La diatomee marine chaetoceros simplex calcitrans paulsen et son environnement,I. Relations avec le milieu de culture; étude de la fraction insaponifiable,des stérols et des acides gras     

Jean-Luc Boutry  Michel Barbier 《Marine Chemistry》1974,2(3):217-227

Detailed analysis of the lipids present in seawater medium before and after growing cultures of the diatom Chaetoceros simplex calcitrans Paulsen in them has been carried out and compared with the lipids found in the diatom itself.Fatty Acids. The seawater contained 1.0 μg fatty acids/ml, C 16:0, C 18:0 and C 18:1 being the predominant components. After removal of 12-day cultures of the diatom, the medium contained 1.1 μg fatty acids/ml and showed 47% decrease of the C 18:0 acid, and decreases of 37% in the C 13:0 and 56% in the C 15:1 contents. The diatom itself contained 10.7% fatty acids of the dry weight, among which C 16:1, C 16:0 and C 14:0 predominated.Sterols. Cholesterol dominated the sterol composition of seawater, which was found to contain 0.15 μg total sterols/ml. The filtered culture medium contained 0.18 μg total sterols/ml, had lost some of its cholesterol content, but contained a significant amount of 24-methylene-cholesterol. Other minor sterols in seawater both prior to and after growing diatoms cultures in it were β-sitosterol, stigmasterol and campesterol.The diatom itself contained 0.47% total sterols of the dry weight with cholesterol and 24-methylene-cholesterol making up ca. 40% of the total each. Minor sterols found were stigmasterol (or fucosterol), campesterol and β-sitosterol.  相似文献   

Formation of magnesium‐smectite during lacustrine carbonates early diagenesis: Study case of the volcanic crater lake Dziani Dzaha (Mayotte – Indian Ocean)     

Vincent P. Milesi  Didier Jzquel  Mathieu Debure  Pierre Cadeau  Franois Guyot  Grard Sarazin  Francis Claret  Emmanuelle Vennin  Carine Chaduteau  Aurlien Virgone  Eric C. Gaucher  Magali Ader 《Sedimentology》2019,66(3):983-1001

The volcanic crater lake of Dziani Dzaha in Mayotte is studied to constrain the geochemical settings and the diagenetic processes at the origin of Mg‐phyllosilicates associated with carbonate rocks. The Dziani Dzaha is characterized by intense primary productivity, volcanic gases bubbling in three locations and a volcanic catchment of phonolitic/alkaline composition. The lake water has an alkalinity of ca 0·2 mol l^?1 and pH values of ca 9·3. Cores of the lake sediments reaching up to one metre in length were collected and studied by means of carbon–hydrogen–nitrogen elemental analyzer, X‐ray fluorescence spectrometry and X‐ray powder diffraction. In surface sediments, the content of total organic carbon reaches up to 20 weight %. The mineral content consists of aragonite and hydromagnesite with minor amounts of alkaline feldspar and clinopyroxene from the volcanic catchment. Below 30 cm depth, X‐ray diffraction analyses of the <2 μm clay fraction indicate the presence of a saponite‐like mineral, a Mg‐rich smectite. The saponite‐like mineral accumulates at depth to reach up to ca 30 weight %, concurrent with a decrease of the contents of hydromagnesite and organic matter. Thermodynamic considerations and mineral assemblages suggest that the evolution of the sediment composition resulted from early diagenetic reactions. The formation of the saponite‐like mineral instead of Al‐free Mg‐silicates resulted from high aluminum availability, which is favoured in restricted lacustrine environments hosted in alkaline volcanic terrains commonly emplaced during early stages of continental rifting. Supersaturation of the lake water relative to saponite is especially due to high pH values, themselves derived from high primary productivity. This suggests that a genetic link may exist between saponite and the development of organic‐rich carbonate rocks, which may be fuelled by the input of CO₂‐rich volcanic gases. This provides novel insights into the composition and formation of saponite‐rich deposits under a specific geodynamic context such as the Cretaceous South Atlantic carbonate reservoirs.  相似文献   

