Average δ15N Values Research Articles

Oceanographic transport along frontal zones forms carbon, nitrogen, and oxygen isoscapes on the east coast of New Zealand: Implications for ecological studies

Characterizing the spatial distribution of δ18O in seawater and δ15N and δ13C in marine particulate organic matter pools can be useful in identifying isotopic discriminators of major water masses and serve as a baseline for food web and other ecological studies. Nevertheless, we do not know how isoscapes of δ18O, δ15N and δ13C are distributed and interact with mesoscale (10–100 km) physical oceanographic features for large parts of the global ocean. Here samples and measurements were collected during research cruises in the austral summer of 2017/18 and 2018/19 along the east coast of the South Island of New Zealand. The physical structure of the water column, δ18O of seawater, and δ15N and δ13C of suspended particulate organic matter were analyzed. Interannual differences in inferred circulation, oceanographic features, and the interaction of Subtropical and Subantarctic water masses in the study area were described. The relationships between nutrient concentrations, physical oceanographic variables and δ18O, δ15N and δ13C isoscapes were investigated by running linear models with all combination of variables, then averaging the most parsimonious ones that best fit the data. Results demonstrate that different environments along the east coast are connected via northward transport of Subtropical Water near the surface and Subantarctic Mode Water at depth (220–500 m). The northward transport of modified STW was associated with nutrient inputs and deepening of the maximum fluorescence depth. The spatial distribution of isotopic values had minimal temporal variability and was primarily linked to patterns of nutrient input (δ15N), coastal productivity (δ13C) and water mass type (δ18O). δ15N values demonstrated significant spatial variation, while δ18O displayed distinct values among depths. The present study was the first to resolve the distribution of δ15N and δ13C isotopes at a regional scale along the east coast of the South Island of New Zealand, δ18O in New Zealand waters, and to investigate the extent to which these distributions were influenced by patterns in physical oceanography. Average values of δ18O, δ15N and δ13C for different fishery management areas and depths are presented to support future ecological studies along Southeast New Zealand.

Trophic structure and resource utilization of the coastal fish community in the western Wadden Sea: evidence from stable isotope data analysis

We studied the trophic structure of the western Wadden Sea fish community through stable isotope analysis (δ13C and δ15N) of 1658 samples from 57 fish species collected between 2012 and 2016. Stable isotope values differed between species but did not vary between years or seasons, and only for some species with fish size. Stable isotope values were not different between immigrating (spring) and emigrating (autumn) fish, suggesting a similar trophic niche of the various fish species in the coastal zone and inside the Wadden Sea. For the majority of species, average δ13C values were within the range of -12 to -20.5‰, showing that both (marine) pelagic and benthic primary producers were at the base of the food web. Average δ15N values varied among species from 13-18‰, resulting in estimated trophic positions (TPs) of 2.1-5.5 with the majority between 2.2 and 3.5. Thick-lipped grey mullet Chelon labrosus, golden grey mullet C. aurata, greater pipefish Syngnathus acus and pilchard Sardina pilchardus had the lowest TP (2.2-2.4). Among the common species (>10 observations), the highest TP values (3.4-3.5) were found for twaite shad Alosa fallax, smelt Osmerus eperlanus, bull-rout Myoxocephalus scorpius, bass Dicentrarchus labrax and cod Gadus morhua. For all species, estimated TPs based on isotope values were lower than those based on stomach content composition (2.0-4.7), which could be explained by species-specific differences in trophic fractionation or by underestimation of the contribution of smaller prey species in the stomach content analysis. The trophic niche space of benthopelagic species was the smallest and overlapped with that of the pelagic and benthic species. In terms of area use, trophic niche space was smaller for juvenile marine migrant species (nursery-type species) and overlapped with that of the (near-)resident species and marine seasonal visitors. Potentially, trophic competition is highest for the functional group of benthopelagic species and the guild of juvenile marine migrant species (nursery-type species).

Changes of δ15N values during the volatilization process after applying urea on soil.

