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A combination of nitrogen isotope analysis and X-ray photoelectron spectroscopy techniques was used to characterize nitrogen isotopic compositions and organic nitrogen forms in a total of 11 coal samples from China. A range of δ15N values between −2.9‰ and +3.6‰ was observed in all coals, and the N-5 peak is predominant. The results show that a correlation exists between the δ15N value and the proportions of the N-5 peak and the sum of the N-6 and N-Q peaks. This suggests that the nitrogen isotopic composition of coal may be controlled by the distribution of nitrogen forms. The pyridinic-structure nitrogen is enriched in 15N compared with the pyrrolic-structure nitrogen.

Atmospheric fine-particle (PM2.5) pollution is frequently associated with the formation of particulate nitrate (pNO3−), the end product of the oxidation of NOx gases (NO + NO2) in the upper troposphere. The application of stable nitrogen (N) (and oxygen) isotope analyses of pNO3− to constrain NOx source partitioning in the atmosphere requires knowledge of the isotope fractionation during the reactions leading to nitrate formation. Here we determined the δ15N values of fresh pNO3− (δ15N–pNO3−) in PM2.5 at a rural site in northern China, where atmospheric pNO3− can be attributed exclusively to biomass burning. The observed δ15N–pNO3− (12.17±1.55 ‰; n = 8) was much higher than the N isotopic source signature of NOx from biomass burning (1.04±4.13 ‰). The large difference between δ15N–pNO3− and δ15N–NOx (Δ(δ15N)) can be reconciled by the net N isotope effect (εN) associated with the gas–particle conversion from NOx to NO3−. For the biomass burning site, a mean εN( ≈ Δ(δ15N)) of 10.99±0.74 ‰ was assessed through a newly developed computational quantum chemistry (CQC) module. εN depends on the relative importance of the two dominant N isotope exchange reactions involved (NO2 reaction with OH versus hydrolysis of dinitrogen pentoxide (N2O5) with H2O) and varies between regions and on a diurnal basis. A second, slightly higher CQC-based mean value for εN (15.33±4.90 ‰) was estimated for an urban site with intense traffic in eastern China and integrated in a Bayesian isotope mixing model to make isotope-based source apportionment estimates for NOx at this site. Based on the δ15N values (10.93±3.32 ‰; n = 43) of ambient pNO3− determined for the urban site, and considering the location-specific estimate for εN, our results reveal that the relative contribution of coal combustion and road traffic to urban NOx is 32 % ± 11 % and 68 %± 11 %, respectively. This finding agrees well with a regional bottom-up emission inventory of NOx. Moreover, the variation pattern of OH contribution to ambient pNO3− formation calculated by the CQC module is consistent with that simulated by the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), further confirming the robustness of our estimates. Our investigations also show that, without the consideration of the N isotope effect during pNO3− formation, the observed δ15N–pNO3− at the study site would erroneously imply that NOx is derived almost entirely from coal combustion. Similarly, reanalysis of reported δ15N–NO3− data throughout China and its neighboring areas suggests that NOx emissions from coal combustion may be substantively overestimated (by > 30 %) when the N isotope fractionation during atmospheric pNO3− formation is neglected.

The degree to which ocean deoxygenation will alter the function of marine communities remains unclear but may be best constrained by detailed study of intervals of rapid warming in the geologic past. The Paleocene–Eocene Thermal Maximum (PETM) was an interval of rapid warming that was the result of increasing contents of greenhouse gases in the atmosphere that had wide ranging effects on ecosystems globally. Here, we present stable nitrogen isotope data from the Eastern Peri-Tethys Ocean that record a significant transition in the nitrogen cycle. At the initiation of the PETM, the nitrogen isotopic composition of sediments decreased by ~6‰ to as low as −3.4‰, signaling reorganization of the marine nitrogen cycle. Warming, changes in ocean circulation, and deoxygenation caused a transition to nitrogen cycle to conditions that were most similar to those experienced during Oceanic Anoxic Events of the Mesozoic., Studying the PETM, a past period of rapid warming ~56 Ma, could provide insights into ecosystem response under future warming conditions. Here, the authors present stable nitrogen isotope data that reveal a dramatic change in the marine nitrogen cycle and the emergence of anoxic conditions.

Although pesticides undergo degradation tests prior to use, determining their export, degradation and persistence under field conditions remains a challenge for water resource management. Compound specific isotope analysis (CSIA) can provide evidence of contaminant degradation extent, as it is generally independent of non-destructive dissipation (e.g., dilution, sorption, volatilization) regulating environmental concentrations. While this approach has been successfully implemented in subsurface environments, its application to pesticides in near-surface hydrological contexts at catchment scale is lacking. This study demonstrates the applicability of CSIA to track pesticide degradation and export at catchment scale and identify pesticide source areas contributing to changes in stable isotope signature in stream discharge under dynamic hydrological contexts. Based on maximum shifts in carbon stable isotope signatures ( Δ δ 13 C = 4.6 ± 0.5‰) of S-metolachlor (S-met), a widely used herbicide, we estimate maximum degradation to have reached 96 ± 3% two months after first application. Maximum shifts in nitrogen isotope signatures were small and inverse ( Δ δ 15 N = − 1.3 ± 0.6 ‰ ) indicating potential secondary isotope effects during degradation. In combination with a mass balance approach including S-met main degradation products, total catchment non-destructive dissipation was estimated to have reached 8 ± 7% of the applied product. Our results show that CSIA can be applied to evaluate natural attenuation of pesticides at catchment scale. By providing a more detailed account of pesticide dissipation and persistence under field conditions we anticipate the contribution of pesticide CSIA to the improvement of regulatory and monitoring strategies.

We report the nitrogen (N) isotope ratios (δ15N) of planktic foraminifera collected from upper-ocean net tows (surface to 200 m), moored sediment traps, and core-top sediments at the Bermuda Time-series Site in the northern Sargasso Sea between 2009 and 2013. Consistent with previous measurements from low-latitude core-top sediments, the annually-averaged δ15N of organic matter bound within the shells of euphotic zone-dwelling, dinoflagellate symbiont-bearing foraminifera collected in net tows (2.3‰ on average) approximates that of shallow thermocline (∼200 m) nitrate (2.6‰), the dominant source of new N to Sargasso Sea surface waters. Deeper-dwelling foraminifer species without dinoflagellate symbionts tend to have a higher δ15N (3.6‰ on average). We observe no systematic difference between the bulk tissue and shell-bound δ15N in net tow-collected foraminifera. A decline in shell N content is observed from net tows (6.8 nmol/mg) to sediment traps (5.4 nmol/mg) and surface sediment (3.0 nmol/mg). On average, shell-bound δ15N rises from net tows (3.1‰) to sediment traps (3.7‰) but does not change further upon incorporation into the sediments (3.7‰). Together, these observations are consistent with preferential loss of shells or shell portions with lower δ15N and higher N content during sinking through the upper 500 m, followed by a non-isotope fractionating decrease in N content between sinking and burial. Time-series data from sediment traps (and to a lesser extent, surface net tows) exhibit seasonal δ15N variations, with a minimum in early spring, a maximum in late spring and a decline from summer to fall. These variations appear to arise from seasonal changes in the δ15N of total upper-ocean biomass, which are, in turn, driven by early springtime nitrate supply, subsequent nitrate drawdown, and an increase in the relative importance of ammonium recycling into the late summer and early fall. The δ15N connection between total upper ocean biomass and foraminifera indicates that foraminifer-bound δ15N records the δ15N of the annual nitrate supply in oligotrophic (e.g., subtropical) environments but will also be sensitive to the degree of nitrate consumption in high-nutrient regions and possibly to changes in upper-ocean ammonium recycling under some conditions.

