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Geowissenschaften

Die Erforschung der Erdgeschichte erfüllt den grundlegenden menschlichen Drang zu wissen, wie die Welt entstanden ist. Im Laufe ihrer 4,6 Milliarden Jahre langen Geschichte hat die Erde eine enorme Transformation durchlaufen, und die Stabilisotopenanalyse steht bei der Erforschung dieser Veränderungsprozesse an vorderster Front. Durch das Verständnis der makro- und mikrozyklischen Mechanismen, welchen die leichten stabilen Isotope in der Lithosphäre durch natürliche Prozesse unterliegen, wächst auch unser Wissen über die Erdgeschichte kontinuierlich.

Paläoklima

Eine der ersten Anwendungen der Stabilisotopenmassenspektrometrie leichter Elemente war die Rekonstruktion des Paläoklimas auf Grundlage der Sauerstoff-Isotopenzusammensetzung (δ18O) von sehr alten, konservierten marinen Carbonaten. Auch heute noch ist dies eine der weitverbreitesten Methoden zur Erforschung der Klimageschichte der Erde. Dieses Paläothermometer basiert auf dem Grundprinzip, dass die Fraktionierung von Sauerstoffisotopen in Calcit temperaturabhängig ist. Das isoprime precisION mit Dual Inlet und MultiCarb ermöglicht eine sehr präzise und zuverlässige, automatisierte Messung von Carbonaten, ideal zur Erzeugung hochauflösender Paläotemperaturaufzeichnungen.

Kosmologie

Die Schwefelisotopenanalyse von extraterrestrischen Sulfidmineralien, z.B. von Meteoriten, hat eine Vielzahl von Erkenntnissen über den Ursprung der Erde und des Sonnensystems ermöglicht. Die Isotopenzusammensetzung von meteoritischem Schwefel (Canyon Diabolo Triolite) wurde auch als der ursprüngliche Bezugspunkt für Erdkruste und -mantel verwendet, von der ausgehend die globalen Fraktionen im Schwefelkreislauf evaluiert werden. Schwefelhaltige Mineralien lassen sich leicht mit unserem vielseitigen Spektrum von EA-IRMS-Systemen analysieren, welche die Advanced Purge and Trap Technologie (APT) für eine unschlagbare Trennung und Peakfokussierung von SO2 nutzen, um eine perfekte Auflösung und eine unvergleichliche Empfindlichkeit für die Mineralschwefelanalyse zu gewährleisten.

Stratigraphie

δ13C-Fluktuationen im Laufe geologischer Zeitalter werden durch Änderungen des Gleichgewichts im Kohlenstoffkreislauf bewirkt. Da die Verweilzeit im Kohlenstoffkreislauf kurz ist (10 ka), werden Änderungen im Kohlenstofffluss im Sediment sehr genau global aufgezeichnet. Als solche sind gelegentliche Spikes im globalen δ13C als stratigraphische Marker für die Chemostratigraphie nützlich, besonders während des Paläozoikums. Der iso FLOW nutzt unsere neuartige UltiTrap-Technologie und ermöglicht so eine präzise, durchgängige Continuous Flow Analyse von Massencarbonaten, um solche Isotopenabweichungen zu identifizieren.

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248 Ergebnisse:

Baseline geochemical characterisation of a vulnerable tropical karstic aquifer; Lifou, New Caledonia
Journal of Hydrology: Regional Studies (2016)
Eric Nicolini, Karyne Rogers, Delphine Rakowski

