Comment & Debate
Some ocean trials did indeed report remarkable results. According to IronEx II reports, their thousand kilogram iron contribution to the equatorial Pacific generated a carbonaceous biomass equivalent to one hundred full-grown redwoods within the first two weeks. Researchers on Wegener Institute’s 2004 Eifex experiment recorded carbon dioxide to iron fixation ratios of nearly 300,000 to 1. Current estimates of the amount of iron required to restore all the lost plankton and sequester 3 gigatons/year of CO2 range widely, from approximately two hundred thousand tons/year to over 4 million tons/year. Even in the latter worst case scenario, this only represents about 16 supertanker loads of iron and a projected cost of less than €20 billion ($27 Billion).
“Fertilizing the Ocean with Iron”. Woods Hole Oceanic Institute. 7 Sep. 2007: ice-core records suggested that during past glacial periods, natural iron fertilization had repeatedly drawn as much as 60 billion tons of carbon out of the atmosphere. Laboratory experiments suggested that every ton of iron added to the ocean could remove 30,000 to 110,000 tons of carbon from the air. Early climate models hinted that intentional iron fertilization across the entire Southern Ocean could erase 1 to 2 billion tons of carbon emissions each year—10 to 25 percent of the world’s annual total.
What is critical for the effectiveness of iron fertilization schemes is the amount of organic carbon that actually sinks from the surface and is sequestered in the depths. Only a small percentage of carbon—in the form of dead cells and fecal pellets—falls to the seafloor and stays there, unused, for millennia. A higher percentage (between 20 and 50 percent) will at least reach middle-depth waters, where the carbon will remain in underwater currents for decades. Proponents consider this result good enough to buy society time to come up with other, more permanent solutions to greenhouse gas increases.
Margaret Leinen PhD, Kevin Whilden, and Dan Whaley. “A Response to Concerns about Ocean Iron Fertilization Raised by Greenpeace”. Climos, Inc. 15 May 2008 – While the recent results of biological pump measurements do not guarantee high efficiency at all times and in all locations, they clearly indicate that export can be substantial – up to 50% of the new production. None of the many JGOFS studies showing high rates of sequestration were considered in the Greenpeace technical note, nor were the rigorous multi-technique VERTIGO studies although they were published before the Greenpeace report. Further, in several sections the Greenpeace technical note refers to the potential for “reduced oxygen levels in subsurface waters” (p. 3). We will discuss low oxygen and anoxia later in this response, but it is important to point out at this time that it is impossible to generate substantially reduced oxygen or anoxia in deep ocean waters without substantial carbon export as the oxygen depletion results from the remineralization of sequestered carbon. If oxygen is reduced in mid- to deep waters after OIF, it is because there has been substantial export. We believe that the results showing substantial export below the level of deep mixing, argue that there may be large regions within the world ocean in which substantial POC can be sequestered by OIF.