Stable Carbon Isotope Research Articles

Paleoclimatic significance of the organic carbon isotopes of the Tajikistan loess in arid Central Asia, on orbital timescales since the last interglacial

During the past few decades, the stable carbon isotope composition of bulk organic matter (δ13Corg) in loess sediments has been increasingly used for reconstructing changes in the terrestrial vegetation and climate in several regions, including Europe, Xinjiang (the eastern part of arid central Asia, ACA), and the Chinese Loess Plateau (CLP). However, previous research indicates significant differences in the climatic significance of δ13Corg between the loess-paleosol sequences of Europe and the western and eastern ACA, compared to the loess of the central and southern CLP in monsoonal Asia. The δ13Corg values of loess-paleosol sequences in western and eastern ACA on different timescales exhibit consistent patterns of variation, suggesting that loess δ13Corg in these areas may be influenced by similar climatic factors and have similar mechanisms. However, the lack of detailed δ13Corg studies in central ACA limits our understanding of their applicability to long loess sequences within this region. This limitation not only constrains our understanding of the paleoclimatic significance of loess δ13Corg in central ACA, but it also affects the practical application of loess δ13Corg as a reliable paleoclimate proxy in this region. Consequently, it impedes a comprehensive understanding and in-depth analysis of loess δ13Corg across the mid-latitude Eurasian continent. To address this deficiency, we conducted a δ13Corg study of the Darai Kalon (DK) loess section, in southern Tajikistan, central ACA, since the last interglacial, with the aim of exploring the environmental significance of loess δ13Corg and the origin of the climatic record of this section, on orbital timescales. The results show that the ecosystem in southern Tajikistan, and throughout ACA, was dominated by C3 vegetation since the last interglacial. Loess δ13Corg records can be used as a precipitation proxy in ACA, at least since the last interglacial. However, regional comparisons revealed negative correlations between loess δ13Corg values and pedogenic intensity in Europe, ACA, and the western CLP, which is the opposite to the positive correlations observed in the central and southern CLP. Comparison of the paleoclimate record of the DK section with those of loess-paleosol sequences from monsoonal Asia indicated that warm, humid conditions occurred during past interglacials (MIS5, MIS1) and interstadials (MIS3), and cold, arid conditions occurred during the glacial/stadial periods (MIS4, MIS2) in both ACA and monsoonal Asia. We propose that changes in Northern Hemisphere insolation were responsible for this in-phase pattern of climate change between these two regions on orbital timescales since the last interglacial.

Similarity recognition approach to identify zero-added MSG soy sauce using stable isotopes and amino acid profiles

Seasonings such as naturally fermented soy sauce without added monosodium glutamate (MSG), are currently a growth market in China. However, fraudulent and mislabeled zero-added MSG soy sauce may cause a risk of excessive MSG intake, increasing food safety issues for consumers. This study investigates stable carbon and nitrogen isotopes and 16 amino acids in typical Chinese in-market soy sauces and uses a similarity method to establish criteria to authenticate MSG addition claims. Results reveal most zero-added MSG soy sauces had lower δ13C values (−25.2 ‰ to −17.7 ‰) and glutamic acid concentrations (8.97 mg mL−1 to 34.76 mg mL−1), and higher δ15N values (−0.27 ‰ +0.95 ‰) and other amino acid concentrations than added-MSG labeled samples. A combined approach, using isotopes, amino acids, similarity coefficients and uncertainty values, was evaluated to rapidly and accurately identify zero-added MSG soy sauces from MSG containing counterparts.

Intercorrelations of Chlorinated Paraffins, Dechloranes, and Legacy Persistent Organic Pollutants in 10 Species of Marine Mammals from Norway, in Light of Dietary Niche.

