海南岛东南部海湾潟湖沉积和碳埋藏变化研究

本文选择海南岛东南部热带小型海湾为研究区, 探讨热带珊瑚礁生态系统对海岸碳埋藏的贡献, 以及小流域系统物质循环过程对极端风暴事件和人类活动的响应。对来自海南岛东南部黎安和新村潟湖的柱状样和表层底质样品, 在室内进行了粒度、有机碳、无机碳和 210 Pb年代指标测试和分析。结果表明, 新村潟湖有机碳和无机碳含量均较高于黎安潟湖, 新村潟湖有机碳埋藏速率(9×105kg/a)为黎安潟湖有机碳埋藏速率(3×105kg/a)的3倍。珊瑚礁生态系统对于这两个潟湖碳埋藏具有重要贡献。新村潟湖柱样岩芯XC-06无机碳含量在1980~2000年期间存在急剧锐减的趋势, 可能与同期该地养殖和过度捕捞致使珊瑚礁生长受限有关。根据沉积物物质守恒原理和沉积物来源分析, 海南岛频繁的台风风暴事件对于新村和黎安潟湖沉积的实际贡献远大于总量的1/3。在未来人类活动和台风活动呈现上升态势背景下, 该地区碳埋藏量将进一步发生变化。海南岛小流域海湾、潟湖碳埋藏量可以达到108~109kg/a 量级, 接近于海南近陆架有机碳通量(2×109kg/a), 表明海湾潟湖对于本区浅海碳埋藏具有重要贡献。     

青海湖近千年来气候环境变化的湖泊沉积记录

本文通过对青藏高原上所钻取的古里雅冰芯和青海都兰树轮高分辨率气候变化记录的对比,分析了过去近2 000a来的气候变化特征.结果表明:1)这两个地区过去2 000a来温度都在波动中逐渐上升,展示了气候逐渐变暖的趋势.进入20世纪以来,气候显著变暖,并有加速变暖的趋势;2)树轮和冰芯均明显地记录了小冰期的3次冷期,其出现的时间基本上一致.小冰期并不是过去2 000a来的最寒冷的时期.冰芯和树轮记录均表明公元初的寒冷程度要大于小冰期;3)古里雅冰芯所记录的温度和降水量揭示出,过去近2 000a来的降水和温度变化的总趋势是正相关关系;但在短时间尺度上,温度和降水的变化并不同步.这主要表现在两个方面,一是温度长期变化中的低频波动频率要大于降水,二是虽然温度和降水的变化在百年级时间尺度上有正相关性,但降水的变化要滞后于温度变化50～100a;4)同时周期分析表明,古里雅冰芯中的δ180和积累量以及都兰树轮记录的变化周期大多数与太阳活动有关,表明青藏高原地区冷、暖、干、湿变化的主要驱动力可能是太阳活动的变化;5)对这两记录的对比研究也揭示了气候变化的区域差异.如中世纪暖期在都兰树轮记录中很强而在古里雅冰芯记录中很弱,而都兰树轮记录中,中世纪暖期以后至1 800A.D.在波动中变冷,但在古里雅冰芯记录中这一时期在波动中变暖.     

