Role of the upper ocean in the energy budget of Arctic sea ice during SHEBA

As part of the 1997-1998 Surface Heat Budget of the Arctic Experiment (SHEBA), a nearly yearlong record of upper ocean observations was obtained below a drifting ice camp in the Beaufort Gyre. A combination of observational and numerical modeling techniques are used to estimate heat fluxes across the under-ice ocean boundary layer. Over the Canada Basin, the upper pycnocline contained moderate heat, but strong stratification effectively insulated it from mixed layer turbulence. Average resulting heat fluxes at the base of the mixed layer (F-pyc) and at the ocean-ice interface ( F-0) were small (0.3-1.2 and 0.2 W m(-2), respectively). Over the Chukchi Borderlands, the presence of relatively warm and salty Pacific origin water increased upper pycnocline heat content and reduced stratification, which permitted moderate F-pyc and F-0 (2.1-3.7 and 3.5 W m(-2), respectively). Solar insolation was the dominant heat source during the final, summertime portion of the drift. During the heating period, F-pyc was relatively small (0.4-1.5 W m(-2)) while F-0 was large (16.3 W m(-2)). The drift-averaged value of F-0 was 7.6 W m(-2). Energy budgets for the ice cover were constructed. The oceanic contribution to the budget during the portion of the drift over the Chukchi Borderlands, supported by entrainment of heat stored in the upper pycnocline, was responsible for a 15% reduction in ice growth. During the summer heating season, the F-0 estimates were larger than the latent energy changes associated with basal melting.