Nearly all extant animal phyla first appeared during the Ediacaran-Cambrian transition. A revolution in primary producer ecology and marine productivity has been proposed as a bottom-up ecological driver for this rapid diversification of metazoans. However, the control(s) driving the evolution of primary producers and primary productivity around the Ediacaran-Cambrian transition, and their potential relationship to the Cambrian Explosion, are not fully understood. In this study, we measured the nitrogen content and the nitrogen isotopic composition of kerogen in the Piyuancun and Hetang Formations, using samples collected from the Chunye-1 well, on the Lower Yangtze Block in western Zhejiang. Our isotope results suggest that nitrate was the dominant N source fueling primary productivity during deposition of the entire Piyuancun Formation and lower Hetang Formation, with only a minor contribution from N 2 fixation. Quantitative reconstructions of paleoproductivity based on organic carbon and pyrite content and sedimentation rate indicate that productivity either stayed the same or increased during the transition from the Piyuancun Formation to the overlying Hetang Formation. Thus, fixed N availability was not the ultimate factor limiting primary productivity during the Ediacaran-Cambrian transition. Combining our data with published nitrogen isotope records from the Early-Middle Ediacaran to Cambrian Stage 4 suggests that NO 3 − was the dominant N species fueling phytoplanktonic productivity during the broad Cambrian Explosion interval, from its earliest roots in the Ediacaran through the main episode in Cambrian Stage 3. Eukaryotes lack the ability to fix nitrogen, and preferentially assimilate nitrate. The NO 3 − -dominated euphotic zone from the Early-Middle Ediacaran to Cambrian Stage 3 may have promoted the radiation of relatively large eukaryote phytoplankton, which may have been an important driver of early animal diversification.

Hydrogen isotopes in archaeological human bone collagen are poorly understood, but present an opportunity to add new depth to our understanding of ancient populations. The competing influences of meteoric water versus protein intake on human bone collagen hydrogen isotope values were examined through comparison with the well-understood proxies of hydroxyapatite oxygen and collagen nitrogen isotopes, respectively. Consideration of the data set as individual points compared to averaged pools of individuals in each of 11 archaeological sites suggested the latter partially eliminates inherent variability due to food choice or regional movement. Collagen hydrogen isotopes were moderately correlated with hydroxyapatite oxygen isotopes (R = 0.695, site averages) and collagen nitrogen isotopes (R = 0.562, site averages). Correlation improved with a multiple linear regression including both oxygen and nitrogen (R = 0.745, site averages). Correlation between meteoric water hydrogen and oxygen isotope values converted from hydroxyapatite and collagen values, respectively, yielded a slope well below the expected value of ∼8 observed directly in meteoric water (i.e. the “meteoric water line”). Correlation between converted meteoric water hydrogen and the measured collagen non-exchangeable hydrogen isotope values showed a slope well below the expected value of 1.0. Theoretical meteoric water hydrogen isotope values and theoretical herbivorous collagen hydrogen isotope values were calculated based on previously established equations in order to construct a hypothetical framework free of trophic level influences. Deviations between actual values and these theoretical values correlated weakly with collagen nitrogen isotope values, suggesting that direct trophic level enrichment/depletion is not controlling the disparity between expected and measured values. The deviations are hypothetically caused by non-local food sources, and a decoupling of expected oxygen and hydrogen relationships as individuals consumed more meat and decreased in vivo non-essential amino acid production. This work presents a new model that facilitates understanding of the complex relationship between meteoric water and protein intake controls on hydrogen isotopes in omnivorous human populations that can potentially inform about past meteoric water values and amounts of animal protein consumption.

Soil organic matter (SOM) often increases with the abundance of short-range-ordered iron (SRO Fe) mineral phases at local to global scales, implying a protective role for SRO Fe. However, less is known about how Fe phase composition and crystal order relate to SOM composition and turnover, which could be linked to redox alteration of Fe phases. We tested the hypothesis that the composition and turnover of mineral-associated SOM co-varied with Fe phase crystallinity and abundance across a well-characterized catena in the Luquillo Experimental Forest, Puerto Rico, using dense fractions from 30 A and B horizon soil samples. The δ13C and δ15N values of dense fractions were strongly and positively correlated (R2 = 0.75), indicating microbial transformation of plant residues with lower δ13C and δ15N values. However, comparisons of dense fraction isotope ratios with roots and particulate matter suggested a greater contribution of plant versus microbial biomass to dense fraction SOM in valleys than ridges. Similarly, diffuse reflectance infrared Fourier transform spectroscopy indicated that SOM functional groups varied significantly along the catena. These trends in dense fraction SOM composition, as well as ∆14C values indicative of turnover rates, were significantly related to Fe phase crystallinity and abundance quantified with selective extractions. Mossbauer spectroscopy conducted on independent bulk soil samples indicated that nanoscale ordered Fe oxyhydroxide phases (nano-goethite, ferrihydrite, and/or very-SRO Fe with high substitutions) dominated (66–94%) total Fe at all positions and depths, with minor additional contributions from hematite, silicate and adsorbed FeII, and ilmenite. An additional phase that could represent organic-FeIII complexes or aluminosilicate-bearing FeIII was most abundant in valley soils (17–26% of total Fe). Overall, dense fraction samples with increasingly disordered Fe phases were significantly associated with increasingly plant-derived and faster-cycling SOM, while samples with relatively more-crystalline Fe phases tended towards slower-cycling SOM with a greater microbial component. Our data suggest that counter to prevailing thought, increased SRO Fe phase abundance in dynamic redox environments could facilitate transient accumulation of litter derivatives while not necessarily promoting long-term C stabilization.

Isotopic investigations of human burials from excavations of the Autonomous University of Campeche (CIHS) at the prehispanic Maya capital of Calakmul in southeastern Mexico, near the border with Guatemala, include determination of radiocarbon dates; carbon and nitrogen isotope ratios in collagen; and strontium, carbon, and oxygen isotope ratios in tooth enamel. A total of 22 human and 5 faunal samples analyzed for strontium isotopes reveal a narrow range of variation in values, pointing to the likely local origin of over two-thirds of the central population of Calakmul, including two of its rulers. Carbon and nitrogen data confirm a typical Classic Maya diet at the site and identify a diet high in meat consumption for one dynastic individual. Interpreted jointly, the isotopic information offers new perspectives on the provenience and lifestyles of the residents of Calakmul, including a potential place of origin for the royal occupant of chamber tomb Burial VII-1.