Short-, medium-, and long-chain chlorinated paraffins (CPs) (SCCPs, MCCPs, and LCCPs) and dechloranes are chemicals of emerging concern; however, little is known of their bioaccumulative potential compared to legacy contaminants in marine mammals. Here, we analyzed SCCPs, MCCPs, LCCPs, 7 dechloranes, 4 emerging brominated flame retardants, and 64 legacy contaminants, including polychlorinated biphenyls (PCBs), in the blubber of 46 individual marine mammals, representing 10 species, from Norway. Dietary niche was modeled based on stable isotopes of nitrogen and carbon in the skin/muscle to assess the contaminant accumulation in relation to diet. SCCPs and dechlorane-602 were strongly positively correlated with legacy contaminants and highest in killer (Orcinus orca) and sperm (Physeter macrocephalus) whales (median SCCPs: 160 ng/g lw; 230 ng/g lw and median dechlorane-602: 3.8 ng/g lw; 2.0 ng/g lw, respectively). In contrast, MCCPs and LCCPs were only weakly correlated to recalcitrant legacy contaminants and were highest in common minke whales (Balaenoptera acutorostrata; median MCCPs: 480 ng/g lw and LCCPs: 240 ng/g lw). The total contaminant load in all species was dominated by PCBs and legacy chlorinated pesticides (63-98%), and MCCPs dominated the total CP load (42-68%, except 11% in the long-finned pilot whale Globicephala melas). Surprisingly, we found no relation between contaminant concentrations and dietary niche, suggesting that other large species differences may be masking effects of diet such as lifespan or biotransformation and elimination capacities. CP and dechlorane concentrations were higher than in other marine mammals from the (sub)Arctic, and they were present in a killer whale neonate, indicating bioaccumulative properties and a potential for maternal transfer in these predominantly unregulated chemicals.

Changes in limpet diet according to habitat type

Limpets are a key taxon regulating the benthic community structure and serving as prey for various predators in rocky shores, however, their role in food web dynamics is still unclear. To determine environmental factors influencing the limpet diet, carbon and nitrogen stable isotopes in limpets and food sources were analyzed on three different coastal habitats. Sediment organic matter contributed the most (86 %) to the limpet diet in bedrocks around tidal flats with abundant sediment supply from the terrestrial matter inflow and the sediment resuspension. Microphytobenthos and macroalgae were the main food sources (57 % and 20 %, respectively) for the limpets around beaches, where benthic flora was abundant. Limpets in bedrocks, erosional habitat, primarily consumed relatively abundant phytoplankton (33 %) and microphytobenthos (28 %). Contrary to previous studies, habitat type, rather than latitude or seawater characteristics, was the most important factor determining the limpet diet. This result also suggests that limpets are non-selective scraper that consume abundant food sources.

Investigation of fraud in the production of butter: a forensic case study of criminal association

Butter is among the most popular and commercially valuable dairy products. Its high commercial value makes it a major target for adulteration, which aims to reduce production costs by using lower-quality fats and oils from other sources. The annual global market is around USD 30 billion (2023), expected to reach USD 36 billion in 2028, which also justifies the enormous interest in adulteration. In this work, a confirmed case of butter adulteration was studied by Nuclear Magnetic Resonance (NMR) and Stable Carbon Isotopic Ratio Analysis (SCIRA) techniques, employed to detect the inclusion in butter production of vegetable oils, such as soybean and palm oils. A total of 21 samples seized by the Brazilian Federal Police were analysed by NMR and SCIR, and compared to original butter obtained from commercial sources. The composition of all the seized samples was a mixture of butter (dairy fat of animal origin) with fat of vegetable origin (soybean and palm oil) and did not contain milk as a major component. While NMR was an unequivocal choice to discriminate the chemical composition of food samples, identifying the short-chain saturated fatty acids present in milk fat, including the butyryl alkyl chain, SCIRA was able to discriminate the origin of fat present in the butter samples as C3 sources, such as palm vegetable oils.

Stable carbon isotopes in scallop shells: A proxy of Antarctic sea-ice persistence

Sea ice is fundamental to global climate and its multiannual persistence or seasonal absence shapes Antarctic marine ecosystems. With sea ice in rapid decline in the Southern Ocean, it is imperative to understand its variability prior to satellite data. The Antarctic scallop Adamussium colbecki has a broad geographic distribution and long fossil history in the Southern Ocean, and its shells could be ideal bioarchives for sea ice with the potential to resolve subannual sea-ice dynamics over multiple years or decades. Here, we evaluate stable isotopes of carbon in A. colbecki shells from two sites on western McMurdo Sound. Each site maintains stable, frigid seawater temperatures, but they differ in sea-ice duration. Explorers Cove has semi-permanent multiannual sea ice, whereas Bay of Sails has annual sea ice that breaks out every year. Our results indicate that seasonal variation in δ13Cshell values may proxy sea-ice persistence. Scallops living under annual sea ice — adults from Bay of Sails and juveniles collected during a fortuitous recent sea ice breakout at Explorers Cove — had higher δ13Cshell values during summer growth than winter growth. Scallops living under multi-annual sea ice had no difference in δ13Cshell values between winter and summer growth. We posit that phytoplankton blooms leverage the seasonal δ13C values of the dissolved inorganic carbon under ice-free conditions, which is in turn recorded in δ13Cshell values and that A. colbecki shells could be used to understand past variability in sea-ice persistence in coastal Antarctica.

