Average Isotopic Values Research Articles

Tusk pairs in the Ziegler Reservoir mastodon (Mammut americanum) assemblage: Implications for site taphonomy and stratigraphy

The Ziegler Reservoir (ZR) mastodon assemblage consists of remains from dozens of individuals that represent one or more populations living in a high-elevation region of the Colorado Rocky Mountains during Marine Isotope Stage (MIS) 5. Several left-right pairs of mastodon mandibular tusks were discovered in different stratigraphic units, challenging previous assumptions that depositional units preserving mastodon remains sample a comparable succession of regional populations through time. It is now recognized as likely that at least some of the specimens contained in these layers were transported from original deposits located on the lake margin, and that successive slumps transported parts of the same skeleton on different occasions, depositing them in different stratigraphic units. Assigning both tusks of a pair to the lowest depositional unit in which either occurs alters the temporal pattern in season of death for ZR mastodons and somewhat modifies a census of individuals, but does not significantly affect the secular trend previously detected in average oxygen isotope values. Two tusks with matching isotope profiles were previously treated as potential evidence of a catastrophic death event that had been proposed to explain the assemblage of remains, but these are now considered to be from the same individual. Newly paired records highlight the importance of careful taphonomic studies for any synthetic analysis of paleoecological history.

Eating out or dining in: modeling diverse dietary strategies in the Middle Period, San Pedro de Atacama, Chile

The Middle Period of the Atacama oases, North Chile, has been characterized as a time of peace, uniform abundance, and widespread access to exotic materials. In the present work, we test this notion through a comparison of Middle Period human isotopic data (δ13Cco, δ15Nco, and δ13Cap) representing two distinct ayllus, Solcor and Tchecar, in the San Pedro de Atacama oases. We employ Bayesian mixture modeling of individual-level isotopic data to quantify and compare dietary composition within and between the cemetery populations of these two contemporary locales. Ultimately, our research shows that dietary diversity, which we take as a proxy for differential levels of participation in long-distance exchange or the access to the products thereof, was unequally distributed, and that the supposedly uniform richness of the Middle Period was similarly discontinuous. While average isotopic values for the two ayllus were similar, variance within each differed significantly, as did variance in dietary composition arrived at through modeling. By all measures, the individuals interred in Solcor 3 had more varied diets, particularly in terms of carbohydrate-rich plants, than their contemporaries interred at Tchecar Tumulo Sur, suggesting that more individuals from Solcor 3 had greater participation in/access to long-distance exchange networks. Besides providing novel insights into the lived experience of the Middle Period residents of far northern Chile, this work also demonstrates the power of Bayesian mixture modeling for the reconstruction of individual paleodiet.

DEW POINT ELEVATION AND OXYGEN AND HYDROGEN ISOTOPIC RATIOS FOR PRECIPITATION SAMPLED AT OSAKA AND MATSUE, JAPAN

Dew point elevation was clarified to be an important factor determining stable isotope values of precipitation. When dew point elevation is high, stable isotope values for precipitation were clarified to increase due to the evaporation process which occurred during dropping from dew point elevation to the ground. In winter wet air from the Japan Sea passes over mountains in the center of Japan and dry air after precipitated at the mountains reaches at the Inland Sea. Subsequently, it is thought that when dew point elevation increases, stable isotope values for precipitation increase with the distance from dew point elevation to the ground then high dew point elevation raises the average isotope value of precipitation. Therefore, the elevation of the precipitation point decreases with an increase of the isotope value. Consequently, altitude effect is thought to be caused by precipitation with high dew point elevation. High dew point elevation and high stable isotope values for precipitation in winter were observed at Osaka in the Inland Sea. On the other hand, these high values at Matsue on the Japan Sea side in winter were rarely observed because of low dew point elevation with wet air.

