AUSTIN, TexasA geologically sluggish region in the Arctic Ocean turns out to have hot spots of activity, according to the first study of the Gakkel Ridge that runs near the North Pole. The study led by a marine scientist at The University of Texas at Austin revealed that the ridge where two tectonic plates meet has at least nine hydrothermal vents releasing hot water as a result of volcanic activity.
“I never in my wildest dreams thought we’d see the extent of activity we saw in the Arctic Ocean,” said Dr. Hedy Edmonds, an assistant professor of marine science and a hydrothermal vent expert.
|
|
||
|
A map of the Arctic Ocean floor, indicating the location of the Gakkel Ridge. The black dots indicate the route taken by scientists aboard a U.S. Coast Guard icebreaker in 2001 on an expedition in which hydrothermal vents were discovered along the ridge. |
||
|
Click on image to view hi-res map. |
Edmonds is lead author of an article about the Gakkel vents that will appear Jan. 16 in the journal Nature. About half as many vents were expected to be found along the Gakkel Ridge, an underwater volcanic mountain chain that snakes for 1,100 miles from north of Greenland to Siberia.
The finding changes scientists’ understanding of the way hydrothermal vents are globally distributed. It also has implications for the way heat and chemicals are exchanged between the Earth’s mantle, the crust overlying the mantle, and oceans, as well as for the way the Earth’s crust forms when tectonic plates pull apart slowly.
Hydrothermal vents are often surrounded by rich underwater ecosystems, supported by micro-organisms that survive on chemicals in the vents. Because the Gakkel Ridge is isolated from its counterparts in other oceans, these new Arctic ecosystems also likely contain previously unidentified organisms, which Edmonds and other scientists hope to discover during future expeditions.
Hydrothermal vents develop along mid-ocean ridges when tectonic plates pull apart, which allows molten material from the Earth’s mantle to edge upward. Water circulating through rocks that form the ocean floor absorbs heat from the molten material, with the water escaping the Earth’s interior in scalding hot vents. The water can reach 350 degrees Celsius (662 degrees Fahrenheit), and contains chemicals on which specialized microbes thrive.
The Gakkel Ridge, which is the slowest spreading of all mid-ocean ridges, was expected to have about four vents based on a previous theory. The theory postulated that slow-moving ridges should produce less molten material and heat to fuel the formation of hydrothermal vents than their faster-spreading counterparts. Based on the 2001 cruise results, hot spots of volcanic activity likely make up for the low level of heat found along much of the ridge.
No one had previously looked for hydrothermal vents on the Gakkel Ridge because of the time and expense involved in breaking surface ice to analyze the water below. Edmonds searched the ridge for vents as an extra scientist on a nine-week research cruise in summer 2001 on the U.S. Coast Guard cutter Healy. The Healy and a companion German icebreaker were being used by geologists to dredge rocks from the ocean floor to study how the Earth’s crust forms.
Whenever the geologists on the Healy lowered their dredging equipment, Edmonds and her colleagues attached a recording device to its steel cable to test the water at different depths for increases in temperature or particles that indicate a nearby hydrothermal vent. Vents release a mixture of chemicals, including iron oxide particles, which are rare in surrounding ocean water. The water from a vent initially stays together to form what is called a plume, allowing its characteristics to be measured.
Edmonds obtained 145 water “profiles” and located nine hydrothermal vents to within a few miles based on the signals of ocean temperatures and suspended sediments as the Healy cruised along. She also pegged three other areas as likely vent locations.
“Eighty-two percent of our water profiles had signatures of plumes in them,” Edmonds said.
During the cruise, the geologists also mapped the ocean floor along the ridge, which allowed Edmonds to confirm that the vents were located in geologic features where hydrothermal vents would likely occur.
As further confirmation, she and colleague David Graham of Oregon State University deployed a more specialized piece of equipment to measure additional water characteristics associated with vent plumes. The device, called a CTD (conductivity-temperature-depth) cast, was lowered into the ocean depths at six locations along the ridge.
The CTD cast included 24 bottles for obtaining water samples at various depths. Edmonds, Graham and British researchers Douglas Connelly and Chris German from the Southampton Oceanography Centre, analyzed the samples after the cruise, and discovered high concentrations of manganese and other vent-associated chemicals at sites that matched Edmonds’ earlier findings.
“With these additional measurements, we could say with certainty that this water was coming from hydrothermal vents,” Edmonds said.
For more information contact: Barbra Rodriguez, media relations, College of Natural Sciences, 512-232-0675, or Dr. Hedy Edmonds, 361-749-6772.
