Conversion of GISP2-based sediment core age models to the GICC05 extended chronology


Marine and lacustrine sediment-based paleoclimate records are often not comparable within the early to middle portion of the last glacial cycle. This is due in part to significant revisions over the past 15 years to the Greenland ice core chronologies commonly used to assign ages outside of the range of radiocarbon dating. Therefore, creation of a compatible chronology is required prior to analysis of the spatial and temporal nature of climate variability at multiple locations. Here we present an automated mathematical function that updates GISP2-based chronologies to the newer, NGRIP GICC05 age scale between 8.24 and 103.74 ka b2k. The script uses, to the extent currently available, climate-independent volcanic synchronization of these two ice cores, supplemented by oxygen isotope alignment. The modular design of the script allows substitution for a more comprehensive volcanic matching, once it becomes available. Usage of this function highlights on the GICC05 chronology, for the first time for the entire last glaciation, the proposed global climate relationships during the series of large and rapid millennial stadial-interstadial events.

Obrochta, S.P., Yokoyama, Y., Morén, J., and Crowley, T.J., 2014, Conversion of GISP2-based sediment core age models to the GICC05 extended chronology, Quaternary Geochronology, 10.1016/j.quageo.2013.09.001.


  • Use to update a GISP2 based chronology to NGRIP.
  • The input series: 2-column in k.y. BP (before 1950), and the conversion range is 0.04027 to 100.643 ka BP. Outside of this range,the input series age is converted to b2k (before 2000) by adding 50 years.
  • If the data entered do not overlap with the coversion range, no results will be returned.
  • The oldest radiocarbon date is optional input. Conversion begins from radiocarbon date if specified. Output is 'GICC05modelext' (GICC05 with ss09sea) in ka b2k

This code is licenced under the GPLv.3 or later.

Data Input

Optional age of oldest radiocarbon date (point at which conversion starts)
Plot (not implemented at this point)



The manuscript is available here.

Conversion Script

To excecute g2n on your own computer, first download the appropriate script for your computing environment:

Most recent datafile

Next, download the datafile. This includes the match points between GISP2 and NGRIP, without which the conversion script will not run. The Matlab/Octave and Python versions use the same file

Supplemental files

The datafile is provided in different formats, but the script will not execute with these files.

Change Log

Version 1.1 (2013-12-18)

Added DOI for isotope ties

Version 2.0 (2014-12-11)

Implemented volcanic ties from Seierstad et al., 2014 10.1016/j.quascirev.2014.10.032