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824 Ergebnisse:

Terrestrial biome distribution in the Late Neogene inferred from a black carbon record in the northeastern equatorial Pacific
Scientific Reports (2016)
Donghyun Kim, Yong Il Lee, Kiseong Hyeong, Chan Min Yoo, T. E. Cerling, T. E. Cerling, E. J. Edwards, C. P. Osborne, C. A. Strömberg, S. A. Smith, C. A. Strömberg, F. A. McInerney, W. D. Tidwell, E. M. V. Nambudiri, S. Singh, A. Awasthi, B. Parkash, S. Ku

The appearance and expansion of C4 plants in the Late Cenozoic was a dramatic example of terrestrial ecological change. The fire hypothesis, which suggests fire as a major cause of C4 grassland is gaining support, yet a more detailed relationship between fire and vegetation-type change remains unresolved. We report the content and stable carbon isotope record of black carbon (BC) in a sediment core retrieved from the northeastern equatorial Pacific that covers the past 14.3 million years. The content record of BC suggests the development process of a flammable ecosystem. The stable carbon isotope record of BC reveals the existence of the Late Miocene C4 expansion, the ‘C4 maximum period of burned biomass’ during the Pliocene to Early Pleistocene, and the collapse of the C4 in the Late Pleistocene. Records showing the initial expansion of C4 plants after large fire support the role of fire as a destructive agent of C3-dominated forest, yet the weak relationships between fire and vegetation after initial expansion suggest that environmental advantages for C4 plants were necessary to maintain the development of C4 plants during the late Neogene. Among the various environmental factors, aridity is likely most influential in C4 expansion.
Schlagworte: carbon , soil , geol , elem

Do forests represent a long-term source of contaminated particulate matter in the Fukushima Prefecture?
Journal of Environmental Management (2016)
J. Patrick Laceby, Sylvain Huon, Yuichi Onda, Veronique Vaury, Olivier Evrard

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident resulted in radiocesium fallout contaminating coastal catchments of the Fukushima Prefecture. As the decontamination effort progresses, the potential downstream migration of radiocesium contaminated particulate matter from forests, which cover over 65% of the most contaminated region, requires investigation. Carbon and nitrogen elemental concentrations and stable isotope ratios are thus used to model the relative contributions of forest, cultivated and subsoil sources to deposited particulate matter in three contaminated coastal catchments. Samples were taken from the main identified sources: cultivated (n = 28), forest (n = 46), and subsoils (n = 25). Deposited particulate matter (n = 82) was sampled during four fieldwork campaigns from November 2012 to November 2014. A distribution modelling approach quantified relative source contributions with multiple combinations of element parameters (carbon only, nitrogen only, and four parameters) for two particle size fractions (<63 μm and <2 mm). Although there was significant particle size enrichment for the particulate matter parameters, these differences only resulted in a 6% (SD 3%) mean difference in relative source contributions. Further, the three different modelling approaches only resulted in a 4% (SD 3%) difference between relative source contributions. For each particulate matter sample, six models (i.e. <63 μm and <2 mm from the three modelling approaches) were used to incorporate a broader definition of potential uncertainty into model results. Forest sources were modelled to contribute 17% (SD 10%) of particulate matter indicating they present a long term potential source of radiocesium contaminated material in fallout impacted catchments. Subsoils contributed 45% (SD 26%) of particulate matter and cultivated sources contributed 38% (SD 19%). The reservoir of radiocesium in forested landscapes in the Fukushima region represents a potential long-term source of particulate contaminated matter that will require diligent management for the foreseeable future.
Schlagworte: carbon , nitrogen , soil , poll , elem

Oxygen isotope fractionation between bird eggshell calcite and body water: application to fossil eggs from Lanzarote (Canary Islands)
The Science of Nature (2016)
Nicolas Lazzerini, Christophe Lécuyer, Romain Amiot, Delphine Angst, Eric Buffetaut, François Fourel, Valérie Daux, Juan Francisco Betancort, Jean-Pierre Flandrois, Antonio Sánchez Marco, Alejandro Lomoschitz

