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.
Each year, an estimated two billion tonnes of dust is raised into the atmosphere; and one-quarter of this reaches the oceans.
What are some of the negative effects of sand and dust storms?
The fertilizing effect of desert dust is thought to have an impact on algal blooms, some of which can be harmful, and may contribute to Sargassum seaweed mats. Unusually large blooms of floating Sargassum seaweed have been noted since 2011 in parts of the Caribbean Sea and along the Atlantic coastlines of West Africa and Brazil. These drifting seaweed mats provide important habitat for many species in the open ocean, but close to shore, they can disrupt shipping, fishing and tourism.
Potential links have also been identified between microorganisms, trace metals and organic contaminants carried in desert dust and some of the complex changes on coral reefs observed in numerous parts of the world. Disease has undoubtedly been an important factor in recent coral reef declines worldwide and several of the diseases that affect corals are associated with microorganisms carried in desert dust.
A wide variety of microorganisms—including fungi, bacteria and viruses—has been found in desert dust. Most of these pathogens come from dryland soils and are highly resistant to desiccation, temperature extremes, conditions of high salinity and exposure to ultraviolet radiation. They are therefore typically able to survive in the atmosphere for many days.
Do sand and dust storms play a role in transporting diseases like COVID-19?
We still have numerous basic questions to answer regarding these desert-derived bioaerosols. It is thought that many of the microorganisms transported in desert dust are capable of causing disease outbreaks in a wide range of organisms, both terrestrial and marine, but we have little data on specific microbes found in dust storms known to cause disease in people and animals.
How does this report contribute to existing knowledge about sand and dust storms?
While our understanding of the dust cycle has improved greatly in recent decades, large uncertainties and knowledge gaps remain. Nonetheless, this knowledge has significant implications for a number of Sustainable Development Goals – particularly Goal 14 on Life Below Water and Goal 15 on Life on Land.
Marking the start of the United Nations Decade of Ocean Science for Sustainable Development (2021–2030), this report explores the impacts of sand and dust storms on oceans—their ecosystem functions, goods and services—which are potentially numerous and wide-ranging. Sand and dust storms thus warrant continued careful monitoring and research.
For more information, please contact Maarten Kappelle: maarten.kappelle@un.org
