重庆羊子洞MIS5a/MIS4转换时期石笋微量元素记录及其气候意义

利用重庆丰都羊子洞石笋Y02 ICP-MS测年数据、微量元素数据和石笋氧同位素数据重建了三峡库区76~69 ka B.P.时段的古气候环境信息。将石笋Y02测试数据与太阳辐射曲线、格陵兰NGRIP冰芯和南海海表温度进行对比分析,结果显示石笋Mg/Ca主要响应降水变化,而Sr/Ca、Ba/Ca和U/Ca更多地响应地表土壤状况和当地大气粉尘活动,间接响应降水变化;石笋Y02 δ18O记录出现偏重的趋势比微量元素比值增大时间晚1 ka多,表明石笋微量元素比值可能还受到温度影响。     

Climatic significance of seasonal trace element and stable isotope variations in a modern freshwater tufa

We present a continuous ∼14-yr-long (1985 to 1999) high-resolution record of trace element (Mg, Sr, Ba, U) and stable isotope (δ¹³C, δ¹⁸O) variations in a modern freshwater tufa from northwestern Queensland, Australia. By utilizing the temperature dependence of the δ¹⁸O signal, an accurate chronology was developed for the sampled profile, which allowed a comparison of the chemical records with hydrological and meteorological observations. As a consequence, it was possible to constrain the relevant geochemical processes relating climate variables, such as temperature and precipitation, to their chemical proxies in the tufa record. Temperatures calculated from the Mg concentrations of the tufa samples provide close approximations of average annual water temperature variations. Furthermore, we demonstrate that temporal changes in (Mg/Ca)_water can be estimated using an empirically derived equation relating (Mg/Ca)_water to the (Sr/Ba) ratio measured in the tufa samples. By means of this relationship, it is theoretically possible to determine the (Mg/Ca) ratio of paleowaters, and hence to derive reliable estimates of former water temperatures from the Mg concentrations of fossil tufas from the study area. Sympathetic variations in Sr, Ba, and δ¹³C along the sampled profile record changes in water chemistry, which are most probably caused by variable amounts of calcite precipitation within the vadose zone of the karst aquifer. This process is thought to be markedly subdued whenever the amount of wet-season precipitation exceeds a given threshold. Accordingly, distinct minima in Sr, Ba, and δ¹³C are interpreted to reflect years with above-average rainfall. The pronounced seasonal and annual variability of the U concentration along the profile is thought to primarily record changes in the U flux from the soil to the water table. We suggest that during intensive rain events U is transported to the phreatic zone by complexing organic colloids, giving rise to conspicuous U maxima in the tufa after above-average wet seasons. This study demonstrates the potential of freshwater tufas to provide valuable information on seasonal temperature and rainfall variations. If tufa deposits turn out to be reasonably resistant to secondary processes, combined investigation of speleothems and tufas from the same area could become a promising approach in future research. While speleothems offer continuous records of long-term paleoenvironmental changes, tufas could provide high-resolution time windows into selected periods of the past.     

Annual trace element cycles in calcite–aragonite speleothems: evidence of drought in the western Mediterranean 1200–1100 yr BP

Each of two calcitic stalagmites from Grotte de Clamouse, Herault, southern France, displays a discrete aragonite layer dated at around 1100 yr BP. The layer of fanning aragonite ray crystals is immediately preceded by calcite with Mg and Sr compositions that are uniquely high for the past 3 kyr. Trace element compositions close to the boundary between original aragonite and calcite are consistent with quasi‐equilibrium partitioning of trace elements between the phases. Study of modern dripwaters demonstrates that pronounced covariation of Mg/Ca and Sr/Ca ratios in dripwater occurs owing to large amounts of calcite precipitation upflow of the drips that fed the stalagmites. Trace element to Ca ratios are enhanced during seasonally dry periods. Ion microprobe data demonstrate a pronounced covariation of trace elements, including Mg and Sr in calcite, and Sr, U and Ba in aragonite. The mean peak spacing is close to the long‐term mean of annual growth rates determined by differences in U‐series ages and so the trace element peaks are interpreted as annual. The trace element chemistry of the stalagmites on annual to inter‐annual scales thus directly reflects the amounts of prior calcite precipitation, interpreted as an index of aridity. The longer‐term context is a multi‐decadal period of aridity (1200–1100 yr BP) possibly correlated with an analogous episode in Central America. The arid period culminated in the nucleation of aragonite, but within a decade was followed by a return to precursor conditions. Copyright © 2005 John Wiley & Sons, Ltd.     

