湖泊沉积物 Mg／Ca作为气候代用指标的局限性

Mg/Ca作为古气候古环境研究的代用指标已得到广泛应用,但是在湖泊沉积物研究中,由于不同区域局地环境的影响,湖泊中Mg/Ca变化的环境气候指示意义有很大差别,甚至出现相悖的情况。本文通过分析太湖沉积物Mg/Ca变化特征与区域环境变化的对应关系,与其他区域研究成果进行对比分析,探讨不同区域环境对湖泊沉积物Mg/Ca的影响。结果表明,湖泊沉积物Mg/Ca在特定区域环境影响下,有着不同的环境指示意义,该指标的应用需要认真研究当地环境的特殊性并与其他气候代用指标结合,以确保气候变化分析的准确性。     

2012-05 科技期刊亮点

青藏高原湖泊沉积重建历史气候环境变迁生活在湖泊中的小型双壳类动物-介形类之壳体和营养体纤细的沉水性植物-轮藻类之藏卵器,能真实记录湖区各种气候和环境变化信息,是研究古环境古气候演变的好材料。中国地质科学院矿产资源研究所郑绵平院士根据西藏台错地区的湖泊沉积物化石,以及化石和碳酸盐的碳氧稳定同位素的测试数据重建了其所代表的41.4—4.5千年期间气候环境,     

近300年来岱海流域气候干湿变化与人类活动的湖泊响应

根据岱海60cm柱状岩芯的磁化率、孢粉、粒度等环境指标的分析结果,对历史时期岱海气候干湿变化和人类活动的湖泊记录进行探讨,岱海湖泊沉积记录近300年来的气候干湿变化可划分七个阶段,与历史记载有较好的一致性;频率磁化率高值段对应气候偏湿阶段,低值对应气候偏干阶段,人类活动特别是人口增加和土地开垦,加剧流域水土流失,导致湖泊沉积物中细颗粒组分增加,频率磁化率升高;孢粉Ulmus的变化受流域人口增加的影响。频率磁化率和孢粉是反映岱海历史时期干湿变化和人类活动的重要环境指标。     

6000 aBP以来洞庭湖沉积记录的环境演变及其同人类活动的关系

通过对东洞庭湖地区ZK01钻孔沉积物的粒度、磁化率、孢粉等古环境指标的分析, 初步揭示了该地区6000 aBP以来湖泊环境及气候演变的历史: 6000~4000 aBP, ZK01钻孔所在区域为水深较大的湖泊环境, 湖泊周围地区分布有亚热带常绿阔叶林植被, 代表较为湿热的气候; 4000~1000 aBP仍为深湖环境, 但后期水深有所减小, 其中4000 aBP的气候有明显变干变凉的趋势, 植被也发生了明显的变化; 1000~600 aBP湖泊演变为浅湖环境, 600 aBP之后进一步演变为浅滩与湖沼交互相环境。 该地区环境演变同史前及历史时期人类活动的相互关系研究表明, 6000~1000 aBP的水文环境及气候变化显著地影响了区域的古代人类文化与历史的进程, 其中4000 aBP的气候变凉及水文环境的变化可能是该地区史前文明迅速衰落的原因; 1000 aBP以来, 人类在长江两岸的筑堤和围垦等活动明显影响了洞庭湖地区的水沙过程及河湖环境的演变历史。     

湖泊沉积物粒度的环境含义

气候特征是冰期和相对温暖的问冰期交替发生。湖泊沉积物以其连续性好、敏感性强和高分辨率的特点,在恢复和重塑各种短时间尺度（千年、百年、十年）的气候和环境演化序列上,具有其它自然历史记录无法替代性。本文主要研究沉积物粒度的环境含义,古气候特征。尘暴,构造运动等环境信息很好的保存在湖泊沉积物粒度上。因此,本文通过对湖泊沉积物柱度的研究进而推断当时的环境特征。     

黄河下游历史时期环境变化的烧失量记录

基于精确14C测年,对黄河下游地区湖泊沉积物岩芯的烧失量进行了分析,结合历史文献资料重建了该区域的气候环境演变历史.研究表明,黄河下游地区沉积物烧失量指示了数次冷暖干湿的大环境变化:2400-1600aBP期间,气候较为温暖,后期转冷;1600-1000aBP期间,气候波动较为复杂,间或有冷暖交替现象;1000aBP至今,气候以暖湿为主,中期有较大波动.     

