C Values Research Articles

Structural Analysis of Hyaluronic Acid Fillers Using Nuclear Magnetic Resonance: Implications for Quality Control and Clinical Performance.

Potential disruptions in the biocompatibility of hyaluronic acid (HA) fillers can arise with mono-linked 1,4-butanediol diglycidyl ether (BDDE) or unreacted (pendant) 1,4-butanediol di-(propan-2,3-diolyl) ether. Assessing the filler's degree of modification involves evaluating improperly cross-linked BDDE. This study analyzed commercially available HA fillers using nuclear magnetic resonance (NMR), focusing on key parameters, such as the degree of modification (MoD), the cross-linker ratio (CrR), and the degree of cross-linking. We assessed thirteen commercially available HA fillers using NMR. The samples were placed in an NMR instrument, and each sample was analyzed for 26 h, including MoD and CrR assessments. MoD 1H ranged from 17.065% to 2.239%, MoD 13C ranged from 12.567% to 1.947%, and CrR 13C ranged from 0.394 to 0.014. Significant distinctions were observed in the CrR 13C values when the MoD values of the products were similar. This study underscores the importance of considering the MoD and the CrR together to ensure optimal cross-linking and minimize the risks associated with residual BDDE impurities. Utilizing NMR for HA gel characterization provides valuable insights regarding product quality control, safety assessments, and clinical performance evaluations for esthetic interventions, contributing to filler product improvements. Further studies correlating NMR findings with real-world outcomes are essential for ensuring safety and efficacy.

Bomb-radiocarbon in the Northern Indian Ocean

Bomb-radiocarbon is a useful tracer to study ocean circulation and air-sea CO2 exchange processes. In the present study bomb radiocarbon distribution in dissolved inorganic carbon of the Northern Indian Ocean around late 2010s has been evaluated. In the late 2010s surface waters in the Northern Indian Ocean had ∆14C values ranging between 9 and 17 ‰ which is comparable or even higher than that of the contemporaneous atmospheric ∆14C values. Water column measurements showed that the bomb 14C inventory in the Arabian Sea and the Bay of Bengal has increased between 1990s and 2010s. During the same period, the eastern and western equatorial Indian Ocean showed either no change or a slight decline in the water column bomb 14C inventory. These bomb 14C inventory values were also used to estimate the air-sea CO2 exchange rate and net CO2 flux over the Northern Indian Ocean region. Bomb 14C-based estimate of net CO2 flux from the Arabian Sea is 75 ± 24 Tg C yr−1 and the Bay of Bengal is 1 ± 7 Tg C yr−1, which is comparable to the estimates reported by previous investigations in the region. The present observations show that the bomb 14C is being transferred to the deeper depths of the ocean, emphasizing the need for continued 14C measurements to gain further insights into subsurface processes in the region.

High δ 15N and δ 13C Values in Aurochs, Cattle and Sheep Bones from Salt Marshes in the North of The Netherlands

ABSTRACT 185 pairs of δ 13C and δ 15N values for aurochs, cattle and sheep bones from the northern Netherlands were studied to establish the influence of salt marsh grazing on bone δ 13C and δ 15N values. The observed values proved significantly increased compared to livestock that grazed inland. The δ 13C and δ 15N values of animals grazing former salt marshes were significantly less increased than those grazing the unembanked salt marsh. Absent regular salt marsh flooding may explain the reduced δ 13C increase in bones of animals grazing there. The δ 15N values of ruminants grazing the embanked salt marshes continued to be increased, presumably due to persisting saline water at shallow depths. The δ 13C values of the salt marsh grazing ruminants correspond with a δ 13C increase of 5‰ compared to eleven modern salt marsh plants from Schiermonnikoog studied in this paper. The δ 15N values of the eleven Schiermonnikoog salt marsh plants proved variable, on average too low to explain the observed 3.5‰ increase in δ 15N values. This suggests that vegetation δ 15N values cannot be the only cause of the high δ 15N values observed in salt marsh ruminants. Other processes may be responsible for the high δ 15N values of salt marsh grazing ruminants as well.

