Kangaroo tooth enamel oxygen and carbon isotope variation on a latitudinal transect in southern Australia: implications for palaeoenvironmental reconstruction

Tooth enamel apatite carbonate carbon and oxygen isotope ratios of modern kangaroos (Macropus spp.) collected on a 900-km latitudinal transect spanning a C₃–C₄ transition zone were analysed to create a reference set for palaeoenvironmental reconstruction in southern Australia. The carbon isotope composition of enamel carbonate reflects the proportional intake of C₃ and C₄ vegetation, and its oxygen isotope composition reflects that of ingested water. Tooth enamel forms incrementally, recording dietary and environmental changes during mineralisation. Analyses show only weak correlations between climate records and latitudinal changes in δ¹³C and δ¹⁸O. No species achieved the δ¹³C values (~?1.0 ‰) expected for 100 % C₄ grazing diets; kangaroos at low latitudes that are classified as feeding primarily on C₄ grasses (grazers) have δ¹³C of up to ?3.5 ‰. In these areas, δ¹³C below ?12 ‰ suggests a 100 % C₃ grass and/or leafy plant (browse) diet while animals from higher latitude have lower δ¹³C. Animals from semi-arid areas have δ¹⁸O of 34–40 ‰, while grazers from temperate areas have lower values (~28–30 ‰). Three patterns with implications for palaeoenvironmental reconstruction emerge: (1) all species in semi-arid areas regularly browse to supplement limited grass resources; (2) all species within an environmental zone have similar carbon and oxygen isotope compositions, meaning data from different kangaroo species can be pooled for palaeoenvironmental investigations; (3) relatively small regional environmental differences can be distinguished when δ¹³C and δ¹⁸O data are used together. These data demonstrate that diet–isotope and climate–isotope relationships should be evaluated in modern ecosystems before application to the regional fossil record.     

Otoliths speak out: why the Pacific halibut in Puget sound are different

Pacific halibut, Hippoglossus stenolepis, is one of the most important commercial groundfish and is managed as a single coast-wide population from Alaska to northern California. Nevertheless, genetic investigations did not show success in detecting the population structure of the species. Here I report stable oxygen and carbon isotope analyses (δ¹⁸O and δ¹³C) in otoliths to discriminate the stock differences from two sample locations between the Washington coast (WC) and the northern Puget Sound (PS), and two sample years in 2007 and 2008. In general the δ¹⁸O values of halibut otoliths from WC ranged from ?0.2 to 1.8‰, higher than the PS samples from ?0.5 to 1.4‰. In contrast, the δ¹³C values from WC ranged from ?3.6 to ?1.0‰, lower than the PS samples from ?3.2 to ?1.2‰. Results from the otolith nuclei (age-0 halibut) and the 8^th (the earliest maturity age for male halibut) and edge otolith rings (the latest location where the fish lived) showed significant differences between halibut samples from PS and WC. In particular, the sample location difference (between PS and WC) in both δ¹³C and δ¹⁸O data was significant and markedly larger than the sample year difference (between 2007 and 2008). These isotopic signatures provide evidence that the PS halibut may belong to a distinct stock that is significantly different from WC halibut.     

Non-climatic variations in the oxygen isotopic compositions of plants

The ¹⁸O content of leaf water strongly influences the ¹⁸O contents of atmospheric CO₂ and O₂. The ¹⁸O signatures of these atmospheric gases, in turn, emerge as important indicators of large-scale gas exchange processes. Better understanding of the factors that influence the isotopic composition of leaf water is still required, however, for the quantitative utilization of these tracers. The ¹⁸O enrichment of leaf water relative to local meteoric water, is known to reflect climatic conditions. Less is known about the extent variations in the ¹⁸O content of leaf water are influenced by nonclimatic, species-specific characteristics. In a collection of 90 plant species from all continents grown under the same climatic conditions in the Jerusalem Botanical Garden we observed variations of about 9‰ in the δ¹⁸O values of stem water, δ_s, and of about 14‰ in the mid-day δ¹⁸O enrichment of bulk leaf water, δ_LW–δ_s. Differences between δ¹⁸O values predicted by a conventional evaporation model, δ_M, and δ_LW ranged between – 3.3‰ and + 11.8‰. The δ¹⁸O values of water in the chloroplasts (δ_ch) in leaves of 10 selected plants were estimated from on-line CO₂ discrimination measurements. Although much uncertainty is still involved in these estimates, the results indicated that δ_ch can significantly deviate from δ_M in species with high leaf peclet number. The δ¹⁸O values of bulk leaf water significantly correlated with δ¹⁸O values of leaf cellulose (directly) and with instantaneous water use efficiency (A/E, inversely). Differences in isotopic characteristics among conventionally defined vegetation types were not significant, except for conifers that significantly differed from shrubs in δ¹⁸O and δ¹³C values of cellulose and in their peclet numbers, and from deciduous woodland species in their δ¹⁸O and δ¹³C values of cellulose. The results indicated that predictions of the δ¹⁸O values of leaf water (δ_LW, δ_M and δ_ch) could be improved by considering plant species-specific characteristics.     

