The iron hypothesis: Basic research meets environmental policy

In October 1993, an interdisciplinary group of scientists spread 445 kg of iron over a 64 km² patch of surface ocean in the eastern equatorial Pacific. They monitored the patch for 9 days, comparing its biology and chemistry to the unfertilized surrounding waters. They found that the phytoplankton (microscopic plants which comprise the base of the food web in the oceans) were three times more productive in the patch than outside it. In other words, the cells were photosynthesizing—i.e., converting CO₂ to organic carbon—at a significantly enhanced rate. The group concluded that iron was the limiting factor in this ecosystem, solving one of the more perplexing puzzles in biological oceanography in recent years. This event marked not only the first unenclosed ocean ecosystem experiment, but also the climax to a complex and fascinating evolution of ideas in biological oceanography. The climax was bittersweet, however, as John Martin, the designer of the experiment and originator of the hypothesis, died shortly before the expedition.