Influences of organic matter and calcification rate on trace elements in aragonitic estuarine bivalve shells

A suite of elements (B, Na, Mg, S, K, Ca, V, Mn, Cr, Sr, and Ba) was measured in aragonitic shells of the estuarine bivalve Corbula amurensis, the Asian clam, using the Sensitive High-Resolution Ion MicroProbe with Reverse Geometry (SHRIMP RG). Our initial intent was to explore potential geochemical proxy relationships between shell chemistry and salinity (freshwater inflow) in northern San Francisco Bay (SFB). In the course of this study we observed variations in shell trace element to calcium ([M]/Ca) ratios that could only be attributed to internal biological processes. This paper discusses the nature and sources of internal trace element variability in C. amurensis shells related to the shell organic fraction and shell calcification rates. The average organic content of whole C. amurensis shells is 19%. After treating whole powdered shells with an oxidative cleaning procedure to remove organic matter, shells contained on average 33% less total Mg and 78% less total Mn. Within our analytical uncertainty, Sr and Ba contents were unchanged by the removal of organic matter. These results show that aragonitic C. amurensis shells have a large component of non-lattice-bound Mg and Mn that probably contribute to the dissimilarity of [M]/Ca profiles among five same-sized shells. Non-lattice-bound trace elements could complicate the development and application of geochemical proxy relationships in bivalve shells. Because B, Ba and Sr occur exclusively in shell aragonite, they are good candidates for external proxy relationships. [M]/Ca ratios were significantly different in prismatic and nacreous aragonite and in two valves of the same shell that had different crystal growth rates. Some part of these differences can be attributed to non-lattice-bound trace elements associated with the organic fraction. The differences in [M]/Ca ratios were also consistent with the calcification rate-dependent ion transport model developed by Carré et al. [Carré M., Bentaleb I., Bruguier O., Ordinola E., Barrett N. T. and Fontugne M. (2006) Calcification rate influence on trace element concentrations in aragonitic bivalve shells: evidences and mechanisms. Geochim. Cosmochim. Acta70, 4906-4920] which predicts that [M]/Ca ratios increase as calcification rates increase and Ca²⁺ channel specificity decreases. This result, in combination with the possibility that there were ontogenetic variations in growth rates among individuals younger than 2 years, underscores the need to develop an independent age model for C. amurensis shells. If growth-rate effects on lattice-bound [M]/Ca ratios can be constrained, it may yet be possible to develop high-resolution geochemical proxies for external solution chemistry in low-salinity regions of SFB.     

Trace-element variations in an annually layered stalagmite as recorders of climatic changes and anthropogenic pollution in Central China

We analyzed variations in the Sr/Ca, Ba/Ca, REE/Ca (REE: rare earth element), Zn/Ca, and Pb/Ca ratios preserved in an annually layered stalagmite, XL21, from central China. The stalagmite record spans the 95 year period AD 1914–2008. The Sr/Ca and Ba/Ca ratios have a significant positive correlation with the stalagmite's growth rate, suggesting that they were primarily controlled by growth-rate variations. Variations in REE/Ca ratios are consistent with local temperature changes, suggesting temperature influenced REE concentrations in the stalagmite over decadal to annual timescales. Higher temperature in this humid area can increase vegetation cover, microbial activity, and organic decomposition in the soil, resulting in enhanced pCO₂, organic matter concentration and reduced pH, and consequently increased REE mobilization from the overlying soil layer and host rock. Higher temperatures may also increase the natural Zn mobilization from the overlying soil mediated by organic matter and consequently may have led to increased Zn retention in XL21. An increasing trend is seen in the Pb/Ca ratios from XL21 since 1985, which is consistent with increased lead production in this area, and indicates an increase in mine-derived lead pollution in the local environment over the past 30 years.     

