Mixing rates in Shagawa Lake,Minnesota, sediments as determined from 106Ru profiles

Rates of surficial sediment mixing and sediment burial are measured in Shagawa Lake, Minnesota, using radionuclide tracers. Based on ¹⁰⁶Ru profiles in 16 cores, mixing rates average 13 cm²/yr within the upper 9 cm of sediment. Two other nuclides, ²¹⁰Pb and ¹³⁷Cs, provide further evidence for calculation of mixing rates. In addition, ²¹⁰Pb profiles estimate sediment burial rates (about 0.4 cm/yr). Mixing estimates are shown to be fairly insensitive both to uncertainties in sediment burial rates and to temporal patterns of ¹⁰⁶Ru deposition.     

Recent chronologies for tree rings and terrestrial archives using C bomb fallout history

Tree rings representing the period from the mid-1950s up to 2001 were studied as part of an investigation of anthropogenic radionuclide input to terrestrial systems. A live specimen of Pinus sylvestris from the east coast of Ireland was felled, sampled and analysed for comparison with a similar tree felled close to the Atlantic seaboard on the west coast of Ireland. Data for the tree ring sequences were examined relative to the radionuclide content of peat profiles sampled in close proximity to the locations of the studied Pine trees.The data indicate that ¹⁴C concentrations in tree ring sequences from the east and west coasts of Ireland are virtually identical. The sequences show maximum ¹⁴C concentrations (185 and 189 pMC at east and west coast sites, respectively) that correspond closely with published data for atmospheric levels during the height of the nuclear weapons test period (1945-1980). The tree ring count for the specimen from the east coast places the ¹⁴C peak precisely at 1964, the year following the known peak in atmospheric concentrations due to above ground testing of nuclear weapons. However, ¹⁴C data show that simple ring counting of the west coast tree did not provide an accurate chronology. The data demonstrate the importance of applying dendrodating techniques using replicated site chronologies, and the value of the ¹⁴C bomb fallout curve for the construction of recent chronologies. Data show no evidence of enhanced uptake at the east coast that might suggest incorporation of output from the Sellafield nuclear complex or from the release of radioactivity resulting from an accidental fire at the plant in 1957.     

Non-destructive alpha-spectrometry and radiochemical studies of deep-sea manganese nodules

A deep-sea Mn nodule handpicked from top of a 20 cm diameter North Pacific tripod core was directly counted by an α-spectrometer with a silicon surface barrier detector. A distinct ²¹⁰Po peak was recorded for the nodule upper side in contact with bottom seawater. Based on the spectrum, the ²¹⁰Po (supported by ²¹⁰Pb with 22 year half life) is thought to be confined in the top few microns of the nodule. Since the ²¹⁰Po peak diminishes considerably for the bottom side resting on sediment, nondestructive α-spectrometry is useful for determining the sea floor orientation of nodules. This method was tested for a western North Pacific dredged Mn nodule, and was successful in identifying the orientation (and also surface loss of the nodule by dredging).Radiochemical analysis was also carried out for carefully scraped samples from the top and bottom of the two nodules. The growth rates of the hand-picked nodule based on excess ²³⁰Th and ²³¹Pa profiles were 1 to 4 mm/10⁶ y and apparently varied with time. The dredged sample has grown at 2 to 6 mm/ 10⁶ y and the growth has likely been episodic. The radionuclide composition was significantly different between the top and bottom. Evidence was found that the radionuclide fluxes of ²³⁰Th and ²³¹Pa into the nodules considerably changed during the growing histories. The ²³⁰Th/²³²Th activity ratios in the nodule tops are comparable with those in bottom seawater suggesting that the top is growing with metals of seawater origin. However it remains unresolved whether the nodule bottoms are growing by utilizing metals in the sediment pore water.     

