Abrupt changes in biomass burning during the last glacial period.

Understanding the causes of past atmospheric methane (CH₄) variability is important for characterizing the relationship between CH₄, global climate and terrestrial biogeochemical cycling. Ice core records of atmospheric CH₄ contain rapid variations linked to abrupt climate changes of the last glacial period known as Dansgaard–Oeschger (DO) events and Heinrich events (HE)1,2. The drivers of these CH₄ variations remain unknown but can be constrained with ice core measurements of the stable isotopic composition of atmospheric CH₄, which is sensitive to the strength of different isotopically distinguishable emission categories (microbial, pyrogenic and geologic)3, 4–5. Here we present multi-decadal-scale measurements of δ¹³C–CH₄ and δD–CH₄ from the WAIS Divide and Talos Dome ice cores and identify abrupt 1‰ enrichments in δ¹³C–CH₄ synchronous with HE CH₄ pulses and 0.5‰ δ¹³C–CH₄ enrichments synchronous with DO CH₄ increases. δD–CH₄ varied little across the abrupt CH₄ changes. Using box models to interpret these isotopic shifts6 and assuming a constant δ¹³C–CH₄ of microbial emissions, we propose that abrupt shifts in tropical rainfall associated with HEs and DO events enhanced ¹³C-enriched pyrogenic CH₄ emissions, and by extension global wildfire extent, by 90–150%. Carbon cycle box modelling experiments7 suggest that the resulting released terrestrial carbon could have caused from one-third to all of the abrupt CO₂ increases associated with HEs. These findings suggest that fire regimes and the terrestrial carbon cycle varied contemporaneously and substantially with past abrupt climate changes of the last glacial period.An increase in wildfire extent and related greenhouse gas emissions can be linked to abrupt climatic changes during the last glacial period. [ABSTRACT FROM AUTHOR]