Shift In δ13C Research Articles

Carbon and sulfur isotopes in tree rings as a proxy for volcanic degassing

Abstract Trees are useful archives of past atmospheric conditions. They have most commonly been used to infer large-scale changes in climate, industrial pollution, and the magnitude and frequency of geological hazards. While geochemical changes in tree rings have been linked to localized anthropogenic smelter pollution, their potential to track geochemical changes in volcanic degassing has not yet been fully realized. Here, we applied a new proxy using sulfur and carbon isotopes in tree rings to examine fluctuations in gas emission at Turrialba volcano, Costa Rica. Since 2009, Turrialba has emitted a persistent gas plume and increasingly frequent explosions and ash eruptions as activity has accelerated. We collected cores from a species of alder tree, Alnus acuminata, at several locations surrounding the volcano. Biannual isotopic analysis of rings demonstrated a notable δ34S shift of –5.2‰ and a similarly sharp δ13C shift of +1.3‰ in trees downwind of the plume following the onset of strong degassing in 2009. We propose that these shifts in the isotopic values of the tree correspond to those of the volcanic SO2 and CO2, and in the case of the δ13C, an additional fractionation caused by leaf impairment from exposure to volcanic SO2. This new proxy can be applied to other volcanoes as a novel method of obtaining a temporal record of degassing, a crucial tool for volcano monitoring.

Siberian Trap volcanism, global warming and the Permian-Triassic mass extinction: New insights from Armenian Permian-Triassic sections

AbstractPermian-Triassic boundary sections from Armenia were studied for carbon isotopes of carbonates as well as oxygen isotopes of conodont apatite in order to constrain the global significance of earlier reported variations in the isotope proxies and elaborate the temporal relationship between carbon cycle changes, global warming and Siberian Trap volcanism. Carbon isotope records of the Chanakhchi and Vedi II sections show a 3–5‰ negative excursion that start in the Clarkina nodosa (C. yini) conodont Zone (latest Permian) with minimum values recorded in Hindeodus parvus to Isarcicella isarcica conodont zones (earliest Triassic). Sea surface temperatures (SST) reconstructed from oxygen isotopes of conodont apatite increase by 8–10 °C over an extrapolated time interval of ∼39 ka with the onset of global warming occurring in the C. iranica (C. meishanensis) Zone of the latest Permian. Climate warming documented in the Armenian sections is comparable to published time-equivalent shifts in SST in Iran and South China suggesting that this temperature change represents a true global signature. By correlating the Armenian and Iranian section with the radiometrically well-dated Meishan GSSP (Global Stratotype Section and Point) section (South China), the negative shift in δ13C is estimated to have occurred 12–128 ka prior to the onset of global warming. This temporal offset is unexpected given the synchrony in changes in atmospheric CO2 and global temperature as seen in Pleistocene ice core records. The negative δ13C excursion is explained by the addition of emission of isotopically light CO2 and CH4 from thermogenic heating of organic carbon-rich sediments by Siberian Trap sill intrusions. However, the observed time lag in the δ13C and δ18O shifts questions the generally assumed cause-effect relationship between emission of thermogenically produced greenhouse gases and global warming. The onset of temperature rise coincides with a significant enrichment in Hg/TOC (total organic carbon) ratios arguing for a major volcanic event at the base of the extinction interval. Whether global warming was a major factor for the Late Permian mass extinction depends on the duration of the extinction interval. Warming only starts at the base of the extinction interval, but with the extinction encompassing a time interval of 60 ± 48 ka, global climate warming in conjunction with temperature-related stressors as hypoxia and reduced nutrient availability may have been one of the major triggers of the most devastating biotic crisis in Earth history.

