THE COMPOSITION AND DISTRIBUTION OF THE PARTICULATE MATTER IN THE STRAIT OF MAGELLAN (CHILE) DURING THE 1991 AND 1995 ITALIAN CAMPAIGNS

During 1991 and 1995, the Italian National Program for Antarctic Research carried out two oceanographic campaigns in the framework of the International (Strait of) Magellan Project. In this paper, we describe the distribution, biochemical composition, and mineralogical characteristics of particulate matter and the characteristics of the water masses deWning microbasins in the Strait of Magellan. The data analyses highlighted diVerences in quality and quantity of the suspended matter and its organic component in the basins that make up the Strait and the PaciWc Ocean. The westernmost basin is subject to an eastward Xow from the PaciWc Ocean, and continental runoV in the surface layers, which are consequently rich in organic matter with a high C:N ratio. The central basin, Isla Carlos III–Segunda Angostura, is characterized by the mixing of Sub-Antarctic PaciWc waters, continental runoV, and glacio-Xuvial waters: The basin has the lowest particulate matter concentration, but at Paso Ancho showed high concentrations of organic matter with a lower C:N ratio. The asternmost basin, Segunda Angostura-Atlantic entrance, is characterized by the mixing of the water column due to strong Atlantic tides and showed high concentration of particulate matter with a high detritic component. Generally, the organic matter concentrations showed signiWcant diVerences during the cruises, being higher in 1991. Using the multivariate discriminant factor analysis to determine whether statistically signiWcant diVerences existed between deWned sampling areas, we determined that temperature, particulate organic carbon, and total particulate matter were the variables most important for the diVerence between areas.