Scientists just back from a research cruise across the northern Pacific say the ocean has soaked up so much carbon dioxide from human burning of fossil fuels that it’s turning more acidic, disrupting growth of coral and the tiny sea creatures salmon and other fish rely on for food.
The chemical signature of the carbon dioxide makes clear it is from human and not natural sources, said Richard Feely, an oceanographer with the federal Pacific Marine Environmental Laboratory in Seattle and chief scientist for the cruise.
Carbon dioxide is known as a greenhouse gas that contributes to global warming by trapping heat in the atmosphere. Oceans help offset that effect by absorbing about a third of the carbon dioxide produced by humans, the researchers said.
But the new findings reveal that all the carbon dioxide is changing the delicate chemical balance of ocean water that lets coral, shellfish and forms of tiny plankton construct their vital shells.
The tiny life forms play vital parts in marine ecosystems by serving as food for larger creatures. Their disruption, coupled with other effects of greenhouse gases such as rising temperatures, could wreak profound changes on the diversity and productivity of oceans, the researchers said.
Escalating ocean acidity can begin to dissolve the shells faster than the creatures can build them.
Researchers estimate the oceans have become about 30 percent more acidic since humans began burning fossil fuels in large quantities, exhausting carbon dioxide into the environment.
While carbon dioxide levels have been higher in the Earth’s past, and oceans more acidic, “the rate at which they’re changing has never been this fast,” said Chris Sabine, another oceanographer on the trip. Ocean life is not used to such sharp shifts.
Carbon dioxide levels in the atmosphere are now higher than they have been at any time in at least 600,000 years. Scientists had expected the rising levels would turn oceans more corrosive.
Northern Pacific waters where researchers detected the shift circulate in currents along the Oregon coast.
“As predicted, the ocean is steadily becoming more acidic,” said Mark Hixon, a professor of zoology at Oregon State University and an authority on coral reefs. “As that continues a threshold will be crossed, and across that threshold these organisms will be unable to make their shells, and they will die.”
He said the findings are unsettling, especially coming only weeks after findings that polar ice sheets are beginning to melt faster than expected in a shift that could raise sea levels worldwide.
“All of this is really scary right now,” said Hixon, who did not take part in the Pacific research cruise. “It’s becoming clear that the biological effects of global warming are accelerating faster than previously anticipated.”
The research cruise, sponsored by the National Oceanic and Atmospheric Administration and the National Science Foundation, traversed the Pacific from Tahiti to Alaska, taking measurements every 60 nautical miles.
Scientists examined the water acidity and chemistry, but also looked closely at pteropods, a shelled form of plankton distantly related to land snails.
Pteropods are an important food source for salmon, herring, cod and other fish, and their sensitivity to water chemistry makes them an important barometer of ocean acidity.
Pteropods and other shellfish build shells from calcium carbonate, with pteropods using an especially delicate form called aragonite. They find enough aragonite only in water near the ocean’s surface, because deeper water becomes too acidic.
They are confined to a thin layer of surface water in the cool northern Pacific, because cold water there holds more carbon dioxide and is more acidic to start out.
As escalating carbon dioxide turns oceans more acidic still, that layer of water gets thinner and thinner until pteropods get squeezed out altogether, said Robert Byrne, a professor at the University of South Florida who was on the research cruise.
“We’re on the threshold of what is going to become a very large effect,” he said.
“People can argue back and forth whether climate is going to change, but they can’t argue that (acidity) is going to change, because we can predict that with certainty and we can see it’s happening,” Byrne said. “The effects in the end are going to be global.”
For more information, go to: www.noaanews.noaa.gov/stories2006/s2606.htm.