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824 Ergebnisse:

Lithostratigraphic analysis of a new stromatolite-thrombolite reef from across the rise of atmospheric oxygen in the Paleoproterozoic Turee Creek Group, Western Australia.
Geobiology (2016)
E Barlow, M J Van Kranendonk, K E Yamaguchi, M Ikehara, A Lepland

This study describes a previously undocumented dolomitic stromatolite-thrombolite reef complex deposited within the upper part (Kazput Formation) of the c. 2.4-2.3 Ga Turee Creek Group, Western Australia, across the rise of atmospheric oxygen. Confused by some as representing a faulted slice of the younger c. 1.8 Ga Duck Creek Dolomite, this study describes the setting and lithostratigraphy of the 350-m-thick complex and shows how it differs from its near neighbour. The Kazput reef complex is preserved along 15 km of continuous exposure on the east limb of a faulted, north-west-plunging syncline and consists of 5 recognisable facies associations (A-E), which form two part regressions and one transgression. The oldest facies association (A) is characterised by thinly bedded dololutite-dolarenite, with local domical stromatolites. Association B consists of interbedded columnar and stratiform stromatolites deposited under relatively shallow-water conditions. Association C comprises tightly packed columnar and club-shaped stromatolites deposited under continuously deepening conditions. Clotted (thrombolite-like) microbialite, in units up to 40 m thick, dominates Association D, whereas Association E contains bedded dololutite and dolarenite, and some thinly bedded ironstone, shale and black chert units. Carbon and oxygen isotope stratigraphy reveals a narrow range in both δ(13) Ccarb values, from -0.22 to 0.97‰ (VPDB: average = 0.68‰), and δ(18) O values, from -14.8 to -10.3‰ (VPDB), within the range of elevated fluid temperatures, likely reflecting some isotopic exchange. The Kazput Formation stromatolite-thrombolite reef complex contains features of younger Paleoproterozoic carbonate reefs, yet is 300-500 Ma older than previously described Proterozoic examples worldwide. Significantly, the microbial fabrics are clearly distinct from Archean stromatolitic marine carbonate reefs by way of containing the first appearance of clotted microbialite and large columnar stromatolites with complex branching arrangements. Such structures denote a more complex morphological expression of growth than previously recorded in the geological record and may link to the rise of atmospheric oxygen.
Schlagworte: C , O , ge , oc , cc , MC

Measurement of compound-specific carbon isotope ratios (δ 13 C values) via direct injection of whole crude oil samples
Rapid Communications in Mass Spectrometry (2016)
Craig D. Barrie, Kyle W. R. Taylor, John Zumberge

RATIONALE: Stable isotope analysis is a powerful tool in understanding the generation, history and correlation of hydrocarbons. Compound-specific δ13C measurements of oils allow detailed comparison of individual compound groupings; however, most studies of these sample materials separate and isolate individual fractions based on the chemistries of particular compound groups, potentially losing considerable valuable isotopic data. Even if all fractions are analyzed, this represents a large increase in the data-processing burden, effectively multiplying data evaluation time and effort by the number of fractions produced. Gas chromatography/isotope ratio mass spectrometry (GC/IRMS) of untreated, whole crude oils allows the immediate collection of a larger suite of valuable isotopic data for these studies. METHODS: Untreated (‘neat’, undiluted), whole crude oils were directly injected and measured on a GC/IRMS system, using split (40:1) injections and a 50 m HP-PONA column. The GC method, 97 min in duration, was designed to maximize baseline separation of target analyte peaks, while an additional oxygen flow was admitted into the combustion reactor to maximize the lifetime of the combustion chemicals. RESULTS: The method and setup utilized allow the measurement of a much greater range of the n-alkanes (n-C4 to n- C25+) than traditional methods, while also retaining important cycloalkane, aromatic and isoprenoid peaks within the same analysis. Carbon isotope (δ13C) evaluation of these additional compound classes reveals trends in maturity and origins which are not identifiable when exclusively assessing the traditional n-alkane package (>n-C12). CONCLUSIONS: The described setup and method open up new possibilities for assessing the origins and histories of crude oil samples. The data generated for the whole oil n-alkanes by this method is equivalent to that reported for isolated n-alkane studies, while also providing valuable additional data on many other important compounds. The end result of this method is a more complete assessment of the carbon isotopic composition of crude oils.
Schlagworte: C , oi , GC

