Weaker Ocean Circulation Could Worsen Warming, Study Finds


As warming weakens ocean circulation, the seas could increasingly become a source of heat-trapping gas, a new study finds.

“Some climate models predict a 30 percent slowdown in the ocean circulation due to melting ice sheets, particularly around Antarctica,” said study author Jonathan Lauderdale, an environmental scientist at MIT.

Ocean currents cycle carbon from the surface into the deep ocean, but they also bring carbon up from those depths. Scientists have long assumed that slower circulation would diminish both the amount of carbon drawn down from the atmosphere and the amount dredged up from deep waters. In this scenario, the ocean would continue to be an overall carbon sink.

But the new modeling study finds that slowing currents could also disrupt the upwelling of nutrients from the deep to the surface, starving the phytoplankton that absorb carbon.

The decline of phytoplankton would be self-reinforcing, as the tiny creatures also convert iron in the ocean into a form that other phytoplankton can consume. The diminution of iron would cause phytoplankton to further decline, meaning they would take up less carbon either from the atmosphere or from the deep. The findings were published in Nature Communications.

The result is that, not only would the ocean absorb less carbon dioxide from the atmosphere, it would also unleash more carbon dioxide from its depths, leading to further warming. Said Lauderdale, “We can’t count on the ocean to store carbon in the deep ocean in response to future changes in circulation.”

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