山西宁武高山湖泊群不同类型湖泊中硅藻记录的过去两千年气候与环境变化研究

Existing palaeoclimate reconstructions in the agro-pastoral transitional zone of eastern and northern China do not show consistent patterns of temperature and moisture variations during the multi-centennial periods of the past 2000 years, such as Medieval Warm Period (MWP) and Little Ice Age (LIA). This study will conduct diatom analysis of lake sediment cores from Ningwu alpine lakes in Shanxi Province, northern China, to improve our understandings of both the pattern of climate change in the East Asian monsoon marginal zone and of the relationship between climate change and agro-pastoral conflict in ancient China. We will choose three lakes that are filled in all seasons, Lakes Mayinghai, Gonghai and Pipahai of different sizes, different trophic states and different phytoplankton community compositions, explore firstly the relationship between modern diatoms and lake habitats and water physicochemical parameters, and then examine diatom-based climate and environmental change during the past 2000 years in the different types of lakes on the same site. We will focus on the analysis of diatoms from Lakes Mayinghai and Pipahai sediment cores, and provide palaeoclimate and palaeoenvironmental interpretations of these two lakes based on the data of diatom relative abundance, absolute concentration, biovolume accumulation rate and dissolution index. We will also compare the Lakes Mayinghai and Pipahai diatom results with extant diatom sequence established from Lake Gonghai, associated with the comparison of conventional proxies such as organic matter content, carbonate content and grain size composition, and improve temperature and/or moisture reconstructions during the past 2000 years in the marginal zone of East Asian monsoon. We will then compare and correlate the palaeoclimate reconstruction results with the frequencies of wars between farming Han Chinese groups and northern nomadic groups, to further explore the impact of climate change on ethnic conflict.

目前中国东部/北方地区农牧交错带过去两千年温度和湿度变化的重建在中世纪暖期和小冰期等特征时期表现出很大的不一致性，制约着季风边缘区气候变化规律的认识，同时也制约着气候变化和农牧冲突之间关系的认识。本项目以山西宁武高山湖泊群为研究对象，选取常年有水、不同大小、不同营养状况、不同浮游植物群落结构组成的三个湖泊马营海、公海和琵琶海，在建立现代硅藻和湖泊环境之间关系的基础上，探究同一地点不同类型湖泊中硅藻记录的过去两千年气候与环境变化。项目集中于马营海和琵琶海湖泊岩芯的硅藻分析，通过硅藻的相对丰度、绝对浓度、生物体积积累速率、溶解指数等参数建立马营海和琵琶海的硅藻变化序列，并结合常规指标与已有的公海硅藻序列进行对比研究，提高季风边缘区过去两千年温度和/或湿度变化的重建。然后对气候变化重建结果和中国古代农牧民族间战争频率数据进行对比和相关分析，探究农牧交错带温度和/或湿度变化对农牧冲突的影响。

中国北方季风边缘区是东亚夏季风和西风带相互作用影响的气候敏感区，本项目选取了山西北部宁武高山湖泊群同一地区相同气候条件下不同类型的两个湖泊马营海和琵琶海，采取湖泊沉积岩芯样品分析和湖泊现代水体样品分析相结合的方案，主要通过硅藻和色素指标一方面重建该地区全新世的气候与环境变化并探索全新世东亚夏季风演化的规律和机制，另一方面追溯人类活动对湖泊环境与生态的影响历史并为当前的湖泊生态修复提供生态背景和修复目标。马营海湖泊岩芯的硅藻群落结构组成的演替揭示了从早全新世到中全新世气候的变暖，浮游硅藻生物体积量的减少反映了从中全新世到晚全新世温度的降低，结合已有的该地区公海孢粉定量重建的中全新世降水最高的结果，可知中全新世该地区气候最适宜、夏季风最强，揭示了北半球冰盖的影响。马营海湖泊岩芯的常规指标、岩芯扫描和硅藻等多个指标揭示了该湖泊在约一千年前左右沉积环境发生了剧烈的变化，这很可能归咎于人类活动的影响，同时人类活动加剧也是最近湖泊富营养化的主要原因。马营海连续一年季节性的现代硅藻观测数据揭示了星杆藻的生态指示意义重在硅而非氮或湖泊分层。