青藏高原介形类电导率转换函数的建立及其在古环境重建研究中的应用

Ostracod ,bivalved microcrustaceans living in all kinds of natural water bodies, given out significant information of habitate condition, were used as a sensitive monitor in palaeo-environmental change. Ostracod transfer function which was based on database of ostracods and environmental factors, was rapidly developing as a quantitave indicator in palaeolimnology research. The Tibetan Plateau which was called as the third pole, providing a natural lab for global past climate changes. .There are plenty of lakes scattered on the plateau could supply sediments for analysing indexes of environment in past climate change research. .This application is planning to research on samples of modern ostracod and its habitate condition, including water sample and water muti-parameter, to produce a database including species of modern ostracods and environmental factors such as temperature, electric conductivity, dissolved oxygen, and so on. A forward transfer function will be set up based on this database and muti-variable gradient analyses using canonical correspondence analysis (CCA), partial canonical correspondence analysis (PCCA) and dentrended correspondence analysis (DCA). The best taxon optima and response model, evaluate by indexes (root mean squared error of prediction and coefficient of estimated and measured value etc.), will be selected as a final transfer function model. Input data of fossil or sub-fossil ostracod from core sediments to the final model will produce reconstucted data. This ostracod transfer function will be used for environment reconstrction of lake Pumayum Co to preview past climate change of this area from mid to late Holocene.

介形类动物群的生长发育与宿生水体环境密切相关，可作为环境变化的敏感指示器应用于过去环境变化。基于现代介形类与环境因子数据库的转换函数研究是定量重建过去环境变化的新方法，在古湖泊学研究中有重要的应用价值。青藏高原上广泛分布的湖泊为过去环境变化研究提供了蕴含丰富信息的湖泊沉积物,但目前利用介形类与水体环境因子建立转换函数进行环境定量重建仍缺少深入研究。本项目拟通过大范围系统采样，从青藏高原湖泊及其他天然水体中采集现代介形类样品，并同步监测宿生水体水质参数，建立现代介形类与环境因子数据库，以此数据库为基础进行环境梯度分析（如CCA、PCCA、DCA等），进而建立介形类-电导率转换函数模型，并将此模型应用到藏南普莫雍错钻孔介形类古电导率恢复中，对比重建结果讨论该湖泊流域中晚全新世以来的环境变化特征。

介形类动物群的生长发育与宿生水体环境密切相关，可作为环境变化的敏感指示器应用于过去环境变化。青藏高原上广泛分布的湖泊为过去环境变化研究提供了蕴含丰富信息的湖泊沉积物,但目前利用介形类与水体环境因子建立转换函数进行环境定量重建仍缺少深入研究。本研究通过大范围系统采样，从青藏高原湖泊中采集现代介形类样品并同步监测宿生水体水质参数，建立现代介形类与环境因子数据库并以此为基础进行环境梯度分析，进而建立介形类-电导率转换函数模型并将此模型应用到藏南普莫雍错钻孔介形类古电导率恢复中，对比重建结果讨论了普莫雍错流域中晚全新世以来的环境变化特征。. 青藏高原湖泊表层沉积物中共发现和鉴定了10属12种介形虫，分别为白玻璃介、西藏玻璃介、玻璃介未定种、吉隆豆形玻璃介、河星介、异星介未定种、吉隆真星介、土星介未定种、湖陆花介、背瘤白花介、中华小白花介和意外湖花介。研究发现介形类属种随湖水电导率变化呈现差异性组合类型，即中华小白花介-背瘤白花介-西藏玻璃介；吉隆真星介-吉隆豆形玻璃介-湖陆花介-白玻璃介；意外湖花介三个组合分别指示淡水-微咸水、微咸水-咸水、咸水-卤水湖泊环境。通过梯度分析，利用介形类-电导率数据建立转换函数，获得的最优模型的实测值与推导值的相关性R2=0.67，推导误差RMSEP=0.47，其跟靴法检验结果（Boot_R2=0.61）显示模型可信度较高，利用介形类-电导率转换函数模型重建了普莫雍错中晚全新世以来的古电导率变化。通过多环境代用指标的综合对比，讨论和恢复了普莫雍错流域过去环境变化，即普莫雍错6000 aBP以来总体的环境变化经历了偏温凉向偏暖发展的演化过程，并伴随着几次代表性的极端气候事件，包括5200 aBP左右的暖事件、2500 aBP左右的高湖面期、1300 aBP左右的强冷事件等。通过与青藏高原及季风区代表性气候记录的对比，认为这一环境演化过程是对季风活动在全新世以来的逐渐减弱的响应与适应。此外，4300 aBP左右可能是季风活动明显减弱导致的重要的气候转变时段，在普莫雍错表现为：4300 aBP可能是冰川融水补给对普莫雍错湖泊水面波动的影响程度由弱到强的转变时段。