Isotope Ratios Research Articles

Synthesis and Characterization of Metallic (Fe‐Ni, Fe‐Ni‐Si) Reference Materials for SIMS 34S/32S Measurements

Secondary ion mass spectrometry (SIMS) is often used to determine the sulfur contents and isotope ratios of metallic alloys in meteorites or high‐pressure experimental samples. However, SIMS analyses involve calibration and the determination of instrumental mass fractionation in reference materials with a matrix composition similar to that of the unknown samples. To provide metallic reference materials adapted to S measurements via SIMS, we synthesised a series of twenty‐eight alloys comprising four FeNi(±Si) compositions (Fe95Ni5, Fe90Ni10, Fe80Ni20, and Fe80Ni15Si5) with S contents varying from 100 μg g−1 to 4 g/100g using the “melt spinning” method, which guarantees that the metal alloys are rapidly quenched at ~ 106 K s−1. Sulfur contents were determined at the Service d'Analyse des Roches et Minéraux at the CRPG and absolute δ34S values were determined by multi‐collector ICP‐MS (MC‐ICP‐MS, ThermoScientific Neptune) and isotope ratio mass spectrometry (Thermoscientific Delta V). A δ34S value of 16.01 ± 0.31‰ was consistently obtained using the MC‐ICP‐MS, which was indistinguishable of the δ34S value of the FeS starting material (15.95 ± 0.08‰). It suggests that S did not undergo isotopic fractionation during the melting process. Of fifteen samples containing ≤ 5000 μg g−1 S, SIMS measurements with 15‐μm‐diameter spots were repeatable to within 10% relative (1 standard deviation, 1s) for S contents and 2‰ for δ34S values. However, samples containing > 5000 μg g−1 S showed FeNi–FeS immiscibility, leading to minor dispersion of the S mass fractions and δ34S values. No matrix effect was observed for Fe‐Ni, Si, or S contents in terms of the calibration curves and instrumental mass fractionation. We ultimately recommend eight samples as reliable reference materials for S isotopic measurements by SIMS, which we can share worldwide with other laboratories.

A long-term study of stable isotope ratios of fingernail keratin and amino acids in a mother-infant dyad.

To evaluate the potential of compound-specific isotope analysis of amino acids (CSIA-AA) for investigating infant feeding practices, we conducted a long-term study that compared infant and maternal amino acid (AA) nitrogen isotope ratios. Fingernail samples were collected from a single mother-infant dyad over 19 months postpartum. Carbon and nitrogen stable isotope ratios were measured in the bulk keratin of the fingernail samples. Selected samples were then hydrolyzed and derivatized for compound-specific nitrogen isotope analysis of keratin AAs. As in previous studies, infant bulk keratin nitrogen isotope values increased during exclusive breastfeeding and fell with the introduction of complementary foods and eventual cessation of breastfeeding. Infant trophic AAs had elevated nitrogen isotope values relative to the mother, while the source AAs were similar between the mother and infant. Proline and threonine appeared to track the presence of human milk in the infant's diet as the isotopic composition of these AAs remained offset from maternal isotope values until the cessation of breastfeeding. Although CSIA-AA is costly and labor intensive, it appears to hold potential for estimating the duration of breastfeeding, even after the introduction of complementary foods. Through the analysis of a full suite of AAs, it may also yield insights into infant physiology and AA synthesis.

Millennial-aged organic matter preservation in anoxic and sulfidic mangrove soils: Insights from isotopic and molecular analyses

Mangrove forests are known as coastal carbon sinks, but the long-term (millennium-scale) preservation processes of organic matter (OM) in their soils and the role of sulphur in these processes are still not fully understood. These processes are crucial for better estimating the impact of sea-level variations on the carbon dynamics in mangrove forests, which are particularly sensitive to sea-level changes due to their direct hydrological interactions with coastal waters. This study focuses on a soil layer enriched in mangrove-derived OM that accumulated during a stable sea-level period of the Holocene in New Caledonia (South Pacific). Radiocarbon dating situates this enriched layer at approximately 4000 cal BP. The aim of this study is to characterize the enriched OM layer using bulk (Rock-Eval), isotopic (δ13C and δ15N), and molecular (lignin and neutral carbohydrates) analyses. This OM has undergone diagenetic processes such as dehydrogenation, and the loss of components such as the main neutral carbohydrates: glucose, xylose, and galactose. However, some Rock-Eval parameters, the total lignin content, and carbon and nitrogen isotopic ratios are characteristic of well-preserved OM, suggesting differential decomposition/preservation processes. In addition, SEM observations highlighted the presence of pyrite associated to preserved root material. Along with high Sorg/TOC ratio, these results suggest potential processes of OM sulfurization preserving it from decomposition. Prolonged sea-level stability in addition to anoxic and sulfidic soil conditions enhanced OM accumulation and long-term sequestration in mangrove soils.

