Isotopic Results Research Articles

Hydrochemical and environmental isotopes characteristic of groundwater and controlling factors for waters’ chemical composition in the iron–copper mine area of Elazığ, SE Turkey

Environmental context Predicting the hydrodynamic structure of water resources based on water chemistry and isotope results is important for understanding their transport and effects on the hydrogeological system. According to the results of this study, hydrogeological characteristics of ground and surface water resources in the Zeryan Stream sub-basin in the iron–copper mining area and their geochemical evolution are mainly controlled by the weathering of silicate and carbonate minerals, and ion exchange. Rationale and hypothesis Groundwater is generally the most important water resource in mine areas, and its circulation processes need to be studied in detail for rational resource exploitation. This work tested the hypothesis that the evolution of groundwater chemistry and recharge by using hydrogeochemical indicators and isotope tracers together are affected by the hydrogeochemical processes that may have taken place during the water-rock interactions in the Zeryan Stream Sub-basin, where the Iron-Copper mine is located. Methodology It used approaches such as hydrochemistry, Piper diagrams, saturation index, ionic ratios, and environmental isotopes to analyze groundwater origin and hydrochemical processes affecting water chemistry. Fifty-seven water samples were collected from 19 points during wet and dry periods. Results Results indicated that the dominance of cations and anions in the mine water follows the trend Mg2+ > Ca2+ > Na+ > K+ and SO42− > HCO3− > Cl−, and most of the water samples are Mg-Ca-HCO3-SO4, Mg-Ca-SO4-HCO3, and Ca-HCO3. Discussion Evaluation of analyzed groundwater chemical data showed that dissolution or precipitation of silicate minerals dominated in the hydrochemical evolution of groundwater, dissolution of carbonate minerals was a secondary process and to a lesser extent, ion exchange processes played a role. The δD and δ18O isotopic contents indicated that the water samples were controlled by local atmospheric precipitation, and affected by secondary evaporation during the recharge process. Tritium levels indicated some well waters are recharged from older groundwater resources from water-rock interaction and residence time. Findings The findings of this study were provided to decision-makers in order to design sustainable implications for groundwater utilization based on the sub-basin.

Isotopic signatures to address the groundwater recharge in coastal aquifers

The dynamics of the coastal aquifers are well-expressed by geochemical and isotopic signatures. Coastal regions often exhibit complex groundwater recharge pattern due to the influence of depression in the Bay of Bengal, tidal variations on surface waters, saline water intrusion and agricultural return flows. In this research, groundwater recharge processes occurring in coastal Tamil Nadu, South India were evaluated using major ion chemistry and environmental isotopes. A total of 170 groundwater samples were collected from shallow and deep aquifers during both post-monsoon (POM) and pre-monsoon (PRM) seasons. The isotopic results showed a wide variation in the shallow groundwater, suggesting contribution from multiple recharge sources. But, the deeper groundwater recharge is mainly from precipitation. The northern part of the study area showed more depleted isotopic values, which rapidly changed towards south from −6.8 to −4.4‰. Alternatively, central and southern parts exhibited relatively enriched isotopic content with variation from −0.58 to −2.7‰. Groundwater was discerned to be brackish to saline with chloride content, 600–2060 mgL−1 and δ18O ranging from −5.8 to −4.5‰, suggesting influence of the saline water sources. A minor influence of anthropogenic activities was also observed in the deeper groundwater during PRM, which was confirmed by tritium and Cl− trends. The old groundwater with depleted isotopic content infer recharged by distant sources while modern groundwater with enriched isotopes points to the influence of evaporated recharge.

Geochemical Characteristics and Genesis of Majiayao Gold Deposit in Jiaodong

Majiayao Gold Mine, located in Qixia City, Shandong Province, is a quartz vein-type gold deposit. In order to explore the source of the metallogenic materials of the Majiayao gold deposit, the previous experimental results of the pyrite and galena in the Majiayao gold deposit were collected in this paper. The S isotopic results show that the δ34S values of gold-related sulfide in Majiayao gold deposit are 4.4‰~8.8‰, indicating that the ore-forming materials come from the mantle and crust. The metallogenic mechanism of the Majiayao gold deposit is the upwelling of mantle-derived magma, and then exchanges material with the metamorphic rocks of the Jiaodong Group to form ore-forming fluids rich in metamorphic components. The ore-forming fluid migrated upward, the temperature and pressure decreased and the atmospheric water was mixed, and the ore-forming fluid was immiscible, resulting in the precipitation of gold.

