delta13C Values Research Articles

Multi-proxy record of ocean-climate variability during the last two millennia on the Mackenzie Shelf, Beaufort Sea

A 2,000 year-long oceanographic history, in sub-centennial resolution, from a Canadian Beaufort Sea continental shelf site (60meters water depth) near the Mackenzie River outlet is reconstructed from ostracode and foraminifera faunal assemblages, shell stable isotopes (delta 18O, delta 13C) and sediment biogenic silica. The chronology of three sediment cores making up the composite section was established using 137Cs and 210Pb dating for the most recent 150 years and combined with linear interpolation of radiocarbon dates from bivalve shells and foraminifera tests.Continuous centimeter-sampling of the multicore and high-resolution sampling of a gravity and piston core yielded a time-averaged faunal record of every approximately 40 years from 0 to 1850 CE and every approximately 24 years from 1850 to 2013 CE. Proxy records were consistent with temperature oscillations and related changes in organic carbon cycling associated with the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). Abundance changes in dominant microfossil species, such as the ostracode Paracyprideis pseudopunctillata and agglutinated foraminifers Spiroplectammina biformis and S. earlandi, are used as indicators of less saline, and possibly corrosive/turbid bottom conditions associated with the MCA (approximately 800 to 1200 CE) and the most recent approximately 60 years (1950–2013). During these periods, pronounced fluctuations in these species suggest that prolonged seasonal sea-ice melting, changes in riverine inputs and sediment dynamics affected the benthic environment. Taxa analyzed for stable oxygen isotope composition of carbonates show the lowest delta 18O values during intervals within the MCA and the highest during the late LIA, which is consistent with a 1 degree to 2 degree C cooling of bottom waters. Faunal and isotopic changes during the cooler LIA (1300 to 1850 CE) are most apparent at approximately 1500 to 1850 CE and are particularly pronounced during 1850 to approximately 1900 CE, with an approximate 0.5 per mil increase in delta 18O values of carbonates from median values in the analyzed taxa. This very cold 50-year period suggests that enhanced summer sea ice suppressed productivity,which is indicated by low sediment biogenic silica values and lower delta 13C values in analyzed species. From 1900CE to present, declines in calcareous faunal assemblages and changes in dominant species (Cassidulina reniforme and P. pseudopunctillata) are associated with less hospitable bottom waters, indicated by a peak in agglutinated foraminifera from 1950 to 1990 CE.

Helicobacter pylori infection and UBT-13C values are associated with changes in body mass index in children and adults.

The urea breath test (UBT-13C) is a non-invasive technique that allows the diagnosis and confirmation of eradication of Helicobacter pylori infection. To evaluate H. pylori positivity and values of UBT-13C among infected Chilean children and adults, and to analyze its variation in relation to sex, nutritional status, and age of the patients. Retrospective study of 1141 patients aged 6 to 94 years, with an indication for a UBT-13C either for diagnosis or for confirmation of eradication of H. pylori infection. 13C enrichment was measured using an infrared spectrometer calculating the delta 13C values before and after the ingestion of 13C marked urea. The clinical data of the patients were obtained at the time of the examination. We included 241 children and 900 adults. Infected children obtained lower UBT-13C delta values than infected adults (16.1 ± 8.7 and 37 ± 52.9, respectively). The rates of infection were higher in males who were recruited for diagnosis. Significant differences were obtained between positivity for H. pylori in overweight and obese children but not adults. UBT-13C titers were significantly associated with the body mass index (BMI) only in adults. H. pylori infection rates are similar between sexes and are higher in children probably because of selection bias. In children, H. pylori positivity is associated with higher BMI and excess malnutrition although with similar UBT-13C values. In adults, H. pylori infection is not related with BMI, but a higher BMI impacts UBT-13C titers.

