Early Spring Oceanic Heat Fluxes and Mixing Observed from Drift Stations North of Svalbard

Abstract

From several drifting ice stations north of Svalbard, Norway, observations were made in early spring of the ocean turbulent characteristics in the upper 150 m using a microstructure profiler and close to the under-ice surface using eddy correlation instrumentation. The dataset is used to obtain average heat fluxes at the ice?water interface, in the mixed layer, across the main pycnocline, as well over different water masses in the region. The results are contrasted with proximity to the branches of the warm and saline Atlantic water current, the West Spitsbergen Current (WSC), which is the main oceanic heat and salinity source both to the region and to the Arctic Ocean. Hydrographic properties show that the surface water mass modification is typically due to atmospheric cooling with relatively less influence of ice melting. Surface heat fluxes of O(100) W m?2 are found within the branches of the WSC and over shelf areas with elevated levels of mixing due to strong tides. Away from the shelves and WSC, however, ocean-to-ice turbulent heat fluxes are typical of the central Arctic. Deeper in the water column, entrainment from below together with equally important horizontal advection and diffusion increase the heat content of the mixed layer and contribute to the heat flux maximum in the upper layers. The results in this study emphasize the importance of mixing along the boundaries, over shelves, and topography for the cooling of the Atlantic water layer in the Arctic in general, and for the regional heat budget, hence the ice cover and cooling of the WSC north of Svalbard, in particular.