长江下游升金湖沉积物记录的过去千年高分辨率气候环境变化

中国东部季风区气候格局具有强烈的时空差异,加强过去千年高分辨率气候变化历史重建及其机制研究对于深刻认识中国东部当今及未来气候变化趋势以及制定应对策略具有重要科学意义。本研究以长江中下游地区典型湖泊升金湖长度为86 cm的沉积岩芯为研究对象,在AMS ¹⁴C测年数据建立可靠年代框架的基础上,利用沉积物粒度、总有机碳（TOC）、总氮（TN）、碳氮比（C/N）和无机碳（IC）等指标高分辨率重建该流域过去千年以来的气候环境变化。研究结果表明：1）阶段Ⅰ（1000~1350 A.D.）,对应中世纪暖期,平均粒径相对较细,TOC、TN、C/N较低,说明湖泊水位总体较高,1100 A.D.后粒度粗粒成分增多和IC波动增长,表明流域气候逐渐向干旱化状态转变;2）阶段Ⅱ（1350~1600 A.D.）,进入小冰期前期,平均粒径和IC含量进一步降低,TOC、TN、C/N上升,指示湖泊水位持续升高,气候偏湿润;3）阶段Ⅲ（1600~1850 A.D.）,进入小冰期后期,平均粒径增大,表明湖泊流域降水减少,水位下降,流域内湿地植被发育从而使得TOC、C/N增大,IC也迅速增加,湖泊流域气候较为干旱;4）阶段Ⅳ（1850~2000 A.D.）,对应现代暖期,平均粒径下降,IC降低,湖泊水位再次上升,气候总体呈暖湿状态,TOC、TN、C/N受气候和人类活动共同影响而持续增长。区域重建结果对比表明,中世纪暖期和小冰期升金湖沉积物记录与长江中下游地区其他研究结果记录的干湿变化较为一致。进一步将升金湖记录与近千年来的东亚夏季风环流、ENSO以及太阳辐照度等记录进行对比分析发现,该地区过去千年以来的气候变化不仅受东亚夏季风变化控制,同时还受到ENSO状态及太阳辐照度变化等显著影响。在中世纪暖期和小冰期后期,以拉尼娜态为主,太阳辐照度较强,升金湖地区气候较为干旱;小冰期前期和现代暖期以厄尔尼诺态为主,升金湖地区气候较为湿润;现代暖期后,升金湖地区气候变化与太阳辐照度关系不明显,推测可能受人类活动影响更为强烈。

     

青海湖近千年来气候环境变化的湖泊沉积记录

本文根据青海湖沉积岩芯（QH00A）碳酸盐含量、TOC和Rb/Sr等环境指标的综合分析，探讨了该地区近千年来的气候变化过程和化学风化史。结果表明：青海湖地区近千年来经历了5次冷湿期和5次暖干期，气候组合类型为冷湿与暖干交替。中世纪暖期、小冰期以及20世纪以来的升温在该沉积岩芯中得到良好的记录。沉积岩芯Rb/Sr较好地记录了湖泊流域化学风化的历史，并揭示流域化学风化的主要控制因素为气温变化。     

过去约8000年来程海摇蚊组合记录的气候与环境变化

季风气候是影响地区古环境变化的主要因素。文章通过程海长556cm岩芯的沉积摇蚊亚化石、粒度、TOC、TN和TOC/TN记录,探讨了季风气候影响下程海地区约7660cal.a B.P.以来的降水变化情况。结果表明,沉积物中摇蚊属种以Procladius Skuse、Chironomus plumosus、Tanytarsus mendax和Microchironomus tener为主。约7660~2800cal.a B.P.时期流域受印度季风影响强烈,气候暖湿、降水量大,湖泊生产力水平较高;约2800cal.a B.P.以来程海流域降水量逐渐减少,湖泊生产力水平降低。Procladius Skuse与T.mendax的组合关系反映了程海在约6850~6500cal.a B.P.、约5500~5000cal.a B.P.、约4150~3700cal.a B.P.、约2800~2300cal.a B.P.和约1400~1100cal.a B.P.这5个时期由于印度季风减弱,发生了短暂性的干旱事件,研究表明季风因素驱动下的程海摇蚊亚化石组合主要受流域降水侵蚀因素的影响。

     

环境地球化学对人体健康的影响

人类与自然环境之间的最本质的内在联系是化学元素,环境中的化学元素通过土壤、空气、水等与人直接联系。而人体中的化学元素的含量与地球化学环境密不可分,所以,环境中的化学元素与人体健康息息相关,环境中某些化学元素组成和含量会影响到人体的生理功能和生长发育。某一地方或区域中某种元素过多则会产生毒性反应,过少或缺乏则会使人体机能出现某种障碍。研究相关的问题成为地球科学工作者面前的新课题。     