The Ediacaran record of glaciogenic dropstones, diamictites and cap carbonates associated with non-metamorphosed banded iron formations (BIFs) in Iran

The Ediacaran period is marked by global icehouse episode, greenhouse period, increasing levels of oxygen-carbon dioxide, syn-glaciogenic structures-BIFs, typical Ediacaran biota and a marked negative carbon isotope excursion. On this global point, field glaciogenic structures, petrographic textures, Ediacaran biota, U-Pb zircon ages, C-O isotopes and geochemical data record an Ediacaran glaciogenic BIFs event in Iran. The Ediacaran (578–547 or 578–541.8 Ma) glaciogenic sequences in Bafq and Hormuz Island mining districts include submarine syn-glaciovolcanic rhyolitic rocks, rhyolitic tuffs, shaly tuffaceous carbonates, dropstone-bearing jaspilitic BIFs, salt minerals, ferruginous diamictites, and cap carbonates. The presence of polygonal, bullet-shape and flatiron forms of gneiss, greenschist, quartz schist, quartzite, marble and magnetite-hematite clasts in a matrix of jaspilitic magnetite-hematite, muddy sandstones and muddy dolomitic rocks records an Ediacaran glaciogenic event. The dropstones occur as lone-stones, dump-stones and deflect their underlying layers. The diamictites contain similar clasts to those of the dropstones, are gradationally covered by buff to dark-grey cap carbonates ± dropstones and resemble the Ghaub, Chuos and Kingston Peak Formation diamictites. C-O isotopes, REE+Y diagrams, high Y/Ho ratios, positive Eu-Y anomalies and subtle Ce anomaly possibly reflect a possible hydrothermal origin for the cap carbonates. Delta 13C values (−0.42 to −6.33‰) in cap carbonates show similar negative signatures to the Ediacaran Shuram glaciogenic event. Average delta 18O (−8.34‰) in the least-altered cap carbonates gives a precipitation temperature of 252.7 °C in the waning stage of the glaciogenic BIFs-hydrothermal system.

Carbonatite-melilitite-phosphate immiscible melts from the aragonite stability field entrained from the mantle by a Pliocene basalt

A plagioclase megacryst containing composite crystal-glass inclusions was ejected in a Pliocene basaltic diatreme in the Carpathian back-arc basin (Pannonian Basin). The megacryst grew from phonolitic melt, relics of which are preserved in the crystal-glass inclusions. Most of the pristine melt has undergone substantial compositional resetting by interaction with several batches of a low-viscosity carbonated, P-rich melilitite melt, which infiltrated and largely replaced the original inclusion content. The melilitite melt also caused partial resorption of the host megacryst and crystallisation of new calcic plagioclase forming stringers and palisades. A P-rich calcic carbonatite melt exsolved from the melilitite and later crystallised to aragonite at ~ 800 °C and 1.9 GPa. The phosphate melt fraction exsolved from the carbonatite and solidified as CO32−-rich A-B type apatite. At a very late evolutionary stage, K- and Si-rich fluids caused potassic and silicic alteration of the solidified melilitite glass along cracks and interfaces between calcic carbonate globules and glass at temperatures below 680 °C. The oxygen isotope composition of the plagioclase megacryst (6.2 ‰ V-SMOW; Vienna Standard Mean Ocean Water) and the 87Sr/86Sr isotope ratio of carbonates in the inclusions (0.7034) are consistent with a mantle-derived melt. 87Sr/86Sr isotope ratios (0.7047–0.7051) in interstitial carbonates from associated syenite and carbonatite xenoliths indicate a metasomatised mantle source contaminated with radiogenic crustal material or altered marine carbonate. The O-isotope ratios in the carbonates, 22.7 ± 0.6 ‰ V-SMOW in calcite and 23.6 ± 0.7 ‰ V-SMOW in aragonite, are also consistent with a sedimentary precursor. Contrasting δ13C values in the calcite, -12.7 ± 0.5 ‰ V-PDB (Vienna PeeDee Belemnite), and the aragonite (-4.6 ± 0.5 ‰ V-PDB) indicate low-temperature modification of calcite assisted by delta13C-depleted CO2 and preservation of primary magmatic delta13C values in aragonite. The microstructural and geochemical evidence points towards heterogeneous silicate-carbonate melt fractions generated during the metasomatism and partial melting of a supra-subduction mantle wedge.