Oxygen and carbon isotope compositions of fossil bird eggshell calcite (δ18Ocalc and δ13Ccalc) are regularly used to reconstruct paleoenvironmental conditions. However, the interpretation of δ18Ocalc values of fossil eggshells has been limited to qualitative variations in local climatic conditions as oxygen isotope fractionations between calcite, body fluids, and drinking water have not been determined yet. For this purpose, eggshell, albumen water, and drinking water of extant birds have been analyzed for their oxygen and carbon isotope compositions. Relative enrichments in 18O relative to 16O between body fluids and drinking water of +1.6 ± 0.9 ‰ for semi-aquatic birds and of +4.4 ± 1.9 ‰ for terrestrial birds are observed. Surprisingly, no significant dependence to body temperature on the oxygen isotope fractionation between eggshell calcite and body fluids is observed, suggesting that bird eggshells precipitate out of equilibrium. Two empirical equations relating the δ18Ocalc value of eggshell calcite to the δ18Ow value of ingested water have been established for terrestrial and semi-aquatic birds. These equations have been applied to fossil eggshells from Lanzarote in order to infer the ecologies of the Pleistocene marine bird Puffinus sp. and of the enigmatic giant birds from the Pliocene. Both δ13Ccalc and δ18Ocalc values of Puffinus eggshells point to a semi-aquatic marine bird ingesting mostly seawater, whereas low δ13Ccalc and high δ18Ocalc values of eggshells from the Pliocene giant bird suggest a terrestrial lifestyle. This set of equations can help to quantitatively estimate the origin of waters ingested by extinct birds as well as to infer either local environmental or climatic conditions.
Schlagworte: carbon , oxygen , ecol , mulitcarb

Trophic interactions between two neustonic organisms: insights from Bayesian stable isotope data analysis tools
Belg. J. Zool (2016)
Gilles Lepoint, Laurent Bernard, Sylvie Gobert, Loïc N Michel

The by-the-wind sailor Velella velella (Linnaeus, 1758) and its predator, the violet snail Janthina globosa (Swainson, 1822) are both floating neustonic organisms. Despite their global oceanic distribution and widespread blooms of V. velella in recent years, many gaps remain in our understanding about prey/predator interactions between these two taxa. Using stable isotope ratios of carbon and nitrogen, we aimed to study the trophic relationship between V. velella and J. globosa and investigate diet variation of V. velella and J. globosa in relation to individuals' size. Bayesian approaches were used to calculate isotopic niche metrics and the contribution of V. velella to the J. globosa diet. Our data showed that the isotopic niche of V. velella differed markedly from that of J. globosa. It was larger and did not overlap that of the J. globosa, indicating a more variable diet but at a lower trophic level than J. globosa. The isotopic niche of V. velella also varied according to the size class of the individual. Small individuals showed a larger isotopic niche than larger animals and low overlap with those of the larger individuals. J. globosa displayed very low isotopic variability and very small isotopic niches. In contrast, there were no isotopic composition nor isotopic niche differences between J. globosa of any size. This very low isotopic variability suggested that J. globosa is a specialist predator, feeding, at least in this aggregation, principally on V. velella. Moreover, outputs of a stable isotope mixing model revealed preferential feeding on medium to large (> 500 mm 2) V. velella colonies. While our isotopic data showed the trophic relationship between V. velella and J. globosa, many questions remain about the ecology of these two organisms, demonstrating the need for more fundamental studies about neustonic ecosystems.

