Sources of autochtonous and allochtonous particulate material to the Cariaco Basin, Venezuela

The temporal variability of physical and biogeochemical oceanographic parameters of the Cariaco Basin, located along the southern margin of the Caribbean Sea, were studied using data collected during two cruises to the eastern half of the Basin in September 2003 and March 2004. Specific objectives were to examine the hydrography of the upwelling plume and the spatial distribution of particles in the area, to help determine the relative importance of particles produced in situ vs. those delivered laterally from terrigenous origins. Particle abundance was examined using continuous vertical profiles of c-beam attenuation and chlorophyll fluorescence. During the dry season (March 2004), Subtropical Underwater (SUW) occupied the entire water column over the northern Cariaco sill. As the SUW entered the basin, this water mass sank about 30-50 m, spreading southward and upwelling along the southeastern corner of the basin. The upwelling plume brought nutrients, dissolved organic carbon (DOC) and colored dissolved organic material (CDOM) to the surface. The particles generated by primary production near the surface spread to the northwest. The vertical flux of this organic material sustains a microbial population with marked vertical structure in biomass as observed in beam attenuation and CDOM fluorescence profiles. During the rainy season (September 2003) the in situ production of organic material is low. However, there is an influx of particles of terrestrial origin, delivered to the basin by local rivers. Though most of the sediment settles within the first 2-3 km from the mouth of the Unare and Neveri Rivers, smaller suspended particles are carried farther within low salinity plumes that reach the CARIACO time series station (10o 30' N; 64o 40' W).