柴达木盆地托素湖不同位置岩芯沉积物指标对比及其环境意义

湖泊不同位置岩芯沉积物相同代用指标的变化是否一致对于重建可靠的区域气候变化历史至关重要.目前多数研究仅利用深水区单一的沉积岩芯来反演区域的气候环境变化,对于不同位置岩芯重建结果的异同尚缺乏研究.本文选择托素湖不同位置、不同水深的4根短钻岩芯沉积物,在放射性核素(210 Pb和137 Cs)定年的基础上,对比分析各岩芯沉积物粒度、碳酸盐含量等代用指标的变化情况.结果显示,湖泊内相近的沉积岩芯沉积物粒度变化相似,但相距较远的岩芯之间粒度变化差异较大;浅水区的沉积物粒度(粒径或组分含量)在短时间尺度上变化很大,而深水区的沉积环境比较稳定,在百年尺度上的变化不明显;有机质与碳酸盐含量总体变化趋势一致且有较好的相关性,表明碳酸盐可能受到湖泊生产力的影响.碳酸盐含量、碳酸盐氧同位素(δ18 O)和TL06孔孢粉的A/C比值变化基本一致,反映的有效湿度变化与同期气象记录的相对湿度一致,但与降水量和蒸发量的变化不一致.因此,托素湖粒度指标仅指示不同位置钻孔沉积环境状况,与气候变化的关系并不明显,用碳酸盐及其同位素等地球化学指标恢复区域气候变化历史更可靠.     

近1200 a来黄河下游梁山泊沉积记录的环境变迁

利用梁山泊670 cm柱状岩芯沉积物,基于精确的AMS-~(14)C年代测定,通过高分辨率的粒度、磁化率、总有机碳、C/N比值等环境代用指标的综合分析,并结合历史文献记载,初步揭示了1200 a来黄河下游地区平原湖泊沉积特征及环境演化历史.结果表明,梁山泊环境演化大致分为5个阶段:790-940 AD期间,为低湖面的沼泽沉积环境,气候冷干;940-1215 AD期间,屡次受到黄河决溢洪水影响,湖盆扩张,湖泊水位上升,为梁山泊极盛期,气候暖湿;1215-1310 AD期间,黄河夺淮入黄海,湖区淤积严重,湖泊萎缩减小;1310-1470 AD期间,再次受到黄河决溢洪水影响,水位上升,面积扩张,但逊于极盛期;1470 AD至现代,黄河河道进一步南移,远离梁山泊,湖盆淤积抬高,梁山泊最终消失,直到1855AD,黄河第6次大改道北移,湖泊再次受到黄河洪水影响,由于前期受到泥沙淤积抬高,该地区仅作为黄河泥沙承载区.在气候变化大背景下,黄河改道决溢是梁山泊演化的主因.     

近0.3 ka来龙感湖流域人类活动的湖泊环境响应

通过210Pb测年、历史事件记载和沉积记录, 对钻孔岩芯沉积物年代进行了确定. 利用花粉、硅藻、磁参数、色素及结合态磷等多环境代用指标分析, 讨论了近0.3 ka来龙感湖流域植被、土壤侵蚀变化与湖泊环境演化之间的关系, 特别是龙感湖营养态的变化. 湖泊经历了两次由贫营养向中等营养的转变, 两次富营养化的发生(1770AD后和1906AD后)与人类活动增强导致的湖泊营养外负荷的增加密切相关. 历史时期降水的变化又是决定该区人类活动强度变化的诱因. 近0.04 ka来, 湿地的严重破坏和流域化学肥料的使用, 使得湖泊富营养化程度呈现明显加重趋势.     

