SYNCHRONOUS CHANGES IN ATMOSPHERIC CH4 AND GREENLAND CLIMATE BETWEEN 40-KYR AND 8-KYR BP

ICE-CORE reconstructions of atmospheric methane concentrations for the past 220 kyr have revealed large variations associated with different climatic periods1-4. But the phase relationship between climate and methane has been uncertain because of dating uncertainties and the coarse sampling interval of available methane records. Here we present a high-resolution record of atmospheric methane from 40 to 8 kyr ago from the GRIP ice core in Greenland. Our improved resolution and dating allow us to conclude that the large changes in atmospheric methane concentration during the last deglaciation were in phase (+/-200 years) with the variations in Greenland climate. Our results confirm the previous observation3 that methane increased to Holocene levels when much of the Northern wetlands was still ice-covered, lending support to the suggestion3 that low-latitude wetlands were responsible for the observed changes. We observe oscillations in methane concentration associated with the warm periods (interstadials) that occurred throughout the glacial period5, suggesting that the interstadials were at least hemispheric in their extent. We propose that variations in the hydrological cycle at low latitudes may be responsible for the variations in both methane and Greenland temperature during the interstadials.