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Dietary preferences of extant reptiles can be directly observed, whereas diet reconstruction of extinct species typically relies on morphological or dental features. More specific information about the ingested diet is contained in the chemistry of hard tissues. Stable isotopes of calcium and strontium show systematic fractionations between diet and skeletal bioapatite, which is applied for diet and trophic-level reconstructions of extant and extinct vertebrate species. Here, we present the first comprehensive analysis of stable calcium and strontium isotopes of bones and teeth from 28 extant reptiles, including lepidosaurs and archosaurs (crocodilians) with distinct herbivorous to faunivorous feeding behaviour, establishing a dietary reference frame. Both calcium and strontium isotopes exhibit systematic offsets between dietary groups, with insectivores having the highest, herbivores intermediate and carnivores the lowest calcium and strontium isotope values. Although the isotopic trophic-level effect is similar to mammals, the absolute calcium isotope values in reptiles are more positive in each diet category. Combining isotopic data with dental microwear texture analysis enables a refined understanding of reptile feeding ecology and the identification of durophagous diets. This toolbox opens new possibilities for improved dietary reconstructions of extinct taxa, such as dinosaurs and other non-mammalian species in the fossil record. [ABSTRACT FROM AUTHOR]

Calcium-aluminum rich inclusions (CAIs) are the oldest condensates in the Solar System. Previous studies have revealed that moderately heavy and trace element isotope anomalies (e.g., Ti, Sr, Mo, and Nd) in CAIs record large nucleosynthetic isotope variations compared to bulk meteorites. Calcium is a major element in CAIs that has six stable isotopes with multiple nucleosynthetic origins. As such, Ca isotopes in CAIs have been an important target of isotopic analysis since the 1970s. However, the Ca isotope compositions of CAIs measured by previous-generation mass spectrometers are less precise than recent isotopic data of heavy elements, which complicates their direct comparisons. Obtaining high-precision Ca isotopic data provides a stronger link between CAI-formation processes from nebular gas and the origin of their source materials. In this study, we report high-precision Ca isotopic compositions of CAIs, amoeboid olivine aggregates, and an Al-rich chondrule from Vigarano-type carbonaceous chondrites. The obtained µ43Ca and µ48Ca values range from +5.8 ± 1.4 to +40.2 ± 5.2 and +181.2 ± 44.8 to +743.1 ± 8.3 ppm, respectively (µXCa represents the mass bias corrected relative deviation in the XCa/44Ca ratio of the sample from a standard material in parts per million). The improved precision of our measurements reveals that the Ca isotopic compositions of CAIs vary over a narrower range than previously thought. Our precise data also show that µ43Ca and µ48Ca values in CAIs are anti-correlated, which cannot be explained by analytical artifacts such as matrix effects. Additionally, the µ43Ca and µ48Ca values of CAIs increase and decrease, respectively, with increasing Ca abundances of the inclusions. These observations suggest the presence of two distinct gaseous reservoirs from which CAIs condensed, one of which was more enriched in 43Ca but depleted in 48Ca, while the other reservoir was more depleted in 43Ca but enriched in 48Ca. Given the distinct nucleosynthetic sources of 43Ca and 48Ca, this change in isotopic signature is best understood if the two reservoirs inherited material derived from distinct nucleosynthetic sites. As such, our results suggest the presence of more than two compositionally distinct gas reservoirs for Ca isotopes in the early Solar System. If correct, this suggests that the infalling material contributing to the CAI-forming reservoirs was not fully mixed. [ABSTRACT FROM AUTHOR]

Bogoliubov many-body perturbation theory (BMBPT) relying on the breaking of U(1) global gauge symmetry has been recently formulated and applied to extend the applicability of standard perturbation theory to ab initio calculations of atomic nuclei away from shell closures. So far, practical applications have been limited to second-order calculations due to the lack of a generic algorithm to constrain the average particle number of the symmetry-broken state. This limitation is presently lifted and a general BMBPT formalism is presented that allows to constrain the particle-number expectation value at arbitrary order P. The constraint can be incorporated in closed form by solving a polynomial equation of degree P - 1 . The numerical procedure is illustrated through BMBPT(3) calculations of calcium isotopes using a nuclear Hamiltonian derived within chiral effective field theory. [ABSTRACT FROM AUTHOR]

Crystalline calcium carbonate isotope compositions have been widely used to reconstruct past environments. However, if their isotopic compositions are modified because of crystallization from an amorphous precursor, their reliability as paleo-geochemical proxies can be compromised. This study explored the changes in the oxygen isotope compositions during the transformation of amorphous calcium carbonate (ACC) into crystalline carbonate under different conditions of relative humidity (RH of 33–95 %), temperature (T of 5 °C and 20 °C) and in the presence/absence of atmospheric CO 2. The data showed that at low RH and T (e.g., RH ≤ 45 % and 5 °C) when a complete ACC-crystalline carbonate transformation did not take place then the original ACC δ18O values (δ18O CaCO3 = −15.9 ± 1.0 ‰, VPDB) were preserved throughout the experimental runtime (up to 144 days). In contrast, in fully crystallized CaCO 3 (e.g., at RH ≥ 60 %) the δ18O CaCO3 values increased rapidly over the first few days, followed by a slower and gradual increase. By the end of the experiments (i.e., after 103–144 days) the crystalline δ18O CaCO3 values ranged from −10.4 ‰ to −8.1 ‰ in the presence of atmospheric CO 2 and from −12.6 ‰ to −9.5 ‰ in the CO 2 -free experiments. These changes in oxygen isotope compositions of the CaCO 3 reaction products (calcite and/or vaterite) were mainly driven by exchange with H 2 O from the hydrated ACC i.e. the synthesis fluid. In CO 2 -present experiments, oxygen isotope fractionation factors between the CaCO 3 reaction products and the synthesis fluid (18α c–w) approached or exceeded oxygen isotope equilibrium values. This could be explained by a decrease in the initially high pH of the aqueous fluid released from ACC dissolution during CO 2 hydration/hydroxylation, which would have increased the oxygen isotope exchange kinetics between H 2 O and dissolved inorganic carbon (DIC). In some experiments, the hydration/hydroxylation of 18O-enriched CO 2 , due to isotopic salt-effects, might have also resulted in 18O-enriched calcium carbonates and calculated fractionation factors that exceeded equilibrium values. In the CO 2 -free experiments, isotopic equilibrium between the crystalline phase and the synthesis fluid was not reached. This oxygen isotope disequilibrium suggests that without the pH lowering effect of the hydroxylation/hydration of CO 2 , the CO 3 2− released during ACC/calcite dissolution-reprecipitation may have not isotopically equilibrated with the high pH synthesis fluid due to the long equilibration times required to reach isotope equilibrium at high pH values, leading to the self-buffering of δ18O CaCO3 values. The results suggest that the oxygen isotopic compositions of natural carbonates formed from ACC transformation in air and at low water/solid ratio (e.g., biominerals or carbonates formed in caves) are complex and cannot be used as simple proxies if the reaction kinetics (RH/CO 2 /T) and H 2 O sources are not known and quantified. [ABSTRACT FROM AUTHOR]

