Potential temperature, oxygen and circulation of bottom water in the Southern Ocean

Abstract

The circulation of bottom and near-bottom water can be determined in a qualitative manner by inspecting parameter distributions. Bottom potential temperature and oxygen (which show a definite relation in the tp-O2 diagram) are very useful for this purpose in the portion of the Southern Ocean dealt with in this paper (20°W westward to 170°W and south of 50°S). Observations used are deeper than 3000 m and within 300 m of the bottom.There are two areas of cold water (<0·0°C): the more extreme emanating from the Weddell Sea and the other from the Ross Sea. The Weddell Sea Bottom Water flows to the east of the South Sandwich Trench into the Argentine Basin, though some water does enter the trench and flows northward The bottom waters of the Scotia Sea come from between the 3000–3200 m level of the Weddell Sea through a passage at 39°W in the South Orkney Ridge. A tongue of this water flows into the southern Drake Passage, confining to the northern Drake Passage the warmer bottom water from the Pacific Ocean. This warmer bottom water forms a rapid easterly current which enters the South Atlantic west of Shag Rocks. The cold Scotia Sea bottom water does not penetrate the Pacific Ocean but is topographically or dynamically restrained. Circulation in the eastern Scotia Sea is weak to moderate.A cold-water tongue in the Bellingshausen Basin is bounded by a band of warm water on its northwest and northeast sides. It is probable that this loop of warm water represents a strong bottom current from the southwest Pacific Basin which overflows the East-Pacific Ridge in the vicinity of a fracture zone. The flow within the cold-water tongue is moderate in its southwestern sections and weak in the southeast.Bottom photographic current evidence is in agreement with the circulation patterns as found from the potential temperature and oxygen distributions. The circulation found by relating the parameter distribution to velocity field is only in relative terms. Direct current measurements are needed to determine volume transport.