EXPLORING EARTHBY SCIENTIFIC OCEAN DRILLING

2050 SCIENCE
FRAMEWORKWRITING AND REVIEWING TEAMLEAD EDITORS
Anthony Koppers .  .  .  .  .  .  .  .  .  .  .  .  .  . Oregon State University, United States
Rosalind Coggon . . . . . . . . . . . . . . . University of Southampton, United Kingdom

AUTHORS
Cara Burberry  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . University of Nebraska–Lincoln, United States
Steve D’Hondt .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . University of Rhode Island, United States
Sarah Feakins  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . University of Southern California, United States
Marguerite Godard  .  .  .  .  .  .  .  .  .  .  .  . Université de Montpellier, France
Patrick Fulton  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Cornell University, United States
Kliti Grice .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Curtin University, Australia
Patrick Grunert .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . University of Cologne, Germany
Chris Lowery  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . University of Texas Institute for Geophysics, United States
Katsuyoshi Michibayashi .  .  .  .  .  . Nagoya University, JapanKen Miller .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Rutgers University, United States
Rob McKay .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Victoria University of Wellington, New Zealand
Antony Morris .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . University of Plymouth, United Kingdom
Richard Norris .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Scripps Institution of Oceanography, United States
Matt O’Regan .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Stockholm University, Sweden
Anais Pages .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Department of Water and Environmental Regulation, Australia
Ross Parnell-Turner .  .  .  .  .  .  .  .  .  .  .  . Scripps Institution of Oceanography, United States
Brian Romans  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Virginia Tech Geosciences, United States
Laura Wallace  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . GNS Science, New Zealand

CONTRIBUTORS
Frederick Colwell  .  .  .  .  .  .  .  .  .  .  .  .  .  . Oregon State University, United States
Jason Sylvan .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Texas A&M University, United States
Susan Straub .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Lamont-Doherty Earth Observatory of Columbia University, United States
Damon Teagle .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . University of Southampton, United Kingdom

REVIEWERS
Donna Blackman  .  .  .  .  .  .  .  .  .  .  .  .  .  . University of California Santa Cruz, United States
Chris Charles  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Scripps Institution of Oceanography, United States
Sean Gulick .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . University of Texas Institute for Geophysics, United States
Masataka Kinoshita  .  .  .  .  .  .  .  .  .  .  . University of Tokyo, Japan
Junichiro Kuroda  .  .  .  .  .  .  .  .  .  .  .  .  .  . University of Tokyo, Japan
Lisa McNeill  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . University of Southampton, United Kingdom
Ken Miller .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Rutgers University, United States
Yuki Morono .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Kochi Core Center, JAMSTEC, Japan
Antony Morris .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . University of Plymouth, United Kingdom
Clive Neal .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . University of Notre Dame, United States
Heiko Pälike .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . MARUM, Universität Bremen, Germany
Julie Prytulak .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Durham University, United Kingdom
Beth Orcutt .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Bigelow Laboratory for Ocean Sciences, United States
Liz Screaton .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . University of Florida, United States
Kristen St. John . . . . . . . . . . . . . . . . James Madison University, United States
Zhen Sun .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . South China Sea Institute of Oceanology, China
Yohey Suzuki .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . University of Tokyo, Japan
Jun Tian .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Tongji University, China
Harold Tobin . . . . . . . . . . . . . . . . . . . University of Washington, United States
Geoff Wheat .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . University of Alaska Fairbanks, United States
Yusuke Yokoyama .  .  .  .  .  .  .  .  .  .  .  .  . University of Tokyo, Japan
EXTERNAL REVIEWERS
Uli Harms .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . International Continental Scientific Drilling Program, GFZ Potsdam, Germany
Victoria Pease .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . International Continental Scientific Drilling Program, Stockholm University, Sweden
Mitch Schulte .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Planetary Science Division, NASA Headquarters, United States

CITATION. Koppers, A.A.P., and R. Coggon, eds. 2020.
Exploring Earth by Scientific Ocean Drilling: 2050 Science
Framework. 124 pp., https://doi.org/10.6075/J0W66J9H.

EXPLORING EARTHBY SCIENTIFIC OCEAN DRILLING
2050 SCIENCE FRAMEWORK

Anthony Koppers and Rosalind Coggon (Lead Editors)
Contact us via eesod2050@iodp.org

SCIENCE FRAMEWORK WORKING GROUP
Anthony Koppers (chair) . . . . . . . . . . .Oregon State University, United States
Cristiano Chiessi .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . University of São Paulo, Brazil
Gail Christeson  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . University of Texas at Austin, United States
Mike Coffin  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . University of Tasmania, Australia
Rosalind Coggon . . . . . . . . . . . . . . . . . . .University of Southampton, United Kingdom
Stuart Henrys .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . GNS Science, New ZealandYoon-Mi Kim .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . KIGAM, Korea
Iona McIntosh  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . JAMSTEC, Japan
Katsuyoshi Michibayashi .  .  .  .  .  .  .  .  .  . Nagoya University, Japan
Yuki Morono .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Kochi Core Center, JAMSTEC, Japan
Antony Morris .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . University of Plymouth, United Kingdom
Richard Norris .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Scripps Institution of Oceanography, United States
Matt O’Regan .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Stockholm University, Sweden
Anais Pages .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Department of Water and Environmental Regulation, Australia
Dhananjai Pandey .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . NCPOR, India
Sandra Passchier .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Montclair State University, United States
Zhen Sun .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . South China Sea Institute of Oceanology, China
Jun Tian .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Tongji University, China
Huaiyang Zhou .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Tongji University, China

EDITING AND DESIGN
Ellen Kappel .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Editor, Geosciences Professional Services Inc.
Johanna Adams .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . Illustrator, Geosciences Professional Services Inc.

CONTENTS
Introduction: Scientific Ocean Drilling Through 2050.  .  .  .  .  .  .  .  .  .  .  .  . 1Prelude.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 1Tools for Probing the Interconnected Earth System. .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 2Frontiers in Scientific Ocean Drilling: The 2050 Science Framework .  .  .  .  .  .  .  .  .  .  .  .  .  . 5Scientific Ocean Drilling: Looking Ahead.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 13

Strategic Objectives.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 14
1. Habitability and Life on Earth.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 15
2. The Oceanic Life Cycle of Tectonic Plates .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 21
3. Earth’s Climate System.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 30
4. Feedbacks in the Earth System. .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 40
5. Tipping Points in Earth’s History. .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 48
6. Global Cycles of Energy and Matter.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 56
7. Natural Hazards Impacting Society. .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 65

Flagship Initiatives .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 72
1. Ground Truthing Future Climate Change. .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 73
2. Probing the Deep Earth .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 78
3. Assessing Earthquake and Tsunami Hazards .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 84
4. Diagnosing Ocean Health. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
5. Exploring Life and Its Origin.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 93

Enabling Elements.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 98
1. Broader Impacts and Outreach .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 99
2. Land to Sea. .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 104
3. Terrestrial to Extraterrestrial.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 108
4. Technology Development and Big Data Analytics .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 112

2050 Science Framework: Document Development
and Involved Countries. .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 118
Figure Credits, Sources, and References.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 120

Mission
The 2050 Science Framework for Scientific Ocean Drilling
guides multidisciplinary subseafloor research into theinterconnected processes that characterize the complex
Earth system and shape our planet’s future.

VisionTo be globally recognized as the authoritative sourceof information about ocean and Earth system history
and its links to society.

Who We Are
We are an international scientific community pioneering
global-scale interdisciplinary research below the seafloorof the world ocean.

WE RESEARCH the processes that connect the solid
Earth, ocean, life, climate, and society.
WE EXPLORE the interconnected Earth in places thatcan only be accessed and understood through scientificocean drilling.
WE TRAVERSE TIME to reveal the many interactions
that shaped Earth’s geologic past to illuminate our future.
WE COMMUNICATE knowledge gained throughscientific ocean drilling to the global community.

INTRODUCTIONSCIENTIFIC OCEAN DRILLING THROUGH 2050

PRELUDETwo hundred million years of Earth history are locked in
sediments and rocks beneath the world ocean. Scientificocean drilling provides access to this archive, allowing scientists to examine the interconnected processes that characterize the Earth system and shape our planet’s future. The
disciplinary breadth and global scope of scientific ocean
drilling requires—and greatly benefits from—international
collaborations that reach across, and in many cases beyond,the boundaries of all Earth science disciplines.
Scientific ocean drilling has fundamentally transformed
our understanding of Earth. The earliest scientific drilling
into oceanic crust in the South Atlantic Ocean verified theseafloor spreading hypothesis and revealed the relative
youth of the seafloor compared to the ~4.5 billion year age
of Earth. Scientific ocean drilling has allowed scientists todecipher the timing of the waxing and waning of Southernand Northern Hemisphere glaciation and to link thatbehavior to global, natural phenomena. Analyses of carefully collected and curated samples recovered by scientificocean drilling have pushed the boundaries of knowledgeof Earth’s climate system, providing geologic context forinterpreting anthropogenic impact on climate and theenvironment. Core analyses have also expanded understanding about the limits of life on Earth, having revealed avast biosphere deep beneath the seafloor.
Over the coming decades, scientific ocean drilling is
poised to contribute vital knowledge to address issues
ranging from the mechanics of fault slip at subduction
zones that lead to great earthquakes and tsunamis, to thehigh-CO2 climate systems of past “greenhouse” worlds andtheir global repercussions. A new phase of scientific ocean
drilling will provide data needed to improve the accuracy ofcomputer models that predict future climate, including thepace of rising sea levels and melting of glacial and polar ice.

Scientific ocean drilling is the only tool available for exploring life in the oceanic crust of our planet—the largest biomeon Earth—providing a glimpse of the types of microbial lifethat might exist elsewhere in our solar system and beyond.
In conjunction with new analytical techniques and innovative big data approaches, scientific ocean drilling will provide a unique lens into deep geologic time and a means
to collect detailed information about currently active Earthprocesses and ground truth data for improving predictive
Earth models. By addressing key questions about Earth’s
past, present, and future through interdisciplinary research
expeditions and ensuing analyses, scientific ocean drilling
will lead to a more profound understanding of Earth as one
integrated, interconnected system.
This international 2050 Science Framework: Exploring
Earth by Scientific Ocean Drilling provides guidance to current and future generations of ocean drilling scientists on
the research objectives that should be pursued. It focuseson the many ways in which scientific ocean drilling will
increase understanding of the fundamental connections
among Earth system components while addressing a
range of challenging natural and human-caused issues
facing society. The Framework calls for strong collaboration
among Earth science disciplines and allied international
research programs to meet scientific goals and promotes
communication of scientific ocean drilling results to abroad global audience. Because this Framework has along time horizon, progress toward achieving it goals will
be assessed every five years. It will be a living online document to enable necessary adjustments and encourage
the evolution of research areas as science advances andsocietal needs evolve.

1TOOLS FOR PROBING
THE INTERCONNECTED
EARTH SYSTEM

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ENVIRON

The dynamic Earth, its climate and environment, and all lifethat emerged and evolved on this planet are linked in
myriad ways. These pieces of the Earth system in turn areconnected to the cycles and rates governing the planet’s
processes and feedbacks, the location and intensity ofnatural hazards, and the health and habitability of the
global ocean. To investigate how the interconnected
Earth system works and to provide the ground truth
needed to test Earth models, scientists rely upon highly
specialized ocean drilling platforms equipped to collectcontinuous cores of sediment and rock and samples of fluids
and microbes from beneath the seafloor, as well as deploy
state-of the-art instruments and long-term observatories
within subseafloor boreholes.

Dynamic Earth. Scientific ocean drilling provides the means to deploy long-term
instruments and sample deep into Earth to reveal the dynamic interconnections
between tectonics, convective mantle processes, earthquake and volcanic hazards,
our planet’s climate system, and Earth’s habitability.

Climate and the Environment. Scientific ocean drilling provides access tolong-term and high-resolution archives of the processes that govern the global
circulation of the ocean and atmosphere, the dynamics of abrupt tipping points
in ecosystems, and the global metronome of orbital climate cycles. Marine sedimentary records reveal the rates at which ice sheets melt, sea levels rise and fall,monsoon systems switch on and off, and past greenhouse warming occurred.

Life. Scientific ocean drilling cores contain details about the evolution, biodiversity, and productivity of marine organisms and the role life plays in thechanging Earth system. Deep drilling and monitoring in borehole observatories
advance research into biodiversity and evolutionary developments in the marine
biome, the distribution of deep microbial life across ocean basins, the limits of lifeon Earth, and the possibility of life on other worlds.

Natural Hazards. Scientific ocean drilling recovers sediment and rock cores that
inform us about hazards related to past earthquakes, tsunamis, volcanic eruptions,submarine landslides, and sea level rise. Borehole instrumentation and cabledmonitoring stations, in conjunction with observations made on land, allow us tobetter evaluate future risks of natural hazards to society.

Cycles and Rates. Scientific ocean drilling acquires detailed information about
the rates and magnitudes of energy, chemical, nutrient, and fluid exchanges
between Earth’s sediments and rocks, ocean, atmosphere, and life. These data
reveal how global cycles moderate Earth’s climate, form natural resources, andcontrol the long-term evolution of life on Earth.

Health and Habitability. Scientific ocean drilling gathers critical informationneeded to more accurately predict Earth’s response to natural and anthropogenic
disruptions to the interconnected life-sustaining systems of our planet. This knowledge helps us evaluate our planet’s future habitability.

3

Scientific Ocean Drilling Discoveries
movements, providing insight into the nature and velocitiesof the large-scale mantle flow over the last 80 million years.
Scientific ocean drilling has also repeatedly transformed
our understanding of how oceanic crust forms at both fastand slow spreading mid-ocean ridges, how the asthenospheric mantle may get structurally exhumed at ultraslow
spreading ridges, how subduction zones are initiated, andhow marginal and full-scale ocean basins evolve. Coring
through megathrust splay faults and installing boreholeobservatories and cabled monitoring have contributed to
our understanding of the mechanisms of giant subduction
earthquakes and “slow slip” earthquake phenomena.
Perhaps most unexpectedly, scientific ocean drilling overthe last two decades has demonstrated that the deepest
reaches within marine sediments, and even the rocky
oceanic crust beneath it, are full of life. This subseafloor realm
harbors the largest and deepest biome on Earth with untold
new varieties of Archaea, Bacteria, Eukarya, and viruses.
New drilling approaches allowed collection of uncontaminated samples, and great advances in DNA research andgenomic sequencing accelerated understanding of thediversity and function of life that can subsist under harshconditions over geologic time.
These examples are among
a multitude of discoveries andscientific advances
made
over
OCEANOBS’19: AN OCEAN
OF OPPORTUNITY
50 years of scientific ocean drillSCIENTIFIC OCEAN DRILLING
ing. Many more can be found in
the March 2019 special issue of
Oceanography on “Scientific Ocean
AN OCEAN
OF OPPORTUNITY
Drilling: Looking
to the Future”(see https://tos.org/oceanography/
issue/​volume-32-issue-01).
The Oceanography Society
1 Research Court, Suite 450
Rockville, MD 20850, USA

ADDRESS SERVICE REQUESTED

Oceanography
T H E O F F I C I A L M AG A Z I N E O F T H E O C E A N O G R A P H Y S O C I E T Y

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Oceanography

Over the past five decades, scientific ocean drilling has
expanded our understanding of the Earth system by piecing
together the basic rhythms of climate, the movement oftectonic plates, and the history of life in the ocean. Scientificocean drilling has demonstrated that minor variations inEarth’s orbit (called Milankovitch cycles) have controlled thetiming of ice ages of the past 2.6 million years, the pulses ofgrowth and decay in the Antarctic ice sheet over the past
50 million years, and changes in global monsoonal precipitation patterns. Drill cores have also revealed the increased
strength and permanency of El Niño-Southern Oscillation
conditions during warmer global climate intervals and thathigh atmospheric CO2 concentrations are implicated in themuch warmer ice-free “greenhouse” worlds of the Eocene(34–56 million years ago) and Cretaceous (66–145 million
years ago). Moreover, scientific ocean drilling has shown that
the Cretaceous was marked by multiple episodes of global
ocean anoxia, that massive amounts of carbon released frommarine sediments may have exacerbated temperature riseat the end of the Paleocene (56–66 million years ago), andthat the rate of sea level rise during the last deglaciation was
greater than 10 times the modern rate of over 3 mm/yr. As
global deglaciation and temperature rise continue over the
next decades, scientific ocean drilling data sets are important for predicting future changes in the rate of sea level rise.
Launched early in the era of plate tectonic theory development, scientific ocean drilling has also revealed much about
how deep Earth mechanisms operate. It has confirmed thatmagma-​dominated rifted margins represent the birth placesof new ocean basins and that oceanic plateaus are the equivalent of continental flood basalts, forming through shortlived massive volcanism. It has shown that the Hawai‘i andLouisville mantle plumes exhibited significant differential

FRONTIERS IN SCIENTIFIC OCEAN DRILLING:
THE 2050 SCIENCE FRAMEWORKThe overarching goal of the 2050 Science Framework is
to guide future subseafloor research that will reveal the
key linkages, processes, feedbacks, and tipping points inthe complex Earth system. Building on the results from50 years of scientific ocean drilling, and taking advantage ofadvances in drilling, logging, and observatory technologies
as well as the development of novel laboratory techniques
and the growth in big data analytics, scientific ocean drilling is poised to advance knowledge at the next frontier—​
understanding Earth as an interconnected system.
As CO2 levels in Earth’s atmosphere are predicted to continue to rapidly increase in the very near term, it is critical tocollect a wide range of paleoclimate records to test contemporary models that provide competing forecasts and thatlay out different future scenarios for sea level rise, global
ocean circulation, ocean acidification, ocean oxygenation,coral reef health, and expanding aridity patterns acrosscontinents. Systematically targeting pre-Holocene epochs
and recovering high-​​resolution sediment sequences overdecadal to millennial timescales in strategic locations
around the world, possibly in grids or along transects, will
provide the required synthesized global paleoclimate database. Comparing those paleoclimate records with theirterrestrial counterparts over widely ranging spatial andtemporal scales will enhance understanding of the Earthsystem and its responses to change.
The next generation of scientific ocean drilling mustalso address many fundamental, unanswered questions
about the life cycle of oceanic crust and the large-scale
structure and functioning of Earth itself. A key exploration
goal is to investigate the nature of the Mohorovičić seismic
discontinuity, or “Moho,” and determine whether it indeed
represents the crust-mantle boundary or it represents
different phenomena in different tectonic settings. Drilling
will collect critical details about how oceanic crust forms
and evolves over tens of millions of years as it interacts withthe hydrosphere and biosphere. It will examine how newplate boundaries initiate, how they evolve, and why theycease to exist. Other frontiers require us to further develop

our understanding of how Earth’s mantle operates andwhy most mantle plumes appear to form along the edgesof large low shear wave velocity provinces that are locatednear the 2,900 km deep core-mantle boundary. These
questions all have implications for how individual components of the Earth system connect.
Major gaps still exist in our knowledge about the processes and timescales of recovery of the Earth systemfollowing mass extinction events caused by both terrestrial
and extraterrestrial natural phenomena. As we may beliving through the sixth mass extinction event on Earthand the first caused by humans, it is critically importantto establish the baseline state of our ocean’s health andexamine potential responses by the Earth system to comparable major perturbations, such as the Paleocene-Eocene
Thermal Maximum 55.8 million years ago when CO2 was
rapidly released into the atmosphere.
Other key frontiers for future scientific ocean drilling
include deepening our understanding of the profoundthreats to society posed by sea level rise, the increasing
frequency and magnitude of extreme monsoonal rains andlarge-scale regional droughts, the deterioration of coral
reef health, massive volcanic eruptions, and major submarine landslides. Subseafloor data are critically needed toassess what governs the occurrence of Earth’s devastating
giant earthquakes and tsunamis at subduction zones.
Scientific ocean drilling also seeks to advance knowledge of fundamental issues in science, such as thoseconcerning the origins, evolution, and rules of life on
Earth and elsewhere in the universe; how and if the ocean
basins may provide long-term subsurface repositories
for CO2 sequestration; how large-scale geologic events
such as earthquakes, landslides, and plate tectonic movements may have shaped Earth’s ecosystems including
subseafloor microbial communities; and how the health of
the global ocean is modulated by the climate system andanthropogenic influences.

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2050 SCIENCE FRAMEWORK COMPONENTS
The 2050 Science Framework captures these exciting frontiers in seven Strategic Objectives, five Flagship Initiatives, andfour Enabling Elements. The Strategic Objectives comprise
broad Earth science research areas that form the foundation of scientific ocean drilling through 2050. Each objective
focuses on understanding the interconnections within the
Earth system. The objectives are wide-ranging and aspirational to allow new science to emerge through bottom-up
proposal development and peer review. Collectively, theStrategic Objectives cover the interconnected processes
and feedbacks of the full Earth system that can be uniquely
investigated with scientific ocean drilling.
The Flagship Initiatives comprise long-term research
efforts that require multi-expedition scientific ocean drilling over 10- to 20-year time intervals. Each multidisciplinary

research endeavor aims to test scientific paradigms andhypotheses that inform issues of particular relevance orinterest to society. The Flagship Initiatives typically combine
research goals from multiple Strategic Objectives. Their
implementation will be shaped by science proposals thatdevelop coordinated strategies that include long-termplanning, technology development, and innovative applications of existing and new scientific ocean drilling data.
The Enabling Elements serve to significantly advancethe goals of scientific ocean drilling through numerous
and varied broader impacts and outreach initiatives,
partnerships and collaborations with organizations thathave complementary scientific goals, and continued
technology development and innovative applications ofadvanced data analytics.

The 2050 Science Framework Structure
STRATEGIC OBJECTIVES

EARTH
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R a tes

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Na
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& Habitab
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Strategic Objectives are multidisciplinary, cutting acrossthe traditional themes of previous scientific ocean drilling
efforts and are open-ended to encourage innovationand evolution of scientific ideas.

FLAGSHIP INITIATIVES

ds
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AMI C
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EA R T H

E
C L I M AT M
ENVIRONTHE INTE
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Broad areas of scientiﬁc inquiry that focus onunderstanding the interconnected Earth system.

Long-term drilling endeavors that aim to
inform issues of particular interest tosociety, typically combining goals frommultiple Strategic Objectives.
Flagship Initiatives will require the community todevelop strategies and technologies to implement
multiple coordinated expeditions, taking advantageof the 25-year timeframe of the Science Framework.

ENABLING ELEMENTS
Key facets of scientiﬁc ocean drilling thatfacilitate our research activities, enhance ourscientiﬁc outputs, and maximize their impact.
Enabling Elements include links with major allied programs,
effective strategies to communicate results to the public,
and the generation of new opportunities through novel
technology and data approaches.

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ENDURING PRINCIPLES
Implementation of the 2050 Science Framework requires aninternational approach and a cohesive set of guiding principles for bringing online future scientific ocean drilling
programs. These eight Enduring Principles follow current
strengths in scientific ocean drilling.
Open access to samples and data. International scien-tists, facility operators, funding agencies, and program
member offices must commit to continuing to provide free
and open access to all samples in all core repositories andto all data deposited in internationally recognized online
data repositories. Open access ensures equity: researchers
from any institution, whether they participated on ascientific ocean drilling expedition or not, can request
samples and access data for their use. It also allows future
generations of scientists and students to apply new analytical techniques to core samples, while the availabilityof FAIR (findable, accessible, interoperable, reusable) data
will allow use of advanced data analytics and modelingto test hypotheses and gain novel insights into the interconnections in the Earth system.
Standard measurements. Numerous Earth science data

sets and observation types are unique to scientific ocean
drilling and can only be collected by seagoing expeditions
using highly specialized drilling platforms. These high-​
quality comparative data sets are the gold standard of scientific ocean drilling and a major requirement for addressing
the research goals in the 2050 Science Framework. To permit
integrative data analytics and predictive modeling efforts,
all data must be made available in standardized formats andcollected by applying standardized analytical approaches.
Bottom-up proposal submissions and peer review.

A strength of scientific ocean drilling has always been its“bottom-up” ethos and focus on transformative frontierresearch. Decisions about deployment of its drilling platforms are reached through an open, meritocratic, peer-​
reviewed proposal system that ensures that the best
science is accomplished by incorporating the perspectivesof hundreds of scientists at the cutting edges of their fields.
Future scientific ocean drilling will also be directed bycommunity-​
generated proposals targeting the Strategic
Objectives and Flagship Initiatives. International collaborative proponent teams will submit research proposals aimed
at transforming the aspirational science goals outlined inthis 2050 Science Framework into successful expeditions andstrategies. The evaluation of proposals and scheduling of
future expeditions will occur through international scienceadvisory panels, external peer review, and facility boards.

Transparent regional planning. To successfully imple-

ment the 2050 Science Framework, future scientific ocean
drilling expeditions need access to the global ocean, including exclusive economic zones and sovereign continental
shelves, which will require an international communitythat engages local and regional stakeholders. Transparent
regional planning by facility boards allows proponent
teams to develop proposals in support of strategically
timed scientific ocean drilling around the world using anarray of specialized ocean drilling platforms.
Promoting safety and success through site characterization. Safe and successful operation of scien-tific ocean drilling expeditions requires comprehensive
pre-expedition site characterization and expert assessment. By leveraging access to integrated data sets of seismicreflection profiles and grids, bathymetry, and other typesof seabed surveys, the data used in site review provide
assurance that drilling occurs in the correct geographic
locations and to the requisite depths, while recovering theappropriate sediment, rock, fluid, and/or biological samples
necessary to achieve the goals laid out in the 2050 Science
Framework. Site characterization ensures that drilling data
are interpreted in the appropriate scientific context.
Regular framework assessments. Progress towardachieving the goals of the 2050 Science Framework will beassessed every five years via a programmatic review. The
review will permit the international scientific ocean drilling
community to make necessary adjustments and propose
new Strategic Objectives and Flagship Initiatives as scienceadvances and as societal needs evolve.
Collaborative and inclusive international programs. Scientific ocean drilling addresses truly global science questions. To make significant progress on the science
goals encapsulated in the Strategic Objectives and Flagship
Initiatives requires collaborative and inclusive approaches
through a united collective of international programs.
Enhancing diversity. Future scientific ocean drillingmust commit to training and mentoring the next generation of scientists, enhancing diversity in that community,
and supporting education of a scientifically literate world.
Scientific ocean drilling will be a leader in driving the push
to widen participation in the Earth and ocean sciencesamong future generations of scientists and in removing
internal barriers to becoming and staying involved.

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STRATEGICOBJECTIVES

1

1

Defining the conditions for, and the role of, life in
the marine realm. Earth is the only planetary body

Habitability andLife on Earthknown to support life. Understanding what makes
our planet habitable, and where and how life origThe Oceanic
Life Cycle ofinated and evolved, requires examining Earth’s
Tectonic Plates
records of habitability and life through time
Investigating the genesis,
Understanding natural
aging,
motion,andand across its myriad different environments.
shazards in the marine
zard
destruction of oceanic
Ha
Scientific ocean drilling provides access tolenvironmentalithosphereAMIC
DYN
the subseafloor environment, providing
EARTH
materials critical to advance understandingof the requirements for and limits of life on
Global Cycles ofEarth’s Climate
Energy and Matter
SystemEarth. Cores contain details about how life in
Determining the
Examining variations&
the ocean and on land has reacted to pastENrole, mechanisms,
in ice sheets, oceanTabrupt environmental changes, the environand magnitudes
and atmosphereyc
lesof Earth system
dynamics, and& Rat smental parameters that led to mass extince
cyclessea leveltions, the conditions that fostered evolution of
Tipping Points
Feedbacks in
our own species, and the global drivers of proin Earth’s History
the Earth System
duction, biodiversity, radiation, and extinction. In
Using Earth’s geologic
Constraining the processes
past to illuminate futurethat regulate or destabilize
comparison with most terrestrial records, marine
environmental change
the Earth systemsediments have excellent chronologies and contain
diverse microfossil groups and novel microbial communities that retain critical environmental information.

2

Defining theconditions for, andthe role of, life in
the marine realm

NaturalHazards
ImpactingSocietyFE

LIE
C L I M AT
M
EN VIR ON& Habitab
alth
ilit
He
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Na
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3

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6

HABITABILITY AND LIFE ON EARTH

5

2

4

THE OCEANIC LIFE CYCLE OFTECTONIC PLATES

3EARTH’S CLIMATE SYSTEM

Investigating the genesis, aging, motion, and destruction of oceanic lithosphere. Earth repaves more than half

Examining variations in ice sheets, ocean and atmospheric dynamics, and sea level. Marine sediments

its surface every ~200 million years. The formation, evolution,and destruction of oceanic lithosphere is an integral part ofthe plate tectonic cycle and establishes boundary conditions for Earth’s climate system. It drives the global cyclingof energy and matter that buffers Earth’s environmental
conditions and makes Earth’s surface habitable. Oceanic
lithosphere cycling produces critical economic resourcesand governs the occurrence of earthquakes, tsunamis, andvolcanoes that pose hazards to society. To date, we have
only explored a small fraction of Earth’s oceanic lithosphereand to relatively shallow depths. To answer fundamental
questions about our planet’s central rock cycle and plate
tectonics requires scientific ocean drilling of crustal sections
that span the life cycle of oceanic lithosphere and the full
spectrum of plate accretion modes, plate boundary types,
intraplate volcanic processes, and subduction styles.

contain the most complete record of the processes, mechanisms, and impacts of natural climate variability andlong-term changes to Earth’s climate system on timescales
from annual to hundreds of millions of years. Scientificocean drilling can increase the continuity, resolution, andaccuracy of paleoclimate reconstructions to enhance ourunderstanding of how Earth’s climate system operates. A
key focus will be to document the onset, interconnectivity,
and resilience of potentially vulnerable components of themodern climate system, including the global ocean meridional overturning circulation, sea ice and ice sheets, andpatterns of precipitation and aridity. By targeting how theclimate system operates across a wide array of past climate
states, scientific ocean drilling will obtain the data necessary
to calibrate and improve numerical models used to project
future climate impacts and inform mitigation strategies.

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4

FEEDBACKS IN THE EARTH SYSTEM

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TIPPING POINTS IN EARTH’S HISTORY

Constraining the processes that regulate or destabilize the Earth system. Feedbacks are pervasive, critical

Using Earth’s geological past to illuminate futureenvironmental change. Parts of the Earth system, par-interconnections among different parts of the Earth system.
Over long timescales, feedbacks have been responsible forreconfiguring of continents, climate alternating between
greenhouse and icehouse states, and the evolution ofvastly different biota during different geologic periods. On
shorter time­scales, feedbacks between the atmosphere,
ocean, and cryosphere have accelerated the growth anddecay of ice sheets, a complex process accompanied bylarge changes in temperature, precipitation, sea level, andvegetation. On human time­scales, changes in ocean circulation and resultant increases and decreases in heat storage
in the deep ocean have caused rapid and sustained shifts inhigh-latitude temperatures and precipitation. Great strides
have been made in identifying feedbacks in the Earth system, but our knowledge of how these feedbacks operate
and interact and the timescales over which given modes
are stable is limited. By providing access to records that
contain evidence of key Earth system processes, scientificocean drilling makes vital contributions to our understanding of the feedbacks that control our planet’s functioning.

ticularly, ice sheets, ecosystems, and ocean circulation do
not respond linearly to external forcings. Changes may be
gradual before a critical threshold is reached—a “tipping
point”—beyond which the system changes rapidly andoften irreversibly into a new state. Because of the interconnected nature of the Earth system, when a tipping
point is crossed in one part, it could trigger a cascade oftipping points being exceeded elsewhere in the system.
Scientific ocean drilling can recover sedimentary and rockrecords that elucidate the environmental boundary conditions when tipping points were crossed, the rates at which
the Earth system built up to tipping points, and how longit took for the system to attain a new stable state. Lessons
learned from the past can help us understand why certain
Earth system components have tipping points and notothers, how exceeding tipping points affects ecosystem
function, and what drives species to extinction. Identifying
tipping points before Earth exceeds them will provide theinformation society needs to decide how to address theconsequences of today’s changing climate.

6

GLOBAL CYCLES OF ENERGY
AND MATTER

7

NATURAL HAZARDSIMPACTING SOCIETY

Determining the role, mechanisms, and magnitudeof Earth system cycles. Energy and matter use multiple

Understanding natural hazards in the marine environment. Earthquakes, landslides, tsunamis, volcanic

pathways to cycle among Earth system reservoirs. Suchcycles are responsible for the continuous sculpting ofour planet’s surface, opening new ocean basins, building
mountains, and eroding continents. They also drive thechemical evolution of the atmosphere and ocean, control the physical and chemical conditions that allow life
to develop and evolve, regulate the recovery from major
perturbations in Earth’s climate, generate natural hazards
that threaten global communities, and contribute to theaccumulation of key resources, including fresh water andcritical metals. Scientific ocean drilling supplies importantdetails and critical missing information about the rates
and magnitudes of energy, chemical, nutrient, and fluid
transfers among Earth’s rocks, ocean, atmosphere, and life.
These data can reveal how global cycles control Earth’s
evolution over a wide range of spatial and temporal scales.

eruptions, mega-floods, and other extreme natural events
directly threaten communities, infrastructure, and theenvironment. Significant progress has been made in theinvestigation of such hazards through scientific ocean drilling, particularly in subduction zones. However, we remain
largely uninformed about the subseafloor conditions that
influence natural hazards in the marine environment. There
are major knowledge gaps in understanding the mechanisms that control hazard recurrence, timing, and possible precursors, and how to assess their future likelihood.
Scientific ocean drilling can help close knowledge gaps by
installing subseafloor observatories to monitor in situ conditions before, during, and after hazardous events and byprobing the stratigraphic record of prehistoric submarine
and terrestrial hazardous events to understand processes
and evaluate long-term magnitude-frequency correlations.

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FLAGSHIP
INITIATIVES

2

1Ground Truthing Future
Climate Change

1

Probing the
Deep Earth

3

Assessing Earthquake
and Tsunami Hazards

5

Exploring Life and
Its Origins

GROUND TRUTHING FUTURE CLIMATE CHANGE

In 2020, atmospheric CO2 concentrations have already exceeded 410 ppm and,without action to reduce anthropogenic CO2 emissions, could surpass 900 ppm
by 2100. Paleoclimate data collected through scientific ocean drilling establishedthat atmospheric CO2 exceeded 410 ppm more than 3 million years ago. Values
approaching 900 ppm were only realized during the hot “greenhouse” climate of the
Eocene ~50 million years ago. Numerical climate and Earth system models are used
to simulate Earth’s response to projected increases in atmospheric greenhouse gas
concentrations. Projections based on those models can provide information about
shifts in rainfall and temperature patterns and rising sea levels that can be usedin the design of mitigation and adaptation strategies. Scientific ocean drilling provides the robust baseline data on global climate evolution over extended geologic
time periods that are critical for improving climate model performance.

2

IMPACT. High-density, global sci-

entific ocean drilling networks
and transects will enable a morerobust identification of feedbacks
and tipping points in Earth’s climate system and improve modeling and IPCC assessments ofclimate sensitivity to atmosphericgreenhouse gases, ocean circulation changes, and other geologic
boundary conditions.

PROBING THE DEEP EARTH

Scientific ocean drilling has long aspired to penetrate deep into Earth’s oceanic crustand its underlying mantle. Since the Mohorovičić seismic discontinuity (“Moho”)
was postulated in 1909, we still haven’t confirmed that it forms the fundamental
boundary between Earth’s crust—oceanic or continental—and mantle and if it
varies globally. Understanding the nature of this seismic boundary in Earth’s overall
structure is fundamental, as the creation of new oceanic crust in response to mantle
upwelling and convection makes Earth unique among our solar system planets.
New multidecadal scientific ocean drilling strategies seek to probe the deep Earthand to finally reach the upper mantle via a series of interconnected, ambitious
expeditions that will take full advantage of emerging drilling, coring, logging, andmonitoring technologies.

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4

Diagnosing
Ocean Health

IMPACT. Deep scientific ocean

drilling will provide a pathway to
Earth’s deep interior where therocks contain fundamental information on Earth’s formation andevolution, geodynamic behavior,and the interrelationship between
geological, geochemical, and climate cycles.

3

ASSESSING EARTHQUAKE AND TSUNAMI HAZARDS

Undersea earthquakes and associated tsunamis cause some of our planet’s deadliest
and costliest natural disasters over the past 20 years. The 2011 magnitude (Mw) 9.0
Tōhoku-oki earthquake and tsunami in northern Japan took over 15,000 lives, witheconomic losses estimated at US$235 billion. The 2004 Mw 9.2 Sumatra-Andaman
earthquake and tsunami in the Indian Ocean killed more than 230,000 people in
15 countries and caused losses of ~US$15 billion. Undersea landslides and gravity
flows can endanger coastal and offshore infrastructure and telecommunications,as happened in the pair of Mw ~7 earthquakes that severed 22 seafloor cables near
Taiwan in 2006. The potential for such earthquake, tsunami, and landslide hazards
along many of the world’s subduction zones remains poorly known. A complete
understanding of the processes leading to the occurrence of large earthquakes
requires high-resolution, continuous measurements of changes in Earth’s crustfor many decades, over different stages of the earthquake cycle, collected at
different locations globally.

4

DIAGNOSING OCEAN HEALTH

Ocean warming, acidification, deoxygenation, and rising and falling nutrient levels
are causing global changes in marine ecosystems. Declining ocean health can leadto devastating losses in biodiversity, habitats, productivity, and fisheries, putting
life at risk. Similarly, in the pre-Anthropocene epochs, episodes of rapid global
warming and cooling, ocean anoxic and acidification events, as well as meteorite
impacts and intervals of flood basalt volcanism perturbed ocean ecosystems.
Scientific ocean drilling retrieves sediment records that preserve key information about the responses of biological activity in the ocean to natural cycles andcatastrophic perturbations over geologic time. By targeting critical periods in Earthhistory, we can assess the impacts of cataclysmic environmental changes on marine
ecosystems and food webs.

5

IMPACT. By directly accessing,sampling, instrumenting, andmonitoring dangerous offshoreand nearshore fault zones worldwide, scientific ocean drilling will
enable more reliable forecasts
and assessments of the risks tovulnerable populations and infrastructure posed by subduction
zone earthquakes and tsunamis
and will facilitate improved hazard preparedness and response.

IMPACT. By diagnosing ocean
health through geologic time,scientific ocean drilling will help
inform society about drivers in
the Earth system that regulate
ocean health, the warning signsof decline, and how long it may
take for the ocean to recover fromperturbations.

EXPLORING LIFE AND ITS ORIGINS

Marine sediments and oceanic crust host a complex, active, globe-spanning ecosystem in which microorganisms live, interact, evolve, and die. The features andstrategies that enable deep life to persist in these geologic habitats, what communities form under these extremely energy-limited conditions, and what geochemical and biochemical processes create their novel biosignatures remain largely
unknown. To sample, monitor, and analyze a representative range of Earth’s diverse
subseafloor environments and the multitude of microbial communities that they
inhabit in Earth’s interior requires sustained scientific ocean drilling exploration.

IMPACT. Scientific ocean drilling
will significantly advance understanding of the rules of life, thelimits of life, and the origins andevolution of life on Earth. It alsooffers the opportunity to establish what life might look like inanalogous environments on otherworlds and what new organisms
and novel biological functions
useful in geobiotechnology reside
in Earth’s subseafloor.

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ENABLING
ELEMENTS

1BROADER IMPACTS AND OUTREACH

Scientific ocean drilling targets a broad array of topics
that are of great interest and importance to society, contributing vital data that will improve climate models,advance earthquake knowledge, and provide insight into
the possibility of life on other worlds. It is a proven modelfor global collaborative research and an incubator for disciplinary partnerships in science and engineering. Widely
recognized as a preeminent training ground for the next
generation of Earth scientists, scientific ocean drilling willcapitalize on its international, cross-disciplinary shipboard
and shore-based science parties to advance participationof traditionally underrepresented groups. Using a variety of social media and web-based platforms, data andresults will be broadly disseminated to educators, policymakers, and the public, securing scientific ocean drilling’s
position as the authoritative source of information about
the Earth system.

3

TERRESTRIAL TO EXTRATERRESTRIAL

Future collaborations between international space agencies and scientific ocean drilling will benefit efforts tobetter understand planetary evolution and structure
and to assess the potential for life elsewhere in the solar
system and beyond. Such collaborations will also enhance
understanding of the hazards posed by past extraterrestrial
impacts and the recovery of life after such events. Perhaps
most importantly, integration of modern satellite data withhistoric paleoclimate records from scientific ocean drilling
will be a powerful new approach to understanding Earth’s
interconnected processes today and climate evolution
into the future.

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2

LAND TO SEA

The scientific ocean and continental drilling communities
have built two of the most successful, long-lasting, international collaborative programs in the Earth sciences.
Strengthened collaborations between these programs will
advance their closely allied objectives to investigate theinterconnected global Earth system. Future collaborativeland-to-sea drilling campaigns will answer fundamental
questions about Earth dynamics and natural hazards, aswell as explore the connections between plate tectonics,
Earth’s climate system, ecosystems, life and habitability, sea level change, and subseafloor freshwater flow
across the coastline.

4

TECHNOLOGY DEVELOPMENT
AND BIG DATA ANALYTICS

Future developments in drilling technology, monitoring,and observatory science are essential to achieve the goals
laid out in this 2050 Science Framework, as is strengthened
collaborations with engineers, computer scientists, andEarth system modelers. Progress increasingly depends on
the ability to compile, integrate, and analyze multiple large
data sets, including those generated through core analyses
and in situ borehole measurements, which are then linked
to regional geophysical observations. Technological developments and big data analytics will drive progress in futurescientific ocean drilling.

SCIENTIFIC OCEAN DRILLING: LOOKING AHEAD
Scientific ocean drilling is a crucial capability for exploring how the Earth system works. It allows us to obtain
unparalleled samples from beneath the seafloor andassemble authoritative data sets that are essential for
revealing the many complex interactions between thesolid Earth, ocean, life, climate, and society. Using age
transects across ocean basins, continuous deep time slices
preserved in sediment and rock cores, a global distributionof research sites, and an array of active observatories andcabled instrumentation, scientific ocean drilling will painta detailed picture of the complex Earth system in the geologic past, with a vision to the future. Research conductedwithin the 2050 Science Framework will provide criticalcontributions to our understanding of ongoing environmental change, allowing society to improve its resilience tonatural hazards, sustainably use marine resources, and consider how to protect the future habitability of our planet.
This research aligns with the goals of the United Nations
Decade of Ocean Science for Sustainable Development.
The long timeframe of the 2050 Science Framework
permits pursuit of the foundational Earth research covered in the Strategic Objectives and Flagship Initiatives
and encourages innovation and discovery through multidisciplinary, multinational, and societally relevant research.
Implementation of this Framework relies heavily on thecontinued cooperation and coordination among numerous partner countries. To increase the yield of our futureinternational scientific endeavors requires collaborationand knowledge sharing with other Earth and space science
programs and a concerted effort to train the next generation of marine geoscientists and microbiologists.
Looking ahead, scientific ocean drilling is positioned
to continue to be a major contributor to studies of how
the linkages, processes, feedbacks, and tipping points in
the interconnected Earth system will impact humankind
in the future. Effective outreach and public engagement
will deliver the important results of our research to thebroadest audiences. Rectifying the underrepresentation ofminorities in leadership roles and enhancing our efforts toremove barriers that hamper participation by historicallyunderrepresented populations in science, technology,
engineering, and mathematics will be critical to the successof future scientific ocean drilling. Through the 2050 Science
Framework we are ready to significantly advance the many
frontiers in the study of the interconnected Earth system.

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STRATEGICOBJECTIVESThe Strategic Objectives comprise broad Earth science
research areas that form the foundation of scientific ocean
drilling through 2050. Each objective focuses on understanding the interconnections within the Earth system.

1 Habitability and Life on Earth
2 The Oceanic Life Cycle of Tectonic Plates
3 Earth’s Climate System
4 Feedbacks in the Earth System
5 Tipping Points in Earth’s History
6 Global Cycles of Energy and Matter
7 Natural Hazards Impacting Society

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1 HABITABILITY AND
LIFE ON EARTHSTRATEGICOBJECTIVE

Defining the conditions for, and the role of, life in the marine realm

SUMMARY
Earth is the only planetary body known to support life. Understanding what makes our planet habitable, and where andhow life originated and evolved, requires examining Earth’s records of habitability and life through time and across its
myriad different environments. Scientific ocean drilling provides access to the subseafloor environment where a large portion of Earth’s biosphere thrives, providing materials critical to advance understanding of the requirements for and limitsof life on Earth. Long, continuous sediment and rock cores recovered through scientific ocean drilling contain details about
how life in the ocean and on land has reacted to past abrupt environmental changes, the environmental parameters that
led to mass extinctions, the conditions that fostered evolution of our own species, and the global drivers of production,
biodiversity, and radiation. In comparison with most terrestrial records, marine sediments have excellent chronologies andcontain diverse microfossil groups and microbial communities that retain critical environmental information.

Botany Plants
Ch

Deep Biosphere

ot
ka

ry

Sulfolobus
Methanogens

Eu

Mit
och
ond
ria

cte

Ba

a

ae

ch
Ar

ria

A habitable world. Starting at the Big
Bang, a cascade of physical and biogeochemical processes led to Earth becoming a habitable planet and enabled theemergence of life—with the tree of life
taking root approximately 4 billion years
ago. Biologists have reconstructed
the terrestrial phylogenetic tree of life
based on the molecular fossils inside
the DNA of living cells. Scientific ocean
drilling provides access to subseafloor
environments and biosphere communities to investigate the conditions andprocesses that were required to develop
and maintain a habitable world andunderstand how it evolved. Modified
from Lineweaver and Chopra (2012),
https://doi.org/10.1146/annurev- ​ e arth042711-105531

Animals Zoology

esCyanobacteria
Gram-positivebacteria

Fungi Mycology

sts

pla
loro

Halophiles

Microbiology

Biochemistry

Geochemistry

O2

CH

4

HCN

CO 2

H2O

NH

Habitability

Geophysics

3

Meteoritics

Fe

Astronomy

H

He

Big Bang

Cosmology

Scientiﬁc
Ocean Drillinginvestigations span
the multidisciplinary
processes that led tothe establishment ofEarth’s biosphere/tree of life .

15

STRATEGICOBJECTIVE

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HABITABILITY AND LIFE ON EARTH

HABITABILITY AND THE
DEEP BIOSPHERE
The marine deep biosphere affords key opportunities toinvestigate habitability on Earth and to consider the habitability of other worlds. Subseafloor environments spanhigh pressures, extreme heat, exceedingly low carbon
availability, and nutrient stress—yet, life survives. By investigating how organisms manage to exist under these challenging conditions and by identifying the deep subsurface
boundaries of the biosphere, scientific ocean drilling will
significantly advance our understanding of the requirements for life. This knowledge in turn can be applied tostudies of the nature and extent of life on Earth and life’s
origins and inform the search for extraterrestrial life.

Scientific ocean drilling reaches otherwise inaccessible
habitats of the deep biosphere to investigate how
environmental conditions directly influence the
distribution, diversity, and survival strategies of
microbial life in subseafloor environments.

Limits of life on Earth. Habitability is an essential concept for developing understanding of the evolution andpersistence of life on Earth. It is defined as the ability of anenvironment to permit at least one organism to survive,
maintain, grow, and reproduce. To date, we do not knowwhat precise combination of conditions is required to makean environment habitable. As we venture into deeper andhotter environments through scientific ocean drilling,
we will better determine those conditions. Liquid water iscurrently recognized as one critical component to sustain
carbon-​based life as we know it, yet its presence alone
is not sufficient. Other parameters that likely influence
habitability include temperature, pressure, pH, salinity,
metal concentrations, mineralogy, and ultraviolet radiation. Using an integrated approach of host substrate andmicrobiological sampling with in situ measurements andmicrobial growth experiments, we will investigate theconditions necessary for habitability in the deep biosphere16

and how the balance between the supply of reactants andavailable energy control the pace and variety of microbial
metabolisms. To make progress in these frontier investigations, new DNA- and RNA-based analytical approaches inmetagenomics, proteomics, lipidomics, and other potential omics techniques can be applied in conjunction with
scientific ocean drilling to explore the limits of life.
Extreme subseafloor biosignatures. The discoveries
that microbial communities persist under energy-limited
conditions in subseafloor sediments for many millionsof years, and that life even inhabits the underlying solid
rocks previously regarded as lifeless environments, havechallenged our understanding of life in general. Major
questions about the microbes, their communities, andtheir energy sources remain unanswered. The slowest
rates at which individual cells can respire, replace biomass,
and reproduce remain unknown. The physiological adaptations and metabolic strategies that allow organisms topersist at extremely low energy fluxes for many millions ofyears are not yet identified. How the nature and suppliesof bioaccessible energy vary across the globe, and theirrelationship to geologic setting and local physico-chemical
conditions, to date are not comprehensively explored.
It remains unknown why microbial food sources such as
buried organic matter can consistently go unconsumed fortens of millions of years.
To resolve these questions, we will characterize thesources of energy and nutrients that sustain microorganisms in subseafloor environments. This knowledge
will allow us to characterize the crossover between habitats whose energy ultimately derives from the Sun andhabitats in which life relies on heat and energy supplied by
Earth itself. This also allows us to define the “bottom of the
deep biosphere” that is the boundary beyond which life
can no longer survive—a goal not yet achieved. Scientificocean drilling offers opportunities to access samples
from depths several kilometers below the seafloor anduses innovative interdisciplinary approaches to study
the presence or absence of microbial communities inextreme subsurface environments. Identifying the biotic/
abiotic contributions to the local chemical conditions in
the deeper and older oceanic crust will provide crucial
insights into the chemical, biological, and environmental
limits of life; the key requirements for habitable conditions;and possible “biosignatures” that allow us to fingerprint
where life thrives.

