Changes In δ13C Research Articles

Glacial water mass structure and rapid δ18O and δ13C changes during the last glacial termination in the Southwest Pacific

Changes in ocean circulation are thought to have contributed to lowering glacial atmospheric CO2 levels by enhancing deep ocean sequestration of carbon that was returned to the atmosphere during glacial terminations. High-resolution benthic foraminiferal δ13C and δ18O records from a depth transect of cores in the Southwest Pacific Ocean presented here provide evidence that both wind- and thermohaline-driven circulation drove CO2 from the ocean during the last deglaciation. Shallow geochemical stratification in the glacial Southern Ocean was followed by a short pulse of rapid δ13C enrichment to intermediate water depths during Heinrich Stadial 1, indicative of better-ventilated intermediate waters co-occurring with documented wind-driven upwelling in the Southern Ocean. Intermediate depth δ13C enrichment paused at the start of the Antarctic Cold Reversal (∼14.7 ka), implying a brief shallow restratification, while deeper layers were progressively flushed of δ13C-depleted and δ18O-enriched waters, likely caused by the increasing influence of deep waters sourced from the North Atlantic. The coincidence of atmospheric CO2 increases with these geochemical shifts in both shallow and deep cores suggests that shifts in both atmospheric and oceanic circulation contributed to the deglacial rise of CO2.

Lipid removal and acidification affect nitrogen and carbon stable isotope ratios of beluga whales (Delphinapterus leucas) and their potential prey species in the Beaufort Sea ecosystem

Carbon and nitrogen stable isotope ratios are ecological tracers that can provide insights into the diets of marine mammals. As a generalist predator, beluga whales (Delphinapterus leucas) consume a variety of prey; however, differences in lipid content and the presence of inorganic carbon in prey may cause variability in the δ13C signal that is not related to food sources. We examined the effects of carbonate and/or lipid removal in beluga and potential prey and tested whether the C:N ratio was a valid indicator of lipid content. The C:N ratio was a good predictor of the change in δ13C after lipid removal in capelin (Mallotus villosus), octopus (Cirroteuthis muelleri), green shrimp (Argis dentata), and circumpolar eualid (Eualus gaimardii). Despite relatively low C:N ratios, lipid removal significantly increased δ13C values, but also affected δ15N. Removal of carbonates from invertebrate samples significantly decreased δ13C values and had variable effects on δ15N. Overall, the variability in δ13C within a species decreased after removing lipids and carbonates. Variability in δ15N did not change for species requiring only lipid removal, but increased after acidification. We also evaluated the effect of these sample preparation methods on niche dispersion metrics. After lipid and carbonate treatments, centroid locations differed significantly in all species except beluga muscle, and niche breadth and mean distance to the centroid decreased. Failure to remove lipids and carbonates for δ13C values may lead to incorrect interpretations for isotopic niche, which may have major ecological implications, such as predicting the impacts of invasive species or determining the dietary linkages of beluga whales.

Soil Organic δ13C Change Along a Vertical Gradient in the Northern Slop of Tianshan Mountains

Soil Organic δ13C Change Along a Vertical Gradient in the Northern Slop of Tianshan Mountains

Sources, transport and deposition of terrestrial organic material: A case study from southwestern Africa

