The “dead zone” off Oregon’s coast is back — larger, thicker, and more lethal than ever. For the fifth year in a row, scientists have witnessed thousands of sea creatures dying in the Pacific Ocean.

This year, the dead zone covers 1,200 square miles, according to Oregon State University marine ecologist Jane Lubchenco.

…”There are no fish down there that we could see,” Lubchenco said. “This is an area where we have measured chronically low oxygen.”

…Scientists found almost no oxygen in the water there. According to OSU marine ecologist Francis Chan, “we’re only half-a-step away from zero — or the absence of oxygen.”

This dead zone is unlike those in the Gulf of Mexico and elsewhere, which result from fertilizer, sewage or runoff from hog or poultry operations carried by rivers. The Oregon zone appears when the wind generates strong currents carrying nutrient-rich but oxygen-poor water from the deep sea to the surface near shore, a process called upwelling.

The nutrients encourage the growth of plankton, which eventually dies and falls to the ocean floor. Bacteria there consume the plankton, using up oxygen.

Jane Lubchenco, a marine biologist at Oregon State University, said the phenomenon did not appear to be linked to recurring El Niño or La Niña currents or to long-term cycles of ocean movements. That made Dr. Lubchenco wonder if climate change might be a factor, she said, adding, “There is no other cause, as far as we can determine.”

The dead zone, which appears in late spring and lasts a matter of weeks, has quadrupled in size since it first appeared in 2002 and this year covers about 1,235 square miles, an area about as large as Rhode Island, Dr. Lubchenco said.

The zone dissipates when winds shift.

Scientists say the oxygen-starved “dead zone” along the Pacific Coast that is causing massive crab and fish die-offs is worse than initially thought.

Scientists say weather, not pollution, appears to be the culprit, and no relief is in sight. However, some say there is no immediate sign yet of long-term damage to the crab fishery.

Oregon State University scientists looking for weather changes that could reverse the situation aren’t finding them, and they say levels of dissolved oxygen critical to marine life are the lowest since the first dead zone was identified in 2002. It has returned every year.

Strong upwelling winds pushed a low-oxygen pool of deep water toward shore, suffocating marine life, said Jane Lubchenco, a professor of marine biology at OSU.

…After a recent trip to the dead zone and an inspection via camera on a remote-controlled submarine, she said, “We saw a crab graveyard and no fish the entire day.”

“Thousands and thousands of dead crab and molts were littering the ocean floor. Many sea stars were dead, and the fish have either left the area or have died and been washed away,” she said. “Seeing so much carnage on the video screens was shocking and depressing.”

Scientists suspect swings in the Earth’s climate tied to global warming may be shifting wind conditions to bring about such grim results.

Seawater turns deadly for marine life when concentrations of the dissolved oxygen they breathe fall below about 1.4 milliliters per liter. On Monday, Chan measured a concentration of .05, or almost 30 times below the lethal level, about 90 feet below the surface.

It is very close to a complete absence of oxygen, a situation rarely known in the world’s oceans, said Jane Lubchenco, a professor of marine biology at Oregon State. New bacteria that take over when oxygen disappears are known to release poisonous hydrogen sulfide gas.