Decreasing δ13C Values Research Articles

A novel ontogeny-related sampling of dental tissues for stable isotopes interpretation of the paleobiology of the cave bear

In cave bear studies, stable isotope analysis of carbon and nitrogen is typically conducted on bone collagen. However, challenges arise due to biases in the classification of bones into age groups, which can be influenced by various factors that affect bone size. To overcome such issues, we present and evaluate a novel approach that involves sampling dental collagen from different ontogenetic stages of 45 fossil teeth, where only a portion of each tooth formed during the periods of interest was sampled. This approach enabled us to obtain a carbon and nitrogen fingerprint specific to a particular period in a cave bear’s life without interference from earlier stages. Stable isotopic analysis revealed a rapid decrease in δ15N values from 3 to 15 months of age. After that, the δ15N values remain stable. Based on the nitrogen isotope composition (15N/14N), cubs aged 0–3 months exclusively consumed milk, while the gradual introduction of solid plant food occurs at 5–10 months, resulting in a shift in δ15N values. Based on similar δ15N values in older age groups, it can be assumed that juveniles did not resume milk suckling after the first hibernation. The δ13C values increase until 15 months, followed by a gradual decrease until adulthood, potentially attributable to hibernation. The δ13C values also seems to indicate isotopic differences between yearlings with low δ13C values that successfully established hibernation and those with high δ13C values that failed to hibernate and starved. This novel observation, i.e., decreasing δ13C values from the second year of life onward, agrees with predicted isotopic skeletal collagen δ13C values calculated from modern brown bear blood plasma. In summary, the ontogenetic sampling strategy facilitated the acquisition of further paleobiological insights into the distinct life periods of cave bears.

Tracking Livestock Diets Using Stable Isotopes in Complex Mixed Farming Systems

Stable isotope analysis of 13C and 15N has been widely used to provide information regarding short- or long-term animal dietary composition as affected by changes in land or ecological system use. In complex mixed-crop−livestock systems, rangeland biomass, crop residues, and feedstuff contribute to livestock diets with high seasonal variations. Particularly in the Limpopo province, South Africa, livestock feed supply varies considerably throughout the year leading to regular feed gaps. Hence, to estimate livestock diet composition in relation to these variations, we analyzed the stable isotopes of C and N of tail hair and feces samples across free-ranging beef cattle in distinct agroecological zones (AEZs) and farm types. Here, farm types were structured according to mixed-crop−livestock farms and livestock-only farms. We found that farm types did not influence the δ13C of feces and hair (P > 0.05), but AEZ had a strong effect on δ13C patterns (P < 0.01). The contribution of C3-C4 plants in the diet varied considerably across farm types and AEZ (P < 0.01). The δ15N values indicated nutritional stress, probably due to low protein concentrations in feed (e.g., rangeland biomass, crop residues) irrespective of AEZ and farm types. In general, cattle exposed to arid conditions (drier AEZ) had significantly decreased δ13C values and increased δ15N values that could potentially be linked to feed gaps. Moreover, the results from the present study indicate that δ13C of feces and hair samples are more meaningful predictors of cattle diet than δ15N as affected by different farm practices. Therefore, stable isotope analyses potentially have an important role in helping improve the understanding of seasonal shifts in livestock diet intake in diverse production systems.

Coupling between chromophoric dissolved organic matter and dissolved inorganic carbon in Indian estuaries

This study investigates the coupling between Chromophoric Dissolved Organic Matter (CDOM) and Dissolved Inorganic Carbon (DIC) in eighteen Indian estuaries across salinity gradient of the east and west coasts during the monsoon season, characterized by significant river discharge. The hypothesis that humic acids (HA) and fulvic acids (FA), prominent in estuarine CDOM, closely correspond to the ‘organic alkalinity’ (Aorg) component of total alkalinity is examined. In most estuaries, specifically those along the northeast coast (NE) and southwest coast (SW), a significant linear relationship exists between DIC, CDOM abundance, and pH level. Notably, minor estuaries along the southeast coast (SE) and northwest coast (NW) exhibit elevated DIC levels beyond what this relationship predicts. These estuaries also reveal heightened ammonium levels, increased δ15N values, and decreased δ13C values, indicative of anthropogenic influence. CDOM properties, such as spectral slope (S300–500) and spectral slope ratio (SR, S275–295:S350–400), align with these findings, with SE and NW estuaries displaying higher values. On average, CDOM contributes 110.5 μM (6.8 %) to DIC in NE, 390.7 μM (11 %) in SE, 24.4 μM (4.8 %) in SW, and 122.2 μM (4 %) in NW estuaries. The relationship between total alkalinity minus DIC (TA-DIC) and pH25 suggests that CDOM, mediated by HA/FA, buffers the inorganic carbon system in estuaries. This buffering capacity weakens at elevated DIC levels, and this condition is marked by anomalous SR values compared to the baseline salinity-SR linear regression. This Study suggests that estuarine CDOM could largely represent “organic alkalinity” and could help monitor acidification in estuaries.

