Isotopic Changes Research Articles

Effect of cocooning conditions on the structure, carbon and nitrogen isotope ratios of silks.

The stable isotope technique provides the possibility to trace ancient textiles because the technique is associated with advantages such as trace indication, fast detection, and accurate results. Since different cocooning conditions may impact cocoons even under identical habitats, it is important to investigate the effects of different cocooning temperatures and humidity on the isotope incorporation values in the cocoons. In this study, silk fibers were reeled under different conditions of temperature and humidity, followed by analysis of the secondary structure of cocoon proteins and isotope incorporation patterns. We found that the deviations in carbon isotope values of silk under different cocooning conditions could reach up to 0.76‰, while the deviation in carbon isotope values at different locations of a single silk was 2.75‰. Further, during the cocooning process, depletion of the 13C-isotope at different locations of the silk fibers was observed, reducing the δ13C values. We proposed that the changes in carbon isotopes in silk were related to the content of sericin and silk fibroin in silk. Finally, we did not observe a significant difference in isotope ratios in degummed cocoons. In summary, the 13C isotope was enriched in sericin, whereas 15N was enriched in fibroin, and these findings provide basic information for tracing the provenance of silks.

Holocene millennial-scale variability of coastal environments on the southern coast of Korea and its controlling factors

AbstractCoastal evolution is influenced by past sea-level changes and resultant shifts from fluvial- to marine-dominant environments and the accompanying significant geochemical and isotopic changes in the water mass and sediments. We investigated the elemental and isotopic features of coastal sedimentary cores (27 m in length) from a small paleo-bay located on the southern coast of Korea to determine such geochemical variability and specify past changes in the bay environment and anoxic conditions and possible links to past climate changes. We analyzed total organic carbon (TOC), total sulfur (TS), their isotopes (δ13CTOC and δ34STS), and pyrite. The δ13CTOC values ranging from −25 to −19‰ (a proxy for terrestrial influence) were lower than average (−22.5‰) before 8300 cal yr BP and since 500 cal yr BP, while the intervening Early to Late Holocene showed higher δ13CTOC values, indicating a shallow coastal environment. The δ34STS values fluctuating between −35 and +5‰ resembled sedimentation rate change. Based on the changes in the ratios of TOC to TS (C/S ratios), sedimentation rate, and δ34STS, we found five possible periods with higher salinity and intensified anoxic conditions at millennial timescales: 8900–8200, 7950–6500, 5200–4300, 3500–2600, and 2000–1100 cal yr BP. These intensified anoxic conditions seem to have been influenced by increased air temperature and sea-surface temperature conditions, which could have intensified the intensity of thermal stratification (less ventilation and mixing) between surface and bottom waters and resultant anoxic conditions.

Characteristics of Hydrogen–Oxygen Isotopes and Water Vapor Sources of Different Waters in the Ili Kashi River Basin

The Ili Kashi River Basin is an area with relatively abundant precipitation within the arid region of Northwest China. Using water samples from atmospheric precipitation, surface water, groundwater, and snow meltwater in the basin from July 2018 to June 2021, the isotope characteristics of the different water bodies in the study area were determined from the perspectives of altitude, season, and interannual changes. Combined with the meteorological data on precipitation and the HYSPLIT model, the water vapor sources of atmospheric precipitation in the Ili Kashi River Basin were tracked and analyzed. Studying the hydrogen and oxygen stable isotopes in the different water bodies in this area can provide substantial scientific support for the generation, development, and change processes of river water resources in Northwest China, and has practical significance for the utilization of water resources. The results derived are as follows. (1) Hydrogen–oxygen isotope changes in the Ili Kashi River Basin were broadly characterized by a continuous enrichment from low-to-high elevations in the summer to a maximum value, followed by gradual depletion, whereas the changes in δ18O and δD were reversed in autumn. (2) The river water values of δD and δ18O fluctuated between −107.15‰ and −68.13‰ and between −18.53‰ and −9.66‰, respectively, during the study period. (3) The variation in δ18O and δD in the precipitation was consistent, showing characteristics of summer enrichment and winter dilution, and the precipitation line equation is δD = 7.30δ18O + 9.29. (4) In autumn and winter, the groundwater δD and δ18O values fluctuated between −99.87‰ and −84.95‰ and between −15.50‰ and −10.38‰, respectively; during spring and summer, the δD and δ18O values varied from −99.27‰ to −87.07‰ and from −15.15‰ to −12.00‰, respectively. The hydrogen–oxygen stable isotope value of the ice–snow meltwater in autumn was higher than that in summer. (5) On the basis of the d-excess variation in each precipitation event over the 3 years and an analysis of the water vapor sources using the HPSPLIT backward trajectory tracking model, the source of water vapor in the study area is primarily the surrounding land water vapor, with the Atlantic Ocean being the main contributor of oceanic water vapor.

