δ13C Signatures Research Articles

Geographic and seasonal variation in δ13C values of C3 plant arabidopsis: Archaeological implications

Archaeologists frequently rely on carbon isotope data to infer past climates, ecosystems, diets, and mobility patterns. Scientists continue to unravel the intricacies of carbon isotope fractionation in C3 plants, and these data work to improve archaeological interpretations. An important question is how δ13C values of a single species vary with climate across sites, years, or seasons when water may not be the limiting factor, which could have important consequences for archaeological interpretation. This article examines δ13C values of one species of C3 plant, Arabidopsis thaliana, grown across five field sites in Europe over two and a half years. The five field sites (Valencia, Spain; Norwich, UK; Köln, Germany; Halle, Germany; and Oulu, Finland) were chosen to represent A. thaliana's native climate range and include both semi-arid and sub-humid climatic zones; site-specific climatic data were collected for each planting. There were significant differences in δ13C signatures of the A. thaliana plants grown at the different sites (p < 0.001) with higher δ13C values seen at lower latitudes or closer to the coast. Further, there were significant differences between years or seasons at Valencia, Spain (p = 0.001), Norwich, UK (p < 0.001) and Halle, Germany (p < 0.001). Principal component analysis of the planting-level climate data illustrates the interconnectedness of the environmental factors at play while also highlighting the importance of daylength on carbon fractionation during photosynthesis in A. thaliana at these sites.

Metal bioaccumulation and transfer in benthic species based on isotopic signatures of individual amino acids in South China Sea cold seep environments

Cold seeps are deep-sea ‘oases’ with dense and dominant coexisting populations of large mussels and tubeworms under extreme environments. Under such natural source of high metal concentrations, the present study investigated the metal bioaccumulation and transfer with trophic positions in six benthic species by the isotopic δ15N and δ13C signatures in the active Haima cold seep, South China Sea. Comparing the isotopic signatures of bulk-tissue and amino acids by compound-specific isotopic analysis (CSIA-AA), we found that the bulk trophic (TPB) values in the benthos except mussels were significantly higher than those of CSIA-based TPGlu-Phe values. The estimated CSIA-based TPGlu-Phe values showed a relatively compressed food chain with much changeable and unique amino acid isotopic heterogeneity, followed slim tubeworms (1.20)<mussels (1.38)<clams (1.52)<brittle stars (1.82)<giant tubeworms (2.16)<shrimps (2.31). All species accumulated relatively high concentrations of Fe, Zn, Cu, and Cr, especially for Zn in clams. Pearson correlation analysis showed that most metals had no significant relationship between their bioaccumulation and trophic positions, whereas Hg showed a significantly positive bioaccumulation through trophic transfer in such a compressed food chain. Water exposure was a major metal source rather than bacterial assimilation for most metals in the cold seep higher consumers. Hyperaccumulation of specific metals in some tissues of different benthos indicated different metal overflows in the Haima cold seep (As and Ni for tubeworms, Zn and Cd for clam gills, Ag and Cu for mussel gills). This study demonstrated high metal adaptations in different species and stable isotopic characteristics of amino acid metabolism in a natural high metal source of an active deep-sea cold seep, which is important for deep-sea development and environmental protection.

IDENTIFICATION IN PORE WATERS OF RECYCLED SEDIMENT ORGANIC MATTER USING THE DUAL ISOTOPIC COMPOSITION OF CARBON (δ13C AND Δ14C): NEW DATA FROM THE CONTINENTAL SHELF INFLUENCED BY THE RHÔNE RIVER

ABSTRACTEstuaries and deltas are crucial zones to better understand the interactions between continents and oceans, and to characterize the mineralization and burial of different sources of organic matter (OM) and their effect on the carbon cycle. In the present study, we focus on the continental shelf of the northwest Mediterranean Sea near the Rhône river delta. Sediment cores were collected and pore waters were sampled at different depths at one station (Station E) located on this shelf. For each layer, measurements of dissolved inorganic carbon concentration (DIC) and its isotopic composition (δ13C and Δ14C) were conducted and a mixing model was applied to target the original signature of the mineralized OM. The calculated δ13C signature of the mineralized organic matter is in accordance with previous results with a δ13COM of marine origin that is not significantly impacted by the terrestrial particulate inputs from the river. The evolution with depth of Δ14C shows two different trends indicating two different Δ14C signatures for the mineralised OM. In the first 15 cm, the mineralized OM is modern with a Δ14COM = 100 ± 17‰ and corresponds to the OM produced during the nuclear period of the last 50 years. Deeper in the sediment, the result is very different with a depleted value Δ14COM = –172 ± 60‰ which corresponds to the pre-nuclear period. In these two cases, the marine substrate was under the influence of the local marine reservoir effect with more extreme Δ14C results. These differences can be largely explained by the influence of the river plume on the local marine DIC during these two periods.