Isotopic evidence for partial geochemical decoupling between a Jurassic epicontinental sea and the open ocean

We report stable isotope ratios (δ13C, δ18O), minor and trace elements (Mn, Fe, Sr, Mg) together with Ca concentrations from bivalve shells and belemnites from the Middle-Upper Jurassic Sundance Seaway (western United States), we compare them with coeval open-ocean Tethyan data, and reconstruct the palaeo-circulation of seaway waters. The Sundance Seaway was a 2000 km long epicontinental sea with a single entrance at mid latitudes (55–60°N), which would have fostered substantial evolution of seawater chemistry relative to its open-ocean source. Samples are distributed across the 13-million-year marine history of the seaway, and across a 540 km east-west transect spanning Wyoming. Delta13C values are in the same range as Tethyan data, and this suggests that they might record global changes in the carbon cycle, with one exception in the Oxfordian. Delta18O values from the seaway are in contrast highly depleted compared with Tethyan data (−2 to −6‰), and they indicate unrealistically high palaeotemperatures (20–40 °C), assuming an isotopic composition of seawater of −1‰, as generally used for the Jurassic. Given more realistic temperature estimates from Mg/Ca ratios of bivalve shells (10–25 °C), we explain such negative δ18O values by the southward inflow of normal-salinity, isotopically depleted (−3, −4‰), Arctic water into the seaway. Such water would become progressively more saline and denser as it flowed towards the southernmost portion of the seaway. In the Late Jurassic, characterised by wetter climate conditions, less dense Sundance waters may have instead exhibited a northward flow, reducing the southward surface flow from the Arctic. The observed partial geochemical decoupling of Sundance Seaway water masses from the open ocean strongly recommends caution in interpreting the geochemical record of ancient shallow seas, where local, regional and global drivers of change all need to be considered.

Long-term fertilizer management in NERICA cultivated upland affects on soil bio-chemical properties

ABSTRACT This study aims to characterize soil chemical properties and microbial biomass, greenhouse gas production, and organic matter dynamics in upland rice field as affected by the long-term fertilizer managements in Uganda. Soil total C (TC) and N (TN) contents were in the relatively smaller range under different fertilizer treatments, even after 20 crop seasons. However, available phosphate contents showed positive correlation with average yield of upland rice. Incubation experiments were conducted under aerobic or under flooding conditions to measure CO2, methane, and nitrous oxide productions. After the incubation, soil samples were extracted to quantify nitrification rate for aerobic condition and ammonification rate for flooding condition. Soil microbial biomass carbon (MBC) and nitrogen were measured. Stable isotope ratio of 13C and 15N were also determined for the soil samples. CO2 production potential under aerobic condition was higher than the flooding condition. The qCO2 (CO2/MBC) in the treatment applied with compost tended to be higher than the other treatments. Positive correlation between nitrous oxide production and nitrification was found. The delta 13C values of the soil samples indicated that the effect of C4 plants before rice cultivation still remained, while the contribution of biological N2 fixation was little according to delta 15N values. These results indicate that soil microbial biomass in upland rice field of the long-term fertilizer experiment in Uganda was characterized with higher qCO2. Greenhouse gas production was affected by fertilizer management, while soil organic C before the long-term experiment still remained in the experiment.

Stable Isotopes from Museum Specimens May Provide Evidence of Long-Term Change in the Trophic Ecology of a Migratory Aerial Insectivore

Identifying the mechanisms of ecological change is challenging in the absence of long-term data, but stable isotope ratios of museum specimen tissues may provide a record of diet and habitat change through time. Aerial insectivores are experiencing the steepest population declines of any avian guild in North America and one hypothesis for these population declines is a reduction in the availability of prey. If reduced prey availability is due to an overall reduction in insect abundance, we might also expect populations of higher trophic level insects to have declined most quickly due to their greater sensitivity to a variety of disturbance types. Because nitrogen isotope ratios (delta 15N) tend to increase with trophic-level, while delta 13C generally increases with agricultural intensification, we used delta 15N and 13C values of bird tissues grown in winter (claw) and during breeding (feathers) from museum specimens spanning 1880–2005, and contemporary samples from breeding birds (2011–2013) to test for diet change in a migratory nocturnal aerial insectivore, Eastern Whip-poor-will (Antrostomus vociferus) breeding in Ontario, Canada. To test if environmental baselines have changed as a result of synthetic N fertilizer use, habitat conversion or climate, we also sampled delta 15N values of three potential prey species collected from across the same geographic region and time period. Over the past 100 years, we found a significant decline in delta 15N in tissues grown on both the breeding and wintering grounds. Prey species did not show a corresponding temporal trend in delta 15N values, but our power to detect such a trend was limited due to higher sample variance. Amongst contemporary bird samples, delta 15N values did not vary with sex or breeding site, but nestlings had lower values than adults. These results are consistent with the hypothesis that aerial insectivore populations are declining due to changes in abundance of higher trophic-level prey, but we caution that museum-based stable isotope studies of terrestrial food chains will require new approaches to assessing baseline change. Once addressed, an ability to decode the historical record locked inside museum collections could enhance our understanding of ecological change and inform conservation decisions.

