The palaeoenvironmental significance of δ¹³C of stalagmite BW-1 from Beijing, China during Younger Dryas intervals inferred from the grey level profile

High-resolution records of carbon isotope composition and grey level were analysed from a stalagmite, BW-1, from Beijing, China, deposited between c.14 and 10.5ka BP, the δ¹⁸O profile of which has been used to discuss the timing and structure of the Younger Dryas (YD) event in north China. The high grey level and low δ¹³C match the milk-white coloured locations on the polished stalagmite surface and coincide with enhanced luminescent bands within which the concentration of both impurities and the total organic carbon (TOC) are high. Additionally, the fluorescence of speleothems was derived from organic acids that have been flushed onto the stalagmite surface along with impurities from the overlying soil by heavy summer rain and co-precipitated with the speleothem calcite. Thus, predominantly low δ¹³C and high grey level values indicate increased summer precipitation that supports abundant vegetation and robust biological productivity. Consequently, three distinct time intervals are defined by the palaeoenvironmental conditions expressed in the δ¹³C and grey level records of stalagmite BW-1: (i) a warm-humid stage (Pre-YD, 13.97 to 12.85ka BP, including a hiatus from 12.99 to 13.21ka BP reported before); (ii) a cool-arid stage (YD, 12.85 to 11.56ka BP); and (iii) a warm-humid stage (Post-YD, 11.56 to 10.39ka BP). The inferences based on our research are generally consistent with other regional vegetation and climatic records.