δ18O of atmospheric oxygen measured on the GRIP Ice Core Document Stratigraphic disturbances in the lowest 10% of the core

δ18O measured on oxygen in the bubble air from ice cores is a proxy for continental ice volume and is used to synchronize cores from Greenland and Antarctica. A record measured on ice samples from the Central Greenland deep ice core GRIP, spanning the Last Glacial Maximum and the Holocene, shows that δ18O of atmospheric oxygen lags δ18O of ice by about 4000 to 1000 years. The smooth isotope record of atmospheric oxygen shows a steady ice sheet decay beginning around 18′000 years BP taking the time lag into account. However, measurements performed on ice from the GRIP core older than 100 kyrs do not correlate with the corresponding Vostok record and show transitions too fast to be typical for ice sheet build-up or decay. Furthermore, the expected time lag between δ18Oatm and δ18O of seawater or δ18O of ice is absent or has even turned into a lead. Climatic interpretation of the fast δ18Oice transitions is not consistent with our δ18Oatm results. The stratigraphy is possibly irregular and if so, this stops us from constructing a steady age-depth relation in the deepest part of the GRIP ice core