豫西渑池盆地沉积剖面粒度特征及其环境意义

渑池盆地是黄河中游的一处峡谷,周边的黄河两岸是中华民族的重要发祥地之一.研究盆地区全新世以来的环境变化过程对新石器时代人类文明的研究具有重要意义.本文通过对渑池盆地池底村古湖泊沉积进行剖面观察、连续采样、14C年代测定(校正为日历年龄)和粒度组成分析,发现剖面沉积物的粒度特征较好地反映了渑池盆地的古气候和古湖泊水位变化情况.剖面粒度组成和粒度参数等变化特征揭示,渑池盆地末次冰盛期以来古湖盆流域的气候环境演化序列为:19 543～8 039 cal.a BP期间,早期对应于末次冰期,气候比较干燥,古湖泊尚未形成,进入全新世气候由干冷向暖湿化方向转变,古湖泊开始形成;8 039～3 473 cal.a BP期间,气候环境处在一个相对比较稳定的时期,此阶段相当于全新世大暖期,气候温暖湿润,湖泊水位最高;3 473～2 897 cal.a BP期问,气候波动剧烈,总体上气候较前一段干旱,湖泊水位下降;2 897～2 422 cal.a BP期间,气候干旱,古湖泊干涸.渑池盆地的环境变化过程与周边地区有较好的对应性.     

湖泊沉积物Rb／Sr比值的古气候含义

由于 Rb、Sr 在表生过程中地球化学性质的明显差异,不同的封闭湖盆接纳的各种气候条件下形成的连续沉积物具有明显不同含量的 Rb、Sr,沉积物 Rb/Sr 比值的变化序列可以反映流域经历的化学风化及气候演变历程。利用湖泊沉积物记录的 Rb/Sr 比值反演流域古环境变迁比利用海洋沉积物、黄土-古土壤更直接,减少了不确定性,优势明显。     

《自然》发表中科院青年科学家最新成果

11月15日出版的《自然》杂志发表中科院广州地化所青年科学家周厚云等人的最新研究成果（第450卷，第E10-11页）。该成果根据华南沿海的气候环境条件和研究地点的地质地理特征，对德国科学家Yancheva等人（Nature，2007，Vol．455：74—77）提出的华南沿海“湖光岩的沉积物主要来自亚洲冬季风搬运的大气粉尘，沉积物的钛（Ti）含量指示亚洲冬季风强度的变化”观点提出了不同的看法。周厚云等人根据该湖泊中存在较粗颗粒的沉积物和湖泊沉积通量偏高等沉积学的证据以及湖泊流域物质中Ti含量较高等特征，提出了湖泊流域应该是湖光岩沉积物的重要来源，湖光岩沉积物中的Ti含量变化反映的可能主要是湖泊水文的变化而不是亚洲冬季风强度的变化观点。该研究观点得到了后续进行的地球化学分析结果的有力支持。对湖光岩沉积物的锶、钕同位素组成和稀土元素的分析结果证明，湖光岩沉积物应该主要来自湖泊流域，而来自中国北方干旱区粉尘的贡献则小得多。     

南四湖湖泊沉积物磁化率特征及其环境意义

黄河下游地区湖泊演化多与黄河河道变迁密切相关，在分析鲁西南南四湖DS2孔沉积物磁化率参数的基础上，结合历史记载资料，探讨历史时期人与自然相互作用下的湖泊沉积物响应.2400aB.P.左右南四湖地区环境演变出现明显的变化，湖泊沉积物磁化率曲线显示黄河泛滥开始影响该区域.公元前400～公元170年与1200～1870年期间是黄河影响DS孔湖泊沉积的主要时期.2400aB.P.以前南四湖地区的独山湖一带湖泊尚未形成.推测当时为泗河、城河冲积扇前缘的洼地.13世纪以来为保证运河漕运进行的人类活动与黄河泛滥加速了现代南四湖形成.     

Environmental magnetic studies of lacustrine sediments

In recent decades, environmental magnetism has become an important method for studying past global climatic and environmental changes. For an environmental magnetic study, it is important to understand the magnetic properties, of various magnetic minerals in lacustrine sedimcuts and the processes involved in the formation, transport,and preservation of these magnetic minerals. The magnetic response of lacustrine sediments to climatic change may vary widely from lake to lake. To reconstruct the processes contributing to paleoclimatic and paleoenvironmental change, it is, therefore, necessary to derive a complete understanding of the potential origin of the magnetic signal observed.     