Carbonatitic Magma Fractionation and Contamination Generate Rare Earth Element Enrichment and Mineralization in the Maoniuping Giant REE Deposit, SW China

Abstract Carbonatite intrusions host the world’s most important light rare earth element (LREE) deposits, and their formation generally requires extraordinary fertile sources, magmatic evolution, and hydrothermal events. However, carbonatitic magma evolution, particularly the role of fractional crystallization and contamination from silicate rocks in REE enrichment, remains enigmatic. The Maoniuping world-class REE deposit in southwestern China, is an ideal target to decipher magmatic evolution and related REE enrichment as it shows continuous textual evolution from medium- to coarse-grained calcite carbonatite (carbonatite I) at depth, to progressively pegmatoidal calcite carbonatite (carbonatite II) at shallow levels. In both types of calcite carbonatites, four generations of calcite can be classified according to petrographic and geochemical characteristics. Early-crystalizing calcite (Cal-I and Cal-II) are found in carbonatite I and exhibit equigranular and a polygonal mosaic textures, while late calcites (Cal-III and Cal-IV) in carbonatite II are large-size oikocrysts (&amp;gt;0.5 mm in length) with strain-induced undulatory extinction and bent twinning lamellae. All these generations of calcite yield similar, near-chondritic, Y/Ho ratios (26.6–28.1) and are inferred to be of magmatic origin. Remarkably, gradual enrichment of MgO, FeO and MnO from Cal-I to Cal-IV is coupled with a significant increase in REE contents (~800 to 2000 ppm), with LREE-rich and gentle-to-steep chondrite-normalized REE patterns ((La/Yb)N = 3.1–26.8 and (La/Sm)N = 0.9–3.9, respectively). Such significant REE enrichment is ascribed to protracted magma fractional crystallization with initial low degree of fractional crystallization (fraction of melt remining (F) = ~0.95) evolving to late stage (F = 0.5–0.6) by formation of abundant calcite cumulates. Differential LREE and HREE behavior during magma evolution largely depend on separation of phlogopite, amphibole, and clinopyroxene from the carbonatitic melt, which is indicated by progressively elevated (La/Yb)N ratios ranging from 3.1 to 26.8. The four generations of calcite have significantly different C and Sr isotopic compositions with δ13CV-PDB decreasing from −3.28 to −9.97‰ and 87Sr/86Sr increasing from 0.70613 to 0.70670. According to spatial relations and petrographic observations, the relative enrichment of δ13C and depletion in 87Sr/86Sr ratios of Cal-I and Cal-II show primary isotopic characteristics inherited from initial carbonatitic magma. By contrast, the variable Sr and C isotopic compositions of Cal-III and Cal-IV are interpreted as the results of contamination by components derived from silicate wall rocks and loss of CO2 by decarbonation reactions. To model such contamination processes, Raleigh volatilization and Monte Carlo simulation have been invoked and the model results reveal that carbonatitic melt-wall rock interaction requires 40% radiogenic Sr contamination from silicate rocks and 35% CO2 degassing from carbonatitic melt. Moreover, positive correlations between decreasing δ13C values and increasing REE contents, together with bastnäsite-(Ce) precipitation, indicate further REE accumulation during the contamination processes. In summary, alongside REE-rich magma sources, the extent of fractional crystallization and contamination during carbonatitic magma evolution are inferred to be important mechanisms in terms of REE enrichment and mineralization in carbonatite-related REE deposits worldwide.

