现代环境研究室知识库

A high-resolution stalagmite oxygen isotope record from Tianmen Cave, located in the south central Tibetan Plateau, characterizes detailed climatic variations between 8.7 and 4.3 ka BP on centennial and decadal time scales, with a temporal resolution of 3 to 7 years. The Tianmen record is in good agreement with speleothem records from Asian monsoon regions (i.e., Dongge Cave, Dykoski et al., 2005; Wang et al., 2005; Qunf Cave, Fleitmann et al., 2003), upwelling records from the Arabian Sea (Gupta et al., 2003, 2005) and peat bog records from southeast Tibetan Plateau (Hong et al., 2003), indicating that the Indian summer monsoon (ISM) gradually weakened as Northern Hemisphere summer insolation declined during the early-mid Holocene and that ISM intensity, rather than temperature, dominates the precipitation delta O-18 on centennial to decadal time scales in the southern TP. On centennial to decadal time scales, the detrended Tianmen record correlates well with the Greenland ice core record, further confirming the mechanistic connection between the ISM and high northern latitude temperature changes. Meanwhile, the Tianmen record bears significant solar activity cycles, suggesting that the solar output changes may affect the variability of the ISM and likely the position of the Intertropical Convergence Zone (ITCZ) as well. Moreover, due to joint effects of changes in monsoon precipitation, moisture source and temperature, the Tianmen delta O-18 record shows much larger amplitude changes than speleothem delta O-18 records from low-elevation Asian Monsoon regions, which is similar to the previously reported Marine Isotope Stage (MIS) 5 record (Cai et al., 20W), suggesting heightened sensitivity of precipitation isotope composition to climate changes over the high-elevation regions and further demonstrating that the stable isotope lapse rate may change under different climatic conditions.