Climatic and environmental conditions in the Western Galilee, during Late Middle and Upper Paleolithic periods, based on speleothems from Manot Cave, Israel

Early Ahmarian, Levantine Aurignacian and Post-Levantine Aurignacian archeological assemblages show that the karstic Manot Cave, located 5 km east of the Mediterranean coast in the Western Galilee region of Israel, was intensively occupied during the Early Upper Paleolithic. The coexistence of these rich archaeological layers with speleothems in Manot Cave provides a window of opportunity for determining the relationships between climatic conditions and the nature of human activity and mobility patterns in the Western Galilee region during the Early Upper Paleolithic period. This study, based on four stalagmites that grew almost continuously from ∼75 to 26.5 ka, covers most of the last glacial, and overlaps with the human occupation of the cave. The speleothems oxygen (δ18O) and carbon (δ13C) isotopic records indicate that climate and environmental conditions fluctuated during the last glacial, some of which correspond with Dansgaard–Oeschger (D-O) cycles 12, 10, 7 and Heinrich (H) events VI and V. Consistent with independent evidence from botanic and faunal remains, these climatic shifts brought about significant environmental changes in the region, ranging from dominant thick Mediterranean forest to more open landscape. A good correlation with less negative δ13C values is most pronounced during the Early Ahmarian time period, but there was also a change to less negative δ13C values during the Levantine Aurignacian and Post-Levantine Aurignacian industries in the Levant. These positive δ13C shifts suggest that environmental transformation towards a more open grassy landscape dominated by C4 vegetation might have played an important role in the development of these cultural entities (mainly the Early Ahmarian) in Manot Cave region.

Linking the Bitter Springs carbon isotope anomaly and early Neoproterozoic oxygenation through I/[Ca + Mg] ratios

The ca. 810 Ma Bitter Springs carbon isotope anomaly is an abrupt and long-lived (5–10 Myr.) departure from the positive carbon isotope values (δ13Ccarb) that otherwise characterize early-middle Neoproterozoic carbonate rocks. The onset of this isotope anomaly is manifested by a globally expressed ~8‰ negative shift in δ13C values in shallow marine carbonate strata. Given increasing evidence that metazoan diversification began well before the Ediacaran Period, the Bitter Springs anomaly is a logical interval to explore the potential relationship between biological innovation, perturbations to the carbon cycle, and oxygenation. The iodine-to-calcium+magnesium ratio (I/[Ca + Mg]) in marine carbonates is a sensitive proxy for seawater redox conditions that is increasingly being applied to reconstruct the oxygenation of the global surface ocean through Earth's history. We report I/[Ca + Mg] ratios, along with carbon and oxygen isotope ratios and major and minor element concentrations from carbonate sections spanning the Bitter Springs anomaly in Svalbard, East Greenland, and the Mackenzie Mountains (northwestern Canada). The results from Svalbard and Greenland collectively show two prominent features. The early stage of the Bitter Springs anomaly is characterized by a negative δ13C shift coupled to low I/[Ca + Mg] ratios compared to carbonates pre- and post-dating the Bitter Springs anomaly. The last stage of the Bitter Springs anomaly displays a positive excursion in I/[Ca + Mg], with the highest values at ~7 μmol/mol yet documented in rocks older than 580 Ma. In contrast, carbonates from the Mackenzie Mountains are uniformly low and display no variation in I/[Ca + Mg] across the Bitter Springs anomaly, which we interpret to be the consequence of alteration of primary signatures during diagenesis. The observed geochemical variations in our Svalbard and Greenland datasets are interpreted to be the result of a shift from pre-Bitter Springs ocean conditions, defined by well oxygenated surface waters and anoxic-ferruginous bottom waters, to syn-Bitter Springs ocean conditions, characterized by expanded euxinia.

Katian (Upper Ordovician) carbon isotope chemostratigraphy in the Neixiang area, central China: implications for intercontinental correlation

AbstractThe Katian (Upper Ordovician) Shiyanhe Formation at the Sigang section, Neixiang area, Henan Province, central China, has been investigated for carbon isotope (δ13Ccarb) chemostratigraphy. The carbon isotopic data document signal between the two major Ordovician positive shifts in δ13C, the early Katian Guttenberg and the Hirnantian excursions. The Kope (Ka1/2), Fairview (Ka2/3), Waynesville (Ka3/4), Whitewater (Ka4) excursions and a doubtful Elkhorn (Ka4) excursion are identified herein. The continuous and well-defined conodont zonal succession of the Sigang section provides a secure biostratigraphic framework for the mid-late Katian carbon isotope chemostratigraphy in China. Correlation between carbon-isotope data curve and the relative sea-level changes shows no clear correspondence, and hence the sea-level change is probably not the main driver of δ13C excursions during the Katian. Intercontinentally, the mid–late Katian carbon isotope excursions, identified mainly in the North American and Baltoscandian successions, are useful for improving long-distance stratigraphic correlations. This further suggests that these excursions represent global perturbations in the carbon cycle.

