It's not the dust, but the iron it contains that helps life thrive, and as the dust moves through the atmosphere, the components of the iron change. the further away from the Sahara the iron contained in the dust moves, the more available it is to marine life. This phenomenon, caused by chemical reactions in the atmosphere, has implications for the ocean ecosystem and carbon cycle projections.
The Sahara Desert in North Africa is the largest hot desert on Earth and the largest source of atmospheric mineral dust. It can be carried by winds over vast distances, with Saharan dust regularly crossing the Atlantic.
The mineral dust supplies important nutrients to the ecosystems in which it falls. In particular, iron is a trace element essential for life, as it enables key functions such as respiration, photosynthesis and DNA synthesis.
But not all forms of iron can be absorbed by living things - some are more bioavailable than others. To assess how the distance that Saharan dust has travelled has affected iron bioavailability, the US-based research team studied drill cores from four locations on the Atlantic seafloor.
"Instead of focusing on total iron content, as has been done in previous studies, we measured the iron that is readily dissolved in the ocean and that marine organisms have access to for their metabolic pathways," says Jeremy Owens, an associate professor at Florida State University and co-author of the study.
Owen and his colleagues measured the concentrations of iron isotopes in the cores of the drill holes with a plasma-mass spectrometer. The collected drill cores are deep enough to reflect 120,000 years of Saharan dust deposition.
Their results show lower iron concentrations in cores located farther from the Sahara, suggesting that marine organisms took up more iron at these sites.
"We conclude that the dust that reaches regions like the Amazon Basin and the Bahamas may contain iron that is particularly soluble and available to life due to the long distance from North Africa, and hence the longer exposure to atmospheric chemistry," says Timothy Lyons, a professor at the University of California, Riverside, and senior author of the study.
In ocean ecosystems, iron is often a limiting resource, meaning that additional iron leads to population increases in organisms such as phytoplankton. Understanding its population dynamics will improve predictions for marine ecosystems that depend on phytoplankton, sometimes called the 'grass of the sea'. | BGNES
