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After the final overnight Argo II photographic survey wrapped up early Tuesday with the remotely operating vehicle's long tether cable receiving a final protective linseed oil bath,
On Thursday afternoon, with the wax coring now history, Texas A&M geologist Jay Miller had barely surfaced from the 15th and last daily two-mile deep dive aboard the manned research submarine Alvin when Atlantis began preparing to head north-northwest back to Manzanillo, Mexico.
But, after unceremoniously vacating the Hess Deep study area for good about suppertime, Capt. George Silva agreed to another short westerly diversion so Klein - staring intensely at a computer lab screen - could scan unsurveyed ocean bottom next to the incipient ridge using Atlantis's Seabeam sonar array (see dispatch 12).
That survey was over by 9 a.m - just as "Blade Runner" began airing on the ship's lounge VCR - and Atlantis "turned the corner" for the three-day transit that would be the Hess Deep expedition's swan song.
As soon became obvious, it was much too soon to celebrate.
With Atlantis now slicing through the water at 12 knots, Friday morning found researchers still hurrying to complete dive transcripts and maps for the burgeoning Hess Deep records. They also had to saw and bubble-wrap rock samples for shipment back to Duke and other participating institutions. But yet another hectic day finally mellowed out at 5 p.m. when Atlantis Stewart Carl Wood held his second on-deck evening cookout.
In a brief Saturday morning change of pace, scientists and graduate students rendezvoused after breakfast to help haul a replacement braided "main line," the long thick rope - appropriately nicknamed "the anaconda" - that links the Alvin to Atlantis's A-frame stern crane (see dispatch 10).
Then a scheduled early afternoon scientific meeting was abruptly canceled so the Hess Deep group would have more time to peck at their computers, or do dirty work like scrubbing off rock dust grime from the wet lab.
But all Saturday afternoon computing activities themselves had to be halted for several hours after Atlantis's vital air conditioning system malfunctioned. Weighing their diminishing options, some researchers used the hiatus to grab quick naps in uncomfortably warm staterooms.
"I think that will start to show up more as people catch up on their rest and the full impact of the study begins to sink in," Karson added in a long, reflective Friday interview. "Basically, we've been over-saturated with fantastic new information. But I think the fatigue and long hours, and just having to keep up with the never-ending rush of incoming data, has done a lot to put a damper on our spontaneity."
Karson, though, had no trouble with repressed emotions.
"This has been far and away the most scientifically gratifying cruise I have ever been on," he beamed, "as well as the most harmonious and, on a personal level, enjoyable.
"I've been trying to do a study like this for 20 years, and it's fantastic that we finally had the right tools to do what I really wanted to do on the sea floor for all that time."
A number of factors converged to create this research cruise of a lifetime, he said. The weather was perfect and the equipment, by and large, all worked - highly unusual success stories in themselves. The team of scientists and students Karson selected also proved both compatible and appropriate for the mission - which are not always givens either.
In addition, the latest generation high-tech devices that Karson's group was able to send to the bottom - the DSL 120 side-scan sonar, Argo II remotely operated photographic surveyor, and Alvin itself - have all benefited from years of technological updating by Woods Hole Oceanographic Institution specialists.
Finally, what the Hess Deep researchers found during their three weeks of intensive studies will do much to overturn prevailing scientific dogma and spawn years of scientific papers, graduate student theses and doctoral dissertations, Karson added.
Hess Deep is a Grand Canyon sized underwater chasm that cuts through a zone where new ocean crust is spreading east from the place is was created: a volcano-dotted mid-ocean ridge called the East Pacific Rise (EPR).
Because it exposes more than a mile thick slice of rock in layer cake fashion, Hess Deep allows scientists to see what is usually buried: the fossil record of about 1 million years of past EPR volcanic activity. Scientists are particularly interested in these fossil crusts because they provide clues about places they cannot directly explore: the very hot and sometimes violent interiors of such ridges.
Mid-ocean ridges make up a global network of spreading zones where the Earth ejects molten lava to make new skin, and scientists have developed general hypotheses about how they behave.
Studies around the world suggest that slow-spreading ridges like the Mid-Atlantic Ridge produce less magma - which erupts on the ocean floor as lava - than do fast spreading ridges like the EPR.
In slow-spreading ridges, volcanic activity is thought to be especially "episodic," Karson said. Crust is made along a ridge in bursts, separated by as much as 1 million years of almost no activity. During the quiet phase, huge fractures develop as the remains of former volcanoes get shoved away from the spreading center like defective parts on an assembly line.
As a result, the structure of new crust is thought to be "more variable" at slow-spreading ridges than at fast-spreading ones, he added.
Because volcanic activity on fast spreading ridges seems to occur more frequently, scientists have hypothesized that the crust produced there has a more regular structures But it is usually impossible to tell for sure, because the lava blanket also hides the underlying structures from inspection.
Since those structures are usually inaccessible, scientists have had to rely on indirect evidence, such as studying how man-made earthquake waves interact with underlying rock (seismic reflection profiling), or visiting the eroded remains of very old ocean crust that have been uplifted onto dry land (ophiolites).
Using this kind of information, scientists developed a "prevailing view" that the uppermost crusts made at fast-spreading ridges is composed of three layers with "very simple horizontal boundaries," and that each of these rock units is "fairly homogeneous," Karson said.
The Hess Deep rift, and the increasing availability of high-tech tools like Woods Hole's deep diving submarine Alvin, have afforded scientists a rare opportunity to test this hypothesis with direct observation.
In 1988, a French team used another manned sub called the Nautile to do just that. And in 1990, Karson and Steve Hurst, a Hess Deep co-principal investigator then at Duke and now at the University of Illinois at Champaign-Urbana, made their own dives in the Alvin.