STUDY REGION Lifou Island, near the main island of New Caledonia. STUDY FOCUS Stable oxygen and hydrogen isotopes of groundwater and rainfall were used to characterise baseline values for the main fresh water aquifer of Lifou Island and describe its recharge. Other stable isotope parameters (nitrates and DIC) were used to investigate the interaction between surface water (rainfall) and groundwater, including anthropogenic effects from human activities. NEW HYDROLOGICAL INSIGHTS FOR THE REGION This study represents the first baseline isotopic characterisation of Lifou Island’s groundwater aquifer composition and provides a reference for future investigative studies on groundwater quality and security. Groundwater sampled in June and October 2012 had nearly identical isotopic composition. Tap water sampled monthly between February 2012 and January 2014 also had a constant isotopic composition similar to the groundwater. Groundwater recharge was found to occur when monthly precipitation exceeded 140mm, with the recharge cycle representing 20–30% of the annual rainfall. Relationships between HCO32− content, pH, soil δ13C DIC and satellite photo interpretation suggests a variance of soil pCO2, which is explained by different vegetation cover and higher water use efficiencies in forested areas (high pCO2, more negative δ13C isotope values). The δ15NNO3 values for most groundwater indicate they are uncontaminated with anthropogenic nitrates, although some samples taken in October (dry season) showed a slight denitrification, possibly of natural origin.
Schlagworte: carbon , nitrogen , geol , elem

Nitrate vulnerability projections from Bayesian inference of multiple groundwater age tracers
Journal of Hydrology (2016)
Jamal Alikhani, Amanda Deinhart, Ate Visser, Richard Bibby, Roland Purtschert, Jean Moran, Arash Massoudieh, Brad Esser

Nitrate is a major source of contamination of groundwater in the United States and around the world. We tested the applicability of multiple groundwater age tracers (3H, 3He, 4He, 14C, 13C, and 85Kr) in projecting future trends of nitrate concentration in 9 long-screened, public drinking water wells in Turlock, California, where nitrate concentrations are increasing toward the regulatory limit. Very low 85Kr concentrations and apparent 3H/3He ages point to a relatively old modern fraction (40-50 years), diluted with pre-modern groundwater, corroborated by the onset and slope of increasing nitrate concentrations. An inverse Gaussian-Dirac model was chosen to represent the age distribution of the sampled groundwater at each well. Model parameters were estimated using a Bayesian inference, resulting in the posterior probability distribution – including the associated uncertainty – of the parameters and projected nitrate concentrations. Three scenarios were considered, including combined historic nitrate and age tracer data, the sole use of nitrate and the sole use of age tracer data. Each scenario was evaluated based on the ability of the model to reproduce the data and the level of reliability of the nitrate projections. The tracer-only scenario closely reproduced tracer concentrations, but not observed trends in the nitrate concentration. Both cases that included nitrate data resulted in good agreement with historical nitrate trends. Use of combined tracers and nitrate data resulted in a narrower range of projections of future nitrate levels. However, use of combined tracer and nitrate resulted in a larger discrepancy between modeled and measured tracers for some of the tracers. Despite nitrate trend slopes between 0.56 and 1.73 mg/L/year in 7 of the 9 wells, the probability that concentrations will increase to levels above the MCL by 2040 are over 95% for only two of the wells, and below 15% in the other wells, due to a leveling off of reconstructed historical nitrate loadings to groundwater since about 1990.

Compositional variation and palaeoenvironment of the volcanolithic Fort Cooper Coal Measures, Bowen Basin, Australia
International Journal of Coal Geology (2016)
S.A. Ayaz, S. Rodrigues, S.D. Golding, J.S. Esterle

