Stable Carbon Isotope Values Research Articles

Growth pattern and turnover of carbon and nitrogen measured by stable isotope ratios in the hair of sika deer (Cervus nippon).

Hair is known to preserve diet history and other physiological information during its growth period and is often used in chemical analyses. However, the growth patterns and turnover of hair vary according to the animal species or habitat, so understanding these patterns in the target animal is necessary for interpreting the results of hair analyses. In this study, we aimed to elucidate the growth pattern and dietary information of winter coat hair in captive sika deer (Cervus nippon). Experiments involving hair-staining and shaving were conducted to elucidate the growth pattern of sika deer hair. A diet-switching experiment was conducted to ascertain what dietary information is reflected in the carbon and nitrogen stable isotope values of the deer winter coat. Hair samples collected from each body site (head, shoulder, back, and hip) were analyzed using an elemental analyser interfaced with an isotope-ratio mass spectrometer. The winter coat grows from early September to early November, and then stops after that. During the growth period of the winter coat, the hair of the shoulder and back grew at a constant rate. The carbon and nitrogen stable isotope values of hair reflected the deer's feeding history during hair growth, but there seemed to be a time lag in the hip hair. The results suggest that the guard hair of the shoulder is suitable for hair analysis in sika deer. The obtained information on growth patterns and isotopic change of hair from captive sika deer according to diet be useful for interpreting the results of future analyses using hair samples of wild deer.

Isotope values reveal “canopy effect” in deer territoriality and maize consumption for dogs from archaeological sites in Kentucky dating to the Middle Woodland through Late Fort Ancient time periods

This research analyzes stable carbon, nitrogen, and oxygen isotope values in tooth collagen and enamel to investigate foraging and territorial behavior in white-tailed deer (Odocoileus virginianus Zimmermann) and maize (Zea mays Linneaus) consumption in dogs (Canis familiaris Linneaus). The study analyzed 22 deer teeth from 13 archaeological sites in Kentucky covering a span of approximately 1,500 years of human occupation. The article presents evidence of foraging and territorial behavior in white-tailed deer, identified through the “canopy effect” observed in deer stable carbon isotope values in remains spanning from the Middle Woodland (200 BCE – CE 500) to Late Fort Ancient (CE 1400 – 1680) time periods in Kentucky. Additionally, teeth samples from nine dog and one wolf (Canis lupus Linneaus) were analyzed and indicate significant consumption of maize in seven of the dog samples. These specimens came from seven archaeological sites in Kentucky dating from the Early through Late Fort Ancient (CE 1400 – 1680) time periods. The study also contributes to the growing database of isotope studies in the Eastern Woodlands by presenting carbon and nitrogen isotope values on deer bone collagen from nine deer bone samples from three of the same archaeological sites dating to the Middle Woodland to Early Late Woodland.

Nutrient Shift in the Yucatan Basin during the late Early Miocene: Evidence from calcareous nannofossils and stable isotopes at ODP Leg 165 Site 998 Hole A

Paleoceanographic reconstructions in the Caribbean Sea during past climate transitions, namely the Late Oligocene to Early Miocene (up to the Miocene Climatic Optimum and Monterey Excursion) are crucial to understanding the effects of the Eastern Pacific interchange with the Atlantic Ocean. Studies of the planktonic domain in the Yucatan Basin during the Early Miocene are limited, with most Caribbean research focused on reconstructing the series of events that precede the final closure of the Isthmus of Panama in the Early Pliocene. Furthermore, paleoceanography of the Yucatan Basin is largely unrefined during this time, even though it is an important transition for ocean gateways, and development of Atlantic deepwater and Atlantic Meridional Overturning Current (AMOC), driving global ocean circulation. Here we conduct a relative percent abundance analysis of calcareous nannofossils and stable isotopes from bulk sediment of drill cores spanning the Upper Oligocene to Lower Miocene in the central Yucatan Basin, collected by the Ocean Drilling Program Leg 165 at Site 998 Hole A. Nannofossil assemblage data record a shift from a eutrophic to oligotrophic system ∼19.2–17.65 Ma. Eutrophic taxa (Reticulofenestra spp. and Cyclicargolithus floridanus) decline at ∼20.23 Ma, while oligotrophic taxa (discoasters and sphenoliths) increase as stable carbon isotope values decline. The palaeoecological turnover coincides with a possible restriction in the Central American Seaway (CAS) ∼20.7–21 Ma. Population dynamics of the Hole 998 A nannofossil assemblage track with global declines in C. floridanus relative abundance between ∼20.2 to ∼20.5 Ma, followed by a subsequent decrease in Reticulofenestra spp. These data suggest water mass stratification in the Yucatan Basin during the Early Miocene ∼19.2–17.65 Ma, likely due to restriction of the CAS.

