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Scientists, crabbers eyeing the dead zone

Posted: Friday, Oct 23rd, 2009

Winds ease, help avoid serious threat to marine life

Close, but no killing fields.

Oregon State University (OSU) researchers, who - with a little help from their friends, including National Oceanic and Atmospheric Administration (NOAA) surveyors and Oregon crabbers - monitored the near-shore waters off Oregon’s coast, say dead zones with severe hypoxia formed during the summer of 2009 near the seashore on the mid- to inner shelf in coastal waters, but were “about average” in size and duration.

“We also saw the now-classic ribbon of low dissolved water near the seafloor extending along the coast,” said Jack Barth, an OSU oceanographer.

The good news: the hypoxia team at OSU’s Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO) that began monitoring in early April observed no anoxic (zero oxygen) zones like the infamous killer off Newport in 2006. In early August, oxygen levels dropped as low as 0.5 milliliters per liter off Newport and Cape Perpetua - at the cusp of “severe” - when the wind backed down.

“We got a break,” Barth noted. “A series of wind reversals late in the summer helped dissipate the low oxygen, in essence allowing the system to ‘flush’ itself.”

Blowin’ in the wind

Unlike hypoxic areas in the Gulf of Mexico caused by agricultural runoff and pollution, low-oxygen water off the Oregon coast is a natural phenomenon triggered by seasonal upwelling - wind-driven mixing of cold, nutrient-rich deep water and surface water.

During the spring transition, coastal wind patterns switch from winter’s southerly flow to summer’s northerly pattern.

The summer pattern favors upwelling that ushers nutrients to the surface, providing nourishment for near-shore marine life. It also brings conditions conducive to hypoxia, or low oxygen levels, in the water, creating “dead zones” that can either suffocate marine animals or force them to migrate to the surface or closer to shore to find adequate oxygen levels.

In 2008, OSU researchers published a study in the journal “Science” based on a review of all available ocean data records, and the hypoxia that has occurred every summer since 2002. Although size, duration, and severity of the dead zone varies from year-to-year, the researchers concluded that those hypoxic events are unprecedented, and could be connected to the stronger, persistent winds stirred up by global climate change.

What changed, Barth said, is the pattern of Northwest wind, and decreasing oxygen levels in the deep, offshore waters that are part of the seasonal upwelling.

“Historically, winds would blow at the coast fro a week or so, then settle down for several days,” he noted. “As the winds eased, so did the upwelling, and low-oxygen water was washed away. Those traditional wind patterns have shifted, and now may last 20 to 30 days instead of a week. The system doesn’t have time to cleanse itself.”

The researchers suggest hypoxic occurrences could become the rule rather than exception under current conditions.

A sea change

Water oxygen levels in these zones now repeatedly reach hypoxic levels, below which most marine animals either suffocate or are severely stressed if they cannot escape the area.

“The 2006 situation was not only the strongest, most widespread hypoxia event yet seen off the Pacific Coast - it was also the most long-lasting,” said Francis Chan, a senior research professor in OSU’s Department of Zoology. “The oxygen levels were off the charts, and they continued through October, which is unheard of. For the first time we’ve ever observed, some parts of the near-shore ocean actually ran out of oxygen altogether.”

If an area becomes anoxic (oxygen levels drop to nil), most - if not all - animals die.

The research report said the 2006 zone covered at least 3,000 square kilometers, and lasted four months. Fish died or fled, thousands of crabs died, and sedentary marine seafloor life faced almost total mortality.

While the cause of all this is less than certain, the researchers said the hypoxic events are “completely consistent” with global climate change.

Chan conducted the survey of all known oxygen level records on the Oregon continental shelf for the past 60 years, gleaning measurements taken from research cruises and other ocean-going vessels from more than 3,000 stations. He said scientists were seeing very low oxygen water “lasting for long periods and closer to shore than at any other time in more than 50 years.”

Coastal upwelling systems like those off the Oregon coast occupy only about 1 percent of ocean area, yet contain about 20 percent of global fishery production. Researchers say those areas have been historically highly productive, and hypoxia or boost in its severity with in those systems would cause concern.

And recovery from the 2006 event has been slow, lending a sense of urgency to monitoring efforts by PISCO and others.

Enhanced monitoring

Oregon is far from alone in experiencing hypoxia zones in its coastal waters. In 2008, scientists and researchers mapped 415 eutrophic (overly nutrient-rich) and hypoxic coastal systems worldwide - 169 of them documented hypoxic areas (dead zones), 233 “areas of concern,” and 13 considered “in recovery.”

Coastal dead zones could appear every summer from now on, said Barth, because ocean and atmospheric conditions “are now primed for their regular, repeated formation.”

The vital concerns are how big those zones become, how long they last, and how often oxygen levels drop to cause marine life die-offs.

OSU scientists run regular transects off Newport using undersea gliders equipped with oxygen sensors, as well as similar instruments aboard four moorings ranging from 15 to 80 meters (49.2 to 262.5 feet) deep.

This season, OSU researchers in a program funded by Oregon Sea Grant worked with Oregon crabbers to use their crab pots as underwater monitoring stations. Sensors attached to the pots gathered vital oceanographic information. Because crab pots are positioned using GPS and distributed throughout much of Oregon’s coastal ocean, researchers can gather data from a much broader geographical range than when using high tech ocean observing methods.

Barth said oceanographers’ ability to monitor and measure hypoxic conditions improves every year, and should take a quantum leap when OSU deploys a new network of undersea gliders and cabled moorings off the coast as part of the national Ocean Observatories Initiative to measure the effects of climate change on the ocean.

Terry Dillman is the assistant editor of the News-Times. Contact him at (541) 265-8571, ext 225, or terrydillman@newportnewstimes.com.

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