Sr Source Research Articles

Sr and O isotopes in western Aleutian seafloor lavas: Implications for the source of fluids and trace element character of arc volcanic rocks

High Mg# andesites and dacites (Mg# = molar Mg/Mg + Fe) from western Aleutian seafloor volcanoes carry high concentrations of Sr (>1000 ppm) that is unradiogenic (87Sr/86Sr < 0.7029) compared to lavas from emergent volcanoes throughout the arc (200–800 ppm Sr, 87Sr/86Sr >0.7030). Data patterns in plots of 87Sr/86Sr vs Y/Sr and Nd/Sr imply the existence of an eclogite-melt source component – formed by partial melting of MORB eclogite in the subducting Pacific Plate – which is most clearly expressed in the compositions of western Aleutian andesites and dacites (Nd/Sr and Y/Sr < 0.02) and which dominates the source budget for Sr in volcanic rocks throughout the arc. When viewed in combination with inversely correlated εNd and 87Sr/86Sr, these patterns rule out aqueous fluids as an important source of Sr because mixtures of fluids from altered oceanic crust with depleted mantle and sediment produce compositions with 87Sr/86Sr higher than in common Aleutian rocks. The unradiogenic nature of Sr in the western Aleutian andesite–dacite end-member may be understood if H2O required to drive melting of the subducting oceanic crust is transported in fluids containing little Sr. Mass balance demonstrates that such fluids may be produced by dewatering of serpentinite in the mantle section of the subducting plate. If the eclogite-melt source component is present throughout the Aleutian arc, melting of the subducting plate must extend into minimally altered parts of the sheeted dike section or upper gabbros, at depths >2 km below the paleo-seafloor. Oxygen isotopes in western Aleutian seafloor lavas, which fall within a narrow range of MORB-like values (δ18O=5.1–5.7), are also consistent with this model. These results indicate that the subducting Pacific lithosphere beneath the Aleutian arc is significantly hotter than indicated my most thermal models.

Calcium biogeochemical cycle at the beech tree-soil solution interface from the Strengbach CZO (NE France): insights from stable Ca and radiogenic Sr isotopes

Calcium (Ca) is the fourth most abundant element in mineral nutrition and plays key physiological and structural roles in plant metabolism. At the soil-water-plant scale, stable Ca isotopes are a powerful tool for the identification of plant-mineral interactions and recycling via vegetation. Radiogenic Sr isotopes are often used as tracers of Ca sources and mixtures of different reservoirs. In this study, stable Ca and radiogenic Sr are combined and analysed in several organs from two beech trees that were collected in June and September in the Strengbach critical zone observatory (CZO) (NE France) and in corresponding soil solutions.At the beech-tree scale, this study confirms the field Ca adsorption (i.e., physico-chemical mechanism and not vital effects) on carboxyl acid groups of pectin in the apoplasm of small roots. The analysis of the xylem sap and corresponding organs shows that although the Strengbach CZO is nutrient-poor, Ca seems to be non-limiting for tree-growth. Different viscosities of xylem sap between the stemwood and branches or leaves can explain δ44/40Ca values in different tree-organs. The bark and phloem 40Ca-enrichments could be due to Ca-oxalate precipitation in the bark tissues and in the phloem. The results from this study regarding the combination of these two isotopic systems show that the isotopic signatures of the roots are dominated by Ca fractionation mechanisms and Sr, and thus Ca, source variations. In contrast, translocation mechanisms are only governed by Ca fractionation processes.This study showed that at the root-soil solution interface, litter degradation was not the main source of Ca and Sr and that the soil solutions are not the complement of uptake by roots for samples from the 2011/2013 period. The opposite is observed for older samples. These observations indicate the decreasing contribution of low radiogenic Sr fluxes, such as recycling, alimenting the soil solutions. Such reduced importance of nutrient uptake and biomass production by the trees could be because the Strengbach trees are ageing and probably weakened by repeated storm events and drought episodes.

