New Production and Carbon Cycling in Marine Plankton Systems

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The export of organic matter from the ocean's surface is an important biological and chemical process. Biologically, this export feeds most deeper dwelling organisms, and chemically it influences the exchange of gases like carbon dioxide and oxygen with the atmosphere. Export usually is defined in terms of carbon. A common approach is to estimate carbon export from a limiting nutrient such as the new (nitrate) component of total plankton production by assuming that 6.6 atoms of carbon are exported for each atom of new production. However, this gear ratio (one of the Redfield ratios) between the surface water carbon and nitrogen cycles has never been rigorously examined. Recent measurements in diverse ocean areas indicate that the net change in inorganic carbon associated with new production exceeds that predicted from the Redfield conversion by more than 50%. Thus, current concepts or nutrient cycling in the ocean may be seriously flawed and the role or the ocean as a carbon sink and as an O2 source may be significantly underestimated. This research represents the first quantitative study of the relationship between new production and net production in terms of both dissolved inorganic carbon and O2 with incubation experiments that can isolate the biological processes from the confounding effects of mixing and gas exchange. These experiments will provide critical relationships that are needed for more accurate estimates of oceanic carbon and oxygen fluxes. The differential recycling of carbon and nitrogen as a reason why the Redfield C:N conversion fails in surface water will also be evaluated.