A Preliminary Study to Determine the Hydrogen and Oxygen Isotopic Compositions of Natural and Bottled Water using High Sensitivity Isotope Ratio Mass Spectrometry

In this study, we introduce the stable isotopic results of water using a recently installed high sensitivity isotope ratio mass spectrometry (HS-IRMS) system at the Korea Institute of Geoscience and Mineral Resources (KIGAM). As a result of analytical method validation through an international proficiency test, the 2020 WICO (Water Isotope Inter-Comparison), organized by the International Atomic Energy Agency, the KIGAM IRMS laboratory showed satisfactory performance. Furthermore, stable isotopic compositions of bottled water samples from South Korea were measured using the HS-IRMS with a high temperature conversion elemental analyzer, and this method was re-validated and confirmed by a comparison with stable isotope results obtained using an equilibrium method.

Origin and tectonic implication of mafic dykes: The Permian diabases in Santanghu Basin, NW China

The Permian mafic dykes of Santanghu Basin offer an opportunity to study the nature of mantle source and tectonic setting of the basin, as well as to provide the theoretical basis for structural transformation of East Junggar region. In this study, zircon U–Pb geochronology, mineral composition analysis, whole‐rock elemental, and Sr‐Nd isotopic geochemistry were conducted to explore the origin and evolution of the primitive magma. LA‐ICPMS zircon U–Pb dating yields ages at 269 Ma. The elemental geochemistry results suggest enrichments in Ba, Pb, and Sr but depletions in Nb, Ta, Zr, and Hf, which indicate that the magma source was influenced by fluid metasomatism. All samples show moderate initial Sr‐Nd isotope results ((87Sr/86Sr)I = 0.704299 to 0.704490 and εNd(t) = +6.16 to +6.83) and have high Sm/Yb ratios, which suggest that the diabases were derived from partial melting of 5%–7% spinel‐garnet Iherzolite lithospheric mantle. Combined with petrological, geochronological data, and the regional tectonic background, it is interpreted that the diabases from Santanghu Basin originated from lithospheric mantle metasomatized by subduction fluids under the background of intracontinental extension.

Copper-base metal supply during the northern Vietnamese Bronze and Iron Ages: metallographic, elemental, and lead isotope data from Dai Trach, Thành Dên, Gò Mun, and Xuân Lâp

We present the results of metallographic, elemental, and lead isotope analyses of one slag and 27 copper-base artefacts from northern Vietnam. These artefacts come from four sites: Dai Trach, Thành Dên, Gò Mun, Xuân Lâp and are attributed to the Đồng Đậu (ca. 1300–1000 BC), Gò Mun (ca. 1000–700 BC), and Đông Sơn (ca. 700 BC–100 AD) cultures, the two former being Bronze Age (18 samples) and the latter Iron Age (10 samples). Twenty-two of the samples have as-cast microstructures, with one having been quenched, three evidencing working and annealing, and one too corroded to tell. Despite variable corrosion levels, all metal samples are identified as bronzes, rather than copper, though seven are leaded bronzes. All the leaded alloys are Iron Age, which is typical for the region. Lead isotope results were notable, in that none of the study samples is consistent with the known prehistoric Southeast Asian copper production signatures, an unusual occurrence in recent regional provenance research. There is some compatibility with Thai Bronze Age copper-base artefacts, but generally it seems there was only weak overlap in exchange systems between northern Vietnam and southern Mainland Southeast Asia, with northern Laos as a possible frontier zone. Further archaeometallurgical prospection and characterisation in northern Vietnam are needed to identify primary production loci, but sources in the southern Chinese provinces of Yunnan, Guangxi, and Guangdong are also probable.

