Soluble and insoluble lithium dust in the EPICA DomeC ice core - Implications for changes of the East Antarctic dust provenance during the recent glacial-interglacial transition

摘要

Continental dust impurities in Antarctic ice provide information on climate changes in the dust source areas and on past atmospheric circulation. We investigated records of dust species from the last 45 ka in the East Antarctic EPICA DomeC (EDC) ice core with special emphasis on the lithium (Li) content of dust. We obtained two complementary Li-records using a new Ion Chromatography (IC) technique in line with Inductively Coupled Plasma-Sector Field Mass Spectroscopy (ICP-SFMS). Concentrations of soluble Li (Li+) were obtained using IC, while total concentrations of Li (Li-T) were obtained using ICP-SFMS, providing an ideal opportunity to investigate the soluble and insoluble chemistry of Li in East Antarctic dust over the last glacial-interglacial transition. The records show that changes in the solubility of Li are associated with climatic changes. For the late glacial period and the Antarctic Cold Reversal (ACR) a large fraction, up to 75%, of the Li-T content is present as insoluble minerals whereas for the Holocene period it seems that Li is present mainly as soluble salts (Li+). We compared the concentrations of Li+ with the concentrations of Ca2+ and the mass and size characteristics of the dust, which were obtained using Coulter Counting (CC). Furthermore we compared the concentrations of Li-T with the concentrations of Ba-T- Our analysis suggests that the changes in solubility of Li along the EDC ice core are related to changes in compositions of the dust minerals. During the late glacial period, changes in the dust composition is characteristic of variations in the strength of the atmospheric circulation, while changes over the last glacial-interglacial transition are indicative of a change in the major dust source areas. The dust characteristics for the glacial and the Holocene periods indicate two different dust types. The glacial dust type partly disappeared after the ACR, while the Holocene dust type appeared significantly after around 16 ka BP and became dominant after the ACR. The relative increase in the Holocene dust type at the glacial-interglacial transition could be due to changed conditions in the potential source area or to changed patterns of atmospheric circulation, resulting in enhanced transport from a source area that was different from the glacial source areas. (C) 2007 Elsevier B.V. All rights reserved.