THE ANTARCTIC ZONE FLUX EXPERIMENT

In winter the eastern Weddell Sea in the Atlantic sector of the Southe rn Ocean hosts some of the most dynamic air-ice-sea interactions found on earth. Sea ice in the region is kept relatively thin by heat flux from below, maintained by upper-ocean stirring associated with the pas sage of intense, fast-moving cyclones. Ocean stratification is so weak that the possibility of deep convection exists, and indeed, satellite imagery from the Weddell Sea in the 1970s shows a large expanse of op en water (the Weddell Polynya) that persisted through several seasons and may have significantly altered global deep-water production. Under standing what environmental conditions could again trigger widespread oceanic overturn may thus be an important key in determining the role of high latitudes in deep-ocean ventilation and global atmospheric war ming. During the Antarctic Zone Flux Experiment in July and August 199 4, response of the upper ocean and its ice cover to a series of storms was measured at two drifting stations supported by the National Scien ce Foundation research icebreaker Nathaniel B. Palmer. This article de scribes the experiment, in which fluxes of heat, mass, and momentum we re measured in the upper ocean, sea ice, and lower-atmospheric boundar y layer. Initial results illustrate the importance of oceanic heat flu x at the ice undersurface for determining the character of the sea ice cover. They also show how the heat flux depends both on high levels o f turbulent mixing during intermittent storm events and on large varia bility in the stratified upper ocean below the mixed layer.