Arctic Ocean full up with carbon dioxide

Loss of sea ice is unlikely to enable Arctic waters to mop up more carbon dioxide from the air.

As climate scientists watched the Arctic’s sea-ice cover shrink year after year, they thought there might be a silver lining: an ice-free Arctic Ocean could soak up large amounts of CO₂ from the atmosphere, slowing down the accumulation of greenhouse gases and climate change.

But research published in Science today suggests that part of the Arctic Ocean has already mopped up so much CO₂ that it could have almost reached its limit¹. Wei-Jun Cai, a biogeochemist at the University of Georgia in Athens and an international team sampled the amount of CO₂ in the surface waters of the Canada Basin, in the western Arctic Ocean. “We found that ice-free basin areas had rather high CO₂ values that approached atmospheric levels,” says Cai. “It was not expected.”

Although the Arctic Ocean accounts for only 3% of the world’s ocean surface area and is mostly covered in ice, it takes up 5-14% of all the CO₂ absorbed by the planet’s oceans. It tends to take in proportionately more CO₂ because gases dissolve more easily in cold water.

Scientists had previously thought that open water would promote the exchange of CO₂ between the air and the ocean and that the increase in light reaching the water would also trigger the microscopic ocean plants called phytoplankton to transfer more CO₂ from the atmosphere to the ocean through photosynthesis².

But that “prediction was based on observations of either highly productive ocean margins or ice-covered basins prior to a major ice retreat,” says Cai. Very few scientists had surveyed CO₂ concentrations in offshore waters.

→ Read more at Nature

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