Regional differences in the carbon isotopic compositions of teak from two monsoonal regimes of India

Inter and intra-annual carbon isotope compositions (δ¹³C) of several annual growth rings of teak trees from two monsoonal regimes from India were studied and compared with the corresponding oxygen isotopic (δ¹⁸O) variations. In teak from both the regimes, amplitudes of intra-annual δ¹³C were ∼2-3 times lower than that observed in δ¹⁸O. Seasonal cycle with lower δ¹³C values at the middle and higher at ring boundaries was observed for teak from central India, dominated by the southwest monsoon. Positive correlations of intra-annual δ¹³C values with the corresponding δ¹⁸O values of the same rings and with relative humidity (RH) of the concurrent period suggest a dominant role of RH in controlling δ¹³C values of teak from central India. Intra-annual δ¹³C variations of teak from southern India, receiving both the southwest and northeast monsoons, revealed an initial decreasing trend followed by an increasing trend before culminating in depleted ¹³C values at the end of the growing season. No correlation was observed between intra-annual δ¹³C and δ¹⁸O variations of teak trees from southern India. Regional differences in the climatology of δ¹³C of atmospheric CO₂ or the lengths of growing season could be likely reasons for differing intra-annual δ¹³C variations of teak from the two climatic regimes.     

Do centennial tree-ring and stable isotope trends of Larix gmelinii (Rupr.) Rupr. indicate increasing water shortage in the Siberian north?

Tree-ring width of Larix gmelinii (Rupr.) Rupr., ratios of stable isotopes of C (δ¹³C) and O (δ¹⁸O) of whole wood and cellulose chronologies were obtained for the northern part of central Siberia (Tura, Russia) for the period 1864–2006. A strong decrease in the isotope ratios of O and C (after atmospheric δ¹³C corrections) and tree-ring width was observed for the period 1967–2005, while weather station data show a decrease in July precipitation, along with increasing July air temperature and vapor pressure deficit (VPD). Temperature at the end of May and the whole month of June mainly determines tree radial growth and marks the beginning of the vegetation period in this region. A positive correlation between tree-ring width and July precipitation was found for the calibration period 1929–2005. Positive significant correlations between C isotope chronologies and temperatures of June and July were found for whole wood and cellulose and negative relationships with July precipitation. These relationships are strengthened when the likely physiological response of trees to increased CO₂ is taken into account (by applying a recently developed δ¹³C correction). For the O isotope ratios, positive relationships with annual temperature, VPD of July and a negative correlation with annual precipitation were observed. The δ¹⁸O in tree rings may reflect annual rather than summer temperatures, due to the late melting of the winter snow and its contribution to the tree water supply in summer. We observed a clear change in the isotope and climate trends after the 1960s, resulting in a drastic change in the relationship between C and O isotope ratios from a negative to a positive correlation. According to isotope fractionation models, this indicates reduced stomatal conductance at a relatively constant photosynthetic rate, as a response of trees to water deficit for the last half century in this permafrost region.     