True digestibility of protein and amino acids in goats using plants naturally enriched in 13C as a label to determine endogenous amino acid excretion

The objective of this study was to determine whether 13C labeling occurs in goats fed diets with different natural levels of 13C enrichment and, if so, to use 13C as a label to determine true amino acid (AA) digestibility. Thirty-six Xiangdong black goats with initial body weights of 7.5±0.5kg were selected as experimental animals and fed dietary treatments consisting of wheat, barley, and soybeans (C3 diet) or corn, sorghum grain, and sugar cane (C4 diet). The 13C abundance of the amino acid fraction (AAF) of the C3 and C4 diets had average delta 13C values of −28.57‰ and −12.93‰, respectively. Three goats/treatment were slaughtered on days 1, 28, 56 and 84 during the labeling phase, and the AAFs of organs were analyzed for 13C abundance. 13C in the blood AAF increased (−21.70‰, −22.65‰, −23.59‰, and −24.43‰, respectively) with increasing feeding durations in goats fed the C3 diet and decreased (−21.13‰, −16.01‰, −13.78‰, and −12.03‰, respectively) in goats fed the C4 diet. Longissimus dorsi, liver and wool AAFs showed similar trends to those observed in the blood. Each tissue showed a significant dietary treatment effect (P<0.05) and a dietary treatment×labeling phase interaction (P<0.01). After the labeling phase (day 85), six goats from each treatment group were placed in metabolism cages and fed at 0700 and 1900. Three of the goats from each treatment group were implanted with the ruminal cannula and duodenal fistulae and given a 14-day recovery period. From days 15 to 21, a total of 4g chromic oxide, used as an indigestible marker, was administered daily via the ruminal fistulae. At 1900 on day 18 of the collection phase, all goats were switched to the opposite diet type. Thereafter, the duodenal fluids and total feces were collected from days 19 to 21. Additionally, one goat that had not been implanted with a ruminal cannula and duodenal fistulae from each treatment group was killed at 0700 (before feeding) on days 19, 20 and 21, and the AAFs of organs were analyzed for 13C abundance. 13C abundance of the blood AAF was used as an index of endogenous protein labeling. Apparent and true protein digestibilities in the forestomach, whole intestine and whole digestive tract were not different (P>0.05) between the diet treatment groups. The levels of true protein digestibility in the forestomach, whole intestine and whole digestive tract in goats fed the C4 diet tended to be higher than for those in goats fed the C3 diet. On average, the true digestibilities of protein, essential AAs and nonessential AAs were 5.30%, 4.28% 3.17% (forestomach), 5.20%, 5.39% 3.75% (whole intestine) and 3.01%, 4.97%, 4.17% (whole digestive tract) higher, respectively, than the apparent digestibilities of these components in goats fed the C3 diet. In summary, goat tissue protein was labeled with 13C using different diets, and the results show that 13C can be used to determine true AA digestibility.

Age, sex, and breeding status shape a complex foraging pattern in an extremely long-lived seabird.

Evidence of age-dependent changes in foraging behavior of free-ranging individuals is scarce, especially at older stages. Using the isotopic niche as a proxy of the trophic niche during both the breeding (blood) and inter-nesting (feather) periods, we report here empirical evidence for age-, gender-, and breeding status-dependent foraging ecology and examine its potential consequences on subsequent reproduction and survival in an extremely long-lived species, the Wandering Albatross (Diomedea exulans). Immature Wandering Albatrosses of both sexes forage in the subtropics (delta13C) and feed at the same trophic position (delta15N) as the adults. In contrast to immature birds, adult females forage, on average, at more northern latitudes than males, with both sexes feeding in the subtropics during the internesting period, and males, not females, favoring subantarctic waters during incubation. In contrast to adult females, males show a unique pattern among birds and mammals of a continuous change with age in their main feeding habitat by foraging progressively farther south in colder waters during both the breeding and inter-nesting periods. In males, foraging at higher latitudes (lower feather delta13C values) is associated with a lower probability of breeding during the following years compared to other birds, but with no effect on their probability of surviving. Foraging in cold and windy waters may be linked to foraging impairment that might explain different life history trade-offs and lower investment in reproduction with age. This key point requires further longitudinal investigations and/or studies examining foraging success and the energy budget of birds feeding in different water masses.

