湛江湖光岩玛珥湖55ka以来植硅体化石记录及古环境变迁

The study of biogenic proxy of tropical and subtropical regions provides important evidence about the process and history of vegetation and environmental changes, and is of globally importance for understanding the dynamic mechanism of paleoclimatic and paleoenvironmental changes. The sediments from the Huguangyan Maar lake in Guangdong Province offer a continuous high-resolution record of the past 55 ka about environmental and vegetational changes. The studies of chronology, and physical, chemical environmental proxies have provided much important information about the paleoenvironmental and paleoclimatic histories. The phytolith, a new biogenicl proxy, has been used to determine the nature and types of plants in this area since the last 55 ka. This study presents a preliminary result about the characteristics of phytolith shapes, the variations of the fossils assemblages, and their significance for environmental changes. Moreover, the author probes the process of special specie evolution and their relationship to climatic parameters. The history of fire has been reconstructed based on the variations in charcoals. The main results and conclusions include: 28 types of phytoliths from 233 samples have been identified. Their environmental meanings are investigated in detail. Based on the variations in phytolith associations, the history and process of climatic and environmental changes in the last 55 kaBP have been established for this region. Climatic changes experienced eight intervals during this period, showing the variations of hot-humid to cool-try climate in the ten thousands years scale, and a shorter dry-hot climate condition in millennial scale. The history of palm plant has been established in this region. Two peaks appeared from 55-39 ka and since the Holocene. Plants in Bambusoideae have been growing in this area all the period, representing the impact of the East Asian summer monsoon. Bamboo plants have similar tendency in their abundance to palm plants, but with a lag of 1-2 ka BP. Panicoideae plants, the representative of C4 plants, have 6 flourishing periods occurred at 54.5, 44, 41.5, 32.5, 14, and 10 kaBP, respectively, reflecting 6 times short-term arid events. Charcoal record from the Huguang Marr lake reveals the history of nature fire, that mostly happened in dry period of last glacial from 55-10 kaBP, centered at 50-45, 40-35, 30-25, and 20-15kaBP, showing about a cycle of 10,000 years.