Contribution of Integrated Crop Livestock Systems to Climate Smart Agriculture in Argentina

Integrated crop-livestock system (ICLS) is a useful practice to enhance soil organic carbon (SOC) compared to continuous cropping systems (CC). However, robust data from different regions around the world remain to be collected. So, our objectives were to (i) compare SOC and its physical fractions in ICLS and CC, and (ii) evaluate the use of δ13C to identify the source of C of SOC in these systems in the Pampas region of Argentina. For that, we compared two farms, an ICLS and a CC having the same soil type and landscape position. The ICLS farm produces alfalfa grazed alternatively with soybean and corn, and the CC farm produces the latter two crops in a continuous sequence. Soil samples (0–5, 5–20, 20–40, and 40–60 cm) were collected and analyzed for SOC, its physical fractions, and their isotopic signature (δ13C). Soils under ICLS showed an increment of 50% of SOC stock compared to CC in the first 60 cm. This increase was related to 100–2000 µm fractions of SOC. The shift in δ13C signature is more in ICLS than in CC, suggesting that rotation with C3 legumes contributed to C sequestration and, therefore, climate-smart agriculture. The combination of on-farm research and isotopic technique can help to study deeply the effect of real farm practices on soil carbon derived from pasture.

In situ Raman spectroscopic measurement of the 13C/12C ratio in CO2: Experimental calibrations on the effects of fluid pressure, temperature and composition

The carbon isotope (δ13C) signature of CO2 within fluid inclusions is of significance to investigate because it can be used to decipher the carbon source of geological fluids. Raman spectroscopy has been applied to determine the δ13C of pure CO2. However, whether this approach can be applied to natural inclusions with complex compositions remains unknown. Here we present Raman spectra of CO2 ± N2 ± CH4 systems with known 13C/12C ratio (0.01–1.12) at temperatures (T) of 21 °C and 40 °C and at pressures (P) ranging from 0.5 to 50 MPa. Peak areas and peak heights of the 13CO2 (∼1370 cm−1) and 12CO2 (∼1285 cm−1) bands were determined to calculate the Raman spectroscopic quantification factors (F- and G-factor ratio). The results show that the quantification factors vary significantly with rising pressure in the low pressure range (e.g., <10 MPa), especially for pure CO2 system. Different fluid systems are characterized by pressure dependences. Specifically, both F- and G-factor ratios for CO2 fluid with a low 13C/12C ratio (e.g., 0.01) are different from that with a high 13C/12C ratio (e.g., 0.13) under the same T-P conditions. Fluid temperature does not result in significant variation in F- or G-factor ratios at the investigated temperatures. Based on these calibrations, we suggest that fluid pressure and composition (x) are prerequisites for Raman spectroscopic measurements of the 13C/12C ratio of CO2. However, the 13CO2 (∼1370 cm−1) band for CO2 from natural fluid inclusions is characterized by low Raman intensity, resulting in large errors in calculated peak area and peak height. Thus, accurate determination of the 13C/12C ratio of fluid inclusion CO2 is not feasible for inclusions with low CO2 density. Nevertheless, this method can be applied to investigate the carbon isotope fractionation in 13C labelled hydrothermal experiments, where CO2 with high a 13C/12C ratio is produced.

