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. Ice-wedge polygons are common features of lowland tundra in the continuouspermafrost zone and prone to rapid degradation through melting of ground ice.There are many interrelated processes involved in ice-wedge thermokarst andit is a major challenge to quantify their influence on the stability of thepermafrost underlying the landscape. In this study we used a numericalmodelling approach to investigate the degradation of ice wedges with a focuson the influence of hydrological conditions. Our study area was SamoylovIsland in the Lena River delta of northern Siberia, for which we had in situmeasurements to evaluate the model. The tailored version of the CryoGrid 3land surface model was capable of simulating the changing microtopography ofpolygonal tundra and also regarded lateral fluxes of heat, water, and snow.We demonstrated that the approach is capable of simulating ice-wedgedegradation and the associated transition from a low-centred to ahigh-centred polygonal microtopography. The model simulations showedice-wedge degradation under recent climatic conditions of the study area,irrespective of hydrological conditions. However, we found that wetterconditions lead to an earlier onset of degradation and cause more rapidground subsidence. We set our findings in correspondence to observed types ofice-wedge polygons in the study area and hypothesized on remainingdiscrepancies between modelled and observed ice-wedge thermokarst activity.Our quantitative approach provides a valuable complement to previous, morequalitative and conceptual, descriptions of the possible pathways ofice-wedge polygon evolution. We concluded that our study is a blueprint forinvestigating thermokarst landforms and marks a step forward in understandingthe complex interrelationships between various processes shaping ice-richpermafrost landscapes.

Pathways of ice-wedge degradation in polygonal tundra under different hydrological conditions