IMPACT OF A DEPTH-VARIABLE ORGANIC MAT ON THAW AND GROUNDWATER FLOW IN CONTINUOUS PERMAFROST

Global climate change is driving rapid increases in arctic temperatures and the thawing of shallow permafrost. The amount of anticipated permafrost thaw has uncertainty because of the limited observations of hydraulic and thermal properties of arctic soils. This is especially true in the ‘organic mat’ that tends to overlie continuous permafrost in the arctic. However, few studies consider how the depth-variability of hydraulic and thermal properties observed in the organic mat could affect how the arctic active layer thaws and laterally transmits groundwater. Here we present high-spatial-density measurements of organic mat hydraulic and thermal properties, as well as model simulations of groundwater flow and freeze-thaw informed by these measurements. Our measurements of water retention, thermal conductivity, organic matter content, porosity, and permeability across multiple watersheds with continuous permafrost illustrate that soil hydraulic and thermal properties vary predictably due to spatial factors such as depth, glacial age, location along a topographic transect, and microtopographic relief. Furthermore, simulations of freeze-thaw and groundwater flow indicate that the observed variability can exert a strong control on active layer thaw and groundwater fluxes. These findings can be used to inform landscape-scale Land Surface Models designed to predict changes in heat, water, and carbon fluxes in arctic watersheds due to increased thaw.