PALEORAINFALL RECONSTRUCTIONS FROM PEDOGENIC MAGNETIC-SUSCEPTIBILITY VARIATIONS IN THE CHINESE LOESS AND PALEOSOLS

The rock magnetic properties of the Chinese loess and paleosols consti tute a unique and sensitive record of East Asian paleoclimate through the Quaternary Period, Systematic variations in the concentration and grain size of the magnetic minerals in these sediments have produced s ystematic variations in the magnetic susceptibility signal, which can be easily and rapidly measured at many sites across the Loess Plateau, Variations in many other rock magnetic properties can be used to iden tify the key shifts in ferrimagnetic grain size, but magnetic suscepti bility alone is sufficiently sensitive to record stadial and interstad ial climate stages, as well as glaciations and interglaciations, Past changes in rainfall and monsoon activity for this region are reconstru cted from the susceptibility variations. The susceptibility record is calibrated using the modern relationship between rainfall and pedogeni c susceptibility on the Loess Plateau. Our rainfall reconstructions id entify enhanced summer monsoonal activity in the Chinese Loess Plateau region in the early Holocene and the last interglaciation. In the pre sently semiarid western area of the plateau, annual precipitation in i nterglacial times was up to 80% higher than at present; in the more hu mid southern and eastern areas, values were up to 20% higher than toda y's levels, During the last glaciation, precipitation decreased across the entire plateau, typically by similar to 25%, The relationship bet ween pedogenic susceptibility, climate, and weathering age was examine d over the Northern Hemisphere temperate zone and the observed positiv e correlation between rainfall and susceptibility indicates that clima te, rather than soil age, is the predominant factor that controls pedo genic susceptibility enhancement in loess soils. (C) 1995 University o f Washington.