Stable Isotope Profiles Research Articles

Seasonal patterns in stable isotope and fatty acid profiles of southern stingrays (Hypanus americana) at Stingray City Sandbar, Grand Cayman

Ecotourism opportunities in the marine environment often rely heavily on provisioning to ensure the viewing of cryptic species by the public. However, intentional feeding of wildlife can impact numerous aspects of an animals’ behavior and ecology. Southern stingrays (Hypanus americana) provisioned at Stingray City Sandbar (SCS) in Grand Cayman have altered diel activity patterns and decreased measures of health. This study looked at seasonal changes in stable isotope (SI) and fatty acid (FA) profiles of provisioned stingrays at SCS. Plasma δ15N was higher in male stingrays (11.86 ± 1.71‰) compared to females (10.70 ± 1.71‰). Lower values for δ15N in males and females were measured in October during low tourist season, suggesting stingrays may be forced to rely on native prey items to supplement the decreased amount of provisioned squid available during this time. Plasma FA profiles were significantly different between sexes and across sampling time points, with FAs 22:6n3, 16:0, 20:5n3, 18:1n3C, 18:0 and 18:1n9T contributing to dissimilarity scores between groups. Dietary FAs primarily contributed to differences between males and females lending further evidence to differences in foraging patterns at SCS, likely due to intraspecific competition. Further, canonical analysis of principal coordinates (CAP) analysis of FA profiles suggest similar diets during peak tourist season and differences in diet between males and females during the low season. This study demonstrates alterations in feeding ecology in stingrays at SCS which is of critical importance for effective management of the SCS aggregation.

Biogeochemical evidence of anaerobic methane oxidation and anaerobic ammonium oxidation in a stratified lake using stable isotopes

Abstract. Nitrate pollution of freshwaters and methane emissions into the atmosphere are crucial factors in deteriorating the quality of drinking water and in contributing to global climate change. The n-damo (nitrite-dependent anaerobic methane oxidation), nitrate-dependent anaerobic methane oxidation and the anaerobic oxidation of ammonium (anammox) represent two microbially mediated processes that can reduce nitrogen loading of aquatic ecosystems and associated methane emissions to the atmosphere. Here, we report vertical concentration and stable-isotope profiles of CH4, NO3-, NO2-, and NH4+ in the water column of Fohnsee (lake in southern Bavaria, Germany) that may indicate linkages between denitrification, anaerobic oxidation of methane (AOM), and anammox. At a water depth from 12 to 20 m, a methane–nitrate transition zone (NMTZ) was observed, where δ13C values of methane and δ15N and δ18O of dissolved nitrate markedly increased in concert with decreasing concentrations of methane and nitrate. These data patterns, together with the results of a simple 1-D diffusion model linked with a degradation term, show that the nonlinear methane concentration profile cannot be explained by diffusion and that microbial oxidation of methane coupled with denitrification under anaerobic conditions is the most parsimonious explanation for these data trends. In the methane zone at the bottom of the NMTZ (20 to 22 m) δ15N of ammonium increased by 4 ‰, while ammonium concentrations decreased. In addition, a strong 15N enrichment of dissolved nitrate was observed at a water depth of 20 m, suggesting that anammox is occurring together with denitrification. The conversion of nitrite to N2 and nitrate during anammox is associated with an inverse N isotope fractionation and may explain the observed increasing offset (Δδ15N) of 26 ‰ between δ15N values of dissolved nitrate and nitrite at a water depth of 20 m compared to the Δδ15Nnitrate-nitrite of 11 ‰ obtained in the NMTZ at a water depth between 16 and 18 m. The associated methane concentration and stable-isotope profiles indicate that some of the denitrification may be coupled to AOM, an observation supported by an increased concentration of bacteria known to be involved in n-damo/denitrification with AOM (NC10 and Crenothrix) and anammox (“Candidatus Anammoximicrobium”) whose concentrations were highest in the methane and ammonium oxidation zones, respectively. This study shows the potential for a coupling of microbially mediated nitrate-dependent methane oxidation with anammox in stratified freshwater ecosystems, which may be important for affecting both methane emissions and nitrogen concentrations in lakes.

