Carbon Isotope Patterns Research Articles

Millennial-scale sedimentary evolution of carbonate platforms during the Permian–Triassic boundary hyperthermal event

The millennial-scale response of shallow-water carbonate platforms to the climatic upheaval at the Permian–Triassic boundary (PTB) remains unclear. This study presents three carbonate platform sections across the Permian–Triassic (P–T) boundary in South China and the Lhasa terrane. A total of 14 types of carbonate microfacies were identified, which show that the Liangfengya and Taiping sections in South China were deposited in an inner ramp, and the Wenbudangsang section on the Lhasa terrane was deposited in an outer ramp. Bulk carbonate carbon isotope patterns through the sections are generally characterized by negative excursions (−2.2 to −3.5‰) during the PTB hyperthermal event. These excursions can be divided into four phases (NC1 to NC4), with NC1 before the negative carbon isotope excursion (NCIE) event, NC2 during the initiation phase of the NCIE, NC3 during the body of the NCIE, and the NC4 marking the recovery stage of the NCIE. The pattern of sedimentary changes in each section through the PTB hyperthermal event, and the relationship between these changes and the carbon isotope stages, was established. In the studied sections, the onset of the NCIEs (NC2 stage) preceded evidence for a carbonate production crisis, with the occurrence of anachronistic facies developed after this crisis but prior to the NC3 stage. In detail, our data show that the carbonate production crisis occurred 11 kyr after the onset of the NCIE, and 47 kyr before the first Permian–Triassic mass extinction (PTME), and that the carbonate production crisis may have been closely related to the environmental stresses associated with greenhouse gas emission from the Siberian Traps Large Igneous Province (STLIP).

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.

Using carbon and oxygen isotopes for global correlation in the Early Triassic Lower Mahil Formation, North Oman, despite potentially misleading diagenetic effect

The study probes into the carbon isotope curves of the Lower Triassic Mahil Formation in two sections situated in the Northern Oman Mountains. The primary objective of the research was to understand the relationship between facies and isotopes, involving the analysis of 174 micrite samples for oxygen and carbon isotopes. Strict measures were implemented during sample selection to mitigate potential influences such as cracks or weathering.The results unveiled diverse δ13C values within the same facies, indicating inconsistencies in carbon isotope trends. Intriguingly, despite notable diagenetic alterations, particularly in the Saiq Plateau section, the Lower Mahil Formation retained carbon isotope patterns with minimal diagenetic impact. However, a note of caution is warranted in the widespread application of these findings, as utilizing whole rock data for carbon isotope analysis may introduce uncertainties.Despite potential diagenetic effects, the carbon isotope records of the Lower Mahil Formation remain valuable for comprehending patterns associated with KS1, facilitating comparisons between local and regional carbon isotope signatures. This research contributes significantly to establishing correlations between outcrop and subsurface data, offering valuable insights into variations in Lower Triassic carbon isotopes.

Tissue-specific carbon isotope patterns of amino acids in southern sea otters.

The measurement of stable isotope values of individual compounds, such as amino acids (AAs), has become a powerful tool in animal ecology and ecophysiology. As with any emerging technique, questions remain regarding thecapabilities and limitations of this approach, including how metabolism and tissue synthesis impact the isotopic values of individual AAs and subsequent multivariate patterns. We measured carbon isotope (δ13C) values of essential (AAESS) and nonessential (AANESS) AAs in bone collagen, whisker, muscle, and liver from ten southern sea otters (Enhydra lutris nereis) thatstranded in Monterey Bay, California. Sea otters in this population exhibit high degrees of individual dietary specialization, making this an excellent dataset to explore differences in AA δ13C values among tissues in a wild population. We found the δ13C values of the AANESS glutamic acid, proline, serine, andglycine and the AAESS threonine differed significantly among tissues, indicating possible isotopic discrimination during tissue synthesis. Threonine δ13C values were higher in liver relative to bone collagen and muscle, which may indicate catabolism of threonine for gluconeogenesis, an interpretation further supported by correlations between the δ13C values of threonine and its gluconeogenic products glycine and serine in liver. This intraindividual isotopic variation yielded different ecological interpretations among tissues; for 6/10 of the sea otter individuals analyzed, at least one tissue indicated reliance on a different primary producer source than the other tissues. Our results highlight the importance of gluconeogenesis in a carnivorous marine mammal and indicate that metabolic processes influence AAESS and AANESS δ13C values and multivariate AA δ13C patterns.

