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Effects of ocean acidification will come 30 years earlier than expected
mongabay.com
November 11, 2008


The Southern Ocean may be 30 years closer to a tipping point for ocean acidification than previously believed, putting sea life at risk, according to research published in this week's Proceedings of the National Academy of Science.

Analyzing seasonal changes in pH and the concentration of carbonate in the Southern Ocean, scientists from the University of New South Wales (UNSW) and CSIRO found that seasonal swings will amplify the effects of carbon dioxide emissions on ocean acidity, speeding up ocean acidification by 30 years relative to previous estimates.

The acceleration of acidification — which reduces the availability of carbonate ions used by calcifying organisms to form calcium carbonate shells — could have significant impacts on marine life. In particular, pteropods, a type of plankton that makes up an important part of the Antarctic food chain, will be challenged by increasingly acidic conditions.

The pteropod or sea butterfly is one marine organism that could suffer in more acidic seas. A recent experiment by Victoria Fabry at California State University San Marcos found that the shells of pteropods, when subjected to conditions as projected by the model for the year 2100, rapidly dissolved. Photo courtesy of USGS.

"Some prominent calcifying plankton, in particular the Pteropod species Limacina helicina, have important veliger larval development during winter and will have to experience detrimental carbonate conditions much earlier than previously thought, with possible deleterious flow-on impacts for the wider Southern Ocean marine ecosystem," write the authors. "Our results highlight the critical importance of understanding seasonal carbon dynamics within all calcifying marine ecosystems such as continental shelves and coral reefs, because natural variability may potentially hasten the onset of future ocean acidification."

Ocean acidification — driven in part by the absorption of carbon dioxide from the atmosphere — is of great concern to scientists. In August members of the U.S. Coral Reef Task Force warned that acidification is among the greatest threats to marine ecosystems and produced the "Honolulu Declaration", a set of measures to address "the survival of coral reefs in an acidifying ocean."

Oceans worldwide absorbed approximately 118 billion metric tons of carbon between 1800 and 1994 according to a report published in 2006 by scientists at the National Center for Atmospheric Research and NOAA, resulting in increased ocean acidity. Should CO2 emissions continue at their current rate, scientists project that global ocean pH levels could drop from 8.1 today to 7.7 by 2100.

In the past, changes in ocean acidity have triggered mass extinction events. According to a study published in the September 2006 issue of Geology, dramatically warmer and more acidic oceans may have contributed to the worst mass extinction on record, the Permian extinction. During the extinction event, which occurred some 250 million years ago, about 95% of ocean's life forms became extinct.

Ben I. McNeil and Richard J. Matear. Southern Ocean acidification: A tipping point at 450-ppm atmospheric CO2. PNAS Early Edition for the week of Nov 10-14