Deadly hypoxic event finally concludes

CORVALLIS, Ore. – The longest, largest and most devastating hypoxic event ever observed in marine waters off the Oregon Coast has finally ended, researchers at Oregon State University say.

During mid-October, a normal shift arrived from summer southward-blowing winds to fall and winter northward-blowing winds, 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 efforts 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, literally, one for the record books.

In 2006, the low-oxygen waters off Oregon stretched further north along the coast, reached closer to shore, and were thicker than any event previously detected. 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 "anoxic" conditions in some places, or the 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 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.

"Given what's happened, it would not be surprising if hypoxic conditions developed next year as well, but we can't say that for sure," Barth said. "And we don't know what is causing the change in wind patterns that ultimately results in marine hypoxia. There's a pressing need to better understand these ocean systems, and all this points to an ongoing need for a better coast-wide observing system."

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 – in some such areas, fishing was very good. But those 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 dead and rotting carcasses.

The event, due to its severity and unusual nature, attracted national media attention.

The next order of business, scientists say, is to continue monitoring the recovery from the dead zone. OSU will work closely with the Oregon Department of Fish and Wildlife, and consult with local fishermen to verify their findings. The event is complex – low oxygen waters are not static, they move up and down the coast and also towards shore, resulting in patchiness and variable effects in some areas.

This winter, the ocean off Newport will be continuously monitored for the first time by a submersible "glider" that will provide information on ocean conditions, and a sophisticated new buoy will be moored off Newport along the central Oregon coast to measure biological productivity, dissolved oxygen, temperature, salinity, current velocity and other data.

"We're very interested now in seeing how the ocean recovers," Chan said. "There is much we don't know about how sensitive or resilient these ocean systems are, but an event of this magnitude gives us the chance to gain some real insights into how marine systems function and can recover. We expect some fish to return fairly quickly, but with other life forms, it's hard to say. And we have deadlines, we need to get a lot of this information before another possible hypoxic event starts next year."

Funding is still inadequate for the types of video monitoring, water sampling, comprehensive ocean observations and research that is needed, the OSU scientists said.

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.

When the system operates normally, upwelling off Oregon is usually a process that brings deep, cold, nutrient rich waters to the surface near the coast, resulting in one of the nation's more productive fisheries. When that process breaks down due to unusual winds, phytoplankton blooms that are healthy in moderation become too extreme, and lead to concentrations of low-oxygen water near the sea floor.

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.

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Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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