The successive outbreak of large-scale Ulva prolifera green tides in the Yellow Sea, China, from 2007 to 2017, is a serious regional environmental issue that attracts worldwide attention. The competitive advantage in nitrogen uptake and utilization is an important factor, making U. prolifera the dominant green-tide-forming seaweed. However, the detailed preference characteristics of U. prolifera for nitrogen uptake and assimilation in common inorganic and organic nitrogen sources is poorly understood and is studied using stable nitrogen isotope (15N) analysis. Our results reveal that various nitrogen sources can be simultaneously and directly taken up by U. prolifera. The uptake rates are in the sequence of NO3− (nitrate) > NH4+ (ammonium) > CO(NH2)2 (urea) > C2H5NO2 (glycine) and C3H7NO2 (alanine). In other words, U. prolifera mostly prefers inorganic nitrogen, such as nitrate and ammonium, although it can also utilize different organic nitrogen sources simultaneously. Moreover, the assimilation of NH4+ is inhibited and its uptake cannot be fitted by the Michaelis–Menten equation when the alga is exposed to multiple nitrogen sources. We propose that at the early and middle stages of green tides the rich inorganic nitrogen sources (especially NO3−) in seawater are very important to support the fast growth of U. prolifera, while at the later stage of green tides, when inorganic nitrogen sources have been exhausted, organic nitrogen sources may contribute importantly to maintaining the growth of U. prolifera, thus lengthening the duration of green tides.

RATIONALE: Stable isotope analysis integrates diet information over a time period specific to the type of tissue sampled. For metabolically active skin of free-ranging cetaceans, cells are generated at the basal layer of the skin and migrate outward until they eventually slough off, suggesting potential for a dietary time series. METHODS: Skin samples from cetaceans were analyzed using continuous-flow elemental analyzer isotope ratio mass spectrometery (EA-IRMS). We used ANOVAs to compare the variability of δ(13)C and δ(15)N values within and among layers and columns (“cores”) of the skin of a fin, humpback, and sperm whale. We then used mixed-effects models to analyze isotopic variability among layers of 28 sperm whale skin samples, over the course of a season and among years. RESULTS: We found layer to be a significant predictor of δ(13)C values in the sperm whale’s skin, and δ(15)N values the humpback whale’s skin. There was no evidence for significant differences in δ(15)N or δ(13)C values among cores for any species. Mixed effects models selected layer and day of the year as significant predictors of δ(13)C and δ(15)N values in sperm whale skin across individuals sampled during the summer months in the Gulf of Alaska. CONCLUSIONS: These results suggest that skin samples from cetaceans may be subsampled to reflect diet during a narrower time period; specifically different layers of skin may contain a dietary time series. This underscores the importance of selecting an appropriate portion of skin to analyze based on the species and objectives of the study.

Excavations at several locations in Verteba Cave have uncovered a large amount of human skeletal remains in association with faunal bones and Tripolye material culture. We aim to establish radiocarbon (14C) dates for eight sites and to evaluate whether these deposits are singular events, or slow accumulations over time.14C measurements, along with stable carbon and nitrogen isotope data from human and faunal remains, were collected from 18 specimens. Stable isotope values were used to evaluate human and animal diet, and whether freshwater reservoir effects offset measured dates. We found diets of the sampled species had limited to no influence from freshwater resources. Human diet appears to be dominated by terrestrial plants and herbivores. Four new sites were identified as Eneolithic. Comparisons of dates from top and bottom strata for two sites (7 and 20) reveal coeval dates, and we suggest that these deposits represent discrete events rather than slow continuous use. Lastly, we identified dates from the Mesolithic (8490±45 BP, 8765±30 BP), Iron Age (2505±20 BP), Slavic state era (1315±25 BP), and Medieval Period (585±15 BP), demonstrating periodic use of the cave by humans prior to and after the Eneolithic.

The Early Cambrian is a key interval in the global development of biological evolution, in which occurred many important environmental events and organic-rich sedimentary layers were deposited, which formed important hydrocarbon source rocks. The Lower Cambrian Niutitang Formation is one of the most important marine sedimentary layers in the Yangtze region, South China, and it records abundant important geological information that can be used for the reconstruction of the Lower Cambrian paleo-climates and paleo-environments. Nitrogen isotope compositions record and reflect variations in the original sedimentary environment and the redox conditions of marine ecosystems. Trace elements are also reliable indicators of sedimentary environments. In this study, we collected samples from the Lower Cambrian Niutitang Formation shale in the upper-middle Yangtze region of South China and measured the nitrogen isotope values of bulk sediments (δ15Nbulk), as well as their organic carbon isotope values (δ13Corg), total organic carbon (TOC) contents, total nitrogen (TN) contents and trace element concentrations. The δ15Nbulk values of the Niutitang shale range from 0.6‰ to 2.8‰, they show a certain positive excursion from bottom to top in the longitudinal direction, and they exhibit a significant correlation with the longitudinal variations in trace elements. These trace element characteristics suggest that the lower section of the Niutitang Formation existed in a strongly reduced sedimentary environment and was located in a hydrothermally active layer. During the deposition of the lower section of black shale, the nitrogen cycle was dominated by anaerobic nitrogen fixation; thus, its nitrogen isotope values are relatively lighter. In contrast, during the deposition of the upper section of the Niutitang Formation, the redox conditions of water column were unstable, the oxygen contents increased, and oxygenated reactions were intermittent or localized; thus producing relatively strong isotopic fractionation and causing the δ15Nbulk values in the upper section of black shale to exhibit a positive excursion. We conclude that the sedimentary environment is the key factor affecting nitrogen isotopes and that the redox conditions of the water column exhibit a significant correlation with the nitrogen isotope values.

Eutrophication, mainly caused by the oversupply of nitrate (NO3−) and phosphate, has become a serious environmental problem in Xiangshan Bay (east China), but the sources of the nitrate are poorly understood. In this study, the estuarine distributions of dual stable isotopes (δ15N and δ18O) of NO3− measured in May 2012 were used in combination with concurrent measurements of salinity, pH, dissolved oxygen, and nutrients (nitrate, nitrite, ammonium, and phosphate) to investigate NO3− sources and the processes that control NO3− distributions within the bay. In the lower bay, high concentrations of NO3− (up to 60.6 μmol L−1), an N/P ratio of 52, and low values of nitrate δ15N (δ15NNO3 = 5.7‰–6.7‰) and δ18O (δ18ONO3 = 1.8‰–3.5‰) indicate that NO3− in this area was likely from the Changjiang and Qiantangjiang rivers as well as local nitrification-associated inputs. In the upper bay, constituent concentrations and high values of δ15NNO3 (up to 8.8‰) and δ18ONO3 (up to 6.8‰) suggest that NO3− distributions here were controlled mainly by the mixing of coastal and fresh waters, phytoplankton assimilation, and inputs of riverine NO3−, possibly derived from manure and sewage. Spatial variations of Δ(15,18), the nitrate δ15N-to-δ18O anomaly, is possibly resulted from the different water residence times across the bay, which could in turn lead to different degrees of nitrification or variable amounts of NO3− from atmospheric deposition.

