Magnitude, Variability and Controls of Particulate Export in the Upper Ocean

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ABSTRACTOCE-0097232Using existing and related international data sets from the Joint Global Ocean Flux Study, researchers at the Woods Hole Oceanographic Institution will study the relationships between export and production and the special role that food web processes may have in controlling upper ocean export. The results thus far indicate that the relative rates of carbon fixation and carbon removal via sinking particles vary widely as a function of local food web dynamics. Given the large number of studies that now use the uranium-238 series radioisotope 234Th as a proxy for POC export, these investigators intend to compile global maps of particulate organic carbon export from the upper ocean. They will look directly at the full range of 234Th export data to assess trends between seasonal, episodic, or regional flux variability and a suite of physical and biological parameters. Because a significant portion of export may occur during short pulses or events, the goal is to help explain export variability in order to better model long-term mean export over larger time or space scales.If common mechanisms can be found for the variations of production and export, these could then be incorporated into more reliable models of the global carbon cycle. While much of the ocean is characterized by low relative POC export, sites of high export are most often characterized by food webs dominated by large phytoplankton, in particular diatoms. If this result holds, models that attempt to predict new and export production from surface chlorophyll or production alone will not resolve the local carbon balance or allow one to model export controls. A mechanistic understanding of the underlying export processes is crucial to being able to incorporate this understanding into models, particularly if we desire to predict fluxes in future climate states.