Abstract Southwestern Africa's coastal marine mudbelt, a prominent Holocene sediment package, provides a valuable archive for reconstructing terrestrial palaeoclimates on the adjacent continent. While the origin of terrestrial inorganic material has been intensively studied, the sources of terrigenous organic material deposited in the mudbelt are yet unclear. In this study, plant wax derived n-alkanes and their compound-specific δ13C in soils, flood deposits and suspension loads from regional fluvial systems and marine sediments are analysed to characterize the origin of terrestrial organic material in the southwest African mudbelt. Soils from different biomes in the catchments of the Orange River and small west coast rivers show on average distinct n-alkane distributions and compound-specific δ13C values reflecting biome-specific vegetation types, most notably the winter rainfall associated Fynbos Biome of the southwestern Cape. In the fluvial sediment samples from the Orange River, changes in the n-alkane distributions and compound-specific δ13C compositions reveal an overprint by local vegetation along the river's course. The smaller west coast rivers show distinct signals, reflecting their small catchment areas and particular vegetation communities. Marine surface sediments spanning a transect from the northern mudbelt (29°S) to St. Helena Bay (33°S) reveal subtle, but spatially coherent, changes in n-alkane distributions and compound-specific δ13C, indicating the influence of Orange River sediments in the northern mudbelt, the increasing importance of terrigenous input from the adjacent western coastal biomes in the central mudbelt, and contributions from the Fynbos Biome to the southern mudbelt. These findings indicate the different sources of terrestrial organic material deposited in the mudbelt, and highlight the potential the mudbelt has to preserve evidence of environmental change from the adjacent continent.

Long (MIS 5e – 3) environmental history of a paleolake in central Poland recorded in the succession from Kubłowo

One of the longest (above 7 m thick) uninterrupted Eemian-Vistulian (Weichselian) pollen successions in Poland is known from Kubłowo (central Poland). The huge importance of this succession is manifested in the possibility of study the evolution of the lake environment under the influence of changing, from interglacial to glacial climatic conditions.The reconstruction of the environmental changes at Kubłowo and its surroundings show the short climate fluctuations and a detailed picture of the natural conditions prevailing in central Poland (central Europe) during the period from approximately 126,000 to 55,000 years BP. Based on the results of multi-proxy analysis, four lacustrine stages linked with a higher water level and three boggy stages (low water level) of evolution of the Kubłowo paleolake were observed.The pollen diagram from Kubłowo reveals a succession of eighteen local pollen assemblage zones (K1-K18 L PAZ). The K1 to K7 LPAZ zones record the interglacial succession correlated with the Eemian. The next pollen zones, K8 to K18, are linked with the Vistulian. The pollen sequence shows, between the Eemian Interglacial (MIS 5e) and the last glaciation (second stadial of the Plenivistulian (MIS 4-3), four cold intervals that are interpreted as stadial phases: Herning, Rederstall, Schalkholtz and Ebersdorf separated by three temperate intervals (interstadials): Brörup, Odderade and Oerel.In the studied sediments, 25 species of subfossil Cladocera were identified, and ten zones of fauna development were distinguished. The unique feature of this profile is the good preservation of above 100,000-year-old Cladocera remains and a high diversity of species, which are primarily littoral. The Middle and Late Eemian were periods convenient to Cladocera development due to high temperatures, high water levels, high trophy and occurrence macrophytes. A deterioration of fauna living conditions started in the Late Eemian and next took place in the Vistulian cold events.The results of isotopic and geochemical analyses of organic matter from Kubłowo have enabled the reconstruction of varying environmental conditions and the origin of organic matter. The organic carbon content (TOC) changes from 1% to 40% and is closely related to climatic conditions. During the Eemian, the amount of TOC systematically increased. The lowest values are recorded in the coldest periods during the Herning, Rederstall and Schalkholz Stadials. The C/N atomic ratio fluctuates from 13 to 34 and the highest values occur in the Brörup Interstadial. The values of δ13C change from −27.9 to −12.9‰, and δ15N values oscillate between −1.6 and +5.3‰.

Carbon and nitrogen isotope systematics in diamond: Different sensitivities to isotopic fractionation or a decoupled origin?

