中国黄土高原西缘甘肃万象洞MIS 5石笋δ18 O记录与南方地区石笋记录的对比研究*

位于青藏高原与黄土高原过渡带的甘肃武都万象洞石笋WXSM51和WXSM52提供了MIS 5(118~79kaB.P.)高分辨率的δ¹⁸ O记录。研究表明, 万象洞石笋δ¹⁸ O值与夏季风强度呈负相关关系, 与我国西南部的贵州董歌洞石笋δ¹⁸ O记录有良好的对应关系, 并与高纬度的格陵兰NGRIP冰芯δ¹⁸ O记录和65°N太阳辐射强度有很好的一致性, 说明万象洞石笋δ¹⁸ O记录了118~79kaB.P.期间亚洲季风强度的变化, 同时也说明东亚季风强度的变化和全球气候变化同步, 而且主要受控于北半球太阳辐射强度的变化。同时它与地中海碳酸盐记录有很好的相似性, 和巴西石笋δ¹⁸ O记录在千年尺度上表现出相反的变化趋势, 说明东亚季风区、地中海地区以及巴西季风区之间存在密切的联系, 指示了南北半球气候在千年尺度上存在"跷跷板"(seesaw)现象。万象洞石笋δ¹⁸ O记录的MIS 5b与MIS 5a突发性转换, 与NGRIP冰芯δ¹⁸ O记录相似, 而与神农架记录存在差异, 说明万象洞地区对亚洲季风强度的响应更为敏感。

COMPARISON OF δ18 O RECORD DURING MIS 5 IN WANXIANG CAVE STALAGMITE, GANSU PROVINCE OF WESTERN LOESS PLATEAU AND THOSE OF SOUTHERN CHINA STALAGMITES

Speleothem, which is suited for precise U-series dating and contains many climate proxies, is widely used in paleoclimate reconstruction. In China, it has been proved that speleothem δ¹⁸ O is suitable for paleomonsoon reconstruction in the south and east regions. But in the northwest region few studies have been done. Here, we report high resolution δ¹⁸ O records of MIS 5 (from 118kaB.P. to 79kaB.P.) from two stalagmites (WXSM51 and WXSM52) collected form the Wanxiang Cave, Gansu Province (33°19'N, 105°00'E).The Wanxiang Cave is located at the transition zone between the Qinghai-Tibetan Plateau and the Loess Plateau. The location is close to the northern limit of the summer monsoon. The results indicate that δ¹⁸ O of stalagmite at this site is inversely related to the East Asian summer monsoon intensity. δ¹⁸ O of the Wanxiang Cave closely resembles the D3 record from the Dongge Cave, and also agrees well with the NGRIP record and the 65°N summer isolation curve. These indicate that δ¹⁸ O of the Wanxiang Cave is a valid and robust proxy for paleomonsoon intensity analysis. These also suggest that the East Asian monsoon varies in step with global climate change and is largely controlled by solar variations in the Northern Hemisphere.The Wanxiang record presents similarity to the Mediterranean speleothem records, and presents an inverse pattern compared with the Brazilian stalagmite BT2 record on the millennial timescales. These indicate that there are climate links among the East Asian monsoon, the Mediterranean and the Brazil summer monsoon regions, and further prove that the north-south climate seesaw did exist.It should be pointed out that the pattern of the transition from MIS 5b to MIS 5a recorded in the Wanxiang records differs from that in the Shennongjia stalagmite records. This difference, which does not seem to be caused by sampling resolution difference, may indicate that δ¹⁸ O of the precipitation in the Wanxiang Cave region is more sensitive to changes in monsoon intensity due to its close location to the northern limit of the monsoon region.