Sulfur isotopic compositions of individual organosulfur compounds and their genetic links in the Lower Paleozoic petroleum pools of the Tarim Basin, NW China
Geochimica et Cosmochimica Acta (2016)
Chunfang Cai, Alon Amrani, Richard H. Worden, Qilin Xiao, Tiankai Wang, Zvi Gvirtzman, Hongxia Li, Ward Said-Ahmad, Lianqi Jia

During thermochemical sulfate reduction (TSR), H2S generated by reactions between hydrocarbons and aqueous sulfate back-reacts with remaining oil-phase compounds forming new organosulfur compounds (OSC) that have similar δ34S values to the original sulfate. Using compound specific sulfur isotope analysis (CSSIA) of alkylthiaadamantanes (TAs), alkyldibenzothiophenes (DBTs), alkylbenzothiophenes (BTs) and alkylthiolanes (TL), we have here attempted to differentiate OSCs due to primary generation and those due to TSR in oils from the Tarim Basin, China. These oils were generated from Cambrian source rocks and accumulated in Cambrian and Ordovician reservoirs. Based on compound specific sulfur isotope and carbon isotope data, TAs concentrations and DBT/phenanthrene ratios, the oils fall into four groups, reflecting different extents of source rock signal, alteration by TSR, mixing events, and secondary generation of H2S. Thermally stable TAs, produced following TSR, rapidly dominate kerogen-derived TAs at low to moderate degrees of TSR. Less thermally stable TLs and BTs were created as soon as TSR commenced, rapidly adopted TSR- δ34S values, but they do not survive at high concentrations unless TSR is advanced and ongoing. The presence of TLs and BTs shows that TSR is still active. Secondary DBTs were produced in significant amounts sufficient to dominate kerogen-derived DBTs, only when TSR was at an advanced extent. The difference in sulfur isotopes between (i) TLs and DBTs and (ii) BTs and DBTs and (iii) TAs and DBTs, represents the extent of TSR while the presence of TAs at greater than 20 μg/g represents the occurrence of TSR. The output of this study shows that compound specific sulfur isotopes of different organosulfur compounds, with different thermal stabilities and formation pathways, not only differentiate between oils of TSR and non-TSR origin, but can also reveal information about relative timing of secondary charge events and migration pathways.

Sulfur isotope constraints on marine transgression in the lacustrine upper cretaceous Songliao Basin, Northeastern China
Palaeogeography, Palaeoclimatology, Palaeoecology (2016)
Hansheng Cao, Alan J. Kaufman, Xuanlong Shan, Huan Cui, Guijie Zhang

Organic-rich Cretaceous source rocks of the petroliferous Songliao Basin in northeast China are considered to be lacustrine in origin, but paleontological and organic geochemical evidence suggest episodic marine incursions. As a test of this hypothesis we applied time-series measurements of elemental and isotopic abundances on core and cutting samples to evaluate fluctuations in the sulfur and carbon cycles across the Santonian-Campanian transition preserved in the upper Yaojia and lower Nenjiang formations. The data reveal a spike in pyrite sulfur abundance and a marked negative excursion in δ34S at the base of the Nenjiang Formation when the basin expanded to its maximal extent. The elemental and isotopic data suggest that flooding was associated with rapid marine transgression that enhanced sulfate concentrations, which promoted microbial sulfate reduction in anoxic bottom waters that were episodically euxinic. Subsequent restriction of the basin and a decline in marine influence is supported by progressive upsection 34S enrichment (up to 30‰) in Nenjiang Member I, which are interpreted to reflect the distillation of sulfate through enhanced pyrite burial, followed by a gradual return to lacustrine conditions that prevailed in overlying strata.

