EAST ASIAN MONSOON/WESTERLY INTENSITY VARIATIONS DURING THE LAST 150KY BASED ON EOLIAN DUST GRAIN SIZE AND ITS N-S CONTRAST IN THE JAPAN SEA

The hemipelagic sediments of the Japan Sea contain significant amount of eolian dust derived from dry areas in inland Asia. The eolian dust grain size is controlled by the distance from the source area and the speed of transport wind, whereas the eolian flux is controlled by the distance and size of the source area as well as intensity of the transport wind. There are two possible paths for eolian dust transport to the Japan Sea. One is through winter monsoon surface winds, and the other is through the westerly jet. For both cases, the distance and size of the source area are influenced by the summer monsoon intensity. Whereas the wind speed is controlled either by the winter monsoon intensity or by the speed of westerly jet. In order to reconstruct the temporal variability of the atmospheric circulation in East Asia, we examined the grain size, content, and composition of eolian dust within the sediment cores from northeastern (KT94-15-PC5; 40‹09f36hNC138‹12f05hE) and southern (IMAGES MD01-2407; 37‹04f06hN, 134‹42f00hE) parts of the Japan Sea. The results revealed millennial-scale variability in eolian dust grain size and content in harmony with Dansgaard-Oeschger Cycles in both cores during the last 150 ky with larger eolian dust median diameters and contents during stadials. We also examined temporal variations of the N-S differences in the eolian dust grain size between the two sites. Eolian dust grain size in the southern site tends to be larger during MIS 1, early MIS 3, MIS 5.1, 5.3, and early MIS 5.5, and smaller during other periods showing oscillations of ca. 20 kyrs periodicity. In addition, N-S difference in eolian dust grain size shows millennial-scale variability with smaller grains size in the southern site during glacial stadials. Based on the comparison of the mineral and elemental compositions between eolian dust of each site and desert and loess of inland Asia, we attributed the cause of the temporal variations in N-S differences in Kosa grain size to the N-S shift either in the dust source area transported by the westerly jets or in the southern limit of dust transport by winter monsoon surface wind.