Absence of oxygen isotope fractionation/exchange of (hemi-) cellulose derived sugars during litter decomposition     

Michael Zech  Roland A. WernerDieter Juchelka  Karsten KalbitzBjörn Buggle  Bruno Glaser 《Organic Geochemistry》2012,42(12):1470-1475

Aiming at developing a novel tool for palaeoclimate research, we recently proposed a new method for determining the oxygen isotope composition of monosaccharides (Zech, M., Glaser, B., 2009. Compound-specific δ¹⁸O analyses of neutral sugars in soils using GC-Py-IRMS: problems, possible solutions and a first application. Rapid Communications in Mass Spectrometry 23, 3522-3532). In order to answer the question whether isotope fractionation and oxygen exchange reactions during litter decomposition affect the climatically controlled δ¹⁸O values of plant derived sugars, such as for instance xylose and arabinose from hemicelluloses, we studied the compound specific δ¹⁸O values of five different litter species having been decomposed in a field litterbag experiment for 27 months.While δ¹⁸O values of bulk organic matter yielded a systematic ¹⁸O depletion of 3.3‰ (pine) to 4.6‰ (spruce) accompanying total cellulose decomposition of 51% (beech) to 86% (ash), δ¹⁸O values of individual sugars show no significant trend with time. In addition to the observed absence of isotope fractionation during decomposition, we also rule out ¹⁸O exchange reactions affecting the δ¹⁸O signature of sugar molecules during diagenetic processes as well as during analytical procedure based on experimental findings and on theoretical biochemical mechanistic considerations. We conclude that our new method may become an analytical tool that elegantly overcomes extraction, purity and hygroscopicity problems of previous ¹⁸O cellulose methods. It furthermore has the potential to be applied to a wide range of climate archives such as tree rings, lacustrine sediments and loess palaeosol sequences.  相似文献   

Impact of recharge variations on water quality as indicated by excess air in groundwater of the Kalahari, Botswana     

Karsten Osenbrück  Jürgen Sültenfuß  Stephan M. Weise 《Geochimica et cosmochimica acta》2009,73(4):911-289

Groundwater is an important and often exclusive water resource in arid and semi-arid regions. The aim of the present paper was to gain insight into the processes and conditions that control the deterioration of groundwater quality in the semi-arid Kalahari of Botswana. Measurements of ³He, ⁴He, ²⁰Ne, ²²Ne, and of ¹⁴C of dissolved inorganic carbon (DIC) were combined with existing isotopic and hydrochemical data to investigate groundwater from the Ntane Sandstone Aquifer, which is affected by high nitrate concentrations of non-anthropogenic origin. All groundwater samples revealed neon concentrations in excess to air-saturated water, which we attributed to the addition of excess air during recharge. Neon concentrations ranged from values close to air saturation for ¹⁴C DIC rich samples (up to 80.5%MC) up to values of 90% in excess to air-saturated water for lower ¹⁴C DIC contents (2.6-61.3%MC). A strong linear correlation of excess Ne with nitrate concentrations suggests an intimate connection between groundwater quality and the processes and conditions during groundwater recharge. Low groundwater recharge rates under present-day semi-arid conditions are associated with low amounts of excess Ne and elevated nitrate concentrations. In contrast to this, higher excess Ne values in groundwater of lower ¹⁴C DIC and nitrate contents indicate that the high quality groundwater end-member presumably is related to higher groundwater table fluctuations during wetter climatic conditions in the past. We attribute the decline in groundwater quality with respect to nitrate to a decreasing rate and temporal variability of groundwater recharge, and to concurrent changes in biogeochemical activities following a transition to a drier climate during the Holocene. Under such conditions, a much stronger decrease in groundwater recharge compared to the release of nitrate from soil organic matter may result in elevated nitrate concentrations in the vadose zone and groundwater. This implies a strong impact of climate change on the transport of solutes like nitrate through the vadose zone which needs to be considered in predictions of future groundwater quality.  相似文献   

Bedform signature of a West Antarctic palaeo-ice stream reveals a multi-temporal record of flow and substrate control     

Alastair G.C. Graham  Robert D. Larter  Karsten Gohl  Claus-Dieter Hillenbrand  James A. Smith  Gerhard Kuhn 《Quaternary Science Reviews》2009,28(25-26):2774-2793

