the Mid-Atlantic Ridge

[Bianca]

A further mystery concerns the migrations of the European eels.

These animals spawn in the Sargasso Sea west of the United States of America.

The newborn eels start their three years long eastbound migration following the Gulf
Stream to the European rivers. Having reached sexual maturity they migrate back to
the Sargasso Sea within four months, however leaving the Azores to their left this time.
It has been proven that the eels need freshwater to reach maturity but why do they
venture on this long journey across the Atlantic Ocean?

Could it be that the eels have a genetic memory of a mainland with freshwater in the
Atlantic Ocean but cannot find it again because it sank? Is that why they keep on
migrating until they reach Europe?




Another phenomenon relates to the suicide of the Norwegian lemmings.

Every year when their homeland is running short of food, these little rodents start
migrating westwards. At the end of their migration they jump into the ocean and
continue swimming westwards until they drown. What is it these animals are after
in the ocean? Are they following a basic instinct driving them into the ocean? Are
they looking for a land that offered them plenty of food a long time ago?

Was this land Atlantis, located in the Atlantic Ocean according to Plato?


http://www.atlantia.de/atlantis_english/myth/atlantis/atlantis_atlantic.htm

[Bianca]

http://www.lostcity.washington.edu/







dhill757
Hero Member

Posts: 330



    Re: ATLANTIS & the Atlantic Ocean
« Reply #69 on: March 31, 2007, 04:25:34 pm » Quote 

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Scientists Seeking Secrets Of "Lost City"

The remarkable hydrothermal vent structures serendipitously discovered last December in the mid-Atlantic Ocean, including a massive 18-story vent taller than any seen before, are formed in a very different way than ocean-floor vents studied since the 1970s, according to findings published July 12 in the journal Nature. The circulation of fluids that forms this new class of hydrothermal vents apparently is driven by heat generated when seawater reacts with mantle rocks, not by volcanic heat.


No one has previously seen a field quite like this but Deborah Kelley, a University of Washington oceanographer and lead author of the Nature paper, says this kind of vent may be common on the seafloor. If so, scientists may have underestimated the extent of hydrothermal venting, the amount of heat and chemicals pouring into the world's oceans and the abundance of life that thrives in such conditions.

"Rarely does something like this come along that drives home how much we still have to learn about our own planet," Kelley says. "We need to shed our biases in some sense about what we think we already know."

The Lost City Field, named partly because it sits on the seafloor mountain Atlantis Massif, was discovered Dec. 4. The expedition was funded by the National Science Foundation and led by Scripps Institution of Oceanography's Donna Blackman, UW's Kelley and Duke University's Jeffrey Karson. Blackman and Karson are among the paper's co-authors.

Lost City is like other hydrothermal vent systems where seawater circulates beneath the seafloor gaining heat and chemicals until there is enough heat for the fluids to rise buoyantly and vent back into the ocean. As the warm fluids mix with cold seawater the chemicals separate from the vent fluids and solidify, sometimes piling up into impressive mounds, spires and chimneys of minerals.

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It was immediately clear, however, that the Lost City Field was unlike other hydrothermal vent systems in a number of ways. First, there was the height attained by some of the structures – the mighty 180-foot vent scientists named Poseidon compares to previously studied vents that mostly reach 80 feet or less. The new vents are nearly 100 percent carbonate, the same material as limestone in caves, and range in color from a beautiful clean white to cream or gray, in contrast to black smoker vents that are a darkly mottled mix of sulfide minerals. And perhaps the Lost City's most distinctive feature is that it is sitting on 1.5 million-year-old crust formed from mantle material.

"We did not realize that hydrothermal activity of this sort could be taking place on seafloor generated millions of years ago," says Margaret Leinen, assistant director for geosciences at the National Science Foundation.

Most previously known vents form along the youngest part of spreading "centers," areas where tectonic forces pull apart the seafloor and magma flows up into the space sometimes during volcanic eruption. Heat from the underlying magma chambers drives hydrothermal vent circulation and generates water temperatures as high as 400°C.

