1. ^*The Niels Bohr Institute, Department of Geophysics, University of Copenhagen, Haraldsgade 6, DK-2200 Copenhagen N, Denmark
2. ^† Science Institute, Department of Geophysics, University of Iceland, Dunhaga 3, IS-107, Reykjavik, Iceland
3. ^‡,  Laboratoire de Modélisation du Climat et de I'Environment, CEA/DSM, CE Saclay 91191, and Laboratoire de Glaciologie et Géophysique de I'Environment, BP 96, 38402 St Martin d'Héres Cedex, France ^§ Lamont-Doherty Geological Observatory, Columbia University, Palisades, New York 10964, USA

Abstract

RECENT results^1,2 from two ice cores drilled in central Greenland have revealed large, abrupt climate changes of at least regional extent during the late stages of the last glaciation, suggesting that climate in the North Atlantic region is able to reorganize itself rapidly, perhaps even within a few decades. Here we present a detailed stable-isotope record for the full length of the Greenland Ice-core Project Summit ice core, extending over the past 250 kyr according to a calculated timescale. We find that climate instability was not confined to the last glaciation, but appears also to have been marked during the last interglacial (as explored more fully in a companion paper³) and during the previous Saale–Holstein glacial cycle. This is in contrast with the extreme stability of the Holocene, suggesting that recent climate stability may be the exception rather than the rule. The last interglacial seems to have lasted longer than is implied by the deep-sea SPECMAP record⁴, in agreement with other land-based observations^5,6. We suggest that climate instability in the early part of the last interglacial may have delayed the melting of the Saalean ice sheets in America and Eurasia, perhaps accounting for this discrepancy.