Magazine article Science News

Seafloor System Has Been Active for Ages. (Long-Term Ocean Venting)

Magazine article Science News

Seafloor System Has Been Active for Ages. (Long-Term Ocean Venting)

Article excerpt

Analyses of mineral deposits in and around a unique set of hydrothermal vents beneath the Atlantic Ocean suggest that the site's tallest towers of minerals have been growing for at least 30,000 years.

The vent system, dubbed the Lost City because its lofty chimneys of carbonate rock can reach the height of an 18-story building, is situated on the side of an undersea mountain about 2,500 kilometers east of Bermuda and 15 km away from the Mid-Atlantic Ridge (SN: 7/14/01, p. 21). The mineral-rich fluids that spew from the ocean floor are warmed by heat-generating chemical reactions between ocean water and subsurface rocks rather than by volcanic activity, a characteristic that sets this vent site apart from all others yet discovered.

The Lost City's formations consist primarily of calcium carbonate, says Gretchen L. Fruh-Green, a geochemist at the Swiss Federal Institute of Technology in Zurich. She and her colleagues used carbon-dating techniques to determine the age of material gathered from active and extinct vent structures, as well as seafloor sediments nearby.

The oldest chimney material analyzed by the scientists was deposited about 25,000 years ago, well before the peak of the last ice age. Carbonate deposits in cracks near the vents are about 32,000 years old. Although the team has dated only a few mineral samples, the Lost City vents appear to have been continually active for at least 30,000 years.

White, feathery formations that surround the active vents are much younger, deposited only in the past few decades, the researchers report in the July 25 Science. …

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