STRATEGICOBJECTIVE

TYPES OF LIFE INHABITINGTHE SUBSEAFLOOR
Subseafloor sediment and underlying rocky substrates
are inhabited by all three major domains of life: Archaea,
Bacteria, and Eukarya. Unique viruses are also known fromsediments and upper crustal rocks. The adaptions of microorganisms in the “deep biosphere” to the environments
they inhabit, the environmental properties that limit theirextent, the nature of their community interactions, andhow they live, die, and evolve are all largely unknown.
For example, little is known about the strategies that subseafloor organisms use to optimize their consumption ofhighly limited resources. Furthermore, while life inhabiting
tens of sedimentary subsurface environments has been
investigated, only a handful of upper crustal subsurface
communities have been studied. Scientific ocean drilling reaches otherwise inaccessible habitats of the deep
biosphere to investigate how environmental conditions
directly influence the distribution, diversity, and survival
strategies of microbial life in subseafloor environments.
Our future research on the deep biosphere will promoteholistic understanding of the deep biome, allowing morecomprehensive understanding of all life on Earth and therole of the deep biosphere in the evolution of the oceanic
crust and the global ocean, and comparisons with microbial communities in terrestrial hot springs and the deeper
realms of Earth’s continental crust.

THE ROLE OF MICROBIAL LIFEIN EARTH HISTORY
About four billion years ago, environmental conditions
on Earth vastly differed from today. No ocean existed, andthe atmosphere lacked oxygen and contained abundant
reduced gases released through intense volcanism. In the

ARCHAEABACTERIA

1

HABITABILITY AND LIFE ON EARTH

absence of an ozone layer, Earth was exposed to harmfulradiation from the Sun. Yet, in this harsh environment,
microbial life started evolving. Through their photosynthetic activity that resulted in the production of oxygen,primordial micro­organisms began changing Earth’s history.
Deposition and burial of the reduced organic matter in theocean left the liberated oxygen in the surface world, where
it increased to higher and higher atmospheric concentrations during Earth’s great oxidization event. Through thisprocess, these organisms also became indirectly responsible for the formation of the protective ozone layer, allowing Earth to become a habitable world for larger, more
complex, multicellular organisms. Primordial life thus
made possible the evolution of complex life—including
humanity—​and it plays a crucial role in the ongoing oxidation of Earth’s surface.
Microbial influence on biogeochemical cycles.
Residing at the interface between a biologically dominated surface world and the abiotic deep subsurface
world, subseafloor life strongly impacts global cycles ofenergy and matter. Subseafloor metabolic activity also
plays key roles in other major biogeochemical cycles. It is
the principal sink of sulfur and bioavailable nitrogen fromthe world ocean and is also a primary source of ocean alkalinity, directly affecting atmospheric CO2 concentration.
Microbes play crucial roles in the formation and destruction of major economic resources, including deposits ofhydrocarbons, phosphate, barite, dolomite, manganese
nodules, and deep-sea metals such as cobalt-rich crusts
that may coat much basalt outcropping on seamounts.
Microbes also are agents consuming pollutants in naturalaquifers and nearshore environments and they may be
crucial players in bioremediation as they promote calcification that could help mitigate the escape of CO2 fromsequestration reservoirs.

Fungi

EUKARYA

Nematodes

Subseafloor sediment and underlying rocky substrates are inhabited by all three major domains of life: Archaea, Bacteria, andEukarya. Here, we show some examples of organisms found in subsurface environments.

17

STRATEGICOBJECTIVE

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HABITABILITY AND LIFE ON EARTH

Effects on climate and ocean health. The effect ofsubsurface communities on ongoing climate change,
and vice versa, remains unexplored. Microbial communities in subseafloor sediment are known sources of greenhouse gases such as methane and CO2 and can also act
as “greenhouse gas sinks” by consuming methane andpreventing it from being released into the atmosphere.
Microbes also may increase the alkalinity of seawaterand thus drive carbonate formation. Much remains to belearned about the rates of these processes, the interactions
between the subseafloor biosphere and biogeochemical
cycling, and how subseafloor life will respond to anthropogenic influences and stresses on ocean health. Scientificocean drilling will explore the coevolution of the biosphereand geosphere over time and quantify the impact of life onbiogeochemical cycles and climate.

THE MARINE BIOME AND THE
BIOLOGICAL PUMPThe ability of the marine biosphere to buffer changes
in atmospheric gases is critical to sustaining planetary
habitability and regulating Earth’s climate system. But
the mechanisms that influence the so-called “biologicalpump” remain poorly understood. It is hypothesized thatthe makeup of the plankton community and ecosystemchanges in ocean frontal systems play key roles in thisprocess, as they may regulate biological production andthe net carbon flux into the sediments on the seafloor.
Past records of ocean productivity. Biological production may respond to basin-scale changes in oceanographic
conditions, such as those of the North Atlantic Oscillation,

Cold Seeps
Low Productivity
Gyre Sediments
Deep-Sea Anoxic
Lakes and Brines
Mud Volcanoes

Gyre

Seamounts

Island
Arc

o
tt

ale
sc

no

Hydrothermal Vents
Deep-Sea Sediments
Bend Fold
Serpentinization
Marine and Continental
Subsurface

18

Examples of extreme environments in the marine realm. Scientific ocean drilling reaches otherwise inaccessible habitats of the deep
biosphere to investigate how environmental conditions directly influence the distribution, diversity, and survival strategies of microbial life
in subseafloor environments. Illustration by Geo Prose, inspired by Figure 1 in Merino et al. (2019), https://doi.org/10.3389/fmicb.2019.00780

STRATEGICOBJECTIVE

the Pacific Decadal Oscillation, the Indian Ocean Dipole,and the El Niño-Southern Oscillation. It is likely that analogues to these cycles govern regional or inter-basin productivity, perhaps on million-year and glacial/​interglacial
timescales. For example, scientific ocean drilling records
have revealed 400,000-year to 3 million-year cycles ofdiatom production in the Pacific, yet the causes of suchcycles will remain unknown until we obtain high-quality
records from other ocean basins to resolve whether thesecycles are synchronous or lag one another.
Biological pump efficiencies. A relatively unexploredaspect of the marine biome is how the biological pump islinked to Earth’s climate evolution. For example, most of
the large increase in atmospheric CO2 during Pleistocene
glacial and interglacial cycles can be attributed to changes
in biological pump efficiency. Conversely, the greenhouseocean of the Eocene appears to have been richly productive, with nearly all productivity recycled in the warm ocean,diminishing any biological pump effects. These changes incarbon burial efficiency rates likely relate to climate-drivenchanges in the physiological activity and composition oflife in marine food webs. This connection raises a numberof questions. Did changes in the global dominance of different plankton groups in the past have similar impacts
on food webs and nutrient cycling? Did changes in ocean
circulation or temperature drive shifts in the dominanceof different plankton groups? Was the Eocene ocean with
its apparently high production (but low carbon burial) a
harbinger of climate change? Novel techniques applied
to marine sedimentary ancient DNA research may shedlight on some of these questions by allowing detection ofplankton groups beyond the skeletal fossil record, enabling
more accurate reconstructions of past marine ecosystems,
improving estimates about past productivity and, ultimately, our understanding of the biological pump.
Marine biodiversity and food webs. Scientific ocean
drilling has recovered unparalleled records of the origins
of biological diversity in the ocean. Molecular taxonomies increasingly show that marine biodiversity is evengreater than we suspected based on conventional micropaleontology. Other environmental clues within cores
have also been understudied. Fossilized teeth, otoliths, andscales from fish and sharks are a common feature of deepsea cores, particularly in pelagic clay, but despite theirpotential to provide key information on vertebrate evolution and production, their record is only now starting to be
explored. Similar gaps exist in our knowledge of biogenic

1

HABITABILITY AND LIFE ON EARTH

silica-rich sediments that are dominated by radiolarians
and diatoms and that are formed away from high productivity regions near continents, ocean upwelling zones,
and divergence in ocean currents. Future drilling targetingcarbonate-poor and silicate-rich sediments deposited indeep ocean water below carbonate compensation depths
will revolutionize our understanding of marine food webs
and how vertebrate diversity—the foundation of modern
fisheries—has responded to shifts in climate and primary
production. As new analytical techniques are developed tointerrogate chemical and isotopic compositions of theseunderstudied sedimentary archives, we can better assist
in diagnosing ocean health through time and identifying
crucial tipping points in Earth’s history.

Our Ancestral Migrations
Scientific ocean drilling has provided archives of terrestrial
climate and ecosystem changes that have been critical tounderstanding the context of human evolution. Researchon the global history of human origins commonly relies onland-derived signals preserved in marine sediments. Pollen,
charcoal, dust flux, leaf wax, and volcanic ash layers recovered from marine drill cores help construct a global pictureof the evolution of terrestrial ecosystems, allowing us tolink archaeological records to the highly resolved global
marine timescale. Marine records of terrestrial proxies goback further in geologic time, provide a direct regional-scale
to global context, and have better deep-time chronologies than anything we can derive from terrestrial archives.
Archaeology and ancient DNA have revealed repeatedmigrations of our ancestors, as well as the rich history ofhominid biodiversity and population crises in our not-so-​distant past. Scientific ocean drilling is a key tool for exploring the environmental history of these events in humanorigins, with direct implications for the habitability and life
on and in the terrestrial Earth.

19

STRATEGICOBJECTIVE

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HABITABILITY AND LIFE ON EARTH

PLANETARY PROCESSES IMPACTING
SUBSEAFLOOR HABITABILITY
The extent to which plate tectonics and other geologic
processes influence the habitability, distribution, anddiversity of subsurface communities remains a frontier inscientific ocean drilling and the Earth sciences. In highly
dynamic regions, such as mid-ocean ridges where new
oceanic lithosphere is created and subduction zones where
this lithosphere reenters the mantle, magmatism and fluid
migration lead to large spatial variations in temperature,pressure, pH, redox, and salinity conditions. These processes create a highly variable succession of habitats thathost radically different subseafloor communities over relatively short distances. Scientific ocean drilling will provide adeeper understanding of the complex exchanges that occur
between the subseafloor biosphere, lithosphere, and atmosphere that led to the development of our habitable world.
To improve our understanding of these interconnections,scientific ocean drilling will need to target new habitats ingeologic settings with diverse sets of environmental conditions. For example, it will be crucial to explore connections
between earthquakes and tsunamis and subseafloor life.
Fault movement can produce hydrogen that feeds subsurface
microbes and may release gas hydrates, and deep communities may migrate through and colonize newly formed
fractures in Earth’s lithosphere. In addition, earthquakes
may cause sediment remobilization and with that transposeorganic matter and its incumbent microbial communities
from shallow to deeper ocean floor environments. On larger
scales of time and distance, we will investigate the effects oflarge igneous province emplacement, seamount and island
arc volcanism, and meteorite impacts on distributions of subsurface communities. The intricacy of potential connections
between geologic events and the subseafloor biome requires
collaboration among geologists, geochemists, geophysicists,hydrogeologists, biogeochemists, and biologists to obtain aholistic understanding of these complex feedbacks in theinterconnected Earth system.

FURTHER READING
Amenabar, M.J., E.L. Shock, E.E. Roden, J.W. Peters, and E.S. Boyd. 2017.
Microbial substrate preference dictated by energy demand, not supply.
Nature Geoscience 10(8):577–558, https://doi.org/10.1038/ngeo2978.
Bao, R., M. Strasser, A.P. McNichol, N. Haghipour, C. McIntyre, G. Wefer, andT. Eglinton. 2018. Tectonically-triggered sediment and carbon export to
the Hadal zone. Nature Communications 9:121, https://doi.org/10.1038/
s41467-017-02504-1.

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Cermeño, P., P.G. Falkowski, O.E. Romero, M.F. Schaller, and S.M. Vallina.
2015. Continental erosion and the Cenozoic rise of marine diatoms.
Proceedings of the National Academy of Sciences of the United States ofAmerica 112:4,239–4,244, https://doi.org/10.1073/pnas.1412883112.
Chapman, C.C., M.A. Lea, A. Meyer, J.B. Sallée, and M. Hindell. 2020.
Defining Southern Ocean fronts and their influence on biologicaland physical processes in a changing climate. Nature Climate
Change 10:209–219, https://doi.org/10.1038/s41558-020-0705-4.
Cockell, C.S., T. Bush, C. Bryce, S. Direito, M. Fox-Powell, J.P. Harrison,
H. Lammer, H. Landenmark, J. Martin-Torres, N. Nicholson, and
L. Noack. 2016. Habitability: A review. Astrobiology 16(1):89–117,
https://doi.org/10.1089/ast.2015.1295.
Colwell, F.S., and S. D’Hondt. 2013. Nature and extent of the deep biosphere. Pp. 547–574 in Carbon in the Earth, Reviews in Mineralogy andGeochemistry, vol. 75. R.M. Hazen, R.J. Hemley, A. Jones, and J. Baross,eds, Mineralological Society of America, Chantilly, VA.
D’Hondt, S., F. Inagaki, B.N. Orcutt, and K.-U. Hinrichs. 2019. IODP advancesin understanding of subseafloor life. Oceanography 32(1):198–207,
https://doi.org/10.5670/oceanog.2019.146.
D’Hondt, S., R.V. Pockalny, V. Fulfer, and A.J. Spivack. 2019. Subseafloor
life and its biogeochemical impacts. Nature Communications 10:3519,
https://doi.org/10.1038/s41467-019-11450-z.
Inagaki, F., and A. Taira. 2019. Future opportunities in scientific ocean drilling: Illuminating planetary habitability. Oceanography 32(1):212–216,
https://doi.org/10.5670/oceanog.2019.148.
Kallmeyer, J., R. Pockalny, R. Adhikari, D.C. Smith, and S. D’Hondt.
2018. Global distribution of subseafloor sedimentary biomass.
Proceedings of the National Academy of Sciences of the UnitedStates of America 109(40):16,213–16,216, https://doi.org/10.1073/
pnas.1203849109.
Lang, S.Q., M.R. Osburn, and A.D. Steen. Carbon in the deep biosphere.
Pp. 480–523 in Deep Carbon: Past to Present. B.N. Orcutt, I. Daniel, and
R. Dasgupta, eds, Cambridge University Press.
Levin, N.E. 2015. Environment and climate of early human evolution. Annual Review of Earth and Planetary Sciences 43:405-429,
https://doi.org/​10.1146/annurev-earth-060614-105310.
Lineweaver, C.H., and A. Chopra. 2012. The habitability of our Earthand other Earths: Astrophysical, geochemical, geophysical, andbiological limits on planet habitability. Annual Review of Earthand Planetary Sciences 40:597–623, https://doi.org/10.1146/
annurev-​earth-042711-105531.
Morono, Y., M. Ito, T. Hoshino, T. Terada, T. Hori, M. Ikehara, S. D’Hondt, and
F. Inagaki. 2020. Aerobic microbial life persists in oxic marine sediment as old as 101.5 million years. Nature Communications 11:3626,
https://doi.org/10.1038/s41467-020-17330-1.
Orcutt, B.N., D.E. LaRowe, J.F. Biddle, F.S. Colwell, B.T. Glazer, B. Kiel
Reese, J.B. Kirkpatrick, L.L. Lapham, H.J. Mills, J.B. Sylvan, and others.
2013. Microbial activity in the deep marine biosphere: Progress andprospects. Frontiers in Microbiology 4:189, https://doi.org/10.3389/
fmicb.2013.00189.
Sibert, E., R. Norris, J. Cuevas, and L. Graves. 2016. Eighty-five million years
of Pacific Ocean gyre ecosystem structure: long-term stability marked
by punctuated change. Proceedings of the Royal Society B 283(1831),
https://doi.org/10.1098/rspb.2016.0189.

STRATEGICOBJECTIVE

2 THE OCEANIC LIFE CYCLEOF TECTONIC PLATESInvestigating the genesis, aging, motion, and destruction of oceanic lithosphere

SUMMARY
Earth repaves more than half its surface every ~200 million years. The formation, evolution, and destruction of oceanic
lithosphere is an integral part of the plate tectonic cycle and establishes boundary conditions for Earth’s climate system.
It drives the global cycling of energy and matter that buffers Earth’s environmental conditions and makes Earth’s surface
habitable. Oceanic lithosphere cycling produces critical economic resources and governs the occurrence of earthquakes,
tsunamis, and volcanoes that pose hazards to society. To date, we have only explored a small fraction of Earth’s oceanic
lithosphere and to relatively shallow depths. To answer fundamental questions about our planet’s central rock cycle andplate tectonics requires scientific ocean drilling of crustal sections that span the life cycle of oceanic lithosphere and the full
spectrum of plate accretion modes, plate boundary types, intraplate magmatic processes, and subduction styles.

ere
osph
Lith

Ocean Islands andLarge Igneous Provinces
Sub
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)

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Scientific ocean drilling collects fundamental data on the plate tectonic cycle. This schematic depicts the three main phasesin the life of an oceanic plate: (left) formation at the mid-ocean ridge, (middle) aging as it moves away from the mid-ocean
ridge, and (right) destruction at a subduction zone. The oceanic plate is dark gray, the continental lithosphere is brown,
and an upwelling mantle plume is orange. The white arrows show plate motion, white circular arrows depict hydrothermal
circulation, and white stars are large earthquakes. Illustration by Geo Prose, inspired by Figure 1 in Crameri et al. (2019),
https://doi.org/10.1016/j.tecto.2018.03.016

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STRATEGICOBJECTIVE

2

THE OCEANIC LIFE CYCLE OF TECTONIC PLATESEXAMINING THE PLATE TECTONIC
LIFE CYCLE
The formation of new oceanic crust at mid-ocean ridges,
its subsequent aging over tens to hundreds of million
years, and its eventual destruction in subduction zones,
recycling through Earth’s mantle, and upwelling via deep
mantle plumes comprise the largest-scale cycle of matterand energy on Earth. Scientific ocean drilling enables us
to better understand the relationships and feedbacks
between this plate tectonic cycle and environmental
changes over a wide range of geologic timescales. We have
limited knowledge about how the plate tectonic cycle
regulates Earth’s climate system, produces critical mineral resources, and generates natural hazards. We havean incomplete understanding of the far-field tectonic andmagmatic processes that may cause major changes in plate
tectonic motions, that may stop portions of the plate cycle,
and that may be implicated in the initiation of new ocean
basins. We also don’t fully comprehend how oceanic crust
accretes and varies along ~60,000 km of the mid-ocean
ridges on Earth; how it is chemically, physically, and biologically altered as it matures; and what fraction may or may
not be recycled into the mantle.
The complex processes governing oceanic crust accretion and aging are recorded by differences in rock chemistry, mineral composition, rock alteration, deformation
fabrics, microbial communities, and more. By sampling
oceanic crust across diverse plate tectonic environments,
and by fully integrating scientific ocean drilling resultswith seafloor mapping and sampling and regional geophysical studies, we can provide important constraints on
the life cycle of oceanic crust, beginning with continental
rifting and the formation of oceanic crust at mid-ocean
ridges, through its final recycling at subduction zones.
The processes accompanying the destruction of plates insubduction zones are best studied by drilling and coringin volcanic arcs, back-arc basins, mud volcanoes, and the
upward-bulging downgoing oceanic plates.

basins. If extensional deformation continues—and the rifting doesn’t fail or stop—the continents break up and new
ocean basins form. The continental margins generated bythese processes are the primary Earth sedimentary sinks
and have high energy resource potential. Scientific ocean
drilling allows us to investigate and test the various models
that have been developed over the last decades for continental breakup and ocean basin formation.
Initial ocean crust formation. Following initial prebreakup extension, the mantle upwells beneath the rift,
partially melting to form magma that becomes the earliest crust that will floor the new ocean basin. This initial
crust, now typically buried by kilometers of sediment,
can be sampled by scientific ocean drilling to decipher
the amount, type, and duration of magmatism; the rate ofextension; and the distribution of faulting as the continents
rift and break up. Scientific ocean drilling thus can provide
critical information on the structure and thermal evolutionof newly formed continental margins in order to decipher
the underlying geodynamic and plate tectonic processes.
Fundamental rifting modes. In some cases, flood volcanism accompanies continental breakup, with mantle
plumes providing an excessive magma supply. In othercases, continental breakup is dominated by faulting andthe development of shallow rift basins. Scientific ocean
drilling can show whether pre-existing structural weaknesses in the continents determine the pattern of breakup
and whether deep-sourced mantle plumes drive breakup
or alternatively are initiated by it. Integration of geophysical and coring data from multiple locations—that covera range of continental extension patterns and related
magmatic production—will permit determination of upliftand subsidence rates, sedimentation histories, and deformation patterns, and the timing, volume, chemistry, andstyle of magmatism. These results provide insight into thefundamental modes of continental rifting and breakup,
from magma-rich to magma-deprived, and the sometimes
rapid transition between these two rifting end members.

CONTINENTAL BREAKUPAND NEW OCEAN BASINSTHE GENESIS OF OCEANIC CRUSTWhen continental lithosphere is stretched beyond its
breaking point due to distant tectonic and/or underlying
magmatic forces, it ruptures into separate, diverging landmasses. Continental rifting and thinning accompany thestretching, resulting in the formation of sedimentary

Scientific ocean drilling and associated marine geologicaland geophysical studies have revealed that the architecture of the oceanic crust is highly variable. Magmaticallyrobust fast-spreading ridges appear to produce relatively simple layered crust of basalts, dikes, and gabbro.

22

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STRATEGICOBJECTIVE

THE OCEANIC LIFE CYCLE OF TECTONIC PLATESTransforming Our Knowledge of Earth’s Interior
geologic timescales. Scientific ocean drilling has transformed
our knowledge of Earth’s interior by pushing the boundaries ofscience exploration deep into oceanic crust. Since confirming
seafloor spreading in 1968, scientific ocean drilling has delivered
critical information about the processes that govern plate tectonics and its impact on the interconnected Earth system. Ocean
drilling has shown that the volume, composition, and architecture of the oceanic crust varies radically with seafloor spreading
rate and the nature of the underlying mantle.

U1309B
1271B
U1415P
335
1275B
U1415J
920B
894G
412A
1272A
1149D
1224F
1268A
U1362A
1274A
483B
1105A
485A
920D
1275D
417A
U1301B
396B
765D
896A
U1383C
333A
332A
417D
801C
418A
395A
332B
U1473A
1256D
U1309D
735B
504B

Holes Deeper than 100 m:

46%
15%
32%
38%
43%
16%
35%
35%
18%
29%
17%
26%
53%
30%
22%
47%
75%
51%
47%
50%
61%
13%
23%
31%
27%
27%
8%
10%
70%
47%

Basaltic Lavas
Lava-Dike Transition
Sheeted Dikes
Gabbros
Serpentinized Peridotites
No Recovery

30%

600

25%

1256D

U1309D400

59%
23% 42%

504B

200

72%
18%
21%

801C

0

800

32%

1,000

28%

1,200

75%
86%

1,400

Depth (meters in basement)

The transfer of residual internal heat from Earth’s formation
4.5 billion years ago, along with energy released by radioactive
decay of isotopes, powers the plate tectonic cycle. Volcanismis the most obvious manifestation of this energy transfer. Morethan 80% of Earth’s volcanism occurs along globe-encircling midocean ridges, creating new oceanic crust. The motion of plates
across Earth’s surface, predominantly driven by the pull of rigid
cool lithospheric slabs as they sink into the mantle at subduction zones, causes oceanic gateways to open and close, which inturn affects ocean circulation, ocean chemistry, and climate on

1,600

14%

1,800

735B
and
U1473A

0

20

2,000

40 60 80 100 120 140 160 180
Ocean Crust Age (million years)

Compilation showing scientific ocean drilling holes that penetrated >100 m into intact oceanic crust and tectonically exposed lower crust and upper
mantle from 1968 to 2018. The bar chart provides the number designation for each hole and the recovery (in percent) for each basement lithology.
The yellow dots indicate the locations of these drill holes on the global map of ocean crustal age; holes that have been particularly instrumental in
informing our understanding of the formation of oceanic crust are labeled (504B, 735B, 801C, 1256D, U1309D, and U1473A). This compilation does
not include “hard rock” drill holes into seamounts, oceanic plateaus, back-arc basement, hydrothermal mounds, or passive continental margins. The
locations of plate boundaries (red) and subducting slabs (blue shading) are also shown. Note that the majority of drill holes are in crust younger
than 40 million years. Sources: Michibayashi et al. (2019), https://doi.org/10.5670/oceanog.2019.136; Hayes (2018), https://doi.org/10.5066/F7PV6JNV;
Müller et al. (2016), https://doi.org/10.1146/annurev-earth-060115-012211

23

STRATEGICOBJECTIVE

2

THE OCEANIC LIFE CYCLE OF TECTONIC PLATES

Moho’s unknown character. We have limited knowledge of how ultramafic rock types of the upper mantle
relate to the position of the Mohorovičić seismic discontinuity (“Moho”) under slow-spreading ridges and how the
Moho differs in the faster-spreading systems. By comparing
ocean crustal sections collected from different spreading
regimes, scientific ocean drilling can shed light on the differences in ocean crustal genesis as a function of spreading
rate, mantle potential temperature,and mantle source composition
over time, and establish the relative
importance of ridge magmatism andnot to scale
tectonic extension in creating oceanic
Crust-Mantle
crust and in determining the location
Boundaryand character of the Moho.

This pattern is different for slow-spreading systems
where tectonic extension usually dominates, leading toheterogeneous crustal structure, the formation of shortlived microplates, or even the absence of a magmatic crust.
In ultraslow spreading environments, tectonic movements
may cause low-​angle detachment faulting that typicallyresults in exposure of mantle rocks such as peridotites
and pyroxenites at the seafloor.

Fast-Intermediate Spreading
Lavas
Sheeted Dikes
GabbroPeridotite

1300°C
Isotherm

Crust
Lithospheric
MantleAsthenosphere

Slow-Ultraslow Normal Spreading

Zone
of Partial
Melting

Magma
Chamber

Lower crust magmatic processes.
It also remains unclear how magma
is distributed throughout the lower
crust—in sections deeper than 1 km—
and how hydrothermal circulation andserpentinization, which may extract
significant amounts of heat fromthese systems, mobilize and concentrate economically important metals
and modulate deeper magmatic
processes. Acquisition of long, deep
crustal sections will permit a better
understanding of what processes drive
variations in crustal accretion and serpentinization and how this interplay
controls the exchanges of heat, mass,elements, critical metals, and volatiles
between Earth’s mantle and its crust,ocean, and atmosphere.

Slow-Ultraslow Detachment-Mode Spreading
Oceanic Core
Complex

24

Scientific ocean drilling and associatedmarine geological and geophysical studies
have revealed differences in the structure ofoceanic crust formed under fast, slow, andultraslow spreading regimes. The large whitearrows depict asthenospheric upwelling andflow induced by plate spreading. The small
white arrows indicate relative fault motion.
The base of the lithosphere is conventionallydefined as the 1300°C isotherm. Illustration by
Geo Prose, inspired by van Wyk de Vries andvan Wyk de Vries (2018), https://doi.org/10.1016/
B978-0-12-809749-6.00007-8

STRATEGICOBJECTIVE

2

THE OCEANIC LIFE CYCLE OF TECTONIC PLATESOCEANIC CRUST MATURATIONSERPENTINIZATION PROCESSES

Throughout its life, the oceanic crust forms the key boundary between the ocean and the mantle. Off-axis magmatism
and tectonics structurally modify the crust as it matures,and thermally driven fluid circulation within the crust andseawater at the seafloor chemically modify the crust overmillions of years. Thus, oceanic crust that is 100 million
years old or older has a very different composition, structure, density, and strength compared to young crust. To
assess changes in past ocean chemistry and understandthe physical and chemical nature and hydration state of theoceanic crust entering subduction zones requires drilling
age transects into mature oceanic crust. Samples recovered will also provide information helpful for determining
the occurrence and magnitude of past natural hazards
such as earthquakes and explosive volcanism.

Up to a quarter of the seafloor formed at slow- and ultraslow-spreading mid-ocean ridges is estimated to be madeup of a diverse patchwork of peridotite and gabbroic
lithologies. This variability indicates that oceanic crust
may be more heterogeneous and more reactive thanoriginally hypothesized for a classically layered crust typically formed at fast-spreading ridges. Changes in physicaland chemical properties due to hydration—in a process
called serpentinization—​thus may be much more extensive in oceanic crust, even to greater depths and into theunderlying mantle, yet this hypothesis is largely untested.
Scientific ocean drilling permits investigation of serpentinization processes in different tectonic environments, fordifferent crustal ages, and to greater crustal depths. Key
unknowns include how serpentinization of slow-spreading
oceanic crust may affect global biogeochemical cycles andplate rheology and structure. We also still need to determine
why serpentinization fronts in oceanic crust appear to be so
abrupt that seismically they may rival the Moho’s signature.

Fluid circulation and cooling plates. We now recognizethat oceanic crust is a highly permeable aquifer throughwhich seawater-derived fluids circulate. High-temperature(up to 400°C) “black smoker” hydrothermal vents along
mid-ocean ridges are the most obvious manifestation ofsuch thermally driven fluid circulation, but we know fromscientific ocean drilling that hydrothermal fluxes throughthe maturing ridge flanks are many orders of magnitude
more voluminous. Conductive heat flow deficits indicatethat fluid circulation is diminishing over geologic time, but
it seems to persist through oceanic crust at temperatures
much less than 100°C and crust as old as 65 million years.
Future scientific ocean drilling will determine when andhow this threshold from advective to purely conductive
heat loss is crossed remains uncertain.
Old crust and CO2 sequestration. Key information onhydrogeology, thermal history, geochemistry, critical metal
deposition, and microbial transitions across the aging
ridge flanks is absent because our current sampling of old(>35 million years) in situ upper oceanic crust is biased
toward areas with anomalously thick overlying sediments
and crust created at intermediate- to fast-spreading rates.
Scientific ocean drilling needs to fill these critical gaps
by exploring a variety of the older ridge flank segments.
Acquisition of oceanic crust samples will also allow us toquantify the extent to which crustal aging buffers Earth’s
climate system through inorganic CaCO3 precipitationand thus how much atmospheric CO2 becomes sequestered in oceanic crust.

…we can explore the links between
serpentinization, aging oceanic crust, the mantle,
and ocean, and their impacts on geochemical cycles,
natural resources, and life.

Bend faults and petit spots. In other instances, during
the final act of lithospheric aging and just prior to subduction, the flexing or bending of the downgoing plate may
initiate new or reactivate old faults that provide late-stage
bidirectional pathways for fluid flow. These new avenues
for seawater penetration lead to the formation of submarine mud volcanoes and serpentinization in the uppermost mantle. This bend faulting also provides pathways formelts, as the uplifted bulge may trigger decompression
melting in the asthenosphere, leading to small-scale but
potentially widespread formation of “petit spot” volcanoes.
Serpentinization fueling microbial life. Serpentinization may play a critical role in providing environments
for microbial life in newly generated oceanic crust to more

25

2

STRATEGICOBJECTIVE

THE OCEANIC LIFE CYCLE OF TECTONIC PLATES

than 100 million-year-old oceanic crust. At slow-spreading
mid-ocean ridges where melt supply is limited, serpentinization of mantle rocks exposed to seawater weakens
the rock, releases heat, and produces a mix of chemicals(including hydrogen and abiotic methane) that is the building block for unique, yet poorly understood, ecosystems,
in conditions that may resemble those of early Earth. The
role serpentinization plays supporting microbial life is an
ongoing scientific ocean drilling research area.
Crustal aging and serpentinization. By drilling age
transects across multiple ocean basins, from mid-ocean
ridges, to subduction zones, to passive margins, we can
explore the links between serpentinization, aging oceanic
crust, the mantle, and ocean, and their impacts on geochemical cycles, natural resources, and life. Integrated
coring and in situ geochemical and microbial monitoring and hydrological experiments along transects will
target critical gaps in ocean crustal sampling with regards
to crustal age, spreading rate, later intraplate volcanic
overprinting, and sediment thickness. Such systematic
sampling is essential to determine the range of crustal
serpentinization effects across the full age spectrum andocean crustal styles.

HOTSPOT VOLCANISM AND
LARGE IGNEOUS PROVINCES
As oceanic crust spreads away from mid-ocean ridges, itcommonly traverses “hotspots” in the underlying mantle
where narrow plumes of material may be upwelling within
Earth’s interior. When these hotspots are long-lived, theymark tectonic plates with age-progressive volcanic chainsfor up to 80 million years or longer, but they also may produce short-lived, high-volume oceanic plateaus. Althoughtens of thousands of volcanic seamounts and many large
igneous provinces (LIPs) are found in the ocean basins,
scientific ocean drilling has explored fewer than a dozen
hotspot systems. Major gaps in our knowledge remain
about the deep mantle heritage and the chemical, isotopic, and mineralogical makeup of mantle sources thatfeed hotspots. Scientific ocean drilling offers opportunities
to learn about the origin and mobility of mantle plumes,
whether two large low shear wave velocity provinces(LLSVPs) in the deepest mantle regions (imaged using seismology) are acting as plume nurseries, if bolide impacts
may be related to the generation of some LIPs, and how
LIPs and excessive intraplate volcanism may drive Earth’s
climate system past tipping points.

Hotspot Volcanic Island Chainand Large Igneous Provinces

Plume
Downgoing SlabLithosphere
Asthenosphere666 kmLower Mantle

LLSVP
ULVZ
Core

not to scale

Core-Mantle Boundary(2,900 km)
Scientific ocean drilling offers the opportunity to learn about the composition and evolution of oceanic plates, mantle
anomalies, mantle plume nurseries, and oceanic volcanic chains. This conceptual sketch illustrates the connections
among these elements in Earth’s interior. ULVZ = Ultra low velocity zone. LLSVP = Large low shear wave velocity province. Illustration by Geo Prose, inspired by Figure 20 in Sager et al. (2016), https://doi.org/​10.1016/​j.earscirev.2016.05.011

26

STRATEGICOBJECTIVE

Mantle plumes modulating Earth’s climate. Longlived mantle plumes play a significant role in broad-scaleregional uplift of oceanic lithosphere, with these topographic fluctuations impacting both sedimentation andocean circulation. For some hotspot systems, these verticalmotions appear more significant when the plumes are
centered on mid-ocean ridges such as Iceland today or on
triple junctions such as Shatsky Rise, Kerguelen Plateau,
and Broken Ridge that formed in the Cretaceous. It remains
unknown whether the plume/ridge and plume/triple junction correlation is random or whether large-scale tectonics
or mantle convection is responsible for the emplacementof plumes in those specific plate-boundary settings. Their
effects on Earth’s climate therefore remain undetermined.
We also don’t know why there are more LIP emplacements
between 150 and 50 million years ago than between
50 million years ago and today. Scientific ocean drilling
can investigate how LIP emplacements affect regional
plate tectonics and mid-ocean ridge spreading, what levelof topographic fluctuation results from long-lived plumes
lifting up oceanic lithosphere, and how the massive magmatism constituting LIP emplacement may have affected
Earth’s climate system and global ocean health.
Chemically zoned and moving plumes. A newresearch avenue centers around understanding the spatial
geochemical zonation of hotspot tracks and what it mightreveal about the internal structure and composition of
mantle plume stems and about LLSVPs from which they may
originate. Scientific ocean drilling is essential for recovering
unaltered igneous rocks that contain tiny parcels of melt
trapped during crystal growth (so-called “melt inclusions”)
that allow us to learn about the pressure, temperature, andcomposition of hotspot mantle source regions. Recoveryof lava erupted from seamounts and LIPs also allows us to
add new paleomagnetic inclination and geochronologicalconstraints on plume mobility—whereby scientific ocean
drilling can test geodynamic computer models of deeprooted plume stems getting deflected in the large-scale
mantle flow—and help refine plate motion histories, which
underpin global tectonic evolution models.

PLATE DESTRUCTION IN
SUBDUCTION ZONES
At subduction zones, the majority of mature, hydrated
oceanic lithosphere descends back into the asthenospheric mantle, recycling igneous rocks, sediments, water,
and carbon back into Earth’s interior. The subduction of2

THE OCEANIC LIFE CYCLE OF TECTONIC PLATES

oceanic lithosphere is responsible for ocean-circling chainsof volcanoes and ocean trenches that extend to 2 km
deeper than the height of Earth’s tallest mountains. Someof the largest earthquakes and tsunamis occur along theroughly 42,000 km of subduction zones. Volatiles released
from the downgoing hydrated oceanic lithosphere give
way to gas-rich explosive eruptions that also endanger thehighly populated regions bordering subduction zones.
Subduction zone behavior and mantle recycling.
The subduction process is remarkably variable in termsof its geometries, speeds of plate descent and trenchrollback, deformation patterns, and chemical exchanges.
It remains difficult to establish how the hydrated oceanic
lithosphere and the overlying sediment and volcanic structures it carries will be processed in the subduction zone.
We don’t know how much of each component will make itinto the arc volcanoes or recycled back into Earth’s mantle.
Scientific ocean drilling can deliver the rock and fluid samples, and the dynamic observations such as temperatureand pore pressure, that are required to define subduction
zone behavior and mantle recycling. Drilling allows us toassess spatial variations in subduction conditions, including enhanced deformation where a seamount or LIP sitson the downgoing slab, that may affect seismic, fluid flow,
magmatic, and landscape responses.

Oceanic Crust Obduction
Not all oceanic lithosphere gets recycled at subduction
zones. Oceanic lithosphere that is exposed on land is called
an ophiolite (e.g., Troodos, Semail) or accreted terrane(e.g., Wrangellia, Siletz). Ophiolites provide invaluable,
accessible windows into the deep Earth. Indeed, the standard model for oceanic crustal structure was long based on
the Troodos ophiolite in Cyprus. However, the origins andemplacement of ophiolites, and hence their interpretationin terms of past seafloor spreading, remain controversial.
Land-to-sea investigations, partnering scientific ocean andcontinental drilling, in places such as the Semail Ophiolite
in Oman or the Izu-Bonin-Mariana and Japan Trenches, will
provide new avenues to elucidate the origins of ophiolites.
By sampling lava sequences in a range of settings, including
in fore-arc and back-arc basins, we will be able to identify
where and why some oceanic crust is able to avoid being
recycled back into Earth’s interior.

27

STRATEGICOBJECTIVE

2

THE OCEANIC LIFE CYCLE OF TECTONIC PLATES

Back-arc basins. The overriding plates typically stretch,
which in many cases progresses from rifting to seafloor
spreading, giving rise to back-arc basins. Scientific ocean
drilling provides the means to seek explanations for theseemingly contradictory occurrence of extensional stressregimes adjacent to areas of major convergence. At present,
these two stress regimes are almost exclusively explored
via geodynamic modeling. Scientific ocean drilling can provide constraints on variables such as basalt geochemistry,timing of cessation of arc volcanism, and temporal changes
in stress regimes that are critical to testing different models
of back-arc extension.

Continental crust formation. Scientific ocean drillingalso helps test hypotheses concerning continental crust formation. Subduction zones not only create new continental
crust; competing processes may destroy continental crustand deeply recycle it. Subduction processes preferentiallyfilter and store certain elements within continental crust,
but they also replenish the mantle. Samples collected byscientific ocean drilling will be key in illuminating how theseelements are fractionated and processed during subduction and how that influences long-term mantle evolution
and its overall chemical makeup. Drilling is needed to better define nascent continental crust formation in oceanic(a) GEOLOGICAL MODEL
Fluid ﬂuxing causes
the mantle to melt further
producing Boninite

Decompression melting of
upwelling mantle produces
Fore-Arc Basalt (FAB)

Philippine plate
Paciﬁc plate(young)(old, dense)
Transform fault(relatively weak)Older, denser
Paciﬁc platefounders andsinks

Asthenosphere
upwells to ﬁll
the void between
the plates

Asthenosphere

Upwellingceases as Paciﬁcslab moves
under Phillipine
plate and thegap between theplates closes

Magma production
rate (cm/year)

0 Myr

Fluid
Dehydration of
the slab tip
drives ﬂuid into
the overlying
mantle~1 Myr(b) DYNAMIC MODEL

~0.34

0.05

0.05

0.05

0
0

0

0

FAB melt
Boninite melt

Depth (km)

20
40
60
80

38 kyr
100
200
150

594 kyr
100

50

0

50

100 200150

855 kyr
100

50

0

50

100 200

150

100

50

0

50

100

Distance from the ﬁnal position of trench (km)T (°C)
400

900

1,400

Drilling results allow us to test subduction initiation models. International Ocean Discovery Program Expedition 352 recovered a continuous, in situ
record of subduction initiation from a segment of the forearc of the Izu-Bonin-Mariana subduction system. (a) Cores show a distinct magmatic progression from mid-ocean ridge-like forearc basalts (FAB) to volatile-rich “boninite” lavas took place over approximately 1 million years (Reagan et al., 2019,https://doi.org/10.1016/j.epsl.2018.11.020). (b) Dynamic numerical modeling reveals that subduction initiation driven by internal, vertical (buoyancy)
forces is needed to reproduce both the temporal and spatial distribution of magmatic products observed in the Expedition 352 cores. Previously models
invoking horizontal external forces are unable to generate the lava types or their distributions. Overlain on the dynamic model results are: regions
where decompression melting is occurring (black outline), regions where melting is occurring in the presence of slab fluid (blue outline), and the regionof the subducting crust that has crossed its solidus (green outline). Modified from Maunder et al. (2020), https://doi.org/10.1038/s41467-020-15737-4

28

STRATEGICOBJECTIVE

arcs, and it will contribute to understanding global-scaleelement fractionation by adding a temporal perspectiveon the scale of millions of years. By combining knowledge
gained from hard rocks and volcaniclastics recovered byscientific ocean drilling with that of widespread (airfall)
tephra deposits on land, we can gain a better understanding of the total mass outflux in volcanic arcs that in turn will
provide a missing component in modeling the overall massbalances across subduction zones.

SUBDUCTION INITIATION
The mechanics of how the subduction process starts isenigmatic. Incipient subduction zones—where oceanic
lithosphere begins to descend into the upper mantle—arerare in today’s plate tectonic configuration. Yet, they are
ideal locations for scientific ocean drilling to test hypotheses about how differences in buoyancy, composition, andlithosphere structure across either convergent, divergent,or transform plate boundaries set the stage for subduction.
A major outstanding question is whether the start of a
new subduction zone is a spontaneous tectonic event or
is induced by a far-field change in Earth’s plate tectonic
configuration, including changes in global plate motion
or the possible presence of mantle plumes. Another major
question is whether there have been peaks and a periodicity in subduction initiation and related increases in arc
volcanism over geologic time. Because subduction is athree-dimensional process, generating regional tectonic
syntheses that combine geophysical and scientific ocean
drilling results will allow us to evaluate the fundamental
structural and magmatic processes involved in the birth of
new subduction zones. Understanding the roles of thermallithospheric rejuvenation, preexisting adjacent transform
faults, differences in crustal age of the downgoing oceanic
lithosphere, and the presence of stretched continental ribbons or transpressional margins is still strongly debated.
Scientific ocean drilling also allows us to delve into thepossibilities that subduction may initiate in Earth’s upper
mantle, that it may start synchronously along entire edgesof single tectonic plates, and that initiation of subduction
itself may cause major changes in the global subduction
zone configuration and in the overall network of interconnected plate tectonic motions.

2

THE OCEANIC LIFE CYCLE OF TECTONIC PLATESFURTHER READING
Alt, J.C., C. Laverne, R.M. Coggon, D.A.H. Teagle, N.R. Banerjee, S. Morgan,
C.E. Smith-Duque, M. Harris, and L. Galli. 2010. Subsurface structure ofa submarine hydrothermal system in ocean crust formed at the East
Pacific Rise, ODP/IODP Site 1256. Geochemistry, Geophysics, Geosystems
11(10), https://doi.org/10.1029/2010GC003144.
Blackman, D.K., B. Ildefonse, B.E. John, Y. Ohara, D.J. Miller, N. Abe,
M. Abratis, E.S. Andal, M. Andreani, S. Awaji, and others. 2011. Drilling
constraints on lithospheric accretion and evolution at Atlantis Massif,
Mid-Atlantic Ridge 30°N. Journal of Geophysical Research 116, B07103,
https://doi.org/10.1029/2010JB007931.
Clapham, M.E., and P.R. Renne.2019. Flood basalts and mass extinctions. Annual Review of Earth and Planetary Sciences 47:275–303,
https://doi.org/​10.1146/annurev-earth-053018-060136.
Coogan, L.A., and K.M. Gillis. 2018. Low-temperature alteration of
the seafloor: Impacts on ocean chemistry. Annual Review of Earthand Planetary Sciences 46(1):21–45, https://doi.org/10.1146/
annurev-earth-082517-010027.
Crameri, F., C.P. Conrad, L. Montési, and C.R. Lithgow-Bertelloni. 2019.
The dynamic life of an oceanic plate. Tectonophysics 760:107–135,
https://doi.org/10.1016/j.tecto.2018.03.016.
Dick, H.J.B., C.J. MacLeod, P. Blum, N. Abe, D.K. Blackman, J.A. Bowles,
M.J. Cheadle, K. Cho, J. Ciążela, J.R. Deans, and others. 2019. Dynamic
accretion beneath a slow-spreading ridge segment: IODP Hole
1473A and the Atlantis Bank Oceanic Core Complex. Journal ofGeophysical Research 124(12):12,631–12,659, https://doi.org/​10.1029/​
2018JB016858.
Gillis, K.M., J.E. Snow, A. Klaus, N. Abe, Á.B. Adrião, N. Akizawa,
G. Ceuleneer, M.J. Cheadle, K. Faak, T.J. Falloon, and others. 2014.
Primitive layered gabbros from fast-spreading lower oceanic crust.
Nature 505(7482):204–207, https://doi.org/10.1038/nature12778.
Hirano, N., E. Takahashi, J. Yamamoto, N. Abe, S.P. Ingle, I. Kaneoka,
T. Hirata, J.-I. Kimura, T. Ishii, Y. Ogawa, and others. 2006. Volcanism
in response to plate flexure. Science 313(5792):1,426–1,428,
https://doi.org/​10.1126/science.1128235.
Ildefonse, B., D.K. Blackman, B.E. John, Y. Ohara, D.J. Miller, andC.J. MacLeod. 2007. Oceanic core complexes and crustal accretion at
slow-spreading ridges. Geology 35(7):623–626, https://doi.org/10.1130/
G23531A.1.
Koppers, A.A.P., and A.B. Watts. 2010. Intraplate seamounts as a window
into deep earth processes. Oceanography 23(1):42–57, https://doi.org/​
10.5670/oceanog.2010.61.
Lymer, G., D.J.F. Cresswell, T.J. Reston, J.M. Bull, D.S. Sawyer, J.K. Morgan,
C. Stevenson, A. Causer, T.A. Minshull, and D.J. Shillington. 2019.
3D development of detachment faulting during continental breakup.
Earth and Planetary Science Letters 515:90–99, https://doi.org/10.1016/​
j.epsl.2019.03.018.
McNeill, L.C., D.J. Shillington, G.D.O. Carter, J.D. Everest, R.L. Gawthorpe,
C. Miller, M.P. Phillips, R.E.L.l. Collier, A. Cvetkoska, G. De Gelder, andothers. 2019. High-resolution record reveals climate-driven environmental and sedimentary changes in an active rift. Scientific Reports
9:3116, https://doi.org/10.1038/s41598-019-40022-w.
Neal, C.R., M.F. Coffin, and W.W. Sager. 2019. Contributions of scientificocean drilling to understanding the emplacement of submarine large
igneous provinces and their effects on the environment. Oceanography32(1):176–192, https://doi.org/10.5670/oceanog.2019.142.
Plank, T., and C.E. Manning. 2019. Subducting carbon. Nature574(7778):343–352, https://doi.org/10.1038/s41586-019-1643-z.
Stern, R.J., and T. Gerya. 2018. Subduction initiation in nature and models:A review. Tectonophysics 746:173–198, https://doi.org/10.1016/​
j.tecto.2017.10.014.