Preliminary Bat Guano Isotope Evidence for Past Vegetation and Climate Change in Southwest Virginia

The Appalachian Mountains, one of the most biologically diverse regions in the temperate world, have been heavily altered by human activity for millennia yet the relative roles of human and other disturbances and climate change in creating modern landscapes are not well understood. Holocene paleoenvironmental records could provide a window into past Appalachian landscapes, but are restricted by a dearth of appropriate sites, such as natural lakes. Recent research suggests that bat guano deposits can serve as valuable archives of past environmental change. Carbon isotope (δ13C) values of guano from insectivorous bats can reflect the relative abundance of forest (C3) versus grassland (C4) vegetation at a regional scale, while guano nitrogen isotope (δ15N) values have been linked to landscape-scale N-cycling and precipitation. To investigate the paleoenvironmental history of an Appalachian site in southwest Virginia, we collected a 170 cm guano core from a limestone cave on Salt Pond Mountain. Bats are no longer active in the cave, but recovered bones indicate the past presence of Myotis species. Preliminary results show clear trends of increasing δ15N values and decreasing δ13C values from deep in the core toward the surface. δ13C and δ15N values are also significantly negatively correlated (R2=0.6, p=5.6e-15). The increase in δ15N values may signal a moistening climate toward the present, a finding consistent with regional Holocene pollen records. Higher δ13C values deep in the core likely indicate a greater prevalence of C4 grassland vegetation on the landscape, which could be linked to drier climate, indigenous burning, or both. Increased variation in δ13C and δ15N values below about 65 cm may indicate more variable climate or increased disturbance during the time represented. Forthcoming radiocarbon dates will anchor these trends in time and inform correction for the Suess effect, while other proxies could help disentangle the drivers of landscape change.

Carbon and nutrient burial within Peruvian coastal marsh driven by anthropogenic activities

This research assessed carbon and nutrient burial during the past ~60 years within a Peruvian coastal marsh ecosystem affected by anthropogenic activities, by examining total organic carbon (TOC), total nitrogen (TN) and isotopes (δ13C and δ15N) tracers in two dated sediment cores. Significantly higher TOC and TN burial, up to 416.4 ± 65.0 and 0.7 ± 0.1 g m−2 year−1 respectively, were observed after an uncontrolled urban expansion starting in the early 1970's to the 1990's. The TOC and TN burial rates were up to twofold higher than those observed for preserved coastal marshes. Furthermore, the decreased δ13C values (−16.1 ± 0.6 ‰) and increasing δ15N values (+10.6 ± 2.6 ‰) indicate higher deposition of algal material and urban sewage during the same period. The higher burial rates during 1970's–1990's and reduced rates thereafter evidenced the role of coastal marsh ecosystems plays in sequestering carbon and nutrients.

Impacts of piscicide-induced fish removal on resource use and trophic diversity of lake invertebrates

Chemical eradication of non-native species has become a widely used method to mitigate the potential negative impacts of altered competitive or predatory dynamics on biodiversity and natural ecosystem processes. However, the responses of non-target species can vary from rapid full recovery to delayed or absent recolonization, and little is known about the potential shifts in resource use and trophic diversity of native species following chemical treatments. We used a before-after-control-impact approach to study the effects of rotenone piscicide treatment on abundance and trophic niche of benthic invertebrates in three untreated and three treated lakes in central Norway, the latter group hosting non-native roach (Rutilus rutilus) and pike (Esox lucius) prior to rotenone treatment. Based on community composition data, the relative abundance of invertebrate grazers and collectors decreased while that of predators increased following fish removal in the treated lakes. The stable isotope data indicated minor shifts in resource use of, and trophic diversity among, benthic invertebrate communities. While the predatory dragonfly larvae (Odonata) and grazer snails (Lymnaeidae) showed increased δ13C values indicating increased reliance on littoral benthic algae, the collector mayfly larvae (Leptophlebia) showed decreased δ13C values following fish removal in treated lakes. Grazer snails also showed a shift to a lower trophic position, while the predatory dragonflies and collector mayflies showed no changes in δ15N values following fish removal. The community-level isotopic niches of benthic invertebrates showed no consistent changes, although the sample-size corrected and Bayesian estimates of standard ellipse areas (SEAC and SEAB) slightly increased in two of the three treated lakes due to an increased range in δ15N. In conclusion, our study findings indicate some changes in species assemblages but minor shifts in the resource use and trophic diversity of benthic invertebrate communities following fish removal in rotenone treated lakes.

Carbon isotope excursions during the late Miocene recorded by lipids of marine Thaumarchaeota, Piedmont Basin, Mediterranean Sea

