Sequestration of carbon dioxide by ocean fertilization

Sequestration of carbon dioxide to the deep ocean by the fertilization of high nutrient, low chlorophyll (HNLC) ocean waters can be an answer to tile concerns arising from the increasing carbon dioxide content of the atmosphere. This approach has the potential to sequester about 400,000,000 tons of carbon dioxide by repeated episodic fertilizations of the Pacific equatorial current for a cost of about $2.00/ton of carbon dioxide and for 1000 to 2000 years. A technology demonstration is planned to fertilize an area of 5,000 square miles of the equatorial Pacific that is expected to sequester between 600,000 and 2,000,000 tons of carbon dioxide in a period of 20 days. The ecological changes expected consist of the increase in diatoms, which double or triple each day until the limiting fertilizing element is used up. No adverse changes are expected, since this is exactly what happens naturally when episodic fertilization occurs in the open ocean. The concept is that fertilization of HNLC waters with chelated iron will cause a bloom of phytoplankton that sink below the thermocline into deep water due to their high density after they die. The experiment, while large by land comparisons, is small in terms of ocean area, about one square degree at the equator. The demonstration protocol will include measurements of the amount of carbon dioxide that is removed from the surface layer and the amount of organic carbon that is produced and exported to the ocean depths as well as other effects in the water column over a period of 20 days. After this time no further effects of iron fertilization are expected to take place because macronutrient elements (N, P and Si) are depleted to limiting concentrations. Since tile iron enrichment is transient, no steady-state modification of the food web will occur. The experiment will be carried out outside the EEZ of any nation, as were the previous five experimental voyages, so, like them, no permits will be required. The five recent ocean experiments observed iron stimulation of phytoplankton growth, but the effects were difficult to quantify in the 9 to 28 square mile experiments since eddy diffusion along the edges of the patch diluted the bloom. This problem will be minimized in the planned technology demonstration because its larger area restricts the diffusion from the center of the patch to less than 2% of the concentration over the 20 day period of the test.