New Source of Unoxidized Iron (II) Found in Deep-Sea Hydrothermal Plumes

Author:  Liu Amy

Scientists have found that iron is spewed out by hydrothermal vents on the ocean floor which could be a source of nutrients for sea life at shallower depths. Published in Nature Geoscience, aquatic organisms can metabolize unoxidized iron more efficiently than its oxidized form, and so this discovery would help elucidate the mechanisms by which sea microorganisms obtain nutrients.

A form of iron known as ferrous iron, or iron (II), is soluble in water. The Roman numeral II refers to the iron atom's oxidation state, or a measure of its electronic charge. Iron can be oxidized, or become less positively charged, when it reacts with oxygen in its environment to form a compound known as iron (III) oxide. This form of iron is insoluble in water and therefore precipitates.

Iron oxidation was previously thought by many scientists to be the normal fate of iron originating from hydrothermal vents. Researchers from the University of Minnesota, University of Southern California, Woods Hole Oceanographic Institution, and Lawrence Berkeley National Laboratory analyzed sediment samples taken 5 meters above the seafloor at the East Pacific Rise, a volcanic mid-oceanic ridge (or split in tectonic plates) in the Pacific Ocean. They found that the iron contained in the samples had slower oxidation rates that the researchers attributed to the presence of organic compounds also in the samples,the organic compounds are thought to form complexes with iron (II), which slows its oxidization.

The researchers propose that unoxidized iron emitted from hydrothermal vents is captured by organic compounds and carried closer to the surface. Here, it can serve as a nutrient for marine organisms that oxidize the iron as they metabolize it.

According to scientists, iron in seawater is analogous to nitrogen on land due to its importance as a nutrient for aquatic life. Nitrogen fertilization in the 20th century led to increased crop yields. Similarly, scientists say that iron fertilization is an important limiting nutrient in the sea; that is, if iron levels were increased, organisms such as microbial colonies living on rocks would grow more quickly. Organisms metabolize iron more efficiently in its pure, rather than rusted, form. "This is one potential mechanism of creating essentially a natural iron fertilization mechanism that's completely unknown," says Katrina Edwards of USC. Future research can help scientists understand iron's role as a nutrient in the ocean's ecological system.

Written by: Amy Liu

Edited by: Jeff Kost (News and Features Editor) and Nira Datta (Professional Reviewer)

Published by: Hoi See Tsao