STUDIUM GENERALE LECTURE – G30 PROGRAMS NAGOYA UNIVERSITY

Fossil Coral Reefs as aWindow into the Historyof Sea-level and ClimateChange
Marc Humblet, Assoc. Prof.
Department of Earth and Planetary Sciences, Nagoya University

Outline Today’s global warming & sea level rise
 Case study: the Great Barrier Reef of Australia

and the history of sea-level and climate change
since 30,000 years ago

 The scientific method and the communication ofscientific results

Global warming & sea level rise The Earth is warming

Evidence from direct measurements of Surface air temperature Sea surface temperatureSurface air temperature
1

ANNUAL ANOMALIES* OF GLOBAL AVERAGE
SURFACE TEMPERATURE (ºC)

0.52019 / +0.43 ºC0

ΔT ~1 ºC

-0.5

1920 / -0.51 ºC

-1
1890

1910

1930

1950

1970

1990

2010

* Relative to average temperature over the period 1981-2010
Data source: Japan Meteorological Agency

 Sea level is rising

Evidence from direct measurements using Tide gauges

 Satellite altimetry

Image credit: adapted from https://oceanservice.noaa.gov/facts/tide-gauge.html, https://www.cmar.csiro.au/sealevel/sl_meas_sat_alt.htmlSea level rise
GLOBAL MEAN SEA LEVEL (GMSL)
250

GMSL (in mm)

200

1990-2020~3.5 mm/year

150100500-501880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010
Data source: Commonwealth Scientific and Industrial Research Organization (CSIRO) Why is it important to study sea level change?
 190 million people in the World living in coastal areas

are directly exposed to sea level rise

- Most at risk are developing countries in Asia
- 20% of Japan population live in cities at elevations <10 m©Wikipedia

Malé, capital of the MaldivesHighest elevation = 2.4 m above mean sea level
Data from Kulp & Strauss (2019 ), Nature Communications Image credit: Hironobu Kan Impacts of sea level rise
- Higher and more frequent coastal flooding- Increased erosion of the coast©Wikipedia

Image credit: Terry Chea/Associated Press (https://www.eenews.net/special_reports/california_crumbling_coast/) What are the causes of sea level rise?
 Melting of ice on land(polar ice sheets, glaciers)

Figure removed due tocopyright restrictions.

 Increasing volume of ocean

water as it warms

Image credit: http://www.bbc.com/earth/story/20160408-this-is-how-far-seas-could-rise-thanks-to-climate-change,Pixabay

RATES OF SEA LEVEL (SL) RISE SEPARATED BY SOURCEFOR THE PERIOD 1993-2003
Rate of SL rise(mm/year)

Potential SL rise

Thermal expansion

1.6 ± 0.5

0.3 m (+ 3°C)

Glaciers and ice caps

0.77 ± 0.2

0.4 m

Greenland ice sheet

0.21 ± 0.077m

Antarctic ice sheet

0.21 ± 0.35

57 m

Observed total SL rise

3.1 ± 0.7

Source of SL rise

Ice cap: surface area < 50,000 km2Ice sheet: surface area > 50,000 km2

Data source: Bertler & Barrett (2014), Changing Climates, Earth Systems and Society

Melting of Greenland ice sheet
1.7 x 106km2
Potential sea level rise = 7m

Image credit: http://flood.firetree.net/

Melting of Antarctic ice sheet
14 x 106km2
Potential sea level rise = 57m

Image credit: http://flood.firetree.net/

Global change in sea level related to variation in thevolume of ocean water

VS.
Local change in sea level related to up/down
movements of the landInfluence of up & down land movements
 Human-induced Natural (earthquakes)

Illustration of a relative sea level fall caused by upward land movement

Sea level appears
to have fallen

Corals©Wikipedia

Actually, it is theland that has beenraised 2007 M8.1 Solomon Islands earthquake raised land by 1-3 m
Image credit: Albert et al. (2007), Coral Reef How fast can sea level rise?

 Today sea level is rising at a rate of 3.5 mm/year…but how fast will it rise in the future?

Predicted sea level rise
PREDICTED SEA LEVEL RISE IN THE 21ST CENTURY

10 mm/yr

FAST WARMING SCENARIO*0.2 – 1 m / 100 yrs

2.5 mm/yr
SLOW WARMING SCENARIO** Depend on how much greenhouse gases (mainly CO2) humanity will emit
https://www.eea.europa.eu/data-and-maps/figures/projected-change-of-global-mean 2021/7/2

Data source: IPCC (2013)

Has sea level ever been changing that fast in the past?
How does the current sea level rise compare with sea
level change in the past?
Is sea level capable of rising even faster?

To answer these questions, we need to study thehistory of sea level change Reconstructing past sea level changeWhat do we need?
 Features of the landscape that can be linked to sea

level (sea level indicators) and that can resist thepassing of time to be studied by geologists

Examples: marine notches, coral reefsmarine notches as sea level indicator

Image credit: Pirazolli & Evelpidou (2013)

Sea

Coral reefs as sea level indicator

Image credit: http://www.coralsoftheworld.org/

Corals need sunlight to grow

Coral

CORAL REEF

PHOTOSYNTHESIS
6H2O + 6CO2 + sunlight → C6H12O6 + 6O2

Coral polypMicroalgae

The position of coral reefs change with sea level
Sea level 30,000 years ago
FossilREEF 1

Sea-level fallSea-level 20,000 years ago
REEF 2

Method to reconstruct past sea level change

Sea level indicator (example = fossil coral reef)
Age = 3000 years
01000 2000 3000 4000 5000 6000
Elevation = +2 m
3
Sea level 3000 years ago

1

Sea level today

LAND

2

SEA

Sea-level fall
0.7 mm/year

0

1
0-1

-1-2-2-3-30

1000 2000 3000 4000 5000 6000

Time (in years)

