NASA, 36 months

In the otherwise oligotrophic Caribbean Sea, distinct seasonal periods of wind-forced upwelling, deposition of Fe-rich Saharan aerosols, and river discharge provide a unique opportunity to examine the persistence of CDOC, provided by 1) physical injection from the aphotic zone, 2) biological release from surface blooms of the cyanophyte, Trichodesmium, and 3) lateral supply from land.  In response to elements 1 and 2 of the NSF/NASA SMP AO, the hypothesis will be tested that after injection of new nitrogen, by coastal upwelling during the winter/spring, by nitrogen-fixation in the summer, and by river runoff in the fall, CDOC of distinct physical and biological origins will continue to contaminate the color signals of the southern Caribbean Sea, seen now by the SeaWiFS and OCTS sensors.  Using concurrent AVHRR imagery of SST and aerosol optical thickness to distinguish different periods of upwelling and of iron-deposition, the time-dependent introduction of CDOC to surface waters, by both physical supply and phytoplankton loss, will be analyzed in relation to the photolysis there of CDOC and to the changing contamination of SeaWiFS/OCTS images.  Validation data of the bio-optical part of the analyses will consist of in-water optical measurements made along the Venezuelan coast, from the mouth of the Orinoco River to the stenohaline Cariaco Basin, as part of a separately funded NASA-SIMBIOS project at USF (F.E. Muller-Karger).

Any analysis of CDOC must be conducted, of course, within the context of temporal and spatial variability of the total DOC stocks, which in turn are only one component of carbon cycling in the sea. Our present time-dependent, 3-d ecological models (driven by wind-forced, baroclinic flow fields with a turbulence closure scheme) consider daily C/N cycling by a minimal set of diatoms, Synechococcus, zooplankton, and bacteria, modulated by ambient temperature and the availability of labile and refractory DOC, light, nitrate, ammonium, and DIC over periods of weeks to an annual cycle of habitat change. A new phytoplankton state variable, with the physiological, buoyancy, and palatability properties of Trichodesmium, would be added to consider in the southern Caribbean Sea 1) the air-sea exchange of carbon dioxide in relation to both local/scatterometer wind fields and the source of new nitrogen, 2) the seasonal and spatial patterns of primary and new production at 4.4 km resolution, in relation to aeolian, riverine, and marine influxes of nutrients, and 3) the in situ color signatures of pigments and CDOC in relation to the total carbon pools of POC and DOC, as measured by F.E. Muller-Karger in a separately funded NSF/CONCIT-CARIACO project on the Venezuelan shelf.