SR Signal Research Articles

Reliability of the Strontium Isotope Stratigraphy approach in marginal seas: Insights from the Miocene Paratethys

The robustness of the Strontium Isotope Stratigraphy (SIS) as a chemostratigraphic tool was tested in the Miocene epicontinental Central Paratethys using new 87Sr/86Sr results obtained for 129 foraminiferal tests and various marine invertebrate shells that were converted to numerical ages using the global 87Sr/86Sr curve for Phanerozoic open oceans. These ages were compared with those expected from either magnetostratigraphic, radiometric or biostratigraphic studies applied to selected sections from different Central Paratethys basins. The results from different basins showed variations in 87Sr/86Sr values for specific time intervals; therefore, it is not possible to construct a unique 87Sr/86Sr curve for the Central Paratethys region that can be used for chemostratigraphic purposes. The 87Sr/86Sr signal in semi-enclosed basins tends to reflect the lithology of the source areas. a: For example, marine basins surrounded by areas of Mesozoic carbonate rock cover are associated with a reduced 87Sr/86Sr signal compared to the global 87Sr/86Sr signal primarily due to the drainage of these Mesozoic carbonate rocks and transfer of their specific Sr signal. By contrast, areas affected by continental runoff from crystalline terrains in combination with limited connection to surrounding marine domains were found to show an elevated 87Sr/86Sr signal compared to the global one. Additionally, it was demonstrated that infaunal, eutrophic and hypoxic species (foraminiferal genus Uvigerina and molluscs) show a shift towards a relatively higher 87Sr/86Sr signal. Therefore, our data show that variable 87Sr/86Sr patterns occur in semi-enclosed domains, primarily reflecting local settings and thus hampering reliable SIS ages. In particular, the best SIS results in the studied Paratethys area occur during periods of maximum marine connectivity, when other (biostratigraphic) methods can be applied, and then become unreliable as connectivity diminishes.

The Core Story: Intertwined Maternal and Progeny Signatures Enclosed in the Otolith

Analytical imaging via synchrotron analysis was used to study sagittal otoliths of four freshwater pipefish species exhibiting amphidromous or freshwater resident lifestyles. We undertook a hyperfine elemental scanning of a 25 μm diameter length area centred on the core, namely the pre-hatch zone, corresponding to the sagitta formed during embryogenesis. We analysed calcium (Ca), strontium (Sr), manganese (Mn), chromium (Cr), cobalt (Co), nickel (Ni) and sulphur (S), with the latter serving to count growth increments. Whatever the species, a Ca pit consistently marked the core; the amphidromous species exhibited Mn enrichment at the core and the sagitta formed a week before hatching. These results illustrate common otolith formation mechanistic processes. Sr and heavy metals’ signals in the pre-hatch zone were compared to their signal in the edge of the otolith, an area encompassing the adult freshwater (adFW) environmental signature. We found that Co and Ni otolith signals had no relation to environmental conditions, but it is worth looking into Cr as a marker of early-life environment. While we caution against the use of a Sr:Ca ratio for life history interpretations at the core because of the Ca pit, the Sr signal analysis uncovered possible variations in the parental behaviour that potentially trigger newly-hatched juvenile migration to sea or residency. Finally, our results demonstrate that the microchemistry of otolith formation during early development is a melting of maternal signal during egg yolk elaboration, of the environmental signal during egg incubation, and of individual physiology during early growth.

Negative muon spin rotation and relaxation on superconducting MgB2

The internal nuclear magnetic field in a superconducting MgB2 powder sample was studied with a µ− SR technique. Although the past µ +SR study on MgB2 reported the appearance of a dynamic behavior even below Tc due to µ + diffusion, µ− SR shows a static behavior in the whole temperature range measured, as expected. The ZF-µ− SR spectra do not suggest any appearance of additional magnetic field below Tc within the experimental accuracy. Considering the small asymmetry of the µ− SR signal, it is a challenge to detect the appearance of an internal magnetic field below Tc caused by the time reversal symmetry breaking.