Abstract Group I mesophilic Thaumarchaeota fix dissolved inorganic carbon (DIC), accompanied by a biosynthetic fractionation factor of ~20‰. Accordingly, the δ13C signature of their diagnostic biomarker crenarchaeol was suggested as a potential δ13CDIC proxy in marine basins if input from nonmarine Thaumarchaeota is negligible. Semi-enclosed basins are sensitive to carbon-cycle perturbations, because they tend to develop thermohaline stratification. Water column stratification typified the semi-enclosed basins of the Mediterranean Sea during the late Miocene (Messinian) salinity crisis (5.97–5.33 Ma). To assess how the advent of the crisis affected the carbon cycle, we studied sediments of the Piedmont Basin (northwestern Italy), the northernmost Mediterranean subbasin. A potential bias of our δ13CDIC reconstructions from the input of soil Thaumarchaeota is discarded, since high and increasing branched and isoprenoid tetraether (BIT) index values do not correspond to low and decreasing δ13C values for thaumarchaeal lipids, which would be expected in case of high input from soil Thaumarchaeota. Before the onset of the crisis, the permanently stratified distal part of the basin hosted a water mass below the chemocline with a δ13CDIC value of approximately −3.5‰, while the well-mixed proximal part had a δ13CDIC value of approximately −0.8‰. The advent of the crisis was marked by 13C enrichment of the DIC pool, with positive δ13CDIC excursions up to +5‰ in the upper water column. Export of 12C to the seafloor after phytoplankton blooms and limited replenishment of remineralized carbon due to the stabilization of thermohaline stratification primarily caused such 13C enrichment of the DIC pool.

Properties of secondary xylem of mature oaks in southwest Germany formed after extreme drought stress in summer 2018

The effect of the extreme summer drought and heatwave 2018 in Central Europe on wood properties of oaks at four sandy valley river sites (Quercus robur L.) and one south-exposed schist slope (Qu. petraea (Matt.) Liebl.) in the middle Rhine and lower Main valley were studied and compared to well-watered trees from a riparian stand. While properties of the 2018 tree rings mostly resembled those of the previous (wet) year, significant decreases in Δ13C, wood density and ring width occurred in 2019 at most drought-prone sites. In the sandy sites, ring widths correlated with previous-year precipitation from June to August over a 20-year period. In organs formed in 2018, in general, decreasing Δ13C values were obtained in the order leaves, twigs, wood and acorns, with the values from acorns often resembling those from 2019-year rings. The observed changes indicated an increased intrinsic water use efficiency and lack of starch reserve formation during the unprecedented hot and dry summer 2018. Qu. petraea revealed quite different values from Qu. robur (lower Δ13C, wider and denser year rings), but qualitatively showed the same reaction to the drought in 2018, except for an enhanced formation of tyloses in recent-year tree rings.

Geochemical and O–C–Sr–Nd Isotopic Constraints on the Petrogenetic Link between Aillikites and Carbonatites in the Tarim Large Igneous Province

Abstract Aillikites are carbonate-rich ultramafic lamprophyres often associated with carbonatites. Despite their common field relationships, the petrogenetic links, if any, between aillikites and carbonatites remain controversial. To address this question, this study reports the results of a detailed geochemical and isotopic examination of the Permian Wajilitag aillikites in the northwestern Tarim large igneous province, including bulk-rock major- and trace-element and Sr–Nd isotope compositions, olivine major- and trace-element and (in situ secondary ion mass spectrometry) oxygen isotope compositions, oxygen isotope data for clinopyroxene separates, and bulk-carbonate C–O isotopic analyses. Olivine in the aillikites occurs in two textural types: (1) microcrysts, 0·3–5 mm; (2) macrocrysts, 0·5–2·5 cm. The microcrysts exhibit well-defined linear correlations between Fo (79–89) and minor and trace elements (e.g. Ni = 1304–3764 μg g–1 and Mn = 1363–3042 μg g–1). In contrast, the olivine macrocrysts show low Fo (79–81), Ni (5·3–442 μg g–1) and Ca (477–1018 μg g–1) and very high Mn (3418–5123 μg g–1) contents, and are displaced from the compositional trend of the microcrysts. The microcrysts are phenocrysts crystallized from the host aillikite magmas. Conversely, the lack of mantle-derived xenoliths in these aillikites suggests that the macrocrysts probably represent cognate crystals (i.e. antecrysts) that formed from earlier, evolved aillikite melts. Olivine phenocrysts in the more primitive aillikite dykes (Dyke 1) have relatively higher Fo (Fo82–89) and mantle-like oxygen isotope values, whereas those in the more evolved dykes (Dykes 2 and 3) exhibit lower Fo (Fo79–86) and oxygen isotope values that trend toward lower than mantle δ18O values. The decreasing δ13C values of carbonate from Dyke 1 to Dykes 2 and 3, coupled with the indistinguishable Sr–Nd isotopes of these dykes, suggest that the low δ18O values of olivine phenocrysts in Dykes 2 and 3 resulted from carbonate melt/fluid exsolution from a common progenitor melt. These lines of evidence combined with the overlapping emplacement ages and Sr–Nd isotope compositions of the aillikites and carbonatites in this area suggest that these exsolved carbonate melts probably contributed to the formation of the Tarim carbonatites, thus supporting a close petrogenetic relationship between aillikites and carbonatites.

