Cambios Espaciales y Estacionales en la Hidrografía y Bioquímica de la Región de la Fosa de Cariaco

The Cariaco Basin is a semi-enclosed basin of tectonic origin composed of two ~1400 m deep sub-basins, aligned in an east-west direction. In the eastern sub-basin, the CARIACO Ocean Time-Series project has been taking biogeochemical and ecological measurements on a regular basis since 1995. However, relatively little is known about the western sub-basin. Two oceanographic cruises (FOSA FOSA 1 and 2) in September 2008 (stratified water column; rainy season) and March 2009 (upwelling; dry season), were conducted to analyze the spatial and seasonal variation in hydrography and geochemistry of both sub-basins. During September 2008, sea surface temperature (SST) was relatively uniform throughout the basin (28–29 °C), and decreased in March 2009, becoming significantly colder in the eastern than in the western sub-basin (22–24 and 25–26 °C, respectively; p < 0.05), due to the seasonal upwelling which occurs in the southeastern part of the basin. Surface salinity was lower in September, due to the influence of surface waters from the Caribbean and the discharge of local rivers. In March, Subtropical Underwater (SUW) reached the surface, raising the salinity values throughout the region. The seasonal hydrographic changes that the basin experiences influenced the surface nitrate and chlorophyll concentrations, both low in September (< 0.1 μM and < 0.3 μg L ^-1 , respectively), and higher in March, especially in the area of upwelling (> 2 μM and > 1.4 μg L ^-1 , respectively). The deep chlorophyll maximum also shallowed during the upwelling period, from 50 to 60 m in September to 0–40 m in March. These results show that while the eastern subbasin responds to the seasonal variability of the region, the western sub-basin has a less pronounced seasonality.