Numerical modeling of the development of a preferentially leached layer on feldspar surfaces

Compositional depth profiles in the leached layer of feldspar surfaces are usually interpreted by using analytical solutions which introduce oversimplifying assumptions. Here we present a general multicomponent interdiffusion numerical model for simulating cation release from a preferentially leached layer on feldspar surfaces in acid solutions. The numerical model takes into account interdiffusion, dissolution of the solid phase (represented by a moving boundary problem), and adsorption in the leached layer. Effective diffusion coefficients of ions vary with concentration along the leached layer. Governing equations of ions diffusion in the leached layer are solved numerically with a finite element method implemented in a multicomponent reactive transport code, CORE^3D, previously verified against analytical solutions of compositional depth profiles. The numerical model is tested with published X-ray photoelectron spectroscopy (XPS) data on early development of compositional profiles of labradorite leached in pH 2 HCl solutions. Model parameters are estimated by fitting depth profiles of Ca and Al measured at 12, 26, 48, 72, and 143 h. The best fit is achieved with tracer diffusion coefficients of 4 × 10⁻¹⁸, 8 × 10⁻¹⁷, 3.4 × 10⁻¹⁷, and 7 × 10⁻¹⁸ cm²/s for H, Na, Ca, and Al, respectively, which fall within the range of values reported in the literature. Our estimate of the retreat velocity corresponding to the dissolution rate is 3 × 10⁻¹³ cm/s. Results of sensitivity runs show that computed compositional profiles are sensitive to most model parameters.     

Determination of chemical weathering rates from U series nuclides in soils and weathering profiles: Principles,applications and limitations

The development of U-series nuclides for investigating weathering processes has been significantly stimulated by the analytical improvement made over the last decades in measuring the ²³⁸U series with intermediate half-lives (i.e., ²³⁴U–²³⁰Th–²²⁶Ra). It is proposed in this paper to present principles and methods that are now being developed to determine weathering rates from the study of U-series nuclides in soils and weathering profiles. Mathematical approaches, developed to calculate such rates, are based on some implicit assumptions that are also presented and must be kept in mind if one wants to correctly interpret the obtained ages.     

Cosmogenic radionuclide dating indicates ice‐sheet configuration during MIS 2 on Nordaustlandet,Svalbard

Hormes, A., Akçar, N. & Kubik, P. W. 2011: Cosmogenic radionuclide dating indicates ice‐sheet configuration during MIS 2 on Nordaustlandet, Svalbard. Boreas, 10.1111/j.1502‐3885.2011.00215.x. ISSN 0300‐9483.0300‐9843 Glacial geological field surveys, aerial image interpretation and cosmogenic radionuclide (CRN) dating allowed us to reconstruct the ice‐sheet configuration on Nordaustlandet, the northernmost island of the European sector on the margin of the Arctic Ocean. The timing of deglaciation was investigated by determining the ²⁶Al and ¹⁰Be ages of glacially scoured bedrock, weathered periglacial blockfields and glacial erratic boulders. Only ¹⁰Be ages were useful for our interpretations, because of unresolved analytical problems with ²⁶Al. Fjords and lowlands on Nordaustlandet yielded Late Weichselian ¹⁰Be ages, indicating that actively erosive ice streams scoured the coastal fjord bathymetry during marine isotope stage (MIS) 2. In Murchisonfjorden, ground‐truthed air‐photograph interpretation and ¹⁰Be ages of boulders indicated a cold‐based glacier ice cover during MIS 2 on higher plateaus. ¹⁰Be ages and lithological studies of erratic boulders on higher and interior plateaus of Prins Oscars Land (>200–230 m a.s.l.) suggest that the Mid‐Weichselian glaciation (MIS 4) might have been more extensive than that during MIS 2.     

长江河口水下三角洲137Cs地球化学分布特征

文章通过对长江口水下三角洲采集的10个柱状样放射性核素¹³⁷Cs的分析可以得知,长江口水下三角洲¹³⁷Cs剖面中均存在清晰的最大蓄积峰,其峰值比活度介于5.68±1.03～21.74±1.39Bq/kg之间,平均值为14.11±1.10Bq/kg,最大蓄积峰所处的深度为55～117cm。剖面中¹³⁷Cs最大蓄积峰应该与1963年的¹³⁷Cs散落沉降相对应。长江口水下三角洲的表层沉积物中的¹³⁷Cs比活度范围介于0～9.19±1.12Bq/kg之间,并且与长江流域其他地区的表层¹³⁷Cs比活度相一致。长江口水下三角洲可探测到的¹³⁷Cs比活度的最大深度范围在88～160cm的范围内变化,¹³⁷Cs蓄积总量为2361.30±174.38～17714.94±262.14Bq/m²,平均值为9664.97±100.05Bq/m²,¹³⁷Cs比活度的最大深度及¹³⁷Cs蓄积总量均表现出从岸向海逐渐增加的趋势。实测的¹³⁷Cs总量均大于长江流域的¹³⁷Cs背景值,说明了长江口水下三角洲的¹³⁷Cs蓄积既有大气散落直接沉降的来源,又有流域侵蚀带来的¹³⁷Cs输入,并且主要以后者为主。通过放射性核素示踪模型分析长江口水下三角洲¹³⁷Cs散落蓄积特征可以得知,长江口水下三角洲¹³⁷Cs的蓄积以长江流域来源为主,说明了放射性核素¹³⁷Cs在长江口水下三角洲沉积物中的蓄积主要受流域侵蚀因素的影响。     

