Isotopic Studies Research Articles

From shore to land: a comparative isotopic study of Neolithic dietary practices in coastal and inland Croatia

From shore to land: a comparative isotopic study of Neolithic dietary practices in coastal and inland Croatia

Southward subduction of the Mongol–Okhotsk Ocean: constraints from Late Triassic granites in the Hailar Basin, NE China

ABSTRACT The southward subduction of the Mongol–Okhotsk Ocean played a crucial role in the tectonic evolution of East Asia during late Paleozoic to Mesozoic. However, the details of the subduction process remain unclear. To better constrain the southward subduction of the Mongol–Okhotsk Ocean, we conducted zircon dating, whole-rock geochemical analysis, and Lu–Hf isotopic studies on Late Triassic granites from the Hailar Basin, NE China. The Late Triassic granites include granodiorites and monzogranites. Zircon U–Pb dating results indicate that the granodiorites and monzogranites were emplaced at 240 Ma and 232 Ma, respectively. The monzogranites are weakly peraluminous, with low concentrations of heavy rare earth elements and high field strength elements, and have low zircon saturation temperatures (average 786℃), indicating an I-type granite affinity. The granodiorites display high Sr/Y values and low concentrations of Y and HREEs, indicating adakitic features. Combining these characteristics with the depleted Hf isotopic compositions suggests that the monzogranites and granodiorites formed through partial melting of juvenile crustal materials and thickened basaltic lower crust, respectively. Based on our data, along with the temporal-spatial distribution of Mesozoic magmatism and episodic variations in crustal thickness along the southern margin of the Mongol–Okhotsk Ocean, we propose that periodic pulses of magmatism in the Erguna and Xing’an blocks are correlated with repeated steepening and shallowing of the Mongol–Okhotsk slab dip. We divided the subduction into five stages: (1) 260 to 225 Ma, the Mongol–Okhotsk Ocean subducted at a shallow angle beneath the Erguna and Xing’an blocks, (2) 225 to 215 Ma, flat-slab subduction occurred, (3) 215 to 205 Ma, the Mongol–Okhotsk Ocean transitioned from flat-slab subduction to slab rollback, (4) 205 to 180 Ma, the Mongol–Okhotsk Ocean experienced a renewed shallow-angle subduction, and subsequently, (5) 180 to 160 Ma, the final ocean closure and continental collision.

Adapting Automatic Water Samplers for the Isotopic Study of Rainfall at High Temporal Resolution.

Stable water isotopes in precipitation are powerful tracers of atmospheric processes. Automatic rain samplers are valuable for high temporal resolution isotopic studies but building them from scratch requires significant financial and material resources. A commercial water autosampler has been modified to prevent post-sampling evaporation and to allow for intra-event precipitation sampling. New sampling bottles were created by reducing the original volume and opening area. Evaporation tests were carried out on different volumes of water for 72 h under laboratory conditions. These were used to determine the minimum amount of rain to collect to minimize the impact of isotopic fractionation by evaporation. The impact of the autosampler's air moisture saturation was also tested. Samples were analyzed by dual-inlet isotope ratio mass spectrometry and cavity ring-down spectroscopy. For samples larger than 10 mL, evaporative heavy isotope enrichment due to Rayleigh distillation remains negligible compared with the overall analytical uncertainty. Intentional saturation of the autosampler's atmosphere significantly reduces post-sampling evaporation but leads to equilibration of the samples with the added water. We have investigated the maximum time that samples must be left for this fractionation to remain negligible. Under these conditions, this autosampler is suitable for intra-event rainfall sampling for isotopic analysis. It is now possible to perform low-cost high-resolution precipitation sampling for isotopic analysis. The intentional air saturation of the sampler, which effectively prevents post-sampling evaporation, had never been proposed before. All instructions for modifying this sampler are now available in open access so the scientific community can easily repeat them.

Pyridine(diimine) Chromium η,1η3-Metallacycles as Precatalysts for Alkene-Diene [2 + 2] Cycloaddition.

