石笋氧同位素指示东亚季风大尺度环流特征

CHARACTERISTICS OF LARGE-SCALE CIRCULATION OF EAST ASIAN MONSOON INDICATED BY OXYGEN ISOTOPE OF STALAGMITES

利用湖北清江和尚洞的两支具有精确年代的年层石笋,建立了20世纪逐年的石笋氧同位素序列,讨论东亚季风石笋氧同位素的气候指示意义。与现代气象观测资料对比,发现近100年来和尚洞石笋δ ^(18)O与当地年总降水量和年均温度的相关性并不显著,但与指示东亚季风环流特征的西太平洋副热带高压指数(WPSH)以及相对应的太平洋年代际振荡指数(PDO)相关性好。在年际和年代际尺度上,当太平洋年代际振荡处于正(负)相位时,副热带高压加强(减弱),石笋的δ ^(18)O相对偏正(负)。因而,石笋δ^(10)O反映了东亚季风大尺度环流特征。

By using of two annually laminated stalagmites with accurate chronology, an oxygen isotope profile with an annual resolution of the 20th Century was established to assess the climate implication of stalagmite δ18O in the East Asian Monsoon area. These two samples were collected in Heshang Cave（30°26′49＂N, 110°25′12＂E）situated south of the Qingjiang valley in Yu Xiakou,Changyang Town,Hubei Province,which is within the Central Asian tropic zone. The region is mountainous and strongly monsoonal, which means that its four seasons are distinct and that with the seasonal reversed winds, the main rain belt shifts from south during the boreal summer to north during the boreal winter. These two samples have laminas able to count year by year and their isotope sequences with annual-resolution are easily obtained. We scraped 105 layers of sample HS6 to construct an accurate chronological stalagmite isotope profile with annual-resolution of the last 100 years in the East Asian monsoon area. The isotope sequence of 61 layers of sample HS4 was also measured as comparative data. According to the isotope equilibrium equation and the modern calcite deposition experiment, the theoretical δ18Oc values calculated by cave temperature and the δ18Ow of precipitation answer to the instrumental δ18Oc of stalagmite,with a tiny deviation（±0.5‰） ,which is a good confirmation of isotope equilibrium. In this paper,the relationship between δ18O and the local climate was discussed. Any correlation between the local temperature and the rainfall amount was hardly found. By a farther correlation analysis,on annual to decadal time scales,the correlation coefficient of 61SO with the annual average temperature and the total rainfall amount are -0.35 （n=78） and 0.08 （n=95）, respectively, less than the credit level, which means the 8＇80 of Heshang Cave stalagmite has a low correlation with the local climate. Thus, a conclusion can be drawn that in the serious East Asian monsoon area,temperature or local precipitation should never be the only force to cause the δ18O change of stalagmites. However,the comparison among the δ18O of stalagmites, the Western Pacific Subtopic High （WPSH）and the Pacific Decadal Oscillation（PDO）index shows a big similarity. On annual to decadal time scales,when PDO is of the warm （cold）phase, the WPSH will be strengthened （weakened）and the δ18O values will get much higher （lower）. The correlation coefficient of the annual δ18O with WPSH is 0.22 （with the ten-year moving average to be 0. 49） ,a perfect correlation. At the same time,0. 25 is also a wonderful correlation coefficient of the annual δ18O with the PDO. A lot of evidence demonstrates that the Western Pacific Subtopic High and Pacific Decadal Oscillation are relevant to the ITCZ, East Asian monsoon, SST, Walker circulation and others, which are closely related to the East Asian monsoon pattern. Thus,the δ18O of Heshang Cave stalagmites indicates characteristics of the East Asian monsoon circulation.