Carbon-use strategies in stem radial growth of two oak species, one Temperate deciduous and one Mediterranean evergreen: what can be inferred from seasonal variations in the δ13C of the current year ring?

Tree ring synthesis is a key process in wood production; however, little is known of the origin and fate of the carbon involved. We used natural 13C abundance to investigate the carbon-use process for the ring development in a temperate deciduous (Quercus petraea (Matt.) Liebl.) and a Mediterranean evergreen (Quercus ilex L.) oak. The sapwood carbon reserves, phloem sucrose contents, stem respired CO2 efflux and their respective carbon isotope compositions (δ13C) were recorded over 1 year, in the native area of each species. The seasonal δ13C variation of the current year ring was determined in the total ring throughout the seasons, as well as in slices from the fully mature ring after the growth season (intra-ring pattern). Although the budburst dates of the two oaks were similar, the growth of Quercus ilex began 50days later. Both species exhibited growth cessation during the hot and dry summer but only Q. ilex resumed in the autumn. In the deciduous oak, xylem starch storage showed clear variations during the radial growth. The intra-ring δ13C variations of the two species exhibited similar ranges, but contrasting patterns, with an early increase for Q. petraea. Comparison between δ13C of starch and total ring suggested that Q. petraea (but not Q. ilex) builds its rings using reserves during the first month of growth. Shifts in ring and soluble sugars δ13C suggested an interspecific difference in either the phloem unloading or the use of fresh assimilate inside the ring. A decrease in ring δ13C for both oaks between the end of the radial growth and the winter is attributed to a lignification of ring cell walls after stem increment. This study highlighted the differences in carbon-use during ring growth for evergreen and deciduous oaks, as well as the benefits of exploring the process using natural 13C abundance.

Diazotrophy Drives Primary Production in the Organic-Rich Shales Deposited Under a Stratified Environment During the Messinian Salinity Crisis (Vena del Gesso, Italy)

Density stratification between freshwater and brine is periodically formed during massive evaporation events, which often associates deposition of organic-rich sediments. Here, we investigated phototrophic communities and nitrogen cycle during the deposition of two organic-rich shale beds of gypsum–shale alternation, representing the initial stage of the Messinian salinity crisis (Vena del Gesso, Northern Apennines, Italy). The structural distributions and the carbon and nitrogen isotopic compositions of geoporphyrins show a common pattern in the two shales, indicating the predominance of a particular phototrophic community under freshwater–brine stratified conditions. The ~6‰ difference in δ13C of total organic carbon between PLG 4 and 5 shales was associated with similar shift in δ13C of the porphyrins derived from chlorophyll c, suggesting that the eukaryotic algae producing chlorophyll c were the major constituent of the phototrophic community. Importantly, these porphyrins show δ15N values (−7.6‰ to −4.7‰) indicative of N2-fixation. We suggest that nitrate-depletion in the photic zone induced the predominance of diazotrophic cyanobacteria, which supplied new nitrogen for the chlorophyll c-producing eukaryotic algae. The large difference in the δ13C values of porphyrins and total organic carbon between PLG 4 and 5 shales are interpreted to reflect the depth of the chemocline, which fluctuates in response to changes in the regional evaporation–precipitation balance. Such variation in the chemocline depth may have dynamically changed the mode of the nitrogen cycle (i.e., nitrification–denitrification–N2-fixation coupling vs. phototrophic assimilation of ammonium) in the density-stratified marginal basins during the Messinian salinity crisis.

