Origin and composition of organic matter in tidal flat sediments from the German Wadden Sea   总被引：5，自引：1，他引：4  

Elke Freese  Jürgen Kster  Jürgen Rullktter 《Organic Geochemistry》2008,39(7):820-829

Two sediment cores of up to 550 cm length from an intertidal flat of the German Wadden Sea near the island of Spiekeroog were investigated for the quantity and composition of fossil organic matter (OM). The lowermost parts of the cores are dominated by grey mud of a salt marsh facies containing mainly terrestrial OM estimated to account for 60–75% of the total OM, based on δ¹³C values and the ratio of short to long chain n-alkanols. The terrigenous origin of the dominant fraction is indicated, among others, by high proportions of C₂₉ sterols and long chain n-alkanes typical of plant waxes. Coarse shell beds overlying the grey mud at 2–2.5 m depth represent a flooding and erosion event possibly related to heavy storm floods in the Middle Ages. Within the intertidal sand-dominated sediments in the upper parts of the cores total organic carbon (TOC) contents are generally low, ranging from 0.1% to 0.5%, and correlate well with the amount of mud fraction (r² 0.90). At the surface, marine OM has not undergone intense diagenetic alteration and so is the dominant fraction. Eroded peat particles are common throughout most of the sequence and values of the Phragmites peat indicator (PPI) > 5 indicate an origin from reed peat due to a high relative abundance of the n-C₂₄ alkane. Changes in the composition of microbial communities over the depth interval investigated are documented by varying compositions of unsaturated fatty acids with 16 and 18 carbons. Eicosapentaenoic acid (EPA) was detected along the entire cores and indicates the presence of EPA-producing bacterial strains.  相似文献   

The Effect of Limited Sample Sizes on the Accuracy of the Estimated Scaling Parameter for Power-Law-Distributed Solar Data     

Elke D’Huys  David Berghmans  Daniel B. Seaton  Stefaan Poedts 《Solar physics》2016,291(5):1561-1576

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The importance of winter in annual ecosystem respiration in the High Arctic: effects of snow depth in two vegetation types     

Elke Morgner  Bo Elberling  Ditte Strebel  & Elisabeth J. Cooper 《Polar research》2010,29(1):58-74

Winter respiration in snow-covered ecosystems strongly influences annual carbon cycling, underlining the importance of processes related to the timing and quantity of snow. Fences were used to increase snow depth from 30 to 150 cm, and impacts on respiration were investigated in heath and mesic meadow, two common vegetation types in Svalbard. We manually measured ecosystem respiration from July 2007 to July 2008 at a temporal resolution greater than previously achieved in the High Arctic (campaigns: summer, eight; autumn, six; winter, 17; spring, nine). Moisture contents of unfrozen soil and soil temperatures throughout the year were also recorded. The increased snow depth resulted in significantly higher winter soil temperatures and increased ecosystem respiration. A temperature–efflux model explained most of the variation of observed effluxes: meadows, 94 (controls) and 93% (fences); heaths, 84 and 77%, respectively. Snow fences increased the total non-growing season efflux from 70 to 92 (heaths) and from 68 to 125 g CO₂-C m⁻² (meadows). The non-growing season contributed to 56 (heaths) and 42% (meadows) of the total annual carbon respired. This proportion increased with deeper snow to 64% in both vegetation types. Summer respiration rates were unaffected by snow fences, but the total growing season respiration was lower behind fences because of the considerably delayed snowmelt. Meadows had higher summer respiration rates than heaths. In addition, non-steady state CO₂ effluxes were measured as bursts lasting several days during spring soil thawing, and when ice layers were broken to carry out winter efflux measurements.  相似文献   

Turbidite stratigraphy in proglacial lakes: Deciphering trigger mechanisms using a statistical approach     

Nore Praet  Maarten Van Daele  Tim Collart  Jasper Moernaut  Elke Vandekerkhove  Philipp Kempf  Peter J. Haeussler  Marc De Batist 《Sedimentology》2020,67(5):2332-2359

Turbidites embedded in lacustrine sediment sequences are commonly used to reconstruct regional flood or earthquake histories. A critical step for this method to be successful is that turbidites and their trigger mechanisms are determined unambiguously. The latter is particularly challenging for prehistoric proglacial lake records in high-seismicity settings where both earthquake-generated and flood-generated turbidites interrupt the background varved sedimentation. This calls for a new method to allow efficient and objective identification and classification of turbidites. This study examined turbidites in five long (9 to 17 m) sediment cores from Eklutna Lake, a proglacial lake in south-central Alaska, using standard core logging and grain-size data. A novel statistical approach is presented, in which varve-thickness distributions were first analyzed to objectively identify the thickest turbidites and distinguish them from background sedimentation. For each turbidite, a selection of variables were then measured, including: basal grain-size, thickness, magnetic susceptibility and spectrophotometric variables. Triggering mechanisms were discriminated by a combination of principal component analysis and clustering, and by calibration with historical events. Using this approach, a 2250 year long lake-wide event stratigraphy was constructed, with 94 prehistoric events, including 24 earthquake and 70 flood events. Basal grain-size and thickness variables turn out to be the most effective proxies for discrimination. This statistical approach is a powerful and new method to identify turbidites and their triggering mechanisms in long prehistoric sediment records. It opens up new prospects for palaeoseismological, palaeohydrological and palaeoclimate studies in proglacial lakes worldwide.  相似文献   