黄东海及朝鲜海峡冰后期陆架沉积物的环境磁学研究

There are four chapters in this dissertation. The first chapter briefly synthesizes the basic theories, methods and present-day applying situation of environmental magnetism. The second chapter probes into the magnetic mineral diagenesis in the post-glacial muddy sediments from the southeastern South Yellow Sea and its response to marine environmental changes, using the muddy sediment of Core YSDP103 formed in the shelf since about 13 ka BP. The third chapter illustrates the high-resolution early diagenetic processes by investigating the rapidly deposited muddy sediments during the last 6 ka in Cores SSDP-102 and SSDP-103 from the near-shore shelf of Korea Strait. The fourth chapter presents the results of detailed rock magnetic investigation of the surface sediments from the fine-grained depositional area on the outer shelf of the East China Sea in an attempt to provide environmental magnetic evidence for the provenance of the fine-grained deposit. Core YSDP103 was retrieved in the muddy deposit under the cold eddy of the southeastern South Yellow Sea, and the uppermost 29.79 m core represents the muddy sediments formed in the shelf since about 13 ka BP. The lower part from 29.79 to 13.35 m, called Unit A2, was deposited during the period from the post-glacial transgression to the middle Holocene (at about 6 ~(14)C ka BP) when the rising sea level reached its maximum, while the upper part above 13.35 m (called Unit Al) was deposited in a cold eddy associated with the formation of the Yellow Sea Warm Current just after the peak of post-glacial sea level rise. For the the uppermost 29.79 m core, detailed investigation of rock-magnetic properties and analyses of grain sizes and geochemistry were made. The experimental results indicate that the magnetic mineralogy of the core is dominated by magnetite, maghemite and hematite and that, except for the uppermost 2.35 m, the magnetic minerals were subject to reductive diagenesis leading to significant decline of magnetic mineral content and the proportion of low-coercivity component. More importantly, ferrimagnetic iron sulphide (greigite) is found in Unit A2 but absent in Unit Al, suggesting the control of marine environmental conditions on the magnetic mineral diagenesis. Magnetic parameters show abrupt changes across the boundary between the Unit Al and A2, which reflects a co-effect of environmental conditions and primary magnetic components of the sediments on the diagenesis. Alternating zones of high and low magnetic parameters are observed in Unit A2 of Core YSDP103, which is presumably due to periodic changes of the concentration and/or grain size of magnetic minerals carried into the study area. Cores SSDP-102 and SSDP-103, two studied sediment cores from the Korea Strait contain mud sequences (14 m and 32.62 m in thickness) that were deposited during the last 6,000 years. Analyses of grain sizes and geochemistry of the cores have demonstrated that the sediments have uniform lithology and geochemical properties, however, marked down-core changes in magnetic properties suggest that diagenesis has significantly impacted the magnetic properties. An expanded view of early diagenetic reactions that affect magnetic mineral assemblages is evident in these rapidly deposited continental shelf sediments compared to deep-sea sediments. The studied sediments can be divided into four descending intervals, based on magnetic property variations. Interval 1 is least affected by diagenesis and has the highest concentrations of detrital magnetite and hematite, and the lowest solid-phase sulfur contents. Interval 2 is characterized by the presence of paramagnetic pyrite and sharply decreasing magnetite and hematite concentrations, which suggest active reductive dissolution of detrital magnetic minerals, the absolute minimum abundance of magnetite is reached at the end of this interval. Interval 3 is marked by a progressive loss of hematite with depth, and at the base of this interval, 82% to 88% of the hematite component was depleted and the bulk magnetic mineral concentration was reduced to the lowest value in the entire studied mud section. Interval 4 has an increasing down-core enhancement of authigenic greigite, which is interpreted to have formed due to arrested pyritization resulting from consumption of pore water sulfate with depth. This is the first clear demonstration from an active depositional environment for a delay of thousands of years for acquisition of a magnetization carried by greigite. This detailed view of diagenetic processes in continental shelf sediments suggests that studies of geomagnetic field behavior from such sediments should be conducted with care. Paleoceanographic and paleoclimatic studies based on the magnetic properties of shelf sediments with high sedimentation rates like those in the Korea Strait are also unlikely to provide a meaningful signature associated with syn-depositional environmental processes. The rock magnetic properties of the surface sediments from the fine-grained depositional area on the outer shelf of the East China Sea, an area surrounded by sands, are investigated with a view to providing information on the sediment provenance. Multiple magnetic parameters such as magnetic susceptibility (%), anhysteretic remanent magnetization (ARM), saturation rernanent magnetization (SIRM), coercivities of SIRM (Her), and S ratios (relative abundance of low-coercivity magnetic minerals) are measured for all 179 surface samples, and partial representative samples are examined for their magnetic hysteresis parameters, temperature-dependence of magnetic susceptibility and x-ray diffraction spectra. Our research indicates that the magnetic mineralogy is dominated by magnetite with a small amount of hematite and is primarily of pseudo-single domain (PSD) to multidomain (MD) nature with a detrital origin. In the surface sediments, the granulometry of magnetic fractions is basically independent of grain sizes of the sediment containing the magnetic grains, and the composition of magnetic minerals remains almost homogeneous, that is, with a relatively constant ratio of low to high coercivity fraction throughout the area. The magnetic concentration in the study area generally decreases to the east or southeast accompanied by magnetic-particle fining to the east or to the northeast. The geographic pattern of magnetic properties is most reasonably explained by a major source of sediment jointly from the erosion of the old Huanghe River deposit and the discharge of the Changjiang River. The rock magnetic data facilitate understanding of the transport mechanism of fine-grained sediments in the outer shelf of the East China Sea.

