云南抚仙湖沉积生物标志物记录的三万年以来温度变化研究

Reliable palaeo-temperature records from southwestern China in low latitude are important for our understanding the driving mechanisms of the Southwest monsoon intensity. This project proposes to get a long lacustrine sediment core from an oligotrophic deep lake – Fuxian Lake in southwestern China to reconstruct paleo-temperature during the past 30 ka. Age-model will be established by a series of dates obtained from various dating methods such as Pb-210, Cs-137 and AMS C-14. Isoprenoid glycerol dialkyl glycerol tetraethers (iGDGTs) as a quantitative index of temperature in the lake will be determined by a systematic study of observations on its modern process, and then an iGDGTs-based mean annual temperature record of lake water will be reconstructed to reveal temperature changes during the Last Glacial Maximum, the last deglaciation and Holocene, and to explore the timing, rate and magnitude of a series of abrupt climatic events over the last 30 ka. Element content and grain size data-based the Southwest monsoon intensity reconstructions will be used to examine possible relationship between temperature in southwestern China and the Southwest monsoon intensity. The simple comparision will be carried out on the paleotemperature records from low and high latitudes to evaluate their phase relationship and explore their driving mechanisms. This project has scientific significance for evaluating regional palaeoclimate models and prediction of future climate change.

我国低纬度西南地区可靠的长尺度温度记录对研究西南季风区季风演化规律和驱动机制具有重要意义。本项目以我国西南地区深水寡营养湖泊—抚仙湖为研究对象，钻取过去30ka以来的连续沉积岩芯，运用多种测年手段（如Pb-210、Cs-137；AMS C-14）精确建立岩芯的年代标尺。基于系统的现代过程研究确定湖相环境中奇古菌iGDGTs所指代温度对应的水层和季节性差异。利用基于奇古菌iGDGTs的TEX86指标定量高分辨率重建30ka以来的温度记录，探寻我国西南地区30ka以来末次盛冰期、冰消期等重大气候突变事件发生的起讫时间、温度变幅和变率。结合常规环境代用指标重建的西南季风强度，探讨西南地区温度和西南季风强度的关系。通过区域和半球尺度对比，认识高、低纬地区温度变化的相位关系，进而探讨其动力学机制。本项目研究将为全球变暖背景下西南季风区气候模拟和趋势预测提供科学依据。

本项目以我国西南地区深水寡营养湖泊——抚仙湖为研究对象，钻取过去26ka以来的连续沉积岩芯（FXH-1孔），运用9个AMS 14C测年及平行钻孔的XRF岩芯扫描比对结果精确建立了岩芯的年代标尺。利用有机生标四醚脂类化合物（6甲基-brGDGTs）和正构烷烃（n-alkanes）指标重建我国西南地区末次冰盛期以来的古气候。获得了西南地区末次冰盛期以来气候变化的框架性总体特征以及末次冰盛期（26~17.7 cal ka BP）、末次冰消期（17.7~11.8 cal ka BP）、全新世早期（11.8~6 cal ka BP）、全新世中期（6~3 cal ka BP）、全新世晚期（3 cal ka BP至今）、YD事件（12.8-11.8 cal ka BP）的起讫时间和变率变幅。同时发现，相较于东亚季风影响区内的湖泊记录，西南地区的大部分湖泊记录的YD气候事件变幅较小。并且，全新世的降水最适期出现在早全新世，而温度最适期出现在中全新世，具有不同步性。区域对比结果证明太阳辐射量对气候演变的驱动可能是通过以季风为代表的热带海洋—气候过程直接作用于中—低纬度地区，而无需经由高纬地区的冰盖涨缩间接传导。