Geochemical fingerprints of early diagenesis in shallow-water marine carbonates: Insights from paired δ44/40Ca and δ26Mg values

We present a suite of major element stable isotope (δ13C, δ18O, δ44/40Ca, δ26Mg), and selected trace element (Sr/Ca and Mg/Ca) data from Pleistocene sediments from the Great Barrier Reef (IODP Expedition 325), as well as Holocene surface sediments from the Bahamas (Triple Goose Creek, Andros Island) to identify geochemical fingerprints associated with early marine and meteoric diagenesis. Sediments from both sites exhibit co-variation in δ13C and δ18O values, depletion in trace elements, and distinct geochemical trends in δ26Mg and δ44/40Ca values that reflect differences between diagenetic alteration in marine and meteoric fluids. While marine diagenesis results in lower Sr/Ca ratios, higher δ44/40Ca values, and little effect on bulk sediment δ26Mg values, meteoric diagenesis leads to lower Sr/Ca ratios, lower δ44/40Ca values, and lower δ26Mg values. Using a numerical model of diagenesis, we show how diagenetic alteration by meteoric fluids must occur after an initial period of diagenetic alteration by marine fluids, a two-stepped diagenetic history that complicates the interpretation of geochemical data in meteorically altered marine carbonate sediments. Finally, we discuss how paired metal isotopes may serve as a robust indicator of meteoric alteration in ancient shallow-water marine carbonate sediments.

Biochemically induced diagenesis of Jurassic micrite: evidence from phase analysis, carbon, oxygen, and strontium isotopes (Franconian Alb, Germany)

The marine Upper Jurassic rocks of the Franconian Alb consist largely of micritic carbonate of partly dolomitized reef mounds and bedded basinal limestone. All carbonates were lithified in the shallow (centimeters, meters) subsurface and have a wide range of ∂13C (≤ + 3‰ to − 10‰VPDB) but always negative ∂18O (− 1 to − 6‰VPDB). Dolomite and reef limestone show the highest ∂18O and ∂13C values. The most negative ∂13C (≥ − 10‰) occurs mainly as cement in dolomite of a basinal, partly dolomitic, biostrome interval. Basinal limestone shows intermediate ∂13C values. Because freshwater diagenesis and elevated temperatures cannot explain the observed isotope values, pH is here considered a major factor influencing the isotope signal of micritic limestone. The bulk sediment isotope signal was reset to lower values, from an original lime mud with ∂13C ≥ 3‰ and a ∂18O of ≥ + 1‰, as a result of biochemically induced diagenesis. Carbonate, probably mostly aragonite but occasionally including dolomite, was dissolved in a zone where low pH developed as a result of organic matter degradation. Dissolved carbonate was translocated by diffusion and re-precipitated as cement (ca. 50vol%) in a zone with elevated pH where all in situ lime mud ∂18O was reset. Imported cement carbonate precipitated in equilibrium with the pore fluid with negative isotope values, whereas ∂13C of the in situ lime mud remained unmodified. The negative shift of the bulk ∂13C and ∂18O is variable and depends on pH and the contribution of 12C from anaerobic sulfate reduction in the zone of cement precipitation. This produced an ubiquitous covariance of ∂18O and ∂13C. Incorporation of seawater-derived Mg2+ during recrystallization of carbonate can account for the local dolomitization. Elevated 87Sr/86Sr ratios are explained as a result of interaction of clay minerals with the stationary pore fluids. This study shows that the isotopic signal produced by biochemically induced shallow submarine subsurface carbonate diagenesis can be indistinguishable from freshwater diagenesis, that ∂18O and ∂13C of the bulk rock are always reset, and that carbonates can show, in the presence of clay minerals, elevated 87Sr/86Sr ratios even when the pore fluids were never exchanged.Graphical

Geochemistry of oils and condensates from the lower Eagle Ford formation, south Texas. Part 6: Carbon isotopes