Reconstruction of Phanerozoic climate using carbonate clumped isotopes and implications for the oxygen isotopic composition of seawater

The oxygen isotope ratio 18O/16O (expressed as a δ18OVSMOW value) in marine sedimentary rocks has increased by ~8‰ from the early Paleozoic to modern times. Interpretation of this trend is hindered by ambiguities in the temperature of formation of the carbonate, the δ18Oseawater, and the effects of postdepositional diagenesis. Carbonate clumped isotope measurements, a temperature proxy, offer constraints on this problem. This thermometer is thermodynamically controlled in cases where carbonate achieves an equilibrium internal distribution of isotopes and is independent of the δ18O of the water from which the carbonate grew; therefore, it has a relatively rigorous chemical-physics foundation and can be applied to settings where the δ18O of the water is not known. We apply this technique to an exceptionally well-preserved Ordovician carbonate record from the Baltic Basin and present a framework for interpreting clumped isotope results and for reconstructing past δ18Oseawater. We find that the seawater in the Ordovician had lower δ18Oseawater values than previously estimated, highlighting the need to reassess climate records based on oxygen-isotopes, particularly where interpretations are based on assumptions regarding either the δ18Oseawater or the temperature of deposition or diagenesis. We argue that an increase in δ18Oseawater contributed to the long-term rise in the δ18O of marine sedimentary rocks since the early Paleozoic. This rise might have been driven by a change in the proportion of high- versus low-temperature water-rock interaction in the earth's hydrosphere as a whole.

Online inventory modeling of a CANDU-6 reactor for nuclear forensic applications

To develop the expected isotopic signatures of online nuclear power plants, a CANDU-6 quarter-core reactor was modeled using Serpent, a Monte Carlo and Burnup code. The reactor model was simulated using nominal operating parameters, steady power levels and standard refueling procedures, to set the baseline for online operations. The model was burned for 500 refuelings totaling 1400 effective full power days. The core was divided into 1140 spatially-discrete fuel bundles with each tracking the density of 237 isotopes. Instantaneous core inventory snapshots were recorded at the time of each refueling to create a continuous inventory database. These snapshots provide the expected isotopic densities and ratios for virtually any fuel bundle position or burnup under nominal operating parameters. These values are useful in the event of accidents, short-cycles, or nuclear proliferation. The time-dependent and spatially dependent results for xenon effluent are used to develop an analytical method for calculating the expected International Monitoring System xenon ratio measurements based on fuel bundle leak rates. A possible false-positive nuclear proliferation scenario for a CANDU-6 operating under nominal parameters is also identified.

Essential amino acid carbon isotope ratios as indicators of marine macrophyte response to environmental variation

Essential amino acid carbon isotope ratios as indicators of marine macrophyte response to environmental variation

An advancement of the gravimetric isotope mixture method rendering the knowledge of the spike purity superfluous

The gravimetric isotope mixture method is the primary method to determine absolute isotope ratios. This method, however, depends on the existence of suitable spike materials and knowledge of their purities. Determining the purity of the spikes can be tedious and labour-intensive. In this publication, an advancement of the gravimetric isotope mixture method, rendering the determination of the purity of the spike materials unnecessary, is presented. The advancement combines mass spectrometry and ion chromatography leading to an approach being independent of the purity of the spike materials. In the manuscript the mathematical background and the basic idea of the novel approach are described using a two-isotope system like copper or lithium.Graphical abstract

The helium and carbon isotopic signature of Ocean island basalts: Insights from Fogo volcano (Cape Verde archipelago)

