Individual δ13C Research Articles

Combined use of carbon, nitrogen and sulfur stable isotopes reveal trophic structure and connections in deep-sea mesopelagic and demersal fish communities from the Southeastern Pacific Ocean

The trophic structure of deep-sea fish communities has been poorly studied in the Southeastern Pacific Ocean. Here, using the analysis of multiple (CNS) stable isotopes, we provide a first approach to characterize the structure of a marine food web including mesopelagic (9 species) and demersal (13 species) fishes. At a species level, Dissostichus eleginoides were the most 13C-depleted and the grenadier Coryphaenoides ariommus the most 13C-enriched species. The most 15N-depleted species was the lanternfish Diogenichthys laternatus and macrourid fishes Trachyrincus villagai and C. ariommus the most 15N-enriched. δ34S values showed less variation, but ranged considerably, varying between 10.5 and 17.7‰: C. ariommus was the most 34S-depleted species and D. eleginoides the most 34S-enriched. At a whole study level, individual δ13C and δ15N values were positively correlated. Relationships between δ13C and δ34S, and δ15N and δ34S were both negative. When analyses were conducted separately for demersal and mesopelagic fishes, δ13C showed a positive correlation with δ15N. There was a negative relationship between δ13C and δ34S in demersal fish but no apparent relationship between δ15N and δ34S. In mesopelagic fishes, there was no statistical support for relationships between δ13C and δ34S or δ15N and δ34S. Mean log-transformed total length (TL) and mean δ15N were related in mesopelagic fishes, but there was no apparent relationship between TL and δ13C or δ34S values. In the case of demersal fishes there was no relationship between TL and either δ15N, δ13C or δ34S. Using cluster analysis, species were classified into 4 distinct trophic groups (G1 - G4) that display different trophic strategies according to the literature. Groups G1 and G2 included zooplanktivorous, micronektonivorous and gelatinovorous fishes associated with pelagic habitats. Groups G3 and G4 include micronektonivorous, piscivorous and generalist fishes foraging in benthic habitats. The demersal fish Dissostichus eleginoides was classified as a member of G1, suggesting that its diet in northern Chile is likely dominated by pelagic prey. In addition, Macrourus holotrachys (G3) showed very marked individual variability in δ15N values indicating considerable intraspecific variation in diet and foraging behavior. Given that this species had isotope values that extended across values typical of benthic and pelagic habitats, it suggests that some individuals may perform vertical migrations. Our results also highlighted that some demersal species (M. holotrachys and Coryphaenoides ariommus) had δ34S values that indicate the assimilation of some chemosynthetic-derived sulfur.Our results provide isotopic information on deep-water species in this region and show likely coupling between the demersal and mesopelagic assemblages. This information improves our understanding of deep-sea ecosystem functioning and provides key information for fisheries management and conservation initiatives.

The role of status, diets, and mobility in understanding the impacts of urbanization in early medieval Bergen, Norway (St. Mary's Church): Insights from stable isotope analyses

AbstractThis research examines the diets and mobility of higher status individuals buried in the St. Mary's (Mariakirken) churchyard (1140 and 1248 AD), located in Bergen, Norway. Stable isotope data are used to explore the role that diets (preferential access, choice of foods) may have played in mitigating the negative impacts of rapid urbanization. Dietary reconstruction involved analysis of carbon (δ13C) and nitrogen (δ15N) stable isotope ratios from paired bone and tooth samples from St. Mary's individuals (N = 25). Oxygen isotope ratios (δ18O) were derived from analyses of tooth enamel carbonate to comment on individuals' origins and mobility (N = 26). Individualδ13C andδ15N collagen values indicate that St. Mary's individuals consumed variable diets, with some relying on marine animal protein almost exclusively, while others primarily consumed C3plants or animals that consumed C3plants as the main source of their dietary protein.δ18O ratios showed that some individuals originated outside of Bergen. Thus, the stable isotope evidence (δ13C andδ15N) indicates that diets of St. Mary's individuals were more varied, and in some cases, relied primarily on imported trade goods such as grain/grain fed animals, and marine resources. This reinforces the view that St. Mary's represented an affluent segment of the growing Bergen population, and that its members were heavily involved in trade. Oxygen isotopes show that some individuals spent time living outside of Bergen during childhood. These data suggest that diets were more variable within the St. Mary's sample than at contemporary Norwegian sites, and that the process of urbanization did not impact the people of Bergen in a unified way.

