IMAGE: BLEACHED CORAL
NOAA via AP
Bleached coral like this specimen are becoming more common as sea temperatures warm. Experts say carbon dioxide absorbed by oceans is adding additional stress to coral and other organisms by making the water more acidic.
msnbc.com
updated 5/23/2008 6:54:15 PM ET 2008-05-23T22:54:15

Waters along North America's Pacific coast are becoming more acidic, posing a threat to marine life, federal scientists reported Friday — adding that while that fits global warming scenarios, no one had expected the acidification to happen so soon.

"We did not expect to see this extent of ocean acidification until the middle to the end of the century," said study co-author Chris Sabine.

"Our results show for the first time that a large section of the North American continental shelf is impacted by ocean acidification," the experts wrote in the study published in the peer-reviewed journal Science.

Acidification describes the process, natural or manmade, of ocean water becoming corrosive as a result of carbon dioxide being absorbed from the atmosphere.

The researchers said anthropogenic, or manmade, emissions of carbon dioxide are likely to blame since the acidified water that is being "upwelled" seasonally from the deeper ocean is from the last 50 years, a period when the burning of fossil fuels raised CO2 levels dramatically.

"Other continental shelf regions may also be impacted where anthropogenic CO2-enriched water is being upwelled onto the shelf," they concluded.

Threat 'right now'
"Ocean acidification may be seriously impacting marine life on our continental shelf right now," study co-author Richard Feely said in a statement released by the National Oceanic and Atmospheric Administration, which co-sponsored the study along with NASA and the National Science Foundation.

Feely, a NOAA oceanographer, noted that while the ability of oceans to absorb carbon dioxide helps mitigate warming, "the change in the ocean chemistry affects marine life, particularly organisms with calcium carbonate shells, such as corals, mussels, mollusks, and small creatures in the early stages of the food chain."

NOAA echoed the experts' findings. "Acidification of the Earth’s ocean water could have far-reaching impacts on the health of our near-shore environment, and on the sustainability of ecosystems that support human populations," said NOAA assistant administrator Richard Spinrad.

"This research is vital to understanding the processes within the ocean, as well as the consequences of a carbon-rich atmosphere," he added.

The team compiled data from 13 survey lines dropped last summer and stretching from the waters of central Canada to northern Mexico. They measured pH levels in seawater to detect acidification, and found lower levels were much closer to the surface than researchers had predicted.

Previous studies found acidification at deeper depths farther from shore. The researchers said the acidified water appears to well up in spring and summer, when winds bring CO2-rich water up from depths of about 400-600 feet onto the continental shelf.

'Train has left the station'
"The water that will upwell off the coast in future years already is making its undersea trek toward us, with ever-increasing levels of carbon dioxide and acidity," co-author Burke Hales, an associate professor at Oregon State University, warned in a statement.

"The coastal ocean acidification train has left the station," Hales added, "and there is not much we can do to derail it."

Hales also cited a strong correlation between recent low-oxygen events off the Northwest coast and increasing acidification.

"The hypoxia is caused by persistent upwelling that produces an over-abundance of phytoplankton," Hales said. "When the system works, the upwelling winds subside for a day or two every couple of weeks in what we call a 'relaxation event' that allows that buildup of decomposing organic matter to be washed out to the deep ocean."

"But in recent years, especially in 2002 and 2006, there were few if any of these relaxation breaks in the upwelling and the phytoplankton blooms were enormous," Hales said. "When the material produced by these blooms decomposes, it puts more CO2 into the system and increases the acidification."

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