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On the launch of the report, Impacts of Sand and Dust Storms on Oceans: A Scientific Environmental Assessment for Policy Makers, author and University of Oxford lecturer, Nick Middleton discusses how the dust cycle affects and interacts with other global-scale biogeochemical cycles.

What exactly are we talking about when we refer to the “dust cycle”?

The dust cycle describes the movement of trillions of tiny particles through the Earth System. Sand and dust is raised by strong winds from areas of bare or sparsely vegetated ground. While some of this material falls back to the surface near the source, the smaller dust particles are carried further in the wind – sometimes thousands of kilometres – before being deposited.

Each year, an estimated two billion tonnes of dust is raised into the atmosphere; and one-quarter of this reaches the oceans.

Is this movement regular and predictable?

These long-distance dust flows are highly seasonal and can vary significantly from year to year.  But most dust comes from deserts and semi-deserts, and a particularly dusty area known as the Dust Belt stretches from the Sahara across the Middle East to the deserts of Central and Northeast Asia.

The planet’s largest sources are in the Sahara. Much Saharan dust is transported south-westward by the Harmattan wind that prevails between November and April. This dust has marked effects on the North Atlantic and the Caribbean Sea, but Saharan dust also impacts the Mediterranean Sea and the Red Sea.

What role do sand and dust storms play in a healthy ecosystem?

Desert dust particles consist of minerals, nutrients, and organic and inorganic matter. Dust plays a role in a range of Earth’s physical, chemical and bio-geological processes, and interacts with the cycles of energy, nitrogen, carbon, and water. All are necessary for Earth system functions.

How do they affect ocean ecosystems? 

Dust carries nutrients such as phosphorus, and trace metals—including iron, manganese, titanium, aluminium—to oceanic ecosystems, elements that are essential for all life forms. In this way, desert dust is a principal driver of oceanic primary productivity, which forms the base of the marine food web.

Marine primary production also fuels the global carbon cycle via the exchange of CO₂ between ocean and atmosphere, so desert dust has impacts on our climate system. Dust also provides some of the building blocks for coral reefs: dust particles are incorporated into coral skeletons as they grow.

Desert dust also provides the primary external source of iron to offshore waters, but controls on iron aerosol solubility are poorly understood. Iron is required for phytoplankton growth, but the iron must be in a form that can be used by living organisms, which is dependent partly on its solubility. Hence, our understanding of how the dust cycle interacts with the iron cycle is critical for our understanding of marine productivity, and hence biodiversity in the oceans.