Compound specific carbon isotope analyses were performed on a well-characterized suite of unconventional oils and condensates produced from the lower Eagle Ford Formation. Thermal maturity is the major influence on the δ13C values of C3–C19 hydrocarbons. From ∼0.8 to ∼1.1 %Ro, the main stage of oil generation, the δ13C values of most measured hydrocarbons remain relatively constant: n-alkanes are ∼ −30 ‰: light aromatic hydrocarbons, cycloalkanes and isoprenoids are ∼ −29 to −28 ‰. Only the C4 to C10 methylalkanes exhibit high variance with carbon number with δ13C values ranging from ∼ −32 to −28 ‰, respectively. Hydrocarbons from samples ∼1.1 to 1.3 %Ro, the late oil generation stage, are 13C-enriched by ∼1–∼2 ‰. This is the range typically assigned to the influence of thermal maturity on oil from many conventional petroleum systems. The onset of significant oil cracking occurs at ∼1.3 %Ro and all measured hydrocarbons systematically become progressively 13C-enriched although the degree varies by compound class and carbon number. The δ13C values of individual hydrocarbons shift by as much as ∼ +9 ‰ for propane and butane to only ∼ +3 ‰ for methylcyclopentane from <1.1 to 1.7 %Ro. The 13C-enrichments observed in the Eagle Ford oils/condensates with increasing maturity are attributed to the kinetic isotope effect (KIE), whereby 12C–12C bonds cleave faster than 12C–13C bonds. No evidence for isotopic equilibrium was found. The consistency of the sums of the weighted δ13C values for C4–C7n-alkane/methylalkane isomers provides support for Mango's (2000a) theory that these hydrocarbons are generated from precursors with a common chemical structure that pass through a similar transition state.Source facies exert only a minor influence on the carbon isotopic composition of Eagle Ford oils/condensates. Small variances in the 13C values of C6+n-alkanes, cyclohexane and methylcyclohexane are consistent with oils produced east of the San Marco Arch being generated from shales with a higher influx of terrestrial high plant matter compared to the shales west of the Arch. Phase fractionation was shown to have a measurable impact on the δ13C values of the most volatile hydrocarbons in evaporated samples and on the least volatile hydrocarbon that underwent phase separation in the subsurface during production.

Molecular and radiocarbon constraints on the fate of sedimentary organic carbon in a human-impacted river-dominated ocean margin

Organic carbon (OC) burial in river-dominated ocean margins plays a pivotal role in the global carbon cycle, impacting atmospheric CO2 levels over the long term. Despite its significance, uncertainties persist regarding the influence of external environmental factors and intrinsic properties on sedimentary OC. In this study, we conducted a comprehensive analysis of surface sediments from the East China Sea, examining geochemical properties (including total OC content [TOC], Δ14C, δ13C, and C/N ratio), terrestrial biomarkers (n-alkanes), and mineral properties (such as specific surface area, Al/Si ratio, and mineral composition). Our aim was to shed light on the fate of sedimentary OC.The surface sediment's Δ14C values displayed significant spatial heterogeneity, delineating four distinct sub-regions. Strong positive correlations (all p < 0.01) were found between the ∆14C values and fine-grained sediments, specific surface area, and clay minerals, suggesting the potentially pivotal role of mineral protection in shaping the fate of sedimentary OC. The proportion of terrestrial OC gradually decreased towards the south, while marine OC proportion increased, corresponding to the enrichment of Δ14C. The co-variation of Δ14C values, mineral properties, and OC source proportions suggests that terrestrial OC may undergo progressive replacement by marine OC during southward transport. Temporal variations in ∆14C values indicated that seabed erosion led to a significant increase in ∆14C values (p < 0.01) in the coastal mud belt, a phenomenon likely common in river-dominated ocean margins globally due to the new sediment cycle during the Anthropocene.

Изотопный состав углерода и кислорода нижнепермских карбонатных пород лосиноостровской свиты (Приполярный Урал, р. Кожым)

