Growing Ocean Acidity May Erode Coastal Ecosystems

John Roach, National Geographic News 22 May 08;

Ocean waters along North America's west coast are becoming more acidic than expected in response to atmospheric carbon emissions, which will likely cause significant changes to economically vital marine ecosystems, a new study says.

At one spot in northern California, waters acidic enough to corrode seashells now rake the shore, researchers point out.

"The models suggested they wouldn't be corrosive at the surface until sometime during the second half of this century," Richard Feely, a chemical oceanographer with the Pacific Marine Environmental Laboratory in Seattle, Washington, said via email.

Scientists have long known that the oceans serve as a giant carbon sink, moderating the effects of global warming by absorbing about a third to a half of human-caused carbon dioxide (CO2) emissions.

But the added carbon dioxide is lowering the oceans' pH, changing their chemistry and biology, explained Feely, whose lab is run by the National Oceanic and Atmospheric Administration.

Acidic waters inhibit marine organisms from producing the calcium carbonate that makes up their exoskeletons and shells.

"Scientists have also seen a reduced ability of marine algae and free-floating plants and animals to produce protective carbonate shells," Feely said.

For example researchers have seen a decline in swimming mollusks called pteropods that are eaten by creatures ranging from shrimplike krill to whales. The mollusks are particularly vital to juvenile salmon and other commercial fish.

"The impact of ocean acidification on fisheries and coral reef ecosystems could reverberate through the U.S. and global economy," Feely said.

Corrosive Upwelling

Feely and colleagues measured the acidity of waters along the west coast of North America from central Canada to northern Mexico.

They found deep-ocean waters corrosive enough to eat away at seashells and coral reefs are upwelling each spring and summer onto the continental shelf.

"The deep waters are always more acidic than surface waters," Feely explained.

In addition to carbon dioxide absorbed from the atmosphere, deep waters contain carbon dioxide that is a by-product of the breathing of marine organisms and the decay of organic matter.

"What's more, there is a 50-year lag between the time when ocean surface waters [are] exposed to the atmosphere, its sinking, and ultimate upwelling on the continental shelf," noted co-author Burke Hales from Oregon State University.

"This means that even if we were to stop instantaneously the current rate of rise of CO2 in the atmosphere ... the corrosivity of these upwelled waters would increase for the next 50 years," he said in a telephone briefing with reporters.

These corrosive waters already reach the surface at one point in northern California. Elsewhere, they reach depths between 130 and 390 feet (40 and 120 meters).

Feely, Hales, and colleagues report their findings in tomorrow's issue of the journal Science.

"Amazing and Frightening"

Ken Caldeira is a geoscientist who studies ocean acidification at the Carnegie Institute of Washington's office in Stanford, California. He said the new finding is dramatic.

"The idea that [calcium carbonate] shells might already be dissolving in coastal waters is pretty amazing, and it's frightening," he said.

Global models, he noted, had predicted corrosion in coastal waters at the Poles around the middle of this century and the California coast sometime next century.

However, the impact of these acidic waters remains uncertain, Caldeira added.

Experiments have shown that ocean acidification makes coral reefs vulnerable to erosion, potentially impacting thousands of species that depend on reef habitat.

Shellfish such as crabs, mussels, and oysters also weaken with increasing carbon dioxide levels, and experiments suggest squid and sea urchins are susceptible to acidic oceans.

But scientists have not conducted any experiments on how entire coastal ecosystems respond to increasing ocean acidification, Caldeira said. Most research has been in the lab and focused on single organisms.

In addition, the chemistry of coastal waters is generally more variable than the open ocean, suggesting coastal environments may be more resilient to the changing conditions.

"It could be either something serious that could completely restructure the coastal ecosystem, or it could be something that within a few years these things basically adapt to," he said.

He added, however, that no experiments have shown an organism becoming more efficient at making shells in response to ocean acidification.

"It looks like the biological capacity for adaptation there in calcification is pretty low."

Human carbon emissions make oceans corrosive: study
Deborah Zabarenko, Reuters 22 May 08;

WASHINGTON (Reuters) - Carbon dioxide spewed by human activities has made ocean water so acidic that it is eating away at the shells and skeletons of starfish, coral, clams and other sea creatures, scientists said on Thursday.

Marine researchers knew that ocean acidification, as it's called, was occurring in deep water far from land. What they called "truly astonishing" was the appearance of this damaging phenomenon on the Pacific North American continental shelf, stretching from Mexico to Canada.

"This means that ocean acidification may be seriously impacting our marine life on our continental shelf right now, today," said Richard Feely of the Pacific Marine Environmental Laboratory, part of the U.S. National Oceanic and Atmospheric Administration.

Other continental shelf regions around the world are likely to face the same fate, he said.

Plenty of natural activities, including human breath, send the greenhouse gas carbon dioxide into the atmosphere, but for the last 200 years or so, industrial processes that involve the burning of fossil fuels such as coal and petroleum have pushed emissions higher.

Oceans have long been repositories for the carbon dioxide, absorbing some 525 billion tonnes of the climate-warming substance over the last two centuries -- about one-third of all human-generated carbon dioxide for that period.

But the daily absorption of 22 million tonnes of the stuff has changed the chemistry and biology of the oceans, turning it corrosive and making it difficult or impossible for some animals to produce their calcium carbonate shells and skeletons, the researchers said.

CHURNING OCEAN WATERS

This change has been observed over the last three decades, the scientists said in research published in the journal Science.