Correlated trace element “vital effects” in tropical corals: A new geochemical tool for probing biomineralization

Micron-scale variations in the trace-element (TE) composition of tropical coral skeletons were measured using laser-ablation ICP-MS (LA-ICP-MS) as part of an investigation into the chemical processes underlying paleoenvrionmental proxy reconstructions. Fluctuations in B, Mg, Sr, Ba and U were measured at high spatial resolution in two Porites corals from the Great Barrier Reef (Australia), and the fine-scale fluctuations (< ∼1.0 mm) were compared with seasonal TE cycles in a third coral. Fine-scale TE variations were found to have a large amplitude over distances corresponding to less than 1 month growth. Variations were quasi-periodic and appeared to have characteristic wavelengths on weekly (6-7 d) and monthly (28 d) scales, although periodicity was not continuous and variations could not be matched either within or between individual corallites. Fine-scale variations between Mg, Sr and U were significantly correlated with each other (Sr and U are positively correlated, but negatively correlated with Mg). This 3D correlation “vector” has the same slope as the seasonal-scale Mg, Sr and U correlations, suggesting that the same chemical/biologic biomineralization process mediates trace element variations at both timescales. Importantly, the fine-scale variations are too large to be caused directly by daily to monthly fluctuations in sea-surface temperature. This means that seasonal variations in these elements cannot reflect purely inorganic temperature-dependent coprecipitation. Models of physicochemical calcification were developed to test whether changes in calcification rate could explain the trace-element correlations. The calculations show that increases in calcification rate will result in correlated decreases in all TE/Ca ratios. The models reproduce the Sr partition coefficient, trace-element correlation slopes, and amplitude of fine-scale variations for an average calcifying pH of 8.5, varying by ±0.2 pH units. The models, however, predict U partition coefficients which are too low, and cannot reproduce the negative correlation between Mg and the other trace elements, which may be caused by crystallographic factors.     

Effects of alteration on element distributions in archean tholeiites from the Barberton greenstone belt,South Africa

Major and trace element and modal analyses are presented for unaltered, epidotized, and carbonated tholeiite flows from the Barberton greenstone belt. Au, As, Sb, Sr, Fe⁺³, Ca, Br, Ga, and U are enriched and H₂O, Na, Mg, Fe⁺², K, Rb, Ba, Si, Ti, P, Ni, Cs, Zn, Nb, Cu, Zr, and Co are depleted during epidotization. CO₂, H₂O, Fe⁺², Ti, Zn, Y, Nb, Ga, Ta, and light REE are enriched and Na, Sr, Cr, Ba, Fe⁺³, Ca, Cs, Sb, Au, Mn, and U are depleted during carbonization-chloritization. The elements least affected by epidotization are Hf, Ta, Sc, Cr, Th, and REE; those least affected by carbonization-chloritization are Hf, Ni, Co, Zr, Th, and heavy REE. Both alteration processes can significantly change major element concentrations (and ratios) and hence caution should be used in distinguishing tholeiites from komatiites based on major elements alone. The amount of variation of many of the least mobile trace elements in the altered flows is approximately the same as allowed by magma model calculations. Hence, up to about 10% carbonization and 60% epidotization of tholeiite do not appreciably affect the interpretation of trace-element models for magma generation.     

Seasonal records of climatic change in annually laminated tufas: short review and future prospects