Behavior of Mg isotopes during precipitation of methane-derived carbonate: Evidence from tubular seep carbonates from the South China Sea

The magnesium (Mg) isotopic composition of marine carbonate has been used as a proxy to constrain the geochemical composition of seawater and to trace the global Mg cycle. Sulfate-driven anaerobic oxidation of methane (SD-AOM) is a prominent process that facilitates the formation of marine authigenic carbonate. Yet the understanding of the impact of SD-AOM on the Mg isotope composition of authigenic carbonate under natural conditions is limited. Here we present the analysis of two tubular methane-seep carbonates from the South China Sea. The tubular carbonates reveal a trend of decreasing δ13C values and increasing carbonate contents from the periphery (i.e., the outer surface of the carbonate) to the inner portion (i.e., close to the inner surface of the carbonate pipes). The tubular carbonates are interpreted as former fluid conduits, indicating intense and lasting seepage that apparently increased with time. The observed variability in composition probably results from changes in the intensity of SD-AOM and correlating carbonate precipitation rates. Trends of enrichment of middle rare earth elements (MREEs), molybdenum (Mo), and uranium (U) from the periphery inward indicate more reducing formation conditions toward the inner surface of the former conduit. Along the same transects, δ26Mg values decrease from periphery to inner portion in one tubular carbonate (−2.63‰ to −3.24‰), while δ26Mg values are close to constant for the second tubular carbonate (−3.42‰ to −3.37‰); such patterns highlight the complexity of Mg isotope fractionation during seep carbonate formation. A positive correlation between δ26Mg and δ13C values and a negative correlation between δ26Mg and Mg/Ca molar ratios suggests that enhanced SD-AOM facilitates the incorporation of light Mg isotopes into the carbonate lattice. However, such assumption contradicts with the fact that higher carbonate precipitation rates reduce Mg isotope fractionation due to incomplete dehydration of Mg ions. It is hypothesized that hydrogen sulfide produced by SD-AOM may enlarge the extent of fractionation by weakening the hydration of Mg. If this interpretation is correct, the effect of sulfide on the fractionation of Mg isotopes can even offset or exceed the effect of precipitation rate. Our study indicates that SD-AOM has an effect on the Mg isotope fractionation during carbonate precipitation. Similar effects may have occurred in geological periods with more widespread carbonate authigenesis. A better understanding of the factors affecting the Mg isotopic fractionation during marine carbonate authigenesis is needed to efficiently use this archive of paleoenvironments and element cycling.

Higher soil organic carbon sequestration potential at a rehabilitated mangrove comprised of Aegiceras corniculatum compared to Kandelia obovata

The present study compared the ecosystem organic carbon (OC) stocks and soil OC sources between two 12-year-old monospecific mangrove sites comprised of different species (Kandelia obovata in tree form and Aegiceras corniculatum in shrub form). We tested whether the carbon sequestration performance following rehabilitation varied with plantation of species in different forms and whether mangrove vegetation sequestrate OC more rapidly than soil pool. The results showed that mangrove rehabilitation increased the ecosystem OC stock relative to that of a non-vegetated bare flat. The accumulation of soil carbon was accompanied by increased soil total nitrogen contents and decreased δ13C values of soil OC, indicating that the increases in OC and TN contents were a function of accumulation of 13C-depleted mangrove materials in the soil. The sequestrated OC over the 12 years was considerably less in soil than in biomass at each mangrove site, suggesting that mangrove vegetation contributes more rapidly than the soil to ecosystem OC sequestration following rehabilitation before the vegetation has reached maturity. Compilation of the carbon stocks from worldwide rehabilitated mangrove forests with various ages further supports this finding. The K. obovata site had an apparently higher biomass OC stock but less OC in the soil than those at the A. corniculatum site. There was a higher standing leaf litter stock on the forest floor and more mangrove materials incorporated into the top 15 cm soil at the A. corniculatum site. These results suggested that the two rehabilitated mangrove sites had different development trajectories of both biomass and soil OC sequestration. Moreover, the performance of ecosystem carbon sequestration was related to plantation of different mangrove species. These carbon sequestration feature of rehabilitated mangrove forests therefore deserve attention in future rehabilitation programs to promote carbon sequestration performance.