What the French team saw was "the textbook view," Karson recalled, with the crustal layers all looking homogeneous and ordered, and the dikes running mostly straight up and down.
The Duke team, however, did not.
"We noted large variations in the thicknesses of the (upper) volcanic unit and (middle) sheeted dike unit," Karson recalled. There was also a tremendous amount of faulting and rotation of crustal blocks in the dike complex in particular."
Moreover, the dikes tended to slope down to the east instead of being vertical. And they observed "deformed dikes" and "cross-cutting dikes" as well, old magma conduits that "cut across the older, more complicated fractured material."
What Karson and Hurst saw in the Alvin suggested that crust made along the East Pacific Rise endures violent changes as it rolls off the assembly line. "So it was natural that people would say that the French dove in a typical place that conforms to the dogma, and that our 1990 dive program was in a place that was anomalous," Karson said.
Even he and Hurst thought that might be the case. And so "the contrast of those two different results was one of the big motivations for us to come back out here," he added.
The goal of the 1999 Hess Deep expedition was to investigate a longer section of the Hess Deep canyon wall than either the previous Nautile or Alvin dives, and to do it more systematically with an array of the most up-to-date tools.
Karson's new team - from Duke and six other institutions - began by sending the DSL 120 side scan sonar along 21 miles of Hess Deep's north face, using sound waves to identify exposed outcrops and general geological features there (see dispatch 3).
The scientists followed that up with the Argo II, which used an array of cameras and lights to photograph the most interesting spots identified by DSL 120 (see dispatch 4 and dispatch 5).
The photographic surveys were so methodical that there was only enough time to document "less than 1 percent" of what DSL-120 "saw," Karson estimated.
Back in labs aboard Atlantis, Hess Deep researchers began the difficult and tedious job of computer melding the Argo II digital images together to create "mosaics" composed of as many as 100 different pictures - something that had never been tried before in an exposed slice of ocean geology (see dispatch 9).
Argo II images were also used to pinpoint the best places to send Alvin during its 15 successive days of daily dives that began March 25 (see dispatch 6). By the time the Alvin dive program concluded, enough Argo II images had been "mosaicked" to allow researchers to know what the places they would visit looked like before they ever squeezed in the submarine - another unprecedented accomplishment.
One Alvin dive team - Bob Varga of the College of Wooster in Ohio and Dan Curewitz, a soon-to-graduate Duke doctoral student - clearly identified Argo mosaic features when they looked through Alvin's thick windows.
All the Hess Deep scientists, graduate students and undergraduates - as well as Duke technician Pete Rivizzigno - made at least one Alvin dive. Different dive teams would emerge from the Alvin each day, tired but pumped up by the excitement of what they had seen.
The reports they delivered at each day's science update were consistent. They observed more of what Karson and Hurst had seen in 1990 - in unprecedented, detail.
"One of the big surprises – and an important lesson in science for us - is that in fact that what appears to be anomalous turned out to be the typical expression of spreading on the East Pacific Rise," Karson said.
"Instead of seeing that textbook form, what we see is that the more complicated structure we found in 1990 is typical of the entire survey area - an area that is tens of kilometers long [one kilometer is .6 miles] and corresponds to more than 1 million years worth of spreading.
"So we can't really regard it as anomalous anymore. In fact, our previous notion of what is typical and what is anomalous is turned on its head here."
The results suggest that still-to-be-pinpointed forces regularly tilt the blocks of crust that are made on the EPR. That tilting is graphically evident in the dikes, which were probably originally completely vertical. As the dikes dip, fractures may form between them that let them slip like leaning books in a bookshelf. That could cause the volcanic layer above them to dip in the opposite direction, a tendency "we've seen beautifully displayed in the Argo images," Karson said.
And the presence of cross-cutting dikes implies that crustal sections begin tilting when they are still on mid-ocean ridge, not later, Karson added. After the initial tilt, new dikes may intrude vertically into the leaning older field of dikes, cross cutting them. Then the section may even tilt some more, tilting the newer dikes off the vertical.
The cross-cutting process will only end when the section moves sufficiently away from its magma source, the spreading center. Without magma there will be no additional dikes.
At an early afternoon summing-up science meeting today in Atlantis's library, Karson wondered aloud what such a "highly variable internal structure" in Hess Deep crustal segments says about "what is going on under the spreading center" - the volcanic seam where the crust is made. What it suggests to Karson is "a much more dynamic and interesting system" than scientists have thought, he said.
Scientists at the meeting also wondered about what they did not find.
Karson and Hurst had actually both expected to see more variety in the tilt of the dikes. Joanna O'Neill, a recently graduated graduate student from the University of California at Santa Barbara, was surprised to see no fossil evidence of "black smokers" - hot water upwelling sites that are found at intervals along the today's East Pacific Rise.
Kathy Gillis, a researcher from the University of Victoria in Canada, wondered why there were not more signs that seeping seawater had penetrating fractures and "altered" the Hess Deep rock's chemistry.
Detailed chemical analysis has yet to begin on samples cut from the 227 rocks that were brought up by Alvin, a collection that Klein called "remarkable." She and Michael Stewart, a Duke doctoral student, will be studying those specimens for some time, as will researchers from other universities (see dispatch 10).
This afternoon, the scientists also began discussing what they would like to do on their next trips to Hess Deep.
Meanwhile, Karson laid out a proposed timetable for presenting the voluminous results of this cruise to the geological community. It would include an initial report to a major peer-reviewed journal by mid summer, a block of presentations at next December's meeting of the American Geophysical Union, and a "nice batch" of detailed scientific papers in about a year.
"We have a tremendous amount of compelling new material to show," he said.
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