Production and respiration in the 1989 North Atlantic spring bloom: an analysis of irradiance-dependent changes

Gross and net O2 production rates at 47°N, 20°W over 13 days during the 1989 JGOFS North Atlantic (Spring) Bloom Experiment were measured. Gross O2 production was measured by H218O uptake or calculated from 14C assimilation, and net O2 production was measured by Winkler titration. Production versus irradiance PB(I) curves were constructed from gross O2 production rates (determined with in situ incubations) normalized to chlorophyll a concentration for the five days of highest total irradiance. Magnitudes of PmB, α and β were high during the bloom. Chlorophyll-normalized gross O2 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 PmB, α and β parameters. 24 h O2 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 O2 production. POC turnover times ranged from two days for near-surface waters up to about two weeks at the base of the euphotic zone.