Effects of algal food quality on sexual reproduction of Daphnia magna
Ecology and Evolution (2016)
Jong-Yun Choi, Seong-Ki Kim, Geung-Hwan La, Kwang-Hyeon Chang, Dong-Kyun Kim, Keon-Young Jeong, Min S. Park, Gea-Jae Joo, Hyun-Woo Kim, Kwang-Seuk Jeong

Schlagworte: C , N , ec , EA

Quantifying the ecological impact of invasive tunicates to shallow coastal water systems
Management of Biological Invasions (2016)
Phil Colarusso, Eric Nelson, Suzanne Ayvazian, Mary R Carman, Marty Chintala, Sinead Grabbert, David Grunden

Coastal ponds, due to their proximity to human activity, may be particularly vulnerable to invasions by non-native species. A number of invasive tunicate species have been documented in several of the coastal ponds on the island of Martha’s Vineyard, Massachusetts. Tunicates are voracious filter feeders, thus our study attempted to examine the impact of their feeding on the normal food web in a coastal pond. In 2012 and 2013, we sampled Stonewall (high tunicate abundance) and Lagoon Ponds (tunicates absent) on Martha’s Vineyard. We used quadrat sampling to quantify tunicate abundance, eelgrass shoot density and eelgrass canopy height. Fish, invertebrates and aquatic vegetation were collected via beach seine, minnow trap, crab traps or by hand. Water samples were run through a filter to collect phytoplankton. These biota samples were processed for carbon and nitrogen isotopic analysis. Temperature loggers were deployed in both ponds to collect water temperature. Detailed bathymetric readings were taken to generate an estimate of the volume of each pond. Tunicate filtration rates from published scientific literature, our volume estimate of Stonewall Pond and our measured tunicate abundance were used in a model to estimate the time needed by tunicates to filter a volume of water equal to Stonewall Pond. That time varied from less than an hour to over 17 hours. Isotopic analysis showed that tunicates were feeding on similar resources as the commercial shellfish species. There was broad overlap in the isotopic signatures between the biota from both ponds, suggesting that tunicates were not having a measurable impact to the food web. Tunicates exhibit significant seasonal abundance changes, with the peak occurring late summer into the early fall. The limited duration of this peak may not be sufficient to be reflected in the isotopic signature of resident biota. As water temperature continues to increase with climate change, the current assemblage of tunicates in these shallow water systems on Martha’s Vineyard will likely change in response. Key
Schlagworte: C , N , ec , EA

Does excess nitrogen supply increase the drought sensitivity of European beech (Fagus sylvatica L.) seedlings?
Plant Ecology (2016)
Christoph Dziedek, Goddert von Oheimb, Leonor Calvo, Andreas Fichtner, Wolf-Ulrich Kriebitzsch, Elena Marcos, Witja Till Pitz, Werner Härdtle

Climate change and atmospheric deposition of nitrogen affect biodiversity patterns and functions of forest ecosystems worldwide. Many studies have quantified tree growth responses to single global change drivers, but less is known about the interaction effects of these drivers at the plant and ecosystem level. In the present study, we conducted a full-factorial greenhouse experiment to analyse single and combined effects of nitrogen fertilization (N treatment) and drought (D treatment) on 16 morphological and chemical response variables (including tissue δ13C signatures) of one-year-old Fagus sylvatica seedlings originating from eight different seed families from the Cantabrian Mountains (NW Spain). Drought exerted the strongest effect on response variables, reflected by decreasing biomass production and increasing tissue δ13C signatures. However, D and N treatments interacted for some of the response variables, indicating that N fertilization has the potential to strengthen the negative effects of drought (with both antagonistic and amplifying interactions). For example, combined effects of N and D treatments caused a sevenfold increase of necrotic leaf biomass. We hypothesize that increasing drought sensitivity was mainly attributable to a significant reduction of the root biomass in combined N and D treatments, limiting the plants’ capability to satisfy their water demands. Significant seed family effects and interactions of seed family with N and D treatments across response variables suggest a high within-population genetic variability. In conclusion, our findings indicated a high drought sensitivity of Cantabrian beech populations, but also interaction effects of N and D on growth responses of beech seedlings.

A novel high-temperature combustion interface for compound-specific stable isotope analysis of carbon and nitrogen via high-performance liquid chromatography/isotope ratio mass spectrometry
Rapid Communications in Mass Spectrometry (2016)
E. Federherr, S. Willach, N. Roos, L. Lange, K. Molt, T. C. Schmidt

