Stable Carbon Isotope Ratios Research Articles

First Retrospective Study of Avian Mercury Exposure in a Tropical ASGM Hotspot.

Artisanal and small-scale gold mining (ASGM) is the largest anthropogenic source of mercury globally. Few studies have explored how this toxicant affects avian wildlife in Indonesia, an ASGM hotspot. Here, we use feather samples from museum specimens (n = 92) of Indonesian birds to examine changes through time in methylmercury (MeHg), diet, and foraging habitat (inferred from stable isotope ratios of nitrogen, δ15N, and carbon, δ13C, respectively). We ask how MeHg changes between time period (1860-1980 vs. 1980-2019) given increases in mercury emissions due to ASGM and describe how foraging guild and among-species variation in diet influence Indonesian bird feather MeHg concentrations. Time period was not a significant factor, with specimens associated with increased ASGM activity (collected post-1980) not significantly higher in MeHg concentrations compared to specimens collected pre-1980. Feather MeHg concentrations varied significantly among species, foraging guilds, and by habitat use. Carnivore and insectivore MeHg concentrations were above thresholds associated with sublethal effects. This is the first report of MeHg in Indonesian passerines, kingfishers, and woodpeckers. It provides critical information on mercury exposure in a region with high avian diversity that is severely impacted by mercury pollution.

Spatiotemporal dynamics of carbon isotope ratios and phytoplankton composition in the eastern Arabian Sea.

Spatiotemporal dynamics of carbon isotope ratios and phytoplankton composition in the eastern Arabian Sea.

Utilisation of Anthropogenic Food by Red Foxes (Vulpes vulpes) in Britain as Determined by Stable Isotope Analysis.

Dietary analyses utilising visual methods to identify stomach and faecal contents have shown that urban red foxes (Vulpes vulpes) in Britain consume human-derived (anthropogenic) food to varying degrees. Anthropogenic foods have been implicated in poor health outcomes for synanthropic species that consume them; therefore, it is important to examine the degree of such foods in the British fox diet. We analysed the carbon (δ13C) and nitrogen (δ15N) stable isotope ratios of whiskers collected from 93 foxes from across Britain to determine: (1) if stable isotope analysis (SIA) distinguished a difference in δ13C and δ15N between rural and urban foxes, and whether any difference was suggestive of anthropogenic food use; (2) the proportion of anthropogenic food consumption in urban foxes compared to rural foxes using a Bayesian mixing model; (3) whether sex, age or season of collection influenced fox diet as assessed by SIA, in relation to anthropogenic food use. We found the following: (1) urban fox diet was significantly different to rural foxes; urban foxes demonstrated significantly higher δ13C and lower δ15N, a pattern consistent with anthropogenic food consumption. (2) Food provided either directly or indirectly by humans contributed an estimated 34.6% of urban fox diet compared to approximately 6% of rural fox diet. (3) Across rural and urban foxes combined, there were significant isotopic differences between males and females, with females demonstrating higher δ13C. (4) No differences in δ13C and δ15N between subadults and adults were observed. (5) Season did not have a significant influence on δ13C and δ15N, despite winter demonstrating the highest δ13C and lowest δ15N seasonal means. Potential negative outcomes of anthropogenic food consumption are likely to disproportionately impact females more than males and urban-dwelling foxes more than rural foxes.

