Posted on 07/01/2003 6:05:26 PM PDT by syriacus
Findings reported from the first ever detailed exploration of the Gakkel Ridge—the northernmost segment of the worldwide mid-ocean ridge system that snakes for 1,100 miles (1,800 kilometers) beneath the Arctic Ocean—underscore the waiting discoveries on the frontiers of Earth science.
For decades scientists longingly eyed the Gakkel Ridge. But since it lies beneath a cover of sea ice, access to it has been limited. Apart from a single submarine study, much of what was known about the undersea region's geology was extrapolated from studies of other, more accessible, ocean ridges.
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But based on rock samples dredged from the ocean floor and detailed sonar mapping, researchers were surprised to discover that the Gakkel Ridge is actually a hotbed of volcanic activity and hydrothermal vents.
(Excerpt) Read more at news.nationalgeographic.com ...
From the NSF, June 25, 2003: Behavior of Arctic Ocean Ridge Confounds Predictions; May Lead to New Insights into Crust Foundation
ARLINGTON, Va.—The discovery that an ocean ridge under the Arctic ice cap is unexpectedly volcanically active and contains multiple hydrothermal vents may cause scientists to modify a decades-long understanding of how ocean ridges work to produce the Earth's crust.[excerpt]
Nature, 16 January 2003: Hydrothermal vents: Arctic hotspots
The Gakkel ridge under the Arctic Ocean is the slowest spreading mid-ocean ridge on Earth, so the recent AMORE survey — conducted with the ice-breakers USCGC Healy and PFS Polarstern — was not expected to reveal much submarine hydrothermal venting there. In fact, abundant venting was discovered, close to volcanic centres on the Gakkel ridge. These vents are physically isolated from the rest of the world's ocean ridges, so may be populated by previously unknown species of thermophilic organisms.[excerpt]
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 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 sea-bed 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 only a quarter-inch 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 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, 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 600-mile 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.
Some of the volcanic domes that the survey detected rise more than a mile from the three-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.
It may be that the composition of the underlying rock, or other factors besides the rate at which the sea floor is spreading, determine whether there is volcanic activity or the kind of cracking and heat that can result in hydrothermal vents, Dr. Michael said.
The findings also raise the tantalizing prospect that the vents nourish novel ecosystems in the Arctic, Dr. Edmonds and other marine scientists said.
The Gakkel's hydrothermal vents, which spew torrents of water heated by magma welling from the planet's fiery depths, are similar to others found elsewhere in the world's oceans, most of them nourishing specialized ecosystems.
But because the Arctic Ocean is connected to the Pacific and Atlantic by relatively shallow passages, it is possible that vents there — isolated for millions of years — might support species not seen anywhere else, the scientists said.
One of the deepest connections is the strait running from the Arctic Ocean past Greenland to the North Atlantic, Dr. Edmonds said. But even there, she said, submerged ridges and Iceland act "like a wall between the Gakkel Ridge and the Mid-Atlantic Ridge," where vent communities have been seen.
The next challenge will be to explore the Arctic vents up close, Dr. Edmonds said. It is one thing to drop dredges and sensors into the Arctic off the stern of a great bluff-nosed icebreaker. It is another thing to consider doing the same thing with a submarine or even a costly unpiloted robotic vehicle. The grinding sea ice has been known to shear through heavy connecting cables.
Oceanographers are developing several new submersibles that by 2005 or 2006 might be able to do the job, Dr. Edmonds said.
Don't you believe it! Not for one minute! Natural my arse. It's all those heavy SUVs pounding across America that cause the fissures to open up. Global warming is still thier fault.
Thursday, June 26, 2003
While fascinating to study, the volcanic and geological action on Gakkel Ridge isn't about to melt the Arctic ice, he adds. It's estimated the geological activity on the ridge has been going on for almost 53 million years, and it hasn't made a dent yet."It's like holding up a small match in a big swimming pool," he says, noting that the water in the Arctic Ocean hovers around -1 or -2 C.
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