Elevation (in m)

2m

23

Fossil coral reefs - Okinawa

Fossil coral reef

100,000-200,000 years old

Fossil coral reefs - Okinawa

Image credit: Marc Humblet (left); http://www.coralsoftheworld.org/ (right)

Fossil coral reefs - The Seychelles Isl.
Fossil coral reef

100,000-200,000 years old

Fossil coral reefs - The Seychelles Isl.

image credit: Nadine HallmannPast sea level change

Photo: Dr. Ron Blakey, Paleogeography and Geologic History of North America

WARM

COLD = ICE AGE

Depth (in m)

Present-day sea level

Age (in thousand of years)
Data source: https://www.dur.ac.uk/, Lisiecky & Raimo (2005)

Case study:

The Great Barrier Reef of Australia andthe history of sea-level and climate overthe past 30,000 years Study case: Great Barrier Reef of Australia

OBJECTIVES:

 Reconstruct sea level change since last Ice Age Reconstruct the history of the Great Barrier Reef

The Great Barrier Reef of Australia

1650 km

AUSTRALIA

Image credit: Google EarthWARM

COLD = ICE AGE

Depth (in m)

Present-day sea level

Peak of Last Ice Age
20,000 years ago

Age (in thousand of years)
Photo: Dr. Ron Blakey, Paleogeography and Geologic History of North America
Data source: https://www.dur.ac.uk/, Lisiecky & Raimo (2005)

Were there coral reefs during the Last Ice Age?
If they were present, where should we look fortheir fossil remains today?

AUSTRALIA

Today

0m

10,000 years ago

20,000 years ago-40 m-120 m
XX
X

A

B

X

X

image credit : Google Earth©Google Earthimage credit : https://www.jamstec.go.jp/e/about/equipment/ships/kaiko7000.html 2021/7/2?
image credit : DOI: 10.1016/j.margeo.2007.08.001

Data source: Hinestrosa et al. (2016); JAMSTEC

BA

How do we take samples?
Modern coral reefABFossil reefs

IODP (Integrated Ocean Drilling Program) Expedition 325

Image credit: IODP

98 m

67 m

110 m

88 m

90 m

47 m

57 m

15 kyr

12.5 kyr

20 kyr

15.5 kyr24 kyr

10.5 kyr12.5 kyr

1 kyr = 1000 years

Image credit: IODPResults-20

Sea Level (in m)-40

ICE AGE-60-80

20 m sea level drop in 1400 years� 140 mm/year

-100
-120

WARMING

COOLING

-140
5,000

10,000 15,000 20,000 25,000 30,000 35,000Time (in years)

Data source: Yokoyama et al. (2018)

-5-25Depth (in m)-45-6520 m rise in < 500 years
 >40 mm/year-85-105
-125
3,000

6,000

9,000

12,00015,00018,000Time (in years)

Data source: Deschamps et al. (2012)

What do we learn from these results?

 Models predicting future sea-level rise produce rates of
2.5 to 10 mm/year by the end of the century.
 Study of fossil reefs show that sea level can change at rates
several times higher than those predicted (up to 40 mm/year
for sea level rise).

?

Is sea level capable of rising that fast in the future?

 We need to investigate mechanisms that generate such fast sea level rise
Data source: IPCC (2013)

The scientific method and thecommunication of scientific results

Outline of the scientific method?

 Define a problem to solve Collect data to solve the problem(observations, experiments)

 Analyze data (to extract useful information)
 Formulate a hypothesis (tentative explanation)
image credit : https://www.irasutoya.com/++or Test your hypothesis against new data Reject / modify / keep as it is(depending on the new results obtained)When scientists work on something, they wantto share the results of their work with others.

Publication in a scientific journal

Scientific journals
Generalist

natureSpecializedEconomics

ECONOMETaRICA
Medicine

THE LANCET
Popular science magazines

SCIENTIFICAMERICAN

Figure removed due to copyright restrictions.

SiencePNAS

PLOS ONEOpen accessFree online

Proceedings of the National Academy ofSciences of the United States of America

Experimental
biology

Cell
American Journal ofPotato Research

Paleontology

Lethaia
Biology

Current Biology

NewScientist
physicstoday

SCIENCE.fr

The peer review process

1. Scientists study
something

2. Scientists write
about their results

5. The article is published
if it meets editorial andpeer standards

3. Journal editor
receives article andsend it to reviewers

4. Reviewers read andprovide feedback toeditor
http://undsci.berkeley.edu/article/howscienceworks_16

Figure removed
due to copyright
restrictions.

Information flow
1. Original source
2. Press release

Figure removed
due to copyright
restrictions.

People3. Scientific news outlet
Figure removed due to copyright
restrictions.
Images : ScienceNews,MONGABAY.COM, ScienceDaily

5. Social media
Figure removed due to copyright
restrictions.
Images : facebook, Twitter, reddit

4. General news outlet
Figure removed due to copyright
restrictions.
Images : The Asahi Shinbun, CNN,
The Yomiuri Shinbun

Information flow
1. Original source
2. Press release

Figure removed
due to copyright
restrictions.

PeopleCheck original source

3. Scientific news outlet
Figure removed due to copyright
restrictions.
Images : ScienceNews,MONGABAY.COM, ScienceDaily

5. Social media
Figure removed due to copyright
restrictions.
Images : facebook, Twitter, reddit

4. General news outlet
Figure removed due to copyright
restrictions.
Images : The Asahi Shinbun, CNN,
The Yomiuri Shinbun

In the Internet Age, in which we areconfronted to a flood of information on aregular basis, it is necessary to analyze
information carefully and verify its sourcein order to take correct decisions

Thank you foryour attention!