黄土高原22万年来的黑碳记录和古火灾害历史重建

The term black carbon is used to describe a relatively inert and ubiquitous form of carbon, comprising a range of materials from char and charcoal to element or graphite carbon produced by the incomplete combustion of fossil fuels and biomass. Due to its inertness, the BC in soils, lacustrine and marine sediments and ice can persist over a long period of time. So BC signatures in geological deposits can be used as evidence of natural fires happened in their surroundings. To study the temporal and spatial changes in paleofires over the Chinese Loess Plateau, black carbon concentrations were analyzed on the loess-paleosol samples from three sections including Lijiayuan, Lingtai and Weinan along a north-south transect. Using the orbitally-tuned time-scales of the sections, the black carbon sedimentation rates (BCSR) were calculated. Meanwhile, with objective to document fine resolution fire history during late Pleistocene and Holocene periods, we measured BC concentrations of loess-paleosol samples at dense sampling intervals since 28 ka BP. in Lijiayuan section. The BCSR of the samples were also calculated. In addition, we also conducted observation on black carbon morphologies to examine their sources. Based on the results, the following remarks can be concluded: 1. In the last two glacial cycles, the BCSR values in glacial periods are 2-3 times higher than in interglacial periods, and the BCSR variability has a relatively strong precession-associated 23 kyr period, suggesting that the glacial cold-dry climate conditions were apt to induce natural fires over the Loess Plateau, 2. Comparison of the BCSR records among the three loess sections demonstrates that natural fire occurrence was much more intensive and frequent in the northern and interglacial periods. 3. Pollen records and carbon isotope analyses of organic matter have shown that the Loess Plateau was covered by an Artemisia-dominated grassland vegetation both during glacial and interglacial periods, So grassland fires were the dominant fire types in the Plateau, which is also corroborated by the observation of black carbon morphology. In addition, statistics and comparison of BC particle sizes among the sections demonstrated that BC records probably reflected local fires. 4. According to previous studies about the effect of fires on vegetation changes, we considered that the fires might play an important role in the expansion of grassland during glacial periods, besides the control of climate changes. 5. The high resolution black carbon record in Lijiayuan section has shown that the BCSR series well documented Younger dryas (YD) and Heinrich (HI和H2) events, suggesting that natural fires in the northwestern part of Chinese Loess Plateau could regularly respond to the millennial scale climate oscillation.

岱海岩芯沉积的粒度组成与湖区全新世降水变化历史

Sediment cores DH99a and DH99b recovered in the central part of Daihai Lake in north-central China were analysed at 2- to 4-crn intervals for grain-size distribution. Grain-size distributions of the lake sediments are inferred to be a proxy for past changes in East Asian monsoon precipitation, such that greater silt-size percentage and higher median grain size reflect increased monsoonal precipitation rates. The grain-size record of Daihai Lake sediments spanning the last ca 11,000 yr indicates that the monsoonal precipitation in the lake region can be divided into three stages: the Early, Middle and Late Holocene. During the Early Holocene before ca 7900 cal yr BP, the median grain size (Md) and the silt-fraction content were relatively low and constant, suggesting relatively low precipitation over the lake region. The Middle Holocene between ca 7900 and 3100 cal yr BP was marked by intensified and highly variable monsoonal precipitation, as indicated by high and variable Md values and silt contents of the lake sediments. During this period, average precipitation rate gradually increased from ca 7900 to 6900 cal yr BP, displayed intense oscillations between ca 6900 and 4400 cal yr BP, and exhibited a decreasing trend while fluctuating from ca 4400 to 3100 cal yr BP Although generally high during the Middle Holocene, both the Md and the silt content assumed distinctly low values at the short intervals of ca 6500-6400, 6000-5900, 5700-5600, 4400-4200 cal yr BP, implying that monsoonal precipitation might have been significantly reduced during these intervals. During the Late Holocene since ca 3100 cal yr BP, grain-size values suggest that precipitation decreased. However, during the Late Holocene, relatively higher Md values and silt contents occurring between ca 1700 to 1000 cal yr BP may denote an intensification of hydrological cycles in the lake area. Changes in the East Asian monsoonal precipitation were not only directly linked with the changing seasonality of solar insolation resulting from progressive changes in the Earth's orbital parameters, but also may have been closely related to variations in the temperature and size of the Western Pacific Warm Pool, in the intensity of the El Nino-Southern Oscillation, and in the path and strength of the North Equatorial Current in the western Pacific.

小兴安岭过去5000年的泥炭δ^13C记录

小兴安岭植物体中δ13C 不仅受区域湿度变化控制,也受温度变化控制。泥炭纤维素的δ13C 曲线,较好地响应了小兴安岭地区过去5000 年来气候,特别是温度和湿度的演变过程。5. 1～3. 0 ka BP、3. 0 ～1. 8 ka BP、1. 8 kaBP 迄今,小兴安岭经历了3 个千年尺度的气候波动,气候演变过程为温暖湿润→温凉较湿→冷凉较湿。在千年尺度的气候波动上,又叠加着百年尺度的气候变化,在3. 0 kaBP 以来更为显著。相应的,泥炭发育也经历了从富营养、中营养到贫营养阶段。

