Increased terrestrial methane cycling at the Palaeocene-Eocene thermal maximum

Area of Science:

• Paleoclimatology
• Biogeochemistry
• Environmental Science

Background:

• The Paleocene-Eocene Thermal Maximum (PETM) was a period of rapid global warming approximately 55 million years ago.
• The primary driver is thought to be a surge in greenhouse gases, with methane hydrate dissociation as a leading hypothesis.
• Previous research suggested terrestrial methane emissions could exacerbate warming, but direct evidence from wetlands was scarce.

Observation:

• The Cobham Lignite deposit in England captures the PETM onset, offering a unique window into wetland ecosystem responses.
• Bacterial hopanoids, a type of biomarker, were identified in mire sediments from this deposit.
• A significant decrease in hopanoid carbon isotope values was observed at the PETM onset.

Findings:

• The carbon isotope shift suggests an expansion of the methanotroph population within the wetland ecosystem.
• This microbial shift points to increased methane production, likely triggered by a warmer and wetter climate.
• The study provides direct evidence for enhanced methane release from the terrestrial biosphere during the PETM.

Implications:

• The findings support the hypothesis that terrestrial methane release acted as a positive feedback mechanism during the PETM.
• This highlights the crucial role of wetland ecosystems in regulating ancient climate dynamics.
• Understanding these past feedbacks is vital for predicting future climate change scenarios.