Lessons learned from setting up the NOWESP research data base: Experiences in an interdisciplinary research project     

Günther Radach  Jens Gekeler 《Ocean Dynamics》1996,48(3-4):231-240

  相似文献   

Time dependence of organic matter decay and mixing processes in Framvaren, a permanently anoxic fjord in South Norway     

David W. Dyrssen  Per O. J. Hall  Conny Haraldsson  Melissa Chierici  Jens M. Skei  H. Göte östlund 《Aquatic Geochemistry》1996,2(2):111-129

Three different layers have been identified in Framvaren, which has a maximum water depth of 184 m. One oxic layer above the redoxcline at 18–20 m. One anoxic layer from 20 to 100 m which is occasionally ventilated by a flow over the sill (which has a depth of 2.5 m), and finally a stagnant layer below 100 m. Using the release rate of silica from the bottom and measurements of the concentration of HTO it is possible to make some calculations on the annual volume of interleaving in the layers 25–50 m, 50–75 m, and 75–100 m together with the advective flows. Reliable values of the sulfide concentration were obtained by precipitating and weighing HgS together with careful protection of all anoxic water samples with argon. The light yellow color of the precipitate in the depth range 25 to 80 m indicates that the occasional ventilation will cause such reactions as 0.50₂ + H₂S S(colloidal) + H₂O. The elemental sulfur, being stabilized with HS^–, is set free upon the precipitation of HgS. The new data for the concentration of sulfide give an acceptable stoichiometry for the decay reaction of organic matter. This is not the case with the data of Yao and Millero. The mean values for the concentrations of ammonium and phosphate agree with the new data of Yao and Millero. The mol/mol C/N ratio of 10.1 found in trapped material by Naess and coworkers (1988) agrees with the stoichiometry of the dissolved constituents, i.e. C/N = 9.92 ± 0.45. A denitrification reaction is suggested to explain the high values of C/N. The vertical diffusion coefficient at 100 m calculated from the depth profile of silica was 0.92 × 10^–6 m² s^–1 which lies in the range of values given by Fröyland. Finally, the ¹⁴C age of the total dissolved inorganic carbon (Ct) in the water below 90 m was about 1600 years indicating a bioproduction in the period 8000 years B.P. to A.D. 1853 when a channel was opened between the fjord outside (Helvikfjord) and Framvaren.  相似文献   

Nitrogen in fluids effecting retrogression of granulite facies gneisses: a debatable mantle connection     

William E. Glassley  David Bridgwater  Jens Konnerup-Madsen 《Earth and Planetary Science Letters》1984,70(2):417-425

The abundance patterns of nitrogen, and chlorine in retrogressed granulite facies gneisses from southern East Greenland exhibit strong enrichment in the vicinity of small-scale shear zones. Sulfur in the shear zones occurs at the same concentration levels as in the adjacent country rock, but is depleted in the transition zone between shear zone and country rock. Within the shear zone sulfur occurs as sulfate, whereas in the country rock granulites it occurs as sulfide. Recrystallization of rock in the shear zone to scapolite-bearing, hornblende-absent assemblages, along with changes in the major element chemistry, demonstrates that these zones define migration pathways of chemically reactive fluids. Consideration of the computed fluid compositions, and of the mass ratios of chlorine/sulfur and nitrogen/sulfur demonstrate that the fluid equilibrated with continental crust prior to its passage through gneisses in the study area. Previous suggestions have been made that the mantle may act as a source region for nitrogen-rich fluids. However, equilibration of these S-, N- and Cl-rich fluids with crustal material precludes the use of element abundances to identify a mantle signature; the bulk of these fluid constituents must be considered crustal derived.  相似文献   

Rb-sr dating of epithermal vein mineralization stages in the eastern Harz Mountains (Germany) by paleomixing lines   总被引：1，自引：0，他引：1  

