Nature Magazine Reports Findings from North Pole Expedition Led by TU Professor
Friday, January 17, 2003
The first major article reporting discoveries made during a scientific expedition led by University of Tulsa professor Peter Michael to the Arctic, which included a stop at the North Pole, appears in the Jan. 16 issue of Nature magazine.
Michael, a geosciences professor, studies the processes that lead to the formation of oceanic crust and the melting of the Earth's mantle. He is one of the main authors of the Nature paper, titled "Discovery of abundant hydrothermal venting on the ultraslow-spreading Gakkel ridge in the Artic Ocean." The principal author is H. N. Edmonds with the University of Texas Marine Science Institute.
The 65-day trip in 2001 involved two icebreakers that conducted 200 dredging operations and retrieved more than 20,000 pounds of rocks from the ocean floor. Michael was the chief scientist on the U.S. Coast Guard's largest ship, the Healy, a 420-foot-long icebreaker. One of the main goals was to learn more about Gakkel Ridge, part of the globe-encircling mid-ocean ridge, which is where the Earth's crust is continually created by seafloor spreading. The ridge lies about three miles beneath the surface of the Arctic Ocean.
On the trip, scientists found more than 10 hydrothermal vent sites, more than in 20 years of exploration on the mid-Atlantic ridge. The vents — evidence that the ridge is volcanically active — are chimney-like structures composed of deposits of precipitated sulfide minerals that have been dissolved from the ocean crust by seawater that has been heated to some 400 degrees Celsius by molten rock.
The vents are places that can host life, and because the Arctic Ocean is a basin that is isolated from other ocean basins, says Michael, it is possible that life forms might be found there that are not present elsewhere.
The vents are also known as "black smokers." Michael explains that cold sea water enters cracks in the crust, and is then heated by volcanic activity within the crust, and the hot water that rises carries dissolved ions of sulfur and metals, creating plumes of cloudy water. When the hot water mixes with the cold seawater, the ions precipitate to form sulfide minerals, which form chimney-like structures.
Scientists used a miniature autonomous plume recorder to record water temperature and clarity at different depths to detect emanations of hot water from volcanic areas. They also sampled the water for helium and manganese, considered as tracers indicating the presence of hydrothermal vents.
Discovery of the large number of vents was completely unexpected. "The discoveries have changed what we believed caused hydrothermal venting," says Michael. It was thought that it was strictly related to the rate of spreading of the ridge, but on slow-spreading ridges there are two key factors. One is that the crust is cold and has cracks, and it is through the cracks that seawater circulates to create the plumes. Secondly, they found that the volcanic activity is highly concentrated in certain locations.
Along the mid-ocean ridge, which runs some 40,000 miles under the oceans, volcanic material is added to crustal plates that move away from each other. For Gakkel Ridge, the seafloor spreading rate is about one centimeter per year, the slowest on Earth, compared to other ridges that spread at up to 20 centimeters per year.