Fertilizing the Oceans

The image to the left shows a satellite image of a 150km long phytoplankton bloom created during the 2002 Southern Ocean Iron (Fe) Experiment (SOFex). The arced distribution is due to oceanic currents and the bloom appeared only six weeks after the initial fertilization.

The fertilization involved adding iron to surface waters in two patches, each 15 kilometers on a side, so that the concentration of this micronutrient reached about 50 parts per trillion, increasing the natural level by about two orders of magnitude.

Each of these blooms consumed over 30,000 tons of carbon dioxide, but the crucial question is whether this carbon dioxide would be returned to the atmosphere, or would sink into deep waters as the phytoplankton died. One of the factors that determines which will occur is what type of organisms form the bloom. Diatoms, for example, are relatively heavy and sink easily. But the abundance of diatoms may be limited by silica as well as iron.

The results were published in the journal Science in 2004 and were reported on quite widely by the press. Here is a nice report by the Sciencedaily website.