The Paleozoic section on the Kozhim River of the Subpolar Urals is the best sequence of the northern Urals. The border of Carboniferous-Permian deposits are observed on the opposite banks of the Kozhim River and are represented by two types of sections: on the right bank — the Kozhym skeletal mound, on the left bank — depression deposits of mixed composition (Losinoostrov Fm.). The article presents the first information on the isotopic composition of carbon and oxygen in the Lower Permian limestones of the Losinoostrov Fm. It is shown that the obtained data on the isotopic composition on the 13C–18O diagram are visually separated into three clusters. The first cluster with the lowest values of 13C (–0.3…1.1 ‰) and 18O (23.5…25.0 ‰) included the most intensively silicified rocks (siliceous bioclastic limestones, secondary silicitolites, siliceous-carbonate-argillaceous mixtolites and siliceous-argillaceous limestone). The third cluster, with the highest values of 13C (3.9…5.1 ‰) and 18O (26.0…26.8 ‰), includes bioclastic and peloid-micritic limestones. In this case, the 13C values correspond to the range of variations in the carbon isotopic composition indicated in review works on the chemostratigraphic correlation of Permian deposits. The second cluster occupies an intermediate position and is characterized by the values of 13C (2.0…2.8 ‰) and 18O (24.3…25.4 ‰). This cluster is predominantly represented by limestones enriched with terrigenous materials. A comparison is made of the isotopic composition of the limestones of the Losinoostrov Formation with the coeval limestones of the Kozhim skeletal mound, which showed higher values of 13C and 18O in the latter.

Comparison of carbon, nitrogen, and oxygen stable isotope ratios and mercury concentrations in muscle tissues of five beaked whale species and sperm whales stranded in Hokkaido, Japan

ABSTRACT We studied δ 13C, δ 15N and δ 18O values, and total mercury (THg) concentrations in muscle samples from deep-sea predators – five beaked whale species and sperm whales – stranded along the coast of Hokkaido, in the north of Japan in 2010 and 2019. The δ 13C, δ 15N and δ 18O values, THg concentrations, and body length (BL) of Stejneger’s beaked whales were similar to those of Hubbs’ beaked whales, which belong to the same genus. In contrast, δ 13C values, THg concentrations, and BL of Sato’s beaked whales were markedly different from those of Baird’s beaked whales, which belong to the same genus. Stejneger’s and Hubbs’ beaked whales living around Hokkaido may compete in their ecological niches, whereas Sato’s and Baird’s beaked whales may segregate their ecological niches. Although Cuvier’s beaked whales and sperm whales belong to different genera and their BLs were significantly different, their δ 13C and δ 15N values were similar, probably because they can dive and stay in deeper waters than other beaked whale species. The δ 13C values in combined samples from all whales increased with increasing BL, probably owing to the larger whale species’ dietary preference for squid. The δ 13C values in combined samples from all whales were positively correlated with THg concentrations, whereas the δ 15N values in the combined samples were negatively correlated. The δ 18O values in combined samples from most whales tended to be positively correlated with THg concentrations. These correlations may be explained by a higher THg load from deep-sea feeding than from pelagic feeding and by a feeding shift towards lower trophic levels.

Southern Ocean humpback whale trophic ecology. II. Influence of fasting and opportunistic feeding on skin stable isotope values of migrating whales

Many baleen whale species migrate between low-latitude breeding grounds and high-latitude feeding grounds, with increasing evidence that humpback whales Megaptera novaeangliae utilise supplemental feeding sites in temperate regions while migrating. The diet of whales while migrating is often unknown, and the impact that temperate feeding and/or fasting has on biochemical tracers used to investigate diet remains unclear. The aims of this study were to (1) determine whether prey consumption at supplemental feeding sites could be detected by carbon (13C) and nitrogen (15C) stable isotope analysis of skin; (2) obtain information on diet during migration; and (3) ascertain the impact of potential fasting on stable isotope values of baleen whales. Skin samples were taken from the eastern Australian humpback whale population on Antarctic feeding grounds and 2 sites on the southward migration route (a sub-tropical site and a temperate site) across 2 yr. At the sub-tropical site, 13C and δ15N were consistent with the last place of foraging 5 mo earlier. One exception was the higher (0.5 ‰) δ15N value in 2011, suggesting that in some years, potentially when blubber reserves are insufficient, δ15N may be influenced by fasting. In both years, skin 13C and δ15N values at the temperate site were higher than those from the Antarctic and sub-tropical sites, indicating that a feeding signal from temperate zones had likely been incorporated, with whales feeding on fish and krill. Importantly, supplemental feeding while migrating could affect the interpretation of whale diet on feeding grounds if sampled early in the season.

