Academic literature on the topic 'Distillation de Rayleigh'

The isotope enrichment of nitrate due to uptake by phytoplankton has previously been measured in a variety of ways, both in the field over time or space, and in vitro. This study provided an unusual opportunity to measure the isotopic fractionation of nitrate over an extended spatial scale. Results are presented from the Otago Continental shelf, New Zealand. δ15N-PON and [NO3–] was correlated using Rayleigh distillation equations to obtain isotope enrichment factors for the uptake of nitrate. The decrease in nitrate concentration during advection landward across the shelf was consistent with removal by phytoplankton, with an average enrichment factor (ϵ) of 8.2 per mil, as calculated using the Rayleigh accumulated product equation. The spatial evolution of δ15N-PON and [NO3–] across the Otago continental shelf led to the conclusion that cross-shelf advection is the predominant process bringing nutrients to the shelf. No Rayleigh distillation-type process is observable from monthly observations. However, in subantarctic surface water (SASW), a seasonal variation in δ15N-PON was seen that was in the opposite phase to that expected for isotopic enrichment of the nutrient pool. In SASW, δ15N-PON peaked at 4‰ in winter months and fell to –2‰ in the spring and summer.

Abstract. The elevation history of the Himalaya–Tibet orogen is central to understanding the evolution and dynamics of both the India–Asia collision and the Asian monsoons. The surface elevation history of the region is largely deduced from stable isotope (δ18O, δD) paleoaltimetry. This method is based on the observed relationship between the isotopic composition of meteoric waters (δ18Op, δDp) and surface elevation, and the assumption that precipitation undergoes Rayleigh distillation under forced ascent. Here we evaluate how elevation-induced climate change influences the δ18Op–elevation relationship and whether Rayleigh distillation is the dominant process affecting δ18Op. We use an isotope-enabled climate model, ECHAM-wiso, to show that the Rayleigh distillation process is only dominant in the monsoonal regions of the Himalayas when the mountains are high. When the orogen is lowered, local surface recycling and convective processes become important, as forced ascent is weakened due to weaker Asian monsoons. As a result, the δ18Op lapse rate in the Himalayas increases from around −3 to above −0.1 ‰ km−1, and has little relationship with elevation. On the Tibetan Plateau, the meridional gradient of δ18O decreases from ∼1 to ∼0.3 ‰ ∘−1 with reduced elevation, primarily due to enhanced sub-cloud reevaporation under lower relative humidity. Overall, we report that using δ18Op or δDp to deduce surface elevation change in the Himalayan–Tibetan region has severe limitations and demonstrate that the processes that control annual-mean precipitation-weighted δ18Op vary by region and with surface elevation. In summary, we determine that the application of δ18O paleoaltimetry is only appropriate for 7 of the 50 sites from which δ18O records have been used to infer past elevations.

Atmospheric rivers (ARs), and frontal systems more broadly, tend to exhibit prominent “V” shapes in time series of stable isotopes in precipitation. Despite the magnitude and widespread nature of these “V” shapes, debate persists as to whether these shifts are driven by changes in the degree of rainout, which we determine using the Rayleigh distillation of stable isotopes, or by post-condensation processes such as below-cloud evaporation and equilibrium isotope exchange between hydrometeors and surrounding vapor. Here, we present paired precipitation and water vapor isotope time series records from the 5–7 March 2016, AR in Bodega Bay, CA. The stable isotope composition of surface vapor along with independent meteorological constraints such as temperature and relative humidity reveal that rainout and post-condensation processes dominate during different portions of the event. We find that Rayleigh distillation controls during peak AR conditions (with peak rainout of 55%) while post-condensation processes have their greatest effect during periods of decreased precipitation on the margins of the event. These results and analyses inform critical questions regarding the temporal evolution of AR events and the physical processes that control them at local scales.