柴达木盆地东部尕海短钻岩芯记录的过去近400 a区域环境变化

干旱区湖泊沉积可以有效记录区域湿度变化及粉尘活动历史,位于柴达木盆地德令哈南部的咸水封闭湖泊尕海具有恢复区域环境变化的潜力.该地区的长序列环境演变研究已开展了较多的工作,但缺乏短尺度、高分辨率的近代以来的环境变化湖泊记录.通过对尕海深水区短钻岩芯放射性核素210Pb和137Cs的年代测定和沉积物各指标分析,认为尕海沉积物碳酸盐含量可以反映区域湿度变化;而粗颗粒组分(66.9μm)主要由风力搬运入湖,其含量可以指示区域粉尘活动历史.区域近400 a的环境变化可划分为3个阶段:1633 1750 AD:各指标出现大幅度波动,表现出该时期气候环境的不稳定和干湿交替,其中1650 1720 AD的变化波动尤为显著,这与太阳活动进入Maunder极小期存在一定的联系.1750 1950 AD:区域气候环境无明显波动,碳酸盐含量逐渐降低,湿度增加.1950 2010 AD:各指标变动剧烈,区域虽降水增多,但由于蒸发加强,湿度降低;1974 AD以后粗颗粒组分含量急剧上升,表现出高强度尘暴事件.     

两种激光粒度仪测量湖泊沉积物粒度结果的对比

湖泊沉积物粒度参数是湖泊沉积与环境演变研究中常用的环境指标,近年来激光粒度仪的发展和广泛使用更是促进了粒度指标的应用并在很大程度上提高了精度和效率.然而不同的激光粒度仪对于同一样品的测量会得到不同的结果,本文利用两种常见的激光粒度仪测量了西藏纳木错的两支岩芯,并对结果进行了对比分析.从仪器的重现性来看,Mastersizer2000型激光粒度仪要优于LS13320型激光粒度仪,而LS13320型激光粒度仪在对含量较少的细颗粒和粗颗粒的检测效果上优于Mastersizer2000型激光粒度仪;两种仪器得到的粒度参数d(0.1)和d(0.5)无论在变化趋势还是绝对数值上都较为相似,而d(0.9)的差异则较大.对比研究结果为利用湖泊沉积物粒度参数提取古环境信息研究提供了基础依据.     

西昆仑山南红山湖沉积反映的过去150年湖区环境变化

采用～２１０Ｐｂ和～１３７Ｃｓ方法对西昆仑山南红山湖 ２号孔（长 １．０７ ｍ）湖泊岩芯进行了定年和沉积速率研究，获得了分辨率达１．４年的过去约１５０年（１８５０～１９９７年）连续湖泊沉积环境序列．该沉积柱子的总有机碳、总氮、元素地球化学、碳酸钙、粒度、介形虫丰度等变化表明，这些环境代用指标具有很好的一致性，反映了湖区环境具有１９世纪下半叶的冷湿、１９世纪末期到２０世纪２０年代的暖湿和２０年代开始的暖干变化背景．２０年代以来又具有次一级的冷暖／干湿波动，可以划分为１９２２～１９６０年间的冷干／暖湿波动、１９６０年以来的强烈暖干化以及出现于７０年代中期到８０年代末期的短暂冷湿过程．其中，７０年代中期至末期的湿润时期和８０年代中期开始的干旱环境在邻近地区的器测气象记录中得到证实，粒度数据与器测降水记录具有较好的相关性．与同一地区的古里雅冰芯记录对比，该孔指示环境冷暖的代用指标（ＴＯＣ）与冰芯中代表温度变化的δ～１８Ｏ变化具有很好的对应关系，但指示干湿程度的指标与冰芯中代表降水大小的冰川积累量变化关系较差．该孔湖泊沉积记录表明，选取的代用指标具有明确的环境意义，湖芯序列能够反映高分辨率的气候环境变化．     

云南错恰湖两百年来气候环境变化与重金属污染

高海拔地区由于特殊的自然环境对气候变化和营养输入的响应十分敏感.在人类活动逐渐加强的背景下,高山湖泊高分辨率的沉积物记录了人与自然相互作用的演变过程.选取云南西北部典型高山湖泊——错恰湖,获取长度37 cm的连续湖泊沉积序列,基于铅铯测年法得到年代深度模型,并对湖芯样品进行总有机碳、总氮及正构烷烃的多指标测定和元素测量,结合气象监测数据探讨分析错恰湖的有机质来源和流域环境演化特征.根据气候代用指标的变化,两百年来错恰湖泊环境及区域气候演化可以分成4个主要阶段：1807-1900年：湖泊水位上升、湖面扩大,有机质丰度下降,有机质以外源贡献为主,内源比例上升;1900-1950年：湖泊水位开始下降、湖面收缩,有机质丰度下降,外源有机质来源增加;1950-1982年：湖泊水位下降、湖面进一步收缩,有机质丰度下降,外源输入比例继续增加;1982-2007年：湖泊水位下降、湖面收缩,有机质含量上升且以陆源输入为主,同时内源贡献比例开始增加.在元素测定结果中,人类活动对应了湖泊沉积重金属含量变化的3个阶段：1950年以前,重金属含量低且稳定,可视作自然背景阶段,人类影响忽略不计;1950年以后,湖泊流域工农业逐渐发展,人为干扰凸显;直到1982年以后,冶炼工业的进步加强了重金属的污染态势,并通过大气传输沉降被湖泊沉积物记录.错恰湖沉积记录的分析讨论在总结该区域气候环境演化历史的同时,加深了对气候人类活动湖泊生态系统相互作用过程的理解,为高山湖泊响应人类活动影响提供了证据.     