Organic matter composition and thermal stability influence greenhouse gases production in subtropical peatland under different vegetation types

Peatlands are a major carbon (C) sink globally. Organic matter quality influence greenhouse gases production. However, little is known about how organic matter from different vegetation types, influences C composition and resultant greenhouse gases production in subtropical peatland. Anoxic incubation experiments were conducted using two types of peats with different botanical origin to assess C composition, CO2 and CH4 production. First peat had cypress dominance and the second knotted spikerush and water lily (spike + lily). Solid-state CPMAS 13C NMR determined C chemical stability, MESTA determined C thermal stability, stable isotopes for C source and gas chromatograph for carbon dioxide (CO2) and methane (CH4). The results indicated dominance of autochthonous C as indicated by δ13C signatures. Low thermal stable C (LTSC) dominated in litter, FL (fermentation layer) and spike + lily sediment, high thermal stable C was dominant in cypress peat. O-alkyl C strongly correlated with LTSC whereas aromatic C correlated negatively with R400 (LTSC:total C ratio). Generally, O-alkyl decreased and alkyl increased along litter-FL-peat continuum. Spike + lily peat exhibited initial stage of decomposition. Indicated by increased alkyl C, aromatic C and aromatic:O-alkyl ratio with increasing peat depth. Also, exhibited 3 times more CH4 and CO2 production compared to cypress peat that dominantly exhibited second stage of decomposition. O-alkyl C exhibited positive relationship with CH4 (P = 0.012, r2 = 0.57) and CO2 (P = 0.047, r2 = 0.41) production whereas R400 related positively with CH4 (P = 0.05, r2 = 0.40). Organic matter thermal and chemical composition varied between the peat types and thermally and chemically labile C influenced CO2 and CH4 production.

Precipitation reconstruction since the last deglacial based on the stable carbon isotopic composition of a loess section in western Central Asia

The topography of the Tianshan Mountains and the Pamir Plateau strongly shapes the seasonality of precipitation in Central Asia (CA): cold-season (October-April) precipitation dominates western CA and warm-season (May-September) precipitation dominates eastern CA. The precipitation/moisture patterns between western and eastern CA are completely opposite at seasonal, decadal and centennial scale. However, the pattern contrasts for millennial or longer time scales remain unknown. In this study, we investigated the precipitation variations in western CA, as recorded in a 6.5-m loess section in southern Kazakhstan, which has accumulated since ~14.4 ka. According to the robust relationship between the surface soil organic matter δ13C and the climatic parameters, the δ13C signature is here considered as a precipitation proxy. The record reveals an overall decreasing precipitation before ~6.0 ka followed by an increasing trend afterward, being consistent with the previously reported precipitation records in western CA. The late-deglaciation precipitation in western CA is in phase with that in eastern CA at millennial scales, which are both driven by the North Atlantic Oscillation (NAO) and the Siberian High.

Atmospheric Black Carbon Loadings and Sources over Eastern Sub-Saharan Africa Are Governed by the Regional Savanna Fires.

Vast black carbon (BC) emissions from sub-Saharan Africa are perceived to warm the regional climate, impact rainfall patterns, and impair human respiratory health. However, the magnitudes of these perturbations are ill-constrained, largely due to limited ground-based observations and uncertainties in emissions from different sources. This paper reports multiyear concentrations of BC and other key PM2.5 aerosol constituents from the Rwanda Climate Observatory, serving as a regional receptor site. We find a strong seasonal cycle for all investigated chemical species, where the maxima coincide with large-scale upwind savanna fires. BC concentrations show notable interannual variability, with no clear long-term trend. The Δ14C and δ13C signatures of BC unambiguously show highly elevated biomass burning contributions, up to 93 ± 3%, with a clear and strong savanna burning imprint. We further observe a near-equal contribution from C3 and C4 plants, irrespective of air mass source region or season. In addition, the study provides improved relative emission factors of key aerosol components, organic carbon (OC), K+, and NO3-, in savanna-fires-influenced background atmosphere. Altogether, we report quantitative source constraints on Eastern Africa BC emissions, with implications for parameterization of satellite fire and bottom-up emission inventories as well as regional climate and chemical transport modeling.

