Surface ocean warming and acidification driven by rapid carbon release precedes Paleocene-Eocene Thermal Maximum

Area of Science:

• Paleoclimatology
• Geochemistry
• Oceanography

Background:

• The Paleocene-Eocene Thermal Maximum (PETM) is characterized by a significant negative carbon isotope excursion (CIE).
• The mass, source, and timing of the carbon injection during the PETM remain subjects of ongoing scientific debate.
• Previous studies suggested transient precursor carbon releases, but a global signal was equivocal.

Purpose of the Study:

• To investigate the presence and characteristics of a potential precursor carbon release before the PETM.
• To analyze the impact of this precursor event on ocean temperature and chemistry.
• To compare the nature of the precursor carbon release with the main PETM CIE and anthropogenic emissions.

Main Methods:

• Analysis of foraminiferal carbon isotope (δ¹³C) records from a marine continental margin section.
• Reconstruction of sea surface temperature and ocean pH based on geochemical proxies.
• Comparison of margin records with deep-sea records to assess the spatial extent and timing of events.

Main Results:

• A negative pre-onset excursion (POE) of 1.0 to 1.5‰ in δ¹³C was identified prior to the main CIE.
• The POE coincided with a sea surface temperature rise of at least 2°C and a decline in ocean pH.
• Recovery of δ¹³C and pH occurred before the CIE onset, and the POE was absent in deep-sea records, suggesting rapid carbon release.

Conclusions:

• The precursor carbon release during the PETM was rapid, occurring on timescales faster than ocean mixing.
• The characteristics of the POE, including its rate and mass, are more comparable to current anthropogenic carbon emissions than the main PETM CIE.
• Deep-sea mixing played a crucial role in the subsequent recovery of the carbon cycle and ocean chemistry.