Lipid residue analysis of ceramic vessels from the Liujiawa site of the Rui State (early Iron Age, north China)

ABSTRACTThe Liujiawa site is located in the Agricultural–Nomadic Transitional Zone in Northern China (ANTZNC), inhabited during the early Spring and Autumn Period (770–476 bc). Little is known about the diets of its inhabitants or agricultural management practices due to scant historical descriptions. In this study, lipid analysis was conducted on pottery sherds collected from two residential areas within the Liujiawa site. The results offer direct evidence for the processing of millet and ruminant and non‐ruminant carcass products by the commoners of the Liujiawa community. The individual δ13C values of fatty acids with positive fluctuation indicate that some ruminant animals and pigs were fed C4 plants as fodder. The routine consumption of ruminant meat by the common inhabitants also reflects a more diverse food source than that proposed in historical descriptions that have suggested dietary heterogeneity between the upper and lower classes: cattle or ovicaprid meat was not a singular privilege enjoyed by the noble classes. On the contrary, commoners also consumed the meat as a food source. Moreover, direct evidence of dairy processing has been found for the first time in pottery residues from an archaeological site within ANTZNC, strongly indicating that milk had been incorporated into the diet as an additional source of food.

A novel isotopic approach to distinguish primary microbial and thermogenic gases in shallow subsurface environments

The stable carbon isotopic compositions of methane and ethane have been used for several decades to characterize petroleum gas in the subsurface. However, difficulties have frequently remained in determining the exact origin of natural gas samples derived from microbial activity, thermal degradation of organic matter (e.g. thermogenic gas), and mixtures of both components. To further refine this approach, we represent the carbon isotope difference between methane and ethane, or Δ13CC1–C2, plotted versus the individual δ13C values of methane and ethane as a new graphical tool for a refined assessment of natural gas origins and their mixtures. In addition, a new mathematical notation using the δ13C values of methane and ethane is also proposed for discrimination of the origin of natural gas samples. This parameter has been termed isotope factor O(C1/C2) and is defined as the ratio [(δ13CC1*1000)/(δ13CC2)3]. When this factor is represented against the δ13C values of methane and ethane, an improved distinction between primary microbial and thermogenic gases is achieved. Our study does not propose mechanisms for microbial generation of ethane, but the data suggest that the isotopic composition of ethane should be taken into account for the characterization of the origin of natural gas samples from shallow subsurface environments. For primary microbial and thermogenic gases with similar δ13C values of methane, the primary microbial gas will be characterized by lower O(C1/C2) values (<1.5) compared to the thermogenic gas (>2), and will have a Δ13CC1–C2 value 10–20‰ more positive than that of thermogenic gas. Gas mixtures have intermediate O(C1/C2) and Δ13CC1–C2 values and are graphically identifiable using the here presented classification tools. The effectiveness of the new graphical tools is demonstrated using natural gas samples from Canadian groundwater wells, low-permeability petroleum reservoirs (including coalbed methane plays) in Canada and the USA, Quaternary primary microbial gas accumulations in China, and secondary microbial gases from Northern Africa and China.

