Gases in ice cores.

Air trapped in glacial ice offers a means of reconstructing variations in the concentrations of atmospheric gases over time scales ranging from anthropogenic (last 200 yr) to glacial/interglacial (hundreds of thousands of years). In this paper, we review the glaciological processes by which air is trapped in the ice and discuss processes that fractionate gases in ice cores relative to the contemporaneous atmosphere. We then summarize concentration-time records for CO2 and CH4 over the last 200 yr. Finally, we summarize concentration-time records for CO2 and CH4 during the last two glacial-interglacial cycles, and their relation to records of global climate change.