Effects of pre-treatment, historical age, and sample characteristics on the stable isotope analyses of killer whale (Orcinus orca) bone.

Stable isotope analysis of bone provides insight into animal foraging and allows for ecological reconstructions over time, however pre-treatment is required to isolate collagen. Pre-treatments typically consist of demineralization to remove inorganic components and/or lipid extraction to remove fats, but these protocols can differentially affect stable carbon (δ13C) and nitrogen (δ15N) isotope values depending on the chemicals, tissues, and/or species involved. Species-specific methodologies create a standard for comparability across studies and enhance understanding of collagen isolation from modern cetacean bone. Elemental analyzers coupled to isotope ratio mass spectrometers were used to measure the δ13C and δ15N values of powdered killer whale (Orcinus orca) bone that was intact (control) or subjected to one of three experimental conditions: demineralized, lipid-extracted, and both demineralized and lipid-extracted. Additionally, C:N ratios were evaluated as a proxy for collagen purity. Lastly, correlations were examined between control C:N ratios vs. historical age and control C:N ratios vs. sample characteristics. No significant differences in the δ15N values were observed for any of the experimental protocols. However, the δ13C values were significantly increased by all three experimental protocols: demineralization, lipid extraction, and both treatments combined. The most influential protocol was both demineralization and lipid extraction. Measures of the C:N ratios were also significantly lowered by demineralization and both treatments combined, indicating the material was closer to pure collagen after the treatments. Collagen purity as indicated via C:N ratio was not correlated with historical age nor sample characteristics. If only the δ15N values from killer whale bone are of interest for analysis, no pre-treatment seems necessary. If the δ13C values are of interest, samples should be both demineralized and lipid-extracted. As historical age and specimen characteristics are not correlated with sample contamination, all samples can be treated equally.

Geochemical analysis of bituminous samples from the Pre-Pottery Neolithic B site of Nahal Efe (Northern Negev, Israel): Earliest evidence in the region and an example of alteration of the Dead Sea bitumen

Thirty-six bituminous samples from the Pre-Pottery Neolithic site of Nahal Efe (8000–7700 cal. BCE, Negev, Israel) were analysed to determine their origins. Most samples are mixtures of bitumen with minerals, predominantly quartz, calcite, dolomite and aragonite. The aragonite is from marine shells, which were crushed to be incorporated into the mixtures.Dead Sea bitumen was identified in all samples. The Nahal Efe geochemical data were compared to samples from Tell Yarmuth (2800–1100 BCE), Tall Dhiban (700–800 cal. BCE), Tel Gezer (1250–700 cal. BCE) and to floating asphalt blocks from the Dead Sea. The stable carbon isotope values of resins and asphaltenes of the Nahal Efe bitumens differ from those of the Dead Sea floating blocks, Tell Yarmuth, Tel Gezer and Tall Dhiban, apparently a consequence of diagenesis. Thus, δ13C values of asphaltenes may not always be a reliable representative of the stable carbon isotope composition of the unaltered source bitumen. Surprisingly, the sterane and terpane patterns of the Nahal Efe samples are not severely biodegraded and clearly indicate a Dead Sea bitumen source. No difference was recorded between mixtures and pure bitumen. Some changes have, however, been observed when using quantitative data on biomarkers. The shifts in δ13C values of resins and asphaltenes is not related to biodegradation but rather to oxidation of the Nahal Efe samples.This is the earliest and most complete evidence of Dead Sea bitumen exploitation and use, which included the preparation of different ‘recipes’, in the Negev and Sinai arid regions.