Lost City is in a part of the ocean where magma chambers are present only rarely and volcanic eruptions happen perhaps every 5,000 to 20,000 years, compared to fast-spreading centers where eruptions may occur every five to 10 years. In the area of the Lost City, spreading and faulting during the last 1 million to 1.5 million years has stripped the mountain down to the underlying mantle rocks. Hydrothermal circulation appears to be driven by seawater that permeates into the deeply fractured surface and transforms olivine in the mantle rocks into a new mineral, serpentine, in a process called serpentinization.

The heat generated during serpentinization appears to drive hydrothermal circulation at the Lost City, Kelley says. The process produces low temperature fluids of 40 to 75°C that are rich in methane and hydrogen.

[Bianca]

Papers published in the early 1990s noted that methane-hydrogen signatures were common over slow- or ultra-slow-spreading centers like the Mid-Atlantic Ridge, where Lost City is. That led scientists to believe that venting was occurring, but there had been no example like the Lost City Field before now, Kelley says.

If the Nature paper is right about the forces driving hydrothermal circulation at the Lost City Field, Kelley says it's easy to imagine there could be many more such systems. Within a mere 50-mile radius of the Atlantis Massif are three similar mountains subject to the same fracturing, the same intrusion of seawater and perhaps the same reactions with mantle material. And those four represent only a tiny fraction of the potential sites along the 6,200 mile Mid-Atlantic Ridge, as well as the Indian ridges and the Arctic Ridge, also considered slow- and ultraslow-spreading centers.

Although large animals that typify other vent environments appear to be rare at Lost City, microbial life seems to thrive there. The microbial samples collected at Lost City show a community that is diverse and so dense in places that magnification reveals rocks so covered with microorganisms that one can't see the minerals, Kelley says. "These environments may host a significant and important amount of microbial life, if these systems prove to be common and operate for long periods on old ocean crust."

Other authors of the paper are Gretchen Fruh-Green of the Institute for Mineralogy and Petrology in Zurich; Pete Rivizzigno of Duke; David Butterfield, Marvin Lilley, Eric Olson, Mathew Schrenk, Kevin Roe and Geoff Lebon, all from the University of Washington or affiliated with the National Ocean and Atmospheric Administration; and the shipboard party on the expedition last December.

[Bianca]

Hydrothermal Vent Systems Could Have Persisted Millions Of Years, Incubated Life
Science Daily — The staying power of seafloor hydrothermal vent systems like the bizarre Lost City vent field is one reason they also may have been incubators of Earth's earliest life, scientists report in a paper published in the July 25 issue of Science.

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Discovered just 2½ years ago during a National Science Foundation-funded expedition in the mid-Atlantic Ocean, Lost City has the tallest vents ever seen the 18-story behemoth at the site dwarfs most vents elsewhere by at least 100 feet. Water is circulated through the vent field by heat from serpentinization, a chemical reaction between seawater and the mantle rock on which Lost City sits, rather than by heat from volcanic activity or magma, responsible for driving hydrothermal venting at sites scientists have been studying since the early 1970s.

If hydrothermal venting can occur without volcanism, it greatly increases the places on the seafloor of early Earth where microbial life could have started. It also means explorers may have more places than previously thought to look for microbial life in the universe.

Although the Lost City vent field is a youthful 30,000 years old, Lost City-type systems might be able to persist hundreds of thousands, possibly millions, of years, says lead author Gretchen Früh-Green of the Swiss Federal Institute of Technology and co-authors from the University of Washington, Duke University and National Atmospheric and Oceanic Administration. One can imagine how such stable, long-lived systems pumping out heat, minerals and organic compounds for millennia might improve the chances for life to spark and to be sustained until it could take hold, say these scientists.

"It's difficult to know if life might have started as a result of one or both kinds of venting," says Deborah Kelley, University of Washington oceanographer, "but chances are good that these systems were involved in sustaining life on and within the seafloor very early in Earth's history."

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As far as longevity and stability, it's possible that black-smoker systems might last as long as 100,000 years but it's unlikely, Kelley says. That's because black-smoker systems typically form where new seafloor is being created, a process that even if a volcanic eruption doesn't bury a hydrothermal vent field in lava will eventually shove the seafloor bearing the vents away from the source of volcanic heat needed to power them.