The acidic waters are coming up onto the continental shelf -- the shallow area near a big land mass like North America -- because of a long-term churning ocean pattern that moves cold deep water up toward the surface in the spring and summer, the scientists said.

The carbon-loaded waters that are now near the U.S. West Coast took about 50 years to get there, starting somewhere on the ocean surface and absorbing their share of carbon dioxide, then sinking deep down and eventually welling upward.

The natural process called ocean respiration could not explain the high levels of carbon dioxide that caused the corrosive water the scientists found on the continental shelf; the addition of human-generated carbon dioxide did.

This acidic water is corroding the shells of clams, mussels, starfish and the free-floating sea-snails called pterapods that nourish young salmon, the researchers said, citing data from a 2007 research cruise.

Corrosion occurred in water that absorbed carbon dioxide from the atmosphere in 1957, when levels of this gas were considerably lower than they are now, the researchers said.

"This means that even if we were to stop instantaneously the current rate of rise of carbon dioxide in the atmosphere, the corrosivity of these upwelling waters would increase for the next 50 years," said Burke Hales, a professor of chemical oceanography at Oregon State University.

(Editing by Will Dunham and Philip Barbara)

The Twilight Age of Coral Reefs
Stephen Leahy, IPSnews 22 May 08;

GIJON, Spain, May 22 (IPS) - Coral reefs will be the first global ecosystem to collapse in our lifetimes. The one-two punch of climate change that is warming ocean temperatures and increasing acidification is making the oceans uninhabitable for corals and other marine species, researchers said at a scientific symposium in Spain.

And now other regions are being affected. Acidic or corrosive waters have been detected for the first time on the continental shelf of the west coast of North America, posing a serious threat to fisheries, Richard Feely, an oceanographer with the U.S. National Oceanic and Atmospheric Administration (NOAA), told attendees in Gijon, Spain Wednesday.

More than 450 scientists from over 60 countries are participating in the "Effects of Climate Change on the World's Oceans" symposium.

"Surface waters off the coast of San Francisco had concentrations of carbon dioxide that we didn't expect to see for at least another 100 years," Feely told IPS.

For hundreds of thousands of years, the levels of carbon dioxide in the ocean and the atmosphere were in balance, but the burning of fossil fuels and deforestation has put more CO2 into the atmosphere over the last 150 years. The oceans have absorbed one-third -- about 130 billion tonnes -- of those human emissions and have become 30 percent more acidic as this extra CO2 combines with carbonate ions in seawater, forming carbonic acid.

Each day, the oceans absorb 30 million tonnes of CO2, gradually and inevitably increasing their acidity and leaving less calcium carbonate in the water for corals and shell-form species like phytoplankton to grow or maintain their skeletons.

On the west coast of North America, there is normal upwelling of deep ocean water onto the continental shelf in the spring and summer. Feely and colleagues took water samples from Canada to Mexico last summer and much to their surprise they found big pools or shoals of corrosive water. These deep waters have been absorbing CO2 for thousands of years and are normally more acidic, but the levels found were far higher and much closer to the shore than anyone had expected.

This is the first evidence that a large section of the North American west coast is being impacted by climate change-driven ocean acidification, Feely and colleagues write in their paper published Thursday in Science. "Other continental shelf regions may also be impacted," they write.

In fact, Feely told IPS that there is evidence that the same process is happening along the west coast of South America.

So what does this mean? "There are likely huge impacts, but this is new and no one has looked to see yet," Feely said.

Continental shelves are among the most productive regions of the oceans and the easiest to fish. The very few studies looking at the impacts of ocean acidification have found that many species cannot survive these new conditions. Brittlestars (a close relative of starfish) die in eight days, and some juvenile clams can't form shells when the CO2 levels are doubled, Feely said. Some of the surface waters last summer were triple the normal CO2 levels.

And there is no information at all on how the marine ecosystem responds when these pools of corrosive water move in for a few days or weeks. "Do species like free-swimming pteropods (a type of snail) know when their thin shells are dissolving so they can get out of the way?" he asked.

That turns out to be an important question for species like salmon, since pteropods can make up 60 percent of their diet.

Temperature rise and acidification are putting one of the planet's key ecosystems at great risk, Feely warned: "This is a very real biological threshold beyond which species will simply cease to exist."

Coral reefs support about 25 to 33 percent of the oceans' living creatures. Some one billion people depend directly and indirectly on reefs for their livelihoods. Sea birds and many species of fish would be affected by the loss of reefs, said Ove Hoegh-Guldberg, a marine scientist at the Centre for Marine Studies at the University of Queensland, Australia.

When CO2 in the atmosphere reaches a concentration of 450 to 500 parts per million (ppm), the oceans will mostly be too acidic for corals to grow. Warmer ocean temperatures of just one or two degrees above normal can not only can cause coral bleaching but also make corals vulnerable to even lower levels of acidification, said Hoegh-Guldberg, who attended the Gijon meet.

CO2 is at 384 ppm currently and rising very fast as nearly every country's emissions continue to grow. Worse, new research also presented in Gijon suggests the oceans themselves are no longer absorbing as much CO2 as they once did. Stabilising the atmospheric concentration of CO2 at less than 450 ppm now looks to be impossible.

"We are witnessing the end of corals as a major feature in the oceans," Hoegh-Guldberg told IPS.

The faint hope for corals is for global society to realise climate change is "a code red emergency" and cut carbon emissions to zero and start reducing the concentrations in the atmosphere right away, he said. "Otherwise in 30 years or so corals will be so thin and brittle if you breathe on them they will fall over."