Abstract220 – University of Copenhagen

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Centre for Ice and Climate > Publications > Scientific papers > Abstracts > Abstract220

A new Greenland ice core chronology for the last glacial termination

Journal of Geophysical Research, Vol. 111, D06102, doi:10.1029/2005JD006079, 2006
S.O. Rasmussen, K.K. Andersen, A.M. Svensson, J.P. Steffensen, B.M. Vinther, H.B. Clausen, S.J. Johnsen, L.B. Larsen and D. Dahl-Jensen
Ice and Climate, The Niels Bohr Institute, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark
M.-L. Siggaard-Andersen
Ice and Climate, The Niels Bohr Institute, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark also at
Alfred-Wegener-Institute for Polar and Marine Research, Bremerhaven, Germany.
M. Bigler
Ice and Climate, The Niels Bohr Institute, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark also at
Climate and Environmental Physics, Physics Institute, University of Bern, Switzerland.
R. Röthlisberger
Climate and Environmental Physics, Physics Institute, University of Bern, Switzerland, now at British Antarctic Survey, Cambridge, UK.
H. Fischer and U. Ruth
Alfred-Wegener-Institute for Polar and Marine Research, Bremerhaven, Germany.
K. Goto-Azuma
National Institute of Polar Reserach, Tokyo, Japan.
M.E. Hansson
Department of Physical Geography and Quaternary Geology, Stockholm University, Sweden.

ABSTRACT.
We present a new common stratigraphic time scale for the NGRIP and GRIP ice cores. The time scale covers the period 7.9-14.8 ka before present, and includes the Bølling, Allerød, Younger Dryas, and Early Holocene periods. We use a combination of new and previously published data, the most prominent being new high resolution Continuous Flow Analysis (CFA) impurity records from the NGRIP ice core. Several investigators have identified and counted annual layers using a multi-parameter approach, and the maximum counting error is estimated to be up to 2% in the Holocene part and about 3% for the older parts. These counting error estimates reflect the number of annual layers that were hard to interpret, but not a possible bias in the set of rules used for annual layer identification. As the GRIP and NGRIP ice cores are not optimal for annual layer counting in the middle and late Holocene, the time scale is tied to a prominent volcanic event inside the 8.2 ka cold event, recently dated in the DYE-3 ice core to 8236 years before A.D. 2000 (b2k) with a maximum counting error of 47 years. The new time scale dates the Younger Dryas - Preboreal transition to 11,703 b2k, which is 100-150 years older than according to the present GRIP and NGRIP time scales. The age of the transition matches the GISP2 time scale within a few years, but viewed over the entire 7.9-14.8 ka section, there are significant differences between the new time scale and the GISP2 time scale. The transition from the glacial into the Bølling interstadial is dated to 14,692 b2k. The presented time scale is a part of a new Greenland ice core chronology common to the DYE-3, GRIP and NGRIP ice cores, named the Greenland Ice Core Chronology 2005 (GICC05). The annual layer thicknesses are observed to be log-normally distributed with good approximation, and compared to the Early Holocene, the mean accumulation rates in the Younger Dryas and Bølling periods are found to be 47±2% and 88 ± 2%, respectively.