Centennial-Scale Climatic Oscillations during the Dansgaard–Oeschger 14 Revealed by Stalagmite Isotopic Records from Shouyuangong Cave, Southern China

During the last glacial, Dansgaard–Oeschger (DO) events are mostly characterized by moderate and shorter fluctuations. Here, we present the three-year-resolution stalagmite isotopic record from Shouyuangong Cave (SYG), southern China, revealing a detailed history of Asian summer monsoon (ASM) and local environmental changes during the middle and late period of DO 14. During this period, the SYG1 δ18O is characterized by the persistence of centennial-scale oscillations. These centennial δ18O enrichment excursions are clearly mirrored in the δ13C signal. This correlation suggests that changes in soil CO2 production at this site are closely correlated with centennial-scale ASM variability. Furthermore, power spectrum analysis shows that δ18O and δ13C display the common periodicities consistent with solar activity cycles, implicating a control of solar activity on the ASM and soil humidity. Particularly, weak solar activity generally corresponds to weak ASM and a decline in soil CO2 production. One possible link between them is that external forcing controls the ASM intensity via the thermal contrast between the ocean and land. Subsequently, the balance of soil moisture co-varies with the hydrological responses. Finally, the soil CO2 production is further amplified by ecological effect.

Metasomatism in the Finero Phlogopite Peridotite: New insights from C and N concentrations and δ13C - δ11B signatures

The interconnection between element recycling and mantle metasomatism may provide powerful insights to unravel the mechanisms governing the transfer, partitioning and residence times of volatiles among the different Earth's reservoirs. In this study, we provide new constraints on the incorporation of C and N in the rock-forming minerals of the Finero Phlogopite Peridotite (FPP) from the Ivrea-Verbano Zone (Southern Alps, Italy), representing a natural laboratory to shed lights on the amounts of volatiles that may be fixed in a deeply metasomatized sub-continental lithospheric mantle (SCLM). Constraints on the relationships between metasomatic events and volatile element enrichment were given by in-situ LA-ICP-MS and micro-Raman investigations together with C (δ13C) and B (δ11B) isotopes.All rock-forming minerals (olivine, clinopyroxene, amphibole and phlogopite) show enrichments in C (270–690 ppm) and N (7–20 ppm) compared to depleted mantle values. The high volatile contents in clinopyroxene and in amphibole are associated with enrichment in incompatible elements (e.g., Li, B, Rb, Sr, Pb, Th, U) and high LaN/LuN ratios (up to 42.0) thus confirming that the metasomatic agent affecting the FPP derive form a hydrous melt with crustal affinity enriched in C and N. Micro-Raman investigations document the occurrence of graphite, carbonate and N2 inclusions, specifically in olivine and clinopyroxene, that are likely responsible for the high CN concentrations reported here. The δ13C signatures measured in mineral separates range from −12.6 to −22.7 ‰, suggesting an overprinting of the C mantle signature by a 12C-rich crustal metasomatic agent. High temperature decarbonation processes, simulated by heating the samples up to 900 °C, indicate that up to10 ppm of C can be residually stored in the SCLM, whereas N is completely released even at lower temperature. The LA-MC-ICP-MS in-situ δ11B signature of amphibole is −5.4 ± 4.1 ‰ (2σ, n = 18), whereas bulk δ11B of olivine and clinopyroxene is −5.51 ± 0.01 ‰ (2σ) and − 1.82 ± 0.06 ‰ (2σ), respectively. Modelling shows that residual slab melts plus variable amounts of 11B-rich serpentinite-derived fluids may account for these B isotope imprints. A subduction-related metasomatizing event during the FPP's evolution is thus proposed to explain the geochemical features documented in our study, in agreement with previous works. At global scale, our results suggest that the metasomatized SCLM might significantly contribute to the so-called hidden C reservoir invoked to match the global C mass balance calculations.

Estimating intra-seasonal photosynthetic discrimination and water use efficiency using δ13C of leaf sucrose in Scots pine.

Sucrose has a unique role in recording environmental and physiological signals during photosynthesis in its carbon isotope composition (δ13C) and transport of the signal to tree rings. Yet, instead of sucrose, total organic matter (TOM) or water-soluble carbohydrates (WSC) are typically analysed in studies that follow δ13C signals within trees. To study how the choice of organic material may bias the interpretation of δ13C records, we used mature field-grown Scots pine (Pinus sylvestris) to compare for the first time δ13C of different leaf carbon pools with δ13C of assimilates estimated by a chamber-Picarro system (δ13CA_Picarro), and a photosynthetic discrimination model (δ13CA_model). Compared with sucrose, the other tested carbon pools, such as TOM and WSC, poorly recorded the seasonal trends or absolute values of δ13CA_Picarro and δ13CA_model. Consequently, in comparison with the other carbon pools, sucrose δ13C was superior for reconstructing changes in intrinsic water use efficiency (iWUE), agreeing in both absolute values and intra-seasonal variations with iWUE estimated from gas exchange. Thus, deriving iWUE and environmental signals from δ13C of bulk organic matter can lead to misinterpretation. Our findings underscore the advantage of using sucrose δ13C to understand plant physiological responses in depth.