Experimental Characteristics of Hydrocarbon Generation from Scandinavian Alum Shale Carbonate Nodules: Implications for Hydrocarbon Generation from Majiagou Formation Marine Carbonates in China’s Ordos Basin

The hydrocarbon source rocks of the marine carbonates of the Ordovician Majiagou Formation in the Ordos Basin are generally in the high-overmature stage and are, therefore, not suitable for hydrocarbon thermal simulation experiments. Their hydrocarbon generation potential and hydrocarbon generation characteristics are not clearly understood. Meanwhile, Nordic Cambrian carbonates are similar in lithology, parent material type, and sedimentary age, and are in the low evolution stage, which is suitable for hydrocarbon thermal simulation experiments. Therefore, in this study, we selected the Nordic carbonates for the gold tube thermal simulation experiment to analyze the content and geochemical characteristics of the thermal simulation products. The experimental results are also compared and analyzed with the characteristics of thermal simulation products of Pingliang Formation mud shale (contemporaneous with the Majiagou Formation) and Shanxi Formation coal (in the upper part of the Majiagou Formation), which are similar to the Majiagou Formation in the Ordos Basin. The results showed that the Nordic carbonate has different hydrocarbon production characteristics from the mud shale of the Pingliang Formation of the same parent material type, and although the hydrocarbon production yields of the two are not very different, the carbonate still produces methane at 600 °C. The hydrocarbon production yield of the Nordic carbonates is almost equivalent to that of type-II2 kerogen, indicating that the hydrocarbon production yield is not related to lithology and only to the organic matter type; however, the Nordic carbonate can produce a large amount of H2S. The alkane carbon isotope changes are mainly controlled by the degree of thermal evolution, showing gradual heaviness with increasing temperature. No carbon isotope sequence reversal occurred during the thermal simulation, and its distribution range is roughly the same as that of the alkane carbon isotope composition of the mud shale of the Pingliang Formation. The ethane carbon isotope composition is as heavy as −21.2‰ at the high-temperature stage, showing similar coal-type gas characteristics. The addition of calcium sulphate (CaSO4) causes the TSR reaction to occur, which has a significant impact on the methane content under high maturity conditions, reducing its content by more than 50% at 600 °C. However, the addition of CaSO4 increases the yield of heavy hydrocarbon gases, such as ethane, and promotes the production of C6-14 hydrocarbons and C14+ hydrocarbons at high-temperature stages, and the addition of CaSO4 substantially increases the yield of H2, CO2, and H2S. The thermal simulation results have implications for the hydrocarbon formation mechanism of the early Paleozoic marine carbonate formation system in the stacked basins of the Ordos Basin and the Tarim Basin in China.

Response of Water Isotopes in Precipitation to a Collapse of the West Antarctic Ice Sheet in High-Resolution Simulations with the Weather Research and Forecasting Model

Abstract The West Antarctic Ice Sheet (WAIS) may have collapsed during the last interglacial period, between 132 000 and 116 000 years ago. The changes in topography resulting from WAIS collapse would be accompanied by significant changes in Antarctic surface climate, atmospheric circulation, and ocean conditions. Evidence of these changes may be recorded in water-isotope ratios in precipitation archived in the ice. We conduct high-resolution simulations with an isotope-enabled version of the Weather Research and Forecasting Model over Antarctica, with boundary conditions provided by climate model simulations with both present-day and lowered WAIS topography. The results show that while there is significant spatial variability, WAIS collapse would cause detectable isotopic changes at several locations where ice-core records have been obtained or could be obtained in the future. The most robust signals include elevated δ18O at SkyTrain Ice Rise in West Antarctica and elevated deuterium excess and δ18O at Hercules Dome in East Antarctica. A combination of records from multiple sites would provide constraints on the timing, rate, and magnitude of past WAIS collapse.

Early Cretaceous magmatism in Yunnan traces the tectonic transition from the Tengchong-Baoshan continental collision to Neo-Tethyan slab rollback

