Fine particulate organic matter (FPOM) transport and processing in littoral interstices – use of fluorescent markers     

Günter Gunkel  Camilla Beulker  Anja Hoffmann  Jan Kosmol 《Limnologica》2009,39(3):185-199

A fluorescent labelling method is presented as a new tool for the investigation of organic particle transport and biogenic carbon cycling processes in sandy littoral interstices at Lake Tegel, Berlin, Germany. Passive particle transport through the pore system was studied by in situ exposition of 2.4 μm monodisperse polymeric resin microparticles stained with 7-amino-4-methylcoumarin (AMC). Uptake of fluorescein-5-isothiocyanate (FITC)-labelled Chlorella vulgaris and fine particulate organic matter (FPOM) by the interstitial fauna was investigated in laboratory and field experiments. The major portion (>85%) of the FITC-labelled particles added to sediment cores was recovered from the topmost centimetre of sediment during the study period of 14 days. Uptake of FITC-labelled FPOM was observed in several benthic groups, e.g. chironomids, microcrustaceans, oligochaetes and tardigrads, whereas C. vulgaris was ingested by oligochaetes only. There is evidence to suggest that both are suitable materials for investigating the fragmentation and ingestion of organic material by herbivorous and detritivorous fauna. Field experiments with inert microparticles and FITC-labelled FPOM (<1 mm) prepared from dried alder leaves were carried out in plexiglass tubes as in situ whole core technique. Within the investigation period of two weeks, the transport of FPOM was restricted to the topmost 2–3 cm of sediment in conjunction with a distinct fragmentation to finer size classes with respect to increasing sediment depth. Vertical FPOM transport was hindered by a high interstitial concentration of natural POM and an intensive settlement of the interstices by algae (mainly epispammic algae, 65–96% of algae cell number) and extra-cellular polymeric substances (EPS), which formed a dense three-dimensional structure.  相似文献   

Experimental impact cratering: A summary of the major results of the MEMIN research unit     

Thomas Kenkmann  Alex Deutsch  Klaus Thoma  Matthias Ebert  Michael H. Poelchau  Elmar Buhl  Eva-Regine Carl  Andreas N. Danilewsky  Georg Dresen  Anja Dufresne  Nathanaël Durr  Lars Ehm  Christian Grosse  Max Gulde  Nicole Güldemeister  Christopher Hamann  Lutz Hecht  Stefan Hiermaier  Tobias Hoerth  Astrid Kowitz  Falko Langenhorst  Bernd Lexow  Hanns-Peter Liermann  Robert Luther  Ulrich Mansfeld  Dorothee Moser  Manuel Raith  Wolf Uwe Reimold  Martin Sauer  Frank Schäfer  Ralf Thomas Schmitt  Frank Sommer  Jakob Wilk  Rebecca Winkler  Kai Wünnemann 《Meteoritics & planetary science》2018,53(8):1543-1568

This paper reviews major findings of the Multidisciplinary Experimental and Modeling Impact Crater Research Network (MEMIN). MEMIN is a consortium, funded from 2009 till 2017 by the German Research Foundation, and is aimed at investigating impact cratering processes by experimental and modeling approaches. The vision of this network has been to comprehensively quantify impact processes by conducting a strictly controlled experimental campaign at the laboratory scale, together with a multidisciplinary analytical approach. Central to MEMIN has been the use of powerful two-stage light-gas accelerators capable of producing impact craters in the decimeter size range in solid rocks that allowed detailed spatial analyses of petrophysical, structural, and geochemical changes in target rocks and ejecta. In addition, explosive setups, membrane-driven diamond anvil cells, as well as laser irradiation and split Hopkinson pressure bar technologies have been used to study the response of minerals and rocks to shock and dynamic loading as well as high-temperature conditions. We used Seeberger sandstone, Taunus quartzite, Carrara marble, and Weibern tuff as major target rock types. In concert with the experiments we conducted mesoscale numerical simulations of shock wave propagation in heterogeneous rocks resolving the complex response of grains and pores to compressive, shear, and tensile loading and macroscale modeling of crater formation and fracturing. Major results comprise (1) projectile–target interaction, (2) various aspects of shock metamorphism with special focus on low shock pressures and effects of target porosity and water saturation, (3) crater morphologies and cratering efficiencies in various nonporous and porous lithologies, (4) in situ target damage, (5) ejecta dynamics, and (6) geophysical survey of experimental craters.  相似文献   

Open-system chemical behavior in deep Wilcox Group mudstones,Texas Gulf Coast,USA     

Ruarri J. Day-Stirrat  Kitty L. Milliken  Shirley P. Dutton  Robert G. Loucks  Stephen Hillier  Andrew C. Aplin  Anja M. Schleicher 《Marine and Petroleum Geology》2010