The presence of a complex bedform arrangement on the sea floor of the continental shelf in the western Amundsen Sea Embayment, West Antarctica, indicates a multi-temporal record of flow related to the activity of one or more ice streams in the past. Mapping and division of the bedforms into distinct landform assemblages reveals their time-transgressive history, which implies that bedforms can neither be considered part of a single downflow continuum nor a direct proxy for palaeo-ice velocity, as suggested previously. A main control on the bedform imprint is the geology of the shelf, which is divided broadly between rough bedrock on the inner shelf, and smooth, dipping sedimentary strata on the middle to outer shelf. Inner shelf bedform variability is well preserved, revealing information about local, complex basal ice conditions, meltwater flow, and ice dynamics over time. These details, which are not apparent at the scale of regional morphological studies, indicate that past ice streams flowed across the entire shelf at times, and often had onset zones that lay within the interior of the Antarctic Ice Sheet today. In contrast, highly elongated subglacial bedforms on sedimentary strata of the middle to outer shelf represent a timeslice snapshot of the last activity of ice stream flow, and may be a truer representation of fast palaeo-ice flow in these locations. A revised model for ice streams on the shelf captures complicated multi-temporal bedform patterns associated with an Antarctic palaeo-ice stream for the first time, and confirms a strong substrate control on a major ice stream system that drained the West Antarctic Ice Sheet during the Late Quaternary.  相似文献   

Polyphase scheelite and stanniferous silicates in a W-(Sn) skarn close to Felbertal tungsten mine,Eastern Alps     

Ordosch  Alexander  Raith  Johann G.  Schmidt  Steffen  Aupers  Karsten 《Mineralogy and Petrology》2019,113(5):703-725

Mineralogy and Petrology - The scheelite exploration target Messelingscharte (Eastern Tyrol, Austria) is located in vicinity of the world-class Felbertal tungsten deposit. W-(Sn) mineralisation...  相似文献   

Primitive andesites from the Taupo Volcanic Zone formed by magma mixing   总被引：1，自引：0，他引：1  

Christoph?BeierEmail authorView author&#;s OrcID profile  Karsten?M.?Haase  Philipp?A.?Brandl  Stefan?H.?Krumm 《Contributions to Mineralogy and Petrology》2017,172(5):33

Andesites with Mg# >45 erupted at subduction zones form either by partial melting of metasomatized mantle or by mixing and assimilation processes during melt ascent. Primitive whole rock basaltic andesites from the Pukeonake vent in the Tongariro Volcanic Centre in New Zealand’s Taupo Volcanic Zone contain olivine, clino- and orthopyroxene, and plagioclase xeno- and antecrysts in a partly glassy matrix. Glass pools interstitial between minerals and glass inclusions in clinopyroxene, orthopyroxene and plagioclase as well as matrix glasses are rhyolitic to dacitic indicating that the melts were more evolved than their andesitic bulk host rock analyses indicate. Olivine xenocrysts have high Fo contents up to 94%, δ¹⁸O_(SMOW) of +5.1‰, and contain Cr-spinel inclusions, all of which imply an origin in equilibrium with primitive mantle-derived melts. Mineral zoning in olivine, clinopyroxene and plagioclase suggest that fractional crystallization occurred. Elevated O isotope ratios in clinopyroxene and glass indicate that the lavas assimilated sedimentary rocks during stagnation in the crust. Thus, the Pukeonake andesites formed by a combination of fractional crystallization, assimilation of crustal rocks, and mixing of dacite liquid with mantle-derived minerals in a complex crustal magma system. The disequilibrium textures and O isotope compositions of the minerals indicate mixing processes on timescales of less than a year prior to eruption. Similar processes may occur in other subduction zones and require careful study of the lavas to determine the origin of andesite magmas in arc volcanoes situated on continental crust.  相似文献   

Local and regional variation of MORB parent magmas: evidence from melt inclusions from the Endeavour Segment of the Juan de Fuca Ridge     

Rachel Sours-Page  Kevin T. M. Johnson  Roger L. Nielsen  Jill L. Karsten 《Contributions to Mineralogy and Petrology》1999,134(4):342-363