Early Cretaceous magmatic rocks of the Tengchong and Baoshan blocks provide insight into the late Mesozoic evolution of southeastern Tibet—Yunnan. We present LA-ICP-MS U-Pb zircon age, zircon εHf(t) isotope, and whole-rock geochemical and Sr-Nd isotopic data for dioritic porphyrite and rhyolite, outcropping in the Eastern Tengchong Belt and the Gaoligong Belt, respectively. The dioritic porphyrite has a 123.0 ± 1.3 Ma (2σ) age, negative whole-rock ℇNd(t) of −1.99 to −2.16, initial 87Sr/86Sr of 0.70690–0.70734, zircon ℇHf(t) of −1.42 to 4.11, and adakitic geochemical features, suggesting an origin from mixing of mantle- and crust-derived magmas; the rhyolite has a 122.2 ± 1.0 Ma age, low whole-rock ℇNd(t) of −9.69 to −8.83, initial 87Sr/86Sr of 0.71104–0.71246, and zircon ℇHf(t) of −8.55 to −2.59, suggesting crustal derivation. Our data—along with the published data—suggest that the Early Cretaceous rocks (140–109 Ma) comprise two magmatic phases with a geochemical and isotopic transition at ∼123 Ma. The 140–123 Ma phase—mainly outcropping in the Gaoligong Belt—is mainly peraluminous, highly silicic, and has negative zircon εHf(t) values, suggesting derivation from remelting of ancient crust in a postcollisional setting; the 123–109 Ma phase is mainly metaluminous, restricted to the Eastern Tengchong Belt, and formed in a continental-arc setting with mantle melt involved. We propose that the ∼123 Ma geochemical and isotopic change marks the transition from contraction due to the Tengchong-Baoshan collision to extension resulting from slab rollback of the Neo-Tethyan lithospheric slab.

Comparison of Intra-Event Characteristics of Hydrogen and Oxygen Stable Isotopes between Rainfall and Throughfall and the Effects of Pre-Event Precipitation

The isotopic composition of precipitation provides valuable information about its source and transportation. However, raindrops interact with vegetation before reaching the earth’s surface, leading to isotopic changes in the infiltrating water. Comparing isotopic composition between rainfall and throughfall helps to understand canopy processes and their impact on isotopic variation. Based on observational data collected during the periods of July 2019, July–August 2020, and July–August 2021 in a planted forest located in the southwest monsoon region of China, this study examines hydrogen and oxygen isotopes in rainfall and throughfall at event and intra-event scales, and investigates the effects of pre-event precipitation (PEP) on the isotopic composition. The results indicate that during the initial stage of precipitation, δ18O was enriched in rainfall and it presented a dilution effect gradually, while the d-excess exhibits a low initial value followed by an increasing trend. The difference in δ18O between throughfall and rainfall initially increased and subsequently converged around 0, whereas the difference in d-excess experiences a decreasing phase, followed by an increasing phase, and finally a decreasing phase. Canopy interception led to a lag effect during the early stage of precipitation; the forest exhibited higher water vapor content compared to open land in the intermediate stage, which reduced the degree of non-equilibrium fractionation in throughfall, and the flow pathway enhanced in the later stage. Evaporation processes become more prominent as precipitation intensity weakens. The rainfall and throughfall were influenced by distinct meteorological factors in different precipitation events, and the role of the forest canopy varied across different precipitation periods. PEP was found to augment the intercept and slope of the linear relationship between the H-O isotopic composition of throughfall and rainfall. This pre-event effect also contributes to heightened fluctuations in the δ18O and d-excess values during subsequent precipitation events. The findings contribute to understanding water dynamics, vegetation interception, and mechanisms governing water input in forested areas during precipitation events, which provides valuable insights for analyzing factors influencing water movement in forest ecosystems.

Provenance of deep-sea sediments in the eastern South China Sea since Marine Isotope Stage 5 (MIS 5) and implications for climate change and volcanic activity

The South China Sea deep-sea basin receives large amounts of marine sediments and volcanic materials from the surrounding continents and islands, and it is an ideal region to study the effects of climate change and volcanic activity on sediment provenance. Core K2 was collected in a water depth of 4078 m in the eastern South China Sea and is mainly composed of diatoms, tephra, volcanic glass and slag. The results of a total of 102 analysed grains show that the depositional processes were dominantly suspension, uniform suspension and overbank-pool facies suspension, with no rolling. Six accelerator mass spectrometry (AMS) 14C ages from planktonic foraminifers and fifty-four δ18O data points of G. ruber suggest that the age of Core K2 is 125 kyr before present (BP). Forty-four clay mineralogical data points show that the clay minerals in the sediments are mainly illite+chlorite (24.3%–49.7%), with a small amount of smectite (2.6%–11%), suggesting a sediment source mainly from Taiwan with a small amount of sediment from Luzon. Forty-five samples yield 143Nd/144Nd and 87Sr/86Sr ratios ranging from 0.512250 to 0.512769 and from 0.704383 to 0.710690, respectively, indicating that sediments in K2 represent a mixture of volcanic inputs from in or around Luzon and sediments from Taiwan and Luzon. Based on calculations of clay minerals and SrNd isotopic data, the relative proportions of sediments from Taiwan and Luzon and volcanic input vary from 8% to 88%, from 1% to 23% and from 0% to 91%, respectively, and the average proportions of sediments from Taiwan and Luzon and volcanic input are 55%, 12% and 33%, respectively. Significant temporal changes in SrNd isotopes are attributed to variations in the volcanic eruption intensity or distance to the sampling location. Moreover, high εNd values and low 87Sr/86Sr ratios of the sediments in Core K2 during interglacial periods could represent volcanic eruptions.

