Snow-cover Effects on the Active Layer Above Permafrost: Results of Long-term Ground Surface Temperature Observations in Northern Alaska

Snow cover impacts the permafrost system through insulative effects. Snow cover is spatially variable in areas affected by permafrost, owing to heterogeneous vegetation types, local topography, and redistribution by wind. Snow depth measurements are difficult to collect over large areas and monitoring sites are sparse in permafrost-affected regions. Long-term (>20 yr) active layer thickness (ALT) and temperature (ground and air) monitoring stations are maintained by the Circumpolar Active Layer Monitoring (CALM) program across Arctic Alaska. CALM records show that summer temperature records cannot fully explain the observed long-term active layer trends. Discrepancies between ALT and summer temperature trends indicate that winter dynamics, specifically snow cover, play an important role in permafrost-climate interactions in this region. We present long-term air and ground-surface temperatures, snow depth, and snow period duration trends employed to explore wintertime characteristics with respect to ALT dynamics. Monthly snow depth and winter precipitation data from SNOTEL sites near CALM sites (Prudhoe Bay, Imnavait Creek, Sagwon) were used in conjunction with snow cameras (located at CALM sites) as indicators for snow cover. Preliminary results show increasing differences in ground surface and air temperatures. Snow cover duration data from three CALM sites show a decreasing trend from 2013-2019. SNOTEL monitoring site records show stability or decreasing trends in snow depth and increasing trends in accumulated precipitation. The results of this work help to better characterize the impacts of heterogenous snow cover on the permafrost system and cast new light on ALT trends not easily explained by summer temperatures alone.