A Dual Stable Isotope Approach Unravels Common Climate Signals and Species-Specific Responses to Environmental Change Stored in Multi-Century Tree-Ring Series from the Tibetan Plateau

Tree-rings are recorders of environmental signals and are therefore often used to reconstruct past environmental conditions. In this paper, we present four annually resolved, multi-centennial tree-ring isotope series from the southeastern Tibetan plateau. The investigation site, where juniper and spruce trees jointly occur, is one of the highest known tree-stands in the world. Tree ring cellulose oxygen (δ18O) and carbon (δ13C) isotopes were analyzed for a common period of 1685–2007 AD to investigate climate–isotope relationships. Therefore, various climate parameters from a local meteorological station and from the CRU 4.02 dataset were used. Tree-ring δ18O of both species revealed highly significant sensitivities with a high degree of coherence to hydroclimate variables during the growing season. The obtained δ18O–climate relationships can even be retained using a species mean. In contrast, the individual δ13C series indicated a weaker and non-uniform response to the tested variables. Underlying species-specific responses and adaptations to the long-term trend in atmospheric CO2 bias even after a trend correction identified dominant environmental factors triggering the tree-ring δ13C at our site. However, analysis of individual intrinsic water-use efficiency in juniper and spruce trees indicated a species-specific adaptation strategy to climate change.

Geographical origin of Chinese wolfberry (goji) determined by carbon isotope analysis of specific volatile compounds

Chinese wolfberry or goji berry (Lycium barbarum) is an important traditional Chinese medicine. Its price and function has a close correlation with its geographical provenance. Illegal mislabeling motivated by commercial gains brings serious food safety problems and damages consumer confidence. In this work, a novel analytical strategy combined with chemometrics statistic tools was developed to determine the geographical origin of wolfberries from different provinces in China. Stable carbon isotopic ratios (δ13C) of wolfberry volatile compounds (i.e. limonene, tetramethylpyrazine, safranal, geranylacetone, and β-ionone) were determined by gas chromatography-combustion-isotope ratio mass spectrometry (GC-IRMS) with headspace-solid phase micro extraction (HS-SPME). Five types of SPME fiber (i.e. DVB/CAR/PDMS, CAR/PDMS, PDMS/DVB + OC, PDMS, and PA), extraction time, temperature and GC-IRMS conditions were comprehensively optimized to obtain the best adsorption of volatile compounds in wolfberry. Method integrity was assessed by comparing volatiles extracted using HS-SPME GC-IRMS with direct injection GC-IRMS and were in good agreement with each other. The geographical variations of volatile compounds using one-way analysis of variance (ANOVA) were explored for individual δ13C values in wolfberry samples from Gansu, Ningxia and Qinghai. Geographical origin of wolfberry was differentiated by linear discrimination analysis (LDA), with an accuracy of 89.16%, 87.77% and 85.87% for these three provinces, respectively. These results showed the combination of SPME and IRMS provides a rapid and valid method to determine the geographical origin of wolfberry.

From field to fish: Tracking changes in diet on entry to two medieval friaries in northern England

Members of religious orders during the later medieval period in Britain were expected to adhere to strict rules governing their daily lives which restricted their consumption of meat. This study aims to investigate whether this switch to a ‘religious diet’ can be isotopically detected in presumed religious individuals upon their entry into a religious order during adolescence. Secondary aims of this study include: 1) a comparison of the carbon (δ13C) and nitrogen (δ15N) stable isotope values between individuals with and without diffuse idiopathic skeletal hyperostosis (DISH); and 2) to compare the mean values of the sites analyzed with geographically and temporally related sites from previously published studies. To achieve these aims, δ13C and δ15N analysis of third molar incremental dentine collagen and bulk rib bone collagen was undertaken on ten presumed religious individuals: five from the Carmelite friary at Priory Close, Northallerton, founded in 1356 CE, and five from the Friars of the Sack-turned-Carmelite friary at Clavering Place, Newcastle-upon-Tyne, founded in 1266 CE. Twelve contemporaneous faunal samples were also analyzed to provide an isotopic baseline. The δ13C and δ15N profiles of all individuals from both sites in this study increased from the beginning of the formation of the third molar at c. 8.5 years to its completion at c. 23.5 years indicating a shift during adolescence from a largely terrestrial mixed diet to one that contained a significant amount of animal and marine protein. Individuals exhibiting skeletal pathology indicative of DISH were found to have individual δ13C and δ15N values that were elevated above the means for each site, and the mean rib collagen δ13C and δ15N values at Priory Close and Clavering Place were in line with published data from other later medieval religious sites in northeastern England. This study provides evidence for a shift in diet experienced by members of religious orders during adolescence and lays the foundation for future studies of dietary changes at different religious institutions.

