The seawater carbon inventory at the Paleocene-Eocene Thermal Maximum

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.