Search

Introduction: The Global Meteoric Water Line (GMWL) describes the linear relationship between stable hydrogen (δ 2H) and oxygen (δ 18O) isotopes in precipitation over large spatial scales and therefore represents a unique reference for water isotopic values. Although trees have the potential to capture the isotopic composition of precipitation, it remains unclear if the GMWL can be reconstructed from tree-ring stable isotopes, since δ 18O and δ 2H undergo in vivo physiological fractionation. Methods: We analyze the tree rings δ 18O and δ 2H values from six regions along a latitudinal gradient from Spain to Greenland. Results: The data show that the covariance between δ 18O and δ 2H closely follows the GMWL, which reflects the isotopic signature of large-scale precipitation patterns. We show that changes in regional tree-ring δ 18O and δ 2H values along wide latitudinal ranges are influenced by the isotopic composition of precipitation with temperature and latitude being the most significant drivers of spatial variation across the studied regions. In contrast, local tree-ring δ 18O and δ 2H values are mainly controlled by plant physiological fractionation processes that mask the isotopic signature of precipitation. Conclusion: We conclude that covariance in tree-ring δ 18O and δ 2H reflects the GMWL at larger spatial scales, but not when evaluating them at individual sites. [ABSTRACT FROM AUTHOR]

IntroductionThe Global Meteoric Water Line (GMWL) describes the linear relationship between stable hydrogen (δ2H) and oxygen (δ18O) isotopes in precipitation over large spatial scales and therefore represents a unique reference for water isotopic values. Although trees have the potential to capture the isotopic composition of precipitation, it remains unclear if the GMWL can be reconstructed from tree-ring stable isotopes, since δ18O and δ2H undergo in vivo physiological fractionation.MethodsWe analyze the tree rings δ18O and δ2H values from six regions along a latitudinal gradient from Spain to Greenland. ResultsThe data show that the covariance between δ18O and δ2H closely follows the GMWL, which reflects the isotopic signature of large-scale precipitation patterns. We show that changes in regional tree-ring δ18O and δ2H values along wide latitudinal ranges are influenced by the isotopic composition of precipitation with temperature and latitude being the most significant drivers of spatial variation across the studied regions. In contrast, local tree-ring δ18O and δ2H values are mainly controlled by plant physiological fractionation processes that mask the isotopic signature of precipitation.ConclusionWe conclude that covariance in tree-ring δ18O and δ2H reflects the GMWL at larger spatial scales, but not when evaluating them at individual sites.

Belowground niche partitioning presents a key mechanism for maintaining species coexistence and diversity. Its importance is currently reinforced by climate change that alters soil hydrological conditions. However, experimental tests examining the magnitude of its change under climate change are scarce. We combined measurements of oxygen stable isotopes to infer plant water‐uptake depths and extreme drought manipulation in grasslands. Belowground niche partitioning was evidenced by different water‐uptake depths of co‐occurring species under ambient and extreme drought conditions despite an increased overlap among species due to a shift to shallower soil layers under drought. A co‐occurrence of contrasting strategies related to the change of species water‐uptake depth distribution was likely to be key for species to maintain some extent of belowground niche partitioning and could contribute to stabilizing coexistence under drought. Our results suggest that belowground niche partitioning could mitigate negative effects on diversity imposed by extreme drought under future climate. [ABSTRACT FROM AUTHOR]

The oxygen isotopes ratio (δ18O) of microbial cell water strongly controls the δ18O of cell phosphate and of other oxygen-carrying moieties. Recently it was suggested that the isotopic ratio in cell water is controlled by metabolic water, which is the water produced by cellular respiration. This potentially has important implications for paleoclimate reconstruction, and for measuring microbial carbon use efficiency with the 18O-water method. Carbon use efficiency strongly controls soil organic matter preservation. Here, we directly tested the effect of metabolic water on microbial cells, by conducting experiments with varying the δ18O of headspace O2 and the medium water, and by measuring the δ18O of cell phosphate. The latter is usually assumed to be in isotopic equilibrium with the cell's water. Our results showed no correlation between the δ18O of O2 and that of the cell phosphate, contradicting the hypothesis that metabolic water is an important driver of δ18O of microbial cell water. However, our labeled 18O water experiments indicated that only 43% of the oxygen in the cell's phosphate is derived from equilibration with the medium water, during late-log to early-stationary growing phase. This could be explained by the isotopic effects of intra-and extra-cellular hydrolysis of organic compounds containing phosphate. [ABSTRACT FROM AUTHOR]

The oxygen isotopes ratio (δ18O) of microbial cell water strongly controls the δ18O of cell phosphate and of other oxygen-carrying moieties. Recently it was suggested that the isotopic ratio in cell water is controlled by metabolic water, which is the water produced by cellular respiration. This potentially has important implications for paleoclimate reconstruction, and for measuring microbial carbon use efficiency with the 18O-water method. Carbon use efficiency strongly controls soil organic matter preservation. Here, we directly tested the effect of metabolic water on microbial cells, by conducting experiments with varying the δ18O of headspace O2 and the medium water, and by measuring the δ18O of cell phosphate. The latter is usually assumed to be in isotopic equilibrium with the cell’s water. Our results showed no correlation between the δ18O of O2 and that of the cell phosphate, contradicting the hypothesis that metabolic water is an important driver of δ18O of microbial cell water. However, our labeled 18O water experiments indicated that only 43% of the oxygen in the cell’s phosphate is derived from equilibration with the medium water, during late-log to early-stationary growing phase. This could be explained by the isotopic effects of intra-and extra-cellular hydrolysis of organic compounds containing phosphate.

Strong variation in plant organic compound δ2H and δ18O values such as leaf waxes or cellulose among species is commonly observed; however, the extent to which this isotopic variation is driven by leaf water or biochemical isotope effects is relatively unknown. Therefore, we compared variation in leaf water and organic compound δ2H and δ18O values (cellulose - δ2H and δ18O, and n -alkanes – δ2H) across 192 species grown in a botanical garden to assess covariation of isotope values (1) between elements in a given compound, (2) between different (organic) compounds of a given element, and (3) across different growing seasons. Our results suggest that variation in leaf water δ2H values are likely not a strong driver for the observed variation in organic compound δ2H values across species, and that this may also be true for δ18O values. Furthermore, even though correlation between leaf water δ2H and δ18O values appears to be transferred to organic compounds, the explanatory power of this correlation is strongly diminished (R2 < 0.04). This indicates that additional biochemical isotope fractionation leads to substantial variation in organic compound δ2H and possibly also δ18O values across species. Moreover, the low explanatory power of the correlation between cellulose and n -alkane δ2H values (R2 = 0.06) suggests that the biochemical pathways associated with the different compounds are accompanied by different isotope effects. Lastly, cellulose δ2H and δ18O values appeared sensitive to environmental differences between growing seasons, while differences in model-predicted source water δ18O and δ2H values and also climate were negligible between years. By contrast, the species pattern in n -alkane δ2H values was highly conserved between the two years. This indicates that the environmental forcing effects on isotope values were not equal between compounds. Therefore, we conclude that variation in organic compound δ2H (and possibly also δ18O) values among species and growing seasons was more strongly driven by biochemical isotope fractionation rather than by isotope values of plant water. This should be considered in the application of organic compound δ2H and δ18O values to reconstruct past climate, where invariable biochemical isotope fractionation is often assumed. Alternatively, organic compound δ2H and δ18O values could be further developed into a tool to extract plant metabolic information. [ABSTRACT FROM AUTHOR]