Megascopic lithotype and microscopic maceral and mineral composition were supplemented by sedimentary logging of the interburden and stable carbon isotope data from a single well to interpret the response of the Late Permian Fort Cooper Coal Measures (FCCM) to regional and global environmental influences. The FCCM are differentiated from underlying, relatively high vitrinite Moranbah Coal Measures, and overlying higher inertinite Rangal Coal Measures in the Bowen Basin by their intercalation with abundant tuff and siliciclastic partings and interbeds. Besides this, there is little described about the variation in the organic composition of the FCCM and its causes. The FCCM can be subdivided into a lower aggradational Fair Hill Formation, transgressed by the shallow marine-derived Black Alley Shale that interfinger with/is overlain by the progradational Middle Main Seams and Burngrove Formation. The coals are dominantly dull with minor bright bands that are more abundant in the Burngrove Formation representing a change in plant composition. The maceral analysis shows that the coals in the Fair Hill Formation and Middle Main Seams are vitrinite-rich (80–90% mmf) albeit with high mineral matter suggesting the formation of precursory peat under rising water levels and with high sediment (tuff) influx and preservation. The coals in the Burngrove Formation have an increased inertinite content (30% mmf) but are also high in mineral matter suggesting a shift to increased decomposition arising from a fluctuating water table, possibly increased aridity and/or microbial activity. Tuffs occur throughout, and although the frequency is higher in the lower Fair Hill Formation, the preservation of thicker tuffs in the Burngrove Formation indicates increased intensity of volcanism that could have modified the environment. Variation in carbon isotope compositions show a parabolic trend, from around −24.1‰ in the Fair Hill Formation to more variable values in the Middle Main Seams with an overall 13C-enrichment upwards in the Burngrove Formation, prior to the δ13C values becoming negative (depleted between −1 to −4% from the average −24.1‰) in the top seams and into the overlying Rangal Coal Measures. The 13C-depletion trend in the upper part of the section is unexpected in view of the high inertinite content of the coals and does not show a positive correlation indicating that the δ13C values/plant composition and inertinite content are decoupled. Similar stable carbon isotope depletion trends have been observed in an equivalent stratigraphic section of the Bowen Basin that suggests the carbon isotope values are responding to local basin tectonics and the climatic transition near end-Permian time, which is represented globally by negative excursions in carbon isotopes before the P-T boundary. Increasing inertinite can also be a function of increasing aridity before the P-T boundary or the result of increased microbial activity as a function of volcanic ash deposition. Overall, the basin was continuously subsiding with excessive sedimentation and volcanic eruptions. The low proportion of bright bands coupled with high vitrinite content suggest a marsh environment, possibly open and wet capable of preserving incoming volcanic ash and clastics resulting in vitrinite-rich and high ash coals.

Identifying recharge and salinization sources of groundwater in the Oussja Ghar el Melah plain (northeast Tunisia) using geochemical tools and environmental isotopes
Environmental Earth Sciences (2016)
Safouan Ben Ammar, Jean-Denis Taupin, Kamel Zouari, Mohamed Khouatmia

The recharge sources and groundwater degradation in the coastal plain of Oussja Ghar el Melah were investigated using geochemical and isotopes tools. We demonstrate that the water quality of shallow groundwater in the phreatic aquifer is impacted by long-term intensive irrigation. We show that the factors controlling the salinity and composition of groundwater are the return flow of the irrigation water, the water–rock interaction in the aquifer and salts formed on the surface by marine sprays. In the low plain where NO3 − content is of up to about 140 mg/L, groundwater is affected by diffuse pollution caused by intensive agricultural activities. In the upstream part of the plain and in the area situated in the SW, stable isotopes and tritium values indicate recent recharge by local precipitation
Schlagworte: hydrogen , oxygen , geol , gashead

Hydrogeological and isotope mapping of the karstic River Savica in NW Slovenia
Environmental Earth Sciences (2016)
Mihael Brenčič, Polona Vreča

Hydrogeological mapping comprises a group of methods with which the area of interest is carefully inspected for the appearance of groundwater related phenomena. During the mapping of groundwater and surface water, samples can be collected for further analysis. On the karstic River Savica (NW Slovenia) the methodology of detailed hydrogeological mapping was tested by which, every 100 m along the river course, samples of water were collected for stable isotopic composition of oxygen (δ 18O). River Savica results from two main tributaries (Velika Savica and Mala Savica) recharging on a high mountain karstified plateau with an average discharge of 5.08 m3/s. Application of hydrogeological mapping methodology to the riverbed resulted in a conceptual model of the groundwater components entering the river. Based on the end member mixing models and with the application of isotope and electrical conductivity data as conservative tracers, it was possible to estimate the contribution of different karstic groundwater components to the river outflow. For the first time it was estimated that, under low and average water conditions, Mala Savica contributes from 12 to 17 % and Velika Savica from 78 to 82 % of the total River Savica discharge, there being only minor inflow from the other sources.
Schlagworte: oxygen , geol , gashead

Stable isotopes and digital elevation models to study nutrient inputs in high-arctic lakes
Rendiconti Lincei (2016)
Edoardo Calizza, Maria Letizia Costantini, David Rossi, Vittorio Pasquali, Giulio Careddu, Loreto Rossi

