One explanation for the abrupt increases in atmospheric CH4, that occurred repeatedly during the last glacial cycle involves clathrate destabalization events. Because marine clathrates have a distinct deuterium/hydrogen (D/H) isotope ratio, any such destabilization event should cause the D/H ratio of atmospheric CH4 (δDCH4) to increase. Analyses of air trapped in the ice from the second Greenland ice sheet project show stable and/or decreasing δDCH4 values during the end of the Younger and Older Dryas periods and one stadial period, suggesting that marine clathrates were stable during these abrupt warming episodes. Elevated glacial δDCH4 values may be the result of a lower ratio of net to gross wetland CH4 emissions and an increase in petroleum-based emissions.
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