Strontium signal lag in otoliths of juvenile sockeye salmon (<i> Oncorhynchus nerka</i>) during transition from the freshwater to marine environments

The shift in strontium (Sr) concentrations in fish otoliths is a commonly used proxy for identification of marine environment entry during diadromous migrations. However, there is still controversy about the appearance of the Sr-based sea entry mark relative to the true point of entry. In this study, the Sr signal lag was assessed in otoliths of juvenile sockeye salmon (Oncorhynchus nerka) under experimental conditions replicating the transition to seawater during juveniles’ seaward migration. A Sr signal delay was observed to average at 8.2 (SD = 5.1) days for fish with a body length of 140–170 mm (and a weight of 30–70 g). This lag may be species-specific and should be taken into consideration when estimating marine entry timing and marine residence duration of juvenile salmon.

Effect of barite-bound Sr on detrital Sr isotope systematics in marine sediments

In marine sediments, the Sr content and isotope composition (87Sr/86Sr) of the terrigenous detrital component are widely used to track changes in provenance and related transport and weathering processes. Accurately separating detrital-Sr from other sedimentary Sr-phases is a prerequisite for such studies. Conventionally, it is assumed that Sr in the carbonate-free residue corresponds to detrital Sr alone. However, the decarbonated residue may contain barite with significant Sr content and a non-detrital 87Sr/86Sr composition; this may substantially affect the measured Sr signal. To examine this chronically overlooked phenomenon, the Mediterranean Sea is an ideal area because 1) detailed provenance studies have been done using Sr and 87Sr/86Sr of the residual fraction, and 2) enhanced levels of barite repeatedly occurred in association with distinct, organic-rich sapropel sediments.Here, we use the most-recent sapropel S1 interval to evaluate the effect of barite-bound Sr in the residual fraction after decarbonation. A total of 130 samples were taken from 10 cores in the eastern Mediterranean Sea (EMS) and 1 core in the western Mediterranean Sea. This selection represents a geographic and bathymetric coverage of the EMS and permits the basin-wide comparison between organic-rich and -lean sediments. After decarbonation using 1 M HCl solution, the residual sediments were subject to NH4Cl extraction (2 M, pH 7), known to selectively dissolve barite. Our results demonstrate the presence of Sr-bearing barite after traditional carbonate removal and its effect on the derived “detrital” Sr signature. This barite-Sr effect is considerable for samples with barite-Ba >400 μg/g in bulk sediment. The impact of barite is prominent if accompanied by a detrital provenance background of high 87Sr/86Sr (>0.713) or low Sr/Al (<1.0 mg/g). In such cases, removal of remaining barite is required to obtain an unbiased detrital Sr signal. We recommend an improved procedure for detrital Sr separation in marine sediments, with an additional NH4Cl leaching step to eliminate any remaining barite after decarbonation. This approach is particularly important for areas/times of high biological productivity, where sediments are often characterized by abundant barite content.

Analysis of Sr and Ba profiles measured by ultra-high-resolution mass spectrometry LA-ICP-MS in otoliths of juvenile anadromous sockeye salmon &lt;i&gt;Oncorhynchus nerka&lt;/i&gt; in the early marine life-history stage as a proxy for fresh to marine water transition

The strontium (Sr) and barium (Ba) profiles in otoliths of juvenile sockeye salmon Oncorhynchus nerka from British Columbia are measured using a Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) system and analyzed. The highest possible measurement resolution (near-daily) was used to assess variability and repeatability of the breakpoint (marine entry) estimates inferred from Sr:Ca and Ba:Ca ratios. Such resolution for the otolith chemical composition (to an accuracy of 2 μm) was reached using the rotating slit, which width was close to the daily circulus width of the otoliths. So, daily or 2-day changes in the elemental composition were recorded during the period of transition to the marine environment. Sr profiles were generally similar among the fish, starting with low values of Sr:Ca in the fresh water and increasing sharply after the marine entry. The Ba:Ca signal was more complex, showing in most cases a dramatic increase immediately before the breakpoint. Besides, multiple peaks in the Ba profiles were recorded prior to the marine transition with a significant difference of their number between fish from different populations. A breakpoint was detectable in the Ba profiles 3–11 µm prior to its appearance in the Sr profiles. The complexity of Ba profiles may cause erroneous estimates of the marine entry date; thus, the Sr signal is a more reliable marker of marine transition for juvenile sockeye.

