Transient deep ocean cooling in the eastern equatorial Pacific Ocean at the Eocene-Oligocene Transition

At the Eocene-Oligocene Transition (EOT), approximately 34 million years ago, Earth abruptly transitioned to a climate state sufficiently cool for Antarctica to sustain large ice sheets for the first time in tens to hundreds of millions of years. Oxygen isotope records from deep-sea benthic foraminifera (δ18Ob) provide the foundation of our understanding of this pivot point in Cenozoic climate history. A deeper insight, however, is hindered by the paucity of independent deep-sea temperature reconstructions and the ongoing challenge of deconvolving the temperature and continental ice volume signals embedded in δ18Ob records. Here we present records of deep-sea temperature change from the eastern equatorial Pacific for the EOT using clumped isotope thermometry, which permits explicit temperature reconstructions independent of seawater chemistry and continental ice volume. Our records suggest that the deep Pacific Ocean cooled markedly at the EOT by 4.7 ± 0.9°C. This decrease in temperature represents the first direct and robust evidence of deep-sea cooling associated with the inception of major Cenozoic glaciation. However, our data also indicate that this major cooling of the deep Pacific Ocean at the EOT was short-lived (∼200 kyrs), with temperatures rebounding to values close to pre-EOT levels by 33.6 Ma. Our calculated record of seawater δ18O suggests that this rebound in ocean temperature occurred despite the continued presence of a large-scale Antarctic ice sheet. This finding suggests a degree of decoupling between deep ocean temperatures in the eastern equatorial Pacific Ocean and the behavior of the newly established Antarctic ice sheet.

Eocene-Oligocene Transition, clumped isotope thermometry, deep-sea temperature

10.1029/2023PA004650

2572-4525

Taylor, V.E.

9a145923-b8f5-4289-81f6-1d3b85d1602a

Wilson, Paul

f940a9f0-fa5a-4a64-9061-f0794bfbf7c6

Bohaty, S.M.

68e3e3ca-01ee-4018-b414-b87e70dd5e61

Meckler, A.N.

96067c6b-c687-48eb-93b8-4c5432cc96f2

24 August 2023

Taylor, V.E.

9a145923-b8f5-4289-81f6-1d3b85d1602a

Wilson, Paul

f940a9f0-fa5a-4a64-9061-f0794bfbf7c6

Bohaty, S.M.

68e3e3ca-01ee-4018-b414-b87e70dd5e61

Meckler, A.N.

96067c6b-c687-48eb-93b8-4c5432cc96f2

Taylor, V.E., Wilson, Paul, Bohaty, S.M. and Meckler, A.N. (2023) Transient deep ocean cooling in the eastern equatorial Pacific Ocean at the Eocene-Oligocene Transition. Paleoceanography and Paleoclimatology, 38 (8), [e2023PA004650]. (doi:10.1029/2023PA004650).

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Accepted/In Press date: 26 July 2023

e-pub ahead of print date: 14 August 2023

Published date: 24 August 2023

Additional Information: Funding Information: This work was funded by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 638467; awarded to ANM) and the Norwegian Research Council (project number 314371; awarded to ANM). This work was also supported by Natural Environment Research Council (NERC) Grants NE/K014137/1 and NE/K008390/1 to PAW, NE/K006800/1 to SMB and PAW, a Royal Society Wolfson Merit Award to PAW, and a NERC SPITIFRE Doctoral Training Program Studentship (NE/L002531/1) awarded to VET and supervised by PAW and SMB. The authors thank Lubna Al‐Saadi, Nil Irvali, Enver Alagoz, and Eirik Galaasen for technical support during sample preparation and clumped isotope analyses at the University of Bergen, Megan Wilding and Bastian Hambach for technical support at the University of Southampton, Phil Rumford and colleagues at the IODP Gulf Coast Core Repository for assistance with sampling, and Alvaro Fernandez and Sevasti Modestou for thoughtful discussions. We thank the Editor, Associate Editor and Reviewers for their constructive and thorough reviews which improved this manuscript. For the purposes of open access, the author has applied a CC BY public copyright license to any Author Accepted Manuscript version arising from this submission. Funding Information: This work was funded by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 638467; awarded to ANM) and the Norwegian Research Council (project number 314371; awarded to ANM). This work was also supported by Natural Environment Research Council (NERC) Grants NE/K014137/1 and NE/K008390/1 to PAW, NE/K006800/1 to SMB and PAW, a Royal Society Wolfson Merit Award to PAW, and a NERC SPITIFRE Doctoral Training Program Studentship (NE/L002531/1) awarded to VET and supervised by PAW and SMB. The authors thank Lubna Al-Saadi, Nil Irvali, Enver Alagoz, and Eirik Galaasen for technical support during sample preparation and clumped isotope analyses at the University of Bergen, Megan Wilding and Bastian Hambach for technical support at the University of Southampton, Phil Rumford and colleagues at the IODP Gulf Coast Core Repository for assistance with sampling, and Alvaro Fernandez and Sevasti Modestou for thoughtful discussions. We thank the Editor, Associate Editor and Reviewers for their constructive and thorough reviews which improved this manuscript. For the purposes of open access, the author has applied a CC BY public copyright license to any Author Accepted Manuscript version arising from this submission. Publisher Copyright: © 2023. The Authors.

Keywords: Eocene-Oligocene Transition, clumped isotope thermometry, deep-sea temperature