Higher δ13C Values Research Articles

Body size, depth of occurrence, and local oceanography shape trophic structure in a diverse deep-pelagic micronekton assemblage

The Gulf of Mexico’s (GOM) deep-pelagic realm is one of the planet’s most speciose pelagic ecoregions, but detailed knowledge of ecosystem structure and function is lacking. Understanding trophic structure is critical to understanding ecosystem dynamics as trophic interactions regulate the flow of energy through ecosystems and influence the resilience of ecosystems to disturbance. Using novel stable isotope (SIA) data and historical stomach content (SCA) data, we examined deep-pelagic trophic structure using 58 species of micronekton from the GOM that encompassed a variety of migratory behaviors, depth distributions, and trophic strategies. We identified major trophic groupings, explored the extent that differences in diet, body size, vertical migration, and presence of a mesoscale feature (Loop Current) explained micronekton isotopic variation and estimated species-specific trophic positions. Cluster analysis of SIA data identified four trophic groups, although species were not strictly clustered by diet. Specifically, non-migratory zooplanktivores with elevated δ15N values were grouped with vertically migrating piscivores, suggesting some non-migratory species could be feeding within food chains with elevated isotopic baselines. The mean δ13C values of species encompassed a narrow range from −21.6 ‰ to −18.1 ‰, with variation in δ13C values of vertically migrating species explained by a positive relationship with body size and higher δ13C values in Loop Current water. In contrast, variation in δ13C values of non-migrators was primarily explained by elevated values in deeper-dwelling species and in larger species. The mean δ15N values of species ranged between 5.0 ‰ and 11.5 ‰, with variation in δ15N values of vertical migrators explained by a positive relationship with body size and lower δ15N values in Loop Current water. Variation in the δ15N values of non-migrators was largely explained by elevated δ15N values in deeper-dwelling species and in larger-bodied species. Trophic position (TP) estimations for the assemblage ranged between 2.6 and 4.9. The elevated δ15N values in non-migratory species led to higher TP estimates relative to estimates derived from stomach content data, but agreement between TP estimates using SIA and SCA was high for vertically migrating taxa. This discrepancy may be a factor of vertical migrating species having a more similar feeding depth than non-migrators. Our results provide important insight into the trophic organization of low-latitude oligotrophic ecosystems and demonstrate that trophic variation within micronekton assemblages is primarily driven by differences in body size, location in the water column and position relative to salient oceanographic features.

Ecological effects of mosquito control with Bti: evidence for shifts in the trophic structure of soil- and ground-based food webs

The microbial control agent Bacillus thuringiensis var. israelensis (Bti) has been successfully used worldwide to reduce abundances of biting Nematocera (Diptera), often with little direct impact on non-target organisms observed. However, the potential for additional indirect effects on other ecosystem properties, including on trophic linkages within food webs, is poorly known. We investigated the effects of multiple-year mosquito control treatments using the Bti product VectoBac®-G on the stable isotope composition of epigeal and soil-based consumers inhabiting replicate floodplains along the River Dalälven, Sweden. We observed significant changes in the isotopic composition of detritivores feeding at the base of floodplain food webs. Enchytraeid worms were characterised by 3.5% higher δ13C values in treated floodplains, suggesting increased consumption of δ13C-enriched food. The overall range of community-wide δ15N values was 56% greater in the treated floodplains, whilst δ15N values of oribatid mites were elevated by 97%. These results suggest extra fractionation in the transfer of nitrogen through floodplain food chains. We conjecture that the ecological mechanisms driving these food web shifts are (1) the mass mortality of high δ13C A. sticticus larvae, which leaves high concentrations of dead mosquito biomass deposited on soils at local scales, after the floodwaters have receded and (2) incorporation of the very high δ13C-enriched corn particles comprising the bulk of the VectoBac®-G product into floodplain food webs. Our results suggest that repeated applications of Bti might have wider, still largely unknown implications for nutrient and energy cycles within floodplain ecosystems.