Stable isotope ratio analysis of breastfeeding and weaning practices of children from medieval Fishergate House York,UK

Rib collagen of 51 juveniles and 11 adult females from the late medieval Fishergate House cemetery site (York, UK) were analyzed using nitrogen and carbon stable isotope ratio analysis to determine the weaning age for this population and to reconstruct diet. The juveniles' ages ranged from fetal to 5–6 years, while the females were of reproductive age. Previous researchers suggested that the children from Fishergate House might have been weaned later than the medieval British norm of 2 years, based on a mortality peak at 4–6 years of age. The results show weaning was complete by 2 years of age, agreeing with previous British weaning studies. The adult female δ¹⁵N values have a mean of 11.4‰ ± 1.1‰ and the δ¹³C values have a mean of ?19.4‰ ± 0.4‰. These findings are consistent with previous isotopic studies of female diet in York during this period, though slightly lower. The weaned juvenile nitrogen values were found to be higher than the adult females (12.4‰ ± 1.0‰ for δ¹⁵N and ?19.7‰ ± 0.5‰ for δ¹³C), which might indicate a dependence on higher trophic level proteins such as marine fish or pork. Marine fish is considered a high status food and children are considered low‐status individuals at this time, making this a particularly interesting finding. Weaning does not appear to coincide with peak mortality, suggesting environment factors may be playing a larger role in child mortality at Fishergate House. Am J Phys Anthropol 152:407–416, 2013. © 2013 Wiley Periodicals, Inc.     

Stable isotope analyses in otoliths of silver carp: a pilot study in identification of natal sources and stock differences

Silver carp, Hypophthalmichthys molitrix, is one of the four major fishes in China for fishing and aquaculture. The Yangtze River and associated waterbodies are important home to silver carp. In this study, we collected 135 otoliths of juvenile silver carp from the two rivers and the Poyang Lake, and analyzed for stable oxygen and carbon isotope ratios (δ¹⁸O and δ¹³C). The isotopic data and correlation of δ¹⁸O versus δ¹³C showed a clear separation and significant differences (p?<?0.001 for both δ¹³C and δ¹⁸O) between otoliths from the Ganjiang River and the Yangtze River at δ¹⁸O values around ?10‰. The Poyang Lake samples were overlapped with those of the Ganjiang River, but distinctly different from the Yangtze River samples. These isotopic signatures agree well with the previous genetic investigation results that there are marked distinctions between one population in the Ganjiang River and the other in the Yangtze River, and the Poyang Lake population belongs to the Ganjiang River rather than to the Yangtze River. Thus we concluded that stable isotope analyses of otoliths can be effectively used to study natal sources and stock differences of silver carp.     

Ontogenetic effects on stable carbon and oxygen isotopes in tests of live (Rose Bengal stained) benthic foraminifera from the Pakistan continental margin

We determined the stable oxygen and carbon isotopic composition of live (Rose Bengal stained) tests belonging to different size classes of two benthic foraminiferal species from the Pakistan continental margin. Samples were taken at two sites, with water depths of about 135 and 275 m, corresponding to the upper boundary and upper part of the core region of the oxygen minimum zone (OMZ). For Uvigerina ex gr. Uvigerina semiornata and Bolivina aff. Bolivina dilatata, δ¹³C and δ¹⁸O values increased significantly with increasing test size. In the case of Uvigerina ex gr. U. semiornata, δ¹³C increased linearly by about 0.105‰ for each 100-μm increment in test size, whereas δ¹⁸O increased by 0.02 to 0.06‰ per 100 μm increment. For Bolivina aff. B. dilatata the relationship between test size and stable isotopic composition is better described by logarithmic equations. A strong positive linear correlation is observed between δ¹⁸O and δ¹³C values of both taxa, with a constant ratio of δ¹⁸O and δ¹³C values close to 2:1. This suggests that the strong ontogenetic effect is mainly caused by kinetic isotope fractionation during CO₂ uptake. Our data underline the necessity to base longer δ¹⁸O and δ¹³C isotope records derived from benthic foraminifera on size windows of 100 μm or less. This is already common practice in down-core isotopic studies of planktonic foraminifera.     

Decrypting stable‐isotope (δ13C and δ15N) variability in aquatic plants

相似文献   

Inter- and intra-annual tree-ring cellulose oxygen isotope variability in response to precipitation in Southeast China

Key message

Compared with annual tree-ring cellulose δ ¹⁸ O, intra-annual cellulose δ ¹⁸ O has potential to reconstruct precipitation with higher resolution and stronger signal intensity.