Signal stability of surface-enhanced laser-induced breakdown spectroscopy for microdroplet analysis using a porous silicon substrate

Surface-enhanced laser-induced breakdown spectroscopy (LIBS) is suitable for the analysis of a small amount of liquid. In this method, a sample solution is dried on a solid substrate and the dry residue is analyzed by LIBS. Porous silicon (Si) loaded with gold nanoparticles is a potential substrate for improving the signal intensity of the surface-enhanced LIBS. In this work, we investigated the position-to-position signal fluctuation of the dry residue in the analysis of a strontium chloride (SrCl2) aqueous solution. A strong Sr signal was stably obtained over the entire surface of the porous Si substrate, while the Sr signal was mainly detected at the periphery of the spread area of the sample solution on a flat Si substrate. The relative standard deviation (RSD) of the Sr signal from 15 laser shots on a single porous Si substrate was ca. 10% and the RSD of the 15-averaged Sr signal from 7 substrates was ca. 10%. The results suggest that the porous Si has great potential for improving both the signal intensity and signal stability.

Absence of μSR evidence for magnetic order in the pseudogap phase of Bi2+xSr2−xCaCu2O8+δ

We present an extended zero-field muon spin relaxation (ZF-$\mu$SR) study of overdoped Bi$_{2+x}$Sr$_{2-x}$CaCu$_2$O$_{8+\delta}$ (Bi2212) single crystals, intended to elucidate the origin of weak quasistatic magnetism previously detected by $\mu$SR in the superconducting and normal states of optimally-doped and overdoped samples. New results on heavily-overdoped single crystals show a similar monotonically decreasing ZF-$\mu$SR relaxation rate with increasing temperature that persists above the pseudogap (PG) temperature $T^*$ and does not evolve with hole doping ($p$). Additional measurements using an ultra-low background apparatus confirm that this behavior is an intrinsic property of Bi2212, which cannot be due to magnetic order associated with the PG phase. Instead we show that the temperature-dependent relaxation rate is most likely caused by structural changes that modify the contribution of the nuclear dipole fields to the ZF-$\mu$SR signal. Our results for Bi2212 emphasize the importance of not assuming the nuclear-dipole field contribution is independent of temperature in ZF-$\mu$SR studies of high-temperature (high-$T_c$) cuprate superconductors, and do not support a recent $\mu$SR study of YBa$_2$Cu$_3$O$_{6+x}$ that claims to detect magnetic order in the PG phase.

The New Kingdom Population on Sai Island: Application of Sr Isotopes to Investigate Cultural Entanglement in Ancient Nubia

Sr isotopes were applied to identify possible allochthony of skeletal remains retrieved from Tomb 26 of the pharaonic cemetery SAC5 on Sai Island (Nubia). Tooth enamel of nine individuals, including the Overseer of Goldsmiths Khummose and his presumed ‘wife’, dating from the New Kingdom, were investigated to gain information whether these individuals were first generation immigrants from Egypt (= allochthonous) or members of the local population inhabiting the area of Sai Island (= autochthonous). The interpretation of supposed allochthony and autochthony was based on the comparison of the Sr of human enamel to an assumed autochthonous Sr isotopic composition. The autochthonous Sr signal on Sai Island during the New Kingdom was derived from archaeological animal samples (rodent, sheep/goat, dog and local mollusc shells dating from the New Kingdom) in combination with local environmental samples (paleo sediments dating from the New Kingdom and literature Sr isotope value of Nile River water for the New Kingdom era). As the Sr values in enamel of all individuals investigated lay within the determined autochthonous Sr range on Sai Island during the New Kingdom, all individuals were classified as supposed members of the local population on Sai Island. Elevated Sr, V, Mn and U mass fractions indicated a high degree of post-mortem alterations of human primary dentine. Hence, a mathematical approach was tested in order to correct the Sr isotope ratios in human primary dentine for diagenetic alteration considering a diagenetic Sr proportion and the Sr isotopic composition of the repository material. The rich funerary equipment associated with the burials in Tomb 26 allowed a dating of the family members of Khnummose and illustrated that they belonged to the Egyptian elite on Sai Island as far as their cultural identity is concerned. In combination with the Sr isotopic analysis, Tomb 26 provided fresh information on the complex coexistence and biological and cultural entanglement of Egyptians and Nubians on Sai Island during the New Kingdom.

