Heat flux through sea ice in the western Weddell Sea: Convective and conductive transfer processes

The heat flux through the snow and sea ice cover and at the ice/ocean interface were calculated at five sites in the western Weddell Sea during autumn and early winter 1992. The ocean heat flux averaged 7 ± 2 W/m2from late February to early June, and average ice/air heat flux in the second‐year floes depended on the depth of the snow cover and ranged from 9 to 17 (±0.8) W/m2. In late February, three of the five sites had an ice surface which was depressed below sea level, resulting, at two of the sites, in a partially flooded snow cover and a slush layer at the snow/ice interface. As this slush layer froze to form snow ice, the dense brine which was rejected flowed out through brine drainage channels and was replaced by lower‐salinity, nutrient‐rich seawater from the ocean upper layer. We estimate that about half of the second‐year ice in the region was covered with this slush layer early in the winter. As the slush layer froze, over a 2‐ to 3‐week period, the convection within the ice transported salt from the ice to the upper ocean and increased total heat flux through the overlying ice and snow cover. On an area‐wide basis, approximately 10 cm of snow ice growth occurred within second‐year pack ice, primarily during a 2‐ to 3‐week period in February and March. This ice growth, near the surface of the ice, provides a salt flux to the upper ocean equivalent to 5 cm of ice growth, despite the thick (about 1 m) ice cover, in addition to the ice growth in the small (area less than 5%), open water regions.