Дисертації з теми "Ca isotope"
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1
Chang, Veronica Tzu-Chun. "Mg and Ca isotope fractionation during CaCO₃ biomineralisation." Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269953.
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Thériault, Réginald J. "Evolution of the ca. 1.9 gallium Taltson magmatic zone, Northwest Territories: A neodymium isotope perspective." Thesis, University of Ottawa (Canada), 1990. http://hdl.handle.net/10393/5788.
Повний текст джерелаАнотація:
The Taltson magmatic zone is a north-trending belt of Early Proterozoic granitoids exposed over an area exceeding 18,000 km$\sp2$ in the Northwest Territories. Three petrologically and chronologically distinct intrusive suites comprise the Taltson zone. These are the 1986 Ma Deskenatlata suite, the 1955 to 1925 Ma Slave suite and the 1935 Ma Konth suite. The Deskenatlata suite is composed of a biotite-hornblende diorite to granite suite whose major and trace element chemistry supports derivation by arc magmatism. The Slave and Konth suites are leucocratic granitoids which contain numerous xenoliths of dominantly pelitic high grade paragneiss and display S-type granite mineralogy which commonly duplicates that of the pelitic gneisses. Bulk rock chemistry for the Konth suite is consistent with a homogeneous crustal magma source whereas the Slave suite is compositionally more heterogeneous. The Deskenatlata suite is considered as continental arc-derived granitoids resulting from eastward subduction of oceanic lithosphere beneath the Churchill Province. The Slave suite is regarded as the result of melting of various segments of heterogeneous Archean crust whereas the Konth may have evolved exclusively from melting of pelitic metasediments. (Abstract shortened by UMI.)
3
MacDonald, Cody J. "Hydrothermal Circulation During Slip on the Mohave Wash Fault, ChemehueviMountains, SE CA: Oxygen Isotope Constraints." Ohio University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1405810104.
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Feasby, Rebecca Susanne Godkin. "Stable isotope evidence for dietary patterns and environmental conditions at Tell Leilan, Syria, ca. 1900-2900 B.C." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ28891.pdf.
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Marriott, Caedmon. "Lithium and calcium isotope fractionation and Li/Ca ratio incorporation into calcium carbonate as potential geochemical proxies." Thesis, University of Oxford, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.418477.
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Du, Vivier Alice Diana Charlotte. "Global evaluation of Os and Ca marine isotope stratigraphy and U-Pb geochronology of the OAE 2." Thesis, Durham University, 2014. http://etheses.dur.ac.uk/10649/.
Повний текст джерелаАнотація:
Oceanic anoxic events occur in response to significant climate perturbations. This study focuses on the late Cretaceous OAE 2, which occurred across the Cenomanian-Turonian boundary (CTB), ~93.9 Ma. Multiple isotope proxies have reviewed the implications of palaeocirculation, volcanism and climate change to assess the driving mechanism(s) associated with global anoxia. Utilising geochemistry and geochronology (Os, Ca and U-Pb) this study provides a greater understanding of palaeoclimate conditions and assesses the global extent of anoxia. Hitherto, analyses have focussed on sections in and around the proto-North Atlantic. Herein, high-resolution 187Os/188Os isotope stratigraphy from 8 globally representative sections is presented; Portland #1 core, Site 1260, Wunstorf, Vocontian Basin, Furlo, Site 530, Yezo Group, and Great Valley Sequence. The Re-Os system is sensitive to regional and global variation in seawater chemistry on the order of the residence time of Os due to ocean inputs: radiogenic Os from continental weathering and unradiogenic Os from hydrothermal inputs. The initial 187Os/188Os (Osi) profiles present a globally ubiquitous trend: radiogenic Os values are attenuated by unradiogenic Os for ~200 kyr, which then gradually return to radiogenic Os. Minor discrepancies illustrate the sensitivity of local water masses as a function of basin connectivity and global sea level; i.e., Portland, Great Valley Sequence and Yezo Group (temporally restricted basins) vs. Site 1260 and Site 530 (open ocean). Furthermore, a temporal framework is developed from existing ages (from the Western Interior, USA) and new U-Pb zircon geochronology (Yezo Group, Japan) to quantify the duration of OAE 2 and volcanic activity at the Caribbean LIP. Age models are applied and support the revision of the stratigraphic position of the OAE 2 onset and the CTB in the Yezo Group. The integration of the Western Interior and Pacific geochronology quantitatively verifies that the OAE 2 was globally synchronous occurring at ~94.4 Ma ± 0.15 Ma. In addition, marine δ44Ca records from 4 global OAE 2 sections are presented. The seawater mixing models reveal that δ44Ca values show no appreciable change to riverine or hydrothermal influx. Herein, I quantitatively demonstrate that fractionation is a parameter for δ44Ca isotopic variation at Portland and Pont d’Issole, which may be attributed to diagenetic reactions in the marl-rich lithology leading to site-specific fractionation. Therefore, marine δ44Ca profiles are different in each section as a function of varying fractionation factor. Ca isotope systematics are highly complex and so further work is crucial in order to develop our understanding of other parameters and to establish which, if any, is the most influential.