Application of Sr-doped octacalcium phosphate as a novel Sr carrier in the α-tricalcium phosphate bone cement

Abstract Strontium has important physicochemical and biological roles in the application of bone repair materials. In our work, Sr-doped octacalcium phosphate (Sr-OCP) and other Sr sources (including Sr-doped α-tricalcium phosphate (α-TCP), SrCO3 and SrCl2) with different actual availability of Sr2+ were imported into α-TCP bone cements; and the effects of Sr2+ on the hydration reaction of cements were comparatively investigated. Compared with other Sr sources, Sr-OCP crystals significantly affected the hydration reaction positively; By the cooperative effects of Sr-OCP crystals and citric acid, the compressive strength of bone cements was increased immediately and the setting time was reduced to 15 ± 2 min. Roles of Sr-OCP as seed crystals in the bone cements in the acidic conditions had been further explored; and the strategy of Sr substitution in α-TCP cements was also discussed. The results show that Sr-OCP crystals can induce rapid crystallization with increased nucleation rate as seed crystals, meanwhile, Sr2+ can also stabilize the formed metastable immediate phases with decreased crystal growth rate. Under the combined action of these factors, the hydration reaction of cement slurry can be carried out quickly with less time to obtain solidified cements for clinical operations and applications. Herein, Sr-OCP crystals were supposed to be applied in the synthesis of calcium phosphate cement as a novel admixture for numerous orthopedic applications.

A strontium isotope and trace element geochemical study of dolomite-bearing bentonite deposits in Bavaria (Germany)

AbstractThe Landshut bentonites that formed from Ca- and Mg-poor rhyolitic tuffs in a fluviatile-lacustrine depositional environment of the Miocene Upper Freshwater Molasse, southern Germany, contain abundant palustrine, pedogenic and groundwater carbonates. Geochemical analyses of dolomites, calcites and smectites from bentonites of various environments by X-ray diffraction, thermal ionization mass spectrometry, inductively coupled plasma-mass spectrometry, and handheld X-ray fluorescence yield new insights into the compositions of fluids and sources of imported components involved in carbonate formation and bentonitization, as well as the timing of bentonite formation. Evaporated, Sr-rich brackish surface water with a molar Mg/Ca ratio of 2–5, derived mostly from the weathering of detrital carbonates, was involved in dolomite and bentonite formation in palustrine and some pedogenic environments. However, Sr-poor groundwater with a molar Mg/Ca ratio of ∼ 1 and a stronger silicate weathering component caused bentonite and calcite formation in strictly pedogenic and groundwater settings. The 87Sr/86Sr and molar Mg/Ca in the smectite interlayers indicate later cation exchange with water having more radiogenic Sr sources and smaller molar Mg/Ca ratios. The Rb-Sr data indicate the common presence of detrital illitic phases in the &lt;0.2 μm fractions of the bentonites. Cogenetic palustrine dolomite and a single smectite residue sample which lacks this detrital illitic phase provide an age constraint for bentonitization at 14.7 ± 4.1 Ma identical to primary ash deposition. Thus a rapid onset of bentonitization of accumulated ash and dolomite formation in evaporation-driven wetland environments is indicated for the genesis of the Landshut bentonites.

Origin of calcium in pedogenic carbonate nodules from silicate watersheds in the Far North Region of Cameroon: Respective contribution of in situ weathering source and dust input

Significant amounts of pedogenic Ca-carbonate nodules have been observed in the Far North Region of Cameroon in the carbonate-free watershed of the Mayo Tsanaga, thus a priori not favourable for carbonate nodules accumulations. These nodules are associated with a Clay-Rich Parent Material (CRPM), covering either a granitic (upstream) or a greenstone bedrock (downstream). In this peculiar context, the amount of pedogenic carbonate nodules represents large quantities of Ca and C. Therefore, determining the Ca sources for pedogenic carbonate nodules is a key point regarding the mechanisms leading to carbonate nodule precipitation and their role in the biogeochemical cycle of Ca. Three sites, two on granite and one on greenstone, were studied by combining Sr et Nd isotope systematics in order to assess the Ca sources of carbonate nodules and the origin of the CRPM associated with nodules.Carbonate nodules have a distinct Sr isotopic composition in each profile, pointing to the contribution of a local source for Ca. Sr isotopic compositions of plagioclases and carbonate nodules display a concomitant variation in each profile, indicating that plagioclases acted as a Sr, and thus Ca, source for the carbonate nodules. Nevertheless, carbonate nodules have a higher Sr isotopic signature than plagioclases, implying the contribution of another more radiogenic Sr source. Sr and Nd isotope data from the CRPM show that it is a mixture of weathered bedrock compounds and Saharan dust. This result highlights two other potential Sr and Ca sources: biotite and Saharan dust. Calculations of their respective contributions demonstrate that in situ weathering significantly adds to the Ca source of nodules. This result contrasts with many other studies from similar settings that highlight the importance of allochthonous - marine, aeolian - inputs. This conclusion points out that a substantial part of Ca is transferred from the local bedrock to the carbonate nodules. This mechanism seems to have been possible as peculiar edaphic conditions preserved the primary Ca sources, making in situ weathering a significant process for providing Ca.

