1996 Volume 35 Issue 2 Pages 87-98
The presence of silt-sized quartz in andesitic or basaltic wethered volcanic ash soils has indicated the additions of non-volcanogenic material through soil accumulation. The oxygen isotope composition of the quartz revealed that it originated from tropospheric dust transported from inland China by the northwest winter monsoon. Thus, the fluctuation of the quartz accumulation rate indicates the fluctuation of northwest winter monsoon intensity. Series of the quartz accumulation rate since the Last Interglacial age, obtained at the Saotome section in the north-Kanto Plain, demonstrate the fluctuation simultaneous with the standard marine oxygen isotope variation. The quartz accumulation rate increases in oxygen isotope stages 2, 4 and 5b, indicating cold climate episodes, and decreases in stages 1, 3 and 5a, indicating warm climate episodes. This fluctuation suggests a strengthening of the northwest winter monsoon during cold stages and weakening during warm stages, a finding that agrees well with variations of quartz accumulation rate in the Tokachi Plain and with variations of the grain size distribution and the accumulation rate of loess-paleosol sequence in the Chinese Loess Plateau.