Stable isotope profile (C, N, O, S) of Irish raw milk: Baseline data for authentication

Grass-based milk production is a major contributor to Irish agricultural output. The study characterized the Irish milk pool using stable isotope ratio analysis of carbon, nitrogen, oxygen and sulphur. Authentic raw milk samples were collected from 50 farms on five occasions over 13 months. Mean values of −27.11, 6.79, −3.27 and 6.16‰ were obtained for δ13C, δ15N, δ18O and δ34S, respectively. δ13C values reflected a high level of grass input and values increased with increasing cereal concentrate feed input (P < 0.001). δ18O values were most negative in spring. There was a significant interaction between feed and season for δ13C and δ15N values (P < 0.05), with the impact of concentrate feeding most evident in spring. δ34S values were lowest at the highest level of concentrate input (P < 0.05). The isotopic values reported here describe the Irish milk pool and may offer the potential to discriminate Irish milk and dairy products from similar commodities from other countries.

High-resolution stable isotope profiles of modern elephant (Loxodonta africana) tusk dentin and tail hair from Kenya: Implications for identifying seasonal variability in climate, ecology, and diet in ancient proboscideans

Stable isotope ratios in tissues of large mammalian herbivores record diet and climate information integrated over large spatial areas and can be used to study modern and fossil ecosystems. Sound interpretation of data requires that tissue growth rates be determined accurately and that ecological and behavioral variables that influence stable isotope ratios of tissues be measured and related to experienced environmental conditions assessed through field observations, remote sensing data, and meteorological records. If well-understood in modern herbivores, stable isotopes from closely-related extinct taxa have tremendous potential for resolving paleodiet, paleoenvironment, and paleoclimate of terrestrial ecosystems. We present multiyear, high-resolution (i.e., weekly) stable isotope records from bioapatite in tusk dentin (δ13Cdentin and δ18Odentin) and tail hair (δ13Chair and δ15Nhair) of an African elephant (Loxodonta africana) from Kenya that was fitted with a GPS collar intermittently over a five year period and observed for nearly a decade. GPS and observational data provide behavioral, life history, and location information. Normalized Difference Vegetation Index (NDVI), precipitation, and isotopic data from plants and water provide further constraints for interpreting isotope profiles. We determine tusk and hair growth rates using a combination of histological and geochemical approaches, including bomb-curve radiocarbon, that confirm approximately weekly resolution in the stable isotope profiles. Tusk dentin isotope profiles spanning the periods 1982 to 1987 and 2000 to 2006 record weekly variability in δ13Cdentin, where increases of up to 4.5‰ from baseline values due to diet switches from predominantly C3 browsing to mixed C3 browsing and C4 grazing occur during the twice-yearly (biannual) rainy seasons. The δ13Chair values show a similar trend. The δ13C profiles served as a proxy for seasonal changes in rainfall, vegetation, and diet. The δ18O of tusk bioapatite varied approximately biannually up to 5‰, likely reflecting increases in the proportion of plant water ingested during the wet season. Using a least squares inverse filter, we show that NDVI can be used to predict δ13C of dentin and vice versa, offering the possibility to reconstruct seasonal changes in vegetation and rainfall in the geologic past. Our results demonstrate that high-resolution tusk isotope profiles serve as a proxy for seasonality of diet and precipitation, and thus can be used to reconstruct aspects of elephant life history, vegetation, and climate at unprecedented resolution from modern and fossil proboscidean samples.