Abstract Austral summer transport of water vapor to the southern South American Altiplano is investigated using in situ measurements of water vapor isotopic composition collected from 1 November 2012 to 10 February 2013 on the Chajnantor Plateau in the Chilean Andes. Onset of the wet season in December was associated with an increase in mixing ratios from an average of 1500 ppmv during the winter dry season to 5400 ppmv in early December. Water vapor isotopes δD and δ18O increased from dry season averages of −235‰ and −31‰, respectively, to wet season averages of −142‰ and −17‰, reaching as high as −70‰ and −17‰, respectively. The highest water vapor δ values were close to those measured in coastal settings, suggesting little condensation during transport to the site. About 5% of the wet season data have δ values that are lower than expected for Rayleigh distillation and are associated with high relative humidity (>75%), easterly winds, and periods of low outgoing longwave radiation over the Altiplano, consistent with moistening by deep convection. The remainder of the data have δ values that are greater than expected for Rayleigh distillation, up to 250‰ above the Rayleigh curve. These data are consistent with mixing between very dry air and moist air from the boundary layer. The data show intraseasonal variability coherently linked to the position of the Bolivian high, with moist air associated with a southward displacement in the Bolivian high. The humidity over the southern Altiplano during the wet season reflects a balance among advective drying, advective moistening with little condensation, and convective moistening.

The genesis of the Zhaxikang Sb-Pb-Zn-Ag deposit remains controversial. Three different geological environments have been proposed to model mineralization: a hot spring, a magmatic-hydrothermal fluid, and a sedimentary exhalative (SEDEX) overprinted by a hot spring. Here, we present the electron probe microanalysis (EPMA) and Fe-Zn isotopic data (microsampled) of four samples from the first pulse of mineralization that show annular textures to constrain ore genesis. The Zn/Cd ratios from the EPMA data of sphalerite range from 296 to 399 and overlap the range of exhalative systems. The δ56Fe values of Mn-Fe carbonate and δ66Zn values of sphalerite gradually decrease from early to late stages in three samples. A combination of the EPMA and isotopic data shows the Fe-Zn contents also have different correlations with δ66Zn values in sphalerite from these samples. Rayleigh distillation models this isotope and concentration data with the cause of fractionation related to vapour-liquid partitioning and mineral precipitation. In order to verify this Rayleigh distillation model, we combine our Fe-Zn isotopic data with those from previous studies to establish 12 Fe-Zn isotopic fractionation models. These fractionation models indicate the δ56Fei and δ66Zni values (initial Fe-Zn isotopic compositions) of the ore-forming system are in the range of -0.5‰​​ ~−1‰ and -0.28‰​ ~0‰, respectively. To conclude, the EPMA data, Fe-Zn isotopic characteristics, and fractionation models support the SEDEX model for the first pulse of mineralization.

Abstract Rain samples were collected for isotopic analyses during the entirety of an extreme rainfall event in Beijing, China, on 21 July 2012, the city’s heaviest rainfall event in the past six decades. Four stages of the storm event have been identified with corresponding isotopic characteristics: 1) isotopes deplete as rain increases, 2) isotopes enrich as rain decreases, 3) isotopes quickly deplete as rain increases, and 4) isotopes remain constant as rain reduces to a small amount. The rainout effect dominates the depletion of isotopic composition in stages 1 and 3. The incursion of a new air mass with enriched heavy isotopes was the main cause for the enriched isotopic composition during stage 2. A Rayleigh distillation model was used to describe the isotopic trends during stages 1 and 3. The Rayleigh distillation model and a binary mixing model were used to estimate the initial isotopic composition of different air masses, which were found to be similar to δ18O of precipitation at nearby Global Network of Isotopes in Precipitation stations representing southwest and southeast trajectories. The results are in agreement with meteorological arrays analysis. This model also indicates that 29% of the initial vapor from the southwest trajectory was precipitated in stage 1, followed by a mixing process between southeast and southwest moisture. In stage 3, up to 56% of mixed moisture was precipitated, among which ~65%–100% was from southeast moisture.

