【作者】 刘冬雁；

【导师】 李巍然；

【作者基本信息】 中国海洋大学 ， 海洋地质， 2009， 博士

【摘要】 亚洲季风的形成和演变是国际全球变化研究中倍受关注的重大科学问题之一。黄土是中国的特色研究材料。目前,以位于东南季风区的中国北方黄土为材料对亚洲季风的研究已取得丰硕成果,而西南季风区黄土研究力度相对薄弱。同时,西风对黄土的搬运和气候记录有重要影响,但相对于亚洲季风来说,西风研究也有待深化。在第四纪黄土古气候演变定量研究中,前人成果多集中于周期分析,突变研究亦需要加强。本文以青藏高原东南缘川西高原甘孜A剖面黄土-古土壤序列为材料研究早更新世晚期以来的气候变化问题。川西黄土形成于早更新世晚期以来；西南季风是该区的主要水汽来源,可以磁化率作代用指标；高空西风、近地面风是该区黄土搬运的主要营力,可以粒度作代用指标。本文对磁化率和敏感粒度指标时间序列进行了定量的周期分析和突变分析,给出了早更新世晚期以来西南季风和高空西风的周期性演变过程和近地面风突变的时间分布,并对相应的气候变化驱动机制进行了初步探讨。磁化率记录的构造时间尺度阶段性特征和100ka滤波曲线特征均表明,西南季风演变过程中存在中更新世气候转型(MPT),该气候转型期与青藏高原东南缘约0.6Ma BP以来的强烈构造抬升在时间上一致,暗示了青藏高原隆升对MPT的贡献。磁化率时序功率谱分析检出典型的地球轨道周期和岁差拍频周期,说明西南季风演变明显受天文因素影响、对太阳辐射具有非线性响应、具有热带特征。磁化率时序经验模态分解(EMD)结果表明：存在100ka周期,其波形特征与偏心率100ka短周期理论值波动过程一致,指示印度季风系统变化的主要驱动因素可能是低纬太阳辐射；存在准200ka周期,其成因需要进一步研究；存在约400ka周期,可能对应理论值为400ka的偏心率长周期。总之,西南季风可能是直接响应轨道驱动。结合甘孜A剖面实测粒度数据,本文采用用三个对数正态分布叠加进行全样粒度频率曲线数据拟合的方法,将全样粒度组成中代表不同动力的粒度组分加以数学分离。分离出的指示高空西风演变的“细粒组分”时间序列EMD结果表明：高空西风演变亦明显受天文因素影响;但检出的准100ka周期在约0.66MaBP以来具有锯齿状波形,指示高空西风演变可能与全球冰量变化100ka周期关系密切；亦存在准200ka周期和约400ka周期；首次检出一个约600-700ka的波动,可能对应约约700ka的偏心率更长周期。在大时间尺度周期上,青藏高原隆升高度可能对高空西风演变有显著影响,该结果支持汤懋苍等的“青藏高原隆升存在气候临界高度”的假说,在约0.66MaBP前后,青藏高原才隆升至水分冻结高度(Hf:3000-3500m)以上。>40μm粗颗粒百分含量时间序列滑动t-检验(MTT)结果表明,近地面风突变点大致位于1.12、1.06、1.0、0.95、0.90、0.85、0.80、0.73、0.64、0.59、0.54、(0.49.) 0.46、0.39、0.29、0.25、0.20、0.14、(0.11、)0.08、0.05、0.03 MaB.P.附近,具有准100ka和准50ka的间隔规律。该突变点系列和青藏高原构造上升的地质记录在年龄上具有对应性；准100ka的间隔规律应当归于“构造-气候旋回”范畴,地球轨道偏心率短周期可能导致了该旋回的形成。古气候突变亦与长江黄河阶地形成时代以及青藏高原构造活动具有良好的对应关系；气候不稳定变化控制着阶地的形成时代；阶地是气候变化和构造抬升耦合的产物,受控于气候-构造耦合系统,具有准100ka和准200ka的旋回周期,亦应归于“构造-气候旋回”范畴。更多还原

