ASIAN PROVENANCE OF GLACIAL DUST (STAGE-2) IN THE GREENLAND ICE-SHEETPROJECT-2 ICE CORE, SUMMIT, GREENLAND

Samples of bust from the Greenland Ice Sheet Project 2 (GISP2) ice cor e, Summit, Greenland, dated within marine isotope stage 2 (between 23, 340 and 26,180 calendar years B.P.), around the time of the coldest, l ocal, last glacial temperatures, have been analyzed to determine their provenance. To accomplish this, we have compared them with approximat ely coeval aeolian sediments (mostly loesses) sampled in possible sour ce areas (PSAs) from around the northern hemisphere. The <5-mu m grain -size fraction of these samples was analyzed on the basis that it corr esponds to the atmospheric dust component of that time and locale, whi ch was sufficiently fine grained to be transported over long distances . On the basis of comparison of the clay mineralogy and Sr, Nd and Pb isotope composition with ice dust and PSAs and assuming that we have s ampled the most important PSAs, we have determined that the probable s ource area of these GISP2 dusts was in eastern Asia. The dust was not derived from either the midcontinental United States or the Sahara; tw o more proximal areas that have been suggested as potential sources ba sed on atmospheric circulation modeling. Except for a brief period dur ing an interstadial, when dust transport was exceptionally low (for gl acial times) and had a mineralogical composition indicative of a sligh tly more southern provenance, the source area of the dust did not chan ge significantly during times of variably higher fluxes of dust with l arger mean grain size or lower fluxes of dust with smaller mean grain size. This includes the high-dust period that correlates with the Hein rich 2 period of major iceberg discharge into the North Atlantic. Vari able wind strengths must therefore be invoked to account for these abr upt and significant changes in dust flux and grain size.