Chloride flux growth of crystalline strontium niobates and nitridation to perovskite SrNbO2N

Highly crystalline (110) layered perovskite Sr2Nb2O7, (111) layered perovskite Sr5Nb4O15 and complex perovskite Sr4Nb2O9 were prepared by NaCl-KCl flux growth method from SrCO3 and Nb2O5. This flux synthesis achieves single strontium niobate phase in contrast to mixed niobates from the solid state reaction with the same heating parameters. A little excess of Sr source was found to be required for the synthesis of Sr5Nb4O15 and Sr4Nb2O9 at elevated temperature due to slight evaporation. The three strontium niobates were converted to perovskite SrNbO2N via thermal ammonolysis under NH3 flow at 900°C. Post-wash treatment was performed to remove the byproduct SrO. This makes additional nanopores in SrNbO2N in the cases of Sr5Nb4O15 and Sr4Nb2O9, and results in increasing surface areas of SrNbO2N with Sr:Nb ratios in the precursors (from 9.9 to 19.8 and 35.5m2/g). On the other hand, the UV–Vis diffusion reflectance spectra reveal decreasing light absorption by defects in SrNbO2N in this order. This suggests fewer low-valent Nb defects in SrNbO2N prepared from precursor with higher Sr:Nb ratio. SrNbO2N prepared from Sr4Nb2O9 would be advantageous for applications that require high surface area and low defect density of the material.

Tracing the circulation of groundwater in volcanic systems using the 87Sr/86Sr ratio: Application to Mt. Etna

The 87Sr/86Sr ratio was investigated in groundwater circulating in the volcanic edifice of Mt. Etna in order to estimate the possible contribution of deep brines circulating in the sedimentary basement. Samples from 14 sites were collected and analyzed for their chemical composition and Sr-isotope ratios. While the most common approach of coupling 87Sr/86Sr ratios with the concentration of dissolved Sr is not effective in distinguishing between the deep brine and seawater contributions, we suggest that the Sr/Cl ratio is a useful complementary parameter that needs to be considered when attempting to clearly identify the Sr sources. The obtained data indicate that the Sr-isotope signature of groundwater is determined by the volcanics hosting the aquifer. The volcanic isotopic signature is modified by very small amounts of brines (<1%), characterized by a high concentration of Sr and a 87Sr/86Sr ratio typical of sedimentary environments, but only at sites where the groundwater circulates almost in contact with the sedimentary basement. Conversely, the contribution of seawater is completely ruled out since this should produce a higher concentration of chloride. The proposed approach is potentially very effective for tracing the circulation of groundwater not only at Mt. Etna but also at volcanic edifices that overlie a bedrock with different 87Sr/86Sr ratios as well as at volcanic islands where freshwater overlies seawater.

REE and Sm-Nd Clues of High-temperature Fluid-rock Interaction in the Riópar Dolomitization (SE Spain)

REE geochemistry and Sm-Nd isotope data of Mesozoic stratabound and patchy dolostones of the Riópar area (Prebetic Zone, SE Spain) are presented. The results, combined with previously published data, suggest the dolomitizing fluid was a warm brine that interacted with siliciclastic rocks of Triassic age and with the host carbonates at low fluid-rock ratios. The positive Eu anomaly, negative ɛNd values and MREE patterns confirm that the dolostones were formed by interaction with warm acidic crustal fluids. C-O isotopic interaction models indicate that these fluids were characterized by δ18O-enriched and δ13C-depleted compositions, pointing to low ratios of fluid to rock volumes. The studied dolostones show two Sr sources: one Sr signature is close to the host carbonate values and the other one is more radiogenic, indicating that fluids became enriched in 87Sr after interacting with siliciclastic rocks. Furthermore, the Sr-Nd isotope data systematic depicts a positive correlation, thus probably the same rock sources are shared for both elements. Moreover, the warm fluids interacted with regional limestones achieving a negative Ce and positive La anomalies, low δ18O compositions and similar δ13C values than the host carbonates.