The development of petrogenetic models of igneous processes in the mantle is dependent on a detailed knowledge of the diversity of magmas produced in the melting regime. These primary magmas, however, undergo significant mixing and fractionation during transport to the surface, destroying much of the evidence of their primary diversity. To circumvent this problem and to determine the diversity of melts produced in the mantle, we used melt inclusions hosted in primitive plagioclase phenocrysts from eight mid-ocean ridge basalts from the axial and West Valleys of the Endeavour Segment, Juan de Fuca Ridge. This area was selected for study because of the demonstrated close association of enriched (E-MORB) lavas and incompatible element enriched depleted (N-MORB) lavas. Rehomogenized melt inclusions from E-MORB, T-MORB, and N-MORB lavas have been analyzed by electron and ion microprobe for major and trace elements. The depleted and enriched lavas, as well as their melt inclusions, have very similar compatible element concentrations (major elements, Sr, Ni and Cr). Inclusion compositions are more primitive than, yet collinear with, the host lava suites. In contrast, the minor and trace element characteristics of melt inclusions from depleted and enriched lavas are different both in range and absolute concentration. N-MORB lavas contain both depleted and enriched melt inclusions, and therefore exhibit the largest compositional range (K₂O: 0.01 to 0.4 oxide wt%, P₂O₅: <0.01 to 0.2 oxide wt%, La_N: 7 to 35, Yb_N: 1 to 13, and Ti/Zr: <100 to 1300). E-MORB lavas contain only enriched inclusions, and are therefore relatively homogeneous (K₂O: 0.32 to 0.9 oxide wt %, P₂O₅: 0.02 to 0.35 oxide wt%, La_N: 11 to 60, Yb_N: 4 to 21, and Ti/Zr: ∼100). In addition, the most primitive E-32 inclusions are similar in composition to the most enriched inclusions from the depleted hosts. Major element data for melt inclusions from both N-MORB and E-MORB lavas suggest that the magmas lie on a low pressure cotectic, consistent with a petrogenesis including fractional crystallization. However, the minor and trace element compositions in melt inclusions vary independently of the major element composition implying an alternative history. When fractionation-corrected, inclusion compositions correlate with their host glass composition. Hence, the degree of enrichment of the lavas is a function of the composition of aggregated melts, not of processing in the upper mantle or lower crust. Based on this fact, the lava suites are not produced from a single parent magma, but from a suite of primary magmas. The chemistry of the melt inclusions from the enriched lavas is consistent with a derivation from variable percentages of partial melting within the spinel stability field by a process of open system (continuous or critical) melting assuming a depleted lherzolite source veined with clinopyroxenite. The low percentage melts are dominantly enriched melts of the clinopyroxenite. In contrast, the depleted lavas were created by melting of a harzburgite source, possibly fluxed with a fluid enriched in K, Ba and the LREE. Such a source was likely melted up to or past the point at which all of its clinopyroxene was consumed. This set of characteristics is consistent with a scenario by which diverse melts produced at different depths travel through the melting regime to the base of the crust without homogenizing en route. The homogeneous major element characteristics are created in the lower crust by fractional crystallization and reaction with lower crustal gabbros. Therefore, the degree of decoupling between major and trace element characteristics of the melt inclusions (and lavas) is dictated by the reaction rate of the melts with the materials in the conduit walls, as well as the residence times and flux rate, in the upper mantle and lower crust. Received: 2 December 1997 / Accepted: 27 August 1998  相似文献   

Long-term displacement of intertidal seagrass and mussel beds by expanding large sandy bedforms in the northern Wadden Sea     

Tobias Dolch  Karsten Reise 《Journal of Sea Research》2010,63(2):93-101

On aerial photographs, sandy tidal flats display (1) large sandy bedforms (> 10 m long, > 3 m wide), indicating effects of strong hydrodynamics on sediment relief, and (2) beds of seagrass and mussels, indicating stable sediment conditions. These physical and biogenic structures have been mapped from aerial photographs taken in a back-barrier tidal basin of the North Sea coast at low tide between 1936 and 2005. Fields of large intertidal sandy bedforms show a consistent spatial distribution in the central part of the basin, and have increased in area from 7.2 to 12.8 km², corresponding now to 10% of the tidal flats. Areal expansion may be linked to a rise in average high tide level and an increase of the expansion rate from the 1960s to the mid 1990s might be traced back to an increased frequency of storm tides during this period. It is shown that expanding fields of large sandy bedforms have replaced mussel beds in the low tidal zone and displaced seagrass beds in the mid tidal zone. Fields of intertidal large sandy bedforms are expected to expand further with an accelerating rise in sea level, and it is recommended to monitor these physical indicators of sediment instability and disturbance of biogenic benthic structures by analysing aerial photographs.  相似文献   