Organic and isotope geochemistry analysis of petroleum condensates from the unconventional portion of the Montney Formation, Western Canada

The Montney Formation is a rather complex petroleum reservoir because it contains in-situ and migrated hydrocarbons. Previous organic geochemistry studies reported for this play were based on biomarker ratios of petroleum fluids from the conventional part of this reservoir. Furthermore, there is no isotope study on liquid hydrocarbons from this formation reported to this date. Therefore, we determined the organic and isotope geochemistry of condensate petroleum from the unconventional portion of the Montney Formation to fill this knowledge gap. The condensates were found to be normal fluids of increasing thermal maturity with increasing depth and from the northeast to the southwest. Light hydrocarbon parameters such as paraffinicity (n-C7/methylcyclohexane) and aromaticity (toluene/n-C7) showed to be governed by thermal maturity according to the known maturity trends (increasing depth, and northeast to southwest). The molecular fingerprint of the condensates is to some extent bimodal (noticeable at n-C13) suggesting the possibility of two hydrocarbon charges in the reservoir. This is further evidenced by the stable carbon isotope profile of n-alkanes where light hydrocarbons (C8-C13) show a normal distribution (decreasing δ13C with carbon number) whereas heavier compounds (C19+) show a reverse trend (increasing δ13C with carbon number). We suggest that condensate petroleum produced in the study area corresponds to a mixture of hydrocarbons sourced by the Montney Formation plus alteration products from a pre-existing oil charge that migrated into Montney reservoirs before further burial and thermal maturation of this rock. Producing intervals were distinguished using the δ13C values of n-C11, n-C12, n-C22, and n-C23.

Intra-tooth stable isotope profiles in warthog canines and third molars: Implications for paleoenvironmental reconstructions

Intra-tooth stable isotope variations have been used to interpret seasonality and aridity in paleoenvironmental reconstructions of paleontological and archeological sites. However, most intra-tooth datasets only permit qualitative interpretations of seasonality, because the measured signal is attenuated due to the duration of enamel mineralization process and sampling geometry. The common warthog (Phacochoerus africanus) is an ideal organism to investigate stable isotope variation in enamel. Their canines grow continuously through the life of the individual and are therefore excellent candidates for mathematical modeling of seasonal signals and of signal attenuation; further, their isotope profiles (a series of isotope measurements) can be compared to isotope profiles of third molars (M3) to provide insights into environmental reconstructions. We first obtained paired intra-tooth enamel samples from ever-growing canines and hypsodont M3s of two extant common warthog specimens from Laikipia, Kenya. Second, from a different set of specimens, we collected data on enamel growth patterns and geometry using histological thin sections and transmitted light microscopy, and enamel mineralization parameters using micro-CT scans in each tooth type. Third, we reconstructed the timeline of unattenuated seasonal δ18O signal from canine enamel using growth rate estimates and the inverse model of Passey et al. (2005). Our results demonstrate that canines, which capture ~1.5 years of time, exhibit near-constant growth rates and simple enamel maturation geometry, whereas M3s, which also represent ~1.5 years of time, exhibit linearly decreasing growth rates and more complex maturation patterns. We compare the timelines of unattenuated seasonal δ18O signal and measured M3 profiles and find an average signal reduction of ~50% in the M3s, providing interpretations of the duration of seasonal cycles that are consistent 75% of the time. We conclude that warthog canines are well suited for the inverse model approach, and we established the model parameters for the forward and inverse methods. Timeline reconstructions based on M3 histology are promising for investigating the pattern of rainfall seasonality in the past. Finally, we found an unexpected carbon isotopic spacing of ~2‰ between canine and M3 enamel, which suggests caution in interpreting δ13C results from suid canine or molar enamel alone.

Forward and inverse methods for extracting climate and diet information from stable isotope profiles in proboscidean molars