Unique distribution pattern and δ13C signature of des-A-triterpenoids from Lake Wuliangsu: Source and paleoenvironmental implications

des-A-triterpenoids have been widely recognized as indicators of terrestrial vascular angiosperms and microbial activities. However, recent studies also suggested complex sources for des-A-triterpenoids in lakes and peatlands, thus complicating their applications in paleoenvironmental reconstructions. Here we present the occurrences of aliphatic and aromatic des-A-triterpenoids from a ∼160-year sedimentary core in Lake Wuliangsu in the upper reaches of the Yellow River, China. In these sediments, des-A-triterpane was not detected, whereas di-unsaturated des-A-triterpenes are more abundant than mono-unsaturated des-A-triterpenes. The δ13C values of di-unsaturated des-A-triterpenes range from –23.0‰ to –17.6‰, with an average value of –21.0‰. Accordingly, aliphatic des-A-triterpenoids from Lake Wuliangsu show a unique distribution pattern and more positive δ13C signatures compared with those sourced from terrestrial vascular angiosperms. By comparing the concentrations and δ13C values of des-A-triterpenoids with n-alkanes and triterpenoids, we suggest that des-A-triterpenoids from Lake Wuliangsu sediments might be degraded from oleanenone, which was produced by submerged macrophytes. In this sense, aliphatic des-A-triterpenes in Lake Wuliangsu could represent a novel proxy for submerged macrophytes, which would be more precise than those of mid-chain n-alkanes, considering that mid-chain n-alkanes are usually from multiple sources. Our results also demonstrate the importance of strong aerobic bacteria activities and photodegradation for the formation of di-unsaturated des-A-triterpenes. The aromatization process of aliphatic des-A-triterpenes show contrasting variation characteristic with the formation of aliphatic des-A-triterpenes over the past ∼160 years, probably due to different rates (production vs consumption of di-unsaturated des-A-triterpenes) and prerequisites (aerobic vs anaerobic conditions) for these two synthesis pathways.

Last millennium hydroclimate and atmospheric circulation change in Northeast China: A dual δ13C and δ18O approach from a mountaintop Sphagnum bog

Northeast China receives most moisture through warm air masses from the western Pacific Ocean and some moisture from the Eurasian Continent predominantly through the westerlies. Changes in the contribution of these different moisture sources affect the amount and isotopic composition of precipitation, which would in turn influence peatland surface moisture and peat moss (Sphagnum) growth. Recently a dual δ13C and δ18O approach from peat-core archive has been used not only as a proxy for peatland moisture/wetness but also as a constraint for interpreting isotope in precipitation and moisture trajectories. Here we used the coupled δ13C and δ18O measurements of peat moss cellulose, along with macrofossil and other proxy data, from a well-dated peat core retrieved from a Sphagnum-dominated ombrotrophic (meteoric water-fed) bog in Northeast China to reconstruct regional climate and moisture sources of precipitation over the last millennium.Our results show no sign of extremely negative δ13C signals that would have been caused by the uptake of respired CO2 by peat moss for photosynthesis, thus we argue that the cellulose δ13C signatures document the peatland moisture conditions, owing to water-film effect. We found a positive correlation between δ13C and δ18O, suggesting that δ18O primarily reflects the δ18O signal in precipitation rather than evaporative 18O-enrichment, because the evaporative enrichment would result in a negative correlation between these isotopes as documented in modern process studies along the hummock-hollow moisture gradients. We propose that the positive δ13C-δ18O correlation is a general feature in regions that are influenced by both summer monsoon and the westerlies, as warm Pacific moisture that has high δ18O values also brings abundant precipitation, resulting in wet conditions that induce high δ13C values, and vice versa. The δ13C results show a decrease of ca. 6‰ from −23 to −29‰, with large-magnitude fluctuations, over the last 1000 years, suggesting a long-term drying trend. An abrupt decrease at 1370 CE of 4‰ in δ18O from >21‰ to ca. 17‰ represents the transition from the warm and wet Medieval Climate Anomaly (MCA) at 815–1370 CE to the cold and dry Little Ice Age (LIA) at 1370–1940 CE, reaching the lowest δ18O value of ca. 15‰ at around 1850 CE. The increase in δ18O to 19‰ after 1900 CE reflects post-LIA climate warming. Enhanced moisture transport from the western Pacific might have contributed to the warm and wet MCA. Three short intervals with pronounced low δ13C and δ18O values occurred at 1370–1450 CE, the 19th Century, and the 1990s, suggesting extreme dry periods with reduced Pacific moisture inputs. The driest period with consistently low δ13C value of < -25‰ (Suess effect-corrected value of −23‰) occurred after 1990 CE, with a corresponding increase in dry-adapted moss Polytrichum.Variability in the regional atmospheric circulation—the western Pacific subtropical high (WPSH)—might have explained the change in moisture sources. The westward extension of the WPSH—often corresponding with the El Niño-like conditions—would block the Pacific moisture from transporting to Northeast China. Our record, together with other paleo-records over monsoon-influenced regions in East Asia, shows synchronous but opposite shifts of summer rainfall anomalies in North or Northeast China and South China on decadal to centennial scales, substantiating a coherent atmospheric circulation pattern associated with WPSH and ENSO variability. We argue that there were major shifts in synoptic-scale atmospheric circulation and associated hydroclimate change during the MCA, LIA, and Current Warming Period in Northeast China.