Using stable isotope data obtained on multiple aliquots of diamonds from worldwide sources, it has been argued that carbon and nitrogen in diamond are decoupled. Here we re-investigate the carbon–nitrogen relationship based on the most comprehensive microbeam data set to date of stable isotopes and nitrogen concentrations in diamonds (n=94) from a single locality. Our diamond samples, derived from two kimberlites in the Chidliak Field (NE Canada), show large variability in δ13C (−28.4 ‰ to −1.1‰, mode at −5.8‰), δ15N (−5.8 to +18.8‰, mode at −3.0‰) and nitrogen contents ([N]; 3800 to less than 1at.ppm). In combination, cathodoluminescence imaging and microbeam analyses reveal that the diamonds grew from multiple fluid pulses, with at least one major hiatus documented in some samples that was associated with a resorption event and an abrupt change from low δ13C and [N] to mantle-like δ13C and high [N]. Overall, δ13C appears to be uncorrelated to δ15N and [N] on both the inter- and intra-diamond levels. Co-variations of δ15N–log[N], however, result in at least two parallel, negatively correlated linear arrays, which are also present on the level of the individual diamonds falling on these two trends. These arrays emerge from the two principal data clusters, are characterized by slightly negative and slightly positive δ15N (about −3 and +2‰, respectively) and variable but overall high [N].Using published values for the diamond-fluid nitrogen isotope fractionation factor and nitrogen partition coefficient, these trends are perfectly reproduced by a Rayleigh fractionation model.Overall, three key elements are identified in the formation of the diamond suite studied: (1.) a low δ13C and low [N] component that possibly is directly associated with an eclogitic diamond substrate or introduced during an early stage fluid event. (2.) Repeated influx of a variably nitrogen-rich mantle fluid (mildly negative δ13C and δ15N). (3.) In waning stages of influx, availability of the mantle-type fluid at the site of diamond growth became limited, leading to Rayleigh fractionation. These fractionation trends are clearly depicted by δ15N–[N] but are not detected when examining co-variation diagrams involving δ13C. Also on the level of individual diamonds, large (≥5‰) variations in δ15N are associated with δ13C values that typically are constant within analytical uncertainty. The much smaller isotope fractionation factor for carbon (considering carbonate- or methane-rich fluids as possible carbon sources) compared to nitrogen leads to an approximately one order of magnitude lower sensitivity of δ13C values to Rayleigh fractionation processes (i.e. during fractionation, a 1‰ change in δ13C is associated with a 10‰ change in δ15N). As a consequence, even minor heterogeneity in the primary isotopic composition of diamond forming carbon (e.g., due to addition of minor subducted carbon) will completely blur any possible co-variations with δ15N or [N]. We suggest this strong difference in isotope effects for C and N to be the likely cause of observations of an apparently decoupled behaviour of carbon and nitrogen isotopes in diamond.

Combined stomach content and δ13C/δ15N analyses of oilfish, escolar, snake mackerel and lancetfish in the western North Atlantic

AbstractLarge, mesopelagic teleost fishes have a potentially keystone position in the ecology of the pelagic water column, yet remain relatively unstudied when compared with large, commercially important, epipelagic fishes. Here, the ecological roles of four, large, vertically migrating teleosts were examined. Stomach content analyses were performed on 48 oilfish (Ruvettus pretiosis), 35 escolar (Lepidocybium flavobrunneum), 32 snake mackerel (Gempylus serpens) and seven lancetfish (Alepisaurus spp.) collected from pelagic longline gear in the Western North Atlantic Ocean from 2007 to 2010. Of these specimens, stable carbon and nitrogen isotope analyses were also performed on white dorsal muscle tissue from 33 oilfish, 16 escolar, 27 snake mackerel and seven lancetfish. Based on literature length‐at‐maturity values, all escolar, snake mackerel and lancetfish specimens were mature, while 13 of the 33 oilfish were juveniles. Crustaceans, annelids, salps, cephalopods and teleosts were present in the stomachs and were presumed to be prey items. A Kruskal–Wallis test showed the four species to be isotopically segregated in both δ13C and δ15N. Escolar were the most depleted in δ13C, followed by adult oilfish, juvenile oilfish and lancetfish, with snake mackerel the most enriched. The depletion in δ13C of adult oilfish and escolar may have been attributable to high C/N values, which were strongly correlated with length in oilfish, weakly correlated with length in escolar and moderately correlated with length in snake mackerel and lancetfish. The high C/N was likely due to the high lipid concentration of these fishes. Other factors that may have contributed to the depletion in δ13C may include spawning or a change in carbon source within the ecosystem. Large escolar occupied the highest trophic level (δ15N = 10.20), followed by snake mackerel (δ15N = 9.66), adult oilfish (δ15N = 9.32), lancetfish (δ15N = 9.05) and juvenile oilfish (δ15N = 7.83). A marked change in oilfish δ13C and C/N at 30–35 cm fork length coincided with a presumed length‐at‐maturity.