Ammonia (NH3) volatilized from soils plays an important role in N cycle and air pollution, thus it is important to trace the emission source and predict source contributions to development strategies mitigating the environmental harmful of soil NH3 volatilization. The measurements of 15N natural abundance (δ15N) could be used as a complementary tool for apportioning emissions sources to resolve the contribution of multiple NH3 emission sources to air NH3 pollution. However, information of the changes of δ15N-NH3 values during the whole volatilization process under different N application rates are currently lacking. Hence, to fill this gap, we conducted a 15-day incubation experiment included different urea-N application rates to determine δ15N values of NH3 during volatilization process. Results showed that volatilization process depleted 15N in NH3. The average δ15N value of NH3 volatilized from the 0, 20, 180, and 360kgN ha-1 treatment was-16.2±7.3‰,-26.0±5.4‰,-34.8±4.8‰, and-40.6±5.7‰. Overall, δ15N-NH3 values ranged from-46.0‰ to-4.7‰ during the whole volatilization process, with lower in higher urea-N application treatments than those in control. δ15N-NH3 values during the NH3 volatilization process were much lower than those of the primary sources, soil (-3.4±0.1‰) and urea (-3.6±0.1‰). Therefore, large isotopic fractionation may occur during soil volatilization process. Moreover, negative relationships between soil NH4+-N and NH3 volatilization rate and δ15N-NH3 values were observed in this study. Our results could be used as evidences of NH3 source apportionments and N cycle.

Livestock as an indicator of socioeconomic changes in Medieval Prague (Czech Republic)

The continuity of occupation at the settlement of Prague, Czech Republic, from the ninth to fourteenth centuries makes it a good case study for investigating the evolution of animal husbandry practices during the Early and High Middle Ages. Previous archaeozoological work shows that people’s dietary behaviour in Prague underwent a transformation at the beginning of the High Middle Ages (thirteenth century). This change has been attributed to large-scale socioeconomic transformations, which may have affected animal management practices. Stable carbon (δ13C) and nitrogen (δ15N) isotope analysis of the tooth dentine collagen of livestock (cattle, domestic pigs, sheep and goats) from three different areas in Prague (the Lesser Town, Prague Castle and the Old Town) presented in this study provides support for this hypothesis. The range of stable isotope values increased over time, which may, in addition to a farm-household model, indicate a more advanced system of livestock supply–for example, through urban markets–and may also be explained by more diversified breeding conditions in the town and its surroundings. The results show an increase in the δ15N values in pig diet over time and suggest that their management changed. This difference may have been caused by increased animal protein intake or higher δ15N value of the dietary sources. It has also been corroborated that the root dentine collagen of High Medieval cattle has slightly higher average δ15N values when compared to cattle from the earlier period, which could be related to gradual changes in landscape utilization and soil processing, such as fertilization.

Stratospheric Incursion as a Source of Enhancement of the Isotopic Ratios of Atmospheric N2O at Western Pacific

AbstractWe present analyses of nitrogen and oxygen isotopic ratios and site‐preference (SP) values of atmospheric nitrous oxide samples obtained from Taiwan in west Pacific. Air samples were collected during September 2013 to January 2016 from Taipei and during November 2011 to December 2014 from Keelung, located in the northeastern coast of Taiwan. The average values of δ15N, δ18O, and SP are 6.4 ± 0.3 ‰, 44.0 ± 0.4 ‰, and 17.1 ± 1.0 ‰, respectively, at Taipei and 6.4 ± 0.2 ‰, 44.6 ± 0.4 ‰, and 17.9 ± 1.3 ‰, for δ15N, δ18O, and SP respectively, at Keelung, comparable to the average values (6.6 ± 0.2, 44.2 ± 0.2, and 18.1 ± 0.5 ‰, scaled to year 2014) from Hateruma, an open ocean station in western Pacific. Strong temporal variations in the delta values, however, are seen. During a subtropical jet‐strengthening period in October to mid‐December 2014, the δ15N, δ18O and SP values increased at the rate of 0.006 ± 0.002 ‰/day, 0.010 ± 0.002 ‰/day and 0.008 ± 0.002 ‰/day, respectively at Taipei and 0.013 ± 0.005 ‰/day, 0.011 ± 0.005 ‰/day and 0.011 ± 0.027 ‰/day at Keelung. This suggests intrusion of air to the lower troposphere from the stratosphere where δ15N, δ18O and SP values are higher. This is consistent with earlier observations of oxygen isotope anomaly in atmospheric CO2 and elevated 35S in sulfate aerosols, indicating frequent stratospheric intrusions in this region. The observed δ15N and δ18O values, along with the oxygen isotope anomaly in CO2 and multiple sulfur isotopes in sulfate, can be used to constrain local emissions from the surface, improving our knowledge of anthropogenic contribution to the global budget of N2O.

