Distribution of Rb and Sr in the Luochuan loess-paleosol sequence of China during the last 800 ka -Implications for paleomonsoon variations

The concentrations of Rb and Sr, and magnetic susceptibility in loess and paleosol samples from the Luochuan profile have been measured. The loess units deposited in different geological periods display a very similar pattern of Rb and Sr distribution while paleosol units exhibit a dramatic increase in the Rb/Sr ratio, ranging from 20% to 120% in increase amplitude. Owing to different geochemical behavior of the two elements, Rb appears to be immobile while Sr appears to be mobile in the processes of weathering and pedogenesis. So variations of the Rb/Sr ratio in the loess-paleosol sequences could reflect intensities of weathering and pedogenesis, thus recording the relative wind strength of the East Asian summer monsoon circulation. This could be supported by the high degree of correlation between the Rb/Sr ratio and the magnetic susceptibility. A continuous record of the Rb/Sr ratio in the Luochuan profile over the last 800 ka bears a striking resemblance to the δ¹⁸O curve of the deep sea sediments and is in accordance with the SPECMAP chronology. Such similarity between the terrestrial and the deep sea records suggests that variability in global ice volume is a primary dynamic factor controlling long-term changes of the East Asian summer monsoon intensity.