Fluid inclusions (FI) entrapped in phenocrysts carried by Ocean Island Basalts (OIB) contain key information on volatiles’ abundance and origin in their mantle sources. Here, we add new piece of knowledge to our understanding of volatile geochemistry in global OIB magmas, by presenting new noble gas (He-Ne-Ar) and carbon (C) isotope results for olivine- and clinopyroxene-hosted FI from enclaves, lavas, tephra and volcanic gas samples from Fogo, the only frequently active volcano at the Cape Verde archipelago (eastern Atlantic Ocean). FI, together with crater fumaroles, constrain the Fogo 3He/4He signature at 7.14–8.44 Rc/Ra (where RC is the air-corrected 3He/4He isotope ratio, and Ra is the same ratio in air), which is within the typical MORB (Mid-Ocean Ridge Basalt) mantle. The carbon isotopic ratio (δ13C vs. Pee Dee Belemnite) of CO2 in FI and fumaroles range from -6.04 to -4.41 ‰. We identify systematic variations of δ13C and He/Ar* with FI entrapment pressure (estimated from a combination of host mineral barometry and FI microthermometry), from which we develop a model for volatile degassing in the mantle-to-crustal magma storage system. The model predicts a crustal-like signature for carbon (δ13C of -0.4 ± 1.0 ‰) in primary melts formed by mantle melting at ∼2200 MPa (∼77 km) and a source He/Ar* ratio of 0.90–0.24, which are indicative of variably depleted mantle metasomatized by carbon enriched melts/fluids from a crustal component. We also use our results to characterise regional (in the Cape Verde and Canary archipelagos) and global trends in C and He isotope composition from OIB. From a comparison with the few other OIB localities for which δ13C are available, we propose that a carbon enriched crustal component could be recurrent at a global scale in OIB magmatism, although often masked by isotope fractionation during magmatic degassing. We additionally find that, at regional scale, He isotopes in OIB scale inversely correlate with the degree of partial melting of the mantle beneath individual islands’ (inferred from the La/Yb ratio of erupted basalts). More widely, our results corroborate previously established global relationships between OIB He isotopic signature, plume buoyancy flux and overlying plate velocity. In this interpretation, the MORB-like 3He/4He (8 ± 1 Ra) at Fogo reflects a combination of (i) low to medium magma productivity, (ii) relatively low plume buoyancy flux (∼1.1 Mg/s), and (iii) slow average velocity (∼3 cm/yr) of the overlying plate.

Regulation of nitrogen isotopic ratios of cellular components

This paper is an attempt to generalize the nitrogen isotope information of the molecules that make up the cell from our point of view. Nitrogen in the cell exists as 20 proteinaceous amino acids, nucleobases, hemes, chlorophylls, and others, and their composition is similar among organisms. Based on a physiologically simple autonomous system that maintains a balance between inputs and outputs, it is theoretically predicted that 15N is distributed to each cellular compound with a certain regularity, and thus a specific relationship in nitrogen isotopic ratios among compounds. Previous studies essentially confirm this. The nitrogen isotopic ratio of compound i constituting the cell can be generalized as δ15Ni = δ15Nplant + Δi (TP − 1) + γi, where TP represents the trophic position, and Δi and γi are the trophic discrimination factor and the intracellular 15N distribution of compound i, respectively. Knowing reliable values of Δi and γi will help us to better understand nitrogen dynamics in the biosphere and advance our understanding of the picture of the Earth’s environment through biogeochemistry.

Hydrogen isotope fractionation in plants with C3, C4, and CAM CO2 fixation.

Measurements of stable isotope ratios in organic compounds are widely used tools for plant ecophysiological studies. However, the complexity of the processes involved in shaping hydrogen isotope values (δ2H) in plant carbohydrates has limited its broader application. To investigate the underlying biochemical processes responsible for 2H fractionation among water, sugars, and cellulose in leaves, we studied the three main CO2 fixation pathways (C3, C4, and CAM) and their response to changes in temperature and vapor pressure deficit (VPD). We show significant differences in autotrophic 2H fractionation (εA) from water to sugar among the pathways and their response to changes in air temperature and VPD. The strong 2H depleting εA in C3 plants is likely driven by the photosynthetic H+ production within the thylakoids, a reaction that is spatially separated in C4 and strongly reduced in CAM plants, leading to the absence of 2H depletion in the latter two types. By contrast, we found that the heterotrophic 2H-fractionation (εH) from sugar to cellulose was very similar among the three pathways and is likely driven by the plant's metabolism, rather than by isotopic exchange with leaf water. Our study offers new insights into the biochemical drivers of 2H fractionation in plant carbohydrates.

