Two oceanographic cruises were conducted during September 2003 and March 2004 in the eastern half of the Cariaco Basin. Specific objectives were to examine the hydrography of the seasonal upwelling plume characteristic of this region, the spatial distribution of particles in the area, and to help determine the source and relative importance of in situ particle production vs. terrigenous particles delivered laterally from the coast. During September 2003, average surface salinities within the basin were higher (36.6) relative to Caribbean Sea waters outside the basin (35.6). Salinity patterns indicated that the Orinoco and Amazon River plumes did not enter or influenced the basin directly. The upwelling plume in March 2004 stimulated primary productivity. Beam attenuation and CDOM fluorescence profiles showed marked vertical structure in biomass of microbial populations, particularly near the oxic-anoxic interface typically located between about 250 and 300 m. There is an increasing difference in temperature and salinity between the Cariaco Basin and the adjacent Caribbean Sea below 200 m. Inside the Basin temperatures and salinities were higher by 4oC and 0.5. The influence of local rivers on the Cariaco Basin was evident during September 2003. Low salinity plumes with high beam attenuation (1m-1) lined the southern margin of the Basin. The primary rivers that affected the basin were the Unare and Neverí Their sediment input affected the shelf near the river mouths, and a surrounding radius of up to 40 Km. Their low salinity plumes were carried northwestward toward the CARIACO time series station. In March 2004, there was minimal or no terrigenous input from local rivers. Near the Manzanares River, off the city of Cumaná and near Cubagua Island, located south of Margarita Island, attenuation due to suspended particles (0.09 m-1) was observed at depth (70-150 m) during both cruises (0.09-0.15 m-1). Therefore, sediment transport from the shelf into the basin seems to occur year-round. More observations are necessary to determine the nature and origin of these particles. In March 2004, there was minimal or no terrigenous input

The Southern Caribbean Sea experiences a strong upwelling process along the coast from about 61°W to 75.5°W and 10-13°N. In this dissertation three aspects of this upwelling system are examined: (A) A mid-year secondary upwelling that was previously observed in the southeastern Caribbean Sea between June-July, when land based stations show a decrease in wind speed. The presence and effects of this upwelling along the whole southern Caribbean upwelling system were evaluated, as well as the relative forcing contribution of alongshore winds (Ekman Transport, ET) and wind-curl (Ekman Pumping, EP). (B) Stronger upwelling occurs in two particular regions, namely the eastern (63-65°W) and western (70-73°W) upwelling areas. However, the eastern area has higher fish biomass than the western area (78% and 18%, respectively, of the total small pelagic biomass of the southern Caribbean upwelling system). The upwelling dynamics along the southern Caribbean margin was studied to understand those regional variations on fish biomass. (C) The most important fishery in the eastern upwelling area off Venezuela is the Spanish sardine (Sardinella aurita). The sardine artisanal fishery is protected and only takes place up to ~10 km offshore. The effects of the upwelling cycle on the spatial distribution of S. aurita were studied. The main sources of data were satellite observations of sea surface temperature (SST), chlorophyll-a (Chl) and wind (ET and EP), in situ observations from the CARIACO Ocean Time-Series program, sardine biomass from 8 hydroacoustics surveys (1995-1998), and temperature profiles from the World Ocean Atlas 2005 used to calculate the depth of the Subtropical Underwater core (traced by the 22°C isotherm). The most important results of the study were as follows: (A) The entire upwelling system has a mid-year upwelling event between June-August, besides the primary upwelling process of December-April. This secondary event is short-lived (~5 weeks) and ~1.5°C warmer than the primary upwelling. Together, both upwelling events lead to about 8 months of cooler waters (-3, averaged from the coast to 100 km offshore) in the region. Satellite nearshore wind (~25 km offshore) remained high in the eastern upwelling area (> 6 m s-1) and had a maximum in the western area (~10 m s-1) producing high offshore ET during the mid-year upwelling (vertical transport of 2.4 - 3.8 m3 s-1 per meter of coastline, for the eastern and western areas, respectively). Total coastal upwelling transport was mainly caused by ET (~90%). However, at a regional scale, there was intensification of the wind curl during June as well; as a result open-sea upwelling due to EP causes isopycnal shoaling of deeper waters enhancing the coastal upwelling. (B) The eastern and western upwelling areas had upwelling favorable winds all year round. Minimum / maximum offshore ET (from weekly climatologies) were 1.52 / 4.36 m3 s-1 per meter, for the western upwelling area; and 1.23 / 2.63 m3 s-1 per meter, for the eastern area. The eastern and western upwelling areas showed important variations in their upwelling dynamics. Annual averages in the eastern area showed moderate wind speeds (6.12 m s-1), shallow 22°C isotherm (85 m), cool SSTs (25.24°C), and phytoplankton biomass of 1.65 mg m-3. The western area has on average stronger wind speeds (8.23 m s-1) but a deeper 22°C isotherm (115 m), leading to slightly warmer SSTs (25.53°C) and slightly lower phytoplankton biomass (1.15 mg m-3). We hypothesize that the factors that most inhibits fish production in the western upwelling area are the high level of wind-induced turbulence and the strong offshore ET. (C) Hydroacoustics values of Sardinella aurita biomass (sAsardine) and the number of small pelagics schools collected in the eastern upwelling region off northeast Venezuela were compared with environmental variables (satellite products of SST, SST gradients, and Chl -for the last two cruises-) and spatial variables (distance to upwelling foci and longitude-latitude). These data were examined using Generalized Additive Models. During the strongest upwelling season (February-March) sAsardine was widely distributed in the cooler, Chl rich upwelling plumes over the wide (~70km) continental shelf. During the weakest upwelling season (September-October) sAsardine was collocated with the higher Chl (1-3 mg m-3) found within the first 10 km from the upwelling foci; this increases Spanish sardine availability (and possibly the catchability) for the artisanal fishery. These results imply that during prolonged periods of weak upwelling the environmentally stressed (due to food scarceness) Spanish sardine population would be closer to the coast and more available to the fishery, which could easily turn into overfishing. After two consecutive years of weak upwelling (2004-2005) Spanish sardine fishery crashed and as of 2011 has not recovered to previous yield; however during 2004 a historical capture peak occurred. We hypothesize that this Spanish sardine collapse was caused by a combination of sustained stressful environmental conditions and of overfishing, due to the increased catchability of the stock caused by aggregation of the fish in the cooler coastal upwelling cells during the anomalous warm upwelling season.