The glacial inception as recorded in the NorthGRIP Greenland ice core: timing, structure and associated abrupt temperature changes

Climate Dynamics, Vol. 26, 273-284, doi:10.1007/s00382-005-0063-y, 2006

A. Landais, V. Masson-Delmotte, J. Jouzel and B. Minster
IPSL/Laboratoire des Sciences du Climat et de l'Environnement, UMR CEA-CNRS, CEA Saclay, 91191 Gif-sur-Yvette, France
D. Raynaud
LGGE, UMR CNRS-UJF, 2-53 Rue Molière, 38 402 St Martin d'Heres, France
S. Johnsen
Ice and Climate, The Niels Bohr Institute, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark
C. Huber, M. Leuenberger and J. Schwander
Physics Institute, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland

ABSTRACT.
The mechanisms involved in the glacial inception are still poorly constrained due to a lack of high resolution and cross-dated climate records at various locations. Using air isotopic measurements in the recently drilled NorthGRIP ice core, we show that no evidence exists for stratigraphic disturbance of the climate record of the last glacial inception (~123-100 kyears BP) encompassing Dansgaard-Oeschger events (DO) 25, 24 and 23, even if we lack sufficient resolution to completely rule out disturbance over DO 25. We quantify the rapid surface temperature variability over DO 23 and 24 with associated warmings of 10±2.5 and 16±2.5^oC, amplitudes which mimic those observed in full glacial conditions. We use records of δ¹⁸O of O₂ to propose a common timescale for the NorthGRIP and the Antarctic Vostok ice cores, with a maximum uncertainty of 2,500 years, and to examine the interhemispheric sequence of events over this period. After a synchronous North-South temperature decrease, the onset of rapid events is triggered in the North through DO 25. As for later events, DO 24 and 23 have a clear Antarctic counterpart which does not seem to be the case for the very first abrupt warming (DO 25). This information, when added to intermediate levels of CO₂ and to the absence of clear ice rafting associated with DO 25, highlights the uniqueness of this first event, while DO 24 and 23 appear similar to typical full glacial DO events.