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

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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 languageEnglish
Article number39
Pages (from-to)1-9
JournalCommunications Earth & Environment
Volume3
Issue number1
DOIs
Publication statusPublished - Dec 2022

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