【作者】 黄元辉；

【导师】 蒋辉；

【作者基本信息】 华东师范大学 ， 第四纪地质学， 2008， 博士

【摘要】 季风是全球中低纬地区的特有现象,对该区气候、环境、政治、经济、文化以及人们的日常生产生活等各个方面均产生重要影响,因此,探讨季风的形成、演变、发展及其对区域与全球气候环境变化的影响已是目前全球变化研究的热点之一。有关东亚季风演变陆上和深海都开展了大量工作。然而,无论是末次冰消期以来南海北部表层海水温度研究还是表层海水盐度研究,已有研究结果彼此之间明显存在一定差异,因此,末次冰消期以来南海北部气候环境变化过程到底如何?东亚季风区气候环境变迁海陆记录是否一致?这是两个至今未能很好解决的问题。针对上述问题,本文对南海北部MD05-2904孔上部0-398 cm段沉积样品进行硅藻分析,从古生态学角度探讨深海硅藻对末次冰消期以来南海北部气候环境变迁的沉积响应,并对东亚季风区内气候环境变迁海陆记录进行了详细对比。本项研究的主要结论和认识如下:1、MD05-2904孔上部0-398 cm段152个硅藻样品中共鉴定硅藻46属98种(含变种),其中既出现淡水种和沿岸种,也出现外洋暖水种,但主要以热带、亚热带浮游硅藻菱形海线藻Thalassionema nitzschioides及其小形变种Thalassionema nitzschioides var.parva为主。2、对MD05-2904孔0-398 cm段硅藻鉴定结果进行主成分分析,结果表明,末次冰消期以来影响MD05-2904孔附近海域沉积硅藻组合特征变化的主要环境影响因子分别为表层海水温度和表层海水盐度;主成分分析结果同时显示,末次冰消期以来南海北部气候环境变迁大致可以划分为五个阶段,分别与波令-阿勒罗德时期(约15.0-12.9 kaBP)、新仙女木期(约12.9-11.6 kaBP)、早全新世(约11.6-8.5kaBP)、中全新世(约8.5-3.8kaBP)和晚全新世(约3.8-0.8kaBP)一一对应,其中:波令-阿勒罗德时期表层海水温度逐渐上升,表层海水盐度波动下降;新仙女木期第一阶段表层海水温度略有下降,其后波动上升,而新仙女木期表层海水盐度明显上升;早全新世表层海水温度波动上升,表层海水盐度持续偏低;中全新世表层海水温度最高,表层海水盐度波动上升;晚全新世表层海水温度逐渐下降,表层海水盐度仍波动上升直至约1.2kaBP后才再次下降。3、对西太平洋边缘海148个表层硅藻样品中菱形海线藻及其小形变种百分含量分布与表层海水温度关系进行研究,确定菱形海线藻小形变种Thalassionema nitzschioides var.parva为典型的暖水种硅藻,而菱形海线藻Thalassionema nitzschioides为广布种;在此基础上,本文探讨了菱形海线藻小形变种与所有菱形海线藻百分含量的比值(简称硅藻Rparva值)可能具有的温度指示意义;结果表明,MD05-2904孔上部0-398 cm段硅藻Rparva值时间序列与根据主成分分析的末次冰消期以来南海北部表层海水温度变化时间序列变化趋势相当一致,表明硅藻Rparva值可以作为一种独立的、有效的温度指数运用于南海北部陆坡末次冰消期以来表层海水温度变化的研究。4、温度变化区域对比结果表明,末次冰消期以来南海北部表层海水温度变化趋势不仅与中国陆上温度变化趋势高度一致,而且与全球温度变化趋势也具有一定的可比性,表明东亚季风区全新世温度变化可能不仅受到区域性气候因子的影响(如季风演变等),可能也是某些全球性气候因子作用的综合结果(如太阳辐射变化等)。5、末次冰消期以来南海北部陆坡处表层海水盐度变化是多种因素的综合结果;季风降水变化、海平面变化以及珠江口冲淡水强度变化可能是其中的三个主要因素;不过,海平面变化及珠江口冲淡水强度变化主要作用于末次冰消期及早全新世时期,在中晚全新世其影响作用明显减弱,而季风降水变化对表层海水盐度变化的影响则持续作用于整个末次冰消期。季风降水变化趋势与南海北部末次冰消期以来表层海水盐度变化趋势基本一致,表明季风降水变化可能是末次冰消期以来南海北部陆坡处表层海水盐度变化的最重要影响因素;盐度变化区域对比结果表明,尽管东海、南海、苏禄海以及西赤道太平洋等同属东亚季风区内,但季风降水对各海区表层海水盐度影响程度并不尽一致,南海北部表层海水盐度对季风降水变化响应最为直接。6、关于新仙女木期南海北部气候环境变化,MD05-2904孔硅藻记录显示:南海北部深海记录中的确存在该事件的相关记录;事件发生期间南海北部表层海水温度并没有发生明显变化,仅在新仙女木期早期略有下降;但南海北部表层海水盐度在新仙女木期明显上升,新仙女木期中期盐度上升尤为显著。7、从末次冰消期以来南海北部表层海水温度和表层海水盐度变化硅藻记录与陆上相关记录对应良好这一结果来看,主要基于陆上研究提出的″东亚环境季风控制″假说同样适用于南海北部,东亚季风演变对南海北部末次冰消期以来的气候环境变迁具有重要影响。更多还原

