Solution-collapse depressions and suspensates in the limnocrenic lake of banyoles (ne Spain)     

M. Canals  H. Got  R. Julia  J. Serra 《地球表面变化过程与地形》1990,15(3):243-254

A high resolution seismic reflection survey in the Banyoles limnocrenic solution lake allowed penetration of dense suspensates occupying cone-like bottom depressions of different size. The depressions result from the dissolution and collapse of underlying Eocene calcareous and gypsiferous materials over which lacustrine sediments of varying thicknesses have accumulated. The suspensates occupying the depressions present three main types of seismic signatures: stratified, semistratified, and transparent. The densities of the suspensates and the water depths of their tops, which fluctuate continuously, vary from one depression to another. The maximum seismically recorded suspensate thickness is 44 m. Morphological and structural features, seismic characters, and variable degrees of hydraulic activity, point to the existence of different stages of maturity in the lake bottom depressions. This work brings new insight on the dynamics and evolution of limnocrenic solution lakes.  相似文献   

Transport and deposition of mud in deep‐water environments: Processes and stratigraphic implications     

Kvin Boulesteix  Miquel Poyatos‐Mor  Stephen S. Flint  Kevin G. Taylor  David M. Hodgson  Stephen T. Hasiotis 《Sedimentology》2019,66(7):2894-2925

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An inspection of the long-term behaviour of the range of the daily geomagnetic field variation from comprehensive modelling   总被引：1，自引：0，他引：1  

J. Miquel Torta  Luis R. Gaya-Piqu  Juan J. Curto  David Altadill 《Journal of Atmospheric and Solar》2009,71(13):1497-1510

This paper attempts to reveal whether long-term trends in the ionosphere are reflected in the amplitude range of the geomagnetic daily variation recorded at ground level. The smooth and regular variation observed in the magnetograms on magnetically quiet days is induced by the ionospheric currents flowing in the dynamo region. So it is likely that trends in the conductivity or in the dynamics of this region could produce changes in the current densities, and consequently in the range of the geomagnetic variation. The crucial aspect is how to separate the changes produced by the geomagnetic activity itself, or by secular changes of the Earth's magnetic field, from the part of the variation produced by factors affecting trends in the ionosphere, which could have an anthropogenic origin. To investigate this, we synthesized for several geomagnetic observatories the daily ranges of the geomagnetic field components with a comprehensive model of the quiet-time, near-Earth magnetic field, and finally we removed the synthetic values from the observed ranges at those observatories. This comprehensive model accounts for contributions from Earth's core, lithosphere, ionosphere, magnetosphere and coupling currents, and, additionally, accounts for influences of main field and solar activity variations on the ionosphere. Therefore, any trend remaining in the residuals, assuming that all the contributions mentioned above are properly described and thus removed by the comprehensive model, should reflect the influence of other sources. Results, based on series of magnetic data from observatories worldwide distributed, are presented. Trends in the X and Z components are misleading, since the current system changes in form as well as in intensity, producing changes of the focus latitude in the course of a solar cycle and from one cycle to another. Some differences exist between the long-term trends in the Y component between the real and modelled ranges, suggesting that other non-direct solar causes to the amplitude changes of the solar quiet geomagnetic variation should not be ruled out. Nevertheless, the results also reflect some short-comings in the way that the comprehensive modelling accounts for the influence of the solar activity on the range of the daily geomagnetic variation.  相似文献   

A Regional Archaeomagnetic Model for the Palaeointensity in Europe for the last 2000 Years and its Implications for Climatic Change     

Fco. Javier Pavón–Carrasco  Maria Luisa Osete  J. Miquel Torta  Luis R. Gaya–Piqué 《Pure and Applied Geophysics》2008,165(6):1209-1225

