Scientists have discovered a new way in which ocean water circulates through deep-sea vents. Click on image for full size (86 Kb) Courtesy of Zina Deretsky/National Science Foundation

Zigzagging some 60,000 kilometers across the ocean floor, Earth's system of mid-ocean ridges plays a pivotal role in many workings of the planet: in plate-tectonic movements, heat flow from the interior, and the chemistry of rock, water and air.

Now, a team of seismologists working in 2,500 meters of water on the East Pacific Rise, some 565 miles southwest of Acapulco, Mexico, has made the first images of one of these systems--and it doesn't look the way most scientists had assumed. The research results, funded by the National Science Foundation (NSF), appear in this week's issue of the journal Nature.

It was not until the late 1970s that scientists discovered the existence of vast plumbing systems under the oceans called hydrothermal vents. The systems pull in cold water, superheat it, then spit it back out from seafloor vents--a process that brings up not only hot water, but dissolved substances from rocks below. Unique life forms feed off the vents' stew, and valuable minerals including gold may pile up.

The hypothetical image of a hydrothermal-vent system shows water forced down by overlying pressure through large faults along ridge flanks. The water is heated by shallow volcanism, then rises toward the ridges' middles, where vents (often called "black smokers," for the cloud of chemicals they exude) tend to cluster.

"The new images show a very different arrangement," said Rodey Batiza, marine geosciences section head in NSF's Division of Ocean Sciences.

The research team's calculations suggest that water moves a lot faster than previously thought--perhaps a billion gallons per year--through these systems. The water appears to descend instead through a buried 200-meter-wide chimney atop the ridge studied on the East Pacific Rise, run below the ridge along its axis through a tunnel just above a magma chamber, then bubble back up through a series of vents further along the ridge.

"If you look at images of hydrothermal vents, you come up with cartoons that don't at all match what we see," said lead Nature paper author Maya Tolstoy, a marine geologist at Lamont-Doherty Earth Observatory in Palisades, N.Y.

The images were created using seismometers planted around the ridge to record tiny, shallow earthquakes--in this study, 7,000 of them over seven months in 2003 and 2004.

The shallow quakes cluster neatly, outlining the cold water's apparent entrance. It dives straight down about 700 meters, then fans out into a horizontal band about 200 meters wide, before bottoming out at about 1.5 kilometers just above the magma. Heated water rises back up through a dozen vents about 2 kilometers north along the ridge.

The researchers interpret the quakes as being the result of cold water passing through hot rocks and picking up their heat--a process that shrinks the rocks and cracks them, creating small quakes.

Seawater, forced down into the resulting space, eventually gets heated by the magma, then rises back to the seafloor--much the same process seen in a pot of boiling water. Tolstoy and co-authors believe the water travels not through large faults--the model previously favored by some scientists--but through systems of tiny cracks.

Their chart of the water's route is reinforced by biologists' observations from submersible dives that the area around the downflow chimney is more or less lifeless, while the surging vents are a covered with bacterial mats, mussels, tubeworms and other creatures that thrive off the heat and chemicals.

It is a mystery where vent organisms originally came from--some evolutionary biologists believe that life on Earth began with them-and how they make their way from one isolated vent system to another.

These findings could add to an understanding of seafloor currents along which they may move, and of the nutrient flows that feed them, said Tolstoy. The work also has large-scale implications for how heat and chemicals are cycled to the seafloor and overlying waters, she said.

Scientists are still retrieving and analyzing data on the vents and their circulation. In 2006, an ocean-bottom volcanic eruption buried many of their instruments; most of the instruments were lost, but the "survivors" provided new information about how undersea eruptions work.

Text above is courtesy of the National Science Foundation.

Scientists have discovered a new way in which ocean water circulates through deep-sea vents. Click on image for full size (86 Kb) Courtesy of Zina Deretsky/National Science Foundation

The Earth has a large system of ridges along the ocean floor that play a big part in the geology of the planet. A team of seismologists (geologists who study earthquakes) has been studying a place called the East Pacific Rise, which is in the ocean floor about 565 miles southwest of Acapulco, Mexico. These scientists have made images of this area and have made some discoveries that change what they thought they knew about these ridges and vents on the ocean floor.

In the late 1970s scientists discovered a large plumbing system under the oceans called hydrothermal vents. These systems pull in cold water, heat the water, and then spit it back out from vents in the seafloor. This process brings up hot water and substances that dissolved from rocks below the ocean floor. Some rare life forms feed off this "stew" of dissolved minerals and hot water.

Scientists used to think that pressure forced the water into the vents through large faults, or cracks in the ridge. Now scientists have learned that the water moves a lot faster in and out of the vents than they had thought (maybe a billion gallons per year!). The water goes down through a large chimney that is buried under the sea floor. Then the water runs underneath the ridge through a tunnel above a hot magma chamber. Finally the water bubbles back up through vents that are further down the ridge.

They have also learned that tiny earthquakes on the ridge are created by the cold water passing through hot rocks and picking up their heat. This process shrinks the rocks and cracks them, creating small quakes. Then seawater is forced down into the new spaces made by the earthquakes. This water gets heated by the magma and rises back to the seafloor. Maya Tolstoy, a marine geologist, says this process is very similar to what happens in a pot of boiling water.

These findings could help scientists understand seafloor currents, the nutrient flows of minerals, and how heat and chemicals are cycled to the seafloor and overlying waters.

Scientists have discovered a new way in which ocean water flows through deep-sea vents. Click on image for full size (86 Kb) Courtesy of Zina Deretsky/National Science Foundation

A group of scientists have been studying an area of the ocean floor called the East Pacific Rise, which is about 565 miles southwest of Acapulco, Mexico. The East Pacific Rise is a ridge along the ocean floor where the sea floor is spreading.

These scientists have learned that tiny earthquakes along this ridge are being created when the cold ocean water passes through hot rocks and picks up their heat. This process shrinks the rocks and cracks them, creating small earthquakes. Then the seawater is forced down into the new spaces made by the earthquakes. This water gets heated by the hot magma and rises back to the seafloor and bubbles through vents in the sea floor back up into the ocean. Maya Tolstoy, a geologist studying this area, says this process is very similar to what happens in a pot of boiling water.

This is a very large system, and the scientists think a billion gallons of water flow through it each year! When the water rises back up into the ocean through the seafloor, it brings up minerals that were dissolved in the hot water below. Some rare animals feed off this "stew" of minerals and hot water, and scientists have been studying these vents to see how some animals can live in such a harsh environment!