Many Recent and fossil freshwater tufa stromatolites contain millimetre‐scale, alternating laminae of dense micrite and more porous or sparry crystalline calcites. These alternating laminae have been interpreted to represent seasonally controlled differences in the biotic activity of microbes, and/or seasonally controlled changes in the rate of calcification. Either way, couplets of these microbially mediated alternating calcified laminae are generally agreed to represent annual seasonality. Combined stable isotope (δ¹⁸O and δ¹³C) and trace element (Mg, Sr, Ba) geochemistry from Recent tufa stromatolites show that seasonal climatic information is available from these calcites. Variability in δ¹⁸O (and in one case Mg concentration) has been shown to be controlled primarily by stream temperature change, usually driven by solar insolation. In arid climates, seasonal evaporation can also cause δ¹⁸O enrichment by at least 1‰. Variability in δ¹³C results potentially from: (1) seasonal change in plant uptake of ¹²C‐enriched CO₂; (2) seasonal change in degassing of ¹²C‐enriched CO₂ in the aquifer system; and (3) precipitation of calcite along the aquifer or river flow path, a process that increases δ¹³C of dissolved inorganic carbon (DIC) in the remaining water. Mechanisms 2 and 3 are linked because calcite precipitates in aquifers where degassing occurs, e.g. air pockets. The latter mechanism for δ¹³C enrichment has also been shown to cause sympathetic variation between trace element/Ca ratios and δ¹³C because trace elements with partition coefficients much greater than 1 (e.g. Sr, Ba) remain preferentially in solution. Since degassing in air pockets will be enhanced during decreased recharge when water saturation of the aquifer is lowest, sympathetic variation in trace element/Ca ratios and δ¹³C is a possible index of recharge and therefore precipitation intensity. High‐resolution geochemical data from well‐dated tufa stromatolites have great potential for Quaternary palaeoclimate reconstructions, possibly allowing recovery of annual seasonal climatic information including water temperature variation and change in rainfall intensity. However, careful consideration of diagenetic effects, particularly aggrading neomorphism, needs to be the next step. Copyright © 2005 John Wiley & Sons, Ltd.     

Trace elements in speleothems as recorders of environmental change

Speleothems are now established as important palaeoenvironmental archives and contain a number of suitable proxies, although trace elements have been much less widely used than oxygen and carbon isotopes. The complexity of the cave environment helps to explain this since the fluids from which speleothems form vary greatly in composition in space (even within a cave chamber), seasonally, and over longer periods. Understanding the forcing factors for this variability is the key to decoding the significance of the trace element records.A variety of techniques are available for trace element work and it is important to understand the strengths and limitations of each and also to seek an understanding, e.g. by micro-imaging techniques, of whether the elements are associated with inclusions in the CaCO₃, or are isolated within the crystal lattice. For some elements there is a more-or-less predictable relationship between element ratios to Ca in the water and in the calcite. Individual trace elements may be derived from atmospheric deposition, superficial deposits or bedrock and can be recycled in soil processes before being transferred to the cave. Some components show an instantaneous response to water infiltration, whereas others are only leached by slow-flowing seepage waters. Changing in the proportion of water from fracture-fed and seepage-flow aquifer compartments is an important factor in influencing trace element supply. High flows lead to higher fluxes of soil-derived colloidally transported elements. Conversely, under relatively dry conditions, degassing of CO₂ results in “prior calcite precipitation” upflow of the site of speleothem deposition and leads to higher ratios of Sr/Ca and Mg/Ca. Some trace element variations in speleothems over time are induced during crystal growth whereby faster growth leads to a greater departure from equilibrium element partitioning.Despite the demonstrated temperature-dependence of Mg partitioning into calcite, attempts at deriving palaeotemperature records from speleothems have been so far confounded by variations in solution Mg/Ca and/or crystallographic effects. A number of case studies have effectively used trace elements such as speleothem Mg as records of palaeo-aridity, using supporting arguments from modern monitoring or covariations with other parameters such as stable isotopes. Sr and U isotopes can also be indicators of palaeohydrology, although Sr isotope variations can also reflect varying aeolian input. Considerable progress has been made in decoding the meaning of annual trace element variations using criteria for understanding dripwater hydrology and pH. This should lead in the future to more specific interpretations of how seasonality evolves through time.     