CO2 flux and carbon dynamics in soil and respired CO2 in a semi‐arid region of western India

AbstractSoil CO2 emissions surpass anthropogenic fluxes by an order of magnitude, with tropical soils exhibiting significant flux variability. We measured soil CO2 flux, stable carbon isotope ratio (δ13C), and radiocarbon (14C) in soil‐respired CO2 as well as in soil pore space CO2 (soil CO2) and soil organic carbon (SOC). The objectives were to estimate CO2 flux, identify influencing factors, and trace the sources of CO2 in soil pore space and surface emissions. Soil CO2 concentrations ([CO2]) ranged from 13,780 to 26,300 ppmv. The surface CO2 flux varied between 4.6 and 8.6 µmolCO2/m2/s. It was strongly influenced by soil moisture content. Under relatively dry summer day with soil moisture content in the range of 7.7%–9.5% by weight, the flux varied between 8.0 and 8.6 µmolCO2/m2/s. Under increased soil moisture conditions (14.3%–17.9%), CO2 flux decreased to 4.6–6.6 µmolCO2/m2/s, with larger fluctuations attributed to moisture variability. The 14C in soil and respired CO2 is predominantly modern, while SOC exhibited much older radiocarbon ages, ranging from 2700 before present (BP) at 10 cm to 12,900 BP at 150‐cm depth. Therefore, the SOC contributes minimally (at most 5%) to both soil and respired CO2. Instead, root respiration and the decomposition of fresh organic matter are the dominant sources, even at deeper soil layers. As a result, the SOC pool and soil CO2 appear to function as largely decoupled systems, suggesting that estimating the mean residence time of SOC based solely on surface CO2 flux may be misleading.

Isotopic Insight Into the Human Diet at Qareh Tepe, Iran, During the Iron Age (c. 1200–750 bce)

ABSTRACTThe period preceding early state formation in Iran (i.e., Early Iron Age) is frequently associated with the prevalence of mobile pastoralists. The analysis of stable carbon and nitrogen isotope ratios of human and animal collagen from Qareh Tepe (c. 1200–750 cal. bc) in Qazvin Plain was performed to understand local subsistence strategy and especially to distinguish between mobile herding and stationary farming, which is crucial in understanding pathways leading to the centralization of power in that time. In total, 53 human dentin samples and 30 animal bone and dentin samples were analyzed. The comparative data come from four other Iranian sites of variable chronology: Sagzabad, Zagheh, Tepe Pardis, and Tepe Hissar. Standard methods of collagen extraction and isotope ratio mass spectrometry were applied. People from Qareh Tepe were characterized by very high δ15N values, clearly higher than at all other sites. There was a significant difference between the sexes, with males having more negative δ13C values. In combined faunal data from the Qazvin Plain, suids composed a separate group, whereas all the herbivores showed a clear correlation between δ15N and δ13C values. Elevated nitrogen isotopic values in humans from Qareh Tepe may be explained by a high level of manuring with animal dung, forced by an increased population size in the limited space of the alluvial fan. The research reveals that, at the dawn of the Median state, the Central Plateau of Iran was most likely not inhabited by nomadic pastoralists but rather by agropastoral communities that knew how to make the best use of limited environmental resources.

Beef Traceability Between China and Argentina Based on Various Machine Learning Models.

Beef, as a nutrient-rich food, is widely favored by consumers. The production region significantly influences the nutritional value and quality of beef. However, current methods for tracing the origin of beef are still under development, necessitating effective approaches to ensure food safety and meet consumer demand for high-quality beef. This study aims to establish a classification model for beef origin prediction by analyzing elemental content and stable isotopes in beef samples from two countries. The concentrations of elements in beef were analyzed using ICP-MS and ICP-OES, while the stable carbon isotope ratio was determined using EA-IRMS. Machine learning algorithms were employed to construct classification prediction models. A total of 83 beef samples were analyzed for the concentrations of 52 elements and the stable carbon isotope ratio. The classification accuracy of the PLS-DA model built on these results was 98.8%, while the prediction accuracy was 94.12% for the convolutional neural network (CNN) and 82.35% for the Random Forest algorithm. The PLS-DA model demonstrated higher classification accuracy compared to CNN and Random Forest, with an explanatory power (R2) of 0.924 and predictive ability (Q2) of 0.787. Combining the analysis of 52 elements and the stable carbon isotope ratio with machine learning algorithms enables effective tracing and origin prediction of beef from different regions. Key factors influencing beef origin were identified as Fe, Cs, As, δ13C, Co, V, Sc, Rb, and Ru.

