西藏昌都崩勒溶洞石笋7ka BP以来高分辨δ18O、δ13C记录的气候变化

摘要

High-precision 230Th dating and carbon and oxygen isotopic analysis were carried out on stalagmite from Benle Cave in Chamdo,Tibet Plateau to establish a mid-Holocene paleoclimate change record in Chamdo of Tibet since 7 ka BP.Carbon and oxygen isotopic records of stalagmite reveal that the climate evolution since mid-Holocene (about 7 ka BP) in Chamdo,Tibet can be approximately divided into three climatic periods.① Warm period of 7000～4500 a BP,during which the overall climate was warm and humid,with temperature slowly cooling.② Temperature falling period of 4500 ～ 2300 a BP.As the temperature continued cooling,the climate became dry.③ Temperature rising period of 2300 a BP,during which the air temperature and precipitation fluctuated and were rising.Carbon and oxygen isotope records of stalagmite show that since the middle Holocene the climate changed from warm and humid,rapidly falling temperature and drought,and to strong fluctuating and rising in the study area.A comparative analysis of isotope records of stalagmite in Dongge cave indicates that the slop and fluctuating amplitudes of δ18O curves of stalagmite in Benle cave are significantly higher than that of stalagmite in Dongge cave.The results above suggest that the climate fluctuation and temperature change in the monsoon region of Eastern Qinghai Tibet Plateau was consistent with that in global,and the isotope record of stalagmite in plateau was more sensitive to climate change.The trend of climate change reflected by the isotope record of stalagmite in Chamdo was positively related to summer solar radiation intensity in low latitude areas,and this indicates that the variation of the solar radiation intensity was an important driving factor in the monsoon area in the Tibetan plateau.%通过对青藏高原崩勒溶洞石笋进行高精度的230Th测年和C、O同位素分析,建立了中全新世7 kaBP以来西藏昌都地区高分辨率的古气候变化记录.石笋C、O同位素记录揭示出,西藏昌都地区中全新世(约7 kaBP)以来的气候演化大致可分为3个气候阶段:7000～4500 a BP为暖期阶段,气候总体处于高温暖湿,伴随缓慢降温;4500～2300 a BP为降温期阶段,出现持续降温,气候变得干旱;2300 a BP至今为升温期阶段,气温及降水均出现波动上升.石笋C、O同位素记录的研究结果表明,中全新世以来研究区存在高温暖湿、快速降温干旱以及后期气候强烈震荡升温的气候过程.通过与董歌洞石笋同位素记录对比表明,崩勒溶洞石笋δ18O同位素曲线变化的斜率、震荡幅度都要明显高于董歌洞石笋记录,揭示出青藏高原东部季风区的气候波动与全球性冷暖变化具有一致性,但高原石笋同位素记录对气候变化更加敏感.昌都石笋同位素反映的气候变化趋势与低纬地区夏季太阳辐射强度变化正相关,表明太阳辐射强度变化是高原季风影响区气候变化的重要驱动因素.