Abstract A simulation of the stable water isotope cycle over South America by the regional circulation model REMOiso is discussed. The performance of the regional model, with a resolution of 0.5° (∼55 km), is compared to simulations by the global circulation model ECHAMiso at two coarser resolutions and evaluated against observations of precipitation and δ18O. Here REMOiso is demonstrated to reproduce reasonably well climatic and isotopic features across South America. This paper explores further insights of δ18O as a climate proxy, based on REMOiso’s improvements as compared to ECHAMiso. In particular, the authors focus on the seasonal variation of the amount effect (δ18O decrease with precipitation amounts) and the anomalous δ18O continental gradient across the Amazon basin, as inferred from the REMOiso, ECHAMiso, and GNIP datasets. The finer resolution of topography in REMOiso enables a detailed analysis of the altitude effect: not only the first, but also the second derivative of δ18O with altitude is considered. It appears that high-altitude grid cells show an isotopic signature similar to Rayleigh distillation, in accordance with experimental studies. Finally, a Lagrangian reference frame is adopted to describe the evolution of δ18O in precipitation along its trajectory, in order to relate the simulation analysis to the fractionation mechanisms. This confirms that the amount effect, via Rayleigh distillation processes, is dominant during the wet season. During the dry season, the δ18O in precipitation is controlled by isotopic reequilibration of rain droplets with surrounding vapor, reflecting the impact of nonfractionating transpiration by the vegetation.

L'utilisation des isotopes du silicium (δ30Si) comme proxy paléocéanographique nécessite une bonne connaissance de la répartition et du devenir des isotopes du silicium à travers l'océan. Au cours des dernières années, des efforts considérables ont été faits pour cartographier la composition isotopique du silicium dissous (acide silicique, DSi) et de la silice biogénique (BSi) dans l'océan. Les diatomées utilisent le DSi pour construire leur frustule fait d’opale (BSi). Durant ce processus, les diatomées discriminent l'isotope lourd de silicium (30Si) en faveur de l'isotope léger (28Si). Ce fractionnement conduit à une BSi qui a un δ30Si inférieur de 1,1 ‰ à 1,5 ‰ par rapport au DSi source. Cela se traduit dans les eaux de surface par de faibles concentrations en DSi en raison de l'utilisation biologique et par des valeurs de δ30Si élevées en raison de la distillation de Rayleigh. Inversement, lorsque la BSi se dissout, il y a une discrimination contre l’isotope lourd et ainsi produit du silicium dissous avec un δ30Si inférieur de 0,55 ‰. Dans le même temps, la circulation océanique et le mélange vertical contribuent à modifier le δ30Si du pool de silicium dissous dans la couche de surface, ce qui complique l'utilisation du δ30Si des diatomées comme proxy pour l’utilisation du DSi durant la saison de croissance. Cette thèse vise à mieux comprendre les processus qui régissent le cycle du silicium et la signature en δ30Si des masses d'eau dans les différentes régions de l'océan. De nouvelles données de δ30Si de silicium dissous sont présentées et discutées. Ces données proviennent de 6 profiles CTD de la campagne ANTXXIII/9 (Atlantique et secteur indien de l'océan Austral), 7 profiles CTD de la campagne ANTXXIV/3 (secteur Atlantique de l'océan Austral), et 5 profiles CTD de la campagne MSM10/1 (région subtropical et tropical de l’océan Atlantique nord). Les échantillons ont été purifiés par chromatographie échangeuse d'ions après préconcentration par précipitation de Mg(OH)2, et le silicium est extrait en utilisant du triéthylamine molybdate. Les analyses isotopiques ont été réalisées sur Spectromètre de Masse Multi-Collection à source Plasma (MC-ICP-MS, Naptune) à moyenne résolution (Ifremer, Brest)
Use of silicon isotopes (δ30Si) as a paleoceanographic proxy requires sound knowledge of the distribution and behaviour of silicon isotopes throughout the ocean. Over the past few years considerable effort has been made to map the silicon isotope composition (δ30Si) of silicic acid (dissolved silicon, DSi) and biogenic silica (BSi) throughout the ocean. Diatoms uptake DSi to build up their opal frustules (BSi). During this process, diatoms discriminate against the heavier isotope of silicon (30Si) in favor of the light isotope (28Si). This fractionation leads to BSi that has a lower δ30Si than the DSi source by 1.1 ‰ to 1.5 ‰. In turn, this results in surface waters with low DSi concentrations due to biological removal, and high δ30Si values due to Rayleigh distillation. Conversely, when the BSi dissolves it is with discrimination against the heavier isotope producing dissolved silicon with a δ30Si lower by 0.55 ‰. At the same time, episodes of upwelling occurring throughout the growing season, ocean circulation and mixing, contribute to modify the δ30Si of the dissolved silicon pool in the surface mixed layer, which complicate the use of diatom δ30Si as a proxy for DSi removal during the growing season. This dissertation aims to better understand the processes driving the Si cycle and the δ30Si signature of water masses in different regions of the ocean. New data of δ30Si of dissolved Si are presented and discussed. These data come from 6 CTD profiles from ANTXXIII/9 campaign (Atlantic and Indian sector of the Southern Ocean), 7 CTD profiles from ANTXXIV/3 (Atlantic sector of the Southern Ocean), and 5 CTD profiles from the campaign MSM10/1 (north Subtropical and Tropical Atlantic Ocean). Samples were purified by ion-exchange chromatography following preconcentration via Mg(OH)2 precipitation and extraction of silicon using triethylamine molybdate. Isotopic analyses were carried on a Neptune MC-ICP-MS at medium resolution (Ifremer, Brest)