Isotope diffusion and re-equilibration of copper and evaporation of mercury during weathering of tetrahedrite in an oxidation zone

To understand the mobility of heavy metals during oxidative weathering of sulfides, we investigated weathering processes of tetrahedrite [(Cu,Fe,Zn,Hg)12(Sb,As)4S13] in an oxidation zone with abundant siderite (FeCO3) and baryte (BaSO4) at Rudňany (Slovakia). The focus of this work lied in the isotopic (δ65Cu, δ202Hg, δ34S) variations of the minerals during weathering and the interpretation of such changes. In the studied oxidation zone, Hg-rich tetrahedrite converts in situ to pockets of powdery cinnabar (HgS) and an X-ray amorphous mixture rich in Sb, Fe, and Cu that slowly re-crystallizes to Cu-rich tripuhyite (FeSbO4). Copper is mobile and precipitates as malachite [Cu2(OH)2(CO3)], azurite [Cu3(OH)2(CO3)2], or less abundant clinoclase [Cu3(AsO4)(OH)3]. The isotopic composition (δ65Cu) of tetrahedrite correlates well with the degree of weathering and varies between 0.0 ‰ and −4.0 ‰. This correlation is caused by isotopic changes during dissolution and subsequent rapid equilibration of δ65Cu values in the tetrahedrite relics. Simple diffusion models showed that equilibration of Cu isotopic values in the tetrahedrite relics proceeds rapidly, on the order of hundreds or thousands of years. Abundant secondary iron oxides draw light Cu isotopes from the aqueous solutions and shift the isotopic composition of malachite and azurite to higher δ65Cu values as the distance to the primary tetrahedrite increases. Clinoclase and tripuhyite have lower δ65Cu values and are spatially restricted near to the weathering tetrahedrite. The Hg and S isotopic composition of tetrahedrite is δ202Hg = −1.27 ‰, δ34S = −1.89 ‰, that of the powdery secondary cinnabar is δ202Hg = +0.07 ‰, δ34S = −5.50 ‰. The Hg isotopic difference can be explained by partial reduction of Hg(II) to Hg(0) by siderite and the following evaporation of Hg(0). The S isotopic changes indicate no involvement of biotic reactions in the oxidation zone, probably because of its hostility owing to high concentrations of toxic elements. This work shows that the Cu isotopic composition of the primary sulfides minerals changes during weathering through self-diffusion of Cu in those minerals. This finding is important for the use of Cu isotopes as tracers of geochemical cycling of metals in the environment. Another important finding is the Hg in the oxidation zones evaporates and contributes to the global cycling of this element through atmospheric emission.

The early lives of the islanders: Stable isotope analysis of incremental dentine collagen from the prehispanic period of the Canary Islands.

This study presents isotopic information for incremental dentine collagen and bone bulk collagen from individuals from the Canary Islands (Tenerife and Gran Canaria) to explore dietary differences during childhood life. Eight individuals have been studied, which comprises 122 δ15 N and δ13 C incremental dentine measurements and eight bulk bone collagen analyses. A baseline of potentially consumed food sources has been developed for comparative purposes. A food reconstruction using isotopic transferred signals (FRUITS) model of probable contributions of each food source towards the diet of each individual has been developed. All samples but one belongs to the later period of indigenous occupation of the archipelago. The dentine collagen data are presented in correlated δ13 C and δ15 N plots per individual, showing the isotopic changes throughout time. δ15 N values for each individual tend to be variable whereas δ13 C data are generally more stable with a range of +9.1 to +14‰ for δ15 N and -17.4 to -20.8‰ for δ13 C. The isotopic analysis allows for the reconstruction of eight dietary profiles, which allow us to estimate the different dietary protein sources. The FRUITS model shows different percentages of the primary food sources for each individual. Where both δ13 C and δ15 N are elevated, this could be indicative of a higher marine contribution to the diet. There appear to be two main dietary profiles identifiable in the dataset and these may be related to changes in status or place of residence. Short-term variations in δ13 C and δ15 N and opposing co-variance of isotopic values can be indicative of nutritional stress, although metabolic changes during growth are also considered.

