Scientists have found the world’s first large-scale area of acidified water in the open ocean in the seas of the western Arctic.
“In other (oceans), you may have a small part with low pH, but the Arctic Ocean is the first one we have observed with a larger scale acidification,” said Wei-Jun Cai of the University of Delaware, co-author of a paper recently published in the journal Nature Climate Change.
Ocean acidification is related to increasing levels of atmospheric carbon dioxide. Waters grow more acidic as they absorb gas from the air.
Previous research has suggested the Arctic Ocean is acidifying faster than any other ocean on Earth. Cai and his colleagues were able to map the rate of that change in the water of the Canada Basin by comparing data from the mid-1990s with that up to 2010.
The say the area of acidified water in the basin has expanded northwards as far as 85 degrees latitude. That’s about 500 kilometres further north.
The pool is also deeper. It’s now found as low at 250 metres, an increase of 100 metres.
“That surprised everyone,” said co-author Richard Feely of the National Oceanic and Atmospheric Administration. “But this builds up very, very quickly over time.”
Feely said acidity in the area has increased twice as fast any other body of water that’s been measured. The acidity is now six times what it was 20 years ago.
The scientists say the buildup is related to the disappearance of summer sea ice. The less ice cover, the longer water is exposed to the CO2-rich atmosphere and the more time there is to absorb the acidifying gas.
“During the summer melt time, the CO2 directly goes to sea water,” Cai said.
The melt water sinks and picks up CO2 generated from organisms living adjacent to the continental shelf.
Currents in the atmosphere are also driving more water from the Pacific into the Canada Basin. The Pacific is generally more acidic than the Arctic, because it’s more exposed to the atmosphere and CO2 generated by plants living in it.
Feely said it’s the combination of those factors that is likely to have created such rapid change.
“If you have a change in circulation, plus acidification, things can happen more rapidly. These different processes may interact.”
Little direct research has been done on how the sea-water changes are affecting the Arctic ecosystem. In other waters, acidification has been shown to damage young shellfish and slow the development of tiny animals called therapods, which are at the base of the northern food web.
Those effects are thought to be at least as significant in places such as the Canada Basin as they are in more southern latitudes.
“It’s a short food web (in the Arctic),” said Cai. “When your food web is not as complex, it’s more vulnerable.”
Cai called what’s happening in the Canada Basin a “natural lab” that could provide insight into how acidification could work in other seas.
“That may be of value in the lower latitudes. The lower latitudes will go through that state in the future.”