华北地块东南缘中生代侵入杂岩中所含榴辉岩类包体矿物微量元素地球化学特征及其意义

华北地块东南缘中生代侵入杂岩中所含榴辉岩类包体中矿物的分析结果表明, 组成榴辉岩类包体的各矿物之间元素的分配在榴辉岩相变质阶段已经达到了化学平衡;石榴石中Al、Fe、Mn, 单斜辉石中Na、Mg、Ca, 角闪石中Na、Mg、Fe等主量元素含量与其全岩之间均呈良好的正相关, 受全岩成分制约;石榴石明显富集HREE、贫LREE, 单斜辉石相对富集LREE、MREE、贫HREE, 两者轻、重稀土含量呈相互消长的互补关系, 石榴石和单斜辉石中分别富集Y、Sr, Ga和过渡族元素Sc、Ti、V、Cr、Co等含量较高, 其含量受全岩成分控制;金红石中稀土元素的含量很少, Fe、Al、Mg、Ca、Mn、Nb、Ta、Cr和Zr含量相对较高, Rb、Sr、Ba含量极低, 部分微量元素(如Nb、Cr、Fe、V、W等)含量与其原岩有继承和对应关系;部分原生或/和退变角闪石的REE配分模式分别与单斜辉石和石榴石相似, 过渡族金属元素等的含量与石榴石、单斜辉石和全岩具有一定的相关性, 角闪石容纳Na、K、Sr、Rb、Ba等元素的能力较强, 其成分除受全岩成分的制约外, 石榴石、单斜辉石对其形成也有影响。榴辉岩类包体与其寄主中生代侵入杂岩中部分高价态/高场强元素(HFSE)和重稀土元素(HREE)呈相互消长的关系。榴辉岩的形成与扬子地块和华北地块之间的俯冲-碰撞作用有关。     

In Situ Multi-Element Analysis of the Mount Pinatubo Quartz-Hosted Melt Inclusions by NIR Femtosecond Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry

Microscopic melt inclusions found in magmatic minerals are undoubtedly one of the most important sources of information on the chemical composition of melts. This paper reports on the successful application of near-infrared (NIR) femtosecond laser ablation (LA) - inductively coupled plasma-mass spectrometry to in situ determination of incompatible trace elements (Li, Rb, Sr, Y, Zr, Nb, Cs, Ba, REE, Ta, Th, U) and ore metals (As, Mo, Pb) in individual melt inclusions hosted in quartz from the Mount Pinatubo dacites, Philippines. The determined elements cover a concentration range of five orders of magnitude. Femtosecond LA-ICP-MS analyses of twenty-eight individual melt inclusions demonstrate the efficiency of the microanalytical technique and suggests a spectacular homogeneity of the entrapped melt, at least with respect to the following incompatible trace elements: Rb, Sr, Nb, Cs, Ba, La, Ce, Pr, Nd, Pb, Th. The analytical precision (1s) for Na, Ca, Rb, Sr, Y, Nb, Ba and LREE ranged from 3 to 20%. Comparison of trace element concentrations in Mt. Pinatubo melt inclusions determined by femtosecond LA-ICP-MS with those of melt inclusions previously analysed by secondary ion mass spectrometry analysis (SIMS) and those of matrix glasses previously determined by nanosecond LA-ICP-MS showed an agreement typically within 30–40%. The homogeneity of trace element concentrations of the Mt. Pinatubo melt inclusions and the matrix glasses is consistent with the melt inclusion origin as homogeneous rhyolitic melt that was trapped in quartz phenocrysts at the final crystallisation stages of the host adakite (dacite) magma.     

Multi-element geochemistry of sediments from the Pearl River system,China

Sediment samples were taken along the West, North, and East rivers of the Pearl River system at 28 locations in 1998, and a total of 49 elements were determined by ICP–AES, ICP–MS and INAA. The probability features of the datasets were studied, and the average concentrations of these elements in sediments of the three rivers were calculated. Significant differences in element concentrations among the three rivers were observed and the results were confirmed by statistical tests including analysis of variance (ANOVA), Kruskal–Wallis test, and t-test. Spatial distribution maps of element concentrations were produced using a geographical information system (GIS). The immobile trace elements (such as Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) are enriched in the West River where limestone dominates the rock types in the watershed. Because of the strong weathering, immobile trace elements are enriched and reside in secondary minerals of the weathering products. All three rivers have high concentrations of rare earth elements (REEs) because of strong weathering, but relatively higher concentrations of REEs are observed in sediments of the East River where granite dominates the rock type. Granite contains high concentrations of REEs and the sediments have inherited this feature from their bedrock. Alkaline element (Li, Na, K, Rb, and Cs) concentrations are elevated in sediments of the East River, these may reside in granitic primary minerals. Relatively high concentrations of alkaline earth elements (Mg, Ca, Sr, and Ba) are observed in the West River, inherited from the limestone bedrock. High Pb and Bi concentrations are found in the North River and are caused by Pb mineralization and the discharge of a smelter in the upper reaches of the river. However, statistical tests did not indicate a significant difference between Pb concentrations in the North River and the other two rivers, which suggests that statistical results should be carefully used and explained.     

