Data collected since the pre-industrial age indicates that the mean surface pH of the world's oceans has declined from 8.2 to 8.1 units with another 0.4 unit decline possible by century's end, according to a new study in Oceanography. A single whole pH unit drop would make ocean waters 10 times more acidic, which could rob many marine organisms of their ability to produce protective shells – and tip the balance of marine food chains, the study warns.

The delicate balance of life in the waters that surround the frozen continent of Antarctica is especially susceptible to the effects of acidification. The impact on the marine life in that region will serve as a bellwether for global climate-change effects.

"The Southern Ocean is a major global sink for carbon dioxide. Moreover, there are a number of unique factors that threaten to reduce the availability of abundant minerals dissolved in polar seawater that are used by marine invertebrates to make their protective shells," co-author Jim McClintock says.

"In addition, the increased acidity of the seawater itself can literally begin to eat away at the outer surfaces of shells of existing clams, snails and other calcified organisms, which could cause species to die outright or become vulnerable to new predators." One recent study, for example, revealed that the shells of post-mortem Antarctic marine invertebrates evidenced erosion and significant loss of mass within only five weeks under simulated acidic conditions.

McClintock says acidification also could exert a toll on the world's fisheries, including mollusks and crustaceans. He adds that the potential loss of such marine populations could greatly alter the oceans' long-standing food chains and produce negative ripple effects on human industries or food supplies over time.

"So many fundamental biological processes can be influenced by ocean acidification, and the change in the oceans' makeup in regions such as Antarctica are projected to occur over a time period measured in decades," McClintock says.

"Evolution simply may be unable to keep up, because it typically takes marine organisms longer periods, hundreds or even thousands of years to naturally adapt," he says. "But ocean acidification is simply happening too quickly for many species to survive unless we reverse the trend of increasing anthropogenically generated carbon dioxide that is in large part driving climate change."


Citation:  Fabry et al., 'Ocean Acidification at High Latitudes: The Bellweather', December 2009, Oceanography, 22(4), 161-171