Influence of the nitrogen concentration on the electrical characteristic of hydrogenated amorphous silicon nitride (a-SiNx:H) based Schottky diodes

The Eskisehir magnesite deposits (Suleymaniye, Margi, and Tutluca) are located in the western part of the Izmir-Ankara Suture Zone, northwestern Turkey. These vein and stockwork type magnesite deposits, which occur along major and minor fault systems, are hosted by Alpine-type ultramafic rocks. The purpose of this study was to understand the origin of the hydrothermal waters responsible and the source of carbon dioxide, and to compare these deposits with similar magnesite occurrences in Turkey and elsewhere. Petrographic and XRD analyses indicate that magnesite was the major carbonate mineral formed. Deposits are predominantly micritic and locally microsparitic, but some also contain secondary calcite and dolomite. The delta13C (V-PDB) values of the Suleymaniye magnesites (-2.7%o to -7.7%o), the Margi magnesites (-7.6%o to -11.2%o), and the Tutluca magnesites (-8.7%o to -10.4%o) indicate that sources of carbon may include atmospheric carbon, dissolved inorganic carbon, freshwater carbonate, and mantle derived CO2. The delta18O (SMOW) compositions of the magnesite range from 27.4%o to 30.8%o and show that the oxygen was derived from marine limestone and metamorphic rocks. The Suleymaniye magnesites have heavier carbon isotopic values than the others because of the greater contribution of mantle sourced CO2, while oxygen isotopic values were similar to those of other altered ultramafic related magnesites in Europe (Former Yugoslavia, Greece). The Margi and the Tutluca magnesite deposits have carbon and oxygen isotopic values similar to those of other ultramafic-related magnesite deposits. Based on isotopic data, we argue that the magnesite deposits in the Eskisehir area formed in a near surface environment at low pressure and temperature. The estimated temperature, using average delta18O values, suggests that magnesite was precipitated from water at 37 °C.

Tracing the biosynthetic source of essential amino acids in marine turtles using delta13C fingerprints.

Plants, bacteria, and fungi produce essential amino acids (EAAs) with distinctive patterns of delta13C values that can be used as naturally occurring fingerprints of biosynthetic origin of EAAs in a food web. Because animals cannot synthesize EAAs and must obtain them from food, their tissues reflect delta13C(EAA) patterns found in diet, but it is not known how microbes responsible for hindgut fermentation in some herbivores influence the delta13C values of EAAs in their hosts' tissues. We examined whether distinctive delta13C fingerprints of hindgut flora are evident in the tissues of green turtles (Chelonia mydas), which are known to be facultative hindgut fermenters. We determined delta13C(EAA) values in tissues of green turtles foraging herbivorously in neritic habitats of Hawaii and compared them with those from green, olive ridley, and loggerhead turtles foraging carnivorously in oceanic environments of the central and southeast Pacific Ocean. Results of multivariate statistical analysis revealed two distinct groups that could be distinguished based on unique delta13C(EAA) patterns. A three-end-member predictive linear discriminant model indicated that delta13C(EAA) fingerprints existed in the tissues of carnivorous turtles that resembled patterns found in microalgae, which form the base of an oceanic food web, whereas herbivorous turtles derive EAAs from a bacterial or seagrass source. This study demonstrates the capacity for delta13C fingerprinting to establish the biosynthetic origin of EAAs in higher consumers, and that marine turtles foraging on macroalgal diets appear to receive nutritional supplementation from bacterial symbionts in their digestive system.

Carbon stable isotopes as indicators of coastal eutrophication.

Coastal ecologists and managers have frequently used nitrogen stable isotopes (delta15N) to trace and monitor sources of anthropogenic nitrogen (N) in coastal ecosystems. However, the interpretation of delta15N data can often be challenging, as the isotope values fractionate substantially due to preferential retention and uptake by biota. There is a growing body of evidence that carbon isotopes may be a useful alternative indicator for eutrophication, as they may be sensitive to changes in primary production that result from anthropogenic nutrient inputs. We provide three examples of systems where delta13C values sensitively track phytoplankton production. First, earlier (1980s) mesocosm work established positive relationships between delta13C and dissolved inorganic nitrogen and dissolved silica concentrations. Consistent with these findings, a contemporary mesocosm experiment designed to replicate a temperate intertidal salt marsh environment also demonstrated that the system receiving supplementary nutrient additions had higher nutrient concentrations, higher chlorophyll concentrations, and higher delta13C values. This trend was particularly pronounced during the growing season, with differences less evident during senescence. And finally, these results were replicated in the open waters of Narragansett Bay, Rhode Island, USA, during a spring phytoplankton bloom. These three examples, taken together with the pre-existing body of literature, suggest that, at least in autotrophic, phytoplankton-dominated systems, delta13C values can be a useful and sensitive indicator of eutrophication.

