Variation In δ13C Values Research Articles

Seasonal variation in the diet of Spoonbill chicks in the Wadden Sea: a stable isotopes approach

We used stable isotope tracers in the growing primary feathers of Eurasian Spoonbill chicks (Platalea leucorodia leucorodia) to study seasonal variation in their diet on one of the Frisian islands, Schiermonnikoog, The Netherlands. Using growing individual primaries as natural samplers over time, samples were taken along the length of primary feathers to estimate both within- and between-individual variation in diet. Absolute isotopic ratios of feather material ranged from −26.2 to −14.7 ‰ for carbon (δ13C) and from 13.0 to 18.7 ‰ for nitrogen (δ15N). The variation in δ13C values suggests the use of a variety of feeding habitats, ranging from freshwater to marine. Across the breeding season, there was a shift from predominantly freshwater prey early on to a more marine diet later in the season. Surprisingly, this shift did not occur within the growth trajectory of early born chicks which instead showed the opposite, but it did occur within individual chicks born later in the season. Stable isotope Bayesian mixing-model (SIAR) outcomes demonstrated that the freshwater/brackish prey had the highest isotopic contribution “(51 %; 95 % confidence interval 39–63 %) to the diet early in the breeding season, whereas marine prey contributed most (78 %; 66–89 %) to the diet later. That chicks fed with either freshwater or marine food items had similar body condition indices suggests that the eating of marine prey did not come at a major cost for growing Spoonbill chicks.

Transport of dissolved carbon and CO2 degassing from a river system in a mixed silicate and carbonate catchment

Assessing the origin, transformation and transport of terrestrially derived carbon in river systems is critical to regional and global carbon cycles, particularly in carbonate terrains, which represent the largest carbon reservoir on the earth’s surface. For this reason, we evaluated sources, cycling, and fluxes of dissolved organic and inorganic carbon (DOC and DIC) and riverine CO2 degassing to the atmosphere in the Santa Fe River in north-central Florida, a sub-tropical river that flows across two distinct hydrogeological settings of a region dominated by carbonate karst. One setting occurs in the upper river catchment, where the carbonate Floridan aquifer is confined by the siliciclastic Hawthorn Group, while the other setting occurs in the lower catchment where the river flows across the unconfined Floridan aquifer. The upper catchment is characterized by DOC-rich and DIC-poor water and the DIC has more variable and lower δ13C values compared to the lower catchment. The river in the upper catchment degasses more CO2 to the atmosphere (1156 g C m−2 yr−1) than in the lower catchment (402 g C m−2 yr−1) because soil respired carbon and organic matter decomposition increase dissolved CO2 concentration, much of which is consumed during carbonate dissolution reactions in the lower catchment. The CO2 flux from the water surface to the atmosphere during a flood event is three times greater than during base flow, suggesting that excess precipitation flushes soil organic carbon to the river through interflow and enhances the loss of terrestrial carbon via river water to the atmosphere. Our values of CO2 fluxes to the atmosphere lie within the range of fluxes from the world’s rivers, but fluxes from the carbonate dominated region are at the low end, while fluxes from the siliciclastic region are at the high end. These results indicate that catchment lithologies, particularly whether carbonate or siliciclastic, as well as flow, are critical to carbon budgets in rivers and thus are linked to the global carbon cycle.

Niche differentiation and dietary seasonality among sympatric gorillas and chimpanzees in Loango National Park (Gabon) revealed by stable isotope analysis

The feeding ecology of sympatric great ape species yields valuable information for palaeodietary reconstructions in sympatric early hominin species. However, no isotopic references on sympatrically living apes and their feeding ecology are currently available. Here we present the first isotopic study on sympatric great apes, namely western lowland gorillas (Gorilla gorilla gorilla) and central chimpanzees (Pan troglodytes troglodytes) from Loango National Park, Gabon. We successfully analyzed the stable carbon and nitrogen isotope ratios in a selection of food plants (n = 31) and hair samples (n = 30) retrieved from sleeping nests to test whether niche partitioning among sympatric chimpanzees and gorillas is detectable using isotope analysis of hair. Ape hair strands with roots were sectioned into sequential segments (n = 100) to investigate temporal isotopic variation related to seasonal variations in food resources. We found significant δ13C differences between herbaceous plants and fruits, most likely due to canopy effects. While the δ13C values of chimpanzees indicate the consumption of fruit, the low δ13C values in gorilla hair indicate folivory, most likely the consumption of 13C-depleted herbaceous vegetation. Our isotopic data also confirmed dietary overlap between chimpanzees and gorillas, which varied by season. Gorillas showed significant variation in δ13C values in response to season due to shifting proportions of herbaceous plants versus fruits. In chimpanzees, significant seasonal variation in δ15N was likely related to the seasonal availability of fruit species with particularly high δ15N values. In summary, we found isotopic evidence for niche partitioning and seasonal dietary variation among sympatric great apes at Loango. These findings provide a valuable reference for palaeodietary research on fossil hominins using δ13C analyses, particularly for studies focusing on sympatric taxa and on temporal isotopic variation within incremental tissues such as tooth enamel.