Jens Schneider  Udo Haack 《Geochimica et cosmochimica acta》2003,67(10):1803-1819

A method is evaluated that enables the dating of binary isotopic paleomixing in hydrothermal alteration assemblages by iterative reconstruction and regression of corresponding two-component mixing lines from conventional Rb-Sr data. The model has been applied to illite-bearing granulometric fractions of hydrothermally altered sedimentary rocks associated with epithermal vein mineralization in the eastern Harz Mountains, Germany. These veins are characterized by a principal quartz-sulfide stage containing quartz, base metal sulfides, and siderite and a subsequent dominant calcite-fluorite-quartz stage. Rb-Sr analyses were performed on untreated granulometric fractions, HCl-treated residues, corresponding HCl leachates, and cogenetic vein minerals obtained from two silicified rock samples related to the quartz-sulfide and the calcite-fluorite-quartz mineralization, respectively.Neither the untreated nor the HCl-leached fractions of these rock samples yield statistically robust and geochronologically meaningful isochrons. When applying the binary mixing model, however, two well-defined paleomixing lines can be reconstructed for the HCl-treated fractions of the rock samples and associated vein minerals at model ages of 226 ± 1 Ma (quartz-sulfide alteration) and 209 ± 2 Ma (calcite-fluorite-quartz alteration). We examine the significance and reliability of these model ages and the corresponding paleomixing lines by means of statistical and geological criteria and discuss the effects of leaching experiments performed on the granulometric fractions using 1 N HCl as well as the nature and origin of the components dissolved in the acid leachates.Our results suggest that the mixing model provides a successful dating concept for isotopic disequilibrium processes during low-temperature hydrothermal events that produce binary mixtures among newly formed alteration phases.  相似文献   

Lead isotope systematics of vein-type antimony mineralization,Rheinisches Schiefergebirge,Germany: a case history of complex reaction and remobilization processes   总被引：1，自引：0，他引：1  

Thomas Wagner  Jens Schneider 《Mineralium Deposita》2002,37(2):185-197

Mesothermal vein-type Sb mineralization in the Rheinisches Schiefergebirge, Germany, is characterized by two different mineralization styles, which are (1) extensional quartz-stibnite vein systems, and (2) (Cu)-Pb-Sb sulphosalt assemblages in overprinted pre-existing Pb-Zn veins. A detailed Pb isotope study of 52 representative samples from both mineralization types indicates distinct compositional patterns. (Cu)-Pb-Sb sulphosalts (meneghinite, boulangerite, bournonite) formed by reaction/remobilization are characterized by Pb isotope compositions (²⁰⁶Pb/²⁰⁴Pb=18.179-18.223), which are identical to the precursor galena (²⁰⁶Pb/²⁰⁴Pb=18.168-18.223). The Pb isotope composition of sulphosalt minerals in these vein systems was controlled by lead inherited from pre-existing galena. Stibnite and Pb-sulphosalts (zinkenite, semseyite, plagionite) formed in quartz-stibnite vein systems display Pb isotope ratios (²⁰⁶Pb/²⁰⁴Pb=18.250-18.354), which are more radiogenic than galenas from Variscan Pb-Zn ore veins (²⁰⁶Pb/²⁰⁴Pb=18.162-18.303). Detailed small-scale investigation of thrust zones hosting Pb-Zn ores and crosscutting quartz-ankerite fissure veins (Ramsbeck deposit) indicates that the Pb isotope compositions of recrystallized (galena) and remobilized phases (boulangerite, semseyite, bournonite) are arranged along a linear trend. This is interpreted as mixing between primary galena with ²⁰⁶Pb/²⁰⁴Pb᜞.206 and overprinting hydrothermal fluids with a more radiogenic composition (²⁰⁶Pb/²⁰⁴Pb⁾.354), expressed by intermediate compositions (²⁰⁶Pb/²⁰⁴Pb=18.256-18.334) of newly-formed sulphosalts. The Pb isotope systematics of the vein-type Sb mineralization is in accordance with a model of Pb extraction from similar crustal sources (Palaeozoic sedimentary sequences) at different times.  相似文献   

Grazing impact on forage quality and macronutrient content of rangelands in Qilian Mountains,NW China     

Alina BARANOVA  Jens OLDELAND  WANG Shun-li  Udo SCHICKHOFF 《山地科学学报》2019,(1):43-53