Stable isotope patterns found in early Eocene equid tooth rows of North America: Implications for reproductive behavior and paleoclimate

Reproductive behaviors of early Eocene equids were likely different from their modern-day counterparts as a result of their small body size and warmer global temperatures. To better understand the paleoenvironment and ecology of these early horses, teeth of Protorohippus montanum jaws from a single stratigraphic locality in early Eocene sedimentary deposits of Wyoming were sampled for oxygen and carbon isotope analysis. These enamel data along with an inferred body mass of ~7.5kg suggests that adult teeth formed over a matter of months, with the final tooth erupting at ~1.3years of age. Thus, average isotopic values from each tooth likely represent environmental conditions from a single season. Results indicate two isotopic patterns. In the case of isotopic “pattern A,” the second forming molars (m/2s) have significantly lower isotopic ratios compared to other teeth within the jaw. This suggests the first forming molars (m/1s) formed during a cooling fall season, followed by formation of the m/2s during the cooler winter. In the case of isotopic “pattern B,” results suggest that m/1s formed during a warming spring season, while the m/2s formed during the following warmer summer season. Isotopic ratios of m/1s may represent an individual's birth season (or in utero season, depending on timing of initial formation), implying that early equids experienced at least two birth seasons per year. These results suggest that temperatures and reduced seasonality of the early Eocene played a strong role in early equid birth cycles. Lastly, the mean and variance in carbon and oxygen isotope ratios was not significantly different across tooth positions of all jaws when all individuals were grouped together, regardless of their pattern assignment. Such results indicate that isotopic data from fourth premolars, first molars, second molars, and third molars can be combined for purposes of temporal reconstructions of paleoclimate, thus increasing the potential sample sizes for these types of studies.

Hábitos alimenticios y migratorios del tiburón blanco Carcharodon carcharias (Lamniformes: Lamnidae) de Isla Guadalupe inferidos por el análisis de isótopos estables de δ15N and δ13C

Stable isotope composition of marine top predator's tissues provides insight information of its trophic ecology and migratory behavior. Previous reports have shown that dermal tissues could record longer patterns of hunting and movement. Based on this, the aim of this study was to describe the feeding and migratory habits of the white shark from Isla Guadalupe, using stable isotopic analysis of dermis. We considered a small subset of many possible prey taxa that the sharks could have eaten throughout their migration: pinnipeds, squid and tuna. We grouped the data in five focal areas: Gulf of California, Coast of California, Isla Guadalupe, SOFA and Hawaii. We performed a Bayesian mixing model to study the trophic ecology of this top predator. Average isotopic values for dermis tissue of white shark were delta13C (-14.5 per thousand) and delta15N (19.1 per thousand). Corrected white shark dermal mean values to resemble muscle were delta13C (-16.6 per thousand) and delta15N (21.2 per thousand). Mixing model data from dermis showed predation in offshore areas such the SOFA and a main importance of pinnipeds as prey of the white shark in Isla Guadalupe.

Biological and environmental influences on the trophic ecology of leatherback turtles in the northwest Atlantic Ocean

Understanding the causes and consequences of variability in trophic status is important for interpreting population dynamics and for identifying important habitats for protected species like marine turtles. In the northwest Atlantic Ocean, many leatherback turtles (Dermochelys coriacea) from distinct breeding stocks throughout the Wider Caribbean region migrate to Canadian waters seasonally to feed, but their trophic status during the migratory and breeding cycle and its implications have not yet been described. In this study, we used stable carbon and nitrogen isotope analyses of bulk skin to characterize the trophic status of leatherbacks in Atlantic Canadian waters by identifying trophic patterns among turtles and the factors influencing those patterns. δ15N values of adult males and females were significantly higher than those of turtles of unknown gender (i.e., presumed to be subadults), and δ15N increased significantly with body size. We found no significant differences among average stable isotope values of turtles according to breeding stock origin. Significant inter-annual variation in δ15N among cohorts probably reflects broad-scale oceanographic variability that drives fluctuations in stable isotope values of nutrient sources transferred through several trophic positions to leatherbacks, variation in baseline isotope values among different overwintering habitats used by leatherbacks, or a combination of both. Our results demonstrate that understanding effects of demographic and physiological factors, as well as oceanographic conditions, on trophic status is key to explaining observed patterns in population dynamics and for identifying important habitats for widely distributed, long-lived species like leatherbacks.