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3 EARTH’S CLIMATE SYSTEM

Examining variations in ice sheets, ocean and atmosphere dynamics, and sea level

SUMMARY
Marine sediments contain the most complete record of the processes, mechanisms, and impacts of natural climate variability
and long-term changes to Earth’s climate system on timescales from annual to hundreds of millions of years. Scientific ocean
drilling can increase the continuity, resolution, and accuracy of paleoclimate reconstructions to enhance our understandingof how Earth’s climate system operates. Major advancements are expected by systematically mapping out the relationshipbetween orbital variability and Earth’s climate, the roles the ocean and continental weathering play in regulating atmospheric greenhouse gases, and the coupled role oceanic and atmospheric circulation play in distributing heat and water
across the planet. A key focus will be to document the onset, interconnectivity, and resilience of potentially vulnerable
components of the modern climate system, including the global ocean meridional overturning circulation, sea ice and ice
sheets, and patterns of precipitation and aridity. By targeting how the climate system operates across a wide array of past
climate states, scientific ocean drilling will obtain the data necessary to calibrate and improve numerical models used toproject future climate impacts and inform mitigation strategies.

DRILLING TO UNDERSTAND THE
CLIMATE SYSTEM
Accounting for 71% of Earth’s surface area, the ocean
plays a central role in the climate system. The ocean stores
1,000 times more heat than the atmosphere, redistributing
this heat through ocean circulation. The ocean also plays
a primary role in the global cycling of carbon, which isimportant in regulating global temperatures and Earth’s
climate by controlling the amount of CO2 in the atmosphere. Ocean water also stores 60 times more carbon than
the atmosphere, but beneath the ocean, even larger quantities of carbon are stored within deeply buried sediments
and in the altered oceanic crust, both of which are recycled
through subduction. This large marine sediment and rocksink for carbon is not well characterized. We can use physical, biological, and chemical signatures in marine sedimentary archives to reveal changes to marine environments
and to terrestrial features, including vegetation, rainfall anddroughts, weathering and the uplift and erosion of mountains, winds, and ice sheets. Acquisition of such information through scientific ocean drilling allows us to address
important questions about Earth’s climate system such as:

30

How does the climate system operate under high atmospheric CO2 concentrations? How does it respond to icefree polar oceans? How resilient are low-latitude monsoon
systems to elevated global temperatures and altered patterns of ocean and atmospheric circulation? How rapidly
and frequently have ice sheet-driven variations in sea leveloccurred in the geologic past?
Past warmer climate analogues. More than 80% of themodern ocean basins were created during the last 100 million years. Past decades of scientific ocean drilling haveallowed us to start reconstructing the warmer climates(such as during the Cretaceous, about 115–66 million yearsago) that followed the breakup of supercontinent Pangaea
and the birth of the Atlantic and Southern Oceans. We havestarted to document the long-term cooling trend and thedevelopment of continental ice on Antarctica over the
past 50 million years and the development of Northern
Hemisphere ice ages in the last few million years. Much
remains to be discovered about the regional patterns ofclimate variability and change, driving mechanisms andrates of change, and the feedbacks and tipping points
that cause irreversible changes.

3

STRATEGICOBJECTIVE

Natural climate variability. In the past century, atmospheric greenhouse gas and aerosol levels have increased,leading to the warming of surface and deep ocean waters,
accelerating rates of sea level rise, the rapid retreat ofpolar and glacial ice, and the emergence of more extreme
and less predictable weather patterns. Climate change isthreatening the infrastructure and resource dependenceof communities across the planet, as exemplified by the
wildfires in Australia and California and the inundation ofPacific islands by increasing sea levels. Humans are now a
key factor in Earth’s climate system, and to understand how

EARTH’S CLIMATE SYSTEM

we are perturbing its inner workings, we must first resolve
the relationships among its basic components and elucidate the driving mechanisms of observed climate change
in the geologic past. We will use the marine sedimentaryarchive collected through scientific ocean drilling to document the influence of orbital variability, carbon storage inthe ocean, tectonic processes, and plate configurations on
the magnitude and origin of natural climate variability atannual through million-year timescales. This information
can be used to improve future climate change projections
and determine the consequences for Earth’s habitability.

Definition of the Climate System
Earth’s climate system consists of five major components: the atmosphere, hydrosphere, cryosphere, lithosphere, and biosphere. The interactions among the components dictate the distributionof heat and water across our planet over timescales from annual and decadal to millions of years.
The climate system is fueled primarily by the amount and distribution of solar energy that reaches
Earth’s surface. It evolves under the influence of external forcings such as volcanic eruptions and solar
variations, as well as internal feedbacks among its components. Illustration by Geo Prose

Solar Energy
Greenhouse
Gases

Atmospheric Circulation Cells

Polar
Jet Stream

Subtropical
Jet Stream

PolarAir

Temperate Air

CarbonExchange

Ice
Sheet

Volcanic
Activity

Heat
Sea Ice

Tropical Air

Clouds andPrecipitation
Wind

Evaporation

Upwelling
Sea Level

Sinking

Plate Motion

Mid-Ocean
Ridge
SpreadingSu

Photosynthesis
not to scale

Aridity

bd

uc

tio

n

Weathering

River Runoﬀ

Photosynthesis

31

3

STRATEGICOBJECTIVE

EARTH’S CLIMATE SYSTEMMILLIONS OF YEARS BEFORE PRESENT
Global Oceanic
Anoxic Event II
100

K/Pg Impact
Event

90

80

EPOCH

Upper Cretaceous

PERIOD

Cretaceous

70

Paleocene/Eocene
Thermal Maximum
60
Paleocene

50

First ContinentalScale Antarctic
Ice Sheet Develops

Mid-Miocene Large
ClimateNorthern
Optimum Ice Sheets

40

20

Eocene30
Oligocene

Paleogene

100Plio Qt

MioceneNeogeneQt–1

Warmerand/orLess Ice

0
1

150
2
100

Coolerand/orMore Ice

Sea Level (m)500Estimates fromSeismic Stratigraphy

3

Benthic δ18O (‰)

PaciﬁcNorth Atlantic
South Atlantic
Southern Ocean

4
5

–50

Calibrated Using Microfossil
Geochemical Proxies

–100

–150

90 Ma
60 Ma
30 Ma
0.02 Ma
Last Glacial Maximum
One hundred million years of climate change captured in scientific ocean drilling records. Significant paleogeographic reorganization and key events inEarth history accompanied a long-term cooling trend that culminated in the development of permanent ice sheets in the polar regions. The geochemicalcomposition (δ18O) of benthic microfossils shown here provides a tool for reconstructing bottom-water temperatures in different ocean basins andcalibrating records of global ice volume and sea level change. (Qt = Quaternary, Plio = Pliocene). The most recent estimate of sea level change for the
Cenozoic is shown and is based on a spliced record derived from multiple scientific ocean drilling cores, while estimates further back in time are largely
based on seismic stratigraphy estimates. The global maps show the changing configuration of the continents and ocean through time (boundary
conditions of the climate system), as well as the extent of the cryosphere. Sources: Cramer et al. (2009), https://doi.org/10.1029/2008PA001683;
Miller et al. (2020), https://doi.org/10.1126/sciadv.aaz1346; Scotese (2016), PALEOMAP PaleoAtlas for GPlates and the PaleoData Plotter Program;
https://www.earthbyte.org/paleomap-paleoatlas-for-gplates/

32

STRATEGICOBJECTIVE

OCEAN CIRCULATION AS A TRIGGER
FOR CLIMATE CHANGE
To understand how Earth’s climate system operates requires
documenting past changes in ocean circulation patterns.
More solar energy reaches the tropics than the poles,
resulting in a latitudinal temperature gradient that drives
atmospheric and oceanic circulation and the location of
windfields and biologically active oceanic frontal zones.
The poleward transport of warm, salty waters, which thencool and sink at high latitudes, propels the modern global
ocean thermohaline circulation. This flow transports heat,carbon, oxygen, and other nutrients around the planet, andprofoundly influences precipitation and temperatures overthe continents. Future scientific ocean drilling is required
to identify the processes that modify ocean deepwater
formation to the point that global thermohaline circulation
patterns are destabilized and to determine the role theopening and closing of tectonic gateways play in modifying ocean circulation patterns over geologic timescales.
Deepwater formation and ocean circulation stability. Today, the temperature gradient between the equator and poles is amplified by the large amount of incoming
solar radiation reflected back into space from polar ice caps
and sea ice. This was not always the case in the geologic
past and may not be so in our future. It is hypothesizedthat continued loss of polar ice will reduce equator-topole temperature gradients and produce more freshwaterrunoff that will impede deepwater production in the polar
regions. The tipping points in the global ocean circulation,and the broader climatic consequences of exceeding them,
are not well understood. Results from climate models thatinvestigate these interrelated processes require groundtruthing based on past analogues that are only obtainable through scientific ocean drilling. Future scientificocean drilling will assess the stability of our modern global
ocean circulation system in different climate states andidentify mechanisms and tipping points that cause it tochange. High-resolution centennial- through millennial-​
scale records are particularly pertinent for tracing patternsof deepwater convection during past interglacial intervals
and can provide analogues of possible future perturbations to ocean circulation.
Oceanic gateway configurations. Scientific ocean
drilling has shown that the locus of deepwater formation
has shifted in the past between the Pacific and Atlantic
Oceans. This seems to be the case in the warmer climates

3

EARTH’S CLIMATE SYSTEM

of the Paleogene and even the more recent Pliocene, but
the mechanisms generating this dynamic behavior, andwhether it acts as a trigger for or response to climatechange, is uncertain. Over the geologic past, the formation and destruction of oceanic lithosphere has moved
continents, opened and closed oceanic gateways, raised
mountains, and thus changed the world’s geography andtopography. These changes in the shape and configurationof ocean basins are primary controls on ocean circulation
patterns and can be reconstructed based on understanding the history of tectonic plate dynamics. Robust tectonic
reconstructions of our ocean basins are needed to understand the mechanisms driving long-term changes in ocean

We will use the marine sedimentary archive
collected through scientific ocean drilling to
document the influence of orbital variability, carbon
storage in the ocean, tectonic processes, andplate configurations on the magnitude and originof natural climate variability at annual
through million-year timescales.

circulation and the related climatic and environmental
consequences. Establishing and validating the influence of
seaways and bathymetric sills on global ocean circulation
is particularly important as their limited geographic extent,
shallow water depths, and dynamic behavior make themdifficult to accurately represent in many models used toinvestigate the global climate system. However, we don’t
understand the histories behind the opening and closing of
those gateways very well. For example, recently there havebeen strong challenges to the hypothesis that the closureof the Central American Seaway was relatively recent, andthe relationship between the opening of the Drake Passage
and changes to global ocean circulation is still strongly
debated. New drilling strategies and targets, for example,
along land-to-sea transects, are needed to resolve theinfluence of ocean basin configuration on global ocean
thermohaline circulation patterns during key climate states
and across critical climate transitions of the past.

33

STRATEGICOBJECTIVE

3

EARTH’S CLIMATE SYSTEM

Critical Oceanic Gateways and Global Thermohaline Circulation
FRAM STRAIT

GREENLAND-SCOTLAND RIDGE
An active seafloor ridge related to Iceland volcanism, whose
dynamic topography controls exit of dense polar watersfrom the Nordic seas to the Atlantic; subsided through theearly-middle Eocene with considerable Neogene variability.

CENTRAL AMERICAN SEAWAY

The only deepwater connection between the Arctic andthe world ocean, allowing exchange between the Arctic andNorwegian-Greenland Sea; open since the middle Miocene.

BARENTS SEA
A shallow seaway allowing inflow of warm Atlantic
waters into the Arctic. Likely aerially exposed for mostof the Paleogene and Neogene, achieving its current
depth due to Quaternary glacial activity.

Narrow land bridge connecting North andSouth America and blocking low-latitude
exchange between the Atlantic and Pacific
Oceans; formed by the early Pliocene.

BERING STRAIT
A shallow, narrow seaway connecting theArctic and Pacific Oceans that first became
submerged near the end of the Miocene.

INDONESIAN SEAWAYSTRAIT OF GIBRALTAR
A narrow seaway allowing exchange
between the Atlantic Ocean andMediterranean Sea, whose closurein the latest Miocene led to the drying out of the Mediterranean.

DRAKE PASSAGE
A deep oceanic gateway between Antarctica andSouth America allowing circum-Antarctic flow;
opened through the late Eocene to Miocene.

A now constricted shallow seaway affecting tropical surface inflow from the Pacific to the Indian
Ocean; established by the early Pliocene.

TASMAN GATEWAY
A deep oceanic gateway between Antarctica
and Tasmania allowing circum-Antarctic flow;
opened through the middle to late Eocene.

TETHYS OCEAN
A major tropical seaway that connected the Indian and
Atlantic Oceans during the Cretaceous to Eocene. The
eastern Tethys closed during the Oligocene to Miocene.

Changes in the shape and configuration of ocean basins are primary controls on ocean circulation patterns. Scientific ocean drilling provides the dataneeded to make robust tectonic reconstructions of ocean basins, permitting a better understanding of the mechanisms driving long-term changes inocean circulation and the related climatic and environmental consequences. This figures is a simplified representation of the global ocean conveyor(blue and red arrows) and critical gateways (orange) that have influenced ocean circulation during the past 100 million years to various extents. Purple
ovals are sites of deepwater formation. Red arrows = Surface currents. Blue arrows = Deep currents. Arrow width indicates relative current strength.
Illustration by Matt O’Regan. Sources: Ocean bathymetry from GEBCO, https://www.gebco.net/; Land mask from NASA Blue Marble; thermohaline circulation modified from NASA Scientific Visualization Studio, https://svs.gsfc.nasa.gov/3881.

34

STRATEGICOBJECTIVE

CHANGING PATTERNS OF
RAINFALL AND DROUGHT
Given the vast societal and ecological consequences ofchanges in rainfall and drought patterns—and associatedincreases in flooding and desertification—there is a pressing need to resolve the interactions within Earth’s climate
system that can alter the global hydrological cycle.
Scientific ocean drilling provides access to slowly and continuously accumulating sediments in the ocean basins thatrecord past extreme climate episodes. Sediment proxies for
rainfall allow mapping of major global monsoon systems.
Mineral dust plumes originating in deserts that were blownout to sea by prevailing winds record progressions toward
greater (glacial) aridity in Earth’s past.
Monsoon systems. Characterized by seasonally reversing winds that bring highly seasonal and abundant rainfall to many of the most densely populated tropical andsubtropical zones, monsoon systems are a critical sourceof water to billions of people. Monsoons are also one of
the most dynamic components of the global hydrological

EARTH’S CLIMATE SYSTEM

cycle on multiple timescales. Scientific ocean drilling canprovide the basic data needed for a global synthesis of
monsoon variations across tectonic, orbital, and millennial
timescales. Past drilling, particularly over the last 10 years,
has contributed the longest high-resolution recordsof regional monsoon activity and documented orbital
controls on its variability back into the Miocene. Futuredrilling is required to balance the geographic distributionof monsoon records, which are currently biased toward
the Northern Hemisphere, and push the overall temporal
range into the greenhouse climates of the Paleogene andCretaceous. These longer-term records can answer important questions about how the monsoons operate in warmer
climates of the past and respond to major global climatechange events, including the inception of polar ice sheets
and sea ice and large-scale perturbations to oceanic andatmospheric circulation. A major questions to answer is
how does seasonality impact our interpretation of pastmonsoonal summer versus winter circulation patterns.
We also need to use scientific ocean drilling and improved
proxies to better differentiate between changing wind,rainfall, and ocean surface circulation patterns.

60°N

North
American

3

South
Asian

North
AfricanEast
AsianWestern
North
Paciﬁc0°SouthAmericanAustralianSouth
African

60°S

120°W

60°W

0°
2

4
6
mm/day

60°E
8

>10

120°E

100 200
Millions of People
per Degree of Latitude

Scientific ocean drilling has contributed to investigations of monsoon systems that impact a significant portion of the world’s population (plot onright). It has provided long, high-resolution records of regional monsoon activity and documented orbital controls on its variability back into the
Miocene (~23 million years ago) to answer questions about how monsoons responded to past climate warming. The map shows global monsoon
regions (white rectangles and labels), illustrated using the average difference in precipitation (mm/day) between Northern Hemisphere summer(June–August) and winter (December–February) between 1979 and 2018. Future drilling will balance the geographic distribution of monsoon records,
which are currently biased toward the Northern Hemisphere, and push the temporal range back to the Paleogene and Cretaceous. Sources: Precipitation:
Climate Prediction Center Merged Analysis of Precipitation 1979–2018; Population: Center for International Earth Science Information Network (CIESIN),
Columbia University (2018)35

STRATEGICOBJECTIVE

3

EARTH’S CLIMATE SYSTEMThe Orbital Heartbeat of Climate Changefooting, as fundamental uncertainties in orbital solutions remain,
and the Cretaceous is still a major work in progress that mostly
lacks orbital control. Equally important to climate science is understanding how subtle shifts in Earth’s orbit propagate through the
Earth system and how changing boundary conditions in Earth’s
climate system have amplified or dampened the climatic response.
Increased temporal and spatial resolutions are vital to be able tomeaningfully investigate the timing of inter-ocean phenomena
such as changing polar ice cover, tectonic processes, atmosphericand oceanic circulation, movement of species and nutrients, andcarbon cycling at century to millennial resolutions. Future scientific ocean drilling requires high-quality sediment cores with significantly increased temporal resolution, as well as the use of big
data analytics, to tease out inter-basin and latitudinal differencesin the expression of astronomically paced climate cycles. These
improved timescales are vital to understanding feedbacks in the
Earth system, the pace at which tipping points are traversed, andthe importance of large igneous provinces and bolide impacts aspotential drivers of mass extinctions.

C22

1262
2

δ 13 C (‰)

22.5°
22.5°
22.5°
22.5°
24.5°
24.5°
24.5°
24.5°

EECO

MECO

1258

1263

1209

U1410

1

0

K/Pg

1260

–1

36

Bartonian

3

OBLIQUITYOBLIQUITYOBLIQUITYOBLIQUITY
4141
41
thousandthousand
years
years
thousandyears
41 thousand years

PRECESSIONPRECESSIONPRECESSIONPRECESSION
19–23
19–23
thousandthousand
years
years
19–23
thousandyears
19–23 thousand years

C19
C18

Lutetian

Ypresian
C23

Thanetian
C25

C24

Selandian

C28

C29

C30

Age

EoceneC26

DanianPaleocene

C20

Epoch

C27

ECCENTRICITYECCENTRICITYECCENTRICITYECCENTRICITY
100–400
100–400
thousandthousand
years
years
100–400
thousandyears
100–400 thousand years

C21

To decipher the causes, consequences, and interconnections ofEarth climate and other environmental processes, it is essential
to understand the temporal relationship of their signatures in thegeologic record. The highest possible quality chronostratigraphy
is key to understanding the timing of critical events. Periodic
climate variations that arise from changes to Earth’s orbit on
timescales of tens to hundreds of thousands of years are exquisitely preserved in marine sediments. These orbital (Milankovitch)
forcings alter the amount and distribution of solar energy reaching Earth in a predictable way, but the climatic response to these
forcings is highly variable and nonlinear. Scientific ocean drilling
was instrumental in identifying pervasive orbital signals in marine
sediments worldwide and continues to facilitate and augment
the construction of a highly resolved astronomical timescale forthe past 66 million years.
Extensive new work is required to achieve a complete orbitally tuned Cenozoic and Cretaceous timescale that allows us tocorrelate global records of temperature, precipitation, and icevolume. The timescale prior to 40 million years ago requires firmer

PETM

Early Eocene
hyperthermals

–2
65

60

1218

55

Age (Ma)

50

45

40

Predictable changes in Earth’s orbit alter the amount and distribution of solar energy reaching Earth’s
atmosphere. Scientific ocean drilling has shown that these Milankovitch cycles (left panels), which operate
on timescales between 100,000 and 400,000 years (eccentricity), 41,000 years (obliquity), and 19,000 and
23,000 years (precession), have a profound impact on Earth’s climate and are captured in the physical, biological, and chemical composition of marine sediments. Marine sediments provide a fundamental tool fordeveloping geochronology and the geologic timescale. The different colors of the δ13C records in the rightpanel correspond to different scientific ocean drilling sites. EECO = Early Eocene Climatic Optimum. K/Pg
= Cretaceous-Paleogene boundary. MECO = Middle Eocene Climatic Optimum. PETM = Paleocene-Eocene
Thermal Maximum. Source: Modified from Littler et al. (2019), https://doi.org/​10.5670/oceanog.2019.122

STRATEGICOBJECTIVE

Aridity and past desertification. Scientific ocean drilling cores containing oceanic dust generated from the continents of Africa, Arabia, and Australia provide evidence ofintervals of extreme droughts and expanding deserts overthe last tens of millions of years. Multiple hypotheses havebeen developed for explaining these periods, including one
that postulates an anti-correlation between the extent of,for example, the Sahara Desert and the African Monsoon
during glacial and interglacial periods, respectively, andanother that suggests they were the result of major changes
in ocean circulation patterns. Future scientific ocean drilling
offshore major continental land masses and along land-tosea transects (including collecting sediment cores in lakes)
are required to further test those hypotheses and to reveal
the more detailed histories of aridification on land. These
results will have direct consequences for understanding
currently changing desertification patterns and the increasing number of wildfires, where the dynamics between
desertification and monsoonal systems are likely to shift
assuming a continued global warming trajectory for Earth.

TELECONNECTIONS IN THE
CLIMATE SYSTEM
Other central features in Earth’s climate system are natural climate oscillations arising from the exchange of heatand moisture, and other feedback processes, between theocean and atmosphere on interannual, multidecadal, andorbital (20–400 kyr) timescales. This interplay between
processes in the ocean and atmosphere are described as
teleconnections in the climate system. A prominent example of a climate teleconnection is the El Niño-Southern
Oscillation (ENSO). Improving our understanding of how
the ocean and atmosphere interact is an a priori requirement for making decadal through centennial-scale climate
predictions. Through collection of high-resolution marine
paleoclimate archives from across the globe, scientificocean drilling can provide high-fidelity records that document natural variability in the frequency and magnitudeof these climate phenomena and establish how far-fieldprocesses (i.e., Asian monsoons and ENSO) are connected.
There is also a need to establish whether this type of naturalinterannual to multidecadal climate oscillations originate
from internal climate dynamics and feedback processes orare forced by changes in solar radiation, a question that isdifficult to fully investigate using the relatively short instrumental time series of modern climate. Exploring the origins
and establishing the teleconnections between highfrequency climate variability presents a particular chal-

3

EARTH’S CLIMATE SYSTEM

lenge for future scientific ocean drilling. It requires acquiring high-resolution time series from the Arctic, to the equator, to the Southern Ocean and working closely with theterrestrial and ice core drilling communities to effectively
integrate marine records with other paleoclimate archives.

THE ROLE OF POLAR ICE
The cryosphere, a primary component of Earth’s climate
system, can change rapidly and over broad regions. The
rapid modern melting of sea ice in the Arctic, and accelerated losses of glacial ice on Antarctica and Greenland,
are trends that pose real concerns for society. Establishingthe impact of these observed trends and elucidating therole of polar ice in Earth’s climate system requires drilling
beneath the polar oceans to establish the geologic historyof the cryosphere.

Scientific ocean drilling can provide thebasic data needed for a global synthesis of
monsoon variations across tectonic, orbital,
and millennial timescales.

High-latitude polar climate records. Scientific ocean
drilling has provided the only Cenozoic marine climate
record from the Arctic Ocean and, through multiple
expeditions, has contributed considerable insights into
the development of the Antarctic ice sheet. Yet, too few
drilling records from high-latitude regions exist to fully
document the geologic history of the cryosphere and ultimately evaluate its feedbacks within the climate system.
For example, while we know that seasonal sea ice existed
briefly in the Arctic as far back as the Cretaceous, we areunable to say when perennial sea ice first formed, whatmechanisms allowed it to form, and how variable it has
been. Other important questions include the extent anddynamics of the Greenland and Antarctic ice sheets during
the long-term global cooling that occurred through the
Neogene and across glacial and interglacial intervals of the
Quaternary. On longer timescales, the extent of Antarctic
ice sheets and bi-polar sea ice in warmer pre-Oligocene
greenhouse climates, and the possible impact they hadon other facets of the global climate system, still needs
to be determined.

37

3

STRATEGICOBJECTIVE

EARTH’S CLIMATE SYSTEM

Polar amplification. The geologic history of the cryosphere must be better resolved if we are to understandpast and future changes in the climate system. Enhanced
poleward transport of heat, the increased absorptionof solar radiation as snow and ice melt, and topographic
changes associated with changing ice cover are thought tocause polar amplification of temperatures—a phenomenon
whereby any change in the net solar radiation fueling theclimate system produces a greater change in temperaturenear the poles than the planetary average. Studies of latitudinal temperature gradients between scientific ocean drilling boreholes document the magnitudes of polar amplification of temperature in the geologic past, and diverse
records of sea surface and terrestrial temperatures reveal
notably higher past polar temperatures, as exemplified bypalm trees in Antarctica, breadfruit trees in Greenland, andalligators in the Arctic. However, the exact amplification
processes are not well understood and numerical climate
models still have trouble explaining how the poles could bewarm enough to sustain these plants and animals throughthe polar winter. This suggests that we may be missing fundamental dynamics in the climate system that may affectour models of a future, possibly much warmer, Earth. What
were the magnitudes and mechanisms driving polar amplification in the warmer and higher CO2 climates of the past?
Answering this question is imperative to understanding
the implications of modern climate change and projecting
the cascading effects of continued polar warming in our
future climate system. To this end, scientific ocean drilling
will reconstruct the geologic history of Earth’s cryosphere,in particular, to constrain the magnitudes and effects ofpolar amplification.
Cryosphere feedbacks. The integration of polar records
with existing and new climate archives from tropical andextratropical regions will allow us to assess feedbacks
between the cryosphere and other components of the climate system. For example, an important, recently observed
feedback in the Earth system concerns the weakening andbroader meandering of the polar jet stream as the Arctic

4.8 m

Antarctic

ArcticPermafrost
Ice
Shelves

West
Antarctica
Sea Ice

Sea Ice
East
Antarctica

4,000 km54.2 m

DSDP
ODP
IODP

Greenland
Ice Sheet

7.4 m

Major components of Earth’s cryosphere, with the bi-polar extent of sea ice shown from June 21, 2019. Past scientific ocean drillingsites located at latitudes greater than 55° illustrate both the ongoing efforts to unravel the evolution and dynamics of the cryosphereandsome ofMajor
the understudied
regionsaroundthe crysophere
Antarctic continent
withinthe Arcticthat innovative
Caption:componentsof theEarth’sin theandpolar
regions
withOcean
the bi-polar
extentdrillingof seastrategies,
iceo expected fromplatforms,
and tools
to target.
The ocean
circular drilling
thermostats
the average
sea level
rise that
illsutrate bothshown from
Junenow
21st,enable
2019.usPast
scientificsitesshow
locatedat latitudes
greaterthancan55be
theof these
ice sheets.
DSDPthe= DeepSea Drilling
Project. ODP
Ocean
Drilling Program.
IODPof= theIntegrated
Ocean Drillingthemelting
on-going
efforts
to unravel
evolutionand dynamics
of=thecrysophereand some
undertsudied
ProgramInternational
Ocean Discovery
Program.
Illustration
Mattocean,
O’Reganthat innovative drilling stratgies, platforms
regionsand
aroundthe Antarctic
continent,
and within
the byArcticand tools now enable us to target.

38

STRATEGICOBJECTIVE

warms, which alters weather and climate patterns acrossmuch of the Northern Hemisphere. Other feedbacks
between Arctic and global climate include thawing of
permafrost, accelerated erosion of polar coastlines, andthe destabilization of gas hydrates that may all inject large
amounts of greenhouse gases in the atmosphere, further
acidifying ocean waters. What were the past magnitudes
and rates of carbon release from these poorly constrained
reservoirs? What influence did they have on local biologic
systems and global climate processes? Answers to thesequestions remain locked in high-latitude marine sediments and are only obtainable through scientific drillingin polar oceans.

ICE SHEETS AND SEA LEVEL RISE
Changes in global sea level over the past 50 million years
are largely the result of the waxing and waning of polar
ice sheets. At present, around 10% of Earth’s land area iscovered by ice sheets, with the potential to raise global
sea level by over 65 m should all ice melt. Scientific ocean
drilling has provided the only firm control on global ice volume prior to the Last Glacial Maximum (around 20,000 to
26,000 years ago) by dating glacial advances across polar
continental margins and through analyses of the geochemical composition of marine microfossils. Results from past
drilling now underpin global sea level reconstructions forthe past 100 million years. Future scientific ocean drilling
will significantly improve the fidelity of ice sheet and sea
level records to better delineate rates and magnitudes ofsea level rise and the processes and events that influenced
past global patterns of sea level change.
Understanding past global sea level change in Earth’s
climate system requires separation of regional tectonic
and glacio-isostatic processes from global changes. Firm
constraints on past sea levels and identifying regions of
ice sheet melt that contributed to these sea level variations require a portfolio of globally distributed recordsof sea level change. Marine-based ice sheets are highly
sensitive to the warming of both ocean and atmosphere.
This fact, combined with uncertainties relating to polar
amplification, ocean-​ice sheet interactions, subglacialhydrology, and dynamic ice processes, lead to serious
concerns that model-​based projections of sea level rise
are underestimated and thus call for greater efforts inground truthing future climate change. We may beapproaching, or have already crossed, the tipping point
for ice sheet collapse in West Antarctica and many of themarine-terminating outlet glaciers draining the Greenland

3

EARTH’S CLIMATE SYSTEM

ice sheet. Scientific ocean drilling provides the only meansof sampling the geologic record on continental margins
that have major ice sheets, which will generate the critical
data needed to build and constrain models for future projections. The need is pressing for scientific ocean drilling todeliver high-quality “ice proximal” records that document
past times of ice sheet collapse, capture major changes inocean and atmospheric circulation, and test and improvemodels that project future sea level rise.

FURTHER READING
Adkins, J.F. 2013. The role of deep ocean circulation in setting glacial
climates. Paleoceanography 28(3):539–561, https://doi.org/10.1002/
palo.20046.
Böhm, E., J. Lippold, M. Gutjahr, M. Frank, P. Blaser, B. Antz, J. Fohlmeister,N. Frank, M.B. Andersen, and M. Deininger. 2015. Strong and deep
Atlantic meridional overturning circulation during the last glacial cycle.
Nature 517:73–76, https://doi.org/10.1038/nature14059.
Dutton, A., A.E. Carlson, A. Long, G.A. Milne, P.U. Clark, R. DeConto,
B.P. Horton, S. Rahmstorf, and M.E. Raymo. 2015. Sea-level rise due
to polar ice-sheet mass loss during past warm periods. Science349(6244):aaa4019, https://doi.org/10.1126/science.aaa4019.
Gallagher, S.J., and P.B. deMenocal. 2019. Finding dry spells in ocean
sediments. Oceanography 32(1):60–63, https://doi.org/10.5670/
oceanog.2019.120.
Gutjahr, M., A. Ridgwell, P.F. Sexton, E. Anagnostou, P.N. Pearson, H. Pälike,
R.D. Norris, E. Thomas, and G.L. Foster. 2017. Very large release of
mostly volcanic carbon during the Palaeocene–Eocene Thermal
Maximum. Nature 548:573–577, https://doi.org/10.1038/nature23646.
Littler, K., T. Westerhold, A.J. Drury, D. Liebrand, L. Lisiecki, and H. Pälike.
2019. Astronomical time keeping of Earth history: An invaluable
contribution of scientific ocean drilling. Oceanography 32(1):72–76,
https://doi.org/10.5670/oceanog.2019.122.
Miller, K.G., J.V. Browning, W.J. Schmelz, R.E. Kopp, G.S. Mountain, andJ.D. Wright. 2020. Cenozoic sea-level and cryospheric evolution fromdeep-sea geochemical and continental margin records. Science
Advances 6(20):eaaz1346, https://doi.org/10.1126/sciadv.aaz1346.
Mohtadi, M., M. Prange, and S. Steinke. 2016. Palaeoclimatic insights
into forcing and response of monsoon rainfall. Nature 533:191–199,
https://doi.org/10.1038/nature17450.
Pross, J., L. Contreras, P.K. Bijil, D.R. Greenwood, S.M. Bohaty, S. Schouten,
J.A. Bendle, U. Röhl, L. Tauxe, J.I. Raine, and others. 2012. Persistentnear-tropical warmth on the Antarctic continent during the early
Eocene epoch. Nature 488:(73–77), https://doi.org/10.1038/
nature11300.
Ruppel, C.D., and J.D. Kessler. 2017. The interaction of climatechange and methane hydrates. Reviews of Geophysics 55:126–168,
https://doi.org/10.1002/2016RG000534.
Stein, R. 2019. The late Mesozoic-Cenozoic Arctic Ocean climate andsea ice history: A challenge for past and future scientific ocean
drilling. Paleoceanography and Paleoclimatology 34(12):1,851–1,894,
https://doi.org/​10.1029/2018PA003433.
Stickley, C.E., K. St John, N. Koç, R.W. Jordan, S. Passchier, R.B. Pearce,and L.E. Kearns. 2009. Evidence for middle Eocene Arctic sea ice fromdiatoms and ice-rafted debris. Nature 460:376–379, https://doi.org/​
10.1038/nature08163.

39

4 FEEDBACKS IN
THE EARTH SYSTEMSTRATEGICOBJECTIVE

Constraining the processes that regulate or destabilize the Earth system

SUMMARY
Feedbacks that amplify or regulate processes within the Earth system are pervasive, crucial to all parts of the system, and act
on all timescales. Over long timescales, Earth system feedbacks have resulted in climate alternating between greenhouseand icehouse states, the evolution of vastly different biota during different geologic periods, and the repeated reconfiguring of continents. On shorter timescales, feedbacks between the atmosphere, ocean, and cryosphere have accelerated thegrowth and decay of ice sheets, a complex process accompanied by large changes in temperature, precipitation, sea level,and vegetation. On human timescales, changes in ocean circulation and resultant increases and decreases in heat storage
in the deep ocean have caused rapid and sustained shifts in high-latitude temperatures and precipitation. Great strides
have been made in identifying various feedbacks in the Earth system, but our knowledge of how these feedbacks operate,
how they interact, the timescales over which they are stable, and the points at which feedback loops break down is limited.
Scientific ocean drilling provides access to the long timescale records needed to investigate the many different feedbacks
within the Earth system and the effects those feedbacks had on our planet’s functioning.

TECTONICALLY DRIVEN FEEDBACKSOver millions of years, tectonic activity continually changes
the topography of Earth’s surface, reconfiguring ocean
basins and continents and uplifting mountain ranges.
Tectonic processes are components of feedback loops andthey also set the boundary conditions within which otherfeedbacks operate.
Mountain building, weathering, and atmosphericCO2. The silicate rock weathering hypothesis posits thatover million- to hundreds of million-year time­scales,there is a negative feedback between the tectonic upliftof mountains and the amount of CO2 in Earth’s atmosphere. Tectonic uplift of mountains causes “relief rainfall”
that increases mechanical erosion on steeper slopes andenhances chemical weathering rates. The amplified chemical weathering consumes more atmospheric CO2, and as
a result, causes global cooling. As cooling increases glaciation, it leads to enhanced erosion and further isostatic
uplift. Scientific ocean drilling will test the hypothesis that
this slow negative feedback regulated atmospheric CO2 in
the past in order to predict whether the Earth system canmodulate the current rapid, massive injection of carbon byhumans and over what timescale.

40

Monsoon systems. Characterized by strong seasonality
in wind and rainfall patterns, monsoons are a major component of the climate system and central to the hydrological cycle. Scientific ocean drilling has shown that althoughinsolation—the amount of solar radiation received on agiven surface in a given time period—is the primary driverof monsoon systems, tectonic features of Earth’s surface
are responsible for large regional differences among them.
Future scientific ocean drilling needs to address the fundamental unknowns in this complex nested feedback systemthat includes tectonic uplift, the timing of monsoonal
initiation, atmospheric greenhouse gas concentrations,the cryosphere, and ocean circulation. By significantly
extending both the spatial and temporal coverage ofhigh-resolution monsoon records around the world andcontinuing to develop new proxies to distinguish global
and regional components in the monsoon system, we will
be able to reveal the feedback sub-loops that together
drive monsoon variations.
Gateways and sills. Geodynamic processes, including
tectonics and plume-related magmatism, control theoccurrence and character of gateways that connect theocean basins (e.g., Drake Passage, Tasman Gateway, Fram
Strait), as well as variations in the water depths of major

STRATEGICOBJECTIVE

4

FEEDBACKS IN THE EARTH SYSTEM

Definition of an Earth System Feedback
gas concentrations causes sea ice to melt, decreasing surface
albedo. The dark ocean waters absorb more solar radiation,
resulting in more sea ice melting and enhanced ocean warming. Positive feedbacks that lead to runaway behavior are particularly important in the Earth system because they can drive
the system past a tipping point, resulting in a dramatic, often
irreversible shift in the system. One perturbation can also leadto multiple loops, some positive and some negative, as in theexample at the bottom of a subset of feedbacks that influence global temperatures. The net effect of such networks ofinterrelated processes depends on the relative strength of thedifferent feedback sub-loops, the timescales over which they
operate, and how they interact. Illustration by Rosalind Coggon

A feedback is a mechanism by which the end products of aprocess influence the ongoing operation of that process. A
perturbation to the Earth system can lead to positive and/or
negative feedbacks, as illustrated in the top panels. Negative
feedbacks (–) help regulate the Earth system and maintainits equilibrium. For example, negative feedbacks between
Earth’s rock cycle (driven primarily by plate tectonics) andglobal biogeochemical cycles (especially for carbon, hydrogen, nitrogen, and sulfur) result in a relatively stable global
climate over long timescales. In contrast, positive feedbacks(+) in the Earth system amplify the responses of processes,
possibly leading to runaway behavior. For example, climate
warming resulting from increasing atmospheric greenhouseGINM

Sea ice, mountainglaciers, andpolar ice sheets
melt

WA
R

WA
R

SIMPLE POSITIVE AND NEGATIVEFEEDBACK LOOPS+AMPLIFYINGFEEDBACKLOOPGlobaltemperature

IN–
REGULATINGFEEDBACKLOOPGlobaltemperature

O
CO

R
WA

M

Ice replaced bydarker sea andland (decreased
albedo)Increasedhydrological cycle
strength
G
IN
M

LI

G

NG

Increasedabsorption ofsolar radiation

Increased physicaland chemical
weathering

CO 2

Increased
CO 2 removal
and burial

MULTIPLE FEEDBACK LOOPS
Sea ice,mountainglaciers, andpolar ice
sheets melt

Increasedwater vapor inatmosphere++
WARMING

Enhancedgreenhouseeﬀect

Globaltemperature
COOLING

Increasedabsorbtionof solarradiation

Increased
evaporation

Weakenedgreenhouseeﬀect

Increased
vegetation
cover
Enhanced
precipitation–

Increased
physical andchemicalweathering

Increased
CO 2 removal
and burial

Decreased
dust supply+
Reducedmarineproductivity

Increased
atmospheric
CO 2

41

4

STRATEGICOBJECTIVE

FEEDBACKS IN THE EARTH SYSTEM

Weakening
Monsoon
CLIMATESTATE

Tropical(Weak Monsoon)

Variable
MonsoonDry

Monsoon0.71950.71650.71350.7115Chemical
Weathering

More clastic
ﬂux to sea

Mass FluxLesschemicalweathering

0.20
0.15
0.10
0.05
0.00

Ti/Ca
Site 1148
Sr/ 86SrLesschemicalweathering

1.1

Chemical
Weathering
MMCO

0.9

1.3

87

WEATHERING PROXIES

K /Al

0.7

Seasonal

84Moreleaching

Smectite/
Kaolinite

12
Clay
Mineralogy

CarbonIsotopesMoreseasonal

23
21
19
17
15
13

Tropical

C4
C3

4
2
0

Less
seasonal
climate∆δ C

13

Hematite/
Goethite

CLIMATE PROXIES

0

Hematite/
Goethite–2

Oligocene30

E. Miocene
25

20

Mid. Mioc.

15
Age (Ma)

L. Miocene
10

Plio.
5

Pl.
0

Robust records of both past weathering and climate are necessary to investigate the temporal relationships
between weathering and climate and, hence, the feedbacks between tectonic and climate processes. A rangeof complementary proxies allow us to reconstruct such records from drill cores, as illustrated here with a compilation of some of the more robust erosion and weathering proxies spanning 25 million years at Ocean Drilling
Program (ODP) Sites 1146 and 1148 in the South China Sea. The upper three panels are proxies for weathering:(top) chemical weathering (K/Al), (middle) mass flux (Ti/Ca) from ODP Site 1148, and (bottom) chemical weathering (Sr isotopes) from ODP Site 1148. The lower three panels are proxies for changing climate. (top) Claymineralogy (smectite/kaolinite), (middle) the difference in isotopic composition of atmospheric and terrestrial
biomass carbon from ODP Site 1148, which reflects shifts between C4 grassland and C3 woodland flora in thecontinental flood plain, and (bottom) the chemical weathering index (CRAT) proxy tracking the relative influenceof chemical weathering versus physical erosion. MMCO = Middle Miocene Climatic Optimum. Modified from
Figure 8 in Clift et al. (2014), https://doi.org/​10.1016/j.earscirev.2014.01.002

42

STRATEGICOBJECTIVE

bathymetric features such as sills (e.g., Greenland-Scotland
Ridge, Strait of Gibraltar, Isthmus of Panama, Bosporus). The
tectonic evolution of oceanic gateways and sills therefore
modifies large-scale ocean circulation, which is a component of multiple climate feedback loops. Targeted drilling
will allow us to reconstruct the timing of the opening andclosing of gateways and changes to ocean circulation patterns to determine the influence gateways have on climate
feedbacks across critical time periods in Earth’s history. For
example, it is still unclear whether large-scale reorganization of ocean circulation that resulted from the opening of
the Drake Passage preceded or followed the expansion of
glacial ice on Antarctica due to climate feedbacks during
the Eocene-Oligocene.

CRYOSPHERE-DRIVEN FEEDBACKS
Ice core records have documented decreases in atmospheric CO2 and CH4 concentrations during glacial intervals when the cryosphere expands and increases during
interglacial intervals when the cryosphere retracts. The
feedbacks responsible for driving these cycles, and thelonger-term interplay between the cryosphere and climate
system, remain widely debated. Scientific ocean drilling has
made major advances in establishing when ice sheets andsea ice nucleated and has provided evidence that changes
in Earth’s orbit drive a major feedback between insolationand cryosphere extent. Future scientific ocean drilling inpolar regions will allow us to better define the development and persistence of the cryosphere and unravel the
many feedbacks between the cryosphere and other components of the climate system.
Carbon burial during cryosphere expansion. Scientific ocean drilling allows us to test hypotheses that
address feedbacks responsible for enhancing carbon storage in seawater and marine sediments during periods ofcryosphere expansion. Examples of how carbon storage
can be enhanced include reductions to the vigor of deepwater circulation, increased nutrient delivery that can fuelthe biological pump, and the growth of sea ice that limits
air-sea gas exchange. Land-to-sea transects drilled across
Arctic shelves can test whether carbon sequestration andrelease from terrestrial and submarine permafrost also playa measurable role in climate feedbacks responsible for the
waxing and waning of ice sheets.

4

FEEDBACKS IN THE EARTH SYSTEM

Volcanic outgassing during deglaciation. It has beentheorized that stress relaxation in the mantle resulting fromdeglaciation enhances volcanic outgassing from deep
Earth magmatic sources. This outgassing increases atmospheric greenhouse gases concentrations, accelerating
warming and melting more ice. Scientific ocean drilling cantest whether volcanic outgassing drives a positive climate
feedback by documenting the frequency of volcanic ash
layers in sediments deposited at time intervals characterized by the growth or decay of the cryosphere.

Scientific ocean drilling allows us to test hypotheses
that address feedbacks responsible for enhancing
carbon storage in seawater and marine sediments
during periods of cryosphere expansion.

Ice sheet grounding and stability. Our ability toreproduce the dynamic behavior of ice sheets in climate
models and examine how ice sheets interact with the restof Earth’s climate system requires detailed knowledge of
their paleo­topography, including surface elevation andareal extent and the elevation of their underlying bedrock.
As ice sheets grow, they cool polar air masses, providing
a positive atmospheric feedback for ice sheet growth byisolating the poles and preventing intrusion of warmer
mid-latitude winds. However, ice sheet growth also introduces a negative feedback to the system. The growing ice
load slowly depresses the underlying lithosphere, causing
the ice sheet to become more marine-based as the land
subsides and ice sheet grounding lines fall below sea
level. This decreases the overall stability of the ice sheet,as marine-based components have a lower frictional coupling to the underlying substrate and are highly sensitive
to oceanic and atmospheric warming. Glacial erosion alongwith lithospheric subsidence is suggested to have resulted
in the current grounding of large portions of the Greenlandand Antarctic ice sheets and most of their outlet glaciersand ice streams below sea level.

43

STRATEGICOBJECTIVE

4

FEEDBACKS IN THE EARTH SYSTEM

Scientific ocean drilling can test the strength of thesecompeting cryosphere-driven feedbacks by reconstructing the paleotopography of the Antarctic continental shelfareas and comparing it to the timing of the waxing andwaning of the Antarctic ice sheet through the Paleogene
and Neogene. Scientific ocean drilling can also improve
constraints on the size of the Greenland ice sheet throughthe Miocene and Quaternary. This information can help

resolve the nature and strength of feedbacks between
atmospheric circulation, surface air temperatures, and sea
ice dynamics during this time. Furthermore, documenting how Quaternary glacial activity reshaped the Arctic’s
shallow continental shelves is critical for reconstructing
the development and influence of the shallow seaways
that are major conduits for inflowing Atlantic and Pacificwaters into the Arctic.
Polar airmasses cool
Polar airmasses cool(a) Cryosphere Paleotopography
Driven Feedbacks(a) Cryosphere Paleotopography
Driven Feedbacks

Ice sheetelevation
increases
Ice sheetelevation
Iceincreases
sheet
growthIce sheetgrowthIce stream
Ice sheetIce stream
mass
l
ve
Ice sheet
Sea lemass
GroundedIce sheet
l
e
v
below
le
Sea
growthsea level
Grounded
Ice
sheet
below
More of thegrowthsea level
lithosphere subsides
sea-level
Morebelowof the++Floating
ice shelf
Floating
ice shelf

lithosphere subsides
below sea-level

Poles isolated
from warmer
mid-latitude
Poles
isolated winds
from warmer
mid-latitude winds

Ice sheetgrowthIce sheetgrowthIce sheetdecay
Ice sheet
decay
More of the ice sheet
is marine-based andlessstableMore ofhence
the ice
sheet

–

–

is marine-based andhence less stable(b) Change in Antarctic Land Area
Since Ice Sheet Inception(b) Change in Antarctic Land Area
Eocene-Oligocene(~34SheetMa) Inception
ModernSince Ice
Modern30Modern ice
sheet extent

Modern ice

Bedrock elevation (km)30

Bedrock elevation (km)Eocene-Oligocene (~34 Ma)–3–3(a) Changes in the paleotopography of both the upper and lower surfaces of ice sheets, as a result of changes in ice sheet mass, can result in
sheet extent
both amplifying and regulatory feedbacks. (b) Comparison between modern and reconstructed (~34 million years ago) bedrock elevation beneath
the Antarctic ice sheet, illustrating how lithospheric loading by the ice sheet, tectonic processes, and glacial erosion have resulted in a 25% reductionin the land area located above sea level since the Eocene-Oligocene. Scientific ocean drilling results are used to reconstruct paleotopography, or
bedrock elevation, which is a critical factor in modeling the nucleation and dynamics of ice sheets. Sources: (a) Original illustration by Matt O’Regan and
Rosalind Coggon. (b) Paleotopography: Paxman et al. (2019), https://doi.org/10.1016/​j.palaeo.2019.109346; Modern bedrock elevation: Fretwell et al. (2013),
https://doi.org/10.5194/tc-7-375-2013

44

STRATEGICOBJECTIVE

MARINE GAS HYDRATES AND
CARBON CYCLE FEEDBACKS
Gas hydrate is an ice-like substance, where low-​molecular-​weight gases (primarily methane, but also CO2, H2S) aretrapped within a frozen lattice of water molecules. It isestimated that gas hydrates account for 15%–50% of Earth’s
total mobile carbon pool, and they appear to exist in continental shelf and slope sediments around the world. Previous
research suggests that gas hydrates may be extremely
sensitive to changes in ocean pressure and temperatureand may destabilize through significant drops in sea levelor warming of intermediate waters. It has also been suggested that most of the methane released in a warming
ocean would be oxidized to dissolved inorganic carbon by
microbes in the form of CO2 in near-seafloor sediments and/or in the water column. By loading intermediate waters with
CO2 that is later upwelled and ventilated to the atmosphere,
hydrate destabilization could play a role as an amplifying
feedback in Earth’s climate system. Scientific ocean drilling provides opportunities to better understand the origin
and quantify the distribution of methane in global hydrate
reservoirs. It can provide new information about how gas
hydrates respond to environmental change and how they
fit into the global cycling of carbon. Scientific ocean drilling can also help elucidate the role gas hydrates may play
in initiating instability on the continental slopes with thepotential for landslide hazards.

