A team of Oregon State
University scientists monitoring near-shore ocean conditions
off Oregon says that oxygen levels in the lower water column
have plummeted, thrusting the region into a hypoxic event for
the sixth consecutive year.
Hypoxia can lead to significant
marine die-offs, the researchers say, depending on the
severity, duration and location of the low-oxygen zone.
Although conditions this summer have not yet duplicated the
severity of the historic hypoxic event of 2006, the outlook
for the remainder of the summer and early fall is uncertain.
Measurements taken by the OSU scientists in late June mirrored
those of last year, but a shift to a southerly wind pattern in
mid-July pushed the mass of low-oxygen water away from the
shoreline. A sizeable mass of low-oxygen water remained,
however, across much of the shelf from Florence to Newport.
Last week, the winds shifted again and these northerly
winds pulled the larger mass of hypoxic water back closer to
shore, where it may endanger reef-dwelling sea creatures that
have limited mobility.
"We are definitely experiencing hypoxia once again," said
Francis Chan, a marine ecologist with OSU and the Partnership
for Interdisciplinary Studies of Coastal Oceans, or PISCO. "By
the beginning of July, conditions were approaching what we
consider 'severe.' But unlike last year, a shift in wind
patterns in mid-July pushed low oxygen waters offshore and
gave us a temporary reprieve.
"The winds have shifted yet again," Chan said, "and we are
now tracking to see how much further oxygen levels will drop.
It is a dynamic system with a lot of uncertainty, which
illustrates the need for more research and monitoring of these
The OSU researchers say the region has not yet fully
recovered from last year's historic hypoxia. Video monitoring
of reefs off the central Oregon coast that were affected by
last year's hypoxia show a significant loss of species
diversity. Most species of sea stars, sea cucumbers and many
bottom-dwellers are still absent, said Jane Lubchenco, the
Wayne and Gladys Valley professor of marine biology at OSU.
"Some rockfish have moved into the area, but the
bottom-dwellers that provide the habitat and food for rockfish
and a diverse array of other species, are slow to return,"
Lubchenco said. "The system is showing early signs of
rebounding, but a full recovery may be a long way off. This
marine ecosystem may take as long to recover as the
terrestrial ecosystem did from the eruption of Mount St.
"Moreover, the current low oxygen conditions may knock the
system back to the starting line, delivering another setback
to an already stressed system," Lubchenco said.
Last year, the largest and most devastating hypoxic
conditions ever observed off the Pacific Northwest coast began
with low oxygen levels of 0.5 milliliters per liter of water
in July off Cape Perpetua -- identical to what the OSU
researchers observed this year. During the next two months,
strong upwelling-favorable winds persisted, fueling massive
phytoplankton blooms, which eventually died and sank to the
bottom, leading to some of the lowest oxygen levels ever
recorded and killing a variety of marine life off the Pacific
For the first time, some areas of the ocean actually ran
out of oxygen altogether, the researchers said.
"The 2006 situation was not only the strongest, most
widespread hypoxia event yet seen off the Pacific Coast – it
also was the most long-lasting," Chan said. "The oxygen levels
were off the charts and they continued through the end of
"We have seen nothing to suggest that conditions this
summer will be any different," Chan added. "In fact, it is
eerily similar to last year."
The OSU scientists have been monitoring offshore conditions
this year since April, deploying instruments, taking survey
cruises and working with the Oregon Department of Fish and
Wildlife on video surveillance of reefs affected by last
By the end of June 2007, the oxygen levels on those reefs
had decreased dramatically, to an average of 0.5 milliliters
per liter. Any level of dissolved oxygen below 1.4 milliliters
is considered hypoxic for most marine life; a normal midsummer
reading may range from 1.5 to 3.0 milliliters.
The next few weeks are critical, says Jack Barth, a
professor of physical oceanography at OSU. If
upwelling-favorable winds are strong and persistent, the
already-low oxygen levels may continue to decline to dangerous
"Last year, summer winds were more intense than normal, and
led to upwelling that was twice as strong as usual," Barth
said. "Summer upwelling winds are a vital part of the system,
but they can become too much of a good thing." Strong and
persistent upwelling winds fuel intense biological production,
leading to hypoxia in near-bottom waters as plankton sink and
decompose at depth.
Barth said it is too early to say with any certainty that
the ongoing hypoxic conditions are a direct result of global
warming, but adds that the symptoms are consistent with global
"There are many variables such as the Pacific Decadal
Oscillation that seem to run in 10- to 15-year cycles," Barth
pointed out. "But this marks the sixth consecutive year that
we have documented significant hypoxia and observed changes in
the circulation and winds that may be responsible."
The OSU-led research team is enlisting a number of other
resources in collecting dissolved oxygen data in near-shore
waters as it seeks to determine the extent of hypoxia along
the West Coast. Stephen Pierce, an OSU oceanographic research
associate, is aboard a vessel that is conducting a biannual
hake survey for the National Marine Fisheries Service. He'll
be testing water samples for dissolved oxygen from Monterey,
Calif., to Vancouver Island.
Already, Pierce and his colleagues have just discovered
hypoxic waters with oxygen levels of about 0.75 milliliters
per liter in the near-shore from Coos Bay to Florence. These
are some of the first recent recordings of hypoxic water along
the southern Oregon coast, which has not been well-monitored,
and will provide important baseline data for the future.
Researchers including NOAA's Bill Peterson, who works at
OSU's Hatfield Marine Science Center in Newport, are taking
dissolved oxygen measurements while conducting a Bonneville
Power Administration-sponsored salmon survey off the Oregon
and Washington coast.
OSU scientists also are working with the Olympic Coast
National Marine Sanctuary and researchers at the University of
Washington to expand hypoxia detection efforts up through the
northern Washington coast.