PNAS - "Our Estimates Confirm Modern Carbon Release Occuring Much Faster Than PETM Carbon Release"
Significance
During the Paleocene–Eocene Thermal Maximum (PETM) (56 Mya), the planet warmed by 5 to 8 °C, deep-sea organisms went extinct, and the oceans rapidly acidified. Geochemical records from fossil shells of a group of plankton called foraminifera record how much ocean pH decreased during the PETM. Here, we apply a geochemical indicator, the B/Ca content of foraminifera, to reconstruct the amount and makeup of the carbon added to the ocean. Our reconstruction invokes volcanic emissions as a driver of PETM warming and suggests that the buffering capacity of the ocean increased, which helped to remove carbon dioxide from the atmosphere. However, our estimates confirm that modern CO2 release is occurring much faster than PETM carbon release.
Abstract
The Paleocene–Eocene Thermal Maximum (PETM) (55.6 Mya) 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 previously undescribed culture calibrations for the B/Ca proxy in planktic foraminifera and use them to calculate relative changes in seawater-dissolved inorganic carbon (DIC) concentration, surmising that Pacific surface-ocean DIC increased by +1,010+1,415−646 µmol/kg during the peak-PETM. Making reasonable assumptions for the pre-PETM oceanic DIC inventory, we provide a 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 +14,900 petagrams of carbon (PgC), pointing to volcanic CO2 emissions as the main carbon source responsible for PETM warming.
EDIT
Subscription-only for full article
https://www.pnas.org/content/early/2020/09/08/2003197117