Trophic interactions between gall-forming molluscs <i>Stilifer </i>spp. (Gastropoda, Eulimidae) and their hosts (Echinodermata)

The trophic relationships between two species of symbiotic gall-forming molluscs from the genus Stilifer (family Eulimidae) and two of their hosts-asteroid species, Linckia laevigata and Culcita noveaguineae, were investigated using the stable isotope analysis of carbon and nitrogen. The aim of present study was to identify the most preferable host tissue in the symbionts’ diet. We analyzed δ15N and δ13C values in tube-feet, gonads and digestive glands of the hosts-starfishes and in muscles of the molluscs. Both symbiont species did not differ to each other both in δ15N and δ13C values. The average δ15N and δ13C values of Stilifer variabilis were significantly different from the digestive glands and gonads of their host Culcita novaeguineae and did not show differences from the tube-feet of starfishes. A similar pattern was found in the symbiotic association of Stilifer utinomi and Linckia laevigata. The tube-feet of analyzed starfishes had significantly higher average δ15N and δ13C values than the digestive glands and gonads. Obtained isotopic signatures indicate that symbionts do not feed on the host's tissues, but take nutrients from their digestive system. It seems that the proboscis of Stilifer spp. absorbs the nutrients from the digestive system of the host-starfish thereby not disturbing significantly the host's immune system.

Chemical and stable isotopic characteristics of PM2.5 emitted from Chinese cooking

This study investigated the characteristics of air pollutants generated from preparing Chinese cuisine and analyzed the isotopic compositions of carbon and nitrogen in particulate matter with a diameter <2.5 μm (PM2.5) to source apportionment study. The CO and CO2 concentrations and temperatures were measured using suitable instruments in real time during cooking, including stir-fry, fry, deep-fry, hot-pot, and mixed cooking, and periods with non-cooking. Personal environmental monitoring instruments were used to collect PM2.5 for carbon and nitrogen elements and isotopes analysis. Our data indicated that the concentrations of CO and CO2 and the temperature were higher during periods of cooking, especially for the fry and stir-fry methods, than during periods with non-cooking. The concentrations of PM2.5, total carbon, and total nitrogen were also higher during cooking; the maximum concentrations were measured during fry. The values of δ13C were considerably lower during the periods of cooking (mean: −28.15‰) than during non-cooking (−27.18‰). The average values of δ15N were 8.63‰ and 11.74‰ during deep-fry and hot-pot cooking, respectively. The δ13C values can be used to distinguish between cooking and other non-cooking sources and further assess the effect of different cooking activities on PM2.5. The δ15N only can be used to investigate the effect of deep-fry on PM2.5. Moreover, the δ13C signature suggested that fry emits higher products of incomplete combustion than do other cooking activities. These findings can assist in pollution source identification of PM2.5, emission control, and the study of combustion characteristics.