The New Kingdom Population on Sai Island: Application of Sr Isotopes to Investigate Cultural Entanglement in Ancient Nubia

Sr isotopes were applied to identify possible allochthony of skeletal remains retrieved from Tomb 26 of the pharaonic cemetery SAC5 on Sai Island (Nubia). Tooth enamel of nine individuals, including the Overseer of Goldsmiths Khummose and his presumed ‘wife’, dating from the New Kingdom, were investigated to gain information whether these individuals were first generation immigrants from Egypt (= allochthonous) or members of the local population inhabiting the area of Sai Island (= autochthonous). The interpretation of supposed allochthony and autochthony was based on the comparison of the Sr of human enamel to an assumed autochthonous Sr isotopic composition. The autochthonous Sr signal on Sai Island during the New Kingdom was derived from archaeological animal samples (rodent, sheep/goat, dog and local mollusc shells dating from the New Kingdom) in combination with local environmental samples (paleo sediments dating from the New Kingdom and literature Sr isotope value of Nile River water for the New Kingdom era). As the Sr values in enamel of all individuals investigated lay within the determined autochthonous Sr range on Sai Island during the New Kingdom, all individuals were classified as supposed members of the local population on Sai Island. Elevated Sr, V, Mn and U mass fractions indicated a high degree of post-mortem alterations of human primary dentine. Hence, a mathematical approach was tested in order to correct the Sr isotope ratios in human primary dentine for diagenetic alteration considering a diagenetic Sr proportion and the Sr isotopic composition of the repository material. The rich funerary equipment associated with the burials in Tomb 26 allowed a dating of the family members of Khnummose and illustrated that they belonged to the Egyptian elite on Sai Island as far as their cultural identity is concerned. In combination with the Sr isotopic analysis, Tomb 26 provided fresh information on the complex coexistence and biological and cultural entanglement of Egyptians and Nubians on Sai Island during the New Kingdom.

The New Kingdom Population on Sai Island: Application of Sr Isotopes to Investigate Cultural Entanglement in Ancient Nubia

Sr isotopes were applied to identify possible allochthony of skeletal remains retrieved from Tomb 26 of the pharaonic cemetery SAC5 on Sai Island (Nubia). Tooth enamel of nine individuals, including the Overseer of Goldsmiths Khummose and his presumed ‘wife’, dating from the New Kingdom, were investigated to gain information whether these individuals were first generation immigrants from Egypt (= allochthonous) or members of the local population inhabiting the area of Sai Island (= autochthonous). The interpretation of supposed allochthony and autochthony was based on the comparison of the Sr of human enamel to an assumed autochthonous Sr isotopic composition. The autochthonous Sr signal on Sai Island during the New Kingdom was derived from archaeological animal samples (rodent, sheep/goat, dog and local mollusc shells dating from the New Kingdom) in combination with local environmental samples (paleo sediments dating from the New Kingdom and literature Sr isotope value of Nile River water for the New Kingdom era). As the Sr values in enamel of all individuals investigated lay within the determined autochthonous Sr range on Sai Island during the New Kingdom, all individuals were classified as supposed members of the local population on Sai Island. Elevated Sr, V, Mn and U mass fractions indicated a high degree of post-mortem alterations of human primary dentine. Hence, a mathematical approach was tested in order to correct the Sr isotope ratios in human primary dentine for diagenetic alteration considering a diagenetic Sr proportion and the Sr isotopic composition of the repository material. The rich funerary equipment associated with the burials in Tomb 26 allowed a dating of the family members of Khnummose and illustrated that they belonged to the Egyptian elite on Sai Island as far as their cultural identity is concerned. In combination with the Sr isotopic analysis, Tomb 26 provided fresh information on the complex coexistence and biological and cultural entanglement of Egyptians and Nubians on Sai Island during the New Kingdom.