Seasonal links between metabolites and traditional seagrass metrics in the seagrass Halophila ovalis in an estuarine system

Monitoring of seagrasses has mainly relied on traditional seagrass metrics (e.g., biomass), which deliver reliable information about mortality but are unable to inform about impacts on seagrass health at the very early stages of stress exposure. Metabolomics is a novel molecular technique which can be used for early stress-detection in plants and also for unravelling the underlying mechanisms of stress response. In the Swan-Canning Estuary, south-west Australia, the seagrass Halophila ovalis is impacted by seasonal changes in sediment-and nutrient-stress. To date, it is unknown how H. ovalis responds to these seasonal stressors on a molecular level. Here, we used a combined approach of traditional seagrass metrics and metabolomics to create a holistic picture of seasonal influences on seagrass condition. Leaf samples of H. ovalis were collected from six different locations in the Swan-Canning Estuary in both summer and spring. We detected strong differences in metabolite profiles and relative metabolite abundance between seasons, with growth- and/or development-related metabolites being up-regulated in spring and stress-related (secondary) metabolites being up-regulated in summer. Metabolites were mostly related to leaf δ13C signatures, a metric that has been previously associated with variation in light and pH in the Swan-Canning. We demonstrate that a holistic approach which includes metabolomics into ecological monitoring can help to improve our understanding of the mechanisms underlying molecular (stress) responses in seagrasses which is crucial knowledge for management and conservation measures locally and globally.

Links between individual performance, trace elements and stable isotopes in an endangered caribou population

Foraging is a key behaviour, and several aspects of foraging remain to be investigated in many wild species. Low energy gain or reduced protein, nutrient, and mineral intake may explain poor individual condition, low reproductive output, high mortality, and, in extreme cases, population declines. Our study explores how foraging ecology, diet composition, and nutritional status could influence individual performance in an endangered population of caribou (Rangifer tarandus caribou). We measured stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) as well as the concentration of 21 trace elements in hairs of 44 caribou (~ 50% of the population). Our results showed that the Atlantic-Gaspésie caribou population consumed mainly lichens, horsetails, deciduous shrubs, and deciduous trees. We found a correlation between diet (described using stable isotope ratios) and accumulation of trace elements in hair using a redundancy analysis, and we detected relationships between diet, trace elements and vital rates using logistic and Cox models. Pregnancy and calf survival probabilities were higher when the δ13C signature of female caribou was higher, and the adult survival probability was higher in caribou that had higher concentrations of zinc and sodium, and lower concentrations of cesium and manganese in their hair. Based on the correlation we found between nutrition and individual performance, our study suggests that nutrition may be an important factor to consider in the recovery of this endangered caribou population.

