Effects of soil warming on CO2 efflux in tundra soil: Response to a 2015 episodic event

Soil carbon emission is vulnerable to changes in temperature, moisture, and the organic carbon stored in tundra soil. Emissions can therefore be affected by recent Arctic climate change and warming. Here, we conducted soil CO2 efflux measurements in the tundra ecosystem of western Alaska, during the growing seasons of 2014 and 2015, in order to assess the effect of soil warming on soil carbon emission from a 2015 episodic warming event. Soil carbon emissions were greater in 2015 than in 2014, resulting from 1) a dry growing season and lower soil moisture, 2) increases in TDDs (total degree days of above 0 °C) for soil temperature at deeper active layers of 50, 70, and 80-cm depths, 3) deeper thaw depth of the active layer, and 4) stronger PAR (photosynthetically active radiation) during the growing season of 2015. These findings demonstrate the response from the decomposability of old-aged organic carbon matter from naturally occurring increased soil temperature at a deeper active layer, and subsequently, enhanced soil carbon emission to the atmosphere (e.g., 9 % higher in 2015 than in 2014) during the growing season. The findings also imply that soil warming-induced soil carbon emissions contribute an additional atmospheric carbon source and an accelerating positive feedback to climate change in the Arctic during the growing season.