Changes In Isotope Ratios Research Articles

Late Cenozoic topographic evolution of the Eastern Cordillera and Puna Plateau margin in the southern Central Andes (NW Argentina)

The Andes constitute an important orographic barrier in the southern hemisphere, impacting atmospheric circulation, the amount and distribution of rainfall, and Earth-surface processes in a highly asymmetric manner. In the Central Andes of NW Argentina, the Andean Plateau (Puna) and the intermontane basins of the adjacent Eastern Cordillera constitute geological archives that furnish spatiotemporal information on surface uplift and associated paleo-environmental change. Today, rainfall in NW Argentina is focused along the windward flanks of the Eastern Cordillera, while its intermontane basins and the Puna constitute high-elevation regions with strongly reduced rainfall. The present-day influence of these topographic characteristics on precipitation patterns is reflected by systematic changes in the hydrogen stable isotope ratios of meteoric water. Proxy archives from basin strata record past environmental conditions and provide insight into the nature of topographic growth through time. We present 34 new hydrogen isotopic compositions of volcanic glass (δDg), extracted from tuffs interbedded with the sedimentary deposits of three different regions across the eastern Andean margin between ca. 24°S and 25°S latitude. Combined with new zircon U-Pb geochronology, our data show clear spatiotemporal variations in δDg correlating with topographic growth and ensuing orographic effects during the Miocene and Pleistocene. In particular, variations in δDg indicate that the Pastos Grandes (Puna) and the Toro (Eastern Cordillera) basins had attained modern elevations by ca. 8 and 6 Ma, respectively. A strong positive shift in the δDg record of the Toro Basin after 840 ka coincides with deposition of thick fluvial/alluvial conglomerates suggesting orographically induced aridification due to progressive range uplift to the east. Other δDg records from the Eastern Cordillera show similar, but diachronous events emphasizing the importance of regional tectonics for environmental change with implications for the formation of orogenic plateaus.

Disentangling environmental from individual factors in isotopic ecology: A 17-year longitudinal study in a long-lived seabird exploiting the Canary Current

Abstract Despite its importance for ecology and conservation, we are still far from understanding how environmental variability interacts with intrinsic factors and individual specialization to determine trophic strategies of long-lived taxa, mostly due to difficulties in studying the same animals over extended periods. Here, by yearly consistently sampling the first primary feather of 99 Cory’s shearwaters (Calonectris borealis) foraging in the Canary Current (CC) upwelling ecosystem, we provide robust evidence on the individual changes of isotopic ratios of carbon (δ13C) and nitrogen (δ15N) over 17 years. We reported a slight longitudinal decline of δ13C values throughout 2001–2017, even after being adjusted for the marine Suess effect (linked to the increasing CO2 emissions). Although CC is often considered to be overexploited by industrial fisheries, we could not detect a decline in Cory’s shearwater trophic level indicating a change in the trophic web structuring, as revealed by δ15N. We found negative correlations of δ13C and δ15N with the CC upwelling intensity, indicating annual variability in baseline isotopic levels propagates through the food chain and it integrates in predators’ tissues. Low individual repeatabilities among years at population level indicates low long-term specialization, suggesting long-lived individuals foraging on highly productive areas can adjust their foraging strategies and diet according to environmental variability. However, individual-level repeatabilities in isotopic values showed a range of individual specialization within the population, indicating most individuals are generalist and a few of them highly specialized. First, although we found a clear influence of the upwelling intensity on the trophic ecology of birds, we could not detect any temporal trend in the trophic level of the Cory’s shearwater population, suggesting a stability in the structure of the pelagic food web of the CC over the last two decades despite the fishing pressure. Second, the existence of individual specialization highlights the importance of considering the repeated sampling of individuals to detect small changes in the trophic ecology of a population. Finally, the coexistence of individuals with different degree of specialization (from extremely flexible [generalists] to highly consistent individuals [specialists]) within a population can have deep implications on the capacity of populations to cope with environmental change.

