Controls on the tropospheric oxidizing capacity during an idealized Dansgaard-Oeschger event, and their implications for the rapid rises in atmospheric methane during the last glacial period

first_imgThe ice core record reveals large variations in theconcentration of atmospheric methane, [CH4], over the last800 kyr. Amongst the most striking natural features are thelarge, rapid rises in [CH4], of 100–200 ppbv, on timescalesof less than 100 years, at the beginning of Dansgaard-Oeschger (D-O) events during the last glacial period (21–110 kyr before present). Despite the potential insight theycould offer into the likelihood of future rapid rises in[CH4], the relative roles of changes in methane sources andsinks during D-O events have been little explored. Here, weuse a global atmospheric chemistry-transport model toexplore—for the first time, in a process-based fashion—controls on the oxidizing capacity during an idealized D-Oevent that features a characteristically rapid rise in [CH4]. We find that the two controls previously identified in the literature as having had significant (though opposing) influences on the oxidizing capacity between glacial and interglacial periods—changes in air temperature and emissions of nonmethane volatile organic compounds from vegetation—offset one another between idealized Heinrich stadial and Greenland interstadial states. The result is, the net change in oxidizing capacity is very small, implying the rapid rises in [CH4] at the beginning of D-O events were almost entirely source-driven. This poses a challenge to earthsystemmodels—to generate a sufficiently large increase inmethane emissions in response to a simulated D-O event,via a more realistic freshwater forcing impacting the strengthof the Atlantic meridional overturning circulation or, possibly,other climate-change mechanisms. Citation: Levine,J. G., E. W. Wolff, P. O. Hopcroft, and P. J. Valdes (2012),Controls on the tropospheric oxidizing capacity during an idealizedDansgaard-Oeschger event, and their implications for therapid rises in atmospheric methane during the last glacial period,last_img read more