Moisture and temperature effects on the radiocarbon signature of respired carbon dioxide to assess stability of soil carbon in the Tibetan Plateau

Abstract. Microbial release of CO2 from soils to the atmosphere reflects how environmental conditions affect the stability of soil organic matter (SOM), especially in massive organic-rich ecosystems like the peatlands and grasslands of the Qinghai–Tibetan Plateau (QTP). Radiocarbon (14C) is an important tracer of the global carbon cycle and can be used to understand SOM dynamics through the estimation of time lags between carbon fixation and respiration, often assessed with metrics such as age and transit time. In this study, we incubated peatland and grassland soils at four temperature (5, 10, 15 and 20 °C) and two water-filled pore space (WFPS) levels (60 % and 95 %) and measured the 14C signature of bulk soil and heterotrophic respired CO2. We compared the relation between the Δ14C of the bulk soil and the Δ14CO2 of respired carbon as a function of temperature and WFPS for the two soils. To better interpret our results, we used a mathematical model to analyse how the calculated number of pools, decomposition rates of carbon (k), transfer (α) and partitioning (γ) coefficients affect the Δ14C bulk and Δ14CO2 relation, with their respective mean age and mean transit time. From our incubations, we found that 14C values in bulk and CO2 from peatland were significantly more depleted (old) than from grassland soil. Our results showed that changes in temperature did not affect the Δ14C values of heterotrophic respired CO2 in either soil. However, changes in WFPS had a small effect on the 14CO2 in grassland soils and a significant influence in peatland soils, where higher WFPS levels led to more depleted Δ14CO2. In our models, the correspondence between Δ14C, age and transit time highly depended on the internal dynamics of the soil (k, α, γ and number of pools) as well as on model structure. We observed large differences between slow and fast cycling systems, where low values of decomposition rates modified the Δ14C values in a non-linear pattern due to the incorporation of modern carbon (14C bomb) in the soil. We concluded that the stability of carbon in the peatland and grassland soils of the QTP depends strongly on the direction of change in moisture and how it affects the rates of SOM decomposition, while temperature regulates the number of fluxes. Current land cover modification (desiccation) in Zoigê peatlands and climate change occurring on the QTP might largely increase CO2 fluxes along with the release of old carbon to the atmosphere potentially shifting carbon sinks into sources.

Effects of long-term application of inorganic fertilizers and organic amendments on the turnover rates of fractionated soil organic carbon and their determining factors in paddy fields

ABSTRACT To investigate how the long-term application of inorganic fertilizer and organic amendments affects the turnover rates of organic matter in physico-chemically fractionated components in paddy soils and how their rates are related to their amounts, we studied the effect of variable management of inorganic fertilizer and organic amendments for > 50 years on the ∆14C values of accumulated soil organic carbon (SOC) in fractionated components of 5 soil samples from three paddy fields. SOC was fractionated into four components based on their physico-chemical properties: (1) light fraction (LF) derived from plant residues, (2) heavy fraction (HF) containing stable aggregates, (3) oxidizable fraction (OxF) and (4) non-oxidizable fraction (NOxF) forming organo-mineral complexes with fine-textured minerals. The ∆14C values were determined by accelerator mass spectrometry using graphitized samples. The ∆14C values of SOC in NOxF (from −305‰ to − 90.5‰) were much lower than those of HF (from −123‰ to − 3.7‰) and OxF (from −215‰ to 21.0‰). Lowest values for NOxF suggested slowest turnover rates as expected, and higher and comparable values for OxF and HF implied much faster turnover rates of SOC in OxF compared with upland soils. This could be one of the characteristics of SOC dynamics in paddy soils, probably reflecting repeated puddling of plow layer soils. ∆14C values in all the fractions increased in response to the application of inorganic fertilizer and organic amendments, suggesting faster turnover rate. Soils with clayey and weathered characteristics had the lowest ∆14C values, or slowest turnover rates among the study fields. The relationship between the ∆14C value and the amount of accumulated C for HF, OxF and NOxF indicated that the more the SOC accumulated, the faster the turnover rate of the SOC was, regardless of the fractions, and the relationship of the HF was considerably different from those of OxF and NOxF. In conclusion, these results can be the basis for understanding the C dynamics and for improving soil fertility status and soil C sequestration in paddy soils.