Tectonic controls on Miocene sedimentation in the Southern Taranaki Basin and implications for New Zealand plate boundary deformation     

Suzanne Bull  Andrew Nicol  Dominic Strogen  Karsten F. Kroeger  Hannu S. Seebeck 《Basin Research》2019,31(2):253-273

Miocene strata in the southern Taranaki Basin (STB), up to 3 km thick, provide a distal record of erosion associated with plate boundary deformation in New Zealand. 2D and 3D seismic reflection data tied to drillhole stratigraphy have been used to constrain four main phases of basin development. These are: (a) Early Miocene (22–19 Ma) subsidence, dominantly bathyal water depths and deposition of minor submarine fans along the eastern basin margin. (b) Middle Miocene (19–14 Ma) widespread submarine fan deposition on a bathyal basin floor in the central STB. (c) Rapid Middle–Late Miocene (14–7 Ma) progradation of the shelf break northwards across the STB. (d) Widespread uplift and erosion of the STB during the latest Miocene–Pliocene (7–4.5 Ma). Bathyal water depths and fan deposition in the Early Miocene were influenced by vertical motions on major reverse faults and regional subsidence produced by subduction of the Pacific plate beneath northern New Zealand. Subsequent submarine fan deposition and northward shelf‐break progradation reflect increasing input of terrigenous material, primarily eroded from an uplifting region to the south of the STB. Sedimentation patterns in the STB are consistent with the age and locations of conglomerates deposited in onshore West Coast basins, related to this uplift and erosion. Sediment transport in the West Coast region was mainly parallel to NNE trending active reverse faults, and in the STB was perpendicular to the NE‐SW orientated shelf break, especially from ca. 14–7 Ma, when sedimentation rates exceeded fault‐displacement rates. Increases in sedimentation rates in the STB coincide with regional increases in the rates of shortening that appear to reflect plate boundary‐wide events and have been attributed to, or correlated with, increases in the plate convergence rate. Miocene sedimentation patterns in the STB thus reflect both intra‐basinal deformation and tectonic signals from the wider developing New Zealand plate boundary.  相似文献   

Impact of multi-purpose aquifer utilisation on a variable-density groundwater flow system in the Gippsland Basin, Australia     

Sunil Varma  Karsten Michael 《Hydrogeology Journal》2012,20(1):119-134

The Latrobe aquifer in the Gippsland Basin in southeastern Australia is a prime example for emerging resource conflicts in Australian sedimentary basins. The Latrobe Group forms a major freshwater aquifer in the onshore Gippsland Basin, and is an important reservoir for oil and gas in both onshore and offshore parts of the basin. The Latrobe Group and overlying formations contain substantial coal resources that are being mined in the onshore part of the basin. These may have coal-seam-gas potential and, in addition, the basin is considered prospective for its geothermal energy and CO₂ storage potential. The impacts of groundwater extraction related to coal-mine dewatering, public water supply, and petroleum production on the flow of variable-density formation water has been assessed using freshwater hydraulic heads and impelling force vectors. Groundwater flows from the northern and western edges towards the central part of the basin. Groundwater discharge occurs mainly offshore along the southern margin. Post-stress hydraulic heads show significant declines near the petroleum fields and in the coal mining areas. A hydrodynamic model of the Latrobe aquifer was used to simulate groundwater recovery in the Latrobe aquifer from different scenarios of cessation of groundwater and other fluid extractions.  相似文献   

Concept and workflow for 3D visualization of atmospheric data in a virtual reality environment for analytical approaches   总被引：2，自引：0，他引：2  

Carolin Helbig  Hans-Stefan Bauer  Karsten Rink  Volker Wulfmeyer  Michael Frank  Olaf Kolditz 《Environmental Earth Sciences》2014,72(10):3767-3780

In the future, climate change will strongly influence our environment and living conditions. Weather and Climate simulations that predict possible changes produce big data sets. The combination of various variables of climate models with spatial data from different sources helps to identify correlations and to study key processes. In this paper, the results of the Weather Research and Forecasting model are visualized for two regions. For this purpose, a continuous workflow that leads from the integration of heterogeneous raw data to 3D visualizations that can be displayed on a desktop computer or in an interactive virtual reality environment is developed. These easy-to-understand visualizations of complex data are the basis for scientific communication and for the evaluation and verification of models as well as for interdisciplinary discussions of the research results.  相似文献