Dissolved iron(II) in the Pacific Ocean: Measurements from the PO2 and P16N CLIVAR/CO2 repeat hydrography expeditions     

S. Paul Hansard  William M. Landing  Chris I. Measures  Bettina M. Voelker 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(7):1117-1129

The redox speciation of dissolved iron in seawater was evaluated at 121 locations in the Pacific Ocean at depths of 15-1000 m, using the method of luminol chemiluminescence. The results indicate that reduced iron, Fe(II), is ubiquitous in surface seawater with a relatively consistent pattern of occurrence. Surface maxima were present in most profiles, with median concentrations of 25-30 pM representing 12-14% of the total dissolved iron. Concentrations decreased monotonically with depth to<12 pM within the upper euphotic zone. This pattern was observed during both day and nighttime sampling events, which suggests that non-photochemical production mechanisms can produce photochemical-like signatures. Further, if theoretical rates of Fe(II) oxidation are applicable to the open ocean, then the employed sampling methods precluded assessment of photochemically-produced Fe(II), regardless of ambient light conditions. For this and other reasons, the concentrations reported here for the upper water column likely represent lower limits of labile iron concentration, and suggest that dissolved iron may be more available for uptake than previously believed. Deeper in the water column, Fe(II) was also frequently detected, though it constituted a small fraction of the total dissolved iron. Possible source mechanisms at these depths include thermal (dark) reduction of Fe(III) organic complexes or remineralization of sinking biogenic particles containing Fe(II). In the northern Philippine Sea between the Japanese coast and the Izu-Bonin volcanic arc system, Fe(II) concentrations were found to be atypically high, possibly because of high atmospheric dust deposition near the surface and transport of sediment-derived iron at depth.  相似文献   

Permeability and degassing of dome lavas undergoing rapid decompression: An experimental determination   总被引：1，自引：1，他引：0  

Sebastian Mueller  Oleg Melnik  Oliver Spieler  Bettina Scheu  Donald B. Dingwell 《Bulletin of Volcanology》2005,67(6):526-538

The gas permeability of volcanic rocks may influence various eruptive processes. The transition from a quiescent degassing dome to rock failure (fragmentation) may, for example, be controlled by the rocks permeability, in as much as it affects the speed by which a gas overpressure in vesicles is reduced in response to decompression. Using a modified shock-tube-based fragmentation bomb (Alidibirov and Dingwell 1996a,b; Spieler et al. 2003a), we have measured unsteady-state permeability at a high initial pressure differential. Following sudden decompression above the rock cylinder, pressurized gas flows through the sample. Two pressure transducers record the pressure signals above and below the sample. A transient 1D filtration code has been developed to calculate permeability using the experimental decay curve of the lower pressure transducer. Additionally an analytical steady-state method to achieve permeability is presented as an alternative to swiftly predict the sample permeability in a sufficiently precise manner. Over 100 permeability measurements have been performed on samples covering a wide range of porosity. The results show a general positive relationship between porosity and permeability with a high data scatter. Our preferred interpretation of the results is a combination of two different, but overlapping effects. We propose that at low porosities, gas escape occurs predominantly through microcracks or elongated micropores and therefore could be described by simplified forms of Kozeny–Carman relations (Carman 1956) and fracture flow models. At higher porosities, the influence of vesicles becomes progressively stronger as they form an increasingly connected network. Therefore, a model based on the percolation theory of fully penetrable spheres is used, as a first approximation, to describe the permeability-porosity trend. In the data acquired to date it is evident, that in addition to the porosity control, the samples bubble size, shape and distribution strongly influence the permeability. This leads to a range of permeability values up to 2.5 orders of magnitude at a given porosity.  相似文献   

Upper bound analysis of tunnel face stability in layered soils   总被引：3，自引：3，他引：0  

Xiao-Wu Tang  Wei Liu  Bettina Albers  Stavros Savidis 《Acta Geotechnica》2014,9(4):661-671

The working face of tunnel constructions has to be kept stable during tunneling to prevent large soil deformations or fatal failure. In layered soils with lower cohesion, failures happen more often and more abrupt than in cohesive soils. Therefore, the maintenance of a proper support pressure at the tunnel working face is of high importance. In this paper, an upper bound analysis is introduced to investigate the minimum support pressure for the face stability in layered soils. A three-dimensional kinematically admissible mechanism for the upper bound analysis is improved to model potential failure within different soil layers. An analytical solution for the support pressure assessment is achieved. The influence of the crossing and cover soil on the face stability is analyzed, respectively. This solution provides an analytical estimation of the minimum support pressure for the face stability. It may be used as a reference for projects under similar conditions.  相似文献   