Dietary niche reconstruction of Pliocene and Pleistocene Equidae from the Linxia Basin of northwestern China based on stable isotope analysis

In this paper, stable isotope (δ13C, δ18O) analyses of five equid species from the Linxia Basin, northwestern China, were conducted to investigate dietary niche turnover during a critical Pliocene-Pleistocene phase in the evolution of Old World Equidae. In the Early Pliocene Shilidun fauna, Proboscidipparion pater is inferred to have mainly fed on C3 grasses in open grasslands as indicated by their relatively high δ13C values (−9.1 ± 0.4‰, five teeth, n = 61), whereas Cremohipparion licenti and Sivalhippus platyodus were possibly mixed feeders inhabiting woodlands and grasslands because of their comparatively low δ13C values (−10.8 ± 0.6‰, seven teeth, n = 36; −10.6 ± 0.6‰, nine teeth, n = 35). Inhabiting the same environments, both C. licenti and S. platyodus went extinct, possibly, because climatic changes led to a decline in woodlands resulting in greater competition. In the Early Pleistocene Longdan fauna, Proboscidipparion sinense had higher δ13C values (−9.1 ± 0.5‰, four teeth, n = 23) than coexisting Equus eisenmannae (−10.2 ± 0.5‰, eight teeth, n = 57), implying that P. sinense had a stronger grazing preference compared to E. eisenmannae. Ecomorphological analyses (body size, tooth crown height, and enamel surface complexity) reveal that P. pater and P. sinense had dental characteristics consistent with a strong grazing preference. Therefore, P. pater might have been preadapted to open grasslands during the warm and humid Early Pliocene, which helped its descendent P. sinense persist into the Pleistocene. The results of this study reveal distinct dietary niches for these equids for the first time and shed light on some aspects of the evolutionary history of Equidae in East Asia.

Is the damage worth it? Testing handheld XRF as a non-destructive analytical tool for determining biogenic bone and tooth chemistry prior to destructive analyses

Isotopic analysis is destructive and requires that a specimen retains its original (biogenic) chemical composition. A specimen's relative abundance of calcium and phosphorous (Ca/P) or carbonate and phosphate (CO3/PO4) is often used to assess preservation. If a specimen's Ca/P or CO3/PO4 is similar to modern specimens, a specimen's isotopic composition may be biogenic. However, most methods for measuring these proxies are destructive. Moreover the relationships between Ca/P, CO3/PO4 and isotopic preservation are poorly established. In this study, we assessed the ability of handheld X-ray fluorescence (hXRF) to non-destructively evaluate a specimen's preservation by characterizing the calcium to phosphorous ratio (Ca/P). We first established that surface Ca/P (Ca/Psurface) for modern specimens was consistent with expectations for unaltered bone (1.3–2.3). Several specimens had slightly larger ratios, suggesting the currently accepted range may need to be expanded. Second, we tested the ability of Ca/Psurface to detect alteration using twenty Quaternary mammal teeth from Big Bone Lick, Kentucky. Ten specimens had Ca/Psurface between 1.3 and 2.3 and ten had larger ratios, suggesting alteration. Because most methods measure Ca/P in powder (Ca/Ppowder), we compared Ca/Psurface, Ca/Ppowder, and the enamel subsurface (Ca/Psubsurface). With two exceptions, Ca/Psubsurface and Ca/Ppowder were below 2.3, regardless of Ca/Psurface, suggesting that Ca/Ppowder and Ca/Psubsurface underestimate alteration. We next compared Ca/Psurface, CO3/PO4, and carbon (δ13C) and oxygen (δ18O) isotope values for the fossil teeth. Fourteen specimens were identified as altered or unaltered by both proxies, but six specimens only had one altered proxy. Specimens with both proxies altered had lower, less variable δ13C values than specimens with both proxies unaltered. Median δ18O values were similar between these groups. Individuals with altered Ca/Psurface but unaltered CO3/PO4 isotopically resembled specimens with both proxies altered. Conversely, specimens with unaltered Ca/Psurface and altered CO3/PO4 were similar to specimens with both proxies unaltered. Notably, all individuals with both proxies altered had relatively low δ13C values, including a horse and mammoth, which are normally considered grazers (and therefore should have higher δ13C values). These and other altered specimens may be isotopically compromised. Overall, our results suggest that Ca/Psurface is effective at detecting alteration non-destructively, quickly, and affordably, making it an attractive approach for analyzing unique specimens.