Stable carbon isotopic composition of amino sugars in heterotrophic bacteria and phytoplankton: Implications for assessment of marine organic matter degradation

AbstractCompound‐specific isotope analysis has opened up a new realm for resolving the sources and transformation processes of marine organic matter. However, the stable carbon isotope patterns of amino sugars remain unknown. We examined δ13C of amino sugars in marine phytoplankton and heterotrophic bacteria, and the variations in amino sugar δ13C during 66‐d planktonic organic matter degradation experiments, to investigate the metabolic sources and transformations of amino sugars by bacterial reworking. The δ13C values of glucosamine (GlcN) and galactosamine (GalN) were comparable in heterotrophic bacteria (difference Δδ13CGlcN–GalN = 0.4–4.0‰) but pronouncedly different in phytoplankton (Δδ13CGlcN–GalN = 4.3–16.6‰), suggesting similar synthesis pathways of GlcN and GalN in bacteria that differed from phytoplankton. Compared to GlcN and GalN, bacteria preferentially use isotopically light organic compounds for muramic acid (MurA) synthesis. During simulated microbial degradation of organic matter, the δ13C difference between GlcN and GalN decreased from 5.8‰ on the initial day to 1‰ at a late stage in the experiment, but the difference between GlcN and MurA remained at 5.3‰. This difference is consistent with the pattern in cultured phytoplankton (average Δδ13CGlcN–GalN = 5.9‰ ± 1.4‰) and heterotrophic bacteria (average Δδ13CGlcN–MurA = 4.6‰ ± 3.4‰), indicating enhanced bacterial resynthesis as degradation proceeded. Based on the difference in δ13C among GlcN, GalN, and MurA, we propose a novel index of variation in amino sugar δ13C, representing amino sugar resynthesis, to describe the diagenetic state of organic matter. Together, these findings suggest that amino sugar δ13C can be used as a new tool to track heterotrophic processes of marine organic matter.

Sources of Hydrocarbon Gases in the Mud Volcano Kedr, Southern Basin of Lake Baikal: Results of Experimental Investigations

Outcrops of the Oligocene-Pliocene coal-bearing Tankhoi suite are traced along the southern shore of Lake Baikal and submerge under its Southern Basin, in which several hydrate-bearing zones of focused discharge of hydrocarbon fluids have been found. To test the hypothesis that coals of the Tankhoi Suite can be sources of hydrocarbon gases in these zones, we collected coal samples from the Shakhterskaya Gorka outcrop. The experiment on gas generation from the selected samples was carried out in a special autoclave at a temperature of 90°C for eight months. This paper presents the results of this study, which confirm the important role of gas generation processes from coals in the formation of fluids in the Kedr mud volcano. Further migration of gases was accompanied by biodegradation and the formation of secondary microbial methane due to CO2 reduction. This was one of the reasons for the observed carbon isotopic pattern in methane (heavier than ‒50‰ VPDB) and carbon dioxide (positive values) taken from near-surface sediments and hydrates of the Kedr mud volcano, as well as for the significant enrichment of authigenic siderites in the heavy 13C isotope.

