Soil temperatures in an Atlantic high mountain environment: the Forcadona buried ice patch (Picos de Europa, NW Spain)

The present study focuses on the analysis of the ground and near-rock surface air thermal conditions at the Forcadona glacial cirque (2227 m a.s.l.) located in the Western Massif of the Picos de Europa, Spain. Temperatures have been monitored in three distinct geomorphological and topographical sites in the Forcadona area over the period 2006–11. The Forcadona buried ice patch is the remnant of a Little Ice Age glacier located in the bottom of a glacial cirque. Its location in a deep cirque determines abundant snow accumulation, with snow cover between 8 and 12 months. The presence of snow favours stable soil temperatures and geomorphic stability. Similarly to other Cantabrian Mountains, the annual thermal regime of the soil is defined by two seasonal periods (continuous thaw with daily oscillations and isothermal regime), as well as two short transition periods. However, the results showed evidence of a significantly different annual thermal regime at the ground and near-rock surface air. Relatively stable soil thermal regimes were observed at the moraine and talus sites, while a more dynamic pattern was recorded at the rock wall site. Here, a higher interannual variability in the number of freeze–thaw days was also detected, which showed evidence of the important role of the snow cover as a ground surface insulator in the area. Seasonal frost conditions are widespread today in the high lands of the massif. No permafrost regime was detected in the area, though mean temperatures measured at 0.5 m depth at the Forcadona buried ice patch during 2006–07 (0.1 °C) suggest that permanent negative values may be reached at deeper layers