玉龙山温冰川浅冰芯记录现代指示意义

Contemporary Significance of Snow and Ice Indicated by the Record in a Shallow Ice Core from a Temperate Glacier in Southwestern Monsoon Region

１９９９年夏季首次在玉龙山最大的白水 １号冰川积累区钻取了一支穿透整个粒雪层的１０ｍ冰芯，获取了近期数年的气候环境记录．深度 ７８ ｍ以上 δ１８Ｏ周期性波动变化特征明显，通过与可溶性离子，电导率和ＰＨ值，以及粒雪中污化冰层位置的对比分析，可鉴别出５个平衡年度的冰雪层，每年平均净积累折合水当量约 ９００ ｍｍ．由于融水渗浸的影响产生“均质化作用”， δ１８Ｏ变化幅度随深度增加而逐渐减小，在 ７．８ｍ以下，δ１８Ｏ值变为均匀分布，气候记录波动变化特征逐渐消失，但由于粒雪层内融水再冻结层的保护作用，仍使以上若干年的气候环境信息得以保存．可溶性离子以Ｃａ２＋和Ｍｇ２＋浓度较高，Ｃ１－和Ｎａ＋含量很低．说明冰芯内以冬季风形成的陆源沉积为主．Ｃ１－和Ｎａ＋的同步变化趋势指示出它们的相同来源，大部分层位上ＳＯ４２－和ＮＯ３－浓度都很低，说明冰川区很少受到人类污染．根据冰芯内年平均净积累厚度和积累区的消融情况，粗略估计粒雪盆的年平均降水量在 ２ ４００～ ３１ ００ ｍｍ之间．

The Mount Yulong is the southmost glacialized area both in China and in Eurasia, where 19 typical subtropics temperate glaciers exist. mainly formed under the climate of southwestern monsoon. In the summer of 1999. a firn core. 10. 10 m long to the glacier ice. was successfully recovered in the accumulation area of the largest glacier. Glacier Baishui No. 1. on the Mount Yulong. Periodic variations of climatic signals above the depth of 7.8 m are apparent. and five-year's boundaries of net accumulation can be identified by the annual changes of isotopic and ionic compositions. verified by some higher values of electrical conductivity and pH as well as the position of refrozen dirty ice layers in summer horizons. Average annual net accumulation from 1994/1995 to 1997 / 1998 is calculated to be about 900 mm water equivalent. Variation amplitude of δ18O decreases with increasing core depth, and isotopic homogenization occurs below the depth of 7.8 m. as a result of meltwater percolation. Above results suggest that, although high melting occurred in the temperate firn core. climatic signals had still kept for some years as a result of a protection effect of percolation-proof ice layers within the firn, especially of the thick ice layers in the summer horizons. However, because of slow melting existed between these ice layers. homogenization and a smoothed distribution of climatic records were finally caused during the formation process of glacial ice. Therefore, the high- melting temperate from core is quite limited for studying long-term climate change. Cycles of δ18O in the core roughly correlate to the variation trend of mean temperature and precipitation at Lijiang Station during the winter months of five balance years. Concentrations of Ca2+ and Mg2+ are much higher than that of Na+ and K+, reflecting that the air mass for precipitation was mainly from continental sources. as well as the materials in the core accumulated during the winter. Cl- and Na+ show a corresponding variation trend, indicating their same genesis. Concentrations of SO42- and NO3- are low. reflecting that the pollution caused by human activities is very low in this area. According to the sum of net income recovered from the core and an estimated ablation amount, the average annual precipitation above the equilibrium line is approximately assumed in the scope of 2 400- 3 100 mm. but it needed to be verified by long-term observation of mass balance.