Intratooth stable isotope profiles in enamel provide time series of dietary and environmental information that if correctly interpreted, serve as archives of seasonal variability in past environments. A major challenge in interpreting these profiles arises from time averaging imparted by enamel mineralization and developmental geometry, whereby the primary (δ13C or δ18O) input signal is attenuated and shifted, which can potentially lead to incorrect interpretations of the magnitude or frequency of seasonal variability. Several forward and inverse models have been developed to reconstruct the primary input signal from intratooth profiles in continuously growing teeth. Here the models developed by Passey and Cerling (2002) and Passey et al. (2005) are extended to molars of Elephantinae, which grow over a long but finite interval of time. Proboscidean molars are particularly attractive for intratooth profiles because they may contain a decade or more of information and they are often well preserved in the fossil record because of their thick enamel and large size.Forward model parameters are established using histological analysis of molar thin sections of extant African elephants (Loxodonta africana) and a mammoth (Mammuthus columbi) and by micro-CT analysis of L. africana molar plates. The density of immature enamel is about 65% of the final density of mature enamel. The appositional length varies from approximately 35 to 55 mm, and the maturation length is about 70 mm. Histological methods are used to determine crown formation time (CFT) in elephant and mammoth molar plates. CFT for the elephant and mammoth molar plates studied in thin section are about 5–6 years and 11 years, which translate to mean growth rates of about 21 mm/year and 16 mm/year, respectively.Coeval molar and tusk profiles from a zoo elephant are compared. The tusk isotope profile serves as a proxy for the primary input signal, and thus provides an opportunity to evaluate the forward and inverse models. The results from the zoo elephant profiles demonstrate that the inverse model accurately reconstructs the amplitude and overall structure of the primary input signal. Inverse model results of mammoth molar profiles show double the range of δ13C in measured enamel profiles. Inversion model results illustrate that improved reconstruction of the primary input signal can lead to more accurate interpretations of the seasonal variability of diet and body water and by extension, vegetation and precipitation in past environments.

Individual phenotyping of feed efficiency in lambs fed stable isotopes through maize silage

Recording feed intake and thus feed efficiency in ruminants is challenging. Hence, there is a need to establish indicator traits that can capture the individual variation in feed efficiency, without requiring individual feed intake recordings. This study aimed to explore whether the methodology established in salmon using individual indicator traits for feed efficiency based on stable isotope profiling could be transferred to lambs since the product for both species is meat. We used a total mixed ration based on maize silage to record the individual indicator traits for feed efficiency. The experiment was done with twelve weaned female lambs of the Norwegian White Sheep grouped equally in three, one group fed a total mixed ration enriched with 13C for 42 days, the second group grazed for 21 days and then fed the total mixed ration for 21 days, and the third group grazed for 42 days. The latter group was included to establish a baseline value for the stable isotope percentage in the back and thigh muscle tissues. Recording of 13C in the back muscle of the animals in the first two groups, resulted in a phenotypic correlation as large as 0.92 between individual feed conversion ratio and the individual indicator traits for feed efficiency based on stable isotope profiling. An assessment through individual indicator traits would be independent of the recording of individual feed intake.

Assessing groundwater recharge and transpiration in a humid northern region dominated by snowmelt using vadose-zone depth profiles

Profiles of the stable isotope ratios of pore water within the vadose zone provide fingerprints of the history of water percolation into a soil. These profiles, combined with profiles of the volumetric water content, can determine the timing and amount of water that has percolated during specific periods. This study aims to: (1) understand water percolation at two sites in Quebec (Canada) that experience thick snow coverage during the winter season; (2) calculate groundwater recharge rates using the peak-shift method; and (3) estimate the transpiration rate based on the water balance budget. A 7-m-deep borehole was drilled at two sites: one site is sparsely covered by vegetation (S1), while the second underlies a pine forest (S2). For all subsamples, δ18O and δ2H from the soil pore water were analyzed, volumetric water content of the cores was measured, and grain-size analyses to estimate the hydraulic properties were performed. For both boreholes, the winter–spring and summer–autumn periods were determined. Given the limited evapotranspiration occurring during the winter–spring period, recharge rates were high at both sites (71 and 75%), while the summer–autumn period had lower recharge rates of 63% (S1) and 41% (S2). A transpiration rate of 0.7 mm/day was estimated for the pine trees covering site S2. This study provides new field observations for estimating recharge based on water stable isotope profiles in a humid northern region dominated by snowmelt. Moreover, it confirms the accuracy of the peak-shift method for assessing groundwater recharge and estimating transpiration.