Human mobility in Byzantine Cyprus: A case study from the Hill of Agios Georgios, Nicosia

The current paper explores human mobility in Byzantine Cyprus, using the site of the Hill of Agios Georgios in Nicosia as a case study. The analysis of mobility is based on strontium isotopic data, with the aim of identifying non-local individuals and estimating their frequency in different periods of use of the site (Early Christian and Late Byzantine/Frankish). As a complementary line of evidence, dental calculus microdebris analysis was conducted to explore the potential existence of imported plants as well as any differences in the diet and environment between local and non-local individuals. The isotopic results identified one individual who likely originated outside Cyprus and several more, the number of which differs pending on the bioavailable baseline used, who were non-local to the burial site. These non-local individuals temporally span both periods under study but they are more common in the Late Byzantine/Frankish assemblage, which is in agreement with historical data pointing to elevated mobility throughout Byzantine times but more so in the later periods. From the analysis of dental calculus microremains, we only retrieved identifiable starches from individuals of non-local origin; thus, these were difficult to interpret. A small amount of starch from the millet tribe, however, allowed us to make important considerations regarding the interpretation of dental calculus data in periods of time and locations where human mobility was high.

Seasonal Dietary Shifts of the Gammarid Amphipod Gondogeneia antarctica in a Rapidly Warming Fjord of the West Antarctic Peninsula

The amphipod Gondogeneia antarctica is among the most abundant benthic organisms, and a key food web species along the rapidly warming West Antarctic Peninsula (WAP). However, little is known about its trophic strategy for dealing with the extreme seasonality of Antarctic marine primary production. This study, using trophic markers, for the first time investigated seasonal dietary shifts of G. antarctica in a WAP fjord. We analyzed δ13C and δ15N in G. antarctica and its potential food sources. The isotopic signatures revealed a substantial contribution of red algae to the amphipod diet and also indicated a significant contribution of benthic diatoms. The isotope results were further supported by fatty acid (FA) analysis, which showed high similarities in FA composition (64% spring–summer, 58% fall–winter) between G. antarctica and the red algal species. G. antarctica δ13C showed a small shift seasonally (−18.9 to −21.4‰), suggesting that the main diets do not change much year-round. However, the relatively high δ15N values as for primary consumers indicated additional dietary sources such as animal parts. Interestingly, G. antarctica and its potential food sources were significantly enriched with δ15N during the fall–winter season, presumably through a degradation process, suggesting that G. antarctica consumes a substantial portion of its diets in the form of detritus. Overall, the results revealed that G. antarctica relies primarily on food sources derived from benthic primary producers throughout much of the year. Thus, G. antarctica is unlikely very affected by seasonal Antarctic primary production, and this strategy seems to have allowed them to adapt to shallow Antarctic nearshore waters.

Potential influence of a planned landfill on a high karst plateau in Southwestern Montenegro to nearby karstic springs

The potential threat of a landfill projected on a high karst plateau in southwest Montenegro is investigated with respect to the subjacent nearby springs. The locality is called Duboki do. As the springs are used for drinking water supply this investigation is urgently needed. For the springs exist two hypotheses concerning their catchment area: I) from the high karst plateau, or II) from a topographically lower area. The stable H- and O-isotope ratios of water samples from the springs are compared with precipitation isotope data, to reveal the catchment area of the springs. The isotope results indicate that the catchment area of the springs is at higher altitude fitting to, and in good agreement with, winter precipitation from the high karst plateau of the planned land-fill locality.