Chemical alteration processes for uranium migration and their significance on uranium isotopic ratio changes

ABSTRACT Gabal Abu Garadi area is covered by metasediments, alkali feldspar granites and stream sediments. Geochemically, silicification, desilicification, sericitisation, fluoritisation and Na-metasomatism are the main alteration features of alkali feldspar granites. The activity concentration of 238U in alkali feldspar granites ranged between 1.7 ± 0.1 Bq g−1 and 3.9 ± 0.3 Bq g−1; between 1.7 ± 0.2 Bq g−1 and 9.4 ± 1.4 Bq g−1 for 234U and between 0.012 ± 0.0002 Bq g−1 and 0.09 ± 0.0001 Bq g−1 for 235U. The activity concentration of 228Th ranges between 1.3 ± 0.1 Bq g−1 and 3.6 ± 0.8 Bq g−1; between 1.5 ± 0.2 Bq g−1 and 2.7 ± 0.7 Bq g−1 for 230Th and between 1.8 ± 0.3 Bq g−1 and 4.1 ± 0.4 Bq g−1 for 232Th. The variability in Chemical Index of Alteration (CIA) with U, Th, 230Th/238U and 230Th/234U for the studied altered granite indicates that U and Th concentrations increased with increasing alteration especially in the silicified and desilicified samples. Changes in U, Th, 230Th/238U and 230Th/234U suggest the role of alteration processes in uranium and thorium mobilisation though thorium is geochemically less mobile or immobile. Thorium mobilisation could be controlled by adsorption in the alteration products of Abu Garadi granites such as clay minerals, manganese and iron oxides. In contrast, 230Th/238U and230Th/234U decreased with increasing CIA values suggesting uranium accumulation. 234U/238U ratios were in equilibrium in most samples; this might suggest the effect of severe chemical weathering or alteration processes that leads to the leachability of the two radionuclides (234U, 238U) with the same ratio probably during kaolinisation processes. In contrast, 230Th/238U and230Th/234U>1 were in disequilibrium, suggesting the changes in the physicochemical conditions accompanying the different alteration processes.

Exploring cycad foliage as an archive of the isotopic composition of atmospheric nitrogen.

Molecular nitrogen (N2 ) constitutes the majority of Earth's modern atmosphere, contributing ~0.79bar of partial pressure (pN2 ). However, fluctuations in pN2 may have occurred on 107 -109 year timescales in Earth's past, perhaps altering the isotopic composition of atmospheric nitrogen. Here, we explore an archive that may record the isotopic composition of atmospheric N2 in deep time: the foliage of cycads. Cycads are ancient gymnosperms that host symbiotic N2 -fixing cyanobacteria in modified root structures known as coralloid roots. All extant species of cycads are known to host symbionts, suggesting that this N2 -fixing capacity is perhaps ancestral, reaching back to the early history of cycads in the late Paleozoic. Therefore, if the process of microbial N2 fixation records the δ15 N value of atmospheric N2 in cycad foliage, the fossil record of cycads may provide an archive of atmospheric δ15 N values. To explore this potential proxy, we conducted a survey of wild cycads growing in a range of modern environments to determine whether cycad foliage reliably records the isotopic composition of atmospheric N2 . We find that neither biological nor environmental factors significantly influence the δ15 N values of cycad foliage, suggesting that they provide a reasonably robust record of the δ15 N of atmospheric N2 . Application of this proxy to the record of carbonaceous cycad fossils may not only help to constrain changes in atmospheric nitrogen isotope ratios since the late Paleozoic, but also could shed light on the antiquity of the N2 -fixing symbiosis between cycads and cyanobacteria.

Traceability of 'Mozzarella di Bufala Campana' production chain by means of carbon, nitrogen and oxygen stable isotope ratios.