BIOLOGICALLY DRIVEN FEEDBACKS
Feedbacks within Earth’s biosphere, and between the biosphere and other components of the Earth system, have
driven evolution and extinction events through Earth’s
history. They have also influenced ocean health and ourplanet’s habitability and climate. Our knowledge ofthe mechanisms that regulate those feedbacks is mostly
incomplete. For example, it is thought that the evolution
and rise to dominance of larger-celled phytoplankton
drove the Mesozoic marine revolution. At that time, many
invertebrate groups took on increasingly complex defenses
against predation. It is posited that the arrival of larger calcareous nannoplankton and diatoms facilitated a more efficient transfer of energy from primary producers to higher
trophic levels, causing diversification of predators andthus a more complex food web with larger energy flows.
These changes to the ocean ecosystem may also have led
to increased removal of both organic and inorganic carbon
from the surface ocean to the seafloor—via the so-called

4

FEEDBACKS IN THE EARTH SYSTEM“biological and alkalinity pumps”—where they becamesequestered in sediments. It has been hypothesized that
this improved capacity of plankton to sequester carbon in
the ocean fundamentally changed the functioning of the
carbon cycle, and that more efficient removal of atmospheric CO2 increased the ocean ecosystem’s resilience
to severe acidification events. The increased plankton
capacity may explain why the numerous large igneous
province emplacements since the Jurassic did not cause
mass extinctions like those in the Permo-Triassic or TriassicJurassic, which occurred before the rise of pelagic calcifiers(i.e., planktic foraminifera).
Scientific ocean drilling can provide access to well-​preserved microfossils in globally dispersed cores to map
out evolutionary pathways in various marine environments
and ecosystems to test these hypotheses. It will also allow
us to further reconstruct ancient changes in both the biological and alkalinity pumps across major climatic eventsand evaluate how climatic or environmental changes cause
shifts in the structure of ecosystems that could lead toother feedbacks. Understanding the role plankton ecology
plays in buffering surface ocean pH and in carbon sequestration is of critical importance as we seek to determine
the future response of the marine biosphere to ongoing
anthropogenic changes.

Understanding the role plankton ecology plays
in buffering surface ocean pH and in carbon
sequestration is of critical importance as we seek
to determine the future response of the marine
biosphere to ongoing anthropogenic changes.

TERRESTRIAL TO MARINE FEEDBACKSThe terrestrial biosphere plays a major role in Earth system
functioning and feedbacks, and there are suggestive correlations between changes in the terrestrial and marine
biospheres. The rise of angiosperms may have increased
terrigenous nutrient flux to the ocean that spurred the evolution of larger marine phytoplankton. Feedbacks between
terrestrial grasslands and marine ecosystems may haveinfluenced the rapid rise in diatom diversity during the45

4

STRATEGICOBJECTIVE

FEEDBACKS IN THE EARTH SYSTEM

last 40 million years. Enhanced productivity due to dust
fertilization during relatively drier Pleistocene glacial intervals has been estimated to account for half of the 80 ppm
changes in atmospheric CO2 during these times. Nutrient
flux thus may be an important feedback in the climate system. However, we currently have a limited understanding
about how land vegetation may have controlled long-term
trends in nutrient fluxes and how it may have affected
global climate and ocean health.
To understand the feedbacks between terrestrial land-

scapes and processes and marine productivity and carbon
burial requires collecting high-quality marine sedimentsthat contain details of terrigenous nutrient flux, marine
primary productivity, and terrestrial vegetation in climatologically sensitive regions and over the last 100 million
years. Core materials provided by scientific ocean drilling
will allow us to establish how marine productivity andcarbon sequestration vary at different nutrient levels. We
will be able to tease out the role atmospheric CO2 plays
in regulating marine productivity through alteration of(a) Modern Carbon Isotope Gradientby the Biological
Pump(a)Produced
Modern Carbon
Isotope Gradient
Produced by the Biological Pump

Sinking
organic
Sinking
matterorganicis
enrichedmatter is
in 12C
enrichedin 12C

Water column
Water column

δ13C (‰)
0 δ13C1(‰) 20
1
2
Planktic
species
Planktic
species

3
3

The biologicalpumpcausesThe
biologicala C isotope
pumpcausesadiﬀerence
C isotope
13
C)(Δδ
diﬀerence(Δδ13C)of ~ 2‰
betweenof~ 2‰planktic
andbetweenbenthic
planktic andforaminifera
benthic
foraminifera

Benthic
species
Benthic
species

Export production, the removal of organic matter from the euphotic zone
to the deep sea, is primarily driven by the biological pump, in which organic
matter such as fecal pellets sink via biological processes combined withgravity. Photosynthesis favors 12C over 13C, enriching organic matter in 12C
and resulting in lower δ13C values. Thus, the functioning of the biologicalpump results in a carbon isotope gradient from 13C-enriched surface waters
to 13C-depleted bottom waters, as recorded by the carbon isotope difference
between planktic and benthic foraminifera (∆δ13C) (a). Hence, foraminifera canbe used to reconstruct past changes in the biological pump, as illustrated bya reduction in ∆δ13C at the Cretaceous-Paleogene (K-Pg) boundary in Ocean
Drilling Program (ODP) Site 1262 cores. The reduction in ∆δ13C indicates a
decline in strength of the biological pump (b). Development of more detailed
records of past changes in the biological pump will allow us to investigate thefeedbacks between the climate system, the marine carbon cycle, and evolution and diversity. Sources: (a) Original graphic by Chris Lowery and Rosalind
Coggon. (b) Modified from Birch et al. (2016), https://doi.org/10.1130/G37581.1

46

1
1

61
61

62
62

δ C (‰)
δ13C 2(‰)
2

3
3

Continued increaseinΔδ13C post-recovery
Continued
increaseofbiologicalpump due
13
C post-recoveryin Δδtoevolution
photoof biological ofpump
due
symbiont-bearing
to evolution of photoplanktics
symbiont-bearing
planktics

63
63

AgeAge
(Ma)
(Ma)

2,000
2,000
3,000
3,000
4,000
4,000

Water
depth
Water
depth
(m)(m)

1,000
1,000

Euphotic Zone
Euphotic Zone

5,000
5,000

Deep water
Deep water

0 0

Surface
Mixedlayer
Surface
Mixed layer
Thermocline
Thermocline–1–1(b) Walvis Ridge Foraminferal
CarbonRecord(ODP Site 1262)(b) Isotope
Walvis Ridge
Foraminferal
Carbon Isotope
Record(ODP Site 1262)
13

Symbiosis
reappears
Symbiosis
reappears
Return to pre-extinction
13
C: biologicalpump
Δδ
Returnto pre-extinction
hasrecoveredbiological pumpΔδ13C:
has recovered

64
64

65
65

66
66

K-Pg
K-Pg

67
67
Surface(K-Pg survivor)
Surface(K-Pg survivor)
Surface
Surface

Increase in Δδ13C:
biologicalinpump
IncreaseΔδ13C:isrecovering
biological pump isrecovering
Collapse in Δδ13C afterthe
K-Pg inboundary:
Collapse
Δδ13C after
weakenedbiological pump
the K-Pg boundary:weakened biological pump
Late Cretaceous Δδ13C:
strongbiological Δδpump
13
Late CretaceousC:strong biological pump
G. cretacea
H.
holmdelensis
G. cretacea
H.
M. holmdelensis
angulata
M.
M. praeangulata
angulata
R. fructicosa
M.
praeangulata
R. fructicosa
Pr.
tauricaGl.
Pr. falsostuarti
taurica
Pr. falsostuarti
inconstansGl.
Pr.
inconstans
N. truempyi

Mixed
Layer
Mixed
Layer
Benthic
N. truempyi
Benthic
Open symbol = photo-symbiont bearing
Open symbol = photo-symbiont bearing

STRATEGICOBJECTIVE

precipitation patterns and vegetation cover, which inturns modifies weathering rates and nutrient fluxes into
the ocean. Purposely designed land-to-sea transects will
permit us to integrate marine records of ocean nutrient
flux, plankton ecology, and carbon burial collected throughscientific ocean drilling with vegetation and climatological records from hinterland regions collected throughcontinental drilling efforts.

POTENTIAL MICROBIALSUBSEAFLOOR FEEDBACKS
Feedbacks between subseafloor microbial life and other
Earth system components are largely unknown. Scientificocean drilling provides the means to explore the extent towhich microbial life in the sediments and underlying igneous crust affects oceanic conditions and tectonic processes
via metabolic reactions. It also provides the tools needed to
examine biological mediation of hydrothermal alterationof the substrate and in turn how ocean conditions andtectonic processes affect habitability beneath the seafloor.
Microbial effects on lithospheric permeability andrheology. Previous scientific ocean drilling has shownthat tectonic and magmatic processes affect the nature of
permeable pathways within the oceanic lithosphere andhence subsurface fluid flow. These processes seem criticalto sustaining a deep microbial biosphere, but we don’tknow to what extent the biosphere might, in turn, influence tectonic and magmatic processes. It has been suggested that biologically moderated mineral precipitation
reduces the porosity and permeability of the upper oceanic
crust. This process is potentially an important feedback
between the biosphere and crustal structure because
the permeability of the crust controls where hydrothermal
fluid and heat exchange occurs along mid-ocean ridges,
which in turn may affect how shallow melts are intruded
into the upper crust.
Similarly, serpentinization reactions associated withmicrobial communities could significantly affect the rheology of the lower crustal or mantle rocks in which theyoccur, in turn influencing the deformational behavior andhazard-generating potential of oceanic lithosphere when
it is consumed in subduction zones. Investigation of thesepotential feedbacks between the deep biosphere and thelife cycle of the oceanic lithosphere relies on scientificocean drilling to recover samples of lithosphere-hosted
microbial communities to enable assessment of how they
modify the rocks they inhabit.

4

FEEDBACKS IN THE EARTH SYSTEM

Deep Earth oxidation state. Subduction of microbiallyaltered sediments and rock may also result in feedbacks
between the subsurface biosphere and Earth’s interior.
Subseafloor life significantly influences Earth’s surface
oxidation and ocean and atmosphere composition, but
the rates at which this happens, and how those rates havechanged over time, are unknown. There is a suggestionthat the redox state of subducted sediment influences
the extent of mantle oxidation, in turn affecting magmatic
evolution, mineral assemblages, gas speciation in volcanic
systems, and the long-term evolution of Earth’s atmosphere. Evaluation of the feedbacks between the ocean
and the atmosphere and biosphere ecology requires direct
sampling by scientific ocean drilling. These records of pastocean conditions and contemporaneous biosphere structure can be deciphered through decoding of sedimentchemistry in combination with microfossils, DNA, andother biomarkers.

FURTHER READING
Escutia, C., R.M. DeConto, R. Dunbar, L. De Santis, A.E. Shevenell, andT. Naish. 2019. Keeping an eye on Antarctic Ice Sheet stability.
Oceanography 32(1):32–46, https://doi.org/10.5670/oceanog.2019.117.
Foley, B.J., and P.W. Driscoll. 2016. Whole planet coupling between
climate, mantle, and core: Implications for rocky planet evolution. Geochemistry, Geophysics, Geosystems 17(5):1,885–1,914,
https://doi.org/​10.1002/2015GC006210.
LaRowe, D., and J. Amend. 2019. Energy limits for life in the subsurface.
Pp. 585–619 in Deep Carbon: Past to Present. B. Orcutt, I. Daniel, and
R. Dasgupta, eds, Cambridge University Press.
Passow, U., and C.A. Carlson. 2012. The biological pump in a high CO2
world. Marine Ecology Progress Series 470:249–271, https://doi.org/​
10.3354/meps09985.
Rohling, E.J., A. Sluijs, H. A. Dijkstra, P. Köhler, R. S. W. van de Wal, A.S. vonder Heydt, D. J. Beerling, A. Berger, P. K. Bijl, M. Crucifix, and others.
2012. Making sense of palaeoclimate sensitivity. Nature 491:683–691,
https://doi.org/10.1038/nature11574.
Scher, H.D., J.M. Whittaker, S.E. Williams, J.C. Latimer, W.E.C. Kordesch,and M.L. Delaney. 2015. Onset of Antarctic Circumpolar Current
30 million years ago as Tasmanian Gateway aligned with westerlies.
Nature 523:580–583, https://doi.org/10.1038/nature14598.
Shaffer, G., M. Huber, R. Rondanelli, and J.O.P. Pedersen. 2016. Deeptime evidence for climate sensitivity increase with warming.
Geophysical Research Letters 43:6,538–6,545, https://doi.org/​10.1002/​
2016GL069243.
Steffen, W., K. Richardson, J. Rockstrom, S.E. Cornell, I. Fetzer,
E.M. Bennett, R. Biggs, S.R. Carpenter, W. de Vries, C.A. de Wit, andothers. 2015. Planetary boundaries: Guiding human development on achanging planet. Science 347(6223):1259855, https://doi.org/10.1126/
science.1259855.
Wang, P.X., B. Wang, H. Cheng, J. Fasullo, Z.T. Guog, T. Kiefer, and Z.Y. Liu.
2017. The global monsoon across time scales: Mechanisms andoutstanding issues. Earth-Science Reviews 174:84–121, https://doi.org/​
10.1016/j.earscirev.2017.07.006.

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5 TIPPING POINTSIN EARTH’S HISTORYSTRATEGICOBJECTIVE

Using Earth’s geologic past to illuminate future environmental change

SUMMARY
Parts of the Earth system, particularly ice sheets, ecosystems, and ocean circulation, do not respond linearly to external
forcings. Changes may be gradual before a critical threshold is reached—a “tipping point”—beyond which the systemchanges rapidly and often irreversibly into a new state. Because of the interconnected nature of the Earth system, whena tipping point is crossed in one part, it could trigger a cascade of tipping points being crossed elsewhere in the system.
Scientific ocean drilling can recover sediment and rock records in multiple tectonic settings, across all ocean basins, andfrom shallow continental shelf areas to the deepest subseafloor environments. These records can elucidate the environmental conditions when tipping points were crossed, the rates at which the Earth system built up to tipping points,
how long it took for the system to attain a new stable state, and how the new state differed from the previous one.
Lessons learned from the geological past can help us understand why certain Earth system components have tipping
points and not others, how exceeding tipping points affects ecosystem function, and what drives species to extinction.
Identifying tipping points before Earth exceeds them will provide the information society needs to decide how to address
today’s changing climate.

TIPPING POINTS IN EARTH’S
CLIMATE SYSTEMThe Earth system is in the midst of a significant transition.
Anthropogenic greenhouse gas emissions are driving
global warming, which is destabilizing ice sheets, raising
global sea level, changing precipitation patterns, reducing
ocean oxygen concentrations, and causing the displacement of both terrestrial and marine ecosystems. What will
happen if the marine-based West Antarctic Ice Sheet enters
into a state of irreversible retreat or if there is widespreadthawing of Arctic permafrost? Will Earth cross a tipping
point and transition to a new equilibrium state? Whatmight this new state look like?
For many components of Earth’s climate system,
modern observational data sets cover too short atime period to answer these questions. Marine sediments contain the longest, best-​preserved, continuous,
high-resolution, in situ records of climate and environmental changes, making scientific ocean drilling ideallysuited for identifying Earth conditions when tipping points
were exceeded in the geologic past and investigating
the consequences of exceeding them. Indicators that key
tipping points may have been crossed in the past include
transitions into and out of glacial intervals, far-reaching
ecosystem changes, shifts in precipitation patterns and48

aridity, and sea level changes. When some tipping points
are crossed—for example, as a result of ocean acidification
and/or oxygen depletion—the marine sedimentary record
provides evidence of rapid, large-scale system changes tothe biosphere, including mass extinctions. In order to combine knowledge of Earth’s past tipping point behavior intomodels of future climate change, we need to understandhow the boundary conditions of the Earth system havechanged with time, and how they affect its stability.

DRIVERS OF TIPPING POINT BEHAVIOR
Components of the Earth system may exceed tipping points
as a result of forcing by internal amplifying feedbacks or
external drivers. A tipping point may also be exceeded ifchanges lower the system’s resilience—its ability to recoverfrom perturbations. Drivers of threshold behavior include
orbitally forced changes in insolation, atmospheric CO2
concentrations, tectonic reconfiguration of the ocean
basins, and global increases in volcanic activity. Scientificocean drilling provides access to high-resolution records
of a wide range of Earth system processes that allow us
to reconstruct the detailed event chronologies required
to decipher which external forcings, geological cycles, or
feedback mechanisms drove the Earth system to exceed
tipping points in the geological past.

5

STRATEGICOBJECTIVE

Changes in ocean basin configuration. Thermohaline
ocean circulation is responsible for distributing heat,
nutrients, salt, and carbon globally. Changes to this global
circulation as tectonic gateways slowly open and close canthus alter regional and global climate. Deep ocean sediment records collected by scientific ocean drilling suggestthat changes in ocean basin configuration were the startof a sequence of events that led to the development ofcontinental-scale ice sheets over most of Antarctica near
the Eocene-Oligocene transition around 34 million years
ago. As global ocean circulation shifted, species turnover in

TIPPING POINTS IN EARTH’S HISTORY

marine plankton groups followed, fundamentally altering
the carbon cycle and marine food webs.
Despite progress in our understanding, the connection
between the opening of Drake Passage and the timingof the initiation of Antarctic glaciation at the EoceneOligocene transition remains controversial. Similarly, therelationship between the closing of gateways such as theCentral American Seaway in the Middle Miocene, which
has been hypothesized to also have affected ocean circulation patterns and global climate, is still debated. A new
focus on latitudinal and longitudinal transects that target(1) The system is kept
in Stable State 1 byregulating feedbacks.
Regulatory
Feedback
Perturbation
Tipping
Point
Potential Energy

Resilience of system— the ability of asystem to recoverfrom change(2) The system will not
shift to Stable State 2 unlessit passes the tipping point(see b and c).

Stable State 1(e.g., ice house world)

Stable State 2(e.g., greenhouse world)aSystem State (e.g., global temperature)

Change in Forcing(a carbon-cycle perturbation
driven by ﬂood basalt volcanism)

Change in System Boundary Conditions(resilience lowered due to achange in continental conﬁgurationand hence ocean circulation)cb
A greater perturbation to
the system causes it topass the tipping point

Change in stability lowers the resilience of thesystem such that the regulatory feedbacks no longer
prevent the system passing the tipping point

Stability landscapes in which valleys represent stable states and the peaks between them represent tipping points. Regulating feedbacks that prevent
perturbations from pushing the system beyond a tipping point keep the system in a stable state (a). In the climate system, changes in insolation are
offset by changes in precipitation and carbon burial. The tipping point may be crossed if the system is perturbed even more, for example, it is subject
to greater forcing as a result of internal amplifying feedbacks or an external driver (b), or if gradual changes in system parameters lead to a change inthe stability landscape that lowers its resilience to perturbations (c). Illustration by Rosalind Coggon

49

5

TIPPING POINTS IN EARTH’S HISTORY

Marbonate Mass
Accumulation
Rate (g cm–2 ky–1)

6

Age (Ma)
4

5Greater
Carbonate
Preservation

0.8 0.2
0.4 0.1

3a

0.0 0.0

Planktic Foraminifera
δ 18 O (‰)

Caribbean (Site 999)
Paciﬁc (Site 846)

Lower
Carbonate
Preservation

0.0

2

CAS
ClosureSTRATEGICOBJECTIVE

Less
Saline

0.5

b

1.0
More
SalineCaribbean (Site 999)
Paciﬁc (Site 1241)

WIDE OPEN

CLOSED

1.5

Central American
Seaway (CAS)c

Surface Water
Deep/Bottom Water
Deep Water Formation
Salinity >36‰
Salinity <34‰
DIFFERENCE

dspecific time intervals—in locations proximal
to ancient oceanic gateways and sills—willenable us to reconstruct latitudinal temperature gradients, map deepwater formation
areas, and determine when ice sheets developed and retreated from continental margins.
Increases in volcanic activity. The emplacement of large igneous provinces (LIPs)
has been hypothesized to lead to tipping
points being crossed in a number of Earthsystem components. Outgassing from suchextensive volcanism increases atmospheric
CO2 and leads to global warming. The same
volcanism produces aerosols that can instead
result in global cooling. It also injects extra
nutrients into the ocean, increasing marine
primary production, which is thought to draw
down dissolved oxygen when the plankton
die off, resulting in the formation of large deadzones. This volcanism may also lead to significant metal pollution when mantle-derived
metals dissolve in high concentrations inseawater at levels potentially lethal for many
marine species. While it has been suggested
that LIP volcanism results in mass extinctions,detailed chronologies of these events andtheir environmental consequences remainunresolved. Consequently, questions remain
as to which LIP-related mechanism, or combination of mechanisms, caused ecosystemtipping points to be crossed.

80°N

40°N

Site 999
0°

CAS

Site 1241
Site 846

40°S

160°E

–3.0

–2.2

–1.4

100°W

–0.6

0.0

0°

0.6

1.4

Sea Surface Salinity Diﬀerence (psu):
Wide Open – Closed

50

2.2

3.0

Drilling records indicate a tectonic-gateway-driven tipping
point in ocean circulation due to closure of the Central
American Seaway (CAS). The divergence of carbonate
preservation records (a) between Ocean Drilling Program
sites in the Caribbean Sea and the Pacific Ocean indicate
a separation of deep water masses around 4.4 million
years ago, while records of sea surface salinity (b)indicate a partitioning of surface waters between the
Caribbean and the Pacific a few hundred thousand years
later. Together, these records indicate the CAS closed
gradually. They are consistent with the modeled effects
of closure of a wide open CAS on global ocean circulation(c) and sea surface salinity (d). Sources: (a and b) modified
from O’Dea et al. (2016), https://doi.org/​10.1126/​sciadv.​
1600883, which is based on data from (a) Haug and
Tiedemann (1998), https://doi.org/​10.1038/​31447 and(b) Sarnthein (2013), https://doi.org/​10.1016/​B978-​0-​444-​
53643-​3.00129-1. (c and d) from figures in Sentman et al.
(2018), https://doi.org/​10.1029/​2018PA003364

5

STRATEGICOBJECTIVE

SCALES AND RATES OF
TIPPING POINTSTIPPING POINTS IN EARTH’S HISTORY

characterized by bi-polar ice sheets, developed by crossing
several major tipping points that cooled our polar regions.
These cooling events thrust Earth’s climate and ocean into
a new steady state. It is hypothesized that these cooling
events were not single global “events” but rather shifts ina number of local parameters (paced by orbital forcings)
that, when combined, resulted in major global change.
There is growing consensus that the Eocene-Oligocenetransition is not a single tipping point, but rather a steppedtipping point toward colder conditions with more ice
cover. Future scientific ocean drilling is needed to establish how multiple smaller events on decadal to centennialtime­scales can combine to create stepped tipping points
that result in larger Earth system events. To be successful inthis effort, scientific ocean drilling must improve the global
coverage of past key climate change intervals and collectcores at increasingly higher temporal resolutions that do
not obscure any decadal- to century-scale system behaviors. Future drilling technology developments are neededthat will enhance core recovery and that along with targeting high-​accumulation-​rate sediments, will improve thetemporal resolution of our records. These improvements

Tipping points in the Earth system can be reached over arange of spatial and temporal scales. Exceeding tipping
points may result in global or regional changes. Changes
may occur in a geologic instant or over millennia to millionsof years, and they may comprise a single event or multiple“stepped” changes in system state. The marine sedimentary record contains key information on the rate, spatial
extent, and nature of the changes to the Earth system as
it approached and crossed tipping points in the past. Suchknowledge is required to evaluate how quickly components of the Earth system may be reaching tipping points
in response to the vast modern-day inputs of atmospheric
CO2 and whether the tipping points are being reachedregionally or globally.
Stepped tipping points. Scientific ocean drilling has
shown that the Cretaceous-Cenozoic record of Earth’s temperature and ice sheet history includes a long progressionof crossing tipping points. Our modern icehouse world,

Eocene-Oligocene
Transition33

60

Age (Ma)50
40

30

Paleogene
Paleocene

EoceneOligocene

Warmer and/or Less Ice

NeogenePeriodMiocene
Epoch
–1
0
1

Cooler and/or More Ice

PaciﬁcNorth Atlantic
South Atlantic
Southern Ocean2
3Benthic δ18O (‰)

a

Qt.
PlioQtFirst
ContinentalScale
Antarctic
Ice Sheet
Develops0

1

2

Coolerand/orMore Ice

140

c

4

120
Calcareous
Nannoplankton 100
Extinction

d

80
60
40

Planktic
Foraminifera

Number of Speciesb28Benthic δ18O (‰)

38

Scientific ocean drilling cores have revealed thedetails of a stepped global tipping point eventat the Eocene-Oligocene boundary. (a) The
oxygen isotopic composition (δ18O) of benthic
foraminifera reveals a general cooling trend
through the late Eocene. (a and b) A major
positive oxygen isotope shift at the EoceneOligocene transition indicates more abrupt
cooling and ice sheet growth, due to tipping
point behavior. The Eocene-Oligocene transition
resulted in major changes in the global ocean.
The carbonate compensation depth deepened
by about a kilometer and North Atlantic Deep
Water began to form, marking a major reorganization of ocean circulation as reflected in thedivergence of benthic foraminiferal δ18O valuesof the different ocean basins. These changes
resulted in a severe and protracted loss of
species in groups that had evolved in a fundamentally different greenhouse ocean, including(c) calcareous nannoplankton and (d) planktic
foraminifera. Sources: (a and b) Cramer et al.
(2009), https://doi.org/​10.1029/​2008PA001683.
(c and d) Lowery et al. (2020), https://doi.org/​
10.1146/​annurev-​earth-​081619-​052818

20
0

51

TIPPING POINTS IN EARTH’S HISTORY

changes in regional rainfall patterns in northern Africa, withphases of intensified precipitation leading to a freshening
and stratification in the Mediterranean Sea. At the otherend of the spectrum, Cretaceous oceanic anoxic events
lasted hundreds of thousands of years may represent global
perturbations of the carbon cycle due to excess burial oforganic carbon. It is thought that increased productivity
resulting from the emplacement of large igneous provinces
drove global ocean anoxic events. In both cases, environmental changes must have caused rapid changes to themarine ecosystems, yet they occurred over markedly dif-Paraná
?

Large
Igneous
Provinces

Chicxulub Popigai Chesapeake Bay

ImpactEvents

?

OAE2

OAE1b

OAE1a

Deccan North Atlantic

Major
Tipping Point
Events100
Planktic
Foraminifera
50

220

200

180

Cretaceous

160

140

120
100
Age (Ma)80

Eocene60

40

20

Plio.-Pliest

Jurassic

Triassic

Miocene0

Oligocene

Nannofossils

Paleocene

Number of Species

150

Morokweng Tookoonooka

T-OAE

Puchezh-Katunki

T-J

Manicouagan

Ontong-Java?
Madagascar?
Caribbean?
High Arctic?

E-O

Central Atlantic
KarooMagmatic Province Ferrar

PETM

Global vs. regional tipping points. Previous scientificocean drilling has shown that organic-rich layers depositedin the Mediterranean represent short (~5,000–6,000 years)
anoxic events driven by variations in Earth’s orbit. These
events appear to be confined to this regional enclosed
inner sea. They are hypothesized to have been caused by

K-Pg

will allow us to carry out robust land-to-sea or ocean-toocean comparisons to look for leads and lags—critical
input for modeling the sequencing and chronology oftipping point behavior.

OAE1d

5

STRATEGICOBJECTIVE

0

High-resolution scientific ocean drilling records of past Earth conditions and biodiversity allow us to identify the drivers of past tipping points in the
Earth system, determine the consequences of exceeding tipping points, and investigate times when ecosystems were resilient to change. Species-level
diversity of calcareous nannoplankton (red) and planktic foraminifera (blue) over the last 230 million years reveal extinction or radiation associatedwith major tipping points (orange lines). Over this interval there were seven impact events that produced craters >50 km in diameter (gray arrows), of
which only Chicxulub is associated with a tipping point in the climate system and marine ecosystem. To better understand the role of large igneous
provinces (brown arrows) in driving tipping point behavior, the timing and duration of these events (e.g., in the Cretaceous) and their environmental
consequences need to be further constrained.
Note that the diversity data are presented in 1 million year bins, though it masks the complete extent of some extinction events, especially the
K-Pg, in which 90% of both planktic foraminifera and calcareous nannoplankton species disappeared. T-J = Triassic-Jurassic boundary. T-OAE =Toarcian ocean anoxic event. OAE = Oceanic anoxic event. K-Pg = Cretaceous-Paleogene boundary. PETM = Paleocene-Eocene Thermal Maximum.
E-O = Eocene-Oligocene boundary. Sources: Modified from Lowery et al. (2020), https://doi.org/​10.1146/annurev-​earth-​081619-​052818; Impact event
ages after Schmieder and Kring (2020), https://doi.org/​10.1089/​ast.2019.2085; LIP event ages after Clapham and Renne (2019), https://doi.org/10.1146/
annurev-earth-053018-060136.

52

STRATEGICOBJECTIVE

ferent spatial and temporal scales. The fundamental differences between both events, in particular how and how fast
tipping points were reached and over what temporal scales,remain unresolved. Scientific ocean drilling will focus on key
time periods and locations around the world to reveal thedifferences in environmental conditions that lead to vastlydifferent scales of Earth system response.

RESILIENCE TO CHANGE
Studies of tipping points in Earth history tend to focus ontimes when the system actually “tipped” and entered a newstate as a result of internal or external drivers. However,periods of stability, such as the Late Cretaceous or middle
Paleocene in which the system remained steady—despite
the presence of drivers that might be expected to cause
global changes—are equally important for constraining
the sensitivity of the Earth system to tipping point behavior. To better understand tipping points, we need to recoverrecords from stable geologic intervals when Earth systemcomponents did not reach tipping points. This criticalinformation will help establish the conditions that makes
system components resilient to threshold behaviors.

CONSEQUENCES AND RECOVERYThe most important downstream consequences of exceeding tipping points are typically found in the biosphere,
which is well preserved in deep-sea sediments. Rapidchanges to the ocean, atmosphere, and climate have driven
both extinction and radiation over the past 200 million
years. Together with macroevolutionary processes, they
have shaped the history of life. An asteroid impact at theCretaceous-Paleogene (K-Pg) boundary around 66 million
years ago resulted in years of global darkness. Primary production declined, which led to marine food webs crossing atipping point that resulted in the extinction of an estimated
75% of marine species, one of the most dramatic mass
extinction events in Earth history. Biodiversity remained
diminished for 10 million years after this global catastrophe. Recovery intervals following several Cretaceous ocean
anoxic events and the Eocene-Oligocene transition also
lasted approximately 10 million years.
The debate as to whether we are living through ahuman-caused “sixth extinction” typically focuses onwhether species loss in the biosphere has already passed
a tipping point that makes collapse inevitable or whether
ecosystems are resilient. Through scientific ocean drilling
we will leverage both the temporal and taxonomic res-

5

TIPPING POINTS IN EARTH’S HISTORY

olution provided by fossilized plankton, benthic microorganisms, biomarkers, and other indicators to determine
the response of ecologically sensitive groups to rapid environmental change, providing a perspective on our modern
marine biosphere and what we might expect for the future
as our climate warms.
Speciation and radiation during recovery. Aspectsof recovery following extinction events—such as speciation and radiation—operate on much shorter timescales.
Scientific ocean drilling can help determine the rates of
speciation and radiation during recovery, how and why
the rates vary geographically, and how recovery affects
the greater Earth system (including carbon cycling andprimary production). This knowledge can lead to a better
understanding of the long-term consequences of human-​Marine Biome Recoveries Following
Major Perturbations
There have been five major mass extinctions over the last
500 million years of Earth history, and we are living througha sixth today. Key questions are: how do life and ocean
health recover from negative anthropogenic pressures andhow long do the effects persist? The Cretaceous-Paleogene(K-Pg) mass extinction provides a useful analogue, as themeteorite impact caused one of the few major changes
in Earth system state that happened faster than modern
climate change. Scientific ocean drilling results have shownthat the ocean was habitable (again) very soon after the
Chicxulub impact, that aerosols and CO2 were important
climate effects that pulled in opposite directions, and thatthe eruptions of massive flood basalts of the Deccan Traps
earlier and later than the impact did not significantly affectthe extinction rate. Despite the short duration of these environmental impacts, it is surprising that ecosystem function,in the form of the biological pump, did not recover for atleast 1.8 million years. The causes for this long recovery
period are not yet understood, but are likely related todisrupted marine food web interactions and temporary successions of dominance by cyanobacteria and smaller-sized
phytoplankton such as algae. Investigations of geographically dispersed sediment cores containing high-fidelity
records of fossils and biomarkers can test these working
hypotheses. The results will significantly advance understanding of marine food web functioning and the global
carbon cycle, with extensions to the modern global ocean
while it undergoes similar changes.

53

STRATEGICOBJECTIVE

5

TIPPING POINTS IN EARTH’S HISTORY

Transitioning Toward an Ice-Free Planet
Although Earth has been free of permanent ice for an estimated 85% of its history, humankind has not lived througha transition to a significantly different cryosphere state. Thistransition to a new state could take place over many thousands of years, or Earth could be free of summer sea ice within
decades and free of marine-based ice sheets in centuries. As
depicted in the figure, Earth has now reached the fork in theroad in the stability landscape. The Earth system can take two
possible paths in the future (dotted lines). Currently, Earth is ona “hothouse” path driven by human emissions of greenhousegases. If Earth exceeds the planetary tipping point, it will follow an irreversible path to a hothouse state. The alternative
path leads to a Stabilized Earth, where human stewardshipof the environment will allow the Earth system to maintain aquasi-​stable state. Scientific ocean drilling provides the globally
distributed samples needed to determine changes in climate
system parameters—such as atmospheric CO2 levels and theamount of ice loss—that caused the cryosphere to tip to newstates in the past. Records that accurately characterize Earth’s
past transitions to ice-free conditions provide the ground truth
data needed for calibrating and testing climate models. Marine
sedimentary records are essential for understanding where
Earth is today on the stability path, whether we are closer tothe planetary tipping point than the figure depicts, and how
much time humankind still has to take steps to prevent Earthfrom hurtling toward a hothouse world. Illustration by Rosalind
Coggon and Geo Prose, inspired by Figure 2 in Steffen et al. (2018),
https://doi.org/10.1073/pnas.1810141115

GlacialInterglacial Cycles

PLEISTOCENE

Last Glacial
Maximum

HOLOCENE

Human
Greenhouse
Gas
Emissions

ANTHROPOCENEPRESENT DAY

RE

TU

FU

ST
AB
ILIT
Y L
AND
S

P L A TA RY
TIP P N E O I N T
IN G PC AP ESTABILIZEDEARTHHOTHOUSE EARTH
cold

54

Global Temperature

hotSTRATEGICOBJECTIVE

induced climate change given our current CO2 scenario. In
addition, determining the specific thresholds crossed that
led to extinctions and the controls on species survivorshipwill help determine the vulnerability of current marineorganisms to various Earth system tipping points. This new
research frontier can be investigated using the very hightemporal and taxonomic resolution offered by the microfossils in scientific ocean drilling sediment cores.
Ocean-basin-scale biodiversity. There remains a significant need for an integrated ocean-basin-scale biodiversity database to determine global timescales and patternsof ecosystem change. Organic-walled and siliceous plankton currently lag behind the calcareous plankton in termsof the fidelity of their species-level biodiversity, particularly
before the Eocene. Benthic micro­organisms are even morediverse than their planktonic counterparts and provide aperspective on the deep sea, which is a fundamentally different environment than the upper water column. Similar
global diversity compilations of benthic microorganisms
will greatly improve our understanding of the marine
biosphere and its long-term evolution, resilience, andadaption potential—in particular through and following
tipping point events.
Most marine plankton in the modern ocean do not leave
fossils behind, while the macrofossils of larger organisms
are normally too large to be recovered in cores. Biomarkers,
paleo-DNA, and fish teeth/bones represent exciting newopportunities to understand these end members of themarine ecosystem. Improved archiving of fossil occurrence
and abundance data sets in community-built databases
will significantly increase our ability to reconstruct marine
biodiversity, evaluate ecosystem resilience to environmental change, determine the ways in which ecosystems evolveas they get closer to tipping points that trigger extinction,and reconstruct the geographic and temporal variability ofextinction and recovery in the ocean.

FURTHER READING
Archer, D., B. Buffett, and V. Brovkin. 2009. Ocean methane hydrates
as a slow tipping point in the global carbon cycle. Proceedings of
the National Academy of Sciences of the United States of America
106(49):20,596–20,601, https://doi.org/10.1073/pnas.0800885105.
Christensen, B.A., W. Renema, J. Henderiks, D. De Vleeschouwer,
J. Groeneveld, I. Castañeda, L. Reuning, K.A. Bogus, G. Auer, T. Ishiwa,
and others. 2017. Indonesian Throughflow drove Australian climate
from humid Pliocene to arid Pleistocene. Geophysical Research Letters
44(13): 6,914-6,925, https://doi.org/10.1002/2017GL072977.
Cramer, B.S., J.R. Toggweiler, J.D. Wright, M.E. Katz, and K.G. Miller. 2009.
Ocean overturning since the Late Cretaceous: Inferences from a newbenthic foraminiferal isotope compilation. Paleoceanography 24(4),https://doi.org/10.1029/2008PA001683.

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TIPPING POINTS IN EARTH’S HISTORY

Scientific ocean drilling provides the globally
distributed samples needed to determine changes
in climate system parameters—such as atmospheric
CO2 levels and the amount of ice loss—that caused
the cryosphere to tip to new states in the past.

DeConto, R.M., and D. Pollard. 2016. Contribution of Antarctica to pastand future sea-level rise. Nature 531(7596):591–597, https://doi.org/​
10.1038/nature17145.
Galaasen, E.V., U.S. Ninnemann, A. Kessler, N. Irvali, Y. Rosenthal,
J. Tjiputra, N. Bouttes, D.M. Roche, H.F. Kleiven, and D.A. Hodell. 2020.
Interglacial instability of North Atlantic Deep Water ventilation. Science367(6485):1,485–1,489, https://doi.org/10.1126/science.aay6381.
Holbourn, A.E., W. Kuhnt, S.C. Clemens, K.G. Kochhann, J. Jöhnck,
J. Lübbers, and N. Andersen. 2018. Late Miocene climate cooling and intensification of southeast Asian winter monsoon.
Nature Communications 9(1):1584, https://doi.org/10.1038/
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Houben, A.J.P., P.K. Bijl, J. Pross, S.M. Bohaty, S. Passchier, C.E. Stickley,
U. Röhl, S. Sugisaki, L. Tauxe, T. van de Flierdt, and others. 2013.
Reorganization of Southern Ocean plankton ecosystem at the onset
of Antarctic glaciation. Science 340(6130):341–344, https://doi.org/​
10.1126/science.1223646.
Hull, P.M., A. Bornemann, D.E. Penman, M.J. Henehan, R.D. Norris,
P.A. Wilson, P. Blum, L. Alegret, S.J. Batenburg, P.R. Bown, and others.
2020. On impact and volcanism across the Cretaceous-Paleogene
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Turgeon, S.C., and R.A. Creaser. 2008. Cretaceous oceanic anoxic event 2
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55

6 GLOBAL CYCLES OF
ENERGY AND MATTERSTRATEGICOBJECTIVE

Determining the role, mechanisms, and magnitudes of Earth system cycles
SUMMARY
Energy and matter use multiple pathways to cycle among Earth system reservoirs. Such cycles are responsible for thecontinuous sculpting of our planet’s surface, opening new ocean basins, building mountains, and eroding continents. They
also drive the chemical evolution of our atmosphere and ocean, control the physical and chemical conditions that allow
life to develop and evolve, regulate the recovery from major perturbations in Earth’s climate, generate natural hazards thatthreaten communities globally, and contribute to the accumulation of key resources, including fresh water and critical
metals. Scientific ocean drilling supplies important details and critical missing information about the rates and magnitudesof energy, chemical, nutrient, and fluid transfers among Earth’s rocks, ocean, atmosphere, and life. These data can reveal
how global cycles control Earth’s evolution over a wide range of spatial and temporal scales.

ENERGYkinetic &thermalimpactenergysolar
energybiochemical
potential
energykinetic &thermalsolarenergy ofenergyocean andatmosphericcirculation

heat
from
radioactive
decay

ENERGYouter core
convection
kinetic&
generates
thermalmagnetic
impactﬁeld
energyprimordialheat

C YC L E

biochemical
potential
energykinetic &thermalenergy ofocean andatmosphericcirculation

56

volcanic
gases

WATER

On this and the facing page, simplified cartoons
depict the different Earth system cycles coveredin this chapter—energy, water, carbon, and metal.
condensation
Illustrations by Rosalind Coggon

heat
from
radioactive
decay

outer core
convection
generates
magneticﬁeld
primordial
heat

electromagnetic
energyevaporationfrom oceans,lakes andstreams

ocean andatmosphereheat
thermally transfer
driventectonic
cycle

transpirationfrom plants

WATER

precipitation

storagein thecryospheresurfacerunoﬀhydrothermal
circulation

groundwater

condensation

C YC L E

electromagnetic
energyevaporationfrom oceans,lakes andstreams

ocean andatmosphereheat
thermally transfer
driventectonic
cycle

precipitationtranspirationfrom plants

surfacerunoﬀ

storagein thecryospheregroundwaterhydrothermal
circulation

BO
CCYACRL E N

TAC YMCEL E L

hydrothermal plume(manganese, iron oxyhydroxide, sulfur, iron)

CO2 in theatmosphereacid rain

particle
fallout

black smokers> 350°C(metal sulﬁdes)diﬀuseventing

STRATEGICOBJECTIVE

EARTH AS A SYSTEM OF
INTERCONNECTED RESERVOIRSENERGYThe continuous cycling of energy
andkinetic& matter among
solar
thermalenergyreservoirs—​large natural storage places—inthe core andimpactenergymantle, the oceanic and continental crust, the ocean, theatmosphere, and biochemical
the biosphere drive Earth’s long-term
electropotential operate over a wide range
magneticofevolution. These cycles
energyenergyheat
fromspatial and temporal scales andare driven by feedbacks
radioactive
ocean anddecay
that regulate or amplify Earth systemprocesses, atmosphere
maintainheattransfer
thermallying equilibrium or pushing Earth past a tipping
point
into
driventectonic
a new stable state.
outer corecycle
kinetic &convection
kinetic & the system includes
thermalgenerates
The
energythatcyclesthroughsolar
thermalenergy ofmagnetic
energyimpact
ocean
and
ﬁeld
thermal(primordial and radioactive)
energy energy from a coolatmosphericprimordial
circulationing Earth, solar energy, energy
heat derived from (bio)chemical
reactions, andbiochemical
the electromagnetic energy that
protectselectropotential
magnetic
energy interior
Earth and life energy
from radiation.
heat Heat from Earth’s
fromradioactive
and the Sun drives convection
within Earth, andoceantheand oceandecayatmosphereheat
and atmosphere, respectively. Convection creates
Earth’s

ENERGYC YC L E
outer core
convection
generates
magneticﬁeld
primordialheat

kinetic &thermalenergy ofocean andatmosphericcirculationtransfer

thermally
driventectoniccycle

6

GLOBAL CYCLES OF ENERGY AND MATTER

magnetic field, drives plate tectonics, sustains life in the
deepest realms of the oceanic crust and sediments, andimpacts Earth’s climate system.
The water cycle, the carbon cycle, the rock/element/
metal cycle, and cycles of volatiles such as
sulfur, nitrocondensation
gen, phosphorous, and oxygen are fundamental matter
cycles operating within Earth. Water transports heat andevaporation
precipitationtranspirationfrom oceans,and chemicalsolutes, impacts rock deformationfrom plantsreactions
lakes andgoverning alteration, and isstreams
essential for life. Carbon is astoragein thebasic component of life, and its cyclingsurface
affects atmospheric cryosphererunoﬀ
carbon dioxide and methane concentrations, ultimately
affecting Earth’s climate system. Element groundwater
cycles exist
hydrothermalfrom nanometer scales, with elemental exchange occurcirculation
ring between minerals, organisms, andcondensation
the environments
in which they exist, to plate tectonic scales, with element
exchanges between oceanicandevaporationcrust and ocean water
precipitation

WATER

WATER

C YC L E
surfacegroundwaterhydrothermal
circulationAL
MCELTE
CY

hydrothermal plume(manganese, iron oxyhydroxide, sulfur, iron)

CO2 in theatmospherevolcanicgases

mid-ocean ridgemagma
degassingorganisms build
carbonate shells

B
CAR ON

silicateweatheringriverinetransportorganic C

buriedhydrocarbons

hydrothermal
CO2 in the
carbonate
atmosphereprecipitation

photosynthesis

C YC L E

acid rain

mid-ocean ridgemagma
degassingorganisms build
carbonate shells

silicateweatheringriverinetransportorganic C

partialmelting andmetamorphismof subductedrockshydrothermal
carbonate
precipitation

C YC L E

buriedhydrocarbons

black smokers> 350°C(metal sulﬁdes)particle
fallout

acid rain

partialmelting andmetamorphismof subductedvolcanic
rocks
gases

in therunoﬀ
atmosphere to protect Earth and life
from harmful incomcryosphere

CCYACRLBEON

photosynthesis

transpirationfrom oceans,fromplants at subducelement recycling backmantlelakesintoand Earth’s
streamstion zones. Volatile cycles determine the capacity of thestorage<2°C
seawater(alkalis,
oxygen)mineralizedchimneysmetalliferous
sedimentshydrothermal
ﬂuid upwelling& mixing

METAL

diﬀuseventing(<300°C)

manganesecrusts &nodules<100°C
mineralization hydrothermal plume(carbonate,(manganese, iron oxyhydroxide,
sulfur,iron)
hightemperature
sulfate &150°C(>350°C) reaction zone
magnesium) leaching(copper, zinc, sulfur leaching)(sodium,
calcium,
black smokers
particlepotassium)> 350°C
fallout
diﬀusemagmatic(metal sulﬁdes)venting
ﬂuids(<300°C)
mineralizedmagma
chimneysmetalliferous<2°C
sedimentshydrothermal
seawater
ﬂuid upwelling(alkalis,
manganese& mixing
oxygen)crusts &nodules

C YC L E<100°C
mineralization(carbonate,sulfate &150°C
magnesium) leaching(sodium,
calcium,
potassium)high temperature(>350°C) reaction zone
(copper, zinc, sulfur leaching)magmatic
ﬂuids

C YC L E

magma

57

STRATEGICOBJECTIVE

6

GLOBAL CYCLES OF ENERGY AND MATTER

ing cosmic radiation, are vital components of the microbial
biome and of human life, and impact mineral resourcesand geohazards.
These complex interconnections among Earth’s reservoirs remain poorly understood. Scientific ocean drilling
allows us to access to the subseafloor to conduct in situ
monitoring and experiments to characterize the pathways,
rates, and magnitude of exchange between reservoirs.
Such investigations are important for resolving how subseafloor life impacts the cycling of energy and matterin the oceanic crust and in Earth’s upper mantle and for
deciphering the role the solid Earth cycle plays in regulating ocean biogeochemistry. Scientific ocean drilling also
helps to map the relative importance of the major controls(tectonics, weathering, life, and atmosphere-ocean interactions) on matter and energy cycles and their impact on
ocean productivity, oxygenation, marine life and evolution,and ocean acidification and health. Through scientificocean drilling we can improve our understanding of theinterrelationships among tectonics and volcanism, climate,
the hydrologic and biogeochemical cycles, and life.

ENERGY CYCLING
Ever since Earth condensed from a cloud of gas and rocks
4.6 billion years ago, its continents, ocean, biosphere, andatmosphere have continuously evolved. The transfer andfeedback of energy through the interconnected Earthsystem is the fundamental driver for change at all spatial
and temporal scales.

Scientific ocean drilling allows us to access to thesubseafloor to conduct in situ monitoring andexperiments to characterize the pathways, rates,
and magnitude of exchange between reservoirs.