The synthesis, characterization, and catalytic cycloaddition reactivity of aryl-substituted pyridine(diimine) (PDI) chromium ether complexes and alkene-diene derived metallacycles are described. The reduction of either (PDI)CrCl2 or (PDI)CrCl3 with sodium and catalytic amounts of naphthalene furnished the corresponding chromium THF or diethyl ether complexes. Exposure of the reduced chromium compounds to a mixture of butadiene and ethylene induced rapid oxidative cyclization and yielded isolable, thermally stable chromium η,1η3 trans-metallacycles. In the presence of pure butadiene, oxidative cyclization was also observed, and a η,1η3 diene-diene chromacycloheptane with vinyl substitution was isolated and crystallographically characterized. Reductive C(sp3)-C(sp3) elimination of the resulting vinylcyclobutane products was promoted by either one-electron oxidation or irradiation with visible light in the presence of diene or coordinating solvents such as THF. Under thermal catalytic conditions, the chromacycles converted butadiene and ethylene to a mixture of vinylcyclobutane arising from [2 + 2] cycloaddition and cis-1,4-hexadiene resulting from competitive hydrovinylation. Visible light irradiation at ambient temperature enabled selective catalytic [2 + 2] cycloaddition. Isotopic labeling studies with 13C-labeled ethylene established that the alkene-diene chromacycle is thermodynamically preferred over the diene-diene alternative and that both oxidative cyclization and reductive coupling steps are reversible. Visible light accelerated the reductive coupling step, while subsequent product displacement from the metal center occurs in the presence of excess diene.

Cooperative Supramolecular Polymerization in Both Polar and Non‐Polar Solvents via Heteroatom‐Driven Amphiphilicity

AbstractSupramolecular polymers in water and non‐polar solvents are extensively studied as model systems to mimic biological processes and as functional materials, respectively. The molecular designs to obtain supramolecular polymers in non‐polar and polar solvents are typically orthogonal. Here, we disclose a molecular design in which we combine hydrogen‐bonding amide units attached to alkyl chains for compatibility with non‐polar solvents and heteroatom in the π‐conjugated core for interaction with polar solvents, leading to supramolecular polymerization of the same monomeric unit in both non‐polar and mixture of polar solvents. Redox‐active phenazine appended with two amide groups was studied as a model monomeric unit and it undergoes cooperative polymerization via intermolecular hydrogen‐bonding resulting in one‐dimensional (1D) nanostructures with co‐facial type packing in non‐polar solvents. Whereas, in a mixture of polar solvents, a J‐type packing was observed with tunable morphology from globular to 1D nanostructures based on the polarity of the cosolvent used. Further, solvent isotopic substitution studies suggest that the amphiphilicity of the system can be attributed to the nitrogen‐atom in phenazine, which is capable of interacting with polar solvent molecules. Thus, this study opens up azaacenes as a new class of π‐conjugated units for functional supramolecular polymers.

Biogeochemical sulfide mineralization in the volcanic-hosted Tongguan hydrothermal field, southern Mid-Atlantic Ridge

Biogeochemical mineralization is increasingly recognized as a significant factor in the formation of submarine hydrothermal sulfide deposits. While several mechanisms by which hydrothermal organisms may facilitate metal deposition have been documented in many seafloor hydrothermal deposits, the potential involvement of biogenic processes in the mineralization of hydrothermal deposits in the southern Mid-Atlantic Ridge (SMAR) has been largely overlooked until now. In this study, we investigate sulfide chimney sample from the volcanic-hosted Tongguan hydrothermal field on the SMAR and present several lines of evidence for biogeochemical mineralization. Mineralogical analysis infers four types of biogenic pyrite and chalcopyrite structures: macrobiotic-related tube structures, microbial-related quasi-stromatolite, quasi-oncolite and globular structures. These biogenic structures exhibit selective enrichment of elements such as Mn, Pb, and Cu in biogenic pyrite compared to abiotic pyrite. In-situ sulfur isotope studies indicate that biogenic minerals possess lower δ34S values than abiotic minerals. We identified three biomineralization mechanisms: an “active” mineralization process mediated by macro-organism, a “passive” mineralization process associated with microbial mats, and a microbial assimilatory sulfate reduction process. Our research suggests that the role of biogenic processes in SMAR hydrothermal mineralization should be given further consideration.

