Timescales and Phasing of Dansgaard-Oeschger Changes in the Summit Greenland ice Cores

EW Wolff (British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET England; +44 1223 362616; e-mail: wolff@bas.ac.uk);

KC Taylor (Desert Research Institute, University and Community College System of Nevada, Reno, NV 89506, USA; e-mail: kendrick@dri.edu);

R Alley (Earth System Science Center and Department of Geosciences, The Pennsylvania State University, University Park, PA 16802, USA; e-mail: ralley@essc.psu.edu)

K Fuhrer (II. Physikalisches Institut, University of Giessen, Heinrich-Buff-Ring 14, 35392 Giessen, Germany; e-mail: fuhrer@exp2.physik.uni-giessen.de)

The GRIP and GISP2 ice cores from Summit, Greenland, both contain a sequence of more than 20 rapid climate oscillations, known as Dansgaard-Oeschger events. At each transition into and out of these events, most ice core parameters change dramatically, some in periods of years to decades. By studying the order of events at transitions, we can narrow down the hypotheses for the causes of such changes. We have selected a small number of transitions, and have used the electrical conductivity method (ECM) records to tie the GISP2 and GRIP records together, and to assess how large a role could be played by noise or spatial variability. We have then studied the speed of response, and the relative phasing, of the signals of oxygen isotopes, ECM, calcium and accumulation rate at each chosen transition. We are able to decide whether there is a rule for the phasing of events at warmings and at coolings. Finally, we discuss how our findings narrow down the possible causes of these rapid climate changes.