The role of atomic chlorine in glacial-interglacial changes in the carbon-13 content of atmospheric methane

Abstract

The ice-core record of the carbon-13 content of atmospheric methane (δ 13 CH 4) has largely been used to constrain past changes in methane sources. The aim of this paper is to explore, for the first time, the contribution that changes in the strength of a minor methane sinkoxidation by atomic chlorine in the marine boundary layer (Cl MBL)could make to changes in δ 13 CH 4 on glacial-interglacial timescales. Combining wind and temperature data from a variety of general circulation models with a simple formulation for the concentration of Cl MBL, we find that changes in the strength of this sink, driven solely by changes in the atmospheric circulation, could have been responsible for changes in δ 13 CH 4 of the order of 10% of the glacial-interglacial difference observed. We thus highlight the need to quantify past changes in the strength of this sink, including those relating to changes in the sea-ice source of sea salt aerosol. Copyright © 2011 by the American Geophysical Union.