Greenhouse Gas Emissions and Lateral Carbon Dynamics at an Eroding Yedoma Permafrost Site in Siberia (Duvanny Yar).

Rapid Arctic warming is accelerating permafrost thaw and mobilizing previously frozen organic carbon (OC) into waterways. Upon thaw, permafrost-derived OC can become susceptible to microbial degradation that may lead to greenhouse gas emissions (GHG), thus accelerating climate change. Abrupt permafrost thaw (e.g., riverbank erosion, retrogressive thaw slumps) occurs in areas rich in OC. Given the high OC content and the increase in frequency of abrupt thaw events, these environments may increasingly contribute to permafrost GHG emissions in the future. To better assess these emissions from abrupt permafrost thaw, we incubated thaw stream waters from an abrupt permafrost thaw site (Duvanny Yar, Siberia) and additionally, waters from their outflow to the Kolyma River. Our results show that CO2 release by volume from thaw streams was substantially higher than CO2 emissions from the river outflow waters, while the opposite was true for CO2 release normalized to the suspended sediment weight (gram dry weight). The CH4 emissions from both thaw streams and outflow waters were at a similar range, but an order of magnitude lower than those of CO2. Additionally, we show that nearshore riverbank waters differ in their biogeochemistry from thaw streams and Kolyma River mainstem: particles resemble thaw streams while dissolved fraction is more alike to the Kolyma River thalweg. In these waters dissolved OC losses are faster than in the river thalweg. Our incubations offer a first insight into the GHG release from permafrost thaw streams that connect exposed and degrading permafrost outcrops to larger river systems.