Wednesday, 27 January 2010 10:52 AM

Carbon Emissions Increasing Acidity of Ocean, Threatening Marine Life

The following article was released by SeaWeb in its latest update (January 26, 2010, Vol. 15, No. 2).There is also an accompanying video which can be accessed at the link provided below to the SeaWeb website.

Industrial nations that attended the Climate Change Conference in Copenhagen this past December have until the end of this month to submit their plans for reducing carbon emissions to the secretariat of the United Nations Framework Convention on Climate Change (UNFCCC)-although the UNFCCC head, Yvo de Boer, stated in a webcast on January 20 that the targets are not legally binding and the deadline is flexible.

The decisions these nations make now could have lasting impacts on marine life, as increasing levels of carbon dioxide in the ocean are making seawater increasingly acidic and, potentially, impeding the survival of many marine organisms.

The ocean absorbs approximately one-third of the carbon dioxide that is emitted by the burning of fossil fuels, which mitigates the impacts of climate change but results in the ocean becoming increasingly acidic. Already, as a recent report from Oceana points out, the ocean is one-third more acidic than it was prior to the Industrial Revolution.

According to a new study in the journal Science, this change in the ocean's chemistry may reduce populations of phytoplankton that form the base of marine food webs. Dalin Shi and colleagues from the Department of Geosciences at Princeton University found that increased seawater acidity decreases the iron intake of phytoplankton. Such a decrease in iron appears to impair phytoplankton's ability to photosynthesize, potentially reducing their populations and hence affecting other ocean life throughout the marine food web.

However, the authors note some of this process could be countered by climate change, which could increase storms that blow iron-rich dust-from, for example, the deserts of Australia and Africa-onto the ocean, where it may eventually settle into surface waters. Additionally, other non-iron-dependent species may fill the void left by declining phytoplankton numbers.

"We're just at the beginning of research on ocean acidification," said study co-author Francois Morel in a press release to announce the findings. "This is the first study published of its kind that looks at uptake of a critical nutrient."

Many previous studies of the impacts of ocean acidification have focused on a decrease in the availability in seawater of carbonate ions, a vital component of the calcium carbonate shells and skeletons of a variety of marine species, including corals, urchins, oysters, clams and mussels. In a low-carbonate ocean, such animals experience greater difficulty in forming their skeletons and shells, and those structures are likely also to prove thinner, less robust and ultimately vulnerable to dissolution.

Such species are at particular risk in the polar regions, largely because calcium carbonate dissolves more readily in lower temperatures. A recent study in the journal Antarctic Science examined what happened when shells from several calcifying Antarctic marine organisms were placed in seawater with a pH of 7.4, a level of acidity that, given present rates of carbon dioxide emissions, researchers predict could occur in coastal waters by the year 2300. Within 35 days of immersion in the water, shells of all four species showed significant signs of deterioration.

Another study, in the journal Biogeosciences, found that shell growth rates of the pteropod (pelagic shelled mollusk) Limacina helicina, a key component of Arctic marine ecosystems, declined by 28 percent in seawater with a pH of 7.78. This is a level of acidity some scientists predict the ocean will reach by 2100. The study's authors conclude that their research supports the "concern for the future of pteropods in a high-CO2 world, as well as of those species dependent upon them as a food resource," noting that a decline in these species' populations "would likely cause dramatic changes to the structure, function and services of polar ecosystems."

If nations do not reduce their emissions dramatically, the Oceana report warns, "scientists project a massive extinction of corals worldwide by the end of this century. As reefs disappear, many commercially important fish species that depend upon reef services will also be in danger."

Sources: Comeau, S., et al. 2009. Impact of ocean acidification on a key Arctic pelagic mollusc (Limacina helicina) Biogeosciences 6:1877-1882; Harrould-Kolieb, E., et al, 2009. Major Emitters Among Hardest Hit by Ocean Acidification. Washington, D.C.: Oceana, 12 pp.; McClintock, J.B., et al., 2009. Rapid dissolution of shells of weakly calcified Antarctic benthic macroorganisms indicates high vulnerability to ocean acidification. Antarctic Science 21(5): 449-456; Shi, D., et al. 2010. Effect of ocean acidification on iron availability to marine phytoplankton. Science Express 10.1126/science.1183517.