云南阳宗海沉积物中细菌脱镁叶绿素含量的气候学意义及全新世古气候定量重建

Quantitative reconstruction of Holocene climate is one of the hot and frontier scientific issues in Quaternary climate research, which requires new technologies or methods. Bacteriopheophytin-a (Bph-a), produced by anaerobic phototrophic bacteria (APB), is a newly identified biochemical index with paleoclimate quantitative reconstruction potential. This bacterial community is mainly concentrated at the bottom of the chemocline and the top of the monimolimnion, where it forms a thin APB layer. Moreover, total APB productivity is mainly affected by the light intensity penetrating to the APB layer, which exponentially increases as the thermocline becomes shallow. Therefore, high Bph-a value in the lake corresponded to the shallowing of thermocline. This study intends to take Lake Yangzong in Yunan Plateau as research object and Bph-a contents in sediments as research method. Through the observation of modern process of lake hydrology, reveal the meteorological factors that affect the water stratification of Yangzong Lake, investigate the species of APB communities and measure their production, obtain the surface sediments of Yangzong Lake and determine the content of Bph-a, then the meteorologic significance of the which is established. Get the short sediment core (~40cm), using 210Pb & 137Cs dating method to establish the time scale, using diffuse reflectance spectra (DRS) to test the relative intensity of Bph-a and redness that represents the erosion intensity, scanning element content by XRF, comparing the Bph-a content and meteorological data since 1960 and establish the function relation which is corrected by combining redness, Fe and S elements that may affect APB productivity. Choose ~10 terrigenous organic residues from the obtained 1140 cm –long sediments core of Yangzong lake, date which using AMS-14C and then correct the data to calendar age. Measure the content of Bph-a of the core sediments, using the transfer function for quantitative reconstruction of the high resolution sequence of Holocene climate of the Yangzong lake basin area.

全新世古气候定量重建是第四纪气候研究的热点与前沿科学问题之一，其实现往往需借助新技术和新方法。细菌脱镁叶绿素(Bph-a)是新近发现的具有定量重建古气候潜力的生化指标，产自于湖泊无氧层中厌氧光合细菌(APB)，其群落规模和生产力主要受光照度控制，化跃层越浅沉积物中Bph-a含量越高。本项目拟选取云南阳宗海为研究对象，以细菌脱镁叶绿素为研究手段，通过湖泊水文学现代过程研究，明确影响水体分层的气象要素，调查水体中APB群落种类并测量其生产量，获取阳宗海表层沉积物并测定Bph-a含量，进而确立其气象学意义；提取沉积物短钻并采用210Pb和137Cs测年法建立年代标尺，利用漫反射光谱测得Bph-a相对含量及红度(代表流域侵蚀强度)，利用XRF扫描元素含量，对比同期器测气象数据，建立两者转换函数，结合红度、Fe元素、S元素含量等可能影响APB生产力的要素对转换函数进行校正；利用已获得的阳宗海11.4 m长沉积物钻孔，选取陆源有机残体，通过AMS-14C测得绝对年龄，校正到日历年龄并建立年代序列，测量沉积物中细菌脱镁叶绿素含量，利用转换函数定量重建该区域全新世以来高分辨率气候演化序列。

全新世古气候定量重建与人地系统耦合演化是第四纪气候研究的热点与前沿科学问题。阳宗海是位于云南高原东部的半封闭暖单循环湖泊，该湖泊沉积连续稳定，气候代用指标指示意义明确，是重建西南季风演化、区域环境变迁的良好载体。项目以阳宗海湖泊沉积物岩芯为主要研究对象，利用AMS14C和137Cs-210Pb测年建立可靠年代序列，分析地球化学元素、粒度、烧失量、碳酸盐含量、细菌脱镁叶绿素a含量等代用指标，重建了阳宗海流域近13000年来气候环境演化和人类活动历史，取得的主要成果有：（1）阳宗海水体各水质参数在春、夏、秋季存在明显的季节性垂向分层特征，在冬季和初春混合均匀，湖泊水体每年对流一次，为典型的暖单循环湖；（2）过去13000年阳宗海流域环境演化可划分4个阶段，13000-11000 cal. a BP气候温凉偏湿；11000-8000cal. a BP 气候温湿；8000-900 cal. a BP 气候暖干；900 cal. a BP至今，气候转温湿，人类活动影响加强；13000年来阳宗海未出现持续稳定分层，沉积物中细菌脱镁叶绿素a仅出现在全新世早期和末期的有限时间段内；（3）公元13-14世纪，即我国历史元朝至明朝初年，大量人口迁入云南，耕地需求扩张，原生植被遭到人为性破坏，地表景观发生显著改变，并由此引发一系列生态环境问题。该时期阳宗海沉积物由浅灰色过渡为砖红色，环境代用指标揭示该时期水土流失加剧、流域化学风化减弱、水循环格局转变并导致阳宗海湖泊扩张，在此背景下，汤池渠挖通使得湖水外流，碳循环模式由此发生重大转变。项目首次揭示了近2000年来由于人口数量和土地政策的变化，导致元-明初阳宗海流域地表植被大规模破坏，引发流域内碳循环和水循环格局转换及水土流失加剧，对于湖泊流域综合治理具有重要指导价值。

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