|Title:||Variations in the methane interpolar gradient during the last glacial termination|
|Author:||Rosen, J., Brook, E., Lee, J.E., Edwards, J.S., Rhodes, R.H. and Blunier, T.|
|Periodical:||American Geophysical Union, Fall Meeting 2012, abstract #C51D-0796|
The interpolar gradient (IPG) in methane is a useful indicator of the latitudinal distribution of its sources. Thus, variations in the IPG yield insights into the changing biogeochemistry of this important greenhouse gas, and can be used to constrain aspects of the global climate that affect methane production, such as the mean position of the ITCZ and the intensity of the Asian monsoon. We present a new highly resolved estimate of the CH4 IPG over the last glacial termination based on measurements from the North Greenland Eemian (NEEM) ice core and the West Antarctic Ice Sheet (WAIS) Divide ice core. Our IPG reconstruction reveals several striking features. First, the IPG remains nearly constant across the abrupt transitions of the deglaciation, including the Oldest Dryas-Bolling/Allerod transition as well as the inception and termination of the Younger Dryas, despite significant changes in the atmospheric mixing ratio of methane. In addition, we observe surprisingly low values in the IPG during Heinrich Stadial 1 (HS1), between ~18 to 16 ka during a period of gradually increasing methane concentration. At this time, concentrations in Greenland and Antarctica were approximately equal. This stands in contrast with modern and reconstructed values of the IPG over the last 40 ka which show a persistent, albeit variable, Northern Hemisphere enrichment. Our record attests to the unique hydrologic conditions of HS1 that have been identified in numerous other paleoclimate records, including Asian speleothems and the δ18O of air.