In the equatorial Pacific Ocean along 160° W, surface-water samples with natural plankton
communities were placed in incubation bottles to which subnanomolar levels of Fe were
added under ultraclean conditions. Addition of 0.1–0.8 nM Fe to seawater samples
containing high NO3 increased stocks of Chl a and POC, NO3 consumption and net growth
rate of phytoplankton in incubation bottles relative to the controls. A large increase in the Chl
a concentration of large-(10 μm) and medium-size (3–10 μm) fractions was observed in the …

Addition of 0.1-0.8 nM Fe to seawater samples containing high NO 3 increased stocks of Chl
a and POC, NO 3 consumption and net growth rate of phytoplankton in incubation bottles
relative to the controls. A large increase in the Chl a concentration of large (> 10 μm) and
medium-size (3-10 μm) fractions was observed in the Fe-enriched samples. The results
indicate that changes n subnanomolar Fe levels affect the equatorial phytoplankton
communities by promoting the growth of large phytoplankton.