Phytoplankton Nutrient Enrichment Experiments off Baja California and in the Eastern Equatorial Pacific Ocean

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Abstract
Natural phytoplankton populations were enriched with various nutrients both singly and as mixtures. After 4 or 5 days of incubation in natural light, the effects of enrichment were assessed by measuring the rate of 14C uptake or changes in chlorophyll. Off Baja California, in June 1964, September 1965, and November 1966, increases in chlorophyll or 14C uptake occurred in treatments containing added nitrate or trace metals. In February 1967, three enrichment experiments done in nutrient-poor water well offshore and both north and south of the Equator showed that nitrogen was the most likely limiting nutrient. In two experiments in equatorial upwelling water, no nutrient appeared to limit phytoplankton growth since chlorophyll increases were nearly as great in controls containing no enrichment as in treatments containing a complete mixture.