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Hydrothermal Vents Found in Arctic Ocean

John Roach
for National Geographic News
January 23, 2003
 
Marine scientists surveying an unexplored mountain range deep beneath the Arctic Ocean have discovered at least nine hydrothermal vents on the Gakkel Ridge, a mid-ocean mountain range that snakes for 1,100 miles (1,770 kilometers) from high above Greenland to Siberia.

Scientists say the underwater hotspots may potentially host unique forms of life previously unknown to science.

"To find as many [hydrothermal vents] as we did was completely unexpected and incredibly exciting," said Henrietta Edmonds, a marine scientist at the University of Texas at Austin and one of the lead researchers that made the discovery. "At first it was difficult to believe, but I soon managed to convince my colleagues."



Scientists have long theorized that only a few vents existed on the ridge and would be difficult to locate.

Edmonds joined a nine-week expedition aboard the US icebreaker Healy and German research vessel Polarstern to map and dredge rocks from the Gakkel Ridge.

To search for the vents, Edmonds attached a recording device—known as a miniature autonomous plume recorder—to steel cables used by other scientists on the research trip to lower instruments to the seafloor to dredge rocks.

The recording device used by Edmonds measures depth, ocean temperature, and the concentration of suspended particulate matter in the water. Scientists plot such data to identify the signature of a hydrothermal plume—a geothermal phenomenon that indicates the presence of an underwater vent.

"Much like the smoke coming out of a house chimney, hydrothermal plumes rise above and spread away from hydrothermal vents, and are much easier to find than an individual vent field," said Edmonds.

By collecting a wide sample of measurements from an area and comparing them, scientists are able to zoom in on the location of vents, which are identified by a high degree of light scattering and warm temperatures.

In addition, the scientists dredged up a fresh sulfide chimney from the ocean floor, which is an indication of active venting.

Edmonds and her colleagues reported their findings in the January 16 issue of the journal Nature.

Slow Spread

Mid-ocean ridges form where two tectonic plates pull apart and hot material from deep within the Earth oozes up to fill in the gap. The Gakkel Ridge spreads at approximately 0.4 inches (1 centimeter) per year, the slowest rate of any ridge on Earth.

Scientists who study the global distribution of hydrothermal activity theorize that the frequency of vents on major ocean ridges is directly related to the spreading rate.

"The slower the plates separate, the less hot material wells up from below to fill the gap," said Edmonds. "This led people to expect very little volcanism on this slowest spreading ridge and also very little hydrothermal activity."

Spreading rate is a rough measure of the amount of magma that oozes up to the ridge each year, and cooling magma is what powers the vent systems, said Ed Baker, a scientist with the National Oceanic and Atmospheric Administration in Seattle, Washington, and study co-author.

At ultra-slow spreading rates like that found at the Gakkel Ridge, scientists believe that even less magma than the spreading rate predicts actually rises to the crust. This led scientists to predict very sparse venting on the Gakkel Ridge.

"The observation of hydrothermal plumes on approximately 80 percent of the [miniature autonomous plume recorder] profiles was completely unexpected," said Baker. "These observations will be a challenge to interpret correctly, especially the determination, or estimation, of how many vent fields actually produce the plumes."

Researchers offered several possible explanations for the number of plumes they discovered. One theory is that a concentration of magma in a few areas efficiently drives hydrothermal venting along the ridge. Another holds that unusually deep faults along the ridge allows seawater access to heat sources not typically available to vents.

"The fact that we found so many vents, and where we found them, is telling us something fundamental about how heat is delivered from the interior of Earth to the surface at these slowest spreading rates," said Edmonds.

Venting Life

Charles Langmuir, an Earth and planetary scientist at Harvard University in Cambridge, Massachusetts, and study co-author, says that hydrothermal vents are central to the function of the Earth system and the life that is part of it.

"Hydrothermal vents at ocean ridges are an essential part of the chemical balance of seawater. They support ecosystems not found anywhere at the surface and are thought to perhaps have been the sites of the early formation and evolution of life," he said.

Scientists are particularly interested in the type of life that may have formed around the hydrothermal vents on the Gakkel Ridge. Iceland blocks the Gakkel Ridge's connection south to the Mid-Atlantic Ridge, leaving it isolated from the rest of the world.

"In the same way that the isolation of the Galapagos led to distinct forms of life that occurred there, the isolation of the Arctic Basin could have similar effects on biological diversity," said Langmuir.

The study of these organisms will give scientists insight to the flexibility and adaptability of life. The water that spews forth from hydrothermal vents can reach temperatures of 662 degrees Fahrenheit (350 degrees Celsius) and is rich in chemicals such as sulfur and salt.

Certain microorganisms have adapted to thrive on these vents and create rich underwater ecosystems that some scientists believe may represent some of the earliest life forms on Earth.

"Biologically, hydrothermal vents have a lot to tell us about the origins of life and the conditions in which life can be found, which is important to our continuing search for life elsewhere," said Edmonds.

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