Did sea level change drive carbon isotopic trends in the Madison Shelf? Sequence stratigraphy and carbon isotopes in the Mississippian Lodgepole Formation of southwest Montana

The Lower Mississippian Lodgepole Formation of Montana and Wyoming records one of the largest positive carbon isotopic excursions of the Phanerozoic. This globally recognized up to 7‰ increase in δ13Ccarb values occurs across the North American Kinderhookian-Osagean boundary (referred to as the KO excursion). It has been argued to reflect significant organic carbon burial, possibly linked to the onset of the Late Paleozoic Ice Age. Previously proposed correlations between carbon isotopic patterns and the sequence stratigraphic framework within these strata suggests that changes in sea level could have played a significant role in the expression and/or magnitude of the KO excursion in the Madison Shelf. This study explores the relationship between carbon isotopic values and sea level change at multiple scales. To accomplish this, we provide a comprehensive overview of the sedimentological and stratigraphic framework and address uncertainty about the number of sequences in the Lodgepole Formation. Our results support a three-sequence model for the Lodgepole Formation. Based on the number of sequences and the placement of sequence stratigraphic surfaces, we see little evidence of statistically significant correlation between carbon isotopic trends and the sequence stratigraphic framework. We argue that sea level change was not the primary driving mechanism for carbon isotopic trends in the Madison Shelf, nor the KO excursion. Instead, we support models that invoke global ocean anoxia and/or destabilization of the global carbon cycle due to land plants.

Control of hydrologic conditions and vegetation composition on carbon dynamics characterized by 13C enrichment in a dune-meadow cascade ecosystem in a semi-arid region

The variation of 13C enrichment (Δ13C and Δδ13C) is an effective indicator of the spatiotemporal dynamics of carbon stock. However, based on 13C enrichment, the effects of global climate change, land use types and historical vegetation succession on carbon dynamics have been found to be equivocal. Taking semi-mobile dune (SD) and meadow wetland (MW) ecosystems in the Horqin Sandy Land as examples, this study examined the stable carbon isotope ratios (δ13C) during the growing seasons in 2019 and 2020, and determined the factors controlling the continuum δ13C. The results revealed that throughout the carbon migration process, under different physiological mechanisms of carbon assimilation, distribution, and respiration, the seasonal variation of carbon isotope patterns exhibited significant differences in the air-plant-soil continuum of dune and meadow ecosystems. The MW with long-term stable vegetation coverage had higher soil carbon turnover than that in SD. In SD, both long-term and short-term restoration-accelerated soil carbon turnover. The effect of soil moisture (Ms) on Δδ13C (the surface soil δ13C minus leaf δ13C) will exceed that of air temperature in SD and MW. In MW, field capacity (FC) was the decisive indicator of various sources of Ms (rainfall, groundwater) affecting 13C enrichment variation. Δ13C (the discrimination of leaf carbon isotope) exerted a positive effect on Δδ13C only when Ms at 0–20 cm < FC, indicating the variable effect of photosynthesis on soil respiration throughout the growing seasons. Moreover, vegetation composition can also affect the extent to which soil respiration responds to photosynthesis.

Sustained mid-Pliocene warmth led to deep water formation in the North Pacific

Geologic intervals of sustained warmth such as the mid-Pliocene Warm Period can inform our understanding of future climate change, including the long-term consequences of oceanic uptake of anthropogenic carbon. Here we generate carbon isotope records and synthesize existing records to reconstruct the position of water masses and determine circulation patterns in the deep Pacific Ocean. We show that the mid-depth carbon isotope gradient in the North Pacific was reversed during the mid-Pliocene compared with today, which implies water flowed from north to south and deep water probably formed in the subarctic North Pacific Deep Water. An isotopically enabled climate model that simulates this North Pacific Deep Water reproduces a similar carbon isotope pattern. Modelled levels of dissolved inorganic carbon content in the North Pacific decrease slightly, although the amount of carbon stored in the ocean actually increases by 1.6% relative to modern due to an increase in dissolved inorganic carbon in the surface ocean. Although the modelled Pliocene ocean maintains a carbon budget similar to the present, the change in deep ocean circulation configuration causes pronounced downstream changes in biogeochemistry. Marine carbon isotope patterns point to substantial deep water formation in the North Pacific during the mid-Pliocene Warm Period, according to a synthesis of carbon isotope records and isotope-enabled climate modelling.

