Ice-core record of methyl chloride over the last glacial-Holocene climate change

Abstract

Methyl chloride (CH3Cl) concentration was measured in air trapped in a deep ice core from Dome Fuji, Antarctica covering the last glacial-present interglacial (Holocene) change. The record shows that the CH3Cl concentration was relatively constant, being similar to the present levels, during the pre-industrial Holocene. In contrast, the CH3Cl concentration was significantly high and variable in the last glacial period, possibly due to impurity-related production of CH3Cl in ice sheet. Under the assumption that the production was the sole cause of the excess CH3Cl, the atmospheric CH3Cl concentration during the last glacial was estimated using simultaneously measured calcium data for the ice core to have been enhanced by 30% compared with the pre-industrial Holocene concentration. Because the major sink of CH3Cl was stronger during the last glacial than during the Holocene, the enhancement of CH3Cl during the last glacial was likely due to the glacial period source being enhanced. Copyright 2007 by the American Geophysical Union.