Scientists and technicians aboard the research vessel Elakha haul in an array of instruments, Tuesday off Cape Perpetua after measuring properties of the water in a dead zone that has developed there. AP Photo

NEWPORT (AP) - His hand on a toggle switch and his eyes on a computer screen, Oregon State University graduate student Anthony Kirincich "flew" an array of scientific instruments up and down through the waters of the Pacific, searching for the deadly low levels of oxygen that mark the return of the dead zone.

Standing next to him in the cramped cabin of the research vessel Elakha, Oregon State University postdoctoral researcher Francis Chan processed water samples, measuring the dissolved oxygen and indicators of phytoplankton, the microscopic plants that are the foundation of the food chain.

"This is definitely a cat-and-mouse game," because the dead zone keeps ebbing to and from the shore and changing characteristics, Chan said. "It really takes us almost daily trips to really pinpoint the data."

Two years ago when local fishermen started hauling up pots filled with dead crabs, scientists figured out that a huge mass of sub-Arctic water with very low levels of oxygen and high levels of nutrients had welled up from the ocean's depths and settled in for the summer on the Continental Shelf off central Oregon.

The dead zone dissipated that fall, and based on 40 years of ocean monitoring and local fishing lore, many thought they would never see it again.

This summer, the dead zone came back, causing scientists to think it may be a sign of a fundamental change in the Pacific Ocean.

"What I think we are seeing is a tipping of the balance of the ecosystem," said Jack Barth, a professor of oceanography at Oregon State University. "We don't fully understand what the cause of that is. We have some good ideas that it is related to some fundamental changes in circulation and the source of water for the Oregon continental shelf."

Chan, in an interview after the research cruise, said the scientists did see several species of healthy rockfish when the scientists partnered with the Oregon Department of Fish and Wildlife, an indication that the dead zone was lower in the water column or further out to sea at the time. Other marine animals seen at the edges of the zone were "somewhat resilient," Chan said, noting that different fish and invertebrates respond to varying levels of oxygen in the water.

There are more than 30 man-caused dead zones - scientists call them hypoxic or low-oxygen events - around the world in enclosed waters, including Hood Canal in Puget Sound, the Mississippi River delta and Chesapeake Bay. There, excess fertilizer from farm fields washing down rivers fuels a surge in phytoplankton. When they die, bacteria decompose them, using up the oxygen in the water and leaving fish, crabs and other sea life to suffocate.

Naturally caused dead zones in open water like the one off Oregon are rare, and less well understood. Others have been found off Peru and South Africa.

The phenomenon is similar to the way the ocean food chain gets kick-started for good salmon returns, Barth said. Strong north winds push down the water along the coast, causing deeper waters laden with plankton to be drawn up.

In this case, a mass of deep ocean water was transported south from the sub-Arctic region by a shift in the California Current and came to rest on the Continental Shelf off Oregon. Already low in oxygen from being deep in the ocean, it lost even more when abundant phytoplankton died and decomposed.

Though Oregon's dead zone is relatively small, "It might be a window into possibly important larger- scale changes in the Pacific," said Jane Lubchenco, professor of marine biology at OSU.

Barth does not think it is related to El Nino, the ocean warming that periodically hits the Pacific. It might, however, be related to the Pacific Decadal Oscillation, a cyclic climate condition in the northern Pacific discovered just 10 years ago that controls upwelling events. It is not behaving as it has in the past.

"Because we think it is potentially a long-term change, to be absolutely certain we need many years of observations," Barth said of the dead zone. "We are still at the fundamental research level, but the impacts could be quite large."

To understand it better, the 54-foot Elakha - Chinook for sea otter - goes out several times a week from the Hatfield Marine Science Center to gather water data in conjunction with PISCO - the Partnership for Interdisciplinary Studies of Coastal Oceans.

On Tuesday, Capt. Perry York motored south through the Dead Zone to Cape Perpetua. On the way, sooty sheerwaters skimmed along the surface, gulls soared, a whale rolled and porpoises showed their dorsal fins.

Water samples Chan processed from near the surface showed low oxygen, but not dead zone low.

The readings on water temperature, dissolved oxygen, depth and salinity coming from the instruments towed behind Elakha told a different story. About five miles out, at a depth of about 150 feet, the green line describing dissolved oxygen slid below the threshold into the Dead Zone.

The zone generally extends from Newport south to Florence, a distance of about 50 miles. On Tuesday, Elakha found it about five miles offshore at a depth of about 150 feet. It lays on the bottom, about 120 feet thick, and extends at least 10 miles out.

- Staff Writer Susan Chambers contributed to this report