The impacts of a linear wastewater reservoir on groundwater recharge and geochemical evolution in a semi-arid area of the Lake Baiyangdian watershed, North China Plain

Sewage leakage has become an important source of groundwater recharge in urban areas. Large linear wastewater ponds that lack anti-seepage measures can act as river channels that cause the deterioration of groundwater quality. This study investigated the groundwater recharge by leakage of the Tanghe Wastewater Reservoir, which is the largest industrial wastewater channel on the North China Plain. Additionally, water quality evolution was investigated using a combination of multivariate statistical methods, multi-tracers and geochemical methods. Stable isotopes of hydrogen and oxygen indicated high levels of wastewater evaporation. Based on the assumption that the wastewater was under an open system and fully mixed, an evaporation model was established to estimate the evaporation of the wastewater based on isotope enrichments of the Rayleigh distillation theory using the average isotope values for dry and rainy seasons. Using an average evaporation loss of 26.5% for the input wastewater, the estimated recharge fraction of wastewater leakage and irrigation was 73.5% of the total input of wastewater. The lateral regional groundwater inflow was considered to be another recharge source. Combing the two end-members mix model and cluster analysis revealed that the mixture percentage of the wastewater decreased from the Highly Affected Zone (76%) to the Transition Zone (5%). Ion exchange and redox reaction were the dominant geochemical processes when wastewater entered the aquifer. Carbonate precipitation was also a major process affecting evolution of groundwater quality along groundwater flow paths.

Determining Seasonal Natural Effects over Isotopic Baselines for CO2 Storage Monitoring

Dissolved carbon stable isotopes in surface waters can be utilized as a monitoring tool of CO2 geological storage and as a good indicator of potential CO2 leakages, since each source of carbon has a specific isotopic signature. The isotopic carbon baseline value and its range will determine whether the situation responds to a leak or a natural modification as part of the system's annual cycle and its seasonal effects. We measured water temperature, pH, dissolved inorganic carbon (DIC) concentration and other geochemical variables, during the different annual stages, in order to characterize the contribution of different sources of carbon to the natural isotopic evolution of DIC in the area of Hontomin. This area is the selected site for the Spanish research facility for CO2 geological storage operated by CIUDEN. The average value for δ13C-DIC at the study site is -10.7 ‰ (V-PDB), which is very different of the CO2 generated during the oxycombustion process (about -28 ‰ vs V-PDB). After statistical analysis of the sampling efforts, we observed light differences on their average isotopic values which imply certain seasonal effects, although we could not find effects over the DIC concentration.

춘천 중도 유적에서 출토된 원삼국시대 토기 탄착물에 대한 화학적 분석

We studied for the chemical characterizations of the charred residues obtained from the ancient potteries in the Proto-Three Kingdom period from archaeological sites in Joong-do, Chuncheon. Organic components of the charred residues were extracted and analysed using mass spectrometry and infrared spectroscopy. Lipid profiles from these samples were not identified in gas chromatography-mass spectrometry. Bulk stable isotope analyses of charred residues was used to infer an average values of the foods prepared. The average carbon isotope values () of the residues are ‰ (ranging from -8.7‰ to -18.4‰, n

Ice-core evidence of westerly and monsoon moisture contributions in the central Tibetan Plateau

AbstractStable isotopes are a primary tool for inferring past temperature changes and atmospheric moisture variability from ice cores. A 33 m ice core representing the period 1850–2004 was retrieved from the Tanggula Mountains, central Tibetan Plateau (5743 m a.s.l.), in August 2005. Annual average stable isotope (δ18O, δD) values generally increase during the period, while the second-order parameter of deuterium excess (d-excess) generally decreases. High annual average d-excess values (18.2‰) throughout the ice core suggest a significant contribution of continental recycled moisture. d-excess values shift from relatively higher values during 1850–1940 to lower values since the 1940s. Annual isotope values and reconstructed accumulation are compared with climate indices, local station temperature records and northern India monsoon precipitation. Significant correlation is observed between δ18O and the Southern Oscillation, NINO3.4 and Dipole Mode indices. Annual average d-excess values revealed a significant negative correlation with the Dipole Mode index. Results suggest a relatively greater contribution of westerly-dominated continental moisture prior to the 1940s and an increase in the contribution of moisture evaporated under more humid conditions since the 1940s.

