May 10, 2011

Hydrothermal Vents Provide Iron For Deep Sea Life

Pyrite nanoparticles from hydrothermal vents provide a rich source of iron for deep sea life, according to new research published in the current issue of the journal Nature Geoscience.

Bacteria and tiny plants living in the ocean need iron for energy and growth, but are without the ability to use natural sources such as leafy greens or red meat.  But scientists have found evidence that points to an iron source on the seafloor: tiny particles of pyrite, or fool's gold, from hydrothermal vents at the bottom of the ocean.

Scientists already knew that the vents' cloudy plumes, which spew forth from the earth's interior, include pyrite particles containing iron.  However, they believed the particles were solids that, once emitted, settled back onto the ocean floor.

In the current study, scientists at the University of Delaware and other institutions showed that the vents emit a substantial amount of microscopic pyrite particles that have a diameter 1,000 times smaller than that of a human hair "“ small enough to be dispersed into the ocean rather than falling to the sea floor.

The researchers noted the importance of the lengthy amount of time pyrite exists suspended in the sea, something known as residence time.

"These particles have long residence times in the ocean and can travel long distances from their sources, forming a potentially important food source for life in the deep sea," said Barbara Ransom, program director in the National Science Foundation's (NSF) Division of Ocean Sciences, which funded the research,

The discovery is "very exciting," she said.

The mineral pyrite, or iron pyrite, has a metallic luster and brass-yellow color that led to its nickname of "fool's gold". In fact, pyrite is occasionally found along with small quantities of gold.

"As pyrite travels from the vents to the ocean interior and toward the surface ocean, it oxidizes gradually to release iron, which becomes available in areas where iron is depleted so that organisms can assimilate it, then grow," said scientist George Luther of the University of Delaware.

"It's an ongoing iron supplement for the ocean--much as multivitamins are for humans."

Growth of tiny plants known as phytoplankton can affect atmospheric oxygen and carbon dioxide levels.

In conducting their research, the scientists made multiple visits to the South Pacific and East Pacific Rise using the manned deep-sea submersible Alvin and the remotely operated vehicle Jason, both operated by the Woods Hole Oceanographic Institution.

The research was published online May 8 in the journal Nature Geoscience.


Image 1: Black smoker from the Mariner vent site in the Pacific Ocean's Eastern Lau Spreading Center. Credit: University of Delaware

Image 2: Transmission electron micrograph (TEM) showing nanoparticles from the Pacific's Kilo Moana vent. Credit: University of Delaware


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