Studies of the Beaufort Sea have shown that once nitrate is depleted from the upper euphotic zone, the concentrations of soluble reactive phosphorus (SRP) and dissolved inorganic carbon (DIC) continue to decrease. Understanding this phenomenon is a crucial step toward assessing the response of net community production and ecosystem productivity to environmental forcing and climate change. Based on the paradigm that phosphorous is recycled more readily than nitrogen in the upper ocean, we hypothesize that the continued depletion of SRP and DIC is not tied to the use of recycled nitrogen by phytoplankton, but to the consumption of an alternate nitrogen form not considered in previous investigations. In this project, we considered the possibility that new nitrogen enters the system via nitrogen fixation by cyanobacteria and that the phytoplankton use allochthonous organic nitrogen directly or via its photochemical degradation into labile inorganic nitrogen forms.
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