云南程海富营养化过程的碳氧稳定同位素示踪

近500年来程海生物成因碳酸盐δ18O和δ13C及其有机质δ13C同位素记录了程海湖泊环境由贫营养到中富营养的演化过程.碳酸盐δ18O记录显示,大约1690年程海成为封闭湖泊后,当时湖泊贫营养环境并没有发生变化,但造成了湖泊水体交换周期加长,碳酸盐δ13C、有机质δ13C及其色素含量、碳酸盐含量变化指示湖泊生产力开始增高.1911～1942年碳酸盐δ18O和δ13C及有机质δ13C突然显著偏负,表明湖泊生物种群结构发生转变,湖泊初级生产力迅速增加,湖泊由贫营养向中营养转化.湖泊沉积物色素含量及碳酸盐含量变化也记录了这一湖泊环境的转换过程.约1986年以来,随着藻类养殖业及其农业耕作方式的转变,程海水环境渐渐转变成目前的中富营养化状态.     

云南程海沉积物粒度对水深的指示意义

不同湖泊盆地构造以及流域水文过程的差异导致湖泊沉积物粒度的指示意义有所不同。文章以云南程海表层岩芯为研究对象,分析取自不同水深的表层岩芯沉积物粒度（1 cm、5 cm以及137Cs-峰层位）和碳酸盐含量（2cm、5cm以及137Cs-峰层位）,探讨其与水深的空间相关性;通过对垂直钻孔岩芯粒度的分析,并结合过去50余年来的湖泊水位记录,探讨沉积物"粒度-水深"在时间尺度上的关系。结果表明：1）在空间分布上,沉积物平均粒径和水深呈显著反相关关系,即程海沉积物平均粒径随水深增加（减小）而变细（变粗）,且该"粒度-水深"空间分布模式得到沉积物碳酸盐含量空间分布规律的支持;2）在时间尺度上,水深的时段沉积物粒度细,水浅的时段沉积物粒度粗;与"粒度-水深"的空间关系一致。我们推测上述"粒度-水深"的时空变化关系与湖泊面积变化导致的采样点与岸边/河口的距离有关。在此基础上,进一步分析了程海近千年的沉积物粒度与水位变化关系：中世纪暖期和现代暖期粒度偏粗,程海处于低湖面;小冰期程海沉积物平均粒度偏细,对应于高湖面。上述基于"粒度-水深"关系推导的水位变化与我们前期基于岸边地质证据得出的水位变化,以及历史文献记载的水位变化一致,验证了本文获得的"粒度-水深"关系的可靠性。     

Research on the carbon isotopic composition of organic matter from Lake Chenghai and Caohai Lake sediments

The carbon isotopic composition of organic matter from lake sediments has been extensively used to infer variations in productivity. In this paper, based on the study of the contents and δ13C values of organic matter in different types of lakes, it has been found that δ13C values of organic matter have different responses to lake productivity in different lakes. As to the lakes dominated by aqutic macrophytes such as Lake Caohai, organic matter becomes enriched in 13C with increasing productivity. As to the lakes dominated by aquatic algae such as Lake Chenghai, δ13C values of organic matter decrease with increasing productivity, and the degradation of aquatic algae is the main factor leading to the decrease of δ13C values of organic matter with increasing productivity. Therefore, we should be cautious to use the carbon isotopic composition of organic matter to deduce lake productivity.     

Lake sedimentary processes and vegetation changes over the last 45k cal a bp in the uplands of south-eastern Amazonia

This study addresses paleoclimate influences in a southern Amazonia ecotone based on multiproxy records from lakes of the Carajás region during the last 45k cal a bp. Wet and cool environmental conditions marked the initial deposition in shallow depressions with detrital sediments and high weathering rates until 40k cal a bp. Concomitantly, forest and C3 canga plants, along with cool-adapted taxa, developed; however, short drier episodes enabled expansion of C4 plants and diagenetic formation of siderite. A massive event of siderite formation occurred approximately 30k cal a bp under strong drier conditions. Afterwards, wet and cool environmental conditions returned and persisted until the Last Glacial Maximum (LGM). The LGM was marked by lake-level lowstands and subaerial exposure. The transition from the LGM to the Holocene is marked by the onset of oscillations in temperature and humidity, with an expansion of forest and canga plants. Cool taxa were present for the last time in the Carajás region ~ 9.5–9k cal a bp. After 10k cal a bp , shallow lakes became upland swamps due to natural infilling processes, but the current vegetation types and structures of the plateaus were acquired only after 3k cal a bp under wetter climatic conditions.     

