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Research tackles key factors in climate change

April 16, 2004

Photo of polar phytoplankton collected in the Southern OceanThe cold waters of the Southern Ocean hold a key to understanding the climatic shifts of the last ice age and help reduce global warming, SFSU researchers have discovered.

Senior research scientist Bill Cochlan and research associates Nicholas Ladizinsky and Julian Herndon -- all of the Romberg Tiburon Center for Environmental Studies -- are part of a muliti-disciplinary field-based research team which demonstrated that supplementing Antarctica's Southern Ocean with minute quantities of iron can kick-start phytoplankton blooms that rival rainforests for their ability to "drawn down" and lock away the greenhouse gas carbon dioxide from the atmosphere. The research results were featured in the cover article in the journal Science published April 16, 2004.

Cochlan and his team were among scientists from 17 universities and institutions nationwide who participated in the massive research effort, known as SOFeX (Southern Ocean Iron Enrichment Experiment). The three-month, three-ship operation took place in some of the roughest, coldest waters at the Antarctic Polar Front Zone between New Zealand and Antarctica. The huge region is packed with nearly all the normal nutrients needed for plants yet supports very little growth – due in large part to a key missing ingredient: iron.

Photo of research associate Nick Ladzinsky collecting a sample from the Southern Ocean"Understanding the biological mechanisms which can shift more CO2 into the sea from the atmosphere is a key part of our research and ultimately in our ability as scientists to provide realistic methods to address global warming," says Cochlan, who notes that there is more phytoplankton biomass in the ocean than plant biomass on land.

The team knew from earlier research that iron deficiencies were a factor in limited growth in both the Southern Ocean and other regions of the World Ocean known as High Nitrate, Low Chlorophyll (HNLC) areas, including the equatorial Pacific and the subarctic Pacific. In this new research voyage, they set out to strengthen evidence that iron supplements could stimulate phytoplankton growth, but more important, to measure whether the biological processes driven by that new photosynthesis could impact climate change through the shifting of carbon dioxide from the atmosphere into the ocean.

According to the U.S. Environmental Protection Agency, atmospheric concentrations of carbon dioxide have increased nearly 30 percent since the industrial revolution and the heat-trapping property of CO2 and other greenhouse gases is undisputed.

"As microscopic plants grow, they take up carbon dioxide from the surrounding waters," Cochlan explains, "and the gases in the ocean in turn equilibrate with the atmosphere." More plant growth in the oceans "pulls down" more CO2 from the atmosphere, which can potentially curb global warming, provided that the CO2 is effectively sequestered into planktonic biomass that sinks to the oceanic depths.

Photo of senior research scientist Bill CochlanFor the experiment, about 20,000 pounds of acidified iron sulfate -- an essential micronutrient needed for plant life -- was pumped slowly in the ship's wake to enrich two test patches of the Southern Ocean, acting as massive test tubes 225 square kilometers in size. Cochlan's team conducted a crucial aspect of the experiments, addressing how the iron enrichment affects the microscopic plants' nutrition, specifically the types of nitrogen used for growth. "Big and small phytoplankton cells tend to prefer different forms of the various nitrogen substrates dissolved in seawater," Cochlan said, "such as ammonium and urea for small cells versus nitrate for larger cells like diatoms. It’s the big ones that tend to sink out quickest and form the majority of the export flux."

Both test patches responded to the iron enrichment with increased growth of phytoplankton, resulting in phytoplankton blooms with increased photosynthetic rates, faster nitrate consumption and depleted concentrations of dissolved carbon dioxide, and other biological processes that enhance the shift of carbon dioxide from the atmosphere into the sea.

"The resulting phytoplankton blooms were so massive that they were easily observable from space with ocean color satellites, and in fact these images were relayed to the ships at sea to aid in the tracking of the patches’ position," noted Cochlan.

Continued mesoscale iron experiments are planned this July and August in the western North Pacific Ocean off Japan. Cochlan just returned from a final logistics meeting at the University of Tokyo to plan for the two-ship operation termed "Subarctic Pacific Iron Experiment for Ecosystem Dynamics Study" (SEEDS-II), an international effort involving scientists from the U.S., Canada and Japan.

The Romberg Tiburon Center contingent, funded by the U.S. Department of Energy and the National Science Foundation, will include both undergraduate and graduate student researchers and two high school teachers specialized in marine science research. The school teachers will be involved in outreach activities on board, and will gain unique hands-on oceanographic experiences to bring back to their classrooms in Torrance, Calif., and Cincinnati, Ohio.

The SFSU researchers will be at sea for six weeks, evaluating longer-term issues associated with large-scale iron enrichment.

-- Ellen Griffin
Photos: Cochlan -- Diane Fenster; Phytoplankton -- Karen Selph, University of Hawaii; Sample collecting -- Kenneth Coale, Moss Landing Marine Laboratories

Note: For more background on the SOFeX project, see a recent article by student Caeli Quinn in the College of Science & Engineering online magazine, InterSci. (Adobe Acrobat required) or see the press release from Moss Landing Marine Laboratories.


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Last modified July 27, 2004 by University Communications