Further investigation into the impact of manuring on stable carbon (δ13C) and nitrogen isotope (δ15N) values in pulses: a four-year experiment examining Celtic bean (Vicia faba)

Plant stable carbon (δ13C) and nitrogen (δ15N) isotope values can be used to directly investigate crop husbandry practices such as manuring; a key variable in understanding the scale and intensity of past farming practices. We present new results from a four-year experiment examining the impact of manuring on the δ13C and δ15N values of a heritage cultivar of the broad or faba bean (Vicia faba), the ‘Celtic black broad bean’. This paper builds upon our previous pilot study (Treasure ER, Church MJ, Gröcke DR (2016) The influence of manuring on stable isotopes (δ13C and δ15N) in Celtic bean (Vicia faba L.): archaeobotanical and palaeodietary implications. Archaeol Anthropol 8:555–562. https://doi.org/10.1007/s12520-015-0243-6). Our results indicate that manuring increased δ15N values in beans, with a mean value of 0.5 ± 0.4‰ in control samples compared to a mean value of 2.1 ± 1.3‰ in the most intensively manured plots. It was not always possible to distinguish between an unmanured and manured crop on the basis of δ15N values, although manured crops consistently exhibited larger variation in δ15N. Bean δ13C values show no clear relationship with manuring, although large variability (> 3‰) was found within crops cultivated under the same conditions. Manuring also increased plant biomass production, seed-size and the bean per plant ratio. Overall, we suggest that high δ15N values (> 1.5‰) in archaeobotanical remains of pulses can be attributed to small-scale, intensive cultivation that is typical of gardens where manuring rates are very intensive.

Mercury concentrations in Seaside Sparrows and Marsh Rice Rats differ across the Mississippi River Estuary

Mercury (Hg) concentrations and their associated toxicological effects in terrestrial ecosystems of the Gulf of Mexico are largely unknown. Compounding this uncertainty, a large input of organic matter from the 2010 Deepwater Horizon oil spill may have altered Hg cycling and bioaccumulation dynamics. To test this idea, we quantified blood concentrations of total mercury (THg) in Seaside Sparrows (Ammospiza maritima) and Marsh Rice Rats (Oryzomys palustris) in marshes west and east of the Mississippi River in 2015 and 2016. We also tested for a difference in THg concentrations between oiled and non-oiled sites. To address the potential confounding effect of diet variation on Hg transfer, we used stable nitrogen (δ15N) and carbon (δ13C) isotope values as proxies of trophic position and the source of primary production, respectively. Our results revealed that five to six years after the spill, THg concentrations were not higher in sites oiled by the spill compared to non-oiled sites. In both species, THg was higher at sites east of the Mississippi River compared to control and oiled sites, located west. In Seaside Sparrows but not in Marsh Rice Rats, THg increased with δ15N values, suggesting Hg trophic biomagnification. Overall, even in sites with the most elevated THg, concentrations were generally low. In Seaside Sparrows, THg concentrations were also lower than previously reported in this and other closely related passerines, with only 7% of tested birds exceeding the lowest observed effect concentration associated with toxic effects across bird species (0.2 µg/g ww). The factors associated with geographic heterogeneity in Hg exposure remain uncertain. Clarification could inform risk assessment and future restoration and management actions in a region facing vast anthropogenic changes.

Mytilus galloprovincialis shell growth – Insights from shell geochemistry

Despite the wide geographic distribution of mussels and their importance in fisheries and aquaculture, understanding of temporal and spatial variations of their growth is still limited. This can be, at least partly, attributed to the lack of distinct growth lines in their shells. Our study uses geochemical properties of shells, particularly oxygen (δ18Oshell) and carbon (δ13Cshell) stable isotope values, to reconstruct mussel growth. Mytilus galloprovincialis specimens were collected from two of the most important bivalve aquaculture sites in the eastern Adriatic - Krka River estuary and Mali Ston Bay. The first site has variable environmental conditions, influenced mainly by the Krka River, resulting in a strong temperature and salinity gradient along the estuary. In contrast, Mali Ston Bay is a relatively shallow enclosed bay with more stable conditions. Samples for δ18Oshell and δ13Cshell analysis were acquired by manual microdrilling cross-sectioned shells from three similar sized shells from each site. In addition, analysis of elemental profiles (Mg/Ca, Sr/Ca, and Ba/Ca) in shells from the Krka River estuary was conducted using laser ablation ICPMS. Temperature and salinity values were obtained for each site through research and monitoring projects and used to calculate predicted δ18Oshell values. By aligning the measured δ18Oshell data along the predicted δ18Oshell curve, it was possible to reconstruct the timing and rate of seasonal shell growth. Results show that M. galloprovincialis shell deposition slows down and/or ceases during high temperature and low salinity periods. Specimens from the Krka River estuary had faster shell growth rates and were characterised by higher δ13Cshell values. Mg/Ca profiles of M. galloprovincialis specimens from the Krka River estuary, confirm growth periodicity data obtained by δ18O analysis. Ba/Ca peaks were also discussed by comparison with δ13C time-series and environmental data. Results have potential applications in fisheries studies as well as in palaeoecology and palaeoceanography research.

