Glacial/interglacial changes in mineral dust and sea-salt records in polar ice cores: sources, transport, and deposition
Sea salt and mineral dust records as represented by Na+ and Ca2+ concentrations, respectively, in Greenland and Antarctic ice cores show pronounced glacial/interglacial variations. For the Last Glacial Maximum (LGM) mineral dust (sea salt) concentrations in Greenland show an increase of a factor of approximately 80 (15) compared to the Holocene and significant shifts by a factor of 15 (5) during Dansgaard Oeschger events. In Antarctica, the dust (sea salt) flux is enhanced by a factor of 15 (3) during the LGM compared to the Holocene and variations by approximately a factor of 8 (1-2) exist in parallel to Antarctic warm events. Primary glacial dust sources are the Asian deserts for Greenland and Patagonia for Antarctica. Ice core evidence and model results show that both changes in source strength as well as atmospheric transport and lifetime contributed to the observed changes in Greenland ice cores. In Antarctica changes in ice core fluxes are in large parts related to source variations both for sea salt and dust, where the formation of sea salt aerosol from sea ice may play a pivotal role. Summarizing our latest estimates on changes in sources, transport and deposition these processes are roughly able to explain the glacial increase in sea salt in both polar regions while they fall short by at least a factor of 4-7 for mineral dust. Future improvements in model resolution and in the formulation of source and transport processes together with new ice core records, e.g. on dust size distributions, will eventually allow to converge models and observations.