Estimating late-winter heat flow to the atmosphere from the lake-dominated Alaskan North Slope

The conductive heat flux through the snow cover (F-a) is used as a proxy to examine the hypothesis that there is a significant heat flow from the Alaskan North Slope to the atmosphere because of the the large number of lakes in the region. F-a is estimated from measurements of snow depth, temperature and density on tundra, grounded ice and floating ice in mid-April 1997 at six lakes near Barrow, northwestern Alaska. The mean F-a values from tundra, grounded ice and floating ice are 1.5, 5.4 and 18.6 W m(-2), respectively. A numerical model of the coupled snow/ice/water/soil system is used to simulate F-a and there is good agreement between the simulated and measured fluxes. The flux from the tundra is low because the soils have a relatively low thermal conductivity and the active layer cools significantly after freezing completely the previous autumn. The flux from the floating ice is high because the ice has a relatively high thermal conductivity, and a body of relatively warm water remains below the growing ice at the end of winter. The flux from the grounded ice is intermediate between that from the tundra and that from the floating ice, and depends on the timing of the contact between the growing ice and the lake sediments, and whether or not those sediments freeze completely. Using the estimated F-a values combined with the areal fractions of tundra, grounded ice and floating ice derived from synthetic aperture radar images, area-weighted F-a values are calculated for six areas. F-a values for the ice vary between 9.8 and 13.8 W m(-2), and those from the ice plus tundra vary between 3.9 and 5.3 W m(-2). The F-a values are similar to those observed in the sea-ice-covered regions of the south and north polar oceans in winter. The North Slope of Alaska may thus make a significant contribution to the regional energy budget in winter.