The Use of Iron Fertilization for Carbon Sequestration

Am. Assoc. for the Adv. Of Sci. 304, 414-417 (2004).

Researchers are looking into new techniques of carbon sequestration to help counteract the negative effects on the climate due to the anthropogenic emission of carbon dioxide.

Ken O. Buesseler, John E. Andrews, Steven M. Pike and Matthew A. Charette performed an experiment called the Southern Ocean Iron Experiment (SOFeX), where they fertilized two sites with four enrichments of iron fertilization. The patch of fertilized water was monitored by 3 boats for 1 month in 2002.

The researches found that in a 1000 km² patch during 21 days, SOFeX resulted in an enhanced flux at 100 m of 1800 tons of carbon. However, because of remineralization that the researchers estimate to have occurred, the true estimate of carbon sequestration is about 900 tons. However, they concluded that because this is such a small amount compared to the 6.5×10⁹ tons/year emitted by humans, there needs to be more research conducted to make this technique useful on a global scale to mitigate climate change.

Researchers have proposed that ocean iron fertilization, which stimulates phytoplankton growth, could be a probable method to mitigate ocean acidification. Long Cao and Ken Caldeira, from Stanford University, examined this idea by creating a simulation that diminished phosphate concentrations in near-surface waters to zero. This placed an upper bound on the maximum possible effect of ocean iron fertilization. This extreme situation, which is unlike real-world conditions, was used to show the basic effects of fertilization on ocean acidification.

When implementing iron fertilization into the simulation, it was determined that fertilization may mitigate ocean acidification in surface waters but if this fertilization also generated carbon credits within the ocean, it would allow greater CO2 emissions to enter the sea and there would be no benefit to the fertilization. However, in all cases it was found that fertilization created greater acidification in deep-sea waters. Because fertilization could lead to worsened deep-sea conditions without aiding surface conditions it is an ineffective mitigating technique.

Can ocean iron fertilization mitigate ocean acidification? Climatic Change, Springer Netherlands. Volume 99, 1-2. DOI: 10.1007/s10584-010-9799-4 (2010)

Science New Series, Vol. 304, No. 5669, pp. 414-417 (2004)

Research by Ken Buesseler, John Andrews, Steven Pike, and Matthew Charette from the Department of Marine Chemistry and Geochemistry at the Woods Hole Oceanographic Institution suggests that iron fertilization could help reduce anthropogenic carbon dioxide in the ocean (though the reduction would be relatively small). Using Thorium 234 (a naturally occurring radionuclide) as a tracer, the researchers observed an increased flux of marine snow (falling organic matter/detritus composed mostly of dead plankton), in the Southern Ocean after injecting iron into the surface layer, demonstrating successful export of particulate organic carbon. Injecting iron into the ocean induces algal blooms (because iron is a limiting nutrient for phytoplankton), resulting in increased uptake of carbon dioxide by phytoplankton in the process of photosynthesis. This results in the increased amounts of marine snow, some of which falls all the way to the ocean floor; storing carbon dioxide in detritus at the bottom of the ocean is a potential method for counteracting ocean acidification.