Vertical distribution of carbon and nitrogen stable isotope ratios in topsoils across a temperate rainforest dune chronosequence in New Zealand

Chronosequences can provide valuable insights into carbon (C) and nitrogen (N) dynamics across natural gradients with C and N stable isotopes serving as powerful tool investigating these dynamics. We studied changes in δ13C and δ15N values in litter, organic layer and mineral soil on dunes across the Haast chronosequence (New Zealand), which spans 120 to 2870 years of pedogenesis beneath a temperate rainforest. Decomposition was approximated from linear regression slopes between C concentrations and δ13C values and termed betaC. Similarly we calculated betaN values to test the relationship between vertical N decrease and δ15N increase. Decreasing δ13C values of litter with age suggests a physiological response of plants to decreased litter N concentrations. A decrease of litter δ15N in the early succession stages and a second decline after 1300 years indicates reduced N2 fixation. BetaC values increased during early ecosystem development and at old sites, and were lowest at the intermediate stages (1500 years), which suggests decomposition did not decrease constantly with time. BetaN values were lowest at the youngest site and increased within the first 200 years, likely because litter as the uppermost part of the vertical depth profile reflected an increased supply of N depleted in 15N provided by fungi. We found relations between betaC and betaN values suggesting that there might be shared processes shaping δ13C and δ15N vertical depth profiles, e.g. microbial cycling, transport or sorption.

Strong coupling of centennial-scale changes of Asian monsoon and soil processes derived from stalagmite δ18O and δ13C records, southern China

The paleoclimate application of speleothem δ13C is influenced by site-specific processes. Here we present four stalagmite δ13C records from two caves in southern China, covering early and late Marine Isotope Stage (MIS) 3 and the Holocene, to investigate the spatio-temporal pattern of calcite δ13C changes and the relationship with Asian monsoon (AM) variability. In each growth period, precessional- to millennial-scale changes are clear in the δ18O record. In contrast, millennial variability is absent in the δ13C record, which characterizes persistent centennial oscillations. However, centennial-scale δ18O variations agree well with those of δ13C, with a larger amplitude in δ13C changes (about twice that of δ18O). This suggests that soil humidity balance associated with regional hydrological circulations is important for these centennial δ13C changes, although evaporation-related kinetic fractionation can induce concurrent enrichments in δ18O and δ13C. In frequency, the detrended δ18O and δ13C records are coupled at a periodicity of about 300 yr during the last glacial period and 150 yr during the Holocene. Those centennial-scale δ13C variations are generally consistent with Greenland temperature variability, indicating a climate response over broad regions. Thus, strong co-variation of δ18O and δ13C records should have a climatic origin, even if it is amplified by kinetic effects.

Stable isotope and calcareous nannofossil assemblage record of the late Paleocene and early Eocene (Cicogna section)