Copyright of Methods in Ecology & Evolution is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Food Safety & Quality is the property of Journal of Food Safety & Quality Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract Stable oxygen isotope (δ18O) compositions from vertebrate tooth enamel are widely used as biogeochemical proxies for paleoclimate. However, the utility of enamel oxygen isotope values for environmental reconstruction varies among species. Herein, we evaluate the use of stable oxygen isotope compositions from pronghorn (Antilocapra americana Gray, 1866) enamel for reconstructing paleoclimate seasonality, an elusive but important parameter for understanding past ecosystems. We serially sampled the lower third molars of recent adult pronghorn from Wyoming for δ18O in phosphate (δ18OPO4) and compared patterns to interpolated and measured yearly variation in environmental waters as well as from sagebrush leaves, lakes, and rivers (δ18Ow). As expected, the oxygen isotope compositions of phosphate from pronghorn enamel are enriched in 18O relative to environmental waters. For a more direct comparison, we converted δ18Ow values into expected δ18OPO4* values (δ18OW‐PO4*). Pronghorn δ18OPO4 values from tooth enamel record nearly the full amplitude of seasonal variation from Wyoming δ18OW‐PO4* values. Furthermore, pronghorn enamel δ18OPO4 values are more similar to modeled δ18OW‐PO4* values from plant leaf waters than meteoric waters, suggesting that they obtain much of their water from evaporated plant waters. Collectively, our findings establish that seasonality in source water is reliably reflected in pronghorn enamel, providing the basis for exploring changes in the amplitude of seasonality of ancient climates. As a preliminary test, we sampled historical pronghorn specimens (1720 ± 100 AD), which show a mean decrease (a shift to lower values) of 1–2‰ in δ18OPO4 compared to the modern specimens. They also exhibit an increase in the δ18O amplitude, representing an increase in seasonality. We suggest that the cooler mean annual and summer temperatures typical of the 18th century, as well as enhanced periods of drought, drove differences among the modern and historical pronghorn, further establishing pronghorn enamel as excellent sources of paleoclimate proxy data.

The cooling associated with the Little Ice Age (LIA) had differential severity across the globe. Within the American Midwest, the local impacts of this cooling have not been established. Our purpose here is to determine its local effects and establish the impacts on the environment encountered at a seventeenth century Native American village in Illinois, USA. We obtained oxygen and carbon stable isotope ratios of freshwater mussel shells from this early seventeenth century site, occupied during one of the coldest periods of the LIA. These data were compared to the oxygen and carbon ratios of freshwater shells from a nineteenth century cabin as well as modern shells. Results demonstrate that shell stable oxygen isotopes capture environmental conditions at the three sites and suggest more arid conditions during the LIA and increased precipitation into the present. Findings also may capture the extensive alteration of the Kankakee region's drainage between the late nineteenth and early twentieth centuries as well as contemporary global warming. Overall, this study illustrates the value of archaeological data to past and contemporary climate studies. [ABSTRACT FROM AUTHOR]

Stable oxygen isotope (δ18O) compositions from vertebrate tooth enamel are widely used as biogeochemical proxies for paleoclimate. However, the utility of enamel oxygen isotope values for environmental reconstruction varies among species. Herein, we evaluate the use of stable oxygen isotope compositions from pronghorn (Antilocapra americana Gray, 1866) enamel for reconstructing paleoclimate seasonality, an elusive but important parameter for understanding past ecosystems. We serially sampled the lower third molars of recent adult pronghorn from Wyoming for δ18O in phosphate (δ18OPO4) and compared patterns to interpolated and measured yearly variation in environmental waters as well as from sagebrush leaves, lakes, and rivers (δ18Ow). As expected, the oxygen isotope compositions of phosphate from pronghorn enamel are enriched in 18O relative to environmental waters. For a more direct comparison, we converted δ18Ow values into expected δ18OPO4* values (δ18OW‐PO4*). Pronghorn δ18OPO4 values from tooth enamel record nearly the full amplitude of seasonal variation from Wyoming δ18OW‐PO4* values. Furthermore, pronghorn enamel δ18OPO4 values are more similar to modeled δ18OW‐PO4* values from plant leaf waters than meteoric waters, suggesting that they obtain much of their water from evaporated plant waters. Collectively, our findings establish that seasonality in source water is reliably reflected in pronghorn enamel, providing the basis for exploring changes in the amplitude of seasonality of ancient climates. As a preliminary test, we sampled historical pronghorn specimens (1720 ± 100 AD), which show a mean decrease (a shift to lower values) of 1–2‰ in δ18OPO4 compared to the modern specimens. They also exhibit an increase in the δ18O amplitude, representing an increase in seasonality. We suggest that the cooler mean annual and summer temperatures typical of the 18th century, as well as enhanced periods of drought, drove differences among the modern and historical pronghorn, further establishing pronghorn enamel as excellent sources of paleoclimate proxy data. [ABSTRACT FROM AUTHOR]

The hydrogen isotopic composition of leaf wax-derived biomarkers, e.g. long chain 푛-alkanes (d2-H푛-alkane), is widely applied in paleoclimatology research. However, a direct reconstruction of the isotopic composition of source water based on d2H푛-alkane alone can be challenging due to the alteration of the soil water isotopic signal by leaf-water heavy-isotope enrichment. The coupling of d2H푛-alkane with d18O of hemicellulose-derived sugars (d18Osugar) has the potential to disentangle this effect and additionally to allow relative humidity reconstructions. Here, we present d2H푛-alkane as well as d18Osugar results obtained from leaves of the plant species Eucalyptus globulus, Vicia faba var. minor and Brassica oleracea var. medullosa, which grew under controlled conditions. We addressed the questions (i) do d2H푛-alkane and d18Osugar values allow precise reconstructions of leaf water isotope composition, (ii) how accurately does the reconstructed leaf-water-isotope composition enables relative humidity (RH) reconstruction in which the plants grew, and (iii) does the coupling of d2H푛-alkane and d18Osugar enable a robust source water calculation? For all investigated species, the alkane 푛-C29 was most abundant and therefore used for compound specific d2H measurements. For Vicia faba, additionally the d2H values of 푛-C31 could be evaluated robustly. With regard to hemicellulose-derived monosaccharides, arabinose and xylose were most abundant and their d18O values were therefore used to calculate weighted mean leaf d18Osugar values. Both d2H푛-alkane and d18Osugar yielded significant correlations with d2Hleaf-water and d18Oleaf-water, respectively (r2 = 0.45 and 0.85, respectively; p < 0.001, n = 24). Mean fractionation factors between biomarkers and leaf water were found to be -156‰ (ranging from -133 to -192‰) for en-alkane/leaf-water and +27.3‰ (ranging from +23.0 to 32.3‰) for esugar/leaf-water, respectively. Modelled RHair values from a Craig-Gordon model using measured Tair, d2Hleaf-water and d18Oleaf-water as input correlate highly significantly with measured RHair values (R2 = 0.84, p < 0.001, RMSE = 6%). When coupling d2H푛-alkane and d18Osugar values the correlation of modelled RHair values with measured RHair values is weaker but still highly significant with R2 = 0.54 (p < 0.001, RMSE = 10%). Finally, the reconstructed source water isotope composition (d2Hs and d18Os) as calculated from the coupled approach matches the source water in the climate chamber experiment (d2Htank-water and d18Otank-water). This highlights the great potential of the coupled d2H푛-alkane-d18Osugar paleohygrometer approach for paleoclimate and relative humidity reconstructions. [ABSTRACT FROM AUTHOR]