Calcium diffusivity in alumino-silicate garnets: an experimental and ATEM study

Concentration gradients in calcium are common in metamorphic or magmatic garnets and can be used to determine the timescales of geological processes. However, the kinetics of Ca diffusion in garnet is poorly constrained and experimental studies have to date yielded widely varying diffusion coefficients. In this paper, we describe a new method for generating diffusion profiles in garnet. We incorporated polished and compositionally homogeneous garnet seeds in a finely ground powder of clinopyroxene and garnet. During the experiments (1.3 GPa, 1,050–1,250°C, and ƒO₂ ≤ the graphite-O₂ buffer), the mineral powder partially melted, recrystallized, and formed a 10–50 μm wide overgrowth zone of compositionally distinct garnet around the seeds. Long duration experiments generated measurable relaxation profiles at these seed/overgrowth interfaces. We performed analytical transmission electron microscope traverses across the interfaces in each experiment. Thirteen usable compositional profiles were obtained with characteristic distances of diffusion ranging from 300 to 1,000 nm. From these profiles, Ca–(Fe, Mg) interdiffusion coefficients were retrieved using an analytical solution for the diffusion equation and the data were cast in an Arrhenius relation. Linear regression of the data yields an activation energy Q _{Ca–(Fe, Mg)} equal to 188 ± 48 kJ mol⁻¹ and a frequency factor D ₀ equal to 6.6 × 10⁻¹⁴ m² s⁻¹. Within the compositional range studied, the composition of garnet has no major effect on the Ca–(Fe, Mg) interdiffusion coefficient. The very slow diffusion rate of Ca is in agreement with natural observations indicating that Ca diffuses more slowly than Fe and Mg. The Ca diffusion coefficients derived from this study are not model-dependent and can be used to determine the durations of geological events from Ca relaxation profiles in natural garnets.

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Chlorine-36 and the initial value problem

 Chlorine-36 is a radionuclide with a half-life of 3.01×10⁵a. Most ³⁶Cl in the hydrosphere originates from cosmic radiation interacting with atmospheric gases. Large amounts were also produced by testing thermonuclear devices during 1952–58. Because the monovalent anion, chloride, is the most common form of chlorine found in the hydrosphere and because it is extremely mobile in aqueous systems, analyses of both total Cl^– as well as ³⁶Cl have been important in numerous hydrologic studies. In almost all applications of ³⁶Cl, a knowledge of the initial, or pre-anthropogenic, levels of ³⁶Cl is useful, as well as essential in some cases. Standard approaches to the determination of initial values have been to: (a) calculate the theoretical cosmogenic production and fallout, which varies according to latitude; (b) measure ³⁶Cl in present-day precipitation and assume that anthropogenic components can be neglected; (c) assume that shallow groundwater retains a record of the initial concentration; (d) extract ³⁶Cl from vertical depth profiles in desert soils; (e) recover ³⁶Cl from cores of glacial ice; and (f) calculate subsurface production of ³⁶Cl for water that has been isolated from the atmosphere for more than one million years. The initial value from soil profiles and ice cores is taken as the value that occurs directly below the depth of the easily defined bomb peak. All six methods have serious weaknesses. Complicating factors include ³⁶Cl concentrations not related to cosmogenic sources, changes in cosmogenic production with time, mixed sources of chloride in groundwater, melting and refreezing of water in glaciers, and seasonal groundwater recharge that does not contain average year-long concentrations of ³⁶Cl. Received, December 1996 · Revised, August 1997 · Accepted, August 1997     

