Deep beneath the ice-sheathed Arctic Ocean, a 1,609km seam in the earth's rocky crust, long thought to be largely dormant, has been revealed as a simmering necklace of volcanoes and hot-water vents that may harbor unique 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 midocean 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 greatly elaborate on initial descriptions of the Arctic sea-floor vents published in the same journal in January.
The Gakkel is the least active of the midocean 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 generally spreads just under a centimeter or so a year in each direction, about a seventh or less of the spreading rate seen in most midocean 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 the summer of 2001 on the two ships included just one vent specialist, said that expert, Dr. Henrietta 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, which were attached to cables as they lowered rock-sampling dredges and checked for rising temperatures and turbidity -- hints of any upstream plume of mineral-rich, volcanically heated water gushing from the sea bed into the frigid sea.
The researchers said they were shocked when more than 80 percent of the instrument deployments detected such emissions over the 966km portion of the ridge that was surveyed. "We were expecting it to be practically dead," said Dr. 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 -- the American Coast Guard vessel Healy and the German Polarstern -- 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 Dr. 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.