The organic and inorganic carbon cycles in lakes are responsive to both natural climate variability and human-induced environmental changes. Here we present an 8600-year sediment record from Xingyun Lake in Yunnan, China that provides insight into carbon cycling and lake primary productivity using stable isotope measurements of organic carbon and nitrogen, carbon to nitrogen ratio, inorganic carbon isotopes, and mass accumulation rates of carbon, nitrogen, and calcite. The early to middle Holocene is characterized by relative stability in most proxies although some variation in organic carbon isotopes reflects fluctuating terrestrial organic matter inputs. The middle to late Holocene, from 5300 to 3300 years BP, is marked by amplified variability in nearly all proxies and suggests either increased C4 vegetation or increased primary productivity. These changes are coincident with declining lake levels and increased aridity throughout the Indian Summer Monsoon region. After 3300 years BP, the greatest variability is in nitrogen isotopes and coincides closely with human settlement in the region. These changes are accompanied by further indications of increased primary productivity, suggesting eutrophic lake conditions. While we cannot definitively link human activity to these changes, the balance of evidence suggests that other mechanisms are unlikely. This study supports previous work that anthropogenic activities began measurably impacting the landscape in southwestern China within the last few millennia.

Rationale Nitrogen and carbon stable isotope ratios (δ15 N and δ13 C values) of carbonate-bound organic materials in otoliths can provide information to address the biological and ecological functions of fish. Correct interpretation of otolith δ15 N and δ13 C profiles requires knowledge of the metabolic routes of nitrogen and carbon isotopes. However, the isotopic assimilation of δ15 N and δ13 C compositions from diets to otoliths has rarely been investigated. Methods This study traced the daily nitrogen and carbon isotopic assimilation between diets and otoliths using nanoscale secondary ion mass spectrometry (NanoSIMS). Isotopically labeled algae (Tetraselmis chui) were fed to tilapia (Oreochromis niloticus) for 14-17 days. NanoSIMS and conventional isotope ratio mass spectrometry were used to measure δ15 N and δ13 C variations in the otoliths and fish muscle, respectively. Results Otolith δ15 N values abruptly surged from natural abundance levels by 1000-2300‰ after the fish ate 15 N-spiked algae with δ15 N values of approximately 2200‰. However, the δ15 N values of fish muscle increased to only approximately 500‰ at the end of the feeding experiment. Much higher δ15 N values (3700-14 000‰) and moderate δ13 C values (60-200‰) were detected in the otoliths after the tilapia ate 15 N- and 13 C-spiked algae with a δ15 N value of 36667‰ and a δ13 C value of 272‰. Mapping analysis showed sub-micrometer-scale distribution of 15 N embedded in the otolith growth increments with a low-to-high δ15 N signal after the tilapia shifted diets from non-spiked to 15 N-labeled algae. Conclusions These results suggest that otolith nitrogen and carbon isotopes from food were directly assimilated on the same day. Food is the major and in some cases only source of otolith nitrogen isotopes but makes only a partial contribution to otolith carbon isotopes. Therefore, the δ15 N values recorded in the sclerochronological layers of the otoliths can be used to determine the trophic levels, food sources and diet changes of fish.

The Late Neolithic and Chalcolithic periods are poorly understood in northeastern Iberia. Most of the information comes from the sepulchral structures rather than habitat settlements. The high number of individuals usually recovered from this types of collective burial spaces, together with the low number of direct radiocarbon dates available on them, forces us to be cautious and consider all the studied assemblages as belonging to the so-called Late Neolithic-Chalcolithic time period. To evaluate human dietary patterns of the Late Neolithic-Chalcolithic populations from the northeast of Iberia, stable carbon and nitrogen isotope analysis was carried out on 78 humans and 32 faunal bones from Cova de la Guineu (Font-rubi, Barcelona) and Cueva de Abauntz (Arraitz, Navarra), both of them sepulchral sites. Results show a common dietary pattern in both sites, indicating an homogeneous protein diet based on C3 terrestrial resources and no isotopic evidence of the consumption of C4 plants. Only one individual from Cueva de Abauntz, who directly dates to the first moments of the use of the cave as a burial place, suggests a different protein intake. The inter-population analysis shows a significant difference between both human and faunal δ13C values, suggesting an environmental influence on the isotope values depending on the geographic location. This effect should not be discarded and always assessed with baseline isotopic values in future studies at each area of Iberia and for different chronological moments.

The Wudalianchi scenic area in NE China has been named an UNESCO “Global Geopark” and “Biosphere Reserve.” During this investigation, the sources of nitrate and the hydrologic system through which it is dispersed were assessed using geochemical data and a multiple isotopic approach. The cold waters from the south and north springs originated from the deep subsurface. Isotopically, these waters exhibited relatively negative δD and δ18O values and nitrate in the water was substantially depleted 15N, suggesting that the mineral water was primarily derived from depth. Lakes within the Wudalianchi region were primarily composed of water from these deep mineral springs and precipitation. Chemical fertilizers were the primary source of nitrate to the Wudalianchi lakes. Groundwater was found in shallow mineral springs and wells plotted above the local meteoric water line, implying that shallow groundwater was primarily derived from precipitation. Elevated concentrations of nitrate in shallow mineral springs and well waters during the summer, autumn, and winter suggest that shallow groundwater within the Yaoquan volcanic area was also polluted by nitrate from human activities. Denitrification of shallow groundwater is slow, reducing the potential for “self-remediation”. The concentration data are supported by nitrogen (N) isotope data; wells and springs exhibited N isotopic ratios between − 5‰ and + 5‰ (typical of fertilizers and precipitation) and exhibited higher oxygen (O) isotope values than water in the Wudalianchi lakes. These relationships suggest that nitrate in shallow mineral springs, wells, and lakes near the Yaoquan volcano was derived from the mixing of chemical fertilizers with local summer rainfall.

Greenland past temperature history can be reconstructed by forcing the output of a firn-densification and heat-diffusion model to fit multiple gas-isotope data (δ15N or δ40Ar or δ15Nexcess) extracted from ancient air in Greenland ice cores using published accumulation-rate (Acc) datasets. We present here a novel methodology to solve this inverse problem, by designing a fully automated algorithm. To demonstrate the performance of this novel approach, we begin by intentionally constructing synthetic temperature histories and associated δ15N datasets, mimicking real Holocene data that we use as “true values” (targets) to be compared to the output of the algorithm. This allows us to quantify uncertainties originating from the algorithm itself. The presented approach is completely automated and therefore minimizes the “subjective” impact of manual parameter tuning, leading to reproducible temperature estimates. In contrast to many other ice-core-based temperature reconstruction methods, the presented approach is completely independent from ice-core stable-water isotopes, providing the opportunity to validate water-isotope-based reconstructions or reconstructions where water isotopes are used together with δ15N or δ40Ar. We solve the inverse problem T(δ15N, Acc) by using a combination of a Monte Carlo based iterative approach and the analysis of remaining mismatches between modelled and target data, based on cubic-spline filtering of random numbers and the laboratory-determined temperature sensitivity for nitrogen isotopes. Additionally, the presented reconstruction approach was tested by fitting measured δ40Ar and δ15Nexcess data, which led as well to a robust agreement between modelled and measured data. The obtained final mismatches follow a symmetric standard-distribution function. For the study on synthetic data, 95 % of the mismatches compared to the synthetic target data are in an envelope between 3.0 to 6.3 permeg for δ15N and 0.23 to 0.51 K for temperature (2σ, respectively). In addition to Holocene temperature reconstructions, the fitting approach can also be used for glacial temperature reconstructions. This is shown by fitting of the North Greenland Ice Core Project (NGRIP) δ15N data for two Dansgaard–Oeschger events using the presented approach, leading to results comparable to other studies.