白洋淀地区全新世以来的气候环境变化

白洋淀是华北平原最大的淡水湖泊,是研究全新世气候变化的理想区域。文章选择白洋淀东垒头剖面（厚382 cm）,在8个AMS-¹⁴C测年数据基础上,通过对其189个样品的地球化学元素、粒度和磁化率等指标分析,高分辨率地揭示了白洋淀地区全新世气候变化过程。研究结果显示：1）11335~10300 cal.a B.P.期间,CaO/MgO比值（多高于4.8）、（CaO+K₂O+Na₂O）/Al₂O₃比值（多高于1.3）、CaCO₃含量（多高于12%）和中值粒径（多高于15 μm）均为整个剖面最大值,干旱指数（平均约为0.019）为剖面次高值,CIA值（多低于45）、Ti含量（多低于0.38%）和低频磁化率值（多低于10×10^-8 m³/kg）为整个剖面的最低值,指示气候冷干,受新仙女木事件影响较大;2）10300~8500 cal.a B.P.期间,CaO/MgO比值、（CaO+K₂O+Na₂O）/Al₂O₃比值、干旱指数和中值粒径明显下降,CIA值、Ti含量、低频磁化率值均不同程度上升,指示气候向暖湿发展;3）8500~6000 cal.a B.P.期间,气候总体温暖湿润,干旱指数（平均达0.014）为剖面的最小值,CIA值和Ti含量较高,CaO/MgO比值、（CaO+K₂O+Na₂O）/Al₂O₃比值较低;但该阶段所有指标波动剧烈,8200 cal.a B.P.和6800 cal.a B.P.左右CaO/MgO比值、（CaO+K₂O+Na₂O）/Al₂O₃比值、干旱指数、CaCO₃含量出现高峰值,CIA值和Ti含量出现低峰值,指示2次明显冷干事件;4）6000~4200 cal.a B.P.期间,CaCO₃含量最低,但干旱指数较高,CaO/MgO比值、（CaO+K₂O+Na₂O）/Al₂O₃比值均有不同程度上升,指示气候湿润度有所下降;其中4500 cal.a B.P.为一次明显冷干事件,干旱指数呈现高峰值;5）4200~1035 cal.a B.P.期间,砂含量（多低于2%）、中值粒径（多低于10 μm）为剖面最小值;干旱指数、CaO/MgO比值、（CaO+K₂O+Na₂O）/Al₂O₃比值、CaCO₃含量明显升高,指示气候向着凉干方向发展;干旱指数在2800 cal.a B.P.呈现高峰值,指示一次明显冷干事件,同时,该时段受人类活动影响,低频磁化率值（多高于20×10^-8 m³/kg）明显高于其他时段。

     

近7000年巢湖沉积物环境磁学特征及其指示的亚洲季风变化

利用巢湖ACN钻孔,通过多参数磁性测量、粒度和AMS14C测年分析,探讨了近7000年以来巢湖沉积物磁性特征变化及其控制因素,并进而探讨了其对亚洲季风变化的指示意义。研究结果表明,ACN钻孔磁性特征由磁铁矿主导,其变化主要受沉积动力环境控制,间接反映了流域降水的变化。总体上粘土含量高的沉积物中磁性矿物含量较低、颗粒较细,形成于高湖泊水位环境,对应了降水量高的时期;而>32μm组分含量高的沉积物磁性较强、颗粒较粗,形成于低湖泊水位环境,对应了降水量低的时期。巢湖ACN的磁性记录(尤其是XARM/X和XARM/SIRM两个参数)揭示了近7000年以来巢湖流域降水具有减少的趋势,导致湖泊收缩和沉积物中磁性矿物颗粒变粗。在这一长期变化的基础上,还存在6000aB.P.,5500aB.P.和3800aB.P.附近的显著干旱事件。这一磁性记录与中国东部地区的石笋、湖泊等记录可以很好地对比,是亚洲季风演变的区域响应结果。     