Energy transfers from the deep Earth. Energy istransferred among Earth’s many reservoirs through a variety of pathways over many different temporal and spatial
scales. Scientific ocean drilling allows us to investigate
many of these pathways, from thermal convection within
Earth’s core that drives global-scale variations in the geo-58

magnetic field to the production of biomass within theoceanic crust. Drilling allows us to track subtle changes in
the orientation and magnitude of Earth’s magnetic field.
With this information, we can map the behavior of thegeodynamo over thousands to millions of years, the geodynamic behavior of the mantle, and upwelling of thermochemical mantle plumes. Through scientific ocean drilling,
we will gain a better understanding of the dynamics ofheat conduction in oceanic lithosphere and the role fluids,
faults, microbial alteration, and metamorphic processes
play in the transport of heat and elements from the mantle
through oceanic lithosphere into the ocean. This will provide insights into the possibility of long-term energy storage in the subseafloor due to the production of biomass
through attendant microbial communities.
Planetary cooling processes. At the longest time­scales,
thermal convection in Earth’s interior is manifested at thesurface through the production, motion, and destructionof tectonic plates over hundreds of millions of years. Only
through recovery of globally representative sections ofoceanic crust and in situ monitoring of subseafloor conditions can we determine how planetary cooling drives plate
tectonics and how it affects the architecture of our planet
and the long-term geochemical evolution of its crustal,mantle, and ocean reservoirs.

MATTER CYCLING: WATER
Water transports heat and dissolved elements, making
it integral to the functioning of our planet and a requirement for all terrestrial life. Seawater circulation throughthe oceanic lithosphere facilitates heat loss from Earth’s
interior. Fluid-rock reactions affect the melting behavior ofmantle source materials and with that the initial composition of tectonic plates. Water also has an impact on rockdeformation and the chemical reactions governing hydrothermal and seawater alteration of oceanic crust. Ocean
currents redistribute heat, carbon, and nutrients globally,
with consequences for Earth’s climate. We have limited
understanding of what pathways in the hydrological cycle
influence global climate change, how ocean circulation
modulates climate sensitivity, and how the hydrological cycle would behave in a warmer world. By collecting
detailed sedimentary records globally across key Cenozoic
climate transitions, we can assess the influx of fluvial andeolian sediments and other water cycle-related proxies toestablish the long-term history of the hydrological cycle.

ROVborehole
deployable
observatory
borehole
observatory
New or legacy
scientiﬁcocean
New or legacy
drilling
boreholes
scientiﬁc
ocean
drilling boreholes

6

STRATEGICOBJECTIVE

GLOBAL CYCLES OF ENERGY AND MATTERINSTRUMENTED
INSTRUMENTED
BOREHOLES
BOREHOLES

Drill
In Situ Investigations of Subseafloor
Hydrogeology and Biogeochemical Cycling
platformDrill
deployable
platformborehole
deployable
observatory
borehole
observatory ROV-The flux of dissolved elements associated withhydrothermal flow that cools the oceanic crustand the processes and timing associated with thisexchange are poorly constrained. Experimentsthat utilize boreholes—after a drilling expeditionis over—have begun to examine the exchange ofelements between circulating sea­water and thehost rock and the resultant fluxes between these
two reservoirs. Exchange processes can be abiotic or
biotic, the latter influenced by endemic subseafloor
microbial communities. Future studies using instrumented boreholes will expand our understandingof exchange processes through novel adaptive sampling, sensors, and experiments within one or multiple boreholes connected for real-time sensor data
return and instrument adjustment.

deployable
borehole
observatory

New or legacy
scientiﬁc ocean
drilling boreholes

INSTRUMENTED
BOREHOLES
Drill
platformdeployable
borehole
observatory

EXAMPLE CAPABILITIESEXAMPLE CAPABILITIESIn situ perturbation, tracer,
andexperiments
In sequestration
situ perturbation,
tracer,and sequestration experiments
Tracer or
perturbation
Tracer or
perturbation

INSTRUMENTS
INSTRUMENTS

Push/pull
experiments
Push/pull
experiments
Pull
Pull

Push
Push

?
?
?
?

?
?

and sequestration experiments
Tracer or
perturbation?

Push/pull
experiments

Push

Temperature andpressure sensors
Temperatureandpressure sensors

In situ condition
manipulationandIn situ condition
response sensing
manipulation
andresponse sensing
Power generation
for instruments

Pull

Tilt, stress, andstrainsensors
Tilt,
stress,and
INSTRUMENTS
strain sensors
In situ ﬂuid samplers
Borehole hydrologic
andchemical
and
In
situ
ﬂuid samplers
and chemical proﬁlers
microbial
analyzers
and chemical andmicrobial analyzers
Sound sources andcoupled hydrophones?
?

Schematic of a cabled array of boreholeobservatories and seafloor instruments
Coupled sensor response to naturaland manmade perturbations
that provide the capability to monitor
Tidal range
in situ hydrogeologic and biogeochemical conditions and conduct in situ
experiments. Photos: (left) DSDP Hole
395A. (right top) IODP Hole U1383C,
a CORK instrumented with two packages. (right bottom) IODP Hole U1383B,
instrumented with a CORK-Lite. Original
Borehole observatory
Boreholeinstruments
observatory
illustration by Rosalind Coggon, Geoff
Seaﬂoor
Wheat, and Geo ProseSound sources andcoupledsourceshydrophones
Sound
and
coupled hydrophones

Adaptive sensing
and sampling
Adaptive
sensingand sampling

Coupled sensor response to naturaland manmade
perturbations
Coupledsensor response
to natural
EXAMPLECAPABILITIES
andmanmade perturbations
Tidal range
Tidal range In situ perturbation, tracer,

Borehole hydrologic
and chemical
proﬁlers
Boreholehydrologic
and chemical proﬁlersPower generation
for instrumentsPowergeneration
for instruments

Temperature andpressure sensors

Adaptive sensing
and sampling
In situ condition
manipulation andresponse sensing

Seaﬂoor instruments

Tilt, stress, andstrain sensors

Data archiveanddistribution
Dataarchiveand distribution

In situ ﬂuid samplers
and chemical andmicrobial analyzers

lecao s alett
cno to stno

Data archiveand distribution

59
Borehole observatory

STRATEGICOBJECTIVE

6

GLOBAL CYCLES OF ENERGY AND MATTER

Hydrothermal fluid flow. Previous scientific ocean
drilling efforts have revealed that oceanic crust hydrogeology is highly heterogeneous. Heat from cooling ocean
lithosphere drives hydrothermal fluid flow through the
mid-ocean ridges and across their flanks, and the accompanying fluid-rock chemical exchanges facilitate thelong-term geochemical evolution of the mantle, crust, andocean over millions of years. This fluid flow and chemicalinteraction are now also understood to deliver energy andnutrients to microbial communities that subsist within
oceanic crust. Subsequent temperature- and pressure-​
regulated dehydration reactions during subduction of
mature and hydrated oceanic crust can release fluids fromthe down­going slab, while compaction and biogeochemical processes in the overlying sediments may alter subsurface pressure gradients and drive fluid flow. Scientificocean drilling at sites of increasing crustal age will allow
us to test models for subseafloor fluid circulation andother hydrogeological processes through the integrationof core and pore fluid analyses; downhole logging data;measurements from in situ borehole hydrological experiments; and measurements of fluid pressure, temperature,
dissolved element concentration, and DNA/RNA from
borehole observatories.
Freshwater aquifers. Scientific ocean drilling allows
us to explore interactions between the submarine hydrogeologic cycle and continental groundwater systems,
including subterranean estuaries where fresh water andsalt water mix. Freshwater aquifers that extend seaward
beneath continental shelves—a relic of past glaciation
when freshwater flow extended seaward—constitute a
crucial non­renewable resource. Similar freshwater lenses
occur beneath atolls, other oceanic islands, and alongcontinental slopes where they may be the only source ofdrinking water available to local communities. In somecoastal systems, fresh water constantly discharges andseeps upward, but we do not know whether such discharges cause instability in the flanks of volcanic islands,change the composition of microbial communities, andpose threats to coastal communities by destabilizing
continental or insular slopes with a potential to cause
submarine landslides. Coastal freshwater reservoirs can bebest investigated through land-to-sea drilling to produce
detailed profiles of porewater chemistry and petrographic
and isotopic analyses of diagenetic minerals and to map
out how freshwater lenses may be affected by unwanted
seawater influxes and/or contaminants.

60

Evaporation effects. Evaporation of seawater canplay a key role in global geochemical cycles. Evaporation
within restricted ocean basins can lead to the depositionof evaporites—​sedimentary rocks rich in a variety of salts.
Such deposits record the history of hypersaline fluid flow
within a basin and can constitute a major sink for elements
such as sodium, chlorine, and sulfur. Scientific ocean
drilling can recover sections through evaporite deposits
to illuminate the nature and consequences of cutting off
these basins from the world ocean and how these changes
affected climate, tectonic, and hydrologic feedbacks. The
mineralogical records from the recovered evaporites willassist in deciphering temporal and spatial changes in ocean
chemistry and in quantifying the contribution of brine-rockinteractions to global cycles of key elements such as sulfur.

MATTER CYCLING: CARBON
The ocean contains 60 times as much carbon as the atmosphere. The ocean reservoir is critical not only because of its
size but also because of the long timescales at which carbon is exchanged across the ocean-atmosphere boundary.
The oceanic crust and upper mantle are also significant
carbon reservoirs. The amount of carbon stored withinthem is poorly understood because of uncertainties in theextent and duration of hydrothermal calcium carbonate
precipitation in oceanic crust, the global role of ultramaficrock serpentinization in CO2 uptake, and the utilizationof the various forms of carbon compounds by microbialcommunities. The fate of carbon stored in mature oceanic
lithosphere during subduction is also unknown because
carbon may be transferred along volatile pathways that are
currently poorly quantified. For example, we do not knowwhat proportion of the crustal carbon budget is recycled
into the mantle, degassed back to the atmosphere via
back-arc volcanism or otherwise returned to the surface
via fluid flow in the forearc. Scientific ocean drilling allows
us to investigate diverse tectonic environments spanning
the oceanic life cycle of tectonic plates to quantify therole oceanic crust and carbonate sedimentation play in thelong-term global carbon cycle.
Cenozoic CO2 decrease. During the last ~50 million
years, long-term decreases in atmospheric CO2 have coincided with substantial and sustained climate cooling—​
except for the unprecedented temperature increase since
the Industrial Revolution. The reason for this coupled trend
has been debated for decades and has been hypothe-

6

STRATEGICOBJECTIVE

GLOBAL CYCLES OF ENERGY AND MATTER

Quantifying the role of mid-ocean ridge spreading in controlling atmospheric CO2
Crustal Age (Ma)Heat ﬂow (mW/m2)

300

180

160

140

120

100

80

60

40

20

0

(a) Global heat ﬂow anomaly

Global observations (±1 s.d.)
GDH1 conductive cooling model
Global heat ﬂow anomaly

250
200

A discrepancy between observed and predictedconductive heat ﬂow.
A “global heat ﬂow anomaly,” indicating
signiﬁcant hydrothermal cooling, is discernable
out to 65 Ma crust on average

150
100

However, basement hydrothermal ﬂuid ﬂow canoccur in crust of all ages if suﬃcient hydrologic
heads can be established

50
0

180 Ma0 Ma(b) Factors thatinﬂuence
low-temperatureridge ﬂank
hydrothermal
exchange

Transform faults
expose lower crustal
and upper mantle rocks
to seawater, facilitating
serpentinization andcarbonation reactions

Unsedimented
seamounts provide
permeable ﬂuid
pathways

Faults provide
permeable ﬂuid
pathways

Serpentinite mud
volcanoes
Seawater inﬁltration along“bend faults” may cause
further carbonation of thecrust and serpentinizationof the upper mantle

Bulk crust CO2 content(weight %)7 Ma intermediate
spreading rate crust:basalt cut by hydrothermal carbonate veins(896A, 6R-3, 30-37 cm)

180 Ma1 cm

Upper lavas (<300 m)
Drill site #Lower lavas (>300 m)

6
5

417/418

4

801

3
2

Atmospheric CO2 (ppm)

1 cm(c) Drill core recordof CO2 uptake by oceanic
crust over the last
180 million years.

Possible Cretaceous rapid
CO2 uptake trajectories

1179

Upp
er
CO lavas: p
2 uptake rogres
siv
traje
Lower lavas:
ctor e 504 896
progressivey
CO2 uptake trajec
1224
1256
tory
1149

843

1
0

132 Ma fast
spreading rate crust:basalt breccia cemented withhydrothermal carbonate(1149B, 30R-1, 56-66 cm)

Impermeable sediments
seal the crust from theoverlying ocean

0 Ma

2000
1000

(d) Atmospheric
CO2 concentrations
over the last
180 million years.

500
200
100
180

Multi-proxy compilation
68% conﬁdence interval
95% conﬁdence interval
Jurassic

160

Cretaceous

140

120

100
80
60
Crustal Age (Ma)

Paleogene

40

Neogene20

0

Scientific ocean drilling is required to quantify the role of natural CO2 sequestration in oceanic crust as a result of hydrothermal exchange between thecrust and overlying ocean in the long-term global carbon cycle. The role mid-ocean ridge spreading plays in controlling past atmospheric CO2, and hence
climate, remains controversial because of uncertainties regarding the rate, extent, and duration of hydrothermal carbonate precipitation. (a) A global
heat flow anomaly indicates that hydrothermal circulation persists across the ridge flanks for ~65 million years on average1, but fluid circulation canoccur at all crustal ages given sufficient hydrologic head and permeability, which are influenced by factors such as local basement cover, topography,
stratigraphy, and structure (b)2. (c) The higher bulk CO2 contents of cored Cretaceous and Jurassic lavas compared to younger lavas is consistent
with either progressive CO2 uptake by the crust (dashed arrows) or with the majority of uptake within 10–40 million years of crustal formation (solid
arrows)3. (d) Global conditions during the Jurassic and Cretaceous, including higher atmospheric CO24 and global temperature, may have enhancedhydrothermal carbonate precipitation. The lithospheric flux of carbon into subduction zones likely depends on the age of the plate, its pathway across
Earth’s surface, its sedimentation and hydrological history, and the physical and chemical conditions of the overlying ocean. To quantify the role ofhydrothermal circulation in the long-term global carbon cycle requires acquiring intermediate age oceanic crust.
Original figure compiled by Rosalind Coggon. 1Modified from Stein and Stein (1994), https://doi.org/10.1029/93JB02222. 2Illustration by Rosalind
Coggon and Geo Prose. 3Modified from Alt and Teagle (1999), https://doi.org/10.1016/S0016-7037(99)00123-4; core photographs from Alt et al. (1993),
https://doi.org/10.2973/odp.proc.ir.148.1993, and Plank et al. (2000), https://doi.org/10.2973/odp.proc.ir.185.2000). 4Modified from Foster et al., 2017,https://doi.org/10.1038/ncomms14845).

61

STRATEGICOBJECTIVE

6

GLOBAL CYCLES OF ENERGY AND MATTERDECODING MAGNETIC FIELD VARIATIONS
have shown unexplained accelerations—with speeds up to 55 km/yr—that are theorized to result from turbulence or eddies in theouter core convection.
Another poorly understood behavior of the geodynamo concernschanges in the overall strength of the geomagnetic field. Current
observations show a decline in strength over the last half century,with implications for how well life on Earth and our infrastructure will
be protected from solar flares in the future. The lowest magnetic field
intensities currently occur in the “South Atlantic Anomaly” and alreadyare significantly affecting spacecraft and satellite orbits, exposing
them to several minutes of damaging strong radiation. Current
models suggest a possible link between the presence of this large
low-​intensity anomaly and the location of the large low shear wave
velocity province (LLSVP) in the lower mantle beneath Africa. The
occurrences of reversed flux patches that signal instability in Earth’s
geodynamo and are seen as a harbinger of a (near) future magnetic
field reversal are also poorly understood. Scientific ocean drilling
cores obtained from areas with high sedimentation rates (e.g., nearcontinents) will provide long-term records with decadal to centurial
resolutions that can assist us in ground truthing computer simulationsof outer core turbulence. These sediment cores will also enable us togain insight into similar future magnetic field variations and declines
in overall field strength. Credit: After Figure 82, https://directory.​
eoportal.org/​web/​eoportal/​satellite-​missions/s/swarm, ESA/DTU Space;and Tarduno (2018), https://doi.org/10.1073/pnas.1819025116

Convection in the liquid-metal outer core gives rise to Earth’s
geodynamo and sustains our planet’s strong magnetic field. The
geomagnetic field shields Earth from damaging cosmic radiationand therefore preserves planetary habitability. Marine sediments
and the underlying volcanic rocks record geohistorical variationsin the magnetic field. Scientific ocean drilling provides magneto-stratigraphic records that—when incorporated in a global database—​are an invaluable tool for constraining the timing and rates ofa wide range of Earth cycles over millions of years. The cores provide
critical data for establishing a common paleomagnetic reference
frame, allowing the movement of Earth’s tectonic plates and upwelling mantle plumes to be mapped through time.
Rock magnetic studies of seafloor core samples allow us to gain
fundamental knowledge about the source of magnetic anomalies
preserved in the oceanic crust and about past paleointensities ofEarth’s magnetic field. Yet, the geomagnetic field and the geodynamo remain one of the least understood planetary phenomena,as the nature of the magnetic field is constantly changing, withlong periods of small changes interspersed with major excursions
or complete polarity “reversals.” Scientific ocean drilling enables
us to investigate the causes and consequences of this highly variable geodynamo behavior, across the world’s ocean basins andover different timescales. Small irregular changes in the character of the magnetic field on short timescales are reflected in the“wandering” of the magnetic poles, which over the last decades

SAA

African
LLSVP

Range associated with
South Atlantic Anomaly (SAA)
20,00030,00040,00050,00060,000

Geomagnetic Field Intensity (nanoTesla)
Reversed ﬂux patches62

Hot dense mantle at thecore-mantle boundary (LLSVP)STRATEGICOBJECTIVE

sized to result from increased chemical weathering on
the continents. When CO2 reacts with rainwater, it forms
carbonic acid, which then bonds with elements such as
calcium or magnesium. In this way, large amounts of carbon are removed from the atmosphere and transferredto the ocean where it is stored in the deep subsurface
reservoirs for millennia. The CO2 removal from the atmosphere cools down Earth. This hypothesis is problematic
because it is not clear what drives up chemical weathering
rates while global temperatures have been dropping overtimescales of millions of years. Scientific ocean drilling canhelp decipher whether increases in chemical weathering
is a feedback and are coupled to increases in mechanicalerosion due to orogenic uplift and increases in glacial erosion. Scientific ocean drilling can also help in the searchof large negative atmospheric CO2 feedback loops thatbalance out over timescales of millions of years and that
could bring down the CO2 concentrations over the courseof the Cenozoic. Candidate processes include organic carbon burial in ocean sediments, inorganic precipitation of
CaCO3, precipitation of silicate minerals on the seafloor via
clay authigenesis, dissolution of ocean crust basalt, deep
biosphere uptake, sulfate reduction, and the subductionof carbonate-rich sediment and recycling and long-term
storage into Earth’s mantle. Scientific ocean drilling also
is uniquely positioned to investigate whether decreasing
ocean bottom water temperatures correlate with decreasing CO2 storage in the oceanic crust.
Volcanism. One of the major inputs into the carbon surface system are volcanic eruptions that introduce mantlederived CO2 into Earth’s atmosphere. It is still unknown
how past eruptions in island arcs, volcanic islands, andlarge igneous provinces (LIPs) influenced the carbon
cycle as a driver of short- and long-term climate change.
Previous scientific ocean drilling has produced limited
evidence for volcanic events as triggers for climate warming, but in many cases the timing is not well constrained
and is asynchronous with other geological records, orthe estimated volume of volcanic CO2 production cannot
explain the levels of increased global warmth. For example,
it has been suggested that there may have been a volcanic trigger for abrupt warming 94 million years ago, but
it remains unclear whether the magma production ratefrom Caribbean and/or Madagascar LIP submarine eruptions could have maintained this Cretaceous greenhousefor roughly 9 million years. This hypothesis is particularly
problematic, as a lot of carbonate would be simultaneously
buried, which would have drawn down atmospheric CO2

6

GLOBAL CYCLES OF ENERGY AND MATTER

and caused Earth to cool. In addition, ocean fertilization bysubmarine volcanism and the injection of large quantities
of sulfate as aerosols also could cause cooling effects leading to “volcanic winters.”
To decipher whether volcanic events triggered the
Paleocene-Eocene Thermal Maximum, the Eocene Thermal
Maximum 1, the Middle Eocene Climatic Optimum, andother global warming events requires scientific ocean drilling. Drilling is also needed to resolve discrepancies between
the relative timing of these events and better estimate thevolume of related CO2 production. This exciting frontier for
scientific ocean drilling can provide better insights in theforcing mechanisms for triggering and maintaining past
hot greenhouse climates.

Scientific ocean drilling allows us to investigate
diverse tectonic environments spanning the oceanic
life cycle of tectonic plates to quantify the role
oceanic crust and carbonate sedimentation play inthe long-term global carbon cycle.

Methane hydrates. Hydrate destabilization could play
an important role as a feedback in the climate system.
Debates are ongoing about how much of the methane andCO2 potentially could be released into the ocean and atmosphere. Scientific ocean drilling provides an opportunity tounderstand the distribution of hydrates, how they respondto environmental change, and how they fit into the global
carbon cycle and climate system. This is another frontier inwhich scientific ocean drilling has great potential to link
paleoceanography to methane hydrate formation anddestruction, and the biosphere.
Microbial processes. The deep biosphere remains alarge and mysterious carbon reservoir. Because it is one of
the largest ecosystems on Earth, we now appreciate thatit may drive subseafloor geochemical processes that affectocean chemistry, the global carbon cycle, and the alteration of sediments and rocks. Deep subseafloor microbial
cells principally fix carbon and nitrogen, but through volcanic processes they also cycle other volatiles such as sulfur,
leading to the accumulation of massive sulfide deposits.

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6

GLOBAL CYCLES OF ENERGY AND MATTER

Oxidation can also be controlled by microbial action,
causing significant pyrite formation on continental slopes
during glacial lowstands and extensive redox reactions
within basaltic crust. These processes provide crucial, bioavailable elements for life and stimulate us to gain a fuller
understanding of microbial-driven cycles in the subseafloor environments.
Sequestration. The sequestration of CO2 in sediments
and rocks buffers climate over geological time­scales,while carbon also forms the engine of all deep biospheremicrobial life and life in general. Subsurface carbon
sequestration is an emerging opportunity for mitigating
anthropogenic climate change. Similar to nature, humankind could possibly sequester CO2 in the subseafloor
in deep saline reservoirs on the continental shelf or inoceanic plateau basalts. The potential exists to actively
pump carbon into spreading ridge flanks that cover vast
expanses of the seafloor. Scientific ocean drilling will play
an important role in exploring opportunities for submarine
CO2 sequestration, as these potential offshore carbon
reservoirs require deep coring capabilities and improved
drilling/​logging technologies.

MATTER CYCLING: METALS
Fluid flow facilitates the cycling of metals between thelithosphere and ocean. Over millions of years, this cycling
can lead to the formation of massive sulfides and ferromanganese nodules on the seafloor. Hydrothermal activity
along mid-ocean ridges and other submarine volcanoes
concentrates key metals in subseafloor ore deposits andprovides useful analogues for understanding ancientdeposits exposed on land that are important sources of
traditional metals (Cu, Zn, Au) and critical metals (Co, Cr, V)
used in green and advanced technologies. Subseafloor
fluid flow may lead to the accumulation of potentially economic metal resources, while at other locations, no deposits
form and seawater can have increased dissolved elemental
concentrations. Scientific ocean drilling can help define thesubseafloor locations and mechanisms and under which
conditions metal resources are formed. It also has thepotential to discover biogenic and non-​biogenic mineraldeposits that result from organic-​​mineral interactions.
Metal concentrations in sediments recovered by scientific ocean drilling can be used as tracers for geologic
events. Mercury can be used to investigate meteorite
impacts and large volcanic eruptions. Other metals canbe used as proxies to help improve our understanding of64

the relationship between global anoxic events and theformation of large igneous provinces and the formationof natural resources (Mn, Co, Ni) in open ocean basins andmore confined back-arc basins and marginal seas.

FURTHER READING
Barry, P.H., J.M. de Moor, D. Giovannelli, M. Schrenk, D.R. Hummer,
T. Lopez, C.A. Pratt, Y. Alpízar Segura, A. Battaglia, P. Beaudry, andothers. 2019. Forearc carbon sink reduces long-term volatile recycling into the mantle. Nature 568:487–492, https://doi.org/10.1038/
s41586-019-1131-5.
Berg, R.D., E.A. Solomon, and F. Teng. 2019. The role of marine sediment diagenesis in the modern oceanic magnesium cycle. Nature
Communications 10:4371, https://doi.org/10.1038/s41467-019-12322-2.
Bradley, J.A., S. Arndt, J.P. Amend, E. Burwicz, A.W. Dale, M. Egger, andD.E. LaRowe. 2020. Widespread energy limitation to life in global
subseafloor sediments. Science Advances 6:eaba0697, https://doi.org/​
10.1126/sciadv.aba0697.
Change, N.C. 2017. Iron entangled. Nature Geoscience 10:157,
https://doi.org/​10.1038/ngeo2913.
Clift, P.D. 2017. A revised budget for Cenozoic sedimentary carbon
subduction. Reviews of Geophysics 55(1), https://doi.org/​10.1002/​
2016RG000531.
Egger, M., N. Riedinger, J.M. Mogollón, and B.B. Jørgensen. 2018.
Global diffusive fluxes of methane in marine sediments. Nature
Geoscience 11:421–425, https://doi.org/10.1038/s41561-018-0122-8.
Gustafson, C., K. Key, and R.L. Evans. 2019. Aquifer systems extending
far offshore on the U.S. Atlantic margin. Scientific Reports 9:8709,
https://doi.org/10.1038/s41598-019-44611-7.
Hazen, R.M., and C.M. Schiffries. 2013. Why deep carbon? Reviews in
Mineralogy and Geochemistry 75(1):1–6, https://doi.org/10.2138/
rmg.2013.75.1.
Kuroda, J., N.O. Ogawa, M. Tanimizu, M.F. Coffin, H. Tokuyama, H. Kitazato,
and N. Ohkouchi. 2007. Contemporaneous massive subaerial volcanism and late cretaceous Oceanic Anoxic Event 2. Earth and Planetary
Science Letters 256:211–223, https://doi.org/10.1016/j.epsl.2007.01.027.
McNeill, L.C., D.J. Shillington, G.D.O. Carter, J.D. Everest, R.L. Gawthorpe,
C. Miller, M.P. Phillips, R.E.L. Collier, A. Cvetkoska, G. De Gelder,and others. 2019. High-resolution record reveals climate-driven
environmental and sedimentary changes in an active rift. Scientific
Reports 9:3116, https://doi.org/10.1038/s41598-019-40022-w.
Nozaki, T., J. Ishibashi, K. Shimada, T. Nagase, Y. Takaya, Y. Kato,
S. Kawagucci, T. Watsuji, T. Shibuya, R. Yamada, and others. 2016. Rapid
growth of mineral deposits at artificial seafloor hydrothermal vents.
Scientific Reports 6:22163, https://doi.org/10.1038/srep22163.
Shalev, N., T.R.R. Bontognali, C.G. Wheat, and D. Vance. 2019. New isotope
constraints on the Mg oceanic budget point to cryptic modern
dolomite formation. Nature Communications 10:5646, https://doi.org/​
10.1038/s41467-019-13514-6.
Tauxe, L., and T. Yamazaki. 2015. Paleointensities. Pp. 461–509 in Treatiseon Geophysics, 2nd ed. G. Schubert, ed., Elsevier.
Vonnahme, T.R., M. Molari, F. Janssen, F. Wenzhöfer, M. Haeckel,
J. Titschack, and A. Boetius. 2020. Effects of a deep-sea mining experiment on seafloor microbial communities and functions after 26 years.
Science Advances 6:eaaz5922, https://doi.org/10.1126/sciadv.aaz5922.

STRATEGICOBJECTIVE

7 NATURAL HAZARDSIMPACTING SOCIETY

Understanding natural hazards in the marine environment
SUMMARY
Earthquakes, landslides, tsunamis, volcanic eruptions, mega-floods, and other extreme natural events directly threatencommunities, infrastructure, and the environment. Significant progress has been made in the investigation of such hazards through scientific ocean drilling, particularly in subduction zones. However, we remain largely uninformed about thesubseafloor conditions that influence hazards; the mechanisms that control their recurrence, timing, and possible precursors; and how to assess their future likelihood. Scientific ocean drilling can help close knowledge gaps by installing
subseafloor observatories to monitor in situ conditions before, during, and after hazardous events and by probing thestratigraphic record of prehistoric submarine and terrestrial hazardous events to understand processes and evaluate longterm magnitude-frequency correlations. Further advances in methodologies to interpret physical properties and processes
from geological and geophysical records are also needed.

DETERMINING PHYSICAL CONTROLSOF GEOLOGIC HAZARDS
Scientific ocean drilling addresses questions about thephysical controls on submarine geologic hazards throughanalyses of rock, sediment, and fluid samples. It also provides access to failure planes and slope failure deposits thatare inaccessible by conventional gravity or piston coring.
Analyses of rock and fluid samples provide information
about the processes that can create geohazards. Fluid
chemistry can inform us about reactions and changes inrock properties that are occurring at depths not reachable
with current drilling capabilities. Collectively, these data
about the present subsurface provide crucial in situ information for the physical models used to determine the risks
from future earthquakes, landslides, and volcanic eruptions.
Although marine geologists and geophysicists have madegreat strides in probing the physical properties, processes,
and conditions controlling geologic hazards, scientificocean drilling is poised to fill critical knowledge gaps.
Slip behavior. Recent study has shown unequivocallythat faults and landslides slip in a wide variety of ways:
while some apparently only slip gradually and steadily overtime and others only fail suddenly and catastrophically,
many others exhibit unstable slip behaviors over a wide
range of magnitudes and durations. Questions such aswhether material properties, physical conditions, or sub-surface geometry of the failure plane control slip behavior,and how subsurface conditions and behavior may change
through time, remain unresolved. By providing access tothe subseafloor to permit long-term measurements ofin situ conditions and to slip planes where rock and sediment samples can be collected, scientific ocean drilling
can address how various slip behaviors influence hazard
potential and how stress state and loading rate affect slip
behavior. Understanding the nature of slip processes, forboth earthquakes and landslides, is particularly importantas it directly influences tsunami hazards.
Submarine explosive volcanism. Scientific ocean drilling can contribute to our understanding of the processes
that control submarine volcanic eruptions. Characterizing
the causal mechanisms of past volcanic eruption-related
tsunamis can improve our understanding of the hazards
associated with potential flank collapse, caldera formation,and pyroclastic flows from submarine volcanoes. Similarly,
understanding whether and why some volcanic flank landslides fail in progressive stages and others catastrophicallyin a single event is important for assessing the potential fortsunamis and/or triggered large-volume eruptions in volcanic arcs. Drilling into volcanic deposits caused by mass
wasting or the volcanic eruptions themselves will provide
direct access to the products from a widespread group oflargely understudied submarine volcanoes.

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NATURAL HAZARDS IMPACTING SOCIETY

Marine Records of Natural Hazards
Large underwater earthquakes and the tsunamis they often generate have been responsible for some of the worst natural disastersof the early twenty-first century, taking hundreds of thousandsof lives and forever altering coastal communities large and small.
Recent events underscore how much we still have to learn aboutplate boundary faults. For example, the 2011 Mw 9.1 Tōhoku-oki(Japan) earthquake, and the effects of the earlier 869 CE Sanriku
earthquake in the same area, have shocked the seismologicalcommunity. Fault slip during the Tōhoku-oki earthquake wasdetermined to be more than 50 m, extending from depth all theway to the trench, resulting in a much larger magnitude earthquake and tsunami than thought possible in this tectonic setting.
Volcanoes both above and below water also pose a variety ofhazards. In 2018, the Anak Krakatau volcanic eruption (Indonesia)
was accompanied by a tsunamigenic flank collapse, creating thedeadliest eruption thus far in the twenty-first century. The humanimpact from the devastating 1883 Krakatoa predecessor eruption
and tsunami was orders of magnitude larger. Although many volcanoes are hidden beneath the ocean, their eruptions can posesignificant hazards. For instance, the unexpected 2010 South
Sarigan Seamount eruption (Northern Mariana Islands) created aplume of ash extending 12 km into the atmosphere, intersecting
airplane routes and disrupting ship and air traffic.
At active and passive tectonic margins, and in plate interiors
and along volcanic flanks, submarine landslides pose hazards
to offshore infrastructure, including seafloor telecommunication cables, drill rigs, and pipelines, and can generate tsunamis.
Debris flows and turbidity currents triggered by earthquakes andtyphoons repeatedly cause damage and major service disruptions
to submarine communication cables worldwide. In 2006, 22 major
cables broke following an earthquake off southern Taiwan. In 2004,
a submarine landslide during Hurricane Ivan destroyed the Taylor
Energy MC20A oil platform in the Gulf of Mexico, rupturing tensof oil wells and creating the longest duration oil spill in US history.
Scientific ocean drilling can fill gaps in our understanding of
hazard processes through targeted investigations into the underlying properties, conditions, and physical mechanisms that control
their occurrence. Drilling can also improve hazard assessments
by helping to constrain the submarine location, magnitude, andfrequency of past hazardous events. Focused studies can help
us understand how changes in climate and sea level affect geologic systems, particularly those with potential landslide hazards.
Through active monitoring, scientific ocean drilling can provide
information on current subseafloor conditions and changes occurring near the hazard source. These data can be used to inform
time-dependent hazard determinations and hazards forecasts.

a(a) The town of Rikuzentakata on the northeast coast of Japan, threedays after the 2011 tsunami reduced the town of 23,000 residents torubble. WorldView-2 satellite image by Robert Simmon, using data ©2011
DigitalGlobe. (b) A drone image of the Anak Krakatau volcano two weeks
after the flank collapsed. The volcano peak that had measured 320 m ismissing. Credit: Deutsches GeoForschungsZentrum (GFZ) (c) Oil slick at
the Taylor MC20 site. Credit: US Coast Guard.

b
Oil
Slick

Old Summitc

New Crater
Sliding Plane

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STRATEGICOBJECTIVE

Variations in slope stability. Uncertainties remain
regarding the causes of large submarine landslides andtheir potential to generate devastating tsunamis, especially where the seafloor gently slopes. It is particularly
important to determine whether the initiation points forthese geohazards, which otherwise appear stable, arepreconditioned for failure and/or are triggered by external
events—for example, by methane release, earthquakes,
or increased sediment supply. Previous scientific ocean
drilling suggests earthquake shaking can strengthen andstabilize sediments through dewatering, making them lesssusceptible to landslides than similar units far from active
margins that have not been shaken considerably. This
strengthening effect, however, can be overwhelmed byhigh sedimentation rates on continental margins, making
the conditions more unstable. Scientific ocean drilling candetermine the primary controls on seafloor stability by providing more detailed characterization of multiple locationsin the ocean basins. This information can be used to informpredictive models of sediment strength, potential methane dissociation, and slope stability.
Hazards triggering hazards. Extreme marine events
often trigger other geohazards. Submarine earthquakes
in subduction zones and along coastal strike-slip systems
can trigger tsunamis, landslides, other earthquakes, andpotentially even volcanic eruptions. Explosive phreatic
volcanic eruptions in island arcs are not only destructiveby themselves, they also often generate tsunamis andlandslides and can be accompanied by large precursor andsyn-volcanic earthquakes. Scientific ocean drilling will target areas in the ocean basins where we can start to establish and test these causal links among various hazards.

RAPID RESPONSE MEASUREMENTS
OF HAZARDOUS EVENTSScientific ocean drilling can collect repeat measurements inthe subseafloor to evaluate how stress state, pore pressure,temperature, and other hydrologic, mechanical, and chemical properties and conditions affect failure evolution at
different stages in the cycles of hazardous events. Scientificocean drilling can also change focus rapidly if there isan opportunity to capture measurements from hazard
events that occur during the lifetime of this 2050 Science
Framework. Rapid response drilling following large,
hazardous events will elucidate processes that occurred
during the events and how the subsurface responded in

7

NATURAL HAZARDS IMPACTING SOCIETY

the aftermath. For example, coring, logging, and boreholeobservatory measurements made through rapid response
scientific ocean drilling after the 2011 Mw 9.1 Tōhoku-oki(Japan) earthquake permitted characterization of thefault’s stress state during and immediately after the earthquake, the physical properties within and around the plateboundary fault zone at depth, and transient processes
during the subsequent aftershock sequence. Given theimportance of in situ and deep measurements, new technologies and operational strategies need to be developed
so that time-sensitive observations and experiments canbe conducted quickly after an event.

By providing access to the subseafloor to permit
long-term measurements of in situ conditions
and to slip planes where rock and sediment
samples can be collected, scientific ocean drilling
can address how various slip behaviors influencehazard potential and how stress state and loading
rate affect slip behavior.

LEARNING FROM PASTHAZARD RECORDS
Increased knowledge of the magnitude and frequency of
past events is important for quantitatively assessing future
hazard potential. Submarine earthquakes and landslides,
tsunamis, volcanic eruptions, hurricanes, and other extreme
events all leave behind evidence in submarine rocks andsediments. Scientific ocean drilling provides the means toaccess this record and to go well beyond the short temporal record provided by shallow piston and long coring.
Interpreting the history of past events—by establishing adetailed event stratigraphy over tens of thousands to millions of years—can be achieved through high-recovery andhigh-resolution core sampling. This strategy requires using
a combination of conventional techniques (e.g., identifying
and dating turbidites) and developing novel techniques tomore robustly obtain a history of past events and to evaluate accurate timing and magnitudes.

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NATURAL HAZARDS IMPACTING SOCIETY

U1439A-2H-4
74 —Centimeters

Glass Shards

50 µm
Ash
Layer
50 µm

Volcanic Ash Layers

103 —Landslide
U1520D-4H-4
1—

Turbidite
Deposits

Volcanic
Eruption

U1520D-5H-6
47 —TsunamiEarthquake
o

tt

no

CentimeterseCentimetersalscFault Zone
Rapid Heating
Signatures

Cartoon highlighting the different marine environmentsthat generate geohazard events and examples of how
scientific ocean drilling can collect important information about them, including volcanic ash layers, turbidite
deposits, and vitrinite reflectance (Ro) that shows higher
thermal maturity inside a fault slip zone. Illustration
by Geo Prose. Inset sources: Kutterolf et al. (2018),
https://doi.org/​10.1002/​2017GC007100; Barnes et al. (2019),
https://doi.org/​10.14379/​i odp.proc.​372B375.​105.2019;
Sakaguchi et al. (2011), https://doi.org/​10.1130/​G31642.1

Microbreccia

Fault Gouge
88 —Microbreccia
63 —

1 cm

68

0.0 Ro (%) 1.0

STRATEGICOBJECTIVE

Eruptive recurrence frequencies. Offshore sediments
contain some of the longest and most complete histories
of large-magnitude volcanic eruptions (VEI > 4; typically,
VEI > 5 to 7). Volcanic ash that settles on the seafloor after
an eruption punctuates the gradual deposition of sediments in marine environments and becomes incorporated
in the sedimentary record. In contrast, ash records preserved onshore can be incomplete, as they are subject toerosion and other subaerial weathering processes.
An active database of ash layer observations in scientificocean drilling cores provides the largest global compilationof eruptions in the geologic record. This database, which iscontinually updated, can be used to guide targeted investigations and further analyses, for example, to constrain
the volume and recurrence of past eruptions. Such records
also provide insights into the operative geochemical andbackground tectonic processes through characteristics
that fingerprint the magma source and style of eruption.
These well-dated ash falls provide important chronologies,
especially in areas such as the Mediterranean, the western margin of the Americas, and near New Zealand andJapan, where radiocarbon chronologies are plagued withinterfering carbon reservoir effects. Ash fall chronologies
provide insights into hazards, but they also offer criticalcontrol on the timescales of global climate change andfeedbacks in the Earth system during glacial/interglacialintervals in the Holocene and Pleistocene as well as deeper
geologic times.

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NATURAL HAZARDS IMPACTING SOCIETY

Ancient earthquake scars. Subseafloor sediments androcks bear the scars of hazard events in other forms as well,such as thermal alteration and microscale deformation
within fault rocks. Determining whether a particular fault—
and particular rock units within it—hosted large, rapid
slip events in the past, particularly at shallow depth, hasdirect implications for earthquake and tsunami hazards.
Continued innovations in identifying and interpretingthese signals for a wide range of geologic compositionsand various conditions are needed.
Scientific ocean drilling provides numerous opportunities to extend analyses of past events beyond a few
targeted locales and to evaluate regional or global differences within the sediment and rock record. We will determine the history of past hazardous events by comparing
global observations using a significantly expanded database in terms of geographic coverage, geologic setting,and timing within the hazard cycle. This analysis will
provide a more robust understanding of the mechanisms
controlling hazards and their potential spatial and temporal variability, which is crucial for assessing earthquake andtsunami hazard potential.

Scientific ocean drilling offers an opportunity
to assess hazard variations over time throughinstallation of offshore subseafloor observatories

Sediment remobilization. Sedimentary sequences
beneath the ocean remain largely undisturbed, but they
can become remobilized during submarine landslides
and debris flows and, particularly in nearshore settings, bytsunamis and tropical cyclones. The remobilized sediments,
including those from land-derived mega-floods, eventually
resettle in slope basins, trenches, and other submarine
depressions. By analyzing sediments deposited in theseenvironments, we can greatly extend the historical recordof earthquakes and landslides. Comparisons of deposits
collected at various global locations and settings can provide insight into how coastal zones respond to extreme
weather, climate, and changing sea levels, as well as rapid
geohazard events. Earthquake-triggered sediment remobilization also appears to drive significant organic carbon
flux to the deep sea, with as yet unstudied consequences
for those microbial communities residing at water depths
deeper than 6 km in Earth’s ocean trenches.

inside or very near faults, at and around landslide
failure planes, and at volcanoes.

SUBSEAFLOOR MONITORINGAND OBSERVATION
A long-standing goal within hazards science has been
to provide robust, time-dependent hazard assessments.
Although precise prediction of the timing of earthquakes,
volcanic eruptions, landslides, and tsunamis is probably
not feasible, improved forecasting of such events and theirpotential magnitude is within reach. Improved forecasting requires understanding the conditions under which
earthquakes, tsunamis, volcanic eruptions, and landslides
are generated and knowledge about how these conditions
evolve, including in the lead-up to major events, during
events, after events, and the long intervals in between.

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NATURAL HAZARDS IMPACTING SOCIETY

Borehole monitoring for precursory hints. Precursory
deformation and seismic activity have now been recognized prior to several large M8 and M9+ tsunamigenic
subduction zone earthquakes and along strike-slip transform boundaries. Knowledge of precursory activity canhelp scientists identify in real time the short-term hazards
expected from large events, much as is commonly donefor volcanoes and some large landslides on land. Becauseof the paucity of instrumentation on and below the seafloor, our observational data sets are limited and much ofwhat is happening beneath the ocean remains unknown.
The potential to use possible event precursors for hazard
assessment is simply unknown and remains an important

target for the next phase of scientific ocean drilling, particularly in parallel with advances in ocean and subseafloor
technology. Scientific ocean drilling offers an opportunity
to assess hazard variations over time through installationof offshore subseafloor observatories inside or very near
faults, at and around landslide failure planes, and at volcanoes. Instrumentation installed deep beneath the seafloor,
where oceanographic noise is minimized and where pressure, temperature, stress and strain, and hydrologic andgeochemical conditions can be directly monitored within
active systems, will provide the data types and resolution
needed for effectively assessing hazards over time and forcomprehending the hazard-generating process itself.

(b) Borehole Temperature2

44,040

0
Nov
2002

40

Mar
2003

Jul
2003

Nov
2003

Mar
2004

Jul
2004

Damage zone

44,060

50

770
780
790
800
810

Fault

Flow Rate

60

Depth (mbsf)

44,080

4

Pressure (kPa)

820

Nov
2004

1 day
Time

(c) Pressure, Fluid Flow Rate, and Strontium Chemistry100

Chemistry (Sr)

750

90

not to scale

44,1006

44,0804

Flow Rate

44,060

2

60
50
40

44,040

0
Nov
2002

70
Pressure (kPa)

750 m
820 m

Pressure

Mar
2003

Jul
2003

Nov
2003

Mar
2004

Jul
2004

Nov
2004

770
Depth (mbsf)

44,1208760
Sr (µM)80

Flow Rate (cm/yr)

Flow Rate (cm yr –1)

44,100670760
Sr (µM)

44,120Pressure

750

90
80

8

December 2012100

Chemistry (Sr)(a) Subseafloor Observatory

780
790
800
810
820

1d

Tim

Subseafloor observatories installed by scientific ocean drilling (e.g., panel a) permit characterization of in situ conditions and their temporal changes
before, during, and after slip events. Observatories have noted changes in borehole (b) temperature and (c) formation pressure, fluid flow rate, andstrontium chemistry during earthquakes and other slip events. Sources: Fulton and Brodsky (2016), https://doi.org/​10.1130/G38034.1; Solomon et al.
(2009), https://doi.org/10.1016/j.epsl.2009.03.022

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STRATEGICOBJECTIVE

Seafloor instrumentation and observatories. Whileless sophisticated, seafloor instrumentation is cheaper toinstall than high-fidelity borehole observatories, but any
network should include both. Subseafloor observatories
can directly sample and monitor at actual failure planes or
hazard source regions and can be designed to characterize in situ properties and processes that cannot otherwise
be determined. They reveal time-dependent variations
required to resolve the physical processes involved in
offshore natural hazards, allow strain buildup and release
to be monitored, and reveal transient behavior that islargely undetectable by surface-based instruments. Withcurrent and future advances in sensor development andtechnologies for managing data and power to and from
instrumentation deep underwater and beneath the seafloor, scientific ocean drilling has the opportunity to bothuse and drive advances in offshore technology and revolutionize science-based assessment of natural hazards inthe marine environment. Many key questions associatedwith hazards revolve around how conditions within thesubsurface change before, during, and after an event.
These changes can be crucial to answering “why, how, andwhen” questions from society about hazard occurrence
and recurrence. These questions cannot be fully answered
without the involvement of scientific ocean drilling andthe in-depth analyses that it affords through innovative
seafloor instrumentation and observatory networks.

FURTHER READING
Araki, E., D.M. Saffer, A.J. Kopf, L.M. Wallace, T. Kimura, Y. Machida, S. Ide,
E. Davis, and IODP Expedition 365 shipboard scientists. 2017. Recurringand triggered slow slip events near the trench at the Nankai Troughsubduction megathrust. Science 356:1,157–1,160, https://doi.org/​
10.1126/science.aan3120.
Embley, R.W., Y. Tamura, S.G. Merle, T. Sato, O. Ishizuka, W.W. Chadwick Jr.,
D.A. Wiens, P. Shore, and R.J. Stern. 2014. Eruption of South Sarigan
Seamount, Northern Mariana Islands: Insights into hazards from submarine volcanic eruptions. Oceanography 27(2):24–31, https://doi.org/​
10.5670/oceanog.2014.37.
Flemings, P.B., H. Long, B. Dugan, J. Germaine, C.M. John, J.H. Behrmann,
D. Sawyer, and IODP Expedition 308 Scientists. 2008. Pore pressure
penetrometers document high overpressure near the seafloor wheremultiple submarine landslides have occurred on the continental
slope, offshore Louisiana, Gulf of Mexico. Earth and Planetary Science
Letters 274(1–2):269–283, https://doi.org/10.1016/j.epsl.2007.12.005.
Fulton, P.M., E. Brodsky, J.J. Mori, and F.M. Chester. 2019. Tōhoku-oki
fault zone frictional heat measured during IODP Expeditions 343
and 343T. Oceanography 32(1):102–104, https://doi.org/10.5670/
oceanog.2019.129.
Garcia-Castellanos, D., A. Micallef, F. Estrada, A. Camerlenghi, G. Ercilla,
R. Periáñez, and J.M. Abril. 2020. The Zanclean megaflood of theMediterranean—Searching for independent evidence. Earth-Science
Reviews 201:103061, https://doi.org/10.1016/j.earscirev.2019.103061.