The SCHA.DI.00 directional model for the geomagnetic field in Europe for the last 2000 years (Pavón–Carrasco et al., 2008) has been updated by modelling the palaeointensity. This model, SCHA.DI.00, was developed from available Bayesian European Palaeosecular Variation Curves using the regional Spherical Cap Harmonic Analysis technique. The comparison of the palaeosecular variation curves, given by the regional model, with available archaeomagnetic data not used in its development showed an improvement with respect to the fit obtained by global archaeomagnetic models. In this paper advantage is taken of recently published palaeointensity databases to develop a complete (direction and intensity) regional archaeomagnetic model for the last 2000 years valid for the European region: the SCHA.DI.00–F model. Not only does this complete model provide an improvement for example for archaeomagnetic data studies, but it is also shown that this new regional model can be used to study the recently proposed link between the centennial secular variation of the geomagnetic field and climate change. The pattern of the archaeosecular variation of the field intensity obtained by SCHA.DI.00–F seems to verify the hypothesis presented by Gallet et al. (2005) about a possible (causal) connection between changes in the geomagnetic field intensity and in climate parameters, opening the door for more discussions on this challenging subject.  相似文献   

Influence of transient storage on stream nutrient uptake based on substrata manipulation   总被引：3，自引：0，他引：3  

Alba Argerich  Eugènia Martí  Francesc Sabater  Roy Haggerty  Miquel Ribot 《Aquatic Sciences - Research Across Boundaries》2011,73(3):365-376

Quantification of the transient storage zone (A_s) has become critical in stream biogeochemical studies addressed to examine factors controlling nutrient uptake. It is expected that higher A_s may enhance the interaction between nutrients and biota and thus, increase nutrient uptake. However, results from the literature are controversial. We hypothesized that besides of the size of A_s, the intrinsic physical and biological characteristics of stream structures that generate A_s are also relevant for nutrient uptake. We performed 24 additions of phosphate, ammonium, and chloride in four reaches of a man-made channel where we introduced three types of naturally colonized substrata packs (mud, sand and cobbles) to modify A_s. We estimated ammonium and phosphate uptake coefficients in both the main channel and A_s using a solute transport model (OTIS-P) and compared the results among reaches with different substrata types. The introduction of substrata packs decreased water velocity and increased A_s similarly among treatments. Nutrient uptake coefficients in the main channel were similar among reaches with different type substrata packs; however, nutrient uptake coefficients measured in A_s differed among them as well as the ratio between ammonium and phosphorus uptake coefficients in A_s, which were 1.6 in reaches with mud packs and 0.02 in reaches with sand or cobble packs. Results obtained in this study suggest that the contribution of A_s in nutrient uptake not only depends on the size of A_s but on the type of materials used to increase A_s, and thus, have biogeochemical implications on restoration projects aimed to modify channel morphology.  相似文献   

Experimental studies of sublimation of highly volatile ices in relevance to the ices of the solar system     

Jacek Leliwa-Kopystyński  Miquel A. Satorre  Carmina Santonja 《Acta Geophysica》2013,61(5):1304-1321

Studies of sublimation of complex ices prepared by deposition of gaseous CO, CH₄, N₂, and NH₃ molecules on a cold plate have been performed. The low pressure and low temperature system was used: 10^?9–10^?5 mbar and the lowermost temperature 10 K. Diagnostic of composition of evaporates (at an actual temperature) was done by means of the mass spectrometer. The latter allowed following simultaneously the partial pressure of five different ions or radicals escaping from the substrate. It has been found that highly volatile molecules that were used simultaneously with the low volatile ones to form the complex ices (mixtures or clathrates) present a different sublimation pattern than the sublimation of pure high-volatile ices. In particular, the high-volatile component sublimes at two or even three different temperature regimes: At low temperature that is typical for sublimation of this component, as well as at much higher temperatures. This effect seems to be important when degassing and outbursts from cometary nuclei are considered. It can be also important for modeling of cryovolcanic processes on the icy satellites.  相似文献   

Long-Term Amateur Ccd Monitoring Of Comet C/1999 S4 (Linear)     

Rodríguez  Juan  Sánchez  Salvador  García  Antonio  Blasco  Manolo  Villalonga  Miquel A. 《Earth, Moon, and Planets》2002,90(1-4):185-194

The results from the analysis of the extensive CCD photometry that we haveobtained during the long-term monitoring (from its discovery until its break-up)of comet C/1999 S4 (linear) are presented here. Our observations showthat the comet did not always behave as expected: it showed activity ahead oftime and in the end became fainter instead of brighter as it approached perihelion.A sequence of images and a lightcurve are shown.  相似文献   

Study of the interaction between U(VI) and the anoxic corrosion products of carbon steel     