Revealing stable SNPs and genomic prediction insights across environments enhance breeding strategies of productivity, defense, and climate-adaptability traits in white spruce.

Exploring the relationship between phenotype, genotype, and environment is essential in quantitative genetics. Considering the complex genetic architecture of economically important traits, integrating genotype-by-environment interactions in a genome-wide association (GWAS) and genomic prediction (GP) framework is imperative. This integration is crucial for identifying robust markers with stability across diverse environments and improving the predictive accuracy of individuals' performance within specific target environments. We conducted a multi-environment GWAS and GP analysis for 30 productivity, defense, and climate-adaptability traits on 1540 white spruce trees from Alberta, Canada, genotyped for 467,224 SNPs and growing across three environments. We identified 563 significant associations (p-value < 1.07 ×10-05) across the studied traits and environments, with 105 SNPs showing overlapping associations in two or three environments. Wood density, myrcene, total monoterpenes, α-pinene, and catechin exhibited the highest overlap (>50%) across environments. Gas exchange traits, including intercellular CO2 concentration and intrinsic water use efficiency, showed the highest number of significant associations (>38%) but less stability (<1.2%) across environments. Predictive ability (PA) varied significantly (0.03-0.41) across environments for 20 traits, with stable carbon isotope ratio having the highest average PA (0.36) and gas exchange traits the lowest (0.07). Only two traits showed differences in prediction bias (PB) across environments, with 80% of site-trait PB falling within a narrow range (0.90 to 1.10). Integrating multi-environment GWAS and GP analyses proved useful in identifying site-specific markers, understanding environmental impacts on PA and PB, and ultimately providing indirect insights into the environmental factors that influenced this white spruce breeding program.

Carbon and Nitrogen Isoscapes of Particulate Organic Matter in the Pacific Ocean

AbstractLarge‐scale geographical distributions in nitrogen and carbon stable isotope ratios (δ15N and δ13C) of particulate organic matter (POM) are essential to understand the variation in the baseline of pelagic food webs in the Pacific Ocean, where phytoplankton production and biological N2 fixation are highly variable because of heterogeneity of nitrate and iron supply. Here, we determined their isoscapes during summer and discussed potential factors characterizing regional ecosystems from the viewpoint of nitrogen cycling. We collected a total of 2,289 and 2,278 isotope values for δ13C and δ15N, respectively, by synthesizing previously published data with our newly measured data, and analyzed their relationships with temperature, concentrations of nitrate and chlorophyll‐a, and N2 fixation activity, obtained from databases. POM δ13C and δ15N regionally varied in ranges of −30 to −18‰ and −4 to 14‰, respectively. POM δ13C was correlated positively with temperature throughout the ocean. In contrast, POM δ15N was negatively correlated with nitrate concentration at high latitudes and with N2 fixation activity at low latitudes. High values (&gt;8‰) of POM δ15N were identified mainly in the marginal area of equatorial upwelling; the highest values (10–14‰) were in the subtropical Southeastern Pacific. Using the isotopic values and nitrate concentration, we classified the ecosystems into 10 groups. Our data demonstrated the distribution patterns of ecosystems with different degrees of nitrate utilization, which are presumably associated with iron supply, and ecosystems sustained by different nitrogen sources: diazotrophic nitrogen and nitrate supplied below the nitracline and/or horizontally advected.

