There was an article in Scientific American a year or so back; it discussed experiments that were done in the open sea to measure effect of "seeding" iron (as ferrous sulfate slurry?) on algae/plankton growth.
"In the 1930s oceanographers first began to suspect that terrestrial dust storms play a key role in phytoplankton growth in the so-called high nutrient, low chlorophyl (HNLC) areas of the ocean, whose concentrations of dissolved iron, an essential micronutrient, are much lower than in other regions. By dissolving carbon in seawater and by fixing it as biomass or inorganic particulate matter, phytoplankton regulates carbon dioxide in the atmosphere and thus helps regulate global climate.
In the 1980s, oceanographer John Martin gathered these facts in his "iron hypothesis," which proposed that by fertilizing plankton growth with iron, global warming could be offset. Iron fertilization can indeed cause plankton "blooms" in HNLC waters, as several expeditions including Soiree (the Southern Ocean Iron Enrichment Experiment) in February 1999 and SOFeX (the Southern Ocean Iron [Fe] Experiment) in January and February 2002 have proved by pouring dissolved iron into HNLC areas in the Southern Hemisphere. "
The SciAm article went on to say that results are controversial (does CO2 absorbed by the blooms actually get sequestered into deep ocean, and at what rate), and that studies are underway to determine ways to best/most cheaply conduct seeding operations. One method proposed was that all out-bound oil tankers from US ports would be filled with aqueous Fe solutions, and be required to de-ballast on their way back to the Persian Gulf...
