Twenty millennia ago, when the Earth was cool and glaciers were at their most massive, scientists believe the deep waters around Antarctica stored up large amounts of carbon dioxide. But as the planet thawed afterward, the sea may have sped the warming up by releasing that carbon back into the atmosphere as greenhouse gas, according to new research published in Science Thursday. If the earth warms up too much, the ocean does it one better and makes it even hotter.
The researchers fear that now, the sea could once again burp up a great load of carbon, which would exacerbate the effects of climate change by trapping even more solar energy and warming the planet further.
“A warmer ocean will be not able to hold as much carbon as it is holding now, and then it will start releasing it back,” said Chandranath Basak, the lead author on the paper and an assistant professor at California State University, Bakersfield. “And that will make it even worse.”
When organisms in the ocean die, they fall to the bottom of the sea and rot, releasing carbon dioxide. If the water column remains stratified into layers, that carbon load can remain in the deep. But if those layers are destabilized by the warming of the ocean, those deep waters circulate to the surface, releasing it back into the atmosphere.
To see whether that happened last time the oceans warmed, Basak and his collaborators looked at isotopes in fossilized fish teeth. They found that during the cooler period, the deep carbon-rich waters near Antarctica didn't churn to the surface much — but that warming had destabilized the water column. No one can predict the future, but I asked Basak whether he’s worried that global warming could again release a great cache of carbon from the ocean, hastening the effects of climate change — rising seas, freak storms and agricultural disruptions.
“Yes,” he said, somberly. “If we keep warming the ocean, especially the deep ocean, it is a possibility.”