1860年以来博斯腾湖碳沉积过程演变

选取博斯腾湖3个不同点位岩芯,在²¹⁰Pb和¹³⁷Cs年代序列基础上,利用沉积物中的各理化指标,分析了该湖碳沉积的时空变化特征,结合各指标的相关性、沉积速率、C/N、同位素特征等,探讨了该湖1860年以来碳沉积环境的变化过程,为干旱区湖泊碳埋藏研究提供了依据.结果表明：1860-1910年,沉积速率相对较小,受人类活动影响较小,磁化率、中值粒径、总无机碳（TIC）较为稳定,总有机碳（TOC）含量相对较低,此时该湖有较多陆源有机质的输入;1910-1950年,湖泊西部浅水域沉积速率明显高于东部深水区,西北湖区水域有大量外源物质的输入,而湖泊初级生产力较低,内源贡献相对较小;1950-1980年,全湖TOC、TIC含量均呈现升高的趋势,尤其是西北近黄水沟水域升高最快,湖泊内源贡献在增加,陆源组分的输入相对前一阶段要少;1980-2002年,沉积速率快速升高,尤其湖泊东部水域最为明显,TOC含量均呈现升高的趋势,湖泊西部水域初级生产力要高于东部深水区,湖面蒸发较强,气候比较温暖;2002年以来,全湖沉积速率相对较高,外源有机质贡献较小.过去150年博斯腾湖沉积物碳累积速率整体上呈现出升高的趋势,尤其是近50年来快速升高,东部湖区碳累积速率比西部湖区高.     

新疆博斯腾湖沉积物粒度的古环境意义初探

湖泊沉积物的粒度分析是一种研究古环境变化常用的手段,但是其环境意义具有多解性,尤其是沙（荒）漠干旱区的湖泊沉积物粒度变化,代表的是沙尘天气的多寡强弱还是其它环境因素的变化值得细致研究。在对我国最大的内陆淡水湖—新疆博斯腾湖的沉积物短岩芯进行了^210Pbex,^137Cs定年的基础上,对近50多年沉积物的粒度进行分析,结果表明平均粒径与粗颗粒含量与区域最大河流—开都河大山口站的最大一天洪量、洪峰流量、天山巴音布鲁克站年降水量、湖泊水位变化以及湖泊附近焉耆站3-6月风力强度变化记录等环境因素对比发现,湖泊中部沉积物中粗颗粒含量变化主要反映的是入湖河流径流量、区域洪水强度及频率、山地降水,而并不反映大风天气或者湖泊水位的变化。对其近千年沉积岩芯的多指标分析结果表明,即使在数百年时间尺度上,博斯腾湖沉积物粒度的环境意义依然与十年时间尺度上一致。     

不同时间尺度下的湖泊沉积物环境记录——以沉积物粒度为例

在湖泊沉积记录与古气候研究中, 沉积物粒度的环境意义常常解释为: 粗粒沉积物指示低水位时期的干旱气候, 细粒沉积物指示高水位时期的湿润气候. 本文通过对云南洱海和程海现代沉积物粒度的研究, 揭示了沉积物粒度在不同时间尺度、不同时间分辨率的研究中具有不同的环境指示意义. 在长时间尺度、低分辨率(百年、千年)研究中, 粗粒沉积物指示湖泊收缩、湖水较浅的干旱气候期; 细粒沉积物指示湖泊扩张、湖水较深的湿润气候期. 在短时间尺度、高分辨率(年际、10 a)研究中, 粗粒沉积物指示降雨量较大的湿润年份; 细粒沉积物指示降雨量相对较小的干旱年份. 由于不同时间尺度研究中沉积分辨率、采样分辨率和定年精度的不同, 湖泊沉积物记录所反映的环境信息在不同尺度下因此可能存在差异. 在由以往的长时间尺度、低分辨率研究转向短时间尺度、高分辨率研究的过程中, 不能简单套用各种指标在长尺度研究中的环境指示意义, 必须结合研究的时间尺度和分辨率, 综合分析各种因素对环境记录的影响方式和程度, 才能得出可靠结论.     

