87SR/86SR AND SR/CA IN SPELEOTHEMS FOR PALEOCLIMATE RECONSTRUCTION

Limestone cave deposits (speleothems) provide archives for past changes in regional temperature, precipitation and moisture source over a range of time scales. To effectively read these archives requires the establishment of proxies other than the commonly used d¹⁸O and d¹³C in speleothem calcite. The concentration and isotopic composition of strontium (Sr/Ca and ⁸⁷Sr/⁸⁶Sr) in speleothems are such proxies that have been explored. In this study, we report further effort in the use of these strontium signals in speleothem calcite to deduce the time variation of the ⁸⁷Sr/⁸⁶Sr ratio in sediments overlying a limestone cave. We show that this ratio reflects climate-driven variations in the provenance and the extent of chemical weathering of the epikarstic sediments. Speleothems that grew in central China under a warm and wet climate have relatively high ⁸⁷Sr/⁸⁶Sr but low Sr/Ca ratios. From the measurements of d¹⁸O, d¹³C, Sr/Ca, and ⁸⁷Sr/⁸⁶Sr made on a stalagmite from Buddha Cave near the Loess Plateau in central China, we reconstruct the variability of the East Asian Monsoon for portions of the time range between 70 and 280 kyr ago, showing that more intense summer monsoons prevailed during interglacial periods than during glacial periods.