When the desert winds kick up, there is no saying where the sand will come to rest. More than likely, it will be thousands of miles away.
Two NASA satellites, named Aqua and Terra, are proving that. If you look at their images — including the one above, which was released today — they show brown swirls in the Atlantic off the coast of Africa.
Scientists say those are not clouds; that is dust from the Sahara desert. Giant sand storms — often larger than Spain — routinely blow all the way across the Atlantic, reaching South America, the Caribbean, and the southeastern United States.
"There have been times when airports in the Caribbean have been closed down for lack of visibility from these dust storms," said Eugene Shinn, a senior geologist at the U.S. Geological Survey in St. Petersburg, Fla. "It shows we're all linked together in one way or the other, that's for sure."
It is a global phenomenon. Windstorms in China have darkened cities in Australia; dust from Mongolia has turned up in Denver.
Shinn has made it his life's work to find out what's in that dust, and what it does to us. You would be surprised, he said.
"It's a complete chemical soup," said Shinn."It's full of living microbes, it has a little mercury in it, small bits of arsenic, you name it, it's in there."
Shinn and his colleagues surprised their fellow scientists two years ago, when they published a study showing that bacteria and fungi could survive transoceanic trips in the upper atmosphere. Apparently, they ride on grains of sand, carried by winds to altitudes of 10,000 feet or more — where many scientists believed they would be killed off by the ultraviolet rays of the Sun. Shinn's team, though, placed dust traps in the U.S. Virgin Islands — and found living microbes that normally grow only in Africa.
This could have serious consequences for human health. Shinn points out that asthma rates on the island of Barbados have increased 17-fold in the last 30 years; the dust from Africa may explain it.
Biologists further suspect the dust may be responsible for damage to coral reefs off the coast of Florida; the coral has no immunity to diseases that settle in the water, carried from places thousands of miles away.
Two Billion Tons a Year
But the dust is also an essential part of life on Earth. Two billion tons of it routinely cross the oceans every year, so much that it's become part of nature's routine.
"African dust blows over almost on a daily basis during our summer, falling in the Caribbean," says Dale Griffin, a microbiologist at the U.S. Geological Survey. "A good number of the plants in the upper canopy of the Amazon rainforest derive all their nutrients from African dust."
As one scientist said, the whole planet is intermixing. If you see a truly spectacular sunset, you may be able to thank a distant desert.