Five major factors control nutrient and organic matter inputs in high-Arctic lakes, all potentially affected by climate change: ice cover; run-off from the watershed; aquatic and terrestrial primary productivity; guano deposition from birds. Quantifying these controls is a key first step to understand what combination of factors underlies the biological productivity in Arctic lakes and drives their ecological response to climate change. Based on C and N elemental content and stable isotope analysis in sediments belonging to three lakes in North Spitsbergen (Svalbard), Digital Elevation Models and drainage maps, we propose an integrated approach for the analysis of nutrient and organic matter inputs in lakes and the role of catchment hydro-geomorphology in determining inter-lake differences in the isotopic composition of sediments. Given its high run-off and large catchment, organic deposits in Tvillingvatnet were dominated by terrestrial inputs, whereas inputs were mainly of aquatic origin in Storvatnet, a lowland lake characterised by low potential run-off. In Kolhamna, organic deposits seemed to be dominated by inputs from birds. Isotopic signatures were similar between samples within each lake, representing precise tracers for studies on the effect of climate change on biogeochemical cycles in lakes. The presented approach proved to be an effective research pathway for the identification of factors underlying nutrient and organic matter inputs within each water body, as well as for the modelling of expected changes in nutrient content associated with changes in isotopic composition of sediments.
Schlagworte: carbon , nitrogen , geol , ecol , elem

Environmental context for the terminal Ediacaran biomineralization of animals.
Geobiology (2016)
H Cui, A J Kaufman, S Xiao, S Peek, H Cao, X Min, Y Cai, Z Siegel, X-M Liu, Y Peng, J D Schiffbauer, A J Martin

In terminal Ediacaran strata of South China, the onset of calcareous biomineralization is preserved in the paleontological transition from Conotubus to Cloudina in repetitious limestone facies of the Dengying Formation. Both fossils have similar size, funnel-in-funnel construction, and epibenthic lifestyle, but Cloudina is biomineralized, whereas Conotubus is not. To provide environmental context for this evolutionary milestone, we conducted a high-resolution elemental and stable isotope study of the richly fossiliferous Gaojiashan Member. Coincident with the first appearance of Cloudina is a significant positive carbonate carbon isotope excursion (up to +6‰) and an increase in the abundance and (34) S composition of pyrite. In contrast, δ(34) S values of carbonate-associated sulfate remain steady throughout the succession, resulting in anomalously large (>70‰) sulfur isotope fractionations in the lower half of the member. The fractionation trend likely relates to changes in microbial communities, with sulfur disproportionation involved in the lower interval, whereas microbial sulfate reduction was the principal metabolic pathway in the upper. We speculate that the coupled paleontological and biogeochemical anomalies may have coincided with an increase in terrestrial weathering fluxes of sulfate, alkalinity, and nutrients to the depositional basin, which stimulated primary productivity, the spread of an oxygen minimum zone, and the development of euxinic conditions in subtidal and basinal environments. Enhanced production and burial of organic matter is thus directly connected to the carbon isotope anomaly, and likely promoted pyritization as the main taphonomic pathway for Conotubus and other soft-bodied Ediacara biotas. Our studies suggest that the Ediacaran confluence of ecological pressures from predation and environmental pressures from an increase in seawater alkalinity set the stage for an unprecedented geobiological response: the evolutionary novelty of animal biomineralization.
Schlagworte: sulfur , geol , arch , elem

Carbon isotopic excursions and detailed ammonoid and conodont biostratigraphies around Smithian–Spathian boundary in the Bac Thuy Formation, Vietnam
Palaeogeography, Palaeoclimatology, Palaeoecology (2016)
Toshifumi Komatsu, Reishi Takashima, Yasunari Shigeta, Takumi Maekawa, Huyen Dang Tran, Tien Dinh Cong, Susumu Sakata, Hung Doan Dinh