Geology, mineralogy, geochemistry, and depositional environment of a Late Miocene/Pliocene fluviolacustrine succession, Cappadocian Volcanic Province, central Anatolia, Turkey

This paper investigates the mineralogy, geochemistry, and depositional environment of Late Miocene/Pliocene fluviolacustrine deposits, including multiple ignimbrite levels and andesitic and basaltic lavas, within the Cappadocian Volcanic Province (CVP) of central Anatolia, Turkey. Palaeosols and calcretes formed within these terrestrial sedimentary rocks under near-surface or surface conditions. The palaeosols are composed predominantly of smectite ± illite with feldspar, quartz, calcite, opal-CT, and amphibole, and the calcretes mainly of calcite with minor feldspar, quartz, and accessory smectite ± palygorskite. The palygorskite occurs on and between the calcite crystals in the calcretes and at the edges of smectite flakes within the palaeosols, indicating an in situ formation from evaporated alkaline water rich in Si and Mg and poor in Al under arid or seasonally arid climatic conditions. In the palaeosols and calcretes, negative Ba, Nb, Ce, Sr, and Ti anomalies and an enrichment of light rare earth elements relative to medium rare earth elements and heavy rare earth elements, with a distinct negative Eu anomaly, likely reflect the alteration of feldspars and amphiboles in the ignimbrite. The alteration of the ignimbrites caused the depletion of SiO2, Al2O3+Fe2O3, TiO2, and K2O through the precipitation of smectite ± illite in the palaeosols and CaO in the form of calcite in the calcretes. The delta18O values of the calcretes and limestones range from –8.71‰ to –10.71‰, which are mainly related to the involvement of high-elevation meteoric water, whereas the delta13C values for the same rocks vary between –1.97‰ and 5.71‰. The positive delta13C values for the limestones reflect calcite precipitation in isotopic equilibrium with meteoric water in a lake. The slightly negative delta13C values of the lacustrine limestone carbonates may indicate precipitation from a relatively thick water column and an inflow of surface or groundwater through the ignimbrites with high Ba/Sr values. Conversely, the calcrete delta13C values (3.0‰ to 4.97‰) may suggest a pedogenic origin with low plant respiration rates and a predominance of C4 plants. Based on stable oxygen isotope values from the lake sediments and calcretes, this study suggests that the global warming trend that followed the Late Miocene continued into the Pliocene within the CVP.

Honey adulteration detection using liquid chromatography/elemental analysis-isotope ratio mass spectrometry

A new method for honey adulteration detection using liquid chromatography/elemental analysis-isotope ratio mass spectrometry (LC/EA-IRMS) was developed. Based on the individual delta13C values detected for 38 authentic honey samples, the limits for the authentic honey samples were proposed: the delta13C difference between protein and honey (Deltadelta13C(P-H)) should be higher or equal to than -0.95 per thousand, the delta13C difference between fructose and glucose (Deltadelta13C(F-G)) should be from -0.64 per thousand to 0.53 per thousand, and the maximum difference of delta13C values between all the components (Deltadelta13Cmax) should be lower than 2.09 per thousand. Based on the above criteria, the 58 positive samples spiked with C4 or C3 plant sugar syrup were confirmed by LC/EA-IRMS method from 150 commercial honey samples, while only 7 samples spiked with C4 plant sugar syrup were confirmed by the official EA-IRMS method. The proposed method represents a significant improvement in comparing with the official EA-IRMS method.