Reconstructing midge consumer-resource dynamics using carbon stable isotope signatures of archived specimens.

Population cycles can be caused by consumer-resource interactions. Confirming the role of consumer-resource interactions, however, can be challenging due to an absence of data for the resource candidate. For example, interactions between midge larvae and benthic algae likely govern the high-amplitude population fluctuations of Tanytarsus gracilentus in Lake Mývatn, Iceland, but there are no records of benthic resources concurrent with adult midge population counts. Here, we investigate consumer population dynamics using the carbon stable isotope signatures of archived T. gracilentus specimens collected from 1977 to 2015, under the assumption that midge δ13 C values reflect those of resources they consumed as larvae. We used the time series for population abundance and δ13 C to estimate interactions between midges and resources while accounting for measurement error and possible preservation effects on isotope values. Results were consistent with consumer-resource interactions: high δ13 C values preceded peaks in the midge population, and δ13 C values tended to decline after midges reached high abundance. One interpretation of this dynamic coupling is that midge isotope signatures reflect temporal variation in benthic algal δ13 C values, which we expected to mirror primary production. Following from this explanation, high benthic production (enriched δ13 C values) would contribute to increased midge abundance, and high midge abundance would result in declining benthic production (depleted δ13 C values). An additional and related explanation is that midges deplete benthic algal abundance once they reach peak densities, causing midges to increase their relative reliance on other resources including detritus and associated microorganisms. Such a shift in resource use would be consistent with the subsequent decline in midge δ13 C values. Our study adds evidence that midge-resource interactions drive T. gracilentus fluctuations and demonstrates a novel application of stable isotope time-series data to understand consumer population dynamics.

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

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

Multi-origin authigenic calcite controlled by the depositional environment and fluid−rock interactions in the Triassic siliciclastic strata, Junggar basin, NW China

Authigenic calcite records geologic fluid activities in sedimentary rocks, and its origin varies with changing sedimentary environments and fluid−rock interactions. This study investigated authigenic calcite with multiple origins in the Triassic siliciclastic strata of the petroliferous Mahu Sag, Junggar Basin, NW China. Detailed core logging was followed by lithological studies including optical, scanning electron and cathodoluminescence microscopic observations together with geochemical analyses of major elements and stable carbon and oxygen isotopes. The results show that there are three stages of calcite in the Baikouquan Formation with significantly differential MnO contents (average = 0.94%, 3.87%, 7.84%, respectively) and obviously negative δ13C values (−57.5‰ to −13.9‰, VPDB). It reflects the evaporation during deposition, and oxidation of hydrocarbon in oxidizing diagenetic environment. Extensive feldspar dissolution promotes the precipitation of late-stage calcite. There are two stages of calcite in the Karamay Formation and Baijiantan Formation. The positive correlation of their MgO and FeO contents reflects the alteration of volcanic materials in the strata. For the early-stage calcite, the low MnO contents (average = 0.50% and 0.61%) and positive δ13C values (>−10‰), demonstrate the paleo-meteoric water input. While the high MnO contents (average = 4.59%) and negative δ13C values (−25‰ to −10‰) of the late-stage calcite in the Karamay Formation indicate hydrocarbon charging and subsequent decarboxylation of organic acid, accompanied by feldspar dissolution. The late-stage recrystallization calcite of the Baijiatan Formation inherits the MnO and carbon isotopic characteristics of the early-stage calcite. This study shows that authigenic calcite is an effective recorder of sedimentary environment and fluid−rock interactions in siliciclastic strata. It enhances the heterogeneity of siliciclastic strata and is beneficial to hydrocarbon accumulation in lithological reservoirs.