Combined use of elemental profiles and stable isotope ratios for the botanical and commercial discrimination of gum Arabic

Gum arabic (GA) is a natural, edible gum with particular characteristics resulting from its complex mixture of polysaccharides and glycoproteins. GA is used extensively in several fields and global demand is steadily increasing; for this reason, the determination of GA origin is fundamental to counteract commercial frauds and ensure food safety.The purpose of the study was to investigate whether elemental and isotopic profiles could discriminate, first, between GA produced from plants belonging to the same genus (Acacia) but to 2 different species (A. senegal, SN; A. seyal, SY), and, second, considering only GA of the same botanical origin (SN), between gums produced from different geographic areas (Kordofan region in Sudan vs other Sub-Saharan areas) and commercially resulting in products with different characteristics. The Principal Component Analysis (PCA), combining elemental and stable isotope profiles, could clearly separate the 45 gum samples in 2 clusters corresponding to the botanical species of origin. Results were screened using a partial least squares regression (PLS-R) model developed following the leave-one-out cross-validation approach and including a validation subset of 8 samples. All the calibration and validation samples showed a 100% correct classification, both for SN and SY.Furthermore, the PCA, using only the C, N, Cs, Mg and Na content, could adequately discriminate the SN samples according to their geographic origin, distinguishing the Kordofan samples, traditionally renowned as top-quality products, from the generic gum samples produced in other Sub-Saharan areas.

On the possibility to restore the climatic signal in the disturbed record of stable water isotope content in the old (0.4–1.2 Ma) Vostok ice (Central Antarctica)

In this work we have presented new detailed (with the resolution of 10 cm) stable water isotope (δD and δ 18 O) profile measured in the central Antarctic Vostok ice core section that contains old ice with the age from 0.4 to 1.2 million years. To interpret these data we have developed a model of molecular diffusion in ice and determined the value of so-called «diffusion length». We have demonstrated that the climatic signal in this ice interval is disturbed by a combination of two processes, ice layer folding (that is accompanied by layer overturning and mixing) and molecular diffusion. The whole old ice interval can be divided in 5 zones that differ in terms of character and intensity of these two processes. In three of these zones the climatic signal is partly preserved and could be restored to some extent. However, in the most interesting and old zone 5 (0.75–1.2 Ma) the climatic signal is nearly completely erased and could hardly be reconstructed. At the same time, the isotopic records obtained from the Vostok old ice have preserved the information on the mean level of the isotopic content of ice in glacial and interglacial stages. This gives an opportunity to reveal and study long-term climatic trends with typical duration longer than main climatic cycles (40–100 ka).

A bat guano deposit in Jamaica recorded agricultural changes and metal exposure over the last >4300 years

Bats are excellent ecological indicators because they are long-lived, globally distributed, and show predictable responses to environmental stressors. Unaltered bat guano deposits, although rare, can serve as environmental archives to reveal changes in dietary patterns over millennial time scales. We inferred changes in agricultural and industrial practices using a continuous 4300-year-old bat guano deposit from Jamaica. Cadmium, mercury, lead, and zinc increased during the Industrial Revolution, (which began in ca. 1760), a period characterized by elevated emissions of metals to the atmosphere. Beginning in the early 20th century, decreases in 206Pb/207Pb isotopes tracked the history of leaded gasoline use. Metal concentrations in the bat guano deposit exceeded those recorded in two nearby lake sediment cores from Jamaica. Carbon, nitrogen, and sulfur stable isotope profiles in bat guano tracked the agricultural history of Jamaica, specifically the introduction of nitrogen fertilizers, sugarcane, and possibly fungicides. Bat populations are under stress globally, and such intact guano deposits provide potentially critical information on long-term changes in their food source and exposure to metals.