Paleoearthquake Investigation along the Chenghai Fault Zone since ~500 ka, Southeast Margin of the Tibetan Plateau

The Chenghai fault zone is located in the Sichuan–Yunnan rhombus block, which is surrounded by the Honghe River, Xianshuihe–Xiaojiang, and Jinsha River fault zones. As a mid-continental active fault, it is one of the most important seismogenic fractures in the southeast margin of the Tibetan Plateau. Geological seismic study is an important supplement to the historical seismic record; therefore, identification of paleoearthquake events in this region is of great significance to reveal the pattern and mechanism of earthquake development. In this study, detailed investigation has been carried out on the earthquake traces that formed in the Quaternary sediments in the Jinsha River section of the Chenghai fault zone, and samples for dating chronology testing were also collected. Many paleoearthquake traces were discovered in the field, including earthquake fissions, dammed lake sediments and landslides, earthquake-generated rock falls, seismic faults, and sand liquefaction veins. The collected samples were tested using optically stimulated luminescence, electron-spin resonance, and U-series methods. A total of 68 chronological samples were dated, combined with the results of field investigations, and 10 large paleoearthquake events were discovered in this region since 500 ka, which are at approximately 450, 400, 345, 300, 250, 190, 155, 105, 75, and 25 ka. Ten tectonic activity periods that produced multiple paleoearthquake events were identified since 500 ka. This study identifies paleoearthquake events in longer scales, larger spaces, and more extensive sediments, which provides new perspectives and new ideas for paleoearthquake research.     

鄱阳湖沉积物近8ka来有机质碳同位素记录及其古气候变化特征

通过对鄱阳湖沉积物的高密度采样和有机质碳同位素分析,讨论了鄱阳湖近 8 ka来的古气候环境.鄱阳湖沉积物有机质δ 13C值为-22.42‰～-32.42‰,属 C3类植物来源.暖湿期δ 13C值相对偏负;冷(凉)干期δ 13C值相对偏正.这些记录表明,鄱阳湖近 8 ka来经历了 4次暖湿和 4次冷(凉)干的气候环境变化, 7 900～3 660 a B.P.、3 440～2 990 a B.P.、2 940～2 170 a B.P.、1 820～6 50 a B.P.属相对温暖湿润的气候环境;3 660～3 440 a B.P.、2 990～2 940 a B.P.、2 170～1 820 a B.P.、650～200 a B.P.为相对冷凉干旱的气候环境,自 200 a B.P.(1 750 A.D.)以来湖区气候开始转暖.暖湿期持续时间较长,冷(凉)干期持续时间较短,1 000 a B.C.左右为一次重要的气候变冷事件.我国全新世几个特征性气候在湖区均有不同的显示,并与孢粉、硅藻、历史记录所反映的古气候环境对应性较好,可以作为恢复古气候变化的灵敏指标.     

滇中星云湖地区200年来的环境演化

在对星云湖的近现代沉积物进行粒度、稳定同位素等测试分析的基础上,综合对比了多项环境指标,并从自然变化和人为影响2个方面揭示湖泊环境演化的动态过程和动力学机制以及各环境要素的内在联系.研究表明该地区近200 a来环境及生态演化具有以下区域性特点:19世纪初期气候较为温暖干旱,之后向温凉湿润转变,20世纪80年代开始,湖泊出现富营养化,1998年以来气温处于回升状态,现在正处于暖干气候阶段,人类活动正在日益深刻地影响着湖泊的环境演化.     