Wilcox Group mudstones have been mechanically and geochemically transformed over a temperature range of 20–200 °C. Our research controlled for provenance and age by sampling from five wells, parallel to the paleodepositional axis, all within the Houston delta system. Across the sampled depths, mudstone porosity has been reduced from ∼25 to <10% and bulk mineralogical change as documented by quantitative X-ray diffraction includes decreases in quartz, K-feldspar and kaolinite content whereas illite + illite − smectite, chlorite, and plagioclase increase. These mineral transformations transfer elements at a scale of less than 1 mm from one mineralogical form to another, however, X-ray fluorescence data suggest that among major elements only Al₂O₃ and TiO₂ are fully conserved within the system (trace-element ZrO₂ is also conserved). K₂O has been added to and SiO₂ released from the Wilcox Group mudstones. Cathodoluminescence and secondary electron imaging did not find this SiO₂ locally precipitated. We, therefore, document an open-system geochemical behavior.  相似文献   

Active mud volcanoes on the upper slope of the western Nile deep-sea fan—first results from the P362/2 cruise of R/V Poseidon   总被引：1，自引：0，他引：1  

Tomas Feseker  Kevin R. Brown  Cecile Blanchet  Florian Scholz  Marianne Nuzzo  Anja Reitz  Mark Schmidt  Christian Hensen 《Geo-Marine Letters》2010,30(3-4):169-186

In February 2008, cruise P362/2 was undertaken aboard R/V Poseidon to the Giza and North Alex mud volcanoes (MVs) on the upper slope of the western Nile deep-sea fan. Emitted fluids were strongly depleted in chloride and rich in hydrocarbons, predominantly of thermogenic origin. In-situ sediment temperature measurements indicate extremely high and moderate levels of activity for the North Alex MV and Giza MV, respectively, and suggest rapid changes from dormant to active stages. Both the physical properties of core sediments (e.g., color and magnetic susceptibility), and their assemblages of micro- and nannofossils point to different sources for the two mud volcanoes. Biostratigraphic dating suggests source depths of 2,100–2,450 mbsf for the Giza MV and 1,150–1,550 mbsf for the North Alex MV. Very high temperatures of up to 70°C in shallow sediments at the North Alex MV can be explained only if the fluid source were warmer and deeper than the sediment source.  相似文献   

Investigating the effect of ballasting by CaCO₃ in Emiliania huxleyi, II: Decomposition of particulate organic matter     

Anja Engel  Lynn Abramson  Jennifer Szlosek  Zhanfei Liu  Gillian Stewart  David Hirschberg  Cindy Lee 《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(18):1408-1419

The quantitative relationship between organic carbon and mineral contents of particles sinking below 1800 m in the ocean indicates that organisms with mineral shells such as coccolithophores are of special importance for transporting carbon into the deep sea. Several hypotheses about the mechanism behind this relationship between minerals and organic matter have been raised, such as mineral protection of organic matter or enhanced sinking rates through ballast addition. We examined organic matter decomposition of calcifying and non-calcifying Emiliania huxleyi cultures in an experiment that allowed aggregation and settling in rotating tanks. Biogenic components such as particulate carbon, particulate nitrogen, particulate volume, pigments, transparent exopolymer particles (TEP), and particulate amino acids in suspended particles and aggregates were followed over a period of 30 d. The overall pattern of decrease in organic matter, the amount of recalcitrant organic matter left after 30 d, and the compositional changes within particulate organic matter indicated that cells without a shell are more subject to loss than calcified cells. It is suggested that biogenic calcite helps in the preservation of particulate organic matter (POM) by offering structural support for organic molecules. Over the course of the experiment, half the particulate organic carbon in both calcifying and non-calcifying cultures was partitioned into aggregates and remained so until the end of the experiment. The partial protection of particulate organic matter from solubilization by biominerals and by aggregation that was observed in our experiment may help explain the robustness of the relationship between organic and mineral matter fluxes in the deep ocean.  相似文献   

MedFlux: Investigations of particle flux in the Twilight Zone     

Cindy Lee  Robert A. Armstrong  J. Kirk Cochran  Anja Engel  Scott W. Fowler  Madeleine Goutx  Pere Masqu  Juan Carlos Miquel  Michael Peterson  Christian Tamburini  Stuart Wakeham 《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(18):1363-1368

The MedFlux project was devised to determine and model relationships between organic matter and mineral ballasts of sinking particulate matter in the ocean. Specifically we investigated the ballast ratio hypothesis, tested various commonly used sampling and modeling techniques, and developed new technologies that would allow better characterization of particle biogeochemistry. Here we describe the rationale for the project, the biogeochemical provenance of the DYFAMED site, the international support structure, and highlights from the papers published here. Additional MedFlux papers can be accessed at the MedFlux web site (http://msrc.sunysb.edu/MedFlux/).  相似文献   

