The effects of added Si and Fe on the rate of silicic acid uptake were examined during two cruises to the equatorial Pacific upwelling zone between 110°W and 140°;W. Maximum uptake rates of Si ( V max ) were highly consistent with a mean of 0.026 ± 0.007 h −1 (n = 29), implying maximum diatom growth rates of ~0.6 d −1 . Half‐saturation constants for Si uptake ( K S ) also showed little variance, averaging 1.7 ± 0.7 mmol L −1 S...

Processes influencing phytoplankton bloom development in the southern Drake Passage were studied using shipboard iron‐enrichment incubations conducted across a surface chlorophyll gradient near the Antarctic Peninsula, in a region of water mass mixing. Iron incubation assays showed that Antarctic Circumpolar Current (ACC) waters were severely iron limited, while shelf waters with high ambient iron concentrations (1–2 nmol L −1...