Every year, dust from the Sahara Desert in Africa travels across the Atlantic Ocean to the Americas, and it is vitally important to our global ecosystem. The nutrient-rich Saharan dust, abundant in phosphorus, nourishes the ocean's phytoplankton and algae, while also acting as a natural fertilizer for the lush Amazon rainforest. That same dust also gets into swimming pools.
Covered in this article:
- The geological history of the Sahara Desert
- How Saharan dust travels across the Atlantic
- Understanding Saharan dust
- The importance of phosphorus in our global ecosystem
- Saharan dust in swimming pools
- Conclusion
The Geological history of the Sahara Desert
The Sahara Desert, the largest hot desert on Earth, boasts a geological history that dates back millions of years.1 Once a region with lush vegetation and abundant water bodies, it underwent significant climatic shifts that led to its current arid state. The transformation began around 7 million years ago, as tectonic movements altered atmospheric patterns.2 Over millions of years, changes in the Earth's orbit and tilt resulted in natural cycles of greening and aridification.
The landscape of the Sahara today is a vast continent of sand dunes and some rocky plateaus. But underneath the surface lies a history of vast freshwater lakes and rivers that once supported abundant life. The main body of water was known as the Tethys Sea, during the late Miocene epoch over 4.5 million years ago.3 Today, the Sahara is still growing, as evidenced by massive freshwater lakes receding into history. Namely, The Bodélé depression of Lake Chad, which is about 5% of its original size, according to NASA.4
The Sahara Desert's sand is not ordinary sands when compared to the beaches we are used to. Indeed, these sands are much older, worn down, and rich in minerals that reveal its history.5 Because of this, the Sahara Desert is a great case study demonstrating the dynamic nature of our planet's climate and geology over time.
How Saharan dust travels across the Atlantic Ocean
Credit: Discover Magazine (photo from NASA, June 18, 2020, DISCOVR Satellite)
For this, we look to NASA. They conducted an amazing study using satellites to track the dust in the air and model how it moves across the Atlantic Ocean.6 Here's their video explaining it:
Just how much Saharan dust is picked up by the wind?
According to NASA, an estimated 182 million tons of dust can be picked up by the wind and transported across the Atlantic. That's roughly equivalent to about 689,290 semi trucks filled with dust.
From NASA's website:
"The data show that wind and weather pick up on average 182 million tons of dust each year and carry it past the western edge of the Sahara at longitude 15W. This volume is the equivalent of 689,290 semi trucks filled with dust. The dust then travels 1,600 miles across the Atlantic Ocean, though some drops to the surface or is flushed from the sky by rain. Near the eastern coast of South America, at longitude 35W, 132 million tons remain in the air, and 27.7 million tons – enough to fill 104,908 semi trucks – fall to the surface over the Amazon basin. About 43 million tons of dust travel farther to settle out over the Caribbean Sea, past longitude 75W.
Yu and colleagues focused on the Saharan dust transport across the Atlantic Ocean to South America and then beyond to the Caribbean Sea because it is the largest transport of dust on the planet.
Dust collected from the Bodélé Depression and from ground stations on Barbados and in Miami give scientists an estimate of the proportion of phosphorus in Saharan dust. This estimate is used to calculate how much phosphorus gets deposited in the Amazon basin from this dust transport." 6
The study cited in that same NASA article calculates that out of the estimated 182 million tons of dust in the atmosphere, there is about 22,000 tons of phosphorus that reaches the Amazon rainforest.
Flying across the Atlantic
The transatlantic journey of Saharan dust is facilitated by a meteorological phenomenon known as the African Easterly Jet.7 This wind pattern originates from the temperature contrast between the hot, dry Sahara and the cooler, wetter regions to the south. In the summer months of the Northern Hemisphere, these winds gain strength and elevate the dust high into the atmosphere.
Once airborne, the Saharan dust is carried westward across the Atlantic Ocean by the trade winds. The journey can take several days to a couple of weeks, and the dust can travel as far as the Caribbean, the Amazon Basin, and even the southeastern United States.8,9 The frequency and intensity of these dust events can vary from year to year, influenced by broader climatic patterns such as the North Atlantic Oscillation and El Niño Southern Oscillation.10
These same wind patterns are related to why the Hurricanes that originate in the Atlantic and Caribbean tend to always move in the same general direction toward Florida and the Southeastern United States. The Caribbean islands are in the middle of not only the hurricanes, but the Saharan dust as well. It should also be noted that Saharan dust doesn't only travel westward across the Atlantic. It affects surrounding regions in all directions, depending on the winds, especially the Eastern Mediterranean areas.11
To better understand the impact this dust has on the global ecosystem, we need to know what it's made of.
Understanding Saharan Dust
Saharan dust is more than just finely ground sand; it is a complex mixture of minerals and organic matter. Some of it consists primarily of quartz, feldspar, and clay minerals, with traces of gypsum and calcite. The dust is also rich in nutrients, namely iron and phosphorus, which are essential for marine and terrestrial ecosystems.
The formation of Saharan dust's mineral composition is a result of geological forces that have shaped the desert terrain for millions of years. Through the processes of weathering and erosion, rocks are gradually ground down into dust. These tiny fragments are then sifted and carried by the wind, eventually coming together to form the ethereal dust clouds that travel across the globe in the atmosphere.
Geology is a slow but steady process. The Sahara looks the way it does thanks to millions of years of wind and friction grinding this landscape into a vast desert of sand and dust. It's hard to comprehend.
