Climatic control of the thermal regime of permafrost, northwest Spitsbergen

The thermal link between the atmosphere and the permafrost is central to considerations of climate change consequences in Arctic areas and interpretations of deep permafrost temperatures that constitute an exceptional archive of past climate change. I studied this link by examining the principal atmospheric factors and heat transfer processes that dictate soil temperatures for an Arctic desert site in north-western Spitsbergen.; Accurate modeling of active layer temperatures requires precise treatment of thermal conduction. Unlike most models that treat soil as homogeneous with fixed thermal properties, I use realistic temporal and spatial variations in soil thermal properties based on in-situ measurements.; The heat transfer model accounted for much of the observed soil thermal regime, and it highlighted three often overlooked components of the energy budget: (1) Although air temperature is generally used as a surface boundary condition during the winter, on a daily average, the snow surface is up to 3.7{dollar}spcirc{dollar}C colder than the air. (2) Heat is delivered rapidly through snow to the active layer when rain falls on snow; it infiltrates, freezes and releases latent heat near the soil surface. (3) Meltwater infiltration and freezing in the soil cause abrupt warming events and deliver nearly half of the energy to the soil in late spring. An increase in frequency or magnitude of infiltration events could mimic simple surface warming.; In view of the natural temporal variability of environmental factors, interannual changes in winter air temperature are considerably more important than other factors in changing soil temperatures, because of the duration and large temperature variability of the cold period. The latter reflects the location of the study site in an air mass boundary zone, and its response to fluctuations in air masses that have vastly different properties during the winter. Since air mass boundaries are likely to shift due to climate change, the thermal future of western Spitsbergen, Alaska and other regions situated at air mass boundary zones may be considerably more complex than simple high latitude warming, and changes in permafrost temperatures are much more likely to reflect changes in circulation patterns than warming of any single air mass.