Lipid and 13C signatures of submicron and suspended particulate organic matter in the Eastern Tropical North Pacific: Implications for the contribution of Bacteria

The contribution of bacterial biomass to total particulate organic matter (POM) in the ocean, including exported material, is poorly constrained. To examine potential signatures for the presence and export of bacterioplankton and their detrital remains, here we provide a detailed compound-specific 13C characterization of fatty acids from membrane polar lipids obtained from a water column profile in the Eastern Tropical North Pacific. POM of submicron size (0.2–0.7μm; “X-POM”) was sampled and analyzed separately from the size class typically collected as “suspended” POM (0.7–53μm; “L-POM”). The distributions of polar head group classes, specific fatty acid side chains, and natural 13C contents all vary, both between particle size classes and with depth in the water column. In general, the polar lipids in submicron material – and by inference, lipids of bacterial origin – have higher 13C content than polar lipids from larger POM and are equally abundant. Lipid signatures from the photic zone appear to be partially conserved in the suspended pool during transit down the water column. However, bacterial heterotrophy and possibly chemoautotrophy partially overprint these surface signatures. In addition, active metabolisms in the oxygen minimum zone (OMZ) appear to mediate the disaggregation of POM transported from the surface, thus adding complexity to the pathways of mid-water carbon flux and providing additional organic substrates to the OMZ and below. This “substrate injection” may provide important fuel for the denitrification and anammox reactions. Finally, examination of 13C content in polar lipids provides a basis for new interpretation of depth-related variations in δ13C values of bulk suspended POM.

Carbon isotope composition as indicator for climatic changes during the middle and late Holocene in a peat bog from Maramureş Mountains (Romania)

The main goal of this study was to use stable carbon isotopic composition of bulk peat sampled in Tăul Mare-Bardău peat bog, Maramureş Mountains, as a tool to provide paleoclimatic information over the middle and late Holocene in this region. A peat core of 3.60 m was sampled for δ13C analysis, and bulk peat samples were analyzed by isotope ratio mass spectrometry (IRMS) method. δ13C values reveal a maximum variation of 4.69‰ along a 3.6-m-long peat core. We examined the vertical variation of δ13C bulk peat and concluded that several factors could contribute to up core trends of δ13C. Four intervals of climatic variability could be related with variations of δ13C values between ~6800 cal. yr BP and present: two wet periods (around 2800 and 545 cal. yr BP) and two dry periods (6760 and 1430 cal. yr BP). We concluded that variability in the δ13C of bulk peat profile could be influenced most heavily by the water availability, which in turn is related to the amount of precipitation at the time. Four intervals of δ13C variations of the peat sequence between 225 and 25 cm can be related with generally accepted intervals of climatic variability that have occurred within the last 2000–2500 years (‘Roman Warm Period’ (RWP), ‘Dark Age Cold Period’ (DACP), ‘Medieval Warm Period’ (MWP) and ‘Little Ice Age’ (LIA)). The climate was probably of warm–cold alternations, as revealed in our peat core by δ13C variations between 2800 cal. yr BP and present. The δ13C values of the peat profile showed two positive signals at 40 and 225 cm depth and two negative signals at 105 and 350 cm depth. We suggest that these could also represent a change in vegetation at the time.