Type-I superconductivity in the Dirac semimetal PdTe2 probed by μSR

The Dirac semimetal PdTe$_2$ was recently reported to be a type-I superconductor with $T_c = 1.64$ K and a critical field $\mu_0H_c = 13.6$ mT. Since type-I superconductivity is unexpected for binary compounds, we have conducted muon spin rotation experiments to probe the superconducting phase on the microscopic scale via its intermediate state. For crystals with a finite demagnetization factor, $N$, the intermediate state forms in applied fields $(1-N)H_c < H_a < H_c$. We have carried out transverse field muon spin rotation measurements on a thin disk-like crystal with the field perpendicular to ($N_{\perp}=0.86$) and in the plane ($N_{\parallel}=0.08$) of the disk. By analysing the $\mu$SR signal we find that the volume fraction of the normal domains grows quasi-linearly with applied field at the expense of the Meissner domain fraction. This then provides solid evidence for the intermediate state and type-I superconductivity in the bulk of PdTe$_2$.

Analysis of contaminated nuclear plant steel by laser-induced breakdown spectroscopy

Laser Induced Breakdown Spectroscopy (LIBS) has the potential to allow direct, standoff measurement of contaminants on nuclear plant. Here, LIBS is evaluated as an analytical tool for measurement of Sr and Cs contamination on type 304 stainless steel surfaces. Samples were reacted in model acidic (PUREX reprocessing) and alkaline (spent fuel ponds) Sr and Cs bearing liquors, with LIBS multi-pulse ablation also explored to measure contaminant penetration. The Sr II (407.77nm) and Cs I (894.35nm) emission lines could be separated from the bulk emission spectra, though only Sr could be reliably detected at surface loadings >0.5mgcm−2. Depth profiling showed decay of the Sr signal with time, but importantly, elemental analysis indicated that material expelled from LIBS craters is redistributed and may interfere in later laser shot analyses.

Multi-Service System: An Enabler of Flexible 5G Air Interface

A multi-service system is an enabler to flexibly support diverse communication requirements for the next generation wireless communications. In such a system, multiple types of services coexist in one baseband system with each service having its optimal frame structure and low out-of-band emission waveforms operating on the service frequency band to reduce the ISvcBI. In this article, a framework for a multi-service system is established, and the challenges and possible solutions are studied. The multi-service system implementation in both the time and frequency domains is discussed. Two representative SFMC waveforms, F-OFDM and UFMC, are considered in this article. Specifically, the design methodology, criteria, orthogonality conditions, and prospective application scenarios in the context of 5G are discussed. We consider both SR and MR signal processing methods. Compared to the SR system, the MR system has significantly reduced computational complexity at the expense of performance loss due to ISubBI in MR systems. The ISvcBI and ISubBI in MR systems are investigated with proposed low-complexity interference cancellation algorithms to enable multi-service operation in low interference level conditions.

Hunting, Gathering, and Fishing on the Coast of the Atacama Desert: Chinchorro Population Mobility Patterns Inferred from Strontium Isotopes

AbstractWe discuss how the Chinchorro population of hunter‐gatherers and fishermen organized their mobility patterns between the rich marine ecosystems of the Pacific coast and the extreme hyperarid core of the Atacama Desert through the application of strontium isotopes (87Sr/86Sr). We analyzed tooth enamel samples of 35 individuals from the coast (n = 28), inland oasis (n = 6), and the Andean highlands (n = 1). The Sr isotopic composition of modern and archaeological bone samples from sea mammals and land herbivores were obtained from 10 localities. Coastal human individuals show a similar Sr signal to sea mammals, confirming that the former were born and raised in the littoral zone. These results along with archaeological data suggest that the Chinchorro maintained logistic mobility along the coast. Similarly, a woman buried in the highlands (Patapatane) has a Sr signal closer to marine values, suggesting that some Chinchorro also maintained a logistic mobility linked to the Andean interior. In contrast, the Sr ratios of individuals from the inland oasis (Tiliviche) are intermediate between marine Sr values and those of local fauna. This seems to indicate that, although these Chinchorro individuals were raised in this oasis, they were part of a broad logistic mobility pattern connected with the coast.