Preparation of sulfur-bearing reference materials for in situ sulfur isotope measurements using laser ablation multicollector inductively coupled plasma–mass spectrometry

In this study, a method for solidifying sulfide and sulfate nanoparticulate powder to prepare bracketing standards and samples for in situ S isotopic analysis using laser ablation multicollector inductively coupled plasma–mass spectrometry (LA-MC-ICP–MS) was developed. Sulfide or sulfate powder was transformed into a stable and mechanically resistant target by mixing it with epoxy resin. Using this method, seven bracketing standards with diverse matrix minerals (pyrite, chalcopyrite, sphalerite, galena, arsenopyrite, barite, and gypsum) were synthesized in the form of resin-preserved powders (RPPs). The effects of ablation behavior, powder particle size, and homogeneity on the S isotopic ratios in these RPPs were rigorously evaluated. The precision of the δ34SVCDT sulfur isotopic results obtained by LA-MC-ICP–MS was better than 0.47‰ (2SD uncertainty, n ≥ 20 over 4 months) for the S-bearing mineral RPPs. Finally, the in situ S isotope results of the seven RPPs measured by LA-MC-ICP–MS were consistent with the values obtained using solution nebulizer (SN)-MC-ICP–MS. The isotopic composition and homogeneity of a range of sulfide mineral RPPs (seven minerals referred to above) were characterized for use as potential reference materials. Our method provides the opportunity to prepare bracketing standards and samples for in situ S isotope analysis for a wide range of sulfur-bearing materials and is particularly appropriate for geologic samples with complex matrices and for which high spatial resolution in situ microbeam analysis is critical. More importantly, this method provides new prospects for the preparation of homogenized reference materials from natural minerals that are urgently needed for matrix-matched calibration and quality control of LA-ICP–MS geochemical and isotope data.

Advances in cocaine signature methodology: Alkaloid and isotope profiles of coca grown in Puno, Peru.

Drug Enforcement Administration's (DEA) Cocaine Signature Program previously identified 19 coca-growing regions within South America and developed methodology to geo-source cocaine using a combination of trace cocaine alkaloids, stable isotopes, and multivariate statistics. Twenty-nine coca leaf samples collected in 2016 and 2019 from a previously unanalyzed coca-growing region located in Puno, Peru, were analyzed with this methodology. Trace cocaine alkaloids and stable isotopes were compared with other Peruvian regions. Minor differences were observed in the extracted cocaine alkaloid profiles when compared with samples collected from the Ucayali-Huallaga Valley and Cusco-Apurimac regions while the stable isotopes of δ2 H (-177.1‰) and δ18 O (23.8‰) were enriched. Puno's alkaloid and stable isotope results are presented in this publication to assist forensic laboratories and enhance their cocaine geo-sourcing capabilities.

Genetic Mechanism and Environment Implications of Siderites in the Lopingian Coal-Bearing Series, Western Guizhou of China: Constrained by Whole-Rock and In Situ Geochemistry

A large number of siderites have been found in the Lopingian (Late Permian) coal-bearing series in western Guizhou, which occurs in various microscopic morphologies and has potential insights into the sedimentary and diagenetic environments. An integrated set of analyses, such as microscopic observation; X-ray diffraction; whole-rock major and trace element, carbon, and oxygen isotope; and in situ major and trace element, has been carried out to unravel the genetic mechanism of the siderites and their environmental implications. According to the microscopic morphology, the siderites can be generally divided into three types and six subtypes, including gelatinous siderites (I), microcrystal-silty siderite [II; microlite siderites (II1), powder crystal siderites (II2)], and spheroidal siderite [III, petal-like siderite (III1), radiating fibrous siderite (III2) and concentric siderite (III3)]. Whole-rock geochemical results show that the iron source for the formation of the siderites was mainly from extensive weathering of the Emeishan high-titanium basalts in hot climate conditions. The carbon and oxygen isotopic results indicate that the origin of CO2 in type I siderites is derived from the dehydroxylation of organic matter. The CO2 in types II1 and II2 siderites is mainly derived from deposited organic matter and marine carbonate rocks, respectively. The CO2 source of type III siderites is sedimentary organic matter and marine carbonate rocks and is affected by different fluids during diagenesis. The whole-rock and in situ geochemical characteristics further point to that type I siderites were formed in the synsedimentary period most strongly affected by seawater. Redox proxies, such as V/Sc, V/(V+Ni), and δ Ce, constrained their formation in a stable and weakly reduced condition. Type II siderites could have been developed in saltwater. Among them, type II1 siderites were formed in the early diagenetic stage, whereas type II2 siderites originated from recrystallization of type II1 siderites and accompanied by metasomatism with calcites under diagenetic fluids of weak reduction to weak oxidation conditions. Type III siderites were formed under the influence of multistage diagenetic fluids. Among them, type III1 siderites formed by the growth of powder crystal siderites (II2) under diagenetic fluids with a weak reducing condition. Type III2 siderites formed by growth around microlite siderites under weak reducing diagenetic fluids. Type III3 siderites formed by concentric growth in diagenetic fluids with weak reduction to weak oxidation conditions and relatively active conditions.