Cross-Analysis of carbon and nitrogen stable isotopes in hairs retrieved from crania of Korean Joseon Dynasty Mummies and Russian Settlers in Siberia

A specific human population’s diet can be estimated by analysis of carbon and nitrogen isotopes in bones or other organic materials unearthed at archaeological sites. In the present study, we investigated the dietary patterns of two agrarian populations of the Eurasian continent to determine if they might show heterogeneities despite their temporal and lifestyle commonalities. Hairs from mummies representative of Joseon Dynasty Koreans and the remains of Russian settlers in Siberia were analyzed by a stable-isotope technique and further compared with corresponding data on Edo-period Japanese. In brief, the 17th to 18th century Russian settlers, a Western population that had partially adopted a native-Siberian dietary strategy, lived on C3 plants and protein-rich foods relative to the Koreans and Japanese. The highest δ13C value among the three groups was observed in the Koreans’ hairs, indicating that their diet had been more C4 plants-based. The second-highest δ15N value (statistically higher than that of the Japanese samples) likewise was found in Korean hairs. In this study, we could conclude that all three Eurasian groups relied on a subsistence agricultural economy during the 16th to 19th centuries but that their dietary lifeways had somewhat diverged.

The arrival of millets to the Atlantic coast of northern Iberia

Despite being one of the most important crops in the recent prehistory of Eurasia, the arrival and exploitation of millets in the westernmost part of Europe are still largely underexplored. Here and for the first time, we report multipronged biomolecular evidence of millet consumption along the Atlantic façade of northern Iberia through a combination of radiocarbon dating, stable isotopes, and dental calculus analyses on the human individuals found in the burial site of El Espinoso cave (Asturias, Spain). The high-resolution chronological framework established for individuals placed the burials between 1235 and 1099 cal. BC. The discovery of high δ13C values on their bone collagen and the identification of polyhedral starch grains within their dental plaque underline the relevance of C4 plants in their diet and highlights the timing of the systematic consumption of millets in the Late Bronze Age. Our data support previous regional archaeobotanical evidence and establish a more precise chronology of the dispersal of millets into northern Iberia during the Bronze Age, becoming an essential crop until the arrival of maize from America after AD 1492. This study emphasizes the importance of multidisciplinary methods to ascertain the origin and development of agricultural practices during recent prehistory.

Stable isotope and elemental profiles determine geographical origin of saffron from China and Iran

Origin verification of high-value saffron is essential for fair trade and to protect consumers' interests and rights. A traceability method using elemental content (% C and % N) and stable isotopes (δ13C, δ2H, δ18O, and δ15N) combined with chemometrics was developed to discriminate saffron from Iran and China and classify major domestic production areas in China. Results showed that Iranian samples had lower % C and % N contents but higher δ13C values than Chinese origin saffron, with δ13C acting as an important variable for origin discrimination. Moreover, δ2H and δ13C isotopes were found to be important variables to classify Chinese regional saffron origin. Two supervised pattern recognition models (PLS-DA) developed to classify Iranian and Chinese saffron, and regional Chinese saffron had a discrimination accuracy of 85.0 % and 80.2 %, respectively. These models provide the basis for a new regulatory inspection procedure to verify saffron origin and label claims, minimizing fraudulent mislabeling and adding value to saffron from specific regions.

Stalagmite evidence of Last Glacial Maximum to early Holocene climate variability in southwestern Iran

ABSTRACTGlacial periods and their terminations are useful for assessing the full scale of natural climate variability in the diverse climate regions of West Asia (i.e. deserts, mountains, alluvial plains, coastal zones). In this study, we report the first stalagmite stable isotope (δ18O and δ13C) records from the southern Zagros Mountains in southwest Iran. The records partially span the period from the Last Glacial Maximum (LGM) to the early Holocene, 24.2–9.6 thousand years before the present. The southwest Iran stalagmite δ18O and δ13C records indicate that climate and environment in the area differed substantially between the LGM and early Holocene. High stalagmite δ13C values are found at the LGM (7‰ greater compared to the early Holocene), and are attributed to sparse vegetation and reduced soil bio‐productivity, and possibly a greater degree of prior calcite precipitation in the epikarst, as a result of a cold and dry climate. Stalagmite δ18O values are also high at the LGM (4‰ greater compared to the early Holocene), and are attributed to lower temperatures (larger water–calcite isotope fractionation) and higher δ18O values of the moisture sources (Mediterranean and Red Seas). Through the deglaciation, stalagmite δ18O, δ13C and/or growth features coincide with the North Atlantic Heinrich Stadial 1, the Bølling–Allerød warm period and the Younger Dryas cold event, supporting a relationship between southern Zagros climate and the North Atlantic millennial events.