The Smithian–Spathian boundary is indicated by the first occurrence of the ammonoid Tirolites cf. cassianus in the Olenekian Bac Thuy Formation, northeastern Vietnam. The boundary is intercalated within organic-rich dark gray mudstone that accumulated under anoxic to dysoxic conditions in the An Chau and Nanpanjiang Basins on the South China Block. In Lang Son area, three conodont zones, Novispathodus ex gr. waageni, Novispathodus ex gr. pingdingshanensis, and Icriospathodus collinsoni, are recognized in the formation. The Smithian–Spathian boundary is intercalated within N. ex gr. pingdingshanensis conodont Zone. The positive excursion inδ13C with values increasing from around −2.3‰ to +5.7‰ was recorded in the uppermost Smithian Xenoceltites variocostatus ammonoid beds and N. ex gr. pingdingshanensis conodont Zone. The δ13C values decrease across the Smithian–Spathian boundary. These δ13C isotopic patterns are correlated with well-known positive excursions around the Smithian–Spathian boundary globally.
Schlagworte: carbon , oxygen , geol , mulitcarb

Water quality and hydrogeochemistry of a basin and range watershed in a semi-arid region of northern New Mexico
Environmental Earth Sciences (2016)
Benjamin Linhoff, Patrick Longmire, Michael Rearick, Denis McQuillan, George Perkins

Hundreds of domestic wells in northern New Mexico, have concentrations of U, As, and NO3 − that exceed the Environmental Protection Agency’s (EPA) maximum contaminant level (MCL) for drinking water consumption. As part of a case study in groundwater quality, we collected groundwater samples from 749 domestic wells throughout the eastern half of the Española Basin. All water samples were analyzed for major ions, trace metals, and alkalinity. Selected samples were also analyzed for stable isotopes of O, H, and N. Of the wells we measured, 15, 173, and 99 had respective NO3 −, U, and As concentrations that exceeded the EPA’s MCL. Total dissolved solids (TDS), U, and HCO3 − were elevated in the Sangre de Cristo mountain block and around the town of Nambé. Our findings suggest that roll-front U deposits and devitrification of volcanic ash result in elevated U near Nambé, while weathering of granitic rocks accounts for high U in the mountain block. Arsenic concentrations were high in much of the study area with the exception of the Santa Fe metro region and the mountain block. Elevated As concentrations can be explained by devitrification of volcanic ash, anion exchange with clays, and mixing with hydrothermal fluids. In wells with high NO3 − concentrations, analysis of N isotopes are consistent with contamination from domestic wastewater effluent. Our findings suggest that the geochemistry of the region is largely influenced by local geology while groundwater contamination from domestic water treatment and wastewater effluent is an emerging issue
Schlagworte: hydrogen , nitrogen , oxygen , geol , elem

Intensification of North Pacific intermediate water ventilation during the Younger Dryas
Geo-Marine Letters (2016)
Ken’ichi Ohkushi, Naoki Hara, Minoru Ikehara, Masao Uchida, Naokazu Ahagon

Modern North Pacific intermediate water (NPIW) is formed in the mixed water region where the Oyashio and Kuroshio currents meet. The source for cooling and freshening of NPIW is intermediate water in the Okhotsk Sea. The Okhotsk intermediate water outflows to the open Pacific, forming the Oyashio intermediate water by mixing with the subarctic gyre water. In the Oyashio region, the intermediate water originating from the Okhotsk Sea flows mainly at depths shallower than 500 m. On the other hand, ventilation of intermediate water in the subarctic Pacific during the deglaciation remains a topic of debate. In this study, foraminiferal δ18O and δ13C signatures were determined in a dated sediment core collected at 777 m water depth to evaluate the intensity and depth distribution of the source of NPIW since the last deglaciation in the Oyashio region. Benthic foraminiferal δ18O increased by 0.3–0.4‰ from the end of the Bølling/Ållerød warm episode to the Younger Dryas cold episode, suggesting intermediate water cooling. Consistent with this trend, benthic δ13C values point to decreased nutrient contents during the cold event. Conversely, benthic δ18O signatures from a nearby core site at a water depth of 1,366 m did not show such cooling. These results suggest that cold intermediate water originating from the north was actively ventilated at depths of at least 700–800 m, and possibly even 1,200 m during the Younger Dryas, implying that NPIW ventilation was thicker and deeper than under modern conditions
Schlagworte: carbon , oxygen , geol , clim , mulitcarb