Assessing the Contribution of Arctic Lakes to the Methane Budget via Upscaling and GOSAT Satellite Derived Flux Data

Abstract:

The considerable contribution of northern lakes and wetlands to global methane emissions is likely to increase as the Arctic warms and carbon within permafrost becomes labile. However, large uncertainties are still present in baseline flux estimates. Satellite remote sensing promises a way to constrain fluxes at continental and hemispheric scales as it is spatially comprehensive and has, or promises, temporal depth. The GOSAT team (Japan) recently released the first global dataset of methane fluxes informed by satellite data. Here, for the Arctic (>66°N), we compare methane flux values from the GOSAT product with up-scaled flux values derived from field observations working in concert with pertinent GIS layers. Upscaling was done within the context of a novel geographic lake classification that recognizes regional differences in lake type and geomorphic history, which, in turn, reflect availability of organic carbon in the catchment/lake ecosystem. The up-scaled (bottom-up) approach yielded an annual flux of 3.89-13.0 Tg CH₄ yr ^-1, with 58-68 percent of the fluxes derived from lakes. This estimate flanks the remotely sensed (top-down) range of 5.36-7.15 Tg CH₄ yr ^-1. Furthermore, both estimates show similar spatial variation in fluxes. The convergence of results from these two independent methods underlines the potential of remotely-sensed methane observation as a new tool in estimating carbon budgets and the importance of regional variation in upscaling flux estimates. Though a first pass attempt at a spatially explicit pan-Arctic methane emission estimate, the results of this work are promising and could aid in closing the global methane budget.