PALAEORAINFALL THROUGH THE HOLOCENE IN THE WESTERN CHINESE LOESS PLATEAU: A HIGH-RESOLUTION RECORD AND A TEST OF PMIP HINDCASTING FOR THE MID-HOLOCENE PERIOD

Formation of strongly magnetic iron oxides in well-drained, buffered, unpolluted soils appears to be controlled by climate, and especially rainfall. If robust, this magnetism/rainfall couple can be used to estimate past, monsoonal rainfall from buried soils, particularly the multiple soils of the Quaternary loess/soil sequences of Central Asia. However, dispute has existed regarding the role of climate versus dust flux for the magnetic properties of modern loessic soils. Kukla and colleagues proposed that the major process responsible for the Chinese loess/soil magnetic contrasts is magnetic ‘dilution’, controlled by a constant ‘rain-out’ of fine-grained magnetite from the atmosphere and a varying rate of accumulation of weakly magnetic windblown dust. According to this model, soils have higher magnetic concentrations due to reduced sedimentation rates and loess units have lower magnetic concentrations due to increased sedimentation rates. Given the scarcity of proxies for robust and quantitative reconstruction of palaeoclimate, essential for testing of climate model postdictions and predictions, and the significance of Asian monsoon variations in this highly-populated region, it is critical to test the validity of these two contrasting interpretations and thence the reliability of the proposed magnetism/rainfall link. Two sets of tests are discussed here: spatial and temporal. Having applied these tests, the magnetism/rainfall link is then used to make quantitative reconstruction of rainfall variations through the Holocene for the western Chinese Loess Plateau, and thereby in turn to test the rainfall hindcasting of the different PMIP models for the mid-Holocene period.