Effects of peat decomposition on δ13C and δ15N depth profiles of Alpine bogs

Decomposition of organic substances is one of the main processes responsible for the signatures of stable carbon and nitrogen isotopes (δ13C and δ15N) in soils and peats. However, the applicability of δ13C and δ15N signatures at the natural abundance level as indicators of the degree of peat decomposition is still debatable. We evaluated δ13C and δ15N depth patterns of peat cores sampled at nine sites in two nearby Alpine peat bogs with varying degree of organic matter degradation. Based on water table depths and past drainage intensities, the peat cores were divided into three degradation classes. We found similar overall depths patterns of δ13C and δ15N across the nine depth profiles and distinct differences between aerobic and anaerobic peat layers. Considerable differences in stable C and N isotope signatures of same depths were detected between profiles of the three classes, whereas depth profiles of peat cores with similar degree in peatland degradation were nearly identical. In the aerobic peat layers, δ13C and δ15N increased with depths at all study sites from 2.6‰ to 4.9‰ for δ13C and 3.2‰ to 7.0‰ for δ15N compared to the initial signatures of the plant biomass. Standardised δ13C of aerobic layers differ distinctly between slightly degraded peats at the open peat bog area, intermediately degraded peats at the tree-covered edge areas and strongly degraded peats at the former peat-cutting site. δ13C signatures of aerobic layers of strongly degraded peats were markedly more negative compared to the slightly degraded peats because of the selective 12C losses by microbial respiration. δ15N were more positive at strongly degraded than at slightly degraded sites in both, aerobic and anaerobic peat layers. The uniform stable isotope ratios in the anaerobic layers deeper than the local maxima of the isotopic signatures support the assumption that minor 13C fractionation occurs under anaerobic conditions. δ13C slightly declining with depth in the waterlogged layers of strongly degraded peat reflects the preferential utilisation and loss of labile organic compounds enriched in 13C. δ15N of strongly degraded peats was higher compared to well-conserved peat. The close relationship between the measured δ15N to δ15N modelled based on C:N ratios and bulk densities supports the assumption that the δ15N signature is the result of isotopic fractionation by peat decomposition. We conclude that peat decomposition strongly affects the δ13C and δ15N depth profiles of peat bogs and most likely overrides other factors, such as differences between plant species, litter components, atmospheric δ13C shift during peat formation, temperature effects, or type of mycorrhizal symbiosis.

Application of a laser-based spectrometer for continuous in situ measurements of stable isotopes of soil CO<sub>2</sub> in calcareous and acidic soils

Abstract. The short-term dynamics of carbon and water fluxes across the soil–plant–atmosphere continuum are still not fully understood. One important constraint is the lack of methodologies that enable simultaneous measurements of soil CO2 concentration and respective isotopic composition at a high temporal resolution for longer periods of time. δ13C of soil CO2 can be used to derive information on the origin and physiological history of carbon, and δ18O in soil CO2 aids in inferring the interaction between CO2 and soil water. We established a real-time method for measuring soil CO2 concentration, δ13C and δ18O values across a soil profile at higher temporal resolutions (0.05–0.1 Hz) using an off-axis integrated cavity output spectroscopy (OA-ICOS). We also developed a calibration method correcting for the sensitivity of the device against concentration-dependent shifts in δ13C and δ18O values under highly varying CO2 concentration. The deviations of measured data were modelled, and a mathematical correction model was developed and applied for correcting the shift. By coupling an OA-ICOS with hydrophobic but gas-permeable membranes placed at different depths in acidic and calcareous soils, we investigated the contribution of abiotic and biotic components to total soil CO2 release. We found that in the calcareous Gleysol, CO2 originating from carbonate dissolution contributed to the total soil CO2 concentration at detectable degrees, potentially due to CO2 evasion from groundwater. The 13C-CO2 of topsoil at the calcareous soil site was found reflect δ13C values of atmospheric CO2, and the δ13C of topsoil CO2 at the acidic soil site was representative of the biological respiratory processes. δ18O values of CO2 in both sites reflected the δ18O of soil water across most of the depth profile, except for the 80 cm depth at the calcareous site where a relative enrichment in 18O was observed.