Bacteria are a key component of the critical zone, because of their role in the nutrient availability for the vegetation. There is still little knowledge on the direct role of bacteria on Ca storage/leaching in soils while it is an essential macronutrient for vegetation growth. In recent years, Ca stable isotopes have shown their potential in understanding the Ca biogeochemical cycle. Preliminary studies highlighted that in the presence of soil bacteria, the plant uptake of nutrients is increased due to the mineral bioweathering. Moreover, Ca isotope signatures of nutrient media also showed differences between growth experiments in batch in the presence and absence of bacteria. In this study, the focus is to verify if Ca adsorption and incorporation into/onto bacterial strains induce such isotopic fractionation. Batch experiments were carried out on Pseudomonas aeruginosa (a Gram-negative bacterium) and on the vegetative and sporulated forms of Bacillus subtilis (a Gram-positive bacterium). These experimentations showed that: (i) no observable isotopic fractionations were induced during calcium/bacteria contact for all experimental parameters (pH, kinetic, bacterial cell number, interaction time, dead/alive bacteria); (ii) Ca was mainly stored in the bacterial cell wall compartments. On the other hand, significant Ca isotopic differences between the spores and the sporulation medium (Δ44/40Caspores–sporulation medium ranging from − 0.53 to − 1.15‰), suggest isotopic fractionation during the sporulation process, likely occurring during the attachment of Ca to carboxyl acid groups as calcium chelates with dipicolinic acid. The absence of Ca isotope fractionation during Ca sorption on vegetative and sporulated bacteria via passive channels indicates that the tested bacteria's contribution to the Ca biogeochemical cycle is indirect primary enhancing bioweathering and Ca bioavailability for vegetation. If confirmed by further studies, only the sporulation mechanisms itself may directly impact the Ca biogeochemical cycle. [ABSTRACT FROM AUTHOR]

A Central European catchment underlain by base-poor orthogneiss was studied using mass budgets and Mg–Ca–Sr isotope systematics. For 50 years, the catchment received large amounts of partly soluble dust from a nearby cluster of coal-burning power plants, while suffering from acid rain and severe spruce die-back. Our objective was to investigate to what extent anthropogenic dust contributes to Mg and Ca in runoff and to identify fractionations affecting Mg and Ca isotope composition of 13 ecosystem pools and fluxes. We hypothesized that if Mg and Ca runoff fluxes were significantly larger than their atmospheric inputs, Mg and Ca isotope ratios in runoff would converge to those of bedrock Mg and Ca. This relationship could be obscured by isotope fractionations. Strontium characterized by negligible isotope fractionations served as a Ca proxy. There was a strong positive correlation between Mg and Ca fluxes via spruce throughfall and catchment runoff. Monitoring of rainfall, canopy throughfall and runoff fluxes revealed a 20-, 15- and 15-fold excess of Mg, Ca and Sr in runoff, respectively, compared to atmospheric deposition fluxes. This sizeable excess per se would indicate predominance of geogenic base cations in runoff. The behavior of Mg and Ca isotopes was de-coupled. Petrographic study indicated that 92% of bedrock Mg was bound to easily dissolving biotite, 97% Ca was present in plagioclase, and nearly all Sr was in orthoclase. While Mg isotope ratios in bedrock and runoff were indistinguishable, corroborating predominantly geogenic Mg in runoff, Ca and Sr isotope ratios in bedrock and runoff were significantly different, consistent with a non-negligible contribution of atmospheric Ca and Sr to runoff. Previous study of sites underlain by felsic rocks indicated that the δ44Ca value of apatite was often higher than the δ44Ca value of plagioclase. Should weathering of apatite and/or plagioclase preferentially release Ca that is isotopically heavier than bulk rock, the geogenic Ca source at JEZ would converge to the mean δ44Ca value of runoff. Calcium isotope data would then become more consistent with a major role of geogenic Ca in JEZ runoff indicated by mass balance data. [ABSTRACT FROM AUTHOR]

Mantle xenoliths provide effective records of the metasomatic processes that affect continental lithosphere evolution, such as interaction with subducted components or modification via small-degree melts. Correlations between major/trace element geochemistry with stable and radiogenic isotope compositions can help constrain the source and timing of this metasomatism. We report new δ18O, δ44/40Ca, and δD values for twelve kimberlite-hosted mantle xenoliths from the Slave Craton (NWT, Canada), which show varying degrees of metasomatism. The δ18O values of olivine (δ18O ol = +5.33 ± 0.13‰; 1σ; n = 12) overlap average mantle values. Clinopyroxene and garnet δ18O values (δ18O cpx = +5.31 ± 0.10‰; δ18O grt = +5.37 ± 0.23‰; 1σ) extend below those reported in most mantle peridotites and are strongly correlated with clinopyroxene δ44/40Ca (avg. = +1.00 ± 0.10‰; 1σ) and garnet δ44/40Ca (avg. = +1.18 ± 0.19‰; 1σ) respectively, extending from typical mantle values to low δ18O and high δ44/40Ca values. In general, Δ18O cpx-ol and Δ18O grt-ol (ranging from −0.19‰ to +0.19‰ and from −0.56‰ to +0.35‰, respectively) are lower than expected equilibrium values at mantle temperatures. Strong negative correlations are found between δ18O grt and Δ18O grt-ol and garnet major and trace element composition (Na 2 O, H 2 O, La/Yb N). Furthermore, phlogopite-bearing kelyphitic rims have δD values (avg. = −126 ± 13‰; 1σ) lower than typical mantle values. Whole rock Sm-Nd model ages and oxygen isotope diffusion modeling suggest that metasomatism occurred during the Mesozoic, shortly before kimberlite entrainment, consistent with indications from diamond-forming fluids from the Slave craton. The combined low δ18O, δD, and high δ44/40Ca signature of the mantle peridotite xenoliths, along with the age constraints, suggest the metasomatic fluid/melt is sourced from a recycled oceanic crust component related to Mesozoic subduction in western North America. [ABSTRACT FROM AUTHOR]

Sharks occupy all living environments of the marine realm as well as some freshwater systems. They display varied and flexible feeding behaviours, but understanding their diet remains challenging due to their elusive ecology and the invasiveness of stomach content analyses in regard of their threatened status. As a potential alternative, we discuss the variability in δ44/42Ca values recorded in the tooth enamel of size‐graded individuals belonging to three species of large sharks with distinct diets (Isurus oxyrinchus, Hexanchus griseus and Carcharodon carcharias). The preliminary results highlight shifts in diet linked to ontogeny (I. oxyrinchus and H. griseus) and spatial distribution (C. carcharias) characterizing feeding behaviour in these species at individual and population level. These outcomes agree with the results of traditional stomach analyses supporting that nontraditional stable isotopes thus represent new perspectives for the study of modern and extinct shark ecology. In addition, for the first time, the Sr/Ca elemental ratios measured in H. griseus reflect sexual differences that could be interpreted in terms of spatial segregation or physiological heterogeneities. [ABSTRACT FROM AUTHOR]

We present a suite of major element stable isotope (δ13C, δ18O, δ44/40Ca, δ26Mg), and selected trace element (Sr/Ca and Mg/Ca) data from Pleistocene sediments from the Great Barrier Reef (IODP Expedition 325), as well as Holocene surface sediments from the Bahamas (Triple Goose Creek, Andros Island) to identify geochemical fingerprints associated with early marine and meteoric diagenesis. Sediments from both sites exhibit co-variation in δ13C and δ18O values, depletion in trace elements, and distinct geochemical trends in δ26Mg and δ44/40Ca values that reflect differences between diagenetic alteration in marine and meteoric fluids. While marine diagenesis results in lower Sr/Ca ratios, higher δ44/40Ca values, and little effect on bulk sediment δ26Mg values, meteoric diagenesis leads to lower Sr/Ca ratios, lower δ44/40Ca values, and lower δ26Mg values. Using a numerical model of diagenesis, we show how diagenetic alteration by meteoric fluids must occur after an initial period of diagenetic alteration by marine fluids, a two-stepped diagenetic history that complicates the interpretation of geochemical data in meteorically altered marine carbonate sediments. Finally, we discuss how paired metal isotopes may serve as a robust indicator of meteoric alteration in ancient shallow-water marine carbonate sediments. [ABSTRACT FROM AUTHOR]