Tracing effects of decalcification on solute sources in a shallow groundwater aquifer, NW Germany     

Bettina A. Wiegand   《Journal of Hydrology》2009,378(1-2):62-71

δ⁸⁷Sr values and Ca/Sr ratios were employed to quantify solute inputs from atmospheric and lithogenic sources to a catchment in NW Germany. The aquifer consists primarily of unconsolidated Pleistocene eolian and fluviatile deposits predominated by >90% quartz sand. Accessory minerals include feldspar, glauconite, and mica, as well as disperse calcium carbonate in deeper levels. Decalcification of near-surface sediment induces groundwater pH values up to 4.4 that lead to enhanced silicate weathering. Consequently, low mineralized Ca–Na–Cl- and Ca–Cl-groundwater types are common in shallow depths, while in deeper located calcareous sediment Ca–HCO₃-type groundwater prevails. δ⁸⁷Sr values and Ca/Sr ratios of the dissolved pool range from 7.3 to −2.6 and 88 to 493, respectively. Positive δ⁸⁷Sr values and low Ca/Sr ratios indicate enhanced feldspar dissolution in shallow depths of less than 20 m below soil surface (BSS), while equilibrium with calcite governs negative δ⁸⁷Sr values and elevated Ca/Sr ratios in deep groundwater (>30 m BSS). Both positive and negative δ⁸⁷Sr values are evolved in intermediate depths (20–30 m BSS). For groundwater that is undersaturated with respect to calcite, atmospheric supplies range from 4% to 20%, while feldspar-weathering accounts for 8–26% and calcium carbonate for 62–90% of dissolved Sr²⁺. In contrast, more than 95% of Sr²⁺ is derived by calcium carbonate and less than 5% by feldspar dissolution in Ca–HCO₃-type groundwater. The surprisingly high content of carbonate-derived Sr²⁺ in groundwater of the decalcified portion of the aquifer may account for considerable contributions from Ca-containing fertilizers. Complementary tritium analyses show that equilibrium with calcite is restricted to old groundwater sources.  相似文献   

First results of operating and monitoring an innovative design of a permeable reactive barrier for the remediation of chromate contaminated groundwater     

Bettina Flury  Urs EggenbergerUrs Mäder 《Applied Geochemistry》2009

An innovative setup of a permeable reactive barrier (PRB) was installed in Willisau, Switzerland to remediate chromate contaminated groundwater. Instead of a conventional continuous barrier, this PRB consists of cylinders installed in rows: a single row for lower expected Cr^VI-concentrations and an offset double row for higher expected Cr^VI-concentrations. The cylinders are filled with reactive grey cast-Fe shavings mixed with gravel to prevent extensive precipitation of secondary phases in the pore space. The treatment of the contaminants takes place both within the cylinders and in the dissolved Fe^II plume generated downstream of the barrier. Monitoring of the contamination situation over a period of 3 a provided evidence of the mobilization, transport and behavior of the contaminants in the aquifer. Groundwater and reactive material were sampled upstream, within and downstream of the barrier by a Multi-Port Sampling System (MPSS) that revealed the geochemical processes as a function of time and space. Comprehensive chemical analyses included sensitive parameters such as Cr^VI, Fe^II/Fe^III, redox potential, dissolved O₂ and pH. Several campaigns using multiple optical tracers revealed a rather complex hydrological regime at different scales, thereby complicating the barrier performance.  相似文献   

Combining global sensitivity analysis and multiobjective optimisation to estimate soil hydraulic properties and representations of various sole and mixed crops for the agro-hydrological SWAP model     

Philipp Stahn  Stefanie Busch  Thomas Salzmann  Bettina Eichler-Löbermann  Konrad Miegel 《Environmental Earth Sciences》2017,76(10):367

  相似文献   

Hafnium isotopes in Arctic Ocean water   总被引：1，自引：0，他引：1  

Bettina Zimmermann  Martin Frank  M. Baskaran  Alex N. Halliday 《Geochimica et cosmochimica acta》2009,73(11):3218-5926