Multi‐isotope (N, O, Ti, and Cr) study of C1 and CM‐like clasts—Probing unsampled C1 material

AbstractA multi‐element isotope (N, O, Ti, and Cr) study was conducted on C1 and CM‐like clasts hosted in achondrites and chondrite breccias to understand the genesis of these chondritic clasts. The mineralogy, O, and N isotopes confirm that CM‐like clasts in howardites and polymict eucrites closely resemble CM chondrite‐like material. The O and Cr isotope composition of C1 clasts in CR chondrites overlaps with those of CR chondrites, implying either formation in a similar nebular environment or resemblance to local CR material that underwent more extensive in situ alteration. Notably, these clasts are less enriched in 15N than bulk CR chondrites. In contrast, C1 clasts in ureilites are enriched in 15N relative to the Earth's atmosphere by ~100‰ setting them apart from any other known solar system material. They display elevated 17O and 18O values and lie along the CCAM line. In addition, a C1 clast from an ureilite represents the most 54Cr‐enriched and 50Ti‐depleted endmember among the carbonaceous chondrites. Altogether, these isotopic characteristics suggest that C1 clasts in ureilites represent material not sampled by any known meteorite group. Overall, this study highlights the presence of primitive, isotopically distinct materials in the early outer solar system, some of which were transported to the inner solar system to the accretion region of the host parent bodies.

Multigenetic origins of pyrite in sedimentary systems: A NanoSIMS sulfur isotope study of the Silurian Longmaxi Formation

Multigenetic origins of pyrite in sedimentary systems: A NanoSIMS sulfur isotope study of the Silurian Longmaxi Formation

Cooperative Supramolecular Polymerization in Both Polar and Non-polar Solvents via Heteroatom-driven Amphiphilicity.

Supramolecular polymers in water and non-polar solvents are extensively studied as model systems to mimic biological processes and as functional materials, respectively. The molecular designs to obtain supramolecular polymers in non-polar and polar solvents are typically orthogonal. Here we disclose a molecular design in which we combine hydrogen-bonding amide units attached to alkyl chains for compatibility with non-polar solvents and heteroatom in the π-conjugated core for interaction with polar solvents, leading to supramolecular polymerization of the same monomeric unit in both non-polar and mixture of polar solvents. Redox-active phenazine appended with two amide groups was studied as a model monomeric unit and it undergoes cooperative polymerization via intermolecular hydrogen-bonding resulting in one-dimensional(1D) nanostructures with co-facialtype packing in non-polar solvents. Whereas, in a mixture of polar solvents, a J-type packing was observed with tunable morphology from globular to 1D nanostructures based on the polarity of the cosolvent used. Further, solvent isotopic substitution studies suggest that the amphiphilicity of the system can be attributed to the nitrogen-atom in phenazine, which is capable of interacting with polar solvent molecules. Thus, this study opens up azaacenes as a new class of π-conjugated units for functional supramolecular polymers.

The Amlah terrane, Yemen – a missing link in the Neoproterozoic tectonic collage of the Arabian Shield

The Amlah terrane, northwest Yemen, comprises a suite of calc-alkaline tonalitic to granodioritic gneisses bounded by mafic volcanic and likely ophiolites. Occupying a key location between the largely juvenile arc terranes of the Saudi Arabian Shield and their correlatives in NW Yemen to the west and continentally influenced terranes of central Yemen to the east, it allows evaluation of models for the final assembly of the Arabian Shield. A field, geochemical, isotopic and geochronological study was undertaken in order to constrain the evolution of the Amlah terrane and its tectonic setting. Calc-alkaline gneisses dated between ca. 760 and 670 Ma have Nd- and Pb- isotopic signatures indicative of minor involvement of older continental crust in their petrogenesis. Syn- and post- tectonic intrusions dated between ca. 635 and 605 Ma show that suturing of the Amlah terrane was complete by around 640 Ma. These data are used to infer that the Amlah terrane developed as an Andean-style marginal arc on an extended western margin of the Palaeoproterozoic continental Abas terrane. The western margin of the Amlah terrane is interpreted as the continuation into Yemen of the Nabitah Suture Zone, which separates eastern (oceanic) and western (continent-influenced) arc terranes in Saudi Arabia.