A climate perturbation at the Middle –Late Jurassic Transition? Evaluating the isotopic evidence from south-central England

The Jurassic greenhouse is punctuated by short cooling intervals. Some published oxygen isotope records of belemnite rostra and fish teeth have been interpreted to reveal a prominent decrease in seawater temperature during the Late Callovian–Early Oxfordian. This is in part the basis for a proposed an ice age at the Middle-Late Jurassic Transition. In contrast relatively constant oxygen isotope records and therefore seawater temperatures as well as carbon isotope values characterized by significant scatter but showing more positive values during the middle and late Callovian have been reported from elsewhere. This research has constructed a stable isotope stratigraphy (from belemnites, Gryphaea and oysters) principally from the Callovian-Oxfordian interval (from southern England) and integrated these data with existing data to assess the pattern of carbon and oxygen isotopic change. Our marine macrofossil record reveals isotopic patterns that are generally comparable with other European basins. Carbon isotopic trends are consistent with bulk carbonate carbon isotope records displaying systematic fluctuations, the largest of which (Middle Callovian, Calloviense/Jason Zones to Early Oxfordian, Mariae Zone) corresponds to previously identified phases of environmental perturbation. Such a trend may have resulted from enhanced burial and preservation of organic matter, leaving the seawater enriched in the heavy carbon isotope. Inferred cooling, derived from our oxygen isotope data from southern England, occurs within the Late Callovian and the Early Oxfordian (Athleta to Mariae zones). Cooling post-dates this positive carbon isotope excursion. Enhanced carbon burial and atmospheric carbon dioxide draw down may have induced cooling. In this study the analysis of a single region (southern England) allows critical factors controlling the oxygen isotopic composition of the carbonates (e.g. temperature and the oxygen isotopic composition of the solution from which the carbonates precipitated) to be more comparable. If Jurassic polar climates were truly warm such a degree of cooling would undoubtedly lead to cooler polar temperatures – but only with seasonal ice.

Stable N and O isotopic indicators coupled with social data analysis revealed long-term shift in the cause of groundwater nitrate pollution: Insights into future water resource management

The stable nitrogen and oxygen isotopic tracers play an important role in determining the causes of groundwater nitrate contamination, natural attenuation capacity, and their extension on a regional scale. However, it is not well known how these pollution characteristics change in response to long-term changes in land use patterns and environmental countermeasures continuously applied, considering that groundwater flows with long residence time. This may be due to the fact that the acquisition of isotope datasets so far has been generally transient, and there has been a lack of datasets to examine the temporal changes on a long-term scale. To test a potential utility of these isotopic indicators in detecting long-term shift in the pollution cause, we collected 243 groundwater samples from regional aquifers in the Kumamoto region to assess isotopic changes in 10 years and analyzed the data with long-term social databases such as estimated nitrogen load and water quality for the past 60 years (1960–2020), for a period comparable to the groundwater residence time. Our analytical results showed that in the recent 10 years (2009–2019) the percentage of groundwater samples mainly affected by chemical fertilizers and livestock waste decreased from 25.0% to 16.2% and increased from 16.1% to 41.3%, respectively, based on our proposed nitrogen isotopic thresholds. This result indicates that the major cause of pollution tends to shift from the application of chemical fertilizers to the leakage of animal waste. The agricultural census data showing gradual long-term shift in the major nitrogen load from application of chemical fertilizers to livestock farming corresponds to the results from isotopic analysis. Furthermore, the long-term nitrate concentration trend analysis revealed that the impact of chemical fertilizer influence decreased for several reasons, whereas that of leakage of animal waste became dominant and has caused the current environmental problems mainly in the north-central part of the study region. The distribution of denitrification has not changed during the past decade. The results of this study suggest that the main factors of nitrate contamination in groundwater can change gradually over time. This study demonstrates that monitoring of nitrogen and oxygen isotopic indicators at regular intervals with long-term continuous social datasets is effective for determining up-to-date conditions and changing processes of groundwater quality, which provide important base information to build critical guidelines for local environmental measure discipline.

Characterization of the GBC-32 Fuel Assembly Source Terms

This paper presents burnup/depletion calculations of the typical Westinghouse 17x17 fuel assembly to be used as a radioactive waste package in a Generic Burnup Credit cask benchmark problem with 32 elements (GBC-32). This first phase is addressing spent fuel source terms calculation while evaluation of the shielding performance of the GBC-32 cask is planned for the second phase. The TRITON-NEWT methodology of the SCALE6.1.3 program package was used in a tandem with ORIGEN-S code for deterministic 2D calculation of the GBC-32 fuel assembly neutron multiplication factor, providing spatial-temporal fluxes and isotopic concentration change. The burnup simulation was done up to 60 GWd/tU with sensitivity analysis of relevant physical parameters influenced by the working cross-section library. This approach also allowed generation of the specific user-defined collapsed cross-section libraries as a function of fuel enrichment and burnup level. Calculation of isotopic concentrations, decay heat, neutron-gamma spectra and major actinides activity for different fuel assembly cooling periods was performed using ORIGEN-ARP module.

