BERYLLIUM-10 IN THE GREENLAND ICE CORE PROJECT ICE CORE AT SUMMIT, GREENLAND

Concentrations of the cosmogenic isotope Be-10 have been measured in m ore than 1350 samples from the Greenland Ice Core Project (GRIP) ice c ore drilled at Summit, Greenland. Although a dust-associated component of Be-10 retained by 0.45 mu m filters in some of the samples complic ates the interpretations, the results confirm that the first-order ori gin of Be-10 concentration variations is changes in precipitation rate associated with different climate regimes. This effect is seen not on ly between glacial and interglacial periods, but also during the short er ''Dansgaard-Oeschger'' interstadials. By contrast, the Be-10 data d o not support the interpretation of rapidly varying accumulation (i.e. , climate) during the last interglacial. They can, however, be used to help place limits on the origin of the ice in these events. After tak ing into account variable snow accumulation effects, variations in the Be-10 flux are observed, probably caused by solar and geomagnetic mod ulation, but possibly also by primary cosmic ray variations. The most dramatic is a Be-10 peak similar to 40,000 years ago, similar to that found in the Vostok ice core, thus permitting a very precise correlati on between climate records from Arctic and Antarctic ice cores. The Cl -36/Be-10 ratio (considering either ''total'' or only ice-associated B e-10) shows significant variability over the whole core depth, thus co nfirming the difficulty in using this parameter for ''dating'' ice cor es.