Functional Spectral Analysis of Paleoclimatic Evolution in Lanzhou Area over the Last 15 ka

In this paper, we make use of the functional spectral analysis to infer the periodicity of paleoelimate in the Hongzuisi section since about 15 ka. Through combined analysis of organic carbon isotope and CaCO3 content, the law of paleoclimatic evolution of the Hongzuisi section is obtained. There were climatic changes from 10 ka to about 0.1 ka over the last 15 ka. Among these cycles, the cycle of several ka is most remarkable. The result indicates that functional spectral analysis is helpful for paleoclimatic study, which can provide useful information about paleoclimatic reconstruction and future forecast.     

云南大理地区1989—2019年期间气候变化及对洱海水质的影响

依据1989年至2019年云南大理地区所辖12个气象站点的气候数据和洱海水质监测资料等文献,分析大理地区气候变化特征和洱海富营养化变化趋势,并总结洱海水质综合营养状态指数与降水量、气温的相互关系。结果表明,1989年至2019年期间,大理地区的年平均气温呈波动上升趋势,气候变暖明显,冬季气温升温幅度最大;年降水量总体呈波动下降趋势,秋季降水量减少最为显著。洱海水质的综合营养状态指数及单因子总氮、总磷、高锰酸盐指数等总体呈升高趋势,而水体透明度呈降低趋势;进一步可分成2个阶段,即2003年之前呈快速上升或下降变化趋势;2003年之后呈波动稳定趋势。洱海综合营养状态指数与年平均气温呈正相关,与年降水量呈负相关关系;总氮、水体透明度分别与年平均气温正相关和负相关,与年降水量则呈负相关和正相关;而总磷与冬季平均气温、高锰酸盐指数与夏季或冬季平均气温均呈正相关关系。年内变化上,洱海污染指数、综合营养状态指数在最近的2015—2019年期间呈现6—10月份明显增高,显示非汛期水质明显好于汛期状况。总之,1989—2019年期间,受大理地区气温升高、降水量减少导致入湖水量减少的影响,洱海综合营养状态指数呈升高趋势,湖泊富营养化进程加剧状况没有得到改善,洱海水环境仍然比较脆弱。     

Shoreline tufa and tufaglomerate from Pleistocene Lake Bonneville,Utah, USA: stable isotopic and mineralogical records of lake conditions,processes, and climate

Shoreline carbonate deposits of Pleistocene Lake Bonneville record the conditions and processes within the lake, including the evaporative balance as well as vertical and lateral chemical and isotopic gradients. Tufas (swash‐zone) and tufaglomerates (cemented, subaqueous colluvium or beachrock) on multiple, well‐developed shorelines near the Silver Island Range, Utah, also present an opportunity to examine physicochemical lake processes through time. Three shorelines are represented by carbonate deposits, including the 23–20 ka Stansbury stage, 15–14.5 ka Bonneville stage, and 14.5–14 ka Provo stage. Mean δ¹⁸O_VSMOW values of all three shorelines are statistically indistinguishable ( ～ 27 ± 1‰), when a few Bonneville samples of unusual composition are neglected. However, differences in primary carbonate mineralogy indicate that the correspondence is an artefact of the different fractionation factors between calcite or aragonite and water. Second, in order to sustain a much smaller, shallower lake during the colder Stansbury stage, the climate must have also been relatively dry. Third, δ¹⁸O values in tufa are higher than tufaglomerate by ～ 0.5‰, consistent with greater evaporative enrichment of lake water in the swash zone. Fourth, mean δ¹³C values for the Provo, Stansbury and Bonneville shorelines (4.4, 5.0 and 5.2‰, respectively) show that carbon species were dominated by atmospheric exchange, with the variations produced by differences in the oxidation of organic matter. Comparisons of shoreline carbonates with deep‐lake marls of the same approximate age indicate that shoreline carbonate was much higher in δ¹³C and δ¹⁸O values (both ～ 2.5‰) during Bonneville time, whereas isotopic differences were minor (both ～ 1‰) in Stansbury time. In particular, the Bonneville stage may have sustained large vertical or lateral isotopic gradients due to evaporative enrichment effects on δ¹⁸O values. In contrast, the lake during the much shallower Stansbury stage may have been well mixed. Differences in the primary mineralogy (Stansbury and Bonneville, aragonite > calcite; Provo, calcite > aragonite) reflect profound differences in lake chemistry in terms of open versus closed‐basin lakes. The establishment of a continuous outlet during Provo time probably reduced the Mg²⁺/Ca²⁺ ratio of lake water. Curiously, regardless of primary mineralogy, tufaglomerate cements are enriched in Na⁺ and Cl^? and depleted in Mg²⁺ relative to capping tufa of the same age. This probably reflects vital or kinetic effects in the swash zone (tufa). We suspect that ‘abiotic’ effects may have been important in the dark pore space of developing tufaglomerate, where the absence of light suppressed photosynthesis. Copyright © 2005 John Wiley & Sons, Ltd.     