Mid-Holocene environmental change and human response at the Neolithic Wuguishan site in the Ningbo coastal lowland of East China

Coastal wetlands provided a favorable settling site for Neolithic people because of their highly exploitable biomass, but were vulnerable to marine hazards such as coastal flooding. The Chinese Hemudu culture persisted for ~2000 years (7200–5300 cal. year BP) in the Ningbo coastal lowland of East China. This study explores the Hemudu people’s survival strategy using sedimentological and chronological records, and organic and acetic-acid-leachable alkaline-earth (Ca, Sr, and Ba) chemistry on a well-dated profile from the coastal Wuguishan site in the Ningbo Plain. Analyses of alkaline-earth elements in surficial sediments collected from present-day alluvial plain, tidal river, and saltmarsh/tidal flat environments in the Ningbo Plain were also undertaken to explain sedimentary environmental changes and their linkage to Hemudu activity at the Wuguishan site. Results indicate high sediment acetic-acid-leachable Ca and Sr contents with high Sr/Ba ratios, and high sediment total inorganic carbon contents at the site during 6300–6000 cal. year BP, which coincided with a marine incursion at the nearby Neolithic Yushan site. However, the increasing sediment total organic carbon contents and decreasing δ13C values suggest that the Wuguishan site evolved from an upper tidal flat to a saltmarsh environment, attracting settlement by the prehistoric Hemudu people after ~6200 cal. year BP. Sr and Ca contents and Sr/Ba ratios decreased after ~6000 cal. year BP, indicating that the site developed into a low-salinity marsh in the supratidal environment after rapid accumulation caused by a storm event at ~6020 cal. year BP. Furthermore, the high Sr and Ba contents in the layers of Hemudu Culture Period III indicate the Hemudu people’s consumption of seafood and their adaption strategy for living in the vulnerable coastal wetland.

Reconstructing diets and subsistence strategies of the Bronze Age humans from the Central Plains of China: A stable isotopic study on the Nanwa site

AbstractA multicrop agricultural system, including millet, wheat, rice, and soybeans, first emerged in China in the Late Longhang period and is considered to be one of the most important basic foundations underpinning the origin and development of early states in China. However, there is still a lack of studies on the specific subsistence strategies of humans from the Bronze Age, specifically addressing how widespread the multicrop agricultural system was. To explore these questions above, carbon and nitrogen isotope analysis on human bones from the Nanwa site (ca 1720–256 BC &amp; 960–1279 AD) was undertaken to investigate the palaeodiet and subsistence strategies of the Nanwa humans. This paper also reviews the existing stable isotope data of Bronze Age humans on the Central Plains of China.The Nanwa humans from the Erlitou and Yinxu periods have a mean δ13C value of −9.4 ± 0.7‰ and −9.1 ± 0.9‰, suggesting a predominantly C4 diet, probably derived from millet agriculture or domesticated animals fed on millet. Nanwa humans of the Eastern Zhou Dynasty have a relatively low mean δ13C value of −10.5 ± 2.4‰, indicating a consumption of much more C3 foods, likely derived from rice, wheat, soybean, or animals that fed on those plants. A temporal stable isotopic comparison from the Erlitou period to the Eastern Zhou Dynasty on the Central Plains of China shows the majority of the Bronze Age humans have high mean δ13C value (−9.5 ± 1.8‰), suggesting a predominantly C4‐based diet. We infer that millet agriculture was still the primary economy for humans during the Bronze Age. However, there is a relatively large proportion of humans from the Eastern Zhou Dynasty that have decreased δ13C values, indicating a much more C3 foods consumption and diversity diet, presumably derived from a multicrop agricultural system of millet, wheat, rice, and soybean. It is possible that the trend moved from a narrowly focused, mainly millet‐based diet, to a more diverse agricultural system and was triggered by a combination of factors such as climate change, agricultural reform, social stratification, wars, migration, and so on.

Mo isotopic response to the end of Neoproterozoic Marinoan glaciation: Evidence from a sedimentary profile in South China