Flood-pulse and trophic position modulate mercury concentrations in fishes from an Amazon floodplain lake

Mercury (Hg) bioaccumulation can be influenced by biological characteristics (e.g., trophic position) and environmental changes (e.g., seasonal flood-pulse), as it can create site conditions conducive to methylation and alter the availability of food to biota. This study aimed to relate total mercury (THg) and methylmercury (MeHg) concentrations in fishes of an Amazonian lake (Catalão Lake) to their dietary changes during different hydrological seasons (rising-, high-, falling-, and low-water). Levels of THg, MeHg, and stable isotopes of nitrogen and carbon (δ15N and δ13C) were determined in the muscles of six fish species: Rhytiodus microlepis, Hemiodus sp., Triportheus albus, Anodus elongatus, Pellona flavipinnis and Acestrorhynchus falcirostris. Triportheusalbus, an omnivorous fish, showed a significant relationship between Hg concentrations and δ13C signatures (negative regression; THg: p = 0.0001 and MeHg: p = 0.0002), as well as between Hg and δ15N signatures (positive regression; THg: p = 0.003 and MeHg: p = 0.021), indicating that changes in feeding habits influenced the Hg concentrations in this species. The herbivorous R. microlepis presented the highest MeHg concentrations during the high-water season, reflecting Hg methylation in its diet (macrophyte roots) during flooded season. The piscivorous A. falcirostris had the lowest THg concentrations during this season because of lower prey availability. Slopes of the regressions between the Hg concentrations and δ15N values followed the sequence of rising- < high- < falling-water seasons (THg: 0.06 < 0.11< 0.15; MeHg: 0.07 < 0.10 < 0.17), indicating that the difference between the THg and MeHg concentrations observed for lower- and higher-trophic-level fish increased during the falling-water season, resulting in trophic biomagnification. The present study shows that feeding habit and the flood-pulse influence mercury concentrations in the muscle of fishes from Catalão Lake.

Olive pits as a high-resolution proxy archive of climate: Δ13C in modern and archaeological olive pits reflecting environmental conditions

Charred olive pits are frequently preserved in archaeological sites in Israel, from ca. 5000 BCE. As olive fruits grow during one season, the carbon comprising their pits reflects their year of growth, making charred olive pits found in situ ideal for radiocarbon dating of archaeological contexts. An additional aspect, up until now not explored, is utilizing the ratio between the stable carbon isotopes (δ13C) in these charred olive pits as a proxy for climate. Olive pits provide multiple advantages as a proxy, allowing for higher resolution of climate reconstruction, both spatially and temporally, reflecting the environment in which the olive trees were growing, and humans were living. Here we show firstly, an analysis of modern olive pits and assess the connection between pit cellulose δ13C and aridity index. Specifically, we identify the threshold Δ13C for olive trees under severe drought stress as below 15.5 ± 0.5‰. Next, as olive pits are usually found charred in archaeological contexts, we evaluated the effect of charring on the δ13C signal of the modern olive pits. Finally, we present Δ13C values of more than 500 charred olive pits from 51 archaeological sites in Israel, spanning ∼6000 years. Based on these values we have identified periods of arid conditions and wet conditions in the past.

Contrasting organic matter composition in pristine and eutrophicated mangroves revealed by fatty acids and stable isotopes (Rio de Janeiro, Brazil)

Mangrove sediments have a high capacity of carbon storage, as the result of larger organic matter (OM) inputs from mangrove trees (litter fall and fine roots production) than OM microbial degradation and export to coastal waters. Mangrove sediments also act as traps for suspended matter and particulate OM (POM) from surrounding water masses. Fatty acids (FAs) markers, δ13C and δ15N signatures were used here to characterize the OM composition in three mangroves located in three coastal embayments of the Rio de Janeiro state (Brazil) with increasing urbanization from a pristine mangrove M1 to a moderately impacted mangrove M2 and a highly impacted mangrove M3. In these mangroves, the δ15N signature of tree leaves and sediments increases with anthropogenic influence, consistent with a large-scale eutrophication gradient along the three regions. At mangrove M1, predominant OM inputs from mangrove trees are highlighted by high proportions of long-chain fatty acids, particularly in the inland station, where high organic carbon concentrations (126 ± 108 mg g−1) indicate limited sedimentation of mineral particles and high carbon storage capacities. The sedimentary OM of M3 mangrove was more labile as confirmed by the higher proportions of algal fatty acids, enriched δ13C signature and the C/N ratio 1.6 times lower (p < 0.001) than in the pristine mangrove M1. At the M2 mangrove site, high contribution of bacterial FAs (around 20%) to sedimentary OM and high proportion of poorly biodegradable saturated fatty acids suggest that bacteria degrade algal labile OM in surface sediments but do not mineralize the most refractory fraction of OM. At the eutrophic M3 site, our findings suggest that deposition of labile POM induced an increase of fungal biomass on the sediment, apparently enhancing the microbial loop, and potentially leading to mineralization of refractory OM and carbon losses through a priming effect.