Preparation, characterization and photocatalytic activities of TiO2-SrTiO3 composites

Series of TiO2-SrTiO3 composites were synthesized by hydrothermal method, using TiO2 nanotube array as a precursor and Sr(OH)2 as a Sr source material. TiO2-SrTiO3 products with various composition were obtained by simply changing the reaction time. The as-synthesized products were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The optical properties were studied by means of UV-Vis absorption spectroscopy and photoluminescence (PL) spectra. Their photocatalytic activities were assessed by photodegradation of rhodamine B (RhB) solution and the photocatalytic reaction mechanism was discussed. The TiO2-SrTiO3 composites obtained at 2 h exhibits the highest activity for photodegradation of RhB.

Assessing the role of submarine groundwater discharge as a source of Sr to the Mediterranean Sea

Submarine groundwater discharge (SGD) has been identified as an important source of Sr to the ocean and the SGD-driven Sr flux to the global ocean has been recently re-evaluated (Beck et al., 2013). However, the uncertainty of this value is still high because of the uncertainties related to the determination of SGD flow rates and the paucity of 87Sr/86Sr data in SGD end-members. As carbonates have high Sr concentrations and are subjected to intense heightened weathering, they might significantly influence the SGD input of Sr to the ocean. Here we present data on Sr concentrations and 87Sr/86Sr ratios in three carbonate dominated sites of the western area of the Mediterranean Sea, a semi-enclosed basin characterized by abundant coastal carbonates. The 87Sr/86Sr ratios in groundwater were lower compared to modern seawater (∼0.70916), as expected for areas dominated by carbonate lithologies. Concentrations of Sr and 87Sr/86Sr ratios in groundwater showed conservative mixing in the studied subterranean estuaries. By using SGD flow rates reported in the literature for the study areas, a flow-weighted fresh SGD end-member characterized by a Sr concentration of 27–30μM and a 87Sr/86Sr ratio of 0.707834–0.708020 was calculated for the eastern coast of the Iberian Peninsula.Integrating these Sr data with literature data (i.e. values of Sr concentration and 87Sr/86Sr ratio from other lithologies as well as SGD flow rates), we also calculated the fresh SGD-driven Sr flux to the entire Mediterranean Sea, obtaining a value of (0.34–0.83)·109moly−1, with a 87Sr/86Sr of 0.7081–0.7086. Thus, for the entire Mediterranean basin, SGD is globally a source of Sr less radiogenic compared to seawater. The SGD Sr flux to the Mediterranean Sea represents 5–6% of the SGD Sr flux to the global ocean and the Mediterranean SGD end-member has higher Sr concentration (5–12μM) than the global SGD end-member (2.9μM). This confirms the significant role of carbonate lithologies on SGD-driven Sr fluxes to seawater.The fresh SGD-driven Sr flux to the Mediterranean Sea is about 20–50% of the riverine Sr input and significantly higher than the input through atmospheric dust deposition. Therefore SGD should be considered as an important continental source of Sr to the basin.

On decay constants and orbital distance to the Sun—part III: beta plus and electron capture decay

The hypothesis that seasonal changes in proximity to the Sun cause variation of decay constants at permille level has been tested for radionuclides disintegrating through electron capture and beta plus decay. Activity measurements of 22Na, 54Mn, 55Fe, 57Co, 65Zn, 82+85Sr, 90Sr, 109Cd, 124Sb, 133Ba, 152Eu, and 207Bi sources were repeated over periods from 200 d up to more than four decades at 14 laboratories across the globe. Residuals from the exponential nuclear decay curves were inspected for annual oscillations. Systematic deviations from a purely exponential decay curve differ from one data set to another and appear attributable to instabilities in the instrumentation and measurement conditions. Oscillations in phase with Earth’s orbital distance to the sun could not be observed within 10−4–10−5 range precision. The most stable activity measurements of β+ and EC decaying sources set an upper limit of 0.006% or less to the amplitude of annual oscillations in the decay rate. There are no apparent indications for systematic oscillations at a level of weeks or months.

