|Title:||An ultra-high resolution continuous record of methane variations during the last glacial-interglacial transition from the WAIS Divide ice core|
|Author:||Rhodes, R.H., Brook, E., McConnell, J.R., Blunier, T., Lee, J.E., Edwards, J.S., Rosen, J.L. and Stowasser, C.|
|Periodical:||American Geophysical Union, Fall Meeting 2012, abstract #C54B-08|
Records of past atmospheric methane mixing ratios developed from ancient air trapped in polar ice cores are integral to our understanding of the global carbon cycle and its interaction with climate. Previously, temporal resolution of these records has been limited by time-, labour- and sample- intensive analytical methods. Here we present an ultra-high resolution, continuous record of the methane mixing ratio across the last deglaciation, obtained using a continuous system in which air extracted from the ice core was analysed on-line by a specially adapted laser spectrometer. 800 m of ice core from the West Antarctic Ice Sheet (WAIS) Divide project, spanning the time period from 10.1 to 22.8 ka, were analysed at a minimum spatial resolution of 4.5 cm depth, which equates to a temporal resolution of better than 2 yr. The variability of our record closely matches that of discrete measurements conducted on the WAIS Divide core. For example, the 130 ppbv increase in the methane mixing ratio over ~250 yr that marks the onset of the B??lling period is extremely well reproduced, as are all other variations in atmospheric methane known from previously published ice core data. Furthermore, we document in great detail variability not previously observed, for example, a methane concentration increase of 45 ppbv occurs within 90 yr at 16.55 ka. The Bolling-Allerod interstadial is characterized by 10-40 ppbv amplitude methane concentration oscillations with periods of 100-200 yr, whilst in the Early Holocene (10,100 to 11,400 yr) the methane signal is dominated by sub-centennial oscillations of 15-20 ppbv amplitude. Spectral analysis of this dataset is ongoing and will explore possible drivers of these high frequency features.