海南三亚地区全新世海滩岩地球化学特征及沉积古地理环境意义

通过野外调查、薄片分析、扫描电子显微镜、X射线衍射技术、¹⁴C年龄测试、微区微量元素分析等,对海南岛南部海岸线上分布的三亚地区海滩岩的表面性质和胶结物特征进行了分析,探讨了海滩岩形成机制及形成的沉积古环境。三亚地区海滩岩由与现在海岸线平行的向海倾斜的低角度岩层构成,岩性为以浅褐色—灰黄色钙质胶结的含砾粗中粒长石(石英)砂岩和以灰黄色钙质胶结的含生物屑砂质砾岩为主,其胶结物主要是钙质,主要由亚稳态碳酸盐相、高镁方解石以及文石组成,从扫描电镜和薄片来看,主要形态是针状、泥晶,是典型的海相潜水沉淀。海滩岩中贝壳AMS ¹⁴C年龄结果为(4570±30) a BP,表明海滩岩形成于全新世中期。胶结物的稀土元素总量较低,总体表现呈微弱的左倾轻稀土亏损型曲线,轻、重稀土分异不强,具有弱的Eu正异常,轻微的Ce负异常及弱的La正异常,Sr/Ba、Th/U、V/Cr、V/(V+Ni)及Sr/Cu比值特征指示了海滩岩形成于海洋环境和干旱气候条件。     

湖泊沉积物中重金属的环境地球化学

概要地回顾了近年来国内外湖泊沉积物中重金属环境污染方面的研究成果,介绍了湖相沉积物重金属研究的主要内容、方法和可能的发展方向.认为就重金属成因方面应加强区分其主要来源是岩石和矿物风化的碎屑产物、大气降尘、人类活动等的研究;重金属污染方面更应重视污染物质的生物有效性、迁移转化机理和重金属“二次污染“的研究;研究手段上,注重运用同位素示踪与定年技术来研究重金属的来源和污染历史,应用高分辨率沉积物钻心研究环境的变迁.最后提出加强多学科的综合研究,建立中国湖泊基准数据库,为探讨湖泊湿地的可持续发展提供依据.     

风成沉积地层化学元素记录的毛乌素沙地气候变化

毛乌素沙地位于东亚季风边缘区,是研究全球气候变化和沙漠变迁的理想场所。选取沙地东缘风成砂/古土壤/湖沼相沉积序列,以常量化学元素含量及比值变化揭示了全新世的气候变化。结果表明：常量化学元素氧化物含量在全剖面上呈SiO₂ > Al₂O₃ > K₂O > Na₂O > Fe₂O₃ > MgO > CaO,且在不同沉积相中含量存在差异;常量化学元素氧化物与<63 μm粉黏组分及磁化率的相关性分析显示,Al₂O₃、Fe₂O₃、MgO三者之间呈显著正相关性,且与粉黏组分、低频磁化率（X_lf）也呈显著正相关性,表明<63 μm粉黏组分、X_lf可以反映夏季风的强弱;全新世气候变化存在多次暖湿冷干波动,10.39 ka BP之前出现3次快速的气候颤动,表现为3层风成砂与3层湖沼相互层沉积,指示存在3次冬夏季风交替变化;10.39~9.34 ka BP、8.68~8.29 ka BP、2.72~1.34 ka BP为3次明显的冬季风势力增强、风沙活动加剧的相对冷干气候;在9.34~8.68 ka BP、8.29~2.72 ka BP、1.34~0.62 ka BP为3次明显的夏季风盛行、降水增多、生草成壤的相对暖湿气候;0.62 ka BP之后与现代气候状况相近。化学元素及其比值反映出毛乌素沙地具有千百年尺度的气候波动,并与北半球其他地区气候变化有着良好的对比。     

Lacustrine sediments provide geochemical evidence of environmental change during the last millennium in southeastern Brazil