Isotopic Evidence for the High Contribution of Wintertime Photochemistry to Particulate Nitrate Formation in Northern China

AbstractStable isotopic constraint and observationally coupled atmospheric chemistry model are two robust means to identify the oxidation mechanisms for atmospheric particulate nitrate (NO3−) production. However, large discrepancies between the two approaches have been noted in the heavily polluted environments of North China Plain (NCP). Herein, daily PM2.5samples (n = 418) were collected at five urban cities across NCP during the winter of 2017–2018; the ionic species (e.g., NO3−and methanesulfonic acid: MSA) and the dual‐isotopic signatures of NO3−were quantified. In this study, we revisited the O isotopic signatures of atmospheric O‐bearing molecules, especially that of OH radical in accordance with the up‐to‐date field measurements conducted in NCP regions. In brief, the δ18O‐OH was determined by the competition between the OH loss reaction rate and its isotopic equilibration reaction with H2O. Our improved isotopic results suggested that the daytime OH oxidation pathway was as important as the nocturnal channels in wintertime nitrate production in NCP (46.4% vs. 53.6%), whereas the exceedingly high loadings of NO3−in haze days were attributed to the heterogeneous chemistry of N2O5hydrolysis. Chemical analysis also confirmed the importance of active photochemistry in secondary components production, as the MSA (a photooxidation product) linearly correlated with the NO3−(R2 = 0.86,p < 0.05). Our preliminary results compared well with the recent model simulations (e.g., sophisticated 3D model and observationally constraint model). To alleviate the winter haze in NCP, future emission regulations should aim to reduce the photochemical oxidants, particularly their precursors of NOxand VOCs simultaneously.

Coeval calc-alkaline and alkaline Cadomian magmatism in the Bafq, central Iran: Insights into their petrogenesis

The Chah-Gaz and Mishdovan areas in the Bafq magmatic complex, central Iran, contain thick series of terrigenous sediments (the Rizu-Dezu complex), and arc-related calc-alkaline and alkaline igneous rocks. Geochemical analyses of igneous rocks from both areas indicate two distinct rock clans: (1) high-K, calc-alkaline-shoshonitic rocks with strong depletions in Nb, P, and Ti, and (2) an alkaline quartz gabbro-diorite, with trace element patterns resembling oceanic island basalts (OIB). New geochronological data reveal that magmatic rocks of both clans crystallized almost simultaneously, with zircon UPb ages of 534 Ma and 537 Ma, respectively. The whole-rock NdSr isotopic data ((87Sr/86Sr)(I) = 0.7052 to 0.7064 and ɛNd(t) = +1.3 to +2.7) of alkaline quartz gabbro-diorite indicate an enriched OIB-like mantle source, while the high-K, calc-alkaline-shoshonitic rocks have εNd(t) = −5.5 to −7.6, clearly reflecting significant contributions from pre-existing Proterozoic basement. Apatite in both the Chah-Gaz and Mishdovan magmatic rocks is of magmatic origin, with light rare earth element (LREE) enrichment patterns. The low Sr/Y and Eu/Eu⁎ values in apatite demonstrate the non-adakitic character of the investigated rocks, while the moderately negative Eu anomaly and inverse correlation between δCe and δEu in the analyzed apatites may reflect reduced parental magmas. The geochemical and isotopic results presented here indicate that slab rollback and opening of an extensional basin could have initiated concurrent Cadomian arc-related calc-alkaline and rift-associated alkaline magmatism in the Chah-Gaz and Mishdovan areas.