Variations in speleothem calcium isotope ratios (δ44Ca) are thought to be uniquely controlled by prior carbonate precipitation (PCP) above a drip site and, when calibrated with modern data, show promise as a semi‐quantitative proxy for paleorainfall. However, few monitoring studies have focused on δ44Ca in modern cave systems. We present a multi‐year comparative study of δ44Ca, carbon isotopes (δ13C), and trace elemental ratios from cave drip waters, modern calcite, and host rocks from two cave systems in California—White Moon Cave (WMC) and Lake Shasta Caverns (LSC). Drip water and calcite δ44Ca from both caves indicate PCP‐driven enrichment, and we used a simple Rayleigh fractionation model to quantify PCP variability over the monitoring period. Modern calcite trace element and δ44Ca data positively correlate at WMC, but not at LSC, indicating a shared PCP control on these proxies at WMC but not at LSC. At both WMC and LSC, we observe an inverse relationship between PCP and rainfall amounts, though this relationship is variable across individual drip sites. Our modeled data suggest that WMC experiences ∼20% more PCP than LSC, consistent with the fact that WMC receives less annual rainfall. This work supports speleothem δ44Ca as an independent constraint on PCP that can aid in the interpretation of other hydrologically sensitive proxies and provide quantitative estimates of paleorainfall. Additional, long‐term monitoring studies from a variety of climate settings will be key for understanding δ44Ca variability in cave systems more fully and better constraining the relationship between PCP and rainfall. Plain Language Summary: Chemical analyses on the minerals that make up stalagmites can provide useful information about how rainfall varied in the past, but most of the chemical parameters measured in stalagmites can respond to several complex environmental influences in addition to rainfall amount. Stalagmite calcium (Ca) isotope ratios can provide more direct information about past rainfall variability but haven't been closely studied in modern cave systems. In this study, we present new Ca isotope measurements of cave drip waters and modern calcite mineral samples collected at a seasonal‐to‐annual resolution from two sites in California that experience different amounts of yearly rainfall. We find that periods of less rainfall at each individual cave generally correspond to higher Ca isotope ratios and that the drier of the two caves experienced less water infiltration overall during the study period. These findings support the idea that Ca isotope ratios in cave systems are controlled by the amount of water infiltrating the cave and can be used in combination with other data from stalagmites to reconstruct rainfall variability in the past. This type of information about past rainfall patterns can help planners assess future water availability, which is especially important in drought‐prone regions such as California. Key Points: Drier periods correspond to higher Ca isotope ratios and more prior calcite precipitation, though there is variability between drip sitesModern calcite trace element ratios positively correlate with Ca isotope data at one of the two cave sitesCa isotope data provides an independent constraint on water infiltration to aid the interpretation of other hydrologically sensitive proxies [ABSTRACT FROM AUTHOR]

Shallow-water platform carbonate δ13C may provide a record of changes in ocean chemistry through time, but early marine diagenesis and local processes can decouple these records from the global carbon cycle. Recent studies of calcium isotopes (δ44/40Ca) in shallow-water carbonates indicate that δ44/40Ca can be altered during early marine diagenesis, implying that δ13C may also potentially be altered. Here, we tested the hypothesis that the platform carbonate δ13C record of the Kinderhookian–Osagean boundary excursion (KOBE), ∼353 m.y. ago, reflects a period of global diagenesis using paired isotopic (δ44/40Ca and clumped isotopes) and trace-element geochemistry from three sections in the United States. There is little evidence for covariation between δ44/40Ca and δ13C during the KOBE. Clumped isotopes from our shallowest section support primarily sediment-buffered diagenesis at relatively low temperatures. We conclude that the δ13C record of the KOBE as recorded in shallow-water carbonate is consistent with a shift in the dissolved inorganic carbon reservoir and that, more generally, ancient shallow-water carbonates can retain records of primary seawater chemistry. [ABSTRACT FROM AUTHOR]

We introduce a new framework for the nuclear structure calculations, which describes the single-particle wave function as a superposition of localized Gaussians. It is a hybrid of the Hartree–Fock and antisymmetrized molecular dynamics (AMD) models. In the numerical calculations of oxygen, calcium isotopes, and |$^{100}{\rm Sn}$|⁠ , the framework shows its potential by significantly improving upon AMD and yielding results that are consistent with or even better than Hartree–Fock(–Bogoliubov) calculations based on harmonic oscillator expansions. In addition to the basic equations, general forms of the matrix elements are also given. [ABSTRACT FROM AUTHOR]

A theoretical comparison has been made for some calcium isotopes ( 2 0 Ca) which are even–even nuclei and have the atomic mass (Z = 20) with its previous experimental data. Theoretical calculations of some 2 0 Ca isotopes (A = 42, 44, 46, 48, 50, 52) adopted by the shell model theory were performed to calculate the transition rate B(E2), theoretical intrinsic quadruple moments ( Q 0 Th ) and theoretical deformation parameters ( β 2 , δ) Th were calculated by two methods by using different effective interactions for each isotope such as, su3fp, fpbm, fprkb, fpd6, kb3. Through code NuShellX@MSU, the single-body density matrix was calculated. The effects of the core polarization were neglected by adopting various effective charges that were employed, effective charges of conventional (Con-E), effective charges of standard (St-E) and effective charges of Bohr and Mottelson (B-M-E) which were calculated. The theoretical values of the B(E2)Th, the Q 0 Th and the ( β 2 , δ) Th were then compared with the previous experimental data where values of the transition rate B(E2)Th, theoretical intrinsic quadrupole moments Q 0 Th and theoretical deformation parameter ( β 2 , δ) Th , using the fpbm, the fpd6 and the kb3 interactions were the best. [ABSTRACT FROM AUTHOR]

Dissolution of calcite in water is fundamental to geochemistry. Laboratory methods generally give consistent dissolution rates under conditions far from equilibrium, but close to equilibrium the measurement of dissolution using isotopes is complicated by poorly understood calcite-fluid isotopic exchange processes. This near-equilibrium isotopic exchange occurs in laboratory experiments at rates of order 10-9 to 10-13 mol/m2/s and decreases with experiment duration approximately as 1/time where time is measured from the start of the experiment. Such rates are fast enough to compete with dissolution in days-long experiments and consequently, net dissolution rates may not be measurable with isotopic tracer methods except in experiments carried out for long enough to allow the background exchange to dissipate sufficiently. To better define what should be expected for isotopic signals during dissolution, we develop a quasi-1D model for calcite dissolution that includes the mechanistically unconstrained isotopic exchange as well as solid state diffusion. We use the model, the observations reported in the literature, and the calcite dissolution rates in seawater reported by Naviaux et al., (2019a) to illustrate ambiguities in measurement of near-equilibrium calcite dissolution rates. The results suggest that the reaction order of calcite dissolution close to equilibrium could be 2 at both room temperature and the lower temperatures of the seafloor. The reaction order of near-equilibrium calcite dissolution is important for understanding calcite mineral surface processes, long-term behavior of dissolution on the seafloor, and alkalinity fluxes from modern seafloor sediments. Distinguishing between net dissolution, which affects fluid saturation state, and "exchange," which doesn't, is important but typically cannot be done with isotopic tracers alone. [ABSTRACT FROM AUTHOR]

Calcium (Ca) is a highly soluble and mobile element during silicate weathering, and its isotopes could be a promising tracer for continental weathering processes. However, it remains controversial whether Ca isotopes fractionate during granitoids' weathering. Here we investigated Ca isotope fractionation (measured by δ 44/42Ca) behaviours on the weathering profile of the late middle Jurassic Fogang granite (165 ± 2 Ma) under a tropical climate with the help of radiogenic anomaly data (i.e., ε40/44Ca) (both relative to the NIST standard SRM 915a), as well as its implications for the Ca isotopic composition in the hydrosphere. A total of 15 saprolite samples, 2 fresh parent rocks, 3 fresh individual minerals of one granite weathering profile from Fogang county, South China, and 8 stream water samples nearby the profile have been analysed for their Ca isotopic compositions by thermal ionisation mass spectrometry using a double spike method. Results reveal extreme radiogenic and stable Ca isotopic variations among saprolites. The saprolites have ε40/44Ca ranging from 0.8 to 55.6, whereas fresh granite rocks exhibit uniform ε40/44Ca close to 0. The large variation of ε40/44Ca in the saprolites can be attributed to the preferential dissolution of plagioclase and exsolved albite in K-feldspar or the variation of K/Ca molar ratios in K-feldspar. In general, saprolites are enriched in lighter Ca isotopes compared to the parent rocks (0.39 ± 0.04 ‰) and have δ 44/42Ca values ranging from −0.45 ‰ to 0.43 ‰. This suggests that newly formed clay minerals preferentially absorb the lighter Ca isotopes (e.g., 40Ca). However, the δ 44/42Ca of stream waters draining highly weathered granite catchments reflect δ 44/42Ca of bedrock, rather than δ 44/42Ca of the saprolites. One possible reason is that too little Ca was adsorbed by secondary clay minerals in the saprolite to shift the Ca isotope composition of dissolved Ca from the bedrock. Our study shows that a combination of radiogenic and stable Ca isotope data is a promising tracer for the sources, migration, and transformation processes of this key element during continental weathering processes. This research contributes to a broader understanding of Ca isotopes as a tracer for tropical weathering and their implications for global biogeochemical cycles. [ABSTRACT FROM AUTHOR]

