News•June 26, 2015

Rapidly Acidifying Arctic Ocean Threatens Species

Parts of the Arctic Ocean within the next 10 years could reach levels of ocean acidification that would threaten the ability of marine animals to form shells, new research suggests.

NOAA and partner scientists collected water samples to measure ocean acidification in the Bering, Chukchi and Beaufort seas on two research cruises aboard USCG cutter Healy.
Click image to enlarge. Credit: Mathis/NOAA

Die-offs in such creatures could have ramifications up the food chain in some of the most productive fisheries in the world and provide a preview of what is in store for the rest of the world’s oceans down the road.

“The Arctic can be a great indicator” of future issues, oceanographer Jeremy Mathis, of the Pacific Marine Environmental Laboratory, said.

Ocean acidification is a process happening in tandem with the warming of the planet and is driven by the same human-caused increase of carbon dioxide in the atmosphere that is trapping excess heat. The oceans absorb much of that excess CO2, where it dissolves and reacts with water to form carbonic acid (also found in soda and seltzer).

As CO2 emissions have continued to grow, so has the amount of carbonic acid in the oceans, decreasing their pH. The ocean generally has a pH of 8.2, making it slightly basic (a neutral pH is 7, while anything above is basic and anything below is acidic). An ocean that is becoming less basic is a problem for the creatures like shellfish and coral that depend on specific ocean chemistry to have enough of the mineral calcium carbonate to make their hard shells and skeletons.

Small snails the size of a human fingernail in polar coastal waters can react very quickly to increased acidity, with their shells dissolving. Such tiny creatures are often the linchpins of marine ecosystems, causing a domino effect up the food chain when they collapse. That’s a major concern in an area that has some of the globe’s most productive fisheries, especially the Bering Sea.

The polar oceans are particularly threatened by ocean acidification, as cold water is better at absorbing CO2 than warm water is. And in regions near the coast, this process is helped along by glacier melt and river runoff that also shift the water’s chemistry toward increased CO2 absorption.

The crew lowers sensors that measure water temperature, salinity and dissolved carbon in the Arctic Ocean.
Click image to enlarge. Credit: Mathis/NOAA

Mathis and his colleagues sampled the levels of calcium carbonate in areas of the Bering, Chukchi and Beaufort seas in the Pacific sector of the Arctic during 2011 and 2012 in an effort to help increase the accuracy of models of the progress of acidification. They found that the models seemed to be performing well, and with the additional data, they could make more refined estimates for when acidification would reach certain critical thresholds.

“That was the major leap forward with this,” Mathis said. The findings were detailed in the journal Oceanography.

In particular, many of the areas studied reached these thresholds sooner than had been anticipated. For the Beaufort Sea, that could be just 10 years from now, in 2025, while the Chukchi could follow close behind, hitting critical levels in 2027. (The Bering Sea has more natural variation in calcium carbonate levels and would take longer to hit these thresholds, around 2044.)

“We knew that the Arctic was on this rapid trajectory,” Mathis said, but the mere 10 years it could take to reach key benchmarks in the Beaufort is “sooner than we had been projecting.”

Already these areas experience hotspots of acidification during the summer months when glacier melt and river runoff are high, Mathis said. He and his team are hoping to study such areas during a research cruise to Alaska this summer to understand what the ramifications are for the local biology.

What’s happening in the Arctic now and what will come to pass over the next decade or two also show what will eventually happen in the rest of the oceans, especially if CO2 emissions continue unabated.

“We need to make sure that people understand that the Arctic is very important, it’s not just this far off place full of snow and polar bears,” Mathis said. “We try to make the case as often as we can that the Arctic really matters to U.S. policy and U.S. food security.”