Palaeoenvironment and taphonomy of a Late Jurassic (Late Tithonian) Lagerstätte from central Poland

A rich assemblage of exceptionally preserved marine and terrestrial fossils occurs in fine-grained limestones in the upper part of the Late Tithonian (Middle Volgian) shallowing upward carbonate sequence in Central Poland. The richest horizon, a deposit known locally as the Corbulomima horizon, is named after the shallow burrowing suspension feeding bivalve Corbulomima obscura, moulds of which occur in densities of up to 500 per square metre on some bedding planes. The fauna in this bed also includes organic and phosphatic remains of a wide range of other creatures including the exuviae of limulids and decapods, disarticulated fish skeletons and rare isolated pterosaur bones and teeth. There are also perfectly preserved dragonfly wings and beetle exoskeletons. The average stable carbon and oxygen isotope values for ostracod shells and fine-grained sediment from this horizon suggest precipitation of the calcium carbonate from warm seawater of normal marine salinity. The carbonate sediments overlying the fossiliferous horizon have been interpreted as nearshore to shoreface facies. These pass abruptly into coarse reworked intraclastic sediments interpreted as possible tsunami or storm surge over-wash deposits. The clasts in this deposit have more positive oxygen isotope values than those in the underlying limestone, which may indicate that they were lithified in a slightly more evaporative, perhaps intertidal, setting. The succession terminates with silicified fine-grained limestones likely to have formed in extremely shallow lagoonal environments. In contrast with the Solnhofen limestones of Lower Tithonian age in south-central Germany the Corbulomima horizon is interpreted as a transitional deposit formed in a shallow marine setting by rapid burial with elements of both Konservat- and Konzentrat-Lagerstätte preservation. □Konzentrat and Konservat-Lagerstätte, Taphonomy, Palaeoenvironment, Paleogeography, Late Jurassic, Poland.

The silicon isotope composition of granites

Because weathering results in preferential incorporation of the lighter Si isotopes into clay minerals, the Si in magmas derived from (meta)sedimentary lithologies enriched in such phases should also be isotopically light, relative to melts derived from igneous sources. With the advent of new high precision techniques it should therefore be possible to resolve such differences. Hence, Si isotopes have to potential to distinguish between, and characterise, different magmatic source regions.To explore this, here we report the Si isotopic compositions of a suite of Phanerozoic I-, S- and A-type granites and mineral separates, as well as samples of associated country rock. The whole-rock data fall between δ30Si=−0.40 and −0.11±0.04‰ (95%s.e.). This range is more limited than that defined by previous low precision measurements of granites, but is significantly broader than that displayed by more recent, high precision, measurements of high-Si extrusive igneous rocks. As predicted, S-type granites are, on average, isotopically lighter than I- and A-type samples, and negative correlations with alumina saturation index (ASI) values and initial 87Sr/86Sr provide evidence that Si isotope variations in granites can be explained by variable incorporation of an enriched sedimentary component. However, the relatively small isotopic perturbations and apparent degree of overlap between granite affinities suggest that Si isotopes are not as sensitive to sedimentary input, relative to more established proxies such as, for example, O isotopes. The average Si isotope value of all granites analysed in this study is δ30Si=−0.23±0.15‰ (2s.d.), which is entirely consistent with a recently published estimate for the continental crust, based on an andesitic bulk composition and the well defined relationship between Si isotopes and magmatic fractionation.

A comparative study on isotopic composition of precipitation in wet tropic and semi-arid stations across southern India

Isotopic composition of monthly composite precipitation samples from Kozhikode (n = 31), a wet tropic station and Hyderabad (n = 25), a semi-arid station across southern India were studied for a period of four years from 2005 to 2008. During the study period, the Kozhikode station recorded an average rainfall of 3500 mm while the Hyderabad station showed an average rainfall of 790 mm. The average stable isotope values in precipitation at the Kozhikode station were δ 18 O= −3.52‰, d-excess = 13.72‰; δ 18 O= −2.94‰, d-excess = 10.57‰ ;a ndδ 18 O= −7.53‰, d-excess = 13.79‰, respectively during the pre-monsoon (March–May), monsoon (June–September) and post-monsoon (October–February) seasons. For the Hyderabad station, the average stable isotope values were δ 18 O= −5.88‰, d-excess = 2.34‰; δ 18 O= −4.39‰, d-excess = 9.21‰ ;a ndδ 18 O= −8.69‰, d-excess = 14.29‰, respectively for the three seasons. The precipitation at the two stations showed distinctive isotopic signatures. The stable isotopic composition of precipitation at the Hyderabad station showed significant variations from the global trend while the Kozhikode station almost followed the global value. These differences are mainly attributed to the latitudinal differences of the two stations coupled with the differences in climatic conditions.