Abstract

Annual tree-ring cellulose oxygen isotope values (δ¹⁸O) of Fokienia hodginsii provide a promising proxy of monsoon-season precipitation in Southeast China. Measuring intra-annual cellulose δ¹⁸O values may reveal the seasonal variability of precipitation and the associated climate influences. Here, we examine intra-annual variation of cellulose δ¹⁸O values in Fokienia hodginsii and Cryptomeria fortune from Fujian Province, Southeast China. Both species exhibited considerable intra-annual variations in cellulose δ¹⁸O (range ~6 ‰) with a consistent pattern of enriched values near the annual ring boundary and depleted values in the central portion of the ring. Seasonal patterns in the tree-ring δ¹⁸O values generally followed changes in precipitation δ¹⁸O values. Compared with annual tree-ring cellulose δ¹⁸O, intra-annual cellulose δ¹⁸O has potential to reconstruct precipitation with higher resolution and stronger signal intensity. July tree-ring cellulose δ¹⁸O is significantly correlated (r = ?0.58, p < 0.05) with July precipitation, and June–August tree-ring cellulose δ¹⁸O and annual tree-ring cellulose δ¹⁸O, respectively, explain 52 and 41 % of the actual variance of April–August precipitation. In addition, May–October cellulose δ¹⁸O values during El Niño years are higher than in La Niña years, and April to October rainfall is lower in El Niño years than in La Niña years. Combining the significant correlations between inter-annual cellulose δ¹⁸O values and sea surface temperatures in the central tropical Pacific, our results support the hypothesis that El Niño–Southern Oscillation affects tree-ring cellulose δ¹⁸O in Southeast China by modulating seasonal precipitation.

     

Tree age,site and climate controls on tree ring cellulose δ18O: A case study on oak trees from south-western France

A main concern of dendroclimatic reconstruction is to distinguish in the tree ring proxy the influence of the climate variables of interest from other controlling factors. In order to investigate age, site and climate controls on tree ring width and cellulose δ¹⁸O, measurements have been performed in nearby groups of young (145 years old) and older (310–405 years old) oak trees in south-western France, covering the period 1860–2010.Within a given site, inter-tree deviations are small, pointing to a common climatic signal. Despite a similar inter-annual variability, the average level of cellulose δ¹⁸O in the young tree group is ∼0.8‰ higher than in the old trees. Such offsets might be caused by different soil properties and differences in the fraction of the source water used by trees from different depths. The δ¹⁸O of water in the top soil layer is directly related to the current growing season precipitation, while deeper water can have a lower and more constant δ¹⁸O. Local cave drip waters at 10 m depth indeed show a constant isotopic composition, which corresponds to pluri-annual mean precipitation.A 2‰ increasing trend is observed in cellulose δ¹⁸O of young trees in the first 30 years of growth, during a period when no trend is visible in older trees. This increase can be quantitatively explained by humidity gradients under the forest canopy, and a changing microclimate around the crown as trees grow higher.While relationships between tree ring width and climate appear complex, the isotopic composition of cellulose is strongly correlated with summer maximum temperature, relative humidity and evapotranspiration (r ≈ 0.70). Weaker correlations (r ≈ 0.40) are identified with precipitation δ¹⁸O from a 15-year long local record and from the REMOiso model output. These results imply that leaf water enrichment has a stronger control on the inter-annual variability of cellulose δ¹⁸O than the δ¹⁸O of precipitation.This study demonstrates the suitability of oak tree ring cellulose δ¹⁸O for reconstructing past summer climate variability in south-western France, provided that the sampling and pooling strategy accounts for the fact that trees from different sites and of different age can introduce non-climatic signals.     

