At the bottom of the ocean, cracks in the seafloor release heat and minerals from within Earth’s crust. These hydrothermal vents support life nearby that would otherwise struggle for survival at such cold, dark depths. Yet UD researchers discovered that the vents may also help nourish organisms thousands of miles away by emitting an important iron source: pyrite nanoparticles.
Measuring only 200 nanometers in size, or roughly one-thousandth the diameter of a human hair, the tiny pieces of pyrite are highly buoyant and can readily disperse into the ocean. Composed of iron and sulfur, pyrite reacts slowly with oxygen in water to rust into oxidized iron, which can then be absorbed by bacteria, plankton, fish and other sea life as a trace nutrient.
“Almost any organism in the ocean is going to need iron,” said George W. Luther, Maxwell P. and Mildred H. Harrington Professor of Oceanography, who reported the findings in Nature Geoscience with his former graduate student Mustafa Yücel in May 2011.
While pyrite, called “fool’s gold” for its shiny surface, was previously known to gush out of hydrothermal vents, scientists thought it emerged only as much larger, heavier pieces that rapidly fell back down on the ocean floor. Luther’s group found that as much as 10 percent of the iron coming out of hydrothermal vents is nanoparticulate pyrite.
At that extremely small size, pyrite may travel up to 4,000 kilometers away through the ocean based on independent analyses of dissolved iron concentrations by other scientists. Given the substance’s slow oxidation rate, pyrite-generated iron can get released in remote parts of the deep sea, akin to time-release capsules.
Finding the nanoparticles in the ocean’s depths was no small feat. In partnership with Woods Hole Oceanographic Institution, UD researchers used remote-controlled titanium samplers, which can withstand the brutally hot temperatures at the hydrothermal vents, to obtain samples from vent plumes 1,800 to 4,000 meters deep in the Pacific. In addition to wet chemical analyses, they used scanning and transmission electron microscopy to closely examine the contents back in the lab.
The findings were part of a broader research project examining how temperature and chemical content in seawater dictates what type of animals thrive in deep-sea environments near hydrothermal vents, such as snails, tubeworms, mussels and other organisms. A chemist by training, Luther focuses his research on the interface between chemistry and biology, with the position that the former drives the latter.
Funded by the National Science Foundation, he will continue the nanoparticle research with colleagues this fall on an excursion to the Mid-Atlantic Ridge to study hydrothermal vents there.
“One of the ideas that we’ve been exploring is that it’s not only iron that’s being transported, but copper, zinc and other elements as well,” Luther said.