Influence of increasing carbonate saturation in Atlantic bottom water during the late Miocene

The late Miocene witnessed the tectonic uplift of the Isthmus of Panama, the onset of modern-like thermohaline circulation, changes in global patterns of deep-sea sedimentation, and a negative shift of ~1‰ in the carbon isotopic composition (δ13C) of marine carbonate sediments. Although previous work has attributed the late Miocene carbon isotopic shift (LMCS) to biological and environmental factors, the reasons for this apparent shift in the global carbon cycle remain incompletely understood. Here we combine both core-based sedimentological and isotopic data from three Walvis Ridge sites in the southeastern Atlantic Ocean with macrostratigraphic data from the entire Atlantic basin to show that the LMCS marks the establishment of modern, glacial/interglacial seawater carbonate saturation levels in the Atlantic. Between 10 and 7 million years ago (Ma) the Atlantic Ocean shows a trend of increasing seafloor area preserving deep-sea carbonate sediments. Neogene carbonate sedimentation in the Atlantic Ocean peaked at 7 Ma, coinciding with a δ13C shift of approximately −0.8‰ in Walvis Ridge benthic foraminifera, similar to the magnitude of LMCS. Northern-sourced waters in the late Miocene likely shifted seawater carbonate chemistry throughout the Atlantic basin by introducing bottom waters with higher carbonate ion concentrations. LMCS reflects the introduction of a carbonate ion effect on North Atlantic Deep Water (NADW) by increasing Northern Hemisphere glacial carbonate weathering. A carbonate ion flux to the Labrador Seawater contribution of NADW raises the possibility of a carbonate burial-mediated feedback with the global climate system that led to additional cooling during the Miocene-Pliocene transition.

Cannibalism and Habitat Selection of Cultured Chinese Mitten Crab: Effects of Submerged Aquatic Vegetation with Different Nutritional and Refuge Values

We examined the food preference of Chinese mitten crabs, Eriocheir sinensis (H. Milne Edwards, 1853), under food shortage, habitat choice in the presence of predators, and cannibalistic behavior by comparing their response to the popular culture plant Elodea nuttallii and the structurally more complex Myriophyllum verticillatum L. in a series of mesocosm experiments. Mitten crabs were found to consume and thus reduce the biomass of Elodea, whereas no negative impact on Myriophyllum biomass was recorded. In the absence of adult crabs, juveniles preferred to settle in Elodea habitats (appearance frequency among the plants: 64.2 ± 5.9%) but selected for Myriophyllum instead when adult crabs were present (appearance frequency among the plants: 59.5 ± 4.9%). The mortality rate of mitten crabs in the absence of plant shelter was higher under food shortage, primarily due to cannibalism. The proportion of molting crabs dying in the structurally more complex Myriophyllum habitats was significantly lower than in the less complex Elodea habitats, indicating that Myriophyllum provides better protection from cannibalistic behavior, likely due to its structurally more complex canopy. Stable isotope analyses of crab samples revealed a trophic shift in both δ13C and δ15N (Δδ13C: 2.2–4.0‰; Δδ15N: 1.5–2.8‰) during the experimental period. Significant positive correlations between body mass and δ13C and δ15N were recorded, suggesting that cannibalistic feeding might further increase crab growth and lead to ontogenetic increases in trophic position with increasing size. Our study overall demonstrates that a combination of submerged aquatic vegetation functioning as a highly suitable food with other less palatable plant species acting as efficient refuges against predators may be the optimal method of plant stocking in mitten crab aquacultures to ensure both high crab growth and a high survival rate.

Amino acid isotope discrimination factors for a carnivore: physiological insightsfrom leopard sharks and their diet.

Stable isotopes are important ecological tools, because the carbon and nitrogen isotopic composition of consumer tissue reflects the diet. Measurements of isotopes of individual amino acids can disentangle the effects of consumer physiology from spatiotemporal variation in dietary isotopic values. However, this approach requires knowledge of assimilation patterns of dietary amino acids. We reared leopard sharks (Triakis semifasciata) on diets of squid (Loligo opalescens; 1250days; control sharks) or squid then tilapia (Oreochromis sp.; switched at 565days; experimental sharks) to evaluate consumer-diet discrimination factors for amino acids in muscle tissue. We found that control sharks exhibited lower nitrogen isotope discrimination factors (∆15N) than most previous consumer studies, potentially because of urea recycling. Control sharks also had large carbon isotope discrimination factors (∆13C) for three essential amino acids, suggesting microbial contributions or fractionation upon assimilation. Compared to controls, experimental sharks exhibited higher ∆13C values for four amino acids and ∆15N values for seven amino acids, corresponding with differences between diets in δ13C and δ15N values. This suggests that not all amino acids in experimental sharks had reached steady state, contrary to the conclusion of a bulk isotope study of these sharks. Our results imply that (1) the magnitude of a shift in dietary δ13C and δ15N values temporarily influences the appearance of discrimination factors; (2) slow turnover of amino acid isotopes in elasmobranch muscle precludes inferences about seasonal dietary changes; (3) elasmobranch discrimination factors for amino acids may be affected by urea recycling and microbial contributions of amino acids.