Primary to post-depositional microbial controls on the stable and clumped isotope record of shoreline sediments at Fayetteville Green Lake.

Lacustrine carbonates are a powerful archive of paleoenvironmental information but are susceptible to post-depositional alteration. Microbial metabolisms can drive such alteration by changing carbonate saturation insitu, thereby driving dissolution or precipitation. The net impact these microbial processes have on the primary δ18O, δ13C, and Δ47 values of lacustrine carbonate is not fully known. We studied the evolution of microbial community structure and the porewater and sediment geochemistry in the upper ~30 cm of sediment from two shoreline sites at Green Lake, Fayetteville, NY over 2 years of seasonal sampling. We linked seasonal and depth-based changes of porewater carbonate chemistry to microbial community composition, insitu carbon cycling (using δ13C values of carbonate, dissolved inorganic carbon (DIC), and organic matter), and dominant allochems and facies. We interpret that microbial processes are a dominant control on carbon cycling within the sediment, affecting porewater DIC, aqueous carbon chemistry, and carbonate carbon and clumped isotope geochemistry. Across all seasons and sites, microbial organic matter remineralization lowers the δ13C of the porewater DIC. Elevated carbonate saturation states in the sediment porewaters (Ω > 3) were attributed to microbes from groups capable of sulfate reduction, which were abundant in the sediment below 5 cm depth. The nearshore carbonate sediments at Green Lake are mainly composed of microbialite intraclasts/oncoids, charophytes, larger calcite crystals, and authigenic micrite-each with a different origin. Authigenic micrite is interpreted to have precipitated insitu from the supersaturated porewaters from microbial metabolism. The stable carbon isotope values (δ13Ccarb) and clumped isotope values (Δ47) of bulk carbonate sediments from the same depth horizons and site varied depending on both the sampling season and the specific location within a site, indicating localized (μm to mm) controls on carbon and clumped isotope values. Our results suggest that biological processes are a dominant control on carbon chemistry within the sedimentary subsurface of the shorelines of Green Lake, from actively forming microbialites to pore space organic matter remineralization and micrite authigenesis. A combination of biological activity, hydrologic balance, and allochem composition of the sediments set the stable carbon, oxygen, and clumped isotope signals preserved by the Green Lake carbonate sediments.

Land cover and space use influence coyote carnivory: evidence from stable-isotope analysis

For many species, the relationship between space use and diet composition is complex, with individuals adopting varying space use strategies such as territoriality to facilitate resource acquisition. Coyotes (Canis latrans) exhibit two disparate types of space use; defending mutually exclusive territories (residents) or moving nomadically across landscapes (transients). Resident coyotes have increased access to familiar food resources, thus improved foraging opportunities to compensate for the energetic costs of defending territories. Conversely, transients do not defend territories and are able to redirect energetic costs of territorial defense towards extensive movements in search of mates and breeding opportunities. These differences in space use attributed to different behavioral strategies likely influence foraging and ultimately diet composition, but these relationships have not been well studied. We investigated diet composition of resident and transient coyotes in the southeastern United States by pairing individual space use patterns with analysis of stable carbon (δ13C) and nitrogen (δ15N) isotope values to assess diet. During 2016–2017, we monitored 41 coyotes (26 residents, 15 transients) with GPS radio-collars along the Savannah River area in the southeastern United States. We observed a canopy effect on δ13C values and little anthropogenic food in coyote diets, suggesting 13C enrichment is likely more influenced by reduced canopy cover than consumption of human foods. We also observed other land cover effects, such as agricultural cover and road density, on δ15N values as well as reduced space used by coyotes, suggesting that cover types and localized, resident-like space use can influence the degree of carnivory in coyotes. Finally, diets and niche space did not differ between resident and transient coyotes despite differences observed in the proportional contribution of potential food sources to their diets. Although our stable isotope mixing models detected differences between the diets of resident and transient coyotes, both relied mostly on mammalian prey (52.8%, SD = 15.9 for residents, 42.0%, SD = 15.6 for transients). Resident coyotes consumed more game birds (21.3%, SD = 11.6 vs 13.7%, SD = 8.8) and less fruit (10.5%, SD = 6.9 vs 21.3%, SD = 10.7) and insects (7.2%, SD = 4.7 vs 14.3%, SD = 8.5) than did transients. Our findings indicate that coyote populations fall on a feeding continuum of omnivory to carnivory in which variability in feeding strategies is influenced by land cover characteristics and space use behaviors.

