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Deep-sea denizen may tell of ocean's past.

Scientists have come up with an Old Man of the Sea that makes Hemingways's character seem a youngster by comparison. This elderly creature of the deep may have its own tale to tell -- not about a giant marlin, but about the ocean's past.

Preliminary carbon-14 dating suggests that the coral-like Gerardia specimen -- retrieved from the Atlantic at a depth of 600 meters -- may have lived for as long as 1,700 years, researchers reported last week at the International Radiocarbon Conference in Tucson, Ariz. While they emphasize that their radiocarbon results await confirmation, they believe Gerardia may provide a valuable record of environmental changes in the deep ocean over the last millennium or more.

Gerardia is not a single organism but a colony of polyps connected to each other by living tissue. Throughout their lives, the polyps slowly build up layers of proteinaceous skeleton. "We're able to get layers like a tree and date them," says Sheila Griffin of the Woods Hole (Mass.) Oceanographic Institution. Griffin and her colleagues suggest that analyses of the skeletal layers could reveal fluctuations in water temperature over time. In addition, measurements of carbon in the skeleton may offer insights into the puzzling carbon cycle of the ocean. As concern over global warning intensifies, understanding how and at what rate the ocean absorbs carbon has become an increasingly important research goal.

Scientists have sought clues to past atmospheric changes by studying the annual rings of the bristlecone pine, which can live for thousands of years. They have also analyzed million-year-old coral reefs to track variations in the shallow sea. However, the past of the ocean's deeper waters has remained closed to observation. Without an oceanic equivalent to the bristlecone, Griffith says, "we've never been able to record things like temperature changes at these depths."

Gerardia's secret to long life is the constant replacement of old polyps with new ones. "The [colonies] are potentially immortal; they can go on forever," says zoologist Malcolm Shick of the University of Maine, Orono. However, he adds, previous specimens have not exceeded a life span of 250 years.

Griffin says it's possibled that her group's preliminary radiocarbon date represents the age of seafloor sediment within the skeleton rather than the age of the skeleton itself. Before publishing their results, the researchers plan to use other isotope tests, and possibly a chemical dating method called amino acid racemization, to confirm the specimen's venerable age.
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Title Annotation:coral-like Gerardia species may provide a record of environmental changes in the deep ocean over the last millennium
Author:Travis, John
Publication:Science News
Date:Jun 1, 1991
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