Transient micropaleontological turnover across a late Eocene (Priabonian) carbon and oxygen isotope shift on Blake Nose (NW Atlantic)

Abstract. The Gulf Stream, a western boundary current transporting warm water into the North Atlantic, plays a key role in climate regulation and oceanographic stability at a regional and global scale as part of the Atlantic Meridional Overturning Circulation (AMOC). Evidence suggests that an ancestral Gulf Stream has existed since the Mesozoic, and it has altered its course repeatedly over Cenozoic times. In this study, we focus on the upper Eocene (Priabonian, ca. 36 Ma) from Ocean Drilling Program Site 1053 on Blake Nose (subtropical North Atlantic). Bulk carbon and oxygen stable isotopes, as well as benthic foraminiferal and calcareous nannofossil assemblages, provide an integrated assessment of the palaeoceanographic changes impacting the area through the water column to the seafloor. Micropaleontological assemblages suggest changes in surface ocean stratification and nutrient supply to the seafloor coeval with a paired negative carbon and oxygen isotope excursion and the return to background conditions higher up in the study section. These transitory changes are compatible with the longitudinal displacement of the proto-Gulf Stream and its related eddies. Our results build on previous work and support the hypothesis that links palaeoceanographic changes in the Blake Nose area with shifts in the proto-Gulf Stream during the middle and late Eocene.

Differential growth rate, water use efficiency and climate sensitivity between males and females of Ilex aquifolium in north-western Spain.

Dioecious plant species, i.e., those in which male and female functions are housed in different individuals, are particularly vulnerable to global environmental changes. For long-lived plant species, such as trees, long-term studies are imperative to understand how growth patterns and their sensitivity to climate variability differentially affect the sexes. Here, we explore long-term intersexual differences in wood traits, namely radial growth rates, water use efficiency quantified as stable carbon isotope abundance of wood cellulose, and their climate sensitivity in Ilex aquifolium trees growing in a natural population in NW Spain. We found that sex differences in secondary growth rates were variable over time, with males outperforming females in both radial growth rates and water use efficiency in recent decades. Summer water stress significantly reduced the growth of female trees in the following growing season, while the growth of male trees was primarily favoured by cloudy and rainy conditions the previous fall and winter combined with low cloud cover and warm conditions in summer. Sex-dependent lagged correlations between radial growth and water availability were found, with a strong association between tree growth and cumulative water availability in females at 30 months and in males at 10 months. Overall, our results point to greater vulnerability of female tress to increasing drought, which could lead to sex-ratio biases threatening population viability in the future.

Ontogenetic, Sexual, and Monthly Niche Segregation of Sepia esculenta in the Northern East China Sea Revealed by Stable Carbon and Nitrogen Isotopes.

Golden cuttlefish play a significant role in the food web of the East and Yellow Seas and are a valuable fishery resource in Chinese coastal waters. Samples of golden cuttlefish were obtained from the northern East China Sea between September 2021 and March 2022, and stable isotope methods were utilized in this study to examine the variations in the forage ecology of golden cuttlefish. Our findings reveal dynamic shifts in carbon and nitrogen stable isotopes (δ13C and δ15N), highlighting intricate foraging strategies tailored to growth and environmental changes. A notable trend emerges: an initial growth-linked rise in δ13C and δ15N enrichment, followed by seasonal fluctuations mirroring seasonal food availability. The ontogenetic niche evolution displays striking habitat shifts and trophic level escalation in small mantle length stages, transitioning to niche overlap and subtle trophic shifts later on. Sex-specific differences emerge, with females occupying higher trophic levels than males in most samples. This comprehensive study underscores the complexity and adaptability of golden cuttlefish feeding ecology, inviting further inquiry into their intricate relationships within the marine ecosystem.

