Role of Ground Ice Dynamics and Ecological Feedbacks in Recent Ice-wedge Degradation and Stabilization
Yuri Shur and Torre Jorgenson stand in front of a large ice wedge, which is protected by only a thin layer of soil that thaws during the summer.
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. In a recent paper published in the Journal of Geophysical Research: Earth Surface, Torre Jorgenson and colleagues from the University of Alaska Fairbanks and the U.S Geological Survey quantified ice-wedge volume and degradation rates, compared thermal regimes and ground-ice characteristics across a sequence of degradation and stabilization stages, and evaluated biophysical feedbacks controlling permafrost stability near Prudhoe Bay, Alaska. By measuring thermokarst pits on imagery from 1949 to 2012, they showed ice-wedge degradation abruptly increased in the 1990s and covered 9% of the area by 2012 (below).
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. The disturbance stimulated plant growth and organic-matter accumulation, providing negative feedbacks that allowed ice to aggrade and heave the surface, thus reducing surface water and soil temperatures in later stages. Due to these ecological feedbacks, mean annual soil temperatures varied by 9 °C, nearly twice as large as projected regional climate warming by century’s end. This greatly complicates efforts to model and project permafrost response to climate change.
Measuring permafrost temperatures below in a recently collapsed thermokarst pit.
Jorgenson, M. T., M. Z. Kanevksiy, Y. Shur, K. Wickland, D. R. Nossov, N. G. Moskalenko, J. Koch, R. Striegl. 2015. Role of ground-ice dynamics and ecological feedbacks in recent ice-wedge degradation and stabilization. Journal of Geophysical Research – Earth Surface 120:2280-2297.