Sr-87/Sr-86 and Sr/Ca in speleothems for paleoclimate reconstruction in Central China between 70 and 280 kyr ago

摘要

Limestone cave deposits (speleothems) provide archives for past changes in regional climates over a range of timescales. While delta(18)O and delta(13)C in speleothem calcite have been commonly used for reconstruction of paleoclimates, we report here further efforts in the use of Sr-87/Sr-86 and Sr/Ca signals in speleothem calcite to deduce paleomonsoon variability near the Loess Plateau of central China. A two end-member mass-balance model of concentration and isotopic composition of strontium in a cave system is used to estimate variation of the Sr-87/Sr-86 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. The measurements of Sr-87/Sr-86 made on a well-dated stalagmite, SFL, from Buddha Cave (33 degrees 40N' 109 degrees 05'E) show ratios of 0.71092 to 0.71133 (+/- 0.00001 as 2 sigma) during relatively cold periods (e.g., Marine Isotope Stage (MIS) 5b, 5d, and 8), lower than ratios of 0.71133 to 0.71194 during relatively warm periods (e.g., MIS 5a, 5c, 5e, and 7). As changes in the Sr/Ca ratio may affect speleothem 87Sr/86Sr, we show that the direct use of speleothem Sr-87/Sr-86 is less ideal than our modeled Sr-87/Sr-86 for the exogenic Sr source above the cave as a paleomonsoon proxy. Using the delta(18)O, delta(13)C, Sr/Ca, and Sr-87/Sr-86 records of the stalagmite, we reconstruct the variability of the East Asian monsoon for the time period between 70 and 280 kyr ago. The results show that summer monsoons were more intense during interglacial periods than during glacial periods. Copyright (c) 2005 Elsevier Ltd.