The paper discusses a photoactivation method for determining the activity of the long-lived isotope Ca relative to the activity of Co in irradiated reactor biological shielding concrete. It is proposed to use photonuclear reactions on cobalt and calcium isotopes: Co( , ) Co, Ca( , ) K, or Ca( , ) Ca Sc to determine the activity of Ca. The sensitivity of the proposed method is on the order of Bq/g, provided that semiconductor spectrometers with an ultrapure germanium detector are used. The structure and chemical compositions of the sample do not affect the proposed method. It avoids the long sample preparation times associated with radiochemical methods. [ABSTRACT FROM AUTHOR]

A‐type granite is a favorable rock for the study of crustal evolution, crust‐mantle interaction and metallogenesis. However, the origin of A‐type granite remains controversial. In this study, we report high‐precision Ca isotopic compositions of a co‐genetic suite of A‐type granites from the Lower Yangtze River Belt (LYRB) in eastern China. Our results show that the δ44/40Ca of the A‐type granites ranges from 0.55 ± 0.11‰ to 1.44 ± 0.06‰, and is negatively correlated with CaO, Sr and Ba contents and Eu/Eu*, indicating that the Ca isotope fractionation of A‐type granites is dominated by plagioclase and potassium feldspar. There is kinetic fractionation of Ca isotopes during A‐type granite magma evolution. Sample BSL‐7, the least evolved sample, revealed that it had a low δ44/40Ca of 0.59‰, which is significantly lower than that of the upper continental crust (δ44/40Ca = 0.71–0.72‰) and the bulk silicate earth (δ44/40Ca = 0.94‰). The low δ44/40Ca can be best explained by partial melting of the enriched mantle metasomatized by subduction material. Combined with the geodynamic background of the LYRB, we propose that the formation of A‐type granites in the LYRB originates from partial melting of the enriched mantle, triggered by early Cretaceous ridge subduction of the Pacific and Izanagi plates. Plain Language Summary: A‐type granite is an important rock type in the study of continental evolution. However, the genesis of A‐type granite has been debated. We try to constrain the origin of A‐type granites by Ca isotopes. The Ca isotopic composition of plagioclase and potassium feldspar in A‐type granites is obviously different, which makes Ca isotopes can be used to trace the magmatic evolution of A‐type granites. In addition, the Ca isotope compositions of different magma source areas vary widely. Therefore, Ca isotopes have great potential to restrict the source feature of A‐type granite magmas. Key Points: The fractionation of Ca isotopes of A‐type granites is dominated by plagioclase and potassium feldsparThere is kinetic fractionation of calcium isotopes during A‐type granite magma evolutionThe ridge subduction model can well explain the genesis of A‐type granites in the LYRB [ABSTRACT FROM AUTHOR]

Major geodynamic processes, including mantle convection and plate tectonics, govern the exchange of mass between Earth's interior and its surface. These processes drive mass-transfer mechanisms such as partial melting and crustal recycling, which have generated a lithologically and compositionally heterogeneous mantle over time. Ocean island basalts (OIB) directly sample these heterogeneities, making them excellent tools to constrain the mantle's dynamic geochemical evolution. In this study, we probe the connection between crustal recycling, mantle mineralogy, and partial melting using the stable Ca isotope compositions of OIB, ultimately contextualizing their Ca isotope variability using conventional mantle "endmember" components including DMM, HIMU, EM-1, and EM-2. Using the state-of-the-art Nu Sapphire collision cell MC-ICP-MS, we measured the Ca isotope compositions of 27 well-characterized OIB samples from 11 different ocean island groups. By supplementing our new data with additional high-precision Ca isotope measurements from the literature, we create an expanded dataset consisting of 15 ocean islands, facilitating a global-scale investigation of Ca isotope variability among hotspots. Our findings reveal that island-averaged Ca isotope compositions form two distinct groups on the basis of their radiogenic isotope compositions. The first group, consisting of OIB with un-enriched radiogenic isotope compositions (non-EM-type), exhibits robust negative correlations with both lithospheric thickness and primitive TiO 2 contents, providing compelling evidence that Ca isotopes are sensitive to the degree of partial melting (F) as well as to the effects of crustal recycling. This joint signal appears to trace the process of decompression melting beneath oceanic lithosphere of variable thickness, as recycled lithologies rich in garnet and pyroxene (i.e., pyroxenites)—which generate large solid-melt Ca isotope fractionations—disproportionally control the Ca isotope composition of the final aggregate melt when F is limited by thick overlying lithosphere. In contrast, the island-averaged Ca isotope compositions of OIB with enriched radiogenic isotope compositions (EM-type) form a distinctly light negative correlation with primitive TiO 2 contents without exhibiting a relationship with lithospheric thickness. In addition to lithology-dependent partial melting effects, the Ca isotope compositions of EM-type OIB appear to be sensitive to the compositional effects of crustal recycling, which may explain their decoupling from the physical controls of partial melting. Calcium isotopes show exceptional potential for elucidating the origin of both enriched and ultra-depleted mantle sources, emphasizing the need to prioritize localities with these signatures in future studies. [ABSTRACT FROM AUTHOR]

Abstract A‐type granite is a favorable rock for the study of crustal evolution, crust‐mantle interaction and metallogenesis. However, the origin of A‐type granite remains controversial. In this study, we report high‐precision Ca isotopic compositions of a co‐genetic suite of A‐type granites from the Lower Yangtze River Belt (LYRB) in eastern China. Our results show that the δ44/40Ca of the A‐type granites ranges from 0.55 ± 0.11‰ to 1.44 ± 0.06‰, and is negatively correlated with CaO, Sr and Ba contents and Eu/Eu*, indicating that the Ca isotope fractionation of A‐type granites is dominated by plagioclase and potassium feldspar. There is kinetic fractionation of Ca isotopes during A‐type granite magma evolution. Sample BSL‐7, the least evolved sample, revealed that it had a low δ44/40Ca of 0.59‰, which is significantly lower than that of the upper continental crust (δ44/40Ca = 0.71–0.72‰) and the bulk silicate earth (δ44/40Ca = 0.94‰). The low δ44/40Ca can be best explained by partial melting of the enriched mantle metasomatized by subduction material. Combined with the geodynamic background of the LYRB, we propose that the formation of A‐type granites in the LYRB originates from partial melting of the enriched mantle, triggered by early Cretaceous ridge subduction of the Pacific and Izanagi plates.