The selection of thermal habitat by fish is strongly regulated by physiology and behaviour. However, delineation of a species lifelong thermal niche remains technically challenging. Lake trout (Salvelinus namaycush) survival and productivity are recognised as being tightly linked to a somewhat restricted thermal habitat. The factors guiding temperature selection during each life stage remain poorly understood.In this study, we tested the significant factors controlling the realised thermal niche of lake trout from two southern Quebec small boreal lakes that experienced supplementation stocking during the last 20 years. We used oxygen stable isotope (δ18O) thermometry of otolith calcium carbonates (aragonite) using secondary‐ion mass spectrometry to estimate experienced lifelong temperatures. We investigated the thermal habitat of lake trout with known genotypes (local, hybrid, and stocked).Ontogeny and genetic origin influenced temperature selection in both studied lake trout populations. Young‐of‐the‐year consistently used warmer, shallower habitats (10.7 ± 2.6°C, 7.5 m depth) prior to a juvenile transition to colder and deeper waters (8.5 ± 3.3°C, 10 m depth). Stocked lake trout, originating from a genetically distinct ecotype, exhibited a more variable thermal niche, with some individuals consistently using warmer habitat (10.4 ± 1°C) than local fish. Their hybrid progeny also occupied a warmer thermal niche, intermediate to the parental strains. We propose that increased fat content and genetic origin are potential explanatory factors for warmer temperature use.This study reiterates that high‐resolution otolith δ18O thermometry is a uniquely well‐suited approach for unravelling the multiple factors that influence lifelong temperature selection in fish. Our results illustrate that the realised thermal niche is influenced by a genetic–environment interaction. [ABSTRACT FROM AUTHOR]

Understanding of the dynamic patterns of plant water use in a changing environment is one of foci in plant ecology, and can provide basis for the development of best practice in restoration and protection of ecosystem. We studied the water use sources of three coexisting dominant plant species Leymus chinensis, Stipa grandis and Cleistogenes squarrosa growing in both enclosed and mowing grassland in a typical steppe. The oxygen stable isotope ratios (δ18O) of soil water and stem water of these three species were determined, along with soil moisture, before and after precipitation events. The results showed that (1) mowing had no significant effect on the soil moisture and its δ18O, whereas precipitation significantly changed the soil moisture though no significant effect detected on its δ18O. (2) C. squarrosa took up water majorly from top soil layer due to its shaollow root system; L. chinensis took up relative more water from deep soil layer, and S. grandis took up water from the middle to deep soil layers. (3) L. chinensis and S. grandis in mowing grassland tended to take up more water from the upper soil layers following precipitation events, but showed no sensitive change in water source from soil profile following the precipitation in the enclosed grassland, indicating a more sensitive change of soil water sources for the two species in mowing than enclosed grassland. The differences in root morphology and precipitation distribution may partly explain the differences in their water uptake from different soil layers. Our results have important theoretical values for understanding the water competition among plants in fluctuating environment and under different land use in the typical steppe.

Summary: Strategies for deep soil water acquisition (WAdeep) are critical to a species' adaptation to drought. However, it is unknown how WAdeep determines the abundance and resource economy strategies of understorey shrub species.With data from 13 understorey shrub species in subtropical coniferous plantations, we investigated associations between the magnitude of WAdeep, the seasonal plasticity of WAdeep, midday leaf water potential (Ψmd), species abundance and resource economic traits across organs.Higher capacity for WAdeep was associated with higher intrinsic water use efficiency, but was not necessary for maintaining higher Ψmd in the dry season nor was it an ubiquitous trait possessed by the most common shrub species. Species with higher seasonal plasticity of WAdeep had lower wood density, indicating that fast species had higher plasticity in deep soil resource acquisition. However, the magnitude and plasticity of WAdeep were not related to shallow fine root economy traits, suggesting independent dimensions of soil resource acquisition between deep and shallow soil.Our results provide new insights into the mechanisms through which the magnitude and plasticity of WAdeep interact with shallow soil and aboveground resource acquisition traits to integrate the whole‐plant economic spectrum and, thus, community assembly processes. See also the Commentary on this article by Tumber‐Dávila & Malhotra, 225: 7–9. [ABSTRACT FROM AUTHOR]

• Combines epidote and fluid compositions from Bacon-Manito Geothermal Field. • Demonstrates disequilibrium between δ 18O epidote and reservoir fluids. • Creates a more comprehensive hydrogeological model of the reservoir. • Demonstrates spatially and temporally changing reservoir processes. The physiochemical evolution of active geothermal systems is important for assessing their long-term viability. Although discharge fluid chemistry provides information on geothermal well conditions, it only typically reflects the current state of the reservoir. Integration of fluid chemistry with rock and mineral chemistry can fill this gap by providing a longer-term record of fluctuations in geothermal conditions. This study examines the stable isotope systematics and the hydrogeological model of the Bacon-Manito geothermal field (Bacman) in the Philippines, a liquid-dominated, volcanic field-type geothermal system in a convergent setting. Geothermal well discharge geochemistry is supported by hydrogen and oxygen isotope data and elemental composition data from hydrothermal epidote and reservoir rocks. Chemical and isotope analysis of well discharges reveal short-term processes that are affecting the Bacman reservoir from the onset of fluid extraction due to field operations. Boiling within the Botong sector and the incursion of peripheral and injection fluids into the main reservoir of Palayang Bayan and Cawayan sectors was observed from the changes in isotope and chemical compositions of well discharges. Meanwhile, changes in epidote morphology and associated mineral assemblages, as well as epidote δ 18O and major-element compositions, are related to reservoir rock composition, fluid chemistry, and temperature. These factors dictate the extent to which water-rock interaction and fluid mixing, the two most prominent processes in the isotopic evolution of epidote and fluids in Bacman, affect each particular sector in the reservoir. We present an updated and expanded hydrogeological model of Bacman by incorporating the exploration sectors of Rangas and Kayabon. A heat source associated with carbonate reservoir rocks is postulated for the Rangas sector. Fluids in the Rangas sector originated in the main reservoir upflow in Botong and are isotopically enriched through interaction with carbonate reservoir rocks, suggesting that water-rock interaction is the dominant process. In contrast, the existence of fluids with variable isotopic compositions in the Palayan Bayan and Cawayan sectors indicates the dominant process is fluid mixing. The present-day fluids evolved through the continuous mixing of isotopically enriched parent waters with isotopically depleted peripheral waters. Furthermore, fluids and epidotes from Kayabon are found to be isotopically and petrologically distinct from those from the rest of the Bacman reservoir, supporting a relatively cooler and waning heat source beneath the sector. [ABSTRACT FROM AUTHOR]

Nitrate pollution is a global issue threatening the health and function of many lowland freshwater ecosystems. Quantifying nitrate loads and instream attenuation associated with land use is a critical requirement for improving freshwater management. One often overlooked nitrate source in catchments is invasive N-fixing trees such as Ulex europaeus (European gorse). This study compared nitrate concentrations in conjunction with stable isotope analyses (nitrate δ15N and δ18O) to investigate the effects of catchment gorse cover on stream nitrate export relative to three other land uses. These were regenerating native forest, low-intensity (dry-stock) and high-intensity (dairying) agriculture. We tested two hypotheses: (1) gorse is a regionally significant nitrate source; (2) instream nitrate attenuation is land-use dependent. The study was conducted in 24 reaches across six small, mixed land-use coastal catchments located on Banks Peninsula, New Zealand. Our results demonstrated that gorse-dominated stream reaches had significantly higher nitrate concentrations than all other land uses. Within the gorse-dominated reaches, nitrate concentration was significantly correlated with upstream catchment gorse cover. Furthermore, nitrate oxygen and nitrogen stable isotope compositions demonstrated that elevated nitrate concentrations in gorse streams were associated with decomposition of dead gorse foliage. The isotope data revealed sub-catchment-scale land-use-specific patterns of nitrate attenuation within streams. All three anthropogenic land uses (gorse, dry stock and dairy) showed distinctly different N-cycling from native-forested reaches where nitrate was efficiently cycled with evidence for highly localised nitrification. Stable isotope data demonstrated that overall nitrate attenuation became less efficient with higher nitrate loads. Our research demonstrates the significant impact N-fixing plants have on nitrate concentrations and instream attenuation. Quantifying the effects of N-fixing plants on water quality is an important step in achieving globally significant goals of sustaining ecosystem health and (sub)catchment-scale nutrient management. [ABSTRACT FROM AUTHOR]

This paper summarises the isotopic characteristics, i.e., oxygen and hydrogen isotopes, of Slovenian milk and its major constituents: water, casein, and lactose. In parallel, the stable oxygen isotope ratios of cow, sheep, and goat’s milk were compared. Oxygen stable isotope ratios in milk water show seasonal variability and are also 18O enriched in relation to animal drinking water. The δ18Owater values were higher in sheep and goat’s milk when compared to cow milk, reflecting the isotopic composition of drinking water source and the effect of differences in the animal’s thermoregulatory physiologies. The relationship between δ18Omilk and δ18Olactose is an indication that even at lower amounts (>7%) of added water to milk can be determined. This procedure once validated on an international scale could become a reference method for the determination of milk adulteration with water.

