抚仙湖沉积有机温标及最近3ka温度记录研究

This proposal mainly focus on modern process and historical temperature reconstructions of Fuxian Lake,the deepest lakes on Yunnan-Guizhou Plateau, based on the distribution of branched glycerol dialkyl glycerol tetraethers (branched GDGTs). During the past decades, paleo-temperature proxy based on branched GDGTs has shown high potential in paleo-climate reconstruction. However, to better employ this proxy in quantitative reconstruction, morden process research is necessary. Here the regional calibration derived from 15 lakes of Yunnan-Guizhou Plateau will be constructed by mean annual GDGTs based temperatures (MBT/CBT-MATs). By comparing with synchronously monitored environmental parameters, MBT/CBT indices of surface sediments at different depth in Fuxian Lake will be applied to evaluate the reliability and sensitivity of the proxy. Furthermore, a quantitative temperature reconstruction for the past 3000 years from sediment cores of Fuxian Lake will be made using multiple proxies, especially MBT/CBT indices. The chronology will be well constrained by a high-resolution (AMS C-14 dates) radiocarbon age-model and Pb-210, Cs-137 dating. The primary objectives of this proposal are: 1)to recognize the timing of initiation and termination, ranges and fluctuating extent of temperature anomaly over the last 3000 years, 2)to evaluate the rates and ranges of temperature rising under global warming in the past decades as well as under the background of climate change in the past millennium, 3)to explore the patterns of temperature variation and driving mechanisms of regional climate change.

本项目以我国西南地区的高原型深水湖泊抚仙湖为研究对象，在进行湖泊不同深度表层沉积物分析的基础上，分析和鉴别生物标志化合物支链GDGTs对温度响应的可靠性和敏感性，从生物标志化合物角度寻找一种或多种可以定量或半定量重建温度的指标。结合对云贵高原区域内多个湖泊现代沉积的同步测试，辅以器测资料，建立基于MBT/CBT指标的区域温度转换函数。然后运用放射性核素（Pb-210、Cs-137、AMS C-14）测年，精确建立抚仙湖岩芯的年代序列。在前述工作的基础上，通过基于支链GDGTs的MBT/CBT指标以及多种常规气候代用指标定量重建研究区过去3ka以来高分辨率的温度变化过程，认识历史上温度异常的不同冷暖期的起止时间、冷暖程度及波动幅度，尤其注意近几十年全球升温的速率和幅度在过去千年的气候变化框架上是否正常，探讨区域气候变化特征和响应机制。

本项目获得西南地区高原型深水湖泊抚仙湖岩芯钻孔2.45m，6个全有机沉积物样品的AMS 14C测年结果显示岩芯底部约为5ka Cal BP。粒度、XRF元素含量、δ13Cbulk、正构烷烃Paq等多种环境指标指示了抚仙湖沉积物中有机质来源以内源水生植物为主，并且自5000 Cal BP以来呈现逐渐增加趋势。间接说明湖泊中的细菌受到陆源输入和内源输入共同影响。因此，对于深水寡营养的抚仙湖而言，基于湖泊沉积物古菌GDGTs的TEX86指标的温度重建结果比基于细菌GDGTs的MBT/CBT指标的温度重建结果更可靠。重建结果显示2200 Cal BP时期抚仙湖表层湖水温度与目前抚仙湖表层水体温度持平,达到历史时期最高值；之后，水位快速下降、温度骤降，存在快速气候变干事件，并且人类活动扰动的因素可以排除。本研究对于探讨中晚全新世西南季风的演化具有重要意义。最后需特别注意上述两类温度重建指标在不同环境条件下的应用和限定条件。