ORLANDO, Fla. – It happens every year: dust from the Sahara Desert in Africa gets lofted thousands of feet into the sky and gets blown across the Atlantic by the trade winds.
While this is a yearly occurrence, typically seen in June or July, this round of dust that has moved through the Caribbean and is impacting the parts of the U.S. is abnormally thick and large. The dust is most known for producing vibrant sunrises and sunsets while also limiting tropical development when present, but there are several more positive and negative impacts from the dust.
Saharan dust and red tide
This is the potentially ugly side of Saharan Dust. Red tide is a harmful algae bloom that develops in the Gulf of Mexico nearly every summer. This bloom is created by microscopic algae that produce toxins that kill fish and make shellfish unsafe to eat. The surrounding air around the bloom can also become harmful for humans to breathe.
A National Oceanic and Atmospheric Association and NASA study in 2001 showed that dust clouds coming off of the Sahara Desert can carry iron into the Gulf of Mexico. That iron promotes the growth of a plant-like bacteria called Trichodesmium. Trichodesmium then creates nitrogen which Karenia brevis, the red tide algae, can use.
"Blooms can get quite large and easily visible," says Dr. Vince Lovko of the Mote Marine Laboratory in Sarasota. "In the low nutrient offshore waters, a Trichodesmium bloom brings new nitrogen into the water. As the bloom dies and decomposes in this region, nitrogen compounds are released, including more complex nitrogen compounds, such as amino acids, that K. brevis is capable of using. Therefore, these degrading Trichodesmiun blooms may be a source of nitrogen for K. brevis blooms."
With more biologically usable nitrogen present in the Gulf of Mexico, the environment becomes better for toxic algae.
Dr. Rick Stumpf, an oceanographer with NOAA’s National Centers for Coastal Ocean Science, notes that while this is a source of nitrogen in the Gulf of Mexico, there are many sources and Karenia brevis can use most of them.
A study by NCCOS in 2008 showed that while some years with a lot of dust had large red tides, other dusty years did not. Some large red tide years have also occurred without any Saharan dust.
Poor air quality & dirty rain
The dust typically hangs out anywhere from 5,000 feet to 20,000 feet above the ground. Rain, thunderstorms and gusty winds can bring some of this dust down to the surface, aggravating allergies and impacting those with respiratory ailments. Air quality when the dust is thick could become unhealthy for sensitive groups.
Some of the raindrops could also contain the dust leaving dirty marks on your car or porch furniture when the raindrops evaporate.
When the sun is low on the horizon in the morning and evening, the sun’s rays have to travel through more of the Earth’s atmosphere. The light scatters more, producing beautiful red, orange and pink colors in the sky. When small dust particles are introduced, more scattering takes place, enhancing the already vibrant colors.
Limits tropical development
The tropics don’t completely shut down when the dust is around, but it certainly makes development much more difficult. Dry air and increased wind shear are the main characteristics of the Saharan Air Layer, the official name of the cloud of Saharan dust. Tropical systems need ample moisture and a relatively calm environment to develop and thrive.
Amazon rainforest fertilizer
The dust cloud contains phosphorous, among other things, which is then transported more than 5,000 miles across the Atlantic often settling in the Amazon. The phosphorous helps to fertilize the soil in the rainforest.
Saharan dust is the ultimate catch 22, bringing significant positives and potentially some negatives as it makes its yearly trans-Atlantic journey.