Simultaneous determination of δ 13 C values of glycerol and ethanol in wine by liquid chromatography coupled with isotope ratio mass spectrometry

A novel procedure was established for the characterization of delta13C values of glycerol and ethanol in wine by liquid chromatography-isotope ratio mass spectrometry (LC-IRMS). Several parameters influencing the separation of glycerol and ethanol from wine matrix were optimized. The precision and accuracy of the proposed method were 0.15 per thousand to 0.26 per thousand and 0.11 per thousand to 0.28 per thousand, respectively. The results obtained for 40 wine samples displayed that the delta13C value of glycerol ranged from--26.87 per thousand to--32.96 per thousand and that of ethanol ranged from--24.06 per thousand to--28.29 per thousand. Close correlations (R = 0.82) were obtained between the delta13C values of glycerol and ethanol. The proposed method didn't need complex sample treatment, and the delta13C values of glycerol and ethanol in wine can be simultaneously determined, thus improving the method in terms of simplicity and speed compared with traditional methods.

Stable carbon isotopes of invertebrate remains: do they reveal past methane release from lakes?

Lakes are a source of methane, an important greenhouse gas in the atmosphere. In order to understand increasing methane emissions in the present, it is important to study the variations of methane release during past periods of climate change. However, records of methane release from lakes over time scales longer than a few years are extremely rare. In this thesis a method is explored to reconstruct past methane availability in lakes based on the stable carbon isotope composition (delta 13C) of aquatic invertebrate remains. Methane-derived 13C-depleted carbon can be an alternative carbon source to plant-derived material for invertebrates in the sediment and water column of lakes, that can lead to markedly depleted delta 13C values in invertebrate tissues. Using culturing experiments, it was demonstrated that methane-derived carbon is incorporated into chironomid head capsules. Also, it was shown that chemical pre-treatments that are commonly used for sediment processing do not have a noticeable effect on delta 13C values of chironomid remains and that a minimum of 20 microgram chitinous material is required for reproducible delta 13C measurements. In study lakes in Sweden and Siberia, delta 13C values of chitinous remains of several invertebrate taxa in surface sediments were negatively correlated with diffusive methane fluxes. Strong and significant correlations are observed between diffusive methane fluxes and delta 13C of Chironomini and Daphnia remains. Similar correlations were also observed within two Swedish lakes, in which surface sediment cores were obtained along depth transects. Delta 13C values of Chironomini and Daphnia were lower in sections of the lake basin in which the sediments had higher methane release rates. This suggests that delta 13C in remains of several invertebrates, especially Chironomini and Daphnia can be indicative of methane availability in lakes. In contrast, Orthocladiinae and Ephemeroptera, always had relatively high delta 13C values, indicating a plant-derived carbon source. In a sediment record from a Siberian thermokarst lake, delta 13C values of the remains of Chironomini and Daphnia showed relatively large negative delta 13C shifts in warm periods (AD 850-1150 and since AD 1970) compared with delta 13C values of Orthocladiinae remains and bulk sediment. Based on the observed correlations between methane fluxes and delta 13C values of Chironomini and Daphnia in surface sediment samples, this suggests that more methane-derived carbon was available in warm periods compared with colder periods. The research in this thesis demonstrates the potential to use taxon-specific stable carbon isotopes analysis of invertebrate remains for qualitative reconstructions of methane availability in lakes. This new method can lead to a better understanding of lake methane emissions in relation to climate change

Microbial community structure and productivity in the oxygen minimum zone of the eastern tropical North Pacific

Microbial abundances and activities (heterotrophic and chemoautotrophic) were profiled in the fall of 2007 along a transect of four stations in the upwelling region between the Tehuantepec Bowl, off the coast of southern Mexico, and the Costa Rica Dome. Heterotrophic potential varied with depth exhibiting relatively low maximum values of 4–8nM leucine d−1, but varied among stations by a factor of 2. Generally, heterotrophic potential varied inversely with nitrate implying NO3− draw down by nitrate-reducing chemoorganotrophs. Dark dissolved inorganic carbon assimilation (≈chemoautotrophy) was also highly variable with depth and reached a maximum value of 6.4μMC d−1 at one station, but only attained maxima of 0.02 and 0.2μMCd−1 at other stations. Elevated values of chemoautotrophy corresponded with enrichments in nitrite concentrations suggesting nitrification as well as with depletions in nitrite and ammonium concentrations suggesting anammox processes. Additions of 30μM NH4+ at selected depths stimulated chemoautotrophic activity up to 33-fold. Fluorescence in situ hybridization (FISH) analyses revealed elevated abundances of Crenarchaeota and β-proteobacteria (up to 1.0×107 and 10.0×107cellsL−1, respectively) associated with NH4+ minima and NO3- maxima. Nitrifying β-proteobacteria were most abundant in the upper oxycline (1.1–1.8×107cellsL−1) at three stations and exhibited a secondary peak of 0.3×107cellsL−1 in the lower oxycline at one station. Anammox bacterial (Planctomycetes) abundances were as high as 2.1×106cellsL−1, but accounted for less than 1% of total DAPI counts. The concentration of diploptene (a hopanoid biomarker found in bacteria) varied from 2 to 15pgL−1 in the upper oxycline and from 51 to 160pgL−1 in the lower oxycline. Delta 13C values of particulate organic carbon (POC) varied from −30 to −21‰ in the water column (avg. −25‰). Distributions of isotopically light POC coincided with enrichments in diploptene, Planctomycetes cells, nitrite, and chemoautotrophy as well as with nitrate and ammonium depletions, suggesting that anammox and nitrification are important for secondary biological production in this system.