Pressure-induced magnetic order in FeSe: A muon spin rotation study

The magnetic order induced by the pressure was studied in single crystalline FeSe by means of muon-spin rotation ($\mu$SR) technique. By following the evolution of the oscillatory part of the $\mu$SR signal as a function of angle between the initial muon-spin polarization and 101 axis of studied crystal it was found that the pressure induced magnetic order in FeSe corresponds either to the collinear (single-stripe) antiferromagnetic order as observed in parent compounds of various FeAs-based superconductors or to the Bi-Collinear order as obtained in FeTe system, but with the Fe spins turned by 45$^{\rm o}$. The value of the magnetic moment per Fe atom was estimated to be $\simeq 0.13-0.14$~$\mu_{\rm B}$ at $p\simeq 1.9$~GPa.

A novel pulse swallow based frequency divider circuit for a phase-locked loops

A new and unique frequency divider circuit has been proposed for this work. In this paper, we have implemented a $$\varDelta \varSigma$$ΔΣ fractional-N PLL using a proposed pulse swallow based frequency divider and a programmable prescaler divider circuit. Advantages of the proposed pulse swallow based frequency divider circuit have been illustrated and its usefulness are described in details. This novel pulse swallow based frequency divider technique does not include any reset or reload signal for the swallow counter as it is normally triggered by the SR latch output signal in conventional pulse swallow based frequency divider circuit. Insertion of a variable delay element at the output of the program counter can be eliminated which is normally used to settle the problem of arrival of the falling edge of the swallow counter pulse. In addition, preset enable signal can be generated without any frequency dependent delay generation block and in few cases without selection of any frequency dependent RC network block. The residual phase noise output of the divider at 1 MHz offset frequency is $$-174.5$$-174.5 dBc/Hz for a carrier signal frequency of 4.7 GHz and power consumption is 9 mW from a 1.2 V power supply. The design of the fractional-N PLL has been carried out in 130 nm standard CMOS process. There is no zero division in the proposed frequency divider's swallow counter for any counting state due to the novel mathematical calculating algorithm for the pulse swallow divider circuit.

Melt-rock interaction near the Moho: Evidence from crystal cargo in lavas from near-ridge seamounts

The Taney Seamounts are a NW-SE trending linear, near mid-ocean ridge chain consisting of five volcanoes located on the Pacific plate 300km west of San Francisco, California. Taney Seamount-A, the largest and oldest in the chain, is defined by four well-exposed calderas, which expose previously infilled lavas. The calderas can be differentiated in time by their cross-cutting relationships, creating a relative chronology. The caldera walls and intracaldera pillow mounds were sampled systematically by a remotely operated vehicle (ROV) to obtain stratigraphically-controlled samples, a unique aspect of this study.The geochemistry of the seamount varies from more differentiated to more primitive with time (6.2–8.6wt.% MgO), suggesting that the sub-caldera reservoir is open and undergoes periodic collapse, replenishment, crystallization, and eruption. The youngest and least differentiated lavas entrained a crystal cargo of plagioclase (An80–90) with melt inclusion volatile saturation pressures indicating entrapment in the lower oceanic crust and upper mantle (6–12km, with 45% between 8 and 10km below the sea floor). Melt inclusions exhibit high Al2O3, low SiO2, positive Sr and Eu anomalies and negative Zr and Nb anomalies when normalized to typical Pacific mid-ocean ridge basalt (MORB). In comparison, the host lavas exhibit positive Sr anomalies, but no concurrent Zr, and Nb anomalies. Based on thermodynamic modeling using alphaMELTS, we develop a melt-rock interaction model defined by melting and assimilation of plagioclase-rich cumulates by hot, primitive mantle-derived melts. Significantly, the variability of the negative Zr and Nb anomalies cannot be explained by either cumulate melting or AFC alone. We propose that the melt inclusions record the interaction between cumulate partial melts and the assimilating melt, demonstrating the importance of cumulate melting during the assimilation process. Later percolating melts underwent diffusive interaction with, and entrained, recrystallized plagioclase cumulates resulting in the positive Sr signal without the concurrent Eu, Zr, or Nb anomalies observed in the host lavas. These results demonstrate that melt-rock interaction at the lower crust or upper mantle is an important process at Taney Seamount-A, and potentially other magmatic systems associated with seamount chains and ridge axes.

