Melt water balance and surface temperature variations in the vicinity of the SHEBA station during spring and summer 1998

The hydrological balance of meltwater on summer pack ice together with the amount of heat in the water are critical elements for determining the surface, lateral and bottom melting of the sea ice. The temporal variation of the pond water present on a floe during the melt season is also a controlling factor in determining the surface albedo (Eicken et al., 2002).

The first objective of this study is to combine surface and bottom ablation observations with changes in freeboard measured with a water-level recorder to determine the changes in total mass of water, M_w, on a representative ice floe. We have adapted the method of Untersteiner (1961) to the present data set and used selected parameters from the summer sea ice observations to calculate the mean water depth and M_w as a function of time. During the SHEBA summer, lateral melting removed up to 5 meters of ice from the edge of the floes, producing a significant contribution to the summer mass loss of the local ice pack. This was driven by the absorption of both short- and longwave radiation in the leads and it is a key step in the ice-albedo feedback system.

Our second objective is to determine the surface temperatures of ice and open water over a wide area near the SHEBA site to determine their relative values, the degree of spatial homogeneity, and their temporal dependence. The results of a comparison of photographic imagery and helicopter-borne infrared photometry will be presented in detail. They show that the temperatures in the leads rose to as much as +2^oC in mid to late July and that the water temperature elevation occurred fairly uniformly in a 50 km box surrounding the ship.