Saharan dust may be bad for our lungs but it also fertilises plant and ocean life

By Harriet Piercy

Published Dec 1, 2020 at 10:53 AM

Reading time: 4 minutes

A Saharan dust cloud may be bad for our lungs but it also fertilises plant and ocean life, which results in a double-edged sword like no other. The storms that are formed by Saharan dust are part of a regular meteorological phenomenon that sends dust from the Sahara Desert in Africa to the Gulf Coast of the US, the Caribbean and South America.

As if 2020 hadn’t brought enough extremities already, this year’s dust cloud, dubbed Godzilla, has proven to be particularly intense, in fact, the most dense cloud to have ever occurred on record. What is the natural purpose of this yearly event, and what health implications did Godzilla bring to humans in its wake?

What is a Saharan dust cloud?

A Saharan dust cloud is formed with a mixture of sand and dust from the Sahara Desert, which is the vast dry area that covers most of North Africa and the largest desert in the world outside of the poles. Wind can, and mostly does, blow strongly over deserts, which whips up dust and sand from the ground high up into the sky, at such high altitudes that it can be transported worldwide. The Sahel is a stripe of land just south of the Sahara that has more of a tropical climate, although also being hot and dry, it has a rainy season and develops dense vegetation.

A meteorologist at the University of Miami and a researcher at NOAA’s Atlantic Oceanographic and Meteorological Laboratory, Jason Dunion, told Vox that “Mother nature has really set up things in an interesting way over Africa, you’ve got the largest [hot] desert in the world, and then just south of that, you’ve got the hurricane nursery for the Atlantic. Over half the named storms that we get each year are coming from this nursery over the Sahel, just south of the Sahara.”

Much of the dust that is in these enormous clouds originates from an ancient dry lake bed at the threshold of the Sahara and the Sahel, the Bodele Depression in Chad. In the early summer, convective storms pick up dry ground and loft particles, sometimes up to 180 million tonnes, of silica, iron and phosphorus into the sky. When airborne, this same dust floats off the west African coast and forms what is called the Saharan Air Layer, which is a segment of the atmosphere that consistently moves every three to five days from the late spring through to early fall each year, across the North Atlantic Ocean. However, although this year’s storm was naturally expected, it wasn’t exactly as we expected. In fact, it was shocking enough to induce fear.

Why was the Saharan dust cloud of 2020 called Godzilla?

Ola Mayol-Bracero, an atmospheric chemist at the University of Puerto Rico checked the readings at the atmospheric observation station that she runs on the northeastern tip of the island, and the numbers were higher than anything the chemist had seen in the entire 16 years of working at the station. “I couldn’t see the sky or clouds, just a greyish layer,” she told National Geographic. “Definitely, we have never seen something like this.”

This year’s dust plume was particularly remarkable in its density. Dust and sand are lung irritative particles that cause disability and death, and 2020 brought significant amounts of it. Sand dunes, consisting of larger particles of sand, don’t usually provide the dust that these clouds carry as they require the fiercest of winds to pick them up, however the finer particles, more like dust, often collect into hollows or flats in the desert landscape that may at one point have held water.

These dust particles usually flood the sky thousands of feet above the ground, but this year it was much lower, meaning much closer to humans and the air that they breathe too. “The parameters we’re looking at have reached values we’ve never seen before, in terms of particulate matter,” says Mayol-Bracero. And the air quality across Puerto Rico became hazardous—even with the windows closed, the dust crept in with fog-like conditions.

Researchers are still unclear as to exactly why the recent Saharan dust cloud was so intense this year as there are so many factors at play. One atmospheric scientist, Colin Seftor told Vox that it may have had to do with the intense rainfall that occurred in the Sahel region in May and June, which potentially led to the local weather to whip up more dust, however, this is just speculation.

Another culprit could be strong tropical waves, which are perturbations in the tropical easterlies that typically move from east to west. They are significant rain producers and are often seen as inverted troughs of low pressure. These tropical waves develop into tropical cyclones.

Climate change provides scientists with an uncertain future trend when it comes to natural patterns and “If the meteorological conditions of the Sahel or even the Sahara change, and there’s more surface dust, it could change,” Seftor said, adding “How it will change, I don’t know.” Technological advances, such as a new generation of geostationary satellites, are allowing these scientists to monitor movements of these dust clouds in real time, which can only benefit human health. That being said, how are these increasingly intense dust clouds affecting our planet?

Why is Saharan dust a vital ingredient to our ecosystems?

Minerals in the dust that these Saharan clouds carry can trigger blooms of phytoplankton, which are microscopic organisms that live in watery environments, both salty and fresh. The importance of these tiny organisms serve as the foundation for many marine ecosystems, as well as being the food that feeds animals ranging from crustaceans to giant whales. Not only this, phytoplankton soak up an enormous amount of carbon dioxide much like plants do on land.

Around 27.7 million tons of these mineral particles also fall onto the Amazon rainforest basin every year, and of the dust that falls, roughly 22,000 tons is made up of phosphorus—a vital nutrient for soil. Without this yearly replenishment of minerals the Amazon rainforest would eventually wither. This is because most of the nutrients in the rainforest are concealed in plants rather than in soil, and what little is left in the ground gets washed away by the frequent rainfall and flooding. The regular Saharan sand deposition keeps this lush rainforest rich in biodiversity.

One of the more surprising effects of the Saharan dust is that it can suppress hurricanes by injecting dry air into the tropics, which form devastating hurricanes when the air is moist and warm. The Saharan air layer also rips storms apart with their sheer speed of up to 50 miles per hour, and the hot air breaks apart cloud formations in its wake as they need cooler air to condense moisture.

The real fascinating fact to remember is that the Earth has figured out how to keep itself alive and healthy, the atmosphere can transport and transfer the minerals it needs, when it needs to do so—effectively this transition of airs acts as a lung of the Earth, and climate change is drastically disrupting how healthily these systems function, which in turn directly affects us. This dust is dangerous: just imagine breathing in a sandstorm! We must change how we act in accordance with nature, as the only way we can heal our planet is to reverse what has harmed it in the first place. A healthy Earth is a common goal for both it and us.

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