RATIONALE: In aqueous samples compound-specific stable isotope analysis (CSIA) plays an important role. No direct method (without sample preparation) for stable nitrogen isotope analysis (δ15N SIA) of non-volatile compounds is known yet. The development of a novel HPLC/IRMS interface based on high-temperature combustion (HTC) for both δ13C and δ15N CSIA and its proof of principle are described in this study. METHODS: To hyphenate high-performance liquid chromatography (HPLC) with isotope ratio mass spectrometry (IRMS) a modified high-temperature combustion total organic carbon analyzer (HTC TOC) was used. A system to handle a continuously large amount of water (three-step drying system), favorable carrier and reaction gas mix and flow, an efficient high-temperature-based oxidation and subsequent reduction system and a collimated beam transfer system were the main requirements to achieve the necessary performance. RESULTS: The proof of principle with caffeine solutions of the system succeeded. In this initial testing, both δ13C and δ15N values of tested compounds were determined with precision and trueness of ≤0.5‰. Further tests resulted in lower working limit values of 3.5 μgC for δ13C SIA and 20 μgN for δ15N SIA, considering an accuracy of ±0.5‰as acceptable. CONCLUSIONS: The development of a novel HPLC/IRMS interface resulted in the first systemreported to be suitable for both δ13C and δ15N direct CSIA of non-volatile compounds. This highly efficient system will probably open up new possibilities in SIA-based research fields.
Schlagworte: C , N , LF

Deciphering processes controlling mid-Jurassic coccolith turnover
Marine Micropaleontology (2016)
Fabienne Giraud, Emanuela Mattioli, Gatsby Emperatriz López-Otálvaro, Christophe Lécuyer, Baptiste Suchéras-Marx, Yves Alméras, François Martineau, Florent Arnaud-Godet, Eric de Kænel

The Middle Jurassic is characterized by major changes within the fossil coccolithophorid community, with a transition from Lotharingius-dominated to Watznaueria-dominated assemblages, concomitant with a significant increase in the pelagic carbonate production. The mechanisms that triggered this overturn remain poorly understood. Here, we present a compilation (new and previously published data) of Lotharingius and Watznaueria abundances through the Early–Middle Jurassic transition. Alongside this, trends in newly-acquired and literature-derived carbon and oxygen isotope data were used to represent paleoceanographic indicators, such as nutrient and temperature changes. The nannofossil data show a rapid (around 1.5Myr) turnover around the Aalenian–Bajocian transition. Across the Aalenian/Bajocian boundary, assemblages dominated by Lotharingius spp. give way to assemblages dominated by Watznaueria spp., coinciding with a peak in a particular morphological group of Watznaueria (species with a cross in the central area). The proliferation of this morphogroup occurred during a time of oceanic opening and rearrangement of ocean circulation. This led on to the evolution of pioneering coccolithophorid taxa, but also to extinctions in several marine groups. In the Early Bajocian, the proliferation of two other morphogroups (Watznaueria without a central-area structure and Watznaueria with a bar) corresponds to the major diversification of Watznaueria, and the beginning of its Mesozoic dominance. The Watznaueria diversification and dominance are associated with radiation in other marine groups, and these biotic changes occurred during a time of putative enhanced oceanic fertility and relatively low temperatures. This study suggests that restructuring of fossil coccolithophorid communities may be favored during short turnover intervals related to major paleoceanographic change.

Scaling the consequences of interactions between invaders from the individual to the population level
Ecology and Evolution (2016)
Blaine D. Griffen

The impact of human-induced stressors, such as invasive species, is often measured at the organismal level, but is much less commonly scaled up to the population level. Interactions with invasive species represent an increasingly common source of stressor in many habitats. However, due to the increasing abundance of invasive species around the globe, invasive species now commonly cause stresses not only for native species in invaded areas, but also for other invasive species. I examine the European green crab Carcinus maenas, an invasive species along the northeast coast of North America, which is known to be negatively impacted in this invaded region by interactions with the invasive Asian shore crab Hemigrapsus sanguineus. Asian shore crabs are known to negatively impact green crabs via two mechanisms: by directly preying on green crab juveniles and by indirectly reducing green crab fecundity via interference (and potentially exploitative) competition that alters green crab diets. I used life-table analyses to scale these two mechanistic stressors up to the population level in order to examine their relative impacts on green crab populations. I demonstrate that lost fecundity has larger impacts on per capita population growth rates, but that both predation and lost fecundity are capable of reducing population growth sufficiently to produce the declines in green crab populations that have been observed in areas where these two species overlap. By scaling up the impacts of one invader on a second invader, I have demonstrated that multiple documented interactions between these species are capable of having population-level impacts and that both may be contributing to the decline of European green crabs in their invaded range on the east coast of North America.