Saharan Dust Helped Build the Bahamas

When some geologists look at the sandy beaches and coral reefs of the beautiful Bahamas, they don't just see the glorious marine life, colorful corals and a nice place for a dive. Looking deeper they can see how layers and layers of limestone were formed by the coral that inhabit these reefs, laying carbonate-rich structures over the past 100 million years. But these reefs present an enigma.

The ocean water surrounding the Bahamas is surprisingly nutrient poor, seemingly lacking a reliable local source of the iron and other minerals needed to keep the ecosystem thriving. For all their abundance, the rich seas don't make a lot of sense.

A new study published in the journal Geology suggests a surprising source for the nutrients that feed the Bahaman splendor: the Sahara desert. The study looked at the concentration of iron and manganese in the sediments found on the Great Bahama Bank, the undersea platform underlying much of the shallow water surrounding the islands. The researchers found that the ratio of minerals in the Great Bahama Bank sediments closely matched the makeup of dust from the Sahara desert.

Every year, great sandstorms blow millions of tons of dust thousands of miles west from the Sahara. This dust has been known to make its way to the Southeast U.S. and cause hazy skies.

The authors speculate that a steady supply of this dust over eons has fueled the growth of cyanobacteria. These bacteria, they think, used the Saharan minerals to grow and fix nitrogen from the atmosphere, supplying nutrients for the whole ecosystem. These bacteria also create carbonate, making whitish sediments and helping to supply coral with the material they use to make their skeletons. 

Saharan dust has been not just a boon for the Bahamas and other Caribbean islands, but it has also helped fertilize the Amazon rainforest, research suggests. And one study found that the red dunes on Bermuda likely hail from the Sahara as well.