Mass spectrometric analysis of the 13C/12C abundance ratios in vine plants and wines depending on regional climate factors (Krasnodar krai and Rostov oblast, Russia)

Distribution of 13C/12C isotopes in vegetative (roots, grapevine, leaves) and generative (berries) parts of vine plants of the West European genetically different varieties Cabernet Sauvignon and Aligote growing on soils of Krasnodar krai and Rostov oblast, as well as autochthonous varieties Sibirkovy and Krasnostop Zolotovsky growing in Rostov oblast, has been studied using isotopic mass spectrometry methods. It has been shown that the variations of δ13C values in plant tissues and berries are related to the climatic conditions of plant growth: moisture (a sum of annual precipitation) and temperature (a sum of annual effective temperatures). The carbon isotope ratios of vegetative and generative parts of vine plants have been found to be noticeably affected by vine varieties. The different 13C contents in ethanol produced from wine of the Aligote and Cabernet Sauvignon varieties grown in two Russian vineyard regions are due to vine growth conditions, variety attribution and wine production techniques. An analytically significant parameter determined as exemplified by the Aligote and Cabernet Sauvignon varieties in fermentation of vine harvested in different seasons and in both vineyard regions was an increased 13C content in ethanol with respect to dry (non-volatile) residue in wine after distillation of ethanol. This characteristic has been determined by a systematic difference of about 1–2‰ between the δ13C value of ethanol and the dry residue. A relative constancy in the carbon isotope composition of ethanol and of the dry residue in the final product is the basis for determining the authenticity of grape wines by means of isotopic mass spectrometry irrespective of natural factors.

Stable oxygen and carbon isotope systematics of exquisitely preserved Turonian foraminifera from Tanzania — Understanding isotopic signatures in fossils

The interpretation of δ18O and δ13C analyses of extinct foraminifera is hampered by insufficient knowledge on the contribution of environmental versus biological factors on the measured values. We present single-species stable isotope data for 18 benthic and 11 planktic foraminiferal species and one calcareous dinoflagellate cyst species from a Turonian equatorial record measured on samples collected in SE Tanzania. All microfossils analyzed were excellently preserved and results are compared to isotopic measurements from bulk sediment of the same material. Remarkably low intra-specific variability (standard deviations < 0.2‰) across the studied interval and consistently large benthic/planktic offsets in δ18O (~ 2.8‰) and δ13C (~ 1.5‰) indicate absence of major long-term environmental fluctuations and presence of a well stratified water column. Stratigraphic isotopic trends show small shifts that are parallel in all studied benthic species (with the exception of the δ13C record of Lenticulina species), but within-sample inter-specific offsets reflect a combination of habitat differences and species-specific isotopic disequilibrium fractionation. Among planktic taxa closely related taxa tend to have similar isotopic values. Biserial taxa have the lowest δ18O values (~− 4.7‰) but also have relatively low δ13C values (~ 1.6‰) indicating that, for the assumption of a surface water habitat, additional metabolic effects need to be involved, which supports the concept of their opportunistic lifestyle. Among trochospiral planktics the keeled taxa with compressed chambers have slightly higher δ18O (~− 4.2‰) and lower δ13C (~ 2.3‰) values than taxa with globular chambers (~− 4.4‰ and ~ 2.4‰, respectively), suggesting differences in habitat or in peak seasonal abundance. Benthic taxa are subdivided into three isotopically distinct groups with differences reflecting mineralogy, life strategy and habitat; Group I: aragonitic taxa (Epistomina, Colomia africana), Group II: calcitic trochospiral taxa with isotopic values seemingly close to equilibrium (Berthelina berthelini, Oridorsalis umbonatus, Lingulogavelinella globosa, Lingulogavelinella convexa) and Group III: calcitic taxa with low δ18O values and large scatter in δ13C values (Lenticulina). Four other benthic species show values between Groups II and III. The wealth and consistency of data, especially for benthic taxa, permit refined conclusions. The five studied species of Epistomina have a similar isotopic signature and are inferred to form their aragonitic shells with close to equilibrium values. Small isotopic offsets are seen among species that differ in orientation of the septal foramen, but no offsets are seen that seem to co-vary with test shape or ornamentation. The conical species C. africana has δ18O values ~ 0.2‰ lower and δ13C values ~ 0.7‰ lower than species of Epistomina. The latter offset probably reflects an infaunal habitat for C. africana. Epistomina and Group II species are recommended for paleoenviromental studies. Mono-specific Lenticulina δ18O values may be used if increased by correction factors of 0.4‰ to 0.9‰, but this taxon's low and variable δ13C values are interpreted to reflect incorporation of respiratory CO2, possibly combined with fast growth rates related to opportunism, rather than equilibrium with benthic dissolved inorganic carbon. The observed stability of inter-specific isotopic offsets suggests disequilibrium isotopic effects are relatively consistent for many taxa in this section, and correction factors are proposed that may help to generate more robust Upper Cretaceous foraminiferal isotopic records. However, δ18O/δ13C covariance in some benthic inter-specific comparisons suggests offsets might vary with changes in temperature, food supply or other factors so the appropriateness of the correction factors should be confirmed before being applied at different sites. Similarities between the observed single-species isotopic patterns from this and other studies are used to present a summarizing scheme of influences on the stable isotopic composition in foraminiferal tests. By applying the new insights from our study to data from other Cretaceous studies we demonstrate that the selection of species for isotopic analysis and understanding these signals are critical to the outcome of paleoceanographic interpretations.