青藏高原东南部巴松措现代沉积过程及其对气候变化的响应

湖泊沉积物是记录气候演化信息的重要载体之一,在探讨过去气候变化过程研究中发挥重要作用.然而,沉积物中的许多代用指标对气候的指示意义存在多解性,不同指标所反映的环境信息相互之间有时会存在矛盾.为了能够更准确地解读湖泊沉积物中指标所记录的环境变化信息,开展现代湖泊沉积物指标与环境之间的关系研究,深入探讨各指标对环境变化的响应机制尤为关键.本文选取青藏高原东南部巴松措湖泊表层沉积物作为研究对象,利用²¹⁰Pb与¹³⁷Cs比活度检测结果建立年代序列,对沉积物中粒度、磁化率、有机质含量等指标进行分析,揭示巴松措现代沉积过程.结合沉积物粒度端元组分分析结果,并将不同指标变化与林芝气象站所记录的数据资料进行对比,得出以下主要结论：该地区沉积物来源主要包括径流搬运的冰川碎屑物质和来自青藏高原南部、西南部上空悬浮于大气中的风成物质两部分;其中,通过风力搬运的物质输入主要集中在冬半年,受季节性风向及风速变化影响明显;径流受到冰雪融水与夏季降水的补给,因此通过径流搬运的物质输入量受到温度与降水综合影响;湖泊中磁性矿物碎屑的产生和输入主要受区域降水量影响的流域侵蚀速率变化控制,该湖泊沉积物磁化率波动可以有效的指示该地区降水量变化;沉积物中总有机碳含量和总氮含量变化主要反映湖泊自身初级生产力的变化,对区域温度变化的响应显著.     

Spatiotemporal patterns of carbon sequestration in a large shallow lake,Chaohu Lake: Evidence from multiple-core records

Lake sediment can sequestrate large amounts of carbon and this issue has become a research hotspot. However, most of research on carbon burial in lakes is based on a single (or a few) sediment core records and so may underestimate the variability of carbon burial features within a single lake. In this study, therefore, Chaohu Lake, a typical large shallow lake in the middle and lower reaches of the Yangtze River, was selected to conduct multiple, high resolution sediment core studies to elucidate that variability. Overall 18 sediment cores are analyzed according to paleolimnological proxies (including ²¹⁰Pb/¹³⁷Cs for 3 master cores); sediment accumulation rate, total organic carbon, grain size and loss of ignition is measured or estimated for most cores. The spatiotemporal variations of organic carbon burial rate (OCBR), carbon storage and their driving factors were examined. Results show: 1) There was a clear temporal difference in carbon burial during the past 150 years, with OCBR varying from 1.1 g C/m²/y to 25.6 g C/m²/y (mean 9.8 g C/m²/y). OCBR began to increase after around 1900, a rapid increase followed after 1950s and a downward trend after 1970s. Total carbon burial amount (OCBA) in the lake since the 1850s is 1.11 x 10¹⁰ g. 2) The average OCBR of six sediment cores in the northwest lake area is 13.4 g C/m²/y, significantly higher than that for sediment cores in other areas (9.6 g C/m²/y). 3) TOC, OCBR, OCBA in all 18 cores exhibited similar temporal patterns (i.e. marked increase since 1950s in most of the cores) but with significant differences in several lake locations. 4) During the last 150 years, carbon burial in Chaohu Lake appears to be greatly affected by changes in regional temperature and population size, according to their significant correlations. OCBR also has a significant correlation with the average lake level in the past 50 years, indicating human activity (notably dam building). This has imposed an important impact on OCBR in Chaohu Lake. This multi-sediment core study reveals the spatiotemporal characteristics of carbon burial in the lake and provides an important basis for increasing the accuracy of calculating carbon storage in large shallow lakes.     

