November 25, 2008

Acidic Ocean Threatens Sea Life

Researchers now believe the ocean is growing more acidic faster than once thought, thanks to increasing levels of atmospheric carbon dioxide.

University of Chicago scientists documented the phenomena in a paper published online in the Proceedings of the National Academy of Sciences.

"Of the variables the study examined that are linked to changes in ocean acidity, only atmospheric carbon dioxide exhibited a corresponding steady change," said J. Timothy Wootton, the lead author of the study and Professor of Ecology and Evolution at the University of Chicago.
The study's authors warned that acidic water can harm some sea animals and could reduce the ocean's ability to absorb carbon dioxide.

The eight-year study was based on 24,519 measurements of ocean pH. It represents the first detailed dataset on variations of coastal pH where the world's most productive fisheries live, in the Pacific Ocean off the coast of Washington.

"The acidity increased more than 10 times faster than had been predicted by climate change models and other studies," Wootton said. "This increase will have a severe impact on marine food webs and suggests that ocean acidification may be a more urgent issue than previously thought, at least in some areas of the ocean."

Experts say the ocean plays a leading role in global carbon cycles.

The study found when atmospheric carbon dioxide dissolves in water it forms carbonic acid, increasing the acidity of the ocean.

However, carbon dioxide levels in the ocean fall because photosynthesis takes it out of the water, but at night, levels increase again. The study documented this daily pattern, as well as a steady increase in acidity over time.

"Many sea creatures have shells or skeletons made of calcium carbonate, which the acid can dissolve," said Catherine Pfister, Associate Professor of Ecology and Evolution at the University of Chicago and a co-author of the study.

"Therefore, the increased acidity of the ocean could interfere with many critical ocean processes such as coral reef building or shellfish harvesting."
The study found a number of mussels and stalked barnacles died as acidity increased, while smaller, shelled species and noncalcareous algae increased.

"Models revealed strong links between the dynamics of species living on the shore and variation in ocean pH," Wootton said. "The models project substantial shifts in the species dominating the habitat as a consequence of both the direct effects of reduced calcification and indirect effects arising from the web of species interactions."

The study, "Dynamical Patterns and Ecological Impacts of Declining Ocean pH in a High-Resolution Multi-Year Dataset," will be published in the Dec. 2 issue of PNAS

"To date there is a lack of information about how the ocean carbon cycle has changed in recent years," Pfister said.

"Atmospheric carbon dioxide concentrations will continue to increase, and our work points to the urgent need to better understand the ocean pH changes that this is likely to drive as well as how these changes will affect marine life."


Image 1: Rocks dominated with mussels represent a prominent habitat that may be in decline as ocean pH falls and acidity increases. Credit: J.T. Wootton, University of Chicago

Image 2: Dead mussels as well as live mussels with open, eroded shells are possible symptoms of stress from declining ocean pH and increasing acidity. Credit: C.A. Pfister, University of Chicago

Image 3: Aerial view of Tatoosh Island in the Pacific Ocean off the coast of Washington, where the study of ocean pH change over eight years was conducted. Scientists took more than 24,519 measurements. Credit: C.A. Pfister, University of Chicago


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