WASHINGTON — Researchers from Oregon State University found that a “flushing” of the deep Pacific Ocean made more carbon dioxide out of the deep sea and into the atmosphere after the last ice age.
A study published on Monday in the journal Nature Geoscience showed compelling evidence for how it happened and warned it could happen again, potentially magnifying and accelerating human-caused climate change.
The flushing was caused by the acceleration of water circulation patterns that begin around Antarctica, sinking and moving northward at great depth a few miles below the surface, according to the study.
It continued all the way to Alaska, where it rises, turned back southward, and flowed back to Antarctica where it mixed back up to the sea surface.
Du Jianghui, the paper’s lead author at Oregon State said it took a long time for the water’s round trip journey in the abyss, almost 1,000 years.
Du and his colleagues found that flow slowed down during glacial maximums but sped up during deglaciation, as the Earth warmed.
This faster flow flushed the carbon from the deep Pacific Ocean and brought the carbon dioxide to the surface near Antarctica, where it was released into the atmosphere.
“It happened roughly in two steps during the last deglaciation: an initial phase from 18,000 to 15,000 years ago, when carbon dioxide rose by about 50 parts per million, and a second pulse later added another 30 parts per million,” Du said.
That total is just a bit less than the amount carbon dioxide has risen since the industrial revolution, making the ocean a powerful source of carbon.
Brian Haley, also an Oregon State oceanographer and co-author on the study, said that carbon tend to fall down into the deep ocean, because up near the surface, plankton grew, but when they died they sunk and decomposed.
“The slower the circulation,” Haley said, “the more time the water spends down there, and carbon can build up.”
“Our evidence that this actually happened in the past will help the people who run climate models figure out whether it is a real risk for the future,” said Du.
According the researchers, the ocean has absorbed about a third of the total carbon emitted from fossil fuels, helping slow down warming.
If the ocean stops absorbing the excess carbon, and instead releases more, it would subtract from our remaining emissions budget set by the Paris Climate Agreement, according to the study.