Forensic Comparison of Soil Samples
(2016)
Jisook Min, Kiwook Kim, Sangcheol Heo, Yurim Jang

As a preliminary experiment to test the discriminating ability of forensic soil analysis techniques and obtain area-specific information, soil samples were collected from eight areas near the eastern branch of the National Forensic Service (NFS) located in Gangwondo, an eastern province of South Korea. The soil samples were collected from five spots within each sample area using a small-scale (1 m2) soil sampling technique; for each of these five spots, two samples were collected from two places in each spot, (i) one from the surface and (ii) another from 30 cm below the surface. For each sample, the color of the sample with particle size in the range 53–500 μm and the major constituents were determined using a spectrophotometer and X-ray fluorescence spectrometer (XRF), respectively. The carbon content and carbon isotope ratio of the part of the sample of particle size below 53 μm were measured using an element analyzer-isotope ratio mass spectrometer (EA-IRMS). The canonical discriminant and XRF analyses showed an excellent color discriminating ability of 87.5 % and 88.8 %, respectively, with respect to the major constituents. The EA-IRMS results showed that the soils obtained from a 30-cm depth below the surface were generally more enriched in δ13C (0/00) than the surface soils, and that the surface soils contained a higher carbon amount (%). The canonical discriminant analysis confirmed 100 % discriminating ability when all three soil characteristics (i.e., color, composition, and content) were used in the analysis. Out of the two functions obtained from the analysis, Function 1 exhibited greater potential for explaining the SiO2, Fe2O3, and TiO2; thus, Area 6 and 7 could be more easily differentiated than the other areas using this function. Function 2 exhibited greater potential for explaining color factor b* (δ13C and C content), and could more efficiently differentiate Area 2 and 5. However, different results were obtained within the same area based on the soil depth. Therefore, when performing a comparative sampling analysis in forensic science, due care should be taken to prevent the mixing of adjacent soils from various depths. Better results can be achieved by collecting soil samples from different spots within the same area.
Schlagworte: carbon , soil , elem

New multiproxy record of the Jenkyns Event (also known as the Toarcian Oceanic Anoxic Event) from the Mecsek Mountains (Hungary): Differences, duration and drivers
Sedimentology (2016)
Tamás Müller, Gregory D. Price, Dávid Bajnai, Anita Nyerges, Dóra Kesjár, Béla Raucsik, Andrea Varga, Katalin Judik, József Fekete, Zoltán May, József Pálfy

The oceanic anoxic event in the Early Toarcian, often referred to as ‘Torcian Oceanic Anoxic Event’, led to widespread deposition of organic-rich black shales and geochemical anomalies in elemental distribution and multiple isotope systems in the Early Jurassic ocean. Best characterized by its hallmark carbon isotope anomaly, the event is widely regarded as a prime example of rapid greenhouse warming-related changes in the Mesozoic Earth system. However, despite numerous studies, details of its forcing mechanisms, exact duration and the role of regional effects remain debated. This article presents new data (high resolution organic carbon isotope, calcareous nannofossil and elemental geochemical analyses) from the black shale-bearing Lower Toarcian section in the Réka Valley, Hungary, with the aim of assessing any regional differences in the sedimentary and geochemical record and their bearing on the underlying oceanographic and climatic processes. Following a short segment with a positive trend at the base of the section, values of the carbon isotope data here are turning to a negative trend with a steep, stepwise drop in two negative shifts, reaching their minimum before a positive trend with oscillations characterizing the top part of the section examined. The shape of the curve and nannoplankton biostratigraphy (recognition of zones NJ5b, NJ6 and NJ7) allow reliable correlation of these data with the global carbon isotope perturbation recorded elsewhere in the Early Toarcian. It is proposed here that it would be fitting to rename the Torcian Oceanic Anoxic Event as the Jenkyns Event, to honour the seminal contributions of Hugh Jenkyns. The cyclostratigraphic analysis in this study suggests that the duration of the negative isotope excursion at Réka Valley is 200 kyr, 350 kyr or 1 Myr, depending on which astronomical forcing parameter controls the most prominent cyclicity. Spectroscopic analyses suggest that the source of the organic matter, marine algae according to previous studies, did not change considerably during the main negative carbon isotope excursion. The variability observed in major element concentrations and enrichments relative to the average shale in the Réka Valley black shales can be regarded as mixtures of terrigenous aluminosilicates and calcium carbonate as two endmembers. Consequently, the terrigenous compositional endmember of the studied black shales consists of a mixture of an illitic/smectitic and a kaolinitic clay, supports previous suggestions of increased weathering under extremely humid climate in the hinterland during the Jenkyns Event.
Schlagworte: carbon , geol , elem

