Are seafloor vents an iron-rich nutrient source for organisms?

Fluids spewing from seafloor hydrothermal vents contain about a million times more iron than seawater. Scientists had thought that when the fluids hit oxygen-rich seawater, the iron immediately oxidizes into a form that has as much nutritional value for organisms as chewing a rusty nail has for patients with anemia.

In a paper published in the March 2009 issue of Nature Geoscience, Brandy Toner and colleagues reported the unexpected discovery that some iron spit out of hydrothermal vents remains in a form that organisms can use. The iron appears to stick to organic matter, and the chemical interaction with carbon seems to protect the iron from oxidizing, said Toner, a NASA postdoctoral fellow at WHOI when the research began and now an assistant professor at the University of Minnesota.

Toner and colleagues used the Lawrence Berkeley National Laboratory's Advanced Light Source synchrotron to focus X-beams on particles in sediments collected at a Pacific Ocean vent--creating elemental maps of the particles on micrometer and nanometer scales. The technique unexpectedly revealed a form of iron called iron(II), a delectable treat for iron-starved organisms in the ocean. Exactly how the iron(II)-laden carbon particles might interact with the marine food web is still to be determined.

"So the question becomes, what are those [carbon-containing] organic compounds?" said co-author Chris German, a WHOI geochemist. "Are they organic compounds like in oils and tars, or is it actually the stuff of life? This paper opens up a whole new line of research that people didn't know they should worry about until now. A bit of work on a tiny nanometer scale can force you to ask questions of global significance."

--Juli Berwald

Research support also came from the National Science Foundation and the WHOI Deep Ocean Exploration Institute.