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| Vol. 17, No. 14 | Dec. 11, 1997 |
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| Vol. 17, No. 14 | Dec. 11, 1997 |
A detailed portrait of the Southwest Indian Ridge (SWIR)-the boundary between the slowly spreading Antarctic and Africa plates-reveals one of the steepest underwater cliffs ever recorded and may shed new light on the origins of primitive life forms, John Madsen, geology, reported today at the American Geophysical Union meeting in San Francisco.
Madsen is part of an international marine geophysical investigating team using remote sensing devices to map this least-studied area of the Mid-Ocean Ridge System. Scientists from major European countries, Japan, South Africa and Korea are participating in the project.
In the spring of 1996, Madsen and a team of scientists spent 48 days aboard the R/V Knorr, operated by the Woods Hole Oceanographic Institute, mapping an area "the size of New England." The ship covered 10,833 nautical miles in 40-degree Fahrenheit weather, all but three of those days in seas of 10- to 20-foot waves. It was the longest cruise the Knorr had ever taken.
During the voyage, the team made a surprising discovery. While charting an area 1,000 miles south of Africa's Cape of Good Hope and above the Antarctic where glaciers begin to thicken into land mass, they discovered a dramatic drop in the ridge, descending from 500 to 20,000 feet in only 10 miles. "It's the steepest change in elevation along the ocean floor that's been mapped any place on the globe," Madsen says.
The topographical maps the trip has produced will help scientists understand the physical characteristics of the sea and ocean floor. Madsen says their work will be useful to the entire oceanographic community, but especially to those studying the biological, seismological and geophysical aspects of the area.
"Some biologists believe life may have originated at hydrothermal vents beginning at 10,000 feet below the surface," he says. That far down, the ocean water is close to freezing and when the 650-degree Fahrenheit hydrothermal flowing through the vents hits the 37 degree water, sulfide deposits are formed. According to Madsen, some scientists believe these vents might hold the key to the beginning of life on this planet.
Aboard the Knorr, Madsen and his colleagues tested a new remote sensing device called the Sea Beam 2112-a multibeam sonar system that details not only depth but also the nature of the ocean floor.
"The multibeam sound signal travels in a variety of directions. For each ping sent to the ocean floor, 128 signals are received back on the ship," he says. These signals are recorded by computers and viewed on monitors. The ship moves ahead 10 knots and the Sea Beam pings again. All of this information ultimately becomes color-coded topographical maps of the evolving Southwest Indian Ridge.
Madsen says the early results of their research suggest that unusual geologic activity and volcanic processes are occurring along the Southwest Ridge, and this information needs to be incorporated into existing knowledge about the global ridge system.
In an article about their findings that has been submitted to Geology, Madsen says that the early results of their research suggest unusual geologic activity and volcanic processes are occurring along the Southwest Ridge that need to be incorporated into the information already known about the global ridge system. The team has submitted two new proposals to the National Science Foundation for charting areas to the east and west of where they've already mapped.
-Barbara Garrison
