Thursday, July 3, 2008
(07-03) 16:22 PDT SAN FRANCISCO -- Ocean waters welling up from the depths along the Pacific Coast from Canada to Mexico are threatening a wide variety of marine organisms as carbon dioxide, the major greenhouse gas, saturates the water and increases its corrosive acidity, government scientists report.
The world's oceans now absorb millions of tons of the global warming gas each year, and thus help to slow the pace of climate change, but the benefit is far outweighed by extreme and damaging changes in the water's chemistry, according to seagoing oceanographers.In separate recent reports in the journal Science and in congressional testimony the scientists warn that the rate of "ocean acidification" is increasing, and say damage to some of the most important living organisms in the sea's food web is becoming more apparent.
The acid can endanger all kinds of marine animals, from the shells of microscopic plankton to the beaks of giant squid, biologists are finding from laboratory experiments and seagoing studies.
Richard A. Feely, a chemical oceanographer in Seattle with the National Oceanic and Atmospheric Administration, estimates that the world's oceans have become at least 30 percent more acidic since the Industrial Age began more than 200 years ago, and that if greenhouse gas emissions continue uncontrolled, the world's oceans in this century will become 150 percent more acidic than they are today.
"While the changes are alarming, it's nearly impossible to predict how this unprecedented acidification will affect entire ecosystems," says Ken Caldeira, an atmospheric scientist with the Carnegie Institute's Department of Global Ecology at Stanford.
Two teams, similar findings
Caldeira and his colleagues raise the issue today in Science, and only two week ago in the same journal, Feely's team from NOAA's Pacific Marine Environmental Laboratory reported on their most recent ocean survey along the West Coast and over the continental shelf aboard NOAA's oceanographic research ship Wecoma, sailing more than 2,000 miles from Queen Charlotte sound in British Columbia to San Gregorio in Baja California.
During May and June of last year the Wecoma's researchers took repeated samples of the upwelling water that rose from the deep sea bottom onto the continental shelf, where depths range from 120 to 1,200 feet, and discovered that the water had been heavily saturated with carbon dioxide and acidified as it lay on the bottom for 50 years.
On another NOAA ship, the MacArthur II, water sampling by Feely's team off the Golden Gate and along other sections of the Northern California coast revealed that the acidified water reached all the way to the surface, the scientists reported.
Each spring along the West Coast, winds from the northwest blow strongly across the sea surface toward the shore and generate strong upwelling currents, Feely explained. The upwelling, in turn, brings water saturated with carbon dioxide from the deep bottom toward the surface. Then, as the gas mixes with seawater, it becomes carbonic acid, and when that acidity of the water becomes strong enough it can dissolve the calcium carbonate shells of many of the sea's most important animals.
Scientists have already reported the severe damage that acidity in seawater is causing to corals - both the shallow coral reefs of the tropics and the lesser-known deepwater corals of the northern oceans that also require calcium carbonate to build their bony skeletal homes.
But mussels, oysters, crabs, urchins, squid, and the kind of microscopic carbonate-shelled plankton that form the diet of creatures ranging in size from krill to whales, are also organisms that can fall prey to increases in the ocean's acidity, according to Feely.
A threat to the food chain
One tiny shelled organism, a swimming snail called a pteropod, is a major food source for juvenile Pacific coast salmon and other fish, Feely noted, and their loss due to increases in the ocean's acidity could in turn seriously endanger one of the most important commercial fisheries on the West Coast - not only salmon, but mackerel, herring and cod.
"We have little idea what ocean acidification will do to fish eggs or fish larvae, or how the loss of organisms at the base of the food chain might affect the larger fish that so many people have come to depend on," Caldeira said last month in testimony to the House Subcommittee on Energy and Environment.
Or as Feely put it in his own testimony before the same congressional committee: "Since ocean acidification research is still in its infancy, it is impossible to predict exactly how the individual species responses will cascade throughout the marine food chain and impact the overall structure of marine ecosystems."
Sea urchins make ideal models for studying the effects of environmental stresses on the development of other marine animals, and their entire genome was sequenced only two years ago.
At UC Santa Barbara Gretchen Hofmann, a leading marine biologist, has collected sea urchins from Antarctica and now cultures their embryos in her laboratory where she varies the concentration of carbon dioxide in sea water to study its effects on the sea urchin genes.
As that concentration doubles and doubles again from 385 parts per million to 1,000 parts per million - the same rate of increase predicted by the International Panel on Climate Change for this century - acidification increases too, Hofmann said Thursday.
"We can see tipping points where genetic changes in the embryos occur all along the way as carbon dioxide in the water rises," she said, "and at 1,000 parts per million the entire metabolism of the embryos crashes, their genes shut deeply down, and they can't make their skeletons at all."
E-mail David Perlman at dperlman@sfchronicle.com
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