The formation of intracellular amorphous calcium carbonate (ACC) by various cyanobacteria is a widespread biomineralization process, yet its mechanism and importance in past and modern environments remain to be fully comprehended. This study explores whether calcium (Ca) isotope fractionation, linked to ACC‐forming cyanobacteria, can serve as a reliable tracer for detecting these microorganisms in modern and ancient settings. Accordingly, we measured stable Ca isotope fractionation during Ca uptake by the intracellular ACC‐forming cyanobacterium Cyanothece sp. PCC 7425. Our results show that Cyanothece sp. PCC 7425 cells are enriched in lighter Ca isotopes relative to the solution. This finding is consistent with the kinetic isotope effects observed in the Ca isotope fractionation during biogenic carbonate formation by marine calcifying organisms. The Ca isotope composition of Cyanothece sp. PCC 7425 was accurately modeled using a Rayleigh fractionation model, resulting in a Ca isotope fractionation factor (Δ44Ca) equal to −0.72 ± 0.05‰. Numerical modeling suggests that Ca uptake by these cyanobacteria is primarily unidirectional, with minimal back reaction observed over the duration of the experiment. Finally, we compared our Δ44Ca values with those of other biotic and abiotic carbonates, revealing similarities with organisms that form biogenic calcite. These similarities raise questions about the effectiveness of using the Ca isotope fractionation factor as a univocal tracer of ACC‐forming cyanobacteria in the environment. We propose that the use of Δ44Ca in combination with other proposed tracers of ACC‐forming cyanobacteria such as Ba and Sr isotope fractionation factors and/or elevated Ba/Ca and Sr/Ca ratios may provide a more reliable approach. [ABSTRACT FROM AUTHOR]

The calcium isotope composition of seawater (δ44/40Ca sw) records important information on the evolution of the calcium and carbon cycles over geologic time. Over the past two decades, many attempts have been made to reconstruct the Neogene δ44/40Ca sw variation using various calcium isotope records of seawater or seawater-like pore fluids. Nonetheless, large discrepancies still exist among these Neogene δ44/40Ca sw records. Here we report δ44/40Ca values in a suite of Neogene island dolomites (20.8–3.4 Ma, n = 18) from the South China Sea. Combining multiple geochemical proxies (δ44/40Ca, δ13C, and δ18O, this study; Sr/Ca, ∑REY, δ7Li, δ26Mg, 87Sr/86Sr, and Δ 47 , previous studies) and evidence from petrography, fluid inclusions, and magnetostratigraphy, we suggest that the dolomitization for these dolomites was buffered by seawater-like fluids in the shallow marine burial domain or even marine diagenetic domain (<180 m) over a considerable period of time (<2 Myr). Then, we apply the equilibrium calcium isotope fractionation factor between dolomite and seawater of −0.52 ± 0.20 ‰ (2SD, n = 13) estimated from the literature to these fluid-buffered dolomites and reconstruct a new Neogene δ44/40Ca sw record. After using the Locally Weighted Regression (LOWESS) curve fitting method, our dolomite-based δ44/40Ca sw record is consistent with the reconciled seawater record from other calcium isotope archives, including shark teeth, corals, foraminifera, brachiopods, barites, phosphates, and bulk pelagic carbonates. Our results support the use of fabric-retentive early marine diagenetic dolomites to trace the evolution of δ44/40Ca sw through Earth's history. [ABSTRACT FROM AUTHOR]

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Copyright of Acta Sedimentologica Sinica is the property of Acta Sedimentologica Sinica Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Large Ca isotope variations recorded in mantle xenoliths and mantle-derived igneous rocks have been widely used to decode the origin of mantle heterogeneity, especially to trace recycled sedimentary carbonates. However, it is still unclear whether and how the subduction of sedimentary carbonate causes significant Ca isotope fractionation in the mantle in correspondence of convergent margins. In this study, we present Ca isotope data for sixteen silica-undersaturated ultrapotassic leucite-bearing rocks and their clinopyroxene (Cpx) phenocrysts from the "Colli Albani" volcano (Italy), and for six carbonate-bearing sediments from nearby Apennine Chain. These subduction-related volcanic rocks have been widely accepted as deriving from a mantle source that involves recycled carbonated sediments indicated by their enriched incompatible trace elements and radiogenic isotopes, and olivine geochemistry. The δ 44/40Ca values (normalized to NIST SRM 915a) of leucite-bearing rocks are uniform (from 0.64 to 0.79 ‰, with one exception of 0.86 ‰) with an average of 0.72 ± 0.03 ‰, 2SE, N = 16, which is 0.12 ± 0.03 ‰ (2SE) and 0.22 ± 0.03 ‰ (2SE) lower than MORBs (0.84 ± 0.02 ‰, 2SE, N = 25) and BSE (0.94 ± 0.01 ‰, 2SE, N = 14) respectively. In contrast, the carbonate-bearing sediments show variable and notably low δ 44/40Ca values, ranging from 0.44 to 0.77 ‰. The δ 44/40Ca of Cpx (0.70 to 0.76 ‰) is indistinguishable from their host rocks (0.73 to 0.76 ‰). In addition, the lack of correlations between δ 44/40Ca and SiO 2 , CaO, Ni and P 2 O 5 , and the Ca isotopic simulation result indicate that Ca isotope fractionation caused by fractional crystallization is insignificant. Given that the Ca isotope fractionation is limited during the melting of spinel wehrlite-like mantle source (within ∼0.04 to 0.11 ‰), the slightly low δ 44/40Ca values of the Italian leucite-bearing rocks require 10 % to 20 % addition of carbonated sediments in their mantle source. This indicates that recycled carbonated sediments can cause slight δ 44/40Ca heterogeneity (∼0.1 to 0.2) of the mantle wedge in local/regional scales. [ABSTRACT FROM AUTHOR]

Torsade de Pointes (TdP), a rare but lethal ventricular arrhythmia, is a toxic side effect of many drugs. To assess TdP risk, safety regulatory guidelines require quantification of hERG channel block in vitro and QT interval prolongation in vivo for all new therapeutic compounds. Unfortunately, these have proven to be poor predictors of torsadogenic risk, and are likely to have prevented safe compounds from reaching clinical phases. Although this has stimulated numerous efforts to define new paradigms for cardiac safety, none of the recently developed strategies accounts for patient conditions. In particular, despite being a well-established independent risk factor for TdP, female sex is vastly under-represented in both basic research and clinical studies, and thus current TdP metrics are likely biased toward the male sex. Here, we apply statistical learning to synthetic data, generated by simulating drug effects on cardiac myocyte models capturing male and female electrophysiology, to develop new sex-specific classification frameworks for TdP risk. We show that (i) TdP classifiers require different features in females vs. males; (ii) male-based classifiers perform more poorly when applied to female data; and (iii) female-based classifier performance is largely unaffected by acute effects of hormones (i.e., during various phases of the menstrual cycle). Notably, when predicting TdP risk of intermediate drugs on female simulated data, male-biased predictive models consistently underestimate TdP risk in women. Therefore, we conclude that pipelines for preclinical cardiotoxicity risk assessment should consider sex as a key variable to avoid potentially life-threatening consequences for the female population.

The Cedars ultramafic block hosts alkaline springs (pH > 11) in which calcium carbonate forms upon uptake of atmospheric CO2 and at times via mixing with surface water. These processes lead to distinct carbonate morphologies with “floes” forming at the atmosphere-water interface, “snow” of fine particles accumulating at the bottom of pools and terraced constructions of travertine. Floe material is mainly composed of aragonite needles despite CaCO3 precipitation occurring in waters with low Mg/Ca (

The stable calcium (Ca) isotopes offer a minimally invasive method for assessing Ca balance in the body, providing a new avenue for research and clinical applications. In this study, we measured the Ca isotopic composition of soft tissues (brain, muscle, liver, and kidney), mineralized tissue (bone), and blood (plasma) from 10 mice (5 females and 5 males) with three different genetic backgrounds and same age (3 months old). The results reveal a distinctive Ca isotopic composition in different body compartments of mice, primally controlled by each compartment's unique Ca metabolism and genetic background, independent of sex. The bones are enriched in the lighter Ca isotopes (δ44/40Cabone = − 0.10 ± 0.55 ‰) compared to blood and other soft tissues, reflecting the preferential incorporation of lighter Ca isotopes through bone formation, while heavier Ca isotopes remain preferentially in blood. The brain and muscle are enriched in lighter Ca isotopes (δ44/40Cabrain = − 0.10 ± 0.53 ‰; δ44/40Camuscle = 0.19 ± 0.41 ‰) relative to blood and other soft tissues, making the brain the isotopically lightest soft tissues of the mouse body. In contrast, the kidney is enriched in heavier isotopes (δ44/40Cakidney = 0.86 ± 0.31 ‰) reflecting filtration and reabsorption by the kidney. This study provides important insight into the Ca isotopic composition of various body compartments and fluids. [ABSTRACT FROM AUTHOR]

