石笋氧碳同位素古气候代用指标研究进展  

Advance in Study of Oxygen and Carbon Isotope Variations in Cave Stalagmites as Palaeo-Climate Proxies

作　　者：孔兴功[1] 

机构地区：[1]南京师范大学地理科学学院,南京210046

出　　处：《高校地质学报》2009年第2期165-170,共6页Geological Journal of China Universities

基　　金：国家自然科学基金(40771009);教育部重点项(207039)共同资助

摘　　要：洞穴石笋以其独立的绝对年龄和稳定的古气候代用指标而成为很好的陆地古气候研究材料。应用U系定年,可以获得独立精确的日历年时间序列,结合年纹层统计,可以获得年际甚至是季节性变化古气候记录。作为古气候代用指标,石笋氧同位素具有全球可对比性,现已建立了氧同位素的全球气候变化曲线,显示了比深海氧同位素及极地冰芯氧同位素记录更多的优势。石笋δ18O的影响因素很多,在东亚季风控制区和其它季风控制区,石笋的δ18O反映了夏季风的强度或者是季风降雨的变化。这些全球可对比的具有高精度绝对定年的石笋δ18O记录,突破了早期的单一温度控制机理,不仅为古气候学家提供了坚实的古气候变化时间序列,而且使古气候研究能从机理上探讨其变化规律。δ13C不如δ18O具有全球可对比性,在同位素平衡的开放体系,石笋δ13C主要反映了洞穴上覆土壤CO2的同位素特征。因此,一般认为石笋δ13C可直接反映当地植被的特征,包括植被类型C3/C4比率的变化及植被的茂盛与衰退,在一些地区也可作为大气降水和温度变化的指标。石笋δ13C很易受到蒸发作用、滴水的快速去气、动力分馏、碳酸盐的先期沉积等影响而使得其数值偏正,应该予以重视。通过介绍石笋氧碳同位素的研究现状,使得读者对石笋的稳定同位素指标有一个初步认识。同时,对今后的研究方向给与一定的探讨。Stalagmites are now regarded as valuable archives in study of climatic conditions on the continents. They are ideal materials for precise U-series dating, yielding ages in calendar years, coupled with annual layer counting, the chronology of stable oxygen-isotope then be made with the resolution higher than year. These absolute precise dating and high resolution records offer a number of advantages relative to other continental climate proxy recorders such as lake sediments and peat cores. In many eases, stalagmite records may provide climate conditions that rival those obtained from marine sediments and ice cores. The controls on stalagmite δ^18O are numerous, under equilibrium condition, the δ^18O values of stalagmites are related to intensity of summer monsoon or amount of the monsoon precipitation at the typical monsoon area. This emphasis on global climate teleconnections has replaced attempts to constrain absolute palaeotemperature, allowing the scientific community to place global climate changes on a firm chronological and climate dynamical footing. Unlike the global comparison of δ^18O, under equilibrium open system conditions, the δ^13C of the dissolved species reflects the isotopic composition of the soil CO2, with no detectable isotopic imprint from the carbonate host-rock. Thus the stalagmite δ^13C is mainly controlled by the vegetation covering the cave, normally by the C3/C4 ratio of the local vegetation. The δ^13C can still be related to the change of precipitation and temperature at special region. We should pay special attention to these processes including evaporation, rapid degassing of cave dripwaters, kinetic fractionation, C02 degassing of dripwaters and consequent calcite precipitation in the vadose zone above a cave that could affect the carbon isotope to a relatively heavier signature. The lilerature is reviewed briefly to provide for the readers a sense of the current research work of the stable isotope of stalagmite and provide some ideas for future research directions.

关 键 词：石笋 氧碳同位素 古气候 

分 类 号：P532[天文地球—古生物学与地层学]