A synchronized dating of three Greenland ice cores throughout the Holocene

As part of the effort to create the new Greenland Ice Core Chronology 2005 (GICC05) a synchronized stratigraphical timescale for the Holocene parts of the DYE- 3, GRIP and NGRIP ice cores is made by using volcanic reference horizons in electri- cal conductivity measurements to match the cores. The main annual layer counting is carried out on the most suited records only, exploit- ing that the three ice cores have been drilled at locations with different climatic con- ditions and differences in ice flow. However, supplemental counting on data from all cores has been performed between each set of reference horizons in order to verify the valid- ity of the match. After the verification, the main dating is transferred to all records us- ing the volcanic reference horizons as tie points. An assessment of the mean annual layer thickness in each core section confirms that the new synchronized dating is consistent for all three cores. The data used for the main annual layer counting of the past 7900 years are the DYE- 3, GRIP and NGRIP stable isotope records. As the high accumulation rate at the DYE- 3 drill site makes the seasonal cycle in the DYE-3 stable isotopes very resistant to firn diffusion, an effort has been made to extend the DYE-3 Holocene record. The new syn- chronized dating relies heavily on this record of �75,000 stable isotope samples. The dat- ing of the early Holocene consists of an already established part of GICC05 for GRIP and NGRIP which has now been transferred to the DYE-3 core. GICC05 dates the Younger Dryas termination, as defined from deuterium excess, to 11,703 b2k; 130 years earlier than the previous GRIP dating.