Precise and accurate Ga isotope ratio measurements of geological samples by multi-collector inductively coupled plasma mass spectrometry

Precise and accurate Ga isotope ratio measurements of geological samples by multi-collector inductively coupled plasma mass spectrometry

Germanium and its isotopes as indicators of hydrogeochemical conditions in a terrestrial geothermal system (Karkonosze granitoid, Sudetes, Poland)

The germanium content and its isotope ratio in thermal waters, aquifer rocks and main silicate minerals in a terrestrial groundwater system located in a granitic pluton (Karkonosze granitoid, Sudetes, Poland) have been investigated. This is the first extensive Ge isotope study carried out in both groundwater and aquifer rocks to better understand previously the identified enrichment of groundwater relative to rocks. This research also provides the first data on δ74/70Ge for hybrid acid rocks formed by mixing magmas from two different sources (mantle- and crustal-derived) and main silicate minerals. The Ge isotopic composition in different facies of granite (porphyritic, equigranular) is comparable (δ74/70Ge of 0.43–1.23‰) to its hybrid rocks (quartz diorite–granodiorite, microgranular magmatic enclaves, composite dykes) – 0.79–1.27‰. However, the range of variability of this feature is quite wide. The minerals have δ74/70Ge values of 1.01–1.04‰ in quartz, 0.84–0.90‰ in alkali feldspars, 0.76–0.88‰ in plagioclase, and 0.36–0.39‰ in biotite. The thermal waters are enriched in heavy Ge isotopes (δ74/70Ge of 1.21–2.78‰) relative to the aquifer rocks (δ74/70Ge of 0.43–1.27‰). Currently, the most likely explanation for this is the influence of secondary mineral phases formed in the geothermal granitic system. This comprises the preferential incorporation and adsorption of light Ge isotopes in/onto iron oxide/hydroxides and clay minerals. The other theoretical explanation, i.e., sulfide formation, is unlikely due to the unfavourable hydrogeochemical conditions in the studied system. The δ74/70Ge values of thermal waters are similar to those of previously studied continental geothermal waters (1.65–3.29‰; Siebert et al., 2011) and fresh groundwater (2.24–4.02‰; Baronas et al., 2020), confirming that groundwater enrichment in heavy Ge isotopes relative to aquifer rocks may be widespread in the upper continental crust. Variation in the isotopic composition of the studied thermal waters is a result of the aquifer rock mineralogy and, in some cases, mixing of the old deep-circulating thermal water with the shallow modern cold groundwater. The general similarities in the chemical composition of the studied waters are due to the influence of porphyritic granite, which is the dominant rock type in this aquifer system. Some differences in chemical composition, including differences in the Ge isotopic composition, are related to the local distribution of hybrid rocks and sulfides. The δ74/70Ge and Ge/Si ratios have been shown to be sensitive indicators of local hydrogeochemical conditions in an alimentation zone and a near-borehole zone of particular water intakes.

Bioarchaeological Perspectives on Late Antiquity in Dalmatia: Paleogenetic, Dietary, and Population Studies of the Hvar—Radošević burial site

Late Antiquity Dalmatia was a time and place of political unrest in the Roman Empire that influenced the lives of those in that region. The Late Antique burial site of Hvar – Radošević, spanning the 3rd to 5th centuries CE, is located on the Croatian Dalmatian island of Hvar. Given the time frame and location on a busy marine trade route, the study of this burial site offers us a glimpse into the lives of the Late Antique population living on this island. It comprises 33 individuals, with 17 buried within a confined grave tomb and the remaining individuals buried in separate locations in the tomb's proximity. The study aims to provide a new perspective on the lives of people on the island during those times by studying ancestry, population structure, possible differences within the buried population, dietary habits, and general health. The genetic analysis of the ancestral origins of the individuals buried at Hvar – Radošević revealed a diverse population reflective of the era's genetic variability. The identification of genetic outliers suggests a range of ancestries from distinct regions of the Roman Empire, possibly linked to trade routes associated with the Late Antique port in ancient Hvar. Stable isotope ratio analysis (δ13C and δ15N) indicated a diet mainly consisting of C3 plants, with minimal consumption of marine foods. High childhood mortality rates, physiological stress markers, and dental diseases suggest a low quality of life in the population. Assessment of kinship and dietary patterns revealed no discernible distinctions between individuals buried within the tomb and those buried outside, indicative of an absence of differential burial practices based on social status and familial ties among this specific buried population.

