Methyl chloride variability in the Taylor Dome ice core during the Holocene

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 CH4 variability.