Irregular glacial interstadials recorded in a new Greenland ice coreNature, 359, p. 311-313, 1992.
S.J. Johnsen, H.B. Clausen, W. Dansgaard, N. Gundestrup, C.U. Hammer, P. Iversen and J.P. Steffensen
Geofysisk Afdeling, Niels Bohr Instituttet for Astronomi, Fysik og Geofysik, Københavns Universitet
The Greenland ice sheet offers the most favourable conditions In the Northern Hemisphere for obtaining high-resolution continuous time series of climate-related parameters. Profiles of 18O/16O ratio along three previous deep Greenland ice cores1-3 seemed to reveal irregular but well-defined episodes of relatively mild climate conditions (interstadials) during the mid and late parts of the last glaciation, but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate, rather than artefacts due to disturbed stratification. Here we present results from a new deep ice core drilled at the summit of the Greenland ice sheet, where the depositional environment and the flow pattern of the ice are close to ideal for core recovery and analysis. The results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt. According to a preliminary timescale based on stratigraphic studies, the interstadials lasted from 500 to 2,000 years, and their irregular occurrence suggests complexity in the behaviour of the North Atlantic ocean circulation.