Fossil-driven secondary inorganic PM2.5 enhancement in the North China Plain: Evidence from carbon and nitrogen isotopes

Measuring isotopic ratios in aerosol particles is a powerful tool for identifying major sources, particularly in separating fossil from non-fossil sources and investigating aerosol formation processes. We measured the radiocarbon, stable carbon, and stable nitrogen isotopic composition of PM2.5 in Beijing (BJ) and Changdao (CD) in the North China Plain (NCP) from May to mid-June 2016. The mean PM2.5 concentrations were 48.6 ± 28.2 μg m−3 and 71.2 ± 29.0 μg m−3 in BJ and CD, respectively, with a high contribution (∼66%) from secondary inorganic aerosol (SIA; NO3−, NH4+, and SO42−).The mean δ13C of total carbon (TC) and δ15N of total nitrogen (TN) values differed significantly between the two sites (p-value of <0.001): −25.1 ± 0.3‰ in BJ and −24.5 ± 0.4‰ in CD and 10.6 ± 1.8‰ in BJ and 5.0 ± 3.1‰ in CD, respectively. In BJ, the average δ15N (NH4+) and δ15N (NO3−) values were 12.9 ± 2.3‰ and 5.2 ± 3.5‰, respectively. The ionic molar ratios and isotopic ratios suggest that NO3− in BJ was formed through the phase-equilibrium reaction of NH4NO3 under sufficient NH3 (g) conditions, promoted by fossil-derived NH3 (g) transported with southerly winds. In BJ, fossil fuel sources comprised 52 ± 7% of TC and 45 ± 28% of NH4+ on average, estimated from radiocarbon (14C) analysis and the δ15N and isotope mixing model, respectively. These multiple-isotopic composition results emphasize that PM2.5 enhancement is derived from fossil sources, in which vehicle emissions are a key contributor. The impact of the coal source was sporadically noticeable. Under regional influences, the fossil fuel-driven SIA led to the PM2.5 enhancements. Our findings demonstrate that the multiple-isotope approach is highly advantageous to elucidate the key sources and limiting factors of secondary inorganic PM2.5 aerosols.

Pig-Breeding Management in the Early Medieval Stronghold at Mikulčice (Eighth–Ninth Centuries, Czech Republic)

ABSTRACT The archaeozoological analysis sets point to the vital role of pigs in the subsistence economy of Early Medieval Mikulčice, an important Great Moravian centre (Czech Republic). The results of slaughtering distribution analyses indicate that pigs were a meat source for a consumer population. Analyses of stable isotopes of nitrogen and carbon suggest that the demand for pork was predominantly met by animals raised by extensive husbandry. . In addition to extensive breeding, small-scale household rearing was also documented. The assumed length of the fattening period represented a more important factor for δ15N values. It has been determined that pigs that were slaughtered at the latest after two years consumed protein-richer fodder when the roots of their third molars were formed. By contrast, the collagen of pigs that were expected from the outset to be used for long-term breeding shows lower values of the isotope in question. It has also been corroborated that the root dentine collagen of domestic pigs from the bailey has slightly higher average δ15N values compared to the collagen of pigs from the acropolis. Such a difference may be explained by different husbandry management techniques having been applied within a single settlement.

Plant response to N availability in permafrost-affected alpine wetlands in arid and semi-arid climate zones

Nutrient cycling in alpine permafrost-affected wetlands remains insufficiently studied, as it is influenced by a complex network of interrelated climatic and environmental factors, at both regional and local scale. Therefore, we applied mathematical models to examine relationship between environmental factors and plant functional traits reflecting N availability in wetland communities developed under locally variable conditions in a geographic and climatic gradient of high-altitude habitats. Moreover, we assessed impact of local differences in soil chemistry on plant fractionation of N isotopes as a response to N availability. Based on environmental data and chemistry of biomass from 192 study sites from the Pamir Mountains (Tajikistan) and Khangai and Khentei Mountains (Mongolia), a matrix of rank correlations was prepared for regional and local factors and community level plant functional traits. For the traits that were highly correlated either with regional or with local drivers (that is plant N:P ratio and plant δ15N), linear models were built, with a limited set of predictors selected according to the Risk Inflation Criterion and the SOS algorithm. The models were fitted for each of the studied regions. Presented regional models indicated significant influence of soil NH4+ and/or PO43− content on plant N:P ratio, which showed increase with altitude and lowering precipitation. Thus, its values clearly distinguished between the Pamir Mountains (high N:P) and the Mongolian ranges (low N:P). Models for plant δ15N showed its strong positive correlations with soil δ15N and soil salinity. Average values of plant δ15N were comparable for both study areas. The studied plant functional traits showed different response to regional and local drivers. Plant N:P ratio was controlled by regional drivers via their influence on soil NH4+ content. Contrastingly, plant δ15N was significantly affected by local factors, namely soil δ15N and soil salinity expressed as Na:EC.