Lost City is already nine miles from the nearest volcanically active spreading center and sits on 1.5 million-year-old crust. Seawater permeating deeply into the fractured surface of the mantle rocks transforms olivine into a new mineral, serpentine. The heat generated during this process is not as great as that found at volcanically active sites where fluids can reach 700 F but it is enough to power hydrothermal circulation and produce vent fluids of 105 to 170 F.

Tectonics, the movement of the Earth's great plates, contributes to the fracturing of the mantle rock. But a big reason this kind of system is so self-sustaining, the Science report says, is that fracturing also happens because rocks undergoing serpentinization increase in volume 20 percent to 40 percent. Kelley likens it to water seeping into tiny cracks in roads, then freezing and expanding to cause ruts and frost heaves in the pavement.

Scientists think many Lost City-type systems were possible on early Earth because so much of the mantle had yet to be skinned over with crust, putting it in contact with seawater and making serpentinization possible, Kelley says.

Lost City is the only vent field of its kind known today but scientists say more could exist. Within a 60-mile radius of Lost City are three similar mountains and there are other, potential sites along thousands of miles of ridges in the mid-Atlantic, Indian Ocean and Arctic.

[Bianca]

Beyond Earth, peridotite the mantle material that reacts with seawater during serpentinization is abundant on all the terrestrial planets in our solar system, says Jeff Karson, Duke University professor. "Peridotite can be exposed by tectonic processes or by major cratering events. This means that Lost City-type venting could occur, or has occurred, in oceans on other planets, and such venting would have the potential to support microbial systems."

Lost City-type systems also may be conducive to life because their fluids are high pH and rich with organic compounds compared to black-smoker systems.

Black smokers get their name because it can appear as if smoke is billowing from the vents. What's actually being seen are dark minerals precipitating when scalding hot vent waters meet the icy-cold ocean depths. Water venting at Lost City, in comparison, is hot enough to shimmer but not "smoke." Because of the different chemistry, black-smoker vents are a darkly mottled mix of sulfide minerals whereas the Lost City vents are nearly 100 percent carbonate, the same material as limestone in caves, and range in colors from white to cream to gray.

The field, named Lost City in part because it sits on a seafloor mountain named the Atlantis Massif, was discovered Dec. 4, 2000, when scientists weren't even looking for hydrothermal vents.

"The discovery of the Lost City vent field is a wonderful example of serendipity in science studying one problem and discovering something totally new and unexpected," says David Epp, program director in NSF's marine geology and geophysics program. "The detailed work is just beginning and should change the way people think about vent systems."

This spring, the NSF funded the first major scientific expedition to Lost City since its discovery. Led by Kelley and Karson, the expedition is documented at: http://www.lostcity.washington.edu/

Other Science co-authors are the Swiss Federal Institute of Technology 's Stefano Bernasconi, University of Washington's Kristin Ludwig and Giora Proskurowski, and National Atmospheric and Oceanic Administration 's David Butterfield.

Note: This story has been adapted from a news release issued by University Of Washington.


http://www.sciencedaily.com/releases/2003/07/030725080845.htm

[Bianca]

HYDROTHERMAL VENT SYSTEM UNLIKE ANY SEEN BEFORE FOUND IN ATLANTIC



 

[Bianca]

A ledge or flange made of carbonate juts out from the side
of a 160-foot chimney in the Lost City hydrothermal vent
field.

The chimney and flange are made of carbonate minerals
and silica dissolved in 160 F fluids that flow out of the sea-
floor and then precipitate when the fluids hit the icy cold
seawater.

The flange is 1 meter across.


(Photo credit:
University of Washington)
 

[Bianca]

A new hydrothermal vent field, which scientists have dubbed "The Lost City," was discovered Dec. 4 on an undersea mountain in the Atlantic Ocean. The unexpected discovery occurred at 30 degrees North on the Mid-Atlantic Ridge during an oceanographic cruise aboard the research vessel Atlantis.

A team of scientists led by Deborah Kelley from the University of Washington, Donna Blackman from the Scripps Institution of Oceanography and Jeff Karson of Duke University conducted the National Science Foundation-supported expedition.

"We thought that we had seen the entire spectrum of hydrothermal activity on the seafloor, but this major discovery reminds us that the ocean still has much to reveal, "says Margaret Leinen, NSF assistant director for geosciences.