湖泊深钻揭示的中更新世以来中国环境的区域分异及其与亚洲季风的关系

根据青藏高原东部若尔盖盆地ＲＭ孔,北部柴达木盆地ＺＫ－３３６及ＣＫ－６孔和滇池盆地参１井等长孔的湖泊深钻记录,探讨了中更新世以来我国环境的区域分异特点,结合黄土－古土壤序列的研究成果,初步分析了导致区域环境分异的原因与亚洲季风的关系,结果表明青藏高原在其中扮演很重要的角色。     

Pacific decadal oscillation impact on East China precipitation and its imprint in new geological documents

This paper briefly introduces the history of the study of the Pacific decadal oscillation (PDO) and explores the relationship between the PDO and sediment grain size from two typical sediment cores from the lower Changjiang (Yangtze River) and Huanghe (Yellow River) estuaries. It is found that the median grain sizes of both cores exhibit relatively high correlation with the PDO. This is because the PDO causes interdecadal variability of precipitation in the East Asia Monsoon region, thus changing the hydrodynamics in both the Changjiang and Huanghe catchments, eventually resulting in variation of sediment grain size. Our analysis also revealed that during different phases of the PDO, the sediment grain size of the Changjiang and Huanghe estuaries showed different variations in cold and warm PDO phases. This is related to movement of the precipitation center driven by the shift in different PDO phases. Moreover, we compared more high resolution geological proxies with the PDO, including stalagmites and tree rings, in East China over the past century. The results indicate that variations of studied geological proxies are generally well correlated with the PDO but have some differences. Finally, longer variations of sediment grain sizes in the Changjiang and Huanghe estuaries are compared with a reconstructed PDO over the last 200 years; sediment grain sizes were still correlated with the PDO, implying that sediment grain size may be used as a new proxy for studying the long-term behavior of the PDO. This result supports previous knowledge of the PDO impact on East China climate evolution and offers a new proxy for further PDO study. Our study will improve paleoenvironment reconstruction in East China on a decadal time scale and benefit future climatic predictions.     

湖泊沉积有机碳同位素与环境变化的研究进展

湖泊沉积有机质稳定碳同位素（δ^13Corg)在区域气候与环境变化方面的应用近年来发展迅速,成果令人瞩目,保存在各类湖泊岩芯中的δ^13Corg记录揭示了晚更新世以来大气CO2浓度的变化、湖泊水位波动、湖区生态与植被的变迁以及气温变化等重要环境信息,由于造成δ^13Corg值变化的影响因素较多,确定个湖与环境变化有关的主导因素时常有赖于其它证据的帮助,诸如地球化学、古湖沼学、孢粉学、分子同位素地层学等等,前人通过研究来自不同类型湖泊、具不同曲线形态特征的δ^13Corg记录,提出了多种环境解释模型,本文对此作了归纳和评述。鉴别和澄清湖泊沉积有机质的源物质以及有机物源随环境变化而发生过的变化,是研究δ^13Corg记录环境意义至关重要的基础性工作,由于有机质含量、碳氮比值、氢指数、生物残留物鉴别等常能提供有关有关湖泊有机质来源、产率、成岩作用等方面的有用信息,这方面的研究结果应该尽可能一并提供,以利于恰当地应用现有的环境解释模型,或者建立个湖新模型,单体生物标志化合物鉴别通常也能为区分湖积有机质中陆生、水生、细菌生等不同碳的来源提供有用信息,特定化合物同位素分析技术近年来成功地应用于建立单体生物标志化合物碳同位素地层学,为湖积有机碳同位素在生态环境演变研究方面的应用提供了思路,我国许多湖泊的湖底沉积岩芯尚未钻取,那些对过去全球变化研究有价值的δ^13Corg记录有待我们去获取和研究。     

Quantifying potential propagule pressure of aquatic invasive species from the commercial shipping industry in Canada

We quantify and compare different measures of potential propagule pressure (PPP) of aquatic invasive species (AIS) from commercial vessels in Canada. We used ship arrivals and ballast water discharge volumes as proxies for PPP from ballast water organisms, and wetted surface area (WSA) as a proxy for hull fouling PPP, to determine their relative contributions to total PPP. For three regions studied, PPP proxies correlated significantly across ports and some vessel categories. Relative contributions of ship arrivals, ballast discharge, and WSAs to PPP, evidenced by non-significant correlations across these measures, varied across regions, ports, vessel types, and seasons. Flow-through (dominant on east and west coasts) and empty-refill (in Great Lakes-St. Lawrence region) were the major ballast water exchange methods employed by the vessels surveyed. These methods have different biological efficacy for AIS removal, influencing PPP. Our study illustrates benefits and limitations of using different PPP proxies to estimate invasion risk.     