Isotopic study of lipids and collagen in bones from archaeological and modern ungulates for the study of paleodiets in Argentina

In this paper we carried out a sequential extraction of lipids and collagen and obtained carbon and nitrogen stable isotope values of archaeological and modern bone samples of native ungulates from the Argentine Patagonia (Lama guanicoe, Pudu puda, Hippocamelus bisulcus) and Northwest (Lama sp., Vicugna vicugna). Collagen and lipids are biomolecules with exceptional survival rates in archaeological bone matrixes and provide complementary information about diet. We studied 28 ungulate specimens and obtained bulk δ13C values (δ13Clip, δ13Ccoll) and δ15N values to evaluate protein diet, whole diet, and offsets between values from lipids and collagen (Δ13Clip-coll). Results showed greater variability in the offsets of the different ungulate species than previously reported for terrestrial herbivores. This variability could be attributed to differences in body mass, particular niche adaptations, seasonal metabolic stress, diet change, and/ or human-ungulate interactions in each case. This study sheds light on the potential of paired lipid-collagen stable isotope values for interpreting paleodiet dynamics and unraveling individual life histories.

Amino acid carbon isotope profiles provide insight into lability and origins of particulate organic matter

AbstractIdentifying the phytoplankton origin of particulate organic matter (POM) in the deep ocean is challenging due to the changing phytoplankton composition and varied extent of decomposition by heterotrophic bacteria and zooplankton. Here, we report vertical distributions of amino acid stable carbon isotope values (δ13C) measured in particles in the South China Sea. Carbon‐weighted amino acid δ13C values generally parallel bulk POM δ13C profiles with a positive offset from 2.4‰ in the surface water to 6.0‰ in deep. Accordingly, a lability model is introduced to describe the relative distribution and isotopic linkage of labile and refractory particulate organic carbon. Temporal changes of amino acid δ13C were observed during the microbial decomposition of two phytoplankton strains, the prokaryote cyanobacterium Synechococcus and the eukaryote diatom Thalassiosira weissflogii. Principal component analysis of individual amino acid δ13C values from the decomposing cells separate samples into two components, reflecting the influence of microbial decomposition and taxonomic differences, respectively. These two components were further applied to particles. A major contribution from decomposing phytoplankton to particles below the euphotic zone was observed, with more prokaryote organic matter in the basin and a larger contribution from eukaryotes at stations near the productive northern shelf. Our findings show the applicability of amino acid δ13C values in tracing the lability and phytoplankton origins of POM in samples with varied extents of decomposition in marine environments.

The intersection of diet, class, and sex during the Eastern Zhou (770–221 BCE): Bioarchaeological evidence from the Dahan cemetery, China

The Eastern Zhou (770–221 BCE) was an important period of social transformation in ancient China. The development of class- and gender-based stratification of this period had profound effects on human diet. We aim to examine the relationships among diet, class, and sex (as a proxy for gender) during this period through comparative investigations of noble individuals and sacrificial human companions. We analyzed the stable carbon and nitrogen isotope values of bone collagen of 61 human (26 nobles and 35 sacrificial companions) and 32 faunal samples from the Dahan (大韩) cemetery (an Eastern Zhou archaeological site). There are statistically significant class-based dietary differences, with the nobles consuming more socially valued foods (high protein food and millets) compared with sacrificial companions, which is also supported by paleopathological evidence. Sex-based differences were specific to class, with no significant dietary differences found in the nobles, whereas males may have had better diets than females in the lower classes. Our dietary analysis suggests that some sacrificial companions may have benefited from the resources of their noble masters, however, most sacrificial companions had a poorer diet. In addition, one noble individual possibly experienced social mobility in his lifetime, as shown by the discrepancy in his burial treatment and his long-term diet. This cemetery-wide study of dietary differences between nobles and sacrificial companions allows for novel insight into the intersection of class, gender, and diet during the Eastern Zhou period.