New techniques are required to guarantee the authenticity of food, especially for PDO (Protected Designation of Origin) trademarks. The genuineness of a product is directly related to the raw material and to the production process used. In this article, the traceability of the Mozzarella di Bufala Campana PDO was investigated, using carbon, nitrogen and oxygen stable isotopes ratios, measured on buffalo feeding, milk and mozzarella, from Caserta and Salerno farms. Furthermore, 37 mozzarella brands were analyzed (carbon, nitrogen and oxygen isotopes) from the different production areas, to characterize their origin. The results of this work showed no changes in carbon and nitrogen isotopic ratios of milk and mozzarella, indicating no fractionation in the production process. The δ13 C of milk was influenced by feeding signal; while, milk δ15 N was regulated by fractionation occurring during ruminant metabolism. Mozzarella oxygen isotopic signal depleted with respect to the milk one. Regarding brand samples, it was found that the geographical differentiation is based more on carbon isotopes than on the nitrogen and oxygen ones. This work gives an important contribution to the knowledge regarding the traceability of such a particular cheese as mozzarella. © 2019 Society of Chemical Industry.

Shift in trophic niches of soil microarthropods with conversion of tropical rainforest into plantations as indicated by stable isotopes (15N, 13C).

Land-use change is threatening biodiversity worldwide, affecting above and below ground animal communities by altering their trophic niches. However, shifts in trophic niches with changes in land use are little studied and this applies in particular to belowground animals. Oribatid mites are among the most abundant soil animals, involved in decomposition processes and nutrient cycling. We analyzed shifts in trophic niches of six soil-living oribatid mite species with the conversion of lowland secondary rainforest into plantation systems of different land-use intensity (jungle rubber, rubber and oil palm monoculture plantation) in two regions of southwest Sumatra, Indonesia. We measured stable isotope ratios (13C/12C and 15N/14N) of single oribatid mite individuals and calculated shifts in stable isotope niches with changes in land use. Significant changes in stable isotope ratios in three of the six studied oribatid mite species indicated that these species shift their trophic niches with changes in land use. The trophic shift was either due to changes in trophic level (δ15N values), to changes in the use of basal resources (δ13C values) or to changes in both. The trophic shift generally was most pronounced between more natural systems (rainforest and jungle rubber) on one side and monoculture plantations systems (rubber and oil palm plantations) on the other, reflecting that the shifts were related to land-use intensity. Although trophic niches of the other three studied species did not differ significantly between land-use systems they followed a similar trend. Overall, the results suggest that colonization of very different ecosystems such as rainforest and intensively managed monoculture plantations by oribatid mite species likely is related to their ability to shift their trophic niches, i.e. to trophic plasticity.

Nutritional stress by means of high C:N ratios in the diet and starvation affects nitrogen isotope ratios and trophic fractionation of omnivorous copepods.

Nutritional stress, from feeding on low-quality diets or starvation, may cause changes in consumers' nitrogen isotope ratios (δ15N = 15N/14N) and trophic fractionation (∆15N = δ15Nconsumer - δ15Nfood source), however, research has shown mixed results in the magnitude and the direction of the change. This is potentially more complex for omnivores whose diets span a wide range of food resources. We conducted seasonal field samplings in Patagonian lakes and analyzed the relationship between seston (SES) quality parameters and the δ15N and ∆15N of an omnivorous copepod, Boeckella gracilipes (Bg). We also performed a 7-day laboratory starvation experiment, an extreme form of nutritional stress, to investigate if lack of food led to changes in δ15NBg values. Our field results showed that increasing values of the seston carbon to nitrogen ratio (C:NSES), chlorophyll a (Chl a), and δ15NSES were related to higher δ15NBg values. C:NSES and Chl a were also positively related to ∆15N; yet, C:NSES alone explained 70% of the variation. C:NSES values correlated with the presence of mixotrophic algae and ciliates that are key food resources for B. gracilipes. In our laboratory starvation experiment, the δ15NBg values increased significantly, pointing to use of internal N sources; yet, the change associated with starvation was less pronounced than that related to C:NSES changes in the field, suggesting depletion of the substrate pool in the former. We found that ∆15N values of omnivorous species consuming a low-quality diet would be higher than that from a conspecific with a high-quality diet; though fasting animals would show intermediate values.