Stable isotopes identify an ontogenetic niche expansion in Antarctic krill (Euphausia superba) from the South Shetland Islands, Antarctica

Antarctic krill (Euphausia superba) occupy a key position in the Southern Ocean linking primary production to secondary consumers. While krill is a dominant grazer of phytoplankton, it also consumes heterotrophic prey and the relative importance of these two resources may differ with ontogeny. We used stable isotope analyses to evaluate body size-dependent trophic and habitat shifts in krill during the austral summer around the South Shetland Islands, Antarctica. We found evidence for an asymmetric, ontogenetic niche expansion with adults of both sexes having higher and more variable δ15N values but consistent δ13C values in comparison with juveniles. This result suggests that while phytoplankton likely remains an important life-long resource, krill in our study area expand their dietary niche to include higher trophic food sources as body size increases. The broader dietary niches observed in adults may help buffer them from recent climate-driven shifts in phytoplankton communities that negatively affect larval or juvenile krill that rely predominately on autotrophic resources.

Diamond from recycled crustal carbon documented by coupled δ18O–δ13C measurements of diamonds and theirinclusions

The origin of variability in δ13C values of cratonic diamonds is controversial, particularly for diamonds associated with eclogitic source rocks. The variability may be due to distinct primordial reservoirs, high-temperature isotope fractionation, recycling of crustal carbon, or any combination of the three. In contrast, the interpretation of variability in δ18O values of silicate minerals in eclogite xenoliths and eclogitic inclusions in diamonds is less contentious—the hypothesis that they represent rocks that were exposed to weathering and hydrothermal alteration at the surface of Earth is broadly, but not universally, accepted. Here, we report high-precision SIMS oxygen isotope measurements of 15 eclogitic garnet inclusions in diamond from the Damtshaa mine, which comprises four kimberlites within the Orapa cluster of kimberlites. The results demonstrate a link between δ18O values of inclusions and δ13C values of their host diamonds. The δ18OVSMOW values range from +4.7‰ to +8.8‰ and have a median value of +5.7‰, similar to the distribution exhibited by cratonic eclogite xenoliths worldwide, at the nearby Orapa Mine, and of oceanic crust. Contrary to previous suggestions, there is no evidence for a unique oxygen isotope distribution for inclusions in diamond. The oxygen isotope ratios do not correlate with garnet compositions; they have, however, a strong negative correlation with the δ13C values of their host diamonds. We interpret this correlation to have geochemical significance. It cannot be due to primordial heterogeneities or high-temperature isotope fractionation, but is most likely due to an association between recycled near-surface crustal rocks and recycled carbon. We suggest that protoliths to the eclogites at Damtshaa that were more strongly affected by low-temperature seafloor weathering (recorded by δ18O≥∼6‰) also have concentrations of primary organic carbon, and, therefore, low-δ13C Damtshaa diamonds are associated with recycling of crustal carbon.

