晚全新世以来福建仙山泥炭钻孔的正构烷烃记录

LATE HOLOCENE ORIGANISM RECORDS FROM PEAT n-ALKANES OF XIANSHAN MOUNTAIN IN FUJIAN PROVINCE,SOUTHEAST CHINA

通过对福建仙山泥炭钻孔中正构烷烃的分析，探讨了研究区近千年以来的气候特征。分析显示：正构烷烃分布范围主要为C16～C35,且以奇碳链为主，奇偶优势明显。正构烷烃与有机质含量（TOC）密切相关，在典型的泥炭层，TOC含量高，长碳链的C27，C29和C31正构烷烃占优势，揭示有机质主要来源于草本或木本等高等植物，盆地处于相对干的沉积环境；在非泥炭层，TOC含量低，钻孔中多含粗砂或粉砂，中碳链的C21或C23正构烷烃占优势，揭示有机质主要来源于水生植物或苔藓植物，表明相对较湿的沉积环境。钻孔中正构烷烃C23／C27比值与前人提出的C23／C29和P等参数呈同向变化，可以作为区域干一湿变化的代用指标。结合地层的年代序列，利用正构烷烃重建了区域距今1400年以来的植被演化和气候变化历史。结果显示，福建仙山地区气候存在3次相对湿润和4次相对较干的时段。在钻孔358—280cm（约公元600—910年），气候相对较干，在280～40cm（约公元910～1640年），降水较多，气候湿润，但中间存在两次变干的阶段；在40-0cm（约公元1640年至今），降水相对较少，气候转干。TOC含量和正构烷烃C23／C27序列与南方旱涝频率序列、石笋和硅藻记录对比显示，研究区在中世纪暖期气候相对较干，而小冰期则相对湿润，揭示出仙山泥炭沉积记录的气候信息具有区域一致性，为认识季风在短时间尺度的变化特征提供了依据。

Sediment core from peatland is a well-established source of paleoenvironmental information. We discussed the regional climate change based on the analysis of n-alkanes from a 358cm-long peat core in Xianshan Mountain of Pingnan County （26°52.4＇N, 118°42.7＇E）, which is located in the central part of Fujian Province, Eastern Subtropical China. The elevation of the study site is 1303m a. s. 1., the mean annual temperature is about 13℃, maximum and minimum extreme temperature respectively 31.5℃ and -12.5℃. The climate exhibits a clear seasonal signal and the mean annual precipitation is ca. 2000mm. Using GC-MS techniques, a series of n-alkanes were identified in peat sediments with a total concentration ranging from 4.2μg/g to 43.2μg/g. The C,6 to C35 n-alkane homologues were detected in all samples and the n-alkane was found dominated by odd carbon chains,with a strong odd-over-even predominance. In typical peat layers,when the value of total organic carbon（TOC） is high, the long chain n-alkanes （C27, C29 or C31 ）were mostly abundant, indicating that the organic matter was mainly originated from trees and grasses and the local environment was dry. Whereas in other non-peat layers, when total organic carbon displays low value, n-alkanes C21 or C23 were abundant in the samples, together with the high contents of sand and gravel in the core, to some degree, indicate that the organic materials in those non-peat layers may have originated from some aquatic plants or sphagnums, and also suggests a wet or under water depositional environment. The ratio of C23/C27 in this core shows strong correlations with C23/C29 and Paq. proposed in previous research,and thus can be used in paleohydrological reconstruction from peat sediments. This peat records show strong agreements with dry-wet anomalies of Southern China, stalagmite δ18O record from Yuhua cave and Tian＇e cave,and also record of the saltwater species percentage in the Southern Okinawa Trough. Based on AMS14C dates, high-resolution peat records were used to reconstruct the past vegetation and climate changes over the past 1400 years. From 600A. D. to 910A. D. ,the organic matter was originated from grasses and aquatic plants or sphagnums, and the climate was dry. From 910A. D. to 1640A. D., the organic matter was primarily originated from aquatic plants or sphagnums, implying a wet climate condition. But this wet period was interrupted by two dry periods, 1270 - 1325A. D. and 1390 - 1450A. D. From 1640A. D. to present,the origin of organic matter was dominated by trees and grasses from water plants or sphagnums, and the climate was dry again. Studies on the characteristics and regularities of climate change in the past millennium have mostly emphasized on three important periods： the Medieval Warm Period （ MWP）, the Little Ice Age （LIA） and the Current Warm Period （CWP）. The n-alkane records in this study show the climate condition during MWP in study site was dry while during LIA was wet, indicating the climate in study area was primarily controlled by monsoons both on multi-decade and century timescales. This study can advanced the knowledge about transformation of historical monsoon changes in China.