Brazil-Malvinas Confluence–1984

The Brazil-Malvinas (Falkland) Confluence is marked by a complex array of strongly contrasting water types. In October 1984 two large poleward meanders of South Atlantic thermocline water, separated by a cold-core cyclonic eddy near 40°S and 50°W, were observed west of 46°W. The western feature extended further south, to 43°S, with a geostrophic volume transport for the upper 1500 decibars (db) relative to 1500 db of 22,5 × 106 m3 s−1. The branch to the east has a somewhat weaker baroclinic structure, though it is associated with warmer and more saline surface water. The warmer temperature reflects less atmospheric cooling than experienced within the western branch, which is exposed directly to the cold prevailing westerlies. The western branch is capped by a low salinity layer, the origin of which appears to be a mixture of continental shelf water with surface water from the Brazil Current. Near 39–40°S the surface water at the Confluence front is of very low salinity, yet too warm to be subantarctic water carried in with the Malvinas Current. It is likely that it represents warm river plume water from the Rio de la Plata, that has “folded-over” the northern tip of the cyclonic trough formed by the Malvinas Current and its return to the south. At depth the most concentrated North Atlantic Deep Water is associated with the western branch. This feature continues flowing south, below the Malvinas Current, indicating that the western boundary separation at depth need not be coherent with the thermocline separation position. South of the western branch are two warm-core eddies; the northern eddy is in the process of separation while the southern eddy has been separated for a period of 2–3 months and has undergone thermohaline modification by the late winter atmosphere. These modified warm-core eddies may not re-coalesce with the main thermocline and hence represent a significant salt flux into the subantarctic zone of the South Atlantic.