Carbon and Oxygen Isotopic Composition of Surface-Sediment Carbonate in Bosten Lake (Xinjiang, China) and its Controlling Factors

Bosten Lake is a mid-latitude lake with water mainly supplied by melting ice and snow in the Tianshan Mountains. The depositional environment of the lake is spatially not uniform due to the proximity of the major inlet and the single outlet in the western part of the lake. The analytical results show that the carbon and oxygen isotopic composition of recent lake sediments is related to this specific lacustrine depositional environment and to the resulting carbonate mineralogy. In the southwestern lake region between the Kaidu River inlet and the Kongqi River outlet, carbon isotope composition (δ13C) values of the carbonate sediment (-1‰ to -2‰) have no relation to the oxygen isotope composition of the carbonate (δ18O) values (-7‰ to -8‰), with both isotopes showing a low variability. The carbonate content is low (<20%). Carbonate minerals analyzed by X-ray diffraction are mainly composed of calcite, while aragonite was not recorded. The salinity of the lake water is low in the estuary region as a result of the Kaidu River inflow. In comparison, the carbon and oxygen isotope values are higher in the middle and eastern parts of the lake, with δ13C values between approximately +0.5‰ and +3‰, and δ18O values between -1‰ and -5‰. There is a moderate correlation between the stable oxygen and carbon isotopes, with a coefficient of correlation r of approximately 0.63. This implies that the lake water has a relatively short residence time. Carbonate minerals constitute calcite and aragonite in the middle and eastern region of the lake. Aragonite and Mg-calcite are formed at higher lake water salinity and temperatures, and larger evaporation effects. More saline lake water in the middle and eastern region of the lake and the enhanced isotopic equilibrium between water and atmospheric CO2 cause the correlating carbon and oxygen isotope values determined for aragonite and Mg-calcite. Evaporation and biological processes are the main reasons for the salinity and carbonate mineralogy influence of the surface-sediment carbonate in Bosten Lake. The lake water residence time and the CO2 exchange between the atmosphere and the water body control the carbon and oxygen isotope composition of the carbonate sediment. In addition, organic matter pollution and decomposition result in the abnormally low carbon isotope values of the lake surface-sediment carbonate.     

医巫闾山变质核杂岩中金矿的稳定同位素特征

医巫闾山变质核杂岩中金矿及相关岩石的氢、氧、铅、硅、碳、硫稳定同位素测试结果为:成矿流体δD为-97‰~-72‰,δ18O为0.3‰~3.8‰,在δ18O-δD分布图上,位于变质水、岩浆水与当地雨水之间;其他稳定同位素数据及综合资料均说明,以排山楼金矿为代表的该区金矿成矿具有长期性、复杂性和多源性;医巫闾山变质核杂岩构造系统对区内金矿有一定控制作用.     

巢湖富营养化过程的沉积记录

土地利用和人类活动加剧所导致的营养元素输入的增加是引起湖泊富营养化趋势增强的重要原因。巢湖沉积钻孔柱状样中总有机碳和总氮自20世纪70年代以来呈明显升高趋势,分别增加了2.5、2.9倍。由柱状样中的TOC/TN比值、TARHC、OEP判断得出,19世纪末到20世纪40年代中期TOC是陆源和内源两种来源并重;20世纪40年代中期到20世纪70年代初期以陆源为主,并可能存在石油污染;20世纪70年代以来沉积物有机质中藻类来源的有机质占主要地位。巢湖沉积柱状样的研究表明20世纪70年代以来巢湖富营养化开始恶化。     

