Page 134 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

Chapter 6. Roles of thermokarst lakes in a warming world Abstract
Permafrost covers a quarter of the northern hemisphere land surface and contains twice the amount of carbon that is currently present in the atmosphere. Future climate change is expected to reduce its near-surface cover by over 90% by the end of the 21st century, leading to thermokarst lake formation. Thermokarst lakes are point sources of carbon dioxide and methane which release long-term carbon stocks into the atmosphere, thereby initiating a positive climate feedback potentially contributing up to a 0.39°C rise of surface air temperatures by 2300. This review describes the potential role of thermokarst lakes in a warming world and the microbial mechanisms that underlie their contributions to the global greenhouse gas budget.
Highlights
• Thermokarst lakes form as a result of permafrost thaw in predominantly ice-rich Yedoma deposits and are therefore an ecosystem that is rapidly expanding with the onset of climate change.
• Thermokarst lakes are net greenhouse gas sources as century-old carbon deposits become bioavailable and are mineralized to CO2 and CH4.
• Methane is a more potent greenhouse gas than CO2. Changed dynamics will therefore disproportionately affect global warming.
• Methane emissions are the net result of CH4 production by methanogenesis and CH4 consumption by aerobic bacteria or anaerobic archaea, with high levels of heterogeneity and intricate interactions.
• Future climate change will have disproportionate effects on the Arctic, which implies potentially strong consequences for future greenhouse gas fluxes and thaw progression.
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