A 7.5 ka chronology of stable carbon isotopes from tree rings with implications for their use in palaeo-cloud reconstruction

Abstract Tree-ring stable isotope chronologies provide very high-resolution palaeoclimatic data, and the number of records is increasing rapidly worldwide. To extend the chronologies back in time, before the period covered by the old living trees, the use of subfossil wood samples is required. Typically, the longest continuous subfossil chronologies consist of regionally collected tree-ring materials, rather than tree rings from a single site, and are likely more sensitive to data heterogeneity. Yet, the characteristics of such datasets remain hitherto unexplored. Here we produce a continuous, decadally resolved chronology of 13C/12C ratio (δ13C) from Finnish Lapland over the past 7.5 ka (5500 BCE to 2010 CE) for which there is replication of at least five Pinus sylvestris trees. Less negative δ13C values were observed as trees age and for western sites (higher in elevation and further from the cold oceanic air flow). The age-related trends in living tree δ13C data were expressed mainly over the first fifty years mimicking the “juvenile effect” whereas the subfossil data showed trend over the trees' lifespan. These findings demonstrated the need to detrend the individual δ13C series before averaging them into the mean chronology. The corresponding biases were removed from the isotopic data using the methods frequently applied for tree-ring width and density proxies, the Regional Curve Standardization (RCS) combined with signal-free approach. While the RCS procedures commonly preserve the long-term variations in the resulting chronology, not all types of them did so as demonstrated for chronologies produced using separate RCS models for the δ13C series with relatively high and low isotopic level (offset from the grand mean). It was shown that these δ13C levels (i.e. the relative isotopic enrichment) result both from the low-frequency climate signal and biogeographical aspects (the site longitude/altitudes). The non-climatic biases were removed from the δ13C series by using separate RCS models for the subsets (western and eastern) of isotopic series. Similar to previous investigations using annually resolved δ13C data from Lapland, our chronology had strong negative correlations to variations in cloud cover. Here, a bootstrapping experiment was used to verify this dendroclimatic association. The resulting palaeo-cloud reconstruction portrayed decadal to multi-millennial variations with centennial anomalies coinciding with the mid and late Holocene events of climate transitions, highlighting the value of subfossil isotope chronologies from tree rings in synthesising climate dynamics from several proxy sources over the present interglacial.

Lipid Evidence for Oil Depletion by Sulfate-Reducing Bacteria during U Mineralization in the Dongsheng Deposit

Fatty acids were extracted from fluid inclusions, and analyzed for distribution and individual δ13C values to determine if there exists sulfate-reducing bacteria (SRB) and what substrates SRB depleted during U mineralization in the Dongsheng deposit. The 10-methylhexadecanoic acid (10Me16:0) has been detected from most of the samples using GC-MS based on relative retention time and co-injection of standard 10Me16:0 compound. Samples with higher 10Me16:0 concentrations, show higher U contents. The presence of 10Me16:0 along with iso-ω7-cis-heptadecenoic acid (i17:1ω7c) and ω7-cis- octadecenoic acid (18:1ω7c) in the fluid inclusions may indicate the occurrence of SRB during the U mineralization. Saturated fatty-acids and unsaturated fatty-acids detected in this study have individual δ13C values from -30.3‰ to -28.5‰ and -30.5‰ to -27.9‰, respectively. These values are close to those of n-alkanes of the associated oils and the bulk oils, but significantly distinct from methane, thus the oils are concluded to have been used as substrate for the microorganisms to survive on. This proposal is supported by oil biodegradation and ore-stage calcite cement with δ13C values from -1.4‰ to -17.2‰.

