Thaw pond expansion enhances greenhouse gas emissions in the Northeast Siberian tundra.

Thaw of surficial permafrost ice bodies (ice wedges and ice-rich mounds) causes formation of ponds with enhanced emission of CH4 and CO2 . Usually these ponds develop in dry Betula nana shrub vegetation, which, when undisturbed, is a sink for both greenhouse gases.

We mapped thaw pond development over time using satellite images of various ages and sources (Corona military intelligence images, recent high resolution images, Sentinel SAR) for the Kytalayk tundra research station in the Indigirka lowlands, Northeast Siberia. Areal expansion of thaw ponds is difficult to quantify because of water level fluctuations. However, ponds appear to expand in number, although ponds also disappear by vegetation succession. There is no evidence of better drainage due to permafrost thaw, as has been suggested for other permafrost areas.

Greenhouse gas emission was quantified by chamber flux measurements. Besides high CH4 and CO2 emissions, occasionally also N2O emissions were also recorded. This indicates that these ponds are an increasing greenhouse gas source. However, vegetation succession studies have shown that their lifetime is short as they are colonized by CO2-sequestering vegetation within a few years. This life time has to be taken into account for quantifying the net greenhouse gas source as shown by our conceptual model.