Combining simulation modeling and stable isotope analyses to reconstruct the last known movements of one of Nature’s giants

The spatial ecology of rare, migratory oceanic animals is difficult to study directly. Where incremental tissues are available, their chemical composition can provide valuable indirect observations of movement and diet. Interpreting the chemical record in incremental tissues can be highly uncertain, however, as multiple mechanisms interact to produce the observed data. Simulation modeling is one approach for considering alternative hypotheses in ecology and can be used to consider the relative likelihood of obtaining an observed record under different combinations of ecological and environmental processes. Here we show how a simulation modeling approach can help to infer movement behaviour based on stable carbon isotope profiles measured in incremental baleen tissues of a blue whale (Balaenoptera musculus). The life history of this particular specimen, which stranded in 1891 in the UK, was selected as a case study due to its cultural significance as part of a permanent display at the Natural History Museum, London. We specifically tested whether measured variations in stable isotope compositions across the analysed baleen plate were more consistent with residency or latitudinal migrations. The measured isotopic record was most closely reproduced with a period of residency in sub-tropical waters for at least a full year followed by three repeated annual migrations between sub-tropical and high latitude regions. The latitudinal migration cycle was interrupted in the year prior to stranding, potentially implying pregnancy and weaning, but isotopic data alone cannot test this hypothesis. Simulation methods can help reveal movement information coded in the biochemical compositions of incremental tissues such as those archived in historic collections, and provides context and inferences that are useful for retrospective studies of animal movement, especially where other sources of individual movement data are sparse or challenging to validate.

City life alters the gut microbiome and stable isotope profiling of the eastern water dragon (Intellagama lesueurii).

Urbanisation is one of the most significant threats to biodiversity, due to the rapid and large-scale environmental alterations it imposes on the natural landscape. It is, therefore, imperative that we understand the consequences of and mechanisms by which, species can respond to it. In recent years, research has shown that plasticity of the gut microbiome may be an important mechanism by which animals can adapt to environmental change, yet empirical evidence of this in wild non-model species remains sparse. Using an empirical replicated study system, we show that city life alters the gut microbiome and stable isotope profiling of a wild native non-model species - the eastern water dragon (Intellagama lesueurii) in Queensland, Australia. City dragons exhibit a more diverse gut microbiome than their native habitat counterparts and show gut microbial signatures of a high fat and plant rich diet. Additionally, we also show that city dragons have elevated levels of the Nitrogen-15 isotope in their blood suggesting that a city diet, which incorporates novel anthropogenic food sources, may also be richer in protein. These results highlight the role that gut microbial plasticity plays in an animals' response to human-altered landscapes.

Aplicação de isótopos estáveis de carbono na avaliação da taxa de crescimento do coral Porites astreoides (Lamarck, 1816) do Atol das Rocas - Atlântico Sul

Corals are often used as natural archives for climate research. These organisms have the ability to incorporate geochemical data into their exoskeletons, which can be used as proxies for different environmental variables. In this work, multiple carbon stable isotope profiles (δ 13 C) were used in different sections of a Porites astreoides (PTM-1) coral colony, collected at Rocas Atoll - South Atlantic. This approach aims to verify the effectiveness of this method as an alternative for the evaluation of coral growth rate of the Scleractinia group. Such method is based on the idea that the coral δ 13 C varies according to the luminosity (i.e. cloud cover), which presents seasonal variability and leave the annual cycles recorded in the corals. Thus, the length of each isotopic cycle corresponds to the growth rate of a coral. In this work, 4 isotopic profiles with 0.5 mm sampling resolution were carried out. The δ 13 C cycles were used to evaluate the growth rate of the PTM-1 colony. The length of the δ 13 C cycles varied from 3 to 12 mm along the profiles and the overall average growth rate estimated for this colony was 6.69 ± 2.39 mm/year, close to those reported for this species in other species. regions, indicating the effectiveness of this method in assessing coral growth rate.

Concentrations of organohalogens (PCBs, DDTs, PBDEs) in hunted and stranded Northern sea otters (Enhydra lutris kenyoni) in Alaska from 1992 to 2010: Links to pathology and feeding ecology.

