Lower Triassic δC isotope curve from shallow-marine carbonates in Japan, Panthalassa realm: Confirmation of the Tethys δC curve     

Micha Horacek  Toshio Koike  Sylvain Richoz 《Journal of Asian Earth Sciences》2009,36(6):481

δ¹³C data from Tethyan sections provide evidence of profound changes in the carbon cycle during the Lower Triassic. Sections from the Panthalassa realm were investigated to establish whether these variations are also present there. In the Jurassic accretionary wedges in Japan, exotic blocks having a Panthalassan affinity, have been incorporated. The majority of the blocks are pelagic cherts but rare shallow-water carbonates are also present. We present a δ¹³C study on the Lower Triassic of a shallow-water carbonate succession deposited on a mid-oceanic seamount and accreted to the Chichibu Belt, Japan. Two sections have been measured at Kamura, central Kyushu Island. The carbon isotope curve shows depleted values across the Permian–Triassic boundary (PTB), subsequently followed by an increase to heavier values into the Dienerian, culminating in a maximum of almost +4‰ V-PDB, before a steep drop at a stratigraphic gap. Low values are recorded in the Smithian, but rise to enriched δ¹³C values > +3.5‰ near the Smithian–Spathian boundary. The observed trend of the stable carbon isotope curve from Japanese sediments mirrors the curves derived from sections in the Tethys (e.g. Italy, Iran, Turkey, Oman and the South China Nanpanjing Basin). Our results support the interpretation of this curve as representing a global trend across the PTB and in the Lower Triassic, although some distinct features are absent around the Dienerian/Smithian boundary. Profound variations of the carbon isotope curve in the Lower Triassic are presented for the first time from a marine section outside of the Tethys. They indicate severe, global changes in the Lower Triassic carbon cycle, and the causative processes must have significantly contributed to the delayed biotic recovery after the PTB. Large amounts of carbon were shifted between carbon reservoirs, most probably between shallow- and deep-ocean waters, and/or ocean and sediment. Anoxia followed by overturn of the ocean water masses may have been the mechanism which quickly altered ecological conditions in the ocean leading to variable availability of nutrients and oxygen, and changes in isotope composition of the available carbon in the surface waters that was incorporated in the precipitated carbonate.  相似文献   

Multiscale characterization of pyritized plant tissues in blueschist facies metamorphic rocks   总被引：2，自引：0，他引：2  

Sylvain Bernard  Karim Benzerara  Olivier Beyssac 《Geochimica et cosmochimica acta》2010,74(17):5054-5068

Pyritized plant tissues with well-preserved morphology were studied in rocks from Vanoise (western Alps, France) that experienced high-pressure, low-temperature metamorphic conditions in the blueschist facies during the Alpine orogeny. Organic and inorganic phases composing these fossils were characterized down to the nanometer scale by Raman microspectroscopy, scanning transmission X-ray microscopy and transmission electron microscopy. The graphitic but disordered organic matter composing these fossils is chemically and structurally homogeneous and mostly contains aromatic functional groups. Its original chemistry remains undefined likely because it was significantly transformed by diagenetic processes and/or thermal degradation during metamorphism. Various mineral phases are closely associated with this organic matter, including sulphides such as pyrite and pyrrhotite, carbonates such as ankerite and calcite, and iron oxides. A tentative time sequence of formation of these diverse mineral phases relative to organic matter decay is proposed. The absence of traces of organic matter sulphurization, the pervasive pyritization of the vascular tissues and the presence of ankerite suggest that the depositional/diagenetic environment of these metasediments was likely rich in reactive iron. Fe-sulphides and ankerite likely precipitated early and might have promoted the preservation of the fossilized biological soft tissues by providing mechanical resistance to compaction during diagenesis and subsequent metamorphism. In contrast, iron oxides which form rims of 100-nm in thickness at the interface between organic matter and Fe-sulphides may result from metamorphic processes. This study illustrates that it may be possible in some instances to deconvolve metamorphic from diagenetic imprints and opens new avenues to better constrain processes that may allow the preservation of organic fossils during diagenesis and metamorphism.  相似文献   

Micro-scale flood risk analysis based on detailed 2D hydraulic modelling and high resolution geographic data   总被引：2，自引：0，他引：2  

Julien Ernst  Benjamin J. Dewals  Sylvain Detrembleur  Pierre Archambeau  Sébastien Erpicum  Michel Pirotton 《Natural Hazards》2010,55(2):181-209

The paper presents a consistent micro-scale flood risk analysis procedure, relying on detailed 2D inundation modelling as well as on high resolution topographic and land use database. The flow model is based on the shallow-water equations, solved by means of a finite volume scheme on multi-block structured grids. Using highly accurate laser altimetry, the simulations are performed with a typical grid spacing of 2 m, which is fine enough to represent the flow at the scale of individual buildings. Consequently, the outcomes of hydraulic modelling constitute suitable inputs for the subsequent exposure analysis, performed at a micro-scale using detailed land use maps and geographic database. Eventually, the procedure incorporates social flood impact analysis and evaluation of direct economic damage to residential buildings. Besides detailing the characteristics and performance of the hydraulic model, the paper describes the flow of data within the overall flood risk analysis procedure and demonstrates its applicability by means of a case study, for which two different flood protection measures were evaluated.  相似文献   

