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October 14, 1996

Research Update: Earth sciences

A two-month cruise off the Pacific Northwest this summer was a slam-dunk success for UCSC hydrogeologist Andrew Fisher and a team of researchers aboard the 470-foot JOIDES Resolution, flagship of the international Ocean Drilling Program (photo).

Fisher, the expedition's cochief scientist, and his team drilled into the seafloor near the Juan de Fuca Ridge, where the planet churns out fresh slabs of oceanic crust. Fluids from the ocean and from within the earth course through these young rocks, driven by heat from below. This relentless cycle alters the character of the seafloor and leaches important minerals into the sea. However, the plumbing of this pervasive percolation has eluded scientists, shrouded as it is by thousands of feet of water and thick layers of sediment.

By drilling as far as 1,900 feet into the seafloor, Fisher's colleagues took the closest look yet at certain details of the fluid cycle. For instance, they collected the first sample of pristine "basement" water--fluid trapped under the seafloor for many thousands of years. Early chemical analysis of these and other samples points to a surprisingly energetic cycling of fluids.

"There's no question the water is moving much faster than we thought," Fisher says. The time it takes for the entire volume of the world's oceans to cycle through these subseafloor systems, he notes, could be "much, much shorter" than the previous estimate of one to two million years.

The scientists also installed deep-sea observatories, called CORKs, in four of the drill holes. The observatories will record the pressures and temperatures of fluids with exquisite sensitivity for several years; manned or robotic vessels will retrieve the data. Fisher expects the CORKs to help paint a complete picture of the forces that impel the fluids.

Meanwhile, students in Fisher's lab will study the permeabilities, grain sizes, and other properties of sediment cores from the voyage. They also will create a numerical model of fluid cycles under the seafloor to simulate how the cycles behave over millions of years.

--Robert Irion