Sources of Uncertainty in Biotransformation Mechanistic Interpretations and Remediation Studies using CSIA.

Compound-specific isotope analysis (CSIA) is a powerful tool to understand the fate of organic contaminants. Using CSIA, the isotope ratios of multiple elements (δ13C, δ2H, δ37Cl, δ15N) can be measured for a compound. A dual-isotope plot of the changes in isotope ratios between two elements produces a slope, lambda (Λ), which can be instrumental for practitioners to identify transformation mechanisms. However, practices to calculate and report Λ and related uncertainty are not universal, leading to the potential for misinterpretations. Here, the most common methods are re-evaluated to provide the basis for a more accurate best-practice representation of Λ and its uncertainty. The popular regression technique, ordinary linear regression, can introduce mathematical bias. The York method, which incorporates error in both variables, better adapts to the wide set of data conditions observed for dual-isotope data. Importantly, the existing technique of distinguishing between Λs using the 95% confidence interval alone produces inconsistent results, whereas statistical hypothesis testing provides a more robust method to differentiate Λs. The propensity for Λ to overlap for a variety of conditions and mechanisms highlights the requirement for statistical justification when comparing data sets. Findings from this study emphasize the importance of this evaluation of best practice and provide recommendations for standardizing, calculating, and interpreting dual-isotope data.

Wintertime decoupling of urban valley and rural ridge hydrological processes revealed through stable water isotopes

Water from fossil fuel combustion can represent >10% of urban specific humidity, but this fraction is difficult to constrain from meteorological measurements alone. Stable water vapor isotopes can be used to estimate the fraction of combustion-derived vapor (CDV) and characterize the contrast between anthropogenically-altered and natural systems due to CDV's distinctive isotope composition. However, accurate estimates of the CDV fraction of urban humidity requires information on vapor isotope ratios in the absence of anthropogenic emissions. We present data from an urban site in Salt Lake City, UT and from a high-elevation site in the adjacent Wasatch Mountains. Urban vapor d-excess values (d-excess = δ2H–8δ18O) closely track CO2 concentrations on diurnal to weekly timescales, but high-elevation vapor values do not. Instead, the high-elevation site captures large-scale atmospheric variability, with d-excess changes largely following changes in δ18O and humidity. Isotope ratios at the two sites remain distinct throughout most of the winter, indicating that these sites are regularly decoupled from each other and that high-elevation winter measurements may rarely be representative of valley conditions in the absence of urban emissions. Furthermore, high-elevation d-excess may be higher than emissions-free values at the same elevation as the urban area, as vapor d-excess changes non-linearly during condensation at low specific humidity, and would result in an overestimate of urban humidity amounts. Therefore, the high-elevation site may not help place additional constraints on the amount of CDV in urban systems, yet the paired sites show changes in vapor isotope ratios, particularly in d-excess, that capture differences in urban and natural impacts on water vapor cycling.

Contributions of Atmospheric Deposition to Pb Concentration and Isotopic Composition in Seawater and Particulate Matters in the Gulf of Aqaba, Red Sea.

Lead concentrations [Pb] and isotope ratios (206Pb/207Pb, 208Pb/207Pb) have been measured in samples of total suspended particulate (TSP) aerosols, seawater, and suspended and sinking particles in the Gulf of Aqaba (GOA), Red Sea. Isotope ratios of Pb in seawater and in the soluble fraction of Pb in atmospheric TSP were similar suggesting that TSP is an important source of Pb in this area. Pb concentrations in seawater measured in this study (max 76.8 pmol kg-1) were much lower than those recorded at the same location in 2003-2004 (up to 1000 pmol kg-1). Changes in Pb isotope ratios in TSP depositions in these years indicate that leaded gasoline was responsible for the high dissolved Pb in GOA more than a decade ago and that recent regulation reduced Pb contamination. The similarity in Pb isotope ratios in suspended and sinking particles implies close interactions between these two size fractions. This study demonstrates the effect of the phasing out of leaded gasoline on TSP and seawater Pb chemistry in the Northern GOA; the rate of change in dissolved Pb concentrations in the GOA is faster than that reported for the open ocean possibly due to higher particle scavenging and the relatively short residence time of deep water in the Basin.