Assessment of the impact of pools on the water isotopic signature of a boreal patterned peatland          下载免费PDF全文

Gwenael E. Carrer  Alain N. Rousseau  Sylvain Jutras  Maxime Fossey 《水文研究》2016,30(8):1292-1307

Recent studies have shown that boreal peatlands exhibit considerable chemical variability but without clear spatial pattern. This chemical heterogeneity illustrates the complex hydrological behaviour of peatlands, particularly patterned fen. Isotopic, chemical and physical tracers were used to describe the hydrological behaviour of a small boreal headwater catchment (13 ha) during the snow‐free period with a special emphasis on the downstream patterned fen. Results showed that shallow pools were mixed every day during the summer, particularly during nights or discharge periods. Despite large water storage capacities in pools, which should induce large buffer effect, hydrological behaviour of patterned fen is more similar to a piston flow process. This is probably because of the division of the fen into successive small cascading streamflow reservoirs. The consequences were a rapid change of the chemical signature throughout the fen, particularly upstream. A spatial pattern was observed downstream in early summer. The isotopic signature passed from an upstream depleted and homogeneous signature to a progressively enriched downstream signature. However, this pattern was not identified during the wetter period (late summer), probably because the discharge, which dominated the water budget, decreased the surface water residence time and flushed a large proportion of stored surface water. We developed for this patterned fen a conceptual model of the surface flow to explain these particular mixing effects and the implications on the dynamics of the chemical signature. To further our understanding of similar boreal headwater catchments, future work should include the development of a multiple mixed‐reservoir model. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Mixing law versus discharge and electrical conductivity relationships: application to an alpine proglacial stream     

Marc Dzikowski  Sylvain Jobard 《水文研究》2012,26(18):2724-2732

Mixing laws have been used in hydrogeology for decades. In glacial hydrology, they are used to determine the contributions of the different reservoirs supplying the proglacial stream. However, some assumptions about discharge–solute matter and discharge–electrical conductivity (EC) relationships have led to erroneous conclusions. Analysis of a theoretical example indicated a hyperbolic relationship between discharge and solute matter concentration/EC for two reservoirs. We applied this approach to experimental data from the Baounet Glacier (Savoie, France), assuming that the proglacial stream is provided by a combination of watershed groundwater flow (diurnally stable and with high EC) and quick drainage from the glacier (low EC and discharge that change very quickly). Applying mixing laws allowed us to characterise these two flows and to separate the quick flows (glacial ablation and rainfalls). Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Growth anomalies on Acropora cytherea corals     

Irikawa A  Casareto BE  Suzuki Y  Agostini S  Hidaka M  van Woesik R 《Marine pollution bulletin》2011,62(8):1702-1707

This ten-year study examined the morphological, physiological, and ecological characteristics of coral growth anomalies on Acropora cytherea on Amuro Island, Okinawa, Japan. The objectives of the study were to assess whether the growth anomalies, identified as diffuse disruptions on the skeleton: (i) were more prevalent on large colonies than on small colonies, (ii) were more common near the center of the colonies than peripherally, (iii) affected colony growth and mortality, and (iv) affected coral-colony fecundity and photosynthetic capacity. We hypothesized that the growth anomalies were signs of the onset of aging. The growth anomalies were more prevalent on colonies >2 m diameter, and were concentrated near the central (older) portions of the colonies. The growth anomalies were also associated with reduced productivity and dysfunctional gametogenesis. Still, the growth anomalies did not appear to affect colony survival. The contact experiments showed that the growth anomalies were not contagious, and were most likely a sign of aging that was exacerbated by thermal stress.  相似文献   

An operational model to simulate post-accidental radionuclide transfers in Toulon marine area: preliminary development   总被引：2，自引：1，他引：1  

Celine Duffa  Francois Dufois  Sylvain Coudray 《Ocean Dynamics》2011,61(11):1811-1821