A 172 cm-long sediment core was collected from a small pristine lake situated within a centripetal drainage basin in a tropical karst environment (Ribeira River valley, southeastern Brazil) in order to investigate the paleoenvironmental record provided by the lacustrine geochemistry. Sediments derived from erosion of the surrounding cambisoils contain quartz, kaolinite, mica, chlorite and goethite. Accelerator mass spectroscopy (AMS) ¹⁴C dating provided the geochronological framework. Three major sedimentary units were identified based on the structure and color of the sediments: Unit III from 170 to140 cm (1030±60–730±60 yr BP), Unit II from 140 to 90 cm (730±60–360±60 yr BP) and Unit I from 90 to 0 cm (360±60–0 yr BP). Results of major and trace element concentrations were analysed through multivariate statistical techniques. Factor analysis provided three factors accounting for 72.4% of the total variance. F1 and F2 have high positive loadings from K, Ba, Cs, Rb, Sr, Sc, Th, light rare earth element (LREE), Fe, Cr, Ti, Zr, Hf and Ta, and high negative loadings from Mg, Co, Cu, Zn, Br and loss on ignition (LOI). F3, with positive loadings from V and non-metals As and Sb, accounts for a low percentage (9.7%) of the total variance, being therefore of little interpretative use. The profile distribution of F1 scores reveals negative values in Units I and III, and positive values in Unit II, meaning that K, Ba, Cs, Rb, Sr, Sc, Th, LREE, Fe, Cr, Ti, Zr, Hf and Ta are relatively more concentrated in Unit II, and Mg, Co, Cu, Zn and Br are relatively more abundant in Units I and III. The observed fluctuations in the geochemical composition of the sediments are consistent with slight variations of the erosion intensity in the catchment area as a possible response to variations of climatic conditions during the last millennium.     

Interactions of Arctic and Atlantic water-masses and associated environmental changes during the last millennium, Hornsund (SW Svalbard)

The fjords of southwestern Spitsbergen (European Arctic) are a climatically sensitive area neighbouring the mixing zone of warm northward-flowing Atlantic water-masses and cold Arctic Water. Owing to reasonably high accumulation rates, these settings are especially suitable for providing high-resolution sedimentary records of regional hydrological and environmental changes. A sediment core spanning the last millennium was retrieved from the outer Hornsund fjord basin, ¹⁴C dated and analysed for sediment grain size, ice-rafted debris (IRD), the distribution of benthic foraminifera and their oxygen and carbon stable isotope composition. The record of sub-centennial resolution reveals three distinctive periods: the Medieval Warm Period, the Little Ice Age (∼AD 1600–1900) and 20th-century warming. The marine record obtained is well correlated with regional high-resolution ice-core records as well as with atmospheric palaeotemperature reconstructions and sea-ice data. The colder periods stay in phase with the greater influence of less saline, cold Arctic Water indicated by subtle changes in benthic foraminifera assemblages and the δ¹⁸O signal, which is dominated by changes in salinity. The IRD record clearly indicates that tidewater glaciers were present in SW Spitsbergen throughout the last millennium, and most actively from the late 16th century until the end of the 19th century.     

Climate variability in the Spanish Pyrenees during the last 30,000 yr revealed by the El Portalet sequence

Palynological, sedimentological and stable isotopic analyses of carbonates and organic matter performed on the El Portalet sequence (1802 m a.s.l., 42°48′00?N, 0°23′52?W) reflect the paleoclimatic evolution and vegetation history in the central-western Spanish Pyrenees over the last 30,000 yr, and provide a high-resolution record for the late glacial period. Our results confirm previous observations that deglaciation occurred earlier in the Pyrenees than in northern European and Alpine sites and point to a glacial readvance from 22,500 to 18,000 cal yr BP, coinciding with the global last glacial maximum. The patterns shown by the new, high-resolution pollen data from this continental sequence, chronologically constrained by 13 AMS ¹⁴C dates, seem to correlate with the rapid climate changes recorded in Greenland ice cores during the last glacial-interglacial transition. Abrupt events observed in northern latitudes (Heinrich events 3 to 1, Oldest and Older Dryas stades, Intra-Allerød Cold Period, and 8200 cal yr BP event) were also identified for the first time in a lacustrine sequence from the central-western Pyrenees as cold and arid periods. The coherent response of the vegetation and the lake system to abrupt climate changes implies an efficient translation of climate variability from the North Atlantic to mid latitudes.     

