HYDROGRAPHIC CONDITIONS IN THE BRAZIL-MALVINAS CONFLUENCE DURING AUSTRAL SUMMER 1990

The Confluence 3 cruise during February 1990 provides the first hydrog raphic survey of the Brazil-Malvinas Confluence region ever obtained w ith such a refined spatial resolution over the continental slope. The closely spaced stations on the slope permit the observation of the bra nching of the Malvinas Current near 40 degrees S. The eastern branch r eturns south, while the eastern one is squeezed along the continental slope, managing to continue northward as far north as 36.3 degrees S. The Brazil-Malvinas (B-M) front has a north-south orientation on the s lope and an east-west direction offshore. The B-M front is marked by v ery strong gradients in temperature and salinity. Fine scale vertical structures and intrusions are numerous in the vicinity of the front an d cover a wide range of scales. The largest intrusion observed is a 50 -km-wide, 350-m-thick subsurface lense of Thermocline Water present on the Malvinas side of the front. The fine scale vertical structure res ults in very high temperature and salinity fluxes across the front of the order of 2 x 10(-2)degrees C m(-1) s(-1) and 10(-3) psu m(-1) s(-1 ). Two types of mode waters are identified as follows: Subtropical Mod e Waters north of the front and Subantarctic Mode Waters on both sides of the front. The Subantarctic mode waters (SAMW) appear to recircula te near the western boundary. A young variety of SAMW (lighter, very o xygenated) propagates northward along the continental slope with the M alvinas Current. It detaches from the coast near 37 degrees S and is s trongly altered in the frontal region. It is then entrained southward with the Malvinas return flow and Brazil Current extension. The Conflu ence 3 hydrographic survey provides a good description of the North At lantic Deep Water (NADW) and Circumpolar Deep Water (CDW) convergence near the western boundary. Strong, fine scale vertical structures are observed in the vicinity of the NADW/CDW front, and the associated tem perature and salinity fluxes induced are strong, 5 x 10(-3)degrees cm/ s and 2 x 10(-3) psu.m/s, respectively.