Isotopic evidence of dietary variations and weaning practices in the Gaya cemetery at Yeanri,Gimhae, South Korea

Stable carbon and nitrogen isotope analyses were conducted to investigate dietary variation in human skeletons (n = 109) from the Gaya cemetery at Yeanri located near Gimhae City, South Korea. The cemetery contained three distinct grave types dating to 4th–7th century AD. The main purposes of this research were to reconstruct palaeodiet in the Gaya population and to explore correlations between stable isotope compositions and burial types, inferred age, and sex of these individuals. The isotopic data indicate that the people at Yeanri consumed a predominantly C₃‐based terrestrial diet supplemented with freshwater and/or marine resources. The comparison of isotopic results reveals significant differences in δ¹³C values among three adult burial types (wood‐cist coffin: ?18.5 ± 0.5‰, stone‐cist coffin: ?18.1 ± 0.6‰, mausoleum: ?17.8 ± 0.9‰). Males in wood‐cist and stone‐cist coffins have relatively more elevated mean δ¹³C and δ¹⁵N values than females. The isotopic ratios from the two adult age groups (21–40 years and 40–60 years) indicate that there was no significant dietary change in individuals with age. The isotope data from the infants and children suggest the weaning was a gradual process that was completed between 3 and 4 years of age in the Gaya population. This evidence indicates that the dietary variations within the cemetery reflect social status, sex, and childhood consumption patterns. Am J Phys Anthropol, 2010. © 2009 Wiley‐Liss, Inc.     

Investigating the potential for Southern Hemisphere climate reconstruction using stable isotopes in Tasmanian tree rings

Few annually dated stable isotope records exist across Oceania. Stable carbon and oxygen isotope ratios have the potential to enhance climate reconstructions currently reliant on tree ring width chronologies. The purpose of this study is to explore the sources of variability in a stable oxygen isotope chronology derived from A. selaginoides from Mount Read, Tasmania. This high elevation site receives abundant rainfall throughout the year and is ∼130 km from the Global Network of Isotopes in Precipitation (GNIP) site at Cape Grim. We crossdated 10 new tree core samples against an existing ring width chronology (954–2011 CE) and analyzed the δ¹⁸O from the individual rings for the period 1960–2018. Using high resolution (0.25 degrees) climate data and ECMWF ERA5 reanalysis data, we disentangled the effects of local climate and source region on the isotopic signatures recorded in the annual rings. In addition, we used HYSPLIT backward trajectory analysis to characterize the source region of precipitation to Mount Read and whether the source region has influence over the δ¹⁸O_TR series. Median δ¹⁸O_TR (n = 10) is correlated with local temperature and vapor pressure deficit in the early growing season. In addition, spatial correlations reveal that median δ¹⁸O_TR is positively correlated with temperature and negatively correlated with precipitation in the source region. However, measurements of δ¹⁸O_TR exhibit high inter-tree variation, particularly between 1960 and 1990. Our results indicate that this δ¹⁸O_TR proxy may provide additional information about past moisture conditions during the growing season, potentially contributing to more robust reconstructions of the Southern Hemisphere climate dynamics; however, additional sampling may be necessary to resolve inter-tree variation in δ¹⁸O_TR.     

Using stable isotope ratios as a tracer of feeding adaptation in released Japanese flounder Paralichthys olivaceus

Release‐recapture experiments were conducted to examine temporal changes of the carbon and nitrogen stable isotope (δ¹³C and δ¹⁵N) ratios in the muscle tissue of artificially produced Japanese flounder Paralichthys olivaceus, juveniles. About 9000 juveniles (mean ± s .d . 43·3 ± 5·2 mm in standard length and 1·07 ± 0·37 g, n = 15) were released in each of three coastal areas: Chojagasaki, Arasaki and Jogashima with different geographical conditions, along Sagami Bay, Pacific coast of central Japan. Recapture efforts were made on 4, 11, 18, 40 and 55 days after the release. The stable isotope ratios, RNA:DNA ratio, stomach content mass (per body mass M_sc) and condition factor (K) of recaptured individuals were measured. The mean ± s .d . δ¹³C and δ¹⁵N values (n = 15) were ?18·3 ± 0·2‰ and 12·2 ± 0·2‰, respectively at the release. Wild Japanese flounder juveniles were captured only in Chojagasaki, and the δ¹³C and δ¹⁵N values (n = 6) were ?14·0 ± 0·4‰ and 13·2 ± 0·7‰, respectively; these values were considered to represent the wild diet. Nutritional conditions of the released and recaptured juveniles as determined by the RNA : DNA ratio, M_SC and K were indicated to be the best in Chojagasaki, in which the stable isotope ratios gradually shifted towards and reached the wild values within 40 days. This result along with stomach content analyses suggested that the released juveniles had acquired a wild feeding habit. In Arasaki and Jogashima, nutritional conditions of the recaptured juveniles were poorer, with no clear changes in the stable isotope ratios. Greatly varied stable isotope ratio values were observed in the juveniles recaptured in Chojagasaki 11 days after the release, ranging from the release levels to the wild levels. The extent of changes in the stable isotope ratios had a positive correlation to the RNA : DNA ratio and K of these juveniles (r = 0·87, n = 10 and r = 0·83, n = 18, respectively). The analyses of stable isotope ratios coupled with nutritional condition were considered to be an effective tool to examine post‐release feeding adaptation of Japanese flounder juveniles.     