Biological nitrogen fixation in field-grown sorghum under different edaphoclimatic conditions is confirmed by N isotopic signatures

The association between sorghum and N2-fixing bacteria has been assessed only under limited conditions. We investigated biological nitrogen fixation (BNF) in situ in fifteen sorghum genotypes with dry or succulent culm types under five edaphoclimatic conditions. One randomized block experiment was established in each of five locations, from the humid to the semiarid regions of Pernambuco state, Brazil. BNF was estimated using the 15N natural abundance method by comparing the average δ15N value of each sorghum genotype with those of the reference species. High levels of productivity, up to 22 Mg shoot biomass ha−1 in the 3-month cycle, were obtained where rainfall was high, and up to 5 Mg ha−1 was obtained under low rainfall. The nitrogen contents showed a similar pattern as biomass production, and the genotypes with the highest productivity accumulated from 200 to 300 kg N ha−1. BNF ranged from 55 to 78% of plant N in one location and from 36 to 56% in another location, but BNF did not occur in the other three locations. Although the factors that blocked effective symbiosis were not determined, symbiosis was not influenced by P or K availability. The proportion of N2 fixation was similar in the grain-producing, dry culm genotypes and in the sugar-rich, succulent culm genotypes. The sorghum genotypes fixed N2, reaching up to 218 kg ha−1 N, without inoculation with diazotrophs. Therefore, sorghum has a high potential to fix atmospheric N2, but the factors that block N2 fixation must be identified for crop management planning.

A comparison of nitrogen isotope compositions of charred and desiccated botanical remains from northern Peru

Isotopic measurements of plant remains from archaeological sites are now routinely used to reconstruct agricultural practices in the Old World. These studies use charred botanical remains as the analytical substrate because (1) these are the materials that are commonly preserved in the archaeological record and (2) the integrity of the isotopic compositions of archaeological plant remains that are uncharred or desiccated has been questioned, particularly for δ15N. By comparing charred and uncharred plant remains from two Late Moche (ad 600–800) sites in the Jequetepeque valley on the north coast of Peru—San Jose de Moro and Cerro Chepen—we sought to directly test the assumption that the isotopic compositions of desiccated plant remains are not representative of the isotopic compositions of the living plants. The average δ15N values of charred (+11.3 ± 4.4‰) and desiccated (+10.1 ± 5.1‰) remains from these two sites did not significantly differ from one another, suggesting that uncharred plant remains can produce reliable isotopic measurements under some circumstances. Furthermore, the relatively high δ15N values of the plant remains from these two sites are consistent with the ancient use of composted camelid manure as a fertilizer.