中国全新世气候变化研究进展

全新世气候变化研究是古气候研究的一个重点。中国全新世气候变化的研究也是全球变化研究中重要的一部分。大量的研究工作为恢复中国全新世气候做了重大贡献。中国地形地貌复杂,又处在具有复杂时空变率的东亚季风控制范围内,这使得不同的研究工作者在一些问题上存在意见分歧。比较统一的意见是:中国全新世始于约10. 5ka BP ;在约9～8 ka BP 左右为一段降温期;7～4 ka BP 为一段温暖期,通常称之为全新世大暖期;大约3 kaBP 左右开始降温,至近代才又升温; 约1300 a A. D. 左右进入小冰期,到1850 aA.D. 左右结束,其间又有几次比较明显的温度振荡。1850 a A. D. 至今为温度的上升期。对于气候变动的驱动因素,不同的学者看法不一;从长时间尺度看,太阳辐射变化是气候变化的主要驱动力。

泥炭的腐殖化度与全新世气候环境

泥炭是第四纪，特别是全新世以来的产物。它的形成和积累主要受控于气候，其次是地质、地貌、水文等因素。因此，泥炭形成过程中包含了大量的古气候、古环境演化信息。腐殖化度在国外早已用于古气候研究，国外学者将它作为湿度代用指标，用以恢复古湿度变迁。本文首次将之引入我国泥炭古气候研究，同时结合青藏高原的气候特点，及泥炭形成过程中温度、湿度对它的影响，赋予了泥炭腐殖化度新的气候内涵。即泥炭的腐殖化度高，指示气候温暖湿润；泥炭的腐殖化度低，指示气候干燥寒冷。本文通过对青藏高原东北部红原泥炭的腐殖化度研究，并与其它研究成果对比，得出如下结论：（1）红原泥炭腐殖化度记录了过去12000年以来当地气候干湿冷暖的变化。其气候变化大致可分为3个阶段：11.8-11.2 kaBP，气候干燥寒冷；11.2-5.5 ka BP，气候温暖湿润；5.5-0 ka BP，当地气候由早中全新世温暖湿润的气候向干燥寒冷的气候波动。红原泥炭腐殖化度记录的气候变化与高原青海湖沉积物、松西错沉积物、敦德冰芯、古里雅冰芯记录的气候变化相似，表明青藏高原12000年以来可能受同一气候系统影响，其气候变化的共同特点为干冷与暖湿交替。（2）泥炭腐殖化度记录了12000年以来印度西南季风在高原的强弱演化。新仙女木期（11.8-11.2kaBP），季风强度最弱；从11.2kaBP到10.8kaBP季风强度快速增强；在10.8ka即到5.5 ka BP，季风强度一直处于强势阶段；从5.5 ka BP开始，印度西南季风强度逐渐减弱，这期间腐殖化度同时记录了百年一千年尺度印度西南季风增强事件，但总体减弱的趋势不变。（3）泥炭腐殖化度记录的百年一千年气候突然变化事件与北大西洋浮冰事件存在遥相关。对应8次浮冰事件，红原地区气候同时变得干冷，而印度西南季风强度也减弱，这表明不但末次冰期印度西南季风与北大西洋气候密切相关，而且在全新世，这种相关性同样存在。（4）泥炭腐殖化度距平值较好的反映了西太平洋副热带高压近5000年来的活动变化。腐殖化度代用指标能很好地记录较长时间西太平洋副热带高压的变化，而对西太平洋副热带高压数十年到百年的频繁波动，则记录不明显。（5）泥炭腐殖化度时间序列的功率谱分析表明，太阳活动对红原地区气．候演化有重要影响，同时太阳活动通过影响全球水循环，进而驱动温盐环流的变化，进一步影响全球气候变化。（6）泥炭腐殖化度能同时记录温度、湿度的变化，并且测定方法简便、快捷，值得进一步研究。

Vegetation and climate variations at Taibai, Qinling Mountains in central China for the last 3 500 cal BP

