Dead zone reappears off the Oregon Coast; outlook uncertain

Dead zone reappears off the Oregon Coast; outlook uncertain

By Terry Dillman
August 01, 2007; Newport News-Times

Oregon State University researchers say near-shore, low-oxygen ocean conditions off the Oregon coast have again created a hypoxic region – colloquially termed a "dead zone" – across much of the underwater shelf from Florence to Newport. Depending on its severity, duration and location, hypoxia (lack of oxygen in the water) can cause "significant marine die-offs" similar to those they witnessed during the historic dead zone episode of 2006.

Conditions this summer have yet to match last season, but the researchers say the outlook remains "uncertain."

"We are definitely experiencing hypoxia again," said Francis Chan, a marine ecologist with OSU and the Partnership for Interdisciplinary studies of coastal Oceans (PISCO). Measurements in late June by the OSU scientists mirrored those of last year’s drastic event, with oxygen levels dropping precipitously.

"By the beginning of July, conditions were approaching what we consider severe," Chan added.

A shift in wind patterns to a southerly flow in mid-July provided a temporary reprieve by pushing the low-oxygen water mass away from shore, although a sizeable section lingered across the shelf from Florence to Newport. Last week, the wind pattern shifted again, and the northerly flow pulled the hypoxic water closer to shore, where it could endanger reef-dwelling sea critters with limited mobility.

Researchers are now monitoring to see how much farther oxygen levels might drop.

Among them is Bill Peterson, who works with the National Oceanic and Atmospheric Administration at OSU’s Hatfield Marine Science Center in Newport. Peterson and others are measuring dissolved oxygen content as part of a salmon survey sponsored by the Bonneville Power Administration off the Oregon and Washington coasts. OSU scientists are also working with other researchers to collect dissolved oxygen data in near-shore waters – including those from the Olympic Coast National Marine Sanctuary and University of Washington – to determine the extent of hypoxia along the entire West Coast.

"It’s a dynamic system with a lot of uncertainty, which illustrates the need for more research and monitoring of these conditions," Chan noted.

Jane Lubchenco, an OSU professor of marine biology, said the region has yet to fully recover from last year’s historic hypoxia. Video monitoring of reefs off the central Oregon coast showed "a significant loss of species diversity." Most species of sea stars, sea cucumbers, and many bottom-dwellers "are still absent."

"The system is showing early signs of rebounding, but a full recovery may be a long way off," Lubchenco noted. "Some rockfish have moved into the area, but the bottom-dwellers that provide the habitat and food for the rockfish and a diverse array of other species are slow to return."

Current hypoxia could deliver another blow to an already stressed system.

Last year’s event was the largest, most devastating conditions ever observed off the Pacific Northwest coast. It began with low oxygen levels of 0.5 milliliters per liter of water in July off Cape Perpetua – identical to what researchers have already measured this year. Strong upwelling-favorable winds persisted through August and September triggered massive phytoplankton blooms that eventually died and sank to the bottom, where oxygen levels dropped to some of the lowest levels ever recorded and killed off a variety of marine life.

A few sections of the ocean were entirely depleted of oxygen for the first time ever.

Not only was the 2006 "dead zone" the strongest, most widespread, but the most long-lasting hypoxia incident ever witnessed. Oxygen levels were "off the charts" until the end of October.

"We have seen nothing to suggest that conditions this summer will be any different," Chan warned. "In fact, it is eerily similar to last year."

The OSU researchers have monitored offshore water conditions since April, taking survey cruises, deploying instruments, and working with the Oregon Department of Fish and Wildlife on video surveillance of reefs devastated by last year’s hypoxia. By the end of June, oxygen levels in those reefs had dropped to an average of 0.5 milliliters per liter of water. Scientists consider any level of dissolved oxygen below 1.4 milliliters hypoxic for most marine life, with a "normal" midsummer reading ranging between 1.5 and 3.0 milliliters.

Jack Barth, an OSU professor of oceanography, said the next few weeks are critical. Strong, persistent winds that favor upwelling could drop oxygen content to dangerously low levels. Last year’s summer winds were more intense than usual, creating upwellings twice as strong as usual.

"Summer upwelling winds are a vital part of the system, but they can become too much of a good thing," Barth said. "Strong, persistent upwelling winds fuel intense biological production, leading to hypoxia in near-bottom waters as plankton sink and decompose at depth."

Lincoln County Commissioner Terry Thompson draws on decades of experience as a commercial fisherman to reach his own conclusion about the dead zone: in most years, it’s ‘a naturally occurring event,’ and this year, he’s "optimistic it won’t be as severe" as 2006.

One concern is the higher-than-usual water temperature, which is hovering near 60 degrees.

But Thompson said the event could breathe life into a neglected aspect of information about marine life migratory patterns.

"We can learn more about fish migration and natural movement of fish," he noted. "We as fishermen know where they are and where they aren’t (and when). This gives us an opportunity to learn why."

Terry Dillman is a reporter for the News-Times. He can be reached at (541) 265-8571 ext. 225, or terrydillman@newportnewstimes.com.
2007-08-01T12:39:00+00:00August 1st, 2007|News|Comments Off on Dead zone reappears off the Oregon Coast; outlook uncertain