Exchange of CO2 and CH4 between a Siberian thaw lake and the atmosphere

Freshwaters are an important component of the continental greenhouse gas (GHG) balance with emissions estimated to correspond to about 80 % of the land GHG sink [Bastviken et al., 2011]. Thaw lakes in permafrost landscapes and especially in Yedoma permafrost are considered to be strong processors of organic carbon and essential emitters of CH4 [Walter et al., 2006]. As the Arctic experiences the recent global warming at a much faster rate than other regions of the world [AMAP, 2015], the importance of thaw lakes in the global GHG budget is expected to rapidly increase due to progressive permafrost degradation. However, especially arctic lakes are highly underrepresented in observational studies on lakeatmosphere GHG exchange. Only a few short-term studies exist, with a majority missing the ice break-up. This event is assumed to result in a spring emission peak that contributes considerably to the annual GHG emissions. In consequence, arctic freshwaters are not adequately represented in modelling approaches and scenarios of climate change. Using a floating eddy covariance (EC) system, we investigate ecosystem CH4 and CO2 flux dynamics between the atmosphere and a Yedoma thaw lake in the Lena River Delta in northern Siberia. The compiled dataset covers the ice break-up and most of the ice-free period 2014. We chose the EC method as it allows direct, automatic and non-intrusive flux measurements in remote areas. The investigated lake is one of > 500 lakes on Kurungnakh Island in the Lena River Delta. The study site lies within the zone of continuous permafrost and belongs to the arctic tundra zone. The lake covers an area of approximately 1.25 km2 with a mean depth of eight meters. We will present first results of this study and discuss the importance of a spring emission peak during ice break-up in the annual GHG budge