Tracking host use by bat ectoparasites with stable isotope analysis

We used C and N stable isotopes of nectarivorous bats and their ectoparasites to determine the extent to which parasites depend on the host individual for food. The difference in stable isotope values between parasites and host tissues (Δ13C and Δ15N) was used as a proxy of host use. First, we tested the hypothesis that movement among individual Mexican long-tongued bats (Choeronycteris mexicana Tschudi, 1844) is more likely to occur in winged flies than in mites as indicated by higher host–parasite isotopic Euclidian distance (ED). Second, we tested the hypothesis that ectoparasite species in two coexisting bat species representing the C3 (Geoffroy’s tailless bat, Anoura geoffroyi Gray, 1838) and the CAM (lesser long-nosed bat, Leptonycteris yerbabuenae Martínez and Villa-R., 1940) food chains were monoxenous as indicated by their isotopic values. We also examined Δ13C and Δ15N of individual parasites in relation to 13C and 15N reference enrichment factors as an indication of host switching. In general, flies in C. mexicana had higher ED and wider ranges of individual Δ13C and Δ15N than mites, suggesting that host switching occurred to a larger extent. Most ectoparasites species collected in both coexisting bats were monoxenous, but one fly species appears to be oligoxenous. Individual Δ13C and Δ15N values varied widely in these parasite species, suggesting movements within species hosts.

Intra- and inter-individual variation in δ13C and δ15N in human dental calculus and comparison to bone collagen and apatite isotopes

There are mixed opinions on the suitability of dental calculus for paleodietary reconstruction using stable isotope analysis. We examine δ13C and δ15N values of calculus samples from two regions, central California in the USA and Sai Island in the Sudan. When atomic C/N ratios are less than 12 in calculus, results show positive correlations at both the regional and individual level between stable isotopes of bone collagen and calculus, suggesting these materials track similar dietary behaviors. Correlations are still positive but lower between δ13C values of calculus and bone apatite. Stable isotope ratios of calculus show between 30% and 50% greater variation than bone, are typically enriched in 15N (mean = 2.1‰ higher), and are depleted in 13C relative to bone collagen (mean = 0.8‰ lower) and apatite (mean = 6.4‰ lower). Calculus from multiple teeth was analyzed separately for seven individuals to examine intra-individual variation. Results show that within an individual δ13C varies up to 1.8‰, and δ15N up to 2.1‰, which may explain some of the weak bone-calculus correlations previously reported in the literature. When atomic C/N ratios are greater than 12, calculus correlates more poorly with bone collagen, suggesting these samples should be treated with caution.

Cautionary lessons from assessing dental mesowear observer variability and integrating paleoecological proxies of an extreme generalist Cormohipparion emsliei

Dental mesowear is an inexpensive and expedient method used to characterize the average diet of herbivorous mammals, capturing wear produced over several months in the lifetime of an animal by both attrition and abrasion. Most dental mesowear methods focus on qualitatively categorizing cusp shapes as sharp, round, or blunt with high or low relief, sometimes classifying teeth into numerical categories that integrate these variables (typically 0 to 6, from sharp/high relief to blunt/low relief). As dental mesowear requires an observer to make subjective judgments regarding tooth categories, we assess observer variability and integrate carbon isotope and dental mesowear data to clarify if mesowear similarly records average dietary information in an extreme generalist herbivore (i.e., Cormohipparion emsliei). Stable carbon isotope samples of C. emsliei from the Bone Valley of Florida (~5Ma) yield a δ13C range of 13.7‰, suggestive of highly generalized dietary behavior ranging from primarily browsing to grazing. While average mesowear values for this population are partially consistent with a mixed feeding diet, individual δ13C values lack significant relationships with all mesowear variables, excluding relief. Further, individuals consuming disparate diets (i.e., individuals with the lowest and highest carbon isotope values of −12.9‰ and 0.8‰, respectively) yield similar dental mesowear values (4.20 and 3.75, respectively). Dental mesowear analyses conducted by experienced versus minimally trained individuals are not significantly different from one another, suggesting that mesowear methods can be easily taught; however, the incorporation of multiple observers can reduce variability. Caution should be exercised when interpreting the diets of individuals based on dental mesowear alone.