The East African Rift System and the impact of orographic changes on regional climate and the resulting aridification     

Anja Sommerfeld  Kerstin Prömmel  Ulrich Cubasch 《International Journal of Earth Sciences》2016,105(6):1779-1794

Several proxy data indicate an aridification of the East African climate during the Neogene, which might be influenced by the orographic changes of the East African Rift System (EARS) induced by tectonic forcing during the last 20 million years. To investigate the impact of the orography and especially of the rifts, the regional climate model CCLM is used, covering the EARS with Lake Victoria in the centre of the model domain. CCLM is driven by the ERA-Interim reanalysis and applied with a double-nesting method resulting in a very high spatial resolution of 7 km. The resolution clearly shows the shoulders and rifts of the western and eastern branch of the EARS and the Rwenzoris within the western branch. To analyse the orographic influence on climate, a new technique of modifying the orography is used in this sensitivity study. The shoulders of the branches are lowered and the rifts are elevated, resulting in a smoothed orography structure with less altitude difference between the shoulders and rifts. The changes in 2 m-temperature are very local and associated with the changes in the orography. The vertically integrated moisture transport is characterised by less vortices, and its zonal component is increased over the branches. The resulting amount of precipitation is mainly decreased west of the western branch and increased in the rift of the western branch. In the eastern branch, however, the changes in the amount of precipitation are not significant. The changes in the precipitation and temperature patterns lead to a shift of biomes towards a vegetation coverage characterised by more humid conditions in the northern part of the model domain and more arid conditions in the South. Thus, the aridification found in the proxy data can be attributed to the orographic changes of the rifts only in the northern model domain.  相似文献   

Geodynamic models R.W. van Bemmelen. Elsevier, Amsterdam, 1972, 267 pp. Dfl. 17.50     

Robert Scholten 《Chemical Geology》1972,10(4):313-314

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Cross-over analysis of Marine magnetic anomalies     

J. Verhoef  R. D. Scholten 《Marine Geophysical Researches》1983,5(4):421-435

Using cross-over analysis the reduction of total magnetic intensity values to magnetic anomalies was studied in an area with ship-tracks which have been made over a period of several years. Under these circumstances the secular variation becomes important. At first we used the old IGRF 1975. This reference field does not correct the secular variation accurately. In the period 1969–1980 the mean values of the differences of the magnetic anomalies at crossing rise to more than 150 nT. The recently adopted reference fields DGRF 1965, DGRF 1970, DGRF 1975 and PGRF 1975 correct the secular variation much better. The mean values now only rise to about 50 nT over the same period. A reduction using a regional determined by filtering along the track removes the secular variation completely. The latter reduction has the disadvantage that the standard deviations of the mean values at the intersections increase, because the regional depends on the orientation of the track line. Calculation of average secular variation in subareas of 4×4 degrees yields a decrease from the northeast to the southwest.  相似文献   

Optically Stimulated Luminescence (OSL) dating of sand‐filled wedge structures and their fine‐grained host sediment from Jonzac,SW France     

Anja Guhl  Pascal Bertran  Christoph Zielhofer  Kathryn E. Fitzsimmons 《Boreas: An International Journal of Quaternary Research》2013,42(2):317-332

Two sand wedge structures and their host sediments, from Jonzac in SW France, were successfully dated using Optically Stimulated Luminescence (OSL) measurements on both small aliquots and single grains of quartz from the 180–212 μm size fraction. One of the sand wedges clearly contains primary infilling. However, grain‐size analysis and field observations do not clearly indicate whether the other feature represents a primary sand wedge or a composite sand wedge with primary and secondary infilling. OSL results and the geological setting justify using the Central Age Model (CAM) for the calculation of age estimates. Grain‐size analysis and detailed investigations of OSL results revealed the contamination of one sand wedge sample with host sediment. However, age calculation using the Finite Mixture Model (FMM) provided what is considered to be a reliable age estimate for the contaminated sample. The age estimates for all samples correspond to Marine Isotope Stage (MIS) 3. While fine‐grained sediments were deposited in the middle of MIS 3 (c. 43–55 ka), the sand wedges unexpectedly correspond to the end of this period (c. 33 ka) or the onset of MIS 2 (c. 27 ka). The sand wedges were probably formed during intense but short cold periods, possibly correlated with a Heinrich event (H2 and/or H3). The results help us to assess how effective luminescence dating is on sand wedges and the limitations involved in correlating sand wedge ages with Heinrich events, and contribute to the debate on the timing of cryogenic formation processes and the permafrost distribution in SW France.  相似文献