Isotopic insights into mesopelagic niche space and energy pathways on the southern Kerguelen Plateau

Mesopelagic fish are an important but poorly understood mid-trophic component of pelagic food webs. There are major uncertainties regarding their trophodynamics and their overall contribution to the broader Southern Ocean food web. This study aimed to investigate the trophic role of mesopelagic fish in the region of the southern Kerguelen Plateau, an area of known importance to an abundant and diverse community of marine predators. We used carbon and nitrogen stable isotopes to quantify the isotopic niches of key mesopelagic fish species (six from the family Myctophidae, and one from Bathylagidae), and assessed variation along the δ15N (resource use) and δ13C (carbon source) axes between species. The assemblage of key mesopelagic fish occupied similar isotopic niche space with overlap among species in both δ13C and δ15N values. Baseline corrected δ15N values provided evidence of latitudinal trends in trophic position (TP). Trophic position estimates of taxa in the southern region of our study area spanned slightly less than 1 TP (mean TP 2.9–3.7); and 1 TP in the northern region (mean TP 3.2–4.2). We found evidence of trophic partitioning between species with differences in niche utilization (resource or habitat use). Factors reducing trophic competition include the relative importance of Euphausia superba as a prey item, vertical distribution of consumer and prey, and migratory behaviours. Size-based trophic structuring between species was evident with larger species displaying higher average δ15N values compared to smaller species. However, fish standard length explained little of the variation in δ15N values at the species level, suggesting within species changes in trophic position with body size is not a predominant driver of trophic structure in our study region. Overall, our analysis demonstrated the structural complexity and spatial variation of the food web in the region of the southern Kerguelen Plateau.

Leaf and Soil δ15N Patterns Along Elevational Gradients at Both Treelines and Shrublines in Three Different Climate Zones

The natural abundance of stable nitrogen (N) isotope (δ15N) in plants and soils can reflect N cycling processes in ecosystems. However, we still do not fully understand patterns of plant and soil δ15N at alpine treelines and shrublines in different climate zones. We measured δ15N and N concentration in leaves of trees and shrubs and also in soils along elevational gradients from lower altitudes to the upper limits of treelines and shrublines in subtropical, dry- and wet-temperate regions in China. The patterns of leaf δ15N in trees and shrubs in response to altitude changes were consistent, with lower values occurring at higher altitude in all three climate zones, but such patterns did not exist for leaf Δδ15N and soil δ15N. Average δ15N values of leaves (−1.2‰) and soils (5.6‰) in the subtropical region were significantly higher than those in the two temperate regions (−3.4‰ and 3.2‰, respectively). Significant higher δ15N values in subtro4pical forest compared with temperate forests prove that N cycles are more open in warm regions. The different responses of leaf and soil δ15N to altitude indicate complex mechanisms of soil biogeochemical process and N sources uptake with environmental variations.

Carbon and nitrogen isotopic composition of commercial dog food in Brazil.

BackgroundBrazil is a low- to medium-income country and has the second largest pet food market in the world with 8% of world pet food consumption. The lowest-income social class spends around 17% of their domestic budget on pet food and other items related to pets. Consumers are frequently misled by advertising as there is no precise information about the main sources of protein, carbohydrates and fat in the labels, and the Brazilian pet food industry can legally claim that their products contain certain items like salmon or beef even if they use just a flavoring compound.MethodsThe stable isotope methodology compares the stable isotope ratios of carbon (13C/12C) and nitrogen (15N/14N) between source and product. The 13C/12C ratio of a specific product (e.g., dog food) reveals the proportions of C4 (maize) and C3 (soybean, rice and wheat) plants in that product and the 15N/14N ratio reveals the proportion of the compounds derived from animals. With this isotopic data, we used MixSIAR, a Bayesian stable isotope-mixing model, to estimate the proportion of maize, grains, poultry and beef in dog food.ResultsThe δ13C values of dry dog food ranged from −24.2‰ to −12.8‰, with an average (± standard-deviation) of −17.1‰ ± 2.8‰. The δ13C values of wet pet food ranged from −25.4‰ to −16.9‰, with an average (± standard-deviation) of −21.2‰ ± 2.4‰, which was significantly lower (p < 0.01). The δ15N values of the dry and wet food ranged from 1.7‰ to 4.2‰, and from 0.5‰ to 5.5‰, respectively. The average δ15N values of dry food (2.9‰ ± 0.5‰) was not higher than the wet food (2.6‰ ± 1.3‰) (p > 0.01). The output of the MixSIAR showed a low proportion of bovine products in dry dog food samples. On the other hand, poultry was obviously the dominant ingredient present in most of the samples. Maize was the second dominant ingredient. Wet and dry dog food showed similar isotopic analysis results. The only difference was a lower proportion of maize and higher proportion of grains in wet dog food.DiscussionThe main finding is that dog food in Brazil is mostly made of approximately 60% (ranging from 32% to 86%) animal-based and 40% (ranging from 14% to 67%) plant-based products. Poultry and maize are the main ingredients. Poultry is added as a by-product or meal, which avoids competition between dogs and humans for meat products, while they can compete for maize. On the other hand, a large proportion of plant-based products in dog food decreases the energy and environmental footprint, since plant-based food products tend to be less harmful compared to animal-based products. Labels can mislead consumers by showing pictures of items that are not necessarily part of the product composition and by not showing the detailed information on the proportion of each ingredient. This information would allow customers to make their own choices considering their pet’s nutrition, the competition between animals and humans for resources and environmental sustainability.