Provenance analysis of rock crystal artefacts from Palaeolithic sites in Moravia (East Central Europe) – a comparative extended approach

The Bohemian Massif and the Alps are regions that are generally known for their rock crystal artefacts and the study thereof. The most important archaeological findspots in the Czech Republic are the Palaeolithic sites at Nová Dědina (East Moravia) and in Žitný Cave (Moravian Karst), which yielded numerous rock crystal artefacts. The study of fluid inclusions as sensitive objects reflecting the conditions of their formation was included in the research. Subsequently, natural sites with the occurrence of rock crystals were selected as potential extraction sites, and a comparative study was carried out. The methodological approach has been completed using microthermometry, Raman spectrometry, EPMA and stable isotopic studies of oxygen. The best match of the fluid inclusion assemblage resulted from samples from the Bory-Cyrilov area (West Moravia, the Moldanubicum geological unit) as the rock crystal source for the Nová Dědina Aurignacian site. Unfortunately, no natural sample that would match the artefacts from the Žitný Cave was discovered in terms of the investigated properties. Certain features of the artefacts suggest a possible origin in the Tauern Window region. The inaccessibility of the Alps during large parts of the Palaeolithic and the properties of fluids may point more to the source area of the Moldanubicum. The applied methodological approach clearly shows that the combination of the methods used and the interpretation of their data defines the formation conditions and provides essential information for a discussion of the provenance of the raw material used for rock crystal artefacts.

The Small-Scale Fluid Heterogeneity in the Tongguan Hydrothermal Field (27.1° S, Mid-Atlantic Ridge): Evidence from Mineralogical and Sulfur Isotope Study of the Hydrothermal Sulfide

Hydrothermal activity on the modern seafloor varies depending on the tectonic setting. In particular, the neovolcanic zones (NVZs) along mid-ocean ridges, where magmatism is intense, generally host high-temperature hydrothermal activities. These high-temperature hydrothermal activities on the NVZs can promote the development of many polymetallic sulfide deposits. Currently, many high-temperature hydrothermal activities and sulfide accumulations have been discovered on the NVZs of major mid-ocean ridges worldwide, but relatively few have been found in the Southern Mid-Atlantic Ridge (SMAR), which limits our understanding of the hydrothermal mineralization characteristics on the NVZs of SMAR. Fortunately, in 2015, a new hydrothermal field—Tongguan—developed on the NVZ of the SMAR was discovered. In this study, we conducted mineralogical and sulfur isotope studies on hydrothermal chimney and massive sulfide samples collected from the Tongguan field. We revealed the mineral composition and growth sequence in the chimney structures and sulfides and discovered two different chimney growth patterns featuring rhythmic banding and opal-filled structures. Additionally, sulfur isotopes suggest the presence of mixing between seawater within the oceanic crust and the upwelling hydrothermal fluid in this hydrothermal field. Our investigation revealed small-scale fluid heterogeneities during the submarine hydrothermal mineralization process, which is due to fluctuations in fluid temperatures and mineral deposition within individual vent frameworks. This work provides a reference for further understanding and comprehension of hydrothermal mineralization on the NVZs of SMAR.

Isotopic study (U Pb, Sm Nd, and Pb Pb) of rocks and auriferous mineralizations from the Volta Grande do Xingu deposits, Bacajá Domain, Amazonian craton

Isotopic study (U Pb, Sm Nd, and Pb Pb) of rocks and auriferous mineralizations from the Volta Grande do Xingu deposits, Bacajá Domain, Amazonian craton

Water Column Structure and Nutrient Supply on the Northwest Atlantic Shelf: A Nitrate Isotope Study

