Physical, Chemical, and Mineralogical Characteristics of Modern Eolian Dust in Japan and Rate of Dust Deposition

Abstract

Physical, chemical, and mineralogical properties of aerosols and air fall sediments collected in Hachimantai, Osaka, Yashiro, Izumo, Oita, and Sasebo from 1981 to 1984 were studied and were compared with those of loess and loess soils in China and Korea. The texture of most aerosols and air fall sediments ranged from silty clay to clay loam. Their median particle diameters (Mds) ranged mostly between 0.003 and 0.026 mm. The aerosols and air fall sediments were characterized by a predominance of SiO₂ and Al₂O₂ and a high amount of K₂O. Their SiO₂/Al₂O₃ and K₂O/SiO₂ molar ratios ranged from 5.35 to 11.40 and from 0.017 to 0.031, respectively. Their dominant minerals were kaolinite, illite, vermiculite, mont-morillonite, quartz, and calcite. These physical, chemical, and mineralogical properties were consistent with those of loess and loess soils in China and Korea. The results suggest that aerosols and fine-grained fractions of air fall sediments collected in Japan are mainly composed of soil materials transported from the arid and semi-arid regions of China and Mongolia by prevailing winds. On the basis of their chemical and mineralogical properties, the aerosols and air fall sediments were divided into the Manchouli (poor in calcite) and the Xi’an (rich in calcite) loess types. The deposition-rate of dust onto the Japanese land surface and its properties were strongly influenced by the meteorological conditions in China and Mongolia, latitude, longitude, and altitude of the sampling site, and season. The dust deposition was considerable from February to May and the flux of eolian dust from the atmosphere to the Japanese land surface ranged approximately from 0.5 to 1.0 g/(cm²·1,000 years) or 3.6 to 7.1 mm/1,000 years in modern times (1.9 to 3.2 g/(cm²·1,000 years) or 13.5 to 22.9 mm/1,000 years in the last Glacial age). The eolian dust could be of significance as parent material of various kinds of soils in Japan, which have existed for 10² to 10⁴ years.

Key Word:

• aerosols
• eolian dust
• loess
• rate of dust deposition