Inter-annual variation of tree-ring width, δ13C and δ18O in juvenile trees of five plantation poplar cultivars (Populus spp.)

The 10-year juvenile records of three hybrid poplar and two aspen cultivars (Populus spp.) from a short rotation coppice (SRC) were assessed by measuring tree-ring width (annual radial increment, i_r) and stable isotope ratios of carbon and oxygen (δ¹³C and δ¹⁸O) of α-cellulose. All cultivars showed common ‘juvenile trends’ that were modeled with nonlinear fit (NLF) functions. The i_r of all cultivars culminated in the middle of the juvenile phase. Within the first ten years, δ¹³C showed a gradual decrease of approximately 2.5 ‰ in all cultivars and δ¹⁸O showed an asymptotic increase which was variable among the poplar cultivars and which was more pronounced in two hybrid poplars. Potential causes of the juvenile inter-annual variability of δ¹³C and δ¹⁸O were discussed. Likely, the maturation related changes in hydraulic architecture, the canopy closure and the resulting increase of the proportion of shaded crown segments which have lower photosynthetic capacities had an effect on δ¹³C. An additional effect of changes in N nutrition on δ¹³C is assumed at the present SRC trial because the NO₃⁻ concentration had significantly decreased after ten years. Interpretation of δ¹⁸O data remained difficult given the lack of soil water δ¹⁸O records.The maturation effect and the respective interaction have resulted in large temporal variability in the present three investigated tree ring traits. However, the impact of two drought vegetation periods (2003 and 2006) was still reflected by the juvenile tree ring records of all traits. Different juvenile trends in the records of the stable isotope ratios δ¹³C and δ¹⁸O, and the trend slopes, which may vary between genetically different cultivars, must be considered in tree ring investigations of SRC poplars.     

Stable isotopic (δ13C and δ18O) signatures of biogenic calcretes marking discontinuity surfaces: a case study from Upper Cretaceous carbonates of central Dalmatia and eastern Istria,Croatia

Biogenic calcretes associated with a regional Cretaceous to Paleogene subaerial unconformity and an intraformational composite (polygenic) surface in Upper Cretaceous intra-platform peritidal successions in central Dalmatia and eastern Istria, Croatia (Adriatic-Dinaridic Carbonate Platform), were analyzed for their δ¹³C and δ¹⁸O signatures in order to provide insight into the conditions of subaerial exposure and calcrete development. The distinctly negative δ¹³C signatures of biogenic calcretes marking the regional subaerial unconformity differ considerably from the δ¹³C values of the host marine limestones. This indicates carbon isotope exchange of primary marine CaCO₃ with CO₂ released by root and rhizomicrobial respiration and subsequent precipitation of pedogenic calcrete. The range of δ¹³C (from ?13.1 to ?8.2 ‰ Vienna PeeDee Belemnite standard, VPDB) and δ¹⁸O (from ?10.1 to ?6.1 ‰ VPDB) values of calcretes are similar to those reported from calcretes elsewhere, and the δ¹³C values of biogenic calcretes with typical Microcodium aggregates (?13.1 to ?12.3 ‰ VPDB) at the ?ibenik locality are very close to, or at the lower limit of, values for soil carbonates formed in isotopic equilibrium with soil CO₂. These values are expected for authigenic pedogenic carbonates formed under the influence of C₃ plant communities, without influence from heavier carbon from pre-existing carbonate and lack of input of atmospheric CO₂. Such low δ¹³C values support the interpretation of Microcodium aggregates as being precipitated under a direct biological control within the soil, although the relationship between formation mechanisms and stable isotope signatures of Microcodium needs further investigation. The δ¹³C values (?4.4 to ?3.6 ‰ VPDB) of rhizogenic calcretes formed inside firmground Thalassinoides burrows of the composite surface at the ?ibenik locality are more negative than the δ¹³C values of the host marine limestones, which confirms that the composite surface went through a phase of meteoric pedo(dia)genesis. However, the overall δ¹³C values of calcretes are less negative than expected, which might reflect contamination from associated primary marine carbonate. This study represents the first detailed stable isotope investigation of calcretes from carbonate successions of the External Dinarides, and the results may be applied to discontinuities present in other shallow-water carbonate rock successions.     

