【作者】 李亮；

【导师】 马春梅；

【作者基本信息】 南京大学 ， 自然地理学， 2017， 硕士

【摘要】 过去2ka是研究气候变化的重要时间段,其中的中世纪暖期、小冰期和现代暖期倍受关注,但是一些气候阶段的起止时间、温湿配置等还存在争议。本文选取赣中玉华山沼泽泥炭钻孔为研究对象,进行AMS14C测年,运用Bacon模型建立完整的年代框架。然后运用孢粉、粒度、腐殖化度、烧失量、Rb/Sr、Zr/Rb等多指标分析研究过去2ka来气候变化,重建了过去2ka的植被变化和火灾历史,并综合分析了特征时段的气候变化规律和驱动机制。具体结果如下:1.岩性、粒度和环纹藻分析结果表明YHS2钻孔在过去2 ka时间里,沉积环境表现为湖泊向沼泽泥炭演化的沉积过程;2.多指标分析揭示过去2 ka来研究区域的气候变化阶段为:(1)0～753 A.D.:以桤木为优势种的乔灌木为主,并伴有蒿属为主的旱生草本,乔灌木多于旱生草本,气候湿润,沉积环境属于泥炭过度到粘土层,可能逐步演化成湖泊;(2)753～981 A.D.:以蒿属为优势种的旱生草本为主并伴有桤木、松属为优势种的乔灌木的植被环境,旱生草本多于乔灌木,该阶段气候较为干旱,时间上大约为隋唐暖期;(3)中世纪暖期(981～1455A.D.)该阶段乔灌木百分比升高,旱生草本减少,植被主要以桤木为优势种的乔灌木。岩性上主要为粘土到沼泽泥炭的过渡阶段,气候上整体表现湿润,但是仍然出现次级波动,表现为”两湿夹一干”格局。(4)小冰期(1455～1947 A.D.):该阶段孢粉浓度有所降低,旱生草本增加,禾本科增加较为明显,乔灌木减少,其中桤木突然减少,几乎为零,整体上表现为冷干,中间存在次级波动,表现为”两干夹一湿”格局。桤木在该阶段迅速减少,结合沉积环境和禾本科增加认为造成这样的变化是由于人类活动和自然环境变化共同作用,而自然环境占有主导地位。(5)1947～2014A.D.:该阶段孢粉浓度较高,乔灌木中松属增加,栗属也出现增加,常绿栎减少,草本植物主要以禾本科、蒿属、伞形科为主。植被类型主要为马尾松林、栎属等为主的乔灌木和经济作物为主的草本植物并存的植被类型。降水偏多,该阶段处于现代暖期,气候主要表现为暖湿。3.研究区与北半球以及我国东部季风区的气候变化具有较好的对应关系,说明过去2 ka以来玉华山泥炭沼泽的气候变化与东部季风区具有相对一致性。4.过去2 ka的特征时期在季风区表现明显,中世纪暖期整体表现为暖湿,而小冰期整体表现为冷干。其中温度变化的主要驱动因子是太阳活动,湿度变化的主要驱动因子是东亚季风和ENSO。更多还原

【Abstract】 The past 2 ka was an important period for studying climate change.The study of the Medieval Warm Period,the Little Ice Age and the Modern Warm Period have attracted much attention.However,many studies disagree on the climate conditions that prevailed during the key phases.In this study,a sediment core obtained from Yuhua Mountain in the middle of Jiangxi Province was constructed.Firstly,we selected samples for AMS 14C dating and built the age framework of Bacon age modeling.Then we combined pollen,grain-size,degree of humification,loss on ignition(LOI),Rb/Sr,Zr/Rb to analyse the climate change and rebuild vegetation changes since the past 2 ka and fire history.The law of climate change and the driving mechanism of the characteristic period are analyzed.The results are as follows:1.Combining with concentricystes changes,we analyzed the grain-size composition.The results indicate process from an active lacustrine environment to stagnant marsh condition.2.Multi-proxies analysis reveals that climate change in the past 2 ka can be classified:1).During 0～753 A.D.,the vegetation was abundant,of that Alnus is the dominant of trees,also have some upland herbs such as Artemisia.The percentage of trees is higher than that of upland herbs.The climate was wet and warm.The semiment indicates a change to lacustrine environment.2).During 753～981 A.D.,Alnus reduced with increasing of Artemisia and Pinus Which indicating the climate turned to dry.The period is about the sui and tang periods.3).Medieval Warm Period(MWP,981～1455A.D.).In this stage,the percentage of shrubs increased,the upland herbs decreased,and the vegetation was mainly planted with Alnus.On the lithology is mainly for the clay to the transition of peat swamp,humid climate on performance,but there is still secondary fluctuations.In details,at 981～1047 A.D.and 1238～1455 A.D.the climate were wet and warn,while at 1047～1238 A.D.the climate was dry and warm.4).Little Ice Age(1455～1947 A.D.).In this stage,the percentage of shrubs decreased and the upland herbs increased.Alnus disappeared rapidly.Poaceae increase rapidly.We think the cause of this is the deforestation of human.The climate of LIA is cold and dry,but there is still secondary fluctuations.In details,at 1455～1626 A.D.and 1836～1947 A.D.the climate were dry and cold,while at 1626～1836 A.D.was wet and cold.In this stage,the percentage of Alnus was decreasing rapidly.Combining with high percentage of Poaceae and the lithology,I think the decreasing of Alnus is due to the combination of human activity and nature change.The nature change maybe the dominant reason.5).Modern Warm Period(1947～2014 A.D.).The dominant vegetation in this stage is Pinus and Poaceae.In this stage trees is higher than upland herbs.The climate was warm and wet.3.The comparative analysis shows that the climate change of the study area respond to the eastern monsoon region climate trends in the past 2 ka.4.High resolution pollen data records indicated unique climate period fluctuate severely,the climate at MWP wa warm-humid,LIA was cold-dry.Solar activity was the fundamental force that drove the temperature and the main driver of humidity change is the east Asian monsoon and ENSO.更多还原