The sedimentary record of recent (last 500 years) environmental changes in the Seixal Bay marsh,Tagus estuary,Portugal

The inner Tagus estuary is essentially a sedimentation basin that receives cohesive sediment from terrestrial, marine, biological and anthropogenic sources. Three short cores from one site in a marsh area of this estuary (Seixal Bay) were analysed for sedimentary, geochemical and micropalaeontological contents (benthic foraminifera and nannoplankton). The length of the cores represents about half a millennium of sedimentation. Textural analysis suggests a highly uniform mud sedimentation for most of the cores but geochemical, mineralogical and micropaleontological results indicate climatic and environmental changes and anthropogenic disturbance. Three Foraminifera zones were identified. The lower part of the lower zone indicates sedimentation in an open channel or a lower domain of an exposed high-energy sandflat. Sediments of the upper part of the lower zone and of the middle zone were deposited in a lower-energy environment, probably associated with a sheltered, vertically aggrading mudflat located within the Seixal Bay. Biological and mineralogical indicators suggest that periods of total or partial closure of this bay occurred. Clay minerals indicate that drier and colder conditions prevailed in the lower half of this zone evolving gradually to a wetter and warmer environment towards the top. The upper zone indicates persistence of low-energy sedimentation and evolution towards the present salt-marsh conditions. Anthropogenic pollution is clear in geochemical proxies at the top of the sedimentary column and was used for dating purposes.     

Environmental changes in the northern Altai during the last millennium documented in Lake Teletskoye pollen record

A high-resolution pollen record from Lake Teletskoye documents the climate-related vegetation history of the northern Altai Mountain region during the last millennium. Siberian pine taiga with Scots pine, fir, spruce, and birch dominated the vegetation between ca. AD 1050 and 1100. The climate was similar to modern. In the beginning of the 12th century, birch and shrub alder increased. Lowered pollen concentrations and simultaneous peaks in herbs (especially Artemisia and Poaceae), ferns, and charcoal fragments point to colder and more arid climate conditions than before, with frequent fire events. Around AD 1200, regional climate became warmer and more humid than present, as revealed by an increase of Siberian pine and decreases of dry herb taxa and charcoal contents. Climatic conditions were rather stable until ca. AD 1410. An increase of Artemisia pollen may reflect slightly drier climate conditions between AD 1410 and 1560. Increases in Alnus, Betula, Artemisia, and Chenopodiaceae pollen and in charcoal particle contents may reflect further deterioration of climate conditions between AD 1560 and 1810, consistent with the Little Ice Age. After AD 1850 the vegetation gradually approached the modern one, in conjunction with ongoing climate warming.     

近千年东亚夏季风演变*

在分析东亚地区夏季海平面气压场与中国东部6区域干湿指数关系的基础上,重建了公元960—2000年近千年东亚地区夏季海平面气压场的格点资料,并对重建效果进行了检验。同时,依据重建的海平面气压场资料定义了近千年东亚夏季风强度指数,探讨了近千年东亚夏季风的变化特征。结果表明：（1）重建的近千年东亚地区的海平面气压场具有一定的可信度,它为研究更长时间尺度的东亚夏季风变化特征提供了基础;（2）东亚夏季风指数存在60～70 a、30～40 a、10～20 a的显著周期变化;（3）近千年东亚夏季风的强度指数主要经历过9次明显的趋势突变。其中,13世纪30年代东亚夏季风的强度指数经历了最显著的振动。     

过去千年年代和百年尺度东亚夏季风变化的模拟分析

利用通用地球系统模式过去千年集成（CESM-LME）试验数据,在验证模式模拟能力的基础上,分析了过去千年（850~1849年）年代和百年尺度东亚夏季风变化及其与中国东部夏季降水的关系。总体上,东亚夏季风在过去千年逐渐减弱,并伴随着年代际和百年尺度波动。在变化趋势上,过去千年土地利用不断增加、后期火山爆发偏多和地球轨道参数变化联合引起欧亚大陆中高纬表面温度降低、东亚区域海陆热力差异减小,东亚夏季风相应减弱;在年代际尺度上,东亚夏季风变化与太平洋年代际振荡有关,后者通过影响北太平洋和中国东部表面温度来改变东亚区域海陆热力差异和夏季风强度;百年尺度东亚夏季风波动受多种因子共同调制,期间欧亚大陆中高纬和北太平洋表面温度变化明显。与此同时,过去千年东亚夏季风逐渐减弱伴随着中国东部降水由南向北呈现负—正—负的变化趋势;在年代际和百年尺度上,东亚夏季风偏强时,中国东部降水表现为南旱北涝型分布。