Stable isotopes of saproxylic beetles reveal low differences among trophic guilds and suggest a high dependence on fungi

AbstractDeadwood stores about 8% of global carbon stock, and its decomposition is a key factor in forest ecosystems. Deadwood‐associated (saproxylic) organisms constitute a food web that sustains a substantial part of biodiversity globally. After fungi, saproxylic beetles are the most prominent agents of structural deadwood decomposition in forests. They are often classified according to their presumed link to the deadwood decomposition gradient, generally as feeding on fresh wood, decayed wood, fungi, or predators. These classifications are, however, based on ecomorphological characters (e.g., trophic morphology, habitat use) while information on their diet is globally limited. Carbon (δ13C) and nitrogen (δ15N) stable isotope ratios represent potential useful tracers to improve knowledge on the trophic ecology of this model group and the whole decomposition food web. We performed stable isotope analysis on 121 beetle species (530 samples) from a mixed‐deciduous forest in Central Europe in order to (1) characterize drivers of saproxylic beetles' isotopic variability with respect to potential food sources along the wood decomposition gradient and in relation to the potentially key intrinsic factors such as phylogeny and body size and (2) to assess how isotope information matches with two trophic guild classifications based on ecomorphological characters which are commonly used in ecological studies. The analysis revealed a clear pattern of δ13C increase and simultaneous C:N ratio decrease across potential food sources along the gradient from fresh to decayed deadwood and fungi. Beetle phylogeny and body size explained a significant part of their isotope variability, with values of δ13C being lower in smaller species. After filtering out these effects, the δ13C values reflected the position of beetle species on the decomposition gradient only loosely. Fungi‐feeding guilds had higher δ13C values than the guilds dependent on fresher deadwood, but otherwise the guilds were indistinguishable. Deadwood consumers did not differ from predators. The isotopic niches of different feeding guilds largely overlapped, and the large observed variation suggests that not only fungi feeders but species from most guilds may depend considerably on fungi and that mixed trophic strategies may be more common in the decomposition food web than currently acknowledged.

Carbon stable isotope values in hair are associated with added sugar intake in adults but not young children: a cross-sectional study.

Carbon stable isotope values in hair are associated with added sugar intake in adults but not young children: a cross-sectional study.

Stable isotope ecology of Quaternary cervid and bovid species in Southeast Asia with implications for wildlife conservation

Southeast Asia, one of the major biodiversity hotspots, is experiencing substantial species loss, with predictions indicating that 13–85% of species are threatened to lose their original habitats. As herbivores play a crucial role in shaping the structure of environments and the ecosystem dynamics of the region, it is crucial to protect these endangered species. Here we measure stable carbon isotopic ratios (δ13C) of tooth enamel samples of eight extant Southeast Asian cervid and bovid taxa, mostly listed as either endangered or vulnerable species by the IUCN and compare the results with their Pleistocene counterparts, in order to investigate their dietary and preferred habitat changes through time. As a result, three distinct categories of ecological patterns among these ruminant taxa are observed: (1) species with dietary and habitat changes through time (i.e. Axis axis, Rucervus eldii, Bos javanicus, and Bos gaurus), (2) those with more restricted diets and habitats today than in the past (i.e. Rusa unicolor and Bubalus arnee), and (3) those with unchanged diets and habitats over time (i.e. Axis porcinus and Muntiacus muntjak). In the case of species with dietary and habitat changes, the Pleistocene C4-grazer enamel isotopes showed a shift towards greater reliance on C3 plants or more closed environments during the Holocene. The isotopic evidence raises the question of whether climatic and environmental changes and/or anthropogenic pressure have significantly driven the population decline of threatened species and can contribute to the understanding of future conservation outlooks of existing wildlife populations in Southeast Asia.

Amino acid stable carbon isotopes in nail keratin illuminate breastfeeding and weaning practices of mother – infant dyads