7

NATURAL HAZARDS IMPACTING SOCIETY

Hüpers, A., M.E. Torres, S. Owari, L.C. McNeill, B. Dugan, T.J. Henstock,
K.L. Milliken, K.E. Petronotis, J. Backman, S. Bourlange, F. Chemale Jr.,and others. 2017. Release of mineral-bound water prior to subductiontied to shallow seismogenic slip off Sumatra. Science 356:841–844,
https://doi.org/10.1126/science.aal3429.
Kioka, A., T. Schwestermann, J. Moernaut, K. Ikehara, T. Kanamatsu,
T.I. Eglinton, and M. Strasser. 2019. Event stratigraphy in a hadal
oceanic trench: The Japan Trench as sedimentary archive recording
recurrent giant subduction zone earthquakes and their role inorganic carbon export to the deep sea. Frontiers in Earth Science 7:319,
https://doi.org/10.3389/feart.2019.00319.
Le Friant, A., O. Ishizuka, G. Boudon, M.R. Palmer, P.J. Talling, B. Villemant,
T. Adachi, M. Aljahdali, C. Breitkreuz, M. Brunet, and others. 2015.
Submarine record of volcanic island construction and collapse in
the Lesser Antilles arc: First scientific drilling of submarine volcanicisland landslides by IODP Expedition 340. Geochemistry, Geophysics,
Geosystems 16:420–442, https://doi.org/10.1002/2014GC005652.
Lopes, C., and A.C. Mix. 2009. Pleistocene megafloods in the northeast
Pacific. Geology 37(1):79–82, https://doi.org/10.1130/G25025A.1.
Mahony, S.H., R.S.J. Sparks, L.M. Wallace, S.L. Engwell, E.M. Scourse,
N.H. Barnard, J. Kandlbauer, and S.K. Brown. 2016. Increased rates oflarge magnitude explosive eruptions in Japan in the Late Neogene andQuaternary. Geochemistry, Geophysics, Geosystems 17(7):2,467–2,479,
https://doi.org/10.1002/2016GC006362.
Sakaguchi, F. Chester, D. Curewitz, O. Fabbri, D. Goldsby, G. Kimura,
C.-F. Li, Y. Masaki, E.J. Screaton, A. Tsutsumi, and others. 2011. Seismic
slip propagation to the updip end of plate boundary subduction
interface faults: Vitrinite reflectance geothermometry on Integrated
Ocean Drilling Program NanTroSEIZE cores. Geology 39(4):395–398,
https://doi.org/10.1130/G31642.1.
Sawyer, D.E., and J.R. DeVore. 2015. Elevated shear strength of
sediments on active margins: Evidence for seismic strengthening,
Geophysical Research Letters 42:10,216–10,221, https://doi.org/​
10.1002/2015GL066603.
Solomon, E.A., M. Kastner, G. Wheat, H.W. Jannasch, G. Robertson,
E.E. Davis, and J.D. Morris. 2009. Long-term hydrogeochemicalrecords in the oceanic basement and forearc prism at the Costa Rica
subduction zone. Earth and Planetary Science Letters 282:240–251,
https://doi.org/​10.1016/j.epsl.2009.03.022.
Talling, P.J., M. Clare, M. Urlaub, E. Pope, J.E. Hunt, and S.F.L. Watt. 2014.
Large submarine landslides on continental slopes: Geohazards,
methane release, and climate change. Oceanography 27(2):32–45,
https://doi.org/10.5670/oceanog.2014.38.

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FLAGSHIP
INITIATIVESThe Flagship Initiatives comprise long-term research efforts
that require multi-expedition scientific ocean drilling over 10- to
20-year time intervals. Each multidisciplinary research endeavoraims to test scientific paradigms and hypotheses that inform
issues of particular relevance or interest to society. The Flagship
Initiatives typically combine research goals from multiple Strategic
Objectives. Their implementation will be shaped by science proposals that develop coordinated strategies, including long-termplanning, technology development, and innovative applicationsof existing and new scientific ocean drilling data.

1 Ground Truthing Future Climate Change
2 Probing the Deep Earth
3 Assessing Earthquake and Tsunami Hazards
4 Diagnosing Ocean Health
5 Exploring Life and Its Origin

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1 GROUND TRUTHING FUTURE
CLIMATE CHANGE

SUMMARY
Predicting how the Earth system will respond to increasing global temperatures is one of the greatest challenges facing
geoscientists. Atmospheric CO2 concentrations have already exceeded 410 ppm in 2020 and could surpass 900 ppm by
2100 without action to reduce anthropogenic CO2 emissions. Paleoclimate data collected through scientific ocean drilling
established that it has been at least 3 million years since atmospheric CO2 exceeded 410 ppm. Values approaching 900 ppm
were only realized during the hot “greenhouse” climate of the Eocene ~50 million years ago. Numerical climate and Earthsystem models are used to simulate Earth’s response to projected increases in atmospheric greenhouse gas concentrations.
Model projections can provide information about shifts in rainfall and temperature patterns and rising sea levels that canbe used in the design of mitigation and adaptation strategies. High-density, global scientific ocean drilling networks andtransects will enable a more robust identification of feedbacks and tipping points in Earth’s climate system and improvemodeling and IPCC assessments of climate sensitivity to atmospheric greenhouse gases, ocean circulation changes, andother geologic boundary conditions.

2,000

+8°C

Atmospheric CO 2 Concentration

Eocene Climatic Optimum+8°C
Miocene Climatic Optimum+3–4°C

1,000
800

Pliocene Warm Period+2–3°C

600

Threshold for Ice Sheet Development+2–3°C

Last Interglacial+1.5°C

CO 2 Today

400+3–4°C

Holocene Climatic Optimum+0.7°C

Leaf Stomata
Boron Isotopes
Alkenones

+1°C

200

2

1

Thousands of Years Ago

2100
2200
2300

3

TRANSIENT EQUILIBRIUM
0
1800
1900
2000

20
10 5
4
Millions of Years Ago

200

30

400

40

800

50

600

Ice Cores, Speleothems,
and Lake Varves

EQUILIBRIUM

Year (CE)

Evolution of CO2 over the past 55 million years, and projected to 2300. Scientific ocean drilling demonstrates the range, rates, and conditions of past
climate changes, including the only opportunity to investigate the Earth system response to atmospheric CO2 exceeding 400 ppm. Drilling provides thecritical parameterization and validation of developing paleoclimate models, including paleo ice sheet and sea level reconstructions. Data from Foster
et al. (2017), https://doi.org/10.1038/ncomms14845, Masson-Delmotte et al. (2013), and DeConto et al. (2008), https://doi.org/10.1038/nature07337

73

FLAGSHIP
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1

GROUND TRUTHING FUTURE CLIMATE CHANGE

Ground Truthing Future
Emissions Trajectories
Future emissions trajectories depend on society’s choices.
Assessments reported by the Intergovernmental Panelon Climate Change (IPCC) range from a “high emission
scenario,” with emissions peaking well after 2100, to
one with “aggressive reductions,” with emissions peaking between 2020 and 2050 and reducing to near zero
before 2100. The latter trajectory is projected to stabilize
atmospheric CO2 concentrations between 350 ppm and420 ppm, which is required to restrict global warming toless than 2°C above the pre-industrial temperatures of
the nineteenth century.
Ocean sediments record Earth’s climate system response
to global “greenhouse” conditions 50–34 million years ago,
which are analogous to high emission scenarios where
CO2 exceeds 650 ppm. They also record Earth’s response
to warmer climates in the “moderate” CO2 worlds of thepast 5 million years. Analysis of past climates, enabled byscientific ocean drilling, will provide vital information about
how the Earth system may respond to climate warming of
2°C over the coming decades and centuries when tipping
points in the climate system may be reached. The historicalknowledge gained from examining sedimentary archives
will inform society about the rates of change in andirreversibility of some Earth system processes such as ice
sheet collapse and permafrost thawing, permitting informal
assessment of mitigation and adaptation measures.

IMPROVING CLIMATE
MODELS THROUGH SCIENTIFIC
OCEANIC DRILLING
Increasingly sophisticated climate models are becoming
better at capturing the complex interactions within Earth’s
climate system that are required to assess potential rates
of future climate change. At best, however, these models
are mathematical representations and simplify important
Earth processes. They contain uncertainties, some of thelargest of which are related to shifts in precipitation patterns
and atmospheric water vapor, the drivers of recent sea ice
trends, marine ice sheet stability, the mantle’s response tomelting ice volumes, and the sources and sinks of carbon.
Many climate models are calibrated to modern instrumental records, so they may overlook or under-represent critical feedbacks and tipping points in Earth’s climate system74

and may fail to capture the full scale of change.
Knowledge gained from studying past climates recorded
in sediments recovered by scientific ocean drilling provides
valuable benchmarks for testing climate models. Stateof-the-art approaches permit us to reconstruct the many
physical, chemical, and biological interactions between
atmosphere-land-ocean systems that are relevant toclimate models and to constrain leads and lags between
components of Earth’s climate system. Incorporating
information about the global ocean’s response to pastnatural climate variability is a robust way to improveand validate model skill and performance. Improving
model skill and performance is especially relevant to thewarmer-than-present climates projected for the end of
the twenty-first century that Earth has not experienced
since the Pliocene, more than 3 million years ago. We willassemble high-resolution paleoclimate records from globally distributed locations to permit more robust identification of feedbacks and tipping points in Earth’s climate
system and significantly improve assessments of climate
sensitivity to atmospheric greenhouse gases, ocean circulation changes, and other geologic boundary conditions.
Results from these studies can be used to improve models
that predict future climate or simulations that focus on the
pre-Anthropocene world.

UNDERSTANDING CLIMATESENSITIVITY
Defined as the average global surface warming that will
occur in response to a doubling of atmospheric CO2 concentration, climate sensitivity is one of the most important
quantitative estimates of climate change. An understanding of Earth’s climate sensitivity requires knowledge ofdifferent magnitudes and rates of feedbacks in Earth’s
climate system, as well as Earth’s complex behavior when
one or more tipping points are crossed. Ocean sediments
contain information about Earth’s past climate sensitivity,
providing unique data-based insights into how Earth may
respond to elevated greenhouse gas concentrations similar
to those projected in climate models that estimate futureanthropogenic emissions pathways.
We know from scientific ocean drilling results that
Earth’s climate is substantially more sensitive to increased
atmospheric CO2 than simulated in most numerical models.
For example, models cannot yet reproduce the warmer
conditions during the Cretaceous and Eocene in the Arctic
known from studies of ocean sediments. In addition, scientific ocean drilling documented that the climate’s response

1

FLAGSHIP
INITIATIVE

to rapid warming following past ice ages was very large incomparison to the small and gradual energy changes initiated by shifts in Earth’s orbit, showing that climate sensitivity may have varied over time.
To assess Earth’s climate sensitivity, scientific ocean drilling will assemble paleoclimate records from globally distributed drill cores to identify what parts of the climate system
are most susceptible to abrupt and irreversible change. The
marine geologic record contains many relevant examplesof perturbations to Earth’s climate that arose from large
and rapid carbon and aerosol input into the atmosphereand resulted in changes to surface temperatures, rainfall
and drought patterns, ice sheet dynamics, and sea level.

RCP 8.5(2081–2100)a

GROUND TRUTHING FUTURE CLIMATE CHANGE

To better constrain the scales and rates at which key
Earth system processes operate and to reduce climate
sensitivity uncertainties in numerical models, the scientificocean drilling community will collaborate with modelers
and climate researchers to assimilate more paleoclimate
data into models. Paleoclimate records also provide information about past variations in Earth’s climate sensitivity
that will help models better predict how sensitivity mightvary in the future. Paleoclimate records can be used to identify what parts of the climate system have been most susceptible to abrupt and irreversible change. This information
can be used to determine whether models fully resolve thewider consequences of crossing tipping points.

b
90°N

0°

90°S

+2.5°C

010
Zonally Averaged
SST Anomaly (°C)

Mid Pliocene Warm Period(3.3 to 3 Ma)
90°N

0°

90°S

+1.7°C

010
Zonally Averaged
SST Anomaly (°C)

Early Eocene Climate Optimum(54 to 48 Ma)
90°N

0°

90°S

Scientific ocean drilling data remain instrumental
in identifying the magnitude of polar amplificationand model-data mismatches in IPCC assessment
reports. Projected sea surface temperature (SST)
anomalies, relative to pre-​industrial values, frommulti-model mean simulations (color maps; a) arecompared to SST anomalies, relative to present site
temperatures, determined from scientific ocean drilling paleoclimate proxy data (discrete data points,plotted using the same color scale as the model
data, and a circle size scaled to estimates of confidence) for the mid-Pliocene warm period and Early
Eocene Climatic Optimum. Model-data mismatches
for these two past intervals help assess the reliability of the modeled 2081–2100 Representative
Concentration Pathway (RCP) 8.5 (top row). The
modeled zonally averaged SST anomalies (b) for
each time interval reveal the degree of polar amplification (shaded band = 2 standard deviations).
Model ensemble simulations are from the Coupled
Model Intercomparison Project Phase 5 (CMIP5)
ensemble using the RCP 8.5 for 2081–2100, andafter Haywood et al. (2013), https://doi.org/​10.5194/
cp-9-191-2013, and Lunt et al. (2012), https://doi.org/​
10.5194/​cp-8-1717-​2012, for the Pliocene and Eocene,
respectively. Modified from Masson-Delmotte et al.
(2013), Box 5.1, Figure 1+9.6°C

010
Zonally Averaged
SST Anomaly (°C)

SST Anomaly (°C)
–12–10 –8 –6 –4 –2

Low

Medium0

2

4

6

ConﬁdenceHigh
Very High

8 10 12

Not Assessed75

1

FLAGSHIP
INITIATIVEGROUND TRUTHING FUTURE CLIMATE CHANGEDISTINGUISHING HUMAN INFLUENCEFROM NATURAL VARIABILITY
Comparing paleoclimate information collected throughscientific ocean drilling with recent instrumental records
of climate variability can help identify where anthropogenic inputs are most influencing Earth’s climate system.
Modern rates of increasing greenhouse gas concentrations are unprecedented in the last 800,000 years, but theamount of released carbon is not unprecedented in the
deeper geologic past. For example, the Paleocene-Eocene
Thermal Maximum 56 million years ago represents a similar
magnitude of carbon release and can inform us about therates and consequences of anthropogenic CO2 increases
on current carbon cycle feedbacks, ocean acidification,
polar amplification, and global rising temperatures. For

some other critical components of Earth’s climate system,
such as precipitation patterns associated with the El NiñoSouthern Oscillation, it remains difficult to differentiate
the role of natural multidecadal and longer climate cycles
from changes in instrumental data sets that are attributed
to anthropogenic activities. By capturing more repeat
climate events, high-resolution marine sediment coresobtained through scientific ocean drilling can help define
the magnitude and causes of natural variability in Earth’s
climate system over timescales of decades, centuries, andmillennia. These marine archives will also provide information that is not available in land-based records andcomplement similar resolution paleoclimate data obtained
from corals, ice cores, lake records, and speleothems, andthey extend the current limit of ~800,000 years of climate
history provided by ice cores.

Climate Sensitivity Estimates (°C per doubling CO 2 )3-6°C(Slow Feedbacks)//Myr

Timescale

2-4°C(Fast Feedbacks)

Multi-Millennia Millennia Centuries Decades

1.2°C(No Feedbacks)
Years
FEEDBACKS
Clouds, water vapor, lapse rate, snow/sea ice
Upper ocean
MethaneLarge-scale gas hydrate (e.g., PETM)
Vegetation
Dust/aerosol (vegetation mediated)
Entire oceansLand ice sheets
Carbon cycle

Weathering
Plate tectonics
Biological evolution (e.g., vegetation)

Instrumental records

Data Resolution

TOOLSETS
HourlyModel-based projections
Lake sediment cores (e.g., ICDP)
Ice cores
Shallow ocean sediment cores
Scientiﬁc ocean drilling

Myr

Paleoclimate models

Climate sensitivity is one of the most important quantitative estimates of climate change. Compared to most other toolsets, scientific ocean drilling allows us to investigate the influence of Earth system feedbacks on climate sensitivity overa wide range of timescales. PETM = Paleocene-Eocene Thermal Maximum. ICDP = International Continental Scientific
Drilling Program. Modified after Figure 1 in Rohling et al. (2012), https://doi.org/10.1038/nature11574

76

FLAGSHIP
INITIATIVESOLID EARTH INTERACTIONS ANDIMPLICATIONS FOR MODELSThe life cycle of oceanic crust and the mantle processes
that underpin it are key building blocks of climate models. For example, Earth’s mantle viscosity and crustal heatflow impact local ice sheet retreat and regional rates of sea
level rise. Major limitations in understanding the controls
on such relationships also extend to the interpretation of
instrumental data sets of modern change. Our poor understanding of how mantle viscosity influences post-glacial
rebound rates limits our ability to use gravimetry or satellite
altimetry data to accurately estimate the total modern-day
ice sheet mass loss.
Scientific ocean drilling can advance understandingof mantle and crustal properties by probing deep Earthstructures and materials and collecting measurementsof geothermal heat flux. This information can improve
spatial constraints on postglacial isostatic rebound rates.
Sea level curves derived from scientific ocean drilling data
can be used to evaluate and test assumptions about sea
levels employed in whole Earth geophysical models. A
priority will be identifying key solid Earth processes that
influence Earth’s surface geography and topography toimprove model performance. Models can point the scientific ocean drilling community to regions with the greatest
uncertainties, such as the Antarctica ice margins wheresediments were deposited during past major climate
shifts, and focus priorities toward capturing data that will
elucidate mantle properties.

THE WAY FORWARD
Scientific ocean drilling will develop high-density networks
in climatically sensitive areas to assess how multidecadal
to centennial-scale natural climate states manifest themselves across the globe and whether polar to low-latitude
teleconnections are appropriately represented in models.
This endeavor will involve latitudinal (polar-to-equator)transects of drill sites, land-to-sea transects, and detailed
grids in regions. Such data will permit better evaluationof the implications to society of increased climate variability and whether this variability is likely to become
more energized or altered under a warmer-than-present,high CO2 climate state.

1

GROUND TRUTHING FUTURE CLIMATE CHANGE

A priority will be identifying key solid Earthprocesses that influence Earth’s surface geography
and topography to improve model performance.

FURTHER READING
Bronselaer, B., M. Winton, S.M. Griffies, W.J. Hurlin, K.B. Rodgers,
O.V. Sergienko, R.J. Stouffer, and J.L. Russell. 2018. Change in futureclimate due to Antarctic meltwater. Nature 564, 53–58, https://doi.org/​
10.1038/s41586-018-0712-z.
Burke, K.D., J.W. Williams, M.A. Chandler, A.M. Haywood, D.J. Lunt, and
B.L. Otto-Bliesner. 2018. Pliocene and Eocene provide best analogs fornear-future climates. Proceedings of the National Academy of Sciencesof the United States of America 115:13,288–13,293, https://doi.org/​
10.1073/pnas.1809600115.
Goldner, A., N. Herold, and M. Huber. 2014. Antarctic glaciation caused
ocean circulation changes at the Eocene–Oligocene transition.
Nature 511:574–577, https://doi.org/10.1038/nature13597.
Golledge, N.R., E.D. Keller, N. Gomez, K.A. Naughten, J. Bernales,
L.D. Trusel, and T.L. Edwards. 2019. Global environmental consequences of twenty-first-century ice-sheet melt. Nature 566:65–72,
https://doi.org/​10.1038/s41586-019-0889-9.
Hakim, G.J., J. Annan, S. Brönnimann, M. Crucifix, T. Edwards, H. Goosse,
A. Paul, G. van der Schrier, and M. Widmann. 2013. Overview of data
assimilation methods. PAGES News 21:72–73, https://doi.org/10.22498/
pages.21.2.72.
Lenton, T.M., J. Rockström, O. Gaffney, S. Rahmstorf, K. Richardson,
W. Steffen, and H.J. Schellnhuber. 2019. Climate tipping points—Toorisky to bet against. Nature 575:592–595, https://doi.org/10.1038/
d41586-019-03595-0.
Masson-Delmotte, V., M. Schulz, A. Abe-Ouchi, J. Beer, A. Ganopolski,
J.F. González Rouco, E. Jansen, K. Lambeck, J. Luterbacher, T. Naish, andothers. 2013. Information from paleoclimate archives. Pp. 383–464 in
Climate Change 2013: The Physical Science Basis. Contribution of Working
Group I to the Fifth Assessment Report of the Intergovernmental Panel on
Climate Change. T.F. Stocker, D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen,
J. Boschung, A. Nauels, Y. Xia, V. Bex, and P.M. Midgley, eds, Cambridge
University Press, Cambridge, UK, and New York, NY, USA.
PALEOSENS Project Members. 2012. Making sense of palaeoclimate
sensitivity. Nature 491:683–691, https://doi.org/10.1038/nature11574.
van der Wal, W., P.L. Whitehouse, and E.J.O. Schrama. 2015. Effect of
GIA models with 3D composite mantle viscosity on GRACE massbalance estimates for Antarctica. Earth and Planetary Science
Letters 414:134–143, https://doi.org/10.1016/j.epsl.2015.01.001.
Zhu, J., C.J. Poulsen, and J.E. Tierney. 2019. Simulation of Eocene extreme
warmth and high climate sensitivity through cloud feedbacks. Science
Advances 5:eaax1874, https://doi.org/10.1126/sciadv.aax1874.
Zhu, J., C.J. Poulsen, and B.L. Otto-Bliesner. 2020. High climate sensitivity
in CMIP6 model not supported by paleoclimate. Nature Climate
Change 10(5):378–379, https://doi.org/10.1038/s41558-020-0764-6.

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2 PROBING THE DEEP EARTHSUMMARY
Scientific ocean drilling has long aspired to penetrate deep into Earth’s oceanic crust and its underlying mantle. Achieving
this objective is still pushing the limits of technology and thus remains elusive. New multidecadal scientific ocean
drilling strategies seek to probe the deep Earth and to finally reach the upper mantle via a series of interconnected,
ambitious expeditions that will take full advantage of emerging drilling, coring, logging, and monitoring technologies.
This deep drilling will lead to a better understanding of Earth’s formation and evolution; the nature of Earth’s deep
interior and its geodynamic behavior; the interrelationships between the deep Earth and geological, biogeochemical,
and climate cycles; and the limits of life.

Inta

ic W

indo
w

Oce
a
Cor nic
Com e
plex

Lithospheric Crust
Mantle

Tect
on

s

tion

ec
ct S

kes
as
Lav ted Di
e
She
bro

Gab

tite

SPR

EAD

ido
Per

78

ING

Understanding the deep Earthcan be achieved by a series of expeditions that drills a transect of shallower
holes through “tectonic windows” (in thiscase, in the footwall of an oceanic corecomplex) or penetrates the full, approximately 6–7 km thick, oceanic crust in one
hole in normal magmatic crust. Illustration
by Antony Morris and Geo Prose

FLAGSHIP
INITIATIVEPROBING EARTH’S INTERIORWITH DEEP DRILLING
Probing the deep Earth remains a key exploration goalof scientific ocean drilling. Since the Mohorovičić seismic
discontinuity (“Moho”) was postulated in 1909, we still
haven’t confirmed that it forms the fundamental boundary between Earth’s crust—oceanic or continental—and
mantle, and if it varies globally. Through this Flagship
Initiative, scientific ocean drilling will peel back the oceanic
crustal layer to reveal the true nature of the Moho and the
mantle beneath for the first time. Understanding the natureof this seismic boundary in Earth’s overall structure is elemental, as the creation of new oceanic crust in response
to mantle upwelling and convection makes Earth uniqueamong our solar system’s planets.
Deep drilling into oceanic crust and the underlying
upper mantle will also contribute to the resolution ofa range of other outstanding questions. How does theoceanic life cycle of tectonic plates control the sources,
sinks, and pathways of heat and chemical transfer among
the lithosphere, hydrosphere, and biosphere? How doseawater-derived fluids control the depth distribution ofmagma during crustal accretion? How does Earth’s upper
mantle permit microbial life to survive at extreme depths?
Deep drilling allows us to investigate the interconnectedmagmatic, tectonic, hydrothermal, and microbial processes
active in seafloor spreading and during the evolution ofoceanic lithosphere that are responsible for the uniquecharacteristics of more than 50% of Earth’s solid surface.
Attempts to understand ocean crustal evolution throughscientific ocean drilling have been hampered by the limited
number of holes drilled, most of which have penetrated
only the uppermost skin of the upper crust. Deeper crustal
rocks have only been accessed where tectonism hasbrought them to shallow levels in dispersed, atypical locations scattered across the ocean basins or where they havebeen tectonically thrust onto continents. From these investigations, the nature of the Moho appears highly variable. It
could be an igneous boundary between magmatic crustal
rocks and mantle peridotites, an alteration front demarking
the depth limit of fluid penetration and serpentinization, or
something else. These distinct hypotheses imply different
outcomes for the hydrological, chemical, and mechanicalmakeup and evolution of oceanic lithosphere and where
and how earthquakes and volcanism may occur during its
eventual subduction tens to hundreds of million years later.
To understand differences in the styles of ocean crust
formation and maturation and the underlying large-scale

2

PROBING THE DEEP EARTH

mantle circulation patterns and evolution requires probing
deep Earth sections globally through scientific ocean drilling. The Pacific represents a mature fast-spreading ocean
basin surrounded by subduction zones along the Ring ofFire, whereas the Atlantic and Indian Oceans represent
mature slower spreading ocean basins mainly bounded bypassive margins. Understanding the role of these different
plate tectonic environments in the formation of oceanic
lithosphere requires planning for more than one total
crustal penetration: one through fast spreading “normal”
oceanic crust in the Pacific and a second one that completely penetrates slower spreading “normal”’ oceanic crustin either the Atlantic or Indian Ocean. This deep drilling
ideally will deliver two representative sections of oceanic
crust that can be compared to shallower drilled sections in
tectonic windows at slow and ultraslow spreading ridges
that are formed with the lowest melt fluxes and may haveatypical upper mantle rocks exposed at the seafloor.

Deep drilling allows us to investigate theinterconnected magmatic, tectonic, hydrothermal,
and microbial processes active in seafloor spreading
and during the evolution of oceanic lithosphere thatare responsible for the unique characteristics ofmore than 50% of Earth’s solid surface.

EXPLAINING DIFFERENCES IN LOWER
CRUSTAL ACCRETION
Our ability to understand oceanic crustal magmatism andcomposition is severely hampered by the limited availability of lower crustal rock samples. Seafloor accretion rates,
which vary from 1 cm/yr to 20 cm/yr, are known to exert
a first-order control on the structure and internal composition of crust formed during spreading. However, we
do not know how differences in spreading rates result invariations in heat and chemical fluxes and in the extent
of hydrothermal circulation and serpentinization. Lack ofaccess to “normal” lower crustal rocks currently hinders ourunderstanding of the nature of magmatism and how meltdelivered from the mantle ultimately leads to construc-79

2

FLAGSHIP
INITIATIVEPROBING THE DEEP EARTH

tion of most of the crust. The roles magma chambers andmagma transport play remain particularly controversial.
The volume of all oceanic crustal rock samples retrieved byscientific ocean drilling to date amounts to about 20 cubic
meters. Even when combined with fragments of ancient
oceanic crust that escaped subduction and are preservedon land, and dredge and deep diving samples recoveredfrom the seafloor, we have barely scratched the surface ofthe rich variety of oceanic crustal types.
To address the many fundamental questions related tolower crustal accretion, it is essential to first penetrate acomplete crustal section through the crust-mantle boundary and into the shallow mantle at a fast-spreading center.
Such centers account for creation of nearly 50% of thepresent-day oceanic crust while covering ~20% of Earth’s
surface. Those results will then be compared with theoutcomes of targeted deep drilling in the slower spreading Atlantic or Indian and elsewhere in the ocean basins.

Sediments

unanswered. How deep does seawater penetrate into
the oceanic crust and upper mantle? What crustal volume becomes hydrated? How do the heat and chemicalsdConvectively Cooled
Lower Crust Model

e
Lavas

1256D
504B

4

Layer
3

?
Crust

?

5
6

Moho

7
4

6
8
VP (km s–1)

Upper
GabbroLower
Gabbro?
Mantle

?

?

?

?

L
re at
le en
as t
ig
e
ne S
ou tr
s ain
cr in
us
t
Co
ol
in
H
yd rate gro
ﬂu theid rm
ﬂ al
H Int ux
T en
al s
te it
ra y o
tio f
n

3

Dikes

?

Moho
Peridotite

he
at

2

8

c

Our lack of knowledge about the transfers of heat andmass via hydrothermal exchange has left many questions

Layer
2

1

2 secsSub-Basement Depth (km)

0

b

a

DECIPHERING OCEANIC LITHOSPHERE
BIOGEOCHEMICAL EXCHANGE

Predicted Crustal Properties
for End-Member
Crustal Accretion Models

Conductively Cooled
Lower Crust Model

Crustal Seismic Structure

A high level of sampling is necessary to ground truth
geophysical images to enable mapping of much greater
volumes of crust formed at fast-spreading ridges. It will alsoenable us to test the depth limits of life in igneous oceanic
crust. The long-term scope of the 2050 Science Framework
will allow us to exploit emerging deep drilling and logging
technologies to achieve the first full penetration of oceanic crust through the Mohorovičić discontinuity and into
the uppermost mantle.

Recovery of a complete crustal section via scientific ocean drilling will allow us to test two competing end-​member crustal accretion models thatwere developed from seismic observations of the oceanic crust combined with geological and petrological evidence from the Oman ophiolite. In thegabbro glacier ductile flow model (c; for example, 1 ) lower crustal cooling is predominantly conductive, whereas in the sheeted sill model (e) of on-axis
intrusions2, there is convective cooling of the lower crust. The two models predict profoundly different variations in a range of crustal properties (d) thatcan be determined from drill cores with depth, providing an opportunity to test these two models.
(a) Average seismic structure of fast/super-fast-spreading oceanic crust older than 7.5 million years. Gray shading: bounds of average “normal” crustolder than 29 million years.3 Green lines: Ocean Drilling Program (ODP) Site 1256.4 Red line: Deep Sea Drilling Project (DSDP) Site 504.5 (b) Example ofa multichannel seismic reflection image showing a crustal column over a sharp, strong single Moho reflection.6 Black arrows in (c) and (e) show the
movement of the solid lower crust, and blue arrows show the dominant zones where hydrothermal circulation removes latent and sensible heat. The
red arrow in (c) shows the tentative movement of magma. (d) Predicted differences in the relative variations of latent heat release, strain rate, coolingrate, hydrothermal fluid flux, and intensity of high temperature (HT) alteration with depth for the end-member gabbro glacier model (orange) andthe sheeted sills model (green) provide an opportunity to test the accretion models using drill cores. (a,b) Illustration by Benoit Ildefonse, (c,e) after
Korenaga and Kelemen (1998), https://doi.org/10.1016/S0012-821X(98)00004-1. (d) Illustration by Rosalind Coggon. 1Henstock et al. (1993), https://doi.org/​
10.1029/92JB02661; Quick and Denlinger (1993), https://doi.org/10.1029/93JB00698. 2Kelemen et al. (1997), https://doi.org/10.1016/S0012-821X(96)00235-X.
3
After Christeson et al. (2019), https://doi.org/10.1029/2019RG000641. 4Teagle et al. (2006), https://doi.org/​10.2204/iodp.proc.309312.2006. 5Swift et al.
(2008), https://doi.org/​10.1029/2008GC002188. 6Modified from Nedimović et al. (2005), https://doi.org/10.1038/nature03944.

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2PROBING THE DEEP EARTH

delivered by fluid circulation support life? What mineral transformations are caused by the alteration of hot
mantle rocks? Answering such broad questions requires
multidisciplinary collaboration in the investigation of
the coupling among hydrological, geochemical, thermal,
mechanical, and biological processes and the relationshipof these coupled processes to the architecture and physicalnature of lithosphere below the ocean.
To establish the rates, distribution, and significanceof fluid exchange within all seafloor components, fromthe overlying sediments to the igneous crust and upper
mantle, requires knowledge of the temporal and spatial
scales of seawater circulation and transport processes.
Seawater circulation facilitates microbial growth beneaththe seafloor and is critical to the transport and distributionof microorganisms. Yet, the size, activity, and connectivityof the crustal oceanic biosphere are unknown, as is its influence on global geochemical and biogeochemical cycles.
To fully quantify the role that the oceanic life cycle oftectonic plates plays in global biogeochemical exchange
and to determine the limits of habitability and life on
Earth, scientific ocean drilling must penetrate the entire
hydrothermally altered portion of the oceanic crust at avariety of locations to capture differing accretion styles anda range of crustal ages.

samples exposed to seafloor weathering and thus are ofquestionable quality. To make progress requires scientificocean drilling to assemble inventories of the chemical compositions of representative ocean crustal sections. Such a
database will allow us to quantify and remove the effectsof alteration by late-stage magmatic fluids and those due
to reaction with seawater. Importantly, a continuous ocean
crustal section will include pristine samples of in situ residual mantle source rocks.

GLOBAL GEOCHEMICAL CYCLING

THE WAY FORWARD

Although the fast-spreading Pacific constitutes about halfof the extant oceanic crust, new crust formed by amagmatic
spreading in the other ocean basins is far more reactive. The
first reason amagmatic spreading is more reactive is thatsignificant chemical reactions occur when mantle-derived
melts and lower crustal rocks come into contact with seawater. The second reason is that slow-spreading environments contain large, tectonically exposed mantle outcrops,
making hydrological exchange at slower spreading ridges
more important than exchanges within new crust formed
at fast-spreading mid-ocean ridges.
To understand the consequences for global chemical
cycles and budgets among large-scale reservoirs in the
mantle and oceanic and continental crust requires accurate
determination of bulk crustal compositions. Currently, we
cannot quantify the extent to which melt-rock interactions
at mid-ocean spreading ridges are affecting estimates ofthe bulk composition of crust. In addition, our understanding of the bulk composition of oceanic crust is based oncomposite sampling profiles of rocks collected in dispersed
shallow drill holes. These analyses include data from

To fulfill the ambition to drill through intact oceanic
crust into the upper mantle requires innovative solutions
to challenges that have thus far hampered progress.
Recovery of pristine hard rock samples from different
ocean crustal locations will provide fundamental insights
into the nature of Earth’s deep interior and its geodynamic
behavior. It will also help constrain the exchange of heat,mass, and volatiles between Earth’s interior and the crust,ocean, and atmosphere.
Achieving full penetration of the oceanic crust requires
a coordinated and phased approach in parallel with significant advances in drilling technology to core igneousrocks at increased depths and temperatures. Solutions
need to be found to overcome challenges of maintaining hole stability, increasing drill bit life, and drilling into
rocks at elevated temperatures where cooler drilling fluids
may cause thermal shattering of the borehole walls. New
logging tools and geologic sensors need to be developedthat can operate above 150°–200°C in crustal sections
younger than 20 million years. These deep holes will also
provide unique opportunities to install long-term observa-

The long-term scope of the 2050 Science
Framework will allow us to exploit emerging
deep drilling and logging technologies toachieve the first full penetration of oceanic crustthrough the Mohorovičić discontinuity and into
the uppermost mantle.

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2

a

b

PROBING THE DEEP EARTHc
EXTRUSIVE
LAVAS

10 cm

(a) Brecciated glassy pillow
lava margin
U1301B 1R-1, 0–18 cm(b) Curved glassy pillow
lava margin
U1301B 24R-1, 17–36 cm

a– c. Lavas (a–c) are from IODP Hole U1301B, which
penetrates ~320 m into 3.5 million year old intact, insitu upper oceanic crust formed at an intermediate-rate
spreading center (~6 cm/yr full rate) now overlain by~265 m of sediment.1(c) Vesicular massive lava flow
U1301B 18R-2, 72–92 cm

def

SHEETED
DIKES(d) Brecciated dike margin
1256D 161R-2, 17–35 cm(e) Sulfide-impregnated dikemargin breccia
1256D 140R-1, 42–45 cm

DEPTH(f) Multiple cross-cutting dikes
1256D 166R-1, 87–102 cm

g

i

j

LOWER CRUSTALGABBROS(g) Dike-gabbro contact: upper
crust-lower crust boundary
1256D 213R-1, 43–61 cm

d–h. The sheeted dike cores (d–f) are from ODP
Hole 1256D, which penetrates ~1,270 m into 15 million
year old intact, in situ oceanic crust formed at a superfast spreading rate (>20 cm/yr full rate) at the East
Pacific Rise, now overlain by ~250 m of sediment.2
Hole 1256D cored ~800 m of lavas and ~345 m of
sheeted dikes, penetrating lower crustal gabbros at
1,157 m subbasement (g) and the uppermost 100 m ofthe dike-gabbro transition zone (h).

(h) Contact between gabbroand quartz-rich oxide diorite
1256D 214R-1, 25–35 cm(i) Gabbro cut by granoblastic dikeU1473A 32R-6A, 29–55 cmh(j) Layered gabbro (coarse
and finer grained layers)
U1473A 13R-1, 12–41 cm

k

l

m

i–j. IODP Hole U1473A, located at the summit of Atlantis
Bank, an 11–13 million year old elevated oceanic corecomplex on the slow-spreading (1.6 cm/yr full rate)
Southwest Indian Ridge, penetrates ~809 m into
uplifted, unsedimented massive gabbros cut by isolated
dikes (i), with intervals of igneous layering within thegabbros defined by variations in grain size ( j) or modal
mineralogy.3

CRUST MANTLE
TRANSITION(k) Gabbro-serpentinite contact
U1309D 227R-2, 27–43 cm(l) Gabbro-troctolite contact
U1309D 11R-1, 86–99 cm(m) Foliated serpentinite cut by
gabbro dike
U1309D 235R-2, 98–113 cm

k– m. IODP Hole U1309D, located on the Atlantis
Massif—a 0.5–2 million year old oceanic core complex
on the slow-spreading (2.4 cm/yr full rate) Mid-Atlantic
Ridge, penetrates into an uplifted and faulted lower
crustal section, cut by diabase sills.4 The U1309D crustal
section comprises a stack of gabbroic bodies that surround pre-​existing serpentinized peridotites and zones
of olivine-rich troctolite formed by interaction with gabbroic melt (k–m).

Scientific ocean drilling has advanced our understanding of the structure and accretion of oceanic crust by recovering cores from different stratigraphic
levels, allowing us to construct “composite stratigraphies” through the oceanic crust. However, this requires the compilation of results from crustal sections of differing age, produced at a range of spreading rates recovered from diverse tectonic settings. To further advance our understanding of crustal
accretion we need longer continuous sections through the lower crust and into the underlying mantle. 1 Fisher et al. (2005), https://doi.org/​10.2204/​iodp.
proc.​301.2005; 2Teagle et al. (2006), https://doi.org/​10.2204/​iodp.proc.​309312.2006; 3MacLeod et al. (2017), https://doi.org/​10.14379/​iodp.proc.​360.2017;4Blackman et al. (2006), https://doi.org/​10.2204/​iodp.proc.​304305.2006

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tories that will, for example, permit seismological monitoring of Earth’s interior in a quiet environment isolated fromon-land, anthropogenic noise.
Assessing global variability of the deep oceanic crust
will require a suite of complementary drilling strategies.
Sections of the lower crust must be recovered from a rangeof spreading regimes. Options include multi-kilometer-​deep sites, networks of sites drilled to 0.2–1.0 km depththat sample different crustal depths exposed by faulting,and an extended array of ~100 m deep holes to document
scales of lateral variability. Only through such an integrated
approach and ceaseless scientific ocean drilling efforts
continuing through 2050 can we reveal the fundamental nature of Earth’s crust and uppermost mantle, whose
dynamics have shaped this planet.

2

PROBING THE DEEP EARTH

Ohira, A., S. Kodaira, Y. Nakamura, G. Fujie, R. Arai, and S. Miura.
2017. Structural variation of the oceanic Moho in the Pacific plate
revealed by active-source seismic data. Earth and Planetary Science
Letters 476:111–121, https://doi.org/10.1016/j.epsl.2017.08.004.
Suzuki, Y., S. Yamashita, M. Kouduka, Y. Ao, H. Mukai, S. Mitsunobu,
H. Kagi, S. D’Hondt, F. Inagaki, Y. Morono, and others. 2020. Deep microbial proliferation at the basalt interface in 33.5–104 million-year-old
oceanic crust. Communications Biology 3:136, https://doi.org/10.1038/
s42003-020-0860-1.
Teagle, D.A.H., B. Ildefonse, P. Blum, and the Expedition 335 Scientists.
2012. Superfast spreading rate crust 4. Proceedings of the Integrated
Ocean Drilling Program, vol. 335, Texas A&M University, Integrated
Ocean Drilling Program Management International Inc., Washington,
DC, https://doi.org/10.2204/iodp.proc.335.2012.
Wilson, D.S., D.A.H. Teagle, J.C. Alt, N.R. Banerjee, S. Umino, S. Miyashita,
G.D. Acton, R. Anma, S.R. Barr, A. Belghoul, and others. 2006. Drilling togabbro in intact ocean crust. Science 312:1,016–1,020, https://doi.org/​
10.1126/science.1126090.

FURTHER READING
Christeson, G.L., J.A. Goff, and R.S. Reece. 2019. Synthesis of oceanic
crustal structure from two-dimensional seismic profiles. Reviews ofGeophysics 57:504–529, https://doi.org/10.1029/2019RG000641.
Dick, H.J.B., C.J. MacLeod, P. Blum, N. Abe, D.K. Blackman, J.A. Bowles,
M.J. Cheadle, K. Cho, J. Ciążela, J.R. Deans, and others. 2019.
Dynamic accretion beneath a slow-spreading ridge segment: IODP
Hole 1473A and the Atlantis Bank Oceanic Core Complex. Journalof Geophysical Research 124(12):12,631–12,659, https://doi.org/​
10.1029/2018JB016858.
Ildefonse, B., N. Abe, D.K. Blackman, J.P. Canales, Y. Isozaki, S. Kodaira,
G. Myers, K. Nakamura, M. Nedimovic, A. Skinner, and others. 2010. The
MoHole: A crustal journey and mantle quest workshop in Kanazawa,
Japan, 3–5 June 2010. Scientific Drilling 10:56–63, https://doi.org/​
10.2204/iodp.sd.10.07.2010.
Kodaira, S., G. Fujie, M. Yamashita, T. Sato, T. Takahashi, and N. Takahashi.
2014. Seismological evidence of mantle flow driving plate motions at a
paleo-spreading centre. Nature Geoscience 7:371–375, https://doi.org/​
10.1038/ngeo2121.
Li, J., P. Mara, F. Schubotz, J.B. Sylvan, G. Burgaud, F. Klein, D. Beaudoin,
S.-Y. Wee, H.J.B. Dick, S. Lott, and others. 2020. Recycling and metabolic
flexibility dictate life in the lower oceanic crust. Nature 579:250–255,
https://doi.org/10.1038/s41586-020-2075-5.
McCaig, A., A. Delacour, A. Fallick, T. Castelain, and G. Früh-Green. 2010.
Detachment fault control on hydrothermal circulation systems:
Interpreting the subsurface beneath TAG hydrothermal field using
the isotopic and geological evolution of oceanic core complexes
in the Atlantic. Pp. 207–239 in Diversity of Hydrothermal Systems on
Slow Spreading Ocean Ridges. P.A. Rona, C.W. Devey, J.D. Bramley, andJ. Murton, eds, Geophysical Monograph Series vol. 188, American
Geophysical Union, Washington, DC.
Michibayashi, K., M. Tominaga, B. Ildefonse, and D.A.H. Teagle, 2019. Whatlies beneath: The formation and evolution of oceanic lithosphere.
Oceanography 32:138–149, https://doi.org/10.5670/oceanog.2019.136.
Neal, C.R., M.F. Coffin, and W.W. Sager. 2019. Contributions ofscientific ocean drilling to understanding the emplacement ofsubmarine large igneous provinces and their effects on the environment. Oceanography 32(1):176–192, https://doi.org/10.5670/
oceanog.2019.142.

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3 ASSESSING EARTHQUAKEAND TSUNAMI HAZARDSSUMMARY
Undersea earthquakes and associated tsunamis have been responsible for some of our planet’s deadliest and costliest natural disasters over the past 20 years. The 2011 magnitude (Mw) 9.0 Tōhoku-oki earthquake and tsunami in northern Japan
took over 15,000 lives, with economic losses estimated at US$235 billion, making it the most expensive natural disasterin history. The 2004 Mw 9.2 Sumatra-Andaman earthquake and tsunami in the Indian Ocean killed over 230,000 people
in 15 countries and caused losses of ~US$15 billion. Undersea landslides and gravity flows can endanger coastal and offshore infrastructure and telecommunications, as happened in the pair of Mw ~7 Taiwan 2006 earthquakes that severed
22 seafloor cables. The potential earthquake, tsunami, and landslide hazards of many of the world’s subduction zones
are poorly known, as many of the large events have no historic record due to their long recurrence intervals. Scientificocean drilling will significantly advance the study of the plate interface where mega-earthquakes nucleate, as it can directly
access, sample, instrument, and monitor these dangerous offshore and nearshore fault zones. Advancing our understanding of the earthquake and tsunami potential of tectonic plate boundaries worldwide will enable more reliable forecasts of
the risks posed to vulnerable populations and infrastructure and improve hazard preparedness and response.

By providing access to major subseafloor fault zones, scientific ocean
drilling advances understanding of the earthquake and tsunami potentialof tectonic plate boundaries. (left) Damage from the 2010 Mw 8.8 earthquake in Chile. Photo credit: Simon Haberle, Australian National University.
(below) Tsunami devastation in Japan after the 2011 Mw 9.0 Tōhoku-oki
earthquake. Photo credit: istock.com/enase.

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TAKING THE PULSE OF THE
EARTHQUAKE CYCLE
A complete understanding of the processes leading to theoccurrence of large earthquakes requires high-resolution,
continuous measurements of changes in Earth’s crust for
many decades, over different stages of the earthquake
cycle. These measurements need to be collected at different locations globally. In the last five years, subseafloor
observatories installed around Japan, New Zealand, andCosta Rica during scientific ocean drilling expeditions havebeen monitoring variations in crustal strain, geochemicaland hydrological properties, and temperature at hightemporal resolution, with detection limits comparable tothe highest sensitivity instruments on land. These observatories are starting to fill major data gaps required tounderstand the physical controls on earthquake dynamics.
They are also permitting investigation of the behavior of
offshore earthquakes and other types of fault slip, potentially leading to identification of recognizable precursors tolarge, damaging earthquakes and tsunamis.
The discovery 20 years ago that slow-motion
earthquakes—aseismic slip events lasting minutes toyears—occur on many of Earth’s major tectonic faults
sparked a revolution in seismology and fault mechanics.
Episodic slow-slip events play an integral role in subduction mega­thrust dynamics by slowly releasing stored
energy. They have also been implicated in the triggeringof subduction earthquakes in 2011 at the northern Japan
Trench (Mw 9.0 Tōhoku-oki) and in 2014 near Iquique, Chile(Mw 8.2). An improved understanding of the relationshipbetween slow slip events and large earthquakes will lead
to better earthquake forecasting, but it requires near-field
monitoring in the submarine source areas of large earthquakes and slow-slip events at subduction zones.
Scientific ocean drilling can provide a sustained subseafloor observational presence through installation of
networks of borehole observatories in numerous fault
zones around the globe. These observatories will collecta full array of spatiotemporal data throughout the earthquake cycle. Although such observatories have alreadybeen installed by scientific ocean drilling in a few subduction zones, more are needed to span a range of properties
and behaviors, with sufficient spatial density in each locale
to resolve the processes operating within the fault zones.
Where logistically and economically feasible, co-locationof subseafloor observatories with seafloor monitoring networks will maximize spatial coverage, enable integrationof borehole monitoring data with other observables, and

3

ASSESSING EARTHQUAKE AND TSUNAMI HAZARDS

enable earthquake monitoring in real time.
Future scientific ocean drilling should also facilitate
rapid response and monitoring efforts following major
earthquakes, similar to the effort mounted following the2011 Mw 9.0 Tōhoku-oki earthquake. Characterizationand monitoring before and after major events areimportant for building a complete picture of the mechanics of fault slip behavior and variations throughout
the earthquake cycle.

Scientific ocean drilling can provide a sustained
subseafloor observational presence throughinstallation of networks of borehole observatories
in numerous fault zones around the globe.

ACCOUNTING FOR PAST
EARTHQUAKES AND TSUNAMIS
Sediments deposited in earthquake- and tsunami-prone
regions contain information about the frequency of pastlarge events. This information can be useful for assessing
the likelihood of earthquakes and tsunamis occurring at
those locations in the future. For example, ground shaking from major earthquakes can mobilize sediment-laden
flows beneath the ocean that transport and redeposit the
sediment into slope basins and trenches. Ground shaking
can also trigger major, coherent submarine landslides.
Such gravity flow deposits, in combination with onshore
evidence for prehistoric earthquakes and tsunamis, havebeen used in places such as the Cascadia subduction zone
and the Japan Trench to assess the spatial and temporal
distribution of earthquakes associated with subduction
plate boundary megathrust faults. Although many ofthese studies have used shallow piston cores that do not
require drilling, scientific ocean drilling can provide complementary, longer prehistoric earthquake records, particularly in regions with high sedimentation rates such as the
Alaskan margin and other continental shelf areas whereshallow coring cannot adequately sample these critical
records of past events.