Sulfur and strontium isotopic study of epithermal mineralization: A case study from the SE Afar Rift, Djibouti

Epithermal mineralization was recently described in synrift volcanic rocks from the SE Afar Rift in Djibouti. To infer fluid sources in this system, coupled sulfur and strontium isotopic analyses were performed on mineralized samples from hydrothermal veins and stockwork zones. Mineralization includes gypsum and chalcedony, and/or quartz±carbonate containing gold and sulfides. Sulfur isotopic compositions of sulfides and sulfates were determined using Multicollector-Inductively Coupled Plasma Mass Spectrometer (MC ICPMS); Laser Ablation MC ICPMS; and Continuous Flow Elemental Analyzer-Isotope Ratio Mass Spectrometry while strontium isotopes were determined by Thermal Ionisation Mass Spectrometry (TIMS) methods. Sulfur isotopic composition of sulfides (mainly pyrite) varies from −9.2 to +6.6‰. These values are classically reported for hydrothermal sulfides resulting from the mixing of variable S sources such as seawater sulfate and magmatic source. In addition, individual pyrite grains within the same sample show both positive and negative δ34S values suggesting multi-phase mineralization processes. Coupled sulfur and strontium isotopic compositions of seven sulfate samples hosted in (i) gypsum mound, (ii) evaporites, (iii) stockwork veins in sediments or in volcanic rocks were also investigated to characterize the sources of Sr and S. The δ34S values of the sulfate ranged from −0.8 to +14.3‰ while the 87Sr/86Sr ranged from 0.70389 to 0.70639 consistent with variable mixing ratios of Sr and S derived from volcanic sources and seawater-derived sulfate. This study shows that, although precious-metal deposition is related to low-sulfidation epithermal environment, both acidic fluid of magmatic and saline origins contributed to the hydrothermal system in the SE Afar Rift.

Synchrotron radiation-based l 1-norm regularization on micro-CT imaging in shale structure analysis

Abstract Synchrotron radiation (SR) X-ray tomography is a main technique in realizing imaging of an object section by section. We apply this technique in recovering shale microstructures which becomes a hot topic recently in non-conventional oil and gas exploration. We first set the experimental setup using SR sources at BL13W1 beamline at Shanghai Synchrotron Radiation Facility to obtain the measured data of the shale sample, and then we establish the l 1 {l_{1}} -norm constrained regularization model to reconstruct the microstructure of the shale. A fast convergent gradient descent method is developed to realize this purpose. It indicates from our test results that the new method possesses higher resolution of imaging than the conventional results given by the commercial software.

Contamination and isotopic composition of Pb and Sr in offshore surface sediments from Jiulong River, Southeast China

Concentrations and isotopic compositions of Pb and Sr in the surface sediment samples from Jiulong River, Southeast China, were determined to trace the sources of Pb and Sr. The average concentrations of Pb and Sr were 110.9 mg/kg and 69.2 mg/kg, approximately 3.2 and 2.0 times of the local soil background values, respectively. Average 62.9% of total Pb and 36.8% of total Sr in the investigated surface sediment samples were extracted by 0.5 mol/L HNO3. Pb and Sr presented slight contamination, and Pb showed low ecological risk for most of surface sediment samples in Jiulong River according to geo-accumulation index (Igeo) and potential ecological risk index (RI). The results of Pb isotopic compositions in sediment samples and potential sources showed that the Pb accumulated in the surface sediments of Jiulong River was mainly from parent material, coal combustion and Fujian Pb-Zn deposit, with the contribution rates of 34.4%, 34.0%, and 31.6%, respectively. The results of Pb isotopic compositions in 0.5 mol/L HNO3-extraction suggested that dilute HNO3-extraction was more sensitive in identifying anthropogenic Pb sources than total digestion. The results of Sr isotopic compositions showed that Sr accumulated in the surface sediments of Jiulong River estuary mainly derived from external source and natural source (parent material) with the contribution rates of 48.1% and 51.9%, respectively.