Oxygen isotope fractionations across individual leaf carbohydrates in grass and tree species

Almost no δ¹⁸O data are available for leaf carbohydrates, leaving a gap in the understanding of the δ¹⁸O relationship between leaf water and cellulose. We measured δ¹⁸O values of bulk leaf water (δ¹⁸O_LW) and individual leaf carbohydrates (e.g. fructose, glucose and sucrose) in grass and tree species and δ¹⁸O of leaf cellulose in grasses. The grasses were grown under two relative humidity (rH) conditions. Sucrose was generally ¹⁸O‐enriched compared with hexoses across all species with an apparent biosynthetic fractionation factor (ε_bio) of more than 27‰ relative to δ¹⁸O_LW, which might be explained by isotopic leaf water and sucrose synthesis gradients. δ¹⁸O_LW and δ¹⁸O values of carbohydrates and cellulose in grasses were strongly related, indicating that the leaf water signal in carbohydrates was transferred to cellulose (ε_bio = 25.1‰). Interestingly, damping factor p_exp_x, which reflects oxygen isotope exchange with less enriched water during cellulose synthesis, responded to rH conditions if modelled from δ¹⁸O_LW but not if modelled directly from δ¹⁸O of individual carbohydrates. We conclude that δ¹⁸O_LW is not always a good substitute for δ¹⁸O of synthesis water due to isotopic leaf water gradients. Thus, compound‐specific δ¹⁸O analyses of individual carbohydrates are helpful to better constrain (post‐)photosynthetic isotope fractionation processes in plants.     

Stable isotope enrichment in laboratory ant colonies: effects of colony age,metamorphosis, diet,and fat storage

Ecologists use stable isotopes to infer diets and trophic levels of animals in food webs, yet some assumptions underlying these inferences have not been thoroughly tested. We used laboratory‐reared colonies of Solenopsis invicta Buren (Hymenoptera: Formicidae: Solenopsidini) to test the effects of metamorphosis, diet, and lipid storage on carbon and nitrogen stable isotope ratios. Effects of metamorphosis were examined in ant colonies maintained on a control diet of domestic crickets and sucrose solution. Effects of a diet shift were evaluated by adding a tuna supplement to select colonies. Effects of lipid content on stable isotopes were tested by treating worker ants with polar and non‐polar solvents. δ¹³C and δ¹⁵N values of larvae, pupae, and workers were measured by mass spectrometry on whole‐animal preparations. We found a significant effect of colony age on δ¹³C, but not δ¹⁵N; larvae, pupae, and workers collected at 75 days were slightly depleted in ¹³C relative to collections at 15 days (Δδ¹³C = ?0.27‰). Metamorphosis had a significant effect on δ¹⁵N, but not δ¹³C; tissues of each successive developmental stage were increasingly enriched in ¹⁵N (pupae, +0.5‰; workers, +1.4‰). Availability of tuna resulted in further shifts of about +0.6‰ in isotope ratios for all developmental stages. Removing fat with organic solvents had no effect on δ¹³C, but treatment with a non‐polar solvent resulted in enriched δ¹⁵N values of +0.37‰. Identifying regular patterns of isotopic enrichment as described here should improve the utility of stable isotopes in diet studies of insects. Our study suggests that researchers using ¹⁵N enrichment to assess trophic levels of an organism at different sites need to take care not to standardize with immature insect herbivores or predators at one site and mature ones at another. Similar problems may also exist when standardizing with holometabolous insects at one site and spiders or hemimetabolous insects at another site.     

