基于对石笋扫描图像灰度值的提取和10个230Th年代数据,建立了末次冰消期万象洞石笋灰度变化时间序列.在17.6～12.8kaB.P.期间,石笋灰度值在千年-亚千年尺度上呈现出明显的9次增大(峰)和9次减小(谷)交替变化的特征.对比分析发现,万象洞石笋灰度与密度指数在高频变化上呈显著的负相关关系,石笋灰度值的减小对应于密度的增大和葫芦洞石笋δ18O值的偏正,指示在末次冰消期期间石笋灰度与密度的变化同时记录了亚洲季风强度的变化.季风的强烈衰退导致环境温度突然降低,洞穴滴水碳酸氢钙过饱和度的升高,形成晶型规则且排列整齐的方解石晶体,使得石笋透光性增强而反射光能力降低,灰度值减小；反之亦然.Heinrich-1冷旋回期间,万象洞石笋灰度值的逐渐增大与季风强烈衰退造成降水减少和植被恶化使得杂质含量增加有关.同时未次冰消期万象洞石笋灰度记录的千年-哑千年尺度上亚洲季风强度的变化与高北纬气候存在密切的联系.%Stalagmite WX42A was collected roughly 1000m deep from the Wanxiang Cave entrance in 2003. Wanxiang Cave(33°19'N ,105°00'E , 1200m above the sea level)is located on the northwest margin of Asian summer monsoon area,where the climate responses are very sensitive to the changes of the summer monsoon. The ventilation of Wanxiang Cave is weak, with a temperature of 11℃ and the relative humidity 100% throughout the year. The stalagmite is 365 mm in length, light yellow, with the growth layers clear and flat at the growth center and vertical to the growth axis. Because several hiatuses exist on the top part of the stalagmite and the growth rate is very low there,the 18. 5 ~ 330. 0mm part of the stalagmite are chosen as our study samples.The digital image of the stalagmite profile is obtained by a scanner with the use of Matlab software,the gray scale data is collected at the center part of the profile. The gray scale data output is described with the numbers between 0 ~255. A higher gray scale indicates a lighter image color. Ten 230Th dating samples were drilled by a 0. 5mm dental drill and analyzed in the chronology lab of the department of geology and geophysics, University of Minnesota.Based on the gray scale data and the 3lTh dating results,the gray scale time series of the stalagmite WX42A grown during the last deglaciation was established. From 17. 6kaB. P. To 12. 8kaB. P. ,the gray scale varied between 125 and 195, with an average of 156. The general variation tendency is horizontal on millennial-sub-millennial scale,the variation of the gray scale presents a 9-peaks and 9-valleys alternating characteristics,9-peaks of the gray scale centered at 12. 8kaB. P., 13. 3kaB. P., 13. 8kaB. P., 14. 2kaB. P., 14. 6kaB. P., 15. 6kaB. P., 15. 8kaB. P., 16. 1kaB. P. And 17. 3kaB. P.,and the 9-valleys centered at 13. 1kaB. P.,13.6kaB. P., 14. 1kaB. P.,14.5kaB. P., 15. OkaB. P., 15. 7kaB. P., 16. OkaB. P., 16. 8kaB. P. And 17. 5kaB. P. Except that the gradually increased trend lasted about 1.4ka between valley 16 and peak 11,the gray scale of the stalagmite WX42A lacks low frequency variations. Further,almost each decreasing of the WX42A gray scale was finished in a less than 100a time interval, and this type of trend was characterized by slow increasing and fast decreasing.In order to remove the low frequency variation trends of the density index,gray scale of WX42A and H82 δ18O record from Hulu Cave,lHz high pass filter based on Fast Fourier Transform( FFT) were used. Through the comparison with the density index of the WX42A stalagmite and the δ18O record from Hulu Cave,which reflects the variation of the Asian monsoon strength,it is found that on the high frequency variations there is an obvious negative relationship between gray scale and the density index. On millennial-sub-millennial timescales, the decreasing of the stalagmite gray scale corresponds to the increasing of the stalagmite density index. The high S X) values of Hulu Cave stalagmite, which indicates that the dramatically retreating of the Asian monsoon led to the abrupt dropping of the environment temperature during the deglaciation, corresponded to the cave drip water's supersaturation increasing in Asian monsoon domain's caves, e. G., Wanxiang cave. That the crystal style and arrangements turned more ordinarily improved the light-transmitting ability and reduced the reflection of the stalagmite so the stalagmite gray scale was reduced consequently. The stalagmite gray scale records from Wanxiang Cave was sensitive in response to the regional climate variations during the last deglaciation.
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