Thermokarst and Microtopography Enhance Carbon Fluxes from an Arctic Tussock Tundra Site

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Abstract. As the Arctic warms, thawing permafrost releases carbon dioxide (CO2) and methane (CH4) into the atmosphere, creating a positive feedback to warming. However, carbon loss from permafrost soils is poorly understood due to the paucity of in-situ carbon flux measurements from Arctic landscapes, complicating efforts to accurately characterize models. To gain insight into the interannual variability of carbon fluxes in response to environmental conditions, as well as the impact of thermokarst landscape features and microtopography on carbon fluxes, we analyzed a six-year (July 2017 – September 2023) eddy covariance tower (EC) dataset from a tussock tundra site with thermoerosional drainage channels near Council, Alaska. Flux chambers located in upland, lowland, and sloped plots near the EC tower measured differences in carbon fluxes by landscape position and inundation status from 2017 – 2019. EC data indicated Council ranged from a weak net carbon sink (-6.50 g C m-2) to a moderate source (30.93 g C m-2) with higher net carbon emissions during warmer temperatures. Growing season CO2 uptake was significantly greater from thermokarst drainage channels south of the tower, but CO2 emissions from these channels were significantly lower in the winter compared to the northern tundra. Similarly, thermokarst, microtopography, and inundation enhanced CH4 emissions. These findings, which establish a baseline for continued long-term monitoring of carbon fluxes and environmental conditions at the Council tundra site, highlight the importance of including the influence of microtopography and landscape features, such as thermokarst, in assessments of current and future carbon balance of the Arctic.

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