Southeastern Atlantic deep-sea warmth across two early Eocene transient global warming events

Paleoclimate Biogeology, Earth Sciences Department, Utrecht University, The Netherlands brbr br br The early Eocene (56–48 Ma) can provide important constraints on the near-future warm climate state (Zachos et al., 2008; Burke et al., 2018) because it is a greenhouse period of highly-elevated CO2 levels and the occurrence of multiple transient global warming events (hyperthermals) (e.g. Lourens et al., 2005; Sluijs et al., 2006; Bijl et al., 2009; Anagnostou et al., 2016; Cramwinckel et al., 2018; Lauretano et al., 2018). Given the large heat capacity of the deep ocean, deep-sea temperatures are arguably the best indicator for mean global temperature change. Here we apply for the first time the clumped isotope technique (Δ47) on early Eocene benthic foraminifera to better constrain absolute deep water temperatures across two hyperthermal events in the Southeastern Atlantic. Our results indicate warmer background deep-sea conditions, and larger high-temperature variability associated with these warming events than previously estimated based on foraminiferal δ18O and Mg/Ca. Assuming our temperatures are representative for the global deep ocean, the robust reconstructions of early Eocene deep-sea temperatures that we provide may indicate higher climate sensitivity for these past warm climates (or alternatively higher CO2 forcing).