Development of an autonomous, monthly and daily, rainfall sampler for isotope research

An autonomous, low cost (<US$750), and open source rainfall sampler has been developed for hydrogen and oxygen isotope research, able to sample daily and monthly for up to 60 days of rainfall, over a three month period. The sampler is designed to use modern fabrication methods such as 3D printing and laser cutting to minimise the need for machined and injection molded components. The sampler can use either paraffin oil or a submerged inlet tube (also known as tube-dip-in samplers) to prevent evaporation, with the use of the inlet tube method facilitated by 3D printed bottle caps. An experiment was performed to identify the most suitable plastic for these caps, with acetone treated ABS (Acrylonitrile Butadiene Styrene) being most suitable, followed by PETG (Polyethylene Terephthalate Glycol), untreated ABS, and PLA (Polylactic acid). In addition, the effectiveness of both paraffin oil and the inlet tube method for preventing evaporation was quantified, with paraffin identified as being the most effective at present. During a 90 day outdoor experiment, the 18O/16O vs. 2H/1H ratios of some water samples evolved along a local evaporation line, with increased isotopic enrichment of samples correlating to water loss. A coupled hydrologic-isotopic model was applied to these data, and successfully predicted the change in isotope ratios based on the amount of water lost from each sample. This modelling approach, combined with daily and monthly sample collection and quantification of evaporation rates within the sheltered environment of the sampler allows for back calculation of the original volume and isotopic composition of daily and monthly rainfall samples. The rainfall sampler thus facilitates cost -and time- effective remote monitoring of the isotopic composition of precipitation to support an array of Earth system research.

An abrupt decrease in Southern Hemisphere terrestrial temperature during the Eocene–Oligocene transition

Earth's climate transitioned from the greenhouse conditions of the Eocene to the icehouse of the Oligocene ∼34 million years ago. Global cooling was triggered by a decrease in atmospheric pCO2 and is associated with the first appearance of large, permanent ice-sheets on Antarctica. The Eocene–Oligocene transition (EOT) is marked by a large two-step increase in the δ18O of benthic foraminifera, reflecting a combination of cooler global temperatures and continental ice growth. We measured the hydrogen isotope composition of hydrated volcanic glasses deposited in Patagonia during the EOT to reconstruct stable isotope hydrology and associated changes in temperature during this critical climate transition. These data show changes in stable hydrogen isotope ratios that are consistent with Patagonian terrestrial mean annual temperature decreasing by ∼5°C during the EOT before returning to 2°C below pre-EOT values by the Early Oligocene. This is approximately synchronous with Northern Hemisphere cooling during the EOT, and indicates close coupling of temperature and atmospheric pCO2.

Using Carbon Isotope Fractionation to Constrain the Extent of Methane Dissolution Into the Water Column Surrounding a Natural Hydrocarbon Gas Seep in the Northern Gulf of Mexico

AbstractA gas bubble seep located in the northern Gulf of Mexico was investigated over several days to determine whether changes in the stable carbon isotopic ratio of methane can be used as a tracer for methane dissolution through the water column. Gas bubble and water samples were collected at the seafloor and throughout the water column for isotopic ratio analysis of methane. Our results show that changes in methane isotopic ratios are consistent with laboratory experiments that measured the isotopic fractionation from methane dissolution. A Rayleigh isotope model was applied to the isotope data to determine the fraction of methane dissolved at each depth. On average, the fraction of methane dissolved surpasses 90% past an altitude of 400 m above the seafloor. Methane dissolution was also investigated using a modified version of the Texas A&amp;M Oil spill (Outfall) Calculator (TAMOC) where changes in methane isotopic ratios could be calculated. The TAMOC model results show that dissolution depends on depth and bubble size, explaining the spread in measured isotopic ratios during our investigations. Both the Rayleigh and TAMOC models show that methane bubbles quickly dissolve following emission from the seafloor. Together, these results show that it is possible to use measurements of natural methane isotopes to constrain the extent of methane dissolution following seafloor emission.

