World's oceans losing appetite for CO2

Between 2000 and 2007, as emissions of the potent greenhouse gas carbon dioxide skyrocketed, the amount of human-made carbon absorbed by the oceans fell from 27 to 24 percent.

In terms of ocean processes, "that's a pretty large drop, and the trend is pretty clear: The ocean can't keep up with human-made carbon," study leader Samar Khatiwala, an oceanographer at Columbia University's Lamont-Doherty Earth Observatory, told National Geographic News.

According to Khatiwala, the total uptake of carbon is not declining, but the rate is just not growing as fast as it used to.

But, if the oceans continue to be overwhelmed by carbon, more of the gas will remain in the already warming atmosphere, the authors say.

"Ultimately the ocean is what's controlling what's going on here," said Chris Sabine, a supervisory oceanographer at NOAA's Pacific Marine Environmental Laboratory in Seattle, Washington.

"It's a big deal that it's becoming less efficient in taking up CO2," he added.

For their study, Khatiwala and colleagues collected data on seawater temperature and salinity recorded from 1765 to 2008.

The team also gathered data on amounts of ocean pollutants called chlorofluorocarbons.

These chemicals act as "tracers," allowing the scientists to figure out the time it takes for a substance to go from the surface of the ocean to the interior.

Based on this data, the team created a mathematical technique that allowed them to "work backward" to determine how much human-made carbon has entered the ocean over the years.

The researchers found that when human-made CO2 began increasing dramatically in the 1950s, the oceans began absorbing more of that carbon.

But, in recent decades, the rate of absorption has declined, and the reasons for the slowdown are still unclear.

It might have something to do with increased carbon dioxide emissions making seawater more acidic, because more acidic waters are less able to dissolve carbon dioxide.

Likewise, CO2 can't dissolve as easily in warmer water-which is why about 40 percent of past carbon emissions were absorbed into the chilly oceans off Antarctica, according to the study.

"The oceans are performing a tremendous service for humankind," NOAA's Sabine said.

"If we throw the oceans' carbon uptake out of whack, the potential is there to completely overwhelm what we're trying to do with limiting our fossil fuel emissions," he added. (ANI)

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