Isotopic analysis of zoological material in archaeological deposits may help identify the origin of predated individuals. Here we assess the utility of carbon, nitrogen, and sulfur isotope values in bone collagen from zooarchaeological remains for determining the degree to which prehistoric Trinidadians relied on terrestrial prey from coastal and inland localities, as well as how this may have changed over time. We analyzed bone collagen from a variety of marine and terrestrial vertebrates from three coastal Ceramic Age sites in southwestern Trinidad. We also collected and analyzed modern foliage from eight sites at varying distances from the ocean to establish expected isotopic values for coastal ( 10 km from the ocean) environments in the southwestern corner of the island. We anticipated that the earliest human inhabitants at these sites initially exploited marine and local (i.e., coastal) terrestrial prey, but that they eventually depleted local resources, necessitating harvesting terrestrial prey from further inland. Unexpectedly, we find no substantial or consistent isotopic trends over time within sites or among different sites. The majority of harvested prey likely lived 1.5–10 km from the ocean. The combination of nitrogen and sulfur isotope values is effective at distinguishing both plants and terrestrial prey from coastal versus inland localities. Although carbon is less informative at elucidating geographic origin, it is quite effective at distinguishing terrestrial and marine prey and may be useful for separating marine turtles from terrestrial tortoises when working with fragmented material. Results from this study can be used as a model for multi-isotopic research in other island and coastal continental settings.

The city of Gabii arose just east of Rome around the 8th century BC. By the Imperial period, it had all but collapsed, its habitation areas either abandoned or repurposed for industrial production. Burials within the city, however, may speak to the urbanization and collapse of Gabii. Twenty-one skeletons from the Imperial era (1st–3rd centuries AD) were analyzed for stable carbon and nitrogen isotopes in an effort to understand palaeodiet. Adults' diets are relatively homogeneous, particularly in comparison with samples from nearby sites dating to the same period, and reflect consumption of terrestrial meats and C 3 plants. Subadult diets do not reflect breastfeeding at the time of death. One individual with anomalous isotopes may have been an immigrant to Gabii.

The paper presents δ13C and δ15N isotope content measurements in human bones from 16 graves, being part of the Yampil Barrow Complex. From the results, conclusions may be drawn about the diet of barrow builders and users. It was based on vegetable foodstuffs and characterised by a varied share of terrestrial animal meat, depending on the period. High δ13C values suggest a share of C4-type plants in the diet, possibly millet.

Oh, Y.; Sohn, H.; Lee, D.; An, Y.-R.; Kang, C.-K.; Kang, M.G., and Lee, S.H., 2018. Feeding patterns of ‘Finless porpoise (Neophocaena asiaeorientalis)’ in the yellow sea as indicated by stable carbon and nitrogen ratios. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 386–390. Coconut Creek (Florida), ISSN 0749-0208.Finless porpoise (Neophocaena asiaeorientalis) is a representative marine mammal that has the largest habitat near the Korean coastal area. However, little information on their trophic ecology has been reported in Korea to date. The stable carbon and nitrogen isotope ratios from muscle samples (n = 60) were analyzed for their trophic ecology. The muscle tissues from the stranded or by caught porpoises in the Yellow Sea were obtained in 2015 (n = 37) and 2016 (n = 23) by Cetacean Research Institute in Korea. The averages of δ13C and δ15N for all the samples were −17.74 ‰ (S.D. = ±0.74 ‰) and 12.96 ‰ (S.D. = ±0.95 ‰), respectively. The mean isotopic values of the porpoise groups obtained from different seasons were −18.13 ‰ (±0.56 ‰) and 12.43 ‰ (±0.73 ‰) and −17.06 ‰ (±0.46 ‰) and 13.87 ‰ (±0.46 ‰) for summer (n = 38) and spring (n = 22), respectively, which were significantly different among the two seasons (t-test; p < 0.01, n = 60, respectively). These increasing isotope values from summer to spring reflected a shift in major prey sources. The small increasing in δ15N values could be caused partly by different body lengths of the porpoises. However, the most plausible reason for the large shift in δ13C value relative to δ15N could be a change from pelagic to benthic prey in the different seasons since benthic diets are reported for enriched δ13C over the pelagic diets. For better understanding, further validation should be conducted.

The data on the content of carbon and nitrogen isotopes in the blood samples of polar bears obtained in the present study confirm that polar bears in the Taimyr region (and the Kara-Barents sea population in general) are partly dependent on the resources of terrestrial origin. However the "terrestrial carbon" evidently reaches bears' tissues indirectly, via marine food webs utilizing organic carbon brought into the polar basin by Siberian rivers.

The δ15N of nitrate (NO3−) and particulate organic nitrogen (PON) was used to study the sources and fate of nitrogen in the impounded Maotiao River, southwest China. During months when the reservoi...

Between 2005 and 2009, 125 skeletons were excavated from the medieval (13th century CE) Hungarian archaeological site of Solt-Tetelhegy. While previous stable isotopic research has examined the diet of medieval European peoples, here we present the first such research conducted on a medieval Hungarian population. Stable carbon and nitrogen isotope analyses were conducted on dental enamel and dentin from first and second molars from 24 individuals to reconstruct their childhood diet, as well as from the rib bones of 21 of the same individuals to reconstruct their adulthood diet. The average enamel δ13C values is − 11.1‰, and the average for dentin δ13C values is 17.4‰. The bone apatite δ13C values have a mean of − 10‰, while the bone collagen δ13C values have a mean of − 17.1‰. These data suggest that C3 plants were the dominant plant type consumed by the majority of the study population, although varying quantities of C4 plants were also eaten, supporting other archaeological evidence that C3 plants were consumed more often than C4 plants in medieval Europe. The dentin δ15N values average at 10.6‰, and the bone δ15N values average at 9.8‰, showing that animal protein constituted a moderate proportion of the diet. Despite signs of status differences indicated by burial location, stable nitrogen isotope values also suggest that the individuals had relatively egalitarian access to animal protein.

Trophic dynamics are often described by following the exchange of naturally occurring isotopes through aquatic communities. However, without experimentally derived isotopic turnover rates and discrimination factors for each species, tissue, and life stage, these trophic models can be misleading. We conducted a laboratory diet shift experiment to describe isotopic turnover and discrimination in age-0 walleye (Sander vitreus) dorsal muscle and gutted carcass samples. Although turnover of dietary δ13C (half-life: 10–12 days) and δ15N (half-life: ∼13 days) signatures was relatively rapid, the diet change was undetected in both tissues during a short transitional period (up to 1.2 times shorter in muscle). Our discrimination estimates generally conform to those of other fishes (ΔCarbon= 0.91, ΔNitrogen= 1.6), but were 30%–50% higher in muscle tissues than in gutted carcass samples. The assumption that young walleye tissues are in equilibrium with their diet is untrue for weeks following a diet shift, and when incorporated, discrimination factors differ between tissues. We provide tissue-specific parameters that remove uncertainty associated with the analysis of field collected isotopic age-0 walleye data.

