DOI: 10.25921/pnba-f878
title: NOAA/WDS Paleoclimatology - North GRIP - Greenland Ice Core Chronology 2005 (GICC05) Holocene section, 20-year resolution

description: 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, Greenland Ice Core Project (GRIP), and North Greenland Ice Core Project (NGRIP) ice cores is made by using volcanic reference horizons in electrical conductivity measurements to match the cores. The main annual layer counting is carried out on the most suited records only, exploiting that the three ice cores have been drilled at locations with different climatic conditions 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 validity of the match. After the verification, the main dating is transferred to all records using 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 synchronized dating relies heavily on this record of ~75,000 stable isotope samples. The dating 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 years before A. D. 2000 (b2k), 130 years earlier than the previous GRIP dating.
description: Greenland Ice Core Chronology 2005 (GICC05) Holocene section. Please cite the relevant papers depending on the time interval used. The dating of the 0-7.9 ka b2k part is described in Vinther et al. (2006) doi: 10.1029/2005JD006921. The dating of the 7.9-14.7 ka b2k part is described in Rasmussen et al. (2006) doi: 10.1029/2005JD006079.

Entire Holocene in 20-year resolution and d18O from NGRIP1, NGRIP2, GRIP, and DYE-3. All ages are given in years b2k (years relative to A.D. 2000). The concept of maximum counting error is introduced in Rasmussen et al. (Journ. Geophys. Res, 2006). Age and depth values refer to the bottom of each interval. Thus the NGRIP1 depth interval 14.15-20.4 m corresponds to the time interval 40 - 60 b2k, in which the NGRIP1 d18O value is -35.11 permille. 

The NGRIP1 core reaches down to a depth of 1372 m. The NGRIP2 core (drilled 20 meters away from the NGRIP1 core) reaches from surface to bedrock, but high-resolution measurements have only been carried out downwards from 1346 m. In the 26 m overlap zone, the cores are offset by 0.43 m on average, probably due to uncertainties in the logging procedure (see Schøtt Hvidberg et al., Ann. Glac. 35, 2002). Thus, the same features appear at larger depths in the NGRIP1 than in the NGRIP2 core. When combining NGRIP1 and NGRIP2 data, we recommend to switch from NGRIP1 to NGRIP2 in the year 9830b2k.

Down to 8313 b2k, DYE-3 is dated year by year. Below 8313 b2k the GRIP-NGRIP based time scale has been transferred to DYE-3 depths using the ECM profiles. This matching introduces a few years of uncertainty which is not included in the maximum counting error (column no. 10).

(*) Note that millennial-scale variations in the DYE-3 d18O data are significantly influenced by upstream effects. Furthermore, due to a problem with standards in the early 1980s, the DYE-3 d18O measurements are slightly off-set (maximum 0.5 permil) towards more negative values during the early Holocene.

For more data downloads, go to www.icecores.dk

LAST UPDATE: Time scale released March 10, 2006. This file released November 27, 2006, received by WDC Paleo 12/2006. Original file name: GICC05_Holocene_20y_27nov2006.