Relationship between fish traits and the methane‐derived carbon contribution to fish in a shallow lake

Abstract Although the transfer of methane‐derived carbon (MDC) to benthic macroinvertebrates such as chironomid larvae and oligochaetes has been well documented, knowledge of the transfer of MDC to fish is limited. We investigated the MDC contribution to 28 fish species through their growth stages and examined the relationship between fish traits including body size, and MDC contribution to fish within species in Lake Kasumigaura, Japan. We used carbon stable isotope ratios and a two‐source mixing model (methane‐oxidation bacteria [MOB] and particulate organic matter) to estimate the MDC contribution to fish. The MDC contribution to individual fish ranged from 0% to 21.5%. Anguilla japonica showed the highest MDC contribution (mean 3.8%). Fish species were classified into four groups according to two criteria: (a) whether the correlation between the MDC contribution and fish size (within species) was significantly negative (negative vs. not significant; ns); and (b) whether the 90th percentile of MDC contribution was 0% or not. The mean MDC contribution was highest (2.18% ± 2.93%, 12 species) for the group with (a)ns/(b)>0%, including the high contribution species such as Abbottina rivularis (mean 5.5%) and Biwia zezera (mean 9.8%). This group (12 species) included relatively high numbers of benthic habitat use (eight species) and omnivores (nine species). The mean MDC contributions were almost zero for the group with (a)ns/(b)=0% (seven species), which included only two species of benthic habitat use and one species of omnivores. The mean MDC contributions were intermediate for the other groups with (a)negative/(b)>0% (1.30% ± 1.17%, seven species) and (a)negative/(b)=0% (0.10%, two species). The negative correlation between fish size within species and MDC contribution in groups with (a)negative/(b)>0% and (a)negative/(b)=0% indicated that ontogenetic habitat and dietary shifts induced changes in MDC transfer. Our results suggest that 21 out of 28 fish species were involved in the MDC transfer in a shallow lake, but variation in MDC transfer could be explained by fish traits (trophic guild and habitat use). Although the mean MDC contribution to all fish species was low (0.61% ± 1.97%), the roughly estimated annual consumption rate of fish on MOB corresponded to approximately 10% of the MOB production in the sediment, suggesting that fish contribute to methane dynamics from the perspective of biogeochemical cycles.

Sourcing and long-range transport of particulate organic matter in river bedload: Río Bermejo, Argentina

Abstract. Fluvial transport of organic carbon from the terrestrial biosphere to the oceans is an important term in the global carbon cycle. Traditionally, the long-term burial flux of fluvial particulate organic carbon (POC) is estimated using river suspended sediment flux; however, organic carbon can also travel in river bedload as coarse particulate organic matter (POMBed). Estimates of fluvial POC export to the ocean are highly uncertain because few studies document POMbed sources, flux, and evolution during long-range fluvial transport from uplands to ocean basins. This knowledge gap limits our ability to determine the global terrestrial organic carbon burial flux. In this study we investigate the flux, sources, and transformations of POMBed during fluvial transport over a ∼1300 km long reach of the Río Bermejo, Argentina, which has no tributary inputs. To constrain sourcing of POMBed, we analyzed the composition and stable hydrogen and carbon isotope ratios (δ2H, δ13C) of plant wax biomarkers from POMBed at six locations along the Río Bermejo and compared this to samples of suspended sediment, soil, leaf litter, and floating organic debris (POMfloat) from both the lowland and headwater river system. Across all samples, we found no discernible differences in n-alkane average chain length or nC29 δ13C, indicting a common origin for all sampled POMBed. Leaf litter and POMfloat nC29 δ2H values decrease with elevation, making it a useful proxy for POMBed source elevation. Biomarker δ2H values suggest that POMBed is a mix of distally derived headwater and locally recruited floodplain sources at all sampling locations. These results indicate that POMBed can be preserved during transport through lowland rivers for hundreds of kilometers. However, the POMBed flux decreases with increasing transport distance, suggesting mechanical comminution of these coarse organic particles and progressive transfer into the suspended load. Our provisional estimates suggest that the carbon flux from POMBed comprises less than 1 % of the suspended load POC flux in the Río Bermejo. While this represents a small portion of the river POC flux, this coarse, high-density material likely has a higher probability of deposition and burial in sedimentary basins, potentially allowing it to be more effective in long-term CO2 drawdown relative to fine suspended particles. Because the rate and ratio of POMBed transport versus comminution likely vary across tectonic and climatic settings, additional research is needed to determine the importance of POMBed in the global carbon cycle.

