The influence of snow cover, air temperature, and groundwater flow on the active-layer thermal regime of Arctic hillslop
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PAPER
The influence of snow cover, air temperature, and groundwater flow on the active-layer thermal regime of Arctic hillslopes drained by water tracks Caitlin R. Rushlow 1 & Audrey H. Sawyer 2 & Clifford I. Voss 3 & Sarah E. Godsey 1 Received: 19 September 2019 / Accepted: 17 April 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Permafrost in Arctic watersheds limits soil biological activity to a thin, seasonally thawed active layer that contributes water to streams. In many hillslopes, relatively wet drainage features called water tracks have distinct freeze-thaw patterns that affect groundwater flow and storage, and thus the export of heat and solutes to Arctic streams. This study uses groundwater flow and energy transport models to examine potential controls on the timing and duration of freeze–thaw conditions and the magnitude of temperature fluctuations within water tracks and their adjacent hillslopes. The simulated length of the active-layer thaw season varies by 1 month over the range of snow-cover and mean annual air-temperature scenarios simulated. The timing and duration of freezing is particularly sensitive to depth and duration of snow cover. Thus, the deeper snowpack covers that can accumulate in water tracks contribute to their more persistent thaw conditions and their ability to conduct groundwater downslope. A threedimensional simulation shows that during the summer thaw season, the water track captures groundwater laterally from half way across the hillslope. The models presented here elucidate key mechanisms driving small-scale variation in the active-layer thermal regime of tundra hillslopes, which may be responsible for changes in drainage-network geometry and Arctic biogeochemical fluxes under a warming climate. Keywords Permafrost . Hillslope . Heat flow . Groundwater modeling . Water track
Introduction The structure and function of Arctic watersheds differs considerably from watersheds in more temperate regions. Water and energy fluxes are extremely seasonal and affected by the presence of continuous permafrost just below the ground surface (Hinzman et al. 1991). Liquid water and the biological activity that depends upon it are typically limited to the active layer, or shallow soil between the ground surface and permafrost that Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10040-020-02166-2) contains supplementary material, which is available to authorized users. * Audrey H. Sawyer [email protected] 1
Department of Geosciences, Idaho State University, Pocatello, ID, USA
2
The Ohio State University, Columbus, OH, USA
3
US Geological Survey, Menlo Park, CA, USA
thaws during the brief summer warm season. The thermal regime and moisture status of the active layer control the distribution, transformations, and flows of water, energy, carbon, and nutrients in Arctic watersheds (e.g., Walvoord and Kurylyk 2016; Hinzman et al. 1991). Despite their critical importance for ecosystem processes, active layer conditio
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