Gross and net O-2 production rates at 47 degrees N, 20 degrees W over 13 days during the 1989 JGOFS North Atlantic (Spring) Bloom Experiment were measured. Gross O-2 production was measured by H-2 O-18 uptake or calculated from C-14 assimilation, and net O-2 production was measured by Winkler 2 titration. Production versus irradiance P-B(I) curves were constructed from gross O-2 production rates (determined with in situ incubations) normalized to chlorophyll a concentration for the five days of highest total irradiance. Magnitudes of P-m(B), alpha and beta were high during the bloom. Chlorophyll-normalized gross O-2 production, integrated over the euphotic zone, was observed to be linearly related to integrated incident irradiance. This linear trend can be simulated with an algorithm using average values of P-m(B), alpha and beta parameters. 24 h O-2 respiration rates for each day appeared to consist of two components: one proportional to the production rate and involving respiration of carbon fixed during the same day's photoperiod, and the other independent of the production rate and respired carbon fixed prior to the day's photoperiod. Integrated over time and depth, these respiration components were of comparable magnitude, and together equalled about 60% of gross O-2 production. POC turnover times ranged from two days for near-surface waters up to about two weeks at the base of the euphotic zone.
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