A coupled sea ice-ocean numerical model has been developed that addresses the role of floe geometry during summertime melting. The model contains a diagnostic equation for average floe diameter in addition to the usual prognostic equations for ice volume per unit area and ice concentration. The partition between melting on the top, bottom, and lateral (side) surfaces of flows is examined using time-dependent simulations with differing initial average floe diameters. The different parameterizations for bottom and lateral melting in the literature are also compared and found to vary significantly. The results show that lateral melting is important only for floes with dimaters less than O(30 m), given atmospheric thermal forcing typical of the central Arctic in summer. This means that the decrease in ice concentration over the summer is a strong function of floe diameter, in keeping with simple geometrical arguments. In all cases, about 80% of the net thermal energy that enters the ocean through leads goes toward melting ice, while the rest warms the ocean. ¿ American Geophysical Union 1992