Putting iron in the ocean to fight global warming

by Mark Schrope
ISNS Contributor
March 10, 2008

Orlando, Fla. -- The highly controversial concept of artificially fertilizing portions of the ocean with iron to fuel plant growth that could take carbon dioxide out of the atmosphere has for years been proposed as a possible method for helping to slow global warming. New research on two Southern Ocean locations where such fertilization occurs naturally, presented at last week's Ocean Science Meeting in Orlando, Fla., suggests that effective artificial fertilization may be more difficult than previously thought.

In most parts of the ocean, how much algae can grow is controlled by nutrients such as nitrogen. But for certain large ocean swaths around the globe, such as the Southern Ocean, further algae growth is prevented by a lack of iron. In such regions, experiments have shown that artificially added iron can fuel massive algae growth, or blooms. The major open question in such work is just how much of the carbon dioxide those plants pull from the atmosphere ultimately gets buried in deeper parts of the ocean, and how much just makes its way back to the atmosphere.

More recently, commercial companies have been exploring the possibility of using artificial iron fertilization as the basis for selling carbon credits in emerging national and global markets to offset the impact of activities that add carbon dioxide or other greenhouse gases to the atmosphere. The concept has grown increasingly controversial with scientists and governments alike urging caution, and debates ongoing.

One of the complications in understanding the impacts of artificial fertilization has been the limited size of past experiments, the largest of which covered only a few thousands square kilometers, a very small slice in ocean terms. But there are also places where iron fertilization occurs naturally over very large areas. At the Ocean Sciences Meeting, researchers from several institutions in the United Kingdom, France, and elsewhere presented results of two major expeditions to study these natural phenomena at the plateaus surrounding the Crozet and Kerguelen Islands in the Southern Ocean. Crozet's annual algae bloom, for instance, covers some 90,000 square kilometers, or about half the area of Florida.

One of the major conclusions is that these naturally occurring algae blooms are ten to 100 times more efficient at taking carbon dioxide out of the atmosphere and burying it than the artificial programs. "The important message is that artificial iron fertilization is a very bad imitation of the natural process, which means that you cannot expect the same results when you add iron artificially as what you can see when you observe the natural process," says Stephane Blain, from the Laboratory of Oceanography and Biogeochemistry in Marseille, France.

However, artificial experiments have been limited in both size and duration, making it difficult to accurately judge their true impacts and complicating comparisons with natural blooms. Significant carbon burial could, for instance, be occurring during the days and weeks after study teams have left experimental fertilization areas. "I think it just highlights the gulf that exists between existing knowledge and what we need to know before effectively using artificial additions to help draw down CO2 from the atmosphere," says Peter Statham, of the National Oceanography Centre in Southampton, UK.

Though the process is still not fully understood, researchers believe the bulk of the iron fueling natural blooms in places such as Crozet and Kerguelen comes from iron-rich sediments in shallower areas around the islands that get mixed with waters above during storms and windy conditions. Researchers with the project believe that because this process is effectively an iron time-release system that continues to fertilize growth over long periods, it is more sustained and efficient than the artificial fertilization. During artificial experiments iron is typically added at the beginning, and a significant portion of this actually sinks away from the algae at the surface.

"I think this will certainly affect thinking about how new experiments are designed," says Margaret Leinen, chief science officer for Climos, of the Southern Ocean natural fertilization research presented at the meeting. Climos hopes to eventually use iron fertilization for commercial removal of carbon dioxide. Leinen says the Southern Ocean work highlights the need for larger artificial fertilization experiments, which some university researchers have also called for. She also points out that past artificial experiments have still shown very significant levels of carbon burial, even if these levels don't match the natural blooms.

Climos has proposed a code of ethical guidelines to govern the company's future work, which Leinen, a former University of Rhode Island biogeochemist and assistant director for geosciences at the National Science Foundation, discussed at the meeting. Pending sufficient venture capital funding, the company hopes to conduct a major iron fertilization experiment in either the North Pacific or the Southern Ocean in 2009. Rather than conduct the work itself, the group proposes to fund academic scientists to do the research as they see fit, with all results freely available for public scrutiny and discussion. The company would only sell carbon credits based on the conclusions of analysis by the academic community. "We're trying to make a very highly credible science experiment," says Leinen, "as well as commercial demonstration experiment."

Mark Schrope is a freelance science writer based in Florida.

***This story is provided free for media use by the Inside Science News Service, which is supported by the American Institute of Physics, a not-for-profit publisher of scientific journals. Please credit ISNS. Contact: Jim Dawson, news editor, at jdawson@aip.org.