Winter Convection Transports Atlantic Water Heat to the Surface Layer in the Eastern Arctic Ocean

A 1-yr (2009/10) record of temperature and salinity profiles from Ice-Tethered Profiler (ITP) buoys in the Eurasian Basin (EB) of the Arctic Ocean is used to quantify the flux of heat from the upper pycnocline to the surface mixed layer. The upper pycnocline in the central EB is fed by the upward flux of heat from the intermediate-depth (similar to 150-900 m) Atlantic Water (AW) layer; this flux is estimated to be similar to 1 W m(-2) averaged over one year. Release of heat from the upper pycnocline, through the cold halocline layer to the surface mixed layer is, however, seasonally intensified, occurring more strongly in winter. This seasonal heat loss averages similar to 3-4 W m(-2) between January and April, reducing the rate of winter sea ice formation. This study hypothesizes that the winter heat loss is driven by mixing caused by a combination of brine-driven convection associated with sea ice formation and larger vertical velocity shear below the base of the surface mixed layer (SML), enhanced by atmospheric storms and the seasonal reduction in density difference between the SML and underlying pycnocline.