Different pacemakers of marine organic carbon burial in the North Yellow Sea from the early to late Holocene

Marginal seas play a crucial role in the global carbon cycle, contributing approximately 20% of the net CO2 uptake by the world's oceans. The North Yellow Sea (NYS), a semi-enclosed marginal sea in the western Pacific Ocean, serves as a significant carbon sink influenced by factors such as sea level changes, monsoon dynamics, ocean currents, and El Niño-Southern Oscillation (ENSO) activity. This study examines a 538 cm-long sediment core W03 from the NYS (10.3 kyr BP to present). We analyzed Organic Carbon (OC) proxies, including total organic carbon (TOC), the stable carbon isotope (δ13C) of TOC, total nitrogen (TN) and marine-produced lipid biomarkers. Our findings demonstrate a strong correlation between OC burial and sea-level fluctuations during the early Holocene, driven by the exposure of the continental shelf. During the mid-Holocene, the intrusion of the Yellow Sea Warm Current increased salinity and temperature conditions and nutrient levels of sea water, thereby enhancing marine OC burial. Over the last 3.3 kyr BP, ENSO variability and intensified East Asian Winter Monsoon (EAWM) strengthened the coastal currents, contributing to better OC preservation. Additionally, human activities on the surrounding mainland increased terrestrial input, altering the OC burial. The heightened activity of the Kuroshio Current also introduced more saline and warm water masses into the NYS, impacting phytoplankton productivity and community structure, as indicated by increased C37 alkenones. This study highlights the complex interplay of geological factors in OC burial processes within the NYS, providing valuable insights into OC dynamics in marginal seas under the impact of global change.

Plant response to decreasing soil moisture under rising atmospheric CO2 levels

Widespread drought driven by global warming is predicted across the 21st century, just as CO2 level is projected to as much as double over the same time period. However, the potential interplay between increasing CO2 and decreasing soil moisture on plant function is uncertain, as previous works have not successfully separated and quantified these two competing effects. Here we evaluated the interaction between soil moisture and CO2 using stable carbon isotope measurements of Arabidopsis grown under the simultaneous modulation of an exhaustive range of both variables. Results showed that both increasing soil water content and increasing CO2 increased isotopic discrimination, and that the soil moisture effect was not influenced by the CO2 level and vice versa. Our data confirm that changes in the carbon isotope record of terrestrial organic matter preserved within the geologic record are best interpreted as deriving from changes in atmospheric CO2.

Chemometrics exploration of monosaccharides, sugar acids, stable carbon isotopes, and volatile organic compounds in Malaysian stingless bee honey from different geographical origins

Chemometrics exploration of monosaccharides, sugar acids, stable carbon isotopes, and volatile organic compounds in Malaysian stingless bee honey from different geographical origins

Compound-specific radiocarbon analysis of sedimentary fatty acids: Potential as a dating tool for lake sediments of Mt. Fuji volcanic region, Japan

Compound-specific radiocarbon analysis (CSRA) is a promising tool for dating sediment sequences where traditional dating methods are impractical. However, the applicability of CSRA of short-chain fatty acids as a dating tool remains poorly understood, especially in lacustrine settings. Accordingly, we determined the radiocarbon content (Δ14C) of individual fatty acids in sediments of Lake Yamanaka (central Japan), as well as their stable carbon and hydrogen isotope ratios, to evaluate the potential of CSRA as a dating tool in volcanic lake environments. We found that the Δ14C values of plant-derived (C24, C26, and C28) n-fatty acids (–99‰ to –149‰) were considerably lower than the Δ14C of charred plants (139‰) within the sediments and those of living aquatic plants (–52‰ to –58‰) in Lake Yamanaka, suggesting that contributions from pre-aged terrestrial and aquatic plant materials likely affect these acids. Similarly, the Δ14C of C16n-fatty acid (–95‰) in surface sediments was much lower than the Δ14C of modern aquatic plants (–52‰ to –58‰), as well as the Δ14C of dissolved organic carbon (DIC) in surface water (–48‰). Together with the stable isotope results, we conclude that in addition to autochthonous aquatic sources, contributions from pre-aged terrestrial carbon sources significantly affect the Δ14C of C16n-fatty acids. Comparing fatty acid Δ14C and concentration data across lakes within the Mt. Fuji region suggests that CSRA of the C16 acid provides valid chronological information only when the C16 originates exclusively from autochthonous aquatic sources, with minor allochthonous terrestrial input.

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.