【Abstract】 Monsoon is a typical phenomenon in low to mid-latitudes which plays a very important role in changing the regional climate,environment,politics,economy as well as the way of people’s living and the mode of production.Consequently it has been one of the hottest topics of global change research on formation,evolution,and development of the monsoon system.Great efforts have been made related to the study of East Asian Monsoon(EAM)with samples from both inlands and deep seas.But it seems irreconcilable among various records of surface seawater temperature(SST)and surface seawater salinity(SSS)from the northern South China Sea(SCS),which is also decoupled from terrestrial records.Thus,the history of climatic change in the northern SCS since the last deglaciation and whether the monsoonal records from inlands and deep seas are comparable to each other remain open to debate.The upper part(0-398 cm)of core MD05-2904 from the northem SCS was applied to carry out diatom analysis in order to investigate how diatoms responded to climatic change around the northern SCS over the last 15 kaBP.Based on the results of diatom analysis,an extensive comparison was made between the monsoonal records from core MD05-2904 and other sites.Primary conclusions are specified as follows:1.A total of 98 diatom taxa belonging to 46 genera had been identified from the upper part (0-398 cm)of core MD05-2904.The dominant diatoms were tropical/subtropical planktonic diatom taxon Thalassionema nitzschioides and Thalassionema nitzschioides var.parva,which were accompanied with small numbers of freshwater species,coastal species,and oceanic species.2.A program of Principal Component Analysis(PCA)was employed here and the first two main environmental factors controlling the characters of sedimentary diatom assemblages in the northern SCS were attributed to SST and SSS.According to the change of SST and SSS,five periods can be confirmed corresponding to Bφlling/Allerφd stage,Younger Dryas stage,early, middle,and late Holocene individually.Bφlling/Allerφd stage was characterized by an increasing SST and a decreasing SSS.During the Younger Dryas stage,SST decreased slightly at the first phase while SSS rose up dramatically.SST was higher in the mid-Holocene which was named Megathermal,and it kept rising or dropping in the early and late Holocene respectively.SSS kept declining sine the early Holocene,but this trend stopped at ca.1.2 kaBP.3.A total of 148 samples from the seafloor of the western Pacific were utilized to ascertain the distribution of Thalassionema nitzschioides and Thalassionema nitzschioides var.parva in waters with different SST.We confirmed Thalassionema nitzschioides var.parva is a warm water species and Thalassionema nitzschioides is a cosmopolitan and purposed the ratio of[T. nitzschioides var.parva /(T.nitzschioides+nitzschioides var.parva)],which is short for Rparva, can be regarded as a SST-index as to document SST changes in the northern SCS.The Rparva-based SST record is consistent with that of PCA analysis.4.Diatom-based SST record in the northern SCS is not only in concert with the terrestrial SST records but also comparable to other SST records around the world,which indicates that temperature change in the EAM area could be involved in both regional and global climatic mechanisms(such as monsoon and solar radiation respectively).5.Diatom-based SSS record was a combined result mainly due to monsoonal precipitation, sea-level change,and runoff from Pearl River.The influence of sea-level change and runoff from Pearl River on SSS declined sine the mid to late Holocene while the effect of monsoonal precipitation had been pervasive over the last 15 kaBP.Consequently monsoonal precipitation might be the most influential factor for the change of SSS around the northern SCS.Comparison between SSS records from East China Sea(ECS),southern and northern SCS,Sulu Sea,and western equatorial Pacific shows that SSS record from the northern SCS responded directly to the change of monsoonal precipitation.6.Younger Dryas event has also been recorded in both our diatom-based SST and SSS record. But change of SST was not as conspicuous as that of SSS.7.Consistency of climatic records between the inlands and deep seas around the EAM area suggests that northern SCS has been under the EAM regime sine the last deglaciation like the inlands.更多还原