Fission-track dating of glass inclusions in volcanic quartz     

Denis Vincent  Roberto Clocchiatti  Yves Langevin 《Earth and Planetary Science Letters》1984,71(2):340-348

We have extended fission-track dating techniques to volcanic pyroclastic rocks, using quartz-bearing uranium-rich glass inclusions. We use both the glass itself and the surrounding quartz as track detectors, the latter having a much higher resetting temperature. We can thus derive the age of the last low-temperature thermal event, as well as that of the most recent deposition of quartz on the walls of the inclusions. This method has been applied to a Sardinian sample and to a Moroccan Precambrian sample.  相似文献   

Acceptance of the 2002 Distinguished Service Award     

Denis M. Shaw 《Geochimica et cosmochimica acta》2003,67(13):2319

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Seismological constraints on the crustal structure beneath the Zagros Mountain belt (Iran)   总被引：5，自引：0，他引：5  

Denis Hatzfeld  Mohammad Tatar  Keith Priestley  Mohsen Ghafory-Ashtiany 《Geophysical Journal International》2003,155(2):403-410

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Numerical modelling of the Storfjorden (Svalbard) polynya development due to wind stress: role of the sea ice rheology and damping forces     

Denis Zyryanov  Jörg Haarpaintner  Reinert Korsnes 《Polar research》2003,22(2):235-245

Remote sensing of the ice cover in Storfjorden (Svalbard) revealed the persistence and evolution of latent heat polynyas during the winter of 1997/98. Latent heat polynyas open mechanically under wind stress or ocean currents that transport the ice cover away. In the present work we used mathematical modelling to simulate the Storfjorden polynya size and geometry caused by wind stress, measured at the meteorological station on the island of Hopen in winter 1997/98. The dependence of the polynya outlines on the wind velocity is presented. Two approaches were used: quasi-static and dynamic. Quasi-static simulations are based on a time-independent, linear ice stress-strain relationship valid for the low strain rates only. Time dependence of the ice cover fracture is joined with stress-strain nonlinearity caused by ice delayed-elastic recovery and viscosity. Results are compared to satellite observations from the synthetic aperture radar (SAR) of ERS-2. The simulation results show that a northern wind opens a larger polynya (ca. 30%) than does a north-eastern wind with the same speed. The results also indicate that the bathymetry and geometry of the fjord might have a stronger influence on the polynya opening and development than the location of individual islands and reefs.  相似文献   

Datation Ar/Ar des leucogranites sous couverture du complexe plutonique de Charroux–Civray (Vienne)Ar/Ar dating of leucogranites in the sediment-covered Charroux–Civray complex (Vienne)     

Paul Alexandre  Christian Le Carlier de Veslud  Michel Cuney  Gilles Ruffet  Denis Virlogeux  Alain Cheilletz 《Comptes Rendus Geoscience》2002,334(16)

⁴⁰Ar/³⁹Ar dating on muscovites, performed on leucogranitic intrusions of Charroux–Civray plutonic complex, points out the existence of two peraluminous magmatic activities, whose equivalents are known in the Limousin: (1) garnet-bearing leucogranitic veins at ca. 340 Ma; (2) a specialised leucogranite associated with W ± Sn deposits at ca 310 Ma. However, available ⁴⁰Ar/³⁹Ar data do not allow us to provide further data concerning the age and the geometry at depth of a large leucogranitic body identified by geophysics. To cite this article: P. Alexandre et al., C. R. Geoscience 334 (2002) 1141–1148.  相似文献   

Pulsed export of carbon in the north-western Mediterranean Sea     

Denis  Michel  Lefevre  Dominique  Thyssen  Melilotus  Jenkinson  Ian R.  Grégori  Gérald 《中国海洋湖沼学报》2023,41(1):189-202

The short term (hourly scale) variability of heterotrophic prokaryote (HP) vertical distribution and respiratory activity, was investigated in the north-western (NW) Mediterranean Sea. HP vertical distribution was determined on board by flow cytometry analysis of seawater samples collected by series of CTD casts. Cell counts and viability were determined for all samples. HP respiratory rates were determined later in the laboratory from filtered seawater samples (23 dm³) from 300–1 150-m depth. The average cell viability was 94.8%±2.2% (n=240). There was no accumulation of dead cells, due to quick decay of damaged cells. In the epipelagic layer, three HP groups were distinguished, two (HNA1, HNA2) whose cells exhibited a high nucleic acid content and one (LNA) with low nucleic acid content cells. HNA2 was most populated at 50 m but not detected at 90 m and below, presumably aerobic anoxygenic photoheterotrophic bacteria (AAPs). The variability in HP abundance was mainly confined in the upper 80 m. A few secondary peaks of HP abundance were observed (80–150 m) in connection with abundance troughs in the surface layer. HP cells were continuously present in a wide layer around 500 m (mean 191×10³ cells/cm³). Below this layer, HP abundance randomly exhibited peaks, coupled to respiratory rate peaks. The HP abundance and variability in the water column was suppressed during a strong wind event. The observed sporadic variability was tentatively interpreted through a pulsed carbon-export mechanism induced by the microorganism production of dissolved polysaccharides, followed by flocculation and rapid sinking. This mechanism would thus contribute to (i) preventing organic matter accumulation in the epipelagic layer, (ii) seeding the water column with live HP cells, and (iii) supplying the aphotic water column with fresh and labile organic matter. This important vertical flux mechanism needs further observations and modelling.