IEECAS SKLLQG

冲绳海槽北部PC-1岩芯24 cal.kaBP 以来孢粉记录的古环境信息

东海陆架是世界上最宽阔的陆架之一，面积达770 000 km2左右。在末次冰盛期（LGM），东海海平面下降120～130 m左右，绝大部分陆架暴露出海面。而冲绳海槽是第四纪以来一直保持海洋环境的东海深海区。本文以冲绳海槽北部PC-1岩芯为材料，通过分析该孔的孢粉，加上详细的AMS 14C测年，恢复了周边地区24 cal.kaBP以来的古植被，并推测古环境和古气候变化，重点讨论了LGM时期出露大陆架上发育的植被。 PC-1孔（31°27.5′N，128°24.8′E）位于黑潮支流对马暖流东侧，水深590 m，柱长812 cm。孢粉分析按间隔8 cm取样，个别为4~6 cm，共分析了103个孢粉样品。利用9个AMS 14C数据建立年龄标尺，用Calib5.1.0软件进行年龄校正。通过相邻样品深度的线性内插获得每个样品的年龄，采用外延法得到顶部和底部的校正年龄分别为351cal aBP、24 280 cal aBP，孢粉样品的时间分辨率平均为230 a。 根据孢粉百分比和沉积率的变化，可划分出四个带：Ⅰ带（812～715 cm，24.2～21.1 cal. kaBP）、Ⅱ带（715～451 cm，21.1～15.2 cal. kaBP）、Ⅲ带（451～251 cm，15.2～10.8 cal. kaBP）、Ⅳ带（251～0 cm，10.8～0.3 cal. kaBP），分别对应MIS 3末期、末次冰盛期、冰消期和全新世。末次冰盛期草本植物花粉占优势，孢粉沉积率较高，此时草本花粉主要来源于出露的大陆架，其上发育了以蒿属为主的草地植被，气候比较寒冷干燥；冰消期海平面开始回升，松属花粉含量升高，草本植物花粉含量下降；全新世以木本植物花粉占绝对优势，栗属－栲属花粉迅速增加，蕨类孢子含量升高，草本植物花粉含量锐减，孢粉沉积率降低，由于海平面回升，大陆架被淹没，此时孢粉主要来源于日本岛，九州地区生长了以栲属、栎属为主的常绿阔叶与落叶阔叶林，气候温暖湿润。 叶枝杉属花粉在整个岩芯中零星出现。叶枝杉属植物分布于菲律宾吕宋北部至塔斯马尼亚和新西兰气候潮湿的山地林中，该属花粉在岩芯中的出现，可能暗示了黑潮的影响或者是较强的夏季风。 草本植物与松属花粉百分比变化很好的反映了海平面的升降，松属花粉含量较高指示海平面较高。对岩芯中主要类型的花粉百分比进行了频谱分析，显示存在千年尺度的准周期变化，有明显的6.8，3.8，2.2，1.6 ka的周期。 孢粉样品中的炭屑统计表明，末次冰消期炭屑含量最高，可能因为末次冰消期降雨量增加，炭屑可被降水带到沉积地点沉积下来；全新世的炭屑浓度较高，尤其在晚全新世，出现了一个峰值，究其原因可能与气候变化和人类活动有关。

Fruits of Lithospermum officinale L. (Boraginaceae) used as an early plant decoration (2500 years BP) in Xinjiang；China

IEECAS SKLLQG

Palaeoenvironmental changes from pollen record in deep sea core PC-1 from northern Okinawa Trough, East China Sea during the past 24 ka

A pollen record of core PC-1 from the northern Okinawa Trough, East China Sea (ECS), provides information on vegetation and climate changes since 24 cal. kaBP. A total of 103 samples were palynologically analyzed at 8 cm intervals with a time resolution of 230 a. Four pollen zones are recognized: zone I (812-715 cm, 24.2-21.1 cal. kaBP), zone II (715-451 cm, 21.1-15.2 cal. kaBP), zone III (451-251 cm, 15.2-10.8 cal. kaBP), zone IV (251-0 cm, 10.8-0.3 cal. kaBP), corresponding to Late MIS 3, Last Glacial Maximum (LGM), deglaciation and Holocene, respectively. The LGM is characterized by the dominance of herbs, mainly Artemisia, and high pollen influx, implying an open vegetation on the exposed continental shelf and a cool and dry climate. The deglaciation is a climate warming stage with Pinus percentage increased and Artemisia percentage decreased and a rapid sea-level rise. The Holocene is characterized by predominance of tree pollen with rapid increase in Castanea-Castanopsis indicating the development of mixed evergreen and deciduous broad-leaved forest and a warm, humid climate. Low pollen influx during the Holocene probably implies submergence of the continental shelf and retreat of the pollen source area. The vegetation indicated by pollen assemblage found in this upper zone is consistent with the present vegetation found in Kyushu, Japan. Originating from the humid mountain area of North Luzon of the Philippines, Tasmania and New Zealand, Phyllocladus with sporadic occurrence throughout PC-1 core probably suggests the influence of Palaeo-Kuroshio Current or intense summer monsoon. The observed changes in Pinus and Herbs percentage indicate fluctuations of the sea level, and high Pinus percentage corresponds to high sea level. Spectrum analysis of the pollen percentage record reveals many millennial-scale periodicities, such as periodicities of 6.8, 3.85 2.2, 1.6 ka.