Linking rhizospheric CH4 oxidation and net CH4 emissions in an arctic wetland based on 13CH4 labeling of mesocosms
Plant and Soil (2016)
Cecilie Skov Nielsen, Anders Michelsen, Per Ambus, T. K. K. Chamindu Deepagoda, Bo Elberling

Aims Poorly drained arctic ecosystems are potential large emitters of methane (CH4) due to their high soil organic carbon content and low oxygen availability. In wetlands, aerenchymatous plants transport CH4 from the soil to the atmosphere, but concurrently transport O2 to the rhizosphere, which may lead to oxidation of CH4. The importance of the latter process is largely unknown for arctic plant species and ecosystems. Here, we aim to quantify the subsurface oxidation of CH4 in a waterlogged arctic ecosystem dominated by Carex aquatilis ssp. stans and Eriophorum angustifolium, and evaluate the overall effect of these plants on the CH4 budget. Methods A mesocosms study was established based on the upper 20 cm of an organic soil profile with intact plants retrieved from a peatland in West Greenland (69°N). We measured dissolved concentrations and emissions of 13CO2 and 13CH4 from mesocosms during three weeks after addition of 13C-enriched CH4 below the mesocosm. Results Most of the recovered 13C label (>98 %) escaped the ecosystem as CH4, while less than 2 % was oxidized to 13CO2. Conclusions It is concluded that aerenchymatous plants control the overall CH4 emissions but, as a transport system for oxygen, are too inefficient to markedly reduce CH4 emissions.
Schlagworte: carbon , soil , gashead

Sensitivity of soil carbon fractions and their specific stabilization mechanisms to extreme soil warming in a subarctic grassland
Global Change Biology (2016)
Christopher Poeplau, Thomas Kätterer, Niki I. W. Leblans, Bjarni D. Sigurdsson

Terrestrial carbon cycle feedbacks to global warming are major uncertainties in climate models. For in-depth understanding of changes in soil organic carbon (SOC) after soil warming, long-term responses of SOC stabilization mechanisms such as aggregation, organo-mineral interactions and chemical recalcitrance need to be addressed. This study investigated the effect of 6 years of geothermal soil warming on different SOC fractions in an unmanaged grassland in Iceland. Along an extreme warming gradient of +0 to ~+40 °C, we isolated five fractions of SOC that varied conceptually in turnover rate from active to passive in the following order: particulate organic matter (POM), dissolved organic carbon (DOC), SOC in sand and stable aggregates (SA), SOC in silt and clay (SC-rSOC) and resistant SOC (rSOC). Soil warming of 0.6 °C increased bulk SOC by 22 ± 43% (0–10 cm soil layer) and 27 ± 54% (20–30 cm), while further warming led to exponential SOC depletion of up to 79 ± 14% (0–10 cm) and 74 ± 8% (20–30) in the most warmed plots (~+40 °C). Only the SA fraction was more sensitive than the bulk soil, with 93 ± 6% (0–10 cm) and 86 ± 13% (20–30 cm) SOC losses and the highest relative enrichment in 13C as an indicator for the degree of decomposition (+1.6 ± 1.5‰ in 0–10 cm and +1.3 ± 0.8‰ in 20–30 cm). The SA fraction mass also declined along the warming gradient, while the SC fraction mass increased. This was explained by deactivation of aggregate-binding mechanisms. There was no difference between the responses of SC-rSOC (slow-cycling) and rSOC (passive) to warming, and 13C enrichment in rSOC was equal to that in bulk soil. We concluded that the sensitivity of SOC to warming was not a function of age or chemical recalcitrance, but triggered by changes in biophysical stabilization mechanisms, such as aggregation.
Schlagworte: carbon , soil , clim , elem

