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1.
Aurélia Mouret Pierre Anschutz Bruno Deflandre Gwénaëlle Chaillou Christelle Hyacinthe Jonathan Deborde Henri Etcheber Jean-Marie Jouanneau Antoine Grémare Pascal Lecroart 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(4):528-540
The relationship between particulate organic carbon (POC) concentrations measured in modern sediment and fluxes of exported POC to the sediment surface needs to be understood in order to use POC content as a proxy of paleo-environmental conditions. The objective of our study was to compare POC concentrations, POC mineralization rates calculated from O2 consumption and POC burial rates. Benthic O2 distributions were determined in 58 fine-grained sediment cores collected at different periods at 14 stations in the southeastern part of the Bay of Biscay with depths ranging from 140 to 2800 m. Depth-dependent volume-specific oxygen consumption rates were used to assess rates of aerobic oxidation of organic matter (OM), assuming that O2 consumption solely was related to heterotrophic activity at the sediment–water interface. Heterogeneity of benthic O2 fluxes denoted changes in time and space of fresh organic material sedimentation. The most labile fraction of exported POC engendered a steep decrease in concentration in the upper 5 mm of vertical O2 profiles. The rupture in the gradient of O2 microprofile may be related to the bioturbation-induced mixing depth of fast-decaying carbon. Average diffusive O2 fluxes showed that this fast-decaying OM flux was much higher than buried POC, although diffusive O2 fluxes underestimated the total sediment oxygen demand, and thus the fast-decaying OM flux to the sediment surface. Sedimentary POC burial was calculated from sediment mass accumulation rate and the organic carbon content measured at the top of the sediment. The proportion of buried POC relative to total exported POC ranged at the most between 50% and 10%, depending on station location. Therefore, for a narrow geographic area like the Bay of Biscay, burial efficiency of POC was variable. A fraction of buried POC consisted of slow-decaying OM that was mineralized within the upper decimetres of sediment through oxic and anoxic processes. This fraction was deduced from the decrease with depth in POC concentration. At sites located below 500 m water depth, where the fast-decaying carbon did not reach the anoxic sediment, the slow-decaying pool may control the O2 penetration depth. Only refractory organic material was fossilized in sedimentary records at locations where labile OM did not reach the anoxic portion of the sediment. 相似文献
2.
Pascal Lazure Valérie Garnier Franck Dumas Christelle Herry Marina Chifflet 《Continental Shelf Research》2009,29(8):985-997
The hydrology of the Bay of Biscay was investigated using the regional ocean model MARS3D (Model for Application at Regional Scale). The simulated hydrology is compared to a set of various data encompassing monthly climatology, remote sensing SST, CTD casts, and coastal salinity measurements. Special focus was put on the validation over the continental shelf. This paper reports that despite some misfits, the climatological hydrology and its seasonal variability are correctly simulated. Various statistics computed over the period from 1999–2004 highlight different aspects of the hydrology. The biases and root mean square errors (RMSE) remain very weak at all depths when comparing salinity (<0.1 and <0.6 psu respectively). The predicted temperature shows a global overestimation of temperature (bias of around 0.8 °C) and the maximum errors are located near the thermocline (rmse of 1 °C at 20–40 m). The model is shown to properly reproduce the annual dynamics of sea surface temperature, as well as the dynamics of large river plumes observed by high frequency time series from coastal salinity gauges. The misfits highlighted by these various comparisons between model and observations are attributed to heat fluxes and mixing parameterisation. 相似文献
3.
