May 05, 2004
Phytoplankton May Partially Limit Global Warming

Dr. David A. Siegel of the University of California, Santa Barbara Institute for Computational Earth System Science and Dierdre Toole now at the Woods Hole Oceanographic Institution have demonstrated with their research on the Sargasso Sea southeast of Bermuda that a gas released by phytoplankton causes cloud formation and reduces the amount of sunlight reaching the Earth.

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.

Ultraviolet radiation causes the phytoplankton to release DMS.

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 environmental stresses, in much the same way as our bodies use vitamins E and C to flush out molecules that cause cellular damage.

Siegel and Toole found that ultraviolet radiation explained almost 90 percent of the variability in the biological production of DMS. They showed that summertime DMS production is "enormous," and that the entire upper layer of DMS content is replaced in just a few days. This demonstrates a tight link between DMS and solar fluxes.

"The significance of this work is that it provides, for the first time, observational evidence showing that the DMS-anti-oxidant mechanism closes the DMS-climate feedback loop," said Siegel. "The implications are huge. Now we know that phytoplankton respond dramatically to UV radiation stresses, and that this response is incredibly rapid, literally just days."

The effects of ozone layer thinning will be partially offset by an increase in cloud cover caused by increased DMS release.

As the Earth's ozone shield thins and greenhouse gases increase, higher ultraviolet radiation will reach the surface layer of the oceans. The findings indicate that phytoplankton will then produce more DMS in response to this increased ultraviolet radiation, causing increasing cloudiness and mitigating the effects of global warming. However, Siegel is careful to note that while the process may mitigate global warming it will not reverse the trend.

Keep in mind that much of global warming is not caused by more ultraviolet light getting through the ozone layer. Carbon dioxide and methane work by reducing heat loss. However, if methods could be developed to increase phytoplankton production of DMS then the resulting cloud cover would still reduce the amount of warming.

Share |      Randall Parker, 2004 May 05 02:23 PM  Climate Trends

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