Temporal changes in the diet composition and trophic level of walleye pollock (Gadus chalcogrammus) inhabiting the middle-eastern coast of Korea

The influences of oceanographic changes on diet composition and trophic level for pollock (Gadus chalcogrammus) inhabiting the East Sea off the Korean coast were examined based on stomach content and stable isotope analyses during 2016 and 2017. The diets of pollock consisted mainly of benthic crustaceans (particularly carid shrimps and euphausiids) and cephalopods, with a predominance of teleosts in the diets of larger individuals in deeper habitats. In 2016, amphipods, carid shrimps and cephalopods featured strongly in pollock diets, and the contribution of amphipods decreased in the diets of larger individuals and deeper depths. In 2017, euphausiids dominated at shallower depths, whereas the contributions of carid shrimps and teleosts increased in deeper habitats. Body-size-related differences in carbon stable isotope (δ13C) values were present in both 2016 and 2017, but size-related differences in nitrogen stable isotope (δ15N) values were only observed in 2017. The increased contribution of euphausiids during 2017 resulted in a distinct decrease in the trophic level of pollock compared to co-occurring higher trophic level predators, which can be linked to changes in habitat water temperature. Combined stomach contents and isotopic analyses provide a more comprehensive understanding of how fish diets and trophic levels fluctuate with changes in the type and abundance of prey resources in response to environmental changes.

Dispersion and fate of methane emissions from cold seeps on Hikurangi Margin, New Zealand

The influence of cold seep methane on the surrounding benthos is well-documented but the fate of dissolved methane and its impact on water column biogeochemistry remains less understood. To address this, the distribution of dissolved methane was determined around three seeps on the south-east Hikurangi Margin, south-east of New Zealand, by combining data from discrete water column sampling and a towed methane sensor. Integrating this with bottom water current flow data in a dynamic Gerris model determined an annual methane flux of 3 x 105 kg at the main seep. This source was then applied in a Regional Ocean Modelling System (ROMS) simulation to visualize lateral transport of the dissolved methane plume, which dispersed over ∼100 km in bottom water within 1 year. Extrapolation of this approach to four other regional seeps identified a combined plume volume of 3,500 km3 and annual methane emission of 0.4–3.2 x 106 kg CH4 y-1. This suggests a regional methane flux of 1.1–10.9 x 107 kg CH4 y-1 for the entire Hikurangi Margin, which is lower than previous hydroacoustic estimates. Carbon stable isotope values in dissolved methane indicated that lateral mixing was the primary determinant of methane in bottom water, with potential methane oxidation rates orders of magnitude lower than the dilution rate. Calculations indicate that oxidation of the annual total methane emitted from the five seeps would not significantly alter bottom water dissolved carbon dioxide, oxygen or pH; however, superimposition of methane plumes from different seeps, which was evident in the ROMS simulation, may have localized impacts. These findings highlight the value of characterizing methane release from multiple seeps within a hydrodynamic model framework to determine the biogeochemical impact, climate feedbacks and connectivity of cold seeps on continental shelf margins.

Barrow Necropolis from the 3rd and 2nd Millennia BC in Western Ukraine. A Bayesian Modeling and Isotopic Study

AbstractThis article discusses the absolute chronology of burials from the 3rd and 2nd millennia BC discovered under the mounds of three barrows in the Kordyshiv cemetery in western Ukraine. Its aim is to create a chronological model of the burials by modeling 27 AMS 14C dates obtained from 21 individuals buried in single and collective graves. Dietary analysis of stable carbon (δ13C) and nitrogen (δ15N) isotope values are presented. The Bayesian modeling of the 14C dates from the three Kordyshiv barrows revealed the extremely important role of these monuments as long-term objects used for ritual purposes. At the end of the 3rd millennium BC, the epi-Corded Ware Culture (epi-CWC) community erected a mound over the central burial in Barrow 2, then interred the graves of three additional deceased. After several hundred years Barrow 2 was reused by Komarów Culture (KC) communities from the Middle Bronze Age (MBA) who interred their deceased in the existing mound. The oldest monument with MBA burials was Barrow 3, in which the dead were buried in a two-stage sequence before and after the mid-2nd millennium BC. The youngest dated grave was Burial 1 in Barrow 1, comprising a collective burial that was interred between 1400 and 1200 BC. The additional analyses of carbon and nitrogen isotopes show significant differences in the diet of epi-CWC individuals buried in Barrow 2 from the individuals representing the KC.

