Grain Size of Quartz as an Indicator of Winter Monsoon Strength on the Loess Plateau of Central China during the Last 130,000 Yr

Abstract

The Chinese loess-paleosol sequence constitutes an important record of variations in Asian monsoon climate over the past 2.4 myr. Magnetic susceptibility of loess and paleosols has been used as a proxy for summer monsoon intensity, while median grain size has been regarded as a measure of the strength of winter monsoon winds that were responsible for most of the dust transport. However, median grain size is only an approximate index of winter monsoon strength because both paleosols and loess have been modified, to various degrees, by weathering processes that have produced pedogenic clay. The quartz component of loess and paleosols is largely unaffected by weathering processes and therefore constitutes a more reliable proxy index of monsoon wind strength. Median grain size (Qmd) and maximum grain size (Qmax) values of monomineralic quartz isolated from the loess-paleosol section at Luochuan in the central Loess Plateau are characterized by two main intervals during the last ca. 130,000 yr when these parameters were significantly greater than 9 and 85 μm, respectively, and three main intervals when they were lower. The data imply that the winter monsoon weakened during the intervals with low Qmd and Qmax values, which coincide with marine oxygen isotope stages 5, 3, and 1, and was strongest ca. 67,000 and 20,000 yr ago during isotope stages 4 and 2. However, both quartz grainsize records display second-order high-frequency, high-amplitude variations, which are lacking in the magnetic susceptibility record, that imply rapid and significant changes in atmospheric conditions that affect dust transport and deposition.

Quantification of aeolian dust (Kosa) contribution to the Japan Sea sediments and its variation during the last 200 ky.

“…The bathymetric contour of -80 m in the East China Sea is illustrated to show the paleo-position of the coastline during glacial stages. Modern summer monsoon limit (Xiao et al, 1995) is also shown.…”

East Asian monsoon climate during the Late Pleistocene: high-resolution sediment records from the South China Sea

“…7; core 17940), values that are characteristic of loess deposits in Central China (Xiao et al, 1995;Porter and An, 1995). Near 18,000 14 C years (940-890 cm c.d.…”

Timing and structure of the mid-Pleistocene transition: records from the loess deposits of northern China

“…To investigate past winter monsoon activity physical grain size and sedimentation rates (SR) are analysed; both of these are expected to increase as the intensi¢cation of the winter monsoon results in more vigorous westerly air movement. A variety of grain size measurements from sites across the loess plateau have been successfully utilised in the reconstruction of past winter monsoon levels at both orbital scales (Ding et al, 1994(Ding et al, , 1995(Ding et al, , 1999Shackleton et al, 1995;Xiao et al, 1995) and sub-orbital scales Chen et al, 1997).…”