Records of radionuclide deposition in two salt marshes in the United Kingdom with contrasting redox and accumulation conditions

Single cores from two salt marshes in the United Kingdom located near different nuclear facilities were investigated to compare chronostratigraphic estimates derived from the natural radionuclide ²¹⁰Pb_excess with estimates from the known times of introduction of artificial radionuclides to the environment. Both cores selected had clear visual indications of redox zonation, and evidence for diagenetic redox perturbation of the radionuclide records was also sought. In the core from Beaulieu Marsh on the south coast of England, the redox zonation was revealed by the profiles of the redox-sensitive elements Mn + I, Fe + P + As, and S, and the records of nuclear discharges were entirely contained within oxidized conditions in the upper 40 cm. The constant flux/constant sedimentation ²¹⁰Pb_excess accumulation estimate was 76% of that derived from the 1963 fallout ¹³⁷Cs level (0.35 vs. 0.46 g cm⁻² yr⁻¹ dry mass), but the constant flux ²¹⁰Pb_excess method indicated that accumulation rates were lower at Beaulieu before ∼1950. On any timescale, ¹³⁷Cs appears earlier in the sediment record than its introduction to the environment, but although downward diffusion of ¹³⁷Cs relative to ²⁴¹Am has clearly occurred, the ¹³⁷Cs peak still appeared in place and there was negligible penetration of ¹³⁷Cs into underlying reduced conditions. This core also contained a peak of the ⁶⁰Co discharges from either or both the Winfrith and La Hague nuclear plants that peaked in 1980 and 1984, respectively. The sediments in the core from Wyre Marsh on the eastern coast of the Irish Sea had accumulated more rapidly than those at Beaulieu, and in this case the redox zonation could be established only from Mn and S profiles. Here, the constant initial activity ²¹⁰Pb_excess accumulation rate estimate was 125% of that derived from the ¹³⁷Cs peak correlated with the 1975 Sellafield discharge maximum (0.79 vs. 0.64 g cm⁻² yr⁻¹). Sellafield discharge ¹³⁷Cs swamps fallout or Chernobyl ¹³⁷Cs signals in this core, but the ¹³⁷Cs and ²⁴¹Am sediment records are well separated and remain consistent with the slightly different discharge patterns over time. This is so despite the fact that the maximum activity levels of both isotopes are now located well into reducing conditions out of which Mn must have migrated. The ²¹⁰Pb profile appeared similarly unaffected by the oxidized/reduced boundary in this case. This core was too short to define the limits of any downward ¹³⁷Cs migration. ²¹⁰Pb_excess accumulation rate estimates for salt marshes should be viewed with some caution because of the steady-state assumptions inherent in all ²¹⁰Pb_excess methods and the potential for fluctuating accumulation conditions and open system behavior in salt marshes.     

Cosmogenic radionuclide <Superscript>7</Superscript>Be concentration in seven species of lichens and its correlation with <Superscript>40</Superscript>K, <Superscript>137</Superscript>Cs and <Superscript>226</Superscript>Ra

In this work, accumulation of cosmogenic radionuclide ⁷Be in seven species of lichens was determined using HPGe detectors in autumn season. Ramsar city which is located in the north of Iran as one of the high-level natural radiation areas in the world was considered. Lichen species represented good potential in accumulation of ⁷Be radionuclide. The foliose species of Xanthoria parietina with the highest activity concentration value of 112.8 ± 1.8 Bq kg^?1 was introduced as bioindicator for accumulation of ⁷Be radionuclide. Cladonia rangiformis species has got minimum concentration of 64.5 ± 0.8 Bq kg^?1. Also from thallus morphology viewpoint, results showed that ⁷Be accumulation in foliose species is higher than in fruticose and crustose lichens species. Also there was relatively large positive correlation between ⁷Be and ²²⁶Ra activity concentrations in lichens species.     