Cette thèse propose d'étudier et de résoudre certaines classes d'équations différentielles algébriques (EDAs), intervenant notamment dans le domaine du génie des procédés. Les EDAs sont des systèmes différentiels généraux qui englobent en outre les équations différentielles ordinaires. On met au point dans cette thèse une nouvelle méthode de résolution des EDAs linéaires et quasi-linéaires. Cette méthode, nommée méthode de déflation, est un processus symbolique itératif dont le but consiste à transformer une EDA, pour obtenir soit une équation différentielle sous contraintes, soit un système d'équations algébriques. La méthode de déflation est donnée par le biais d'un algorithme formel ; on analyse les propriétés de ce dernier en détail. Le premier chapitre de cette thèse parcourt les méthodes de résolution des EDAs les plus significatives de la littérature. Ces méthodes de résolution sont présentées et illustrées. Dans le second chapitre, la méthode de déflation est décrite et analysée. On montre notamment le caractère géométrique de la méthode, à savoir qu'elle préserve la géométrie des systèmes étudiés, à travers l'étude des équations modélisant le mouvement d'un pendule simple en dimension n. La méthode de déflation est mise en pratique sur des systèmes mécaniques contraints à corps multiples. On montre également la baisse caractéristique de l'indice de Kronecker durant l'application de la méthode de déflation. Plus précisément, on prouve que l'indice de Kronecker diminue de un entre chaque étape de la méthode. Enfin, nous résolvons formellement dans le troisième chapitre des EDAs quasi-linéaires modélisant des phénomènes de distillation de Rayleigh
This thesis deals with the study and the resolution of several classes of differential algebraic equations (DAEs), especially involved in the process engineering field. DAEs are general differential systems which include ordinary differential equations. We establish in this work a new resolution method for linear and quasilinear DAEs. The method, called the deflation method, is an iterative symbolic process which transforms DAEs into either constrained differential equations or algebraic equations. The deflation method is provided by a symbolic algorithm. We analyse properties of this algorithm in detail. The first chapter of the thesis describes the most significant resolution methods of DAEs known in the actual literature. These methods are presented and illustrated. In the second chapter, the deflation method is studied. We show the geometric aspect of the deflation method (the method preserves the geometry of the studied systems) through the study of the equations of the n-pendulum. The deflation method is used on constrained multibody systems. We also show how the Kronecker index decreases during the application of the method. In the last chapter, we solve quasilinear DAEs provided by Rayleigh distillation models