Similar patterns of individual niche use are revealed by different time‐integrated trophic tracers (stable isotopes and parasites)

AbstractTwo unconnected time‐integrated tracers of niche use provided similar conclusions about individual foraging behaviour and niche adaptations (functional traits in head shape) within a subarctic lake population of Arctic charr (Salvelinus alpinus). Zooplanktivorous individuals mainly from the pelagic zone were characterised by having low δ13C values, high infections of the parasites transmitted by pelagic copepods (especially Diphyllobothrium spp.) and slender heads with long snouts. In contrast, fish individuals that had consumed benthic prey in the littoral zone were enriched in δ13C and had high abundances of parasites transmitted by Gammarus lacustris (Cyathocephalus truncatus and Cystidicola farionis) and a robust head shape. There were strong positive correlations between individual δ13C values and the abundance of the two parasite species transmitted by Gammarus, but a negative correlation between δ13C and the infection of copepod‐borne parasites. The close relationships between diet variation (foraging behaviour), the time‐integrated ecological tracers (SI and parasites) and functional trophic morphology (niche adaptations) evidently reflect long‐term temporally stable niche use of each individual predator. The two independent time‐integrated tracers both gave valuable information of specialised trophic behaviour at the individual level, which is an important basis for studies related to ecological (e.g., resource partitioning) and evolutionary (e.g., polymorphism) topics within a population.

Feeding on the edge: δ13C analysis of a macrofauna food web from disappearing seagrass beds in a polluted urban harbour – implications for biomonitoring and restoration efforts

Abstract Thirty‐five macrofaunal species were collected from several eelgrass (Zostera marina) beds in Boston Harbour to determine whether food provenance and carbon flow as measured by δ13C analysis differed for a seagrass community exposed to dense urbanization compared with those documented for populations distant from cities, and whether such isotopic determinations might be used for purposes of biomonitoring such disturbance. In support of other studies and a previous global synthesis, the majority of benthic and epibenthic fauna inhabiting Boston Harbour eelgrass beds were found to have δ13C values within the range, –20 to –17 ‰, indicative of epiphytic algae being the most important food source. However, the proportional abundance‐weighted assessment of the distribution of individual δ13C measurements was found to be quite different from that revealed by non‐quantitative, species‐only assessments. Because the chink shell, Lacuna vincta, which was the only species to demonstrate primary assimilation of eelgrass δ13C, numerically dominated the benthic food web in Boston Harbour, over three‐quarters of the total abundance of macroinvertebrates were likely to be directly dependent upon eelgrass carbon. Nevertheless, food web transfer, as measured through δ15N analysis, was extremely limited as no direct mechanism appeared to presently exist by which eelgrass carbon could be exclusively passed from chink shells to animals of higher trophic positions. The dietary fidelity of these animals while experiencing severe habitat loss due to anthropogenic pollution – neither a shift toward increased vascular plant detritivory nor toward increased planktonic algivory occurred – indicates that pathways of carbon flow may offer little use as an early warning biomonitor for gauging either individual stress or community‐level disturbance from coastal development. Because epiphytic algae are the major food source for most macrobenthos species rather than the vascular plants themselves, the possibility exists that seagrass simulacra might be used as interim installations in order to sustain communities until such time as the aquatic conditions improve to such a degree as to enable the successful restoration of the degraded beds. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Bulk Sediment and Diatom Silica Carbon Isotope Composition from Coastal Marine Sediments off East Antarctica

