by The dust carried from the Sahara Desert provides a crucial nutrient to life at the bottom of the marine food chain. Without the iron carried far and wide by this mineral cloud, oceanic phytoplankton would struggle to thrive.
According to a new study led by the University of California, Riverside, the longer it stays in the atmosphere and the further it travels, the iron is converted into a form that is easily accessible to the biosphere below.
“The transported iron appears to stimulate biological processes, just as iron fertilization can influence life in the oceans and on continents,” say biogeochemist Timothy Lyons. “This study is a proof of concept and confirms that iron-bound dust can have a major impact on life at large distances from the source.”
Arid desert dust from North Africa is the largest source of airborne particles on Earth. Every year, winds move about 800 million tons of it westward, all the way to the Americas, carrying with it isotopes of iron scoured from the desert’s exposed surface.
The metal plays a crucial role in biochemical pathways that convert carbon in the atmosphere into organic molecules. However, as essential as iron is to life, its availability is limited, meaning the distribution of this nutrient largely determines where life is found on Earth.
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Not all forms of iron are easy for living organisms to use. Conditions in the atmosphere can make a big difference to the iron menu that eventually settles on the ocean surface.
“Dust reaching regions such as the Amazon Basin and the Bahamas may contain iron that is particularly soluble and available to life, thanks to its great distance from North Africa, and thus longer exposure to atmospheric chemical processes,” Lyons explains.
Biogeochemist Bridget Kenlee and colleagues discovered this by analyzing drill cores from the bottom of the ocean. They found that although the total amount of dust decreased with transport distance, the amount of biologically useful iron that dissolved in water actually increased with that distance.
“This relationship suggests that chemical processes in the atmosphere convert less bioreactive iron into more accessible forms,” says Owens.
With its heavy mass of bioactive iron, the dust feeds a vast food chain thousands of kilometers from its origin, fertilizing ocean phytoplankton and plants as far away as the Amazon. These two systems produce much of the oxygen we all breathe.
Previous studies have suggested that these patterns of bioactive iron correspond to areas of increased biological activity. This includes increased microbe activity at the surface of Caribbean coral reefs and fertilization of the Amazon.
A seven-year study found that an average of 28 million tons of North African dust also supplies the Amazon River basin with about 22,000 tons of fertilizing phosphorus.
Other research has found that dust from Asia has fertilized Hawaii’s rainforests for millennia.
The Saharan dust clouds can also cause problems with their presence, such as causing allergies in people. They even have the power to smother hurricanes.
Despite the arid origins of this high-altitude soil and all the problems it could cause, grains from the Sahara Desert contain essential fuel for life on Earth, providing yet another example of how incredibly connected our planet’s physical processes are to the life that calls her home. .
This research was published in Frontiers in marine sciences.