Compound-specific stable carbon isotope analysis of amino acids (CSIA-AA) is widely used in ecological studies to analyze food-webs and is gaining use in archaeology for investigating past diets. However, its use in reconstructing breastfeeding and weaning practices is not fully understood. This study evaluates the efficacy of stable carbon isotope analysis of amino acids in early life diet reconstruction by analyzing keratin from fingernail samples of three mother-infant pairs during late gestation and early postpartum periods. Our results show that stable carbon isotope ratios (δ13C) of glycine, and to a lesser extent glutamate, effectively trace the onset of exclusive breastfeeding and the end of weaning in infants. We propose that glycine’s ‘conditionally essential’ metabolic pathway during infancy allows it to reflect maternal glycine δ13C, indicating breastmilk consumption. Subtle changes in glutamate δ13C likely result from its ‘non-essential’ status. Additionally, δ13C values of glycine and glutamate indicate maternal physiological and pathological stress due to catabolic effects such as gluconeogenesis. These findings have significant implications for ecological and archaeological research using CSIA-AA for dietary reconstructions. They highlight the need to understand how metabolic pathways affecting δ13C of amino acids may change over an individual’s lifespan or be altered due to various forms of stress.

Geographical Variation in Carbon and Nitrogen Stable Isotope Ratios and Feeding Habits of Japanese Jack Mackerel (Trachurus japonicus)

ABSTRACTJapanese jack mackerel (Trachurus japonicus) is subject to substantial and escalating commercial harvesting activities, yet its habitat structure is poorly understood. We analyzed the carbon and nitrogen stable isotope ratios (δ13C and δ15N) of this species to evaluate geographical fluctuations in these ratios, allowing a delineation of the jack mackerel feeding habits. Fish specimens were collected across the East China Sea (ECS) and Sea of Japan (JS), and isotopic data were retrieved from two previous studies. Six subareas were considered: the southern, central, and northern ECS; Tsushima Strait; and eastern and western JS. The residuals of isotope ratios predicted from fork length showed significant geographical variation in the ratios (a lower δ13C in the JS than in the ECS and Tsushima Strait; a lower δ15N in the eastern JS and southern ECS than in other areas). Comparisons of stable isotope ratios between jack mackerel and prey candidates also revealed geographical differences in potential prey selection. The potential prey was identified as anchovy larvae and larger Copepoda in the western and eastern JS, respectively, whereas various prey species contributed to the diet in the other areas. Both δ13C and δ15N increased with fork length, suggesting ontogenetic changes in foraging habitat, associated with habit shifts into demersal layers of jack mackerel during their growth. Collectively, our results suggest that stable isotope ratio values—and consequently, the feeding habits—of jack mackerel differed between the ECS and JS but that they possess a limited migration range after an ontogenetic shift to demersal layers.

The power and pitfalls of amino acid carbon stable isotopes for tracing origin and use of basal resources in food webs

AbstractNatural and anthropogenic stressors alter the composition, biomass, and nutritional quality of primary producers and microorganisms, the basal organisms that synthesize the biomolecules essential for metazoan growth and survival (i.e., basal resources). Traditional biomarkers have provided valuable insight into the spatiotemporal dynamics of basal resource use, but lack specificity in identifying multiple basal organisms, can be confounded by environmental and physiological processes, and do not always preserve in tissues over long timescales. Carbon stable isotope ratios of essential amino acids (δ13C‐EAA) show remarkable promise in identifying and distinguishing clades of basal organisms with unique δ13C‐EAA fingerprints that are independent of trophic processing and environmental variability, providing unparalleled potential in their application. Understanding the biochemical processes that underpin δ13C‐AA data is crucial, however, for holistic and robust inferences in ecological applications. This comprehensive methodological review, for the first time, conceptualizes these mechanistic underpinnings that drive δ13C‐EAA fingerprints among basal organisms and incorporates δ13C values of non‐essential amino acids that are generally overlooked in ecological studies, despite the gain of metabolic information. We conduct meta‐analyses of published data to test hypothesized AA‐specific isotope fractionations among basal organism clades, demonstrating that phenylalanine separates vascular plant δ13C‐EAA fingerprints, which strongly covaries with their phylogeny. We further explore the utility of non‐essential AAs in separating dietary protein sources of archaeological humans, showing the differences in metabolic information contained within different NEAAs. By scrutinizing the many methodologies that are applied in the field, we highlight the absence of standardized analytical protocols, particularly in sample pretreatments leading to biases, inappropriate use of statistical methods, and reliance on unsuitable training data. To unlock the full potential of δ13C‐EAA fingerprints, we provide in‐depth explanations on knowledge gaps, pitfalls, and optimal practices in this complex but powerful approach for assessing ecosystem change across spatiotemporal scales.