Stable carbon isotopic characterization of rice vinegar protein as an intrinsic reference for discriminating the authenticity of brewed rice vinegar.

Rice vinegar plays an important role in daily life. However, some unscrupulous manufacturers may deliberately add synthetic acetic acid in vinegar products to reduce fermentation time and save production costs. To protect the rights and health of consumers, vinegar authenticity must be controlled. The rice vinegar protein was used as an intrinsic reference and its stable carbon isotope ratio (δ13Cprotein) was analyzed by elemental analyzer-isotope ratio mass spectrometry. The stable carbon isotope ratio difference between the acetic acid and the rice vinegar protein (Δδ13Cacetic acid-protein) was calculated to evaluate vinegar authenticity. Sixteen rice vinegar samples were analyzed and a stable carbon isotopic pattern of rice vinegar was established by the 95% confidence interval for Δδ13Cacetic acid-protein (0.27‰-2.10‰). An acetic acid adulteration curve of Δδ13Cacetic acid-protein was also assumed according to the data from rice vinegar samples, and its validity was confirmed by rice vinegar deliberately blended with acetic acid at different ratios (25, 50, and 75%). The Δδ13Cacetic acid-protein values of the adulterated vinegars decreased with increasing amounts blended acetic acid, but the δ13Cprotein values did not, showing that rice vinegar protein could be used as an intrinsic reference for identifying the adulterated rice vinegar. The rice vinegar adulterated with acetic acid at higher than approximately 10% could be detected.

Geochemical characteristics, origin and carbon isotope reversal of the presalt natural gas in the Lower Paleozoic Ordovician carbonates, Ordos Basin, China

The origin and potential source of the presalt natural gas in the Lower Paleozoic Ordovician carbonates within the Ordos Basin, China, is heavily debated, and the causes of carbon isotope reversal are currently unclear. This study analyzes the source and origin of the presalt natural gas and determines the reasons for carbon isotope reversal. The results show that the nonhydrocarbons contain CO2, H2S, and N2 and some gas samples have high H2S contents of 9.02%–23.58%. The dryness coefficient (C1/C1+) of 91.06%–99.99% (ave. 98.34%) suggests that the presalt gas is mainly a dry gas with some wet gas and that it originates from a high-to over-mature source. However, the results show that the presalt natural gas is primarily a wet-gas-cracking gas, rather than a kerogen-cracking gas, with a certain amount of coal-type gas mixing and it mainly originated from oil-prone marine carbonate source rocks rather than the Permian–Carboniferous coal measures. The gas has different types of carbon isotope reversal patterns, and the δ13C2 values become negative at Roequ > 1.5%. The mixing between the oil-cracking and wet-gas-cracking gas at Roequ > 1.5% results in carbon isotope reversal (δ13C1 > δ13C2), rather than Rayleigh and migration fractionation. The occurrence of thermochemical sulfate reduction (TSR) is supported by the high abundance of H2S in the presalt gas, reservoir bitumen in dissolved pores, secondary calcite with negative δ13Ccarbonate of −21.1‰ to −9.7‰, and diagenetic cubic pyrite. It is evident that the heavy δ13C2 values (greater than −28‰) and the carbon isotope reversal of δ13C2 > δ13C3 of the presalt natural gas at Roequ < 1.5% are related to TSR. This study also establishes a new model of the carbon isotope reversal of the natural gas, which is primarily controlled by its thermal maturity and TSR. Six carbon isotope patterns can be well explained and are supported by real gas samples from the presalt strata, and two types of carbon isotope reversal are predicted.