Ammonia degassing is a common process in natural alkaline waters and in the atmosphere. To quantitatively assess the nitrogen cycle in these systems, the essential parameter of nitrogen isotope fractionation factors associated with ammonia degassing is required, but still not constrained yet. In this study, we carried out laboratory experiments to examine the nitrogen isotope behavior during ammonia degassing in alkaline conditions. The experiments started with ammonium sulfate solution with excess sodium hydroxide. The reaction can be described as: NH4+ + OH− (excess) → NH3·nH2O → NH3 (g)↑. Two sets of experiments, one with ammonia degassing under static conditions and the other with ammonia degassing by bubbling of N2 gas, were carried out at 2, 21, 50, and 70 °C. The results indicate that kinetic isotopic effects are dominated during efficient degassing of ammonia in the bubbling experiments, which yielded kinetic nitrogen isotope fractionation factors αNH3(g)–NH3(aq) of 0.9898 at 2 °C, 0.9918 at 21 °C, 0.9935 at 50 °C and 0.9948 at 70 °C. These values show a good relationship with temperature as 103lnαNH3(g)–NH3(aq) = 14.6 − 6.8 × 1000/T. In contrast, isotopic effects during less efficient degassing of ammonia in the static experiments are more complicated. The results do not match either kinetic isotope fractionation or equilibrium isotope fractionation but sit between these two. The most likely cause is that back dissolution of the degassed ammonia occurred in these experiments and consequently shifted kinetic isotope fractionation toward equilibrium isotope fractionation. Our experimental results highlight complicated isotopic effects may occur in natural environments, and need to be fully considered in the interpretation of field data.

Stable nitrogen isotopes (δ15N) are used as indicators of trophic position (TP) of consumers. Deriving TP from δ15N of individual amino acids (AAs) is becoming popular in ecological studies, because of lower uncertainty than TP based on bulk δ15N (TPbulk). This method would also facilitate biomagnification studies provided that isotope fractionation is unaffected by toxic exposure. We compared TPAA and TPbulk estimates for a sediment-dwelling bivalve from two coastal sites, a pristine and a contaminated. Chemical analysis of PCB levels in mussels, sediments, and pore water confirmed the expected difference between sites. Both methods, but in particular the TPAA underestimated the actual TP of bivalves. Using error propagation, the total uncertainty related to the analytical precision and assumptions in the TP calculations was found to be similar between the two methods. Interestingly, the significantly higher intercept for the regression between TPAA and TPbulk in the contaminated site compared to the pri...

RATIONALE Squid is an important seafood resource for Asian and European countries. With the continuous development of processed squid products, an effective traceability system has become increasingly prominent. Here, we attempt to trace the fishery products of the main target species, jumbo squid (Dosidicus gigas), by using biochemical tracers. METHODS Carbon and nitrogen isotope ratios (δ13 C and δ15 N values) and fatty acid profiles were identified in squid from three harvest locations in the eastern Pacific Ocean by isotope ratio mass spectrometry and gas chromatography/mass spectrometry, respectively. Comparative analysis was used to evaluate the geographic variations in tracers and to identify the suitable discriminatory variables among origins. RESULTS Significant spatial variations were found in isotopic values and fatty acid profiles in squid muscle tissues, possibly because of different food availability and/or oceanographic conditions that each group experiences at a given location. The stepwise discriminant analysis indicated that δ15 N, C16:1n7, C17:1n7, C18:2n6, C20:1 and C20:4n6 were effective variables at differentiating origin. CONCLUSIONS Combined use of stable isotope ratios and fatty acid analyses could trace geographic origins of jumbo squid. This study provides an alternative approach for improving authenticity evaluation of commercial squid products.

Establishing links between migration patterns and trophic dynamics is paramount to ecological studies investigating the functional role habitats provide to resident and transient species. Natural tags in fishes, such as otolith chemistry and tissue stable isotopes, can help reconstruct previous environmental and dietary histories, although these approaches are rarely combined. A novel multiproxy natural tag approach was developed to estimate immigration patterns of juvenile Atlantic croaker Micropogonias undulatus, across contrasting salinity gradients in three subtropical estuaries of the western Gulf of Mexico. Juvenile young-of-year Atlantic croaker were collected along a latitudinal gradient that included positive, neutral, and negative estuaries, based on physicochemical (temperature, salinity, dissolved element) and isotopic (δ15N and δ13C) parameters. Otolith elemental chronologies of Sr/Ca and Ba/Ca were used to classify migratory types within each estuary, while tissue-specific isotope ratios revealed time since recent (liver~weeks) and longer term (muscle~months) diet shifts. Nitrogen isotopes in both liver and muscle tissues were highly correlated, suggesting tissue equilibrium and estuarine residence of at least 3 months, with geographic δ15N gradients reflecting the magnitude of anthropogenic nutrient enrichment within each estuary. Differences in isotopic equilibrium of muscle-liver δ13C values and variation in marginal edge otolith Sr/Ca and Ba/Ca suggested recent shifts in carbon source and habitat utilization, reflecting individualized movement across seascapes and connectivity of habitat mosaics. The multiproxy approach presented here identified diverse migration patterns and linked feeding and movement on regional (inter-estuary), local (intra-estuary), and individual scales to improve our understanding of habitat function across estuarine gradients.

Recent excavations at the sites of Strandvagen and Kanaljorden in Motala, Eastern Central Sweden, have unearthed complex and varied funerary remains from the Mesolithic. The two sites are situated ...

We report here stable nitrogen isotope values of amino acids and stable carbon and nitrogen isotope values of collagen in human (n = 18) and faunal remains from Tell el-Kerkh, which was a large settlement in the northern Levant during the Neolithic period. A unique outdoor communal cemetery involving > 240 individual burials was found in the Pottery Neolithic levels at Tell el-Kerkh. To test the hypothesis that the burial locations of individuals within the cemetery were determined by household units sharing food resources, we separated individuals from one layer into seven groups within the cemetery, and compared the isotope values of collagen, glutamic acid, and phenylalanine. The results of analysis of individual skeletons in the cemetery suggest that the early farmers had different isotope values based on their burial locations, perhaps indicating distinct household burial spaces.

Rationale Pesticide self-poisoning is a major method of suicide in many agricultural communities worldwide. In addition, there are a number of known crime cases related to people being harmed by insecticides. Methomyl, a prohibited insecticide in the Republic of Korea, has high toxicity and is frequently used for self-poisoning. In this study, we investigated the source of origin of methamyl in a fatal poisoning case using stable isotope ratio analysis. Methods Two bottles of Soju from a crime scene were seized and nine different brands of methomyl products were collected from the neighborhood for analysis. In addition, the gastric contents and energy drink from the person who had committed suicide were analyzed. Isotope analysis using GC/Isolink/IRMS was conducted to determine the source of the methomyl by comparing their carbon and nitrogen isotope ratios. Linear discriminant analysis was utilized to verify the results. Results Isotope ratio analysis showed that the isotope ratio ranges of methomyl found in the Soju, the gastric contents of the suicide victim, and the energy drink bottle were similar to those of a seized methomyl product, Samgong methomyl 2011 (SG11). Thus, it was assumed that SG11 was used in this fatal poisoning case. Conclusions This study demonstrates the potential of stable isotope ratio analysis for the determination of insecticide origin in fatal poisoning cases.