Continental paleoclimate proxies with near-global coverage are rare. Land snail δ18O is one of the few proxies abundant in Quaternary sediments ranging from the tropics to the high Arctic tundra. However, its application in paleoclimatology remains difficult, attributable in part to limitations in published calibration studies. Here we present shell δ18O of modern small (<10 mm) snails across North America, from Florida (30°N) to Manitoba (58°N), to examine the main climatic controls on shell δ18O at a coarse scale. This transect is augmented by published δ18O values, which expand our coverage from Jamaica (18°N) to Alaska (64°N). Results indicate that shell δ18O primarily tracks the average annual precipitation δ18O. Shell δ18O increases 0.5–0.7‰ for every 1‰ increase in precipitation δ18O, and 0.3–0.7‰ for every 1°C increase in temperature. These relationships hold true when all taxa are included regardless of body size (ranging from ~1.6 to ~58 mm), ecology (herbivores, omnivores, and carnivores), or behavior (variable seasonal active periods and mobility habits). Future isotopic investigations should include calibration studies in tropical and high-latitude settings, arid environments, and along altitudinal gradients to test if the near linear relationship between shell and meteoric precipitation δ18O observed on a continental scale remains significant. [ABSTRACT FROM AUTHOR]

Oxygen isotope ratios of the core region of otoliths were examined in Anguilla japonica glass eels collected from two rivers in Japan to verify the possible temperature and depth layer experienced by these eels when they were at the egg stage in their spawning area. To determine the relationship between otolith δ 18 O values and water temperature, the otoliths of glass eels reared under four different temperatures (15, 20, 25 and 30 °C) were analyzed. The otolith δ 18 O values showed an inverse relationship to ambient water temperature. Linear regression of the fractionation between otolith oxygen isotopic ratio from the δ 18 O of seawater and water temperature produced a precisely determined relationship from 15 to 30 °C: δ 18 O otolith,PDB  − δ 18 O seawater,SMOW  = −0.153 ×  T (°C) + 1.418. The δ 18 O core,PDB values of the otolith core region of the glass eels from the two locations were −2.53 ± 0.12 and −2.59 ± 0.07 respectively, and could be converted to water temperatures of 26.3 ± 0.8 °C and 26.7 ± 0.4 °C, respectively, using the equation and assuming a seawater δ 18 O seawater,SMOW  = 0.06‰. The water depth corresponding to these temperatures is ∼150 m in the water column in the spawning area of Japanese eels, which corresponds to the upper-most part of the thermocline and chlorophyll maximum in the vertical hydrographic profile. These results were consistent with the field studies that egg development after the beginning of otolith formation and hatching occurs around the upper-most part of thermocline, suggesting that stable isotope micro-analysis is a powerful method to extrapolate unknown spawning ecology of fishes. [ABSTRACT FROM AUTHOR]

The Oldowan site HWK EE (Olduvai Gorge, Tanzania) has yielded a large fossil and stone tool assemblage at the transition from Lower to Middle Bed II, ∼1.7 Ma. Integrated tooth wear and stable isotope analyses were performed on the three most abundant ungulate taxa from HWK EE, namely Alcelaphini, cf. Antidorcas recki (Antilopini) and Equus oldowayensis (Equini), to infer dietary traits in each taxon. Some paleodietary changes were observed for cf. A. recki and E. oldowayensis based on tooth wear at the transition from the Lemuta to the Lower Augitic Sandstone (LAS) interval within the HWK EE sequence. Stable carbon and oxygen isotope data show no significant changes in bulk diet or hydroclimate between the Lemuta and LAS intervals. The combined tooth wear and stable isotope data suggest similar paleoecological conditions across the two HWK EE intervals, but that differences in vegetation consumed among ungulates may have resulted in changes in dietary niches. Integrating tooth wear and stable isotope analyses permits the characterization of ungulate diets and habitats at HWK EE where C 4 dominated and minor mixed C 3 and C 4 habitats were present. Our results provide a better understanding of the paleoenvironmental conditions of the Lemuta and LAS intervals. The LAS assemblage was mostly accumulated during relatively dry periods at Olduvai Gorge when grasses were not as readily available and grazing animals may have been more nutritionally-stressed than during the formation of the Lemuta assemblage. This helps to contextualize variations in hominin and carnivore feeding behavior observed from the faunal assemblages produced during the two main occupations of the site. [ABSTRACT FROM AUTHOR]

Stock and flow pollution differentiation is the basis for efficient pollution-abatement mechanism designs. The focus of our research has been marine pollution from land-based sources. Stable isotope analysis of groundwater is an acknowledged method for karst aquifer characterisation. We have tested whether stable isotopes of water, when used as a proxy for groundwater dynamics in the karst, could also be used as an indicator of marine pollution differentiation in terms of flow and stock pollution. The focus has been on two close coastal locations characterized by differences in terms of open and closed sea as well as anthropogenic pressure. A static Estimated General Least Squares (EGLS) statistical model described the closed bay location suggesting stock pollution. For a good description of the open sea location, we have had to resort to dynamic Generalised Method of Moments (GMM) statistical modelling, indicating flow pollution. Stable isotopes of groundwater together with appropriate statistical tools have proved to be a useful tool of marine pollution differentiation into stock or flow. [ABSTRACT FROM AUTHOR]

Abstract: Soil phosphate oxygen isotope analysis (δ18OP) emerges as an effective method to trace the cycling of phosphorus (P) in soils. This study uses δ18OP measurements to learn how the nutrient status (P and N) affects the biological turnover rates of P in the soil of a Mediterranean holm oak Savanna. Such ecosystems cover >3 × 106 ha at the Iberian Peninsula. The analysis was part of a large‐scale nutrient manipulation experiment, where N and P were added. We followed the changes in δ18O values of soil bioavailable P during incubation of soils with a pulse of P and in addition measured the δ18OP in soil sampled at the site. In the incubations, the δ18OP values changed from the original value of the added P and approached a steady state of 16.3‰, which is 3.8‰ higher than the isotopic equilibrium with water. The steady state was higher with 18O‐enriched incubation media water. The change in δ18OP values was more pronounced under trees, indicating a faster microbial P turnover rate. Incubation of soils fertilized with either P or N showed faster P turnover rate than control, implying N and P colimitation. Soil samples from P‐fertilized plots displayed higher δ18OP than the fertilizer, rather than the expected decrease toward steady‐state values, found at the control and N plots. The microbial P turnover rates during incubations were slower than the rates reported for lowland tropical forest with lower bioavailable P concentrations but resemble ecosystems with similar concentrations. [ABSTRACT FROM AUTHOR]