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Efficient ensemble forecasting of marine ecology with clustered 1D models and statistical lateral exchange: application to the Red Sea     

Denis Dreano  Kostas Tsiaras  George Triantafyllou  Ibrahim Hoteit 《Ocean Dynamics》2017,67(7):935-947

Forecasting the state of large marine ecosystems is important for many economic and public health applications. However, advanced three-dimensional (3D) ecosystem models, such as the European Regional Seas Ecosystem Model (ERSEM), are computationally expensive, especially when implemented within an ensemble data assimilation system requiring several parallel integrations. As an alternative to 3D ecological forecasting systems, we propose to implement a set of regional one-dimensional (1D) water-column ecological models that run at a fraction of the computational cost. The 1D model domains are determined using a Gaussian mixture model (GMM)-based clustering method and satellite chlorophyll-a (Chl-a) data. Regionally averaged Chl-a data is assimilated into the 1D models using the singular evolutive interpolated Kalman (SEIK) filter. To laterally exchange information between subregions and improve the forecasting skills, we introduce a new correction step to the assimilation scheme, in which we assimilate a statistical forecast of future Chl-a observations based on information from neighbouring regions. We apply this approach to the Red Sea and show that the assimilative 1D ecological models can forecast surface Chl-a concentration with high accuracy. The statistical assimilation step further improves the forecasting skill by as much as 50%. This general approach of clustering large marine areas and running several interacting 1D ecological models is very flexible. It allows many combinations of clustering, filtering and regression technics to be used and can be applied to build efficient forecasting systems in other large marine ecosystems.  相似文献   

Estimating Pesticide Attenuation From Water Dating and the Ratio of Metabolite to Parent Compound          下载免费PDF全文

Julien Farlin  Michael Bayerle  Denis Pittois  Tom Gallé 《Ground water》2017,55(4):550-557

Although pesticides are primarily degraded in the topsoil, significant attenuation can be expected in groundwater systems where the transit time of pesticides usually are orders of magnitude longer than in the soil. Because degradation and transport processes in the subsurface take place at time scales of months to years or even decades, direct measurements of natural attenuation are hampered by practical and logistical limitations (for instance the limited duration of sampling or a correct estimation of the pesticide flux into groundwater). Indirect methods such as measuring the changes in the ratio of degradation product to parent compound as a function of transit time in the aquifer, along a flow line provide a possible alternative. This paper presents a simple mathematical formulation of the relationship between transit time in the subsurface and changes in that ratio, and allows estimating the transformation rate of both parent compound and degradation product. The applicability of the method is illustrated in a case study investigating atrazine attenuation in a fractured sandstone aquifer.  相似文献   

Large roots dominate the contribution of trees to slope stability     

Filippo Giadrossich  Denis Cohen  Massimiliano Schwarz  Antonio Ganga  Roberto Marrosu  Mario Pirastru  Gian Franco Capra 《地球表面变化过程与地形》2019,44(8):1602-1609

Tree roots provide surface erosion protection and improve slope stability through highly complex interactions with the soil due to the nature of root systems. Root reinforcement estimation is usually performed by in situ pullout tests, in which roots are pulled out of the soil to reliably estimate the root strength of compact soils. However, this test is not suitable for the scenario where a soil progressively fails in a series of slump blocks – for example, in unsupported soils near streambanks and road cuts where the soil has no compressive resistance at the base of the hillslope. The scenario where a soil is unsupported on its downslope extent and progressively deforms at a slow strain rate has received little attention, and we are unaware of any study on root reinforcement that estimates the additional strength provided by roots in this situation. We therefore designed two complementary laboratory experiments to compare the force required to pull the root out. The results indicate that the force required to pull out roots is reduced by up to 50% when the soil fails as slump blocks compared to pullout tests. We also found that, for slump block failure, roots had a higher tendency to slip than to break, showing the importance of active earth pressure on root reinforcement behaviour, which contributes to reduced friction between soil and roots. These results were then scaled up to a full tree and tree stand using the root bundle and field-measured spatial distributions of root density. Although effects on the force mobilized in small roots can be relevant, small roots have virtually no effect on root reinforcement at the tree or stand scale on hillslopes. When root distribution has a wide range of diameters, the root reinforcement results are controlled by large roots, which hold much more force than small roots. © 2019 John Wiley & Sons, Ltd.  相似文献   

NanoSr – A New Carbonate Microanalytical Reference Material for In Situ Strontium Isotope Analysis     

Michael Weber  Federico Lugli  Bodo Hattendorf  Denis Scholz  Regina Mertz‐Kraus  Damien Guinoiseau  Klaus Peter Jochum 《Geostandards and Geoanalytical Research》2020,44(1):69-83

The in situ measurement of Sr isotopes in carbonates by MC‐ICP‐MS is limited by the availability of suitable microanalytical reference materials (RMs), which match the samples of interest. Whereas several well‐characterised carbonate reference materials for Sr mass fractions > 1000 µg g^?1 are available, there is a lack of well‐characterised carbonate microanalytical RMs with lower Sr mass fractions. Here, we present a new synthetic carbonate nanopowder RM with a Sr mass fraction of ca. 500 µg g^?1 suitable for microanalytical Sr isotope research (‘NanoSr’). NanoSr was analysed by both solution‐based and in situ techniques. Element mass fractions were determined using EPMA (Ca mass fraction), as well as laser ablation and solution ICP‐MS in different laboratories. The ⁸⁷Sr/⁸⁶Sr ratio was determined by well‐established bulk methods for Sr isotope measurements and is 0.70756 ± 0.00003 (2s). The Sr isotope microhomogeneity of the material was determined by LA‐MC‐ICP‐MS, which resulted in ⁸⁷Sr/⁸⁶Sr ratios of 0.70753 ± 0.00007 (2s) and 0.70757 ± 0.00006 (2s), respectively, in agreement with the solution data within uncertainties. Thus, this new reference material is well suited to monitor and correct microanalytical Sr isotope measurements of low‐Sr, low‐REE carbonate samples. NanoSr is available from the corresponding author.  相似文献