An important indicator of the rangeland health, associated with land degradation, is the ability of semi-natural rangelands to provide forage of sufficient quality for livestock production. In Qilian Mountains(Gansu Province, NW China) biomass production and forage quality are dependent on the seasonality of precipitation and temperature; most of the precipitation falls during summer season, when sheep, goats and yaks graze mountain rangelands. To sustain the rangelands and to improve the management strategies, the assessment of the forage quality should be implemented. The purpose of this research was to study the response of biomass, forage quality and macronutrient content different levels of grazing intensity in Qilian rangelands. We sampled aboveground biomass in the growing seasons in 2012 and 2013 within spring/autumn or summer grazing regimes in two altitudinal zones below and above 3000 m a.s.l.(montane-subalpine and subalpine-alpine respectively). In order to estimate forage quality, biomass was sampled in 1 m × 1 m plots, assigned to the center of 10 ×10 m sites, fromwhich we collected different indicator parameters of rangeland health. Mineral and fiber content of forage biomass was estimated under different levels of grazing intensity with regard to the growing period. It was found that an increase in grazing intensity led to a decrease in dry matter weight. No linearity was observed in the relationship between nutritive value and grazing intensity. The highest fiber content(59.20 %) was found in plots mostly disturbed by grazing. The highest protein(16.30 %) and the lowest fiber(51.30 %) contents were associated with slightly grazing intensity. Concentrations of the mineral elements, such as Zn, P, K and S varied significantly and showed maximum values under low grazing intensity.  相似文献   

The reaction of carbonates in contact with laser-generated,superheated silicate melts: Constraining impact metamorphism of carbonate-bearing target rocks     

Christopher Hamann  Saskia Bläsing  Lutz Hecht  Sebastian Schäffer  Alex Deutsch  Jens Osterholz  Bernd Lexow 《Meteoritics & planetary science》2018,53(8):1644-1686

We simulated entrainment of carbonates (calcite, dolomite) in silicate impact melts by 1-bar laser melting of silicate–carbonate composite targets, using sandstone, basalt, calcite marble, limestone, dolomite marble, and iron meteorite as starting materials. We demonstrate that carbonate assimilation by silicate melts of variable composition is extremely fast (seconds to minutes), resulting in contamination of silicate melts with carbonate-derived CaO and MgO and release of CO₂ at the silicate melt–carbonate interface. We identify several processes, i.e., (1) decomposition of carbonates releases CO₂ and produces residual oxides (CaO, MgO); (2) incorporation of residual oxides from proximally dissociating carbonates into silicate melts; (3) rapid back-reactions between residual CaO and CO₂ produce idiomorphic calcite crystallites and porous carbonate quench products; (4) high-temperature reactions between Ca-contaminated silicate melts and carbonates yield typical skarn minerals and residual oxide melts; (5) mixing and mingling between Ca- or Ca,Mg-contaminated and Ca- or Ca,Mg-normal silicate melts; (6) precipitation of Ca- or Ca,Mg-rich silicates from contaminated silicate melts upon quenching. Our experiments reproduce many textural and compositional features of typical impact melts originating from silicate–carbonate targets. They reinforce hypotheses that thermal decomposition of carbonates, rapid back-reactions between decomposition products, and incorporation of residual oxides into silicate impact melts are prevailing processes during impact melting of mixed silicate–carbonate targets. However, by comparing our results with previous studies and thermodynamic considerations on the phase diagrams of calcite and quartz, we envisage that carbonate impact melts are readily produced during adiabatic decompression from high shock pressure, but subsequently decompose due to heat influx from coexisting silicate impact melts or hot breccia components. Under certain circumstances, postshock conditions may favor production and conservation of carbonate impact melts. We conclude that the response of mixed carbonate–silicate targets to impact might involve melting and decomposition of carbonates, the dominant response being governed by a complex variety of factors.  相似文献   

The Chelyabinsk meteorite: Thermal history and variable shock effects recorded by the 40Ar-39Ar system     

Mario Trieloff  Ekaterina V. Korochantseva  Alexei I. Buikin  Jens Hopp  Marina A. Ivanova  Alexander V. Korochantsev 《Meteoritics & planetary science》2018,53(3):343-358

