中文摘要：

本文提供西藏普若岗日冰芯高分辨率的孢粉记录，证实普若岗日冰帽15世纪以来植被主要经历由寒冷干旱荒漠草原向寒冷潮湿的草甸草原和温暖干旱草原发展的演替过程。在大约550年来植被与生态环境变化中，明显出现AD1500-1515年（75007300cm）、AD1565—1575年（7200-7000cm）以及AD1635-1640年（6300—6200cm）期间是当地土壤和空气较为湿润的时期，发育草甸草原植被。在AD1770-1800年（4700—4200cm）、AD1815--1825年（4000-3800cm）、AD1850-1865（3400-3200cm）以及AD1980年（500cm）以后是气温升高时期，气候温暖干燥，干旱草原植被逐渐扩大。冰芯记录的草原和草甸植被中主要植物花粉的百分含量与高原中部历年夏季温度呈正相关，推算最近150年内在19世纪70、90年代和20世纪90年代曾出现高于现今当地气温约1．9℃的高温期，而在19世纪60、80年代和20世纪初，20世纪50和60-70年代是相对寒冷的时期。过去100年中20世纪晚期的渐暖现象尤其明显，与整个青藏高原年平均温度显著相关，也与青藏高原记录的冰川缩小较一致。

英文摘要：

The ice core pollen from the Puruogangri ice cap （PRGR） provides a sensitive record of the fifteenth century climatic changes and vegetational response in the central Tibetan Plateau at time scales ranging from centuries to decades. Pollen analysis of the last 550 years suggests that there were humid periods of AD1500-1515,AD1565-1575 and AD1635-1640, when meadow-steppe vegetation dominated in the Puruogangri area. Relatively dry and warm episodes occurred at AD1770-1800, AD1815-1825, AD1850-1865 and after AD1980, when steppe vegetation apparently expanded. Pollens preserved in the ice core approach an annual resolution for the PRGR ice cap during the past 150 years. The summer temperature history on the central Tibetan Plateau during 1860-2002 was revealed based on a linear regression model between sum of the steppe and meadow pollen components and Naqu summer temperature, which accounts for 66% of recorded summer temperature variance for the period of 1955-2002. Three remarkable warm periods of 1870s, 1890s, and 1990s, and five cold periods of 1860s, 1880s, 1900s, 1950s, and 1960- 70s were identified. The late-20th century warming is remarkable during the last 100 years, which may be mainly responsible for the shrinkage of most glaciers on the Tibetan Plateau. The pollen record is also significantly correlated with average annual temperature of the entire Tibetan Plateau, suggesting that the pollen record can represent temperature changes of the Tibetan Plateau. The striking similarity between the pollen record and ice core δ18O series shows that both records are reliable indicator of temperature change at annual to multi-year timescales in this region.