KEY POINTS:
A significant increase in the acidity of the Pacific Ocean has been detected by scientists, who believe it could upset the delicate balance of marine ecosystems and lead to their collapse.
Rising ocean acidity is one of the results of increasing levels of carbon dioxide in the atmosphere
and scientists are worried that the phenomenon could make it impossible for key species in the marine food chain to make their protective shells.
The scientists, led by Richard Feely of the US National Oceanic and Atmospheric Administration (NOAA), surveyed 13 spots off the west coast of North America, and found higher-than-expected levels of acidity.
"Our results show for the first time that a large section of the North American continental shelf is impacted by ocean acidification," the scientists said in their study, published online in the journal Science.
The survey took place in May and June last year using a research ship that collected seawater samples as it sailed across the North American continental shelf from Queen Charlotte Sound in Canada to San Gregorio Baja California Sur in Mexico.
The scientists said that other regions of the world may also be affected to a similar extent, because rising levels of man-made carbon dioxide in the air cause ocean acidity to increase wherever the gas dissolves in seawater to form carbonic acid.
Over the past 250 years, since the start of the industrial revolution, the amount of CO2 in the atmosphere has increased by about 100 parts per million and about a third of this extra carbon dioxide is estimated to have dissolved in the oceans, raising acidity levels.
"This phenomenon, which is commonly called 'ocean acidification', could affect some of the most fundamental biological and geochemical processes of the sea in the coming decades, and could seriously alter the fundamental structure of pelagic [free-swimming] and benthic [seafloor] ecosystems," the scientists said.
Dr Feely said many species of fish that are not directly affected by rising acidity levels would nevertheless still be indirectly affected by the inability of key marine organisms to make their protective shells.
"The best example, of course, is coral reefs. They support 25 per cent of the entire biodiversity of the world's oceans. If they should be lost, then many of the fish species that depend on them would also be lost," Dr Feely said.
"Coral reefs also provide food resources for 500 million people throughout the world. Deep-water corals have been found along the US coast, from California to Alaska," he said.
Microscopic plankton also form shells that eventually sink to the sea floor to become beds of limestone.
Some of these organisms, called coccolithophores, increase their shell-making capacity in response to rising levels of carbon dioxide, but Dr Feely said this may also alter the balance of the marine habitat.
"With some species of coccolithophores increasing in abundance at the expense of others, the ocean ecosystem might shift towards species that carry more carbon away from the surface, causing greater uptake of carbon into the oceans."
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