SEM/SIMS imaging and analysis of δ 18 O and δ 13 C in sandstones from a transect through the Illinois Basin (USA) show systematic μm-scale isotopic zonation of up to 10‰ in both carbonate and quartz cements of the middle-Ordovician St. Peter and Cambrian Mt. Simon formations. Quartz δ 18 O values are broadly consistent with the model of Hyodo et al. (2014), wherein burial and heating in the Illinois Basin is recorded in systematically zoned quartz overgrowths. Observations of zoned dolomite/ankerite cements indicate that they preserve a more extended record of temperature and fluid compositions than quartz, including early diagenesis before or during shallow burial, and late carbonates formed after quartz overgrowths. Many carbonate cements show innermost dolomite with δ 18 O values (21–25‰ VSMOW) that are too low to have formed by deposition at low temperatures from ancient seawater (δ 18 O > − 3‰) and most likely reflect mixing with meteoric water. A sharp increase in Fe content is commonly observed in zoned carbonate cements to be associated with a drop in δ 18 O and an abrupt shift in δ 13 C to higher or lower values. These changes are interpreted to record the passage of hot metal-rich brines through sandstone aquifers, that was associated with Mississippi-Valley Type (MVT) Pb-Zn deposits (ca. 270 Ma) of the Upper Mississippi Valley. Local variability and individual trends in δ 13 C are likely controlled by the sources of carbon and the degree to which carbon is sourced from adjacent carbonate units or thermal maturation of organic matter. Quartz overgrowths in sandstones provide an excellent record of conditions during burial, heating, and pressure-solution, whereas carbonate cements in sandstones preserve a more-extended record including initial pre-burial conditions and punctuated fluid flow events. [ABSTRACT FROM AUTHOR]

Hydroelectric dams can alter downstream water temperatures, impacting thermal habitat available for fishes. Decreases in river water temperatures resulting from hydroelectric dam operations may be beneficial to coldwater species and could potentially offset warming resulting from climatic trends. We used two coldwater fish species, Slimy Sculpin ( Cottus cognatus) and Brook Trout ( Salvelinus fontinalis) to assess the impact of a cool water draw below a 15 MW hydroelectric dam on fish thermal habitat use relative to a nearby naturally flowing river. Cooler water temperatures below the dam corresponded with significantly cooler mean growth season temperature use for Slimy Sculpin, but not Brook Trout, relative to the natural river. As well, mean growing season temperature use by Slimy Sculpin was significantly cooler relative to Brook Trout in both rivers, and significantly different amongst studied sites in the regulated river. Fish condition was significantly correlated with temperature use for Slimy Sculpin in the naturally flowing river only. Our results indicate that manipulating river water temperatures through hydroelectric dam operations to benefit multiple fish species will be difficult given the complexity of riverine thermal habitat and species-specific differences in thermal preferences and behaviour. [ABSTRACT FROM AUTHOR]

Agroforestry parklands, in which annual crops are grown under scattered mature trees, constitute the most prevalent farming system in semiarid West Africa, covering vast areas of land. The most dominant tree species in these systems is Vitellaria paradoxa , an indigenous tree to West Africa. Despite the importance of this tree in the region, no study to our knowledge has examined its sources and patterns of water uptake. In this study, we used oxygen stable isotopes at natural abundance levels to investigate water sources used by V. paradoxa both in the dry and wet season in an agroforestry parkland in Burkina Faso. We found that during the wet season soil moisture was highest near the soil surface (<10 cm depth), yet during this time V. paradoxa preferentially accessed water from slightly deeper soil depths, obtaining ca. 90% of its water from 10 to 50 cm depth. In contrast, soil moisture in the upper soil layers was significantly lower during the dry season and as a result V. paradoxa shifted to deeper water sources, obtaining ca. 30% of its water from groundwater and ca. 50% from 30 to 600 cm depth. We also found a negative relationship between tree size and the contribution of groundwater during the dry season, whereas during the wet season V. paradoxa predominantly used water near the soil surface regardless of tree size. Knowledge about the sources and patterns of tree water uptake provides crucial information to better understand how trees influence the local water balance. [ABSTRACT FROM AUTHOR]

The Brazil Current (BC) is a relevant feature in the Atlantic Meridional Overturning Circulation (AMOC). Its behavior during slowdown or intense AMOC remains poorly known because of the lack of paleoceanographic records, especially for the Holocene. Here, we investigate changes in a western boundary upwelling system (Cabo Frio, off Southeastern Brazil) which are driven by variations in the BC and NE winds during the last 9 kyr. To assess the variability of the BC, we used δ18O, Mg/Ca, and assemblages of planktonic foraminifera. Our results indicate five oceanographic phases during the last 9 kyr. During Phase I (from 9.0 to 7.0 cal kyr BP), the BC diverged offshore from the modern upwelling area because of the low sea level, increasing the influence of shelf waters and coastal upwelling plumes on foraminifera assemblages. Phase II (7.0–5.0 kyr BP) was marked by the approach of the internal front of the BC with low intensity and episodes of strong productivity that were linked primarily to the upwelling of the South Atlantic Central Water (SACW) and/or Subpolar Shelf Waters (SPSWs) (cold). Phase III (5.0–3.5 kyr BP) was a transition, marking a large oceanographic and climatic change from the weakening of the AMOC. The internal front of the BC became warm and subsurface SACW upwelling was stronger. In Phase IV (3.5–2.5 kyr BP), the BC acquired its modern dynamics, but weak NE winds weakened the SACW’s contribution to upwelling events. Finally, in Phase V (last 2.5 kyr BP), the NE winds reintensified, promoting frequent episodes of upwelling and intrusion by SPSWs during the Medieval Climate Anomaly. [ABSTRACT FROM AUTHOR]

The Krafla geothermal system is located in Iceland's northeastern neovolcanic zone, within the Krafla central volcanic complex. Geothermal fluids are superheated steam closest to the magma heat source, two-phase at higher depths, and sub-boiling at the shallowest depths. Hydrogen isotope ratios of geothermal fluids range from −87‰, equivalent to local meteoric water, to −94‰. These fluids are enriched in 18O relative to the global meteoric line by +0.5-3.2‰. Calculated vapor fractions of the fluids are 0.0-0.5 wt% (~0-16% by volume) in the northwestern portion of the geothermal system and increase towards the southeast, up to 5.4 wt% (~57% by volume). Hydrothermal epidote sampled from 900 to 2500 m depth has δD values from −127 to −108‰, and δ18O from −13.0 to −9.6‰. Fluids in equilibrium with epidote have isotope compositions similar to those calculated for the vapor phase of two-phase aquifer fluids. We interpret the large range in δ DEPIDOTE and δ18 OEPIDOTE across the system and within individual wells (up to 7‰ and 3.3‰, respectively) to result from variable mixing of shallow sub-boiling groundwater with condensates of vapor rising from a deeper two-phase reservoir. The data suggest that meteoric waters derived from a single source in the northwest are separated into the shallow sub-boiling reservoir, and deeper two-phase reservoir. Interaction between these reservoirs occurs by channelized vertical flow of vapor along fractures, and input of magmatic volatiles further alters fluid chemistry in some wells. Isotopic compositions of hydrothermal epidote reflect local equilibrium with fluids formed by mixtures of shallow water, deep vapor condensates, and magmatic volatiles, whose ionic strength is subsequently derived from dissolution of basalt host rock. This study illustrates the benefits of combining phase segregation effects in two-phase systems during analysis of wellhead fluid data with stable isotope values of hydrous alteration minerals when evaluating the complex hydrogeology of volcano-hosted geothermal systems. [ABSTRACT FROM AUTHOR]

