Spatial and seasonal variability of dissolved organic matter in the Cariaco Basin

Dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP) were measured monthly at the CARIACO Time Series station (10 degrees 30N, 64 degrees 40W) in the southeastern Caribbean Sea between 2005 and 2012. Marked seasonal variability in DOC concentrations was observed, with lower values (similar to 66 mu M) in the upper water column (<75m) during the upwelling season (December-April) due to the injection of cool, DOC-impoverished Subtropical Underwater from the Caribbean Sea. During the rainy season (May-November) waters were stratified and upper layer DOC concentrations increased to similar to 71 mu M. Interannual variability in surface (1m) concentrations of DOC was also observed in response to the variable strength in upwelling and stratification that the Cariaco Basin experienced. DON and DOP showed no such seasonality. At depths >350m, DOC concentrations were 564.7 mu M, roughly 10 mu M higher than those in the Caribbean Sea over the same depth range. DON and DOP showed similar vertical profiles to that of DOC, with higher concentrations (6.81.2 mu M N and 0.15 0.09 mu M P) in the upper water column and invariant, lower concentrations at depth (4.81.6 mu M N and 0.10 +/- 0.08 mu M P). Wind-driven advection of surface DOC out of the Cariaco Basin was estimated to support a net export similar to 15 Gmol C yr(-1) into the Caribbean Sea; this rate is comparable to the flux of settling particulate organic carbon to depths >275m within the basin.