Radioisotopic Measurements to Determine Plankton Nutrient Sources and Carbon Export at Station ALOHA

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ABSTRACTOCE-9906634There is mounting ecological evidence that the oceanic ecosystem of the central North Pacific Ocean my be undergoing a shift from a system in which nitrogen limits primary production to one limited by the availability of phosphorous. Before we can evaluate this possibility and its oceanographic and ecological significance, we must first understand the biogeochemical mechanisms working in the cycling of phosphorous in the oceanic water column. To that end, the principal investigator on this project will conduct a study of phosphorous cycling and particulate organic carbon (POC) export in the North Pacific gyre using the naturally-occurring, short-lived radionuclides Phosphorous-32, Phosphorous-33, Thorium-234, and Beryllium-7. The P isotope measurements would permit the estimation of P residence times in the dissolved and particulate pools. The work would be carried out in conjunction with an already established monthly U.S.JGOFS-HOT (Hawaiian Ocean Time Series) cruise program.