Hydrologic controls on radiogenic Sr in meltwater from an alpine glacier system: Athabasca Glacier, Canada

Filtered subglacial meltwater samples were collected daily during the onset of melt (May) and peak melt (July) over the 2011 melt season at the Athabasca Glacier (Alberta, Canada) and analyzed for strontium-87/strontium-86 (87Sr/86Sr) isotopic composition to infer the evolution of subglacial weathering processes. Both the underlying bedrock composition and subglacial water–rock interaction time are the primary influences on meltwater 87Sr/86Sr. The Athabasca Glacier is situated atop Middle Cambrian carbonate bedrock that also contains silicate minerals. The length of time that subglacial meltwater interacts with the underlying bedrock and substrate is a predominant determining factor in solute concentration. Over the course of the melt season, increasing trends in Ca/K and Ca/Mg correspond to overall decreasing trends in 87Sr/86Sr, which indicate a shift in weathering processes from the presence of silicate weathering to primarily carbonate weathering.Early in the melt season, rates of carbonate dissolution slow as meltwater approaches saturation with respect to calcite and dolomite, corresponding to an increase in silicate weathering that includes Sr-rich silicate minerals, and an increase in meltwater 87Sr/86Sr. However, carbonate minerals are preferentially weathered in unsaturated waters. During the warmest part of a melt season the discharged meltwater is under saturated, causing an increase in carbonate weathering and a decrease in the radiogenic Sr signal. Likewise, larger fraction contributions of meltwater from glacial ice corresponds to lower 87Sr/86Sr values, as the meltwater has lower water–rock interaction times in the subglacial system. These results indicate that although weathering of Sr-containing silicate minerals occurs in carbonate dominated glaciated terrains, the continual contribution of new meltwater permits the carbonate weathering signal to dominate.

Modeling elemental strontium in human bone based on in vivo x-ray fluorescence measurements in osteoporotic females self-supplementing with strontium citrate.

An in-house custom I-125 excited in vivo x-ray fluorescence (IVXRF) system was used to perform bone strontium (Sr) measurements in individuals suffering from osteoporosis and/or osteopenia. These individuals, who were self-administering with Sr supplements of their choice, were measured frequently, ranging from weekly to biweekly to monthly, over four years, as part of the Ryerson and McMaster Sr in Bone Research Study. Based on these data collected, data from eight subjects were used to perform kinetic modeling of Sr in human bone. Power and exponential models were used to model the data based on one and two compartmental systems. Model parameters included: mean normalized baseline bone Sr signal, half-life and bone Sr uptake. A one compartmental exponential model applied to finger and ankle bone measurements gave half-lives of (508 ± 331) d and (232 ± 183) d, respectively, but did not show statistically significant differences (p = 0.087 96). However, the values fall within literature estimates.When a two compartmental model was applied to finger bone measurements, half-lives of (300 ± 163) d and (2201 ± 1662) d were observed. Ankle bone data gave half-lives of (156 ± 117) d and (1681 ± 744) d. A two sample t-test, assuming unequal variances, showed these half-lives to be statistically different in both the finger and ankle bone measurements (p = 0.0147 and p = 0.00711, respectively). Common kinetic parameters amongst the different subjects could not be unambiguously identified due to the wide scatter of data, leading to an inconclusive kinetic model. The wide distribution of data is suggested to be physiological since technical and positioning factors were eliminated as possible causes. This outcome indicates the need for a more controlled study and further understanding of the physiological mechanism of Sr absorption.