The Early Mississippian K-O (Kinderhookian-Osagean) carbon isotope (δ13C) excursion or TICE (mid-Tournaisian carbon isotope excursion) is one of the most prominent positive δ13C excursions of the Phanerozoic. Recent studies raise uncertainties about the representative shape (single vs. double spikes) and magnitude of this δ13C excursion (3‰ to ≥ 6‰ in South China; ≥ 5.5‰ in Europe; and ≥ 7‰ in North America) and the 3‰ unidirectional increase in nitrogen isotopes across the δ13C excursion, which is unanticipated considering the amount of organic carbon burial required to form the δ13C excursion and the resultant oxygen increase and global cooling. To test if stratigraphic completeness and spatial isotope variations caused such uncertainties, we have conducted paired carbonate carbon (δ13Ccarb), organic carbon (δ13Corg) and nitrogen (δ15N) isotope analyses across the K-O interval in two well-exposed sections of the southern Great Basin, western United States. The two sections represent proximal shallow-water and distal deep-water depositional settings of a west-dipping carbonate ramp. In the distal ramp section where no exposure surface is present, both δ13Ccarb and δ13Corg show double spikes with peak δ13Ccarb values up to 7‰ and a negative shift down to 4‰ between the peaks. In the proximal shallower-water section where two karstic disconformities are observed, δ13Corg shows similar double spikes but δ13Ccarb displays only a single peak with the highest value of 5.5‰. The missing δ13Ccarb spike is likely caused by diagenetic alteration below a karstic disconformity that lowered δ13Ccarb but not δ13Corg values, resulting in smaller magnitude of the δ13Ccarb excursion. These features suggest that the 7‰ magnitude and double spikes are more representative of the K-O δ13C excursion in the southern Great Basin. The smaller magnitude of the K-O δ13Ccarb excursion in some sections of the Great Basin and the TICE in other sections globally may have overprinted with local environmental/diagenetic signal or resulted from stratigraphic hiatus/truncation, which needs to be clarified in future research. The δ15N across the K-O δ13C excursion in the distal ramp section is decoupled from δ13C, with the majority of δ15N values around 4 ± 1‰ that do not show any obvious temporal trend. In contrast, δ15N values in the shallow-water section is coupled with the K-O δ13C excursion, with a 3‰ positive shift from 4‰ to 7‰ at the rising limb of the δ13C excursion and a negative shift from 7‰ to 1–2‰ at the falling limb of the δ13C excursion. The δ15N trend from the distal ramp section is, in some extent, comparable with that documented from a section in South China, while the coupled δ13C–δ15N pattern in the proximal section seems better explain the potential redox change across a prominent δ13C excursion. Considering the sensitivity of δ15N to redox conditions of depositional environments, a more comprehensive δ15N study in a broader paleogeographic context is required to better understand the interactions between carbon and nitrogen cycles across the K-O interval—a critical transition from the mid-Paleozoic greenhouse clime to Late Paleozoic Ice Age (LPIA).

This study explores the use of compound-specific nitrogen isotopes of amino acids (δ 15 N AA ) of coupled dissolved and particulate organic nitrogen (DON, PON) samples as a new approach to examine relative sources, transformation processes, and the potential coupling of these two major forms of N cycle in the ocean water column. We measured δ 15 N AA distributions in high-molecular-weight dissolved organic nitrogen (HMW DON) and suspended PON in the North Pacific Subtropical Gyre (NPSG) from surface to mesopelagic depths. A new analytical approach achieved far greater δ 15 N AA measurement precision for DON than earlier work, allowing us to resolve previously obscured differences in δ 15 N AA signatures, both with depth and between ON pools. We propose that δ 15 N values of total hydrolysable amino acids (THAA) represents a proxy for proteinaceous ON δ 15 N values in DON and PON. Together with bulk δ 15 N values, this allows δ 15 N values and changes in bulk, proteinaceous, and “other-N” to be directly evaluated. These novel measurements suggest three main conclusions. First, the δ 15 N AA signatures of both surface and mesopelagic HMW DON suggest mainly heterotrophic bacterial sources, with mesopelagic HMW DON bearing signatures of far more degraded material compared to surface material. These results contrast with a previous proposal that HMW DON δ 15 N AA patterns are essentially “pre-formed” by cyanobacteria in the surface ocean, undergo little change with depth. Second, different δ 15 N AA values and patterns of HMW DON vs. suspended PON in the surface NPSG suggest that sources and cycling of these two N reservoirs are surpisingly decoupled. Based on molecular δ 15 N signatures, we propose a new hypothesis that production of surface HMW DON is ultimately derived from subsurface nitrate, while PON in the mixed layer is strongly linked to N 2 fixation and N recycling. In contrast, the comparative δ 15 N AA signatures of HMW DON vs. suspended PON in the mesopelagic also suggest a possible PON source for some HMW DON in the mid-water column. Together, these results suggest that conversion of relatively labile ON to less labile DON by heterotrophic bacteria (a “microbial nitrogen pump”) may be the key pathway for production and alteration of DON in both the surface and the mesopelagic oligotrophic ocean. Finally, in contrast to THAA, δ 15 N values of the other-N were substantially less affected by heterotrophic alteration, which may be consistent with a larger than expected contribution of amino sugars, or other less labile nitrogenous organic molecules.

Great attention has been paid to the origin of anomalously low nitrogen isotope values during the Late Cretaceous. Nitrogen isotope values are often as low as − 3 ‰ and are typically less than + 2 ‰ , even in relatively organic matter-lean sediments. Here we evaluate nitrogen isotope variability during a relatively quiescent phase of the Late Cretaceous Greenhouse, between Oceanic Anoxic Events 2 and 3, using the black shales of Demerara Rise (DR). Selection of this site allows us to isolate some of the factors that control nitrogen cycle dynamics and contribute to low nitrogen isotope values. New N-isotope measurements from ODP Site 1259 reveal δ 15 N values that range from + 0.2 ‰ to −3.5‰ and oscillate by 1.5‰ to 3‰ over 1.6 million years (Ma). Temporal calibration of our data using a new astronomical time scale reveals a strong ∼100 thousand year (ka) eccentricity cyclicity in δ 15 N. We attribute this cyclicity to oscillations in the position of the intertropical convergence zone (ITCZ) over DR that modulate upwelling intensity, chemocline depth and the degree of 15N-depletion. We also recognize a statistically significant correlation ( p = 0.0022 ) between the TEX86 indices and δ 15 N, with the lowest δ 15 N corresponding to the highest TEX86 indices. This relationship suggests that the activity and ecology of ammonia oxidizing Thaumarchaeota and the δ 15 N of dissolved inorganic nitrogen utilized by primary producers are linked. We therefore interpret the observed variability in the δ 15 N data and TEX86 indices as primarily reflecting fluctuation of upwelling intensity and chemocline depth, and the significant inverse relationship between these data sets suggests that caution should be exercised when interpreting the TEX86 in terms of temperature in similar paleoenvironmental settings.

Stable isotope ratios (13C/12C and 15N/14N) of South African lambs from different regions were measured by isotope ratio mass spectrometry (IRMS). Homogenised and defatted meat of the Longissimus lumborum muscle was assessed. The Ruens and Hantam Karoo regions had the lowest (P≤0.05) δ13C values related to the presence of C3 plants (lucerne and Karoo bushes, respectively). The Northern Karoo, Namibia and Bushmanland had the highest δ13C values likely due to a high proportion of dietary C4 grass species. The δ15N values were highest for Central Karoo, Semi-extensive, Namibia and Hantam Karoo, while Ruens and Feedlot had the lowest nitrogen isotope values (P≤0.05). Classification of origin (Karoo vs. Non-Karoo) using discriminant analysis allowed 95% and 90% correct classification of the samples for the estimation model and validation models, respectively. The results confirm that IRMS provides sufficient discriminative power to classify lamb meat of varying origin.

