Scientists discover vast iron plume beneath South Atlantic

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Scientists discover vast iron plume beneath South Atlantic

August 21, 2013 - 18:37

Hydrothermal vents billowing 600-mile long plume along Mid-Atlantic Ridge

The figure plots ocean depth and sampling location, with elevated iron concentrations indicated by warm colors (red, orange, etc)

Scientists have discovered a vast iron plume more than 600 miles long billowing from hydrothermal vents beneath the South Atlantic Ocean. The finding not only calls into question past estimates of iron abundances, but may also challenge assumptions about iron sources in the world's seas.

The researchers weren’t actually seeking iron, instead setting out to map chemical composition and microbial life along a route between Brazil as Namibia. Sampling seawater at frequent intervals and multiple depths, they gathered information to learn more about the ocean’s chemical composition.

En route, they passed over the Mid-Atlantic Ridge, the band of mountains and valleys traversing the Atlantic Ocean floor from the Arctic to the Antarctic. Along this ridge are hydrothermal vents, fissures in the Earth's crust. The vents of the slow-spreading ridges have yet to be extensively studied, as they are believed to be less active than fast-spreading ones.

Sample analysis revealed a surprise: exceptionally high iron and manganese levels. Upon mapping the samples’ origins, they found that the samples formed a distinct plume.

"We had never seen anything like it," said researcher Mak Saito. "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."

In contrast to previous beliefs, the findings seemed to indicate slow-spreading ridges aren't iron deprived. In addition, questions were raised about the use of helium as an indicator for iron flux in hydrothermal vents. As iron is a critical element for ocean life, this has huge implications for future studies.

"We need to understand where iron is in the ocean and where it's coming from to understand the role of iron in the marine carbon cycle with any confidence," said Saito .

The researchers plan future studies that may reveal the plume’s exact shape and extent. This could help determine how much iron and other micronutrients persist and rise to the surface, revealing a little bit more about the ocean's nutrient cycle.