A Comparison of the Foraging Ecology and Bioenergetics of the Early Life-Stages of Two Sympatric Hammerhead Sharks

Juvenile scalloped hammerhead sharks, Sphyrna lewini (Griffith and Smith, 1834), were collected in northwest Florida to examine foraging ecology, bioenergetics, and trophic level [30-60 cm fork length (FL); mean FL= 41.5 cm; N = 196]. Diet analysis was performed using single and compound measures of prey quantity, as well as seven broad diet categories. Diet composition and estimated daily ration were compared to previously published information on bonnethead sharks, Sphyrna tiburo (Linnaeus, 1758). Diet overlap was low between species. Juvenile S. lewini feed on relatively small (85% of prey items < 5% shark length) teleosts (mostly bothids and sciaenids) and shrimps, whereas juvenile S. tiburo has been documented to feed mostly on crustaceans and plant material. Plant material contributed little to the diet of S. lewini. Estimated daily ration was significantly lower for S. lewini than for S. tiburo, regardless of whether plant material was included in the model. Trophic level was calculated at 4.0 for S. lewini and 2.6 for S. tiburo. stable isotope analysis showed S. lewini had significantly higher (delta)15N values and significantly lower (delta)13C values than S. tiburo, consistent with the difference observed in calculated trophic level. These results provide evidence that juvenile hammerhead species coexist in coastal northwest Florida by feeding at separate trophic levels.

Isotopic signature (15N/14N and 13C/12C) confirms similarity of trophic niches of millipedes (Myriapoda, diplopoda) in a temperate deciduous forest

The species composition, abundance, and isotopic signature of millipedes (Myriapoda, Diplopoda) were investigated in seven biotopes of Kaluzhskie Zaseki State Nature Reserve. Nine Diplopoda species were found in total, and the local species diversity (within a sampling plot) reached seven species. The Diplopoda tissues were similar to the plant litter in the isotopic composition of nitrogen (delta15N was by 0.4% per hundred higher, on average), but were more strongly enriched in heavy carbon (delta13C was by 4% per hundred higher, on average). Removal of mineral carbon from the cuticle reduced delta13C of Diplopoda by about 1.4% per hundred on average. Differences in the delta15N and delta13C values between the species did not exceed 2.5 per hundred. Differences in the isotopic compositions of the considered species are insignificant, and thus, it is impossible to distinguish particular trophic guilds in the Diplopoda community. Analysis of the published data confirmed that isotopic differentiation of millipedes was much less pronounced than in other investigated groups of soil animals. Hence, millipedes of the deciduous forest form a uniform trophic group.

A general hypothesis‐testing framework for stable isotope ratios in ecological studies

We propose a framework for hypothesis-testing of stable isotope ratios in ecological studies. Statistical procedures are based on analysis of nested linear models and a residual permutation procedure (RPP) that is employed to evaluate probabilities associated with test statistics. We used simulated examples and a real data set to illustrate the utility and generality of the method. First, we developed a test for differences in centroid location and dispersion of delta13C and delta15N values within and among groups of isotopic data. Second, we evaluated magnitude and direction of change in centroid position (termed "path") of a pair of isotopic samples separated in space/time relative to paths of other paired sample sets. Third, we compared attributes of path trajectories (size, direction, and shape) over sample sets containing more than two samples to provide a quantitative description of how patterns of isotopic ratios change in response to spatial and temporal gradients. Examples are limited to the bivariate case (delta13C-delta15N biplots), but the statistical method can readily be applied to univariate and multivariate cases.