Quantification, morphology and source of humic acid, kerogen and black carbon in offshore marine sediments from Xiamen Gulf, China

Three types of macromolecular organic matters (MOMs), i.e. humic acid (HA), kerogen+black carbon (KB), and black carbon (BC) were extracted from marine sediments of Xiamen Gulf, southeast of China. The chemical composition, morphological property and source of the three extractions were characterized by elemental analyzer/isotope ratio mass spectrometry (EA/IRMS) and scanning electron microscope (SEM). The results showed that KB was the predominant fraction in MOMs, which accounted for 61.79%-89.15% of the total organic content (TOC), while HA consisted less than 5%. The relative high contents of kerogen and BC, and low contents of HA in the samples indicated that anthropogenic input might be the major source of organic matter in marine sediments near the industrial regions. The characterization of SEM, not only revealed morphological properties of the three fractions, but also allowed a better understanding of the source of MOMs. The δ13C values of the three fractions suggested that materials from terrestrial C3 plants were predominant. Furthermore, the anthropogenic activities, such as the discharge of sewage, coal and biomass combustion from industry nearby and agricultural practices within drainage basin of the Jiulong River, were remarkably contributed to the variations in δ13C values of MOMs in the offshore marine sediments.

Trophic characteristics of a mangrove fish community in Southwest Thailand: Important mangrove contribution and intraspecies feeding variability

Mangrove production has been found to make a major contribution to the nutrition of a fish community in the Sikao Creek mangrove estuary, Southwest Thailand. Gut content analysis and carbon and nitrogen stable isotope analysis were used to assess fish feeding behavior and trophic reliance on different primary producers (mangrove leaves, phytoplankton, microphytobenthos) focusing on 19 dominant fish species, and 4 potential fish food items. Cluster analysis identified 5 trophic groups and the IsoSource model indicated the importance of primary food sources in trophically supporting different fish species. Most analyzed fish species had carbon isotopic signatures that were more depleted than those reported in previous studies, and the IsoSource model indicated that mangrove leaves were an important primary food source. This may be a specific characteristic of our study site, which is not well connected to other productive coastal habitats that provide alternative primary food sources. Thus we suggest that food chains in trophically isolated mangrove estuaries of southwest Thailand are more dependent on mangrove tree production. We also assessed the relationship of individuality in fish feeding habits and variability of δ13C values and showed that several mangrove fish species have significant intraspecies variability in feeding habits, possibly due to high intraspecific competition.

Stable isotope compositions of recent and fossil sun/shade leaves and implications for palaeoenvironmental reconstruction

Stable carbon isotope values (δ13C) obtained from terrestrial plant leaves are increasingly being used to infer palaeoenvironmental trends. However, there are considerable variations in δ13C values even among leaves of a single plant due to different microhabitats, which can bias palaeoenvironmental interpretations. One important factor causing microhabitat variations is leaf position on a tree (i.e. sun and shade leaves). It is extensively known that δ13C varies markedly between sun and shade leaves in modern plants, with sun leaves containing more enriched 13C. Yet, the δ13C variations of fossil leaves in this respect are not investigated systematically. Here, we examine bulk carbon and nitrogen isotopic variabilities of fossil Liquidambar leaves between sun and shade leaves. For comparison, bulk isotopic data are analyzed in modern Liquidambar. Our results show that carbon and nitrogen content, C/N ratio, δ13C and nitrogen isotope composition (δ15N) are notably different between sun and shade morphotypes in modern Liquidambar. When these criteria are applied to fossil Liquidambar, we found that the difference in stable carbon isotope compositions between fossil sun and shade morphotypes is narrow (only 0.33‰) and statistically not significant (P>0.2). Also, the aforementioned other parameters do not present apparent differences between sun and shade morphotypes (P>0.2). Comparing isotope data with anatomic characteristics previously studied in fossil Liquidambar miosinica, we conclude that anatomical characters are better indicators to distinguish sun/shade leaves for fossil L. miosinica. Here, carbon and nitrogen contents of the sun morphotype are higher than that of the shade morphotype in fossil Liquidambar leaves, suggesting that sun leaves perhaps are more resistant against decomposition. Moreover, the variation of δ13C values is more profound in sun leaves than that in shade leaves for both modern and fossil Liquidambar, suggesting that sun leaves may be more sensitive to environmental changes. Together, our data indicate that δ13C of sun morphotypes is a better proxy in reconstructing palaeoenvironments.

