Gas records from the West Greenland ice margin covering the Last Glacial Termination: a horizontal ice core

Certain sites along ice sheet margins provide an easily accessible and almost unlimited supply of ancient ice at the surface. Measurements of gases in trapped air from ice outcropping at Pakitsoq, West Greenland, demonstrate that ancient air is mostly well preserved. No alterations in δ18Oatm and δ15N of N2 are apparent, and alterations in methane are found in only a few ice sections. Using measurements of these gases, we have unambiguously identified a stratigraphic section containing ice from the end of last glacial period as well as Bølling–Allerød, Younger Dryas and Preboreal intervals. Extensive sections of ice from the Holocene and most ages within the last glacial period are probably also present. Very accurate dating has been possible in the ice section containing the Younger Dryas–Preboreal abrupt climate transition signal. The ice at Pakitsoq is folded and non-uniformly thinned, with many cross-cutting bands of bubble-free ice and dust. The cross-cutting features are associated with anomalies in both the gas and the ice records. With careful sampling to avoid these, the ice at Pakitsoq is suitable for recovery of large-volume samples of the ancient atmosphere for analysis of trace constituents such as 14CH4.