Trace and minor element geochemistry of the rhyolitic volcanic rocks,Central North Island,New Zealand

Analytical data are presented for the following elements: Cs, Rb, Ba, K, Sr, Ca, Na, Fe, Mg, Cu, Co, Ni, Li, Sc, V, Cr, Ga, Al, Si, La, Y, and Zr. Eight samples were analysed by the spark source method for rare earths, Tl, Pb, Hf, Sn, Nb, Mo, Bi, and In. In addition to data on rhyolitic volcanics, a small number of intermediate volcanics and eugeosynclinal sediments were analysed for comparative purposes. The following features are shown by the trace element data:

1. The rhyolitic rocks have consistently lower concentrations of most trace and minor elements when compared with recent estimates of average concentrations in granites. None of the criteria for strong fractionation (e.g. low K/Rb, Ba/Rb and K/Cs ratios) are present.
2. The data do not indicate any systematic differences between the rhyolitic lavas and ignimbrites, although the very young rhyolitic pumices are consistently more “basic” in their element concentrations compared to the other rhyolitic analyses.
3. The residual glasses (and devitrified matrices) are depleted, relative to the total rock compositions, in Fe, Mg, Ca, Sr, V, Sc, and Al, and enriched in Cs, Rb, K, Ba, and Si. Zr is depleted in the residual glasses separated from rhyolites, but not in the andesitic residual matrices.
4. The rare earth fractionation patterns of the rhyolitic and andesitic extrusives are very similar, being intermediate between chondritic and sedimentary patterns i.e., there is no evidence of strong fractionation. The rhyolitic patterns also indicate a slight Eu depletion.
5. Comparable trace and minor element behaviour (with the possible exception of Zr) seems to exist through the rhyolite-andesite compositional range. This is supported by the whole rock-residual liquid trends for the various elements studied, which broadly coincide with the observed whole rock trends, both through the rhyolitic-andesitic compositonal range, and within the rhyolitic compositional range.

The data are finally discussed in the light of the possible origin of the rhyolitic magmas. It is believed that the analytical data presented are qualitatively consistent with the recently proposed idea that the magmas are derived by partial fusion of the associated Triassic-Jurassic eugeosynclinal greywacke-argillite sedimentary sequence.     

Determination of Trace Elements in Calcite Using Solution and Laser Ablation ICP-MS: Calibration to NIST SRM Glass and USGS MACS Carbonate, and Application to Real Landfill Calcite

We report new data on the trace element concentrations of Mg, Cr, Mn, Co, Ni, Cu, Zn, Sr, Cd, Ba, La, Ce, Nd, Pb and U in USGS carbonate reference materials (MACS-1 and MACS-2) and compare solution ICP-MS and LA-ICP-MS trace element determinations on landfill calcites using calibration to different reference materials (MACS-1 and MACS-2 carbonate and NIST SRM 612 glass). Very good agreement (differences below 10% relative) was found between laser ablation and solution ICP-MS data for MACS-1 with higher concentrations of trace elements (values between 100 and 150 μg g⁻¹), with the exception of Cu and Zn. Similarly good agreement was found for MACS-2 with lower trace element concentrations (units to tens of μg g⁻¹), with the exception of Cr, Co and Zn. The MACS-1 reference material for calibration of LA-ICP-MS was found to be extremely useful for in situ determination of trace elements in real-world carbonate samples (landfill calcites), especially those present in calcite in higher concentrations (Mn, Sr, Ba; < 5% RSD). Less accurate determinations were generally obtained for trace elements present at low concentrations (∼ units of μg g⁻¹). In addition, good agreement was observed between the instrument calibration to MACS and NIST SRM 612 glass for in situ measurements of trace elements in landfill calcites K-2, K-3 and K-4 (differences below 15% relative for most elements). Thus, the application of MACS carbonate reference materials is promising and points to the need for the development of new carbonate reference materials for laser ablation ICP-MS.     