Natural radionuclide concentrations in thermal springs of east Algeria

The variation of the natural radionuclide concentrations depends on the chemical composition of each site. In this work, two thermal springs in the east of Algeria have been chosen to assess the activity concentration of natural radionuclide, mainly the three natural radioactive series ²³⁸U, ²³⁵U and ²³²Th, and ⁴⁰K. The high-resolution gamma ray spectroscopy was used to determine these concentrations. In these water samples, ²³⁵U, ²³⁴Th, ²¹⁰Pb, ²²⁶Ra radionuclides are less than the minimum detectable activity. The activity of ²³⁸U is dominant. The ²³⁸U activity was determined by taking the mean activity of two separate photo-peaks of daughter nuclides ²¹⁴Pb at 351.92 (37.2%) keV and ²¹⁴Bi at 609.31 (45%) keV. The measured activity concentrations of ²³⁸U in water samples obtained from the concentrations of ²¹⁴Bi and ²¹⁴Pb ranged from 0.56 ± 0.20 to 1.13 ± 0.20 Bq/L. The annual effective dose value due to the ingestion of the measured radionuclide ²³⁸U in 1 L of water, for an adult, ranged from 9.20 to 18.56 µSv.     

A search for small-scale clumpiness in dense cores of molecular clouds

We have analyzed HCN(1-0) and CS(2-1) line profiles obtained with high signal-to-noise ratios toward distinct positions in three selected objects in order to search for small-scale structure in molecular cloud cores associated with regions of high-mass star formation. In some cases, ripples were detected in the line profiles, which could be due to the presence of a large number of unresolved small clumps in the telescope beam. The number of clumps for regions with linear scales of ～0.2–0.5 pc is determined using an analytical model and detailed calculations for a clumpy cloud model; this number varies in the range: ～2 × 10⁴–3 × 10⁵, depending on the source. The clump densities range from ～3 × 10⁵–10⁶ cm^?3, and the sizes and volume filling factors of the clumps are ～(1–3) × 10^?3 pc and ～0.03–0.12. The clumps are surrounded by inter-clump gas with densities not lower than ～(2–7) × 10⁴ cm^?3. The internal thermal energy of the gas in the model clumps is much higher than their gravitational energy. Their mean lifetimes can depend on the inter-clump collisional rates, and vary in the range ～10⁴–10⁵ yr. These structures are probably connected with density fluctuations due to turbulence in high-mass star-forming regions.     

Long-core profiles of137Cs,134Cs,60Co and210Pb in sediment near the Rhône River (Northwestern Mediterranean Sea)

Various anthropogenic radionuclides and²¹⁰Pb were analyzed in a 4.3-m-long core, sampled near the Rhône River mouth in March 1991, to evaluate the extent of industrial releases that accumulate in this area. The whole core was significantly marked by radionuclide inputs from the nuclear facilities located along the river (¹³⁷Cs,¹³⁴Cs,⁶⁰Co). Irregular profiles in natural and artificial radionuclides should be related to variations in their respective inputs from the Rhône River to the Mediterranean Sea. Minimum concentrations were found during high flow periods. Using both the¹³⁷Cs/¹³⁴Cs profile in the core and the range of this ratio in Rhône waters, mean apparent accumulation rates were estimated to range between 37 cm yr^?1 and 48 cm yr^?1. This core would then represent a sedimentary record over a 7–10 year period. However, the presence of a signal from the Chernobyl accident, which occurred on April 26, 1986, was not clearly observed in the core. Inventories of both artificial and natural radionuclides were greater than expected from atmospheric inputs. The increased sedimentation occurring in close vicinity to the mouth of the Rhône River is thus responsible for trapping of elements transported by the river to the Mediterranean Sea. In this area, inventories of artificial radionuclides are well in excess of aerial deposition from Chernobyl and atmospheric weapons tests and are linked primarily to industrial releases.     

