Huge Plume of Iron Billows for 1,000km Below Sea

A newly discovered ocean plume could be a major source of iron and the researchers who've found it suggest their discovery may change assumptions about how many iron sources are in the world's seas.

In the South Atlantic Ocean, a 1,000 kilometer long plume of iron and other micronutrients was discovered billowing from hydrothermal vents deep below the surface.

"This study and other studies like it are going to force the scientific community to reevaluate how much iron is really being contributed by hydrothermal vents and to increase those estimates, and that has implications for not only iron geochemistry but a number of other disciplines as well," said Mak Saito, associate scientist at Woods Hole Oceanographic Institute (WHOI) and lead author of the study.

The research team included scientists from WHOI and the University of Liverpool, who began their the "Cobalt, Iron and Micro-organisms from the Upwelling zone to the Gyre" (or CoFeMUG, pronounced "coffee mug") expedition in 2007.

CoFeMUG was intended to map the microbial and chemical composition of the ocean along a route from Brazil to Namibia. Along the route, the researchers collected water samples from various depths and frequent intervals.

Along the CoFeMUG route the ship passed an underwater range of mountains where several of Earth's tectonic plates are slowly spreading apart. The hydrothermal vents along these fissures are known to release helium and it has been presumed that only a little iron would have been in the mix.

Saito and his colleagues were surprised when they analyzed the water samples and found high levels of both iron and manganese. When the data of where the water samples were collected was plotted out, the researchers saw it came from a stretch of sea more than 1,000 kilometers long at depths of 1,500 to 3,500 meters.

"We had never seen anything like it," Saito said. "We were sort of shocked -- there's this huge bull's-eye right in the middle of the South Atlantic Ocean. We didn't quite know what to do with it, because it went contrary to a lot of our expectations."

The plume's iron-to-helium ratio is 80 times greater than in other areas of the ocean.

"We've assumed that low helium means low iron, and our study finds that that's not true," Saito said. "There's actually quite a lot of iron coming out of these slow-spreading regions in the Atlantic, where people thought there would be little to none."

Saito and his colleagues' research will be published in the journal Nature Geoscience.