Department of Earth System Science

Methyl chloride (CH₃Cl) is a naturally occurring, ozone-depleting trace gas and one of the most abundant chlorinated compounds in the atmosphere. CH₃Cl was measured in air from the Taylor Dome ice core in East Antarctica to reconstruct an atmospheric record for the Holocene (11–0 kyr B.P.) and part of the last glacial period (50–30 kyr B.P.). CH₃Cl variability throughout the Holocene is strikingly similar to that of atmospheric methane (CH₄), with higher levels in the early and late Holocene, and a well-defined minimum during mid-Holocene. The sources and sinks of atmospheric CH₃Cl and CH₄ are located primarily in the tropics, and variations in their atmospheric levels likely reflect changes in tropical conditions. CH₃Cl also appears to correlate with atmospheric CH₄ during the last glacial period (50–30 kyr B.P.), although the temporal resolution of sampling is limited. The Taylor Dome data provide information about the range of natural variability of atmospheric CH₃Cl and place a new constraint on the causes of past CH₄variability.