The equation of state of Al,H-bearing SiO2 stishovite to 58 GPa     

Dmitry L. Lakshtanov  Carine B. Vanpeteghem  Jennifer M. Jackson  Jay D. Bass  Guoyin Shen  Vitali B. Prakapenka  Konstantin Litasov  Eiji Ohtani 《Physics and Chemistry of Minerals》2005,32(7):466-470

We have determined the P-V equation of state of Al-rich H-bearing SiO₂ stishovite by X-ray powder diffraction at pressures up to 58 GPa using synchrotron radiation. The sample contained 1.8 wt% Al₂O₃ and up to 500 ppm H₂O, and had a composition that would coexist with Mg-silicate perovskite in a subducted slab. By fitting a third-order Birch-Murnaghan equation of state to our compression data, we obtained a bulk modulus K _T0=298(7) GPa with K′=4.3(5). With K′ fixed to a value of 4, the bulk modulus K _T0=304(3) GPa. Our results indicate that Al³⁺ and H⁺ have a small effect on the elastic properties of stishovite. Compared with data obtained up to 43.8 GPa, peak intensities changed and we observed a decreased quality of fit to a tetragonal unit cell at pressures of 49 GPa and higher. These changes may be an indication that the rutile↔CaCl₂ transition occurs between these pressures. After laser annealing of the sample at 58.3(10) GPa and subsequent decompression to room conditions, the cell volume is the same as before compression, giving strong evidence that the composition of the recovered sample is also unchanged. This suggests that Al and H are retained in the sample under extreme P-T conditions and that stishovite can be an agent for transporting water to the deepest lower mantle.  相似文献   

Trends and climate evolution: Statistical approach for very high temperatures in France   总被引：3，自引：0，他引：3  

Sylvie Parey  Farida Malek  Carine Laurent  Didier Dacunha-Castelle 《Climatic change》2007,81(3-4):331-352

The existence of an increasing trend in average temperatures during the last 50 years is widely acknowledged. Furthermore, there is compelling evidence of the variability of extremes, and rapid strides are made in studies of these events. Indeed, by extending the results of the “extreme value theory” (EVT) to the non-stationary case, analyses can examine the presence of trends in extreme values of stochastic processes. Definition of extreme events, their statistical significance as well as their interpretations have to be handled with great care when used for environmental concerns and public safety. Thus, we will discuss the validity of the hypothesis allowing the use of mathematical theories for these problems. To answer safety requirements, respect installation norms and reduce public risk, return levels are a major operational goal, obtained with the EVT. In this paper, we give quantitative results for observations of high temperatures over the 1950–2003 period in 47 stations in France. We examined the validity of the non-stationary EVT and introduced the notion of return levels (RL) in a time-varying context. Our analysis puts particular accent on the difference between methods used to describe extremes, to perform advanced fits and tests (climatic science), and those estimating the probability of rare future events (security problems in an evolving climate). After enouncing the method used for trend identification of extremes in term of easily interpretable parameters of distribution laws, we apply the procedure to long series of temperature measurements and check the influence of data length on trend estimation. We also address the problem of choosing the part of observations allowing appropriate extrapolation. In our analysis, we determined the influence of the 2003 heat wave on trend and return-level estimation comparing it to the RL in a stationary context. The application of the procedure to 47 stations spread over France is a first step for a refined spatial analysis. Working on the behavior of distribution parameters while assessing trend identification is a primary tool in order to classify climatic change with respect to the location of the station and open a systematic work using the same methodology for other variables and multivariate studies.  相似文献   

Comparing GPS-only with GPS + GLONASS positioning in a regional permanent GNSS network   总被引：1，自引：1，他引：1  

Carine Bruyninx 《GPS Solutions》2007,11(2):97-106

Within the regional EUREF Permanent Network (EPN) all positioning is purely based on GPS. This paper investigates, using the Bernese GNSS analysis software, the influence of adding GLONASS observations to the EPN processing using fixed orbits from the International GNSS Service (IGS) as well as from the CODE analysis centre. The GPS-only coordinates and GPS + GLONASS coordinates will be compared and the change in their repeatabilities will be investigated. The influence of the used orbits will also be outlined. The results show that a combined GPS + GLONASS data analysis can be set up without major efforts and that it will not degrade the positions obtained within the EPN.  相似文献