Substantial sea ice melt has taken place in the western Arctic Ocean basin, a photo taken in September 2008 shows. (Zongyong Gao, State Ocean Administration of China/Courtesy of Science)

Optimistic predictions that warming Arctic waters will soak up lots of carbon dioxide from the atmosphere are unlikely to come true, a new study suggests.

Carbon dioxide levels in surface waters of the Arctic Ocean have been rising rapidly and they probably can't hold much more of the greenhouse gas, reported a scientific paper published Thursday online in Science Express.

That's because carbon dioxide from the atmosphere has been seeping quickly into the thin surface layer of water, and it takes a long time for the carbon dioxide to move into deeper layers, reported the international team of scientists led by Wei-Jun Cai of the University of Georgia.

"That doesn't mean that nothing goes down into the deeper water," said E. Peter Jones, an emeritus research scientist at the Bedford Institute of Oceanography in Halifax, who co-authored the paper. "But it's not going to be the huge sink that some people, anyway, had thought it would be in an ice-free ocean."

Increasing levels of carbon dioxide in the atmosphere have been linked to global climate change that might be slowed down if some of the carbon dioxide were to be removed by a large carbon sink.

The earlier prediction that the Arctic might act that way was based on observations in very specific areas, such as ice-covered basins or ocean margins — areas where continental shelves drop off into deep oceans, the paper said.

2008 Canada Basin survey

However, Cai, Jones and their collaborators did a much more detailed 2008 survey of the Canada Basin, a section of the Arctic Ocean just inside the Bering Strait. From a ship, they collected water samples at different depths and measured the carbon dioxide levels. Compared with an earlier underway survey in summer 1999, the researchers reported, temperatures had increased by three degrees, and a substantial amount of ice had melted.

Jones, who has been researching the nutrients, alkalinity and carbonate content in Arctic waters for decades, said his main job in this project was transferring the water from the collection bottles and preparing them for lab analysis on board the ship.

By comparing their results to those in 1994 and 1999, the researchers found carbon dioxide levels were much higher in surface waters now except in ice-covered areas. They also found that there was a negligible increase or possibly even a slight decrease in carbon dioxide absorption due to photosynthesis. They suggested that was largely because there are few nutrients in the surface waters to support the growth of photosynthesizing organisms such as algae.