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| Making Sense of Increasing Anoxia The lead author of this study (summarized below) in the February 15 2008 Issue of SCIENCE, Francis Chan, was my undergraduate student thesis advisee. His thesis on the economic valuation of coral reefs, which was unfortunately never published, is far superior to anything in the literature. The data they show in the paper shows progressively decreasing oxygen. The pattern of increasing anoxia is a global one, not confined to California. But what is unstated in this paper is what the cause of the decline is. But it is likely to be global warming, which 1) has been shown by the CALCOFI long term study to have resulted in a temperature rise of several degrees in California surface waters, which 2) decreases the solubility of oxygen, 3) increases the warm cap of surface water, and so prevents upwelling of cold deep nutrient rich waters to the surface, thereby 4) decreasing primary production, and 5) causing a large documented decrease in zooplankton, while 6) causing an increase in micorbial utilization of oxygen in respiration and carbon decomposition, while at the same time 7) nutrient and organic carbon loading from land based sources of pollution are increasing also. This results in different causes of anoxia in zones overloaded from the land in places like Louisiana downstream from the Mississippi River mouth or the East China Sea, versus those affected more by physical circulation changes like the California Current system. Thomas J. Goreau, PhD President Global Coral Reef Alliance
SEATTLE POST-INTELLIGENCER Coast has seen deadly drop-off in oxygen levels for sea life Friday, February 15, 2008 By ROBERT MCCLURE Where scientists previously found a sea bottom abounding with life, two years ago they discovered the rotting carcasses of crabs, starfish and sea worms, swooshing from side to side in the current. Most fish had fled -- and those that didn't or couldn't joined the deathfest on the sea floor. Extraordinarily low oxygen levels were to blame -- swept up from the deep ocean into normally productive waters just off the Pacific Northwest coast by uncharacteristically strong winds. On Thursday scientists announced they had documented that low oxygen levels that killed the sea life in 2006 were the lowest in a half-century -- and that for the first time, parts of the ocean off our coast were measured with zero oxygen in the water; 2007 looked only a bit better. Strong winds and low oxygen levels have persisted for eight summers now, leading scientists to conclude that the ocean may be "poised for significant reorganization"-- their way of saying an ecosystem gone awry. It looks like the Pacific has reached a "tipping point," a threshold where low-oxygen levels are becoming the rule, researchers said. And while scientists can't prove it's caused by a changing climate, that's consistent with what is predicted by computer projections built to anticipate global warming. "The real thing in the back of our minds is: Is this the first signs of what global warming might be like?" said Bill Peterson, a federal scientist and co-author of the research published in the journal Science. But because it's not conclusive proof, he said, "We tried not to go there too much." Whatever the cause, it's worrisome, researchers said, because shallow, productive ocean areas like those off the Northwest coast occupy just 1 percent of the globe's oceans -- yet produce 20 percent of the fish we eat. "People keep asking us, 'Is this situation really all that different or not?' " said Jane Lubchenco, a co-author and prominent ocean researcher, in a news release about the research. "Now we have the answer to that question, and it's an unequivocal 'yes.' The low oxygen levels we've measured in the last six years are abnormally low for our system. We haven't seen conditions like this in many, many decades." Only once during the past seven years did the strong northerly winds of spring and summer go away -- and that time, in spring and early summer of 2005, the pendulum swung wildly the other way, with little wind at all until partway through summer. That set off a chain of events that scientists concluded were responsible for a startlingly widespread wave of seabird deaths -- from the Farallon Islands off San Francisco to Vancouver Island. After that, researchers from Oregon State University, the National Oceanic and Atmospheric Administration and the Oregon Department of Fish and Wildlife looked intensely at waters off the Oregon coast for the research announced Thursday. And the same thing is happening off Washington's coast. Mary Sue Brancato and her colleagues first noticed it on a visit to the coast in 2000 or 2001. "We were out there for another (research) project and we were like, 'What is it with these thousands of dead crabs?' " said Brancato, a marine biologist who works at the Olympic Coast National Marine Sanctuary. Those were Dungeness crabs. Later other species were affected, Brancato said, leading scientists to surmise it was some widespread cause. By 2004 they were taking measurements to document low levels of dissolved oxygen, the kind of oxygen sea creatures can use. By the time the biggest oxygen drop-off happened in 2006, it lasted for two weeks and researchers noted species of rockfish, eels and crabs normally found in deep water were along the coast instead, she said. "It could be climate change, but we don't have definitive proof of that," Brancato said She said the findings mirror a Canadian study that has been going on for 50 years that also detected declining dissolved oxygen levels. Brancato was not on the team of researchers whose work is being published this week. Those researchers had realized for years that they were seeing "really low" oxygen levels, said lead author Francis Chan. "But the key is, what is the norm?" Chan said. To ascertain that, Chan conducted a painstaking search for recordings of oxygen off the Northwest coast. He was able to find reliable records extending back into the 1950s. "Now we know exactly what the norm looks like and we see that the kinds of values we've gotten (in 2000-2006) are really unprecedented for our system," Chan said. Oxygen levels in the spring and summer of 2007 also were depressed, but not as much as 2006. The way the strong spring and summer winds reduce oxygen levels is complex. When these winds blow from the north as the Earth is turning toward the east, the water in the shallows along the coast is forced farther out to sea. This allows water from deeper in the ocean -- colder water with little oxygen but lots of nutrients -- to seep up near the coast. It's filled with nutrients because it contains dead plankton, fish excrement and more. Once in the shallow water, these nutrients feed an explosion of one-celled plants. They die, falling to the bottom -- only to fuel a massive buildup in bacteria that gobble up the oxygen while they eat the dead microscopic plants. It's possible that such low-oxygen periods occurred before reliable measurements were made starting in the '50s, Chan said. But 50 years is enough time to have covered many oscillations between the El Niño and La Niña phases of ocean activity. "If this was because of El Niño or La Niña cycles, we should have seen it in the past," Chan said. Researchers would like to find out now how much oxygen levels have varied over the course of tens of thousands of years around here. But already, Chan said, "if we look at the deeper past, it gives us an idea that changes in climate do lead to changes in the intensity of low-oxygen zones. "Oxygen is such a basic, critical (need) for the ecological processes for marine life that changing that number in a rapid and dramatic way, is likely to have some big ecological consequences," Chan said. P-I reporter Robert McClure can be reached at 206-448-8092 or robertmcclure@seattlepi.com. Read his blog on the environment at datelineearth.com. © 1998-2008 Seattle Post-Intelligencer |
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