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Ostracod response to monsoon and OMZ variability over the past 1.2 Myr

Ostracod response to monsoon and OMZ variability over the past 1.2 Myr
Ostracod response to monsoon and OMZ variability over the past 1.2 Myr

We present the first continuous middle through late Pleistocene record of fossil ostracods from the Maldives in the northern Indian Ocean, derived from sediment cores taken at Site U1467 by Expedition 359 of the International Ocean Discovery Program (IODP). Site U1467 lies at 487 m water depth in the Inner Sea of the Maldives archipelago, an ideal place for studying the effects of the South Asian Monsoon (SAM) system on primary productivity, intermediate depth ocean circulation, and the regional oxygen minimum zone (OMZ). The Inner Sea acts as a natural sediment trap that has undergone continuous sedimentation for millions of years with minor terrestrial influence. Our record spans from Marine Isotope Stage (MIS) 35 to the present, covering the mid-Pleistocene transition (1.2–0.6 Ma) and the Mid-Brunhes Event (MBE, at ~480 ka) the time when ice age cycles transitioned from occurring every 40,000 years to 100,000 years. The ostracod data is interpreted alongside the existing datasets from the same site of sedimentological (grain-size) and XRF-elemental analyses, and new organic biomarker data also from Site U1467. These datasets support the paleoenvironmental interpretation of the ostracod assemblages. Ostracods are abundant and diverse, displaying a prominent change in faunal composition at the MBE related to the increase in the amplitude of glacial-interglacial cycles, which deeply affected the monsoon system and thereby the past oceanographic conditions of the Maldives Inner Sea. Furthermore, ostracods exhibit distinctly different assemblages across glacial-interglacial cycles, particularly after the MBE, and these changes convincingly correspond to variability of the OMZ. Glacial periods are characterized by ostracod indicators of well‑oxygenated bottom water due to the intensification of the winter monsoon and the contraction of the OMZ. Abundant psychrospheric ostracods during glacials suggests that a southern sourced water mass, such as Antarctic Intermediate Water (AAIW) and/or Subantarctic Mode water, bathed the Maldives Inner Sea during glacial periods. In contrast, interglacial stages are characterized by ostracod species and biomarker data that indicate low-oxygen conditions and sluggish bottom water circulation pointing to an expansion of the regional OMZ due to the strengthening of the summer monsoon. Our results highlight the sensitivity of ostracods to oceanographic and climate variability.

Expedition 359, IODP Site U1467, Indian Ocean paleoceanography, Oxygen Minimum Zone, Pleistocene, South Asian monsoon, The Maldives
0377-8398
1-19
Alvarez Zarikian, Carlos A.
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Nadiri, Chimnaz
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Alonso-garcía, Montserrat
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Rodrigues, Teresa
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Huang, Huai-hsuan M.
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Lindhorst, Sebastian
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Kunkelova, Tereza
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Kroon, Dick
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Betzler, Christian
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Yasuhara, Moriaki
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Alvarez Zarikian, Carlos A.
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Nadiri, Chimnaz
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Alonso-garcía, Montserrat
22dc5967-2964-4ac0-9ad2-c269665a316f
Rodrigues, Teresa
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Huang, Huai-hsuan M.
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Lindhorst, Sebastian
4150d290-1c61-4962-a792-f8d0a6bea8fb
Kunkelova, Tereza
32818c35-f763-4ba3-8640-b9334ad4ae6e
Kroon, Dick
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Betzler, Christian
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Yasuhara, Moriaki
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Alvarez Zarikian, Carlos A., Nadiri, Chimnaz, Alonso-garcía, Montserrat, Rodrigues, Teresa, Huang, Huai-hsuan M., Lindhorst, Sebastian, Kunkelova, Tereza, Kroon, Dick, Betzler, Christian and Yasuhara, Moriaki (2022) Ostracod response to monsoon and OMZ variability over the past 1.2 Myr. Marine Micropaleontology, 174, 1-19, [102105]. (doi:10.1016/j.marmicro.2022.102105).