Sources and turnover of organic carbon and methane in fjord and shelf sediments off Northern Norway
Geochemistry, Geophysics, Geosystems (2016)
Simone Sauer, Wei-Li Hong, Jochen Knies, Aivo Lepland, Matthias Forwick, Martin Klug, Florian Eichinger, Soma Baranwal, Antoine Crémière, Shyam Chand, Carsten J. Schubert

To better understand the present and past carbon cycling and transformation processes in methane influenced fjord and shelf areas of Northern Norway we compared two sediment cores from the Hola trough and from Ullsfjorden. We investigated (1) the organic matter composition and sedimentological characteristics to study the sources of organic carbon (Corg) and the factors influencing Corg burial, (2) pore water geochemistry to determine the contribution of organoclastic sulfate reduction and methanogenesis to total organic carbon turnover, and (3) the carbon isotopic signature of hydrocarbons to identify the carbon transformation processes and gas sources. High sedimentation and Corg accumulation rates in Ullsfjorden support the notion that fjords are important Corg sinks. The depth of the sulfate-methane-transition (SMT) in the fjord is controlled by the supply of predominantly marine organic matter to the sediment. Organoclastic sulfate reduction accounts for 60% of the total depth-integrated sulfate reduction in the fjord. In spite of the presence of ethane, propane and butane, we suggest a purely microbial origin of light hydrocarbons in the sediments based on their low δ13C values. In the Hola trough, sedimentation and Corg accumulation rates changed during the deglacial-to-post-glacial transition from approximately 80 cm ka−1 to erosion at present. Thus, Corg burial in this part of the shelf is presently absent. Low organic matter content in the sediment and low rates of organoclastic sulfate reduction (only 3% of total depth-integrated sulfate reduction) entail that the shallow depth of the SMT is controlled mostly by ascending thermogenic methane from deeper sources.
Schlagworte: carbon , geol , gashead

Adaptation to a high protein diet progressively increases the postprandial accumulation of carbon skeletons from dietary amino acids in rats
American Journal of Physiology - Regulatory, Integrative and Comparative Physiology (2016)
Magdalena Stepien, Dalila Azzout-Marniche, Patrick C Even, Nadezda Khodorova, Gilles Fromentin, Daniel Tomé, Claire Gaudichon

We aimed to determine whether oxidative pathways adapt to the overproduction of carbon skeletons resulting from the progressive activation of amino acid (AA) deamination and ureogenesis under a high protein (HP) diet. Ninety-four male Wistar rats, of which 54 were implanted with a permanent jugular catheter, were fed a normal protein diet for one week and were then switched to an HP diet for 1, 3, 6 or 14 days. On the experimental day, they were given their meal containing a mixture of 20 U-[15N]-[13C] AA, whose metabolic fate was followed for 4 h. Gastric emptying tended to be slower during the first 3 days of adaptation. 15N excretion in urine increased progressively during the first 6 days, reaching 29% of ingested protein. 13CO2 excretion was maximal as early as the first day, and represented only 16% of the ingested proteins. Consequently, the amount of carbon skeletons remaining in the metabolic pools 4 h after the meal ingestion progressively increased to 42% of the deaminated dietary AA after 6 days of HP diet. In contrast, 13C enrichment of plasma glucose tended to increase from 1 to 14 days of the HP diet. We conclude that there is no oxidative adaptation in the early postprandial period to an excess of carbon skeletons resulting from AA deamination in HP diets. This leads to an increase in the postprandial accumulation of carbon skeletons throughout the adaptation to an HP diet, which can contribute to the sustainable satiating effect of this diet.