Calcium (Ca) isotopes (δ44/42Ca) in serum and urine have been suggested as novel sensitive markers of bone calcification. The response of δ44/42Ca to acute changes in Ca homeostasis, has not yet been demonstrated. We measured serum Ca and δ44/42Ca in rats maintained on a standard and a 50% Ca reduced diet for 4 weeks, and after injection of 1 mg/kg of the calcimimetic AMG-416, 24 h prior to sacrifice. AMG-416 decreased serum Ca by a maximum of 0.38 ± 0.10 and 0.53 ± 0.35 mmol/l after 12 and 6 h, respectively, in the standard and low-Ca diet groups (p = 0.0006/0.02), while serum δ44/42Ca did not change over 24 h in both groups. Urinary Ca concentrations were higher 24 h after AMG-416 injection in both groups (p = 0.03/0.06), urine δ44/42Ca was not different compared to the untreated control groups. Our data does not show acute changes in δ44/42Ca in response to a single dose of AMG-416 within 24 h after injection, possibly due to a lack of bone calcification. • An acute, calcimimetic induced decrease in serum Ca concentration did not alter serum and urine Ca isotope ratios. • The non-response of the Ca isotopes was also observed with 4 weeks of Ca deficient diet. • Our findings suggest rapid deposition of Ca in non-mineralized pools rather than bone calcification. [ABSTRACT FROM AUTHOR]

Isotopes in fossil tooth enamel provide robust tools for reconstructing food webs, which have been understudied in Australian megafauna. To delineate the isotopic composition of primary consumers and understand dietary behaviour at the base of the food web, we investigate calcium (Ca) and strontium (Sr) isotope compositions of Pleistocene marsupial herbivores from Wellington Caves and Bingara (New South Wales, Australia). Sr isotopes suggest small home ranges across giant and smaller marsupial herbivores. Ca isotopes in Pleistocene marsupial herbivores cover the same range as those in modern wombats and placental herbivores. Early forming teeth are depleted in heavy Ca isotopes compared to late-forming teeth of a given individual, suggesting a weaning signal. Distinct Ca compositions between taxa can be interpreted as dietary niches. Some niches conform to previous dietary reconstructions of taxa, while others provide new insights into niche differentiation across Australian herbivores. Combined with the small roaming ranges suggested by Sr isotopes, the Ca isotope niche diversity suggests rich ecosystems, supporting a diversity of taxa with various diets in a small area.

Small mineral particles present in soils, such as clay minerals and some oxyhydroxides, constitute important nutrient reservoirs. This behavior is due to the negative charges and high specific surface areas of these particles allowing them to adsorb cations such as calcium (Ca), a macronutrient that occupies key physiological and structural functions in plant metabolism. Although the chemical reactivity of clay minerals is rather well-known in the literature, especially toward macronutrients such as Ca, that of oxyhydroxides such as phyllomanganate minerals remains largely unexplored. To enhance our understanding of the mechanisms at the origin of the storage/release of the different isotopes of Ca in a soil solution, the possible fractionation between 40Ca and 44Ca during adsorption and desorption of Ca on a synthetic phyllomanganate, abiotically precipitated in the laboratory [synthetic analog of vernadite (δ-MnO 2)], was studied. Experiments were performed in batch (closed system), and several parameters (time, pH of the solution, Ca concentration and nature and concentration of the desorbent) were tested to cover a large range of physicochemical conditions. This study demonstrated that the light 40Ca isotope is preferentially adsorbed on δ-MnO 2 , with Δ44/40Ca (the apparent fractionation of the aqueous solution at the stationnary state of adsorption compared to the initial one) of the adsorbed Ca that can reach 1.19 ± 0.15‰. The results showed that this isotopic fractionation occurs at chemical equilibrium in a closed system and that the isotopic fractionation measured in this study during Ca adsorption on phyllomanganate is significantly higher than that reported in the literature during Ca adsorption on other soil constituents such as clay minerals. At pH below 4 Ca occupies only the interlayer/basal sites whereas above this pH Ca fills interlayer/basal sites (∼86%) and edges sites (∼14%). By combining the experimental data obtained at different pH values, initial Ca concentrations and interaction times, our results suggest that isotopic signature of the Ca adsorbed on δ-MnO 2 is dependent on the nature of the site involved in the adsorption step (i.e., enriched in 40Ca in the interlayer with Δ44/40Ca equal to −0.43‰ and enriched in 44Ca when bound to the edges with Δ44/40Ca equal to +3.5‰). As revealed by surface complexation modeling, such contrasting behavior between the two types of adsorption sites could be due to the bidendate nature of the Ca adsorption occurring on edges and to ion exchange of Ca2+ with H+ in the interlayer sites. Finally, desorption experiments point to total but not instantaneous Ca desorption, probably due to a partial collapse of the interlayer with some ions used to desorb Ca2+ (K+, NH 4 +, hexaamine-cobalt). This suggests that the amount of bioavailable Ca in soils by simple ion-exchange reactions is highly dependent on the nature of the ions which could desorb Ca present in the soil solution. [ABSTRACT FROM AUTHOR]

Recent experimental studies of the isoscalar giant monopole resonance (ISGMR) region in the Ca isotope chain are analyzed within the microscopic model of the phonon–phonon coupling based on the Skyrme energy-density functional. The inclusion of two- and three-phonon configurations leads to a substantial redistribution of the ISGMR strength to lower energy states and also higher energy tail. It is shown that the gross structure of the ISGMR in the calcium isotopes Ca is caused by the complex configurations. [ABSTRACT FROM AUTHOR]

The nuclear shell model is one of the prime many-body methods to study the structure of atomic nuclei, but it is hampered by an exponential scaling on the basis size as the number of particles increases. We present a shell-model quantum circuit design strategy to find nuclear ground states by exploiting an adaptive variational quantum eigensolver algorithm. Our circuit implementation is in excellent agreement with classical shell-model simulations for a dozen of light and medium-mass nuclei, including neon and calcium isotopes. We quantify the circuit depth, width and number of gates to encode realistic shell-model wavefunctions. Our strategy also addresses explicitly energy measurements and the required number of circuits to perform them. Our simulated circuits approach the benchmark results exponentially with a polynomial scaling in quantum resources for each nucleus. This work paves the way for quantum computing shell-model studies across the nuclear chart and our quantum resource quantification may be used in configuration-interaction calculations of other fermionic systems. [ABSTRACT FROM AUTHOR]

Several studies have exploited the stable calcium (Ca) and strontium (Sr) isotope compositions of marine carbonate rocks to investigate ancient carbon cycle dynamics, seawater geochemistry, and controls on carbonate production and preservation. However, the two proxies have rarely been applied together. Based on knowledge achieved to date, the δ44/40Ca-δ88/86Sr multi-proxy can distinguish signatures imparted by mass-dependent fractionation and reservoir mixing, including early diagenesis and shifts in the isotopic composition of seawater. In detail, the δ44/40Ca-δ88/86Sr multi-proxy represents a five-isotope system because the determination of δ88/86Sr values requires analysis of fractionation-corrected 87Sr/86Sr ratios, which provide additional constraints on mixing. Here, we apply the novel δ44/40Ca-δ88/86Sr multi-proxy to two Marinoan (ca. 635 Ma) "cap carbonate" sequences from Namibia. Cap carbonates were widely deposited after the Neoproterozoic Marinoan Snowball Earth Event, but controversy surrounds their origin. We find that the rocks archive primary environmental signals deriving from a combination of seawater-glacial meltwater mixing and kinetic isotope effects. In an outer platform section, dolostone δ44/40Ca and δ88/86Sr values define a line predicted for kinetic mass-dependent isotope fractionation. This dolostone mostly precipitated from meltwater. Moreover, stratigraphically higher samples exhibiting the fastest precipitation rates display elevated 87Sr/86Sr ratios, consistent with long-held expectations that a rapid deglacial weathering pulse forced cap carbonate formation. An inner-platform dolostone shows greater effects from water-mass mixing but still reveals that precipitation rates increased up-section. Overlying limestones show greater Ca and Sr contributions from seawater. Amplification of local coastal processes during global ice sheet collapse offers a simple but sufficient proposition to explain the Ca isotope heterogeneity of cap carbonates. Detection of kinetic isotope effects provides evidence for predominantly rock-buffered diagenesis and further offers a basis for developing the δ44/40Ca-δ88/86Sr multi-proxy as an indicator of saturation state and p CO 2. [ABSTRACT FROM AUTHOR]