Calculation of Single Cell Assimilation Rates From SIP-NanoSIMS-Derived Isotope Ratios: A Comprehensive Approach.

The nanoSIMS-based chemical microscopy has been introduced in biology over a decade ago. The spatial distribution of elements and isotopes analyzed by nanoSIMS can be used to reconstruct images of biological samples with a resolution down to tens of nanometers, and can be also interpreted quantitatively. Currently, a unified approach for calculation of single cell assimilation rates from nanoSIMS-derived changes in isotope ratios is missing. Here we present a comprehensive concept of assimilation rate calculation with a rigorous mathematical model based on quantitative evaluation of nanoSIMS-derived isotope ratios. We provide a detailed description of data acquisition and treatment, including the selection and accumulation of nanoSIMS scans, defining regions of interest and extraction of isotope ratios. Next, we present alternative methods to determine the cellular volume and the density of the element under scrutiny. Finally, to compensate for alterations of original isotopic ratios, our model considers corrections for sample preparation methods (e.g., air dry, chemical fixation, permeabilization, hybridization), and when known, for the stable isotope fractionation associated with utilization of defined growth substrates. As proof of concept we implemented this protocol to quantify the assimilation of 13C-labeled glucose by single cells of Pseudomonas putida. In addition, we provide a calculation template where all protocol-derived formulas are directly available to facilitate routine assimilation rate calculations by nanoSIMS users.

Advanced Photonic Sensors Based on Interband Cascade Lasers for Real-Time Mouse Breath Analysis.

A multiparameter gas sensor based on distributed feedback interband cascade lasers emitting at 4.35 μm and ultrafast electro-spun luminescence oxygen sensors has been developed for the quantification and continuous monitoring of 13CO2/12CO2 isotopic ratio changes and oxygen in exhaled mouse breath samples. Mid-infrared absorption spectra for quantitatively monitoring the enrichment of 13CO2 levels were recorded in a miniaturized dual-channel substrate-integrated hollow waveguide using balanced ratiometric detection, whereas luminescence quenching was used for synchronously detecting exhaled oxygen levels. Allan variance analysis verified a CO2 measurement precision of 1.6‰ during a 480 s integration time. Routine online monitoring of exhaled mouse breath was performed in 14 mechanically ventilated and instrumented mice and demonstrated the feasibility of online isotope-selective exhaled breath analysis within microliters of probed gas samples using the reported combined sensor platform.

Adult nutrition and reproductive physiology: a stable isotope analysis in a eusocial paper wasp (Mischocyttarus mastigophorus, Hymenoptera: Vespidae)

