As researchers dig into data about the Earth's distant past for clues about how the planet will change in the future, understanding the influence of desert dust -- soil particles in the atmosphere -- could provide an important piece of the puzzle.
In a talk at the annual meeting of the American Association for the Advancement of Sciences in San Diego Feb. 19, Natalie Mahowald, associate professor of earth and atmospheric sciences, said that the concentration of desert dust in the atmosphere could affect global systems including climate, precipitation, vegetation, ocean acidity and carbon dioxide levels.
Desert dust, which can be carried thousands of miles in the atmosphere, interacts with radiation and other elements as it travels; and it serves as a key source of vital nutrients such as iron when it lands. Using the first 3-D earth systems model to incorporate the carbon cycle and the limits to plant growth based on nitrogen availability, Mahowald and colleagues added historical and current data about desert dust and analyzed the resulting changes.
Data from polar ice cores show that dust accumulation has decreased by a factor of 10 to 20 since the last glacial maximum 20,000 years ago, Mahowald said, while cores from lower latitudes show a much more moderate decrease, suggesting a global change of a factor of three or four.
The researchers found that dust in the atmosphere has a modest impact on global climate, as well as on ocean productivity, and can have a large impact on regional climate and biogeochemistry.
In the Sahel region of North Africa in the late 20th century, for example, times of high atmospheric dust have correlated with times of drought.
"Mostly what people think drove this drought was sea surface temperatures off the coast in the North Atlantic, but we argue that dust could have also contributed as well," she said in an interview before her talk.
Meanwhile, low dust, and therefore low iron deposition, likely explains why certain ocean regions support less life than otherwise would be expected. Desert dust may also be an important source of phosphorous to tropical rain forests.
The current studies are not conclusive and will continue to be refined as more data is available, she noted. The researchers will also do similar analyses using other models (there are about 20 by different researchers around the world) to see which results remain consistent across models.
"Our main goal is to improve our projections of the climate going into the future and our understanding of what causes what," she said, "and understanding past and future regional changes requires inclusion of desert dust impacts."