Responses of C4 grasses to aridity reflect species‐specific strategies in a semiarid savanna

AbstractThe C4 Poaceae are a diverse group in terms of both evolutionary lineage and biochemistry. There is a distinct pattern in the distribution of C4 grass groups with aridity; however, the mechanistic basis for this distribution is not well understood. Additionally, few studies have investigated the functional strategies of co‐occurring C4 grass species for dealing with aridity in their natural environments. We explored the coordination of leaf‐level gas exchange, water use, and morphology among five co‐occurring semiarid C4 grasses belonging to divergent clades, biochemical subtypes, and size classes at three sites along a natural aridity gradient. More specifically, we measured predawn and midday water potential, stomatal conductance, water use efficiency, and photosynthesis. Leaf tissue was also collected for the analysis of stable isotopes of carbon and oxygen as well as for measurement of specific leaf area (SLA) and leaf width. Species differences in responsiveness of stomata to changes in vapor pressure deficit (VPD) were also assessed. It was expected that NAD‐me species would maintain higher rates of photosynthesis, higher water use efficiency, and have more responsive stomata than other co‐occurring species based on observed biogeographic patterns and past greenhouse studies. We found that Aristidoideae and Chloridoideae NAD‐me‐type grasses had greater stomatal sensitivity to VPD, consistent with a more isohydric strategy. However, midgrasses had both greater apparent water access and water use efficiency, regardless of subtype or lineage. PCK‐type species had less responsive stomata and maintained lower levels of photosynthesis with increasing aridity. There were strong interspecific differences in δ13C, leaf width, and SLA; however, these were not significantly correlated with water use efficiency. C4 grasses in our study did not fit discretely into functional groups as defined by lineage, biochemistry, or size class. Interspecific differences, evolutionary legacy, and biochemical pathway are likely to interact to determine water use and photosynthetic strategies of these plants. Control of water loss via highly responsive stomata may form the basis for dominance of certain C4 grass groups in arid environments. These findings build on our understanding of contrasting strategies of C4 grasses for dealing with aridity in their natural environments.

Geochemical fingerprints of Dongpu Depression crude oils in Bohai Bay Basin, northern China: Insights from biomarkers and isotopic compositions of selected alkylnaphthalenes and alkylphenanthrenes

The Dongpu Depression is a rift lake in the Bohai Bay Basin of eastern China, where abundant oil and gas resources were discovered. Previous geochemical investigations of Dongpu Depression oils have revealed a notable lack of data regarding the isotopic compositions of individual polycyclic aromatic hydrocarbons (PAHs) from the discovered Cenozoic crude oils. Using gas chromatography-mass spectrometry (GC–MS) and gas chromatography-isotope ratio mass spectrometry (GC-IRMS), a novel approach combining molecular parameters and stable carbon isotope compositions of individual PAH was applied to study the depositional environment conditions, the different source inputs, the maturation stage and to identify the potential family of five crude oils selected from Dongpu Depression.A decrease of Ga/C30H together with low Pr/Ph ratios and changes in isotopic compositions indicate that the five Dongpu Depression oils were derived from OM deposited in an anoxic saline environment with a stratified water column where mixing of saline water and freshwater occurred. The low isoprenoid, tricyclic and tetracyclic terpane ratios in combination with the δ13C values of 1,6-DMN, 1,2,5-TMN, 1,3,6,7-TeMN, 9-MP and 1-MP attest that their sources have a mixed origin with high aquatic organism (planktonic) input and a lower land plant (C3 plant) contribution. The δ13C values of phenanthrene between −30.0 ‰ and −20.0 ‰ indicate that the studied Dongpu Depression oils belong to a single family generated from the peak to the late oil generation stage (Rc-TNR-2 between 0.85 and 1.15 %). A correlation with various basins indicates that oil samples featured by δ13C values of Phen between −30.0 ‰ and −20.0 ‰ correspond to crude oils derived from mixing of aquatic and high plant contributions with different degrees of mixtures, which have not yet reached their cracking stage (Rc < 2.0 %). Crude oils from the Carboniferous and Mesozoic-Cenozoic Tarim rocks, Australian petroleum systems, Termit Basin, Bongor Basin, Fushan Depression and the studied Dongpu Depression oils belong to that group of oils. Crude oils characterized by lighter phenanthrene isotopic compositions (δ13C values of Phen < −30.0 ‰) are mainly derived from marine/aquatic input and have already entered the cracking window (Rc > 2.0 %). This group of oils is represented in this study by the Cambrian-Ordovician Tarim Basin oil samples. The research shows the importance of the aromatic isotopic compositions in petroleum system characterization and could be used as a reference for a practical exploration campaign of petroleum.