Geological characteristics and exploration breakthroughs of coal rock gas in Carboniferous Benxi Formation, Ordos Basin, NW China

To explore the geological characteristics and exploration potential of the Carboniferous Benxi Formation coal rock gas in the Ordos Basin, this paper presents a systematic research on the coal rock distribution, coal rock reservoirs, coal rock quality, and coal rock gas features, resources and enrichment. Coal rock gas is a high-quality resource distinct from coalbed methane, and it has unique features in terms of burial depth, gas source, reservoir, gas content, and carbon isotopic composition. The Benxi Formation coal rocks cover an area of 16×104 km², with thicknesses ranging from 2 m to 25 m, primarily consisting of bright and semi-bright coals with primitive structures and low volatile and ash contents, indicating a good coal quality. The medium-to-high rank coal rocks have the total organic carbon (TOC) content ranging from 33.49% to 86.11%, averaging 75.16%. They have a high degree of thermal evolution (Ro of 1.2%–2.8%), and a high gas-generating capacity. They also have high stable carbon isotopic values (δ13C1 of –37.6‰ to –16‰; δ13C2 of –21.7‰ to –14.3‰). Deep coal rocks develop matrix pores such as gas bubble pores, organic pores, and inorganic mineral pores, which, together with cleats and fractures, form good reservoir spaces. The coal rock reservoirs exhibit the porosity of 0.54%–10.67% (averaging 5.42%) and the permeability of (0.001–14.600)×10−3 μm2 (averaging 2.32×10−3 μm2). Vertically, there are five types of coal rock gas accumulation and dissipation combinations, among which the coal rock-mudstone gas accumulation combination and the coal rock-limestone gas accumulation combination are the most important, with good sealing conditions and high peak values of total hydrocarbon in gas logging. A model of coal rock gas accumulation has been constructed, which includes widespread distribution of medium-to-high rank coal rocks continually generating gas, matrix pores and cleats/fractures in coal rocks acting as large-scale reservoir spaces, tight cap rocks providing sealing, source-reservoir integration, and five types of efficient enrichment patterns (lateral pinchout complex, lenses, low-amplitude structures, nose-like structures, and lithologically self-sealing). According to the geological characteristics of coal rock gas, the Benxi Formation is divided into 8 plays, and the estimated coal rock gas resources with a buried depth of more than 2 000 m are more than 12.33×1012 m3. The above understandings guide the deployment of risk exploration. Two wells drilled accordingly obtained an industrial gas flow, driving the further deployment of exploratory and appraisal wells. Substantial breakthroughs have been achieved, with the possible reserves over a trillion cubic meters and the proved reserves over a hundred billion cubic meters, which is of great significance for the reserves increase and efficient development of natural gas in China.

Using stable carbon isotopes of lignin-derived methoxy to improve historical apportionments of particulate organic matter and sediment sources incorporating multiple Suess corrections

PurposeSoil erosion models are essential to improving sediment management strategies. Sediment source fingerprinting is used to help validate erosion models. Fingerprinting sediment sources with organic isotopic tracers faces challenges from aquatic sources and co-linearity. To address these complexities, integrating another land-use-specific tracer is essential. Suess corrections incorporating multiple mean-residence-times are necessary to accurately model historical sediment apportionments. In previous studies, compound specific isotopic tracers indicated forest as the dominant source. We hypothesize that there is an overestimation of forest contribution, attributed to the misclassification of particulate organic matter as forest.MethodsIn this study, we utilize stable carbon isotope (δ13C) values of fatty acids and the average chain length in combination with the δ13C values of lignin-derived methoxy groups as an additional tracer. We apply different Suess corrections to explore the effect of the changing atmospheric δ13CO2 values on sediment apportionment. The performance of the unmixing model is evaluated with 300 mathematical mixtures. To determine shifts in sediment sources throughout the last 130 years, particulate organic matter contributions are determined and removed to apportion sediment soil sources. We investigate the potential misclassification of forest contributions by merging particulate organic matter and forest sources to simulate tracers which are unable to discriminate.ResultsThe inclusion of δ13C values of lignin methoxy groups and the alkane average chain length as additional tracers successfully removed tracer co-linearity. Additionally, we used an updated concentration dependent point in polygon test to identify sediment with increased potential for incorrect source apportionments. Changes in the dominant sediment sources over time (Forest: pre-1990, Pasture: 1910–1940, Arable: post 1940) highlight the effect of policy-induced land-use changes. Additionally, the inability to discriminate particulate organic matter and forest sources was revealed to cause a 37% overestimation of forest contributions from 1944 to 1990.ConclusionUsing δ13C values of lignin methoxy groups as an additional tracer, we identified critical points in the 130-year sediment history of Lake Baldegg. Furthermore, we highlight the importance of incorporating multiple Suess effects. Through mathematical mixtures, we assessed the confidence that should accompany apportionment estimates. While merging forest and particulate organic matter sources did not result in forest as the dominant source over the last 130 years, separating these sources resulted in more accurate apportionment. These insights offer valuable information to enhance the accuracy of sediment fingerprinting, which can then be used to assist soil erosion models employed for sediment mitigation policies.