Spatial heterogeneity of food web structure in a large shallow eutrophic lake (Lake Taihu, China): implications for eutrophication process and management

The knowledge of food web spatial heterogeneity is important for ecologists and lake managers to understand ecosystem complexity and lake management. Lake Taihu, a large shallow eutrophic lake in China, has two distinct zones: algae- and macrophyte-dominated. In this study, we assessed the spatial heterogeneity of food webs in the two lake zones using stable isotope analysis and isotope mixing model. The basal sources and consumers showed significant differences in δ13C and δ15N ratios between the two lake zones, except for the filter-feeding fishes. Overall, more δ13C-depleted and δ15N-enriched ratios were found in the algae- than the macrophyte-dominated zones for basal sources and consumers. Although the consumers in the algae-dominant zone had higher average δ15N values, the food web of the macrophyte-dominated zone had longer food chain length and more diverse trophic linkages. These spatial differences may have resulted from resource availability and environmental stress of Lake Taihu ecosystem. Factors associated with spatial trophic heterogeneity should be considered for the management and restoration of this shallow eutrophic lake.

Stable carbon and nitrogen isotope compositions of bulk aerosol samples over the South China Sea

The marine aerosols is mainly produced primary sea salt and secondary form of non-sea salt (nss) sulfate and organic species from marine emission, but get modified significantly by the anthropogenic and terrestrial materials, such as total carbon (TC) and total nitrogen (TN), which transported by the atmospheric circulation from land to the ocean. Rarely studies focus on the TC and TN in marine aerosol in the open ocean due to the sampling difficulty, let alone the annual observation. Concentrations of TC and TN, and their isotope compositions (δ13C-TC and δ15N-TN) were measured in total suspended particulate (TSP) which sampled at Yongxing Island over the South China Sea from March 2014 to February 2015, and coastal mega-city Guangzhou in April/May and October/November 2014. The annual average concentrations of TC and TN at Yongxing Island were 4.20 ± 2.38 μg m−3 and 0.77 ± 0.47 μg m−3, respectively. Much higher concentration of TC and TN were observed at Guangzhou. Contributions of NO3− and NH4+ (inorganic nitrogen, IN) to TN at Yongxing Island averaged 55.7% and 6.8%, respectively, while they averaged 27.4% and 12.2% at Guangzhou, respectively. The average values of δ15N in TN were +0.7 ± 3.3‰, +6.8 ± 6.3‰ and −0.7 ± 2.7‰ during winter, transitional and warm seasons, respectively, with an annual average value of +1.1 ± 4.3‰. The δ13C of TC varied from −16.2 to −26.8‰, with an annual average value of −22.7‰. The average of values of δ13C were −22.9 ± 1.7‰, −22.9 ± 1.4‰, and −22.4 ± 2.6‰ during winter, transitional and warm seasons, respectively. The average values of δ15N in TN and δ13C of TC were +13.2 ± 0.9‰ and −25.8 ± 0.4‰ in winter season, +13.6 ± 0.8‰ and - 26.5 ± 0.3‰ in warm season at Guangzhou, respectively. Based on aerosol δ15N and δ13C values, the marine realm may be an important source of aerosol TN, while aerosol TC may dominantly contributed by the combustion of fossil fuels and biomass burning from continental mass over the South China Sea. The secondary aerosol formation and long-range transport on aerosol chemistry also varied the concentrations and isotopic composition of TN and TC at Yongxing Island.