Hydrothermal Methane Venting and Its Microbial Oxidation Along the Eastern Southwest Indian Ridge, 63.5°–68°E

AbstractMethane concentration and its stable carbon isotope ratio studies were carried out in deep waters of ultraslow‐spreading eastern Southwest Indian Ridge (eSWIR), 63.5°–68°E, to identify hydrothermal plumes and associated biogeochemical processes. High methane concentrations (1.0–37.8 nmol/kg) confirm the presence of 11 hydrothermal plumes along the ∼500 km long section of eSWIR. Among these 11 plumes, eight are reporting for the first time. Detailed investigations near 67.67°E; 26.61°S show the presence of three plumes at various depths and their dispersion &gt;100 km along the ridge in east‐west directions. Stable carbon isotope ratios of these plumes show lighter and heavier isotope enrichment (−40‰ to −3‰). Lighter isotope enrichment may indicate that methane could be derived from a combination of abiotic and thermogenic sources and, heavier isotope enrichment is mainly because of microbial methane oxidation. We report strong evidence for the presence of an active hydrothermal field at 67.67°E; 26.61°S in the eSWIR for the first time.

The return of raptors to Scotland's skies: Investigating the diets of reintroduced red kites and white-tailed eagles using stable isotopes.

Species reintroductions are increasingly seen as important methods of biodiversity restoration. Reintroductions of red kites Milvus milvus and white-tailed eagles Halieaeetus albicilla to Britain, which were extirpated in the late 19th and early 20th centuries, represent major conservation successes. Here, we measured stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) in feather keratin and bone collagen of museum specimens of red kites and white-tailed eagles, which were collected from across Scotland between the 1800s and 2010s. Our objectives were to investigate dietary differences between species and between the pre- and post- reintroduction periods. Among reintroduced birds, δ13C values were significantly less negative and δ15N values higher in feather keratin and bone collagen of white-tailed eagles compared to red kites, likely reflecting a greater reliance on marine resources by the former. Our stable isotope data showed a wide range, confirming the dietary diversity observed in conventional diet studies of both taxa, with white-tailed eagles, in particular, having wide dietary niches and a considerable degree of inter-individual variability. Isotopic data from pre-introduction red kites mostly fell within the range of post-reintroduction birds, suggesting they had similar diets to the pre-reintroduction birds, or the prey base for modern birds is isotopically indistinguishable from that of their historic counterparts. For white-tailed eagles, several pre-reintroduction birds were isotopically distinct from the post-reintroduction population. These differences may indicate a changing prey base, although these conclusions are complicated by shifting distributions and small population samples. Overall, our study demonstrates the utility of natural history collections in examining changes in diet, environment, and interactions with humans in reintroduced species compared with pre-extirpation indigenous populations.

Dietary Shifts Among the Developmental Stages of the Ectoparasite, Argulus japonicus (Crustacea; Branchiura), Mirror Ontogeny as Shown Through Differences in Stable Isotope Ratios of Carbon (δ13C) and Nitrogen (δ15N).

