While many areas of the ocean are rich in other nutrients, they often lack iron—a critical element for marine life. Dissolved iron in seawater can originate from three main sources: dust from the atmosphere, sediment dissolution along continental margins, and fluids from hydrothermal vents.
(Jack Cook,Woods Hole Oceanographic Institution )

When scientists studied a deep hydrothermal plume of water in the Pacific Ocean, they were surprised to find that iron particles persist for more than 2,500 miles.

The iron comes from vents along volcanic mountain ridges deep in the ocean. Microscopic organisms called phytoplankton—a key part of the marine food chain—need iron to survive. Phytoplankton serve as food for the fish that feed people all over the world.

“No one ever knew how far these metal particles, which are 7,000 to 8,000 feet deep in the ocean, could travel away from their source vents,” says Jessica Fitzsimmons, assistant professor in oceanography at Texas A&M University. “So we couldn’t understand what effect they had on the overall chemistry of the world’s oceans.

“By measuring hundreds of seawater samples along the track of the plume, the team found that iron particles persisted for thousands of miles.

The biggest surprise was that through exchange between hydrothermal iron particles and the iron dissolved in seawater, the slowly sinking particles caused the dissolved iron to sink by 1,000 feet while it was carried west.

“This iron exchange, facilitated by the natural organic compounds to which iron is bound, controls where the eventually upwelled to the surface ocean. This is critical, since it is this supply of iron to phytoplankton at the surface that affects carbon dioxide sequestration from the atmosphere.”

Fitzsimmons’ team’s conclusions, published in Nature Geoscience, suggest that the supply of iron by hydrothermal vents and subsequent transformations when mixing with seawater are important for scientists to understand in order to predict how the oceans could help to reduce the carbon dioxide levels emitted by fossil fuels.

The National Science Foundation and Chemical Oceanography funded the work. Collaborators are from Rutgers University, the University of South Carolina, the University of Minnesota, and the Woods Hole Oceanographic Institute.

Published in Nature Geoscience

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