Functional traits of riparian trees in the lower Fitzroy River, Western Australia

AbstractRiparian trees are critically important for maintaining the ecological function of freshwater ecosystems. Globally, anthropogenic changes to water regimes are impacting the health and distribution of riparian trees. Understanding the physiological constraints on the distribution of riparian tree species in relation to the water regime is essential for informed water resource management that seeks to limit impacts on riparian trees. To fill an identified knowledge gap for the Fitzroy River, a significant river in the wet–dry tropics of north‐western Australia, we used a trait‐based approach to characterise nine common riparian tree species in relation to their distribution along a hydrological gradient. We assessed key functional traits related to drought and flood flows. Leaf mass per unit area (LMA), leaf dry matter content (LDMC), foliar carbon content (% C) and the ratio of carbon to nitrogen (C:N) are broadly related to plant productivity and durability and may reflect resistance to fluvial stress. Traits related to water availability were stem specific density (SSD), mean xylem vessel diameter and xylem vessel density, as well as foliar δ13C which is related to water use efficiency, and leaf osmotic potential at full hydration (π100) as a measure of drought tolerance. We found that π100, δ13C and SSD values reflected species hydrological habitat preferences, with higher δ13C values and lower π100 for species distributed in the drier floodplain habitats, compared with species constrained to the riverbank. Low SSD values for species close to the riverbank may be indicative of aerenchyma tissue in response to flooding. Differences in leaf trait values were primarily attributed to differences between evergreen Myrtaceous and deciduous non‐Myrtaceous species, rather than hydrological habitat preferences. LMA was greatest for the Myrtaceous study species, with deciduous non‐Myrtaceous species associated with wetter habitats having the lowest values. The physiology of riparian trees in northern Australia is not well described for the majority of species. Our study provides insight into plant functional strategies in response to both flooding and drought and is a critical step in understanding plant responses to future water‐take scenarios to support evidence‐based decision making.

Seasonality of precipitation in the southwestern United States during the late Pleistocene inferred from stable isotopes in herbivore tooth enamel