Lower–Middle Ordovician carbon and oxygen isotope chemostratigraphy at Hällekis, Sweden: implications for regional to global correlation and palaeoenvironmental development

A high-resolution chemostratigraphical (coupled δ13Ccarb and δ18Ocarb) study of the topmost Floian through the middle Darriwilian (Ordovician) succession at the Hällekis quarry, Kinnekulle, southern Sweden, shows relatively steady isotopic values with overall minor changes, although some notable short- and long-term shifts are discernible. A pronounced positive shift in δ13C in the uppermost part of the study succession is identified as the Middle Darriwilian Isotopic Carbon Excursion (MDICE), representing the only named global isotopic excursion in the data set. Regional and global comparisons suggest that few details in the different carbon and oxygen isotope curves can be confidently correlated, but longer-term patterns appear quite consistent. Trends in the isotope data are in agreement with palaeogeographical reconstructions. Differences in stratigraphical patterns of both carbon and oxygen isotopes between localities suggest strong secular development at several spatiotemporal scales; any global signal involving relatively minor isotopic shifts is often masked/subdued by local and regional overprinting and care should be taken not to overinterpret data sets. Collectively, the data suggest rising sea levels and cooling climates through the studied time interval, but detailed interpretations remain problematic.

High‐resolution reconstruction of 8.2‐ka BP event documented in Père Noël cave, southern Belgium

ABSTRACTA distinct shift in δ18O, δ13C and trace element contents of the Père Noël (PN) stalagmite from southern Belgium revealed an abrupt climatic anomaly at 8.13 ± 0.03 ka BP (before present = before 1950 AD). This anomaly is characterized by a maximum drop in the δ18O (−1.4‰ compared the mean) between 8.13 and 8.10 ka BP (±0.03). This drop of δ18O coincides with a decrease in δ13C and trace element (Sr, Ba and Mg) concentrations suggesting drier conditions. Our precise chronology provides the timing of the outburst of proglacial lakes Agassiz and Ojibway that caused the δ18O, δ13C and trace elemental anomalies at 8.13–8.10 ± 0.03 ka BP, which corresponds to the 8.2‐ka BP event. The PN stalagmite bears δ18O values in fluid inclusions that covary with the δ18O values in calcite, suggesting that the speleothem calcite δ18O primarily reflects variations in the rainfall δ18O. Comparison of the PN record with different marine and terrestrial archives during the 8.2‐ka BP event shows a good agreement in timing and duration, suggesting that the PN speleothem can be regarded as a valuable proxy to better understand the 8.2‐ka BP event.

Environmental changes and carbon cycle perturbations at the Triassic–Jurassic boundary in northern Switzerland

The Triassic–Jurassic boundary is characterized by strong perturbations of the global carbon cycle, triggered by massive volcanic eruptions related to the onset of the Central Atlantic Magmatic Province. These perturbations are recorded by negative carbon isotope excursions (CIEs) which have been reported worldwide. In this study, Triassic–Jurassic boundary sections from the southern margin of the Central European Basin (CEB) located in northern Switzerland are analyzed for organic carbon and nitrogen isotopes in combination with particulate organic matter (POM) analyses. We reconstruct the evolution of the depositional environment from Late Triassic to Early Jurassic in northern Switzerland and show that observed negative shifts in δ13C of the total organic carbon (δ13CTOC) in the sediment are only subordinately influenced by varying organic matter (OM) composition and primarily reflect global changes in the carbon cycle. Based on palynology and the stratigraphic positions of isotopic shifts, the δ13CTOC record of the studied sections is correlated with the GSSP section at Kuhjoch (Tethyan realm) in Austria and with the St. Audrie’s Bay section (CEB realm) in southwest England. We also show that in contrast to POM analyses the applicability of organic carbon/total nitrogen (OC/TN) atomic ratios and stable isotopes of total nitrogen (δ15NTN) for detecting changes in source of OM is limited in marginal depositional environments with frequent changes in lithology and OM contents.

