On the Direction and Magnitude of Oxygen Isotope Fractionation Between Calcite and Aragonite at Thermodynamic Equilibrium     

Gen-Tao Zhou  Yong-Fei Zheng 《Aquatic Geochemistry》2006,12(3):239-268

Oxygen isotope fractionation factors between calcium carbonates and water have been applied to ancient marine geochemistry principally for the purpose of geothermometry. The problem was encountered, however, with respect to the direction and magnitude of oxygen isotope fractionation between calcite and aragonite at thermodynamic equilibrium. This basically involves sound understanding of both thermodynamics and kinetics of oxygen isotope fractionation between inorganically precipitated carbonate and water at low temperatures. Thus the crucial issues are to acknowledge the processes of chemical reaction and isotopic exchange during precipitation of CaCO₃ minerals in solution, the kinetic mechanism of isotope equilibrium or disequilibrium, the effect of polymorphic transition from metastable aragonite to stable calcite under hydrous or anhydrous conditions, and the presence or absence of isotope salt effect on oxygen isotope exchange between carbonate and water in response to the hydrous or anhydrous conditions at thermodynamic equilibrium. Because good agreements exist in carbonate–water oxygen isotope fractionation factors between theoretical calculations and experimental determinations, it is encouraging to applying the thermodynamic and kinetic data to isotopic paleothermometry and geochemical tracing.  相似文献   

Environmental geochemistry of calcium isotopes： Applications of a new stable isotope approach     

刘占民刘丛强  韩贵琳王中良薛紫晨  宋照亮杨成 《中国地球化学学报》2006,25(2):184-194

1IntroductionIn nature, calcium has six naturally occurring sta-ble isotopes with atomic mass units (amu) and the a-bundances of40Ca (96.941%),42Ca (0.647%),43Ca (0.135%),44Ca (2.086%),46Ca (0.004%)and48Ca (0.187%) are presented in this paper.These analyt…  相似文献   

黄龙嗜冷细菌两种胞外单糖对碳酸钙矿化影响   总被引：2，自引：0，他引：2  

于璐嘉  李琼芳  陈超  吕治州  王旭辉 《岩石矿物学杂志》2018,37(3):497-504

为了探究黄龙水体中嗜冷细菌的胞外代谢产物对钙华沉积速率及沉积产物的影响,本文从黄龙钙华水体中分离到优势土著嗜冷细菌,并以其标志性胞外代谢产物D-葡萄糖和D-核糖作为研究对象,研究了两种单糖组分在低温环境下对钙华沉积的影响,并通过X射线衍射(XRD)、扫描电子显微镜(SEM)、红外吸收光谱(FT-IR)等分析手段对碳酸钙晶型、形貌以及结构组成进行了表征。实验表明:D-葡萄糖在低温条件下能促进方解石型碳酸钙的沉积,并加快沉积速率。低浓度下(20 mg/L和40 mg/L)的沉积产物均为方解石型碳酸钙并对其形貌有一定的影响;高浓度下(80 mg/L和160 mg/L)能诱导少量的文石型碳酸钙的合成。D-核糖在低温条件下能促进碳酸钙的沉积,加快沉积速率。与D-葡萄糖不同,D-核糖仅能合成方解石型碳酸钙,但对方解石晶面的生长表现为抑制作用,且随浓度增大抑制作用益明显。此结果可为黄龙钙华生物成因的探究提供一定的理论研究基础。  相似文献   

气动雾化进样-微波等离子体炬质谱法快速测定水样中的钙离子   总被引：1，自引：1，他引：0  

杨美玲  钟涛  裴妙荣  张兴磊  乐长高  王广才  陈焕文 《岩矿测试》2015,34(5):586-591

环境水样中金属元素的分析通常采用电感耦合等离子体质谱法(ICP-MS),检出限低、线性范围宽,但仍存在使用功率高、耗气量大、分析成本高以及不适用于现场分析等不足。本文为降低金属元素分析成本,建立了微波等离子体炬(MPT)与有机质谱耦合的方式检测水样中钙离子的新方法。详细探究了载气流速和维持气流速对钙离子响应信号的影响,方法检出限为224.56 ng/L,相对标准偏差(RSD)为1.2%~9.8%,加标回收率在86.3%~110.4%之间。本方法无需样品预处理,分析速度快、灵敏度和精确度高,为环境水样中金属离子的测定提供了新途径,有望应用于金属离子的实时在线分析。  相似文献   

