Late quaternary atmospheric CH₄ isotope record suggests marine clathrates are stable

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 (δD_CH4) to increase. Analyses of air trapped in the ice from the second Greenland ice sheet project show stable and/or decreasing δD_CH4 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 δD_CH4 values may be the result of a lower ratio of net to gross wetland CH₄ emissions and an increase in petroleum-based emissions.