"These structures, which tower 180 feet above the seafloor, are the largest hydrothermal chimneys of their kind ever observed," said Deborah Kelley, a University of Washington geologist and co-principal investigator on the cruise.

Most previously studied vents are less than 80 feet high, the tallest being a 135-foot vent dubbed Godzilla, on the seafloor off the Washington state coast. It toppled in half a few years ago.

"If this vent field was on land, it would be a national park," Duke University structural geologist Jeff Karson said of the new find. Karson, a second co-principal investigator, joined Kelley in the submersible Alvin on a dive to the site on Dec. 5.

Perhaps most surprising is that the venting structures are composed of carbonate minerals and silica, in contrast to most other mid-ocean ridge hot spring deposits, which are formed by iron and sulfur-based minerals. The low-temperature hydrothermal fluids may have unusual chemistries because they emanate from mantle rocks.

[Bianca]

[Bianca]

The top of this 18-story-tall chimney in the Lost City
hydrothermal vent field is nearly 30 feet in diameter
and is actively venting fluids.

(Photo credit:
University of Washington)

[Bianca]

Nothing like this submarine hydrothermal field has ever been previously observed, say the scientists. These events are unique, they believe, because they rest on one-million-year-old ocean crust formed tens of kilometers beneath the seafloor, and because of their incredible size. Dense macrofaunal communities such as clams, shrimps, mussels, and tube worms, which typify most other mid-ocean ridge hydrothermal environments, appear to be absent in this field. The Lost City Field was discovered unexpectedly while studying geological and hydrothermal processes that built an unusually tall, 12,000-foot-mountain at this site. In this area, deep mantle rocks called serpentinized peridotites, and rocks crystallized in subseafloor magma chambers, have been uplifted several miles from beneath the seafloor along large faults that expose them at the surface of the mountain.
"As so often happens, we were pursuing one set of questions concerning building of the mountain and we stumbled onto a very important new discovery," said Donna Blackman, a geophysicist from the Scripps Institution of Oceanography and chief scientist of the expedition. She added that "the venting towers are very spectacular and, although they bring up a whole new set of questions, we will learn about the evolution of the mountain itself as we study the vents carefully in the future."

 

 Observations using the submersible Alvin and deep-towed vehicle Argo, operated by Woods Hole Oceanographic Institution, show that the field hosts numerous active and inactive hydrothermal vents. The steep-sided, 180-foot-tall deposits are composed of multiple spires that reach 30 feet in width at their tops. They are commonly capped by white, feathery hydrothermal precipitates. The tops and sides of the massive edifices are awash in fluids that reach temperatures up to 160 degrees.
From the sides of the structures, abundant arrays of delicate, white flanges emerge. Similar to cave deposits, complex, intergrown stalagmites rise several meters above the flange roofs.

Underneath the flanges, trapped pools of warm fluid support dense mats of microbial communities that wave within the rising fluids. Downslope, hundreds of overlapping flanges form hydrothermal deposits reminiscent of hot spring deposits in Yellowstone National Park. During the Alvin dive, expedition leader Patrick Hickey collected rocks, fluids, and biological samples for shore-based analyses.

"By studying such environments, we may learn about ancient hydrothermal systems and the life that they support," suggested Kelley.

[Bianca]

Cone-shaped pinnacles, about 20 feet can be seen, rise from
a 160-foot-tall edifice in the Lost City hydrothermal vent field.

White-colored chimneys are actively venting fluids in contrast
to the beige-colored edifices that are no longer venting.


(Photo credit:
University of Washington)
 

[Bianca]

Kelley, Blackman and Karson are at sea until Saturday, Dec. 16, and return to their home institutions from there.

The three principal scientists may be contacted aboard ship until Sat. Dec.16. (Note: e-mail is only sent and received three times a day.)



Donna Blackman

Debbie Kelley

Jeff Karson



Expedition web site:

http://earthguide.ucsd.edu/mar

 www.washington.edu/.../12-00archive/k121200.html


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                                                                    'DHILL"



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                                                   "ATLANTIS & THE ATLANTIC OCEAN"



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