Planktonic carbon and nitrogen budgets for the N-NW Spanish shelf: The role of pelagic nutrient regeneration during upwelling events
Antonio Bode, Manuel Varela
Carbon and nitrogen fluxes through several components of the pelagic ecosystem in the N-NW Spain upwelling area were estimated from published biomass results. Additional information concerning primary productivity and biomass of microheterotrophs in the area is given. The measured primary production rates during upwelling events in the annual thermal stratification period could be based up to 50 % on recycled nitrogen in the water column. Microbial-loop organisms accounted for up to 80 % of the estimated carbon and nitrogen flow through heterotrophs. Our estimations of consumption, respiration and production of mesozooplankton agree well with direct measures in the study area. Additional support of rapid nutrient cycling is indicated by the significant amounts of recently fixed carbon (up to 65 %) that is excreted in short-term incubations of upwelled water. In spite of differences in biomass and productivity, high grazing rates resulted in all the selected upwelling examples. Coastal areas receiving export phytoplankton and nutrients from the nearby productive estuaries appeared to act more as accumulation than as production sites, when compared to other upwelled areas on the shelf. Export of organic matter to other systems is more likely in the former areas, whereas rapid active grazing could be responsible for the degradation of organic matter produced by the upwelling induced phytoplankton blooms in the latter.
Keywords: Coastal upwelling, C and N budgets, heterotrophic plankton, new and regenerated production, N-NW Spain.
Sci. Mar. 58(3) : 221-231
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