The Link between Climate and Terrigenous Deposition in the Cariaco Basin, Venezuela

We are investigating seasonal variations in terrigenous input to the Cariaco Basin, Venezuela, by studying the major and trace element chemistry in sediment trap material gathered over two years (1996-1998) as part of the CARIACO program. Our main goal is to compare changes in the flux and composition of the terrigenous matter with meteorological and hydrological records (e.g., precipitation and SST) in order to discern the modern climate forcing of terrigenous deposition in the Basin. Previous studies have used chemical proxies of the terrigenous component to infer changes in the paleoposition of the Intertropical Convergence Zone (ITCZ). Our study aims to discriminate the sources of this material and understand how modern shifting of the ITCZ controls changes in these sources' relative contributions. Understanding this link in the modern is crucial to help calibrate the paleorecords and interpret past climate changes in this tropical setting. Preliminary results from two traps (275m and 440m) show that the detrital component has its highest concentration during the wet season. However, terrigenous flux does not show seasonality, which suggests that parameters other than river run off are affecting the terrigenous deposition. Some chemical tracers of the detrital fraction clearly document fluctuations between a rainy and a dry season signal, suggesting seasonal changes in the relative contribution of at least two different sources. Multivariate statistical analysis suggests mixing between two or three compositional end-members. We are also studying shelf sediments (Unare Platform). These sediments record a dilution pattern as more proximal samples show the highest concentrations of Ti, Al, Fe, and other detrital tracers while the more distal samples show the lowest concentrations (biogenic dilution). Thus, for example, variations in Ti concentration in marine cores may reflect dilution, not real changes in the terrigenous flux. Considering the reported composition of potential sources and the results we have at this point, changes in the contribution of local rivers, Saharan aerosol, and the Orinoco River may contribute to the observed seasonality. On-going work by our team is assessing the importance of these potential sources.