The beginning of the Romano-British period in the 1st century AD was marked by changes in agriculture, economy and material culture at varying rates. Rural areas such as Oxfordshire may have been slower to incorporate Roman agriculture practices, possibly as a result of limited demand from urban centres or local conditions. In order to gauge the scope of agricultural continuity in rural areas, this study uses stable carbon and nitrogen isotope analysis of bone and tooth dentine collagen from forty cattle and sheep from five sites from the Chalk Downs of the Ridgeway and the adjacent Vale of the White Horse to determine where these animals grazed. While no significant differences in δ13C are present, the data show a clear distinction in δ15N values, suggesting that herds from the Downs and the Vale were largely kept separately, while a small number of outliers also suggest that some individual animals were moved between different pastures earlier in their lives. This mirrors very similar findings from the Early-Middle Iron Age in the same study area (Schulting et al., 2019), suggesting long-term continuity in at least some aspects of animal husbandry. The results of this study suggest that local environment and the identities of rural communities may have had a major impact in determining which agricultural practices were adopted or rejected.

The Ordovician-Silurian (O/S) transition was a critical geological interval, during which significant biological events and dramatic environmental changes occurred. Extensive research has proven that changes in the ocean environment are one of the main causes of events that affect the biosphere. However, the redox structure and related geochemical evolution of the ocean during the O/S transition remain under debate. N isotopes are thought to have significant potential for further elucidating the oceanic redox structure and related geochemical evolution during the O/S transition, and are an effective supplement to the former environmental proxies of bottom sediments. This study presents high-resolution N isotope data from a well-sequenced drill core across the O/S transition from the Lower Yangtze Platform, South China, showing an interesting isotopic variation with high δ15N values (+1‰ to +4‰) during the Late Katian to Hirnantian ages of the Ordovician and much lower values (−1‰ to +1‰) during the Rhuddanian Age of the earliest Silurian. This δ15N variation is mostly controlled by ocean redox conditions and the corresponding changes in the nitrate reservoir. Combined with previously reported δ15N data, a redox-stratified ocean with a relatively deep redox transition zone was reconstructed according to the distribution of δ15N profiles across different palaeogeographic locations. The lower δ15N values and more reducing conditions in deep water sections demonstrate that glacio–eustatic fall, rather than increased upwelling, was likely the main driver of the global redox change during the Late Ordovician. Furthermore, a global δ15N decrease during the Late Katian may be associated with the debated Boda warm event, and the up to six positive δ15N excursions observed during the Hirnantian might suggest the cyclicity of the glaciation process.

Our aim is to measure the interstellar 14N/15N ratio across the Galaxy, to establish a standard data set on interstellar ammonia isotope ratios, and to provide new constraints on the Galactic chemical evolution. The (J, K) = (1, 1), (2, 2), and (3, 3) lines of 14NH3 and 15NH3 were observed with the Shanghai Tianma 65 m radio telescope (TMRT) and the Effelsberg 100 m telescope toward a large sample of 210 sources. One hundred fourty-one of these sources were detected by the TMRT in 14NH3. Eight of them were also detected in 15NH3. For 10 of the 36 sources with strong NH3 emission, the Effelsberg 100 m telescope successfully detected their 15NH3(1, 1) lines, including 3 sources (G081.7522, W51D, and Orion-KL) with detections by the TMRT telescope. Thus, a total of 15 sources are detected in both the 14NH3 and 15NH3 lines. Line and physical parameters for these 15 sources are derived, including optical depths, rotation and kinetic temperatures, and total column densities. 14N/15N isotope ratios were determined from the 14NH3/15NH3 abundance ratios. The isotope ratios obtained from both telescopes agree for a given source within the uncertainties, and no dependence on heliocentric distance and kinetic temperature is seen. 14N/15N ratios tend to increase with galactocentric distance, confirming a radial nitrogen isotope gradient. This is consistent with results from recent Galactic chemical model calculations, including the impact of superasymptotic giant branch stars and novae.

For nitrogen (N) migration and transformation from unsaturated soil to groundwater, the N stable isotope (δ15N) was modified due to the isotope fractionation effect. To quantitatively evaluate the N cycle in groundwater systems, the determination of isotope fractionation is decisive. In this research, for the first time, incubation experiments were conducted to quantitatively investigate the N isotope enrichment factor (ϵp/s) associated with ammonification in unsaturated soil. Under weak isotopic fractionation, the Rayleigh function cannot be directly applied during ammonification. Thus, we proposed a different method calculating the ϵp/s values during ammonification, which were −0.03‰ for 15 °C and −2.34‰ for 30 °C. Moreover, for the first time, experimental equipment is presented to explore the isotopic fractionation effects under the co-occurrence of nitrification and volatilization. The results indicated that the isotope effect of volatilization during nitrification can be ignored in this study, and the ϵp/s values during nitrification were −10.59 and −6.81‰ at 15 and 30 °C, respectively. This work provides a novel arrangement determining the crucial parameters for identifying nitrate pollution sources in groundwater systems.

The δ13C, δ15N and C/N ratio of the particulate organic matter (POM) in western Guangdong waters were determined to evaluate the impacts of the coastal currents on the POM in spring and summer. The predominance of photosynthetic organic matter in the nearshore was triggered by nutrients brought by the coastal currents in spring and summer, while the proportion of terrestrial organic matter in the offshore was very high in spring but low in summer. In spring, the weaker and narrower coastal currents carried insufficient nutrients (phosphate deficiency) to the offshore and prohibited phytoplankton production. This scenario contributes to the dominance of terrestrial organic matter transported by the cyclonic circulation beyond the coastal currents in the offshore in spring. The Bayesian mixing model reveals that the proportion of terrestrial organic matter (with 75.8% of C3 plants) in the offshore was higher in spring than in summer (with 33.7% of C3 plants).

The surface distribution of lipid biomarkers, elemental and isotopic compositions ( δ 13 C and δ 15 N, C/N) were investigated from coastal sediments of Brunei Bay, in order to understand the sources and biogeochemical processes of the organic matter. Fatty acid biomarkers from terrestrial higher plants (e.g., long-chain fatty acids > 20), phytoplankton (e.g., 20:5n-3 and 22:6n-3) and microbial activity (e.g., iso-, anteiso fatty acids, 10Me-16:0) were identified. The ratios of carbon and nitrogen isotopes ( δ 13 C, δ 15 N) and C/N had values ranging from –30.62 to –27.43‰, 1.70 to 3.57‰, and 4.07 to 15.62 respectively, suggesting the prevailed inputs of terrestrially-derived organic matter sources with typical characterization of mangrove estuaries. Principal component analysis separated lipids of autochthonous aquatic production as the major source, followed by allochthonous terrestrial derived input. The presence of bacterial derived lipids and short chain lipids with low and C/N ratios suggest the preferential utilization and decomposition of organic matter by microbial activity. An enrichment of the δ 15 N ratios could be due to marine cage culture activities and surface runoff from cultivated areas via fluvial transport.