Origin of the magnetic susceptibility signal in Chinese loess

The quality of the loess magnetic susceptibility (MS) record as a climate proxy has been compared to the ice core and deep-sea records, yet the source and causes of the MS signal remain poorly understood. Four explanations are currently in circulation. The dominant hypothesis, that MS variations largely result from post-depositional weathering and/or formation of magnetic phases by pedogenic processes, has led to the use of MS data as a palaeoprecipitation proxy. We present a different view based on analyses of samples of monthly dust falls over 4 years in North China. These have MS values comparable to those of Pleistocene loess and palaeosols but, unlike the latter, their variations are seasonal and so cannot be explained by weathering differences. Our experiments confirm that MS enhancement in the palaeosols is caused principally by fine-grain magnetic minerals, but, in contrast with previous proposals, the major source of the ultrafine magnetic minerals appears to be decomposed plant litter. Copyright (C) 1997 Elsevier Science Ltd.