Acidification of the Pacific

Carbon dioxide in the 

tropical Pacific Ocean is 

increasing faster than 

expected

Ocean acidity is also rising rapidly

NOAA,
26 March, 2014

New NOAA research has revealed unprecedented changes in ocean carbon dioxide in the tropical Pacific Ocean over the last 14 years, influencing the role the oceans play in current and projected global warming and ocean acidification. Natural variability has dominated patterns in ocean CO2 in this region, but observations now show human activity contributes to increasing CO2 levels.

“Carbon dioxide in tropical Pacific waters has been increasing up to 65 percent faster than atmospheric CO2 since 1998,” says Adrienne Sutton, a research scientist with the NOAA Joint Institute for the Study of the Atmosphere and Ocean at the University of Washington and lead author of the paper in the journal Global Biogeochemical Cycles. “Natural cycles and human-caused change appear to be combining to cause more rapid change than our models predict.”

The new research documents the rise in the level of CO2 that the tropical Pacific Ocean gives off into the atmosphere. While this region emits CO2, global oceans overall are an important sink for CO2 and absorb more than 25 percent of fossil fuel emissions annually. But 70 percent of the change from year to year in the global oceanic uptake of atmospheric CO2 is driven by variations in the tropical Pacific Ocean. So changes in this region can affect the global carbon system.

“We have a 30-year record of CO2 collected from instruments on ships, but this new data tell us the tropical Pacific has changed more rapidly in the past 14 years than observed previously,” says coauthor and NOAA Senior Scientist Richard Feely.

Driving these rapid increases in oceanic CO2 is likely a combination of human impact and natural cycles, with human impacts now playing a large role. The burning of fossil fuels produces an increasing level of CO2 in the atmosphere, which is partially absorbed into the oceans. Natural cycles also influence the tropical Pacific. Deep ocean water is naturally high in CO2. This water is driven to the surface by a process known as upwelling. Since 1998, higher winds have increased the upwelling of water enriched with CO2 from human and natural sources. The higher winds are believed to be connected to a shifting pattern called the Pacific Decadal Oscillation.

"Rates of change in CO2 and acidity in seawater are just as rapid in the Tropical Pacific as in polar regions, which are considered one of the harbingers of ocean acidification,” says Sutton.

Rising acidity

NOAA and Cooperative Institute scientists have documented a decline in the pH of the tropical Pacific from 1998 to 2011. A declining pH means that the ocean's acidity is rising. Black, orange, green, and gray are each pH data from different buoys. (NOAA)

Rising acidity (lowering pH) in the oceans, or ocean acidification, is a chemical change caused by the ocean’s absorption of CO2 emissions. More acidic seawater can corrode the calcium carbonate shells of many marine organisms.

The new research relies on observations from CO2 sensors that scientists and engineers with NOAA Research’s Pacific Marine Environmental Lab Carbon Group have placed on moored buoys within the Tropical Atmosphere Ocean array, a network of buoys that stretches across the Pacific. This study examines data from 1997-2011.

“Sustaining these mooring observations in the tropical Pacific helps us distinguish long-term change from natural variability,” Sutton says. “This level of understanding will help us predict and prepare for potential impacts of climate change in tropical marine ecosystems.”

The paper is available online through the journal Global Biogeochemical Cycles.