Otolith-derived estimates of mean marine temperatures used by West Greenland 1SW Atlantic salmon (Salmo salar) of North American origin were determined for fish collected in 2009 and 2010. Otolith material corresponding to the second summer at sea was subsampled, via micromilling, and analysed by mass spectrometry to produce stable oxygen isotope (δ18O) values from which temperature use estimates were obtained from a salmonid-based fractionation equation. Mean temperature estimates did not differ significantly by period (early vs. late summer), or capture year. The mean and variation estimates were also consistent with temperature use values previously published in the literature or derived from the limited number of data storage tags that have been retrieved for Atlantic salmon, with 80% of all individuals occupying temperatures in the 3.9-9.78°C range. Among-individual differences in temperature use did not correlate with measured otolith growth zone widths. Given the temporal, spatial and methodological variation associated with the derivation of marine temperature use estimates for Atlantic salmon, the data were interpreted to define a range of preferred temperatures within which among-individual differences in growth were driven by the interaction of feeding and temperature use, possibly as a result of the opportunistic feeding behaviour known to predominate among Atlantic salmon. [ABSTRACT FROM AUTHOR]

Changes in oxygen isotope ratios from shell carbonates are mainly dependent on sea surface temperature, which enables the estimation of temperatures during periods of shell growth and helps to determine the season of the year when the mollusk died. The marine topshell Phorcus lineatus (Da Costa, 1778) is commonly found in Holocene archaeological deposits of Atlantic Europe and is one of the most abundant subsistence resources utilized during the Mesolithic in northern Spain. Before applying isotopic techniques to ancient samples, calibration of the past isotopic data and its variability must be performed through the study of modern specimens to test their potential as paleoclimate proxy and their suitability for determining the collection season. Although previous studies performed in the region highlighted the existing relationship between sea surface temperatures and isotopic signatures, no systematic works have been done so far. In this paper, calibration of modern P. lineatus shells from northern Spain was carried out using δ18O analysis. The results showed (1) the existence of a robust inverse correlation between instrumental temperatures (Tmeas) and δ18Oshell (R2 > 0.9), accompanied by the lack of significant dependence from δ18Owater variations (R2 = 0.06); (2) the existence of conditions of (or close to) isotopic equilibrium during the formation of the aragonite in the P. lineatus shells; and (3) that using mean annual δ18Owater values, past temperatures could be calculated with a maximum uncertainty of ±3°C. Moreover, results suggested that P. lineatus generally grew without substantial slow/cessation throughout the year, reflecting the four annual seasons. Therefore, our study not only confirms the potential of oxygen isotope analysis on P. lineatus for paleoclimate reconstruction and archaeological studies highlighted in previous studies but also shows for the first time that the aragonite of those shells grew under conditions of isotopic equilibrium, opening new avenues for future research. [ABSTRACT FROM AUTHOR]

The giant clam Tridacna maxima presents a strong potential for paleoclimatic reconstructions but its use remains limited by the fact that the relationship between the shell stable oxygen isotopes ratio ( δO), the sea surface temperature (SST), and the stable oxygen isotopes ratio of seawater ( δO) has not been calibrated yet. In this study, a T. maxima specimen was stained with calcein and grown in a tank for 1.5 yr. The tank seawater was monitored weekly for sea surface salinity, and the stable oxygen isotopes ratio of seawater ( δO) and SST was recorded hourly. Microscopic observations of outer shell layer thin sections revealed micrometric, simple and complex, growth increments. The staining experiment demonstrated that these growth increments were deposited on a daily basis. The weekly δO record showed that the shell was precipitated in isotopic equilibrium with seawater and that 63 % of the ( δO − δO) variations were explained by SST variations. A conventional linear function (1) linking T. maxima high-resolution δO record, in situ δO, and SST data was calculated as:where SST is in degree Celsius and Δ δO is the difference between the stable oxygen isotopes ratio of the shell and of the seawater ( δO − δO), in ‰ VPDB. The root mean square error of the SST reconstructed by this equation is ±1.41 °C revealing the potential of T. maxima for paleoclimatic studies. An average SST = f( δO − δO) equation for giant clam is proposed by compiling the equations from the present study and previous worksThis equation permits one to obtain SST records from isotopic values of giant clams species that have not been calibrated yet or from fossil giant species that do not have living modern conspecifics. [ABSTRACT FROM AUTHOR]

The availability of instrumental climate data in West and Central Africa is very restricted, both in space and time. This limits the understanding of the regional climate system and the monitoring of climate change and causes a need for proxies that allow the reconstruction of paleoclimatic variability. Here we show that oxygen isotope values (δ 18 O) in tree rings of Entandrophragma utile from North-western Cameroon correlate to precipitation on a regional to sub-continental scale (1930–2009). All found correlations were negative, following the proposed recording of the ‘amount effect’ by trees in the tropics. The capacity of E. utile to record the variability of regional precipitation is also confirmed by the significant correlation of tree-ring δ 18 O with river discharge data (1944–1983), outgoing longwave radiation (a proxy for cloud cover; 1974–2011) and sea surface salinity in the Gulf of Guinea (1950–2011). Furthermore, the high values in the δ 18 O chronology from 1970 onwards coincide with the Sahel drought period. Given that E. utile presents clear annual growth rings, has a wide-spread distribution in tropical Africa and is long lived (> 250 years), we argue that the analysis of oxygen isotopes in growth rings of this species is a promising tool for the study of paleoclimatic variability during the last centuries in West and Central Africa. [ABSTRACT FROM AUTHOR]

The North Brazil Current in the western equatorial Atlantic is the main route for poleward heat transfer and therefore is a key component of the climate system. To understand the parameters that influence this region, we present a paleoceanographic reconstruction of the last 40 kyr based on study of sediment core MC 10/3. This reconstruction is based on: i) the oxygen isotope composition of the planktonic foraminifer Globigerinoides ruber (white); ii) census counts of the planktonic foraminifera assemblage to estimate sea surface temperature (SST) via the Modern Analogue Technique (SST MAT ) and to deduce characteristics of the water column; and iii) values of δ 18 O ivc-sw (a proxy for sea surface salinity (SSS)). The oxygen isotope composition of G. ruber showed a strong shift of greater than 1‰ after 21 cal kyr BP. Such a change can be attributed mainly to a salinity reduction of two units, as well as a slight SST increase (~ 1 °C), between 21 and 17.5 kyr BP. This change may be related to a southward displacement of the Intertropical Convergence Zone (ITCZ) and its belt of convective activity, which would have increased precipitation over the region and diminished surface salinity. The structure of the planktonic foraminiferal assemblage also indicates such conditions. The productive/thermocline-dwelling Globigerinita glutinata showed higher abundance prior to 21 cal kyr BP. Other productive/deep-dwellers, i.e., Neogloboquadrina dutertrei , Globorotalia truncatulinoides (left- and right-coiling) and Globorotalia inflata , were slightly more abundant prior to 21 cal kyr BP and became less frequent with the development of low-salinity surface water that created more stratified and oligotrophic conditions in the water column. However, the warm/oligotrophic surface-dwellers ( G. ruber , Globigerinoides sacculifer and Globigerinella siphonifera ) became more abundant after 21 cal kyr BP. The species Globorotalia menardii was nearly absent during the Last Glacial Maximum (LGM), and its growth in abundance, mainly after 17.5 cal kyr BP, may indicate the resumption of the Agulhas leakage, which would have reached the study area via the South Equatorial Current (SEC). The return of high salinity values synchronous with the G. menardii increase also denotes the influence of Agulhas leakage into the western equatorial Atlantic. [ABSTRACT FROM AUTHOR]

