Seasonal and spatial evolution of albedo in a snow‐ice‐land‐ocean environment

In the course of a program studying Arctic coastal processes we have investigated the albedos for the range of surfaces in the region and their response to seasonal changes in a land‐ice‐ocean regime near Barrow, Alaska. From April through June in the years 2000, 2001, and 2002, spectral and wavelength‐integrated albedos were measured along 200‐m survey lines. These lines were installed at four sites and included sea ice, lagoon ice, fresh ice, and tundra. Initially, all sites were completely snow‐covered, and the albedo was high (0.8–0.85) and spatially uniform. The concentration of absorptive contaminants in the snow was enough to produce a slight reduction below the pure snow values. As the melt season progressed, albedos decreased at all sites. The decrease was greatest and most rapid at the tundra site, where the albedo dropped from 0.8 to 0.15 in only 2 weeks. The spectral signature also changed as the wavelength of maximum albedo at the tundra site shifted from 500 nm for snow to 1100 nm for vegetation. As the snow cover melted, there was rapid and extensive ponding, resulting in a decrease of the spatially averaged, wavelength‐integrated albedo from 0.6 to 0.2 in only 5 days. Extensive pond drainage and below‐freezing temperatures caused the albedo to rebound briefly to 0.55 before resuming a steady decrease. Comparison of these results with data collected in the central Arctic show that albedos of fast ice in the coastal regime evolve significantly faster than pack ice albedos. Interannual seasonal variations showed additional melting phases that might be expected during protracted warming. The albedo evolution in the coastal lagoon was different each of the 3 years because of variations in sediment loading of the ice during freeze‐up and in the melt/freeze pattern the following spring. The record early melt in May 2002 followed by a pronounced freezing event 2 weeks later produced a distinct melt regime that gave rise to reduced melt pond coverage and higher albedo. Such events provide insight into processes associated with the melt ponds that will be important for modeling sea ice in a warming climate.