δ13C referential in three Pinus species for a first archaeological application to Paleolithic contexts: “Between intra- and inter-individual variation and carbonization effect”

Tree-ring studies, particularly those focusing on the δ13C isotopic signal, have become a reliable method to reconstruct past climatic and environmental conditions. Unfortunately, wood remains are notably absent from the very ancient archaeological record, due to degradability of plant tissue. For archaeological studies, the analysis of isotopic signals from charcoal of Pinus species, which is more reliably preserved over time, and continuously represented among archaeological remains, would yield more robust findings. However, methodological confirmation of this approach is required prior to the archaeological implementation of this tool. Here, we present a wood-charcoal reference set, focused on the intra-genus Pinus spp. Δ13C data (Pinus halepensis L., Pinus sylvestris Mill., Pinus nigra subsp. nigra Arn.), which addresses both natural variability and the isotopic impact of the carbonization. Our results show the potential application of an average isotopic signal from different Pinus spp. either from wood and charcoal. Moreover, carbonization results offer a baseline from which to create a general correction of the δ13C shift introduced during pyrolysis temperature gradients. Lastly, a primary reference set was established in the context of climatic and environmental parameters for future archaeological analyses of charcoal remains.

Significance of carbon, nitrogen and their isotopic changes in a Permian-Triassic non-marine boundary section at Carlton Heights (Karoo Basin), South Africa

We performed analyses of Corg, Norg, δ13C org, and δ15N org from the non-marine Permian-Triassic boundary section at Carlton Heights in the Karoo Basin, South Africa. The Carlton Heights section is thus far unique in the Karoo in containing the Permian-Triassic palynological boundary between the Upper Permian Klausipollenites schaubergeri Zone and the Lower Triassic Kraeuselisporites-Lunatisporites Zone, separated by a 1-m thick “fungal event” zone, marked by abundant fungal cell remains (Reduviasporonites) and woody debris. The Corg values obtained are very low (below 0.05%), but reach a maximum of 0.1% in the middle of the fungal event zone. Norg varies little from 0.02%, except in the middle and top of the fungal event, where it rises to 0.04%. C/N ratios are extremely low throughout the section (less than 3), reaching a maximum of 2.49 during the fungal event, coincident with the peaks in Norg and Corg. The very low C/N ratios resemble those found in modern burned soils with low bacteria/fungi ratios, and the lack of variation suggests no change in the organic matter source. δ15Norg values vary between 2.46‰ and 4.25‰, showing no significant changes in the fungal event zone. The δ13Corg values are all below −25‰, and reach a low of −27.41‰ in the fungal event zone. This negative shift in δ13Corg is an example of the global negative shift in δ13C found associated with the end-Permian extinctions and fungal event.

Carbon cycle history through the Middle Jurassic (Aalenian – Bathonian) of the Mecsek Mountains, Southern Hungary

AbstractA carbonate carbon isotope curve from the Aalenian–Bathonian interval is presented from the Óbánya valley, of the Mecsek Mountains, Hungary. This interval is certainly less well constrained and studied than other Jurassic time slices. The Óbánya valley lies in the eastern part of the Mecsek Mountains, between Óbánya and Kisújbánya and provides exposures of an Aalenian to Lower Cretaceous sequence. It is not strongly affected by tectonics, as compared to other sections of eastern Mecsek of the same age. In parts, a rich fossil assemblage has been collected, with Bathonian ammonites being especially valuable at this locality. The pelagic Middle Jurassic is represented by the Komló Calcareous Marl Formation and thin-bedded limestones of the Óbánya Limestone Formation. These are overlain by Upper Jurassic siliceous limestones and radiolarites of the Fonyászó Limestone Formation. Our new data indicate a series of carbon isotope anomalies within the late Aalenian and early-middle Bajocian. In particular, analysis of the Komló Calcareous Marl Formation reveals a negative carbon isotope excursion followed by positive values that occurs near the base of the section (across the Aalenian–Bajocian boundary). The origin of this carbon-isotope anomaly is interpreted to lie in significant changes to carbon fluxes potentially stemming from reduced run off, lowering the fertility of surface waters which in turn leads to lessened primary production and a negative δ13C shift. These data are comparable with carbonate carbon isotope records from other Tethyan margin sediments. Our integrated biostratigraphy and carbon isotope stratigraphy enable us to improve stratigraphic correlation and age determination of the examined strata. Therefore, this study of the Komló Calcareous Marl Formation confirms that the existing carbon isotope curves serve as a global standard for Aalenian–Bathonian δ13C variation.

