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Carbon-Collecting Iron Traced to Dusty Sahara Desert

Jul 03, 2014 02:47 PM EDT
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Iron, though present in miniscule amounts in seawater, is a major player in the ocean's carbon cycle. Now scientists have assessed the various sources of dissolved iron in the north Atlantic Ocean, finally tracing the source of this precious metal to the dusty Sahara Desert.
(Photo : Dreef / Fotolia)

Iron, though present in miniscule amounts in seawater, is a major player in the ocean's carbon cycle. Now scientists have assessed the various sources of dissolved iron in the north Atlantic Ocean, finally tracing the source of this precious metal to the dusty Sahara Desert.

Their research established that between 70 and 90 percent of iron comes from dust that blows in from the Sahara desert, making it the largest iron source for the North Atlantic.

Given that there is so little iron in ocean water - the amount of iron found in a ton of water weighs only as much as an eyelash - you would think that its role in the ocean is inconsequential. However, it is one of the most essential elements of life.

"The key reason that everybody cares about iron is because it limits the growth of phytoplankton, such as algae, in maybe a fifth of the ocean," Seth John, an assistant professor in the department of marine science at the University of South Carolina, said in a statement.

Algae and phytoplankton, especially in this climate changing world, are critical because they take carbon dioxide out of the atmosphere and convert it into proteins and other carbon-based molecules that constitute living cells. Iron is what allows this process to continue, and a little iron goes a long way - in a typical cell, for every atom of iron, there are about a million atoms of carbon, John added.

Knowing how iron moves into the oceans is thus crucial for scientists to fully understand the details of the carbon cycle on earth.

Based on the ratio of iron isotopes, iron-56 and iron-54, in sediment samples from the north Atlantic Ocean floor, researchers determined that dissolved iron in seawater is blown in from the Sahara's dust particles.

"It could help us understand past climate change, like glacial-interglacial cycles," John said. "There would have been huge changes in dust fluxes to the ocean in glacial times, and so understanding how much iron comes from dust in the modern day helps us figure out whether that was an important driver of glacial-interglacial cycles."

The study's findings were published in the journal Nature.

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