Isotopic turnover of carbon δ13C and nitrogen δ15N in the muscle tissue of tambaqui Colossoma macropomum juveniles fed diets containing different levels of digestible protein

The technique that uses natural stable isotopes rises as a safe alternative to evaluate the deposition of potential food constituents’ elements. Diets with distinct isotopic signatures can be used to measure turnover rates in all animal tissues, improving knowledge of metabolic processes in fish nutrition. The aim of the study was to evaluate the growth and turnover of stable isotopes of carbon and nitrogen in the muscle tissue of tambaqui juveniles fed diets containing different levels of digestible protein. A total of 1750 tambaquis were used (weight 6.53 ± 0.43 g and length 7.58 ± 0.18 cm) and distributed in 35 tanks (450 L), with a density of 50 fish per tank. Seven isoenergetic (3378.4 cal g−1) experimental diets were formulated with digestible protein (DP) levels of 14%, 17%, 20%, 23%, 26%, 29% and 32%. During 120 days of experiment, the animals grew over time in all treatments (P < 0.05); and in the evaluated periods, the protein levels of 29% and 32% stood out from the first biometric evaluations, at 30 days, with similar weight averages (P > 0.05) and higher than the averages in the other treatments (P < 0.05). The speed of isotopic changes in muscle tissue was influenced by the characteristics of the diets, and the rates of carbon and nitrogen turnover were more accelerated the higher the protein level. The trial period of 120 days was sufficient for the fish to reflect the isotopic composition of the diets in all treatments (P < 0.05). However, the isotopic contribution of the diet to the tissue as a function of time was different, with indices that reached about 96–97% in 49–63 days of feeding for the diets of 29% and 32% DP and indices of 81–82% for diets of 14% and 17% DP in the same period. The isotopic data analyzed by exponential equations and exploratory analysis showed the formation of three groups with homogeneous characteristics in response to the effects of protein levels: a grouping of diets with 14%, 17% and 20% DP (P > 0.05); another with intermediate levels (23% and 26%); and a third with the highest levels (29% and 32%). Thus, the diet containing 29% of digestible protein proved to be the most attractive for the productive performance of tambaqui juveniles in the growth phase studied.

Modeling periodicity in equid serial enamel isotopes as a proxy for precipitation seasonality

Seasonality shapes environments by driving vegetation patterns and faunal community composition, and identifying seasonality patterns in the past can provide unique insight into paleoenvironments and how they changed over time. Many environmental proxies operate on too large a time scale to glean data about intra-annual seasonality. However, serial enamel isotope samples from the teeth of high-crowned ungulates show promise for providing this temporal resolution of data. Interpreting these data remains a challenge due to the complexity of factors related to animal physiology and the isotopic values of environmental inputs. This study seeks to establish a method for interpreting intra-tooth isotopic change in modern equid teeth as a signal of seasonality by applying a linear mixed effect model to the isotope data to detect periodicity in serial enamel isotope values. Using a modern assemblage of zebra (Equus quagga) from Ol Pejeta Conservancy in Kenya, where long-term climate data has been collected, allows us to compare known climatic seasonality patterns to periodicity in the zebra tooth enamel isotopes. The results of the linear mixed effect modeling, in tandem with the climate data from Ol Pejeta, demonstrate the impact high precipitation variability can have on an environment. While our isotope results point towards measured precipitation seasonality patterns at Ol Pejeta, noise in our data and the variation identified by the models illustrate the challenges of working with serial enamel isotope data. Future refinement and application of this model will allow us to better characterize seasonality in both modern and fossil enamel datasets.

Response of stable isotopes (δ2H, δ13C, δ15N, δ18O) of lake water, dissolved organic matter, seston, and zooplankton to an extreme precipitation event

Lake ecosystems process and cycle organic substrates, thus serving as important bioreactors in the global carbon cycle. Climate change is predicted to increase extreme weather and precipitation events that can flush nutrients and organic matter from soils to streams and lakes. Here we report changes in stable isotopes (δ2H, δ13C, δ15N, or δ18O) of water, dissolved organic matter (DOM), seston, and zooplankton in a subalpine lake at short time resolution following an extreme precipitation event between early July to mid-August 2021. Water from excess precipitation and runoff remained in the lake epilimnion and coincided with increasing δ13C values of seston (−30 ‰ to −20 ‰), due to the input of carbonates and terrestrial organic matter. Particles settled into deeper lake layers after two days and contributed to the uncoupling of C and N cycling as the lake responded to this extreme precipitation event. Following the event, there was an increase in bulk δ13C values of zooplankton (from −35 ‰ to −32 ‰). Throughout this study, δ13C values of DOM remained stable throughout the water column (−29 ‰ to −28 ‰), while large isotopic fluctuations in DOM δ2H (−140 ‰ to −115 ‰) and δ18O (+9 ‰ to +15 ‰) values suggested DOM relocation and turnover. Integrating isotope hydrology, ecosystem ecology, and organic geochemistry offers an element-specific, detailed approach to investigating the impact of extreme precipitation events on freshwater ecosystems and particularly aquatic food webs.