藏南羊卓雍错近代沉积物碳酸盐氧同位素特征及其环境意义

20世纪80年代以来气候变暖加剧,青藏高原冰川物质负平衡趋势增强,导致众多湖泊水位上升,但位于藏南地区的羊卓雍错,湖泊水位近年来却呈现出显著的波动下降趋势。本研究通过对羊卓雍错YZYC2沉积岩芯(长23 cm)进行²¹⁰Pb活度测定,建立沉积物的年代序列;分析公元1989年以来沉积物全样碳酸盐含量及其氧同位素组成,并结合现代气象及水文观测数据,揭示羊卓雍错沉积物碳酸盐氧同位素(δ¹⁸O)的环境意义及其对气候变化的响应过程与机制。结果表明,YZYC2岩芯碳酸盐矿物以自生成因的文石为主,其含量变化范围为23.3 % ~39.7 %,δ¹⁸O值变化范围为-4.7 ‰ ~-3.2 ‰。沉积物碳酸盐δ¹⁸O值总体呈波动上升趋势,较好地记录了近30年来羊卓雍错湖泊水位变化。1989~2019年羊卓雍错水位变化总体由降水与蒸发共同作用下的湖区有效湿度变化主导,同时也可能受到羊湖电站运行的影响。

     

Carbon and Oxygen Isotopic Composition of Surface‐Sediment Carbonate in Bosten Lake (Xinjiang,China) and its Controlling Factors

Bosten Lake is a mid-latitude lake with water mainly supplied by melting ice and snow in the Tianshan Mountains. The depositional environment of the lake is spatially not uniform due to the proximity of the major inlet and the single outlet in the western part of the lake. The analytical results show that the carbon and oxygen isotopic composition of recent lake sediments is related to this specific lacustrine depositional environment and to the resulting carbonate mineralogy. In the southwestern lake region between the Kaidu River inlet and the Kongqi River outlet, carbon isotope composition (δ13C) values of the carbonate sediment (?1‰ to ?2‰) have no relation to the oxygen isotope composition of the carbonate (δ18O) values (?7‰ to ?8‰), with both isotopes showing a low variability. The carbonate content is low (<20%). Carbonate minerals analyzed by X-ray diffraction are mainly composed of calcite, while aragonite was not recorded. The salinity of the lake water is low in the estuary region as a result of the Kaidu River inflow. In comparison, the carbon and oxygen isotope values are higher in the middle and eastern parts of the lake, with δ13C values between approximately +0.5‰ and +3‰, and δ18O values between ?1‰ and ?5‰. There is a moderate correlation between the stable oxygen and carbon isotopes, with a coefficient of correlation r of approximately 0.63. This implies that the lake water has a relatively short residence time. Carbonate minerals constitute calcite and aragonite in the middle and eastern region of the lake. Aragonite and Mg–calcite are formed at higher lake water salinity and temperatures, and larger evaporation effects. More saline lake water in the middle and eastern region of the lake and the enhanced isotopic equilibrium between water and atmospheric CO2 cause the correlating carbon and oxygen isotope values determined for aragonite and Mg–calcite. Evaporation and biological processes are the main reasons for the salinity and carbonate mineralogy influence of the surface-sediment carbonate in Bosten Lake. The lake water residence time and the CO2 exchange between the atmosphere and the water body control the carbon and oxygen isotope composition of the carbonate sediment. In addition, organic matter pollution and decomposition result in the abnormally low carbon isotope values of the lake surface-sediment carbonate.     

应用氢、氧同位素研究苏干湖盆地大、小苏干湖湖水补给来源

苏干湖盆地是嵌套在柴达木盆地中的一个封闭盆地,大、小苏干湖是盆地地表水和地下水的汇集中心,两湖相距20km,但大苏干湖为咸水湖、小苏干湖为淡水湖。文章通过氢、氧同位素分析盆地中大、小苏干湖湖水补给来源,解释了两湖虽近,但矿化度差别较大的原因。为解决敦煌盆地地下水资源短缺问题,政府部门计划从苏干湖盆地地下水的主要补给源——大哈尔腾河引水至党河当中,但湖水补给源的不同,导致引水对两湖影响不一。结果表明,大苏干湖湖水补给来源为大、小哈尔腾河上游4 800m以上冰雪融水补给,且径流路径长,蒸发强烈。小苏干湖主要由来自党河南山西段和阿尔金山区雨水补给,径流路径短。因此,大、小苏干湖矿化度差别较大,补给源的不同导致引水对大苏干湖湖水影响较大,而对小苏干湖湖水影响较小。     