A Pilot Study on Bioaccumulation and Tissue Distribution of Mercury in Barn Swallow (Hirundo rustica).

Although extensive research has been carried out on the occurrence of mercury (Hg) in biota, bioaccumulation and tissue distribution of Hg in songbirds have not been well characterized. In the present study, Hg was investigated in insects and barn swallows (Hirundo rustica) to explore the bioaccumulation characteristics of Hg. Hg in swallow feathers and tissues including muscle, liver, and bone was investigated to determine the tissue distribution of Hg. The concentrations of Hg were 1.39 ± 1.01 μg/g, 0.33 ± 0.09 μg/g, 0.47 ± 0.10 μg/g, and 0.23 ± 0.09 μg/g in feather, muscle, liver, and bone samples, respectively. The trophic magnification factor of Hg in swallows and insects was higher than 1. However, the Hg concentrations in swallow feathers were not significantly correlated with stable isotope values of carbon or nitrogen, which implies the complex food sources and exposure processes of Hg for swallows. Feathers had significantly higher concentrations of Hg than liver, muscle, and bone samples (p < 0.01 for all comparisons). Feather, muscle, bone, and other organs had fractions of 64.4 ± 11.9%, 6.07 ± 2.06%, 20.0 ± 8.19%, and 9.56 ± 2.96% in total body burden of Hg in swallows. Hg in feathers contributed more than half of Hg in the whole body for most swallow individuals. Swallows may efficiently eliminate Hg by molting, and the excretion flux of Hg and other contaminants via molting deserves more investigation.

Preserved particulate organic carbon is likely derived from the subsurface sulfidic photic zone of the Proterozoic Ocean: evidence from a modern, oxygen-deficient lake.

Biological processes in the Proterozoic Ocean are often inferred from modern oxygen-deficient environments (MODEs) or from stable isotopes in preserved sediment. To date, few MODE studies have simultaneously quantified carbon fixation genes and attendant stable isotopic signatures. Consequently, how carbon isotope patterns reflect these pathways has not been thoroughly vetted. Addressing this, we profiled planktonic productivity and quantified carbon fixation pathway genes and associated organic carbon isotope values (δ13 CPOC ) of size-fractionated (0.2-2.7 and >2.7 μm) particulate matter from meromictic Fayetteville Green Lake, NY, USA. The high-O2 Calvin-Benson-Bassham (CBB) gene (cbbL) was most abundant in the <2.7 μm size fraction in shallow oxic and deep hypoxic waters, corresponding with cyanobacterial and eukaryote algal populations. The low-O2 CBB gene (cbbM) was most abundant near the lower oxycline boundary in the larger size fraction, coincident with purple sulfur bacteria populations. The reverse citric acid cycle gene (aclB) was equally abundant in both size fractions in the deepest photic zone, coinciding with green sulfur bacteria populations. Methane coenzyme reductase A (mcrA), of anaerobic methane cyclers, was most abundant at the lower oxycline boundary in both size fractions, coinciding with Methanoregula populations. δ13 CPOC values overlapped with the high-O2 CBB fixation range except for two negative excursions near the lower oxycline boundary, likely reflecting assimilation of isotopically-depleted groundwater-derived carbon by autotrophs and sulfate-reducers. Throughout aphotic waters, δ13 CPOC values of the large size fraction became 13 C-enriched, likely reflecting abundant purple sulfur bacterial aggregates. Eukaryote algae- or cyanobacteria-like isotopic signatures corresponded with increases in cbbL, cbbM, and aclB, and enrichment of exopolymer-rich prokaryotic photoautotrophs aggregates. Results suggest that δ13 CPOC values of preserved sediments from areas of the Proterozoic Ocean with sulfidic photic zones may reflect a mixture of alternate carbon-fixing populations exported from the deep photic zone, challenging the paradigm that sedimentary stable carbon isotope values predominantly reflect oxygenic photosynthesis from surface waters.