Generation Potential and Characteristics of Kerogen Cracking Gas of Over-Mature Shale

To investigate the characteristics and generation potential of gas generated from over-mature shale, hydrous and anhydrous pyrolysis experiments were carried out on the Longmaxi Formation in the Anwen 1 well of the Sichuan Basin of China at temperatures of 400–598 °C and pressures of 50 Mpa, with (hydrous) and without (anhydrous) the addition of liquid water. The results show that in the presence of water, the total yield of carbon-containing gases (i.e., the sum of methane, ethane, and carbon dioxide) was increased by up to 1.8 times when compared to the total yield from the anhydrous pyrolysis experiments. The increased yield of carbon dioxide and methane accounted for 89% and 10.5% of the total increased yield of carbon-containing gases. This indicated that the participation of water could have promoted the release of carbon from over-mature shale, like we used in this study. The methane generated in the hydrous pyrolysis experiments was heavier, with a δ13C value of −21.27‰ (544 °C) compared to that generated in the anhydrous pyrolysis experiments, which showed a lighter δ13C of −33.70‰ (544 °C). It is noteworthy that the δ13C values of the methane from hydrous pyrolysis at &gt;500 °C were even heavier than that of the kerogen from the over-mature shale, although the δ13C values of the methane show an overall increasing trend with increasing temperature both in hydrous and anhydrous pyrolysis. The carbon dioxide from hydrous pyrolysis was less enriched in 13C relative to that from anhydrous pyrolysis. Specifically, the δ 13C values of the carbon dioxide increased with the increasing temperature in anhydrous pyrolysis, whereas they remained nearly constant with increasing temperature in hydrous pyrolysis. The overall lighter δ13C values of the carbon dioxide generated in the hydrous pyrolysis experiments likely indicate that water tends to prompt the release of lighter carbon and/or suppress the release of heavier carbon from over-mature shale in the form of carbon dioxide, especially at higher temperatures, for example, of &gt;510 °C.

Assessments of groundwater recharge process and residence time using hydrochemical and isotopic tracers under arid climate: Insights from Errachidia basin (Central-East Morocco)

The aquifer systems in the Errachidia basin, located to the south of the High Atlas limestone, are constituted by three superimposed and exploitable aquifers (Senonian, Turonian, and Infracenomanian). These aquifers hold economic significance for the central-east region of Morocco. This area experiences an arid to Saharan climate characterized by low precipitation, high temperatures, and very high evaporation. It is one of the most exposed and vulnerable regions to climate change in Morocco. The low local rainfall cannot explain the recharge of the deep aquifers. However, the significant spring discharges from these aquifers indicate the existence of other recharge contributions.The aim of this study is to elucidate the recharge processes of the Cretaceous aquifers in the investigated basin, clarify hydraulic relationships between them and the Jurassic aquifers of the High Atlas Mountains and estimate the residence time of groundwaters. Water samples from aquifers are collected and analyzed for chemical and isotopic elements. Several statistical methods (SOM, discriminant factorial analysis, CPA) are employed. The results reveal that many samples from different aquifers exhibit clear similarities in chemical characteristics, providing evidence of water transfer between aquifers. Isotopic findings are consistent with chemical characterization and mineralization anomalies.Recharge of the investigated aquifers originates from the Jurassic limestone of the High Atlas Mountains, facilitated by the karstic nature of the Jurassic in contact with the permeable formations of the Cretaceous basin. Age dating results, using 3H and 14C values, confirm that most of the investigated groundwater results from a mixing of old and recent recharges. This process of groundwater renewability is relevant. All the findings are valuable for decision-makers to enhance their understanding of the aquifer system's functioning and inform sustainable management strategies for future sustainability.

Distribution and stable isotope ratio characteristics of Japanese eel leptocephali in relation to hydrographic structure of their Pacific Ocean spawning area

AbstractTo understand the larval distribution, size variation, and stable isotope ratios of Japanese eel leptocephali in relation to the salinity front and their feeding ecology, larvae from 7 research cruises (2002–2013) in the North Equatorial Current (NEC) spawning area were examined. The smallest early‐stage larvae were distributed south of or near the salinity front, confirming that the salinity front is an important oceanic feature to understand spawning locations of the Japanese eel. Larger size larvae tended to distribute into higher latitudes. Transport to northern latitudes with their growth would facilitate transport into the Kuroshio region, but retention in the Subtropical Countercurrent (STCC) might be detrimental. Preleptocephalus isotope ratios reflected maternal ratios, but feeding‐stage leptocephali (8–56 mm) tended to have higher ∂15N values at lower latitudes typically in areas south of a salinity front. Feeding larvae quickly assimilate isotope ratios from the NEC after spawning and early growth. Large differences of ∂13C values of larvae between the NEC and STCC might vary with spatial baselines in the two currents. However, diel vertical migrations should be considered, because the isotope ratios in particulate organic matter distinctly depend on the depth. Comparisons among Japanese eel larvae and other taxa of leptocephali in the NEC illustrate the need for further studies on the trophic ecology of leptocephali.