The first isotopic compositions of dissolved hafnium in seawater from across the Arctic Ocean are reported. Most samples from the four sub-basins of the Arctic Ocean have values within error of an average of ε_Hf = +0.8. Combined Hf-Nd isotope compositions do not fall on the well-established positive correlation for mantle and crustal rocks. Instead, Arctic waters have Hf that is more radiogenic than that typically found in rocks with similar Nd isotope compositions, a feature previously found in ferromanganese crusts and waters from the Pacific Ocean. Arctic seawater samples generally fall on the lower part of the ferromanganese crust array, reflecting influences of inputs from Arctic rivers and interactions of shelf waters with underlying sediments. Arctic rivers have much higher Hf concentrations (7-30 pM) than Arctic seawater (0.36-4.2 pM). Water from the Mackenzie River has the least radiogenic Hf, with ε_Hf = −7.1 ± 1.7, and plots furthest away from the ferromanganese crust array, while waters from the Ob, Yenisey, and Lena Rivers have values that are indistinguishable from most Arctic waters. In the Amundsen, Makarov, and Canada basins, Hf concentrations are highest at the surface and lowest in the deeper waters, reflecting the influences of riverine inputs and of waters that have flowed over the extensive Siberian continental shelves and have Nd and Hf characteristics that reflect water-sediment interactions. This is in contrast to the relatively low near surface Hf concentrations reported for locations elsewhere. The Pacific water layer in the Canada Basin exhibits the highest value of ε_Hf = +6.8 ± 1.8, reflecting the Hf isotopic composition of waters entering the Arctic from the Pacific Ocean. Mixing relationships indicate that a substantial fraction of the Hf in the Mackenzie River is lost during estuarine mixing; the behaviour of Hf from other rivers is less constrained.  相似文献   

Strontium isotopic evidence for prehistoric transport of gray‐ware ceramic materials in the eastern Grand Canyon region,USA     

Sidney W. Carter  Bettina Wiegand  Gail A. Mahood  Francis O. Dudas  Joseph L. Wooden  Alan P. Sullivan  Samuel A. Bowring 《Geoarchaeology》2011,26(2):189-218

Through a novel application of strontium (Sr) isotopic analysis, we evaluate geological sources for prehistoric ceramics in the eastern Grand Canyon region of northern Arizona, focusing on two gray‐ware traditions in the Upper Basin of the Coconino Plateau. Building on a conceptual framework for the general potential of Sr isotopes in the analysis of geological materials, we suggest that the eastern Grand Canyon is specifically well suited archaeologically and geologically for: (1) exploring the utility of Sr isotopes for ceramic provenance research and (2) testing long‐standing hypotheses that gray‐ware ceramics were invariably made with local materials. Sr isotopic compositions indicate that the ceramic samples represent at least three different geological sources, and that different raw materials were used in the manufacture of the two gray‐ware traditions found in the Upper Basin. One of the gray‐ware traditions is not compositionally consistent with local geology, indicating that either the ceramics or the raw materials were transported at least 20 km to the Upper Basin. © 2011 Wiley Periodicals, Inc.  相似文献   

Role of wave–mean flow interaction in sun–climate connections: Historical overview and some new interpretations and results     

Terrence R. Nathan  John R. Albers  Eugene C. Cordero 《Journal of Atmospheric and Solar》2011,73(11-12):1594-1605

Quasi-decadal variations in solar irradiance – termed the 11-year solar cycle (SC) – have been linked to variations in a variety of atmospheric circulation features, including the polar vortex, the Brewer–Dobson circulation, and the quasi-biennial oscillation. These features share an underlying commonality: they are all rooted in wave–mean flow interaction. The purpose of this paper is to provide a historical overview of the connection between the SC and wave–mean flow interaction and to propose a more complete theoretical framework for solar modulated wave–mean flow interaction that includes both zonal-mean and zonally asymmetric ozone as intermediaries for communicating variations in solar spectral irradiance to the climate system. We solve a quasi-geostrophic model using the WKB formalism to highlight the physics connecting the SC to planetary wave-drag. Numerical results show the importance of the zonally asymmetric ozone field in mediating the effects of solar variability to the wave-driven circulation in the middle atmosphere.  相似文献   

The position of the Rupelian/Chattian boundary in the southern Upper Rhine Graben based on new records of microfossils     

Claudius Pirkenseer  Jean-Pierre Berger†  Bettina Reichenbacher 《Swiss Journal of Geoscience》2013,106(2):291-301

This study analyses the regressive phase of the marine Froidefontaine Subgroup and the subsequent fluvio-lacustrine Niederroedern formation in the southern Upper Rhine Graben during the Late Rupelian and the position of the Rupelian/Chattian boundary. The study is based on the sedimentary record and several microfossil groups from two boreholes, with a focus on new records of fish otoliths, Bolboforma and Charophyta. The biostratigraphic evaluation of these groups provides evidence for a position of the Rupelian/Chattian boundary within the upper Niederroedern Formation. This is contrary to the results from a previous sedimentological approach, which places the boundary at the base of the Niederroedern Formation. The fish fauna indicates a biogeographic relation to southern France, the Molasse Basin of Switzerland and southern Germany.  相似文献