June 12, 1996 Contact: Robert Irion (408) 459-2495; irion@ua.ucsc.edu

DRILLING EXPEDITION OFF PACIFIC NORTHWEST COAST TO PROBE THE RELENTLESS FLOW OF FLUIDS BENEATH THE SEAFLOOR

470-foot research vessel JOIDES Resolution docks at San Francisco's Pier 30/32 June 16-19

FOR IMMEDIATE RELEASE

SAN FRANCISCO, CA--Rains and rivers run endlessly into the ocean, nourishing its life and affecting its chemistry for better or worse. Another cycle of water may determine the character of the sea even more profoundly--a cycle hidden under the ocean itself, within sediments and rocks just beneath the dark seafloor.

Driven by the heat of the planet's interior, water courses through pores and cracks under the ocean in earth's upper crust. The water leaches minerals as it flows, altering the crust and suffusing the ocean with important elements. This process occurs dramatically at "black smokers" and other hot vents along volcanic midocean ridges. It happens to a far greater extent along the sweeping flanks of these ridges, and possibly under most of the rest of the ocean as well. But because the seafloor is so remote, scientists know precious little about the details.

Now, a floating community of researchers hopes to take the closest look yet at this intricate cycle by drilling into the seafloor off the Pacific Northwest, where new oceanic crust churns toward the continent. Their voyage, Leg 168 of the international Ocean Drilling Program, sets steam June 20 from San Francisco on a two-month expedition aboard the 470-foot JOIDES Resolution.

The team will implant four sophisticated instruments in drill holes to record fluid pressures and temperatures over time--the first attempt to monitor adjacent spots within a marine hydrothermal system. Researchers will study cores of rock and sediment hauled onto the ship for telltale signs of fluid flow and chemical interactions. The work should help reveal how quickly water moves through crustal rocks, how deep within the crust this flow occurs, and the extent to which heat and minerals stream into the ocean.

"We've come to realize that this kind of water circulation is much more important than we believed just a few years ago," says Earl Davis of the Geological Survey of Canada, cochief scientist for the mission. "We suspect these processes take place within a large part of the seafloor, perhaps most of it, and play important roles in forming mineral deposits and in helping to control the composition of seawater."

Joining Davis as cochief scientist is Andrew Fisher, assistant professor of earth sciences at the University of California, Santa Cruz. About two dozen other scientists will sail on Leg 168 from the U.S., Canada, Great Britain, France, Germany, Sweden, and Japan. They'll be aided by about 80 technicians, drillers, and crew members on the JOIDES Resolution, which stocks five miles of drill pipe and a derrick one-fifth the height of the Eiffel Tower.

The ship's destination is the eastern flank of the Juan de Fuca seafloor ridge, about 130 miles west of the border between the U.S. and Canada. New oceanic crust created at this ridge spreads slowly toward North America, where it plows under the continent and gives rise to the earthquakes and volcanoes of the Pacific Northwest. Before this crust subducts into the planet, a wedge of sediment settles on top of it and prevents the rock below from directly exchanging fluids and heat with the ocean.

"Usually it takes about 65 million years for sediments to seal off the oceanic crust," says Fisher, who will embark on his seventh Ocean Drilling Program expedition. "Here, because the continent is so close to the spreading zone, it takes only a few million years. So we can sample a large range of the evolution of oceanic crust within a very short distance."

Davis, Fisher, and their colleagues plan to drill into two types of crust near the thin "toe" where continental sediments begin to build up. At one series of sites, the crust is flat and smooth. At the other sites, the crust has crumpled into peaks and troughs underlying the layer of sediments. "We think these hills can create an extra instability," Fisher says. "One of the things we will test is whether fluids flow more vigorously in such regions."

The researchers will place two instrument packages, called "CORKs," at different spots along each of the two series of drill holes. As tall as a three-story building, each CORK contains devices that will record, with exquisite sensitivity, pressures and temperatures inside the drill holes. As their names imply, the CORKs also plug the tops of the holes, allowing the fluid flows beneath to return to their natural states within a few weeks or months. Scientists will retrieve the data over the next several years with manned submersibles or remotely operated vehicles.

Results from the expedition promise to go beyond mere academic interest in the plumbing of earth's oceanic crust. Davis notes that the entire volume of the world's oceans cycles through these hydrothermal systems every one or two million years. "That greatly influences the chemistry of the ocean," he says. He adds that fluids and other foreign materials plunge back into the earth with the oceanic crust at subduction zones. That drives the nature of many volcanoes--high water content can make magma more explosive, for example.

Editor's notes: You may contact the scientists as follows: Earl Davis--(604) 363-6453 or davis@pgc.emr.ca Andrew Fisher--(408) 459-5598 or afisher@earthsci.ucsc.edu

The researchers will be at the San Francisco port call for the JOIDES Resolution at Pier 30/32 from June 16 through June 19. Tours and other activities for reporters, the public, and invited guests are planned. For a schedule of events, contact John Barron at the U.S. Geological Survey, Menlo Park: (415) 329-4971 or jbarron@isdmnl.wr.usgs.gov

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