We studied three lithologies (light and dark chondritic and impact melt rock) differing in shock stage from the LL5 chondrite Chelyabinsk. Using the ⁴⁰Ar-³⁹Ar dating technique, we identified low- and high-temperature reservoirs within all samples, ascribed to K-bearing oligoclase feldspar and shock-induced jadeite–feldspar glass assemblages in melt veins, respectively. Trapped argon components had variable ⁴⁰Ar/³⁶Ar ratios even within low- and high-temperature reservoirs of individual samples. Correcting for trapped argon revealed a lithology-specific response of the K-Ar system to shock metamorphism, thereby defining two distinct impact events affecting the Chelyabinsk parent asteroid (1) an intense impact event ~1.7 ± 0.1 Ga ago formed the light–dark-structured and impact-veined Chelyabinsk breccia. Such a one-stage breccia formation is consistent with petrological observations and was recorded by the strongly shocked lithologies (dark and impact melt) where a significant fraction of oligoclase feldspar was transformed into jadeite and feldspathic glass; and (2) a young reset event ~30 Ma ago particularly affected the light lithology due to its low argon retentivity, while the more retentive shock-induced phases were more resistant against thermal reset. Trapped argon with ⁴⁰Ar/³⁶Ar ratios up to 1900 was likely incorporated during impact-induced events on the parent body, and mixed with terrestrial atmospheric argon contamination. Had it not been identified via isochrons based on high-resolution argon extraction, several geochronologically meaningless ages would have been deduced.  相似文献   

Geophysical signature of Målingen,the minor crater of the Lockne–Målingen doublet impact structure     

Irene Melero-Asensio  Jens Ormö  Erik Sturkell  Gabrielle Stockmann  Joakim Mansfeld 《Meteoritics & planetary science》2018,53(7):1456-1475

Målingen is the 0.7 km wide minor crater associated to the 10 times larger Lockne crater in the unique Lockne–Målingen doublet. The craters formed at 458 Ma by the impact of a binary asteroid related to the well-known 470 Ma Main Belt breakup event responsible for a large number of Ordovician craters and fossil meteorites. The binary asteroid struck a target sequence including ~500 m of sea water, ~80 m of limestone, ~30 m of dark mud, and a peneplainized Precambrian crystalline basement. Although the Lockne crater has been extensively studied by core drillings and geophysics, little is known about the subsurface morphology of Målingen. We performed magnetic susceptibility and remanence, as well as density, measurements combined with gravity, and magnetic field surveys over the crater and its close vicinity as a base for forward magnetic and gravity modeling. The interior of the crater shows a general magnetic low of 90–100 nT broken by a clustered set of high-amplitude, short wavelength anomalies caused by bodies of mafic rock in the target below the crater and as allogenic blocks in the crater infill. The gravity shows a general −1.4 mgal anomaly over the crater caused by low-density breccia infill and fractured crystalline rocks below the crater floor. The modeling also revealed a slightly asymmetrical shape of the crater that together with the irregular ejecta distribution supports an oblique impact from the east, which is consistent with the direction of impact suggested for the Lockne crater.  相似文献   

Interfacing MHD Single Fluid and Kinetic Exospheric Solar Wind Models and Comparing Their Energetics     

Sofia-Paraskevi Moschou  Viviane Pierrard  Rony Keppens  Jens Pomoell 《Solar physics》2017,292(9):139

An exospheric kinetic solar wind model is interfaced with an observation-driven single-fluid magnetohydrodynamic (MHD) model. Initially, a photospheric magnetogram serves as observational input in the fluid approach to extrapolate the heliospheric magnetic field. Then semi-empirical coronal models are used for estimating the plasma characteristics up to a heliocentric distance of 0.1 AU. From there on, a full MHD model that computes the three-dimensional time-dependent evolution of the solar wind macroscopic variables up to the orbit of Earth is used. After interfacing the density and velocity at the inner MHD boundary, we compare our results with those of a kinetic exospheric solar wind model based on the assumption of Maxwell and Kappa velocity distribution functions for protons and electrons, respectively, as well as with in situ observations at 1 AU. This provides insight into more physically detailed processes, such as coronal heating and solar wind acceleration, which naturally arise from including suprathermal electrons in the model. We are interested in the profile of the solar wind speed and density at 1 AU, in characterizing the slow and fast source regions of the wind, and in comparing MHD with exospheric models in similar conditions. We calculate the energetics of both models from low to high heliocentric distances.  相似文献