Paleodiet reconstruction of human and animal bones at the Dalujiao cemetery in Early Iron Age Xinjiang, China

AbstractLong before the East–West “Silk Road” appeared, cultural communication as well as exchanges of materials and technologies had existed between different populations across the Eurasian Steppe. Xinjiang, located at a crossroads of the East and the West, is particularly important for exploring human interactions. The present paper contributes to this end from a stable isotopic perspective. Carbon and nitrogen stable isotope analysis were applied to 51 human and four animal bone remains collected from three types of tombs—namely, the earthen vertical tomb‐pit, earthen vertical tomb‐pit with second‐tier ledge, and earthen vertical tomb‐pit with side chamber—excavated from the Dalujiao cemetery, dated to the Early Iron Age (542 BCE–59 CE), in Xinjiang of northwest China. The δ13C (mean: −18.6 ‰) and δ15N (mean: 7.5‰) results of the faunal remains suggest that the two herbivore species (horse and sheep) were fed mainly by C3 terrestrial plants. By contrast, the human bone specimens differ in δ13C values (from −16.0‰ to −11.6‰, with a mean of −14.1‰ ± 1.1‰, n = 51). People buried in vertical tomb‐pits show a narrow range of δ13C values, an indication that they consumed quite stable sources of food. In contrast, those buried in vertical tomb‐pits with a second‐tier ledge or with a side chamber consumed more diverse foods and probably adopted different subsistence strategies. Taking into consideration both isotopic results and types of tombs, we propose that at least three groups of populations with diverse dietary and subsistence strategies are identifiable at the Dalujiao cemetery. Our study reveals not only human diets and subsistence patterns in the study area but also interactions among different populations prior to the rise of “Silk Road.”

Provenance and depositional history of the Mesozoic Sanjiang Basin (northeastern China): implications for the uplift history of the northeastern Asian continental margin

AbstractThe uplift history of northeastern Asian continental margin has been the subject of much debate. The Sanjiang Basin is an ideal area to investigate the uplift history of this margin. We present new data from sandstone petrology, whole-rock geochemistry, U–Pb geochronology and Hf isotopy of detrital zircons to trace the provenance of the basin and to unravel the uplift history of the northeastern Asian continental margin. We investigated the chemical and plagioclase indices of alteration and index of compositional variability (CIA, PIA and ICV, respectively) in samples from two formations. The geochemical proxies indicate that source rocks were subjected to an intensified weathering process. Based on the high SiO2/Al2O3 values and low K2O, we infer that the two basinal strata experienced silicification and insignificant potassium metasomatism. Sandstone petrography is indicative of low degrees of sedimentary sorting, suggesting a proximal deposition. The provenance fingerprints of light rare earth, high-field-strength and transition metal elements indicate that parts of the provenance included recycled sediments, and that first-cycle sediments were derived mainly from felsic rocks with a minor contribution from intermediate and mafic rocks. The combined detrital zircon U–Pb ages and Hf isotopic results constrain the contributions of different source terranes over time. The provenance results, in combination with seismic profile interpretations from the Sanjiang Basin, suggest that the northeastern Asian continental margin experienced at least three stages of uplift, which were driven by subduction initiation of the Paleo-Pacific Ocean during the Jurassic Period, a plate motion change during the Early Cretaceous Epoch, and a shallowing of the slab dip angle during the Late Cretaceous Epoch.

Mechanism of anomalous manifestations δ13C CO2 underground water on Tashkent geodynamic range