Record type: Article

Abstract

We present the first continuous middle through late Pleistocene record of fossil ostracods from the Maldives in the northern Indian Ocean, derived from sediment cores taken at Site U1467 by Expedition 359 of the International Ocean Discovery Program (IODP). Site U1467 lies at 487 m water depth in the Inner Sea of the Maldives archipelago, an ideal place for studying the effects of the South Asian Monsoon (SAM) system on primary productivity, intermediate depth ocean circulation, and the regional oxygen minimum zone (OMZ). The Inner Sea acts as a natural sediment trap that has undergone continuous sedimentation for millions of years with minor terrestrial influence. Our record spans from Marine Isotope Stage (MIS) 35 to the present, covering the mid-Pleistocene transition (1.2–0.6 Ma) and the Mid-Brunhes Event (MBE, at ~480 ka) the time when ice age cycles transitioned from occurring every 40,000 years to 100,000 years. The ostracod data is interpreted alongside the existing datasets from the same site of sedimentological (grain-size) and XRF-elemental analyses, and new organic biomarker data also from Site U1467. These datasets support the paleoenvironmental interpretation of the ostracod assemblages. Ostracods are abundant and diverse, displaying a prominent change in faunal composition at the MBE related to the increase in the amplitude of glacial-interglacial cycles, which deeply affected the monsoon system and thereby the past oceanographic conditions of the Maldives Inner Sea. Furthermore, ostracods exhibit distinctly different assemblages across glacial-interglacial cycles, particularly after the MBE, and these changes convincingly correspond to variability of the OMZ. Glacial periods are characterized by ostracod indicators of well‑oxygenated bottom water due to the intensification of the winter monsoon and the contraction of the OMZ. Abundant psychrospheric ostracods during glacials suggests that a southern sourced water mass, such as Antarctic Intermediate Water (AAIW) and/or Subantarctic Mode water, bathed the Maldives Inner Sea during glacial periods. In contrast, interglacial stages are characterized by ostracod species and biomarker data that indicate low-oxygen conditions and sluggish bottom water circulation pointing to an expansion of the regional OMZ due to the strengthening of the summer monsoon. Our results highlight the sensitivity of ostracods to oceanographic and climate variability.

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Ostracod response to monsoon and OMZ variability over the past 1.2 Myr - Accepted Manuscript
Restricted to Repository staff only until 20 February 2023.
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Accepted/In Press date: 13 February 2022
e-pub ahead of print date: 20 February 2022
Published date: June 2022
Additional Information: Funding Information: Expedition 359 was funded by the US National Science Foundation (NSF); the European Consortium for Ocean Research Drilling (ECORD); the Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT); the Ministry of Science and Technology (People's Republic of China); the Korea Institute of Geoscience and Mineral Resources; the Australian Research Council and the New Zealand Institute for Geological and Nuclear Sciences; and the Ministry of Earth Sciences (India). CAAZ acknowledges financial support from the U.S. Science Support Program at Columbia University under post-expedition award OCE14–50528 and NSF award no. OCE-1326927. MAG and TR would like to acknowledge funding from FCT (CCMAR UID/Multi/04326/2019 and WarmWorld project (PTDC/CTA-GEO/29897/2017). MY acknowledges funding from the Research Grants Council of the Hong Kong Special Administrative Region, China (project code: HKU 17302518), the Seed Funding Programme for Basic Research of the University of Hong Kong (project code: 202011159122), the Small Equipment Grant of the University of Hong Kong, the Seed Funding of the HKU-TCL Joint Research Centre for Artificial Intelligence, SKLMP Seed Collaborative Research Fund of City University of Hong Kong (project code: SKLMP/SCRF/0031), and the Faculty of Science RAE Improvement Fund of the University of Hong Kong. This research used samples and data provided by the International Ocean Discovery Program (IODP). This study would not have been possible without the dedicated effort of the drilling crew, ship's crew, and scientific staff of the drillship JOIDES Resolution during IODP Expedition 359. The Ministry of Fisheries and Agriculture of the Republic of the Maldives is thanked for granting the research permit. Thomas Stephens is thanked for assistance during the SEM imaging. Gene Hunt for helping with ostracod taxonomy. We thank Simone N. Brandâo and an anonymous reviewer for their thoughtful comments and suggestions for improving this manuscript. Publisher Copyright: © 2022 Elsevier B.V.
Keywords: Expedition 359, IODP Site U1467, Indian Ocean paleoceanography, Oxygen Minimum Zone, Pleistocene, South Asian monsoon, The Maldives

Identifiers

Local EPrints ID: 456163
URI: http://eprints.soton.ac.uk/id/eprint/456163
ISSN: 0377-8398
PURE UUID: 7240ad34-0bb6-4631-9411-e7fcee15aadf

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Date deposited: 26 Apr 2022 15:10
Last modified: 20 Jan 2023 18:03

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Contributors

Author: Carlos A. Alvarez Zarikian
Author: Chimnaz Nadiri
Author: Montserrat Alonso-garcía
Author: Teresa Rodrigues
Author: Huai-hsuan M. Huang
Author: Sebastian Lindhorst
Author: Dick Kroon
Author: Christian Betzler
Author: Moriaki Yasuhara

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