Spring and winter water mass composition in the Brazil-Malvinas Confluence
Abstract:Hydrographic data of the Confluence 1 cruise collected during austral spring (November 1988) have been analyzed to estimate relative mixing proportions of the various water masses of the Brazil-Malvinas Confluence region using a multiparameter analysis. Seven source water types (SWT) are identified in this region, and all are retained for the analysis: Thermocline Water (TW), Subantarctic Surface Water (SASW), Antarctic Intermediate Water (AAIW), Upper Circumpolar Deep Water (UCDW), North Atlantic Deep Water (NADW), Lower Circumpolar Deep Water (LCDW) and Weddell Sea Deep Water (WSDW). Tracers selected are temperature, salinity, dissolved oxygen and nutrients. Mixing proportions are quantified and plotted along five zonal sections at 35.4, 36.5, 37.9, 41 and 41.6S. The solution obtained during the springtime cruise is consistent with the wintertime (September 1989) data set (Maamaatuaiahutapu et al., 1992): both show the large local recirculation of AAIW and the separation of NADW from the coast south of the thermocline front. However, noticeable changes in water mass mixing proportions can be detected between the winter of 1989 and the preceding spring. The seasonal change for the upper layers of TW and SASW is related to temporal and spatial fluctuations of the thermohaline front. The marked differences in SWT proportions between the two seasons occur at the same location for TW, SASW and AAIW; suggesting that the upper waters have a large impact on the AAIW movement. The deep waters undergo great spatial changes between the two cruises. The variation of the deep convergence position (revealed by the variation of spatial occupancy of the CDW and NADW) seems influenced by the movement of the thermocline front.
Document Type: Research Article
Publication date: May 1, 1994
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