The Origin of the Millimeter-Scale Lamination in the Neoproterozoic Lower Beck Spring Dolomite: Implications for Widespread, Fine-Scale, Layer-Parallel Diagenesis in Precambrian Carbonates

Abstract The Neoproterozoic lower Beck Spring Dolomite exhibits a prominent, millimeter-scale, light–dark, planar lamination commonly interpreted as a primary depositional fabric. Microscopic examination reveals that the dark laminae are composed of micrite and contain a micrometer-scale, wavy fabric, whereas the light laminae are composed of relatively coarse-crystalline pseudospar that engulfs, surrounds, and crosscuts the dark laminae. Nearly all of the light laminae surround, or occur in proximity to, elongate (long axis fabric-parallel), spar-filled cavity structures. The average δ18O values for dark and light laminae are −1.8‰ (std. dev. 1.6) and −3.0‰ (std. dev. 1.3) VPDB, respectively. Cavity-filling cements are even more depleted in 18O, with an average isotopic value of −6.2‰ (std. dev. 1.1). These characteristics suggest that the coarse-crystalline, light laminae are the result of the preferential, aggrading neomorphism of a thinly laminated, micritic host rock and that the (now cemented) cavity structures acted as conduits for the fluid responsible for recrystallization. The oxygen isotope distributions are consistent with progressive recrystallization by an 18O-depleted fluid, likely of meteoric origin. Therefore, we interpret the prominent millimeter-scale, light–dark layering in the lower Beck Spring Dolomite to result from widespread, laminae-parallel, diagenetic processes—perhaps controlled by fine-scale layer-parallel differences in initial porosity and permeability—and not from primary sedimentary processes. Extensive, layer-parallel diagenesis on such a fine scale is rare in Phanerozoic shallow marine deposits, due to disruption by bioturbation. However, before the advent of metazoan burrowing, fine-scale, layer-parallel fluid flow would have been more common. Thus, the diagenetic fabric of the lower Beck Spring Dolomite may represent a mode of carbonate diagenesis restricted to the Precambrian. Similar diagenesis may also occur in Phanerozoic environments devoid of vertical bioturbation.

Concentration-dependent Stable Isotope Analysis of Consumers in the Upper Reaches of a Freshwater-dominated Estuary: Apalachicola Bay, FL, USA

The goals of this study were to quantify organic matter source utilization by consumers in the freshwater-dominated region (East Bay) of a high river flow estuary and compare the results to consumers in marine-influenced sites of the same estuary to understand how organic matter utilization by consumers may be changing along the salinity gradient. We used the results from these evaluations to establish the baseline against which we isotopically determined trophic level for consumers in East Bay. Average isotope values for consumers sampled in East Bay ranged from −20.1‰ to −24.8‰ for carbon and from 8.9‰ to 14.3‰ for sulfur. These values were well-constrained by the four identified sources: plankton, benthic organic matter, macroalgae, and terrestrial detritus. Application of a concentration-corrected mixing model resulted in contributions of benthic production and detrital sources (averaged over the food web) to East Bay consumers of 41% and 33%, respectively, with the remainder made up of plankton and benthic macroalage. While benthic organic matter was an important organic matter source for consumers at both sites, we found that the influence of terrestrial detritus varied significantly throughout the bay. Terrestrial detritus contributed only 18% of average total organic matter in organisms inhabiting marine-influenced sites. Although terrestrial detritus did contribute to all consumers examined, most fish species in Apalachicola Bay reflect a greater reliance on autochthonous sources. Our results suggest that, while terrestrial detritus does appear to be a major contributor to commercially important shellfish species (most notably oysters and penaeid shrimp), it is not the major source fueling the diversity of secondary production in Apalachicola Bay. Thus, production in Apalachicola Bay is highly dependent on riverine influx in two ways: (1) economically important bivalves and crustaceans are being fueled by terrestrial organic matter supplied by river flooding and (2) secondary and above consumer fish species are supported by in situ production which, in turn, is reliant on nutrients supplied by the Apalachicola River. These findings are significant in light of decisions regarding water usage and river flow restrictions in the Apalachicola-Chattahoochee-Flint drainage basin. The results of this study confirm that in situ estuarine organic matter is the dominant source supporting secondary production in this river-dominated estuary.

