The Seawater Carbon Inventory at the Paleocene-Eocene Thermal Maximum

Abstract:

The Paleocene-Eocene Thermal Maximum (PETM, 55.6 Ma) was a geologically rapid carbon release event that is considered the closest natural analog to anthropogenic CO₂ emissions. Recent work has used boron-based proxies in planktic foraminifera to characterize the extent of surface ocean acidification that occurred during the event. However, seawater acidity alone provides an incomplete constraint on the nature and source of carbon release. Here we apply new culture calibrations for the B/Ca proxy in planktic foraminifera and use them to calculate relative changes in seawater dissolved inorganic carbon concentration (DIC), surmising that Pacific surface ocean DIC increased by + 1100 µmol/kg during the peak-PETM. Making reasonable assumptions for the pre-PETM oceanic DIC inventory, we provide the first fully data-driven estimate of the PETM carbon source. Our reconstruction yields a mean source carbon δ¹³C of -10‰ and a mean increase in the oceanic C inventory of +14,700 PgC, pointing at volcanic CO₂ emissions as the main carbon source responsible for PETM warming.