The Surface Heat Balance of the Arctic (SHEBA) program is an ambitious observation and modelling program designed to improve parameterizations of interacting atmosphere-ice- ocean processes which determine the net heat flux balance in the Arctic Ocean. The role of the upper ocean in the Arctic surface heat balance is being assessed by a year-long measurement of vertical ocean heat fluxes at the SHEBA ice camp, which started it s drift in the Beaufort Sea in October 1997. A slowly profiling automated CTD with a thermal microstructure packaged clipped on has been used throughout the experiment to determine upper ocean thermal structure dissipation rates, allowing profiles of vertical heat fluxes to be estimated whenever the mean vertical temperature gradients exceed 10 micro degrees/m.
A preliminary analysis of heat flux timeseries in the upper pyconcline (and mixed layer during strong wind forcing events) will be shown. Through much of the experiment, unusually warm water was observed near the top of the salinity stratified pycnocline, resulting in very high upward fluxes by turbulent entrainment during wind storms. This significant winter-time transfer of heat from the pycnocline into the ice cover suggest an additional complication in correctly modelling the net Arctic heat balance.
Comparisons between the dissipation-based fluxes in the upper pycnocline and in situ eddy correlation based estimates within the mixed layer during a strong storm in March 1998 will be shown to estimate the entrainment efficiency based on a simple ice covered, wind driven mixed layer model.