Lara Duro  Souad El Aamrani  Miquel Rovira  Joan de Pablo  Jordi Bruno 《Applied Geochemistry》2008

The objective of this study was to investigate the removal mechanism of U(VI) from groundwater by magnetite as the main product of anoxic steel corrosion. For this purpose, a systematic sequence of batch experiments was conducted to focus the active role of magnetite in the reduction of U under different conditions. Results indicated that under anoxic conditions U(VI) was sorbed at the magnetite surface, whereas under reducing conditions at different H₂(g) pressures, U was present in tetravalent form as amorphous UO₂.  相似文献   

Environmental isotopes (N, S, C, O, D) to determine natural attenuation processes in nitrate contaminated waters: Example of Osona (NE Spain)   总被引：1，自引：0，他引：1  

Laura Vitria  Albert Soler  ngels Canals  Neus Otero 《Applied Geochemistry》2008,23(12):3597-3611

Nitrate-contaminated groundwater from an aquifer in the Osona region (NE Spain) was chemically and isotopically (δ¹⁵N_NO3,δ¹⁸O_NO3,δ³⁴S_SO4,δ¹⁸O_SO4, δD, δ¹⁸O_H2O and δ¹³C_DIC) characterized. Diffuse- contamination reached values of 366 mg/L. Nearly 75% of the 37 sampled sites had higher concentrations than the 50 mg/L in limit for drinking water. To identify the source of pollution δ¹⁵N_NO3 and δ¹⁸O_NO3 were used with results, for most samples, in the range of pig manure . Nitrification processes were evaluated by means of the δ¹⁸O of and water. Isotopic data suggested that natural attenuation of was taking place. This process was confirmed using the δ¹⁸O_NO3 coupled with the ratio, avoiding the influence of continuous inputs. A further insight on denitrification processes was obtained by analyzing the ions involved in denitrification reactions. Although the role of organic matter oxidation could neither be confirmed nor discarded, this approach showed a link between denitrification and pyrite oxidation. Therefore, in areas with no adequate infrastructure (e.g. multipiezometers), such as the one studied, this approach could be useful for implementing better water management.  相似文献   

Particulate organic matter and ballast fluxes measured using time-series and settling velocity sediment traps in the northwestern Mediterranean Sea     

Cindy Lee  Michael L. Peterson  Stuart G. Wakeham  Robert A. Armstrong  J. Kirk Cochran  Juan Carlos Miquel  Scott W. Fowler  David Hirschberg  Aaron Beck  Jianhong Xue 《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(18):1420-1436

Prompted by recent data analyses suggesting that the flux of particulate organic carbon sinking into deep waters is determined by fluxes of mineral ballasts, we undertook a study of the relationships among organic matter (OM), calcium carbonate, opal, lithogenic material, and excess aluminum fluxes as part of the MedFlux project. We measured fluxes of particulate components during Spring and Summer of 2003, and Spring of 2005, using a swimmer-excluding sediment trap design capable of measuring fluxes both in a time-series (TS) mode and in a configuration for obtaining particle settling velocity (SV) profiles. On the basis of these studies, we suggest that distinct OM–ballast associations observed in particles sinking at a depth of 200 m imply that the mechanistic basis of the organic matter–ballast association is set in the upper water column above the Twilight Zone, and that the importance of different ballast types follows the seasonal succession of phytoplankton. As in other studies, carbonate appears to enhance the flux of organic matter over opal. Particles must be at least half organic matter before their settling velocity is affected by ballast concentration. This lack of change in ballast composition with SV in particles with <40% OM content suggests that particle SV reaches a maximum because of the increasing importance of inertial drag. Relative amounts of OM and opal decrease with depth due to decomposition and dissolution; carbonates and lithogenic material contribute about the same amount to total mass, or increase slightly, throughout the water column. The high proportion of excess Al cannot be explained by its incorporation into diatom opal or reverse weathering, so Al is most likely adsorbed to particulate oxides. On shorter time scales, dust appears to increase particle flux through its role in aggregation rather than by nutrient inputs enhancing productivity. We suggest that the role of dust as a catalyst in particle formation may be a central mechanism in flux formation in this region, particularly when zooplankton fecal pellet production is low.  相似文献