Abstract. We present records of stable carbon and oxygen isotopes, CaCO3 content, and changes in calcareous nannofossil assemblages across an 81 m thick section of upper Paleocene–lower Eocene marine sedimentary rocks now exposed along the Cicogna Stream in northeast Italy. The studied stratigraphic section represents sediment accumulation in a bathyal hemipelagic setting from approximately 57.5 to 52.2 Ma, a multi-million-year time interval characterized by perturbations in the global carbon cycle and changes in calcareous nannofossil assemblages. The bulk carbonate δ13C profile for the Cicogna section, once placed on a common timescale, resembles that at several other locations across the world, and includes both a long-term drop in δ13C and multiple short-term carbon isotope excursions (CIEs). This precise correlation of widely separated δ13C records in marine sequences results from temporal changes in the carbon composition of the exogenic carbon cycle. However, diagenesis has likely modified the δ13C record at Cicogna, an interpretation supported by variations in bulk carbonate δ18O, which do not conform to expectations for a primary signal. The record of CaCO3 content reflects a combination of carbonate dilution and dissolution, as also inferred at other sites. Our detailed documentation and statistical analysis of calcareous nannofossil assemblages show major differences before, during and after the Paleocene–Eocene Thermal Maximum. Other CIEs in our lower Paleogene section do not exhibit such a distinctive change; instead, these events are sometimes characterized by variations restricted to a limited number of taxa and transient shifts in the relative abundance of primary assemblage components. Both long-lasting and short-lived modifications to calcareous nannofossil assemblages preferentially affected nannoliths or holococcoliths such as Discoaster, Fasciculithus, Rhomboaster/Tribrachiatus, Sphenolithus and Zygrhablithus, which underwent distinct variations in abundance as well as permanent evolutionary changes in terms of appearances and disappearances. By contrast, placoliths such as Coccolithus and Toweius, which represent the main component of the assemblages, were characterized by a gradual decline in abundance over time. Comparisons of detailed nannofossil assemblage records at the Cicogna section and at ODP Site 1262 support the idea that variations in the relative and absolute abundances, even some minor changes, were globally synchronous. An obvious link is through climate forcing and carbon cycling, although the linkages between variations in calcareous nannoplankton, changes in δ13C records and oceanography will need additional work.

Biogeochemical processes and response to climate change recorded in the isotopes of lacustrine organic matter, southeastern Qinghai-Tibetan Plateau, China

Large amount of labile organic matter sequestered in Qinghai–Tibetan Plateau (QTP), the highest plateau in the world. However, large uncertainties remained in the response of biogeochemical cycling to climate change due to the lack of spatial and temporal resolution of climatic and ecosystem records in the plateau. Here, we present the stable carbon (δ13C) and nitrogen (δ15N) isotope records from Muge Co, a lake in the southeastern QTP, in order to investigate the response of biogeochemical processes to climate change. In this record, changes in δ13C and δ15N values were more likely to reflect the rate of organic matter decomposition in the catchment and within the lake, while early diagenesis, changes in organic matter sources and aquatic primary productivity may only play an insignificant role. The trend of the greenhouse gases efflux index (GGEI) based on the δ13C and δ15N records is similar to that of other archives which record the organic matter mineralization, and that of climate change records from the eastern QTP and the adjacent regions, with higher GGEI values indicating a higher degree of decomposition of organic matter is associated with a warmer and wetter climate, and vice versa.

Effects of Ontogeny on δ13C of Plant- and Soil-Respired CO2 and on Respiratory Carbon Fractionation in C3 Herbaceous Species.

Knowledge gaps regarding potential ontogeny and plant species identity effects on carbon isotope fractionation might lead to misinterpretations of carbon isotope composition (δ13C) of respired CO2, a widely-used integrator of environmental conditions. In monospecific mesocosms grown under controlled conditions, the δ13C of C pools and fluxes and leaf ecophysiological parameters of seven herbaceous species belonging to three functional groups (crops, forage grasses and legumes) were investigated at three ontogenetic stages of their vegetative cycle (young foliage, maximum growth rate, early senescence). Ontogeny-related changes in δ13C of leaf- and soil-respired CO2 and 13C/12C fractionation in respiration (ΔR) were species-dependent and up to 7‰, a magnitude similar to that commonly measured in response to environmental factors. At plant and soil levels, changes in δ13C of respired CO2 and ΔR with ontogeny were related to changes in plant physiological status, likely through ontogeny-driven changes in the C sink to source strength ratio in the aboveground plant compartment. Our data further showed that lower ΔR values (i.e. respired CO2 relatively less depleted in 13C) were observed with decreasing net assimilation. Our findings highlight the importance of accounting for ontogenetic stage and plant community composition in ecological studies using stable carbon isotopes.