Habitats in the Pre-Taghanic (Givetian, Middle Devonian) muddy carbonate ramp at Miłoszów (Holy Cross Mountains, Poland): geochemical and microfacies evidence

The well-known fossiliferous and lithologically variable Middle Devonian Shaly-Calcareous Skały Formation in the Łysogóry Region (northern part of the Holy Cross Mountains, central Poland) was studied for the first time in terms of elemental geochemistry, carbon isotope stratigraphy and limestone microfacies. Three Lower to Middle Givetian marly-limestone successions, exposed at Miłoszów, represent middle to outer facies belts of the vast carbonate ramp, characterized by very rich epifaunal and infaunal benthic life in muddy, oxic, eutrophic, and photic zone habitats. Brachiopods and occasionally corals (in mesophotic association), erect branching bryozoans, and tiny crinoids played a leading role among flourishing sessile suspension-feeders. High-energy storm events, possibly even a tsunami, during the brief Early Givetian time strengthened a prolific carbonate ooze delivery system from shallow ramp areas, including restricted back-ramp lagoons and a variety of organic buildups, populated by corals and stromatoporoids. The ecologically mixed skeletal grain association is characterized by the rich occurrence of a typical lagoonal biota, calcispheres and amphiporoids. The effective carbonate factory declined stepwise regionally during the Middle Givetian because of an intermittent progradation of the deltaic system of the Świętomarz Beds, linked with climate cooling and the activation of block movements. The regional carbonate crisis resulted in the demise of diverse benthic life, including the prolific calcified microbiota. The higher Skały Formation succession, deposited between the important Kačák and Taghanic bioevents, is noticeable for a background carbon-isotope pattern in carbonate and organic matter signatures, with the baseline δ 13 C carb values between 1‰ and 2‰. The microfacies and chemostratigraphic data confirm that at least the lower pumilio bioevent was not recorded in the Łysogóry Region.

Origin of the Xitieshan Pb-Zn deposit, Qinghai, China: Evidence from petrography and S-C-O-Sr isotope geochemistry

The Xitieshan Pb-Zn deposit in the North Qaidam orogenic belt, contains a geologic resource of 64 million tons grading 4.86 percent Zn and 4.16 percent Pb. The mineralized zones are hosted by the Tanjianshan Group, a metamorphosed succession of volcanic-sedimentary rocks in a Middle to Late Ordovician back-arc basin. Lower greenschist to middle amphibolite facies metamorphism and deformation of the original Xitieshan Pb-Zn ores and host rocks resulted in zones hosted in marble and schist. Sulfides in the marble consist of pyrite, sphalerite, galena, and marcasite with accessory chalcopyrite with undeformed textures that reflect the original carbonate replacement mineralization. Pyrrhotite, pyrite, sphalerite, and galena are the major sulfides in the schist-hosted ores, which occur as laminated sulfide layers that pinch, swell, and conform to the foliation of the schist. The schist-hosted mineralization occurs as a remobilized paragenetic assemblage that reflects the recrystallization and physical migration of the original sulfides across the brittle-ductile boundaries of these minerals during dynamic metamorphism. The sulfur isotopic compositions of ore-stage sulfides cluster around values of −1‰ to +5‰, consistent with sulfur derived from leaching volcanic rocks in the host sequence, or magmatic-related fluids. Carbon, oxygen, and strontium isotope patterns of the altered marble (δ13C = −3.8 to −1.5‰, δ18O = 8.7 to 12.2‰, and 87Sr/86Sr = 0.713092 to 0.713503) indicate extensive isotopic exchange with hydrothermal fluids. Gangue minerals, including ankerite and siderite, intergrown with sulfides at Xitieshan have C, O, and Sr isotopic compositions (δ13C = −1 to +1.7‰, δ18O = 2.3 to 7.8‰, and 87Sr/86Sr = 0.715707 to 0.722918) and textures indicative of replacement reactions between an originally marine carbonate rock and magmatic-related hydrothermal fluids. Considering the Xitieshan ore fluids replaced carbonate in a volcanoclastic sequence together with the similarities of host rocks, mineralogy, alterations, and sulfur isotope composition, the most likely genetic model for the deposit is an intrusion-related carbonate replacement deposit that underwent subsequent metamorphism and deformation.