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3ASSESSING EARTHQUAKE AND TSUNAMI HAZARDS

Exciting new approaches have been developed forrecognizing past earthquake slip on subseafloor faults.
These techniques include quantifying the heating within afault zone during seismic slip by probing the geochemical
characteristics of rocks recovered through scientific ocean
drilling and investigating the thermal maturity of organic
material within them through laboratory experimentation.
Various novel thermal proxies are being developed toestimate the amount of past frictional heating on faults.
Estimates of temperature increases experienced by thesefault rocks, particularly those in the near surface, can constrain the maximum displacement and seaward extent of
past earthquakes in these fault systems. These parameters
ultimately affect the earthquake magnitude and resulting
tsunami extent and allow quantification of the frictional
work accomplished during earthquake rupture. These andother approaches offer a tantalizing means to use scientificocean drilling to improve records of past earthquake occurrence and assess the potential for near-surface rupture
and tsunami generation.

WHAT FACTORS LEAD TO MASSIVESUBDUCTION EARTHQUAKES?
The massive earthquakes in 2011 in Japan and in 2004
in the eastern Indian Ocean highlight our lack of understanding of the factors that promote and amplify seismic
slip at subduction zones. In both cases, slip was larger
and/or extended farther seaward toward the trench than
expected. Scientific ocean drilling has already played an
important role in revealing some of the physical propertiesof the subduction faults that led to the earthquakes andtsunamis in these two regions. To make significant headway in understanding the slip potential of major subduction zone faults globally requires collecting a broad rangeof observations from diverse environments at different
stages in the earthquake cycle.
To understand how and why earthquakes occur requires
knowledge about how fault zone lithology, chemical environment, and physical conditions such as temperature and

Idealized borehole observatory and integrated seafloor
network. Scientific ocean drilling can provide a sustained
subseafloor observational presence through installationof networks of borehole observatories in numerous
fault zones around the globe. Illustration by Geo Prose,
inspired by Ocean Networks Canada and DONET

Hydrophone
Array
CameraPlatform

Instrument
Platform

Node
SeaﬂoorCameraInstruments
Repeaters

Backbone
Cable

Branching
Units

Junction
Boxes

no
t

to

Nodes

Borehole
Observatory

sc
al
e

Shore
StationBoreholes

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Observatory

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effective stress control the sliding stability and slip behavior of faults. Cores and in situ physical and chemical measurements collected within active fault zones, along withrecovery of sedimentary sequences and oceanic crustfrom regions before they enter the subduction zone, canprovide that needed information. To date, such investigations have been undertaken in only a few locations globally and most have targeted the earthquake-generating
segments of subduction zones. Even there, only relatively
shallow depths have been sampled and with limited spatial
coverage. It is equally important to collect similar data on
subduction zone faults that appear to creep without large
earthquakes to resolve which properties cause some fault
zones to lock up between large earthquakes while others
creep without generating significant earthquakes, or
why some may slip both slowly (aseismically) and rapidly(seismically) along the same part of a fault zone over time.
Scientific ocean drilling will advance understanding of the
key factors that generate large earthquakes and tsunamis,
as it provides the only way to directly access, sample, andinstrument major offshore fault zones.
The factors that produce sudden, large seafloor displacements that can generate tsunamis remain poorly
understood. In particular, a class of earthquakes known as“tsunami earthquakes” generates much larger tsunamis
than expected given the earthquake’s magnitude. These
events are a challenge for tsunami warning, as they do
not generate strong shaking—typically the indicator that
prompts evacuation from the coast and low-lying regions.
The earthquake and landslide processes that cause large
seafloor displacements and therefore tsunamis of all types
remain poorly understood. Targeted scientific ocean drilling to reveal the physical conditions that promote tsunami
generation in different tectonic or structural environments
is needed to identify the sources of potential hazards.

THE WAY FORWARD
The underlying physical processes governing the spectrum of observed fault slip behaviors at subduction zones
can only be addressed with an integrated, system-levelapproach that combines evidence of past and present fault
behaviors, ground truth data on the physical conditions
and materials within plate boundaries, and data collectedby robust, high-precision, subseafloor instruments that
continuously monitor the fault zones. This multifaceted
approach requires a sustained scientific ocean drilling
effort in a representative range of the world’s subduction
environments. Because many of the faults that produce

3

ASSESSING EARTHQUAKE AND TSUNAMI HAZARDS

devastating earthquakes and tsunamis, or faults’ slip effects,
reach across the coastlines, there are numerous opportunities to integrate observations from scientific ocean drillingwith those from onshore geophysical networks, surface
geology, and continental drilling. Such an effort willcontribute important information about how some of theworld’s largest and most active undersea faults work andultimately will improve hazard preparedness and response.

FURTHER READING
Araki, E., D.M. Saffer, A.J. Kopf, L.M. Wallace, T. Kimura, Y. Machida,
S. Ide, E. Davis, and the IODP Expedition 365 shipboard scientists.
2017. Recurring and triggered slow slip events near the trench at
the Nankai Trough subduction megathrust. Science 356:1,157–1,160,
https://10.1126/science.aan3120.
Chester, F.M., C. Rowe, K. Ujiie, J. Kirkpatrick, C. Regalla, F. Remitti,
J.C. Moore, V. Toy, M. Wolfson-Schwehr, S. Bose, and others. 2013.
Structure and composition of the plate-boundary slip zone forthe 2011 Tōhoku-oki earthquake. Science 342(6163):1,208–1,211,
https://doi.org/10.1126/science.1243719.
Davis, E.E., H. Villinger, and T. Sun. 2015. Slow and delayed deformation
and uplift of the outermost subduction prism following ETS andseismogenic slip events beneath Nicoya Peninsula, Costa Rica. Earthand Planetary Science Letters 410:117–127, https://doi.org/10.1016/​
j.epsl.2014.11.015.
Fulton, P.M., E.E. Brodsky, Y. Kano, J. Mori, F. Chester, T. Ishikawa,
R.N. Harris, W. Lin, N. Eguchi, S. Toczko, and Expedition 343,
343T, and KR13-08 Scientists. 2013. Low coseismic friction on
the Tōhoku-oki fault determined from temperature measurements. Science 342(6163):1,214–1,217, https://doi.org/10.1126/
science.1243641.
Goldfinger, C. 2011. Submarine paleoseismology based on turbidite
records. Annual Reviews of Marine Science 3:35–66, https://doi.org/​
10.1146/annurev-marine-120709-142852.
Hüpers, A., M.E. Torres, S. Owari, L.C. McNeill, B. Dugan, T.J. Henstock,
K.L. Milliken, K.E. Petronotis, J. Backman, S. Bourlange, and others.
2017. Release of mineral-bound water prior to subduction tied toshallow seismogenic slip off Sumatra. Science 356(6340):841–844,
https://doi.org/​10.1126/science.aal3429.
Kitajima, H., and D.M. Saffer. 2012. Elevated pore pressure and anomalously low stress in regions of low frequency earthquakes along
the Nankai Trough subduction megathrust. Geophysical Research
Letters 39(23), https://doi.org/10.1029/2012GL053793.
Niemeijer, A., G. Di Toro, W.A. Griffith, A. Bistacchi, S.A.F. Smith, andS. Nielsen. 2012. Inferring earthquake physics and chemistry using
an integrated filed and laboratory approach. Journal of Structural
Geology 39:2–36, https://doi.org/10.1016/j.jsg.2012.02.018.
Sakaguchi, A., F. Chester, D. Curewitz, O. Fabbri, D. Goldsby, G. Kimura,
C.-F. Li, Y. Masaki. E.J. Screaton, A. Tsutsumi, and others. 2011. Seismic
slip propagation to the updip end of plate boundary subduction
interface faults: Vitrinite reflectance geothermometry on Integrated
Ocean Drilling Program NanTroSEIZE cores. Geology 39(4):395–398,
https://doi.org/10.1130/G31642.1.
Tobin, H., G. Kimura, and S. Kodaira. 2019. Processes governing giant
subduction earthquakes: IODP Drilling to sample and instrument subduction zone megathrusts. Oceanography 32(1):80–93, https://doi.org/​
10.5670/oceanog.2019.125.
Wallace, L.M., M.J. Ikari, D.M. Saffer, and H. Kitajima. 2019. Slow motion
earthquakes: Taking the pulse of slow slip with scientific ocean
drilling. Oceanography 32(1):106–118, https://doi.org/10.5670/
oceanog.2019.131.

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4 DIAGNOSING OCEAN HEALTH

FLAGSHIP
INITIATIVESUMMARY
Ocean warming, acidification, deoxygenation, and rising and falling nutrient levels are causing global changes in marine
ecosystems. Declining ocean health can lead to devastating losses in biodiversity, habitats, productivity, and fisheries,
putting life at risk. Similarly, in the pre-Anthropocene epochs, periods of rapid global warming and cooling, ocean anoxic
and acidification events, as well as meteorite impacts and episodes of flood basalt volcanism perturbed ocean ecosystems.
Scientific ocean drilling will target these critical times in Earth history to assess the impacts of catastrophic environmental
changes on marine ecosystems and food webs and the overall planetary carbon footprint. By drilling sites globally andusing new analytical techniques and big data approaches, the high-resolution multidisciplinary data collected throughscientific ocean drilling will offer a diagnosis of ocean health through geologic time that will in turn inform society about
the expected rates, durations, and magnitudes of future ocean health deterioration.

Cretaceous Ocean Anoxic Event
CO2
CO2
CO2

Acidiﬁcation

CO2

Modern-Day Factors

CO2

Warming
Ocean
WarmingCO2
Metalnutrients

Planktonproduction
enhanced bynutrients

Human-caused
greenhouse gas
emissions

CH4

N2O
CO2
CO2
CH4
Warming

Mud slide

CO2

Coral bleaching
Decaying
organic
mattersinks

ANOXIA
Ocean
warming
causesstratiﬁcation

Black shale

Isolationof deep ocean
prevents
oxygen mixing

Ocean
WarmingNutrient
pollutionfrom runoﬀ
stimulates
marinealgal blooms

Acidiﬁcation

Sediments
Lithosphere
Asthenosphere

CO2

Algal blooms
sink and decay
causing anoxic
conditions
Anoxic “deadzones” oncontinental
shelves growANOXIA

Plastic
Pollutionnot

Scientific ocean drilling retrieves marine sediment records that preserve key information on changes in ocean health through geologic
time. Knowledge of how the ocean biosphere responded to major environmental perturbations in the past—for example as a result of
volcanic perturbations to the carbon cycle during the Cretaceous (left)—will provide insights on the future of ocean health through the
Anthropocene (right). Illustration by Rosalind Coggon and Geo Prose

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4DIAGNOSING OCEAN HEALTH

Day 0

OCEAN HEALTH THROUGHGEOLOGIC TIME

Ocean Acidification’s Ability
to Transform Ecosystems

Scientific ocean drilling retrieves sediments that
preserve key information on the interactions
among life on Earth, ocean health, and Earth’s
climate system. These deep-time archives record
the responses of biological activity in the ocean tonatural cycles and occasional catastrophic perturbations over geologic time. Of particular interest
is how shifts in biogeochemical cycles affected
the recovery of life following mass extinctions
and rapid climate change. Scientific ocean drilling
will document the state of the pre-Anthropocene
ocean. By comparing this baseline information
to data from the modern ocean, we will gain
important insights into how the ocean biosphereresponds to greenhouse gas emissions, nutrient
levels, and weathering, and what the possible
consequences might be if humankind continues
to over-exploit marine organisms.

Anthropogenic CO2 emissions not only cause
greenhouse warming, they also acidify theocean. The ecological effects of acidification
are many. In the coastal ocean, they include
reduced biomineralization, carbonate dissolution of reef deposits and shelled organisms,
and changes in the competitive balance ofsurvival between microalgae and corals. In the
open ocean, acidification affects fish physiology and the biomineralization of calcareous
phytoplankton and pteropods, an important
prey group for fisheries.
Scientific ocean drilling will collect preAnthropocene sediments to allow comparisonof the rates of prehistoric ecosystem changewith the rates of change today. Marine sediment archives can reveal how long episodesof acidification lasted and can be used to calibrate biogeochemical and ecosystem models
to understand the feedbacks present in Earth’s
modern carbon cycle. By studying the numerous global warming events of the Cretaceousand Paleogene (from 145 to 23 million yearsago), we will be able to gauge the impact ofpast acidification on ecosystem structure andproductivity. Understanding how past ocean
acidification transformed communities ofcarbonate-​​shelled organisms, including corals,
and how fast they recovered, will inform scenarios of future ocean health and habitability.

OCEAN ACIDIFICATION
AND WARMING
Current CO2 emissions are altering the radiative
heating of our planet, dialing up its thermostat.
They are also lowering the ocean’s pH towardlevels that Earth has not encountered for tens of
millions of years. Globally distributed deep-sea
sedimentary records acquired through scientificocean drilling will reveal how increased rates ofchange in ocean temperature and acidification
affect marine ecosystems and will illuminate
the mechanisms and timeframes of adaptation
and recovery.
Increasing seawater acidity reduces biomineralization of pelagic and benthic calcifiers in theocean, affecting their physiology. Many of theseorganisms play key roles in marine food webs as
primary producers or as prey for larger animals,
directly affecting the global carbon cycle. Risingseawater temperatures—even by a modest 0.5°C
to 1.0°C over the last century—are making coralmicrobial communities (including bacteria,
archaea, protists, fungi, and viruses) vulnerable todisease (bacterial or viral infection) and algal competition. These circumstances are increasingly
causing coral bleaching events. By applying novel
genomic methods, biomarkers, and pH and iso-

~5 mm

Pteropods, tiny snails with aragonitic shells, thrive
in shallow waters and play an important role inpolar ecosystems. These photos show the time
sequence of shell dissolution of the Antarctic
pteropod Limacina helicina in waters simulating thesaturation state of surface seawater with respect
to aragonite that is projected for the Southern
Ocean (Orr et al., 2005, https://doi.org/10.1038/
nature04095) by 2100 under the IS92a businessas-usual CO2 emissions scenario. These experimental results indicate that pteropods may cease toexist in polar latitudes by the middle of the twenty-​
first century, with potential major repercussions toorganisms up the food chain. Source: The photos
were taken in the laboratory of Victoria Fabry fromMarch 31, 2007, to May 15, 2007. Photo credit: David
Liittschwager, National Geographic StockDay 4589

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4DIAGNOSING OCEAN HEALTH

topic sea surface temperature proxies to ancient coral reef
deposits obtained through scientific ocean drilling, we canestablish a highly relevant geologic baseline for the stateof health of today’s coral ecosystems and the global ocean.

DECLINING OCEAN OXYGEN LEVELS
Modern observations reveal that oxygen availability has
been declining in the global ocean over the past 50 years.
Earth system models suggest that future deoxygenation
may expand the world’s oxygen minimum zones by 60%
over the next 80 years in response to anthropogenic
warming, with implied large impacts to all global marine
ecosystems. The situation is particularly acute where
nutrient-​rich runoff fuels algal blooms and leads to theformation of “dead zones” where decomposition during
die-off consumes most oxygen. Current models lack reliable data such as reproducible ocean oxygen records, orthey underestimate the current decline in oxygen concentrations and fluxes between the ocean and atmosphere.
Oxygen minimum zones such as those in the eastern
tropical Pacific and northern Indian Ocean have changed
over time due to numerous interconnected chemical,
biological, and climatic processes acting on global scales.
Scientific ocean drilling will fill critical gaps in our understanding of the mechanisms and history of oxygen fluctuations throughout Earth’s ocean. To tease out various levelsof ocean deoxygenation from the sedimentary record

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requires continued efforts to develop and calibrate reliablebiotic and geochemical biomarker proxies.
At times in Earth’s geologic past, oxygen became limitedin the ocean at significant depths and over large paleogeographical areas. Many of these global ocean anoxic
events are due to increased primary productivity in the surface ocean related to emplacement of large igneous provinces. Nutrient-rich runoff from rapidly weathering rocks
and freshwater stratification in smaller basins such as theMediterranean Sea, Sea of Japan, and Black Sea have led
to the deposition of sapropels—layers of organic-rich sediment that formed under hypoxic conditions. These organicmatter-rich layers can span periods ranging from a few
thousand years to more than 400,000 years. The abundanceof oxygen-depletion events in the geologic record permits
examination of the triggers and tipping points of anoxic
events and their global scope and biological impacts.
Know­ledge of the ecological consequences of anoxic zone
expansions, for example, during the Cretaceous, can beused to better predict the impact to ecosystems of declining oxygen levels in the modern ocean. By obtaining infor-(below) Using proxies for pH and sea surface temperature, records ofmarine biodiversity, and cores from ancient coral reef deposits, scientific ocean drilling will provide insights into the global changes that candevastate coral ecosystems, as illustrated by these images of a coral
reef in American Somoa—before (left) and after (right) a bleaching event.
Credit: XL Catlin Seaview Survey

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mation about the key controls on past ocean oxygen andnutrient levels, scientific ocean drilling can help to establish
how future climate change and excessive nutrient inputs
may affect oxygen availability in the ocean and the magnitude and extent of the resulting ecological responses.

NUTRIENT AVAILABILITY
IN THE OCEAN
Humankind is altering nutrient availability in the ocean.
Agricultural runoff and aerosol deposition of excess nitrogen and phosphorus modify the ocean’s nutrient levels,
enhancing ocean primary productivity. Anthropogenic
CO2 emissions are causing the planet to warm, leading tosurface ocean warming and increased upper ocean stratification. In mid-latitudes, increased thermal stratification—
which serves as a barrier between nutrient-depleted surface waters and nutrient-rich subsurface waters—is widely
predicted to decrease the productivity of food webs in the
open ocean, particularly in the ocean gyres. Reduction inpolar sea ice is projected to increase nutrient availability
in the upper ocean in these regions through increased
upwelling and mixing and, combined with increased lightlevels, will increase phytoplankton biomass, resulting inecosystem-wide changes.
Scientific ocean drilling is well suited to explore theresponse of Earth’s ocean ecosystems to past changes inocean nutrient levels. There are numerous examples fromsediment record of dramatic changes in ocean nutrient
supplies, whether from enhanced weathering on land due
to increased intensity of the hydrological cycle, changes inintensity of coastal upwelling systems, increased thermal
stratification, changes to organic matter cycling, or changes
at the poles from ice-covered to ice-free environments.
Scientific ocean drilling will obtain cores globally from anarray of past environments that exhibit significant changes
in nutrients levels to investigate how those changes
affected ocean ecosystems. This information can be used
to assess the potential rates, magnitudes, and global distribution of the anticipated future decline in ocean healthdue to human inputs.

ECOSYSTEM DYNAMICS IN
A GREENHOUSE WORLD
Global warming is severely disrupting marine and terrestrial habitats, threatening even the most remote ecosystems. In the tropics, increased stress on coral reefs causedby changes in temperature, light, or nutrients is causing

4

DIAGNOSING OCEAN HEALTH

many of them to bleach, while at the cold extreme, the lossof Arctic sea ice is transforming fisheries. Understanding
changes in ecosystem functioning in the geologic past
provides insight into how impaired, transformed, andpotentially new ecosystems will respond to future warming. There are numerous opportunities for scientific ocean
drilling to explore the biodiversity and ecosystem
dynamics of viruses to microbial life and phytoplankton
to micro- and macro-fauna, as well as land plants (throughevidence of forests to grasslands delivered by wind andrivers to the nearby seafloor). Scientific ocean drilling will
expand its high-resolution sediment archives to permit
increased understanding of the future health, abundance,
functioning, and resilience of marine ecosystems on awarmer and ice-free planet.

Globally distributed deep-sea sedimentary records
acquired through scientific ocean drilling will
reveal how increased rates of change in ocean
temperature and acidification affect marine
ecosystems and will illuminate the mechanisms andtimeframes of adaptation and recovery.

THE WAY FORWARD
To better understand how human inputs to the ocean
might impact ocean health, and the timescales of recovery from major perturbations, scientific ocean drilling
will explore times in the geologic past that were punctuated by significant changes in ocean conditions. Drilling
campaigns could examine cyclic anoxia/euxinia in the
Mediterranean Sea and Southern Ocean, the oxygen minimum zone of the northern Indian Ocean, or widespreadocean acidification during the Paleocene–Eocene Thermal
Maximum. Scientific ocean drilling will enable a moreaccurate global assessment of ocean health through timeby collecting cores from globally distributed sites that span
the ocean basins and the transition from land to sea. The
fossil record in the cores chronicle the evolution of ocean
properties, including temperature, oxygen concentration,
pH, and nutrients, and provide information on biodiversity
and biological productivity. Multidisciplinary approaches,state-of-the art analytical techniques, novel paleogenomic

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200

4
–3.0

DIAGNOSING OCEAN HEALTH

Benthic δ13C (‰)
–1.5
0.0

1.5

Relative Sizeof Nuttallides
truempyi

Carbonate ooze
(light colors)Age (+/– ka PETM)

150

Clay-rich sediments(dark colors) wherecarbonate has been
dissolved during
ocean acidiﬁcation

100

50

0

–50

PETM

10

20 30 40 50 60
Number of foraminifera
species at ODP Site 1263

Determining Future Biodiversity Shifts
The Paleocene-Eocene Thermal Maximum (PETM) and the Early
Eocene Climatic Optimum (EECO) are excellent intervals to use
in investigations of marine biodiversity and ocean health during
past “greenhouse” climate states. Scientific ocean drilling cores
are replete with fossilized skeletal and molecular remains of past
life, whose chemistry, biology, and diversity reveal the health andresilience of ancient ecosystems and food webs. Future scientificocean drilling could target bleaching episodes, for example,
during a relatively brief interval of the PETM, when planktonic
foraminifera discarded their algal symbionts in a process similar towhat happens in corals exposed to higher temperatures. On longer
timescales, larger benthic foraminifera and calcareous algae outcompeted corals during the PETM and EECO, replacing coral-algal
reefs with foraminifer-algal banks on a worldwide basis for morethan 10 million years. These foraminifer-algal banks dominatedcoastal ecosystems throughout the tropics and can be found on
atolls and guyots in the central Pacific. Deep-time reef records
targeted by scientific ocean drilling can show us how long-lasting
global warming can flip ecosystems such as coral reefs to an alternate state for millions of years.

The PETM (55.8 million years ago) provides an analogue for exceptionally high rates of ocean acidification and carbonate dissolution in the ocean of ahigh-CO2 world. Scientific ocean drilling cores from Ocean Drilling Program (ODP) Site 1263 (Walvis Ridge) reveal a rapid and enormous loss of speciesof shell-forming foraminifera (blue line) occurs during ocean acidification, coeval with a carbon isotope (δ13C) excursion in shells of deep-sea benthic
foraminifera. Surviving species, such as the depicted Nuttallides truempyi (all specimens to scale), show a severe reduction of test size. Species diversity
eventually recovers, although at a much slower pace over tens of thousands of years. From Thomas (2012), https://doi.org/10.22498/pages.20.1.37

tools, and integrated data sets will allow us to diagnose
past ocean health at centennial and millennial timescales.
All the evolutionary and paleoenvironmental data collected from physically archived marine sediment cores will
feed into publicly accessible databases for Earth systemmodeling and big data exploration and interpretation.
Integrated data sets allow identification of teleconnections,feedbacks, and tipping points in ocean health, and allow us
to put the rates and scales of current changes in context.

FURTHER READING
Eiler, J., J. Cesar, L. Chimiak, B. Dallas, K. Grice, J. Griep-Raming,
D. Juchelka, N. Kitchen, M. Lloyd, A. Makarov, and others. 2018.
Analysis of molecular isotopic structures at high precision andaccuracy by Orbitrap mass spectrometry. International Journal of Mass
Spectrometry 422:126–142, https://doi.org/10.1016/​j.ijms.2017.10.002.
Hesselbo, S.P., S.A. Robinson, and F. Surlyk. 2004. Sea-level change
and facies development across potential Triassic–Jurassic boundary
horizons, SW Britain. Journal of the Geological Society 161(3):365–379,
https://doi.org/​10.1144/0016-764903-033.

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Hoegh-Guldberg, O., P.J. Mumby, A.J. Hooten, R.S. Steneck, P. Greenfield,
E. Gomez, C.D. Harvell, P.F. Sale, A.J. Edwards, K. Caldeira, and others.
2007. Coral reefs under rapid climate change and ocean acidification. Science 318(5857):1,737–1,742, https://doi.org/10.1126/
science.1152509.
Hönisch, B., A. Ridgwell, D.N. Schmidt, E. Thomas, S.J. Gibbs, A. Sluijs,
R. Zeebe, L. Kump, R.C. Martindale, S.E. Greene, and others. 2012. The
geological record of ocean acidification. Science 335(6072):1,058–1,063,
https://doi.org/10.1126/science.1208277.
Hu, S.Y., S.J. Barnes, A. Pagès, J. Parr, R. Binns, M. Verrall, Z. Quadir,
W.D.A. Rickard, W. Liu, D. Fougerouse, and others. 2020. Life on theedge: Microbial biomineralization in an arsenic-and lead-rich deep-sea
hydrothermal vent. Chemical Geology 533:119438, https://doi.org/​
10.1016/j.chemgeo.2019.119438.
Norris, R.D., S.K. Turner, P.M. Hull, and A. Ridgwell. 2013. Marine ecosystem responses to Cenozoic global change. Science 341(6145):492–498,
https://doi.org/10.1126/science.1240543.
Schaefer, B., K. Grice, M.J.L. Coolen. R.E. Summons, X. Cui, T. Bauersachs,
L. Schwark, M.E. Böttcher, T.J. Bralower, S.L. Lyons, and others.
2020. Microbial life in the nascent Chicxulub crater, in press.
Geology 48(4):328–332, https://doi.org/10.1130/G46799.1.
Zeebe, R.E., J.C. Zachos, K. Caldeira, and T. Tyrrell. 2008. Carbon emissions
and acidification. Science 321(5885):51–52, https://doi.org/​10.1126/
science.1159124.

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5 EXPLORING LIFE
AND ITS ORIGIN

SUMMARY
Marine sediments and oceanic crust host a complex, active, globe-spanning ecosystem in which microorganisms live,
interact, evolve, and die. The features and strategies that enable deep life to persist in these geologic habitats, what
communities form under these extremely energy-limited conditions, and what geochemical and biochemical processes
create their novel biosignatures remain largely unknown. To sample, monitor, and analyze a representative range of Earth’s
diverse subseafloor environments and the multitude of microbial communities that they inhabit in Earth’s interior requires
scientific ocean drilling. A sustained drilling effort will significantly advance understanding of the rules of life, the limits oflife, and the origins and evolution of life on Earth. It also offers the opportunity to establish what life might look like in analogous environments on other worlds and what new organisms and novel biological functions useful in geobiotechnology
reside in Earth’s subseafloor.

EUKARYA
Animals

Fungi
PlantsBACTERIA
Other
bacteria

Cyanobacteria
Proteobacteria

ARCHAEA
Crenarchaeota

Euryarchaeota

Algae

a

Bac

ise to chthat gave r
teria
Bac

loroplasts

Ciliatesdria
hat gave rise to mitochon
ria t
te

c

~25 µmb~500 nm~10 µmCell

PRIMITIVEANCESTRAL CELLS

The tree of life, based on analysis of DNA sequences from organisms across all three domains of life: Bacteria, Archaea, and Eukarya. Scientificocean drilling allows researchers to access environments below the seafloor that resemble early Earth and/or are analogues to environments foundelsewhere in the solar system (after illustration by Jayne Doucette in Teske and Edwards, 2005). By analyzing microbial communities in these environments, we can better predict what primitive ancestral cells may have looked like as well as clarify what types of lifestyles likely exist on extraterrestrial
bodies. (a) Microbial colonization (orange dots) of mineral incubation experiments in subseafloor oceanic crust on the Juan de Fuca Ridge flank (Orcutt
et al., 2011, https://doi.org/10.1038/ismej.2010.157). (b) A microscopic view of microbial life in a subseafloor sediment core sample obtained by drilling
vessel Chikyu off Shimokita Peninsula, Japan. Green particles represent microbial cells (Morono et al., 2009, https://doi.org/10.1038/ismej.2009.1). Photo
credit: JAMSTEC. (c) A microscopic image of a microbial cell (white) on a 2 km deep, 20-million-year-old coal particle (black) obtained by Chikyu during
IODP Expedition 337 (Site C0020; Inagaki et al., 2015, https://doi.org/10.1126/science.aaa6882; Trembath-Reichert et al., 2017, https://doi.org/10.1073/
pnas.1707525114). Photo courtesy of Elizabeth Trembath-Reichert, Caltech

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5EXPLORING LIFE AND ITS ORIGIN

DEFINING THE RULES OFMICROBIAL LIFE
The communities that live inside rocks, in the pore spaces
between sediment grains, in fault zones, and in hydrothermal vents are different from those we are more familiar within other, more accessible environments. These ecosystems
remain essentially untouched by human activities. Resultsfrom previous scientific ocean drilling studies indicate thatmicrobes living in subseafloor sediment have severely
limited access to energy; on average, they respire and turnover their biomass hundreds to thousands of times more
slowly than microbes in the surface world. The rules thatpredict an organism’s behavior and structure at such slow
rates of activities are essentially unknown. The rates of cell
division and evolution in subseafloor populations as wellas the extent and nature of communication within its communities are virtually a blank slate. We also know practicallynothing about the adaptations that enable organisms topersist in subseafloor environments, far from the abundant
energy at Earth’s surface in the photosynthetic world.

By studying the life that inhabits extreme
subseafloor environments, we will gain insight
into the potential adaptations of primordial
life, the constraints under which it evolved,
and hence the origin of life on Earth.

Marine sediments and the underlying crustal rocks comprise fundamentally different environments. The microbesthat inhabit the variable substrates in these different environments probably also differ. Marine sediments comprisea porous, but relatively impermeable, environment where
diffusion usually dominates dissolved chemical transport,
and opportunities for organismal mobility are limited. In
this environment, we hypothesize that organismal lineages
are introduced early in sediment deposition and then are
subjected to burial for many millions of years. In contrast,
the upper basaltic oceanic crust is a fracture-permeable
but generally relatively low porosity environment, where
fluid advection is probably the dominant process. There,organisms may be continually introduced by inflow ofseawater from the deep ocean. How and why community

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interactions, organismal adaptations, population turnover,and evolution vary from marine sediments to the underlying rock is almost completely unexplored. The diversityof habitats is plausibly linked to biotic diversity in termsof the overall pace of metabolic activity, favored metabolisms, complexity of biological consortia, and abundance ofliving material. As yet, we have little notion of the inherent
degree of complexity of these different biomes. In short, therules of life within these two very different globe-spanningbiomes are unknown.
Solving these fundamental unknowns will require scientific ocean drilling to target a diverse, yet representative
range of sediment regimes and rock environments withbiological, chemical, and geological sampling; biologicalexperimentation; and continuous subsurface monitoringand manipulation via borehole observatories. This integrated, globe-spanning effort will ultimately elucidate
the rules of life for the organisms that persist and thrive inthese extraordinary systems.

EXPLORING THE LIMITS OF LIFE
Scientific ocean drilling provides an opportunity to explore
the limits to habitability on Earth. The depths to which life
extends beneath the seafloor and the properties that limitthat extent of life, whether it is high heat, a low energy flux
directly available to microbes, absence of liquid water, orsome other property, are completely unknown and likely
differ from one subseafloor environment to another. We
will drill deep into the seafloor in diverse environmentswith the expectation of reaching the depths at which life
is no longer able to survive. Such environments will spandifferent combinations of potentially life-limiting factors,
such as temperature, bioavailable energy flux, pressure,dissolved metal concentrations, water availability, andpH. We will sample and conduct in situ experiments at
high-temperature hydrothermal systems, in deep hot sediment, in high-pH serpentinization zones, and at the greatest, but thus far unknown, depths where liquid water exists
in oceanic crust. Analytical approaches in metagenomics,
proteomics, lipidomics, and other potential omics techniques will guide scientific ocean drilling in exploring thelimits of life.
There are numerous examples of advances in biotechnology and medical fields based on studies of life in these
extreme environments. There is a high potential for discovery of new organisms, enzymes, and more from deep-sea
and subseafloor environments. Scientific ocean drilling canprovide crucial information on the environmental factors

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that will allow better cultivation and isolation of a variety oforganisms from these biomes that will help understand thepotential for life beyond Earth.

CONSTRAINING THE ORIGIN OF LIFE
Constraining the fundamental conditions of life’s origin
and the core characteristics of the earliest life on Earthremains a significant scientific challenge. The origin ofEarth-based life more than 3.5 billion years ago is only
preserved in a very few ancient continental rocks. A direct
assay of Earth’s earliest life is not possible by scientific ocean
drilling because the oldest ocean basins are only about
200 million years old. However, scientific ocean drilling canconstrain aspects of life’s origin by sampling modern deep
subseafloor environments that are analogous to the early
Earth, including the “warm pools” of hot vents, “clay mineralfactories,” impact-generated hydrothermal systems, andsulfide-rich seeps. Scientific ocean drilling provides accessto the organisms that persist, and perhaps thrive, underthese extreme subseafloor environmental conditions, suchas constant anoxia, darkness, high pressure, locally high

5

EXPLORING LIFE AND ITS ORIGIN

temperatures, highly restricted energy sources, and minerals that catalyze life-sustaining reactions. By studying thelife that inhabits extreme subseafloor environments, wewill gain insight into the potential adaptations of primordial life, the constraints under which it evolved, and hence
the origin of life on Earth.

DISCOVERING THE SIGNATURES OF LIFE
The discovery that life exists beyond our planet would
demolish the notion that Earth-based life is unique in theuniverse. Multiple discoveries would demonstrate theorigin and persistence of life to be universally commonplace. How can we drive such discoveries? To gain further
insights into the origin of life on Earth and the possible
occurrence of life on other worlds, it is essential to effectively detect signatures of ancient life in sediments androcks. A biosignature is “an object, substance, and/or pattern whose origin specifically requires a biological agent”
that includes, but is not limited to, organic biomarkers,
microfossils, stable isotopic compositions of minerals andorganic compounds, and paleo­genomic data sets.

Moho

Lithospherenot to scale

Asthenosphere

Scientific ocean drilling can access an array of potential habitats deep beneath the seafloor. It has provided vital samples that have yielded microbes,
illuminating the features and strategies that enable deep life to persist in these diverse geologic habitats. Illustration by Geo Prose, inspired by
Figure 4 in D’Hondt et al. (2019), https://doi.org/10.5670/oceanog.2019.146. Photo credits: (left) Deep sediments. From Figure 2 in Inagaki et al. (2015),
https://doi.org/10.1126/science.aaa6882. (middle) Young oceanic crust. From Figure 3 in Ramirez et al. (2019), https://doi.org/10.3389/fmicb.2019.01983.
(right) Old oceanic crust. Courtesy of Jason Sylvan, Texas A&M University

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Scientific ocean drilling offers the opportunity to assess
the preservation potential and meaning of biosignatures
through deep time and under diverse environmental(e.g., oxygenated versus non-oxygenated) and chemical(e.g., high concentrations of sulfur or iron) conditions. Suchknowledge will enable us to establish proxies for ancient
life, document biosphere responses to past major environmental perturbations, and build new methods to predict
biosphere response to future environmental changes.
Scientific ocean drilling will enable us to explore genomic(biotic) and chemical (abiotic or prebiotic) evolutions.
Further, if life did evolve on other worlds, it may be that in
the now dry, former surface water bodies on Mars there still
exists a rock record containing fossils of life that has been
largely blasted away in the ~3.8 billion year old “heavy
bombardment” of Earth, or the subsequent erosional andtectonic remolding of our planet’s surface. Impact craters
represent a potential microbial habitat for thermophilic life
both on Earth and other planets. Continued explorationof the records of impact-generated hydrothermal ecosystems could yield insights into locations for exploration onother worlds. Terrestrial to extraterrestrial collaborations
between the scientific ocean drilling and space science
communities offer an avenue to predict what signatures oflife may look like on the moons and planets of our solar
system and beyond.
Sampling living subseafloor communities is a technical challenge. The ability to detect biosignatures requires
minimizing contamination and the ability to preserve
organisms for study at viable temperature and pressure
conditions, cultivate communities within subseafloor
boreholes, and image cells in their environmental context(a) Microbial Cell Counts in the
Sediment-Hosted Deep Biosphere
10

–2

10

0

Cell concentration (cells/cm3)
10 2
10 4
10 6

10

8

10

10

(b) Evidence of Ocean CrustHosted Microbial Life

10 –3

Depth below seaﬂoor (m)

10

–2

10 –3

Oﬀ Shimokita
Equatorial PaciﬁcBering Sea
South Paciﬁc
North Paciﬁc Gyre
South Paciﬁc Gyre
ODP sites

10 0

10 1

10 2

10 3

2,466 mIODP Expedition 337

10

1 mm

4

New MQL(<10 cells cm–3 )Previous MQL(~105 cells cm–3 )(a) Scientific ocean drilling has made great advances in sampling the biosphere within the ocean sediment column globally, mapping regional variationsin the exponential decrease in cell abundance with depth. Novel techniques have allowed scientists to lower the minimum quantification limit for sedimentary microbial cell enumeration (MQL) by several orders of magnitude and demonstrate that microbial life extends more than 2 km beneath theseafloor where cell counts were as low as 10 cells/cm3 (yellow dots clustered around 2,466 meters below seafloor constitute the deepest subseafloor
sediment samples examined for life to date; IODP Expedition 337 Site C0020; Inagaki et al., 2015, https://doi.org/​10.1126/science.aaa6882). (b) Scientificocean drilling is also significantly enhancing knowledge of the composition, origin, and heterogeneous distribution of communities in subseafloor
igneous crust, as illustrated here by the microbial colonization of a basalt hosted hydrothermal celadonite vein (light [left] and fluorescence microscopy[right] of SYBR Green I-stained microbial cells). A future goal is to obtain microbial samples from within oceanic crust of all ages to determine cell counts
and to investigate how the distribution of microbes relates to fluid pathways and the extent to which the biosphere facilitates hydrothermal exchange.
(a) From: D’Hondt et al. (2019), https://doi.org/​10.5670/oceanog.2019.146. (b) From Suszuki et al. (2020), https://doi.org/10.1038/s42003-020-0860-1

96FLAGSHIP
INITIATIVE

5EXPLORING LIFE AND ITS ORIGIN(within sediment and rock). Detection of biosignatures willaid in identifying, characterizing, and understanding life
below the seafloor and will directly benefit the search forextraterrestrial life, where similar barriers to discovery exist.
Advancement of such shared interests between the scientific ocean drilling and space science communities requires
identification of the best subseafloor analogues to extraterrestrial habitats. We will team with space agencies todesign and test tools and to formulate criteria that will best
assess biosignatures and aid in understanding habitability
in Earth’s subseafloor and on other worlds.

The quest to understand the origins, diversification, andevolutionary processes of life on Earth and the pursuit of lifeon other worlds are challenges of the first order. To accomplish these goals, the scientific ocean drilling community
must collaborate with space science communities to identify the best Earth drilling targets that might be analogues
to extraterrestrial habitats and develop the technologies
most likely to yield insights about the organization of life
below the seafloor and elsewhere in our solar system.

THE WAY FORWARD

Armbrecht, L.H., M.J.L. Coolen, F. Lejzerowicz, S.G. George, K. Negandhi,
Y. Suzuki, J. Young, N.R. Foster, L.K. Armand, A. Cooper, and others.
2019. Ancient DNA from marine sediments: Precautions and considerations for seafloor coring, sample handling and data generation. Earth-Science Reviews 196:102887, https://doi.org/10.1016/​
j.earscirev.2019.102887.
Cai, L., B.B. Jørgensen, C.A. Suttle, M. He, B.A. Cragg, N. Jiao, and R. Zhang.
2019. Active and diverse viruses persist in the deep sub-seafloor
sediments over thousands of years. The ISME Journal 13:1,857–1,864,
https://doi.org/10.1038/s41396-019-0397-9.
Colwell, F.S., and S. D’Hondt. 2013. Nature and extent of the deep
biosphere. Pp. 547–574 in Carbon in Earth. R.M. Hazen, R.J. Hemley,
A. Jones, and J. Baross, eds, Reviews in Mineralogy and Geochemistryvolume 75, https://doi.org/10.2138/rmg.2013.75.17.
Inagaki, F., K-U. Hinrichs, Y. Kubo, M.W. Bowles, V.B. Heuer, W.L. Hong,
T. Hoshino, A. Ijiri, H. Imachi, M. Ito, and others. 2015. Exploring deep
microbial life in coal-bearing sediment down to similar to 2.5 km below
the ocean floor. Science 349(6246):420–424, https://doi.org/10.1126/
science.aaa6882.
Jones, R.M., J.M. Goordial, and B.N. Orcutt. 2018. Low energy
subsurface environments as extraterrestrial analogs. Frontiers in
Microbiology 9:1605, https://doi.org/10.3389/fmicb.2018.01605.
Orcutt, B.N., D.E. LaRowe, J.F. Biddle, F.S. Colwell, B.T. Glazer, B. Kiel
Reese, J.B. Kirkpatrick, L.L. Lapham, H.J. Mills, J.B. Sylvan, and others.
2013. Microbial activity in the deep marine biosphere Progress andprospects. Frontiers in Microbiology 4:189, https://doi.org/10.3389/
fmicb.2013.00189.
Orsi, W.D., B. Schink, W. Buckel, and W.F. Martin. 2020. Physiologicallimits to life in anoxic subseafloor sediment. FEMS Microbiology
Reviews 44:219–231, https://doi.org/10.1093/femsre/fuaa004.
Stamenković, V., L.W. Beegle, K. Zacny, D.D. Arumugam, P. Baglioni,
N. Barba, J. Baross, M.-S. Bell, R. Bhartia, J.G. Blank, and others. 2019.
The next frontier for planetary and human exploration. Nature
Astronomy 3:116–120, https://doi.org/10.1038/s41550-018-0676-9.

The globe-spanning deep biome can only be understood
through sustained scientific ocean drilling efforts to sample,
monitor, and analyze sediments, rocks, and organisms froma representative range of Earth’s subseafloor environments.
Direct study of natural communities and hypothesis-driven
experiments are critical for advancing understanding ofthese extraordinary biomes. Scientific ocean drilling willallow us to delineate the conditions in which subseafloor
communities live and in which they fail to live, and characterize how these organisms evolve, interact, and die.
Experiments, including in situ manipulations, will elucidate
the features and strategies that enable microbes to persist
and communities to form under specific subseafloor conditions and will allow us to identify the biochemical processes that create biosignatures.
Life detection and description will require interdisciplinary teamwork—a hallmark of scientific ocean drilling.
Astrobiologists will analyze the DNA and RNA of the sparseorganisms that must exist near the limits of life as well as thecontrasting diverse communities in more energy-rich environments. Hydrologists will determine the connectivity ofthe deep-sea plumbing system to answer how life moves
around and how it is interconnected in the confined worldsof sedimentary grains and rock fractures. Geologists will
evaluate the trace fossil remains of microbial communities.
Geochemists will examine the host of chemical and mineralogical waste products left by metabolic reactions andanalyze authigenic minerals that record past pore waterchemistry conditions influenced by microbial processes.
Integration of these multiple lines of evidence to answer
our fundamental questions regarding the origin of life
will require big data analytics, which will aid us in robustly
mapping the novelty of the various communities sampledthroughout Earth’s globe-encircling deep biosphere.

FURTHER READING97

ENABLING
ELEMENTSThe Enabling Elements serve to significantly advance the goalsof scientific ocean drilling through numerous and varied broader
impacts and outreach initiatives, partnerships and collaborations with organizations that have complementary scientificgoals, and continued technology development and innovative
applications of advanced data analytics.

1 Broader Impacts and Outreach
2 Land to Sea
3 Terrestrial to Extraterrestrial
4 Technology Development and Big Data Analytics

98

ENABLING
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1 BROADER IMPACTS
AND OUTREACH

SUMMARY
Scientific ocean drilling targets a broad array of topics that are of interest andimportance to society, contributing vital data that will improve climate models,advance earthquake knowledge, and provide insight into the possibility of life onother worlds. It is a proven model for global collaborative research and an incubator for disciplinary partnerships in science and engineering. Widely recognized
as a preeminent training ground for the next generation of Earth scientists, scientific ocean drilling will capitalize on its international, cross-disciplinary shipboard
and shore-based science parties to advance participation of traditionally underrepresented groups. Using a variety of social media and web-based platforms,
data and results will be broadly disseminated to educators, policymakers, and the
public, securing scientific ocean drilling’s position as the authoritative source of
information about the Earth system.

ECORD Summer School 2016 in Bremen,
Germany. The goal of the summer
schools is to train the next generation ofscientists. Credit: MARUM – Zentrum fürMarine Umweltwissenschaften, Universität Bremen, V. Diekamp99ENABLING
ELEMENT

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BROADER IMPACTS AND OUTREACH

THE IMPACT OF SCIENTIFIC OCEAN DRILLING
Scientific ocean drilling advances understanding of how the Earth system has operated in the past by providing the means
to access archives of sediment and rock that lie deep beneath the seafloor and by instrumenting borehole observatories
to monitor the subseafloor and conduct experiments. Scientific ocean drilling has an impact on a wide range of issues ofbroad interest to society, exemplified here.
Advancing earthquake studies
Studies of earthquake generation
at subduction zones are hampered
by a lack of in situ samples andmeasurements from active plateboundary faults. In a rapid responseto the magnitude 9.1 Tōhoku-oki
earthquake in 2011, scientific ocean
drilling penetrated the fault zone that ruptured during theearthquake and measured the frictional heating generated
by it. Such data provide important constraints on the forcesthat influence earthquake hazards. Only by deploying adrilling platform that can penetrate into deep fault zones
and by implementing sophisticated downhole technologies under challenging borehole conditions can scientists
collect and record such important in situ data.
Improving climate models
Studies of cores recovered globally
through scientific ocean drilling haveallowed reconstruction of the past
180 million years of Earth’s climate
history. Continued advances in drilling technology and analytical techniques and recovery of cores fromcarefully selected sites will increase the temporal and spatial resolution of assembled paleoclimate and paleoceanographic records. These records are needed to ground truth,
and thus improve, global climate forecasts. They will also
be used to test more refined hypotheses about the rates ofchange in temperature and sea levels as our climate warms
and to pinpoint tipping points in the climate system.
Discovering the deep biosphere
Through new approaches to drillingand coring that allow collection ofpristine samples, scientific ocean
drilling has contributed to advancing understanding of the quantity,
diversity, and global significance oflife in subseafloor sediments and100

rocks. This deep biosphere may be the largest ecosystem
on Earth, driving subseafloor geochemical processes, theglobal carbon cycle, and the alteration of sediments androcks. Deep biosphere studies also seek to reveal how life
can survive in hot, nutrient-deprived, high-pressure environments. These studies will lead to a better understanding of the limits of life on Earth and the potential for life
elsewhere in the universe. Simultaneously, discoveries of
new species within the subseafloor biosphere may offer
opportunities to develop novel pharmaceuticals.
Assessing future ocean health
Seafloor sediments preserve information about the responses of ocean
biological activity to natural cycles
and catastrophic perturbations overgeologic time. Shifts in biogeochemical cycles modulate the recovery oflife following mass extinctions andepisodes of rapid climate change. Cores recovered by scientific ocean drilling will provide baseline information about
the abundance and diversity of microscopic organisms
living in the pre-Anthropocene ocean. Comparing thesedata to contemporary responses of the ocean-biospheresystem to changes in greenhouse gas emissions, nutrient
levels, weathering, and the exploitation of marine organisms will contribute to projections of the ocean’s future
health and habitability.
Investigating the deep Earth
Geochemical exchanges between thesolid Earth, ocean, atmosphere, andbiosphere have influenced Earth’s
surface environment throughout its
history. Emerging drilling, coring,
logging, and monitoring technologies, will permit investigation of theinterconnected magmatic, tectonic, hydrothermal, andmicrobial processes in seafloor spreading and oceanic
lithosphere evolution that are responsible for the uniquecharacteristics of Earth’s surface.