全新世／冰期西赤道太平洋边缘海碳酸钙沉积旋回及其古海洋学意义   总被引：7，自引：1，他引：7  

李铁钢  薛胜吉 《海洋地质与第四纪地质》1994,(4)

本文所研究的区域是西赤道太平洋的两个边缘海盆─—南中国海和苏禄海。分别对南中国海的ＧＧＣ—６孔和苏禄海的ＧＧＣ—２９孔的ＣａＣＯ＿３含量、浮游有孔虫动物群及氧同位素地层进行分析，并用浮游有孔虫转换函数方法对古温度进行分析，用以确定地层年代的气候分期。研究结果表明，本区Ｃａ－ＣＯ＿３旋回模式与太平洋型相反，而与大西洋型一致。即冰期时ＣａＣＯ＿３含量低，全新世冰后期ＣａＣＯ＿３含量高。冰期陆源物质供应的加强是控制本区ＣａＣＯ＿３旋回的主要因素。此外，冰期时南中国海海水溶解作用的加强是控制本区低ＣａＣＯ＿３含量的又一重要因素，而苏禄海受海水溶解作用的影响相对很小。  相似文献   

Barium Increasing Prior to Opal during the Last Termination of Glacial Ages in the Okhotsk Sea Sediments     

Masayasu M. Sato  Hisashi Narita  Shizuo Tsunogai 《Journal of Oceanography》2002,58(3):461-467

Ba and Ti in a sediment core (10 m long) from the Okhotsk Sea, covering the last 120 kyrs, were measured. The authigenic Ba (Ba_ex) contents were calculated and compared with the opal. The correlation coefficient between Ba_ex and opal was quite small (r = 0.34), but it greatly grew larger (r = 0.90), if the Ba_ex contents were multiplied by a simple function increasing with depth, except for two intervals. This may be due to the gradual change in the sedimentation environment during the glacial ages. One of the exceptional interval is found at 60–170 cm in depth, corresponding to 10–17 calendar kyr ago, the last termination period of glacial ages, where the Ba_ex began to increase prior to opal. Since the calcium carbonate contents similarly increased prior to the opal increase, the Ba_ex may be also related to calcareous organisms besides siliceous ones. The other is the last interglacial period around 120 kyr ago when the opal contents were high, but those of the Ba_ex were not increased. This can be explained, if the Ba_ex was reduced to sulfide and dissolved away in a strongly anoxic environment during the biologically productive period. During the glacial ages, the mass accumulation rate (MAR) of lithogenic Ti was about twice the amount of that during the interglacial ages. For opal, however, the contrast between the glacial and interglacial ages was more remarkable in its MAR than in its concentration in sediments, due to the larger variation in the bulk sedimentation rates. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Leaching of rock-concrete interfaces   总被引：1，自引：1，他引：0  

O. Buzzi  M. Boulon  M. Hervé  K. Su 《Rock Mechanics and Rock Engineering》2008,41(3):445-466

Summary  It has been shown that contacts between host rock and engineered barriers may be critical in the design of deep radioactive waste repositories. Water is expected to reach the interface zone after the resaturation of the geological massive and its presence may lead to concrete leaching. Such a phenomenon could increase the interface transmissivity and compromise the confinement of radioactive waste. This paper intends to investigate the influence of concrete leaching on the hydromechanical behaviour of host rock-concrete interfaces. Some concrete specimens have been subjected to an accelerated leaching process using ammonium nitrate. The hydromechanical response of degraded concrete-rock interfaces has been studied under shearing and compared to that of sound interfaces. Consistent with the results available in the literature on bulk concrete, a loss of mechanical strength has been observed for the degraded interface. Unlike the sound specimens, the degraded interfaces do not dilate when sheared and they tend to be closed, thereby preventing water from flowing. Correspondence: O. Buzzi, Centre for Geotechnical and Materials Modelling, School of Engineering, University of Newcastle, 2308 Callaghan NSW, Australia  相似文献   

Daytime deposition and nighttime dissolution of calcium carbonate controlled by submerged plants in a karst spring-fed pool: insights from high time-resolution monitoring of physico-chemistry of water   总被引：6，自引：0，他引：6  