A high-resolution integrated study has been performed in a super-expanded marine record (sedimentation rate spanning from 11 cm/100 years to 20 cm/100 years) from the continental shelf area of the southeastern Tyrrhenian Sea. Planktonic foraminiferal distribution illustrates 6 major environmental changes during the past 2000 years: (i) the Roman Period-Dark Age transition (from herbivorous-opportunistic to carnivorous species); (ii) the Dark Age-MCA transition (from carnivorous to herbivorous-opportunistic species); (iii) the Medieval Classic Anomaly-Little Ice Age transition (a further and definitive change from carnivorous to herbivorous-opportunistic species); (iv) the period during the Maunder event between approximately 1720 AD and 1740 AD (turnover from the carnivorous planktonic foraminifer Globigerinodes ruber to the herbivorous-opportunistic planktonic foraminifer Turborotalita quinqueloba); (v) the Industrial Period (dominance of herbivorous-opportunistic planktonic foraminifera); and (vi) the Modern Warm Period at approximately 1940 AD (the last turnover in favor of herbivorous-opportunistic planktonic foraminifers, associated with an increase in benthic foraminifera). Our studies lead us to link this latter feature to an anthropogenic impact associated with the damming of Sele River (Salerno Gulf) at 1934 AD, which induced a change in the sediment input with a strong decrease in coarse-grained fraction and a probable alteration in nutrient supply. The δ18O G. ruber record of the past 2000 years shows the alternation of warm/wet and cold/dry events related to the Roman Period, the Dark Age, the Medieval Classic Anomaly, the Little Ice Age, the Industrial Period and the Modern Warm Period. The 5 evident δ18O G. ruber oscillations (between approximately 1325 AD and 1940 AD) coincide with the 5 minima in the solar activity record (Wolf, Spörer, Maunder, Dalton and Damon events). [ABSTRACT FROM AUTHOR]

Abstract: We performed δ18OC (Globigerinoides ruber, 250–300μm white) and SST (modern analogue technique) paleoceanographic reconstructions for the western tropical South Atlantic Ocean at the northeast Brazilian margin to assess millennial- to centennial-scale climatic shifts that may be propagated by the thermohaline circulation. The results show a progressive SST increase (~1°C) over the Holocene, with a prominent shift occurring during the mid-Holocene that may be linked to changes in insolation distribution. Furthermore, spectral and coherency analyses reveal several centennial- to millennial-scale modes of variability that are similar in both proxy records (4.1–3.8kyr, 1.5–1.0kyr, ~700yr, 570–560yr, ~390yr, ~350yr and ~330yr). Such variability could be the result of (1) solar-induced atmospheric changes at northern high latitudes (possibly propagated southward by the meridional overturning circulation and hence inducing shifts in tropical δ18Oc and sea surface temperature), and/or (2) salinity anomalies propagated from the Southern Atlantic Ocean and transmitted to the study site through the Agulhas Leakage. These climate oscillations may have had substantive effects on the Holocene climate system, especially over the tropical western South Atlantic Ocean and the South American continent. Our data show that the western tropical South Atlantic may respond to multi-centennial to millennial oscillations that are possibly triggered by external (solar) and internal (northern and southern high latitudes) climate forcing. Further investigations are necessary to illuminate the role of the western tropical South Atlantic in inter-hemispheric heat transfer. [Copyright &y& Elsevier]

Abstract: Predicted increases in temperature associated with climate change are expected to have consequences for fish, in particular for Arctic charr, Salvelinus alpinus, a cold-adapted fish species. Despite differences in predicted hydroecological responses to climate change in fluvial and lacustrine environments, little is known of whether fluvial and lacustrine Arctic charr populations may respond differently to increasing temperatures. In order to compare growth and thermal habitat use between habitat types, otolith-inferred average water temperatures estimated from whole otoliths and fork lengths at capture were measured for young-of-the-year (YOY) Arctic charr obtained from two proximal fluvial and lacustrine sites in Labrador, Canada. Otolith-inferred average experienced water temperatures were not significantly correlated with air temperatures at both sites, suggestive of behavioural thermoregulation by YOY. The majority of Kogluktokoluk Brook (fluvial) YOY were found using water temperatures consistent with laboratory determined preferred temperatures for juvenile Arctic charr, whereas most Tom's Pond (lacustrine) YOY were found using temperatures ranging between preferred temperatures and optimal temperatures for growth. There was no consistent difference between mean water temperatures used between YOY from the two sites. Otolith-inferred average experienced water temperatures were only correlated to fork lengths in Tom's Pond YOY. The lack of correlation in Kogluktokoluk Brook YOY is argued to reflect resource partitioning occurring as a result of territoriality known to occur among stream salmonids. The limited range of temperatures used by fluvial YOY in this study, particularly the lack of cooler temperatures, also suggests that fluvial YOY may face barriers to thermal refugia, and as a result may be particularly vulnerable to climate change. [Copyright &y& Elsevier]

Abstract: Episodic discharges from the Laurentide Ice Sheet are considered to be one of the major causes of climate oscillations during the glacial to interglacial transition. These outburst floods disrupted thermohaline circulation and might have caused cooling events in the North Atlantic region and beyond, including the Younger Dryas, Preboreal Oscillation, and 8.2-ka events. However, few terrestrial sedimentary records show regional climate changes directly linked to outburst floods during the early Holocene. Here we present lithologic and isotopic data from Silver Lake in northern New Jersey to document temperature and moisture changes during the early Holocene and to discuss possible linkage with outburst flooding events. The lithologic record shows multiple intervals with coupled decreases in carbonate and increases in organic matter during the early Holocene, suggesting lower lake levels and drier climate conditions. Simultaneous with these changes were decreases in carbonate δ18O values, likely reflecting a decrease in air temperature during these dry periods. The apparent correlation of these sedimentary events at Silver Lake with documented outburst floods from the melting ice sheet suggests a possible causal connection, implying that the climate in the Mid‐Atlantic region was extremely sensitive to perturbations of ocean circulation. [Copyright &y& Elsevier]

Abstract: The timing and magnitude of surface uplift provide important constraints on geodynamic models of orogen formation. Oxygen isotope (δ18O) and mass-47 isotopolog (Δ47) compositions from terrestrial carbonate sediments have been used with modern isotope and temperature lapse rates to infer past surface elevations of the Andes. However, these paleoaltimetry interpretations are contentious because variations in the oxygen isotope composition in meteoric water (δ18Op) are caused by changes in elevation (orographic) and regional climate. Here, we use a limited-domain isotope-tracking general circulation model to simulate changes in δ18Op and isotopic lapse rates in response to Andean surface uplift, and to re-evaluate δ18O and Δ47 changes in late Miocene carbonates previously associated with rapid Andean growth. Results indicate that Andean surface uplift leads to changes in low-level atmospheric circulation and an increase in precipitation along the eastern Andean flank which influences isotopic source and amount effects. Simulated changes in Andean δ18Op are not systematic with an increase in surface elevation, but are instead a function of orographic thresholds that abruptly change regional climate. A δ18Op decrease of >5‰ over the central Andes and an increase in isotopic lapse rates (up to 0.8‰km−1) coincide with Andean surface uplift from 75 to 100% of modern elevation. These changes in the isotopic signature could account for the entire 3–4‰ δ18O depletion in late Miocene carbonate nodules, and suggest an Andean paleoelevation of ~3000m (75% of modern elevations) before 10Ma. [Copyright &y& Elsevier]

Abstract: Combined oxygen (O) and nitrogen (N) stable isotope analyses are commonly used in the source determination of nitrate . The source and fate of are studied based on distinct O and N isotopic signatures (δ18O and δ15N) of various sources and isotopic effects during transformation processes, which differ between sources like fertilizer, atmospheric deposition, and microbial production (nitrification). Isotopic fractionation during production and consumption of further affects the δ18O and δ15N signal. Regarding the δ18O in particular, biochemical O exchange between O from and H2O is implicitly assumed not to affect the δ18O signature of . This study aimed to test this assumption in soil-based systems. In a short (24 h) incubation experiment, soils were treated with artificially 18O and 15N enriched . Production of from nitrification during the incubation would affect both the 18O and the 15N enrichment. Oxygen exchange could therefore be studied by examining the change in 18O relative to the 15N. In two out of the three soils, we found that the imposed 18O enrichment of the declined relatively more than the imposed enrichment. This implies that O exchange indeed affected the O isotopic signature of , which has important implications for source determination studies. We suggest that O exchange between and H2O should be taken into consideration when interpreting the O isotopic signature to study the origin and fate of in ecosystems. [Copyright &y& Elsevier]