In the geological time, atmosphere and ocean have experienced two important oxidation events which are the Paleoproterozoic Great Oxidation Event and the Neoproterozoic Oxidation Event. These events had a great influence on the origin and evolution of life and the system of atmosphere, ocean and earth surface. The record of early metazoan fossils and the radiation of marine algae occurred following the Marinoan glaciation in the Neoproterozoic. Hence, an ocean oxygenation event at the boundary of Cryogenian and Ediacaran is closely associated with the biological evolution. Here, we present new TOC contents, Mo concentrations, C-O-Mo isotopic data of sedimentary rocks collected across the boundary (~635 Ma) between the Nantuo and Doushantuo Formations in the Shennongjia area, South China. Based on the isotopic data, three intervals can be distinguished: Interval I, the Nantuo Formation beneath the cap carbonate of the Doushantuo Formation, has the highest TOC (0.03%) and Mo concentration (5.494 ppm) and similar tendency of the δ13C values and the δ98Mo values, which represent the enhanced chemical weathering, the raised nutrient input and the higher primary productivity. Interval II, the cap carbonate, possesses low TOC and Mo concentrations and the consistently diminished carbon composition and the fluctuating δ98Mo values. Interval III, the sediments above the cap carbonate of the Doushantuo Formation, is characterized by low TOC and Mo concentration, which is similar with the Interval II, but displays decreasing δ13C values and increasing δ98Mo values. These features of the Interval II and III were contributed by the end of high intensity chemical weathering, resulting in the atmosphere and shallow-ocean enriching oxygen. The δ98Mo values elevated until the interval III, indicating that the response of Mo isotope system lagged the shallow-ocean oxygenation. Our data, therefore, indicate an oxygenation from the Cryogenian to Ediacaran, which is in good agreement with the emergence of the Ediacaran biota.

Carbon isotopes of n-alkanoic acids in Antarctic ornithogenic sediments as indicators of sedimentary lipid sources and paleocological change

Sedimentary n-alkanoic acids are ubiquitous in the environment and their carbon isotopic composition is increasingly used to identify the source of organic matter and to reconstruct past climatic and ecological changes. Here we investigate the distribution and carbon isotope ratios of n-alkanoic acids in two sediment profiles influenced by animal excrement in Antarctica. We found that organic matter input from animal excrement is the predominate source of short- and mid-chain n-alkanoic acids in the ornithogenic sediments. Decreased δ13C values are closely related to increased excrement input of penguins and seals that occupied the study site, especially in C16n-alkanoic acid. Long-chain (>C24) n-alkanoic acids likely originate from moss and heterotrophic microbes, and the δ13C values of C26n-alkanoic acid were consistent with organic biomarkers and bio-elements from animal excrement. Two possible processes are suggested to explain the close relationship between C26n-alkanoic acid δ13C values and animal excrement input. All the results indicate that the carbon isotopes of n-alkanoic acids in ornithogenic sediments can be used to indicate historical population change of penguins or seals in Antarctica.

Speleothem δ13C record suggests enhanced spring/summer drought in south-eastern Spain between 9.7 and 7.8 ka – A circum-Western Mediterranean anomaly?

South-eastern Spain is one of the driest regions in Europe and thus, prone to drought. Terrestrial climate records covering the late Glacial and Holocene from this area are sparse. Here, we present a flowstone record from Cueva Victoria, south-eastern Spain, which covers the late Glacial (15 ka) to the mid-Holocene (7 ka) including the Younger Dryas (YD). Between the onset of the Bølling/Allerød (B/A) and the early Holocene, flowstone δ18O values progressively decrease in accordance with sea-surface temperatures in the Alboran Sea, indicating an increase in precipitation in south-eastern Spain and a supra-regional signal of North Atlantic temperature change. At the same time, decreasing δ13C values suggest progressively increasing precipitation and vegetation density. This trend is interrupted by both colder and drier conditions during the YD. Between 9.7 ± 0.3 and 7.8 ± 0.2 ka, a large positive excursion of the δ13C values indicates a strong reduction in vegetation density, probably as a consequence of very dry spring/summer conditions. In combination with the continuously low speleothem δ18O values and a nearly unchanged growth rate, this suggests increased seasonality (i.e. drier spring/summer conditions, but not a strong reduction in annual precipitation). This is consistent with several other climate records from the Western Mediterranean region, showing that the Western Mediterranean realm (Spain, Italy) experienced pronounced spring/summer drought during this time interval. Interestingly, the timing of this dry period coincided with the African Humid Period. This may be part of a teleconnection with the North African Monsoon via the Hadley cell circulation.