【Abstract】 The formation and evolution of Asian Monsoon is an important subject in the study of global changes.Loess is a research material characteristic of China.So far, while great achievements have been made in research on Asian monsoon utilizing loess in north China which locates in the south-east monsoon region as main research material, research on loess in south-west monsoon region is relatively weak. The westerly plays an important role in the transportation of loess and has an significant influence on climatic recording. Compared with Asian monsoon, research on the changes of the westerly is to be furthered. Former quantitative studies on paleoclimate using Chinese loess were mostly concentrated on the climate periodicity, while that on the abrupt changes needs to strengthen.This thesis studies the changes of paleoclimate since the late early Pleistocene,using the loess-paleosol sequences in Garze A section on West Sichuan Plateau as research materials.Previous research shows that the widely distributed loess on West Sichuan Plateau came into being since the late early Pleistocene; Southwest monsoon is the main transporter of water vapor,which can be studied using the magnetic susceptibility as its proxy;the westerly and the near-surface wind are the major driving forces for the transportation of loess in this region,which can be studied using the grain size as its proxy. This thesis studies the quantitative periodical analysis and abrupt change analysis of paleoclimate proxies for their magnetic susceptibility and the grain size and discusses the mechanism of paleoclimatic evolutionary in this region.Both of stage feature of the magnetic susceptibility sequence in tectonic time scale and the feature of 100kyr filter curve suggest that there exists mid-Pleistocene Transition (MPT)in the evolutionary process of southwest monsoon. This transition was consistent in time with the dramatic uplift on the southeast rim of Qinghai-Tibet Plateau,which implies the contribution of the uplift of Qinghai-Tibet Plateau to the climatic transition in the mid-Pleistocene. The orbital period and precession beat periods detected from power spectrum analysis of magnetic susceptibility time sequence suggest that the evolution of southwest monsoon is influenced by astronomical factors, Indian monsoon system has nonlinear responds to solar insolation and southwest monsoon has tropical features. Experimental mode decomposing(EMD) results of magnetic susceptibility time sequence shows that there exists the 100kyr cycle whose waveform feature is consistent with the theoretical value of the fluctuation period of eccentricity (100kyr), suggesting that the main driving force of the Indian monsoon system is not global ice volume but solar insolation at low latitudes; there also exists quasi-periodic 200kyr cycle whose formation needs further study; a 400kyr cycle is detected and it probably corresponds to the long period of eccentricity whose theoretical value is 400kyr.In all,the southwest monsoon is probably driven by the orbital forcing but not the global ice volume.This thesis introduces the concrete way of data fitting of sample grainsize frequency by superposing three lognormal distributions into a mixed distribution and uses it to partition the bulk sample into three components mathematically.One of the partitioned component has the significance of single genesis.EMD is used for analyzing time-frequency characteristic of the fine grained component,which may indicate upper westerly. The results indicate that, the evolution of upper westerly is influenced by astronomical factors as well.The quasi-periodic 100kyr cycle has changed in sawtooth shape since 0.66MaBP,which suggests that evolution of upper westerly has close relationship with the change of global ice volum (quasi-periodic 100kyr cycle); The quasi-periodic 200kyr cycle and 400kyr cycle are also detected;and the 600-700kyr period is detected for the first time,which probably corresponds to the quasi-700kyr eccentricity long period. On a large time scale, the evolution of upper westerly responds remarkably to the uplift height of Qinghai-Tibet Plateau probably. The Qinghai-Tibet Plateau reached the freezing height above 3000 to 3500m, at about 0.66MaBP.Results of the abrupt change by moving-t technic(MTT) of the time sequence of the percentage of>40μm bulk grain size component suggests that the abrupt change points of near-surface wind appeared at about 1.12,1.06,1.0,0.95,0.90,0.85,0.80, 0.73,0.64,0.59,0.54 (0.49),0.46,0.39,0.29,0.25,0.20,0.14(0.11),0.08,0.05,0.03 MaBP, at intervals of 100kyr and 50kyr. This abrupt change points sequence correspond well with ages from other geological records of tectonic uplift on the southeastern Qinghai-Tibet Plateau. The quasi-periodic cycle of 100kyr should be attributed to the tectonic-climatic circulation which results from the period of the earth’s eccentricity.The time for abrupt change of paleoclimate is well correlated to the formation time of the Yangtze River and the Yellow River terraces as well as the tectonic activity of Qinghai-Tibet Plateau. The forming age of terraces was controlled by the climatic instadibility.River terraces with quasi-periodic cycle of 100kyr and 50kyr is the coupling product of the climatic change and tectonic uplift, so it should belong to the category of tectonic-climatic circulation.更多还原