Evidence of rainfall variations in Southern Brazil from trace element ratios (Mg/Ca and Sr/Ca) in a Late Pleistocene stalagmite

Trace element ratios in the Bt2 stalagmite from Botuverá cave, Southern Brazil, are explored as a proxy for changes in the local rainfall recharge during the last 116 ky. BP Mg/Ca and Sr/Ca ratios, measured with an electron microprobe, are significantly positively correlated with one another throughout the entire record, and vary in a way that is very consistent with variations of δ¹⁸O in the same speleothem during the last glacial period. We suggest that prior calcite precipitation in the vadose zone of the cave system is the main factor affecting the incorporation of Mg and Sr into calcite of the stalagmite. This interpretation is supported by trace element correlation patterns and by results from a hydrochemistry study performed in a cave located in the same region and in a similar environmental setting. Therefore, we conclude that higher (lower) Mg/Ca and Sr/Ca values are associated with lower (higher) levels of recharge into the karstic aquifer, as such conditions lead to an increase (decrease) in the volume of calcite precipitated in the unsaturated zone above the cave during dry (wet) climate periods.Trace element variations point to generally dryer (wetter) conditions during lower (high) phases of summer insolation in the southern hemisphere. These periods coincide with decreased (increased) activity of the South American summer monsoon, as revealed by δ¹⁸O stalagmite records. In addition trace element variations show that rather wet conditions persisted throughout most of the last glacial period from approximately 70 to 17 ky BP. We suggest that during this period the glacial boundary conditions, especially ice volume buildup in the northern hemisphere, played an important role for monsoon rainfall intensification in the region.     

Element partitioning during precipitation of aragonite from seawater: A framework for understanding paleoproxies

This study presents the results from precipitation experiments carried out to investigate the partitioning of the alkaline earth cations Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ between abiogenic aragonite and seawater as a function of temperature. Experiments were carried out at 5 to 75 °C, using the protocol of Kinsman and Holland [Kinsman, D.J.J., Holland, H.D., 1969. The coprecipitation of cations with CaCO₃ IV. The coprecipitation of Sr²⁺ with aragonite between 16 and 96 °C. Geochim. Cosmochim. Acta33, 1-17.] The concentrations of Mg Sr and Ba were determined in the fluid from each experiment by inductively coupled plasma-mass spectrometry, and in individual aragonite grains by secondary ion mass spectrometry. The experimentally produced aragonite grains are enriched in trace components (“impurities”) relative to the concentrations expected from crystal-fluid equilibrium, indicating that kinetic processes are controlling element distribution. Our data are not consistent with fractionations produced kinetically in a boundary layer adjacent to the growing crystal because Sr²⁺, a compatible element, is enriched rather than depleted in the aragonite. Element compatibilities, and the systematic change in partitioning with temperature, can be explained by the process of surface entrapment proposed by Watson and Liang [Watson, E.B., Liang, Y., 1995. A simple model for sector zoning in slowly grown crystals: implications for growth rate and lattice diffusion, with emphasis on accessory minerals in crustal rocks. Am. Mineral.80, 1179-1187] and Watson [Watson, E.B., 1996. Surface enrichment and trace-element uptake during crystal growth. Geochim. Cosmochim. Acta60, 5013-5020; Watson, E.B., 2004. A conceptual model for near-surface kinetic controls on the trace-element and stable isotope composition of abiogenic calcite crystals. Geochim. Cosmochim. Acta68, 1473-1488]. This process is thought to operate in regimes where the competition between crystal growth rate and diffusivity in the near-surface region limits the extent to which the solid can achieve partitioning equilibrium with the fluid. A comparison of the skeletal composition of Diploria labyrinthiformis (brain coral) collected on Bermuda with results from precipitation calculations carried out using our experimentally determined partition coefficients indicate that the fluid from which coral skeleton precipitates has a Sr/Ca ratio comparable to that of seawater, but is depleted in Mg and Ba, and that there are seasonal fluctuations in the mass fraction of aragonite precipitated from the calcifying fluid (“precipitation efficiency”). The combined effects of surface entrapment during aragonite growth and seasonal fluctuations in “precipitation efficiency” likely forms the basis for the temperature information recorded in the aragonite skeletons of Scleractinian corals.     

