Seeding Ocean No Panacea to Warming

By GAIL GALLESSICH

Scientists are learning about the history and possibly the future of climate change by fertilizing the ocean with iron to create blooms of microscopic plants.

These microscopic marine plants in the Southern Ocean may have played a pivotal role in developing the Earth's climate during past ice ages, explained Mark Brzezinski, professor of biology and deputy director of the UCSB Marine Science Institute.

He took part in a major ocean fertilization study, known as SOFeX, for Southern Ocean Iron Enrichment Experiments, involving many institutions that was initiated 12 years ago. The research was funded by the National Science Foundation and the Department of Energy. The results of the research project were described last month in the journal Science.

There are three major areas of the ocean where iron is a limiting factor in the growth of these plants: the sub-Arctic Pacific, the Equatorial Pacific, and the Southern Ocean. By adding iron to the ocean's surface, the tiny plants, called phytoplankton, increase in number in these locations. The plants draw carbon dioxide—an important greenhouse gas—from the atmosphere to live.

Iron was more plentiful in the atmosphere during the ice ages because the Earth was drier at that time. The dryness caused more iron-ladened dust to be picked up by the wind, which then fertilized the ocean. More plant productivity in the ocean meant a reduction in carbon dioxide in the atmosphere.

Brzezinski, one of 17 principal investigators, took part in a major expedition to the Southern Ocean to test the theory. He spent 42 days at sea. With UCSB technician Janice Jones and graduate student Mark Demarest, he took part in dropping iron sulfate into two areas of the Southern Ocean. The goal was to observe the growth and fate of the marine plants under such enriched conditions.

In order to simulate ice-age conditions, the scientists added iron to surface waters in two patches, each 15 kilometers on a side, so that the concentration of this micronutrient reached about 50 parts per trillion—a 100-fold increase over ambient concentrations. Even at this low concentration, massive blooms of phytoplankton covered thousands of square kilometers. Each of these blooms consumed over 30,000 tons of carbon dioxide.

Certain plants, like diatoms, are heavy and sink into the deep ocean. "If they are eaten, or decomposed by bacteria, and if that occurs at depth, then the carbon dioxide is retained in the deep sea where it is sequestered for at least 1,000 or more years," said Brzezinski.

Some of the findings from the study suggest that, when extrapolated over large regions, iron fertilization could cause billions of tons of carbon to be removed from the atmosphere each year. Removal of this much atmospheric carbon dioxide could have helped cool the Earth during ice ages.

Similarly, some have proposed that a massive iron fertilization program could help mitigate the current trend toward global warming. Brzezinski, however, is not optimistic about preventing global warming through fertilization of the ocean.

He said that his measurements did not show a strong enough result to expect that fertilization could reverse global warming. "It's still an open question as to whether or not this is a viable way to export carbon to the deep sea," he said.