Dissolved Iron in North Atlantic Ocean Linked to Sahara Desert Dust and Sand

Sea water contains all sorts of nutrients, including iron. Yet in a ton of ocean water, there's only enough iron to weigh as much as a single eyelash. Even with so little of it, iron plays a huge role as one of the essential elements of life and now, scientists have assessed the iron found in the north Atlantic Ocean and have found that a surprising amount actually comes from the Sahara desert.

"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," said Seth John, one of the researchers, in a news release.

Understanding how iron moves into the oceans is crucial to understanding the details of the carbon cycle on Earth. When algae and other phytoplankton grow, they take carbon dioxide out of the atmosphere. Yet a limitation on iron keeps these producers in check.

In order to better understand the movement of iron, the researchers collected ocean samples over the past several years and developed analytical techniques for quantifying different natural isotopes of iron in seawater. This allowed them to track the origins of the dissolved metal. More specifically, the ratio of the stable natural isotopes iron-56 and iron-54 can tell scientists what sort of processes the iron underwent, which can then tell them exactly where the iron is from in the first place.

So where does the iron come from? The scientists found that the largest source of iron in the north Atlantic, somewhere between 70 and 90 percent, comes from dust that blows in from the Sahara desert.

"It could help us understand past climate change, like glacial-interglacial cycles," said John. "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 findings are published in the journal Nature.