Food web architecture and trophic interactions between organisms can be studied using ratios of naturally occurring stable isotopes of carbon (13C/12C) and nitrogen (15N/14N). Most studies, however, focused on free-living organisms, but recently, there has been growing interest in understanding trophic interactions of parasites. The crustacean ectoparasite Argulus japonicus is a well-studied parasite of freshwater teleost fish, which has low host specificity and a cosmopolitan distribution. Little is known about the trophic interactions between various developmental stages of this parasite and its host. This study compares stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) among developmental stages of A. japonicus. It was hypothesised firstly that stable isotopes would vary among the developmental stages of the parasite with differences matching ontogenetic development of the parasite. Secondly, fractionation patterns among developmental stages would relate to different fish tissues and particles, such as algae, ingested by the parasite. Goldfish, Carassius auratus, were infected with A. japonicus, and different developmental stages of the parasite were isolated and prepared for stable isotope analysis. Differences in stable isotope enrichment correlated with the ontogenetic development of the parasite. In adult parasites, δ15N was higher than in the host's tissues, whereas stage two larvae showed the lowest δ15N values. Infection by A. japonicus alters δ13C ratios between infected and uninfected hosts, where the latter group showed lower δ13C compared to uninfected hosts. Source contribution comparison showed that algae was not incorporated into the diet of A. japonicus and tissues of the host served as the only dietary source of nourishment. These results further suggest that the diet of the parasite is mixed and correlates to the ontogenetic development of A. japonicus.

Identification of 3-methoxytyramine as a specific biomarker for beet-sugar-fed honey: A two year surveillance study in South Korea

Identification of 3-methoxytyramine as a specific biomarker for beet-sugar-fed honey: A two year surveillance study in South Korea

Ecosystem engineers alter the evolution of seed size by impacting fertility and the understory light environment

AbstractIt has been hypothesized that the extinction of the dinosaurs, and later the Pleistocene megafauna, created a darker forest subcanopy benefiting large‐seeded plants. Larger seeds and their fruit, in turn, opened a dietary niche space for animals thus strongly shaping the ecology of the Cenozoic, including our fruit‐eating primate ancestors. In this paper, we develop a mechanistic model where we replicate the conditions of tropical forests of the early Paleocene, with small animal body and small seed size, and the Holocene, with small animal body and large seed size. We first calibrate light levels in our model using stable carbon isotope ratios from fossil leaves and estimate a decrease of understory light of c. 90 μmol m−2 s−1 (a 19% decrease) from the Cretaceous to the Paleocene. Our model predicts a rapid increase in seed size during the Paleocene that eventually plateaued or declined slightly. Specifically, we find a dynamic feedback where increased animal sizes opened the understory causing negative feedback by increasing subcanopy light penetration that limited maximum seed size, matching the actual trend in angiosperm seed sizes in mid/high latitude ecosystems. Adding the ability of larger animals to increase ecosystem fertility to the model, further increased mean animal body size by 17% and mean seed size by 90%. Our model is a drastic simplification and there are many remaining uncertainties, but we show that ecological dynamics can explain seed size trends without adding external factors such as climate change.

A high-resolution record of Late Holocene drought in the eastern Sierra Nevada (California, USA) from June Lake carbonate geochemistry

AbstractAs historic drought conditions become more common in western North America, Late Quaternary hydroclimate records become vital for putting present anthropogenic conditions into a longer-term context. Here, we establish a high-resolution record of drought for the eastern Sierra Nevada (California) using lacustrine carbonates from well-dated sediment cores. We used oxygen and carbon stable-isotope ratios, combined with high-resolution scanning X-ray fluorescence counts of calcium (Ca) and titanium (Ti), to reconstruct the drought record over the last 4600 years in June Lake. We found elevated δ18O and δ13C carbonate isotope values coinciding with peaks in both total inorganic carbon and Ca/Ti, suggesting enhanced carbonate precipitation in response to evaporative concentration of lake water. At least six intervals of prolonged (centennial-scale) carbonate deposition were identified, including three pulses during the Late Holocene Dry Period (LHDP; ~3500–2000 cal yr BP), the Medieval Climate Anomaly (~1200–800 cal yr BP), and the Current Warm Period, which began around 100 cal yr BP. This record highlights the complexities of the LHDP, an interval that was more variable at June Lake than has been previously described in regional records.