SEPARATION OF LOCAL SIGNALS FROM THE REGIONAL PALEOMONSOON RECORD OF THE CHINESE LOESS PLATEAU - A ROCK-MAGNETIC APPROACH

We propose a method based on thermal unblocking of low-temperature sat uration remanent magnetization for a quantitative estimation of the su perparamagnetic [Cullity, 1972] fraction (size, d < 30 nm) of magnetit e produced by pedogenesis in the Chinese loess plateau [Liu, 1988]. We applied this method to the proxy climatic records of the last 130 ka from two sites 250 km apart, but separated by the mountain range Liupa n-shan. Xifeng to the east (35.7-degrees-N, 107.6-degrees-E) and Baica oyuan to the west (36.2-degrees-N, 105.0-degrees-E) currently have hum id and arid microclimates, respectively. As expected, the superparamag netic fraction increases during known warm temperature intervals at ea ch site. Furthermore, the more humid site clearly has higher overall s uperparamagnetic fractions during most of the last 130 ka. However, du ring the period 5 to 10 ka ago, the relative humidity at both sites wa s the same within experimental errors. Bulk grain size evidence confir ms the magnetic data, and we suggest that the present easterly summer monsoon in China came from a more southerly direction during this time to flow parallel to Liupan-shan, resulting in very similar summer hum idity at Xifeng and Baicaoyuan.