Variations in 87Sr/ 86Sr ratios of calcites in Chinese loess: a proxy for chemical weathering associated with the East Asian summer monsoon

• Published in: Palaeogeography, palaeoclimatology, palaeoecology palaeoclimatology, palaeoecology, 2000-03, Vol.157 (1), p.151-159
• Main Authors: Yang, Jiedong, Chen, Jun, An, Zhisheng, Shields, Graham, Tao, Xiancong, Zhu, Hongbin, Ji, Junfeng, Chen, Yang
• Format: Article
• Language: English
• Subjects: chemical weathering; east Asian monsoon; loess and paleosols; soil carbonates; Sr isotope
• ISSN: 0031-0182; 1872-616X
• DOI: 10.1016/S0031-0182(99)00159-5

87Sr/ 86Sr ratios of loess–paleosol calcites of Luochuan in China over the past 130 ka display a regular change with increasing trend of 87Sr/ 86Sr ratios in the following order: loess calcite→weakly pedogenetic, paleosol calcite→paleosol calcite→pure secondary calcite. The observed variations in the 87Sr/ 86Sr record of loess–paleosol calcites correlate closely with the records of the magnetic susceptibility, coarse-grain fraction content in the same profile [An et al., Chin. Sci. Bull. 39 (1994) 182–184] and the SPECMAP stacked δ 18O record of global ice volume [Imbrie et al., in Berger et al. (Eds.), Milankovitch and Climate, Part I, Reidel, Boston, 1984, pp. 269–305]. Strata from the last glacial consist mostly of loesses and weakly developed paleosols and have lower 87Sr/ 86Sr ratios, averaging 0.71079. Paleosols which developed during the last interglacial have higher 87Sr/ 86Sr ratios, averaging 0.71131. The four periods (ca. 125–110, 98–90, 80–75 and 9–5 ka B.P.) of increased summer monsoonal rainfall coincide with the four peaks in 87Sr/ 86Sr values. A series of 87Sr/ 86Sr high frequency, high amplitude fluctuations is superimposed on the last glacial–interglacial cycle over the past 130 ka, occurring on millennium timescales with an average time span of about 3 ka during the last glacial. The fluctuations of the 87Sr/ 86Sr ratios of the Luochuan loess–paleosol calcites lie in the range 0.71036–0.71176 for the past 130 ka. The study shows that the Sr isotopic system in loess–paleosol calcites may therefore be an excellent proxy of chemical weathering on continents associated with the East Asian summer monsoon.