Circulation and bottom water production in the Weddell Sea

Abstract

A study is made of the distribution of temperature and salinity in the Weddell Sea. From this a clear picture emerges of the main features of the circulation over the continental shelf and continental slope. The main feature of the horizontal circulation is the Antarctic coastal current which enters the Weddell Sea from the east. This current leaves the coast near Halley Bay ( 75 1 2 ° S, 27 1 2 ° W ) and flows along the edge of the continental shelf as a ribbon of cold fresh water between cold salty water on the shelf and the warm salty water characteristic of the circumpolar region. There is a circulation on the shelf in the vertical plane which carries about 10 6 m 3sec −1 of water off the shelf. The horizontal circulation on the shelf probably carries a flux of the same order. At the edge of the shelf in the western Weddell Sea, there is a V-shaped double front, above which lies the cold fresh water from the coastal current. The descending cold salty water from the shelf meets the warmer fresher water of the open-ocean pycnocline at the base of the V and the two waters mix to form bottom water which then runs down the continental slope. The characteristics of the bottom water formed vary with distance along the edge of the shelf, the bottom water becoming saltier and heavier with distance westwards. Bottom water is produced throughout the year, since there is always a supply of dense water from the continental shelf. The time taken for the dense water to run off the shelf and be replaced is several years. The mechanism by which the water on the shelf acquires its salinity is discussed. It is concluded that surface processes are responsible and that there is a net brine release over the continental shelf area because the pack ice is continually being blown off shore. It is estimated that the net brine release in a year is equivalent to the freezing of 1 m or more of ice. Discussion of water properties in the cold regions requires a proper appreciation of the equation of state. Attention has been drawn in the past to the variation of the thermal expansion coefficient with temperature, but the fact that it also varies strongly with depth has not been taken into account in many previous studies. Some consequences of this are discussed.