The late Pleistocene was a climatically dynamic period, with abrupt shifts between cool-wet and warm-dry conditions. Increased effective precipitation supported large pluvial lakes and long-lived spring ecosystems in valleys and basins throughout the western and southwestern U.S., but the source and seasonality of the increased precipitation are debated. Increases in the proportions of C4/(C4+ C3) grasses in the diets of large grazers have been ascribed both to increases in summer precipitation and lower atmospheric CO2 levels. Here we present stable carbon and oxygen isotope data from tooth enamel of late Pleistocene herbivores recovered from paleowetland deposits at Tule Spring Fossil Beds National Monument in the Las Vegas Valley of southern Nevada, as well as modern herbivores from the surrounding area. We use these data to investigate whether winter or summer precipitation was responsible for driving the relatively wet hydroclimate conditions that prevailed in the region during the late Pleistocene. We also evaluate whether late Pleistocene grass C4/(C4+ C3) was higher than today, and potential drivers of any changes.Tooth enamel δ18O values for Pleistocene Equus, Bison, and Mammuthus are generally low (average 22.0 ± 0.7‰, 2 s.e., VSMOW) compared to modern equids (27.8 ± 1.5‰), and imply lower water δ18O values (−16.1 ± 0.8‰) than modern precipitation (−10.5‰) or in waters present in active springs and wells in the Las Vegas Valley (−12.9‰), an area dominated by winter precipitation. In contrast, tooth enamel of Camelops (a browser) generally yielded higher δ18O values (23.9 ± 1.1‰), possibly suggesting drought tolerance. Mean δ13C values for the Pleistocene grazers (−6.6 ± 0.7‰, 2 s.e., VPDB) are considerably higher than for modern equids (−9.6 ± 0.4‰) and indicate more consumption of C4 grass (17 ± 5%) than today (4 ± 4%). However, calculated C4 grass consumption in the late Pleistocene is strikingly lower than the proportion of C4 grass taxa currently present in the valley (55–60%). δ13C values in Camelops tooth enamel (−7.7 ± 1.0‰) are interpreted as reflecting moderate consumption (14 ± 8%) of Atriplex (saltbush), a C4 shrub that flourishes in regions with hot, dry summers.Lower water δ18O values, lower abundance of C4 grasses, and the inferred presence of Atriplex are all consistent with general circulation models for the late Pleistocene that show enhanced delivery of winter precipitation, sourced from the north Pacific, into the interior western U.S. but do not support alternative models that infer enhanced delivery of summer precipitation, sourced from the tropics. In addition, we hypothesize that dietary competition among the diverse and abundant Pleistocene fauna may have driven the grazers analyzed here to feed preferentially on C4 grasses. Dietary partitioning, especially when combined with decreased pCO2 levels during the late Pleistocene, can explain the relatively high δ13C values observed in late Pleistocene grazers in the Las Vegas Valley and elsewhere in the southwestern U.S. without requiring additional summer precipitation. Pleistocene hydroclimate parameters derived from dietary and floral records may need to be reevaluated in the context of the potential effects of dietary preferences and lower pCO2 levels on the stability of C3 vs. C4 plants.

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

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

Origin of microbial–hydrothermal bedded dolomites in the Permian Lucaogou Formation lacustrine shales, Junggar Basin, NW China

Dolomite is widely developed in the shale sequences of saline lakes and has significance in paleoenvironmental, paleoclimatic, and petroleum geology research. In this study, a new end-member type of dolomite is discovered from the Permian Lucaogou Formation in the Junggar Basin, northwest China, along with its geological significance. The microbial–hydrothermal origin of the bedded dolomite is evident from the development of hydrothermal minerals (including barite and cubic pyrite) and methanogenic micro-organisms. In terms of geochemistry, the bedded dolomite has high (Ba/La)N ratios (~2.8) and Sr contents (~594.9 ppm) and positive Sr anomalies (Sr/Sr* ~3.8). Chondrite-normalized rare earth element (REE) patterns exhibit light REE enrichment, heavy REE depletion, slightly positive Ce anomalies, and negative Eu anomalies. The bedded dolomite has relatively low 87Sr/86Sr ratios (~0.705283), high δ13C values (~6.63‰ ), and low δ18O values (~−9.92‰ ). All these indicate that the dolomitizing fluid is a mixed source of hydrothermal fluids and lake waters, and the hydrothermal fluids and microbial methanogenesis provided the Mg2+ and C, respectively. The combination of microbial and hydrothermal activity overcame the limitation of dolomitization hydration shells around Mg2+. In terms of geological significance, the studied Lucaogou Formation was deposited in an extensional tectonic setting under hot–arid climatic conditions, which controlled the high-frequency interbedding and meter-scale cyclicity of sediment deposition of dolomites and shales. The combined effects of tectonism and paleoclimate may be important factors for the formation of bedded dolomite, enrichment of organic matter and hydrocarbons in saline lacustrine shales.

