Warm deep-sea temperatures across Eocene Thermal Maximum 2 from clumped isotope thermometry

Tobias Agterhuis; Martin Ziegler; Niels J. de Winter; Lucas J. Lourens

doi:10.1038/s43247-022-00350-8

Warm deep-sea temperatures across Eocene Thermal Maximum 2 from clumped isotope thermometry

Tobias Agterhuis^*
, Martin Ziegler
, Niels J. de Winter
, Lucas J. Lourens

^*Corresponding author for this work

Vrije Universiteit Amsterdam

Research output: Contribution to Journal › Article › Academic › peer-review

Abstract

The early Eocene hothouse experienced highly elevated atmospheric CO₂ levels and multiple transient global warming events, so-called hyperthermals. The deep ocean constitutes an assumed setting to estimate past global mean temperatures. However, available deep-sea temperature reconstructions from conventional benthic foraminiferal oxygen isotopes and magnesium/calcium ratios rely on uncertain assumptions of non-thermal influences, associated with seawater chemistry and species-specific physiological effects. Here we apply the carbonate clumped isotope thermometer, a proxy not governed by these uncertainties, to evaluate South Atlantic deep-sea temperatures across two hyperthermal events in the early Eocene (Eocene Thermal Maximum 2/H1 and H2; ~54 Myr ago). Our independent reconstructions indicate deep-sea temperatures of 13.5 ± 1.9 °C (95% CI) for the background conditions and average hyperthermal peak temperatures of 16.9 ± 2.3 °C (95% CI). On average, these absolute temperatures are three degrees warmer than estimates from benthic oxygen isotopes. This finding implies a necessary reassessment of (1) the Eocene seawater isotope composition and (2) pH changes in the deep ocean and its potential influence on benthic foraminiferal oxygen isotope records.

Original language	English
Article number	39
Pages (from-to)	1-9
Number of pages	9
Journal	Communications Earth & Environment
Volume	3
Early online date	24 Feb 2022
DOIs	https://doi.org/10.1038/s43247-022-00350-8
Publication status	Published - 2022

Bibliographical note

Publisher Copyright:
© 2022, The Author(s).

Funding

This research was conducted under the program of the Netherlands Earth System Science Centre (NESSC), financially supported by the Ministry of Education, Culture, and Science (OCW) of the Netherlands. M.Z. acknowledges additional funding from the Dutch Research Council (NWO), research grant 016.161.365. This work used samples and data provided by the Ocean Drilling Program (ODP). We thank the three anonymous reviewers and Sevi Modestou for their comments and suggestions that helped to improve this manuscript. We are grateful to Ilja J. Kocken (Utrecht University) for processing the raw clumped isotope data in R and Arnold E. van Dijk (Geolab of Utrecht University) for technical support in the lab. We acknowledge Alvaro Fernandez, Niklas Meinicke, Joep van Dijk, and Anna N. Meckler for sharing their Matlab scripts and output files to propagate errors. We thank Lucy Stap for picking of foraminifera. This research was conducted under the program of the Netherlands Earth System Science Centre (NESSC), financially supported by the Ministry of Education, Culture, and Science (OCW) of the Netherlands. M.Z. acknowledges additional funding from the Dutch Research Council (NWO), research grant 016.161.365. This work used samples and data provided by the Ocean Drilling Program (ODP). We thank the three anonymous reviewers and Sevi Modestou for their comments and suggestions that helped to improve this manuscript. We are grateful to Ilja J. Kocken (Utrecht University) for processing the raw clumped isotope data in R and Arnold E. van Dijk (Geolab of Utrecht University) for technical support in the lab. We acknowledge Alvaro Fernandez, Niklas Meinicke, Joep van Dijk, and Anna N. Meckler for sharing their Matlab scripts and output files to propagate errors. We thank Lucy Stap for picking of foraminifera.

Funders	Funder number
Horizon 2020 Framework Programme	843011
Universiteit Utrecht
Ministerie van Onderwijs, Cultuur en Wetenschap
Nederlandse Organisatie voor Wetenschappelijk Onderzoek	016.161.365
Netherlands Earth System Science Centre

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

SDG 14 Life Below Water

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10.1038/s43247-022-00350-8

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title = "Warm deep-sea temperatures across Eocene Thermal Maximum 2 from clumped isotope thermometry",

abstract = "The early Eocene hothouse experienced highly elevated atmospheric CO2 levels and multiple transient global warming events, so-called hyperthermals. The deep ocean constitutes an assumed setting to estimate past global mean temperatures. However, available deep-sea temperature reconstructions from conventional benthic foraminiferal oxygen isotopes and magnesium/calcium ratios rely on uncertain assumptions of non-thermal influences, associated with seawater chemistry and species-specific physiological effects. Here we apply the carbonate clumped isotope thermometer, a proxy not governed by these uncertainties, to evaluate South Atlantic deep-sea temperatures across two hyperthermal events in the early Eocene (Eocene Thermal Maximum 2/H1 and H2; \textasciitilde{}54 Myr ago). Our independent reconstructions indicate deep-sea temperatures of 13.5 ± 1.9 °C (95\% CI) for the background conditions and average hyperthermal peak temperatures of 16.9 ± 2.3 °C (95\% CI). On average, these absolute temperatures are three degrees warmer than estimates from benthic oxygen isotopes. This finding implies a necessary reassessment of (1) the Eocene seawater isotope composition and (2) pH changes in the deep ocean and its potential influence on benthic foraminiferal oxygen isotope records.",

author = "Tobias Agterhuis and Martin Ziegler and \{de Winter\}, \{Niels J.\} and Lourens, \{Lucas J.\}",

note = "Publisher Copyright: {\textcopyright} 2022, The Author(s).",

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AB - The early Eocene hothouse experienced highly elevated atmospheric CO2 levels and multiple transient global warming events, so-called hyperthermals. The deep ocean constitutes an assumed setting to estimate past global mean temperatures. However, available deep-sea temperature reconstructions from conventional benthic foraminiferal oxygen isotopes and magnesium/calcium ratios rely on uncertain assumptions of non-thermal influences, associated with seawater chemistry and species-specific physiological effects. Here we apply the carbonate clumped isotope thermometer, a proxy not governed by these uncertainties, to evaluate South Atlantic deep-sea temperatures across two hyperthermal events in the early Eocene (Eocene Thermal Maximum 2/H1 and H2; ~54 Myr ago). Our independent reconstructions indicate deep-sea temperatures of 13.5 ± 1.9 °C (95% CI) for the background conditions and average hyperthermal peak temperatures of 16.9 ± 2.3 °C (95% CI). On average, these absolute temperatures are three degrees warmer than estimates from benthic oxygen isotopes. This finding implies a necessary reassessment of (1) the Eocene seawater isotope composition and (2) pH changes in the deep ocean and its potential influence on benthic foraminiferal oxygen isotope records.

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Warm deep-sea temperatures across Eocene Thermal Maximum 2 from clumped isotope thermometry

Abstract

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Funding

UN SDGs

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