Julie C. Gattacceca Christine Vallet-Coulomb Adriano Mayer Christelle Claude Olivier Radakovitch Enrico Conchetto Bruno Hamelin 《Journal of Hydrology》2009,378(1-2):46-61
The coastal plain bordering the southern Venice Lagoon is a reclaimed lowland characterized by high subsidence rate, and ground level and water-table depth below sea level. In this agricultural region, where the surface hydrologic network is entirely artificially controlled by irrigation/drainage canals, salinization problems have long been encountered in soils and groundwaters. Here we use isotopic and geochemical tracers to improve our understanding of the origin of salinization and mineralization of the semi-confined aquifer (0–40 m), and the freshwater inputs to this hydrological system. Water samples have been collected at different seasons in the coastal Adriatic Sea, lagoon, rivers and irrigation canals, as well as in the semi-confined aquifer at depths between 12 and 35 m (14 boreholes), and in the first confined aquifer (three boreholes drilled between 40 and 80 m depth). Stable isotopes (δ18O and δD) and conductivity profiles show that direct saline intrusion from the sea or the lagoon is observed only in a restricted coastal strip, while brackish groundwaters are found over the entire topographic and piezometric depression in the centre of the study area. Fresh groundwaters are found only in the most western zone. The sharp isotopic contrast between the western and central regions suggests disconnected hydrological circulations between these two parts of the shallow aquifer. The border between these two regions also corresponds to the limits of the most strongly subsiding zone.Our results can be interpreted in terms of a four end-member mixing scheme, involving (1) marine water from the lagoon or the open sea, (2) alpine and pre-alpine regional recharge waters carried either by the main rivers Adige, Bacchiglione and Brenta (irrigation waters) or by the regional groundwater circulation, (3) local precipitation, and (4) evaporated waters infiltrated from the surface. Infiltration from the surface is also revealed by the stratification of the electrical conductivity profiles, showing that the brackish groundwaters are overlain by a shallow layer of less saline water all over the central depression. In the first confined aquifer, the groundwaters have isotopic compositions similar to the deep groundwaters of the Venetian confined aquifers (40–400 m depth). The isotopic data and the Br/Cl ratio show that the origin of the salinization of the phreatic aquifer can be ascribed to seawater intrusion alone, with no indication of the involvement of deep brines (identified at 450 m depth) in the process.The chemical composition of the saline and brackish groundwaters is characterized by an excess of sodium and a deficit of calcium compared to conservative mixing between fresh groundwaters and seawater. This suggests that the phreatic aquifer is progressively freshening, as a consequence of the beneficial influence of the extensive irrigation/drainage network, including raised canals acting as a hydraulic barrier along the coast. This freshening tendency may have been lasting since the reclamation in the mid-twentieth century, and has probably been accelerated by the ban on groundwater abstraction since the 1970s. 相似文献
4.
Guillaume Favreau Christian Leduc Christelle Marlin Abdou Guéro 《Comptes Rendus Geoscience》2002,334(6):395-401
In southwest Niger, the Continental Terminal water table displays a natural hollow shape about 10 m in depth over an area of 4000 km2. A 10-year survey of this hollow aquifer has shown that current recharge is above . The water table has risen continuously since the 1950–1960s as a result of land clearance. This shows a disequilibrium in the aquifer balance. The long-term recharge rate is estimated by radioisotopes to be around . This figure fits with the only possible origin of the piezometric depression, i.e. evapotranspiration losses in its centre. To cite this article: G. Favreau et al., C. R. Geoscience 334 (2002) 395–401. 相似文献
5.
E Mottin C Caplat T Latire A Mottier ML Mahaut K Costil D Barillier JM Lebel A Serpentini 《Marine pollution bulletin》2012,64(9):1911-1920
Two types of exposures were performed to assess the effects of zinc released from sacrificial anode degradation: a chronic exposure, in which oysters were exposed to 0.53±0.04mgZnL(-1) for 10weeks, and an acute exposure, where oysters were exposed to 10.2±1.2mgZnL(-1) for 1week. At the end of the acute exposure experiment, 81.8% mortality was recorded. In contrast, no mortality was detected after 10weeks exposure. Moreover, all of the immune system biomarkers studied, except the number of circulating haemocytes, were stimulated by a moderate level of zinc and inhibited by a high level. Our exposure conditions did not induce SOD or MXR mRNA expression in gills and digestive gland. However, an increase of MT mRNA is observed in these tissues. The results indicate that oysters are sensitive to acute zinc toxicity but are only moderately affected by a mild zinc concentration. 相似文献
6.
Jean-Denis Taupin Gaëlle Gaultier Guillaume Favreau Christian Leduc Christelle Marlin 《Comptes Rendus Geoscience》2002,334(1):43-50
The isotopic content of rainfall was measured in Niamey (Niger) over a period of eight years (1992–1999). Seasonal distribution of rainy events depends on the monsoon movement over the region. At the beginning and at the end of the rainy season, low rainfall, high temperatures and low relative humidity favour isotopic enrichment. In the middle of the rainy season, heavy rainfall, low temperatures and relative humidity close to saturation lead to isotopically depleted contents because of the mass effect; moreover, in the case of low rainfall, marked vertical convective development favours high altitude condensation. How far the Intertropical Front moves north, determines the quality of the rainy season and influences the isotopic contents. Thus the isotopic contents of rainfall are good climatic indicators. To cite this article: J.-D. Taupin et al., C. R. Geoscience 334 (2002) 43–50 相似文献
7.
