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551.
Molecular characterization of dissolved organic matter in pore water of continental shelf sediments 总被引:1,自引:0,他引:1
Dissolved organic matter (DOM) in sediment pore water is a complex molecular mixture reflecting various sources and biogeochemical processes. In order to constrain those sources and processes, molecular variations of pore water DOM in surface sediments from the NW Iberian shelf were analyzed by ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and compared to river and marine water column DOM. Weighted average molecular element ratios of oxygen to carbon ((O/C)wa) and hydrogen to carbon ((H/C)wa) provided general information about DOM sources. DOM in local rivers was more oxygenated ((O/C)wa 0.52) and contained less hydrogen ((H/C)wa 1.15) than marine pore water DOM (mean (O/C)wa 0.50, mean (H/C)wa 1.26). The relative abundance of specific compound groups, such as highly oxygenated aromatic compounds or nitrogen-bearing compounds with low H/C ratios, correspond to a high concentration of lignin phenols (160 μg/g sediment dry weight) and a high TOC/TN ratio (13.3) in the sedimentary organic matter and were therefore assigned to terrestrial sources. The lower degree of unsaturation and a higher relative abundance of nitrogen-bearing compounds in the pore water DOM reflected microbial activity within the sediment. One sampling site on the shelf with a high sediment accumulation, and a humic-rich river sample showed a wide range of sulfur compounds in the DOM, accompanied by a higher abundance of lipid biomarkers for sulfate-reducing bacteria, probably indicating early diagenetic sulfurization of organic matter. 相似文献
552.
Florian Scholz Christian Hensen Rolf L. Romer Anette Meixner Matthias Haeckel 《Geochimica et cosmochimica acta》2009,73(18):5444-206
The chemical and isotopic composition of pore fluids is presented for five deep-rooted mud volcanoes aligned on a transect across the Gulf of Cadiz continental margin at water depths between 350 and 3860 m. Generally decreasing interstitial Li concentrations and 87Sr/86Sr ratios with increasing distance from shore are attributed to systematically changing fluid sources across the continental margin. Although highest Li concentrations at the near-shore mud volcanoes coincide with high salinities derived from dissolution of halite and late-stage evaporites, clayey, terrigenous sediments are identified as the ultimate Li source to all pore fluids investigated. Light δ7Li values, partly close to those of hydrothermal vent fluids (δ7Li: +11.9‰), indicate that Li has been mobilized during high-temperature fluid/sediment or fluid/rock interactions in the deep sub-surface. Intense leaching of terrigenous clay has led to radiogenic 87Sr/86Sr ratios (∼0.7106) in pore fluids of the near-shore mud volcanoes. In contrast, non-radiogenic 87Sr/86Sr ratios (∼0.7075) at the distal locations are attributed to admixing of a basement-derived fluid component, carrying an isotopic signature from interaction with the basaltic crust. This inference is substantiated by temperature constraints from Li isotope equilibrium calculations suggesting exchange processes at particularly high temperatures (>200 °C) for the least radiogenic pore fluids of the most distal location.Advective pore fluids in the off-shore reaches of the Gulf of Cadiz are influenced by successive exchange processes with both oceanic crust and terrigenous, fine-grained sediments, resulting in a chemical and isotopic signature similar to that of fluids in near-shore ridge flank hydrothermal systems. This suggests that deep-rooted mud volcanoes in the Gulf of Cadiz represent a fluid pathway intermediate between mid-ocean ridge hydrothermal vent and shallow, marginal cold seep. Due to the thicker sediment coverage and slower fluid advection rates, the overall geochemical signature is shifted towards the sediment-diagenetic signal compared to ridge flank hydrothermal environments. 相似文献
553.
An estimate of the glacier ice volume in the Swiss Alps 总被引:1,自引:0,他引:1
Daniel Farinotti Matthias Huss Andreas Bauder Martin Funk 《Global and Planetary Change》2009,68(3):225-231
Changes in glacier volume are important for questions linked to sea-level rise, water resource management, and tourism industry. With the ongoing climate warming, the retreat of mountain glaciers is a major concern. Predictions of glacier changes, necessarily need the present ice volume as initial condition, and for transient modelling, the ice thickness distribution has to be known. In this paper, a method based on mass conservation and principles of ice flow dynamics is applied to 62 glaciers located in the Swiss Alps for estimating their ice thickness distribution. All available direct ice thickness measurements are integrated. The ice volumes are referenced to the year 1999 by means of a mass balance time series. The results are used to calibrate a volume–area scaling relation, and the coefficients obtained show good agreement with values reported in the literature. We estimate the total ice volume present in the Swiss Alps in the year 1999 to be 74 ± 9 km3. About 12% of this volume was lost between 1999 and 2008, whereas the extraordinarily warm summer 2003 caused a volume loss of about 3.5%. 相似文献
554.
Massimo Vellante Matthias Förster Michael Pezzopane Norbert Jakowski Tie Long Zhang Umberto Villante Marcello De Lauretis Bruno Zolesi Werner Magnes 《Earth, Moon, and Planets》2009,104(1-4):25-27
Cross-spectral analysis of ULF wave measurements recorded at ground magnetometer stations closely spaced in latitude allows accurate determinations of magnetospheric field line resonance (FLR) frequencies. This is a useful tool for remote sensing temporal and spatial variations of the magnetospheric plasma mass density. The spatial configuration of the South European GeoMagnetic Array (SEGMA, 1.56 < L < 1.89) offers the possibility to perform such studies at low latitudes allowing to monitor the dynamical coupling between the ionosphere and the inner plasmasphere. As an example of this capability we present the results of a cross-correlation analysis between FLR frequencies and solar EUV irradiance (as monitored by the 10.7-cm solar radio flux F10.7) suggesting that changes in the inner plasmasphere density follow the short-term (27-day) variations of the solar irradiance with a time delay of 1–2 days. As an additional example we present the results of a comparative analysis of FLR measurements, ionospheric vertical soundings and vertical TEC measurements during the development of a geomagnetic storm. 相似文献
555.