The response of Tampa Bay to a legacy mining nutrient release in the year following the event

IntroductionCultural eutrophication threatens numerous ecological and economical resources of Florida’s coastal ecosystems, such as beaches, mangroves, and seagrasses. In April 2021, an infrastructure failure at the retired Piney Point phosphorus mining retention reservoir garnered national attention, as 814 million liters of nutrient rich water were released into Tampa Bay, Florida over 10 days. The release of nitrogen and phosphorus-rich water into Tampa Bay – a region that had been known as a restoration success story since the 1990s – has highlighted the potential for unexpected challenges for coastal nutrient management.MethodsFor a year after the release, we sampled bi-weekly at four sites to monitor changes in nutrients, stable isotopes, and phytoplankton communities, complemented with continuous monitoring by multiparameter sondes. Our data complement the synthesis efforts of regional partners, the Tampa Bay and Sarasota Bay Estuary Programs, to better understand the effects of anthropogenic nutrients on estuarine health.ResultsPhytoplankton community structure indicated an initial diatom bloom that dissipated by the end of April 2021. In the summer, the bay was dominated by Karenia brevis, with conditions improving into the fall. To determine if there was a unique carbon (C) and nitrogen (N) signature of the discharge water, stable isotope values of carbon (δ13C) and nitrogen (δ15N) were analyzed in suspended particulate material (SPM). The δ15N values of the discharge SPM were −17.88‰ ± 0.76, which is exceptionally low and was unique relative to other nutrient sources in the region. In May and early June of 2021, all sites exhibited a decline in the δ15N values of SPM, suggesting that discharged N was incorporated into SPM after the event. The occurrence of very low δ15N values at the reference site, on the Gulf Coast outside of the Bay, indicates that some of the discharge was transported outside of Tampa Bay.DiscussionThis work illustrates the need for comprehensive nutrient management strategies to assess and manage the full range of consequences associated with anthropogenic nutrient inputs into coastal ecosystems. Ongoing and anticipated impacts of climate change – such as increasing tropical storm intensity, temperatures, rainfall, and sea level rise – will exacerbate this need.

Neutronic Performance Analysis of Inner-Side Chromium Coatings for Accident Tolerant Fuel

To address concerns about the degradation of unprotected internal surfaces of nuclear fuel claddings, inner-side coatings have been proposed as a complementary approach to the accident tolerant fuel protective coating concept. In addition to the increased coping time during severe events, these coatings are expected to provide enhanced protection in normal operation conditions. This study analyzes the neutronic performance of chromium (Cr) inner-side coatings in VVER-type fuel assemblies. Different aspects, such as reactivity and cycle length penalties, enrichment requirements, neutron flux, and the associated isotopic concentration changes are discussed, considering both the coating thickness and position. The results show that for the same thickness, reactivity penalties due to the use of inner-side Cr coatings will be (~30% on average) less compared to external coatings. The fuel assembly operating cycle showed reductions by ~ 5.5 effective full-power days when a 10-µm-thick internal Cr coating is introduced, while a 10-µm two-sided coated assembly possessed an ~13.6-day shorter operating cycle compared to an uncoated fuel assembly of the same specifications. The neutron flux showed slight shifts and hardening in the thermal energy region. The analysis of nuclide inventories showed relative increases in these inventories, which were proportional to the thickness. For the fissile plutonium isotope 239Pu, this relative increase reached a peak of 0.25% and 0.42% (for the 10-µm and 20-µm internal Cr coatings) at a fuel burnup of 18 MWd/kg heavy metal (HM). While for 241Pu, the observed highest relative increases for the 10-µm- and 20-µm-thick internal Cr coatings were 0.74% and 1.03%, respectively. The 135Xe isotopic concentration showed a relative increase that reached 0.2% and 0.4% for the 10-µm and 20-µm internal Cr coatings at a burnup of 34 MWd/kgHM, while the 149Sm concentration increased by 0.2% and 0.5% for the 10-µm and 20-µm internal Cr coatings, respectively. While these observed isotopic concentration changes were generally small for the studied inner-side coatings, the results showed that the changes remain subject to further increases as the amount of coating material gets higher. Therefore, it is important for the coating thickness to be optimized, taking into account the impact of such nuclide inventory changes. Possible fuel-clad gap reductions and the associated effects on heat transfer, as well as gap tolerance to fission products and fuel relocations, will require further studies, especially so that additional enrichments may be applied.