Steeve Bonneville Thilo Behrends Christelle Hyacinthe 《Geochimica et cosmochimica acta》2006,70(23):5842-5854
A kinetic model for the microbial reduction of Fe(III) oxyhydroxide colloids in the presence of excess electron donor is presented. The model assumes a two-step mechanism: (1) attachment of Fe(III) colloids to the cell surface and (2) reduction of Fe(III) centers at the surface of attached colloids. The validity of the model is tested using Shewanella putrefaciens and nanohematite as model dissimilatory iron reducing bacteria and Fe(III) colloidal particles, respectively. Attachment of nanohematite to the bacteria is formally described by a Langmuir isotherm. Initial iron reduction rates are shown to correlate linearly with the relative coverage of the cell surface by nanohematite particles, hence supporting a direct electron transfer from membrane-bound reductases to mineral particles attached to the cells. Using internally consistent parameter values for the maximum attachment capacity of Fe(III) colloids to the cells, Mmax, the attachment constant, KP, and the first-order Fe(III) reduction rate constant, k, the model reproduces the initial reduction rates of a variety of fine-grained Fe(III) oxyhydroxides by S. putrefaciens. The model explains the observed dependency of the apparent Fe(III) half-saturation constant, , on the solid to cell ratio, and it predicts that initial iron reduction rates exhibit saturation with respect to both the cell density and the abundance of the Fe(III) oxyhydroxide substrate. 相似文献
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9.
Belkacem Bekkoussa Herve Jourde Christelle Batiot-Guilhe Mohamed Meddi Abdelkader Khaldi Habib Azzaz 《水文科学杂志》2013,58(5):1111-1127
Résumé L'origine de la salinité dans les eaux de la nappe Plio-Quaternaire de la plaine de Ghriss (Nord-Ouest de l'Algérie) et la compréhension de ses comportements hydrodynamiques et géochimiques, en réponse à certains forçages naturels et anthropiques, ont été approchées par l’étude combinée des rapports ioniques et d'analyses statistiques des données hydrochimiques. Cette étude a identifié l'alimentation latérale de l'aquifère Plio-Quaternaire par les deux principaux aquifères de la région. La salinisation des eaux de la nappe Plio-Quaternaire résulte essentiellement de la dissolution des évaporites (halite et gypse), de l'infiltration des eaux de ruissellement, et du retour à la nappe des eaux d'irrigation qui sont chargées en sels initialement reconcentrés dans le sol ou dans la zone non saturée. Les concentrations élevées en nitrates et en chlorures sont l'indice d'une pollution anthropique d'origine urbaine ou agricole qui affecte toute la plaine de Ghriss en proportions variables. Citation Bekkoussa, B., Jourde, H., Batiot-Guilhe, C., Meddi, M., Khaldi, A., et Azzaz, H., 2013. Origine de la salinité et des principaux éléments majeurs des eaux de la nappe phréatique de la plaine de Ghriss, Nord-Ouest Algérien. Hydrological Sciences Journal, 58 (5), 1111–1127. Editeur Z.W. Kundzewicz; Editeur associé S. Faye 相似文献
10.
Description and first results of an explicit electrical scheme in a 3D cloud resolving model 总被引:2,自引:0,他引:2
The three-dimensional non-hydrostatic mesoscale model MésoNH of the French community offers the numerical environment to develop a cloud electrification scheme in a consistent way with the original mixed phase microphysical scheme. The charge separation mechanisms are entirely due to non-inductive processes and result from elastic ice–snow, ice–graupel and snow–graupel collisions. The electric charges carried by each of the five hydrometeor categories are transported along the airflow and are exchanged according to the various microphysical mass transfer rates but assuming a power law distribution of the individual charges as a function of the particle size. The electric field is diagnosed at each time step after integrating the electric potential induced by a net charge density in the Poisson equation. Finally, a lightning ash is triggered when the electric field locally steps over a given threshold. It propagates in two opposite directions until the magnitude of the electric field falls below a prescribed value. A fractal branching algorithm is then activated to extend lightning streamers away from the main channel and toward cloudy regions where substantial charge densities are present. Charges are neutralized along the tortuous lightning path with a simple procedure that preserves total charge conservation.The complete electrification scheme tested for an ideal case of vigorous supercellular storm shows an intense electrical activity all along its lifecycle. We show that the model is able to produce a direct tripolar structure of the charges as the result of a temperature charge reversal of − 10 °C and of the different sedimentation rates of the hydrometeors. 相似文献