AbstractThe Northwest Atlantic continental shelf is a highly productive marine region with major uncertainties regarding the supply mechanisms of nutrients fueling productivity. This study uses nitrate isotopes (δ15NNO3 and δ18ONO3) from the Atlantic Zone Monitoring Program 2020 fall mission and an Optimum Multiparameter Analysis to evaluate on‐shelf nutrient transport versus biological supply pathways across three transects from the Laurentian Channel to the central Scotian Shelf. Surface waters showed an imprint of remineralized production, with partial nitrification creating an isotopically light (δ15NNO3 ≥2.7‰) surface lens extending from Cabot Strait across the coastal Scotian Shelf. A concurrent enrichment in δ15NNO3 and δ18ONO3 (<8.5‰, <7.4‰) alongside decreasing nitrate concentrations further indicated phytoplankton assimilation over the deep central shelf (overlying Emerald Basin), a process not observed across Cabot Strait or coastal shelf stations. Subsurface nutrients in Cabot Strait are highly regenerated (<43%), with increased bottom water δ15NNO3 signaling sedimentary denitrification in the deep Laurentian Channel. Conversely, subsurface nutrients on the Scotian Shelf were predominantly preformed (<86%), sustained by Cold Intermediate Water from the Gulf of St. Lawrence and warm North Atlantic Central Water (NACW) from offshore. Derived water mass contributions and a distinct isotopically light subsurface layer offshore (δ15NNO3 of >4.2‰)−characteristic of N2 fixation in shallow NACW−indicate a stronger NACW imprint on the central Scotian Shelf compared to the Laurentian Channel and eastern shelf. Our results confirm the importance of slope water advection in supplying subsurface nutrients to the shelf while highlighting the seasonal imprint of recycled production on near‐shore surface waters during fall.

The Rossosh Domain Is a Fragment of the Mesoarchean Granite–Greenstone Area of Sarmatia: Results of Geochronological and Isotopic Studies of Felsic Volcanic Rocks

The Rossosh Domain Is a Fragment of the Mesoarchean Granite–Greenstone Area of Sarmatia: Results of Geochronological and Isotopic Studies of Felsic Volcanic Rocks

Geochemical and isotopic studies of the Douda-Damerjogue aquifer (Republic of Djibouti): Origin of high nitrate and fluoride, spatial distribution, associated health risk assessment and prediction of water quality using machine learning.

Geochemical and isotopic studies of the Douda-Damerjogue aquifer (Republic of Djibouti): Origin of high nitrate and fluoride, spatial distribution, associated health risk assessment and prediction of water quality using machine learning.

Highly Heterogeneous Parent Body of the Rare Andesitic Erg Chech 002 Meteorite Revealed by the Revisited Mn–Cr Isotopic Systematics

Abstract Erg Chech 002 (EC 002), an andesitic meteorite, has been dated to be the oldest magmatic rock in the solar system. However, controversy has arisen due to inconsistent dating results and isotopic compositions in previous studies, which complicates understanding the evolution of andesitic magmatism in the early solar system. In this study, we conducted comprehensive Cr isotopic studies on two fragments of EC 002, identifying distinct nominal crystallization ages (4567.3 ± 0.8 and 4565.9 ± 0.6 Ma, respectively), as well as nucleosynthetic 54Cr anomalies (ε 54Cr values of −1.12 ± 0.16 and −0.57 ± 0.16, respectively) and ε 53Cr values (−0.37 ± 0.06 and −0.06 ± 0.06, respectively). These results highlight the highly isotopically heterogeneous nature of the EC 002 meteorite. The difference in nominal crystallization ages likely reflects the initial 53Mn/55Mn heterogeneity among various EC 002 fragments. The highly isotopically heterogeneous nature of the EC 002 meteorite may be directly inherited from its surrounding nebula, suggesting subplanetesimal-scale heterogeneity of the inner solar nebula during the formation time of EC 002. We affirmed the oldest crystallization age for EC 002 among all achondrites at ∼4565.9 Ma. Previous discrepancies in dating results and isotopic compositions should arise from the isotopic heterogeneity in the EC 002 meteorite.

Mining coral-derived terpene synthases and mechanistic studies of the coral biflorane synthase.

