Arctic Seabed Yields
Volcanic Secrets

Arizona Republic
Posted July 23, 2003

1,000-mile-long seam in Earth's crust not as quiet as believed.

By Andrew C. Revkin.

Deep beneath the ice-sheathed Arctic Ocean, a 1,000-mile seam in the Earth's rocky crust, long thought to be dormant, has been revealed as a simmering necklace of volcanoes and hot-water vents that may harbor unusual life forms.

Earlier surveys in the depths near the North Pole had identified a couple of seabed volcanoes in one place along the seam, which is called the Gakkel Ridge and bisects the polar ocean from Greenland to Siberia.

But sonar and seismic readings, rock samples and water measurements gathered during a recent joint expedition by German and American ice-breaking ships have created a detailed overview of the surprisingly dynamic geology of the ridge.

Researchers and experts not directly involved in the new work said the findings challenged longstanding notions about such mid-ocean ridges, which are the geologic factories forging Earth's ever-changing crust.

The charts and two accompanying papers appear in the current issue of the journal Nature and elaborate on descriptions of the Arctic sea-floor vents published in the same journal in January.

The Gakkel is the least active of the mid-ocean ridges found throughout the world's seas. These are the gutter-shaped valley and mountain systems where the crust of the sea floor spreads out to each side and hot magma pushes to the surface.

Earlier surveys measuring the magnetic signature of rocks in the Gakkel ridge found that it spreads only a quarter-inch or so a year in each direction, about a seventh or less of the spreading rate seen in most mid-ocean ridges.

The slow spreading rate was presumed until now to inhibit the surge of magma, the researchers and other experts said.

The likelihood of finding volcanoes and life-sustaining vents was so low that the 30-member team that put to sea in summer 2001 included just one vent specialist, said Henrietta N. Edmonds, a geochemist from the University of Texas.

"I was brought along as a funky add-on," she said. "They were saying, 'Man, she's going to be bored for a couple of months.' "

That was before the results started pouring in from her instruments.

"We were expecting it to be practically dead," said Peter J. Michael, the lead author of one of the new Nature papers and a geologist at the University of Tulsa. "Instead we got so many readings that we thought the equipment was not working right."

By chance, that summer the polar ice pack was exceptionally thin and widely dispersed, so the ships were able to collect far more data than had been expected. Until this expedition, the only surveys of the ridge had been done sporadically by Navy submarines that, while submerged, cannot maintain precise coordinates on their positions.

"I think we know the topography of Mars and the moon better than that area of the Arctic," said Wilfried Jokat, a lead author of one of the Nature papers and a senior scientist at the Alfred Wegener Institute for Polar Research in Bremerhaven, Germany.

Some of the volcanic domes that the survey detected rise more than a mile from the 3-mile-deep bottom of the rift valley running down the center of the Gakkel Ridge.

The hot spots found along the ridge appear to have existed fairly consistently for up to 25 million years in some cases, according to the papers.

The findings raise the tantalizing prospect that the vents nourish novel ecosystems in the Arctic, Edmonds and other marine scientists said.

Arizona Republic

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