Eddies found to be deep, powerful modes of ocean transport

Apr 28, 2011
Black smoke rises vigorously at vents when the hot, chemically-altered seawater mixes with the cold, oxygenated bottom water. The hydrothermal alterations to seawater occurring at these relatively isolated locations affect the global ocean chemical budget and sustain thriving and strange communities, including these giant tubeworms, Riftia pachyptila, and gastropod limpets grazing on their tubes. (Woods Hole Oceanographic Institution)

(PhysOrg.com) -- Researchers from Woods Hole Oceanographic Institution (WHOI) and their colleagues have discovered that massive, swirling ocean eddies -- known to be up to 500 kilometers across at the surface -- can reach all the way to the ocean bottom at mid-ocean ridges, some 2,500 meters deep, transporting tiny sea creatures, chemicals, and heat from hydrothermal vents over large distances.

The previously unknown phenomenon, reported in the April 28 issue of the journal Science, helps explain how some travel huge distances from one vent area to another, said Diane K. Adams, lead author at WHOI and now at the National Institutes of Health.

"We knew these eddies existed," said Adams, a biologist. "But nobody realized they can affect processes on the bottom of the . Previous studies had looked at the upper ocean."

Using deep-sea moorings, current meters and sediment traps over a six-month period, along with computer models, Adams and her colleagues studied the eddies at the underwater mountain range known as the East Pacific Rise. That site experienced a well-documented eruption in 2006 that led to a discovery reported last year that larvae from as far away as 350 km somehow traveled that distance to settle in the aftermath of the eruption.

The newly discovered depth of the powerful eddies helps explain that phenomenon but also opens up a host of other scientific possibilities in oceans around the world. "This atmospherically generated mechanism is affecting the deep sea and how larvae, chemical and heat are transported over large distances," Adams said.

The eddies are generated at the surface by atmospheric events, such as wind jets, which can be strengthened during an El Niño, and "are known to have a strong influence on surface ocean dynamics and production," say Adams and Dennis J. McGillicuddy from WHOI, along with colleagues from Florida State University, Lamont Doherty Earth Observatory, and the University of Brest in France. But this "atmospheric forcing…is typically not considered in studies of the deep sea," they report.

Moreover, the eddies appear to form seasonally, suggesting repeated interactions with undersea ridges such as the Eastern Pacific Rise. The models "predict a train of eddies across the ocean," Adams said. "There may be two to three eddies per year at this location," Adams said. Each one, she says, "could connect the site of the eruption to other sites hundreds of miles away." Elsewhere, she adds, "there are numerous places around the globe where they could be interacting with the deep sea."

In her 2010 report on larvae traveling great distances to settle at the eruption site, WHOI Senior Scientist Lauren S. Mullineaux , along with Adams and others, suggested the larvae traveled along something like an undersea superhighway, "jets" travelling up to 10 centimeters a second. But conceding that even those would not be enough to carry the larvae all that distance in such a short time, the researchers speculated that large eddies may be propelling the migrating larvae even faster.

Adams's current work follows up on that possibility. "The mechanism we found helps explain what we saw in the first paper," Adams said.

It is the larger picture, over longer periods of time, however, that Adams and her colleagues find particularly intriguing. "Transport [of ocean products] could occur wherever…eddies interact with ridges—including the Mid-Atlantic Ridge, the Southwest Indian Ridge, and the East Scotia Ridge—and the surrounding deep ocean," the researchers say.

And because the eddies appear to form repeatedly, the high-speed, long-distance transport can last for months. "Although the deep sea and in particular are often naively thought of as being isolated from the surface ocean and atmosphere, the interaction of the surface-generated eddies with the deep sea offers a conduit for seasonality and longer-period atmospheric phenomena to influence the 'seasonless' deep sea," Adams and her colleagues write.

"Thus, although hydrothermal sources of heat, chemical and larval fluxes do not exhibit seasonality there is potential for long-distance transport and dispersal to have seasonal to interannual variability."

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Provided by Woods Hole Oceanographic Institution

5 /5 (2 votes)

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User comments : 4

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sender
not rated yet Apr 28, 2011
Magnetic Vortices are another interesting deep sea phenomenon, studied for the past few decades.
barakn
not rated yet Apr 29, 2011
Care to provide a source for your statement about deep sea magnetic vortices?
deepsand
3 / 5 (10) Apr 29, 2011
Magnetic Vortices are another interesting deep sea phenomenon, studied for the past few decades.

Beyond having been conjectured to explain the so-called Bermuda Triangle phenomena, where else is there a nexus between such vortexes and the deep seas?
GSwift7
1 / 5 (1) May 03, 2011
Huge eddies/vortices also form in the deep ocean when the tide moves the ocean back and forth accross the ridges. It's strange that they don't mention that here, especially since that's a viggorous daily occurance.

On land, the fastest way to transport seeds and larvae over large distances is in the belly or stuck to the outside of an animal. There may not be very much life down there, but there is some. Do the deep sea animals make journeys from one vent to another? It would seem to me that it makes sense for a deep sea animal to visit the vents. They might even be able to hear the vents from hundreds of miles away and be attracted to them like bugs to light. I wonder if the above study has thought about that?