Mechanism of variations in environmental magnetic proxies of lake sediments from Nam Co, Tibet during the Holocene

High-resolution environmental records from the Tibetan Plateau are essential to understand past global climatic and environmental changes. Magnetic minerals in lake sediments are important proxies to reconstruct environmental and climatic changes. Nam Co (lake) is a typical great lake in the transitional region of southwest monsoon in the Tibetan Plateau. Previous studies have extensively focused on geochemistry, microfossils, sedimentology and biochemistry analysis of Nam Co, which provides sound interpretation of paleoclimatic and paleoenvironmental changes. However, up to now, no systematic environmental magnetic studies have been carried out. Therefore, high-resolution and systematic magnetic studies combined with geochemical parameters were carried on lake sediments of core NC 08/01 from Nam Co for the Holocene period (11.3 cal ka BP) in order to explore how magnetic properties of the sediments respond to climatic changes. Based on variations of magnetic proxies, the sequence can be separated into 3 units. Unit 1 (236-199 cm, 11.3-7.8 cal ka BP) contains dominantly coarse-grained magnetite with homogeneous grain size. A positive correlation between magnetite and Ti strongly suggests that these coarse-grained detrital magnetites reflect detrital input signals due to insignificant effects of postdepositional dissolution processes on these coarse-grained magnetite particles. For Unit 2 (198-102 cm, 7.8-2.1 cal ka BP), magnetic grain size is finer and the corresponding concentration of magnetite is also reduced. This is mainly due to significant dissolution of these fine-grained detrital magnetite particles, which were transported under reduced water flow conditions during this period. For Unit 3 (101-0 cm, 2.1-0 cal ka BP), the bulk magnetic properties are dominated by a mixture of single domain biogenic magnetite and detrital magnetite. The concentration of magnetic minerals is not correlated with the Ti content. In conclusion, the preservation of magnetic minerals in the lake sediment and thus the corresponding magnetic properties are related to the initial grain size. Combination of magnetic properties (including variation of grain size and concentration) and other proxies of detrital inputs (e.g. Ti) can be used to infer the variation of redox conditions in Nam Co. These results provide a viable framework for reconstructing the paleoenvironmental changes of this lake.     

New progress of lake sediments and environmental changes research in China

Environmental change recorded by lake sediments is one of the important branches of the past global changes study. The new progress of lake sediments and environmental changes in China since the late 1980s has been comprehensively discussed. The highlights emphasized are Asian paleomonsoon migration reflected by lake level fluctuation, uplift of the Qinghai-Xizang Plateau recorded by lacustrine sediments, saltlake sediments and environmental evolution, lake response to the natural-human interaction and modern lake biogeochemical process. Meanwhile important suggestions for the lake sediments and environmental research in the future are proposed, which include studies on the quantitative relationship between lake environment proxies and climate factors, high-resolution evolutionary sequence and spatial differentiation of environments, modern lake dynamic process and environment, Quaternary Chinese lake database and global changes.     

达连海沉积物粒度特征及其古环境意义

利用达连海湖心浅井的粒度资料,分析了粒度组成、粒度频率曲线等粒度特征,并探讨了达连海粒度代表的古气候意义。结果表明,达连海沉积物频率曲线主要是正态单峰型,反映流水作用为主要沉积作用。湖心底部降水较多,湖面高,沉积物以细组分占绝对优势,频率曲线显示物源较单一,为深水沉积环境,但后期环境有所变化;中下部降水相对稀少,湖面降低,沉积物以粗组分含量增加,环境可能进一步恶化;中上部湖面上升,细组分含量增加,频率曲线显示物源由复杂变单一,为浅水沉积向深水沉积过渡环境;上部沉积物粗细间隔连续变化,频率曲线显示物源复杂,反映湖区环境进一步恶化,风砂活动频繁。沉积物粒度特征反映了达连海中全新世以来降水、流水和风力作用以及湖面水位高低的变化。达连海5 000多年来的古气候环境演化大致经历了5 600~5 100 cal a BP的湿润、5 100~2 500 cal a BP的干旱、2 500~800 cal a BP的偏湿和800 cal a BP以来的偏干4个阶段。     

