Dominant wind patterns shaping grain-size records at IODP Site U1430 in the East (Japan) Sea since the early Pleistocene: Northwesterly surface winds vs. upper westerlies

Abstract

Grain-size records of detrital components at IODP Site U1430 in the East (Japan) Sea, spanning the last 2.3 million years, are examined to understand how variations in the intensity of the East Asian Winter Monsoon influenced these records through two distinct dust-transporting wind patterns: low-level northwesterly winter monsoon winds and upper-level westerlies. By applying end-member (EM) modelling to grain-size distributions, we identified five EMs corresponding to fine-mode dust carried by upper-level westerlies (EM1), coarse-mode dust transported by northwesterly surface winds (EM2), and marine tephra of varying modes (EM3, EM4, and EM5). To isolate the dust components, we excluded marine tephra contributions and developed a dust-size distribution model based solely on EM1 and EM2. The mean size variations of this modeled dust at Site U1430 exhibited strong consistency in both cyclicity and amplitude, with similar stacked size records from the Chinese Loess Plateau (CLP). Given that the CLP size records near the source deserts were primarily influenced by northwesterly surface winds, the synchronization between these records and those from Site U1430 suggests that the records from Site U1430 were also predominantly governed by changes in the intensity of northwesterly surface winds rather than upper westerlies. The spatial variations in size records from the loess sections across the CLP, along with modern dust size observations, imply that the vertical and lateral sorting of dust during uplift and downwind transport likely contributed to the smaller dust sizes recorded at Site U1430.