Olgite矿物的合成、发光性能和结构特征

以Na2CO3, BaCO3, SrCO3, NH4H2PO4和Eu2O3为原料,利用高温固相反应法合成了Eu3+离子掺杂的磷锶钡钠石(Ba,Sr)(Na,Sr)2Na(PO4)2粉末样品.用X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)、傅里叶变换拉曼光谱(FT-Raman)和扫描电镜(SEM)等技术对其物相组成、结构和晶体形貌进行了表征.探讨了不同晶体结构中Sr/Ba比对晶体结构和发光性能的影响.实验通过对Eu3+的发光特点的表征和研究,分别测试了Eu3+离子的室温激发光谱和发射光谱.研究结果表明:(Ba,Sr)(Na,Sr)2Na(PO4)2属简单六方晶系,所有的振动均来自PO43-阴离子团,Eu3+占据非反演中心的格位,该材料中阳离子位置具有高度扰动性的特点.     

Atmospheric pollution indicated by trace elements in snow from the northern slope of Cho Oyu range,Himalayas

Samples collected from a 0.87 m snow pit at a high altitude site in the Cho Oyu range, Himalayas were measured for V, Cr, Mn, Co, Ni, Cu, Zn, As, Rb, Sr, Cd, Sn, Sb, Ba, Tl, Pb, Bi, Th, and U using inductively coupled plasma mass spectrometry. In addition, major ions, oxygen stable isotopes, and microparticles were also measured to assist the interpretation of seasonal variation of trace elements. The trace elements show a distinct seasonality, i.e., higher concentrations during the non-monsoon season than those during the monsoon season. Significant correlation is observed between Ba and the other trace elements. Crustal enrichment factor (EF_c) analysis indicates that V, Mn, Co, Ni, Rb, Sr, and Th originate mainly from crustal dust, while anthropogenic inputs make an important contribution to the other trace elements (i.e., Cu, Zn, As, Cd, Sn, Sb, Ti, Pb, Bi, and U). Evidence from air mass back trajectories suggests that atmospheric trace element pollution reaching the studied area is transported dominantly by Indian summer monsoon during the monsoon season, while it is transported mainly by the westerlies during the non-monsoon season.     

Barium partitioning in coccoliths of Emiliania huxleyi

The coccolithophore Emiliania huxleyi was grown in seawater under different Ba concentrations. The relationship of coccolith Ba/Ca ratio and seawater Ba/Ca ratio was found to be linear. The linear regression yields the apparent Ba exchange coefficient of 0.10. Our data support a recently proposed generic model (Langer G., Gussone N., Nehrke G., Riebesell U., Eisenhauer A., Kuhnert H., Rost B., Trimborn S., and Thoms S. (2006) Coccolith strontium to calcium ratios in Emiliania huxleyi: the dependence on seawater strontium and calcium concentrations. Limnol. Oceanogr.51, 310-320.) developed for explaining apparent exchange coefficients of metabolically inert divalent trace metals, such as Sr, in E. huxleyi. This model represents the first approach combining cell physiological processes and data from inorganic precipitation experiments, which quantitatively explains coccolith apparent Sr and Ba exchange coefficients.     

黄土高原南部全新世黄土-古土壤 序列若干元素分布特征及意义*

选择黄土高原南部的XJN,XMC和JYC全新世剖面为研究对象。通过对地层中Ca,Ba,Rb和Sr元素分布的研究,发现Ba/Sr和Rb/Sr比值在不同地层中含量差异十分明显,并与成土作用强度显著正相关,可作为良好的气候替代指标;表生环境中Rb和Ba较稳定,Sr和Ca元素十分活跃,易于迁移,其中Ca的迁移能力高于Sr元素;从XJN→XMC→JYC剖面,Rb和Ba元素含量增加,而Sr和Ca元素含量降低,这与区域环境差异有关;全新世中期暖湿的亚热带气候主要出现关中盆地地区,六盘山以西则是暖温带气候。