Effects of lipid extraction on stable isotope ratios of carbon and nitrogen in muscles of freshwater fish

ABSTRACT The extraction of lipids by the Folch method from the muscles of all the fish studied led to statistically significant differences in the values of δ 15N. At the same time, lipid extraction led to a statistically significant increase in δ 13C in pike and roach, and to a statistically insignificant decrease in δ 13C in perch and bream. Thus, lipid extraction cannot serve as a universal method of sample preparation for the analysis of the isotopic composition of carbon (13C/12C) and nitrogen (15N/14N) in fish muscles. The differences between the δ 13C values in the samples before and after lipid extraction were statistically investigated by different models. It is shown that mathematical correction method models can be used, but the results are depending on the fish types.

14C and 14C‐10Be terrestrial age dating system for meteorites—New data for four recently fallen meteorites

AbstractWe perform a systematic and detailed study of the 14C and 14C‐10Be dating systems for meteorite terrestrial ages. Physical model calculations indicate that neither the 14C production rates nor the 14C/10Be production rate ratios are constant enough to be reasonably approximated by average values. By using simple averages, one introduces a significant size‐dependent bias into the database for meteorite terrestrial ages. By combining modeled 14C production rates and 14C/10Be production rate ratios with (22Ne/21Ne)cos ratios and assuming ~80% ablation losses, relatively easy to use correlations of 14C production rates and 14C/10Be production rate ratios as a function of (22Ne/21Ne)cos are established. The new correlations enable the determination of terrestrial ages that are more accurate than ages based solely on average values for 14C and/or 14C/10Be. We validate the model predictions by measuring 14C activity concentrations, 14C/10Be production rate ratios, 21Necos concentrations, and (22Ne/21Ne)cos ratios in four recently fallen meteorites: Mt. Tazerzait, Boumdeid (2011), Bensour, and SaU 606. The experimental data confirmed the model predictions, although the available data are insufficient to be conclusive. More data from freshly fallen meteorites are needed for validating the model predictions for different chondrite sizes and chondrite types.

Multi-tracer approach to constrain groundwater flow and geochemical baseline assessments for CO2 sequestration in deep sedimentary basins

Geological storage of gases will be necessary in the push to net zero and the energy transition to reduce carbon emissions to atmosphere. These include CO2 geological storage in suitable sandstone reservoirs. Understanding groundwater flow, connectivity and hydrogeochemical processes in aquifer and storage systems is vital to prevent risk and protect important water resources, such as the Great Artesian Basin. Here, we provide a ‘tool-box’ of geochemical assessment methods to provide information on flow patterns through the basin's aquifers (changes in chemistry along flow path), stagnant versus flowing conditions (cosmogenic isotopes and noble gases), inter-aquifer connectivity and seal properties (major ions, Sr and stable isotopes), water quality (major ions and metals) and general assessments on residence times of groundwater (cosmogenic isotopes and noble gases). This information can be used with reservoir and groundwater models to inform on possible changes in the above-mentioned processes and serve as input parameters for CO2 injection impact modelling. We demonstrate the use and interpretation on an example of a potential CO2 storage geological sequestration site in the Surat Basin, part of the Great Artesian Basin, and the aquifers that overly the reservoir. The stable water isotopes are depleted compared to average rainfall and most likely indicate greater contributions from monsoonal rain events from the northern monsoonal troughs, where amount and rainout effects lead to the depletion rather than colder recharge climates. This is supported by the modern recharge temperatures from noble gases. Inter-aquifer mixing between the Precipice Sandstone reservoir and the Hutton Sandstone aquifer seems unlikely as the Sr isotope ratios are distinctly different suggesting that the Evergreen Formation is a seal in the locations sampled. Mixing, however, occurs on the edges of the basin, especially in the south-east and east where the Surat Basin transitions into the Clarence-Moreton Basin. Groundwater flow appears to be to the south in the Precipice Sandstone, with a component of flow east to the Clarence-Morton Basin. The cosmogenic isotopes and noble gases strongly indicate very long residence times of groundwater in the central south Precipice Sandstone around a proposed storage site. 14C values below analytical uncertainty, R36Cl ratios at secular equilibrium as well as high He concentrations and high 40Ar/36Ar ratios support the argument that groundwater flow in this area is extremely slow or groundwater is stagnant. The results of this study reflect the geological and hydrogeological complexities of sedimentary basins and that baseline studies, such as this one, are paramount for management strategies.

