East Asia winter monsoon variations on a millennial time-scale before the last glacial-interglacial cycle

Grain size and magnetic susceptibility measurements on samples from a typic al loess-palaeosol sequence on the central Chinese Loess Plateau are used t o reconstruct the Pleistocene East Asian monsoon climate. The coarse-graine d fraction, i.e. the weight percentage > 30 mu m of the bulk grain-size dis tribution, is used as a sensitive proxy index of the East Asia winter monso on strength. On the basis of an absolute time-scale, time-series variations of this proxy show that winter monsoon strengths varied on millennial time -scales during the periods 145-165, 240-280, 320-350, 390-440, 600-640, 860 -890, 900-930 and 1330-1400 kyr BP. The wavelength of these climatic oscill ations varied between 1.89 and 4.0 kyr, as is shown by spectral analysis us ing the multitaper method. Although numerical simulation experiments show t hat high frequencies also can arise from measurement errors in the grain-si ze analysis, the frequencies prove to be sufficiently stable when the spect ral analysis is repeated with a different number of tapers. For the time be ing, we do not correlate these climatic oscillations with palaeoclimatic re cords in the North Atlantic deep-sea sediments because both time-scales nee d to be further improved. Our data, however, certainly demonstrate that mil lennial-scale East Asian winter monsoon variations in the last 1.4 million years can be detected from terrestrial loess records. Copyright (C) 1999 Jo hn Wiley & Sons, Ltd.