Diagenesis has been recognized for decades to significantly alter the trace elements biogenic signatures in fossil tooth enamel and bone that are routinely used for paleobiological and paleoenvironmental reconstructions. This signature is modified during diagenesis according to a complex continuum between two main processes, addition and substitution. For an additive-like, or early diagenesis, the trace elements biogenic profiles can be restored by leaching secondary minerals, but this technique is inefficient for a substitutive-like, or extensive diagenesis for which secondary trace elements are incorporated into the biogenic mineral. This scheme is however unclear for Ca, the major cation in tooth enamel and bone hydroxylapatite, whose stable isotope composition (δ44/42Ca) also conveys biological and environmental information. We present a suite of leaching experiments for monitoring δ44/42Ca values in artificial and natural fossil enamel and bone from different settings. The results show that enamel δ44/42Ca values are insensitive to an additive-like diagenesis that involves the formation of secondary Ca-carbonate mineral phases, while bone shows a consistent offset toward 44Ca-enriched values, that can be restored to the biogenic baseline by a leaching procedure. In the context of a substitutive-like diagenesis, bone exhibits constant δ44/42Ca values, insensitive to leaching , and shows a REE pattern symptomatic of extensive diagenesis. Such a REE pattern can be observed in fossil enamel for which δ44/42Ca values are still fluctuating and follow a trophic pattern. We conclude that Ca isotopes in fossil enamel are probably not prone to extensive diagenesis and argue that this immunity is due to the very low porosity of enamel that cannot accommodate enough secondary minerals to significantly modify the isotopic composition of the enamel Ca pool. [ABSTRACT FROM AUTHOR]

The end-Triassic mass extinction was among the most severe biotic crises of the Phanerozoic. It has been linked with the global expansion of marine anoxia, and the prolongation of these conditions within epeiric seas has been proposed as a cause for the suppression of biodiversity during the early Jurassic Hettangian Stage. Testing this interpretation is complicated by spatially heterogeneous patterns of local marine redox conditions within the western Tethys European Epicontinental Shelf. In this study, we assess the redox state within this region by focusing on two carbonate successions in Italy, a peritidal platform at Mount Sparagio, Sicily, and an offshore ramp deposit at Val Adrara in the Southern Alps. Based on previously published I/Ca ratios, these locations record distinct local background redox conditions, with Val Adrara showing a notably lower pre-extinction oxygen saturation state than Mount Sparagio. Here, we measure δ13C and δ18O at Mount Sparagio and δ44Ca and trace element ratios at both sites to identify the roles of mineralogical and diagenetic effects on the preservation of primary redox signals. A numerical framework of multiple elemental (Sr, Mg, Mn, I) and isotopic (δ13C, δ18O, δ44Ca, δ238U, and δ34S CAS) ratios was constructed to recognize modes of carbonate diagenesis and source-mixing in the data. While diagenesis is impossible to completely rule out, our state-of-the-art approach provides robust evidence against common forms of diagenetic alteration as the main drivers of the overall paleoredox proxy trends. Where the redox signals are largely preserved, we interpret differences in pre-extinction I/Ca between the two sites to reflect distinct local oxygenation states. Drawing from published Community Earth System Model simulations, we propose that ocean circulation and hydrological regime could have been important drivers of spatial heterogeneity in paleo-redox conditions across the European Epicontinental Shelf. Conceptual flow chart for the data reduction process employed in this study. Categories of geochemical tracers (major element isotope ratios, redox proxies, and minor/trace elemental ratios; rounded boxes) can be paired with calcium isotope ratios (δ44Ca) by an analytical method (blue diamonds) to identify pre- (source mixing) and post-depositional (diagenesis) geochemical transformations (grey ellipsis) which together (connected by solid curved lines) inform interpretations of original mineralogy and signal preservation (red ellipsoids). Arrow line styles connect the inputs with the outputs. [Display omitted] • Pairing δ44Ca with redox proxies (δ238U, δ34S CAS , I/Ca) offers a reliable approach to assess post-depositional geochemical alteration. • Two Italian sites, Mount Sparagio and Val Adrara, spanning the Triassic-Jurassic boundary, show diagenesis yet retain redox signals. • Ocean circulation strength and depth of vertical mixing may explain the difference in local redox conditions. [ABSTRACT FROM AUTHOR]

Stable calcium (Ca) and iron (Fe) isotopes could provide a new way to investigate granite petrogenesis, and their isotope fractionation mechanisms in felsic magmas have been increasingly understood through continuous efforts in recent years. However, comprehensive Ca and Fe isotope fractionation during highly fractionated magmas is still unclear. This study presents Ca and Fe isotope data for some fractionated granites from Southern Myanmar. The δ56/54Fe values of the less fractionated Eocene granites range from 0.11 ± 0.03 ‰ to 0.23 ± 0.04 ‰. The highly fractionated Late Cretaceous and Paleocene granites clearly exhibit 0.15 ‰ and 0.42 ‰ variations in δ56/54Fe values, respectively. These δ56/54Fe values are negatively correlated with those of Fe 2 O 3T , TiO 2 contents and (La/Yb) N ratios, suggesting that more evolved melts are enriched in heavy Fe isotopes, primarily as a result of fractional crystallization of Fe-rich minerals enriched in light Fe isotopes (e.g., biotite and ilmenite). Some Late Cretaceous granites with low Nb/Ta and Zr/Hf ratios display relatively low δ56/54Fe values, which may be modified by exsolved fluids enriched in light Fe isotopes. Moreover, the δ44/40Ca values of the Late Cretaceous, Paleocene, and Eocene granites range from 0.71 ± 0.07 ‰ to 0.90 ± 0.06 ‰, 0.62 ± 0.08 ‰ to 0.89 ± 0.06 ‰, and 0.66 ± 0.06 ‰ to 0.75 ± 0.05 ‰, respectively. Most of the studied granites have relatively consistent Ca isotopic compositions with those of the continental crust. Combined with high δ44/40Ca values (up to 0.90 ‰), the studied granites have a weakly negative correlation between δ44/40Ca values and Eu/Eu⁎ ratios. This evidence suggests that fractional crystallization of plagioclase with light Ca isotopes may also be a reason for Ca isotope fractionation during felsic magma differentiation, in addition to crustal magma sources and crustal contamination. Additionally, a Late Cretaceous granite with a high (Dy/Yb) N ratio has the lowest δ44/40Ca value (0.52 ± 0.06 ‰), possibly reflecting the presence of residual garnet in the source. The affirmation of significant Ca and Fe isotope fractionation in highly evolved melts strengthens the utility of Fe and Ca isotopes as tracers of magma differentiation. • Heavy Fe isotopes in fractionated granites resulted from fractional crystallization of Fe-rich minerals. • Ca isotopic variations in fractionated granites were mainly controlled by plagioclase crystallization. • Ca Fe isotopic systems could serve as a proxy for deciphering magma evolution. [ABSTRACT FROM AUTHOR]

We conducted hydroponic experiments growing soybean (Glycine max), rice (Oryza sativa), and wheat (Triticum aestivum) under K and Ca replete conditions to establish the degree of K isotopic fractionation by plants, and compare the isotopic fractionation of Ca and K. Each of the test plants displays fractionation relative to the growth solution favoring the light isotopes of K and Ca. The average δ41K values of the roots from the three plant species were similar, and have an overall average of -0.55 ± 0.24‰ 2s, while the overall average δ44Ca for roots is -0.67 ± 0.44. For leaves, the overall average of δ41K is -0.97 ± 0.4‰, compared to an overall average leaf δ44Ca of -0.83 ± 0.09‰. In the case of the soybean plants, the lightest K and Ca occurs in the stems with average δ41K of -1.31 ± 0.40‰ 2s and average δ44Ca of -1.20 ± 0.19 ‰ 2s. We present a simple box model involving the relative fluxes of K and its isotopic fractionation that reproduces our K isotopic observations and suggests a fractionation of ∼0.8‰ with K uptake from solution by roots. Directly comparing the per amu fractionation of K and Ca reveals an average factor of 2.05 ± 0.50 2s greater fractionation of K isotopes which may reflect their different roles and behaviors in plants.

