ALBERT

Description: The influence of climate and hydrological variables on opposite anomaly in active layer thickness between Eurasian and North American watersheds The Cryosphere Discussions, 6, 2537-2574, 2012 Author(s): H. Park, J. Walsh, A. N. Fedorov, A. B. Sherstiukov, Y. Iijima, and T. Ohata This study not only examined the spatiotemporal variations of permafrost active layer thickness (ALT) during 1948–2006 over the terrestrial Arctic regions experiencing climate changes, but also identified the associated drivers based on observational data and a simulation conducted by a land surface model (CHANGE). The focus on the ALT extends previous studies that have emphasized ground temperatures in permafrost regions. The Ob, Yenisey, Lena, Yukon, and Mackenzie watersheds are foci of the study. Time series of ALT in Eurasian watersheds showed generally increasing trends, while ALT in North American watersheds showed decreases. An opposition of ALT variations implicated with climate and hydrological variables was most significant when the Arctic air temperature entered into a warming phase. The warming temperatures were not simply expressed to increases in ALT. Since 1990 when the warming increased, the forcing of the ALT by the higher Annual Thawing Index in the Mackenzie and Yukon Basins was offset by the combined effects of less insulation caused by thinner snow depth and drier soil during summer. In contrast, the increasing Annual Thawing Index together with thicker snow depth and higher summer soil moisture in the Lena contributed to the increase in ALT. The results imply that the soil thermal and moisture regimes formed in the pre-thaw season(s) provide memory that manifests itself during the summer. While it is widely believed that ALT will increase with global warming, this hypothesis may need modification because the ALT also shows responses to variations in snow depth and soil moisture that can over-ride the effect of air temperature. The dependence of the hydrological variables driven by the atmosphere further increases the uncertainty in future changes of the permafrost active layer.