Many organohalogen compounds (OHCs) are persistent organic pollutants (POPs) found in appreciable concentrations in marine predators. While production of some POPs has declined or ceased in recent decades, their capacity for global transport and bioaccumulation results in observations of unchanging or increasing concentrations in marine systems. Sea otters (Enhydra lutris) have been advocated as an environmental sentinel for contaminants due to their longevity, site fidelity and prey species that often overlap with human consumption. Using archived (1992-2010) samples of livers from Northern sea otters (n = 50) from Alaska we examine concentrations of chlordanes (CHLs), polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDTs), and polybrominated diphenyl ethers (PBDEs) and associated metabolites. We found some evidence for declining ΣPCBs over the two decades, however for most animals concentrations were low compared to toxicological thresholds. Six animals had relatively high concentrations of ΣPCBs (mean = 262,000 ng/g lipid weight), ΣDDTs (mean = 8,800 ng/g lw), and ΣPBDEs (mean = 4,600 ng/g lw), with four of these six animals experiencing hepatic parasitism or hepatitis. In order to assess whether differences in POP concentrations are associated with feeding ecology, we examined stable isotopes of C and N in archived muscle and whisker samples. In general, there were no significant relationships between ΣPOP concentrations and stable isotope ratios. There were small differences in stable isotope profiles in animals with high POP concentrations, although it was unclear if these differences were due to feeding ecology or disease processes. This study highlights the importance of considering feeding ecology and necropsy (health and disease status) data while conducting contaminant surveys, and confirms some previous reports of trends in OHCs in Alaska marine mammals.

Geographical assignment of polar bears using multi-element isoscapes

Wide-ranging apex predators are among the most challenging of all fauna to conserve and manage. This is especially true of the polar bear (Ursus maritimus), an iconic predator that is hunted in Canada and threatened by global climate change. We used combinations of stable isotopes (13C,15N,2H,18O) in polar bear hair from > 1000 individuals, sampled from across much of the Canadian Arctic and sub-Arctic, to test the ability of stable isotopic profiles to ‘assign’ bears to (1) predefined managed subpopulations, (2) subpopulations defined by similarities in stable isotope values using quadratic discriminant analysis, and (3) spatially explicit, isotopically distinct clusters derived from interpolated (i.e. ‘kriged’) isotopic landscapes, or ‘isoscapes’, using the partitioning around medoids algorithm. A four-isotope solution provided the highest overall assignment accuracies (~80%) to pre-existing management subpopulations with accuracy rates ranging from ~30–99% (median = 64%). Assignment accuracies of bears to hierarchically clustered ecological groups based on isotopes ranged from ~64–99%. Multivariate assignment to isotopic clusters resulted in highest assignment accuracies of 68% (33–77%), 84% (47–96%) and 74% (53–85%) using two, three and four stable isotope groups, respectively. The resulting spatial structure inherent in the multiple stable isotopic compositions of polar bear tissues is a powerful forensic tool that will, in this case, contribute to the conservation and management of this species. Currently, it is unclear what is driving these robust isotopic patterns and future research is needed to evaluate the processes behind the pattern. Nonetheless, our isotopic approach can be further applied to other apex mammalian predators under threat, such as the large felids, providing that isotopic structure occurs throughout their range.

Onset and demise of coral reefs, relationship with regional ocean circulation on the Wyville Thomson Ridge