Temporal variations in geochemistry of hydraulic fracturing fluid and flowback water in a tight oil reservoir

Hydraulic fracturing facilitates the development and exploitation of unconventional reservoirs. In this study, the injected hydraulic fracturing fluid (HFF) and flowback and produced water (FPW) in tight oil reservoirs of the Lucaogou Formation in the Junggar Basin are temporally sampled from day 1 to day 64. Freshwater is used for fracturing, and HFF is obtained. The chemical and isotopic parameters (including the water type, total salinity, total dissolved solids (TDS), pH, concentrations of Na+, Cl−, Ba+, K+, Fe2+ + Fe3+, and CO32−, δD, and δ18O) are experimentally obtained, and their variations with time are systematically analyzed based on the flowback water. The results show that the water type, Na/Cl ratio, total salinity, and TDS of the FPW change periodically primarily due to the HFF mixing with formation water, thus causing δD and δ18O to deviate from the meteoric water line of Xinjiang. Because of water–rock interaction (WRI), the concentrations of Fe2+ + Fe3+and CO32− of the FPW increase over time, with the solution pH becoming more alkaline. Furthermore, based on the significant changes observed in the geochemistry of the FPW, three separate time intervals of flowback time are identified: Stage I (< 10 days), where the FPW is dominated by the HFF and the changes in ions and isotopes are mainly caused by the WRI; Stage II (10–37 days), where the FPW is dominated by the addition of formation water to the HFF and the WRI is weakened; and finally, Stage III (> 37 days), where the FPW is dominated by the chemistry of the formation water. The methodology implemented in this study can provide critical support for the source identification of formation water.

Preservation of stable isotope signatures of amino acids in diagenetically altered Middle to Late Holocene archaeological mollusc shells

Stable isotope proxies measured in the proteinaceous fraction of archaeological mollusc shell represents an increasingly important archive for reconstructing past ecological and biogeochemical conditions of nearshore environments. A major issue, however, is understanding the impact of diagenetic alteration in sub-fossil shell isotope values. “Bulk” stable isotope values of nitrogen (δ15N), and especially carbon (δ13C) often shift strongly with increasing C/N ratios in degraded shell, resulting in unreliable data. Here, we examine preservation of an entirely new set of shell paleo-proxies, compound-specific isotopes of amino acids (CSI-AA). We examine carbon (δ13CAA) and nitrogen (δ15NAA) patterns and values from the organic fraction of California mussel (Mytilus californianus) shells from the California Channel Islands. Archaeological shell samples ranging in age from ca. 6,100 to 250 cal BP exhibiting a wide range of degradation states were collected from varied depositional environments (e.g., exposed coastal bluff, buried strata, etc.), and were directly compared to modern shells of the same species and region.Our results indicate organic matter C/N ratios as the best bulk diagnostic indicator of the relative degradation state of shell organic fraction, including changes at the molecular level. Modern shell organic C/N ratios ranged from 2.8 to 3.5, while those in archaeological shell were substantially elevated (3.4–9.5), exhibiting strong and significant negative correlations with bulk δ13C values, weight %C, and weight %N, and a significant but weaker correlation with δ15 N values. An additional “cleaning” step using weak NaOH helped to remove possible exogenous contaminants and improved bulk values of some samples. However, relative molar AA abundances revealed that some AAs, especially the two most abundant, Glycine and Alanine, progressively decreased with increasing C/N ratio. The loss of these amino acids permanently alters bulk isotope values regardless of removal of contaminants. Modeling the bulk isotope change expected due to amino acid molar composition showed major and predictable shifts in bulk δ13C values from selected AA loss, and similarly large but far more variable impacts from exogenous contaminants.In contrast to bulk data, key CSI-AA values and patterns remained almost entirely unaltered, even in the most degraded shell samples, closely matching expected biosynthetic isotope patterns in modern mussel shell. AA isotope proxies for “baseline” (δ15N-Phenylalanine and average δ13C-Essential AAs) and planktonic trophic structure (δ15N-Glutamic Acid and δ15N-Phenylalanine) were not statistically altered with degradation in any sample. Overall, we conclude that while bulk isotopes, particularly δ13C, are very likely to be unreliable in archaeological or subfossil shell with C/N ratios higher than ∼4.0, CSI-AA proxies can still be used to reconstruct past climatic and ecological conditions of the nearshore marine environment.