Rare earth elements and 87Sr/86Sr isotopic characterization of Indian Basmati rice as potential tool for its geographical authenticity

The increasing demand for premium priced Indian Basmati rice (Oryza sativa) in world commodity market causing fraudulent activities like adulteration, mislabelling. In order to develop authentication method for Indian Basmati rice, 87Sr/86Sr ratios and REEs composition of Basmati rice, soil and water samples were determined and evaluated their ability as geographical tracer in the present study. In addition, the possible source of Sr in rice plant has also been examined. Basmati rice samples (n=82) showed 87Sr/86Sr ratios in the range 0.71143–0.73448 and concentrations of 10 REEs (La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er, Yb) in ppb levels. Statistical analysis showed strong correlation between 87Sr/86Sr ratios of rice, silicate and carbonate fractions of soil. Good correlation and closeness of 87Sr/86Sr of rice with water indicate its uptake in rice from water. Rice grown in southern Uttar Pradesh contains higher 87Sr/86Sr compared to other region of Indo-Gangetic Plain due to higher 87Sr/86Sr of the Ganga compared to other rivers. 87Sr/86Sr ratios can be used as a tracer for differentiating Indian Basmati rice from the other country originated rice samples.

Field Measurements of Magnets for Modern SR Sources and FEL

Magnets for modern accelerators and storage rings may have a rather complex field distribution and strict quality requirements. The Budker Institute of Nuclear Physics (Novosibirsk, Russia) is a well-known producer of magnets for various accelerator projects worldwide. This paper describes our magnet measurement facility with examples of NSLS-II booster magnets, small-aperture X-FEL quadrupoles, and PETRA-III dipoles. NSLS-II booster dipoles have quadrupole and sextupole components with a rather high field quality of $1\cdot 10^{-3}$ in the good field region of ±2 cm, providing booster operation at energy from 170 MeV to 3.15 GeV with a 2-Hz repetition rate. We designed a special bench with a ceramic rotation coil to measure X-FEL quadrupoles. The equipment provided measurements of the magnetic axis with accuracy better than 5 $\mu\text{m}$ . We used the system of three temperature-stabilized Hall sensor arrays distributed vertically to obtain a three-dimensional field map from a single measurement of PETRA-III dipole magnets.

Application of advanced X-ray methods in life sciences

BackgroundSynchrotron radiation (SR) sources provide diverse X-ray methods for the investigation of structure–function relationships in biological macromolecules. Scope of reviewRecent developments in SR sources and in the X-ray tools they offer for life sciences are reviewed. Specifically, advances in macromolecular crystallography, small angle X-ray solution scattering, X-ray absorption and fluorescence spectroscopy, and imaging are discussed with examples. Major conclusionsSR sources offer a range of X-ray techniques that can be used in a complementary fashion in studies of biological systems at a wide range of resolutions from atomic to cellular scale. Emerging applications of X-ray techniques include the characterization of disordered proteins, noncrystalline and nonequilibrium systems, elemental imaging of tissues, cells and organs, and detection of time-resolved changes in molecular structures. General significanceX-ray techniques are in the center of hybrid approaches that are used to gain insight into complex problems relating to biomolecular mechanisms, disease and possible therapeutic solutions. This article is part of a Special Issue entitled “Science for Life”. Guest Editors: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo.

87Sr/86Sr, Ca/Sr, and Ge/Si ratios as tracers of solute sources and biogeochemical cycling at a temperate forested shale catchment, central Pennsylvania, USA

Plant uptake and biological cycling processes are commonly the largest flux of nutrients in terrestrial ecosystems. Hydrologic and other losses are offset by inputs from atmospheric deposition and weathering. This multi-tracer study investigates these effects using 87Sr/86Sr, Ca/Sr, and Ge/Si ratios from solid (soil profiles and bedrock), biological (leaves and sap waters), and water (pore-, ground-, stream-waters) samples to study Ca, Sr, Ge, and Si sources and cycling in a forest catchment underlying gray shale in the temperate climate of central Pennsylvania. Leaves and sap waters were found to have similar Ge/Si ratios <1μmol/mol which is consistent with biological fractionation occurring at the root–soil water interface. Ge/Si ratios in soil porewaters were higher near the surface and increased over the growing season suggesting plant preferential uptake of Si over Ge. Ca/Sr ratios in oak leaves (1360±40mol/mol) were significantly higher than those in maple leaves (650±20mol/mol). Ca/Sr ratios were also generally higher in leaves than in sap waters which are consistent with preferential Sr adsorption or Sr uptake during transpiration. 87Sr/86Sr ratios in both leaves and sap waters were similar for a given site implying that trees access similar pools of Sr and Ca, although there are site-to-site differences. Additionally, 87Sr/86Sr ratios in plant tissues were most similar to shallow pore waters (0–50cm) suggesting that mineral nutrients are obtained by trees from the near sub-surface. 87Sr/86Sr ratios in soil solutions from ridgetop and swale sites are best explained by mixing Sr derived from shale and atmospheric deposition. Valley bottom soil reservoirs and stream and groundwater samples include Sr and Ca derived from dissolution of two isotopically distinct generations of carbonates. A preliminary estimate of the Sr and Ca stream fluxes and isotopic mass balances imply propagation of a carbonate weathering front of ca. 300m Myr−1, a value larger than previously reported for regolith weathering advance rates calculated based on cosmogenic nuclides and U-series isotopes. The data for Ca, Sr, Si, and Ge in soil, soil solutions, and stream waters reflect the interaction of slower weathering processes with rapid, biologically driven cycling between soils and biomass.