Distribution and relationship of radionuclides to streambed gravels in a small watershed

In White Oak Creek watershed in eastern Tennessee, the radionuclides⁶⁰Co,⁹⁰Sr, and¹³⁷Cs were retained by streambed gravels on different sites:⁶⁰Co was associated with manganese in the hydrous oxide coatings on rocks and minerals;⁹⁰Sr occurred primarily as an exchangeable cation although small amounts were held in a nonexchangeable form; and¹³⁷Cs was held very selectively, presumably by illite in shale fragments composing the sediment. The distribution of radionuclides on sediments was size dependent: the 0.85–3.35 mm fine-gravel fraction was higher in radionuclide concentration than the sand fraction. An areal survey of radionuclide concentrations on streambed gravels from throughout the watershed, located numerous contamination sources. These radionuclide concentrations, when combined with both distribution coefficients of radionuclides between gravel and water and drainage area, were used to rank subsections of the watershed by their relative contribution to the overall contamination of the watershed. For⁹⁰Sr, this ranking procedure agreed with the measured discharges of subsections of the watershed which are routinely monitored. Research sponsored by the Oak Ridge National Laboratory (operated by U.S. Department of Energy under contract W-7405-eng-26 with Union Carbide Corporation. Publication No. 2017, Environmental Sciences Division, ORNL.     

现代沉积年分辨的137Cs计年──以云南洱海和贵州红枫湖为例

1964,1975及1986年三个¹³⁷CS时标计算出红枫湖和洱海沉积物平均堆积速率完全一致,说明1975年和1986年次级蓄积峰作为计年时标的可靠性。洱海沉积物平均堆积速率为0．047±0．002g／(cm²·a),与²¹⁰Pb方法所获得的结果一致;红枫湖为0．17±0．01g／(cm²·a),与其建湖以来沉积物实际堆积的观察结果吻合。洱海1964年沉积物中¹³⁷CS的比活度(校正到沉积年代)仅46．4Bq／kg,而红枫湖达145Bq／kg。由于红枫湖沉积物堆积速率约为洱海的3．7倍,所以其1964年层节沉积物中¹³⁷CS蓄积量比洱海大11.5倍。红枫湖沉积物中¹³⁷CS累计值的99．4％分配于1985年以前,而洱海的19．4％分配于1986年以后,显示出¹³⁷CS在洱海沉积物中的较大扩散能力。     

Inventories and sorption-desorption trends of radiocesium and radiocobalt in James River estuary sediments

Anthropogenic radionuclides (¹³⁷Cs,¹³⁴Cs,⁶⁰Co) have been introduced to the James River estuary as a result of low-level releases from the Surry Reactor site since 1973 and worldwide atmospheric fallout from nuclear weapons tests since the early 1950s The total radionuclide burden in the estuary sediments has been estimated by integrating radionuclide activities in 29 box cores and extrapolating these integrated values over surface areas subdivided on the basis of sediment type, rates of accumulation, and proximity to the reactor release site. Our results indicate that 30% of the⁶⁰Co, but only 15% of the¹³⁴Cs released from the reactor site, has been retained in the estuary sediments, and about 40% of the¹³⁴Cs and⁶⁰Co sediment inventory is in areas that represent less than 5% of the total estuarine surface area. Depletion of the¹³⁴Cs in downstream sediments forms a noticeable trend in the James River estuary, and we postulate that seawater cation competition and exchange is primarily responsible.     

Chlorine-36 in groundwater of the United States: empirical data

Natural production of the radionuclide chlorine-36 (³⁶Cl) has provided a valuable tracer for groundwater studies. The nuclear industry, especially the testing of thermonuclear weapons, has also produced large amounts of ³⁶Cl that can be detected in many samples of groundwater. In order to be most useful in hydrologic studies, the natural production prior to 1952 should be distinguished from more recent artificial sources. The object of this study was to reconstruct the probable preanthropogenic levels of ³⁶Cl in groundwater in the United States. Although significant local variations exist, they are superimposed on a broad regional pattern of ³⁶Cl/Cl ratios in the United States. Owing to the influence of atmospherically transported ocean salt, natural ratios of ³⁶Cl/total Cl are lowest near the coast and increase to a maximum in the central Rocky Mountains of the United States. Electronic Publication     