Cryogenic vacuum distillation vs Cavitron methods in ecohydrology: Extraction protocol effects on plant water isotopic values

Stable isotope ratios of hydrogen and oxygen in plant water are widely used for water tracing in ecohydrology studies. In this approach, plant water is extracted for isotopic analysis of δ2H and δ18O. Among the extraction methods, cryogenic vacuum distillation (CVD) has been the most popular, but its impact on the isotopic composition of plant water is currently under debate. Newer Cavitron method have been proposed to replace CVD method for xylem water extraction. These recommendations have been largely based on comparisons between Cavitron-xylem water with low temperatures CVD-xylem water. However, the CVD protocol (extraction temperature and time) varies widely across laboratories, and no direct, systematic comparison has yet been made between extraction temperature and time protocols vs. the Cavitron approach. Here we compared the isotopic values of xylem water from the same tree obtained through CVD extraction at 60 °C (60, 120, 240, 360 min), 100 °C (30, 60, 120, 240 min), 140 °C (15, 30, 60, 120, 240 min), and 200 °C (15, 30 min). Subsequently, we compared the results of CVD-xylem water with Cavitron-xylem water. Our data show that isotopic values for CVD-xylem water became more positive with increasing extraction time under the same extraction temperature. Such extractions also became more isotopically positive with increasing extraction temperature for the same extraction time. When total extraction efficiency exceeded 98 %, there was no δ18O difference in CVD-xylem water among any of the different protocols (p > 0.05). However, lower extraction temperatures resulted in more negative δ2H when compared to higher temperature extraction (p < 0.05). Cavitron-xylem water was close to CVD-xylem water (average difference of 3 ‰ for δ2H and 0.5 ‰ for δ18O, n = 79) when total extraction efficiency for CVD was below 98 %. But for extraction efficiencies beyond 98 %, the Cavitron-xylem water was more negative in δ2H (17.3 ‰, n = 70) and δ18O (1.7 ‰, n = 70) than CVD-xylem water. Compared to Cavitron-xylem water, CVD-xylem water at 200 °C with extraction efficiency > 98 % was closer to the soil water. Further study is necessary to conduct a complete cross-comparison between Cavitron and CVD at different temperatures with different species at various water and salt stress conditions. But our results suggest that abandoning CVD for plant water maybe premature until such complete comparison work is done.

Isotope-based inferences of the trophic niche of short-finned pilot whales in the Webbnesia

Knowledge of predator-prey interactions is key in ecological studies and understanding ecosystem function, yet this is still poorly explored in the deep-sea environment. Carbon (δ13C: 13C/12C) and nitrogen (δ15N: 15N/14N) stable isotope ratios of a deep-diving species, the short-finned pilot whale (Globicephala macrorhynchus), were used to explore knowledge gaps on its ecological niche and foraging habitats in the Webbnesia marine ecoregion (Tenerife Island, n = 27 animals vs. Madeira, n = 31; 500 km apart) where animals display distinct levels of site fidelity. Specifically, we tested whether intraspecific isotopic variation results from differences between geographic areas (due to possible foraging plasticity between regions), sexes, and/or years (2015–2020) using Generalized Linear Models. In general, significant differences (p < 0.05) were found in the stable isotope profiles of pilot whales between the two archipelagos, which were also reflected in their isotopic niche. The higher mean and wider range of δ15N values in Tenerife suggest that pilot whales consume prey of higher trophic levels and more diverse than Madeira. The higher mean and wider range of δ13C values in Madeira suggest that in that island, pilot whales rely on prey from more diverse habitats. There was significant variation between some years, but not between sexes. Finally, we discuss pilot whales' foraging strategies worldwide and infer the reliance on benthic or benthopelagic food sources in the Webbnesia.