As part of its development of post-accident management tools, the French Institute for Radiological Protection and Nuclear Safety is setting up a model to simulate radionuclide dispersion in the Toulon marine area (one of France’s main military ports). The model is based on the MARS 3D code developed by IFREMER. It reproduces hydro-sedimentation phenomena in the Bay of Toulon with a horizontal spatial resolution of 100 m and 30 vertical sigma levels and also factors in radioactive decay and dissolved/particulate distribution of the radionuclides studied. With no tide, the major currents in this area are generated by the wind. The model effectively reproduces the resulting hydrodynamic phenomena, which were measured throughout the summer of 2009 in the channel that links the Little Bay to the Large Bay of Toulon. When the Mistral (wind from the West/Northwest) blows, a surface current quickly appears, which pushes water southwards from the Little Bay, and which is offset by a bottom current (upwellings). When the wind blows from the East, the currents move in the opposite direction, and southeasterly waves, dependent on wind strength and fetch, occur in the Large Bay. Here, we give an example of the simulated dispersion of radionuclides released directly into the surface waters near the Arsenal, demonstrating the constraint relative to dispersion generated by the half-closed configuration of the Little Bay. Sediment in the Little Bay also forms an area where the most highly reactive radionuclides would accumulate, and where the lack of waves has the effect of considerably limiting the phenomena of resuspension.  相似文献   

Failure of dams arranged in series or in complex     

Benjamin Dewals  Sébastien Erpicum  Sylvain Detrembleur  Pierre Archambeau  Michel Pirotton 《Natural Hazards》2011,56(3):917-939

A practical methodology has been developed for predicting flows generated by dam failures or malfunctions in a complex or a series of dams. A twofold approach is followed. First, the waves induced in the downstream reservoirs are computed, as well as hydrodynamic impacts induced on downstream dams and dikes are estimated. Second, the flood wave propagation and the inundation process are simulated in the downstream valley, accounting for possible dam collapse or breaching in cascade. Two complementary flow models are combined: a two-dimensional fully dynamic model and a simplified lumped model. At each stage, the methodology provides guidelines to select the most appropriate model for efficiently computing the induced flows. Both models handle parametric modeling of gradual dam breaching. The procedure also incorporates prediction of breach formation time and final width, as well as sensitivity analysis to compensate for the high uncertainties remaining in the estimation of breach parameters. The applicability of the modeling procedure is demonstrated for a case study involving a 70-m high-gravity concrete dam located upstream of four other dams.  相似文献   

Growth of the European abalone (Haliotis tuberculata L.) in situ: Seasonality and ageing using stable oxygen isotopes     

Sabine Roussel  Sylvain Huchette  Jacques Clavier  Laurent Chauvaud 《Journal of Sea Research》2011,65(2):213-218

The ormer, Haliotis tuberculata is the only European abalone species commercially exploited. The determination of growth and age in the wild is an important tool for fisheries and aquaculture management. However, the ageing technique used in the past in the field is unreliable. The stable oxygen isotope composition (¹⁸O/¹⁶O) of the shell depends on the temperature and oxygen isotope composition of the ambient sea water. The stable oxygen isotope technique, developed to study paleoclimatological changes in shellfish, was applied to three H. tuberculata specimens collected in north-west Brittany. For the specimens collected, the oxygen isotope ratios of the shell reflected the seasonal cycle in the temperature. From winter-to-winter cycles, estimates of the age and the annual growth increment, ranging from 13 to 55 mm per year were obtained. This study shows that stable oxygen isotopes can be a reliable tool for ageing and growth studies of this abalone species in the wild, and for validating other estimates.  相似文献   

Validation of Forecast Cloud Parameters from Multispectral AIRS Radiances     

Louis Garand  Ovidiu Pancrati  Sylvain Heilliette 《大气与海洋》2013,51(2):121-137

The well-known CO₂ slicing technique which provides retrievals of cloud parameters (effective height and amount) is adapted in light of model validation using multispectral infrared sounders. The technique is applied to both real Atmospheric Infrared Sounder (AIRS) radiances and to corresponding radiances simulated from global 6 h and 12 h forecasts for the 31 days of July 2008. The forecast model is the one used operationally at the Canadian Meteorological Centre. Radiances are simulated from the Radiative Transfer for the Television and Infrared Observation Satellite (TIROS) Operational Vertical Sounder (RTTOV) model. When compared to model output of cloud parameters, simulated retrievals help us understand systematic biases linked to the retrieval technique. Systematic errors of interest, attributed to forecast cloud parameters, are then more clearly assessed from real retrievals. This is the central idea of this paper. The proposed definition of model cloud top, based on cloud transmittance, corresponds well to the height derived from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) instrument. These lidar-derived cloud heights, in turn, confirm the nature of the biases produced by the CO₂ slicing technique (e.g., a negative bias increasing with height to about 2 km (approximately 50 hPa) for the highest clouds at 16 km (approximately 100 hPa)). Results suggest that the model has a tendency to produce an excess of low-level clouds below 2 km, compensated for by a deficit from 3 to 6 km. No significant differences are found between 6 h and 12 h forecast monthly fields, an indication that the model has sufficiently spun-up after a few hours. Retrieved global monthly cloud parameter fields are compared to independently derived products available from the Moderate Resolution Imaging Spectrometer (MODIS) and AIRS standard processing. Significant differences are noted, linked to the different retrieval approaches, input data and resolution. This is further evidence that, for validation purposes, definitions of observed and model parameters must be consistent.  相似文献