Influence of riparian thinning on trophic pathways supporting stream food webs in forested watersheds

AbstractResource managers seek to thin second‐growth riparian forests to address multiple stream and riparian management objectives, including enhancing aquatic productivity via light‐mediated trophic pathways in watersheds of the Pacific Northwest (USA). However, such increases in aquatic productivity depend on complex food web dynamics that link riparian forests and streams. To evaluate how riparian forest thinning influences stream food webs, we conducted a replicated, manipulative field experiment in three northern California watersheds composed of second‐growth redwood forests and tracked responses across multiple trophic levels (periphyton, macroinvertebrates, amphibians, and fish) 1 year pre‐ and post‐treatment. Riparian thinning treatments increased light to the stream channel, yet we observed mixed responses by stream food webs. Thinning did not change stream periphyton biomass on natural substrates but increased periphyton accrual on ceramic tiles. Periphyton accrual appeared to be partially muted by top‐down effects from invertebrate scrapers, which were more abundant in thinned reaches. Prey in the diets of top predators—coastal giant salamanders (Dicamptodon tenebrosus) and coastal cutthroat trout (Oncorhynchus clarkii clarkii)—did not change in biomass, composition, or structure in response to thinning and instead varied more seasonally and between predators. Stable isotope analysis indicated that shifts in carbon (δ13C) signatures of stream periphyton associated with thinning were reflected to varying extents by primary consumers but did not propagate up to top predators. Top predator biomass responses varied between species, where salamander biomass remained unchanged, but cutthroat trout biomass increased slightly in thinned reaches. However, trout biomass responses were not supported by diets or isotopes and correlated weakly with changes in light associated with thinning, suggesting little evidence that responses could be attributed directly to changes in autotrophic pathways. Furthermore, we found no evidence that local trophic responses to thinning propagated into downstream reaches. Taken together, we observed that trophic pathways supporting stream food webs remained largely intact immediately after riparian thinning treatments. Collectively, these results suggest that riparian thinning does not necessarily enhance aquatic productivity in forested streams, indicating that contextual factors driving realized ecological responses should be accounted for when considering thinning as a restoration strategy for stream–riparian ecosystems.

Genesis of the Florida Canyon Nonsulfide Zn Ores (Northern Peru): New Insights Into the Supergene Mineralizing Events of the Bongará District

Abstract The Florida Canyon Zn deposit in the Bongará Province of northern Peru consists of sulfide and nonsulfide mineralizations within dolomitized strata of the Triassic Chambará Formation, a member of the Triassic-Jurassic Pucará Group. The nonsulfide mineralization, which represents one third of the total resource, formed by supergene alteration of Mississippi Valley-type sulfide bodies. The nonsulfide assemblages occur in stratabound or fault-related, discordant zones that mimic the shapes of the former sulfide zones. Two nonsulfide facies can be distinguished: facies 1 – red zinc ores, which are characterized by smithsonite, or hemimorphite-dominant bodies that formed by direct replacement of primary sulfide assemblages, and facies 2 – white zinc ores, which are characterized by masses of colloform smithsonite formed by replacement of wall rock. The facies are distinct in bulk chemical composition and stable isotope geochemistry. Facies 1 shows high concentrations of Zn, Pb, Fe, Ge, Mn, and As, whereas facies 2 shows only high Zn and Cd concentrations. Enrichments in Ge, which have been reported in other Zn deposits of the Bongará Province, are associated with hemimorphite, Fe hydroxides, and remnant sphalerite in facies 1. The δ13C and δ18O signatures of smithsonite in both facies suggest that meteoric waters infiltrating the precursor sulfide bodies were affected by kinetic fractionation and originated from multiple sources at different altitude.