Source rock potential, crude oil characteristics and oil-to-source rock correlation in a Central Paratethys sub-basin, the Hungarian Palaeogene Basin (Pannonian basin)

Eocene and Lower Oligocene rocks are potential source rocks for crude oil accumulations in the Hungarian Palaeogene Basin. To enhance the understanding of the hydrocarbon system, this study (i) assesses the petroleum potential of Palaeogene formations, (ii) characterises the source rock facies of the accumulated oils, and (iii) provides an oil-to-source correlation. Rock-Eval data of samples from three boreholes (W–1, W–9 and W–12) show that most Palaeogene formations are mature at depths exceeding 2.1–2.5 km. The coal-bearing Kosd Formation includes good to excellent gas- (and oil-) prone source rocks. The overlying Buda Marl Formation is typically organic matter-lean but contains oil-prone rocks with up to 2.3 wt% TOC and a fair petroleum potential in borehole W–9. The Tard Clay Formation in W–12 reaches up to 1.9 wt% TOC and shows HI values up to 440 mg HC/g TOC, characterising the deposits as good petroleum source rocks. Based on low TOC contents, the Kiscell Clay Formation is not considered a source rock. Molecular parameters of 12 crude oil samples indicate a shaly source rock deposited in a marine/brackish environment. Salinity stratification, causing the development of oxygen-depleted conditions, is likely. The organic matter is dominated by aquatic biomass, including algae, dinoflagellates and chemoautotrophic bacteria. Minor angiosperm-dominated organic matter was transported into the basin from the shoreline. Specific V-shaped compound-specific carbon isotope patterns of n-alkanes observed in crude oils and extracts from the Tard Clay prove the dominant source rock. Minor differences between biomarker ratios are related to vertical and lateral facies variations within the Tard Clay Formation. The accumulated oils are slightly more mature than the Tard Clay in borehole W–12.

Root Endophytic Fungal Community and Carbon and Nitrogen Stable Isotope Patterns Differ among Bletilla Species (Orchidaceae).

Orchids of the genus Bletilla are well-known ornamental plants and sources of traditional medicine in Asia that rely on the symbiotic relationship with root endophytic fungi throughout their whole life cycle. However, little is known about their fungal partners, infection pattern, and pathways of carbon gain. We investigated carbon and nitrogen stable isotope patterns in different organs of three Bletilla species, identified the root endophytic fungal community composition, and determined mycorrhizal colonization rates. The three Bletilla species were comprised by a polyphyletic group which belongs to different trophic modes, such as saprotroph, pathotroph, and symbiotroph; however, the dominant species and their abundances varied among Bletilla spp. Mycorrhizal infection rates also varied among Bletilla species, with B. striata (65% ± 25%) being significantly higher than those of B. formosana (35% ± 16%) and B. ochracea (22% ± 13%). Compared with surrounding autotrophic plants, all Bletilla spp. were significantly enriched in 13C with B. striata to a significantly higher level than other two Bletilla species. Among different organs, stems had higher δ13C values, while leaves and flowers had higher δ15N and total N content values across all three species. Our results indicate that the symbiotic relationship of Bletilla and its root endophytic fungi is not strictly specific. Although mycorrhizal infection rates were highly variable, the three Bletilla species had the same infection pattern with hyphae penetrating the cortex cell by the pathway cell. Different Bletilla species have different strategies for C allocation among plant organs. These findings provide new insights into the ecological adaptation of orchids and will contribute to Bletilla germplasm conservation and sustainable utilization.

