The new study indicated carbon that had built up in the oceans over millennia was released in two big pulses, one about 18,000 years ago and one 13,000 years ago, said Thomas Marchitto and Scott Lehman of CU-Boulder's Institute of Arctic and Alpine Research, who jointly led the study. While scientists had long known as much as 600 billion metric tons of carbon were released into the atmosphere after the last ice age, the new study is the first to clearly track CO2 from the deep ocean to the upper ocean and atmosphere and should help scientists better understand natural CO2 cycles and possible impacts of human-caused climate change.
"This is some of the clearest evidence yet that the enormous carbon release into the atmosphere during the last deglaciation was triggered by abrupt changes in deep ocean circulation," said Marchitto. Marchitto and Lehman are both faculty members in the CU-Boulder geological sciences department.
While much of the CO2 released by the oceans after the end of the last ice age about 19,000 years ago was taken up by the re-growth of forests in areas previously covered by ice sheets, enough remained in the atmosphere to pump up CO2 concentrations significantly, the authors said. Today, CO2 levels are higher than at any time in at least the past 650,000 years because of increased fossil fuel burning.
"The timing of the major CO2 release after the last ice age corresponds closely with deep-sea circulation changes caused by ice melting in the North Atlantic at that time," said Lehman. "So our study really underscores ongoing concerns about the ocean's capacity to take up fossil fuel CO2 in the future, since continued warming will almost certainly impact the mode and speed of ocean circulation."