Biflorane diterpenoids are unique natural products often seen in marine animals. Recent studies have reported a small number of biflorane synthases. However, the catalytic mechanism and structural basis for biflorane formation remain unclear. To address these issues, we conducted genome mining of terpene synthases from the sea whip coral Paramuricea clavata, resulting in the discovery of a biflorane synthase PcTS1. We performed a series of isotope labeling, crystallography, quantum mechanics/molecular mechanics calculations, and mutagenesis studies toward PcTS1 to investigate the mechanism. Isotopic labeling studies, together with calculations, elucidate a cascade of 1,10-cyclization, 1,3-hydride shift, 1,6-cyclization, 1,2-hydride shift, 2,6-cyclization, cyclopropane ring opening, and deprotonation by the generated pyrophosphate, forming the biflorane scaffold. Crystallography, quantum mechanics/molecular mechanics, and mutagenesis studies confirmed the cascade and produced different terpene scaffolds. Our work demonstrated the mechanism of marine biflorane formation, elucidated the second crystal structure of a coral terpene synthase, and realized the terpene skeleton expansion.

Minimizing Stress in White Sharks: Non-Invasive Epidermal Biopsies for Isotopic and Vitellogenin Analyses.

The great white shark (Carcharodon carcharias), a keystone predator vital to marine ecosystem stability, is increasingly exposed to anthropogenic threats, including endocrine-disrupting chemicals (EDCs). This study highlights the use of non-invasive epidermal biopsies to assess physiological and ecological parameters in 28 live specimens sampled from the Dyer Island Nature Reserve, South Africa. Epidermal tissue was analyzed for vitellogenin (Vtg), a biomarker of estrogenic exposure, while dermal tissue was used for stable isotope analyses of carbon and nitrogen, essential for understanding the feeding habitat of white sharks. Vitellogenin, typically restricted to sexually mature females, was unexpectedly detected in males and immature females, indicating significant exposure to estrogenic pollutants. This finding raises concerns about the potential reproductive and population-level impacts on this vulnerable species. Stable isotope analyses confirmed that dermal tissue alone is sufficient for trophic studies, eliminating the need for deeper muscle sampling. By demonstrating that epidermal and dermal tissues provide critical data for both biomarkers and isotopic studies, this research supports the adoption of minimally invasive techniques. Shallower biopsies reduce stress on the animals, making this method a valuable tool for conservation research and management of C. carcharias.

Seasonal water level fluctuations cause opposite changes in fish trophic dynamics in Amazonian black-water and white-water lakes.

Amazonian floodplain lakes, distinguished by their water types, are crucial ecosystems for fish biodiversity. In these ecosystems, the annual hydrological cycle, known as the "flood pulse," is the primary driving force for fish productivity, providing habitat and feeding opportunities. However, how seasonal water level changes affect fish assemblages and feeding guild responses in floodplains with varying watershed characteristics is still poorly understood. We conducted a comparative stable isotope study in both a white-water and a black-water floodplain lake to investigate fish trophic dynamics during periods of rising and low water levels. Analyses of a broad taxonomic range of fish (seven orders and 27 families, with 73 and 82 taxa in the studied lakes, respectively) revealed that the fish assemblages in the studied white-water and black-water lakes exhibited different trophic dynamics in response to changes induced by the hydrological cycle. In contrast to the white-water lake, a strong, trophic guild-related effect shaped the δ13C and δ15N dynamics in the black-water lake. As a result, the fish assemblage in the black-water lake experienced significant trophic shifts with generally opposite dynamics over the water levels compared to the white-water lake. In the black-water lake, water level changes caused alterations in trophic niche width in almost all analyzed guilds (carnivorous, detritivorous, herbivorous, invertivorous, omnivorous, planktivorous), while this was less consistent in the white-water lake. Our results suggest that the fish assemblage in the nutrient-poor black-water lake is more dependent on the annual flood pulse and associated resources than in the white-water lake. These findings may further imply a relatively higher vulnerability of the black-water lake to alterations in the regular flood pulse compared to the white-water lake, indicating greater stability in feeding conditions and fish trophic dynamics in the latter.