A mid-Cretaceous carbon isotope reference curve for the SE Neo-Tethys region (Zagros, W Iran)

Stable carbon isotope chemostratigraphy and the associated reference curves have proved to be valuable tools for stratigraphic calibration and long-distance correlations. Nonetheless, the reference curves covering the Cretaceous have mostly been produced from localities located within the W Neo-Tethys. In order to establish a reference curve for the SE Neo-Tethys margin, an Aptian–Albian hemipelagic carbonate-rich succession deposited along the Zagros Basin (SW Iran) was examined for planktic foraminifera biostratigraphy, carbon isotope stratigraphy, and sedimentological characteristics. Eight biozones including Globigerinelloides ferreolensis, Globigerinelloides algerianus, Hedbergella trocoidea, Paraticinella bejaouaensis, Muricohedbergella planispira, Ticinella (T.) primula, Biticinella breggiensis, and Pseudothalmanninella (P.)ticinensis as well as two subzones enclosing T. praeticinensis and P. subticinensis assign the strata to the early late Aptian–late Albian age. A carbon isotope record constrained by the planktic foraminifera zonation scheme shows good concordance with existing composite reference curves from the W Neo-Tethys region. Several carbon isotope excursions (CIEs) characterizing global marine events including Oceanic Anoxic Event (OAE) 1a, OAE1b, OAE1c and associated sub-events can be identified in the studied section. Deoxygenated bottom waters associated with the formation of OAE1a and OAE1b are indicated by distinct lithological signatures including enrichment in pyrite and glauconite, nodular and stratiform chert beds, as well as enhanced organic matter contents. We integrate the here-studied interval with a previously published upper Albian−Turonian succession from the same outcrop section, forming a composite, stratigraphically well-constrained section. This results in a high-resolution carbon isotope record for the SE Neo-Tethys margin, considered to represent an expedient reference Aptian–Turonian curve for this region. Correlation of this new curve with previously published records from the Middle East has helped to address ambiguities regarding the stratigraphic positions of the early/late Aptian and Aptian/Albian boundaries identified by previous studies.

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.

Environmental microbiology explains the largest positive carbon isotope excursion in Earth history, the Lomagundi-Jatuli Event.

The geological record of stable carbon isotopes preserved in marine carbonate rocks spans nearly 4 billion years. Numerous perturbations mark this record, but one stands out for its magnitude, the Lomagundi-Jatuli Event, which spanned the transition of the Earth's surface from an anoxic to an oxic state. An Applied and Environmental Microbiology article by D. Y. Sumner (90:e00093-24, 2024, https://doi.org/10.1128/aem.00093-24) provides, for the first time, a biological explanation for its initiation, cessation, environmental specific restriction, and geological singularity.

Characterizing water solubility of fresh and aged secondary organic aerosol in PM2.5 with the stable carbon isotope technique

Abstract. The investigation of the water-soluble characteristics of secondary organic carbon (SOC) is essential for a more comprehensive understanding of its climate effects. However, due to the limitations of the existing source apportionment methods, the water solubility of different types of SOC remains uncertain. This study analyzed stable carbon isotope and mass spectral signatures of total carbon (TC) and water-soluble organic carbon (WSOC) in ambient PM2.5 samples for 1 year and established stable carbon isotope profiles of fresh and aged SOC. Furthermore, a Bayesian stable isotope mixing (BSIM) model was employed to reveal the water solubility characteristics of fresh and aged SOC in a coastal megacity of China. WSOC was dominated by secondary sources, with fresh and aged SOC contributing 28.1 % and 45.2 %, respectively. Water-insoluble organic carbon (WIOC) was dominated by primary sources, to which fresh and aged SOC contributed 23.2 % and 13.4 %. We also found that the aging degree of SOC has considerable impacts on its water solubility due to the much higher water-soluble fraction of aged SOC (76.5 %) compared to fresh SOC (54.2 %). Findings of this study may provide a new perspective for further investigation of the hygroscopicity effects of SOC with different aging degrees on light extinction and climate change.