中文摘要：

通过青藏高原可可西里马兰冰芯记录，重建了1887-1998年时期的净积累量变化，揭示出在研究时段内其变化呈弱的上升趋势。谱分析结果表明，马兰冰芯净积累量变化存在10.8a的显著周期。这表明太阳黑子活动对马兰冰芯净积累量变化存在一定的影响。统计分析发现，在20世纪80年代中期之前马兰冰芯净积累量变化与太阳黑子相对数变化之间存在显著的负相关关系，而在20世纪80年代中期之后却呈正相关关系。

英文摘要：

Precipitation along with temperature plays an important role in environmental evolution. In dry regions, precipitation usually is more important for vegetations than other Climatic factors. In the Northern Tibetan Plateau, the precipitation is less than 400mm, but in its large part usually less than 200mm. Study on the variation in precipitation in this region has an environmental significance. However, few meteorological stations exist there. Ice cores can provide some data of climatic changes. In 1999, we retrieved an ice core from the Malan ice cap （35°50′N, 90°40′E）with an area of 195km^2 in Kekexili of the Northern Tibetan Plateau, where the climate is mostly controlled by the westerly. Using the seasonal variations of δ^18O and annual dust layers,we dated the upper 23.3m of the Malan ice core, and found that it contained 122 annual layers,i, e.,the time span of this upper part of the ice core was from 1887A. D. to 1998A. D. Based on the thickness of each annual layer of the Malan ice core, we reconstructed the variation of net accumulation rate over the period of 1887 - 1998. By comparison of the net accumulation rate with meteorological data at the Wudaoliang station（35°13′N,93°05′E） , which is relatively close to the ice core drilling site,it was found that the net accumulation rate was a good proxy of summertime precipitation （note that 92% of the annual precipitation,272.5mm, is concentrated in the period of May through September at the Wudaoliang station）. The record of net accumulation rate（its long-term average was 186mm w. eq.）indicated that 1887-1907, 1918-1930, 1934-1949, 1958-1962, 1967-1986 and 1996-1998 were the spells with less precipitation, while 1908-1917, 1931-1934, 1950-1957, 1963-1966 and 1987 -1995 were the spells with relatively more precipitation. Over the whole study period, the net accumulation rate showed a weak increasing trend and two significant periodicities,i.e.： 10.8 and 2.3 yrs. These imply that variation of the net accumulation rate might be i