Anaerobic biodegradation of MTBE in a field site above the Israeli Coastal Aquifer: evidence from δ13C compound‐specific isotope analysis

AbstractBACKGROUNDThe fuel additive, methyl tert‐butyl ether (MTBE), is one of the most frequently occurring groundwater pollutants worldwide. The present study focused on assessing microbial degradation of MTBE in groundwater below a gasoline station situated above the Israeli Coastal Aquifer. Groundwater was monitored in six monitoring wells over a time period of 2.5 years.RESULTSThe site water geochemistry indicated that anaerobic conditions prevailed in two of the most contaminated wells. During a year MTBE concentrations declined from 81 to 4.2 mg L−1, concurrently, with a significant change in δ13C from −31.4 to −11.8 ‰ in a source area monitoring well. MTBE biodegradation during microcosm experiments under sulfate reducing and methanogenic conditions resulted in carbon isotopic enrichment factors (ε) of −17.2 ± 1.1 ‰.CONCLUSIONSignificant decrease in MTBE concentrations, along with pronounced changes in carbon isotope composition, indicates in situ degradation of MTBE occurring at the site. This evidence was supported by a microcosm experiment with indigenous microbial cultures. The estimated rate of biodegradation is 0.7 year−1, which is about 70% of the total natural attenuation (NA) processes. © 2016 Society of Chemical Industry

Compound specific δD and δ13C analyses as a tool for the assessment of hydrological change in a subtropical wetland

Compound specific carbon and deuterium stable isotope values (δ13C and δD) and the relative abundance of mid-chain n-alkanes (Paq) were determined for a series of dominant wetland plants, a surface slough-to-ridge soil transect, and slough and ridge soil cores, to assess historical vegetation successions induced by hydrological modification in an anthropogenically impacted, subtropical wetland, the Florida Everglades, USA. A difference of as much as 3.6 and 130 ‰ in their δ13C and δD values was observed between the two most abundant emergent macrophyte species (Cladium and Eleocharis), respectively. A clear n-alkane δD value depletion (−130 to −167 ‰) and decreasing Paq was observed along the slough-to-ridge soil transect, likely the result of an eco-hydrological transition from slough-to-ridge dominated vegetation (Eleocharis to Cladium). In agreement with the relatively constant Paq values, the lack of significant changes in the δD depth profile for the slough core, suggest a consistent slough type of vegetation composition over time at that location. In contrast, changes of both n-alkane δ13C and δD values for the ridge core, especially after ~1960 AD, coincide with the expected plant successions from historically long hydroperiod (>8 months), slough type plants (Eleocharis, Utricularia, Nymphaea) to present day, shorter hydroperiod (<8 months), ridge type plants (Cladium). These δ13C and δD changes seem to be driven by vegetation shifts associated with hydrological change. The application of the compound-specific stable isotope determinations may strongly complement the biomarker approach for paleo-hydrological assessments in wetland ecosystems.

Dissolved organic carbon lability and stable isotope shifts during microbial decomposition in a tropical river system

Abstract. A significant amount of carbon is transported to the ocean as dissolved organic carbon (DOC) in rivers. During transport, it can be transformed through microbial consumption and photochemical oxidation. In dark incubation experiments with water from the Tana River, Kenya, we examined the consumption of DOC through microbial decomposition and the associated change in its carbon stable isotope composition (δ13C). In 15 of the 18 incubations, DOC concentrations decreased significantly by 10 to 60 %, with most of the decomposition taking place within the first 24–48 h. After 8 days, the remaining DOC was up to 3 ‰ more depleted in 13C compared with the initial pool, and the change in δ13C correlated strongly with the fraction of DOC remaining. We hypothesize that the shift in δ13C is consistent with greater microbial lability of DOC originating from herbaceous C4 vegetation than DOC derived from woody C3 vegetation in the semi-arid lower Tana. The results complement earlier findings that the stable isotope concentration of riverine DOC does not necessarily reflect the proportion of C3 and C4-derived DOC in the catchment: besides spatial distribution patterns of different vegetation types, processing within the river can further influence the δ13C of riverine OC.

