22 / 2025-03-25 10:06:34

Pronounced methane cycling in northern lakes coincided with a rapid rise in atmospheric CH4 during the last deglacial warming

permafrost,methane,biomarker,Last deglaciation to glaciation,thermokarst lakes

Theme 4: Microbial and Biogeochemical Evolution through Time > Session 4d: Biogeochemical Methane Cycle: Past, Present, and Future

Atmospheric methane concentration (AMC) surged by ~50% during the last deglaciation, with northern (>30°N) sources contributing ~40% of the rise. However,  hypothesized northern sources, including expanding lakes, peatlands, and destabilized permafrost or hydrates, fail to explain this rapid increase. Here, we use radiocarbon data, biomarkers, and compound-specific isotopes to assess temperature change, permafrost thaw and methane cycling from a Tibetan thermokarst lake that encompasses the Younger Dryas-Preboreal (YD-PB) transition. Extremely low δ¹³C values (-80.3‰) of methane-diagnostic lipids suggest intense methane cycling during the YD-PB, co-eval with the AMC surge and the fastest rate of warming (3.1°C/100yr). By contrast, methane cycling was weak during the Holocene Climatic Optimum despite the highest temperatures. These findings question the view that freshwater methane production positively correlated with absolute temperature, suggesting instead a greater dependence on warming rates. Rapid warming likely intensified emissions from existing northern lakes, fueling the elusive yet clearly amplified northern methane source that contributed to the deglacial abrupt rise in AMC.