Promising Global Warming Solution Possibly Flawed

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New Mexico Tech chemistry professor Oliver WingenterÂ?s research findings concerning gases produced or consumed by ocean-dwelling, single-cell algae known as phytoplankton have raised doubts about plans to use the marine microorganisms to remove, or "sink", carbon dioxideÂ?a greenhouse gas that warms the EarthÂ?from the atmosphere into the deep ocean.

Wingenter was one of more than 70 scientists involved in the Southern Ocean Iron Enrichment Experiments (SOFeX) research expedition, the longest lasting and most comprehensive ocean iron fertilization experiment to date, which was carried out in January and February 2002 aboard three research ships in the Southern Ocean, between New Zealand and Antarctica.

The SOFeX expedition sought to test what has become known as "John Martin’s Iron Hypothesis," in which Martin suggested, before he passed away in 1993, that an increase in the flow of iron-rich dust from the world’s deserts to oceanic surfaces during glacial periods with iron caused phytoplankton populations to also increase in size. Similarly, deliberate iron fertilization could in theory increase phytoplankton "blooms", subsequently removing more carbon dioxide from surface waters, thus reducing the buildup of the greenhouse gas in the atmosphere.

During the SOFeX expedition, researchers tested the effectiveness of iron fertilization of ocean waters by adding an iron sulfate solution to two 100 square mile patches of the Southern Ocean to stimulate the growth of phytoplankton in those areas.

The experiments proved successful. Phytoplankton numbers rose quickly during SOFeX as a result of the alleviation of the iron deficiency and the area of the blooms spread to thousands of square kilometers, and were visible in satellite images. Raising the possibility that fertilization of the Southern Ocean with iron could cut in half the build up of carbon dioxide if the entire Southern Ocean south of 500 S latitude were fertilized with iron.

In addition, water samples taken by Wingenter during the SOFeX expedition showed marked increases in other climate-relevant gases produced by phytoplankton, most notably methyl bromide, which depletes the protective ozone layer at higher altitudes, and isoprene, a hydrocarbon that generates greenhouse gases and contributes to clouds seeding at lower altitudes, and methane an important greenhouse gas.

Dimethyl sulfide (DMS) increased by about 4 times. Emissions of DMS are the main source of sulfate particle formation to the region and seed much of the cloud formation in the region, Wingenter points out.

"If massive iron enhancements were to be carried out, the result would be a major cooling of the region because of increased DMS," Wingenter says. "Iron fertilization of the entire Southern Ocean could result in a ten to 20 percent decrease in sunlight to the area, possibly negatively impacting not only the Southern Ocean, but also summertime temperatures and agriculture in parts of Australia, New Zealand, South Africa, Chile, and Argentina."

Wingenter and his research colleagues involved in SOFeX first reported their preliminary findings in the December 2002 issue of Nature.

An updated article about their most recent findings is featured in this week’s issue of The Proceedings of the National Academy of Science. Wingenter and coworkers measured over 60 organic gases in water and air samples during SOFeX and will report further results in upcoming articles.


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Oliver Wingenter