Division of labor in social groups can be influenced by differential nutrition. Consumption of more food or higher-quality food often affects individuals’ capacities for reproduction. In social insects, nutrients consumed during immature (e.g., larval) stages often affect adult reproductive capacity, but adult nutrition may also impact reproductive status. This study tested whether ovary development, an indicator of reproductive status, corresponded to higher trophic-level feeding for adults in the primitively eusocial paper wasp Mischocyttarus mastigophorus. Our main prediction was that females’ ovary development would correlate positively with evidence of feeding at higher trophic levels, as indicated by stable isotope ratios of nitrogen (δ15N) and carbon (δ13C). We first asked whether isotope ratios of mature females co-varied with ovary development. δ15N values were higher for mature females with better-developed ovaries, as expected if they fed on a diet richer in animal tissue. There was a negative relationship of δ13C with ovary development in mature females, as would be expected if females with developed ovaries had higher body lipid stores. To test for evidence of nutritional biasing of caste during immature development, we measured changes in isotope ratios across pupal development leading up to early adulthood (i.e., immediately before and after adult eclosion). The δ15N and δ13C values for mature pupae were similar to those of newly emerged adults and to those of mature adults lacking developed ovaries. In contrast, mature females with developed ovaries showed N-isotope signatures of a more prey-based diet and C-isotope signatures of elevated lipid content. We conclude the N and C isotopic signatures of ovary-developed mature females diverged from their levels at the end of immature development. The findings suggest reproductive caste status was associated with differences in nutrient acquisition and reflects differences in consumption of animal-derived versus plant-based foods during adulthood. Pre-adult nutrition is known to affect caste development, and thereby influence division of labor, in diverse insect societies. In temperate independent-founding (IF) paper wasps, the effects of larval nutrition on adult caste may reflect adaptations for overwintering and diapause by reproductive females. We asked whether adult nutritional content showed caste-related trophic differences in the Neotropical IF paper wasp Mischocyttarus mastigophorus. Previous studies suggested interactions among adult nest-mates affected food sharing and caused biased nutrient flow within colonies. Our data suggest adult nutrition affected reproductive physiology. We propose this pattern may be widespread in tropical IF paper wasps, where opportunities for adult reproductive plasticity are favored by long colony cycles and relatively aseasonal nest founding.

Effects of acidification on the isotopic ratios of Neotropical otter tooth dentin.

Stable carbon and nitrogen isotope ratios are widely used in ecological studies providing important information on the trophic ecology and habitat use of consumers. However, some factors may lead to isotopic variability, which makes difficult the interpretation of data, such as the presence of inorganic carbon in mineralized tissues. In order to remove the inorganic carbon, acidification is a commonly used treatment. The effects of two methods of acidification were tested: (i) dentin acidification with 10% HCl using the 'drop-by-drop' technique, and (ii) dentin acidification in an 'HCl atmosphere', by exposing the dentin to vaporous 30% hydrochloric acid. Results were compared with untreated subsamples. The stable carbon and nitrogen ratios of untreated and acidified subsamples were measured using an elemental analyzer coupled to an isotope ratio mass spectrometer. The nitrogen isotopic ratios were statistically different between the two acidification treatments, but no significant changes in carbon isotopic ratios were found in acidified and untreated samples. The results indicated that acidification had no effect on carbon isotopic ratios of Neotropical otter tooth dentin, while introducing a source of error in nitrogen isotopic ratios. Therefore, we conclude that acidification is an unnecessary step for C and N stable isotope analysis.

Assessing the effect of chlorinated hydrocarbon degradation in aquitards on plume persistence due to back-diffusion

This modeling study aims to investigate how reactive processes in aquitards impact plume persistence in adjacent aquifers. For that purpose the migration of a trichloroethene (TCE) plume in an aquifer originating from dense non-aqueous phase liquid (DNAPL) source dissolution and back-diffusion from an underlying reactive aquitard was simulated in a 2D-numerical model. Two aquitard degradation scenarios were modeled considering one-step degradation from TCE to cis-dichloroethene (cDCE): a uniform (constant degradation with aquitard depth) and a non-uniform scenario (decreasing degradation with aquitard depth) and were compared with a no-degradation scenario. In the no-degradation scenario, a long-term TCE tailing above the Maximum Contaminant Level (MCL) caused by back-diffusion after source removal was observed. In contrast, in the aquitard degradation scenarios, TCE back-diffusion periods were shorter, whereby the extent of back-diffusion reduction depended on the aquitard degradation depth and the rate. For high degradation rates (half-life: 30–80days), an aquitard degradation depth greater than 65cm prevented TCE plume persistence after source removal but generated a long-term tailing above the MCL for the produced cDCE. For slow degradation rates (half-life: <200days), TCE was only partially degraded after source removal, independent of the aquitard degradation depth, leading to a long-term dual contamination of the aquifer by cDCE and TCE. A sudden enrichment of 13C in TCE and cDCE was observed after source removal in the uniform and non-uniform degradation scenarios that was distinct from δ13C patterns observed when aquifer degradation occurs (continuous enrichment of 13C along the plume axis) and for when there is absence of degradation (no change of isotope ratios). This demonstrates that δ13C measurements in the aquifer can be used as a diagnostic tool to demonstrate aquitard degradation, which simplifies the identification of reactive processes in aquitards, as aquifers are usually easier to monitor than aquitards.

