CORVALLIS - The so-called "dead zone" in the ocean off Oregon has finally ended, researchers at Oregon State University say. It was the most severe episode of this kind that had been observed off the Oregon coast.

During mid-October, a normal shift in wind direction took place, resulting in the end of the upwelling season and a rise in dissolved oxygen to levels that can generally support marine life, scientists said. The oxygen levels should continue to increase throughout the next month.

Monitoring will continue, new technology will be utilized, federal funding will be sought for more work in the area, and work is already under way to identify the amounts of biological damage done by this event, the fifth dead zone in five years and one for the record books.

In 2006, low-oxygen waters off Oregon stretched farther north along the coast, reached closer to shore, and were thicker than detected before. The event was four times larger than any previous episode and lasted four times as long. More important, the oxygen levels were by far the lowest ever recorded on the near shore of Oregon, approaching a complete lack of oxygen.

"The figures were just off the charts this year," said Francis Chan, a marine ecologist with OSU and the Partnership for Interdisciplinary Studies of Coastal Oceans, or PISCO.

Any level of dissolved oxygen below 1.4 milliliters per liter is considered hypoxic - low in oxygen - for most marine life, and many areas were below that, some 10-30 times lower than normal, others approaching zero.

"We had stronger and more persistent winds from the north, causing greater upwelling and more severe hypoxic conditions, than we had ever seen before," said Jack Barth, OSU professor of oceanic and atmospheric sciences. "The winds were outside the normal summer range of anything seen in decades."

Even though hypoxic concerns erupted for the fifth year in a row, the events are still considered an anomaly, Barth said.

This year's hypoxic event began in mid-June, and in the Heceta Bank off Florence oxygen levels were unusually low for four months. Many species fled to areas with more oxygen, such as a shallow refuge near shore where wave action raised oxygen levels n in some such areas, fishing was very good.

But species that could not swim away or get out, including thousands of crabs, sea stars and marine worms, carpeted vast areas of the ocean floor with rotting carcasses.

Changes in oceanic and atmospheric conditions are expected as a result of global climate change, and events such as this summer's stronger and more persistent winds from the north, contributing to hypoxia, are consistent with such predictions, the OSU researchers said. However, at this point there is no data or basis to suggest such cause and effect mechanisms, they said. There are also no known links to other marine or atmospheric events such as El Nino or the Pacific Decadal Oscillation.

This type of dead zone is different than those that have occurred elsewhere in the United States and widely around the world, which are usually caused by nutrient pollution. It is similar to some that have been documented in the past off the coasts of Peru, Chile, Namibia and South Africa.