EVIDENCE FOR GENERAL INSTABILITY OF PAST CLIMATE FROM A 250-KYR ICE-CORE RECORD

RECENT results1,2 from two ice cores drilled in central Greenland have revealed large, abrupt climate changes of at least regional extent du ring the late stages of the last glaciation, suggesting that climate i n the North Atlantic region is able to reorganize itself rapidly, perh aps even within a few decades. Here we present a detailed stable-isoto pe record for the full length of the Greenland Ice-core Project Summit ice core, extending over the past 250 kyr according to a calculated t imescale. We find that climate instability was not confined to the las t glaciation, but appears also to have been marked during the last int erglacial (as explored more fully in a companion paper3) and during th e previous Saale-Holstein glacial cycle. This is in contrast with the extreme stability of the Holocene, suggesting that recent climate stab ility may be the exception rather than the rule. The last interglacial seems to have lasted longer than is implied by the deep-sea SPECMAP r ecord4, in agreement with other land-based observations5,6. We suggest that climate instability in the early part of the last interglacial m ay have delayed the melting of the Saalean ice sheets in America and E urasia, perhaps accounting for this discrepancy.