Variations in Denitrification and Ventilation Within the Arabian Sea Oxygen Minimum Zone During the Holocene

AbstractThe continental slope of India is exposed to an intense perennial oxygen minimum zone (OMZ) supporting pelagic denitrification. Sediments that are presently in contact with the lower boundary of the denitrification zone indicate marked changes in the intermediate and bottom waters ventilation of OMZ during the past 9,500 years. The δ15N of sediment suggests that the OMZ waters were less ventilated during the early Holocene (between 9.5 and 8.5 ka BP) resulting in intensified denitrifying conditions with an average δ15N value of 7.8‰, while at the same time stable Mo isotope composition (average δ98Mo of −0.02‰) indicates that the bottom waters that were in contact with the sediments were better oxygenated. By the mid‐Holocene OMZ became more oxygenated suppressing denitrification (average δ15N of 6.2‰), while bottom waters gradually became less oxygenated (average δ98Mo of 1.7‰). The mid‐Holocene reduction in denitrification coincided with a global decrease in atmospheric N2O as inferred from ice core records, which is consistent with a decreased contribution from the Arabian Sea. Since ~5.5 ka BP OMZ waters have again been undergoing progressive deoxygenation accompanied by increasing denitrification.

Upper trophic structure in the Atlantic Patagonian shelf break as inferred from stable isotope analysis

The Patagonian Shelf is a very productive region with different ecosystem structures. A long history of fishing in the Southwestern Atlantic Ocean combined with a complex hydrographic structure, with a permanent front over the shelf-break and different coastal frontal regions, and a wide non-frontal area in between have made the food web in this area more complex and have resulted in changes to the spatialtemporal scale. Stable isotopes of carbon and nitrogen were used to determine the trophic structure of the Patagonian shelf break which was previously poorly understood. The results indicated that the average δ15N value of pelagic guild (Illex argentinus) was remarkable lower than those of the other guilds. The δ13C values of almost all species ranged from -17‰ to -18‰, but Stromateus brasiliensis had a significant lower δ13C value. Compared with the southern Patagonian shelf, short food chain length also occurred. The impact of complex oceanographic structures has resulted in food web structure change to the temporal-spatial scale on the Patagonian shelf. The Patagonian shelf break can be considered as a separated ecosystem structure with lower δ13C values.

Stable carbon isotopic composition indicates large presence of maize in Brazilian soy sauces (shoyu)

Carbon and nitrogen (N) isotopic compositions were used to test the presence of C4 carbon in soy sauces (shoyu) produced in Brazil. Seventy samples of Brazilian shoyu were analyzed and compared with the same product from Japan, China, Singapore, Taiwan, and United States. The average (±standard-deviation) δ13C of the Brazilian shoyu was −15.0 ± 3.4. The average (±standard-deviation) δ13C of five shoyu samples from Japan was −25.2 ± 0.6‰. The δ13C of shoyu from US (−25.3‰) and Singapore (−25.9‰) were close to Japanese samples. Shoyu δ13C values from China were equal to −20‰ and −15.4‰, and from Taiwan equal to −20.2‰. The average δ15N value of Brazilian shoyu was 0.3 ± 1.2‰. The variability of δ15N values among shoyu from other countries was much lower than Brazilian shoyu, and the average was 1.4 ± 0.3‰. Using a simple isotopic mass balance, we estimated that most of the shoyu in Brazil contains <20% soy, and the dominant cereal is maize, probably because in Brazil maize is cheaper than soybean.