The results of long-term isotope and gas measurements of various groundwater sources in the Tashkent artesian basin are presented. In addition to areal studies, the results of regime observations of selected wells at the Tashkent geodynamic test site are also presented to identify prognostic features as a precursor to strong earthquakes. The first results were obtained related to the manifestation of the Nazarbek earthquake on December 11, 1980, with a magnitude of 5.3, a source depth of 10 km. On the basis of this earthquake, the behavior of isotopic and gas precursors at the Ulugbek well, Tashkent geodynamic test site, was analyzed. A quantitative analysis was made of the anomalous manifestation of the gas and isotopic composition of groundwater in the Ulugbek borehole during the preparation and execution of the Nazarbek earthquake. Determination of CO2 release from rock samples recovered from deep wells of the landfill made it possible to quantify the ratio of “background” CO2 mixing from carbonate decomposition to anomalous. Judging by the obtained ratio, the rocks during the preparation of the earthquake should emit 2 times more carbon dioxide than the background CO2. This was confirmed by observations of the CO2 content in the well, when an increase in its relative concentration of 250% was recorded. The analysis of the δ13C time series, obtained as a result of long-term regime observations of the carbon isotopic composition of CO2 in the groundwater of the Tashkent geodynamic test site, made it possible to identify significant anomalies in the carbon content.

The potential of marine bivalve Spisula sachalinensis as a marine temperature record

• The potential of Spisula sachalinensis as a high resolution temperature indicator • δ 18 O inversely correlates to seasonal ocean temperature but δ 13 C is less cyclical • Annual growth lines are formed during the warmest part of the year • Annual and non-annual growth lines are distinguishable via stable isotope analysis • Archaeological S. sachalinensis offer a valuable regional palaeoclimate record This paper presents a four year subannual isotope marine temperature record using modern Spisula sachalinensis specimens from Tomakomai (Hokkaido's Pacific coast, Japan). This species is commonly found in pre- and protohistoric shell middens and faunal assemblages from around the Seas of Japan and Okhotsk, so has significant potential as an indicator of past marine and, by inference, climatic conditions. However, previous sclerochronological research on the species’ growth has shown significant geographical variation in growth pattern, rendering palaeoclimatic interpretation difficult. To address this issue, this study applied sequential isotopic analysis to two sectioned modern valves, providing a proxy for sea surface temperature (SST) and allowing the direct identification of seasonality during shell growth. The sequences span four years of growth, as confirmed by visually identified growth patterns and the oxygen stable isotope results, which show clear annual cycles in δ 18 O. δ 13 C seasonality is less clear, but shows a weak inverse correlation with temperature potentially relating to primary productivity. Annual growth lines show that shell growth occurs during both warmer and cooler SSTs, but is more rapid during the cooler seasons. This is consistent with warm-season growth minima seen in shells from Hakodate Bay by Kato and Hamai (1975) , but not with their suggestion that it is associated with shells growing at the southern limits of their distribution. Comparison to average local SST shows that δ 18 O-derived temperature falls within the expected range, but, contrary to expectations given preferential cool-season shell growth, appears biased towards warmer temperatures. Factors that could contribute to this are discussed. Overall, stable isotope analysis of Spisula sachalinensis is considered a useful complement to macro/microscopic sclerochronological research in building a holistic picture of shell growth, and has significant potential as a high resolution proxy for palaeoenvironmental studies of past SST.

Exploring the paleoceanographic changes registered by planktonic foraminifera across the Cenomanian-Turonian boundary interval and Oceanic Anoxic Event 2 at southern high latitudes in the Mentelle Basin (SE Indian Ocean)

