COLLAPSE OF THE DEEP-SEA CIRCULATION DURING THE PETM WITH IMPLICATIONS FOR THE EXTINCTION OF BENTHIC FORAMINIFERA

During the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma), a rapid injection of isotopically depleted carbon into the atmosphere led to a ~5 °C global temperature rise, ocean acidification, and extinction of benthic foraminifera. In this study, DeepMIP climate sensitivity experiments have been carried out with the Community Earth System Model CESM1.2 to evaluate how changes in the CO₂radiative forcing could have contributed to Eocene hyperthermal events. The analysis of our simulations suggests that a substantial warming from pre-PETM conditions (corresponding to 3x CO₂PAL) to the PETM (corresponding to 6x CO₂PAL) occurred that could have generated severe environmental stress for benthic foraminifera. The lower equator-to-pole temperature gradient compared to present-day is due to the lack of an ice sheet and an increase in greenhouse gases. Topographic effects like the closure of the Drake Passage and the more southern location of Australia during the Eocene as well as a lower-than-present meridional temperature gradient contributed to a much weaker surface ocean circulation near the Antarctic continent as compared to the current pronounced Antarctic Circumpolar Current and a strong formation of deep water around Antarctica consistent to previous modeling studies and paleo-proxies. The formation of southern component water collapses with an increase of CO₂radiative forcing, thus leading to increased stratification, deep-water warming, reduced export production, and ocean acidification that likely contributed to the benthic extinction event during the PETM.