Mother Natures Coastal Killing Fields

Margaret Munro ,
Canwest News Service

Published: Thursday, February 14, 2008

VANCOUVER - Oxygen-deprived water rose up from the deep ocean two years ago, cutting a deadly swath along the Pacific Northwest coast, say scientists, who watched in awe as fish fled and crabs, sea stars and worms died en masse, creating a rotting carpet on the sea floor.

The "dead zone" was unprecedented say the researchers, who have been combing through the historic records to understand the phenomenon that bathed at least 3,000 square kilometres, from the Canadian border south to the central Oregon coast, in low-oxygen water in 2006.

The scientists report their findings in the journal Science on Friday. They say it appears to be an increasingly common phenomenon as winds patterns shift along the Pacific coast.

Low-oxygen water has appeared in varying degrees since 2000, in bad years coming within just two kilometres of shore, says oceanographer Francis Chan of Oregon State University, lead author of the Science report that notes how sensitive the marine ecosystem off the Northwest Pacific is to "rapid reorganization."

Canadian researchers say they have been seeing changes in the winds and a drop in oxygen in waters off the B.C. coast as well. But so far "we're escaping the killing, low-oxygen levels," says Bill Crawford, a research scientist with Fisheries and Oceans Canada.

He and his colleagues are hoping to secure federal funding to install a continuous oxygen monitoring station off southwest Vancouver Island, which Crawford says is probably the most vulnerable region in Canadian waters. But he suspects oceanographic conditions, including the massive outflow of water from the Fraser River, protect Canada from the "killing waters" that have been smothering sea life across the border.

"It would be tricky for really low-oxygen water to cross and get into Canada," says Crawford, "but I'm not saying it couldn't happen."

Low-oxygen water off Oregon in 2006 left a normally thriving marine habitat covered with dead and rotting crabs, sea stars and anemones. Rock fish disappeared and worms that burrow into sediments could be seen floating on the bottom along with "marine snow" - fragments of dead marine life, mostly jellyfish and other invertebrates colonized by bacteria that sucked the remaining oxygen out of the water.

Southerly winds eventually blew in and flushed out the deadly water, allowing the ecosystem to come back to life.

Chan and his colleagues looked back through 50 years of coastal monitoring records which show that since 2000 the summer waters have been experiencing an unprecedented low oxygen level, with 2006 being most pronounced. They trace it to a shift in winds.

The problem starts in the spring and summer when winds from the north drive deep, low-oxygen water towards the surface "like a conveyor belt," says Chan. The water is so nutrient-rich it acts like fertilizer, triggering a massive growth of plants and plankton, much of which dies, sinks to the bottom and decays, a process that further depletes the oxygen.

It has long been known a giant pool of low-oxygen water sits offshore, about 600-800 metres below the surface. But in the last decade winds have brought more of it to the surface, in effect, speeding up the conveyor, says Chan. 

"What's been remarkable is that we're getting oxygen values that not only approach what you see in the very deep, offshore pool, but we've actually surpassed how low it is in waters that are only 50 metres deep," says Chan. The killing water has been come to within a couple of kilometres of the surf zone. "It is a very, very near-shore phenomenon," he says.

While the scientists say climate change is shifting the winds and currents off the coast, Chan stresses they have not directly linked the changes to rising greenhouse gas emissions. But he says the increasing incidence of low-oxygen water "gives a really important insight" into how coastal ecosystems can be impacted as winds and current shift, phenomena expected to become more common as the planet warms.