Abstract: Soils are the major source of the greenhouse gas nitrous oxide (N2O) to our atmosphere. A thorough understanding of terrestrial N2O production is therefore essential. N2O can be produced by nitrifiers, denitrifiers, and by nitrifiers paradoxically denitrifying. The latter pathway, though well-known in pure culture, has only recently been demonstrated in soils. Moreover, nitrifier denitrification appeared to be much less important than classical nitrate-driven denitrification. Here we studied a poor sandy soil, and show that when moisture conditions are sub-optimal for denitrification, nitrifier denitrification can be a major contributor to N2O emission from this soil. We conclude that the relative importance of classical and nitrifier denitrification in N2O emitted from soil is a function of the soil moisture content, and likely of other environmental conditions as well. Accordingly, we suggest that nitrifier denitrification should be routinely considered as a major source of N2O from soil. [ABSTRACT FROM AUTHOR]

Abstract: Stable carbon, oxygen, and strontium isotope records were obtained from uppermost Hauterivian to lowermost Aptian belemnite rostra, which were collected in well-dated sections from the Vocontian Trough (southeastern France). This data set complements previously published belemnite-isotope records from the uppermost Berriasian-Hauterivian interval from the same basin. The belemnite carbon and oxygen isotope record is compared to the carbonate bulk-rock isotope record from the same sections, and from additional Italian sections. With regards to their long-term trends, both belemnite and whole-rock δ18O records are well correlated, except for the uppermost Hauterivian-lower Barremian interval, within which they deviate. This discrepancy is interpreted to be linked to the latest Hauterivian Faraoni oceanic anoxic event and its early Barremian aftermath. The Faraoni level is characterized by enhanced sea-water stratification, probably induced by the onset of a warmer and more humid climate along the northern Tethyan margin. The early Barremian was characterized by stronger vertical sea-water mixing reflected by a decrease in density contrast between sea-surface and deeper waters. The belemnite oxygen isotope record shows a more stable evolution with smaller fluctuations than its bulk-rock counterpart, which indicates that deeper water masses were not as much subjected to density fluctuations as sea-surface water. The comparison of belemnite and bulk-rock carbon isotope records allows observing the impact of regional influence exerted by platform carbonate ooze shedding on the carbon cycle. Discrepancies in the two records are observed during time of photozoan carbonate platform growth. The strontium isotopic record shows a gradual increase from the uppermost Berriasian to the uppermost lower Barremian followed by a rapid decrease until the uppermost Barremian and a renewed small increase within the lowermost Aptian. The major inflection point in the uppermost lower Barremian appears to predate the onset in the formation of the Ontong-Java volcanic plateau. [Copyright &y& Elsevier]

Woody plant encroachment into semiarid ecosystems has become a global trend in recent decades. Due to stream channel incision, the semiarid riparian montane meadows of the southern Sierra Nevada Mountains, USA are experiencing long-term declines in soil moisture. A woody shrub, Artemisia rothrockii A. Gray (Rothrock sagebrush, Asteraceae) is invading these herbaceous meadows. We used an analysis of the stable oxygen isotope ratios of plant and soil water to measure the depth of plant water acquisition during the early stages of this woody plant encroachment. Sagebrush used deeper water on average than most herbs, but it also acquired 10–30% of its water from shallow (<30 cm) soil. Most of the young sagebrush seedlings (1–3 years old, <15 cm) that we sampled used deep water like the older shrubs. Many, but not all of the herb species we sampled were also able to acquire deep water. These findings are consistent with a scenario of shrub encroachment in which channel incision causes shallow-water-dependent herbs to die back, allowing shrub seedlings to establish in disturbed areas during wet years. At least during the early stages of the invasion, some herbs appear to coexist with sagebrush by using deep root systems to cope with the declining shallow soil moisture. [ABSTRACT FROM AUTHOR]

Abstract: We present a record of monsoon variations for the early and middle Holocene that is inferred from the geochemistry of sediment cores from Ahung Co, a lake in central Tibet. The resolution of this record is better than 50 yr and the age model is derived from radiocarbon ages of terrestrial charcoal, which eliminates errors associated with the lake hard-water effect. We made down-core geochemical measurements of % carbonate, % organic carbon, C/N and δ 13C of bulk organic matter, δ 13C and δ 18O of carbonate, and % dolomite. Proxy calibration and modern water-balance reconstruction show that these are proxies for lake depth and the amount of monsoon precipitation. We find that lake level and monsoon precipitation have been decreasing at Ahung Co since the early Holocene (∼7500 cal yr B.P.). Superimposed on this trend are rapid declines in monsoon rainfall at 7000–7500 and 4700 cal yr B.P. and seven century-scale wet–dry oscillations. The cores do not contain sediment from the last ∼4000 yr. Surface sediments from the lake accumulated during the 20th century, however. From this, we argue that lake levels have risen again recently following a late Holocene dry period. [Copyright &y& Elsevier]

δ18Obenthic values from Leg 194 Ocean Drilling Program Sites 1192 and 1195 (drilled on the Marion Plateau) were combined with deep-sea values to reconstruct the magnitude range of the late middle Miocene sea-level fall (13.6–11.4 Ma). In parallel, an estimate for the late middle Miocene sea-level fall was calculated from the stratigraphic relationship identified during Leg 194 and the structural relief of carbonate platforms that form the Marion Plateau. Corrections for thermal subsidence induced by Late Cretaceous rifting, flexural sediment loading, and sediment compaction were taken into account. The response of the lithosphere to sediment loading was considered for a range of effective elastic thick- nesses (10 < Te < 40 km). By overlapping the sea-level range of both the deep-sea isotopes and the results from the backstripping analysis, we demonstrate that the amplitude of the late middle Miocene sea-level fall was 45–68 m (56.5 ± 11.5 m). Including an estimate for sea-level variation using the δ18Obenthic results from the subtropical Marion Plateau, the range of sea-level fall is tightly constrained between 45 and 55 m (50.0 ± 5.0 m). This result is the first precise quantitative estimate for the amplitude of the late middle Miocene eustatic fall that sidesteps the errors inherent in using benthic foraminifera assemblages to predict paleo-water depth. The estimate also includes an error analysis for the flexural response of the lithosphere to both water and sediment loads. Our result implies that the extent of ice buildup in the Miocene was larger than previously estimated, and conversely that the amount of cooling associated with this event was less important. [ABSTRACT FROM AUTHOR]

A set of 27 samples of human skeletal remains, collected at 3 different sites in European Russia, was measured for the oxygen isotope composition of their phosphate (δ18Op). The age of these samples (cultural age derived from archaeological evidence) ranges from about 5000 to about 500 years BP. The samples come from the steppe Volga–Don area of southern European Russia. The δ18O values of palaeoenvironmental water (δ18Ow) were calculated from the δ18Op of fossil samples by means of the isotope equations calibrated on modern specimens. The results obtained and the results from other sets of data from European Russia reported elsewhere suggest a δ18Ow temporal pattern indicating an overall climatic improvement from about 10,500 until about 2300 years BP followed by a degradation in terms of temperature. Three cold events may be suggested at about 4.6/4.7 ka BP, 3.9/4.0 ka BP and 200 BP, respectively, as well as a warm event at about 2300 years BP. These climatic events are in good agreement with the climatic condition existing in central and northern Europe during the same periods. Markedly arid environmental conditions dominated the steppe area during the time interval covered by this work. [Copyright &y& Elsevier]