Planktonic foraminiferal population dynamics and benthic foraminiferal and radiolaria distributions combined with δ13C and δ18O measurements of both bulk carbonate and foraminifera provide clues concerning the paleoceanographic changes across the Cenomanian-Turonian boundary interval and the Oceanic Anoxic Event 2 (OAE 2) at southern high latitudes. Samples analyzed are from Integrated Ocean Discovery Program (IODP) Expedition 369 Site U1516 in the Mentelle Basin (eastern flank of the Naturaliste Plateau, Indian Ocean, SW Australia). Site U1516 was located at 60°–62°S paleolatitude during the mid-Cretaceous, and it is the first high latitude locality in the Southern Hemisphere where planktonic foraminifera are consistently recorded across the OAE 2 interval and its associated positive δ13C excursion. The sedimentary record at Site U1516 consists of a sequence of alternating black, dark greenish gray, and light greenish gray claystone in the Cenomanian that grade to white and light gray calcareous chalk interbedded with chert in the Turonian. The correlation between the δ13C and δ18O profiles at Site U1516 and the European reference section at Eastbourne (England) coupled with the integrated calcareous plankton biostratigraphy and stable isotopic data at Site U1516, indicate that a complete record of OAE 2 at Site U1516 was recovered. Below and in the lower part of OAE 2, the planktonic foraminiferal assemblages are dominated by small-sized (125–38 μm) opportunistic species of Microhedbergella and radiolaria indicating a dominantly eutrophic regime. Above the onset of OAE 2, a trough in the δ13C profile (Plenus Carbon Isotope Event: P-CIE) coinciding with a δ18O increase may correspond to the Plenus Cold Event as observed at low latitudes, although no evidence of cooling is registered in the microfossil assemblages. At Site U1516, the middle part of OAE 2 at the initiation of the plateau phase of the δ13C profile is masked by absence of carbonate, by the highest TOC values, and high biogenic silica (dominance of radiolaria) indicating this interval corresponded to a time of highly stressed eutrophic conditions with possible shoaling of the Carbonate Compensation Depth (CCD). Above this interval, bulk isotopic results yield lower δ13C values, and the CaCO3 increases are associated with the presence of even smaller-sized Microhedbergella showing cyclic fluctuations in absolute abundances with benthic foraminifera indicating dominantly eutrophic conditions likely affected by upwelling of nutrient-rich and δ13C-depleted intermediate water masses. Toward the top of OAE 2 and across the Cenomanian-Turonian boundary interval, the planktonic foraminiferal assemblages show changes in composition (e.g., Microhedbergella is replaced by Muricohedbergella), species occupying relatively deep ecological niches appear and an overall increase in diversity is observed. These features coupled with the foraminiferal species-specific δ13C and δ18O patterns reveal that Site U1516 occupied a paleoceanographic setting still affected by eutrophy likely related to enhanced input of nutrients but with episodes of stability with ecological/thermal separation in the surface waters. This interval also records the highest sea surface water paleotemperatures values estimated as 20°–23°C based on δ18O values of foraminiferal test and assuming seawater δ18O values of −1‰V-SMOW. Mesotrophic to oligotrophic conditions persisted after the OAE 2 and throughout the Turonian as evidenced by a diverse planktonic foraminiferal assemblage with different species occupying separate ecological niches in the mixed layer and thermocline.

Big data and environmental sustainability based integrated framework for isotope hydrology applications in India

Water contains environmental isotopes, which can act as tracers to study the source, origin, and distribution of water in the hydrological cycle. Recently, the environmental isotopes have been widely applied in hydrological investigations and it is established that the spatio-temporal variations in isotopic abundance provide valuable information to enhance the qualitative and quantitative understanding of hydrological processes such as mixing of different flow components and recharge rate, identify origin of water, delineation of groundwater recharge zones, geothermal dynamics, paleo-recharge and many others. Here, a review of case studies is presented to highlight the impact of isotope applications in water resource management in India. Along with a review of studies across India, a study is carried out for the assessment of groundwater interactions using isotopes of water (18O, 2H and 3H) in dry/semi-arid region (Jaipur) and wet/humid region (Guwahati). The major outcome of the study is the formulation of groundwater baseline for Guwahati (post-monsoon in 2017 and 2018: δD= 4.98 δ18O + 7.50) and Jaipur (post-monsoon and pre-monsoon in 2018: δD= 4.85 δ18O – 9.49). The results indicate that tritium has strong negative correlation (R2 = 0.59) with depth in Jaipur, indicating increasing groundwater age with depth. In Guwahati, the tritium shows weak positive (R2= 0.25) relationship which might be because of the presence of sandyclay layers in the shallow zone limiting vertical recharge to aquifer. Moreover, based upon the review and isotope results of the two study sites, a novel integrated framework for isotope hydrology application for India is proposed, incorporating the principles of environmental sustainability, economic efficiency and social equity. The isotopic techniques in hydrological investigations not only complements the traditional methods used in water resource management but also provides new insights and an enhanced understanding of the hydrological systems.