THE FORMATION OF A HALINE SHELF FRONT IN WINTERTIME IN AN ICE-COVEREDARCTIC SEA

During rome winters, the water overlying Mackenzie shelf in the southe astern Beaufort Sea becomes quite saline (33-35) and at freezing tempe rature throughout. Although this water is found at the surface, its de nsity is that of waters within the halocline of the arctic basin, and ventilation of the halocline occurs. The formation of sea ice is a nec essary, but not a sufficient condition for the production of this wate r. Observations from the winter of 1980-1981 are presented which illus trate that a two-stage preconditioning of shelf waters is also require d: first, surface waters of low salinity must be driven from the shelf by strong westerly winds; then, more saline water must upwell onto th e shelf in response to prolonged easterly winds. A haline front forms on the outer shelf separating cold, saline shelf waters from slightly warmer, less saline slope waters. The characteristics of this front ar e controlled by the input of negative buoyancy from ice growth over th e shelf, and by turbulent entrainment and mixing driven by under-ice c onvection. A simple model to predict the position, dimension and buoya ncy contrast of this front is presented. The cross-isobath circulation is examined and found to be relatively ineffective at flushing dense waters from the shelf over a winter. Thus shelf waters accumulate almo st all the salt expelled from growing sea ice over the same time. The magnitude of the contribution by this shelf to renewal of waters in th e arctic halocline is estimated to average 0.04 x 10(6) m3 s-1 over a period of years. Although small relative to the overall rate of renewa l (1 x 10(6) m3 s-1), this contribution is in proportion to the fracti on of the arctic shelf area which this region represents.