Carried by the winds over thousands of kilometers, Sahara dust plays an essential role in marine life in the Atlantic Ocean. Rich in iron, the chemical transformations it undergoes during its journey over the sea make this iron more readily available to marine organisms, particularly phytoplankton. A hitherto unsuspected impact, revealed by recent research.
By Laurie Henry
Cover photo: Saharan dust plume over the North Atlantic Ocean, June 18, 2020, via NASA-NOAA’s Suomi NPP satellite © NASA Worldview
Unexpectedly, dust from the Sahara could have a profound influence on ecosystems far beyond its point of origin. As it crosses the Atlantic, it appears to play a crucial role in enriching the oceans with iron, a micronutrient essential to certain biological functions (such as photosynthesis and respiration), but often limited.
Published in the journal Frontiers in Marine Science, the results of recent work by teams from the Universities of California at Riverside and Florida, in collaboration with the International Ocean Discovery Program (IODP), show how the chemical transformations undergone by the iron contained in this dust make it more accessible to phytoplankton.
Iron, an essential biological driving force
To understand how Saharan iron, transported over long distances, becomes bio-reactive, the researchers undertook an in-depth analysis of sedimentary cores from four strategic sites in the Atlantic. These cores, extracted as part of the International Ocean Discovery Program (IODP), represent up to 120,000 years of dust deposits, making it possible to trace variations in iron availability at different distances from the Sahara.
Samples were taken at increasing distances from the Sahara: two cores near the coast of Mauritania (200 and 500 km to the west), one in the middle of the Atlantic and one near the Bahamas, 500 km off the coast of Florida. Scientists analyzed total iron content and iron isotopes using plasma mass spectrometry.

Location of survey sites with iron data. The base map shows estimates of dust deposition, in particular the transport of African dust across the ocean surface. © T. W. Lyons et al., 2024
These analyses revealed a decrease in total iron concentration in sediments far from the Sahara. At the same time, by taking a closer look at the chemical forms of iron present in the sediments (notably compounds such as goethite, hematite and pyrite), they observed that these minerals, initially non-bio-reactive, undergo geochemical modifications during their atmospheric transport. Altered by humidity, temperature variations and interactions with atmospheric compounds (such as sulfuric or nitric acids), these iron particles are transformed into more soluble forms that can be assimilated by phytoplankton.
Phytoplankton at the heart of the carbon cycle
Phytoplankton are single-celled organisms at the base of the marine food chain. Every year, it is estimated to capture around 40% of the atmospheric CO₂ produced by human activities, according to researchers’ estimates. Its growth depends on the availability of iron, which is often limited in the oceans. In this context, bio-reactive iron from Saharan dust is an essential resource for its development. “ This iron directly stimulates the proliferation of phytoplankton, which boosts the productivity of marine ecosystems and supports the global carbon cycle,” explains Dr. Timothy Lyons of the University of California, Riverside.
Analyses of sediment cores show a clear correlation between the distance travelled by dust and the use of iron by marine organisms. In areas such as the Bahamas, more than 5,000 kilometers from the Sahara, a significant proportion of Saharan iron is assimilated by suspended phytoplankton. Only 30% reaches the ocean floor. Near the Sahara, however, this percentage rises to 70% of iron. “ These data confirm that Saharan iron is not just transported over long distances, but actively supports marine life and influences carbon sequestration processes in the oceans,” concludes Dr Lyons.”

(A) African dust transport over the North Atlantic in summer (JJAS) and winter (DJFM), illustrated by aerosol optical depth (AOD), a measure of the amount of particles in the atmosphere. (B) Iron flux modeled with ecoGEnIE, showing dust transport from Africa to the Atlantic (gray arrow). T. W. Lyons et al. 2024
Analyses of sediment cores show a clear correlation between the distance travelled by dust and the use of iron by marine organisms. Near the Sahara, up to 70% of iron reaches the sediments. By contrast, in remote areas such as the Amazon basin, this proportion drops to less than 30%, indicating massive iron uptake by suspended phytoplankton. “ These data confirm that Saharan iron is not simply transported over long distances, but actively supports marine life and influences carbon sequestration processes in the oceans,” concludes Dr. Lyons.
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The discovery of the crucial role played by Saharan dust in enriching the oceans with bio-reactive iron offers a new perspective for climate modelling. Phytoplankton, thanks to their ability to fix amospheric carbon dioxide (CO₂) in their biomass, play a central role in the carbon cycle. Once dead, these organisms sink to the ocean floor, taking organic carbon with them, a process known as the “biological pump”. By integrating data on the influence of Saharan dust on phytoplankton blooms, climate models will now be able to more accurately estimate the amount of CO₂ sequestered in the oceans. According to this new study, variations in Saharan dust deposits, dictated by winds and climatic conditions, could significantly alter carbon fluxes on a planetary scale.

Simplified oceanic iron cycle. (A) Saharan dust rich in oxides and silicates. (B) Transport by wind, fine particles travel far. (C) Atmospheric processes increasing solubility (FeSol). (D) FeSol is used by phytoplankton or precipitates rapidly.(E) Nearby areas: high FeSol in sediments. (F) Remote areas: FeSol reduced by biological assimilation. © T. W. Lyons et al., 2024
The researchers also point out that large-scale natural processes, such as atmospheric dust transport, need to be included in climate forecasts to reduce uncertainties. “ These results clearly show that elements such as Saharan iron have a major impact on the productivity of marine ecosystems and, by extension, on global climate,” explains Dr Timothy Lyons. Indeed, the increased bioaccessibility of iron promotes interconnected ecological and climatic dynamics. Integrating these data into existing models could provide more reliable forecasts of climatic responses to natural and anthropogenic variations in biogeochemical cycles.
Future prospects and challenges
This study highlights the need for further research, in particular to better understand the impact of climate change on these processes. Changes in wind and precipitation patterns, as a consequence of global warming, could alter the transport of Saharan dust, and consequently influence iron availability for marine ecosystems. These uncertainties call for a finer integration of these data into climate models to anticipate future developments in biogeochemical cycles.
These results also highlight the complexity of large-scale natural interactions. “ Deserts, often perceived as barren, play a vital role in providing essential nutrients to the oceans, demonstrating a global interconnectedness ,” recalls Dr Jeremy Owens of Florida State University. These scientific advances reinforce the idea that even seemingly isolated terrestrial processes, such as dust storms, directly influence ecological and climatic dynamics thousands of kilometers away. They also serve as a reminder of the urgent need for sustainable management of terrestrial ecosystems in the face of environmental challenges, to preserve this fragile balance that is essential to the functioning of our planet.
Source : Timothy W. Lyons et al., “Long-range transport of dust enhances oceanic iron bioavailability”, Frontiers in Marine Science (2024).