Organic carbon and nitrogen source of sunken wood communities on continental shelves around Japan inferred from stable isotope ratios

Abstract The food source for animals associated with sunken wood on the deep-sea floor has not been clearly identified. In the present study, we analyzed carbon- and nitrogen-stable isotope ratios of these animals to clarify (a) whether or not species that are potentially able to ingest wood (direct user) really digest and use it as their food source in situ , or (b) whether or not sunken wood is the organic source for the species that cannot feed on it directly (indirect user). The average isotopic values of the direct user, wood-boring bivalves, were δ 13 C:−24.14±0.38‰ ( n =13) and δ 15 N:4.05±0.27‰ ( n =11). The value of δ 15 N was close to that of their host wood (1.97±1.87‰ ( n =7)) and lower than that of suspended particles assumed from that of suspension feeding species, suggesting that direct users do not use either their host wood or suspended particles as their nitrogen source. Given ambient nitrogen gas value (δ 15 N: around 0.5‰), bacteria symbiotic with the direct user appear to autotrophically fix ambient nitrogen gas and the bacteria are probably the major nitrogen source for the direct user. The average δ 13 C of wood was −26.85±1.13‰ ( n =7), suggesting that wood is the carbon source of the direct user. On the other hand, the average δ 13 C of the indirect user (−23.29±0.99‰ ( n =27)) was distinctly higher than that of wood and they were considered to use organic matter derived from both phytoplankton and their host wood.

Stable isotopic constraints on the tectonic, topographic, and climatic evolution of the northern margin of the Tibetan Plateau

This study presents oxygen and carbon isotopic records from lacustrine, paleosol, alluvial, and fluvial carbonate sampled in thirteen Cenozoic sedimentary sections that span the northern margin of the Tibetan Plateau. Isotopic analyses of 1475 carbonate samples yield δ 18O values that range from 13.1 to 38.9‰ (SMOW), and δ 13C values range from − 11.5 to 3.7‰ (PDB). Based on these analyses, we see two isotopic trends regionally. We interpret a Paleogene decrease in average oxygen isotope values to result from an increase in the mean elevation of the study region's drainages as they tapped waters from a growing Tibetan Plateau to the south of the study area. We interpret a Neogene increase in both carbon and oxygen isotope values to result from the initiation of local mountain building in the study area and the withdrawal of marine waters, which increased basin isolation, aridity, and temperatures. The timing of inferred initiation of uplift in this region is consistent with structural, thermochronological, and sedimentological evidence for a tectonic transition in the early and middle Miocene from accommodation of India–Eurasia convergence through extrusion along the Altyn Tagh fault to accommodation of convergence through active shortening and mountain building in this region. This study also supports tectonic models for the differential uplift of the Tibetan Plateau, in that mountain building in this study region significantly postdates estimates for the attainment of high elevation from isotopic studies of the central Tibetan Plateau.

Retrospective characterization of ontogenetic shifts in killer whale diets via δ13C and δ15N analysis of teeth

Metabolically inert, accretionary structures such as the dentin growth layers in teeth provide a life history record of individual diet with near-annual resolution. We constructed onto- genetic δ 13 C and δ 15 N profiles by analyzing tooth dentin growth layers from 13 individual killer whales Orcinus orca collected in the eastern northeast Pacific Ocean between 1961 and 2003. The individuals sampled were 6 to 52 yr old, representing 2 ecotypes — resident and transient — collected across ~25° of latitude. The average isotopic values of transient individuals (n = 10) are consistent with a reliance on mammalian prey, while the average isotopic values of residents (n = 3) are consis- tent with piscivory. Regardless of ecotype, most individuals show a decrease in δ 15 N values of ~2.5‰ through the first 3 yr of life, roughly equivalent to a decrease of one trophic level. We interpret this as evidence of gradual weaning, after which, ontogenetic shifts in isotopic values are highly variable. A few individuals (n = 2) maintained relatively stable δ 15 N and δ 13 C values throughout the remainder of their lives, whereas δ 15 N values of most (n = 11) increased by ~1.5‰, suggestive of an ontogenetic increase in trophic level. Significant differences in mean δ 13 C and δ 15 N values among transients col- lected off California suggest that individuality in prey preferences may be prevalent within this eco- type. Our approach provides retrospective individual life history and dietary information that cannot be obtained through traditional field observations of free-ranging and elusive species such as killer whales, including unique historic ecological information that pre-dates modern studies. By providing insights into individual diet composition, stable isotope analysis of teeth and/or bones may be the only means of evaluating a number of hypothesized historical dietary shifts in killer whales of the northeast Pacific Ocean.

