Role of ground ice dynamics and ecological feedbacks in recent ice wedge degradation and stabilization

Abstract

Ground ice is abundant in the upper permafrost throughout the Arctic and fundamentally affects terrain responses to climate warming. Ice wedges, which form near the surface and are the dominant type of massive ice in the Arctic, are particularly vulnerable to warming. Yet processes controlling ice wedge degradation and stabilization are poorly understood. Here we quantified ice wedge volume and degradation rates, compared ground ice characteristics and thermal regimes across a sequence of five degradation and stabilization stages and evaluated biophysical feedbacks controlling permafrost stability near Prudhoe Bay, Alaska. Mean ice wedge volume in the top 3 m of permafrost was 21%. Imagery from 1949 to 2012 showed thermokarst extent (area of water‐filled troughs) was relatively small from 1949 (0.9%) to 1988 (1.5%), abruptly increased by 2004 (6.3%) and increased slightly by 2012 (7.5%). Mean annual surface temperatures varied by 4.9°C among degradation and stabilization stages and by 9.9°C from polygon center to deep lake bottom. Mean thicknesses of the active layer, ice‐poor transient layer, ice‐rich intermediate layer, thermokarst cave ice, and wedge ice varied substantially among stages. In early stages, thaw settlement caused water to impound in thermokarst troughs, creating positive feedbacks that increased net radiation, soil heat flux, and soil temperatures. Plant growth and organic matter accumulation in the degraded troughs provided negative feedbacks that allowed ground ice to aggrade and heave the surface, thus reducing surface water depth and soil temperatures in later stages. The ground ice dynamics and ecological feedbacks greatly complicate efforts to assess permafrost responses to climate change.

Effects of changing permafrost and snow conditions on tundra wildlife: critical places and times

“…These wetlands provide high-quality habitats for numerous waterfowl species throughout the Arctic (Gauthier et al 1996). Ice wedges, the dominant massive ice type in Arctic tundra, develop near the surface in regions where winter temperatures enable thermal contraction cracking (Fortier and Allard 2005;Jorgenson et al 2015). Over decades or even centuries, ice wedges grow from water that fills the cracks and refreezes, a process that heaves the soil and disturbs the surface drainage favoring the formation of small catchment basins typical of low-centered polygons (Fig.…”

Thermo-erosion gullies boost the transition from wet to mesic tundra vegetation

“…Vegetation was sensitive to this process, and mesic environment plant species gradually replaced hydrophilic species within 5 to 10 years, although the full transition has yet to be reached. This vegetation turn-over can have substantial consequences on wildlife biology, permafrost stabilization and ecosystem-level greenhouse gas emissions (Blok et al, 2010;Doiron et al, 2014;M. T. Jorgenson et al, 2015;McEwing et al, 2015).…”

“…Several forms of ground and massive ice can be found within permafrost (Rowland et al, 2010), especially ice wedges in regions where winter temperatures enable thermal contraction cracking (Fortier and Allard, 2005;Kokelj et al, 2014;M. T. Jorgenson et al, 2015;Sarrazin and Allard, 2015).…”

Landscape Change Detected over a Half Century in the Arctic National Wildlife Refuge Using High-Resolution Aerial Imagery

“…In comparison, ice-wedge degradation was observed at a few of 206 photointerpreted plots in the Arctic Network of National Parks [50]. Within small, targeted areas in northern Alaska, the extent of ice-wedge degradation increased from 0.5% to 4.4% near Fish Creek [21] and increased from 0.9% to 7.5% (1949-2012) near Prudhoe Bay [30]. Farquharson et al [51] found thermokarst troughs and pits covered 7% of 12 small mapped areas across northern Alaska.…”