ENABLING
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BROADER IMPACTS AND OUTREACH

PLATE TECTONICSMASSEXTINC
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INSPIRING EDUCATORS AND THE
PUBLIC THROUGH DISCOVERY
A growing number of geoscience initiatives are working toincorporate real data into undergraduate classrooms andlaboratory learning. Free and openly available, scientificocean drilling data are a valuable resource for such projects.
They cover a range of topics and disciplines that capture
the imagination: asteroid impacts that led to the demiseof dinosaurs, hot climates in the geologic past that may
be akin to what a future Earth may look like, and extreme
environments deep beneath the seafloor where microbes
thrive. The scientific ocean drilling community will actively
partner with education initiatives globally to ensure incorporation of drilling data into curriculum modules.
Web-based tools are available to broadly educate thepublic about scientific ocean drilling and disseminate
information about exciting discoveries. For example, interactive websites and live ship-to-shore broadcasts can beincorporated into classroom lessons and museum exhibits.
Online “story maps” can convey how scientific ocean drilling works, including technologies, life on the ship, tours
through the laboratories, and the process from “core oningIllustration by Rosalind Coggondeck” to answering a scientific question. As they are carried out over multiple expeditions, the Flagship Initiatives
will provide unified messaging for research findings delivered as a story map, film, animation, or instantly sharable
video that shows the moment of discovery. The lengthy
timeframe of the Flagship Initiatives ensures ample time
to develop focused messaging through workshops andexternal projects.
The public can discover scientific ocean drilling and
its achievements through a growing number of venues.
Traditional news media and social media outlets both canbe leveraged to increase the profile of ocean drilling and its
achievements. The scientific ocean drilling community will
use the 2050 Science Framework to develop common story
themes, graphics, and educational materials as a basis forconsistent messaging across the platforms. Photos, videos,animations, and artwork from individual expeditions canprovide the public with an inspiring bird’s-eye view of how
science is conducted and what the results might mean
for the planet. Partnerships with museums will provide
opportunities to engage directly with the public throughhands-on exhibits. Tours while the drillships are in port willallow for in-person ship-based educational initiatives.

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BROADER IMPACTS AND OUTREACH

TRAINING THE NEXT GENERATIONOF SCIENTISTS

Sc
hScientific ocean drilling is a superb training ground for the
next generation of geoscience researchers and university
educators. Drilling expeditions will continue to provide
large numbers of graduate students and early career scientists with the opportunity to contribute to the scientificendeavor, from the early planning stages to the publicationof results. Through shipboard and shore-based participation, they hone analytical, research, and writing skills andlearn from teams of international scientists representing
a range of disciplines. The program’s core repositories anddatabanks are entry points for many who are interested inscientific ocean drilling—including some who have not
had the opportunity to go to sea on a specialized drilling
platform. As the next generation takes the helm of the
program, scientific ocean drilling will strive to advanceparticipation of traditionally underrepresented groups andpromote a more diverse group of students and researchers
to become co-chief scientists of future drilling expeditions
and leaders in the scientific community.
Development of the next generation of scientists must
start at a younger age, at both the schoolchild and undergraduate levels, and from a broad spectrum of schools.
Scientific ocean drilling will expand the suite of available
educational resources for all age levels. Partnering withother programs and organizations that have experienceand influence in the schoolchild and undergraduate
arena will broaden distribution and use of these valuable
materials. Because scientific ocean drilling covers andintegrates so many science, technology, engineering, andmathematics (STEM) areas, the possibilities for developing
successful programs and relationships are immense.

102

ADVANCING DIVERSITY
AND INCLUSION
The geosciences are among the least diverse in the STEM
disciplines. To date, scientific ocean drilling largely reflects
this reality. Numerous pathways are available to help
increase participation of underrepresented groups in scientific ocean drilling, where mentoring the next generation is embedded in their culture. Approaches to increasing
diversity include actively recruiting diverse science parties,
codifying the enhancement of diversity and inclusion in
expedition objectives and as enduring principles in futurescientific ocean drilling programs, conducting ship-toshore video conferences with minority-serving institutions,promoting diversity in the selection processes for scientific

ck
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to-Shore Bro
ipad

c
ts

Examples of some ofour broader impacts andoutreach endeavors.

Scientific ocean drilling is a model of international cooperation and interdisciplinary collaboration in science.
Before, during, and after each expedition, the expedition
scientists, technicians, and engineers bring their diverse
expertise and perspectives to bear on the scientific investigation at hand. Collaborations last for years as drilling plans
are developed, refined, and executed, and the results analyzed and published. Scientific and technical relationships
endure over decades as the science matures, additionalcore is recovered on new expeditions, and analytical tools
are improved and/or invented. Graduate students particularly benefit from these international collaborations. Manyare provided with the opportunity to spend time conducting analyses at laboratories abroad, while others move into
postdocs or jobs with scientists they met on a scientificocean drilling expedition.

as

ENGAGEMENT

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INTERNATIONAL COLLABORATION

Do

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Li
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ENABLING
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tariesenmcuENABLING
ELEMENTocean drilling speaker and sponsored seminar programs
and leadership roles, and linking early career scientists witheducators from communities that are underrepresented in
the STEM fields. As a large international research community
in the geosciences, we will vigorously expand on these andother efforts to broaden the representation and participation in all aspects of the scientific ocean drilling endeavor.
Over the last half century, scientific ocean drilling has
been successful in growing the number of women participating in and leading expeditions. Today, 34% of the science
parties are women, compared to 12% in the earliest daysof ocean drilling. Forty-one percent of graduate students
and half of the co-chief scientists on drilling expeditions are
women. While the trajectory is clearly positive, there is stillwork to be done. Future efforts will focus on bringing fullgender parity to all aspects of scientific ocean drilling.
The scientific ocean drilling community will use thesame successful approaches for achieving gender parity
to enhance overall diversity and inclusion. Scientific ocean
drilling community will be a leader in driving the push to
widen participation in the Earth and ocean sciences among
future generations of scientists and in removing internalbarriers to becoming and staying involved.

KNOWLEDGE SHARINGThe outcomes, data, and samples from scientific ocean
drilling are made freely available via open-access publications, databanks, and core repositories. Scientists and graduate students from around the globe, even those who havenever been involved with scientific ocean drilling, can use
these materials. They often access international archivesof carefully curated scientific ocean drilling cores anddatabanks for decades beyond the end of an expedition to

tio
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ENGAGING WITH OTHER FIELDS
Scientific ocean drilling can build strong, mutually beneficial collaborations with other fields, such as engineering,
astrobiology, and space sciences. Collaboration with
scientists and engineers from other disciplines is vital for
addressing fundamental technical challenges such as
improving and deepening our recovery of undeformed
sediments, minimizing contamination in order to collectthe most pristine samples of the deep biosphere, andimproving our ability to recover cores in hot crust andunstable, tectonically deformed terrain. The discovery of abiosphere deep beneath the seafloor has attracted to scientific ocean drilling microbiologists who are now taking
leading roles in planning and implementing expeditions
and in developing new tools to collect and analyze samples. Investigation of life in the high-temperature, nutrientand light-limited environments deep below the seafloor
can assist space scientists and engineers in designing tools
and experiments that can be employed on space missions
to investigate other potentially habitable worlds.

B o o ks

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BROADER IMPACTS AND OUTREACH

answer questions that were never envisaged by the original
seagoing participants. Expedition archives should include
social media posts, photographs, interview recordings, andvideos that convey how discoveries are made and how
the drilling platforms work. Collectively, the archives frommultiple expeditions capture and document the scientificprocess of discovery, personal stories, and post-cruise findings and inform the public, inspire future generations, andeducate everyone about the Earth system.

Te

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2 LAND TO SEASUMMARY
The scientific ocean and land drilling communities have built two of the mostsuccessful, long-lasting, international collaborative programs in the Earthsciences. The International Ocean Discovery Program (IODP 2013–2023) andthe International Continental Scientific Drilling Program (ICDP) have brought
together more than 30 countries, building on initiatives and programs first
implemented in 1968 and 1996, respectively. Strengthened collaborations
between these programs will advance their closely allied objectives to investigate the interconnected global Earth system. Future collaborative land-to-sea
drilling campaigns will answer fundamental questions about Earth dynamics
and natural hazards, as well as explore the connections between plate tectonics, Earth’s climate system, ecosystems, life and habitability, sea level change,and subseafloor freshwater flow across the coastline.

104

Copper River Delta glacier runoff flows into
the coastal waters of the Gulf of Alaska.
NASA Earth Observatory image by RobertSimmon and Jesse Allen, using Landsat 8
data from the USGS Earth Explorer.

2

ENABLING
ELEMENTLAND TO SEANEW SCIENCE FRONTIERS IN
LAND-TO-SEA DRILLINGThe Strategic Objectives and Flagship Initiatives that
underpin the 2050 Science Framework for scientific ocean
drilling aim to understand how the complex, interconnected Earth system works. This priority strongly aligns
with research initiatives in allied programs such as the ICDP,
which focuses on understanding geodynamic processes,
geohazards, georesources, and environmental change
through drilling and coring across continents, lakes,
and oceanic islands.
Strengthening collaborations in land-to-sea drilling
campaigns will advance several complementary scientificobjectives. A unified database on Earth’s paleoclimate,
prepared jointly, will help to improve model projectionsof future climate and environmental changes by providing
access to a wider array of ground truth data. Collaborative
drilling will enhance our understanding of the interplay
between freshwater and seawater along coastlines, thedevelopment of drought and desertification patterns
and increased wildfire potential, the transition between
continental and oceanic crust, and the formation of sustainable georesources from microbial life, volcanoes, andrelated element cycles. Together, scientific ocean and land
drilling can furnish a more holistic assessment of natural
hazards from earthquakes, tsunamis, and explosive volcanism, many of which occur close to Earth’s coastlines.
It can also deepen our understanding of how the Earthsystem recovers following large meteorite impacts or theemplacement of large igneous provinces on land, alongcontinental margins, and in the ocean. The following provides details of some key opportunities for scientific ocean
and land drilling collaborations.
Causes and consequences of sea level change.
Ongoing sea level rise is having a significant impact oncoastal communities and island nations. Projections ofglobal sea level rise exceed 1 m by 2100. Determining therates, amplitudes, and mechanisms that control sea level
rise as well as its consequences requires sampling on bothsides of the modern shoreline. Sea level is controlled primarily by global temperature, ice volume, and regional
subsidence or uplift on human timescales and by tectonics
on longer timescales. Global warming causes seawater toexpand and ice sheets to melt, raising sea level. Removalof thick ice sheets since the last ice age is still causing uplift
in some regions and subsidence in others. Plate tectonic
changes related to rates of oceanic crust production, con-

Sea level records collected across the shorelineby scientific drilling will allow us to unravel
feedbacks between Earth’s climate system,
deep Earth and surface processes, and sea level.

tinental collisions, and mantle dynamic topography affectboth global and regional sea levels.
Knowledge of how these processes contributed to past
sea level rise will inform the future. Sea level records collected across the shoreline by scientific drilling will allow
us to unravel feedbacks between Earth’s climate system,
deep Earth and surface processes, and sea level. Past studies have yielded critical constraints on the amplitude andtiming of sea level change and the rates of rise due to ice
sheet collapse. Critical environments for sea level studies
include coral reefs, passive continental margins, polar
margins, and deep-sea regions where geochemical proxies
will yield information on ice volume changes. In addition,
coordinated ocean and coastal drilling studies of more
active settings will provide constraints on how deep andshallow Earth processes affect regional and local subsidence and uplift.

not to scale

Ice sheet
Icebergs

Sea ice
Grounding line
Subglacial
sediments

Progradingwedge

Ice-raeddebrisBasement

Continental
shelf

Continental
slope

Continental riseabyssal plain

Conceptual cross section across the Antarctic margin. Subglacial to ice-​
proximal (coastal-​
shelf) to ice-distal depositional environments that
contain the sedimentary record of past ice sheet dynamics result fromchanging atmosphere-ice sheet-ocean interactions. Land-to-sea drilling
is required to target all parts of this system. Modified from Escutia et al.
(2019), https://doi.org/10.5670/oceanog.2019.117

105

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ENABLING
ELEMENTLAND TO SEA

Future sea level investigations need to build on our
understanding of the interconnections within the Earth system and how they affect sea level. Transects of continuous
drill cores and logs across the shoreline in coral reefs, passive continental margins, polar margins, and active margins
will provide the materials needed to advance understanding of the relationship between Earth system interactions
and sea level. Such a coordinated research strategy will
provide a better understanding of the roles CO2 and astronomical forcing play in sea level changes and how sea level
responded to past rapid climate warming and ice sheet collapse, and to evaluate the response of the Earth system in
ice-free “hothouse,” ice-transitional cool “greenhouse,” andice-dominated “icehouse” worlds.

address this goal. Such a comprehensive record will also
provide the ultimate age model—an atomic clock andtimescale from a couple of thousand to millions of years
ago—that is essential for understanding the timing, rates,
and complex interconnections among the processes that
operate within the Earth system. The combined paleoclimate database will include informa­tion from marine
sediments, lake sediments, ice cores, land stratigraphic sections, speleothems, and tree rings collected by scientists
within and beyond the established drilling programs.

Fluid flow across the coastline. Land-to-sea drillingof active freshwater aquifers and hydrothermal systems
in coastal and marginal regions will allow us to determine
these systems’ roles in global water, carbon, and metal
cycling and their impact on georesources, habitability of
Toward an integrated global paleoclimate record.
A common objective of scientific ocean and continental
the subsurface, and life. Groundwater is an essential natudrilling is to improve understanding of feedbacks andral resource, supplying many communities with water for
tipping points within the Earth system and how they affectdrinking and for irrigation of crops. Groundwater circulaenvironmental conditions and the planet’s habitability.
tion does not stop at the coastline; freshwater aquifers canWorking together, the two communities can assemble aextend offshore, beneath the seafloor, but salt water cantruly global, high-resolution, and fully integrated marine
also flow inland and underground. Freshwater sustainabiland terrestrial knowledge base of Earth’s paleoclimate toity in a greenhouse climate is critical, especially in regionsof increasing desertification. Coastal
aquifers may also support life beneaththe surface by carrying nutrients to thesubseafloor microbial biosphere.
To determine the current natureand extent of coastal aquifers and how
they may respond to changing climate
and sea level requires knowledge ofthe magnitude, rates, directions, andmechanisms of fluid flow throughthem. Onshore and offshore drilling
will collect vital information about theUvigerina
Globorotalia
physical and chemical properties ofinterruptacostata
pseudomiocenica
the rocks that comprise the aquifers,
the fluid pressure and temperature

Globigerinoides
tenellus
2 cm

106

MelonisaffinisScale bars = 100 µm

Paleoclimate information can be extracted fromboth land (left) and ocean (right) rocks andsediments. (left) Scientists analyze the thickness and chemical composition of speleothem
layers to reconstruct climate changes overthousands to hundreds of thousands of years.
(right) Microfossils in marine sediment cores
collected by scientific ocean drilling have been
instrumental in providing a continuous record ofglacial history since the Cretaceous.

ENABLING
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WatWa
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SeaFresh water

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Salt waterni ti oImpermeable bedrock

not to scale

Groundwater flow patterns and the fresh water-salt water transitionzone in an idealized coastal aquifer. Mixing of fresh water and salt waterin the transition zone induces circulation of salt water from the sea
to the transition zone and then back to the sea. From Barlow (2003),
https://doi.org/​​10.3133/cir1262

conditions within the aquifers, and the horizontal and vertical extent of the aquifers. Installation of observatories inboreholes will allow us to sample fluids and quantify flow
rates and solute fluxes through the aquifers. Land-to-sea
drilling will also permit evaluation of the processes that
affect the extent of offshore aquifers and salt water influx
and the potential future impacts of ground­water extraction
on these aquifers.
Active volcanic islands such as Iceland and Hawai‘i often
host onshore-to-offshore hydrothermal systems. Similar
to deep-sea hydrothermal systems, energy and matter
cycle through these “coastal” fluid flow systems as a resultof fluid-rock reactions. In regions where the coastline comprises ancient uplifted oceanic crust (ophiolites), modern
groundwater circulation results in lower-temperature
fluid-rock reactions. The reactions within these coastal
systems form ore deposits, sequester or trap atmospheric

2

LAND TO SEA

CO2 in calcium carbonate minerals, and produce hydrogen through serpentinization of peridotites. Each ofthese processes can also impact subsurface habitability
by supporting chemolithotrophic organisms in the deep
microbial biosphere. The rocks that host these systems
contain a mineralogical and biogeochemical record of
past fluid-rock exchange. Land-to-sea drilling of the terrestrial and submarine portions of these systems and in situ
monitoring and fluid sampling will enable determinationof the hydrogeologic, chemical, and microbial transitions
between them, and the nature and extent of biogeochemical exchange within the systems and the microbial communities they support.
Earth dynamics and natural hazards. Plate tectonic
processes along active margins are responsible for generating most of the world’s destructive earthquakes, tsunamis,and explosive volcanoes. Efforts to understand the mechanisms controlling the magnitude and recurrence time ofthese natural hazards and assess hazard potential tocoastal populations will benefit from coordinated studies
that cross the shoreline. Stratigraphic sections recovered
both offshore and on land provide opportunities to determine the rates and magnitude of crustal uplift, subsidence,and tilting across fault zones and reconstruct more fully
the activity and slip history of faults. Installation of borehole observatories in and above seismogenic zones willallow continuous monitoring of pressure, temperature,and stress and strain, and collection of hydrologic andgeochemical data to help assess the evolution of hazard-​
generating processes. Land-to-sea drilling provides anopportunity to recover complementary paleoseismology
records from submarine and lacustrine deposits. These
sediments can contain information on the magnitude andfrequency of past earthquakes and tsunamis, which can beused in assessments of hazard potential.

FUTURE COLLABORATION
Future plans for both scientific ocean and continental drilling emphasize the need to study
Earth as an interconnected system, including the links between Earth processes, the environment, and society. The new focus requires development of integrated land-to-sea drilling
campaigns where the science crosses the shoreline. Such studies will reinforce collaborations between the two scientific drilling communities, but more importantly, it will drive newopportunities for the mutually beneficial development of shared science strategies, novel
analytical tools, syntheses of truly global data sets, and improved drilling technologies.

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3 TERRESTRIAL TO

EXTRATERRESTRIALSUMMARY

Future collaboration between international space agencies and scientific ocean drilling
will benefit efforts to better understand planetary evolution, evaluate the potential forindigenous life elsewhere in the universe, and assess the risks posed by extraterrestrial
impacts. Through space exploration, humankind aspires to discover the fundamental
physical laws of the universe, decipher the conditions required to promote planetary
formation and evolution, and ultimately, unravel the origin of the universe and life.
Scientific ocean drilling’s investigations into Earth’s structure, magnetic field, and volcanism and the requirements for planetary habitability have similar goals. Earth’s ocean
basins provide a reference frame for exploring challenging environments and offer anatural laboratory for testing remote and space exploration robotic technologies.
Integration of modern satellite data with historic records from scientific ocean drilling
will be a powerful new approach to understanding Earth’s interconnected processes
today and climate evolution into the future.

108

A team of transatlantic scientists,
using reanalyzed data from NASA’s
Kepler space telescope, discovered
an Earth-size exoplanet orbiting in
its star’s habitable zone, the areaaround a star where a rocky planet
could support liquid water. This
artist’s illustration shows what
Kepler-1649c could look like from its
surface. Image credit: NASA/Ames
Research Center/Daniel Rutter

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TERRESTRIAL TO EXTRATERRESTRIAL

UNDERSTANDING PLANET EARTH
The overarching goal of all space agencies­—to explore
space and its planetary bodies—includes the study ofEarth. Satellite-based sensors collect real-time data thatare essential for understanding a wide variety of Earthprocesses and properties such as weather, plate motions,and active tectonics, including earthquakes, tsunamis,
and volcanism. These data also provide calibration for the
long-term records of Earth history that we access throughscientific ocean drilling. The synthesis of remote-sensing
data and drill core records of Earth processes and properties will enhance our ability to achieve our Strategic
Objectives and implement our Flagship Initiatives.
Sensors aboard satellites are also documenting a wide
range of global environmental change indicators, fromatmospheric greenhouse gas concentrations, to global
and regional sea levels, to sea ice thickness. As we continue to observe the many far-reaching environmental
changes, decision-makers will need to increasingly rely
on model-based scenarios of future climate to informplanning. Climate models require robust baseline dataof global climate evolution over extended geologic time
periods to test model performance. For example, satellite
observations paired with long climate histories obtained
from scientific ocean drill cores will allow us to test different assumptions used in physical and dynamic models ofEarth’s climate system, as well as define boundary conditions and recognize potential tipping points.
During the last half century, space agencies have played a
key role in providing data sets of global weather patterns andchlorophyll distributions throughout the ocean. Over the
next decades, space agencies will continue launching new
Earth satellite missions to further enrich our understanding
and predictability of modern weather and ocean circulation
patterns. To fully comprehend the extent to which the Earthsystem is fundamentally changing due to climate warming
requires comparing modern data sets collected by satellites
to the long-term records of global climate and ocean system evolution recovered by scientific ocean drilling. Space
agencies and scientific ocean drilling can support futureclimate system modeling by collaborating on the locationof future drill sites and integrating results.
Exploring planetary evolution. Planetary scientists
use remote sensing to investigate features at the surfaceof planetary bodies and rovers, landers, probes, and sample return to study the near-surface environment. Thesemissions stand to gain from scientific ocean drilling inves-

Space agencies and scientific ocean drilling can
support future climate system modeling bycollaborating on the location of future drill sites
and integrating results.

tigations in Earth’s ocean basins. By examining Earth’s history recorded in sediments and rocks beneath the seafloor
and by viewing this history in a planetary-analogue reference frame, it becomes possible to gain a holistic picture ofEarth’s dynamics, its climate system, and its biologicalevolution over geologic time, including the geologic andbiologic processes of impact events. Investigations
into the formation, cooling, and environmental evolutionof other planetary bodies will benefit from a partnership
between scientific ocean drilling and space agencies.
There has long been interest in exploring Mars. It is now
hypothesized that the Red Planet’s environment had once
been much wetter and could have hosted carbon-based
life. Stabilizing liquid water on the surface of Mars would
have required a much thicker atmosphere, which could
have been supplied by martian mantle plume volcanism.
However, because of the small size of Mars, this low-gravity
planet is not likely to have retained an atmosphere. The

NASA’s Curiosity Mars rover captured this mosaic as it explored the“clay-bearing unit” on February 3, 2019. This unit has been an importantscientific destination because it indicates that water may have played acritical role in its formation. Image credit: NASA/JPL-Caltech/MSSS

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halting of its geodynamo when the planet was relatively
young, which resulted in a weak (residual) magnetic field,
likely accelerated the loss of the atmosphere, killing any
life that emerged or forcing it underground. Scientificocean drilling studies of active plume volcanism on Earthand changes in the behavior of Earth’s geodynamo overgeologic timescales can be used to understand the development and retention of atmospheres on other planetary
bodies and the possibility that life once developed there.
Investigations of mantle plume and rift volcanism on Earth
are also important for understanding how terrestrial planetary bodies in our solar system transfer heat, cool advectively, and influence surface landforms.
Searching for life in the universe. A primary pursuit ofspace agencies is to unravel the origin of the universe andlife. The US National Aeronautics and Space Administration(NASA) Mars 2020 and European Space Agency (ESA)
ExoMars missions will be the first to specifically examine
the implications of a “thicker atmosphere” enveloping earlyMars by seeking traces of ancient life at or near the surface.
The 2019 NASA Roadmap to Ocean Worlds aims to identify
new ocean worlds, characterize their oceans, evaluate theirhabitability and potential for preserving life, and ultimately
understand any form of life that would be found. To groundtruth and complement these important objectives, weneed to determine the potential biosignatures in each hab-itable niche on planets. Such an endeavor requires learning
first-order lessons from the evolution of life on Earth. By
investigating the continuum from no life to life on Earth,scientific ocean drilling can provide a more holistic pictureof the requirements for biochemical functioning of life andplanetary habitability. Such knowledge will inform thesearch for life elsewhere in the universe and help identify
the best candidates for extraterrestrial exploration.

This artist’s impression shows the planet K2-18b, its host star, and anaccompanying planet in this system. K2-18b is now the only super-Earthexoplanet known to host both water and temperatures that could support life. Credits: ESA/Hubble, M. Kornmesser.

Samples from Extreme Environments
Sample return from extraterrestrial bodies has greatly advanced our knowledge of the formation andevolution of the solar system. To obtain determinative evidence of martian life, various space agencies,
including NASA, ESA, JAXA, and the Canadian Space Agency, started the Mars Sample Return project,which began with the launch of the Perseverance rover launch in July 2020. This rover will cache samples
for return to Earth in the 2030s. Collaboration with scientific ocean drilling will offer space agencies anopportunity to first develop and test technologies on microbial samples collected in extreme environments through drilling in the ocean basins, before applying those techniques to extraterrestrial samples.
A United Launch Alliance Atlas V rocket with NASA’s Mars 2020 Perseverance rover on board was launched Thursday,
July 30, 2020, at Cape Canaveral Air Force Station in Florida. The rover’s mission on the Red Planet is to search forsigns of ancient life and collect samples to send back to Earth. Image credit: NASA/Joel Kowsky

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Investigating impact craters. Tracking of near-Earthasteroids for planetary protection is a priority of space
agencies. Although asteroid impacts pose a clear natural
hazard to our planet, the impact processes and environmental aftermath on a planetary scale are poorly understood. Scientific ocean drilling will provide greater insight
into the processes involved in impact crater formation
by investigating meteorite impact structures, such as
Chicxulub in Mexico and in Chesapeake Bay in Virginia,
USA, and their ejecta across Earth. These scientific ocean
drilling investigations will permit comprehensive studies of
the consequences of impacts on local, regional, and global
scales and the process of the impacts themselves and theimmediate planetary implications. They will also provide
insights into recovery after the impact event, including
a better understanding of the resource potential fromany post-impact hydrothermal circulation. Samples ofmaterial in and around the impact craters recovered byscientific ocean drilling will capture pre-impact conditions,the impact itself, post-impact recovery processes, andimpact-induced hydrothermal habitats.

3

TERRESTRIAL TO EXTRATERRESTRIAL

Scientific ocean drilling will provide
greater insight into the processes
involved in impact crater formation by
investigating meteorite impact structures
and their ejecta on Earth.

(a) Schrödinger Basin
Lunar Far Side316 km diameter(a) Mosaic of images from the Schrödinger
Basin, an impact crater on Earth’s moon. The
impact structure looks very similar to the that ofthe (b) Chicxulub impact that occurred ~66 million years ago on Earth, here shown in gravity
measurements. (a) From http://lroc.sese.asu.edu/​
posts/161. (b) Modified from Lowery et al. (2019),
https://doi.org/​​10.5670/​oceanog.2019.133.

(b) Chicxulub Crater
Yucatán, Mexico
195 km diameter

FUTURE COLLABORATION
The perspectives of scientific ocean drilling and space agencies regarding the Earth system arecomplementary, presenting opportunities for mutually beneficial collaborations. For example,
scientific ocean drilling requires teams to effectively and efficiently collect new scientific data inchallenging and unexplored environments, which in turn can inform approaches for missions
beyond Earth. We anticipate that close cooperation between scientific ocean drilling and spaceorganizations will foster scientific and technological breakthroughs in drilling, coring, and analytical techniques and will facilitate new directions for scientific ocean drilling and remote robotic
investigations of planetary bodies. Partner organizations will benefit by combining technicalstrengths to better recognize, extract, and preserve life signatures in extreme environments on
Earth and other planets; by telling a unified story about how the Earth system functions; and bytraining the next generation of researchers to think in a fully interdisciplinary fashion.

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4 TECHNOLOGY DEVELOPMENT

AND BIG DATA ANALYTICSSUMMARY

Progress in addressing the ambitious scientific objectives of the 2050 Science Framework
requires continued development of drilling, coring, logging, observatory, and laboratory tools and techniques. And, as capturing information from these sources becomes
ever more digital and higher resolution, the requirements for maintaining the cyberinfrastructure to store, process, analyze, and model the resultant large data sets anddiverse data types are growing significantly. Big data analytical techniques applied toscientific ocean drilling data will play an increasing role in advancing the science andinforming policy. The five-year review cycle of the 2050 Science Framework will allow
scientific ocean drilling to update its approaches to investigating the interconnected
Earth system as innovations in drilling and coring technologies, downhole and shipboard analytical tools, and big data analytics reshape how science gets done.

112

The International Ocean Discovery
Program (IODP) Bremen Core
Repository at MARUM. Cores fromthe Atlantic and Arctic Oceans
and the Mediterranean, Black,and Baltic Seas are stored here.
Image credit: MARUM − Zentrum
für Marine Umweltwissenschaften;
Universität Bremen; V. Diekamp

ENABLING
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4REVOLUTIONIZING SCIENTIFIC
OCEAN DRILLING
Since its inception, scientific ocean drilling has established an excellent track record of developing innovativetechnologies in response to new scientific challenges andparadigms and exploring new scientific avenues that open
up through external technological developments. Over thelast two decades, the pace of such developments has been
impressive and will keep driving progress in future scientific ocean drilling. Key innovations include installationof cabled borehole observatories that transmit real-timedata of subsurface conditions and changes, developmentof improved coring techniques for sampling fault zones,
application of the highest contamination control measures
for microbial sampling, implementation of onboard X-CT
scanning of core sections to ensure capture of critical intervals, and assimilation of proxy climate data from scientificocean drilling cores into numerical climate models to eval-

TECHNOLOGY DEVELOPMENT AND BIG DATA ANALYTICS

uate and improve model performance.
Future developments in technology, monitoring, andobservatory science will be needed to achieve the Strategic
Objectives and implement the Flagship Initiatives of the2050 Science Framework. Some examples include theneed to continue to improve and deepen the recovery ofundeformed sediments. Core orientation advancements
will help minimize magnetic overprinting so we can obtain
the best quality paleomagnetic records. Another goal is tominimize sample contamination to enable collection ofpristine samples of the deep biosphere. We need to continue to improve our ability to recover cores in hot crustand unstable, tectonically deformed terrain. These technical innovations should be matched with better capturing
shipboard and land-based measurements to improve ourability to visualize complex data and instantly be able tocompare new data streams with those collected on previous expeditions. Innovations in analytical tools and laboratory techniques will allow us to maximize the scientific

Pioneering Research and Engineeringin the Ocean
Scientific ocean drilling pioneered drilling in deep ocean basins at atime when the petroleum industry was only operating on the shallow
continental shelves. Drilling in the deep ocean required engineering
innovations such as development of a dynamic positioning system tomaintain location over a drill site for several weeks at a time, despite
wind and ocean currents. This versatile system is now regularly
deployed on research vessels, commercial drillships, cable-laying ships,
and even cruise ships. Over subsequent decades, scientific ocean drilling invented and refined hydraulic piston coring tools that today allow
us to retrieve continuous, high-fidelity sediment cores that provide a
detailed history of Earth’s climate. Borehole observatories developedby scientific ocean drilling isolate the drill holes from the ocean, allowing physical, chemical, and biological conditions within the boreholes
to be monitored during and after the fluids have re-equilibrated.

Comparison of sediment core quality between rotary drilling and piston coring.

Rotary Cored

Piston Cored

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TECHNOLOGY DEVELOPMENT AND BIG DATA ANALYTICS

Hy
d

ty
ivi

ea
the
r

W

Interface
Housing
Hydraulic
Power

SCIENTIFICOUTPUTSalt
Bas

We are at a technical inflection point where prior operational successes, multidisciplinary needs, and broad scientific support will accelerate the pace of technological advancement to further our understanding of processes that shapethe evolution of the oceanic crust. For example, several Flagship Initiatives will
benefit from the design, fabrication, and commissioning of a remotely operated
vehicle-manipulated platform that, when lowered to the seafloor, will allow a
flexible array of sensors and samplers to be deployed in existing scientific ocean
drilling boreholes in the upper volcanic oceanic crust. Such a platform will benefit
from the availability of many off-the-shelf sensors, samplers, and systems within aflexible and modular framework. Such a tool will benefit experiments and exploration today, while allowing future generations of sensors and samplers to beincorporated. Illustration by Geoff Wheat, Claudia Paul, and Geo Prose.

Micr
ob
ia
l

gy
lo
ro

ct
A

Example Technological Innovation for Future Drilling

ies

4

ro
pe
rt

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lP
ta
s
u
Cr

ROV-MANIPULATED
PLATFORM
Flotation

Wet Mates

Instrument
Package “POD”

REMOTELYOPERATED VEHICLE

Release Pad
Base Plate
Adjustable
Reentry Cone
Grip

SEDIMENT

Borehole
Reentry
Cone

INSTRUMENT
PACKAGE “POD”

CameraBattery
Main
Controller
Packer
with
Pump
Water
Sampler
TracerPump
Manipulator
CameraBASALT

Packer
with
Pump

Water
Sampler
Sensors(e.g., CTD,
hydrophone,camera)Instrument
Package“POD”

114

not to scale

ENABLING
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potential of five decades of scientific ocean drilling coreshoused in our core repositories, make new discoveries fromthese legacy samples, and inform new avenues of inquiry
for scientific ocean drilling.
Science leading innovation. Given the long timeframeof this 2050 Science Framework, the science proposed in
the Scientific Objectives and Flagship Initiatives can drive
technological developments. Probing the deep Earth will
require us to drill deeper than ever before into oceanic lithosphere, leading to the development of new coring capabilities to operate at more extreme in situ temperatures andpressures. Assessing tsunami and earthquake hazards
will be most effective if it includes real-time monitoringof the critical in situ pore fluid pressures, temperatures,and strain in the fault zone. Such monitoring will require
improvements in or development of rig-deployable borehole instruments and development of affordable infrastructure to transmit data between observatories and theshore. Exploring life and its origin on Earth and assessing
the pharmaceutical potential of the deep biosphere will
require new techniques to conduct in situ manipulative
experiments and methods to isolate and culture subsurface
life. Among the technologies requiring development are
coring tools that can be used in difficult-to-sample environments and that can preserve critical fabrics in uncemented
sandy sediments.

TECHNOLOGY DEVELOPMENT AND BIG DATA ANALYTICS

Industry innovation enabling science. Scientificocean drilling recognizes that external technology developments will enable new scientific opportunities. Industry
is continually introducing novel coring approaches andplatforms, downhole tools, artificial intelligence applications, and core-log interpretation protocols. Scientificocean drilling into exposed rock outcrops and recoveryof hard rock material have been particularly challenging,in part because historically industry did not work in suchenvironments. The frontier exploration in basalt-hosted oil
and gas reservoirs on some continental margins and ultrahard formations on the Brazil margin has led to industry
development of new hard rock drilling technologies that
could be adopted for scientific ocean drilling purposes.
Scientific ocean drilling will also benefit from futureindustry-led developments in seismic reflection data acquisition. These new techniques will yield higher resolution
site survey data that will significantly improve targeting ofcoring sites and penetration depths and provide invaluable
regional context. Scientific ocean drilling will continue tobenefit from collaboration between its scientists and engineers and industry experts, allowing us to realize our scientific ambitions and ensuring successful and safe scientificocean drilling operations.

Since its inception, scientific ocean drilling has
established an excellent track record of developing
innovative technologies in response to new scientificchallenges and paradigms and exploring newscientific avenues that open up through external
technological developments.

State-of-the-art contamination control was used for microbiological sampling from sediment cores during International Ocean Discovery Program
Expedition 370. In order to avoid the intrusion of drilling fluid into theinner part of the “mbio” sample, the outer part was carefully removed
with sterile tools inside an anaerobic chamber. From Heuer et al. (2019),
https://doi.org/10.5670/oceanog.2019.147

Need for big data analytics. Although the foundationof scientific ocean drilling is the recovery of core samples
from marine environments, each drilling expedition alsocollects an array of geophysical, geochemical, and biological data that are equally important. Core analyses, insitu downhole measurements, and monitoring data from
borehole observatories are all linked to regional geologicaland geophysical observations. Automation of data collection in laboratories will expand and become routine, vastly

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Data Innovation for Future Drilling
For many of the science goals laid out in the 2050 Science
Framework, the objective quantification of the subsurface is mandatory to reach useful conclusions and avoid misleading results.
This applies to all rock types recovered by scientific ocean drilling
but is especially true of hard rock coring, where recovery is usually
incomplete and biased to more robust rocks. The rocks that record
the greatest hydrothermal exchanges and biological activity are
the most fragile, fractured, and/or altered. Core-log integration
to characterize the missing materials remains challenging andhuman intensive and requires improved high-resolution imaging
tools to more precisely locate these intervals.
New approaches already used by industry and some terrestrial
scientific drilling experiments, such as the Oman Drilling Project incollaboration with the International Continental Scientific Drilling
Program, allow cores to be more thoroughly recorded before
splitting and further processing. Optical imaging of the externalsurface of cores freshly released from the core barrels provides
high-resolution digital records of the cores when they are mostintact, preserving context and enabling feature recognitionand objective quantification by artificial intelligence/machinelearning (AI/ML) approaches. Digital observations need not be
restricted to the visual spectrum, and current photographic imag-

ing of exterior and split surfaces can be supplemented by visible
to short wavelength infrared (VSWIR) spectroscopy, so-called“hyperspectral scanning” by industry, that allows mineral identification and mapping at submillimeter spatial resolution. X-ray
computation tomography (XCT) complements these surface
imaging techniques by providing three-dimensional density
maps of the core interiors, assisting with the recognition of veins,fabrics, and layering, and revealing hitherto unavailable internal
imaging of faults and breccias.
With the right instrumentation, these approaches can be
fit into onboard workflows. It is critical to recognize up front
that they produce very large amounts of data and demand big
data analytical approaches that until recently remained in thedomains of particle physics or astronomy, but are increasingly
required for Earth and environmental sciences. Supervised andunsupervised convoluted neural networks (CNN) can objectively
recognize, measure, and quantify the presence of minerals andfeatures, arguably better than the most experienced scientist
over a two-month drilling expedition. These approaches should
never take the scientists “out of the loop” but will improve theconsistency, efficiency, and accuracy of observations once
calibrated and tested.

Digital Observations of Oman Drilling Project Core GT2A-120Z2
and Machine Learning Image Interpretations
0

4500

10
4000

Core Length (cm)20

30

Example of existing non-destructive corescanning approaches and automatedinterpretations of digital data for hydrothermally altered gabbros from the lower
oceanic crust of the Semail ophiolite,
Oman. Note the damage caused to theupper 12 cm of this section (split core
optical image) as a result of cutting with adiamond saw blade. Credits: Optical images
from the Oman Drilling Project. Machinelearning automated interpretation fromPeter Hopkins, Blair Thornton, and Damon
Teagle. VSWIR from Rebecca Greenberger
and Bethany Ehlmann. XCT analysis from
Katsu Michibayashi.

3500

ML Key
40
3000

2500

60

CT value

116

114

EpidoteClinozoisite
ZeoliteVSWIR Key

50

70

Background rock
Altered Gabbro
Altered olivine

360° coreexterior
optical image

ML automatedcore exterior
interpretation

Split core
optical
image

VSWIR
mineralmaps

XCT imageslice parallelto split surface

Left panel
Chlorite
Chlorite + epidote/clinozoisite
Epidote/clinozoisite
Prehnite + epidote/clinozoisite
Prehnite
Prehnite + chlorite
Chlorite + epidote/clinozoisite + prehnite
Right panel
ZeoliteClinopyroxene
Amphibole

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increasing the number and size of data files. Progress inscientific ocean drilling increasingly depends on the compilation and integration of these very large and varied data
sets (“big data”) and the sophisticated computational tools
used to analyze them.
Intergovernmental Panel on Climate Change climate
projections can be improved by incorporating real dataon past climates acquired through scientific ocean drilling. These ground truth data must be aggregated fromhundreds of globally distributed sites spanning millions ofyears of Earth’s climate history and acquired over many
scientific ocean drilling expeditions. Similarly, to make significant progress in exploring life and its origin on Earth
may require building a databank of subseafloor microbes.
The vast amounts of data that will be collected by scientificocean drilling through 2050 will be complemented by anequally vast legacy database from the previous 50 yearsof scientific ocean drilling, including the supplementary
data collected prior to drilling during site surveys andpost-expedition, as well as data collected by downhole
instruments. By compiling these huge data sets, mining theholdings, and examining them with big data tools, previously unrecognized patterns, correlations, and trends may
be revealed, advancing the science and informing policy.

Mini-Map
Ct Depth(meters)Den
DE Density Dimensionless
Section Names

Ct Depth(meters)

Sonic
GRA Density
Dimensionlessg/cc

TECHNOLOGY DEVELOPMENT AND BIG DATA ANALYTICS

Progress in scientific ocean drillingincreasingly depends on the compilation andintegration of these very large and varied
data sets (“big data”) and the sophisticatedcomputational tools used to analyze them.

To achieve Strategic Objectives and Flagship Initiatives outlined in this 2050 Science Framework, we need to maximize
the scientific potential of all existing and future scientificocean drilling data. These data must be findable, accessible,
interoperable, and reusable (FAIR) in order to take advantage of new and existing data analytics tools that will reveal
patterns and trends within the interconnected Earth system. A key strength of scientific ocean drilling has always
been ensuring open access to its databases. By focusing on
FAIR data practices, and by developing common standards
among the future platform providers, scientific ocean drilling will continue to produce data that will benefit the global
science community and the wider public.

CT Cleaned:
XZ Slice

CylinderUnwrap

Acoustic
Borehole Image
ABI_AMPLITUDE 506-697

CT Cleaned
Histogram

Screenshot of Virtual Core visualization software with various types of data added. Left to right: Mini-Map (navigation tool), X-ray computerized tomography (CT) density, sonic well log and multisensor core logger (MSCL) density, CT XZ slice, CT unwrapped, acoustic borehole image, and CT cleaned
histogram. From Figure F13 in Gulick et al. (2017), https://doi.org/10.14379/iodp.​proc.​364.​102.​2017117

Countries Involved in
Developing the2050 SCIENCE
FRAMEWORK
Australia, Austria, Brazil, Canada, China, Denmark,Finland, France, Germany, India, Ireland, Italy, Japan,
Netherlands, New Zealand, Norway, Portugal,
South Korea, Spain, Sweden, Switzerland,
United Kingdom, United States of America

1182050 SCIENCE FRAMEWORKDocument Development

Six international planning workshops were organized in 2018 and 2019 in India, Japan, Europe,
Australia and New Zealand, the United States of America, and China. More than 650 scientificocean drilling scientists participated; about 30% were female and 40% early to mid-career
scientists. The results from those workshops were presented, discussed, and distilled inJuly 2019 during the first meeting of the Science Framework Working Group. The 19 international scientist delegates in this working group—representing all current International
Ocean Discovery Program (IODP) member countries and consortia—established a consensus
roadmap to develop a new science framework in support of Future Scientific Ocean Drilling
Through 2050. In August 2019, a draft of this proposal was posted on IODP.org for commenting by the overall IODP community, and based on the constructive and positive community
input, a final revised proposal was presented to and endorsed by the IODP Forum during its
September 2019 meeting in Osaka, Japan.
A diverse international writing and reviewing team was established, including more than
45 scientists from all career stages, with an emphasis on early to mid-career scientists. This
team has worked on four different drafts, involving two internal reviews. Two full drafts ofthe 2050 Science Framework were circulated for community review in February and July 2020.
Following those reviews, the final framework documents were endorsed by consensus during
the virtual IODP Forum meeting in September 2020.
The outcome of this extensive peer review process and the high level of community input
and involvement has resulted in an exciting outlook on more than 25 years of future scientific ocean drilling, with a focus on new scientific frontiers and a strong emphasis on researchthat will have societal impact as seen through the lens of a diverse next generation of Earthscientists. The 2050 Scientific Framework demands strong interdisciplinarity in scientific ocean
drilling, enhanced by collaborations with external partner organizations. It also shows how
our science informs society, while addressing foundational Earth system research questions.

119

FIGURE CREDITS, SOURCES, AND REFERENCES
Cover	�������������� Microbes: Jason Sylvan, Texas A&M University.
Hydrothermal Vent: MARUM − Zentrum für Marine Umweltwissenschaften, Universität Bremen (CC-BY 4.0,
https://creativecommons.org/licenses/by/4.0/).
Hurricane Damage: iStock.com/skrum.
Coral Reef: iStock.com/xrender.
Desert: iStock.com/gorsh13.
Glacier: iStock.com/Bernhard_Staehli.
Volcano: iStock.com/KalypsoWorldPhotography.
Earth Image: https://www.ngdc.noaa.gov/mgg/image/etopo1_large.jpg.
TOC	����������������� (left) Publications Specialist Ekant Desai (IODP/JRSO) and others on the catwalk with a core during International Ocean		
Discovery (IODP) Expedition 383, Pacific Antarctic Circumpolar Current. Credit: Sian Proctor & IODP.
(middle) Structural Geologist Joann Stock (California Institute of Technology, USA), Igneous Petrologist S. Khogenkumar Singh (National
Centre for Antarctic and Ocean Research, India), and Co-Chief Scientist Daniel Lizarralde (Woods Hole Oceanographic Institution,USA) examine a core on the description table during IODP Expedition 385, Guaymas Basin. Credit: Andreas Teske & IODP.
(right) Sipan Issa rinses off the core halves after splitting during the Expedition 381 onshore science party at the Bremen Core
Repository. Credit: V. Diekamp ECORD/IODP/MARUM.
Mission	���������� Marble Earth: iStock.com/pixalot.
Page 3	������������ Dynamic Earth: iStock.com/KalypsoWorldPhotography.
Climate and the Environment: iStock.com/Bernhard_Staehli.
Life: iStock.com/xrender.
Natural Hazards: iStock.com/skrum.
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Health and Habitability: iStock.com/IBorisoff.
Page 4	������������ Background Photo | Glomar Challenger.
Inset Photos (from left to right)
D/V Chikyu: JAMSTEC.
JOIDES Resolution: William Crawford, IODP/TAMU.
Icebreakers Vidar Viking, Oden, and Sovetskiy Soyuz: IODP-ECORD.
Page 10	��������� Ground Truthing Future Climate Change: iStock.com/Byronsdad.
Probing the Deep Earth: Illustration by Rosalind Coggon.
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Diagnosing Ocean Health: iStock.com/byrneck.
Exploring Life and Its Origins: iStock.com/artisteer.
Page 13	���������� Photo credit: John Beck, IODP/TAMU.
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Hydrothermal Vents: CMARUM, University of Bremen and NOAA Pacific Marine Environmental Laboratory.
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(b) Modified from: Suszuki, Y., S. Yamashita, M. Kouduka, Y. Ao, H. Mukai, S. Mitsunobu, H. Kagi, S. D’Hondt, F. Inagaki, Y. Morono, andothers. 2020, Deep microbial proliferation at the basalt interface in 33.5–104 million-year-old oceanic crust. Communications
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Page 100	������� Advancing Earthquake Studies: iStock.com/MasaoTaira.
Improving Climate Models: NASA/Goddard/Maria-José Viñas.
Discovering the Deep Biosphere: iStock.com/appledesign.
Assessing Future Ocean Health: iStock.com/armiblue.
Investigating the Deep Earth: NOAA Office of Ocean Exploration and Research.
Page 102	������� School of Rock: https://joidesresolution.org/for-educators/school-of-rock/.
Live Ship-to-Shore Broadcasts: https://www.ukiodp.org/for-educators.
Documentaries: ECORD-IODP.
Page 103	������� Exhibition Materials: https://www.mysteriesofthedeep.org/resources.
Children’s Books: https://joidesresolution.org/for-educators/node2998/.
Teaching Materials: https://joidesresolution.org/activities/from-the-mountains-to-the-ocean/.
Ship Tours: https://joidesresolution.org/about-the-jr/jr-vessel-tour/.
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Page 106	������� (left) From: US Geological Survey archived Paleoclimate page: https://www2.usgs.gov/landresources/lcs/paleoclimate/archives.asp.
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Page 118	�������� (clockwise from the top)
(1) Core Description Scientist Jianghong Deng (University of Science and Technology of China) and Organic Geochemist Olivier Sissmann(IFP Energies Nouvelles, France) sample a core, International Ocean Discovery Program (IODP) Expedition 366, Mariana Convergent
Margin. Credit: Tim Fulton, IODP/JRSO.
(2) Sedimentologist Francesca Meneghini (Università degli Studi di Pisa, Italy), Structural Geologist Heather Savage (Lamont-Doherty
Earth Observatory [LDEO], Columbia University, USA), Sedimentologist Hannah Rabinowitz (LDEO, Columbia University, USA), andStructural Geologist Ake Fagereng (Cardiff University, UK) describe a core during IODP Expedition 375, Hikurangi Subduction Margin.
Credit: Tim Fulton, IODP/JRSO.
(3) Engineer Yuichi Shimmoto (JAMSTEC, Japan) and Physical Properties Specialist Aida Farough (Kansas State University, USA)examine a core during IODP Expedition 376, Brothers Arc Flux. Credit: William Crawford, IODP/JRSO.
(4) IODP Expedition 381 Science Party and ECORD Science Operator team in the Bremen Core Repository. Credit: V. Diekamp,
ECORD/IODP.
(5) Paleontologist Thiago Pereira dos Santos (Universidade Federal Fluminense, Brazil) works at the sample table, IODP Expedition 361,
South African Climates. Credit: Tim Fulton, IODP/JRSO.

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