Soil thawing and warming in the High Arctic and the potential breakdown of previously frozen

The Arctic has accumulated substantial stores of carbon within permanently frozen soils during the Holocene. Recent, unprecedented warming in the Arctic may release considerable carbon within this region. Record high temperatures and melting of the Greenland Ice Sheet occurred this past summer and we have recorded significant thawing of the permafrost in the High Arctic of Greenland. Our decade long soil temperature record at our High Arctic sites at Thule, Greenland reveals a significant increase in the thawed depth and soil temperature. The rate of breakdown of soil organics depends on soil temperature as well as moisture content. The balance between wet, anaerobic soils versus dry soils is recognized but not often studied. Our data on soil temperature, moisture, and microclimate provide insights into the covariance of these parameters and relative estimates of how soil organic carbon decomposition can vary under the changing conditions. Our previous work has shown that soil organic carbon in the High Arctic was underestimated by over an order of magnitude, particularly in the most barren sites. The primary source of the previously missed carbon was carbon at depth that is nearly always or continuously frozen. The deepening of the thawed layer is documented at our Thule sites. We present a conceptual model of the potential carbon release. These soils continue to undergo freeze-thaw cycles that may also mix the soils by cryoturbation and bring more carbon to the upper, better drained portion of the active layer. As the soil warms, it may allow greater development of vegetation; however this will also depend on the soil stability and the potential for a stable substrate for vegetation. Some arctic studies indicate a greater rate of carbon mineralization while others indicate increased vegetation biomass. The complex interplay will ultimately determine the rate of carbon release. Clearly the arctic system is unique in storing substantial carbon below the ground surface, and we now need to understand how this will change as the soil climate changes.