sediments in France (Eicher et al., 1981) and Switzerland. (Oeschger ..... H. Clausen for providing us with their unpublished Byrd ... John Wiley & Sons, 287-318.
Gtadas-Oceatt-AtmomteK Interactions/Proceedings of the International Symposium held at St Petersburg, September 1990). IAHS Publ. no. 208,1991.
The last déglaciation in Antarctica; evidence of a "Younger Dryas" type climatic event J. JOUZEL (1, 2), J.R. PETIT (1, 2), J. CHAPELLAZ (1), J.M. BARNOLA (1) 1. Laboratoire de Glaciologie et Géophysique de l'Environnement, BP 96, St-Martin-d'Hères 38402, Cedex, France 2. Laboratoire de Géochimie Isotopique, CEA CEN, Saclay 91191, Cedex, France N.I. BARKOV, V.N. PETROV Arctic and Antarctic Research Institute, Beringa 38, St Petersburg 199226, USSR ABSTRACT The Younger Dryas was a cold event which occurred during the last climatic transition, following the warming trend of the Bôlling-Allerod and spanning approximately a millennium from 11 to 10.2 kyr B.P. Isotopic Dome C results have shown that the transition is a two-step process with two warming trend periods interrupted by a slightly colder period estimated to have taken place from about 13.2 to 11.7 kyr B.P. This cooling event is also well recorded in the Vostok record but again during a time interval preceding the Younger Dryas by about 1 kyr. Recent measurements of methane and dust concentration in the Vostok core are discussed as useful information for linking Northern and Southern Hemisphere observations. INTRODUCTION The Younger Dryas is a climatic stage which took place during the second half of the last déglaciation and was originally defined for a pollen zone in Europe (Jensen, 1938; Iversen, 1954) . It corresponds to a cold event spanning approximately a millennium from ~ 11 to 10 kyr B.P. which followed the warming trend of B0lling and Allerôd interstadials. Available data on the Younger Dryas were recently compiled by Rind e_t al. (1986) both for Europe where this event is best recognized, and for the whole world. They comprise terrestrial pollen records which indicate that trees, which have started growing in response to the climatic warming of the déglaciation, were suddenly replaced by shrubs and herbs, and characteristics of a glacial regime, and isotope records from the Camp Century and Dye 3 Greenland ice cores (Dansgaard e_t al. , 1973; Oescheger et al. . 1984) and isotope records from lake 269
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sediments in France (Eicher et al., 1981) and Switzerland (Oeschger et. al. . 1980) .
-38 -36 -34 -32 -30 -28(%o)
FIG. 1 Detailed 5180 profile along a 120 m increment of the Dye 3 deep core containing ice deposited during the entire Pleistocene to Holocene transition (middle curve) . CO 18
2
concentration in air bubbles and 5 0 for lime sediments in the Swiss lake Gerzen are shown on the right and left curves respectively (adapted from Dansgaard & Oeschger, 1989). This is illustrated in Fig. 1 which shows the remarkable correlation between lake Gerzensee (Switzerland) and Dye 3 (Greenland) climatic records, as deduced from 5 0 profiles, over this period. At Dye 3 the cooling corresponding to the Younger Dryas is estimated to be ~ 7 C and recent studies (Dansgaard et al.. 1989) have shown that this event ended very abruptly and possibly in less than 20 years with a transition characterized by a sudden shift in nearly all parameters studied in this core (deuterium-excess; chemical trace elements; acidity and continental dust). The deuterium and oxygen 18 concentrations are expressed in S units (