Results from a vibrocore collected on the northern edge of the Scottish continental shelf at around 300 m water depth, on the Wyville Thomson Ridge, enable to reconstruct the history of cold water coral (CWC) reef growth and demise during the Holocene period. We report on significant age differences between U/Th and 14C dates obtained on pristine well-preserved CWC (Lophelia pertusa), which may reflect an diagenetic process that standard quality tests have failed to highlight. Additional 14C dates derived from bivalve fragments (Venus sp.) and foraminifera (Cibicides refulgens) samples show a gradual ageing with core depth but with significant age inversions in the lower section of the sediment core, which we consider reflects sedimentary mixing. We thus chose to derive an independent age model using planktonic foraminifera Globigerina bulloides stable isotope profiles. The vibrocore record is divided into 3 phases: 1- Mixed sediment deposits of glacial age corresponding to the base of the core with ages older than 13 cal ka BP, 2- The end of the deglacial/early Holocene between 13 and 9 cal ka BP and 3- Finally, the Holocene period from around 9 cal ka BP with abundant Lophelia pertusa fossils. Siliciclastic grain size and clay mineralogical composition show two significant shifts at around 13 and 9 cal ka BP indicating changes in sedimentary sources and transport associated with the dynamics and flow patterns of surface currents during the deglaciation and Holocene. Our results show that the onset of CWC reef growth on the Wyville Thomson Ridge occurred around 9 cal ka BP and was associated with a shift in flow patterns of surface currents in this area. This change of circulation patterns induced favourable sedimentological and hydrological conditions for corals to grow, and is associated with large scale modifications of North Atlantic circulation patterns at the end of the deglaciation.

Assessing groundwater sustainability under changing climate using isotopic tracers and climate modelling, southwest Ohio, USA

ABSTRACTGroundwater, an essential resource, is likely to change with global warming because of changes in the CO2 levels, temperature and precipitation. Here, we combine water isotope geochemistry with climate modelling to examine future groundwater recharge in southwest Ohio, USA. We first establish the stable isotope profiles of oxygen and deuterium in precipitation and groundwater. We then use an isotope mass balance model to determine seasonal groundwater recharge from precipitation. Climate model output is used to project future changes in precipitation and its seasonal distribution under medium and high climate change scenarios. Finally, these results are combined to examine future changes in groundwater recharge. We find that 76% of the groundwater recharge occurs in the cool season. Climate models project precipitation increase in the cool season and decrease in the warm season. The total groundwater recharge is expected to increase by 3.2% (8.8%) under the medium (high) climate change scenarios.

Selection for feed efficiency in Atlantic salmon using individual indicator traits based on stable isotope profiling

BackgroundWe used stable isotope profiling (15N and 13C) to obtain indicator phenotypes for feed efficiency in aquaculture. Our objectives were to (1) examine whether atom percent of stable isotopes of nitrogen and carbon can explain more of the variation in feed conversion ratio than growth alone, and (2) estimate the heritabilities of and genetic correlations between feed efficiency, growth and indicator traits as functions of nitrogen and carbon metabolism in various tissues. A 12-day experiment was conducted with 2281 Atlantic salmon parr, with an average initial weight of 21.8 g, from 23 full-sib families that were allocated to 46 family tanks and fed an experimental diet enriched with 15N and 13C.ResultsUsing leave-one-out cross-validation, as much as 79% of the between-tank variation in feed conversion ratio was explained by growth, indicator traits, and sampling day, compared to 62% that was explained by growth and sampling day alone. The ratio of tissue metabolism, estimated by a change in isotope fractions relative to body growth, was used as an individual indicator for feed efficiency. For these indicator ratio traits, the estimated genetic correlation to feed conversion ratio approached unity but their heritabilities were low (0.06 to 0.11). These results indicate that feed-efficient fish are characterized by allocating a high fraction of their metabolism to growth. Among the isotope indicator traits, carbon metabolism in the liver had the closest estimated genetic correlation with feed conversion ratio on a tank level (− 0.9) but a low estimated genetic correlation with individually recorded feed efficiency indicator ratio traits. The underlying determinants of these correlations are largely unknown.ConclusionsOur findings show that the use of indicator ratio traits to assess individual feed efficiency in Atlantic salmon has great prospects in selection programs. Given that large quantities of feeds with contrasting isotope profiles of carbon and/or nitrogen can be produced cost-effectively, the use of stable isotopes to monitor nitrogen and carbon metabolism in various tissues has potential for large-scale recording of individual feed efficiency traits, without requiring individual feed intake to be recorded.