Abstract
Modeling and observation of ground temperature dynamics are the main tools for understand-ing current permafrost thermal regimes and projecting future thaw. Until recently, most studies on perma-frost have focused on vertical ground heat fluxes. Groundwater can transport heat in both lateral andvertical directions but its influence on ground temperatures at local scales in permafrost environments isnot well understood. In this study we combine field observations from a subarctic fen in the sporadic per-mafrost zone with numerical simulations of coupled water and thermal fluxes. At the Tavvavuoma studysite in northern Sweden, ground temperature profiles and groundwater levels were observed in boreholes.These observations were used to set up one- and two-dimensional simulations down to 2 m depth across agradient of permafrost conditions within and surrounding the fen. Two-dimensional scenarios representingthe fen under various hydraulic gradients were developed to quantify the influence of groundwater flow onground temperature. Our observations suggest that lateral groundwater flow significantly affects groundtemperatures. This is corroborated by modeling results that show seasonal ground ice melts 1 month earlierwhen a lateral groundwater flux is present. Further, although the thermal regime may be dominated by ver-tically conducted heat fluxes during most of the year, isolated high groundwater flow rate events such asthe spring freshet are potentially important for ground temperatures. As sporadic permafrost environmentsoften contain substantial portions of unfrozen ground with active groundwater flow paths, knowledge ofthis heat transport mechanism is important for understanding permafrost dynamics in these environments.
