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 years from the Greenland Ice Core Project (GRIP) ice core shows a huge dynamic range (factor >100). The relationship between dust concentrations and temperature (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 concentrations during the Dansgaard-Oeschger interstadial periods and high levels 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 relationship between Ca concentration and temperature. Previous authors [Biscaye et al., 1997] have suggested that the most likely source for the increased dust is eastern Asia. For the first time, we consider each possible cause of both rapid and slow increases from source to deposition. We suggest that, to account for the size and rapidity of the fast changes, significantly higher wind speed in the source area is required, although changes in atmospheric residence time could also play a role. For the slower long-term variability, changes in transport speed or, possibly, route are probably also involved. Changes in the size of the source area could give some change on longer time periods. The probable importance of changes in source area wind speed, almost simultaneous with Greenland temperature changes, confirms that climatic parameters in high and low latitudes were strongly coupled through the atmosphere during glacial climatic changes. This adds to evidence that the atmospheric circulation system underwent almost instantaneous large-scale changes during the last glacial period.