Organic carbon occluded in diatom silica is assumed to be protected from degradation in the sediment. δ13C from diatom carbon (δ13C(diatom)) therefore potentially provides a signal of conditions during diatom growth. However, there have been few studies based on δ13C(diatom). Numerous variables can influence δ13C of organic matter in the marine environment (e. g., salinity, light, nutrient and CO2 availability). Here we compare δ13C(diatom) and δ13C(TOC) from three sediment records from individual marine inlets (Rauer Group, East Antarctica) to (i) investigate deviations between δ13C(diatom) and δ13C(TOC), to (ii) identify biological and environmental controls on δ13C(diatom) and δ13C(TOC), and to (iii) discuss δ13C(diatom) as a proxy for environmental and climate reconstructions. The records show individual δ13C(diatom) and δ13C(TOC) characteristics, which indicates that δ13C is not primarily controlled by regional climate or atmospheric CO2 concentration. Since the inlets vary in water depths offsets in δ13C are probably related to differences in water column stratification and mixing, which influences redistribution of nutrients and carbon within each inlet. In our dataset changes in δ13C(diatom) and δ13C(TOC) could not unequivocally be ascribed to changes in diatom species composition, either because the variation in δ13C(diatom) between the observed species is too small or because other environmental controls are more dominant. Records from the Southern Ocean show depleted δ13C(diatom) values (1-4 ‰) during glacial times compared to the Holocene. Although climate variability throughout the Holocene is low compared to glacial/interglacial variability, we find variability in δ13C(diatom), which is in the same order of magnitude. δ13C of organic matter produced in the costal marine environment seems to be much more sensitive to environmental changes than open ocean sites and δ13C is of strongly local nature. © 2012 Springer Science+Business Media B.V.

Variation in δ13C and δ15N diet-vibrissae trophic discrimination factors in a wild population of California sea otters (Enhydra lutris nereis)

The ability to quantify dietary inputs using stable isotope data depends on accurate estimates of isotopic differences between a consumer (c) and its diet (d), commonly referred to as trophic discrimination factors (TDFs) and denoted by Δc-d. At present, TDFs are available for only a few mammals and are usually derived in captive settings. The magnitude of TDFs and the degree to which they vary in wild populations is unknown. We determined δ13C and δ15N TDFs for vibrissae (i.e., whiskers), a tissue that is rapidly becoming an informative isotopic substrate for ecologists, of a wild population of sea otters for which individual diet has been quantified through extensive observational study. This is one of the very few studies that report TDFs for free-living wild animals feeding on natural diets. Trophic discrimination factors of 2.2‰ ± 0.7‰ for δ13C and 3.5‰ ± 0.6‰ for δ15N (mean ± SD) were similar to those reported for captive carnivores, and variation in individual δ13C TDFs was negatively but significantly related to sea urchin consumption. This pattern may relate to the lipid-rich diet consumed by most sea otters in this population and suggests that it may not be appropriate to lipid-extract prey samples when using the isotopic composition of keratinaceous tissues to examine diet in consumers that frequently consume lipid-rich foods, such as many marine mammals and seabirds. We suggest that inherent variation in TDFs should be included in isotopically based estimates of trophic level, food chain length, and mixing models used to quantify dietary inputs in wild populations; this practice will further define the capabilities and limitations of isotopic approaches in ecological studies.

Improved detection of honey adulteration by measuring differences between13C/12C stable carbon isotope ratios of protein and sugar compounds with a combination of elemental analyzer - isotope ratio mass spectrometry and liquid chromatography - isotope ratio mass spectrometry (δ13C-EA/LC-IRMS)

The detection of honey adulteration with invert sugar syrups from various C3 and C4 plant sources was realized by coupling an isotope ratio mass spectrometer both to an elemental analyzer and to a liquid Chromatograph (EA/LC-IRMS). For 451 authentic honeys measured, the individual δ13C values of bulk honey, its protein fraction, fructose, glucose, and di- and trisaccharides ranged from −22.5 to −28.2‰ and did not show differences (Δδ13C) of more than ± 0.9‰ (average), with a maximum standard deviation of 0.7‰ The Δδ13C (fructose — glucose) value was significantly lower (0 ± 0.3‰). Based on the obtained results and considering a confidence level of 99.7%, the following limits for Δδ13C values of authentic honey are proposed: Δδ13C max.: ± 2.1‰ (maximum difference between all measured δ13C values); Δδ13C fru —glu: ± 1.0‰; Δδ13C (‰) protein — honey: ⩾ − 1.0‰ The newly developed EA/LC-IRMS method and the purity criteria defined represent a significant improvement compared to existing methods.

