ELECTRICAL-CONDUCTIVITY MEASUREMENTS FROM THE GISP2 AND GRIP GREENLAND ICE CORES

THE direct-current electrical conductivity of glacial ice depends on i ts acidity1-3, and can also indicate changes in climate, as ice formed in cold, dusty periods has a high concentration of alkaline dust1,4,5 , which significantly reduces the conductivity6,7 compared to warmer, less dusty periods. Here we present electrical conductivity records fo r the Greenland Ice Sheet Project 2 (GISP2) and Greenland Ice-core Pro ject (GRIP) ice cores, drilled 28 km apart to enable direct comparison of the results. The upper parts of both records are consistent with p revious evidence from other Greenland cores4,8-12 for a stable Greenla nd climate during the Holocene, and a series of warm events punctuatin g the last glacial period. However, there is a significant discrepancy between the two records in the bottom 10% of the cores, calling into question recent reports of climate variability in the last interglacia l4,8 and the penultimate glaciation8. At this stage, it is too early t o say what exactly is causing the discrepancy, although ice flow may h ave introduced some discontinuities into the records. Further work wil l be necessary to establish how much climatic information it will even tually be possible to extract from the lower parts of the two cores.