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Coupled evolution of temperature and carbonate chemistry during the Paleocene–Eocene; new trace element records from the low latitude Indian Ocean

Coupled evolution of temperature and carbonate chemistry during the Paleocene–Eocene; new trace element records from the low latitude Indian Ocean
Coupled evolution of temperature and carbonate chemistry during the Paleocene–Eocene; new trace element records from the low latitude Indian Ocean

The early Paleogene represents the most recent interval in Earth's history characterized by global greenhouse warmth on multi-million year timescales, yet our understanding of long-term climate and carbon cycle evolution in the low latitudes, and in particular the Indian Ocean, remains very poorly constrained. Here we present the first long-term sub-eccentricity-resolution stable isotope (δ 13C and δ 18O) and trace element (Mg/Ca and B/Ca) records spanning the late Paleocene–early Eocene (∼58–53 Ma) across a surface–deep hydrographic reconstruction of the northern Indian Ocean, resolving late Paleocene 405-kyr paced cyclicity and a portion of the PETM recovery. Our new records reveal a long-term warming of ∼4–5 °C at all depths in the water column, with absolute surface ocean temperatures and magnitudes of warming comparable to the low latitude Pacific. As a result of warming, we observe a long-term increase in δ 18O sw of the mixed layer, implying an increase in net evaporation. We also observe a collapse in the temperature gradient between mixed layer- and thermocline-dwelling species from ∼57–54 Ma, potentially due to either the development of a more homogeneous water column with a thicker mixed layer, or depth migration of the Morozovella in response to warming. Synchronous warming at both low and high latitudes, along with decreasing B/Ca ratios in planktic foraminifera indicating a decrease in ocean pH and/or increasing dissolved inorganic carbon, suggest that global climate was forced by rising atmospheric CO 2 concentrations during this time.

Indian Ocean, Paleocene-Eocene Thermal Maximum, Paleogene, paleoceanography, paleoclimate, trace elements
0012-821X
Barnet, James S.k.
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Harper, Dustin T.
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Levay, Leah J.
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Edgar, Kirsty M.
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Henehan, Michael J.
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Babila, Tali L.
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Ullmann, Clemens V.
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Leng, Melanie J.
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Kroon, Dick
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Zachos, James C.
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Littler, Kate
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Barnet, James S.k.
f8741ea4-8403-423c-bf5d-ef57a1b0a014
Harper, Dustin T.
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Levay, Leah J.
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Edgar, Kirsty M.
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Henehan, Michael J.
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Babila, Tali L.
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Ullmann, Clemens V.
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Leng, Melanie J.
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Kroon, Dick
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Zachos, James C.
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Littler, Kate
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Barnet, James S.k., Harper, Dustin T., Levay, Leah J., Edgar, Kirsty M., Henehan, Michael J., Babila, Tali L., Ullmann, Clemens V., Leng, Melanie J., Kroon, Dick, Zachos, James C. and Littler, Kate (2020) Coupled evolution of temperature and carbonate chemistry during the Paleocene–Eocene; new trace element records from the low latitude Indian Ocean. Earth and Planetary Science Letters, 545, [116414]. (doi:10.1016/j.epsl.2020.116414).

Record type: Article

Abstract

The early Paleogene represents the most recent interval in Earth's history characterized by global greenhouse warmth on multi-million year timescales, yet our understanding of long-term climate and carbon cycle evolution in the low latitudes, and in particular the Indian Ocean, remains very poorly constrained. Here we present the first long-term sub-eccentricity-resolution stable isotope (δ 13C and δ 18O) and trace element (Mg/Ca and B/Ca) records spanning the late Paleocene–early Eocene (∼58–53 Ma) across a surface–deep hydrographic reconstruction of the northern Indian Ocean, resolving late Paleocene 405-kyr paced cyclicity and a portion of the PETM recovery. Our new records reveal a long-term warming of ∼4–5 °C at all depths in the water column, with absolute surface ocean temperatures and magnitudes of warming comparable to the low latitude Pacific. As a result of warming, we observe a long-term increase in δ 18O sw of the mixed layer, implying an increase in net evaporation. We also observe a collapse in the temperature gradient between mixed layer- and thermocline-dwelling species from ∼57–54 Ma, potentially due to either the development of a more homogeneous water column with a thicker mixed layer, or depth migration of the Morozovella in response to warming. Synchronous warming at both low and high latitudes, along with decreasing B/Ca ratios in planktic foraminifera indicating a decrease in ocean pH and/or increasing dissolved inorganic carbon, suggest that global climate was forced by rising atmospheric CO 2 concentrations during this time.

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Accepted/In Press date: 8 June 2020
Published date: 1 September 2020
Additional Information: Funding Information: This work was principally funded by a European Consortium for Ocean Research Drilling (ECORD) Research Grant, the International Association of Sedimentologists (IAS) Postgraduate Research Grant Scheme, and the Natural Environment Research Council (NERC) Isotope Geosciences Facility ( IP-1581–1115 ), awarded to James Barnet and Kate Littler. We also thank participants of the International Ocean Discovery Program Expedition 353 and Ocean Drilling Program Expedition 121 for collecting the sediment cores, as well as the Kochi Core Center for taking the requested samples on our behalf. LJL acknowledges funding from the IODP-JRSO ( NSF grant 1326927 ), KME acknowledges funding from NERC grants NE/H016457/1 and NE/P013112/1 , and CVU acknowledges funding via NERC grant NE/N018508/1 . Lastly, we thank two anonymous reviewers for their comments which helped to improve the manuscript. The complete stable isotope and trace element datasets supporting this manuscript have been archived online in the PANGAEA database: https://doi.pangaea.de/10.1594/PANGAEA.910789 . Publisher Copyright: © 2020 The Author(s)
Keywords: Indian Ocean, Paleocene-Eocene Thermal Maximum, Paleogene, paleoceanography, paleoclimate, trace elements

Identifiers

Local EPrints ID: 444444
URI: http://eprints.soton.ac.uk/id/eprint/444444
ISSN: 0012-821X
PURE UUID: b94d7584-9fca-4ec1-b8d3-d7b4c7bd6151
ORCID for Tali L. Babila: ORCID iD orcid.org/0000-0001-9948-9341

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Date deposited: 19 Oct 2020 16:33
Last modified: 22 Oct 2022 01:53

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Contributors

Author: James S.k. Barnet
Author: Dustin T. Harper
Author: Leah J. Levay
Author: Kirsty M. Edgar
Author: Michael J. Henehan
Author: Tali L. Babila ORCID iD
Author: Clemens V. Ullmann
Author: Melanie J. Leng
Author: Dick Kroon
Author: James C. Zachos
Author: Kate Littler

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