Ability of thermal energy from rainfall to warm and thaw soils at a thermokarst site in south-central Alaska

Abstract:

Northern-high latitudes are experiencing rapid climate change. These changes are resulting in permafrost thaw, landscape subsidence, and the release of long-stored carbon into the atmosphere. To better understand how high latitude systems will behave in the future, we instrumented a collapse scar bog and surrounding permafrost plateau in south-central Alaska that has a warm and wet climate, similar to that expected in more northern permafrost regions in the future. Our data indicate that thermal energy from rain was able to alter soil temperature. Directly following a 3-cm rain event, we observed up to 60 cm of thaw in the permafrost plateau and warming of soil to a depth of 2.1-meters (our deepest sensor) in the bog. Motivated by these soil responses, we used two years of field data along with physically-based modeling to quantify the belowground thermal input from rain and track how that thermal input is dissipated through the permafrost plateau and bog. Rain is an overlooked transporter of thermal energy into northern soils, but our data indicate it is an important factor influencing soil temperature, which in turn controls rates of thaw and wetland biogeochemistry. The role of rain in these thermally sensitive processes will likely grow in importance as northern high latitudes get warmer and wetter.