Magazine article USA TODAY
Polluted Dust Storms Reduce Global Warming
A surprising link may exist between ocean fertility and air pollution over land, according to Georgia Institute of Technology, Atlanta, research, which provides new insight into the role that the sea plays in the complex cycle involving carbon dioxide and other greenhouse gases in global warming.
When dust storms pass over industrialized areas, they can pick up sulfur dioxide, an acidic trace gas emitted from industrial facilities and power plants. As the storms move out over the ocean, the sulfur dioxide they carry lowers the pH (a measure of acidity and alkalinity) level of dust and transforms iron into a soluble form. This conversion is important because dissolved iron is a necessary micronutrient for phytoplankton--tiny aquatic plants that serve as food for fish and other marine organisms as well as reduce carbon dioxide levels in Earth's atmosphere via photosynthesis. Phytoplankton carry out almost half of Earth's photosynthesis even though they represent less than one percent of the planet's biomass.
"I knew that large storms from the Gobi deserts in northern China and Mongolia could carry iron from the soil to remote regions of the northern Pacific Ocean, facilitating photosynthesis and carbon-dioxide uptake," reports Nicholas Meskhidze, a postdoctoral fellow at Georgia Tech's School of Earth and Atmospheric Sciences. "But I was puzzled because the iron in desert dust is primarily hematite, a mineral that is insoluble in high-pH solutions such as seawater. So, it's not readily available to the plankton."
Meskhidze examined how variations in air pollution and mineral dust affect iron mobilization. The differing--and surprising--results can be attributed to the concentration of sulfur dioxide existing in large and small dust storms, Meskhidze points out. Large storms are extremely alkaline because they contain a higher proportion of calcium carbonate. Thus, the amount of sulfur dioxide picked up from pollution is not enough to bring the pH down below 2--the level needed for mineral iron to convert into a dissolved form that would be available to phytoplankton. …