Understory ferns alter soil carbon chemistry and increase carbon storage during reforestation with native pine on previously degraded sites

Reforestation with native species and resulting understory succession can exert important influences on soil organic matter (SOM) storage and chemistry, but a mechanistic understanding of these effects is lacking. We studied different aged Masson pine (Pinus massoniana L.) plantations with and without the understory fern, Dicranopteris dichotoma (Thunb.) Berhn., in subtropical China to assess how SOM over a 30 year sequence of pine growth and fern expansion. To do this, we measured total SOM, lignin-derived phenols, soil carbon (total C and 13C), soil nitrogen (total N and 15N), and soil microbial community composition via phospholipid fatty acid (PLFA) analyses. We found that the accumulation of newly-formed SOM outweighed decomposition of old SOM, with the majority of this increase being derived from fern detrital inputs. Where ferns were present, ferns contributed 54–61% of total soil C storage in surface (0–10 cm depth) soils, which was 62–91% higher than pre-reforestation soil C storage. We found that the abundance of lignin-derived compounds was lower in fern dominated soils, perhaps because soils under ferns supported more soil fungi, the primary decomposers of the lignin in soil. Fern soils also showed higher ratios of syringyls to vanillyls and decreased δ13C values, an indicator that ferns altered the composition of SOM at the molecular level while contributing significantly to SOM accumulation. Reforestation especially when accompanied by fern expansion also improved soil N and phosphorus (P) status, with observed declines in soil δ15N in fern dominated soils aligning with increased nutrient retention and observed increases in soil C storage. Our study highlights the potentially important role of understory ferns in mediating SOM chemistry and soil C storage during ecosystem recovery.

Ecologic shift and aridification in the northern Tibetan Plateau revealed by leaf wax n-alkane δ2H and δ13C records

Two competing factors, the global cooling and the uplift of Tibetan Plateau, have been proposed to drive the central Asian aridification, but their relative role has seldom been discriminated in paleoclimate and paleoenvironment records. Here, we reconstruct a 14-million-year-long record of paleohydrology and paleoecology in the western Qaidam Basin by applying the compound-specific hydrogen (δ2H) and carbon (δ13C) isotope analyses to terrestrial leaf wax long-chain n-alkanes. The δ2H values are low during the interval of 14.6 to 13.0 Ma. Then the δ2H increases from 13.0 to 12.2 Ma and maintains high values from 12.2 to 3.2 Ma with a peak high value of −156.1‰ at 8.0 Ma. After 3.2 Ma, the δ2H values are low and vary larger than 30‰. The δ13C values decrease from 14.6 to 13.0 Ma and are low from 13.0 to 3.2 Ma except a high value at 3.8 Ma. Then they decrease slightly after 3.2 Ma. Low δ2H values indicate relatively wet climate between 14.6 and 13.0 Ma. The decreasing δ13C values during the same time period support the ecologic shift with the decline of warm component of conifers after the Mid-Miocene Climatic Optimum. High δ2H values since 13.0 Ma are synchronous with the uplift of northern Tibetan Plateau, implying tectonics-driven aridity. Large-amplitude variation in δ2H values since ca. 3.2 Ma seen in East and West Qaidam and lower δ13C values reveal the climatic cyclic responses to the Northern Hemisphere Glaciation.

The Central Paratethys during Oligocene as an ancient counterpart of the present-day Black Sea: Unique records from the coccolith limestones

Four isochronous Oligocene coccolith limestone horizons from the Carpathians were examined in order to reconstruct paleoceanographic conditions in the Central Paratethys. The dominance of small and size-uniform pyrite framboids, the occurrence of low-diversity dinoflagellate cysts and coccolithophorids and the presence of biomarker molecule 28,30-dinorhopane indicate that the water column was stratified with the upper water column being relatively well‑oxygenated, but the bottom water being anoxic. The latter is confirmed by the fine and consistent horizontal laminations in various parts of the basin, scarcity of benthic organisms and their trace fossils. The limestones exhibit typical marine δ13C values, but are significantly depleted in 18O and enriched in 87Sr relative to contemporaneous ocean water. These isotopic compositions result from a decreased salinity of the surface waters caused by an increased riverine input. This is confirmed by the lack or impoverishment of planktonic foraminifers, presence to abundance of goniodomid dinoflagellate cysts and massive occurrence of low-diversity nannoplankton assemblages, which indicates decreased salinities as low as 17‰ and high productivity in the upper water column. These observations indicate that the limestones were formed during periods when connection of the Central Paratethys with the global ocean was limited, which impeded water exchange causing the development of low-salinity conditions of surface water and bottom-water anoxia. During the deposition of the oldest Tylawa horizon, primary productivity was enhanced and chemocline was positioned exceptionally high in the water column. Moreover, decreased δ13C values in both carbonates and organic matter of this horizon suggest that widespread methane venting took place in the basin during NP23. All these data show that during the Oligocene the Central Paratethys experienced similar conditions to those of the current Black Sea, which can be used as a modern analogue, especially for the Tylawa horizon. Therefore, the Tylawa horizon can be perceived as a potential effect of future post-depositional processes of coccolith marls analogous to those having been deposited in the Black Sea for 2.7 kyr.