Validation of Mg Isotopic Measurements for the Characterisation of Ten Carbonate Reference Materials with Ultra‐Low Mg Mass Fractions

Magnesium isotope ratios in carbonate rocks and minerals play an important role in tracing geological and biological processes. We report δ26MgDSM3 values for the first time in ten carbonate reference materials (GBW07865, GBW07114, GBW(E)070159, GBW07136, GBW07108, GBW03109a, GBW07120, GBW07214a, IAEA‐B‐7 and IAEA‐CO‐8) with calcium to magnesium mass ratios around 1300 g g−1 and ultra‐low Mg mass fractions of 295 μg g−1. A combination of AG MP‐50 (100–200 mesh) and AG 50W‐X12 (200–400 mesh) resins for the matrix extraction and multi‐collector inductively coupled plasma‐mass spectrometry (MC‐ICP‐MS) were used for the isotopic measurements. This measurement procedure is applicable to materials with high and low Mg mass fractions (e.g., carbonates, lunar highlands anorthosites, ice core). It was validated using various types of reference material. In‐house synthetic solutions with 1000 and 1300 g g−1 [Ca]/[Mg] mass ratios yielded δ26MgDSM3 values at 2s = ±0.05‰ (n = 62), ‐4.89‰ and ‐4.89‰, respectively, indistinguishable from those of the pure Mg solutions, at ‐4.91‰. δ26MgDSM3 values in well characterised carbonatite and carbonate reference materials (such as JDo‐1, COQ‐1, GBW07133, GBW07217a and GBW07129), with varying MgO and CaO mass fractions, were in agreement with literature values.

Melting of Totten Glacier, East Antarctica since the Last Glacial Maximum Revealed by Beryllium Isotope Ratios of Marine Sediment

The Totten Glacier of East Antarctica drains a basin containing about 3.5 m of sea-level rise equivalent ice. While Totten Glacier is generally considered somewhat more stable than the rapidly retreating sectors of the West Antarctic Ice Sheet, such as the Amundsen Sea Embayment and Getz Ice Shelf, our understanding of its intricate dynamics and interaction with the Southern Ocean since the Last Glacial Maximum remains incomplete. Situated in a precarious position grounded below sea level, Totten Glacier represents a critical yet enigmatic component of East Antarctic ice dynamics. Its susceptibility to marine ice sheet instability raises concerns, as positive feedback from grounding line retreat could trigger irreversible ice discharge or even complete collapse. A meticulous reconstruction of the retreat history of the Totten Glacier is imperative to comprehensively grasp the glacier's response to present and future climate changes.Here, we present a beryllium isotope ratio analysis of marine sediment from the continental slope proximal to Totten Glacier, the first such record from this location, supplemented by grain size data from the same sediment core. The results, when evaluated together with nearby proxy records, reveal that the initial deglaciation of the Totten Glacier sector of the East Antarctic Ice Sheet began at ca. 21 ka BP. The rapid deglaciation from ca. 7 ka BP that followed is determined to be caused by the intrusion of modified Circumpolar Deep Water, leading to melting at the grounding zone of the Totten Glacier and causing instability of the glacier system. The southward shift and intensification of Antarctic easterlies may be one of the causes of this intrusion. These results contribute to the body of knowledge regarding the dynamical response of marine-terminating glaciers to climate variability during the last deglaciation.

Water isotope ratios reflect convection intensity rather than rain type proportions in the pantropics.

Against the traditional view, a recently published theory argued that isotope ratios are higher in convective precipitation but lower in stratiform precipitation and proposed that isotope ratios reflect rain type proportions. This theory has been widely cited despite some early reservations. Whether the theory represents a faithful reflection of signals of water isotope ratios remains unclear. Here, we reassess its validity from different timescales and broader observations from the pantropics. Unexpectedly, our findings contradict the theory on daily, monthly, and even annual timescales. Pantropical precipitation isotope ratios remain strongly correlated to convection intensity but are independent of rain type proportions because stratiform precipitation isotope ratios cover a large range of values. We find that the theory has many serious weaknesses related to preferential data selection and suggest that new theories need to be validated at more locations on different timescales before gaining widespread acceptance.