Quantifying the Variability of CH4 Emissions from Pan-Arctic Lakes with Lake Biogeochemical and Landscape Evolution Models

Abstract:

Recent studies in the arctic and subarctic show that CH₄ emissions from pan-arctic lakes are playing much more significant roles in the regional carbon cycling than previously estimated. Permafrost thawing due to pronounced warming at northern high latitudes affects lake morphology, changing its CH₄ emissions. Thermokarst can enlarge the extent of artic lakes, exposing stable ancient carbon buried in the permafrost zone for degradation and changing a previously known carbon sink to a large carbon source. In some areas, the thawing of subarctic discontinuous and isolated permafrost can diminish thermokarst lakes. To date, few models have considered these important hydrological and biogeochemical processes to provide adequate estimation of CH₄ emissions from these lakes. To fill this gap, we have developed a process-based climate-sensitive lake biogeochemical model and a landscape evolution model, which have been applied to quantify the state and variability of CH₄ emissions from this freshwater system. Site-level experiments show the models are capable to capture the spatial and temporal variability of CH₄ emissions from lakes across Siberia and Alaska. With the lake biogeochemical model solely, we estimate that the magnitude of CH₄ emissions from lakes is 13.2 Tg yr^-1 in the north of 60 ºN at present, which is on the same order of CH₄ emissions from northern high-latitude wetlands. The maximum increment is 11.8 Tg CH₄ yr^-1 by the end of the 21st century when the worst warming scenario is assumed. We expect the landscape evolution model will improve the existing estimates.