Repository Core Re-Discovery Program

Received date

2023/05/23

Proposal No.

ReC-001(ReCoRD)

New / RevisedNew(Above For Official Use Only)

Proposal Form
Basic Information
Title: Tracing Intermediate Water Current Changes and Sea Ice
Expansion in the Indian Ocean
Keywords: Miocene, Indian Ocean, intermediate water, sea ice(5 or less)Lead Proponent: Junichiro Kuroda
Affiliation: The University of Tokyo
Address: 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564 Japan
Phone: +81 4 7136 6120
E-mail: kuroda@aori.u-tokyo.ac.jp
Permission is granted to post the coversheet/site table on www.j-desc.org.
☒ I permit.
☐ I don’t permit.

Scientific Objectives (250 words or less)Within the proposed ReCoRD, we aim to understand the effect of changing climaticconditions during the “near-future warm period analogs” such as the Miocene Climatic
Optimum (MCO), and subsequent cooling during the Middle and Late Miocene andPliocene had on intermediate water formation and circulation. Model studies indicatethat climatic changes lead to a positional shift of the westerlies, related to the expansion
and contraction of sea ice around Antarctica. These changes further modulated
intermediate water circulation and nutrient transport in the global oceans (seeLaufkotter, C. & Gruber, N., 2018; Science 359, 1103–1104).
Based on this hypothesis, we aim to identify and correlate evidence for intermediatewater current changes and potential sea ice expansion in the Neogene by reinvestigating key Ocean Drilling Project (ODP) Sites in the wider Indian Ocean. Our
strategic sampling plan involves a transect through key features of Indian Ocean watermasses targeting ODP Sites 707 and 752, as well as DSDP Site 266
The objectives are, therefore:
1) Analyze Site 707 and 752 to define the sedimentological changes related to thehypothesized reorganization of intermediate water circulation.
12) Provide new digital core archives which can be directly correlated to existingvisual core descriptions to better quantify current winnowing or ice-rafted
debris at the target Sites.
3) Targeted sampling of the study sites for subsequent laboratory-based studies tobetter define intermediate water changes that provide information regarding theorigin and nutrient load of the water masses interacting with the sediment ateach Site.

Proposed Target CoresLeg/Exp.

Site-HoleCore115

707A

1H – 15H

121752A

1H – 10H

28266[Note: Only cores in KCC are available.]

1R – 22R

Proposed analysis prior to sampling
X-ray CT scans of cores (AH) are requested to allow comparison of sedimentologicaldescription and the application of machine learning to evaluate CT-scanned corematerial expected drift deposits during the ReCoRD. Site 266 will also be used toground truth machine learning approaches for ice-rafted debris (IRD) identification incore CT-scanning data of legacy cores. DSDP Site 266 is considered uniquely qualified
for this approach as it is located close to Antarctica and has a proven record of IRD
based on the shipboard reports.
[Note: Please describe above any analysis needed prior to sampling. Standard set is X-ray
CT, split surface image (WH and/or AH), digitizing smear slide and/or thin section
microscopic images.]

Summary of previous studies of the target cores
ODP Site 707 is located in the tropical western Indian Ocean, at the Mascarene
Plateau (present water depth of 1552 m). This site was selected to elucidate theNeogene variation of the Indian Central Water (ICW). Identification of water
properties and history of ocean circulation in the western Indian Ocean through theNeogene have long been studied by benthic carbon isotopic records from Site 707 (e.g.,Smart, 1998, Ramsay et al., 1998; Smart et al., 2007). In addition to those studies, an
important work on Nd isotope was conducted to reconstruct the Indian Ocean
circulation over the last 25 Ma (see Fig. 1d below) (Gourlan et al., 2008). The Neogene
history of marine primary productivity, ecosystem and biogeochemistry in the tropicalwestern Indian ocean have been investigated based on coccolith assemblages of thesediments from Site 707 (e.g., Sucheras-Marx and Henderiks, 2014; Supraha and2Henderiks, 2020; Karatsolis et al., 2022). Although Site 707 represents a key lowlatitude site in the Indian Ocean, the sedimentological effects of the recorded current
dynamics are, as of yet, poorly documented.
ODP Site 752 is located in the southeastern Indian Ocean, on the Broken Ridge(present water depth of 1086 m), where is close to the eastern flow path of SubAntarctic Mode Water. This site is particularly important to elucidate the history ofTasman Leakage through the Neogene, on the basis of benthic carbon isotopic recordsof sediments (e.g., Ridha, 2020; Christensen et al., 2021). Neogene climate change andatmospheric circulations have also been investigated by dust fraction of sedimentsfrom Site 707 (Hovan and Rea, 1992). However, the Neogene section of Site 752 is
critically understudied in terms of biostratigraphy as well as sedimentological changes
related to current changes.
DSDP Site 266 is located on the south flank of the Southeast Indian Ridge. Ice-rafted
debris (IRD) were described in the sedimentary cores from Site 266 based on theshipboard description, and a limited number of studies on the bulk sedimentgeochemistry has been done to identify the sedimentary provenances (Vlastelic et al.,2005). Neogene ecosystem and oceanographic variability have been studied based onorganic carbon isotope ratios (Sackett, 1986), biogenic Si (Brewster, 1980), andmicrofossil assemblages such as diatom (Barron, 1996) and radiolaria (Keany, 1978).
The new study on the Miocene sediment from Site 266 may provide a key (lowresolution) record of Miocene IRD in the southern high latitudes of the Indian Oceanby applying new CT-based core scanning methods.

Proponent ListFirst Name

Last Name

Affiliation

Country

Expertise

GeraldAuer*

University of Graz

Austria

Micropaleontology,
Stratigraphy,
Paleoceanography

Werner E.

Piller*University of Graz

Austria

Micropaleontology,
Stratigraphy,
Sedimentology

DavidDe
University of Munster Germany
Vleeschouwer*

Stratigraphy,
Paleoceanography

Anna Joy

Drury*

UKDigital Core Description,
Data Processing,
Stratigraphy,
Paleoceanography

BethChristensen*

USA

Paleoceanography,
Micropaleontology,
Sedimentology

Roawn University3Theresa

Nohl*

University of Vienna

Austria

JingLyu*

University of Munster Germany

Stratigraphy,
Paleoceanography

TamaraHechemer*

University of Graz

Austria

Paleoceanography,
Micropaleontology

XabierPuentes-Jorge*

University of Graz

Austria

Paleoceanography,
Micropaleontology

Jumpei

Yoshioka

University of TokyoJapan

Sedimentology

Sedimentology[Note: For proponents who do not have J-DESC memberships, please put an asterisk (*)
AFTER his/her last name.]
In the following pages, please provide a free-format document (3-pages maximum)
including figures, tables, and references.

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