Pacific Ocean getting warmer and more acidic

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Pacific Ocean getting warmer and more acidic
Rhett A. Butler, mongabay.com
March 31, 2006

The Pacific Ocean is getting warmer and more acidic, while the amount of oxygen is decreasing, due to increased absorption of atmospheric carbon dioxide say scientists from the National Oceanic and Atmospheric Administration's Pacific Marine Environmental Laboratory and the University of Washington.

Researchers report that the pH of saltwater in the Pacific has dropped 0.025 units since the early 1990s and warn that oceans could become even more acidic by the end of the century given current atmospheric carbon dioxide levels. Since there is a lag time in the absorption of carbon dioxide by oceans, the impact of past carbon emissions are not yet fully apparent.

Carbon dioxide is a byproduct of fossil fuels combustion. Scientists estimate that the oceans have soaked up about half--118 million tons of atmospheric carbon dioxide--of all fossil fuel emissions over the past 200 years. Had oceans not absorbed this carbon, current atmospheric carbon dioxide would be much higher than the current 381 parts-per-million (ppm)--probably closer to 500-600 ppm say climatologists.

This absorption has made the world's oceans significantly more acidic since the beginning of the industrial revolution. According to Mark Jacobson, an assistant professor of civil and environmental engineering at Stanford University, between 1751 and 2004 surface ocean pH dropped from approximately 8.25 to 8.14. James Orr of the Climate and Environmental Sciences Laboratory estimates that ocean pH levels could fall another 0.3 - 0.4 units by 2100.

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.

Ocean acidification is of great concern due to its potential impact on marine life. Coral and other marine organisms use free carbonate ions in sea water to build calcium carbonate shells and exoskeletons, but as atmospheric carbon dioxide levels rise and more carbon dioxide is absorbed by the world's oceans, sea waters become increasingly acidic by stripping out carbonate ions. Lower carbonate ion concentrations make it more difficult for organisms to form shells, leaving them vulnerable to predators and environmental conditions.

In the past, changes in ocean acidity have caused mass extinction events. According to a study published in the September 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. The same fate could befall modern day marine life. In September 2005, a team of scientists writing in Nature warned that by 2100, the amount of carbonate available for marine organisms could drop by 60%. In surface ocean waters, where acidification starts before spreading to the deep sea, there may be too little carbonate for organisms to form shells as soon as 2050.

The loss of these small organisms would have a disastrous impact on predators -- including salmon, mackerel, herring, cod -- that rely on them as a food source and could spell trouble for other species.

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