Measurements of Net and Gross O-2 Production, Dark O-2 Respiration, and C-14 Assimilation at the Marine Light-Mixed Layers Site (59-Degrees-N, 21-Degrees-W) in the Northeast Atlantic-Ocean

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Journal of Geophysical Research-Oceans
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Apr 15
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Rates of primary production and respiration were determined at a moderately eutrophic site (1-4 mg Chl a m(-3)) in the northeast Atlantic Ocean from in vitro changes in dissolved oxygen and C-14 uptake. The oxygen rates were measured with new instruments called productivity autosamplers (PA's), which automate the process of water sampling, incubation, and O-2 measurement. Measurements of net and gross production and respiration were obtained at two depths over an 8-day period in May and a 7-day period in August 1991. Carbon 14 uptake was measured in dawn-to-dusk and 24-hour incubations at six depths during the same periods. The results indicate that gross O-2 production and C uptake were tightly coupled; the ratio of gross O-2 production to dawn-to-dusk C-14 uptake averaged 1.4 +/- 0.1 (SE). Net autotrophic O-2 production, estimated as gross O-2 production minus a floristically determined chlorophyll a specific respiration rate times the chlorophyll a concentration, was compared for the first time with C-14 uptake. These two processes were not tightly coupled; the ratio of net autotrophic O-2 production to C-14 uptake varied from 1.0 at 2 m to 0.2 at 15 m. Particulate organic carbon (POC) turnover rates (k(POC)) in the mixed layer, estimated from day-to-day changes in the water column POC inventory, were compared with turnover rates estimated from the in vitro O-2 and C-14 incubations. The 24-hour C-14-based turnover rates (k(14C)) exhibited little relationship to in situ POC turnover rates. Turnover rate based on 24-hour net community O-2 production (k(O2)) converted to carbon using a molar ratio of O-2 produced to CO2 assimilated (PQ) of 1.4 was a more useful indicator of k(POC).


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