David Siegel, professor of geography at the University of California, Santa Barbara, and director of the Institute for Computational Earth System Science, made the discovery with his former Ph.D. student Dierdre Toole, who is now based at Woods Hole Oceanographic Institute.
In an article in the May 6 issue of the journal Geophysical Research Letters, the scientists explain their research in the Sargasso Sea, approximately 50 miles southeast of the island of Bermuda. Siegel's research group has been making observations at this location since 1992.
Phytoplankton are tiny, single-celled floating plants. They inhabit the upper layers of any natural body of water where there is enough light to support photosynthetic growth. They are the base of the ocean's food web, and their production helps to regulate the global carbon cycle. They also contribute to the global cycling of many other compounds with climate implications.
One of these compounds is a volatile organic sulfur gas called dimethyl sulfide or DMS. Scientists had previously theorized that DMS is part of a climate feedback mechanism, but until now there had been no observational evidence illustrating how reduced sunlight actually leads to the decreased ocean production of DMS. This is the breakthrough in Toole and Siegel's research.
They describe how the cycle begins when the ocean gives off DMS to the lower atmosphere. In the air, DMS breaks down into a variety of sulfur compounds that act as cloud-condensing nuclei, leading to increased cloudiness. With more clouds, less sunlight reaches the Earth and the biological processes which produce DMS are reduced.
According to their research, it appears that phytoplankton produce organic sulfur
compounds as a chemical defense from the damaging effects of ultraviolet radiation and other e
Contact: Gail Gallessich
University of California - Santa Barbara