Assessment of water-rock interaction processes in the Karst Springs of Makook Anticline (Kurdistan Region, Iraq) using Sr-isotopes, rare earth, and trace elements

This work characterizes the karst springs of the Makook karst system (Kurdistan Region, Iraq) in terms of geochemistry of Sr-isotopes, rare earth, and trace elements. The aim of the work is to better understand water-rock interaction by geochemical means. Sources of elements, correlation of flow rate and the geochemistry of carbonate aquifers, and effects of organic matter on the rare earth elements were investigated. Furthermore, the degree of karstification and the length of flow path were assessed. The 87Sr/86Sr ratio of two spring waters was similar to the ratio of rocks forming the aquifer, indicating that these rocks are their main and dominant Sr source. In the remaining six spring waters, the 87Sr/86Sr ratios were significantly higher than their corresponding aquifer rocks at the spring outlet and thus pointed to additional Sr sources. A temporal variation of 87Sr/86Sr in the Sarwchawa spring corresponds to flow rate changes. The chemical composition of the spring water reflects some important features of the chemical composition of their aquifers. Springs that stem from the Kometan aquifer (mainly limestone) are characterized by higher mineralization compared to springs that drained from dolomites of the Bekhme aquifer. Low to medium V2+, Rb+, P3+, and Si4+ contents in waters correspond to springs fed by limestone and dolomite aquifers, whereas higher concentrations of these elements reflect water from a marly limestone aquifer (Shkarta spring). The release of these elements is related to the clay fraction of this aquifer. In contrast, the highest concentrations of Ni2+, Se4+, Mo6+, SO4 2−, Sr2+, F¯, and Ba2+ were found in the spring fed by pure limestone but having the highest flow rate and the longest flow path. Therefore, these elements were enriched in the water due to longer interaction of the water with the rock. The temporal variation of REE concentrations in karst waters are controlled by flow, dissolved organic carbon (DOC), temperature, and redox reactions.

Pb and Sr concentrations and isotopic compositions in prehistoric North American teeth: A methodological study

We present Pb and Sr isotopic compositions and elemental concentrations for dentin and enamel from 28 human teeth from 10 locations in the southwestern United States. These teeth represent Native American communities that were functioning between 300BCE and 1200CE. We wished to assess whether Pb isotopic data can extend the interpretations made from Sr isotopic data alone, and to determine the analytical requirements for doing Sr and Pb analyses from single samples. Pb concentrations in our samples are between 0.06 and 48ppm, with Sr concentrations between 10 and 3300ppm. 87Sr/86Sr compositions lie between 0.708 and 0.712. Pb isotopic compositions are more variable, with 206Pb/204Pb ranging between 17.9 and 21.7. Isotopic compositions and elemental concentrations for both Sr and Pb can be determined on samples smaller than 1mg, but there is real heterogeneity between samples of this size. Neither concentrations nor isotopic compositions are reproducible to within analytical uncertainty in replicate aliquots from individual teeth. We cannot determine whether this variability is an in-vivo or a diagenetic effect. Combined Pb and Sr isotopic data discriminate most locations, and the inclusion of Pb data provides a stronger basis for archeological interpretations. Our data suggest that Pb is more susceptible to post-mortem exchange than Sr. Background isotopic data are needed to characterize Pb and Sr sources in the study areas. Pb concentration data for enamel samples indicate a blood Pb load of 0.1–0.2μgPb/dL for preindustrial Native Americans.