New study maps ocean acidification at global scale

This map shows the global distribution of aragonite saturation at 50 meters depth. The graphic shows areas that are most vulnerable to ocean acidification since they are regions where the saturation of aragonite is lower. Aragonite is a calcium carbonate mineral that shellfish use to build their shells.
This map shows the global distribution of aragonite saturation at 50 meters depth. The graphic shows areas that are most vulnerable to ocean acidification since they are regions where the saturation of aragonite is lower. Aragonite is a calcium carbonate mineral that shellfish use to build their shells. Graphic courtesy NOAA.

U.S. West Coast seen as vulnerable

Staff Report

There’s little doubt that all the world’s oceans are being acidified by the release of carbon dioxide, but some areas are more vulnerable than others, scientists said this week after measuring levels of aragonite, a substance that’s critical for shell-building organisms.

The new study, led by National Oceanic and Atmospheric Administration researchers, says the Arctic and Antarctic oceans, and the upwelling ocean waters off the west coasts of North America, South America and Africa as regions are especially vulnerable to ocean acidification.

When cold waters in those regions, already loaded with CO2, circulate to the upper layers of the oceans they mix with surface waters that are absorbing carbon dioxide from the atmosphere, subjecting them to a double whammy of sorts, according to the scientists. The carbon dioxide from the atmosphere is coming primarily from human-caused fossil fuel emissions.

“These findings will help us better understand and develop strategies to adapt to the severity of ocean acidification in different marine ecosystems around the world,” said Richard A. Feely, a NOAA oceanographer and co-author of the study, which has been accepted for publication and can be read online in the American Geophysical Union journal Global Biogeochemical Cycles.

Ocean acidification happens when excess carbon dioxide enters the ocean, reacts with water, decreases ocean pH and lowers carbonate ion concentrations, making waters more corrosive to marine species that need carbonate ions and dissolved calcium to build and maintain healthy shells and skeletons.

Scientists can assess acidification by measuring levels of chemicals like aragonite. Waters with higher aragonite saturation state tend to be better able to support shellfish, coral and other species that use this mineral to build and maintain their shells and other hard parts.

The new study showed the aragonite saturation state in waters shallower than 328 feet or 100 meters depth decreased by an average of 0.4 percent per year from the decade spanning 1989-1998 to the decade spanning 1998-2010.

“A decline in the saturation state of carbonate minerals, especially aragonite, is a good indicator of a rise in ocean acidification,” said Li-Qing Jiang, an oceanographer with NOAA’s Cooperative Institute for Climate and Satellites at the University of Maryland.

“When oyster larvae are born they must draw on the energy in their yolk to build their aragonite shells to protect themselves from predators and grow into healthy adults,” said Feely. In waters depleted of carbonate ions, young oysters must expend more energy to build their shell and may not survive. This has significant consequences for the seafood industry.”

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