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Mission’s End Brings Great Lakes Mysteries To The Surface

August 12, 1986

DETROIT (AP) _ Scientists probing the Great Lakes report mysterious crescent-shaped mounds on Lake Superior’s floor and a cloudy belt of organisms that may hamper the battle against pollution in the lakes.

Researchers aboard the ship Seward-Johnson ended a month-long expedition Monday, the second of five annual expeditions on the Great Lakes financed by the National Oceanic and Atmospheric Administration.

The ship, which cruised lakes Huron and Superior, had a crew of 26, including eight scientists, and served as base for the Johnson-Sea Link II, a four-passenger minisubmarine.

Previous scientific missions had spotted the outlines of the Lake Superior mounds using sonar from surface ships. But the high-technology submarine allowed the first gaze by humans, said Richard Cooper, director of the undersea research program at the University of Connecticut.

The mounds have the same shape but sizes vary and they face different directions. Some are 7 feet to 10 feet high, Cooper said.

″There seemed to be whole fields of them. They stretch on for miles and miles and miles,″ Cooper said in a telephone interview. ″We really don’t know what caused them. It’s very perplexing.″

Samples from the mounds may confirm whether they are made of sand and gravel, as scientists believe, and whether they were formed by currents. A more exotic hypothesis holds that the mounds were formed by glacial water seeking escape from 10,000 years beneath the giant lake’s floor.

The belt of organisms just above the lake floor comprise what is known as a nepheloid layer. The scientists thought they would find a thin nepheloid layer similar to those in the oceans. ″We expected it to be a few inches thick - a veneer that hugged the bottom,″ Cooper said.

Instead, after taking the submarine through 500 feet of clear water at Lake Huron’s Mackinac Basin, they encountered ″what looked like a very dense snowstorm of particulate matter″ 20 feet to 30 feet deep, Cooper said. In other spots, the layer was several feet thick.

About 70 percent to 80 percent of the cloud is living organisms, he said, and it also is believed to contain clay-like material that may harbor pollutants.

Cooper’s brother, William, chairman of the Michigan State University zoology department, said it’s likely that organic pollutants such as DDT stick to the nepheloid particles and remain in the food chain instead of settling to the lake bottom. However, he said no conclusions can be drawn until the new data is studied.

About $650,000 was to be spent on the project, according to Michigan State, which also took part. The data is to be shared by about 100 scientists from a dozen universities.

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