Isotopic and zooarchaeological investigation of later medieval and post-medieval cattle husbandry at Dudley Castle, West Midlands

Zooarchaeological analysis of a substantial assemblage of animal bones excavated from Dudley Castle, West Midlands, revealed two significant changes in cattle management in the late medieval and post-medieval periods: a statistically significant increase in size in the later 14th century; and a gradual reduction in slaughter age. To explore whether these altered husbandry practices were accompanied by modifications to the diet and environment of these animals, a targeted study of carbon and nitrogen stable isotope values from 135 cattle bones was conducted. This analysis revealed that δ13C and δ15N values were broadly consistent between the mid-13th and mid-18th centuries. Only two statistically significant diachronic variations were identified: a temporary decrease in δ13C values in phase 7 (1397–1533); and lower variation in δ13C values in phase 9 (1647–1750). A number of explanations for these changes are offered. While the zooarchaeologically attested shifts in cattle husbandry were not accompanied by isotopically detectable changes to diet and environment, the analysis of stable isotopes highlighted other changes that were not detected using traditional zooarchaeological analysis. The complimentary benefits of zooarchaeological and isotopic approaches are extolled.

Spatial variations in δ13C and δ15N values of primary consumers in a coastal lagoon

The analysis of the contribution of a food source to a consumer's diet or the trophic position of a consumer is highly sensitive to the variability of the isotopic values used as input data. However, little is known in coastal lagoons about the spatial variations in the isotopic values of primary consumers considered ‘end members’ in the isotope mixing models for quantifying the diet of secondary consumers or as a baseline for estimating the trophic position of consumers higher up in the food web. We studied the spatial variations in the δ13C and δ15N values of primary consumers and sedimentary organic matter (SOM) within a selected area of the Cabras lagoon (Sardinia, Italy). Our aim was to assess how much of the spatial variation in isotopic values of primary consumers was due to the spatial variability between sites and how much was due to differences in short distances from the shore. Samples were collected at four stations (50–100 m apart) selected randomly at two sites (1.5–2 km apart) chosen randomly at two distances from the shore (i.e. in proximity of the shore –Nearshore – and about 200 m away from the shore –Offshore). The sampling was repeated in March, May and August 2006 using new sites at the two chosen distances from the shore on each date. The isotopic values of size-fractionated seston and macrophytes were also analyzed as a complementary characterization of the study area. While δ15N did not show any spatial variations, the δ13C values of deposit feeders, Alitta (=Neanthes) succinea, Lekanesphaera hookeri, Hydrobia acuta and Gammarus aequicauda, were more depleted Offshore than Nearshore. For these species, there were significant effects of distance or distance × dates in the mean δ13C values, irrespective of the intrinsic variation between sites. SOM showed similar spatial variations in δ13C values, with Nearshore-Offshore differences up to 6‰. This indicates that the spatial isotopic changes are transferred from the food sources to the deposit feeders studied. In contrast, δ13C and δ15N values of suspension feeders, Ficopomatus enigmaticus and Amphibalanus amphitrite, did not show major variations, either between sites, or between Nearshore and Offshore. These different patterns between deposit feeders and suspension feeders are probably due to a weaker trophic link of the latter with SOM. We suggest that the Nearshore-Offshore gradient might be an important source of isotopic variation that needs to be considered in future web studies in coastal lagoons.

Stable isotopes identify dietary changes associated with beak deformities in Black-capped Chickadees (Poecile atricapillus)

ABSTRACT. A large number of beak deformities of unknown etiology have recently been reported in Black-capped Chickadees (Poecile atricapillus) and other resident avian species in Alaska. We investigated the potential association between diet and beak deformities. We analyzed carbon (δ13C) and nitrogen (δ15N) isotopes in whole blood of Black-capped Chickadees captured at three semiurban sites in south-central Alaska. For dietary analysis, we included natural foods (arthropods, seeds, and berries) and anthropogenic items commonly provided in bird feeders (sunflower seeds, peanut butter, and suet). Blood samples from individuals with beak deformities exhibited lower δ15N values and more variable δ13C values than birds with normal beaks. Isotopic values of blood also differed by location for both carbon and nitrogen, but we did not detect a difference in natural dietary items across the three sites. Contributions of individual diet items differed between birds with and without beak deformities, a pattern that...

