藏南沉错沉积物有机质δ^(13)C对湖区环境冷暖变化的响应

THE RESPONSE OF ORGANIC MATTER δ^(13)C TO COLD/WARM FLUCTUATION OF CHEN CO LAKE SEDIMENT, SOUTHERN TIBET

湖泊沉积物有机质碳同位素δ13C是一种重要的环境代用指标,其对环境变化的响应较为复杂。通过研究藏南沉错CC1孔216cm柱状沉积物中有机质δ13C的变化,认为其波动是对湖区环境冷暖变化的良好响应,且在暖期偏低,而在冷期偏高。以δ13C的变化为基础并结合其他地球化学指标包括总有机碳(TOC)、氢指数(HI)、碳氮比(C/N)等,讨论了研究区近1400a来的冷暖变化,进一步划分出了4个暖期和4个冷期以及若干冷暖过渡期。其中4个暖期依次和“隋唐温暖期”、中世纪温暖期(包含中间2个暖期)和20世纪变暖相对应;而4个冷期中的后3个分别对应于小冰期的3个冷期,其时间范围分别约为1460—1510AD、1660—1770AD、1850—1900AD。CC1孔δ13C值波动所指示的冷暖时期与青藏高原其他地区和我国东部地区利用冰心、树轮、物候资料、史料及观测等资料的研究结果较为相似,反映了湖泊沉积物有机质δ13C作为环境代用指标的有效性以及藏南沉错地区气候变化与其他地区的相似性。

The stable isotope of organic carbon δ^13 C in lacustrine sediment is an important environmental proxy and is widely used in lake sediment and environmental change studies, but its response to environmental change is comparatively complicated. In this study, we use a 216 cm lake sediment core from Chen Co, located in Southern Tibet to distinguish the environmental significance of organic matter δ^13 C The results indicate that the fluctuation of organic matter δ^13 C well responds to the cold/warm variation of the lake areas; the corresponding way is that δ^13 C had relatively low values during the warm periods and high values during the cold periods. Based on the variation of δ^13 C as well as other geochemical proxies such as total organic carbon （TOC）, hydrogen index （HI）, and carbon hydrogen ratio （C/N）, the cold/warm fluctuation of the past ca. 1 400 years in the study area was discussed, four warm periods and four cold periods as well as some interims between them were distinguished. The four warm periods corresponded to ＂warm period in Sui and Tang Dynasty＂, ＂Medieval Warm Period＂ （ including the two middle warm periods） and ＂Global Warming in 20th Century＂ respectively; while the latter three cold periods correlated to the three cold periods of the Little Ice Age and the time range are 1460--1510AD, 1660--1770AD and 1850--1900AD, respectively. The warm/cold periods indicated by δ^13 C of CC1 core have some similarity to those from other studies by ice core, tree rings, phenological data, historical records and measurement data in other areas on Tibetan Plateau and the eastern part of China, reflecting the lacustrine sediment organic matter （313C is effective as a environmental proxy while the environmental change in Southern Tibet area is similar to the counterparts in other areas.