Spatial and temporal changes of summer monsoon on the Loess Plateau of Central China during the last 130 ka inferred from Rb/Sr ratios

The Rb/Sr ratios for samples from six loess-paleosol sections on the Chinese Loess Plateau during the last glacial-interglacial cycle, and for samples from 18 modern surface soils, have been analyzed. The six sections are along north-south and west-east transects respectively. The results show that the spatial distribution of Rb/Sr is characterized by a remarkable increase from north to south while Rb/Sr ratio changes little from west to east, whose latitude indicates shift of summer monsoon intensity. A regression equation between Rb/Sr ratios and mean annual pre-cipitation (MAP) has been constructed through statistical analysis for the modern surface soils. Paleorainfall during the last 130 ka is estimated for the six sections based on the regression equa-tion. It is evident that precipitation increased remarkably during marine isotope stages 3 and 5, exhibiting the high and similar gradients of variation with latitude. This demonstrates that the envi-ronmental effect is more prominent in the south of the Loess Plateau than in the north during the dominance of summer monsoon.