NOAA/WDS Paleoclimatology - Talos Dome and WAIS Divide, Antarctica Atmospheric Methane 13C and Deuterium Data from 50-15 KyrBP

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). The drivers of these CH4 variations remain elusive 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). Here, we present decadal-scale measurements of d13C-CH4 and dD-CH4 from the WAIS Divide and Talos Dome ice cores and identify abrupt 1‰ enrichments in d13C-CH4 synchronous with HE CH4 pulses and 0.5‰ d13C-CH4 enrichments synchronous with DO CH4 increases. dD-CH4 varied little across the abrupt CH4 changes. Using box models to interpret these isotopic shifts and assuming a constant d13C-CH4 of microbial emissions, we hypothesize that abrupt shifts in tropical rainfall associated with HE and DO Events enhanced 13C-enriched pyrogenic CH4 emissions, and by extension global wildfire extent, by 90 to 150%. Carbon cycle box modeling experiments suggest that the resulting released terrestrial carbon could have caused 1/3 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.