Ra-226 and Rn-222 in saline water compartments of the Aral Sea region

The Aral Sea has been shrinking since 1963 due to extensive irrigation and the corresponding decline in the river water inflow. Understanding of the current hydrological situation demands an improved understanding of the surface water/groundwater dynamics in the region. ²²²Rn and ²²⁶Ra measurements can be used to trace groundwater discharge into surface waters. Data of these radiometric parameters were not previously available for the study region. We determined ²²²Rn activities after liquid phase extraction using Liquid Scintillation Counting (LSC) with peak-length discrimination and analyzed ²²⁶Ra concentrations in different water compartments of the Amu Darya Delta (surface waters, unconfined groundwater, artesian water, and water profiles from the closed Large Aral Sea (western basin).The water samples comprise a salinity range between 1 and 263 g/l. The seasonal dynamics of solid/water interaction under an arid climate regime force the hydrochemical evolution of the unconfined groundwater in the Amu Darya Delta to high-salinity Na(Mg)Cl(SO₄) water types. The dissolved radium concentrations in the waters were mostly very low due to mineral over-saturation, extensive co-precipitation of radium and adsorption of radium on coexisting solid substrates.The analysis of very low ²²⁶Ra concentrations (<10 ppq) at remote study sites is a challenge. We used the water samples to test and improve different analytical methods. In particular, we modified a procedure developed for the α-spectrometric determination of ²²⁶Ra after solid phase extraction of radium using 3M Empore™ High Performance Extraction Disks (Purkl, 2002) for the analysis of the radionuclide using an ICP sector field mass spectrometer. The ²²⁶Ra concentration of 17 unconfined groundwater samples ranged between 0.2 and 5 ppq, and that of 28 artesian waters between <0.2 and 13 ppq. The ICP-MS results conformed satisfactorily to analytical results based on γ-measurements of the ²²²Rn ingrowth after purging and trapping on super-cooled charcoal. The ²²⁶Ra concentrations were positively correlated with the salinity and the dissolved NaCl concentrations. The occurrence of unusually high ²²⁶Ra activities is explained by radium release from adsorption sites with increasing salinity. The inferred spatial variability of ²²²Rn in the Aral Sea and of ²²²Rn and ²²⁶Ra in the groundwater of the Amu Darya Delta is discussed in the context of our own previous hydrochemical studies in the study sites. Relatively low ²²²Rn activities in the unconfined GW (1–9.5 Bq/l) indicate the alluvial sediments hosting the GW to be a low-²³⁸U(²²⁶Ra) substrate. Positive correlations between U and ²²⁶Ra, and U and ²²²Rn are likely related to locally deposited Fe(Mn)OOH precipitates. The ²²²Rn activity of the GW, however, distinctly exceeds the ²²²Rn concentration in the Aral Sea (10 mBq/l), in principle, making ²²²Rn a sensitive tracer for the inflow of GW. The high water volume of the Large Aral Sea and wind induced mixing of its water body, however, hamper the detection of local groundwater inflow.     

Analysis of coupled Sr/Ca and Sr/Sr variations in enamel using laser-ablation tandem quadrupole-multicollector ICPMS

We present in this study results obtained with a laser-ablation coupled with both a quadrupole and a multi-collector ICPMS. The simultaneous in situ Sr/Ca and ⁸⁷Sr/⁸⁶Sr measurements along growth profiles in enamel allows the concomitant diet and migration patterns in mammals to be reconstructed. Aliquots of the powdered international standard NIST “SRM1400 Bone Ash” with certified Sr and Ca contents, was sintered at high pressure and temperature and was adopted as the reference material for external reproducibility and calibration of the results. A total of 145 coupled elemental and isotopic measurements of herbivores enamel from the Kruger National Park, South Africa, gives intra-tooth Sr/Ca and ⁸⁷Sr/⁸⁶Sr variations that are well larger than external reproducibility. Sr/Ca profiles systematically decrease from the dentine-enamel junction to the outer enamel whereas ⁸⁷Sr/⁸⁶Sr profiles exhibit variable patterns. Using a simple geometric model of hypsodont teeth growth, we demonstrate that a continuous recording of the ⁸⁷Sr/⁸⁶Sr variations can be reconstructed in the tooth length axis. This suggests that the mobility of a mammal can be reconstructed over a period of more than a year with a resolution of a ten of days, by sampling enamel along growth profiles. Our geometric model of hypsodont teeth growth predicts that an optimal distance between two successive profiles is equal to the enamel thickness. However, this model does not apply to the Sr/Ca signal which is likely to be altered during the enamel maturation stage due to differential maturation processes along enamel thickness. Here, the observed constant decreases of the Sr/Ca ratios in the ungulates of Kruger National Park suggests that they did not changed of diet, while some of them were migrating.