Observational study of relationships between incoming radiation, open water fraction, and ocean-to-ice heat flux in the Transpolar Drift: 2002-2010

Abstract

Ocean/ice interface heat fluxes (F0) are calculated from upper ocean measurements obtained from autonomous systems repeatedly deployed in the Arctic Ocean Transpolar Drift between 2002 and 2010. Average F0 values over the nine summer heating season realizations varied between 4.6 and 10.5 W m-2 with an average summer value of 7.6 W m-2. Between 2002 and 2010, summer-averaged F0 passed through a clear minimum, with most inter-annual variability in F0 dominated by differences in ocean heat content, rather than by differences in surface forcing. We test if Transpolar Drift F0 is supported primarily by local, radiative energy flux entering the upper ocean through areas of open water (Frw). Frw is estimated by combining re-analysis solar radiation products with satellite-borne passive microwave ice concentration products and observed divergence of drifting buoys. Inter-annual variability of summer-averaged surface insolation is relatively small (0.04 normalized standard deviation, NSTD), so differences in open water fraction (0.30 NSTD) are the most likely sources of the observed F0 variability. Ensemble-averaged over the 2002-2010 summers, the satellite and buoy-divergence Frw, are equal to 8.1, and 8.0 W m-2, respectively. Therefore, over the course of the summer season, sufficient energy enters the upper ocean through open water to wholly support the observed F0. Reasonable agreement between the two open water fraction estimates further indicates that mechanical processes, rather than lateral melting, are controlling the amount of radiation entering the upper ocean, implying that ocean ice-albedo feedbacks were not strong in the Transpolar Drift in the last decade. © 2012. American Geophysical Union.