Intra-interglacial cold events: an Eemian-Holocene comparison

Abstract

This paper is included in the Special Publication entitled 'Geological evolution of ocean basins: results from the Ocean Drilling Program', edited by A. Cramp, C.J. MacLeod, S.V. Lee and E.J.W. Jones. Rapid oscillations between warm and cold climates have been found in the oxygen isotope record of the Greenland Ice-core Project (GRIP) ice core during the Eemian/Marine oxygen Isotope Stage (MIS) 5e. In contrast, the variability in Greenland Ice Sheet Project 2 (GISP2) ice core is significantly different and some Atlantic deep-sea records suggest no such climate variations. We present here a high-resolution (50-300 years) set of marine proxies from the low-latitude east Atlantic margin (ODP Site 658), which suggest that in general the Eemian was climatically very similar to the Holocene. We, however, observe that the upwelling intensity off the West African coast was greatly reduced during the early Eemian, corresponding to the very mild climate observed in the European lake records. We observe that MIS 5e contains one significant short cold spell (<400 years), which is marked by a reduction of upper North Atlantic deep water ventilation. We suggest this cold event may correlate with the cold interval found in the European terrestrial records. The cause of the intra-Eemian event was likely to be the freshening and cooling observed in the Norwegian Sea. This brief cold spell, however, did not affect the overall stability of MIS 5e, and moreover it has an analogue event in the Holocene 'Sub-Boreal' period. Marine and terrestrial records thus seem to be incompatible with those of the GRIP ice core record, supporting the suggestion that the GRIP record has been altered by ice tectonics.