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Scientists Still Eyeing the ‘Dead Zone’

 


Hypoxia team keeps watch on coastal waters

Spring transition is the time of year when coastal wind patterns switch from winter’s southerly flow to summer’s northerly pattern. The summer pattern favors upwelling, the ocean process 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 other areas closer to shore to find adequate oxygen levels.

For the past decade, the hypoxia team at Oregon State University (OSU)’s Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO) has monitored the waters off Oregon’s coast.

During the summer of 2002, oxygen levels in water near the Oregon coast dropped so low that fish, crabs and other marine life had to flee the area or die by suffocation. Scientists said the low oxygen levels – known as hypoxia – were more extreme than they had ever documented so shallow and so close to shore in the prior 50 years. Since then, the dead zone has recurred every summer at varying intensities, some severe. The most severe occurred in 2006, when oxygen levels dropped to all-time lows, including a few places with no oxygen, and created huge areas of hypoxia along both the Oregon and Washington coasts.

Climate Change

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 the 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.

The researchers suggested hypoxic occurrences could be the rule rather than exception under current conditions.

“In this part of the marine environment, we may have crossed a tipping point,” PISCO’s lead scientist Jane Lubchenco said at the time.

“Levels of oxygen in the summertime have suddenly become much lower than levels in the previous 50 years,” added Lubchenco, who now heads up the National Oceanic and Atmospheric Administration. “And 2006 broke all records, with parts of the shallow shelf actually becoming anoxic, meaning that they lacked oxygen altogether. We’ve never seen that before.”

Water oxygen levels in these zones have repeatedly reached hypoxic levels, below which most marine animals either suffocate or are severely stressed if they cannot escape the area. If oxygen levels drop to zero, most – if not all – animals die. The research report said the massive 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.” Chan’s survey encompassed several El Nino and La Nina events – both of them suspects in any change that occurs in Pacific Ocean conditions – as well as shifts in what’s called the Pacific Decadal Oscillation, which affects short-term climate trends. None of that trio appeared to have any relation to the hypoxia, the scientists noted.

In 2008, Lubchenco said 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. “These areas have historically been highly productive,” she added. “The appearance or increase in severity of hypoxia in these ecosystems would be cause for concern.”

In addition, recovery from the 2006 event was slow, lending a sense of urgency to the monitoring efforts by PISCO and others.

This rapid, disturbing shift of ocean conditions in what is traditionally one of the world’s most productive marine areas – what’s known to scientists as the California Current Large Marine Ecosystem – has received much attention during the past decade or so, raising questions about whether it has occurred before and what’s causing it. Researchers say the situation is definitely different than anything that has happened before, but still aren’t sure exactly what’s causing the hypoxic conditions, other than it being consistent with climate change.

Jack Barth, an OSU oceanographer and another PISCO lead scientist, said unusual weather events – hurricanes, droughts and changes in wind patterns – have always occurred naturally, making it difficult to pinpoint whether any particular event is the direct result of climate change.

“Having said that, we expect global warming to generally cause stronger and more persistent winds,” he said. “These winds contribute to the hypoxic events by increasing plankton production and holding low-oxygen water on the continental shelf for longer periods.”

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.

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 for 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.”

Water oxygen levels in those 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 Chan. “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.

Researchers expect hypoxia to continue. In fact, hypoxic occurrences could become the rule rather than exception under current conditions, which is why the PISCO team and others are watching so intently.

Crabbers Pitch In

In 2009 and 2010, 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, including data that could provide the answers to why and when hypoxia zones form in coastal waters. 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 using high tech ocean observing methods.

Historically, fishermen are leery of researchers for fear that the information could be used to close fisheries or restrict catches and seasons. Scientists are often skeptical of the quality of data gathered by fishermen. Representatives from the fishery and the university said this effort demonstrated the effectiveness of such collaboration by collecting excellent data, cutting research costs and – as a bonus – provide good information for the Dungeness crab fishery, which is Oregon’s most valuable.

Developing trust took time, but “we’ve figured out that engaging the fishermen actually improves the data,” said Michael Harte, director of OSU’s Marine Resource Management Program. “This is fantastic for us. It would cost many thousands of dollars to deploy one scientific buoy, but by working with the crab fishermen, we can deploy fixed buoys for about $100 each.”

Led by oceanographer Kip Shearman, the researchers worked with 10 Oregon crabbers, attaching sensors to about 60 crab pots deployed between Port Orford and Astoria. Because many crabbers use anywhere from 300 to 500 pots, the researchers could select locations, where the sensors recorded temperatures every 10 minutes during the crab season (December through August). Researchers scanned and uploaded that information to analyze and evaluate. They later developed larger sensors that could record both temperature and dissolved oxygen levels in the water surrounding the crab pots. The information gleaned is moving the scientists closer to understanding and predicting hypoxia and the appearance of dead zones.

“Fishing has been good to me and I’m happy to be giving something back,” Al Pazar, one of the crabbers involved in the project, said at the time. “I love working with OSU, and Sea Grant in particular has helped establish a good connection between Oregon’s fishing industry and academia. It’s a no-brainer to utilize the local volunteers from the fishing fleets and their gear.”

The project offered valuable information for both groups, but bringing folks together who traditionally are at odds was a plus.

“No oxygen means dead crabs (as in 2006) or no crab, so the crab fishermen are happy to work with us,” Harte noted. “They and their crab pots are going to be out there anyway, and we don’t need huge research grants to tap into this ready-made ocean observing system. We’re learning that scientists and fishermen, working together, can collect valid scientific data in a robust way using a relatively inexpensive system that improves our understanding of the ocean.”

The researchers said 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 Barth.

But the hypoxia team observed no anoxic (zero oxygen) zones like the infamous killer off Newport, Oregon 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 and they – according to Barth – “caught a break” that weakened and shortened the hypoxia.

They know such luck won’t always intervene, and they point to other areas around the world – such as the Benguela Current off South Africa and Humboldt Current off Chile – undergoing the same process as the Pacific Northwest. Such areas, scientists say, have historically endured hypoxic conditions, including more extreme upwelling and more frequent marine die-offs than the Pacific Northwest. The main concern is whether or not those similar systems are harbingers of the future for the Pacific Northwest.

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.

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.

In 2010 and 2011, hypoxic events were less severe and less widespread, with no recorded mass die-offs of any marine life, according to PISCO. As of the end of August 2012, multiple ocean observations from various locations indicated “moderate to severe hypoxia occurring along parts of the central Oregon shelf” from Cape Perpetua to Newport, with the most severe levels “as usual” found south of Newport. They expected conditions conducive to hypoxia to exist through late September or early October.

Terry Dillman can be reached at tdwordwright@gmail.com.

 
 
 
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