祁连山北坡稳定同位素生态水文学研究的初步进展与成果应用

2012年以来祁连山北坡稳定同位素生态水文学研究的初步进展包括：（1）云下蒸发和水汽再循环是降水稳定同位素演化的重要因子;（2）各水体稳定同位素年内变化指示了地表水和地下水的不同转化模态;（3）海拔2 000 m以上山区水汽再循环贡献了约24%的降水;（4）冰雪冻土带贡献了出山径流的80%左右。上述结果为祁连山国家公园范围区划和生态保护提供了科技支撑。     

Fluid Inclusions and Stable Isotopic Characteristics of the Yaoling Tungsten Deposit in South China: Metallogenetic Constraints

The Yaoling tungsten deposit is a typical wolframite quartz vein‐type tungsten deposit in the South China metallogenic province. The wolframite‐bearing quartz veins mainly occur in Cambrian to Ordovician host rocks or in Mesozoic granitic rocks and are controlled by the west‐north‐west trending extensional faults. The ore mineralization mainly comprises wolframite and variable amounts of molybdenite, chalcopyrite, pyrite, fluorite, and tourmaline. Hydrothermal alteration is well developed at the Yaoling tungsten deposit, including greisenization, silicification, fluoritization, and tourmalinization. Three types of primary/pseudosecondary fluid inclusions have been identified in vein quartz, which is intimately intergrown with wolframite. These include two‐phase liquid‐rich aqueous inclusions (type I), two‐ or three‐phase CO₂‐rich inclusions (type II), and type III daughter mineral‐bearing multiphase high‐salinity aqueous inclusions. Microthermometric measurements reveal consistent moderate homogenization temperatures (peak values from 200 to 280°C), and low to high salinities (1.3–39 wt % NaCl equiv.) for the type I, type II, and type III inclusions, where the CO₂‐rich type II inclusions display trace amounts of CH₄ and N₂. The ore‐forming fluids are far more saline than those of other tungsten deposits reported in South China. The estimated maximum trapping pressure of the ore‐forming fluids is about 1230–1760 bar, corresponding to a lithostatic depth of 4.0–5.8 km. The δD_H2O isotopic compositions of the inclusion fluid ranges from ?66.7 to ?47.8‰, with δ¹⁸O_H2O values between 1.63 and 4.17‰, δ¹³C values of ?6.5–0.8‰, and δ³⁴S values between ?1.98 and 1.92‰, with an average of ?0.07‰. The stable isotope data imply that the ore‐forming fluids of the Yaoling tungsten deposit were mainly derived from crustal magmatic fluids with some involvement of meteoric water. Fluid immiscibility and fluid–rock interaction are thought to have been the main mechanisms for tungsten precipitation at Yaoling.     

淮河下游地区地表水与地下水同位素特征分析

为探明淮河下游地区地表水与地下水稳定同位素的组成特征,于2020年11月对该区域进行代表性采样,共采集地表水样13个,地下水样82个.结合全球大气降水同位素监测网(GNIP)公布的南京降水同位素数据,根据最小二乘法得出当地大气降水线(LMWL)方程为:δD=8.49δ18O+17.71,其斜率和截距高于全球大气降水线(...     

吉林西部盐碱化土壤碳酸盐的碳稳定同位素特征

对吉林西部盐碱化土壤的物理性状进行了实地调查,并对不同土地利用类型的土壤碳酸盐碳稳定同位素作了系统的测定。结果表明,研究区内盐碱地土壤碳酸盐的δ¹³C值的变化趋势可以反映本区土壤盐碱化的进程。盐碱化土地在0～50 cm的深度范围内,土壤碳酸盐的δ¹³C值变化规律为：0～30 cm深度内,土壤碳酸盐的δ¹³C值随深度的增加而逐渐减小;在30～50 cm范围内,如果有盐积层或碱积层的存在,则土壤碳酸盐的δ¹³C值迅速增加。