First Late Triassic Record of a Paleoentomofauna from South America(Malargüe Basin,Mendoza Province,Argentina)   总被引：1，自引：0，他引：1  

Carsten BRAUCKMANN  Oscar F. GALLEGO  Norbert HAUSCHKE  Rafael G. MARTINS-NETO  Elke GROENING  Jan-M. ILGER  María B. LARA 《《地质学报》英文版》2010,84(4):915-924

<正>Late Middle Triassic to early Late Triassic insects from Argentina have been previously described from the Bermejo and Cuyana Basins where they have been recovered from the Ischichuca-Los Rastros and Potrerillos-Cacheuta Formations,respectively.The insect fauna discussed herein was collected during field studies in 1986/1987 from the Llantenes section(Norian to Rhaetian? Late Triassic),which is situated in the Malargue Basin in southern Mendoza province.The insect remains were found in the upper part of the Llantenes section (Llantenes Formation),which is built up of two coarsening-upwards cycles reflecting a deltaic progradation of a fluvial into a lacustrine environment(lower part),succeeded by repeated progradations into a floodplain-dominated environment(upper part;with finds of insects,conchostracans,fish remains,plant fragments,and drifted logs).The new finds represent the youngest Triassic insect records described from Argentina and even from South America in its entirety.There is only one contemporaneous fossil assemblage in Gondwana:in the Clarence/Moreton Basin(Aberdare Conglomerate;Late Norian)in Australia.The new Triassic insects include an impression of an isolated Mecopterida-like wing(Mendozachorista volkheimeri gen.et sp.nov.; Mendozachoristidae fam.nov.),coleopteran elytra of the Permosynidae(Ademosyne rosenfeldi sp.nov.and Ademosyne llantenesensis sp.nov.)and other isolated body fragments.This new Late Triassic entomofauna from Argentina is of considerable importance in the reconstruction of the biotic recovery of continental environments in Gondwana after the catastrophic mass extinction at the P/T boundary.  相似文献   

Sensitivity of an ecosystem model to hydrology and temperature     

Annett Wolf  Eleanor Blyth  Richard Harding  Daniela Jacob  Elke Keup-Thiel  Holger Goettel  Terry Callaghan 《Climatic change》2008,87(1-2):75-89

We tested the sensitivity of a dynamic ecosystem model (LPJ-GUESS) to the representation of soil moisture and soil temperature and to uncertainties in the prediction of precipitation and air temperature. We linked the ecosystem model with an advanced hydrological model (JULES) and used its soil moisture and soil temperature as input into the ecosystem model. We analysed these sensitivities along a latitudinal gradient in northern Russia. Differences in soil temperature and soil moisture had only little influence on the vegetation carbon fluxes, whereas the soil carbon fluxes were very sensitive to the JULES soil estimations. The sensitivity changed with latitude, showing stronger influence in the more northern grid cell. The sensitivity of modelled responses of both soil carbon fluxes and vegetation carbon fluxes to uncertainties in soil temperature were high, as both soil and vegetation carbon fluxes were strongly impacted. In contrast, uncertainties in the estimation of the amount of precipitation had little influence on the soil or vegetation carbon fluxes. The high sensitivity of soil respiration to soil temperature and moisture suggests that we should strive for a better understanding and representation of soil processes in ecosystem models to improve the reliability of predictions of future ecosystem changes.  相似文献   

Routine analysis of sediment pore water of high ionic strength     

Peter Herzsprung  Elke Bozau  Olaf Büttner  Anja Duffek  Kurt Friese  Matthias Koschorreck  Martin Schultze  Wolf v. Tümpling  Katrin Wendt‐Potthoff 《洁净——土壤、空气、水》2006,34(6):593-607

Pore water of sediments plays an important role in aquatic systems as mediator and as the reactive zone between the sediment and surface water. Sediment pore waters with high ionic strength from acidified pit lakes were investigated to obtain information about the influence on the lake water quality. The analysis of soluble reactive phosphorus, nitrate, ammonium, silica, dissolved organic carbon, ferrous iron, sulfate, chloride, sodium, potassium, calcium, magnesium, manganese, and total dissolved iron was predetermined as the dataset required for evaluation of water quality. The data collection procedure was optimised by designing a methodology for stabilisation, dilution of pore water samples and adaptation of analytical methods. The developed methodology was evaluated with respect to the effort required in the laboratory under routine conditions. In the first round of analyses, 72% of 638 individual analyses from a random selection of pore water profiles were found to be within the calibration ranges. Remedial actions to handle the remaining 28% of invalid analytical results are exemplified. Differences between comparative analyses of some ions by continuous flow analysis, ion chromatography, and atomic emission spectroscopy were evaluated. The majority of results measured by ion chromatography differed on a highly significant level from results measured by atomic emission spectroscopy. Possible reasons, originating from the extreme sample matrix, are discussed. Finally, the designed methodology and the results of the method comparison are used to recommend the selection of analytical methods under specific conditions.  相似文献   