The giant inoceramid Platyceramus platinus as a high-resolution paleoclimate archive for the Late Cretaceous of the Western Interior Seaway

Platyceramus platinus was a giant inoceramid bivalve that inhabited the outer shelf environments of the Western Interior Seaway (WIS) in North America. With axial heights typically exceeding 1 m, the shells of this species potentially serve as a unique high-resolution geochemical proxy archive for Late Cretaceous paleoclimate. Here we present the first sclerochronological investigation of P. platinus shells to evaluate the usefulness of this species as an archive of short-term (e.g., seasonal to inter-annual) paleoenvironmental variability. We analyzed the growth patterns, the stable oxygen (δ18O) and carbon (δ13C) isotope values of well-preserved P. platinus shell fragments from the Santonian Niobrara Formation at Monument Rocks (Kansas, USA), a National Natural Landmark. A series of diagenetic tests, including cathodoluminescence (CL), scanning electron microscopy (SEM), and geochemical (LA-ICP-MS) analysis, confirmed the good state of preservation of the material. Shell microgrowth patterns suggested lunar daily (circalunidian) growth and that P. platinus grew nearly uninterruptedly throughout the year. Assuming a δ18Ow value of −3.45 ± 0.26‰, reconstructions based on shell δ18O data suggest average seasonal temperature variations between 12.5 ± 3.0 and 25.5 ± 1.1 °C and a mean annual temperature of 17.0 ± 4.1 °C for the outer shelf environment of the WIS. Repeated sudden negative δ13C shifts of up to 2.00‰ and Mn-rich shell growth bands (Mn/Ca ratios up to 90.21 μmol/mol) suggest that P. platinus filter-fed on suspended organic detritus which sank from the upper water column during episodic events. The availability of large amounts of suspended food, however, slowed shell accretion rates of P. platinus. This shell growth behavior combined with the positive δ13C values (0.03–3.96‰) possibly indicate a chemosymbiotic lifestyle that allowed P. platinus to survive under oxygen-depleted conditions at the seafloor.

The Cretaceous-Paleogene transition at Galanderud (northern Alborz, Iran): A multidisciplinary approach

We investigated the Cretaceous-Paleogene (K/Pg) transition at the Galanderud section, northern Alborz (Iran) to identify the pattern of mass extinction of planktic foraminifera and to unravel the associated paleoenvironmental changes in a little-studied area of the eastern Tethys. We applied a high-resolution quantitative and multidisciplinary study based upon benthic and planktic foraminiferal assemblages, clay mineralogy, rock magnetic properties, stable isotopes, and geochemistry. In this section, the K/Pg boundary is marked by an abrupt change in lithology from marl to a clay boundary layer, a marked decrease in magnetic susceptibility, a negative 2.2‰ δ13C excursion, and a peak in iridium. In the uppermost Maastrichtian, foraminifera are well preserved and diversified suggesting a stable, mesotrophic environment. By contrast, the K/Pg boundary and basal Danian is marked by high values of epifaunal benthic morphogroups, low planktic diversity, and high percentages of opportunistic species (Guembelitria cretacea and Cervisiella operculata) suggesting highly stressed and variable conditions, partly due to the dramatic collapse of calcareous primary producers. Benthic foraminiferal assemblages indicate outer neritic-uppermost bathyal depths with slight bathymetric variations. The most peculiar and unique aspect of the Galanderud section is the occurrence of the three thin chalk layers interbedded within clays above the K/Pg boundary, each marked by positive shifts in δ13C and δ18O values, and consisting of >80% carbonate. We propose that the chalk/clay deposits in the basal Danian reflect changes in seawater chemistry and dynamic changes in circulation (upwelling) alternating with episodes of enhanced weathering and runoff. This section on the northern margin of eastern Tethys provides new clues about the pattern of the K/Pg mass extinction and the paleoenvironmental changes occurring during the biotic recovery phase.