Isotopic paleoecology of mammals and the Middle Miocene Cooling event in the Madrid Basin (Spain)

The Middle Miocene underwent profound climatic perturbations detected in worldwide marine and continental records. The Miocene Climatic Optimum (~17 to 14Ma), a warm and humid period, was followed by the Middle Miocene Cooling (~14–13.8Ma) characterized by a sharp drop in temperatures and an increase in aridity triggered by the reestablishment of the Eastern Antarctica ice sheet. The Madrid Basin, located in the central Iberian Peninsula, has furnished a considerable number of Miocene fossil sites with a very complete succession of localities from the Lower Middle Miocene to the Upper Middle Miocene (Middle and Upper Aragonian, MN5 and MN6, local zones Db to G). Mammalian fossil tooth enamel of different taxa including rhinoceros, equids, gomphothere, suids and ruminants from 16 fossil sites spanning from ~15.9Ma to ~13.2Ma were analyzed for δ13C, δ18OCO3 and δ18OPO4 values with the aim of determining regional paleoecological, paleoenvironmental and paleoclimatic changes across this important climate transition. The δ13C values vary between −11.9‰ and −6.4‰ (VPDB), indicating a C3 environment ranging from woodlands to more open conditions. The rhinoceros Alicornops simorrense and Hoploaceratherium tetradactylum, the gomphothere Gomphotherium angustidens, the cervid Heteroprox moralesi and the paleomerycid Triceromeryx pachecoi may be regarded as browsers inhabiting more closed environments, whereas the equid Anchitherium, the rhinoceros Hispanotherium matritense and the bovid Tethytragus langai show a mixed feeding diet related to more open conditions. Furthermore, the variation in δ13C values across the fossil sites and local zones indicates drier conditions in local zones Db and Dc (~15.9–14.8Ma), a more humid period in local zone Dd (~14.8–14.1Ma), before a return to a drier environment in local zones E, F and G (~14.1–13.2Ma). The δ18OCO3 and δ18OPO4 values and calculated δ18Ow values all track a declining trend from local zones Db to Dd (~15.9–14.1Ma), with minimum values in local zone E (δ18OCO3=26.5±2.1‰, δ18OPO4=18.4±2.4‰, and δ18Ow=−5.3±2.9‰). The minimum in δ18O values in local zone E (~14.1–13.7Ma) appears to coincide with a drop in temperature at the time of the Middle Miocene Cooling (~14–13.8Ma). After this minimum, δ18OCO3, δ18OPO4 and δ18Ow values recover in local zones F and G (13.7–13.2Ma). The calculation of Δ13Cleaf values allowed us to determine plausible biomes that might have existed in the Madrid Basin during the Middle Miocene (i.e., a tropical rain forest, a tropical deciduous forest, a temperate evergreen forest and a xeric woodland–scrubland), although this method was not able to detect more savanna-like environments. Finally, δ13Cdiet, meq values were used to infer mean annual precipitation, with values ranging from ~250mm/yr (local zone Dc) to ~670mm/yr (local zone Dd) which are in accordance with the proposed biomes suggested by the Δ13Cleaf values and fossil mammal assemblages.

Fossil organic matter characteristics in permafrost deposits of the northeast Siberian Arctic

[1] Permafrost deposits constitute a large organic carbon pool highly vulnerable to degradation and potential carbon release due to global warming. Permafrost sections along coastal and river bank exposures in NE Siberia were studied for organic matter (OM) characteristics and ice content. OM stored in Quaternary permafrost grew, accumulated, froze, partly decomposed, and refroze under different periglacial environments, reflected in specific biogeochemical and cryolithological features. OM in permafrost is represented by twigs, leaves, peat, grass roots, and plant detritus. The vertical distribution of total organic carbon (TOC) in exposures varies from 0.1 wt % of the dry sediment in fluvial deposits to 45 wt % in Holocene peats. Variations in OM parameters are related to changes in vegetation, bioproductivity, pedogenic processes, decomposition, and sedimentation rates during past climate variations. High TOC, high C/N, and low δ13C reflect less decomposed OM accumulated under wet, anaerobic soil conditions characteristic of interglacial and interstadial periods. Glacial and stadial periods are characterized by less variable, low TOC, low C/N, and high δ13C values indicating stable environments with reduced bioproductivity and stronger OM decomposition under dryer, aerobic soil conditions. Based on TOC data and updated information on bulk densities, we estimate average organic carbon inventories for ten different stratigraphic units in northeast Siberia, ranging from 7.2 kg C m−3 for Early Weichselian fluvial deposits, to 33.2 kg C m−3 for Middle Weichselian Ice Complex deposits, to 74.7 kg C m−3 for Holocene peaty deposits. The resulting landscape average is likely about 25% lower than previously published permafrost carbon inventories.