The contribution of human foods to honey bee diets in a mid-sized metropolis

Concern for honey bee health has implicated both urbanization and nutritional stress as factors contributing to honey bee declines. The expansion of urban areas has resulted in reduced foraging habitat for bees, while at the same time introducing new food sources, such as foods unintentionally provided by humans as litter or in waste containers. While human foods play an important role in the diets of other urban animals, the extent to which honey bees feed on these resources has not been well characterized. Here, we compared the amount of human foods in honey bee diets across a rural-urban gradient in North Carolina, USA, using stable isotopes of carbon (δ13C). Human-produced sugars—primarily sugarcane and corn syrup—have a characteristic isotope signature that can be used to quantify the relative amount of human foods in animal diets. We predicted that urban bees would have an increase in δ13C if they were feeding on human-produced sugars, but we found no change in δ13C between urban and rural colonies. Instead, we found an increase in δ13C in managed bees in both habitats, which is indicative of supplemental sugar feeding by beekeepers. Rather than switching to human food sources, urban bees seem to be feeding on urban flowers or insect-produced honeydew. This suggests an important role for urban flowers and green spaces in maintaining healthy pollinator populations in cities.

Black carbon concentration and isotopic composition of surface sand from deserts and dune fields in Northern China

Black carbon (BC) is a continuum of incomplete combustion products of vegetation and fossil fuels. It can be used as a proxy for wildfires and paleovegetation reconstruction. Nevertheless, BC can be transported by wind and water via atmospheric and fluvial transport. To research the characteristics of BC in deserts and dune fields that are directly connected with the Chinese Loess Plateau (CLP) in Northern China, and to evaluate the possibility that BC in deserts and dune fields occurs as exogenous BC in the CLP, we investigated surface sand from the Mu Us dune field, the Tengger Desert, and the Badain Jaran Desert, and analyzed the stable carbon concentration and carbon isotopes of organic carbon (SOC%, δ13CSOC) and BC (BC%, δ13CBC). The δ13CSOC, δ13CBC values ranged from −27.4‰ to −22.5‰, and −28.2‰ to −23.0‰, respectively, which mainly reflected δ13C changes in surface C3 grasses. A positive correlation was observed between δ13CBC and δ13CSOC, suggesting that local vegetation mainly controls δ13CBC. The difference between δ13CBC and δ13CSOC ranged from −0.2‰ to +3.5‰, and the difference is likely to be due to carbon isotope discrimination occurring during burning and SOC decomposition. The SOC% and BC% in these deserts and dune fields are very small (averaging 0.048% and 0.011%). The BC% of surface sand in these areas is about 5.5% of BC% in the CLP surface soils, and the Δ-δ13СBC value between surface sand in deserts and surface soils in CLP ranged from −0.3‰ to −6.3‰, so the change of δ13СBC in the CLP surface soils, deduced by exogenous BC from deserts, is less than 0.35‰. All these findings suggest that BC in deserts has a limited impact on BC in the CLP and is unlikely to affect interpretations of the BC record of wildfires and paleovegetation information in the CLP.