The dendroclimatic value of oak stable isotopes

Tree-ring stable oxygen and carbon isotope ratios (δ¹⁸O and δ¹³C) are an important archive for climate reconstructions. However, it remains unclear whether the polyvinyl acetate emulsion, often used for the preservation and fixation of wood samples, influences δ¹⁸O and δ¹³C signals. Further uncertainties are associated with the possible effects of geographical origin and cambial age of historical samples. Here, we present annually-resolved and absolutely-dated δ¹⁸O and δ¹³C measurements of 21 living oaks (Quercus robur and Q. petraea) from the Czech Republic. We find that the δ¹⁸O and δ¹³C signals in the extracted alpha-cellulose are not affected by polyvinyl acetate treatment. Covering the entire 20^th century and reaching until 2018 CE, our dataset reveals spatial and temporal coherency within and between the individual δ¹⁸O and δ¹³C chronologies of different oak species, sample locations, and tree ages. Highly significant (p < 0.01) Pearson’s correlation coefficients of the site-specific δ¹³C and δ¹⁸O chronologies range from 0.48–0.77 and 0.36–0.56, respectively. The isotopic inter-series correlations of Q. robur and Q. petraea from the same site are 0.75 and 0.43 for the mean δ¹³C and δ¹⁸O values, respectively. Significant (p < 0.01) correlations of 0.49 and 0.84 are found for δ¹³C and δ¹⁸O, respectively, when all measurements from all sampling locations and tree ages are included. Our study shows that non-pooled oak δ¹⁸O and δ¹³C measurements from both species, different locations, and diverse tree ages can be combined into robust isotopic chronologies for climate reconstructions.     

Stable isotope differences of polar bears in the Southern Beaufort Sea and Chukchi Sea

The life-history, genetic, and habitat use differences between the 2 polar bear (Ursus maritimus) subpopulations in Alaska, USA, have been used to determine the geographic border separating them, but it has sparked a debate of the correct placement of the border for several years. Recently, the Southern Beaufort Sea (SBS) polar bear subpopulation has declined because of sea ice loss, while the Chukchi Sea (CS) subpopulation appears stable. To provide additional information about potential differences between the SBS and CS subpopulations, such as differences in prey sources, we used stable isotope analysis of carbon and nitrogen from bone collagen of polar bears in these 2 neighboring subpopulations. We analyzed polar bear bones from 112 individuals collected from 1954–2019. Our purpose was to determine if the SBS and CS subpopulations could be distinguished based on the stable isotope signatures of bone collagen. A difference >1‰ in stable carbon isotope (δ¹³C) values suggests a change in carbon sources, such as nearshore to offshore, while a 3‰ change in stable nitrogen isotope (δ¹⁵N) values equates to a change of about 1 trophic level. Our study indicated a difference in δ¹³C values (P ≤ 0.001) but not δ¹⁵N values (P = 0.654) between the CS (−13.0 ± 0.3‰ and 22.0 ± 0.9‰, respectively) and SBS bears (−14.7 ± 1.3‰ and 22.2 ± 1.0‰, respectively). Our findings indicate that the 2 subpopulations are consuming similar high trophic level prey, while feeding in ecosystems with different δ¹³C baselines. We performed a logistic regression analysis using δ¹³C and δ¹⁵N values of the polar bears to predict their placement into these 2 subpopulations. Using Icy Cape, Alaska as the geographical boundary, the analysis correctly placed polar bears in their respective subpopulations 82% of the time. Overall accuracy of placement changed to 84% when using the current geographical boundary at Utqiaġvik, Alaska. We predicted samples collected from the Wainwright, Alaska region as 58% CS and 42% SBS polar bears. This suggests that the area between Wainwright and Icy Cape is a polar bear mixing zone that includes bears from both subpopulations. Bone collagen has a long-term, potentially life-long, stable isotope turnover rate, and our results could be used to determine the association of harvested polar bears to Alaska subpopulations, thus aiding in transboundary harvest quota management.