气候环境变化的河流响应

通过综述前人及笔者的已有研究工作,指出气候环境变化可能引发各种河流地貌过程,如河流的侵蚀与加积、河口的溯源侵蚀与溯源堆积等;流域气候环境变化在河口沉积物的矿物和元素组成上也得以反映,如SX97孔中的粘土矿物和石英的含量变化教育与该孔孢粉资料所揭示的气候环境演化规律相吻合,也与早期对华南海岸沙丘和海滩岩的研究所揭示的区域气候环境演化一致,但由于局部因素的干扰,气候环境变化的河流响应体系可能变得较为复杂,在研究工作中应对此予以足够注意。     

渤海沿岸全新世海面升降与半干旱湖区演化的对比研究

全新世时,渤海沿岸海面升降变化与半干旱区湖泊的演化具有明显的同步性。形成的主要原因是与全球性气候变化有关。在弄清不同时间尺度自然变化规律,并考虑到人为因素的影响,可对未来环境演化趋势进行预测。     

Abrupt Holocene changes of the Asian monsoon at millennial- and centennial-scales: Evidence from lake sediment document in Minqin Basin, NW China

Considerable research is now focusing on abrupt Holocene changes at millennial- and centennial-scales all over the world. This study shows that the changes in the Holocene summer monsoon can be divided into two main periods, based on climatic proxy records of lake sediments from the Sanjiaocheng section located at the NW boundary of the summer monsoon, Gansu Province. The early and middle Holocene was humid with stronger summer monsoon, while the late Holocene is dry with weak summer monsoon. Detailed results also show a series of millennial- and centennial-scale changes in the intensity of the summer monsoon, with a periodicity of {dy1600} years during the whole Holocene, and with a periodicity of 800 years during the early Holocene. Ten dry events during the Holocene are associated with the weakening of the summer monsoon. These rapid climatic changes may be representative of a global climatic change pattern during the Holocene.     

Humid medieval warm period recorded by magnetic characteristics of sediments from Gonghai Lake,Shanxi, North China

Variations in monsoon strength, moisture or precipitation in eastern China during the MWP reflected by different climatic records have shown apparent discrepancies. Here, detailed environmental magnetic investigations and mineralogical analyses were conducted on lacustrine sediments of Core GH09B1 (2.8 m long) from Gonghai Lake, Shanxi, North China, concerning the monsoon history during the MWP. The results demonstrate that the main magnetic mineral is magnetite. The sediments with relatively high magnetic mineral concentrations were characterized by relatively fine magnetic grain sizes, which were formed in a period of relatively strong pedogenesis and high precipitation. In contrast, the sediments with low magnetic mineral concentrations reflected an opposite process. The variations of magnetic parameters in Gonghai Lake sediments were mainly controlled by the degree of pedogenesis in the lake drainage basin, which further indicated the strength of the Asian summer monsoon. The variations in the and S 300 parameters of the core clearly reveal the Asian summer monsoon history over the last 1200 years in the study area, suggesting generally abundant precipitation and a strong summer monsoon during the Medieval Warm Period (MWP, AD 910–1220), which is supported by pollen evidence. Furthermore, this 3–6-year resolution environmental magnetic record indicates a dry event around AD 980–1050, interrupting the generally humid MWP. The summer monsoon evolution over the last millennium recorded by magnetic parameters in sediments from Gonghai Lake correlates well with historical documentation (North China) and speleothem oxygen isotopes (Wanxiang Cave), as well as precipitation modeling results (extratropical East Asia), which all indicate a generally humid MWP within which centennial-scale moisture variability existed. It is thus demonstrated that environmental magnetic parameters could be used as an effective proxy for monsoon climate variations in high-resolution lacustrine sediments.     

湖泊沉积物中细菌含量影响因子分析

为探讨湖泊沉积物中的生源要素对细菌含量的影响,采用实时定量PCR技术检测沉积物中的细菌含量,运用统计学方法找出中值粒径、总有机碳、总氮、总磷等环境因子与细菌含量之间的相关关系,并据此对影响细菌含量的环境因子进行分析.结果表明:湖泊沉积物中细菌含量随深度的增加而减少;沉积物粒径影响营养元素的赋存从而对细菌含量产生影响;总氮、总磷、总有机碳对沉积物中细菌含量的影响与湖泊水域环境、不同季节温度有关.