The importance of phosphorus in our global ecosystem
It's a good thing this dust travels, however. It may seem like pollution when you look at the satellite images of the Saharan dust cloud, but this dust plays a vital role in fertilizing the Amazon rainforest and feeding algae and phytoplankton in the ocean; both of which are massive consumers of carbon dioxide.
Both phosphorus and iron play a crucial role in the nutrition of phytoplankton in the Caribbean Sea.12 These microscopic plants form the base of the marine food web and are pivotal in carbon cycling. Phosphorus acts as a fertilizer, stimulating phytoplankton and algae blooms that can increase biodiversity and support fish populations.
Beyond the ocean, when Saharan dust settles on the lush canopy of the Amazon rainforest, the phosphorus replenishes nutrients that are annually washed away by heavy rains. This transcontinental nutrient transfer is a remarkable natural phenomenon that sustains the productivity of one of the world's most biodiverse regions, highlighting the interconnectedness of our global ecosystem.
Saharan dust in swimming pools
An Orenda Customer in Grenada (a Caribbean island near South America) reached out to us in 2024 about Saharan Dust and other issues with his swimming pool. This image shows Saharan dust in a rain puddle on his lounge chair. Rain takes dust out of the sky. Photo used with permission. Credit: Ben Unger
While Saharan dust nourishes the rainforests and phytoplankton, it also complicates pool chemistry. Not only can this dust cloud the water and increase filter pressure, the composition of the dust leads to bigger issues too.
The iron in the dust is likely to increase chlorine demand as it gets oxidized, and can lead to staining. The organic components of the dust can also lead to brownish red staining. The sooner you can get this dust out of the pool, the easier it will be to manage.
Dealing with phosphates is simple. Phosphate removers like PR-10,000 will easily remove them from the water. By its very nature, however, phosphate removal is a reactive strategy. It doesn't make sense to put phosphate remover in before the phosphates arrive.
Enzymes, however, are a proactive strategy that you can use before the dust arrives. Having a residual of CV-600 or CV-700 enzymes in the pool will be very helpful for managing carbon that makes it into the water.
The chemistry strategy we recommend is identical to how we manage pools near wildfires, which have phosphate and carbon-rich soot and ash traveling hundreds of miles. It's also similar to how we recommend handling desert dust storms in Arizona (called Haboobs). While we don't know the exact chemical makeup of desert sands in Arizona, they still create challenges in pool care.
For all three of these situations, nothing will replace the importance of physically cleaning the dust/debris out of the pool and filter. This means vacuuming to waste, cleaning the filter(s) thoroughly, and using a leaf blower to get the dust on the ground away from the pool.
Regular maintenance is key. Additionally, pool owners may consider protective coverings during peak dust seasons to minimize contamination and reduce cleaning efforts. It should be noted, however, that automatic pool covers will have dust on top of them, which will still get into the pool due to how these covers roll up. The top of a pool cover comes in contact with the bottom side as it rolls up into a reel.
Conclusion
While Saharan dust can make pool care more complex, its trans-Atlantic journey is essential to our global ecosystem. There's nothing we can to do stop it; we just have to deal with it. In that way, it's similar to wildfires Western North America each year (many of which are naturally ignited by lightning), and Haboob dust storms in Arizona.
Managing Saharan dust is similar to managing wildfire soot and ash and other nutrient-rich debris that might get in the pool. CV-600 and CV-700 Enzymes are a phenomenal proactive defense to manage carbon that may get in the pool, and PR-10,000 will effectively remove the phosphates from the water after the fact. But nothing will replace the need to physically clean the pool and filters. We recommend using a leaf blower to blow the dust as far away from the pool as you can (don't worry, the grass and flowers will love it).
1 While researching this topic, we learned that we need to specify the Sahara is the world's largest hot desert, because technically Antarctica is also considered a desert, and it's larger than the Sahara. The arctic is also considered a desert, even though it's not one cohesive landmass.
2 Zielinski, S. (2014). The Sahara is Millions of Years Older than Thought. Smithsonian Magazine.
3 Zhang, Z., Ramstein, G., Schuster, M., Li, C., Contoux, C., Yan, Q. (2014). Aridification of the Sahara Desert caused by Tethys Sea shrinkage during the Late Miocene. Nature, 513, pp. 401-404.
4 NASA Earth Observatory (2004). Dust Storms from Africa's Bodélé Depression.
5 Rocha-Lima, A., Vanderlei Martins, J., Remer, L., et.al. (2018). A detailed characterization of the Saharan dust collected during the Fennec campaign in 2011: in situ ground-based and laboratory measurements. Atmospheric Chemistry and Physics. Vol. 18, pp. 1023-1043.
6 Garner, R. (2015). NASA Satellite Reveals How Much Saharan Dust Feeds Amazon's Plants. NASA.gov.
7 Bercos-Hickey, E., Nathan, T. R., & Chen, S. (2020). On the Relationship between the African Easterly Jet, Saharan Mineral Dust Aerosols, and West African Precipitation. Journal of Climate, 33(9), pp. 3533-3546.
8 NASA SVS (Retrieved 2024). Dust from Africa leads to large toxic algae blooms in Gulf of Mexico, study finds. NASA.gov.
9 Segal, R., Tucker, R. (2024). Huge Saharan dust plume reaches parts of US. Fox59 News.
10 El Niño and other Oscillations. Woods Hole Oceanographic Institution.
11 Athanasopoulou, E., Protonotariou, A., Papangelis, G., Tombrou, M., Mihalopoulos, N., Gerasopoulos, E., (2016). Long-range transport of Saharan dust and chemical transformations over the Eastern Mediterranean. Atmospheric Environment. Vol. 140, pp. 592-604.
12 Iron Fertilization. Woods Hole Oceanographic Institution.