A multiproxy record of the Younger Holsteinian Oscillation (YHO) in the Ossówka profile, eastern Poland

The laminated lacustrine succession at Ossówka in eastern Poland, which is largely the equivalent of MIS 11c, is amongst the best‐developed sites in Europe that cover this time period. Close inspection of the depth interval between 35.0 and 42.5 m in a 55‐m‐long core shows an environmental crisis at a depth of 40.95 m that lasted approximately 800 years and resulted in almost complete extinction of fir (Abies) from the communities existing at that time. Geochemical analyses reveal a simultaneous increase in sulphur in the deposits and a change in stable carbon and oxygen isotope ratios towards higher values, as well as a significant increase in the thickness of the laminae (up to 5 mm). Diatom studies show a clear increase in benthic diatoms in this interval, implying a decrease in water level. However, the predominance of such forms was probably caused by the elimination of planktonic diatoms by invasive blooms of Tetraedron, rather than lower lake levels, evidence of which was not noted in the pollen spectra. Hence, all these changes in the lake may have been triggered by the destruction of fir trees, the gradual decomposition of dead trunks and some inconspicuous geomorphological disturbances caused by wind throw. They resulted in a supply of micronutrients to the basin, an increase in varve thickness and rapid oscillations in the abundance and composition of algae and changes in the geochemical status of the lake. Rapid and significant drops in winter temperatures appear to be responsible for the extinction of fir. Alternatively, late frost in spring or hot and dry summers may have affected microsporophyll growth and the fir physiology as known from extant Abies populations. This environmental crisis, which is termed the Younger Holsteinian Oscillation (YHO), is noted at only a few sites. At Dethlingen (Germany), where hornbeam communities disappear at that time, a drop in summer temperatures is suggested to have been the driving force. We suggest that, at Ossówka, a drop in winter temperatures, late frost, or summer drought at the very start of the YHO are possible causes of the near‐extinction of fir.

Early mining and smelting lead anomalies in geological archives as potential stratigraphic markers for the base of an early Anthropocene

This article reviews possible lower boundaries for an early Anthropocene period. Although a noticeable environmental impact of humans, caused by hunting, the use of fire, forest clearance, animal domestication and agriculture had already occurred in the Neolithic, these early signals are strongly diachronous and localised. Here, we examine early significant, synchronous and regional stratigraphic signals indicating an anthropogenic influence as consequences of mining and smelting-related trace metal contamination. A first regional lead contamination event in the Northern Hemisphere is recognized during the (Eastern Mediterranean) Late Bronze Age to Early Iron Age, between 3500 and 2800 BP, with a peak at around 3000 BP. Another pronounced anthropogenic lead peak is recorded around 2000 BP, during the Roman period. These events, as defined by lead enrichment and changes in lead isotope ratios, accompanied by other trace metal enrichments, are found in several types of archives, such as Arctic ice-cores and European peat-bogs, speleothems as well as fluvial, lake and marine records. Potential stratigraphic correlations and secondary markers may be present using tephrochronology, climate events, and magnetostratigraphy. Such a definition of the base of a formally defined (early) Anthropocene stage/period allows the application of the GSSP (Global Stratotype Section and Point) concept by using a point in a physical archive, and, in contrast to the late Anthropocene, includes a significant quantity of anthropogenic strata as evidence for an Anthropocene chronostratigraphic unit.