556.
Well-defined analytical interrelations exist between the geostatistical estimation variance performing an expression of degree of geological exploration and the task-oriented entropy as a concept of information theory. The example of normal distribution shows that this relationship can be expressed in mathematical terms. An extensive practical use could consist in the improvement of exploration optimization on the common basis of continuous geological parameters as is demonstrated by means of an example. 相似文献
557.
Geochemistry of xenolithic eclogites from West Africa, part 2: origins of the high MgO eclogites 总被引:1,自引:0,他引:1
Matthias G Barth Roberta L Rudnick Ingo Horn William F McDonough Michael J SpicuzzaJohn W Valley Stephen E Haggerty 《Geochimica et cosmochimica acta》2002,66(24):4325-4345
Oxygen isotope, mineral trace element, and measured and reconstructed whole-rock compositions are reported for the high MgO eclogite xenolith suite (16 to 20 wt% MgO in the whole rock) from the Koidu Kimberlite complex, Sierra Leone. In contrast to the previously published data for low MgO eclogites (6 to 13 wt% MgO) from this area, high MgO eclogites equilibrated at higher temperatures (1080 to 1130°C vs. 890 to 930°C) have only mantlelike δ18O and show variable degrees of light rare earth element (REE) enrichment. Analyses of multiple mineral generations suggest that the heterogeneous REE patterns of the high MgO eclogites reflect variable degrees of metasomatic overprinting. High MgO and Al2O3 contents of the eclogites suggest a cumulate origin, either as high-pressure (2 to 3 GPa) garnet-pyroxene cumulates or low-pressure (<1 GPa) plagioclase-pyroxene-olivine cumulates. Trace element modeling suggests a low-P origin for eclogites with flat heavy REE patterns and a high-P origin for eclogites with fractionated heavy REE. Flat heavy REE patterns, the presence of Sr anomalies, and low to moderate transition element contents in the low-P group are consistent with a low-pressure origin as metamorphosed olivine gabbros and troctolites. These metagabbroic high MgO eclogites either could represent the basal section of subducted oceanic crust or foundered mafic lower continental crust. In the former case, the metagabbroic high MgO eclogites may be genetically related to the Koidu low MgO suite. Crystal fractionation trends suggest that the metapyroxenitic high MgO eclogites formed at lower pressures than their current estimated equilibrium pressures (>4 GPa). 相似文献
558.
Matthias Münnich 《Dynamics of Atmospheres and Oceans》1996,23(1-4)
Standing internal waves, so-called seiches, are ubiquitous in reservoirs and lakes. Although the stratification in such basin is often continuous, the modeling of seiches has been confined mostly to two-layer models. Such models are unable to give reliable insights into the vertical structure of the seiches, which might be crucial for the understanding of vertical mixing in natural water basins. To obtain this kind of information a two-dimensional computer model has been developed, which takes both continuous stratification and bottom topography into account. The results of this model are presented. The computed seiche modes reveal that (1) several large-scale modes can exist with similar eigenfrequencies, (2) the modes have a tendency to develop narrow jets and (3) only the lowest modes are strongly influenced by the bottom topography. 相似文献
559.
560.
Katja U. Heeschen Hans Jürgen Hohnberg Matthias Haeckel Friedrich Abegg Manuela Drews Gerhard Bohrmann 《Marine Chemistry》2007,107(4):498-515
Two newly developed coring devices, the Multi-Autoclave-Corer and the Dynamic Autoclave Piston Corer were deployed in shallow gas hydrate-bearing sediments in the northern Gulf of Mexico during research cruise SO174 (Oct–Nov 2003). For the first time, they enable the retrieval of near-surface sediment cores under ambient pressure. This enables the determination of in situ methane concentrations and amounts of gas hydrate in sediment depths where bottom water temperature and pressure changes most strongly influence gas/hydrate relationships. At seep sites of GC185 (Bush Hill) and the newly discovered sites at GC415, we determined the volume of low-weight hydrocarbons (C1 through C5) from nine pressurized cores via controlled degassing. The resulting in situ methane concentrations vary by two orders of magnitudes between 0.031 and 0.985 mol kg− 1 pore water below the zone of sulfate depletion. This includes dissolved, free, and hydrate-bound CH4. Combined with results from conventional cores, this establishes a variability of methane concentrations in close proximity to seep sites of five orders of magnitude. In total four out of nine pressure cores had CH4 concentrations above equilibrium with gas hydrates. Two of them contain gas hydrate volumes of 15% (GC185) and 18% (GC415) of pore space. The measurements prove that the highest methane concentrations are not necessarily related to the highest advection rates. Brine advection inhibits gas hydrate stability a few centimeters below the sediment surface at the depth of anaerobic oxidation of methane and thus inhibits the storage of enhanced methane volumes. Here, computerized tomography (CT) of the pressure cores detected small amounts of free gas. This finding has major implications for methane distribution, possible consumption, and escape into the bottom water in fluid flow systems related to halokinesis. 相似文献