Coupling of Sinking Biogenic Particulate Fluxes and Primary Production in the Euphotic Zone of the Cariaco Basin, Venezuela

Only 1% of the organic matter produced in the upper ocean by photosynthesis reaches depths below 1500 m due to dissolution and microbial degradation. Recent work shows that the vertical flux of particulate organic carbon (POC) is strongly correlated with the settling flux of minerals like calcium carbonate, opal and lithogenic material. These act as ballast and also provide physical protection against degradation of POC. Results from the CARIACO (Carbon Retention in a Colored Ocean) time series program support this hypothesis. For over ten years, CARIACO has been studying the connections between primary production (PP) and the biogeochemical features of sinking particles in the Cariaco Basin, Venezuela, with moored sediment traps that collect settling matter at five depths between 125 and 1300 m on a bi-weekly basis. The geomorphology of the basin restricts deep water ventilation, leading to anoxia below 250 m. Although the Cariaco Basin exhibits strong seasonal production cycles related to wind-driven upwelling, the flux of biogenic matter at all depths below the oxic-anoxic interface is not significantly correlated to primary production. In order to understand the flux of particles in the upper 100 m of the water column, deployments of drifting sediment traps in the Cariaco Basin were carried out from March to July 2007, collecting settling material at 50 and 100 m. The hypothesis is that the flux of sinking material through the euphotic zone may be less affected by decomposition and dissolution than material reaching the deep moored traps. Initial results show significant differences in POC, PON and carbonate flux rates between 50 and 100 m. They also exhibit significant differences in the flux rates of these components between upwelling vs. relaxation periods, suggesting potential connections among seasonal changes in surface chlorophyll a concentrations, plankton community structure, and the vertical export of biogenic materials. We describe results from this research, including comparisons between shallow and deep sediment trap data.