Microbial metabolism amplified warming in three Phanerozoic hyperthermal events

Area of Science:

• Paleoclimatology
• Oceanography
• Biogeochemistry

Background:

• The ocean's biological carbon pump (BCP) is vital for climate regulation, sequestering atmospheric CO2.
• Understanding BCP dynamics during past extreme warming events (hyperthermals) is crucial but limited.

Purpose of the Study:

• To investigate changes in the BCP during the Permian-Triassic, early Toarcian, and Paleocene-Eocene hyperthermals.
• To identify the mechanisms driving BCP alterations under rapid warming.

Main Methods:

• Utilized vertical carbon isotope (δ13C) gradients between surface and mid-waters as a proxy for BCP activity.
• Analyzed data from three distinct geological hyperthermal events.

Main Results:

• Observed a two- to three-fold increase in vertical δ13C gradients during hyperthermals.
• Attributed increased gradients to enhanced organic matter remineralization via microbial respiration.
• Documented a two- to six-fold reduction in particulate organic carbon transfer efficiency.

Conclusions:

• Warming-induced microbial metabolism significantly impacted the BCP during ancient hyperthermals.
• Reduced carbon export to the deep ocean may have limited sequestration.
• Enhanced microbial metabolism likely amplified global warming through a positive feedback loop.