Africa Pays Another Visit to North America

Forrest M. Mims III

If you live in or have recently visited the Caribbean, Cuba, Mexico or the Southeastern United States and have noticed that the sky has been hazier than usual, you may have been seeing dust from Africa.

African dust has been blowing across the Atlantic for millennia. I've been measuring it indirectly by means of sun photometry since 1990. In 2001 my daughter Sarah used crossed polarizers and a $30 microscope to verify that dust she collected on filter paper and microscope slides was not from Texas. She used satellite images to prove the dust had come from the Sahara Desert. This research earned her some major science awards, and led to her discovery (also see here) that smoke arriving in Texas from Central America is loaded with living fungal spores and bacteria.

Recently a huge cloud of dust from the Sahara Desert blew over the Atlantic Ocean west of Africa. The cloud was twice the size of the United States! The same trade winds that blow hurricanes across the Atlantic carried the dust cloud to the Caribbean and then on to the Gulf of Mexico.

The dust cloud blanketed the Caribbean, Cuba, Florida, Mexico and South Texas. It caused brilliant, red sunsets and colorful twilight displays. Most of the cloud stayed south of San Antonio, but some reached at least as far as my Geronimo Creek Observatory.

The good news about Sahara dust is that it provides nutrients for various plants. It is especially important to epiphytes, plants such as bromeliads that live on the trunks and branches of trees. Some scientists believe that epiphytes in South America depend on Sahara dust for their iron supply.

Sahara dust also forms a major part of the soil of islands in the Caribbean. It forms a small part of Florida and Texas soil. It even covers the floor of much of the Atlantic between North Africa and Central and South America.

The down side of African dust is that it causes asthma problems for people who inhale large amounts of it. This is especially true for people of the Caribbean.

Sahara dust is more than its name suggests, for it also comes with mold spores and bacteria. Some research shows that certain spores in the dust may be harmful to coral.

It’s quite possible that the mold spores in the dust may be responsible for the asthma attacks for which the dust itself is blamed.

As my daughter Sarah has so ably shown, Sahara dust is a great topic for high school science fair projects. If you are a student looking for a project, keep your eye on the sky and begin preparing your project before summer is over. If you live in the Southeastern U.S., chances are you'll be visited by Africa before summer is over.

Colorful twilights are your clue that Sahara dust is in the air. So make the most of it and join those who have earned scholarships and many awards for their studies of these annual African visitations.

Forrest M. Mims III and his science are featured online at www.forrestmims.org.

This feature was originally published in Forrest Mims's weekly science column in the Seguin Gazette-Enterprise, Seguin, Texas. The column is written for a general audience.