Abrupt changes in biomass burning during the last glacial period

Area of Science:

• Paleoclimatology
• Atmospheric Chemistry
• Terrestrial Biogeochemistry

Background:

• Atmospheric methane (CH4) variability is crucial for understanding past climate dynamics and the carbon cycle.
• Ice core records show rapid CH4 fluctuations linked to abrupt climate events like Dansgaard-Oeschger (DO) and Heinrich events (HE).
• The precise drivers of these CH4 variations remain unclear, necessitating isotopic analysis.

Purpose of the Study:

• To investigate the causes of abrupt atmospheric CH4 changes during the last glacial period.
• To constrain the sources of CH4 variability using stable isotope measurements.
• To link CH4 emissions to abrupt climate shifts and their impact on the carbon cycle.

Main Methods:

• Multi-decadal-scale measurements of stable isotopes (δ13C-CH4 and δD-CH4) from Antarctic ice cores (WAIS Divide and Talos Dome).
• Analysis of isotopic shifts synchronous with CH4 pulses during DO and HE events.
• Application of box models to interpret isotopic data and infer emission source changes.

Main Results:

• Abrupt ~1‰ enrichments in δ13C-CH4 observed synchronous with HE CH4 pulses.
• Abrupt ~0.5‰ enrichments in δ13C-CH4 observed synchronous with DO CH4 increases.
• Minimal variation in δD-CH4 across abrupt CH4 changes, suggesting limited shifts in microbial or geologic sources.

Conclusions:

• Abrupt tropical rainfall shifts during HEs and DO events likely enhanced 13C-enriched pyrogenic CH4 emissions by 90-150%, indicating increased global wildfire extent.
• These fire-driven CH4 emissions could account for one-third to all of the abrupt CO2 increases associated with HEs.
• Fire regimes and the terrestrial carbon cycle demonstrably varied in concert with past abrupt climate changes.