We employed MC‐ICP‐MS to measure the mass‐dependent Ca isotope compositions of Vesta‐related meteorites. Eucrites and diogenites show distinct Ca isotope compositions, which is caused by crystallization of isotopically heavy orthopyroxene. The Ca isotope data support a model where the two lithologies are linked, where the diogenites, mainly composed of orthopyroxene crystallized from an eucritic melt. As normal eucrites are the main Ca reservoir on Vesta, their δ44/40Ca values (per mil 44Ca/40Ca ratios relative to NIST 915a) best represents that of bulk silicate Vesta (0.83 ± 0.04‰). This value is different from those of bulk Earth (0.94 ± 0.05‰) and Mars (1.04 ± 0.07‰), suggesting that there exists notable Ca isotope heterogeneity between inner solar system bodies. The δ44/40Ca difference between chondrules and these planets does not support the pebble accretion model as the main mechanism for planetary growth. Plain Language Summary: Calcium is a major, refractory element in solar system, and its mass‐dependent isotope fractionation effect is a robust proxy for probing planetary magmatic evolution and tracing the genetic relationships between solar system materials. We report high‐precision Ca isotope data for the howardite‐eucrite‐diogenite and mesosiderite meteorites, which potentially derive from the asteroid 4 Vesta, to better understand the origin and differentiation of Vesta. Eucrites and diogenites have different mass‐dependent Ca isotope compositions, which is caused by orthopyroxene crystallization from a magma ocean. We have modeled the Ca isotope evolution of this magma ocean and find that eucrites and diogenites can have formed from this melt. Eucrites show similar Ca stable isotope compositions to howardites and mesosiderites, consistent with a mixing model of eucrites and diogenites for howardites and the silicate portion of mesosiderites originating from Vesta. The Ca‐rich eucrites can best represent the Ca isotope composition of bulk Vesta. It shows Earth, Mars, and Vesta do not share a common Ca isotope composition, suggesting their potentially different precursor material. All these planets and asteroids possess different Ca isotope composition from the chondrules formed in the inner solar system, which does not support a chondrule‐rich model for accretion of terrestrial planets. Key Points: Eucrites possess isotopically light Ca than diogenites; the Ca isotope modeling shows they are co‐geneticEarth, Mars, and Vesta do not share a common Ca isotope reservoir, reflecting isotopic heterogeneities in the inner solar systemThe Ca stable isotopes of the planets/asteroids do not overlap those of chondrules, which does not support a chondrule‐rich model for planet accretion [ABSTRACT FROM AUTHOR]

Chondrites are undifferentiated meteorites that can provide information on the compositions of materials in the early solar System, including the building blocks of the terrestrial planets. While most chondrites belong to well-defined groups based on their mineralogy and chemical composition, a minor fraction have unusual characteristics and are classified as ungrouped chondrites. These ungrouped chondrites reflect the diversity of chondritic materials in the early solar system; however, they are not as well studied as grouped meteorites and their origins are poorly understood. In this study, we present high-precision mass-independent Cr, Ca and Mg isotope data for 17 ungrouped chondrites. The ε54Cr and ε48Ca (ε expresses parts per ten thousand mass-independent isotope deviation) data for ungrouped chondrites also provide important constraints for assessing their relationships to the known chondrite groups, and the radiogenic Mg isotope ratios (μ26Mg*) can be used to track the early solar system history. We also present the first high-precision data for a Kakangari (KC) chondrite, an enstatite chondrite, and for four enstatite-rich meteorites. The ε54Cr and ε48Ca values for the KC are −0.44 ± 0.04 and −1.30 ± 0.25, respectively, and ε48Ca value for SAH 97096 (EH3) is −0.19 ± 0.22 that overlaps with that of those of Earth-Moon system and ordinary chondrites. All the carbonaceous chondrite-like (CC) ungrouped chondrites show positive ε54Cr and ε48Ca values, and all the non-carbonaceous chondrite-like (NC) ungrouped chondrites and KCs (also belong to the NC trend) show zero or negative ε54Cr and ε48Ca values. This observation confirms the CC-NC dichotomy for primitive solar system materials. LEW 87232 (KC) also shows the highest 55Mn/52Cr ratio and ε53Cr value amongst all the chondrites. There is a positive trend between 55Mn/52Cr ratios and ε53Cr values among all the chondrites that mostly reflects a mixing between multiple chondritic components. Previously it has been reported that there is a bulk 26Al-26Mg correlation line amongst chondrites. This correlation has been interpreted as being due to mixing of CAIs (high 27Al/24Mg ratios and μ26Mg* values) and other silicate material (e.g., chondrules and matrix). By providing additional 26Al-26Mg chondrite data, we show that there is no 26Al-26Mg correlation line for the chondrites, ruling out the two-endmember (i.e., CAIs and other silicates) mixing model. [ABSTRACT FROM AUTHOR]

Diffusion is a significant driver of isotope fractionation at high temperatures, but its precise role is difficult to evaluate in many situations due to the sparsity of data on the isotopic mass dependence of the diffusion coefficient. Such data are lacking particularly for diffusion in minerals. The ratio of diffusion coefficients of two isotopes of the same element in the same material can be characterized as the inverse mass ratio raised to an empirical exponent β , but experiments to determine β are challenging and few measurements have been reported. Here, a method is developed to empirically determine β based on numerical modelling of the diffusion-controlled elemental and isotopic redistribution between minerals during slow subsolidus cooling, and comparison of the results to data from natural mineral pairs. The method is applied to the Ca redistribution between orthopyroxene (opx) and clinopyroxene (cpx), where the elemental partitioning equilibrium as a function of temperature has been well characterized experimentally and Ca isotope fractionation data are available in natural samples that experienced slow cooling. We show that the Ca isotope fractionation during cooling is insensitive to the initial temperature, cooling rate or grain size over a broad range of conditions, provided that diffusion is sufficient to re-homogenize opx grains at near-peak temperatures during early cooling. Furthermore, we find that the Ca isotope fractionation established during cooling is much more strongly dependent on the value of β in opx than the value of β in cpx, as long as cpx dominates the Ca budget in the system. Transient heating events produce fractionation in the opposite sense to that developed during cooling, which can diminish or reverse the isotope fractionation for samples that experienced such events after cooling. Based on the largest Ca isotope fractionation that has been documented between opx and cpx in natural samples, it is inferred that for Ca, β opx = 0.04(1). Despite the relatively small inferred value of β opx , diffusive fractionation of Ca isotopes between opx and cpx is significant over a broad range of cooling rates. Similar behavior during sub-solidus cooling is anticipated for other elements with temperature-dependent inter-mineral partition coefficients, and the method developed here has the potential to be used to place constraints on β for many elements, even in minerals where experimental measurements are not feasible. [ABSTRACT FROM AUTHOR]

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