Variations in dust event frequency over the past century reflected by ice-core and lacustrine records in north China

In this paper, we analyzed the variations of dust proxies in the Dunde, Malan and Chongce ice cores from the northern Tibetan Plateau and the Hongjiannao lacustrine sediment core from north Shaanxi Province, and found that they all showed a general decrease trend over the past century. Owing to the fact that all these ice cores and lacustrine core were retrieved from the margins and/or the leeward sides of the major areas of dust events in north China, their records could suggest that the dust event frequency in north China declined over the study period. This decrease trend might be attributed to increasing precipitation and weakening westerly. However, human activities have made the areal extent of desertification expand acceleratingly in north China. This status could make it possible that dust events would occur on a large spatial scale under the future climate change, which would be a big environmental issue we shall face.     

Variability of natural and bomb-produced radionuclide distributions in abyssal red clay sediments

The nature of sedimentation and mixing are examined in abyssal red clay sediments from the North Central Pacific using three types of indicators: ²³⁰Th/²³²Th, organic¹⁴C, and¹³⁷Cs and ^239.240Pu.²³⁰Th/²³²Th analysed revealed that the clay sedimentation rate in three box cores collected within a 50 km radius was less than 1.0 mm/10³ yr. However, analyses of the organic carbon in thin layers of sediment revealed that radiocarbon was present much deeper in the cores (down to 20 cm) than was expected from the ²³⁰Th/²³²Th distribution. In addition, both the stratigraphy and inventory of radiocarbon was significantly different between box cores. The distributions and inventories of¹³⁷Cs and^239.240Pu were similar to that found for radiocarbon, further illustrating the spatial variability of radionuclides in oligotrophic North Pacific red clays. These data suggest that bioturbational processes are important for transporting organic carbon down into the sediment column.     

The effects of sewage organic matter on biogeochemical processes within mid-shelf sediments offshore Sydney, Australia

A laboratory incubation experiment was conducted using replicate cores collected from a muddy-sand sediment facies offshore Sydney, Australia to determine what components and processes would be affected by the addition of sewage organic matter. Sewage effluent has a solid phase composition of 40% carbon (35% organic carbon), 5% nitrogen, 1% phosphorus and 5% silicate. The molecular C:N:P ratio is 92:10:1, compared to the Redfield ratio of 106:16:1 in marine phytoplankton. Sediment cores were incubated at in situ temperature in a darkened room for periods up to 95 days. Sewage organic matter was added to the cores at three different loads equivalent to 0 (T0), 65 (T1) and 130 (T2) g m⁻² of sediment. Following the addition of sewage organic matter, fluxes of oxygen (into the sediments), ammonia and phosphate (from the sediments) increased, reflecting an enhanced organic carbon supply to the sediments. Oxygen penetrated to a depth of 6 mm in the ambient cores, but the sediment oxygen content was severely depleted following the addition of the sewage-derived organic matter. Sediment porewater data, together with nutrient flux data indicate that oxygen reduction, nitrate reduction and sulphate reduction occurs within these sediments. Following the addition of sewage organic matter, increases in total nitrogen, total phosphate and total organic carbon were measured to depths of 5 cm in the sediments, suggesting that bioturbation influences nutrient and organic carbon distributions. Additionally, irrigation of the surficial sediments may play an important role in the metabolism of organic matter. These results indicate that oxygen penetration, oxygen fluxes, nitrate concentrations within porewaters, ammonia flux rates, and solid phase concentrations of total organic carbon and nutrients may be useful indicators of sediments affected by high rates of organic matter deposition onto Sydney's offshore sediments. The EPA has recently predicted maximum deposition rates of sewage particulate matter to be approximately 1 g m⁻² day⁻¹. Because of the similarities in CNP ratios of sewage organic matter and marine organic matter, the effects of sewage organic matter and marine organic matter inputs to coastal sediments may not be easily distinguishable.