The importance of small but local vs. large rivers in the region on the Cariaco Basin, Venezuela

Two cruises were conducted to sample the eastern half of the Cariaco Basin, located along the southern margin of the Caribbean Sea, during September 2003 and March 2004. The objectives of these cruises were to examine the seasonal influence of the Caribbean Sea and of rivers in the region on the hydrography of the Cariaco Basin. Specifically, the cruises sought to clarify whether strong seasonal salinity variation observed in surface waters at the CARIACO time series station (10.5oN, 64.66oW) is due to influence of the Orinoco and Amazon River or due to dispersal of plumes from local rivers entering the basin along its southern margin. During the rainy season (September 2003), surface salinities inside the basin were generally higher relative to Caribbean Sea waters outside the basin. Salinity patterns indicated that the Orinoco and Amazon don't influence the basin directly. However, there is a strong correlation between DOC concentration and CDOM absorption in the Cariaco basin for March 2004 (r2 = 0.846), regardless of the location sampled. The influence of local rivers was evident during the rainy season. Low salinity plumes lined the southern margin of the Cariaco Basin relative to the north around the sill. The primary rivers that affect the basin are the Unare and Neveri. While their sediment input is limited and affects mostly the shallow platform, their plumes are carried northwestward toward the CARIACO time series station near the surface. Near the Manzanares river, off the city of Cumana, and near Cubagua Island, located south of Margarita Island, large particle concentrations were observed at depth (70-150 m), pointing to a possible deep sediment pool year-round. However, more observations are necessary to determine the nature and origin of these particles. The high resolution climate record contained in Cariaco Basin sediments can only be properly interpreted by considering the significant influence of small local rivers relative to the small to minimal influence of large rivers of the region.