Diet-shift driven δ13C and δ15N changes in liver and muscle tissues of juvenile clownfish Amphiprion frenatus: A laboratory experiment

A laboratory-based diet-shift study using juvenile clownfish (Amphiprion frenatus) was performed to determine 1) isotopic turnover rates and 2) trophic fractionation of δ13C and δ15N in liver and muscle tissues. A brood of A. frenatus was first fed shrimps (Acetes erythraeus) with δ13C=−19.2‰ and δ15N=8.3‰ for 29days to provide an isotopic baseline. Subsequently, they were fed muscle filets from a predatory reef fish (Sparus latus) with isotopic signature of δ13C=−15.9‰ and δ15N=11.3‰. The results showed significant differences in δ13C and δ15N between liver and muscle throughout the most of the experiment, indicating different incorporation of isotopes by these two tissues. δ13C in muscle tissue was less depleted than liver tissue before the diet shift and more depleted after. The change in isotopic composition was significantly faster for liver than muscle tissue after the diet-shift. A hyperbolic saturation model provided a good fit for predicting the time scale of isotopic turnover. The model showed that liver tissue approaches isotopic saturation 3–4 times faster than muscle tissue. Isotopic fractionations extrapolated from the model output at saturation were remarkably similar for liver and muscle tissues (Δ13C of −0.5 and −0.3‰, and Δ15N of 2.6 and 2.8‰, respectively), which indicates that fractionation is independent of tissue or organ in A. frenatus. Liver tissue therefore appears more useful than muscle tissue as a short-term dietary indicator for A. frenatus and possibly also for other fish species.

Temperature and air pollution affected tree ring δ13C and water-use efficiency of pine and oak trees under rising CO2 in a humid temperate forest

To better predict forest productivity under rising atmospheric CO2 concentration ([CO2]), it is critical to understand how intrinsic water-use efficiency (WUEi) and its relationship with tree growth are affected by the concomitant changes in environmental conditions such as precipitation, temperature, and air pollution that either enhance or undermine any potential CO2 fertilization effect. We investigated changes in δ13C and WUEi in annual rings and basal area increment (BAI) of Pinus densiflora (from 1968 to 2007) and Quercus variabilis (from 1970 to 2007) trees in relation to precipitation, temperature, and air pollution in a humid temperate forest. The WUEi of P. densiflora increased by 39.9%, whereas that of Q. variabilis did not change over time in the study period. The WUEi was not affected by precipitation for both species but increased (P<0.001) with temperature for P. densiflora and with SO2 emissions for both species. Multiple regression models suggested that the effect of [CO2] on tree growth was much higher than temperature; however, for the period (1998 to 2007) when SO2 emissions data were available, SO2 emission was the driver of changes in BAI and WUEi, and temperature effects became stronger than [CO2]. Overall, BAI and WUEi were positively (P<0.001) correlated for P. densiflora, but not for Q. variabilis. We conclude that temperature and air pollution rather than precipitation were key determinants of WUEi at the study site and that the two species had contrasting responses to environmental changes.

Genetic and physiological differences of European beech provenances (F. sylvatica L.) exposed to drought stress

Prolonged summer droughts constitute to a major risk for the cultivation of beech in Central Europe. Therefore the identification of beech ecotypes that cope with growth conditions expected in future is highly desirable for forest practitioners. In a pot experiment under controlled conditions, the influence of longterm water deprivation on growth, root/shoot ratio, nitrogen (N)- and carbon (C) assimilation of seedlings from 6 European beech (Fagus sylvatica) provenances, originating from Central Europe (Germany), the Balkan Peninsula (Croatia), and south-east Europe (Bulgaria, Greece) were examined. Genetic diversity and relationships between the provenances were analysed by molecular markers such as nuclear EST microsatellites (EST-SSRs), SNPs and chloroplast microsatellites. Genetic diversity within provenances was high and highlighted close relationships between plants from Greece, Croatia and Germany, whereas beech from Bavaria (Germany) seemed to be admixed with genotypes from Bulgaria. Significant changes in fine root δ13C and C/N ratio as well as the intrinsic Water Use Efficiency (iWUE) demonstrate a better adaptability to future environmental conditions of beech ecotypes genetically related to the Greek beech population.