Stable carbon isotope characteristics of desert plants in the Junggar Basin, China

AbstractDesert plants have unique strategies for survival and growth to cope with the limited water availability in arid regions. The stable carbon isotope (δ13C) provides an integrated measurement of internal plant physiological and external environmental properties affecting photosynthetic gas exchange and water use efficiency. The δ13C values of 84 species in the Junggar Basin were categorized into two groups (ranged from −30.1 to −23.3‰ for C3 and −14.9 to −9.9‰ for C4 species, respectively). No life form differences in δ13C values were detected in C3 (p = 0.78) and C4 plants (p = 0.63). Small differences among life forms were observed in δ13C values in C4 species with shrubs slightly depleted (−13.3‰) relative to perennials (−13.1‰) and annuals (−12.5‰). These differences suggested that δ13C value could not represent a plant functional group classification based on life forms in C4 plants in extremely arid regions. Ephemerals are all using C3 photosynthetic pathway and no significant differences (p = 0.92) in δ13C values were observed between annuals (−26.5‰) and perennials (−26.4‰). The δ13C values of Tulipa iliensis (an important ephemeral species distributed widely in the Junggar Basin) among nine natural populations were positively correlated with leaf (r2 = 0.46, p = 0.046) and soil (r2 = 0.67, p = 0.007) total nitrogen content, and negatively correlated with leaf (r2 = 0.48, p = 0.039) and soil (r2 = 0.79, p = 0.001) water content. This indicated that the variation in δ13C values of T. iliensis was probably caused by both water availability associated stomatal openness and nitrogen availability associated photosynthetic capacity. T. iliensis is very sensitive to water and nitrogen availability in soil.

Imprint of the Late Palaeozoic Ice Age on stratigraphic and carbon isotopic patterns in marine carbonates of the Orogrande Basin, New Mexico, USA

AbstractThe Permian records one of the most extreme climate transitions of the Phanerozoic, yet the climatic and environmental dynamics of this interval and their effects on neritic carbonate systems remain poorly constrained. New stratigraphic and carbon isotope records from uppermost Pennsylvanian to Lower Permian strata of the Orogrande Basin in south‐central New Mexico, USA, provide fresh insights into the response of palaeotropical carbonate systems to the growth and demise of ice sheets on Gondwana. The earliest Permian acme of glaciation is recorded in the Orogrande Basin as a series of subaerial exposure surfaces marked by highly variable δ13C values that tend toward values as low as −6‰. These stratigraphic and isotopic patterns are interpreted to reflect the retreat of the sea from the basin during glacial expansion. Younger (Lower Sakmarian to Kungurian) strata, deposited during the long decline of the Late Paleozoic Ice Age, are characterized overall by higher and more uniform δ13C values (+2 to +5‰) and show no evidence of long‐term subaerial exposure. However, these strata record two short‐lived excursions toward more negative δ13C values. These excursions occur through intervals that record shifts toward shallower and more restricted conditions in the Orogrande Basin. The timing of these shifts corresponds to two periods of glacial expansion across eastern Australia during Late Sakmarian to Early Artinskian and Kungurian time. These relationships suggest that pulses of glacial expansion in eastern Gondwana were of sufficient magnitude to have caused relative sea‐level fall, and possibly environmental change, in the Orogrande Basin. The results from this study suggest that marine chemistry, depositional environments and sea‐level in the Orogrande Basin were profoundly influenced by epochs of Gondwanan glaciation. These inferences help improve the understanding of how palaeotropical carbonate systems responded to the effects of cryospheric changes during the acme and waning stages of the Late Palaeozoic Ice Age.

Clarifying the influence of water availability and plant types on carbon isotope discrimination by C3 plants

We are pleased that the results of Kohn (1) so strongly support our findings published earlier in PNAS (2). Both studies (1, 2) analyzed published measurements of the carbon isotope composition of plants and quantified relationships between isotopic fractionation and environmental factors at large spatial scales. These relationships will be useful when interpreting archives of plant-derived carbon, such as fossils, soil organic matter, and plant biomarkers. Kohn (1) emphasized differences between the two papers, particularly the coefficients and proportion of variance explained in regression models, but the major findings were the same: water availability [estimated by mean annual precipitation (MAP)] explains most of the observed variability in δ13C values …