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Newly found ocean plume could be major source of iron

According to researchers at the Woods Hole Oceanographic Institution, a massive plume of iron and other micronutrients has been discovered in the South Atlantic Ocean. The plume is more the 1,000 km long surging from hydrothermal vents. The discovery brings previous approximations of iron supply into question, and may dispute researchers’ presumptions about iron sources in the world’s oceans.

“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 lead author Mak Saito, a Woods Hole Institution researcher.

Saito and his colleagues weren’t looking for iron plumes in the South Atlantic. In fact, they launched an expedition aboard the R/V Knorr in 2007 in order to map chemical composition and microbial life along the ship’s path between Brazil and Namibia. During the expedition, the researchers sampled the ocean water on numerous occasions for further analysis in a laboratory.

Their path took the researchers over the Mid-Atlantic Ridge. The Mid-Atlantic Ridge is a chain of mountains and valleys stretched out along the Atlantic Ocean floor from the Arctic to the Antarctic where several of the planet’s major tectonic plates are gradually moving apart.

Hydrothermal vents are located along the ridge, but researchers haven’t exhaustively examined these vents because gradually-moving ridges are believed to be less active than quickly-moving ones. Previous studies utilizing helium have discovered very little originating from mid-Atlantic vents, and researchers have taken this to mean that vents spit out little iron as well.

Needless to say, Saito and his colleagues were taken aback by what their ocean water samples showed when later examined in a laboratory. After being filtered and evaluated, some of the ocean water revealed surprisingly high levels of iron and manganese. The researchers mapped the sites were the iron-rich samples were obtained and discovered that the samples created a distinct plume. The plume of nutrients stretches in depth from 1,500 to 3,500 meters for more than 1,000 km of the South Atlantic Ocean.

“We had never seen anything like it,” Saito posited. “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.”

According to a news release, the plume’s ratio of iron to helium was 80-times higher than ratios recorded for quickly-moving ridges in the southeastern Pacific Ocean.

According to Saito, the finding rejects the presumption that gradually-moving ridges are iron-poor, and it brings into question the utilization of helium as a sign of iron flux in hydrothermal vents.

“We’ve assumed that low helium means low iron, and our study finds that that’s not true,” Saito noted. “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.”

This is a major discovery for researchers studying ocean water, because iron is a crucial element for ocean life. Given the fact that more than 50 percent of the Earth’s seafloor ridges are gradually-moving, the study’s results put forth the idea that there may be a lot more iron in these locations than previously approximated.

The researchers hope future research will show the specific shape and extent of the plume.

The study’s findings are described in greater detail in the journal Nature Geoscience.