The ocean is growing more acidic faster than previously thought, according to research from University of Chicago scientists.

The research, published by the Proceedings of the National Academy of Sciences this month, also found that the increasing acidity correlates with increasing levels of atmospheric carbon dioxide.

Lead author of the study and Professor of Ecology and Evolution at the University of Chicago, J. Timothy Wootton, said of the variables the study examined that are linked to changes in ocean acidity, only atmospheric carbon dioxide exhibited a corresponding steady change.

The researchers said increasingly acidic water harms certain sea animals and could reduce the ocean's ability to absorb carbon dioxide.

Scientists have long predicted that higher levels of atmospheric carbon dioxide would make the ocean more acidic, however empirical evidence of growing acidity has been limited.

The new study is based on 24,519 measurements of ocean pH spanning eight years, which represents the first detailed dataset on variations of coastal pH at a temperate latitude, where the world's most productive fisheries live.

Professor Wootton said the study found that the acidity increased more than 10 times faster than had been predicted by climate change models and other studies.

"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," he said.

The ocean plays a significant role in global carbon cycles. When atmospheric carbon dioxide dissolves in water it forms carbonic acid, increasing the acidity of the ocean. During the day, 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.

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

"Therefore, the increased acidity of the ocean could interfere with many critical ocean processes such as coral reef building or shellfish harvesting."

She says to date there is a lack of information about how the ocean carbon cycle has changed in recent years.

"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."

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