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Up until now, researchers have usually assumed that dust from the Sahara was the only significant source of iron to the North Atlantic Gyre. Now ETH geochemists Tim Conway and Gregory de Souza have discovered another source: cold, iron-rich seawater from the North American continental slope, which is captured by meanders of the Gulf Stream and carried out to the North Atlantic Gyre. Their study was recently published in the journal Nature Geoscience.
These "water pockets" are visible at the ocean's surface as circular eddies, the largest of which have a diameter of 200 kilometres. Beneath them are cylinder-shaped columns that reach down to 1,000 metres, rotating anticlockwise on their own axes. They last for about two years, during which time their rotation slows as they mix with the water of the North Atlantic Gyre and enrich it with iron. Some of the water columns return to be reabsorbed by the Gulf Stream.
Amount - Iron - Source - Order - Magnitude
"The amount of iron from this source is probably of the same order of magnitude as that delivered by Saharan dust, since Gulf Stream eddies are constantly forming, while dust storms are usually just brief events," says de Souza, Senior Assistant at the Institute of Geochemistry and Petrology at ETH Zurich.
de Souza and former postdoc Conway (now Professor at the University of South Florida) found the iron-carrying Gulf Stream eddies serendipitously. Purely out of curiosity, the two researchers examined some recently published data that had been gathered during a research cruise from the North American coast to Bermuda. This data included the concentrations of iron and zinc dissolved in seawater from the surface to the ocean floor.
Location - Gulf - Stream - ETH - Researchers
At one location close to the Gulf Stream, the ETH researchers noticed elevated iron concentrations inear the surface of the otherwise iron-poor North Atlantic Gyre, reaching values similar to those of coastal water....
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