Rapid Acidification of the Ocean During the Paleocene-Eocene Thermal Maximum

TLDR

The Paleocene‑Eocene Thermal Maximum was driven by the rapid release of ~2000 × 10^9 t of methane, which should have lowered deep‑sea pH and caused a rapid shoaling of the calcite compensation depth. This study aims to constrain the timing and extent of massive sea‑floor carbonate dissolution during the PETM using new geochemical data from five South Atlantic deep‑sea sections. Geochemical analyses of sediment cores from 2.7–4.8 km water depth were used to track carbonate dissolution and CCD changes. The data reveal that the CCD shoaled by more than 2 km within <10,000 years and recovered over >100,000 years, indicating that >2000 × 10^9 t of carbon dissolved in the ocean and was permanently sequestered through silicate weathering feedback.

Abstract

The Paleocene-Eocene thermal maximum (PETM) has been attributed to the rapid release of ∼2000 × 10 9 metric tons of carbon in the form of methane. In theory, oxidation and ocean absorption of this carbon should have lowered deep-sea pH, thereby triggering a rapid (&lt;10,000-year) shoaling of the calcite compensation depth (CCD), followed by gradual recovery. Here we present geochemical data from five new South Atlantic deep-sea sections that constrain the timing and extent of massive sea-floor carbonate dissolution coincident with the PETM. The sections, from between 2.7 and 4.8 kilometers water depth, are marked by a prominent clay layer, the character of which indicates that the CCD shoaled rapidly (&lt;10,000 years) by more than 2 kilometers and recovered gradually (&gt;100,000 years). These findings indicate that a large mass of carbon (»2000 × 10 9 metric tons of carbon) dissolved in the ocean at the Paleocene-Eocene boundary and that permanent sequestration of this carbon occurred through silicate weathering feedback.