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Ice-wedges are common permafrost features formed over hundreds to thousands of years of repeated frost cracking and ice vein growth. We used field and remote sensing observations to assess changes in areas dominated by ice-wedges, and we simulated the effects of those changes on watershed-scale hydrology. We show that top melting of ice-wedges and subsequent ground subsidence has occurred at multiple sites in the North American and Russian Arctic. At most sites, melting ice-wedges have initially resulted in increased wetness contrast across the landscape, evident as increased surface water in the ice-wedge polygon troughs and somewhat drier polygon centers. Most areas are becoming more heterogeneous with wetter troughs, more small ponds (themokarst pits forming initially at ice-wedge intersections and then spreading along the troughs) and drier polygon centers. Some areas with initial good drainage, such as near creeks, lake margins, and in hilly terrain, high-centered polygons form an overall landscape drying due to a drying of both polygon centers and troughs. Unlike the multi-decadal warming observed in permafrost temperatures, the ice-wedge melting that we observed appeared as a sub-decadal response, even at locations with low mean annual permafrost temperatures (down to −14 °C). Gradual long-term air and permafrost warming combined with anomalously warm summers or deep snow winters preceded the onset of the ice-wedge melting. To assess hydrological impacts of ice-wedge melting, we simulated tundra water balance before and after melting. Our coupled hydrological and thermal model experiments applied over hypothetical polygon surfaces suggest that (1) ice-wedge melting that produces a connected trough-network reduces inundation and increases runoff, and that (2) changing patterns of snow distribution due to differential ground subsidence has a major control on ice-wedge polygon tundra water balance despite an identical snow water equivalent at the landscape-scale

Ice wedges are common features of the subsurface in permafrost regions. They develop by repeated frost cracking and ice vein growth over hundreds to thousands of years. Ice-wedge formation causes the archetypal polygonal patterns seen in tundra across the Arctic landscape. Here we use field and remote sensing observations to document polygon succession due to ice-wedge degradation and trough development in ten Arctic localities over sub-decadal timescales. Initial thaw drains polygon centres and forms disconnected troughs that hold isolated ponds. Continued ice-wedge melting leads to increased trough connectivity and an overall draining of the landscape. We find that melting at the tops of ice wedges over recent decades and subsequent decimetre-scale ground subsidence is a widespread Arctic phenomenon. Although permafrost temperatures have been increasing gradually, we find that ice-wedge degradation is occurring on sub-decadal timescales. Our hydrological model simulations show that advanced ice-wedge degradation can significantly alter the water balance of lowland tundra by reducing inundation and increasing runoff, in particular due to changes in snow distribution as troughs form. We predict that ice-wedge degradation and the hydrological changes associated with the resulting differential ground subsidence will expand and amplify in rapidly warming permafrost regions.

Schematic overview of a typical terrestrial and shallow-marine permafrost landscape during summer and winter. Permafrost is defined as ground that remains continuously at or below 0°C for at least two consecutive years; some 24% of the land surface in the northern hemisphere is classified as permafrost. This schematic figure (summer) pictures a terrestrial and shallow marine permafrost system. A permafrost landscape is characterized by its large heterogeneity with morphological permafrost-related features such as polygonal patterned ground with underlying ice wedges, thaw ponds, thermokarst lakes, and wetland areas. During winter, the terrestrial landscape is covered with snow, and water bodies and the ocean are typically covered with ice.The last pictures shows schematically the fluxes (not scaled) that occur between the terrestrial and marine environment and atmosphere.

This report summarizes temperature, wind, and snow-cover data for the Kuparuk River Basin in Arctic Alaska spanning the five-year period of 1994-%1995. Comparison of results from five meteorological towers is presented to illustrate both the differences and similarities of the regional climate and weather along a 200-km transect. A picture emerges of the Arctic Slope as a region dominated by subfreezing tempera- tures for most of the annual cycle. The five sites showed a good deal of similarity in both seasonal variation and meteorological forcing on a time scale of a few days. While the Kuparuk Basin is typified by almost constant moderate winds, winds greater than 10 m(s-1) are fairly rare. The observed patterns of temperature and wind have important ramifications for the winter snow cover of the Kuparuk Basin, explaining why the snow cover forms first in the foothills and last near the coast. The surprisingly low wind speeds across the network in October and November help to explain the presence of thick but low-density layers observed in the basal snowpack. A pronounced warming event occurring each November capped this early snow with a melt crust or wind slab or both, protecting it from subsequent wind erosion.