Theory of oceanic levelling for improving the geoid from satellite altimetry     

Elke Stöcker-Meier 《Journal of Geodesy》1990,64(3):247-258

The problem of improving the geoid from satellite altimetry is formulated and studied within the scope of geophysical fluid dynamics. The oceanic levelling is defined by analogy to the astrogeodetic levelling and it is used to determine the sea surface topography as a function of current velocity, atmospheric pressure and viscosity. Simulating strong currents like the Gulf Stream or the Kuroshio the numerical treatment of the oceanic levelling shows that the sea surface topography can come up to an order of magnitude of1–2 m, whereby the results depend on latitude and slightly on the actual pressure conditions.  相似文献   

Ram-pressure stripping of disc galaxies orbiting in clusters – II. Galactic wakes     

Elke Roediger  Marcus Brüggen 《Monthly notices of the Royal Astronomical Society》2008,388(2):465-486

We present 3D hydrodynamical simulations of ram-pressure stripping of a disc galaxy orbiting in a galaxy cluster. In this paper, we focus on the properties of the galaxies' tails of stripped gas. The galactic wakes show a flaring width, where the flaring angle depends on the gas disc's cross-section with respect to the galaxy's direction of motion. The velocity in the wakes shows a significant turbulent component of a few     . The stripped gas is deposited in the cluster rather locally, i.e. within     from where it was stripped. We demonstrate that the most important quantity governing the tail density, length and gas mass distribution along the orbit is the galaxy's mass-loss per orbital length. This in turn depends on the ram pressure as well as the galaxy's orbital velocity.
For a sensitivity limit of     in projected gas density, we find typical tail lengths of     . Such long tails are seen even at large distances (0.5 to     ) from the cluster centre. At this sensitivity limit, the tails show little flaring, but a width similar to the gas disc's size.
Morphologically, we find good agreement with the H  i tails observed in the Virgo cluster by Chung et al. 2007 . However, the observed tails show a much smaller velocity width than predicted from the simulation. The few known X-ray and Hα tails are generally much narrower and much straighter than the tails in our simulations. Thus, additional physics like a viscous intracluster medium (ICM), the influence of cooling and tidal effects may be needed to explain the details of the observations.
We discuss the hydrodynamical drag as a heat source for the ICM but conclude that it is not likely to play an important role, especially not in stopping cooling flows.  相似文献   

Sources of dissolved silica to the fjords of northern Patagonia (44–48°S): the importance of volcanic ash soil distribution and weathering          下载免费PDF全文

Elke Vandekerkhove  Sébastien Bertrand  Brian Reid  Astrid Bartels  Bernard Charlier 《地球表面变化过程与地形》2016,41(4):499-512

Dissolved silica (DSi) plays an important biogeochemical role in the fjords of northern Chilean Patagonia (44–48°S), where it drives high biogenic productivity and promotes carbon burial. It is generally believed that the DSi riverine input to lakes and coastal environments is controlled by a combination of factors including lithology, climate, topography, vegetation, and meltwater input. In northern Chilean Patagonia several authors have proposed that the postglacial volcanic ash soils (andosols) may play a significant role in the high supply of DSi to the regional fjords. To assess the influence of andosols on DSi concentrations in north Patagonian rivers, we mapped andosol thickness and compared our results with river chemistry. The mineralogical and geochemical composition of three representative andosol profiles was also examined to evaluate the efficiency of weathering processes. The andosol thickness map clearly demonstrates that volcanic ash was predominantly deposited on the eastern side of the regional volcanoes, reflecting the influence of the prevailing westerly winds on the distribution of pyroclastic material. Mineralogical and geochemical results show that the andosol parent material has the typical andesitic basaltic signature of the regional volcanoes, i.e. high amounts of amorphous material, plagioclase, K‐feldspar, and pyroxene. Down‐profile variations in soil mineralogy and geochemistry indicate increased leaching of silica with depth, resulting from weathering of the volcanic parent material. For the five studied watersheds, a highly positive correlation (R²=0.98) was found between average andosol thickness and DSi concentrations, suggesting that andosol thickness is the main parameter affecting DSi concentrations in north Patagonian river systems. On seasonal timescales, increased precipitation (winter) and glacial meltwater (summer) input can significantly reduce DSi concentrations. We argue that the weathering of andosols constitutes the most important source of DSi to the lakes and fjords of northern Chilean Patagonia, explaining the particularly high regional rates of biogenic silica production. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献