Zaihua Liu  Xiangling Liu  Changjun Liao 《Environmental Geology》2008,55(6):1159-1168

Water temperature, dissolved oxygen (DO), pH, and specific conductivity (spc) were measured in a time interval of 15 min in a karst spring and the spring-fed pool with flourishing submerged plants in Guilin, SW China under dry weather for periods of 2 days. Measurements allowed calculation of calcium and bicarbonate concentrations ([Ca²⁺] and [HCO₃ ⁻]), and thus CO₂ partial pressure ( ) and saturation index of calcite (SIc). Results show that there were not any diurnal variations in the physico-chemical parameters of the water for the spring. However, during daytime periods, pool water decreased to far less than the spring water in a few hours, pH and SIc increased to greater than the spring, and [Ca²⁺] and [HCO₃ ⁻] decreased to less than the spring. During nighttime periods, pool water returned to or even increased to greater than the spring, pH and SIc decreased to less than the spring, and [Ca²⁺] and [HCO₃ ⁻] increased to greater than the spring. The decrease in [Ca²⁺] and [HCO₃ ⁻] to less than the spring during daytime periods implies daytime deposition of calcium carbonate, while the increase in [Ca²⁺] and [HCO₃ ⁻] to greater than the spring during nighttime periods implies nighttime dissolution of calcium carbonate. The direction of the observed changes depended essentially on the illumination, indicating that daytime photosynthetic and nighttime respiratory activities in the pool aquatic plant ecosystem, which were further evidenced by the increase and decrease in DO during daytime and nighttime periods respectively, were the main processes involved. The large variations of the components of the carbonate system imply considerable changes of the capacities of CO₂ and O₂ in water. The finding has implications for water sampling strategy in slow-flowing karst streams and other similar environments with stagnant water bodies such as estuaries, lakes, reservoirs, and wetlands, where aquatic plant ecosystem may flourish.  相似文献   

生物膜脂参与的非晶碳酸钙形成和稳定     

倪杰  周根陶 《地学前缘》2008,15(6):83

非晶碳酸钙(amorphous calcium carbonate,ACC)是碳酸钙矿物体系中极不稳定的矿物相。但由海鞘类动物的研究表明,ACC可作为碳酸钙晶体矿物的前驱体在生物体内稳定存在,并且这些生物成因的ACC常常是由膜包裹着的。文中选用生物膜的主要成分卵磷脂(PC)为主要矿化调节剂,通过调控与碳酸钙矿化过程密切相关的无机离子Mg2+的浓度,模拟生物膜表面碳酸钙矿化作用过程。在空气/水界面处的膜脂调控下合成出可在溶液中稳定存在数天的非晶碳酸钙。该结果有力地证明了在生物矿化过程中,除了受生物体中可溶性有机大分子调控外,生物膜可能对ACC的形成和稳定也有显著的调控作用。  相似文献   

Burial of organic carbon and carbonate on inner shelf of the northern South China Sea during the postglacial period     

Shouye YANG  Wyss W.-S. YIM  Min TANG  Guangqing HUANG 《Frontiers of Earth Science》2008,2(4):427-433

Two vibrocores from the inner shelf off Hong Kong are investigated to compare the contents of organic and inorganic carbon in postglacial sediments. The compositions of organic elements and carbonate are highly variable in the core sediments, but overall drop within the compositional ranges of modern seabed sediments in the Zhujiang estuarine and its shelf area. The Holocene sediments in the inner shelf have never been subject to subaerial exposure and the organic matter and carbonate can be preserved well. The burial of carbon in river-dominated shelf environments is highly dependent on the river flux with time. Nevertheless, it is difficult to establish a simple relationship between carbon burial in sediments in relation to climatic changes of basin-wide scale due to complex controls of production, transport and deposition of organic matter and carbonate. Our study suggests that the organic carbon to nitrogen ratio can not reliably identify the sources of depositional organic matters because of selective decomposition of organic matter components during humification and sedimentation. Caution is therefore needed in using organic elemental compositions as indicators of organic matter sources and paleoenvironmental changes in the East Asian continental shelves where intense river-sea interaction and variable carbon flux in geologic record occur.  相似文献