High Phytoplankton Growth and Production Rates in the North Pacific Subtropical Gyre

Rates of phytoplankton growth and production were measured with14C techniques at stations near the Hawaiian Islands and at about 28⚬N, 155⚬W in the North Pacific subtropical gyre during August and September 1985. Ratios of light-saturated assimilation averaged 9.5 ± 1.4 g C (g Chl a)-1 h-1 during the photoperiod. Doubling times in the upper 30 m of the water column averaged 14± 3 h. Relative growth rates were estimated to be 85-90% of nutrient-saturated values. Over the upper 200 m of the water column photosynthetic rates uncorrected and corrected for grazing and phytoplankton respiration losses were 315 ± 26 and 450 ± 37 mg C m-2 d-1, respectively. The former figure is comparable to the highest daily photosynthetic rates inferred from14C studies at this station during 1968-1980 and is about twice the mean of those historical productivity numbers. These results contradict the paradigm of subtropical gyres as vast biological deserts characterized by constantly low biomass and low turnover rates limited by the supply of nutrients. However, further studies will be reeded to determine whether these high growth and production rates are typical or atypical of the central regions of the oceans.