Distribution of black carbon in sediments from mangrove wetlands in China

Black carbon (BC) is a carbonaceous residue generated by the incomplete combustion of fossil fuels and biomass. It forms an important component of the mangrove carbon pool. Although coastal and marine sediments have long been recognized as important sinks for BC, there are few reports on its distribution in mangrove sediments. This study investigated BC distribution and the associated environmental implications in sediments of various size fractions. Mangrove sediments were collected from 44 sites in the Guangdong, Guangxi, Hainan, and Fujian Provinces of China. Sediments from the Hainan Province were found to have much higher organic carbon (OC) and BC content than those from other provinces. Sediment OC and the BC content showed a significant positive relationship. Sediments from the Guangdong, Guangxi, and Hainan provinces showed significant BC accumulation with an enrichment factor &amp;gt; 1, especially in the size fractions 0.053–0.25 mm and 0.25–2 mm. Sediments from different sampling sites did not show significantly different BC distribution between the various size fractions. A higher mass loading of BC was observed among fine particles in samples from the Fujian Province, and among the larger particles in samples from the Guangdong, Guangxi, and Hainan provinces. Among all the samples, the BC/OC ratio ranged from 0.21 to 0.29, indicating that BC originates from a combination of biomass and mineral combustion. The average δ13C values in the sediments varied between the sampling plots. The highest δ13C values were recorded in the Fujian province, which indicates the proportion of BC from biomass combustion in mangroves in Fujian Province is higher than that in other Provinces.

Fault zone fluid pathways in the carbonate Irecê basin, NE Brazil

AbstractWe applied field structural data and isotope geochemical (δ13C, δ18O and 87Sr/86Sr) analyses to understand the relationship among calcite veins, fault damage zones and carbonate host rocks in a thrust fault damage zone in the Achado quarry, Irecê Basin in the São Francisco Craton, NE Brazil. Our results reveal three hydrological packages with different rheological behaviours in a stratified carbonate succession. The upper package includes the Achado fault damage zone that is characterised by interlayered dolomitised grainstones and mudstones. These rocks display high positive δ13C values (10‰–13‰), negative δ18O values (mean −6.34‰) and radiogenic (87Sr/86Sr) isotope values (0.70885–0.71519). A second package is marked by a cataclastic brittle shear zone lateral parallel to dolograinstones bedding. These rocks show low to positive δ13C values (−3.41‰ to +8.85‰), more positive δ18O values (mean −3.73‰) and radiogenic (87Sr/86Sr) isotope values (0.71039–0.71373). The lower package is characterised by well‐preserved pristine limestone succession that shows δ13C values ranging between −0.46‰ and +3.17‰, mean δ18O = −5.41‰ and less radiogenic 87Sr/86Sr values (0.70762–0.70818). In contrast to the upper and intermediate packages, rocks from the lower one exhibit very low permeability and behaved as a seal for fluid migration. Fluid flow occurred several times during basin evolution, for example along syn‐rift fault damage zones, bedding‐parallel carbonate breccia, thrust faults, cataclastic shear zones, synorogenic conjugate shear fractures or joints and opening mode I fracture‐fill calcite veins. These fractures allowed pervasive fluid flow in the porous intermediate cataclastic shear zone where fluids flowed and formed veins, as diffuse fluid flow in randomly oriented fracture swarms, or channelised fluid flow in aligned fracture corridors. They record significant centimetre‐scale to km‐scale hydrological behaviour within carbonate layers. Most carbonates that are associated with veins, fault damage zones and hydraulic breccia were formed by fluids of the same origin with low δ13C (−6.0 to −2.0‰) and δ18O (−6.0 to −8.5‰) values, and more radiogenic 87Sr/86Sr values compared to the carbonate host rocks.

Technical note: Examining the use of ethylenediaminetetraacetic acid for humic extraction of ancient bone

We examined the efficacy of ethylenediaminetetraacetic acid (EDTA) for removing humic contaminants from collagen extracted from ancient bone. Humic contaminants must be removed to obtain reliable stable isotope values from ancient bone collagen, given that humic acids have consistently lower δ13C values than collagen. The purpose of our research was to examine if EDTA treatment could effectively remove humic contaminants from bone collagen and thus serve as an alternative to the commonly implemented sodium hydroxide (NaOH) treatment, which may be associated with large collagen losses in poorly preserved samples. We compared the isotopic and elemental composition of ancient samples treated with EDTA alone, samples demineralized in hydrochloric acid (HCl) and rinsed in EDTA, samples treated with HCl alone, and samples demineralized in HCl and rinsed with NaOH. The samples used in the analyses were selected because they presented evidence of substantial humic contamination. We found that NaOH was the most effective agent for reducing humic contaminants as evidenced by the samples treated with this agent having higher δ13C values and lower C:N ratios relative to other treatments. The results from samples treated with EDTA suggest that this chemical cannot effectively remove humic contaminants given that these samples had significantly higher C:N ratios and lower δ13C and δ15N values relative to the HCl/NaOH treatment. Our results demonstrate that when performing stable isotope analysis of ancient bone collagen suspected to be contaminated with humic acids, NaOH is the most effective chemical agent to remove humic contaminants, while EDTA cannot perform this task.

