The Sahara dust plume regularly headlines headlines as it sweeps across the sky, coloring it with orange hues as winds push dust southward. This phenomenon affects infrastructure by lowering solar power generation and can trigger respiratory issues in people. New scientific work tracks how radioactive elements ride along with the dust as it settles on territories including Spain and other parts of Europe.
Europe faced a notable dust episode in February 2021, prompting a civic science effort focused on snow regions such as the Pyrenees. Volunteers and scientists gathered snow samples to understand how dust travels through mountain environments. The campaign was guided by researchers from major European meteorological institutions in France and involved a collaboration with community participants to map dust deposition in high-altitude snowpacks.
Across the European Pyrenees and the Alps, from sea level up to elevations around 2,500 meters, researchers collected multiple snow samples. Melted material from each sample was sent to laboratories for filtration and drying before analysis of powder particles. The effort spanned hundreds of kilometers and encompassed a diverse range of alpine settings to capture the full extent of dust deposition during the event.
The study, published in Earth System Science Data, reports that a total of 152 snow samples were gathered from 70 sites over four weeks. The observed powder volumes varied widely, influenced by distance from the Sahara. Heavier, larger particles tended to deposit closer to the dust source, while the wind carried finer material farther into the mountains, explaining a gradient in particle size with distance from the desert.
Powder composition shifts with distance
Because deposition patterns differ with proximity to the dust source, the chemical makeup of the powder changes across the study area. Iron-rich particles were found to be more concentrated closer to the Sahara, with about 11 percent iron detected in samples from the Pyrenees, dropping to roughly 2 percent iron in the Swiss Alps farther north.
Dust accumulation in icy and snow-covered ecosystems can alter albedo, darkening the surface and reducing reflectivity. This leads to more solar absorption, warming, and faster snowmelt. A similar mechanism occurs when dark clothing absorbs more heat, contrasting with white materials that reflect sunlight and help keep wearers cooler. In a notable example, a 2018 dust event shortened the snowy season by as much as thirty days in some places.
Elements of concern: cesium, beryllium and lead
The February 2021 haze prompted widespread media attention about radionuclides in the dust, with references to historical nuclear activities in the Sahara region. The researchers verified this concern by analyzing sediment and snow samples from the Pyrenees, where elevated levels of cesium and certain short-lived radionuclides were detected. Increased concentrations of beryllium and lead were also observed, consistent with fallout patterns linked to atmospheric dust and recent snowfall carrying those contaminants.
The study noted that plutonium levels did not show a notable deviation from background concentrations typically observed in the northern hemisphere due to earlier tests conducted during the mid-20th century. The authors suggested that differences in fuel and engine types could influence the nuclear footprint detected in these dust episodes, potentially distinguishing the Sahara dust signature from other regional sources.
The team highlighted that cesium and lead signals seen in the Sahara align with global fallout patterns from historic tests by major world powers, rather than representing a unique French signature. These findings reflect the complex mix of dust origins and historic contamination that can accompany large-scale dust transport events.
Scientists emphasize that the French nuclear tests in the Sahara carried only a fraction of the power of earlier tests by the United States and the Soviet Union, underscoring that the measured signatures are the result of widespread, long-range atmospheric processes rather than a single national action.
The researchers call for continued work to assess how the expected increase in dust events could influence water resources, snow and ice dynamics, avalanche risk, and the management of ski resorts. Ongoing monitoring and modeling are needed to understand the future impacts on alpine hydrology and winter tourism infrastructure.
Reference work: essd.copernicus.org articles 15 3075 2023
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