Root-derived resources fuel earthworms predominantly via bacterial and plant energy channels – Insights from bulk and compound-specific isotope analyses

Soil food webs rely on both brown and green energy, i.e., litter material and root-derived resources such as exudates. Earthworms have traditionally been viewed as macro-detritivores fuelled by brown energy and playing a central role in nutrient cycling and belowground energy flux. However, the role of root-derived resources for earthworm nutrition remains controversial. We studied the dietary contribution of root-derived resources from different plant functional groups to earthworms using bulk and compound-specific stable isotope analyses in a microcosm experiment with five earthworm species, grasses and legumes in monoculture and mixture, and an unplanted control by preventing leaf litter from entering the microcosms. The presence of plants consistently depleted bulk 13C values of the five earthworm species studied suggesting that root-derived carbon contributed to earthworm nutrition in each of the species. The response of bulk 15N values was less consistent, which is in line with the assumption that root-derived resources fuel soil food webs mainly via carbon-based root exudates. These observations were corroborated by 13C values of essential amino acids suggesting that most of the tissue carbon of earthworms was incorporated via bacterial- (∼60%) and plant-derived resources (∼30%), with the presence of legumes enhancing the incorporation via plant-derived resources. The high proportion of bacterial resources in the earthworms was consistent with the relative dominance of bacteria in the experimental soil and suggests that bacteria serve as important link in the acquisition of food resources. However, it remains an open question whether earthworms feed directly on soil bacteria, bacterial residues in soil or rely on nutritional supplementation by gut microorganisms. Overall, our results show that when root-derived resources are available, earthworms, as macro-detritivores, also incorporate green energy, with these resources being assimilated mainly via the bacterial energy channel, pointing to the importance of bacterial energy channelling in ecosystems with high earthworm biomass.

Dissolved nitrogen uptake versus nitrogen fixation: Mode of nitrogen acquisition affects stable isotope signatures of a diazotrophic cyanobacterium and its grazer.

Field studies suggest that changes in the stable isotope ratios of phytoplankton communities can be used to track changes in the utilization of different nitrogen sources, i.e., to detect shifts from dissolved inorganic nitrogen (DIN) uptake to atmospheric nitrogen (N2) fixation by diazotrophic cyanobacteria as an indication of nitrogen limitation. We explored changes in the stable isotope signature of the diazotrophic cyanobacterium Trichormus variabilis in response to increasing nitrate (NO3-) concentrations (0 to 170 mg L-1) under controlled laboratory conditions. In addition, we explored the influence of nitrogen utilization at the primary producer level on trophic fractionation by studying potential changes in isotope ratios in the freshwater model Daphnia magna feeding on the differently grown cyanobacteria. We show that δ 15N values of the cyanobacterium increase asymptotically with DIN availability, from -0.7 ‰ in the absence of DIN (suggesting N2 fixation) to 2.9 ‰ at the highest DIN concentration (exclusive DIN uptake). In contrast, δ 13C values of the cyanobacterium did not show a clear relationship with DIN availability. The stable isotope ratios of the consumer reflected those of the differently grown cyanobacteria but also revealed significant trophic fractionation in response to nitrogen utilization at the primary producer level. Nitrogen isotope turnover rates of Daphnia were highest in the absence of DIN as a consequence of N2 fixation and resulting depletion in 15N at the primary producer level. Our results highlight the potential of stable isotopes to assess nitrogen limitation and to explore diazotrophy in aquatic food webs.