Plant and soil lipid modification under elevated atmospheric CO 2 conditions: II. Stable carbon isotopic values ( δ13C) and turnover

Future enrichment of atmospheric CO 2 and its effect on ecosystems were studied using grassland free air CO 2 enrichment (FACE) experiments. Plant waxes have been shown to be directly modified under elevated CO 2 concentration. Lipids, as major components of plant waxes, are important constituents of plant surfaces and their position at the plant/atmosphere interface makes them susceptible to environmental change. The main focus of this study was to improve knowledge about modifications to stable carbon isotopic ( δ 13C) values of individual lipids within plant biomass and soils as a result of the increased atmospheric CO 2 concentration, implying an addition of 13C labelled CO 2. The isotopically labelled biomass facilitates turnover time determination of lipids in soils due to the direct comparison of identical plants grown under ambient and 13C-depleted atmospheric conditions. We demonstrate which lipids were influenced by modified CO 2 concentration and how the lipid isotopic values of plant biomass and soil were influenced under elevated vs. ambient CO 2 conditions. Most plant carboxylic acids and alkanes were uniformly depleted in 13C by ca. 6‰ when compared to plant biomass bulk isotope values. In soil, short chain carboxylic acids (< C 20), derived mainly from microbial sources, revealed a lower depletion in isotope value than plant-derived long chain acids (⩾C 20). The isotopic differences between individual compounds in soil under ambient vs. elevated CO 2 conditions varied significantly between 2 and 6‰ for individual acids and 0–6‰ for individual alkanes. This argues against plant/soil turnover determinations for individual compounds. Preferably, weighted mean average isotopic values of the most abundant lipids provide reliable calculation of replaced carbon proportions and turnover times. Carboxylic acids were turned over fastest in grassland soil, followed by bulk carbon, whereas alkanes exhibited the slowest turnover times. This is in contrast to previous studies of arable soil, but confirms observations made on peaty soil indicating that alkanes may be part of the relatively stable carbon fraction in soils. The turnover of total organic carbon, carboxylic acids and long chain alkanes was observed to be significantly greater in soil under Lolium perenne (ryegrass) than in soil under the leguminose plant Trifolium repens (white clover).

Biomarker and Stable Isotope Characterization of Coastal Pond-Derived Organic Matter, McMurdo Dry Valleys, Antarctica

Small coastal ponds that contain photosynthetic microbial mat communities represent an extreme environment where a potentially significant source of labile organic carbon can be found within the McMurdo Dry Valleys, Antarctica. To distinguish coastal pond-derived organic matter from other sources of organic matter in the Dry Valleys, bulk organic carbon, nitrogen, and sulfur isotope signatures and phospholipid fatty acid (PLFA) profiles of benthic microbial mats located at two sites--Hjorth Hill coast and Garwood Valley--were investigated. The average isotope values at Hjorth Hill coast and Garwood Valley are, respectively, -10.9 per thousand and -10.2 per thousand for delta(13) C, 3.7 per thousand and -1.3 per thousand for delta(15)N, and 8.1 per thousand and 16.7 per thousand for delta(34)S. Microbial mats from all ponds are dominated by monounsaturated PLFAs (indicative of Gram-negative bacteria) and polyunsaturated PLFAs (indicative of microeukaryotes). Biomarkers specific to aerobic prokaryotes, eukaryotes, and photoautotrophic microeukaryotes, as well as sulfur-reducing bacteria, are present in all samples. Benthic mats at Garwood Valley are thicker and more laminated, have a higher biomass, and have a greater carbon and nitrogen content, which suggests greater productivity than mats at Hjorth Hill coast. Greater productivity is supported, as well, by higher dissolved oxygen contents likely derived from heightened photosynthetic productivity. More productivity at Garwood Valley likely results from a larger influx of terrestrial surface waters together with a concomitant nutrient loading.