Timescales for dust variability in the Greenland Ice Core Project (GRIP) ice core in the last 100,000 years

The calcium (representing dust) concentration record of the last 100,000 ye ars from the Greenland Ice Core Project (GRIP) ice core shows a huge dynami c range (factor >100). The relationship between dust concentrations and tem perature (represented by the oxygen isotope ratio) is not a simple one, as has often been assumed. A rapid alternation (factor of 5-10) between low co ncentrations during the Dansgaard-Oeschger interstadial periods and high le vels in colder periods is superimposed on a long-term trend encompassing a further factor of 5-10. Within climate periods, there is only a very weak r elationship between Ca concentration and temperature. Previous authors [Bis caye et al., 1997] have suggested that the most likely source for the incre ased dust is eastern Asia. For the first time, we consider each possible ca use of both rapid and slow increases from source to deposition. We suggest that, to account for the size and rapidity of the fast changes, significant ly higher wind speed in the source area is required, although changes in at mospheric residence time could also play a role. For the slower long-term v ariability, changes in transport speed or, possibly, route are probably als o involved. Changes in the size of the source area could give some change o n longer time periods. The probable importance of changes in source area wi nd speed, almost simultaneous with Greenland temperature changes, confirms that climatic parameters in high and low latitudes were strongly coupled th rough the atmosphere during glacial climatic changes. This adds to evidence that the atmospheric circulation system underwent almost instantaneous lar ge-scale changes during the last glacial period.