Simultaneous Analysis of the Stable Carbon Isotope Ratios of Acetoin and Acetic Acid by GC-C-IRMS for Adulteration Detection in Brewed Rice Vinegar Products.

In this study, we developed a method to simultaneously measure the stable carbon isotope ratio for acetic acid (δ 13Caceticacid) and acetoin (δ13Cacetoin) in rice vinegar by gas chromatography-combustion-isotope ratio mass spectrometry. The method showed good precision and accuracy. With this method, data from 16 brewed rice vinegars and 10 acetic acid samples were used to evaluate the feasibility of adulteration detection. On the basis that all δ13Cacetoin values of brewed rice vinegars are nearly constant, a characteristic pattern of the stable carbon isotope in rice vinegar was built with the 95% confidence intervals for δ13Caceticacid (-26.97 to -25.38‰), δ13Cacetoin (-28.14 to -27.09‰), and Δδ13C (0.61 to 2.27‰). An adulteration detection curve of Δδ13C was proposed based on the results of vinegar and acetic acid samples and confirmed by vinegar spiked with different amounts of acetic acid. This method could be useful in estimating the blending ratio of adulterated rice vinegar products. Products containing more than 10% of synthetic acetic acid could be possibly identified.

A model of algal organic carbon distributions in the Pearl River estuary using the amino acid carbon isotope values

To better understand the sources and behavior of estuarine labile organic matter, we measured stable carbon isotope patterns of individual amino acids in suspended particles and surface sediments from the Pearl River Estuary in China; samples were taken along a salinity transect in December, 2016. Here we demonstrate that carbon isotope values (δ13C) of individual amino acids in these samples gradually increase with salinity downstream, reflecting the increase in δ13C values of algal-derived organic carbon along the salinity gradient. The isotopic difference between amino acids and bulk organic carbon varies, most likely due to changes in the relative contributions of algal-derived organic matter and refractory terrestrial input. In addition, algal-derived organic matter can consist of labile and semi-labile organic matter in varied proportions depending on degradation state. This isotopic difference between amino acids and bulk organic carbon is much larger in surface sediments than in suspended particles, suggesting that labile organic carbon contributed more to suspended particles than to sediments. Using the relative abundances and δ13C ratios of amino acids and total organic carbon, a Lability Model was constructed to evaluate the relative contributions of three forms of estuarine organic carbon: labile algal material as amino acids, semi-labile algal material as lipids and acid-insoluble material, and refractory terrestrial organic material. The model suggests highly dynamic contributions of semi-labile algal-derived organic carbon and terrestrial organic carbon to estuarine particulate organic carbon. This evaluation of organic carbon sources illustrates the importance of decomposition in shaping the molecular composition and isotopic signature of particulate organic carbon in the estuary.

Evolution patterns of seawater carbon isotope composition during the Cambrian and their stratigraphic significance

Our current understanding of the Cambrian carbon cycle mostly comes from geologically rapid carbon isotope excursions (CIEs) of marine carbonate. In addition to carbon cycle indicators, stable carbon isotopes of marine carbonates can be used as stratigraphic correlation tools. Previous studies have recognized 10 CIEs in the Cambrian, but only 3 of them appear to have global significance. This limits the application of CIEs in chronostratigraphic correlation of Cambrian successions with the 10 successive stages. Here, we present a continuous carbon isotope record from a stratigraphically complete Cambrian section at Xiaoerbulak, Aksu region in the Tarim Basin, Xinjiang, China. Its comparison with more than 40 sections across the world shows the carbon isotope record of the Cambrian can be divided into 10 units based on the variation patterns. Each pattern has occurrences in at least two Cambrian tectonic plates, suggesting global significance. A generalized curve consisting of the 10 patterns, Carbon Isotope Pattern Curve (CIPC) has been compiled. Based on the fossil records, the 10 patterns are correlated with the 10 stages of the chronostratigraphic system of the Cambrian. The pattern Angularianis correlated with Fortunian Stage and the lower half of Stage 2, Dampingian with the upper part of Stage 2, Boxian with Stage 3, Rabbitian with Stage 4, Chairian with the lower half of Wuliuan, Zigzagian with the upper Wuliuan Stage, Stickian with the Drumian and Guzhangian stages, Towerian with the Paibian Stage and Lower Jiangshan Stage, Shelfian with Upper Jiangshan Stage and the lower half of Stage 10, and Hillian with the upper half of Stage 10.We suggest that the application of CIPC makes the chronostratigraphy of non‐fossiliferous successions realizable.