Diet of the social groups of long-finned pilot whales (Globicephala melas) in the Strait of Gibraltar

The Strait of Gibraltar is inhabited throughout the year by a group of pilot whales (Globicephala melas), but their spatial distribution varies between Summer and Autumn. In this paper, we have used carbon (13C/12C) and nitrogen (15N/14N) stable isotope signatures to investigate the differences in diet amongst seasons, sex and stable social units. Skin samples were collected from 56 individually photo-identified pilot whales during Autumn 2005 and Summer 2006. These individuals were genetically sexed and their isotopic signature determined. The level of inter-individual association both within and between stable social units were compared to Euclidean distances between individual isotopes signatures. No differences in either δ15N or δ13C were found according to the sex of individuals, but significant seasonal differences were found in δ15N, although not in the δ13C values. This suggests that pilot whales are resident year round in the Strait, a finding supported by independent photo-identification. The variation in δ15N could reflect a shift in pilot whale diet through the year, with pilot whales feeding at a higher trophic level in Autumn compared to Summer. This could also represent a change in the diet of pilot whale prey species. The δ13C values were significantly different amongst the four stable social units sampled and individual δ13C values were significantly related to the level of inter-individual association, while no relationship was found for δ15N. These results suggest that within the same general area (i.e. the Strait of Gibraltar), there is some level of specialisation in habitat or prey choice between pilot whales social units.

Maastrichtian North Atlantic warming, increasing stratification, and foraminiferal paleobiology at three timescales

Analysis of 944 single specimens of three species of late Maastrichtian planktonic foraminifera (Racemiguembelina fructicosa, Contusotruncana contusa, and Rugoglobigerina rugosa) from 38 samples spanning the last 3 Myr of the Cretaceous shows consistent isotopic trends through time, consistent isotopic differences among taxa, and high within‐sample isotopic variability throughout. Within‐sample variability does not change systematically through time for any taxon, but average δ18O values decrease by ∼1.5‰, and average δ13C values diverge up section. Comparing taxa, average δ18O values are similar within most samples, but average δ13C values generally decrease from R. fructicosa to R. rugosa to C. contusa. In addition, the within‐sample variability of individual δ13C measurements is larger for R. fructicosa than for either C. contusa or R. rugosa, an observation which is consistent with a photosymbiotic habitat for R. fructicosa. In terms of Maastrichtian paleoceanography the negative δ18O trend of ∼1.5‰ corresponds to a temperature increase of ∼6°C, and the divergence of δ13C values up section suggests an increasingly stratified water column in the western Atlantic through the late Maastrichtian. We suggest that these trends are best explained by increasing import of South Atlantic waters into the North Atlantic and an intensification of the Northern Hemisphere polar front.

Seasonal and annual changes in leaf δ13C in two co‐occurring Mediterranean oaks: relations to leaf growth and drought progression

1. Changes of δ13C and its relation to leaf development, biochemical content and water stress were monitored over a 2 year period in two co‐occurring Mediterranean oak species: the deciduous Quercus pubescens and the evergreen Quercus ilex. 2. The time course of leaf δ13C showed different patterns in the two species. Young Q. pubescens leaves had a high δ13C and a marked decrease occurred during leaf growth. In contrast, leaves at budburst and maturity did not differ significantly in the case of Q. ilex. We suggest that the difference between δ13C of young leaves was linked to differential use of reserves of carbon compounds in the two species. 3.δ13C values of mature leaves were negatively correlated with minimum seasonal values of predawn water potential, suggesting that a functional adjustment to water resources occurred. 4. There was a significant correlation between individual δ13C values for two successive years. This interannual dependence showed that δ13C rankings between trees were constant through time.