Five Years of Variability in Snow Depth and Active Layer Hydrologic and Thermal Regime Across an Ice Wedge Polygon in Barrow, Alaska

Ice wedge polygons, common to the low-gradient Arctic tundra, give rise to several microtopographical units and a diverse range of ecosystem microcosm over short distances (meters). The rims of low-centered polygons, mounds of high-centered polygons, basins (centers) of low-centered polygons and polygon troughs result in a somewhat systematic mosaic of surface and subsurface characteristics due to the organized network of ice wedges. In order to assess the importance of specific ice wedge features on larger-scale (> km2) fluxes of energy, water and carbon, including their geomorphological stability, it is necessary to quantify the sub-meter scale variations in ice wedge polygon snow depth and active layer hydrologic and thermal regime. An ice wedge polygon having both troughs, a low center and a wide rim was instrumented in fall 2007 within the Barrow Environmental Observatory, Barrow, Alaska. Hourly measurements included soil temperature at three depths and near-surface soil moisture at 29 sites. Snow and active layer depth was measured manually in April/May and September, respectively. The results present large variability in snow depth, active layer depth, time of freeze-up, and near-surface soil temperature that are correlated to feature type (trough, low center and rim). For example, end-of-winter snow depth is about twice as deep in the troughs as on the rims, resulting in an >10 °C soil temperature difference during cold spells. Further, a complete freeze up, defined as the rapid soil cooling that follows the end of phase change, occurs about a month later in the troughs than the exposed and dry rims. The identified fine-scale spatial variability in active layer and surface characteristics of ice wedge polygon landscapes may impose important controls large-scale energy, water and carbon exchange.