Ecophysiological Responses of Tall Wheatgrass Germplasm to Drought and Salinity.

Tall wheatgrass (Thinopyrum ponticum (Podp.) Barkworth and D.R. Dewey) is an important, highly salt-tolerant C3 forage grass. The objective of this work was to learn about the ecophysiological responses of accessions from different environmental origins under drought and salinity conditions, to provide information for selecting superior germplasm under combined stress in tall wheatgrass. Four accessions (P3, P4, P5, P9) were irrigated using combinations of three salinity levels (0, 0.1, 0.3 M NaCl) and three drought levels (100%, 50%, 30% water capacity) over 90 days in a greenhouse. The control treatment showed the highest total biomass, but water-use efficiency (WUE), δ13C, proline, N concentration, leaf length, and tiller density were higher under moderate drought or/and salinity stress than under control conditions. In tall wheatgrass, K+ functions as an osmoregulator under drought, attenuated by salinity, and Na+ and Cl− function as osmoregulators under salinity and drought, while proline is an osmoprotector under both stresses. P3 and P9, from environments with mild/moderate stress, prioritized reproductive development, with high evapotranspiration and the lowest WUE and δ13C values. P4 and P5, from more stressful environments, prioritized vegetative development through tillering, showing the lowest evapotranspiration, the highest δ13C values, and different mechanisms for limiting transpiration. The δ13C value, leaf biomass, tiller density, and leaf length had high broad-sense heritability (H2), while the Na+/K+ ratio had medium H2. In conclusion, the combined use of the δ13C value, Na+/K+ ratio, and canopy structural variables can help identify accessions that are well-adapted to drought and salinity, also considering the desirable plant characteristics. Tall wheatgrass stress tolerance could be used to expand forage production under a changing climate.

Micromilling vs hand drilling in stable isotope analyses of incremental carbonates: The potential for δ13 C contamination by embedding resin.

RationaleEmbedding resins are commonly used to facilitate high‐resolution sampling for stable isotope analysis but anomalous δ13C values have been observed in some cases. Here we compare the results of microsampling strategies for hand‐drilled versus resin‐embedded micromilled samples from the same marine shells to assess whether resin contamination is implicated in δ13C spikes. The comparison allows assessment of the relative benefits for spatial resolution, seasonal range for both δ18O and δ13C, and sample failure rates.MethodsHand‐drilled samples were obtained from two bivalve shells (Spisula sachalinensis), corresponding to micromilled samples on the same shells where high δ13C spikes were observed. All carbonate powders were analysed using a dual‐inlet Isoprime mass spectrometer and Multiprep device. Results from both sample sets were compared statistically.ResultsNo anomalous high δ13C values and no failures due to insufficient gas were observed in the hand‐drilled samples in contrast to the embedded micromilled sequences. Spatial resolution was reduced (~2.5×) in the former compared with the latter, resulting in a small reduction in the total range observed in the micromilled δ13C and δ18O values. Reduced sampling resolution between the two datasets was only significant for δ18O.ConclusionsFor S. sachalinensis (as with other similar bivalves), rapid growth mitigates the reduced sampling resolution of hand drilling and does not significantly impact observed isotopic range and seasonal patterning. Occurrence of anomalous δ13C values were eliminated and failure rates due to insufficient sample size greatly reduced in the hand‐drilled dataset. We can find no other explanation for the occurrence of δ13C spikes than contamination by the embedding agent. We conclude that the logistical and interpretational benefits of careful hand drilling may be preferable to resin embedding for micromilling in marine shells, corals or speleothems where growth rate is rapid and the highest resolution is not required.