Characterizing niche differentiation among marine consumers with amino acid δ13C fingerprinting.

Marine food webs are highly compartmentalized, and characterizing the trophic niches among consumers is important for predicting how impact from human activities affects the structuring and functioning of marine food webs. Biomarkers such as bulk stable isotopes have proven to be powerful tools to elucidate trophic niches, but they may lack in resolution, particularly when spatiotemporal variability in a system is high. To close this gap, we investigated whether carbon isotope (δ13C) patterns of essential amino acids (EAAs), also termed δ13CAA fingerprints, can characterize niche differentiation in a highly dynamic marine system. Specifically, we tested the ability of δ13CAA fingerprints to differentiate trophic niches among six functional groups and ten individual species in the Baltic Sea. We also tested whether fingerprints of the common zooplanktivorous fishes, herring and sprat, differ among four Baltic Sea regions with different biochemical conditions and phytoplankton assemblages. Additionally, we investigated how these results compared to bulk C and N isotope data for the same sample set. We found significantly different δ13CAA fingerprints among all six functional groups. Species differentiation was in comparison less distinct, due to partial convergence of the species' fingerprints within functional groups. Herring and sprat displayed region‐specific δ13CAA fingerprints indicating that this approach could be used as a migratory marker. Niche metrics analyses showed that bulk isotope data had a lower power to differentiate between trophic niches than δ13CAA fingerprinting. We conclude that δ13CAA fingerprinting has a strong potential to advance our understanding of ecological niches, and trophic linkages from producers to higher trophic levels in dynamic marine systems. Given how management practices of marine resources and habitats are reshaping the structure and function of marine food webs, implementing new and powerful tracer methods are urgently needed to improve the knowledge base for policy makers.

Modeling hydrocarbon accumulation based on gas origin and source rock distribution in Paleozoic strata of the Ordos Basin, China

Paleozoic gases in the Ordos Basin, China, are produced from upper Paleozoic tight sandstones, Ordovician weathered-crust, and ‘pre-salt’ (beneath gypsum deposits) dolomite reservoirs. Their origins have been debated, particularly as to whether Carboniferous–Permian (CP) or Ordovician source rocks contributed more gas to the lower Paleozoic gas reservoirs. The expanded exploration of lower Paleozoic gas to the eastern, western, northern, and southern regions of the basin has re-initiated the debates. In this study, geochemical characteristics of gas samples from newly drilled wells in different regions of Ordos Basin in combination with the source rock evaluation were used to determine the gas origin. The carbon and hydrogen isotope of alkane indicate that gas mixing occurred in both upper Paleozoic and Ordovician weathered-crust gases, and that TSR occurred in pre-salt gases. A modified δ13C–1/Cn plot was suggested to be useful to determine the carbon isotopic patterns of gases generated from the different source rocks. The light hydrocarbon characteristic shows that oil-type gas mainly distributes in the eastern basin. A study of source-rock distributions also indicates that the most favorable Ordovician source rock is located in the eastern basin. Based on the distribution of CP coal measures, limestones and lower Paleozoic carbonate source rock, a gas accumulation history was established. The results of this study provide applicable method for identifying gas origin in Ordos Basin. Moreover, the accumulation history proposed in this study is useful for further exploration of the lower Paleozoic gas in Ordos Basin.