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Wogsland, Brittan Valhalla. "Organomineralization of Microbialites from Storr’s Lake, San Salvador Island, Bahamas: Calcium Stable Isotope Analysis using TIMS and a 42Ca-43Ca double spike." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1587723502946554.
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Horowitz, Michael (Michael Joshua) 1962. "Western South Atlantic holocene and glacial deepwater hydrography derived from benthic foraminiferal Cd/Ca and stable carbon isotope data." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/69183.
Повний текст джерелаАнотація:
Thesis (S.M.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1999.Includes bibliographical references (leaves 16-21).
Today, deep waters produced in the North Atlantic are exported through the western South Atlantic. Antarctic intermediate water (AAIW) also enters the Atlantic in this region. Circumpolar deep water (CDW) fills the depths below AAIW and above and below northern source waters. A depth transect of cores from 1567-3909 m water depth in the western South Atlantic are ideally located to monitor inter-ocean exchange of deep water, and variations in the relative strength of northern versus southern source water production. Last glacial maximum (LGM) Cd/Ca and 813C data indicate a nutrient-depleted intermediate-depth water mass. In the mid-depth western South Atlantic, a simple conversion of LGM 813C data suggests significantly less nutrient enrichment than LGM Cd/Ca ratios, but Cd/Ca and 613C data can be reconciled when plotted in CdW/ 13C space. Paired LGM Cd/Ca and S13C data from mid-depth cores suggest increasingly nutrient rich waters below 2000 m, but do not require an increase in Southern Ocean water contribution relative to today. Cd/Ca data suggest no glacial-interglacial change in the hydrography of the deepest waters of the region. To maintain relatively low Cd/Ca ratios (low nutrients) in the deepest western South Atlantic waters, and in CDW in general, during the LGM requires an increased supply of nutrient-depleted glacial North Atlantic intermediate water (GNAIW) and/or nutrient-depleted glacial Subantarctic surface waters to CDW to balance reduced NADW contribution to CDW. LGM Cd/Ca and 513C data suggest strong GNAIW influence in the western South Atlantic which in turn implies export of GNAIW from the Atlantic, and entrainment of GNAIW into the Antarctic Circumpolar current.
by Michael Horowitz.
S.M.
9
Perez, Fernandez Andrea. "Etude expérimentale sur l'échange isotopique dans le système eau-roches carbonatées." Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30398.
Повний текст джерелаАнотація:
Les signatures isotopiques des minéraux carbonatés sont utilisées pour caractériser de nombreux processus géochimiques. Cette thèse a pour but de déterminer les vitesses auxquelles ces signatures isotopiques peuvent être altérées lors des interactions entre les fluides et les minéraux. A cette fin, une série d'études expérimentales a été conduite avec la dolomite (CaMg(CO3)2), la magnésite (MgCO3) et la calcite (CaCO3). On a mesuré l'évolution temporelle des compositions isotopiques de Ca et Mg pendant une série d'expériences de dissolution en réacteur fermé de la dolomite à des températures de 50°C à 126°C. A T < 120°C la composition isotopique du calcium dans la phase fluide est identique à celle de la dolomite initiale, mais au-delà de cette température, la signature isotopique du calcium dans le fluide (delta(44/42)Ca fluid) après 4 semaines était 0.6±0.1‰ plus lourde que l'originale. En revanche, le rapport delta(26/24)Mg du fluide reste égal à celui de la dolomite à toutes les températures étudiées. Ces résultats indiquent un double transfert de calcium vers et depuis la structure de la dolomite à T > 120°C. En outre, ces résultats suggèrent que la difficulté de la dolomite à précipiter à température ambiante doit être la conséquence de l'incapacité de Mg à s'incorporer dans la structure du minéral. Dans une autre étude on a conduit des expériences de dissolution de la magnésite à 25°C en solution aqueuses pour différents pH et pression de CO2. On a trouvé que la composition isotopique du fluide à proximité de l'équilibre chimique était différente de celle du solide, ce qui reflète un double transfert de Mg en direction et hors du minéral à température ambiante. Cependant, un seul mécanisme de fractionnement ne peut expliquer le comportement isotopique de Mg observé. La dernière partie de ce travail, consacrée au fractionnement isotopique du carbone dans le système calcite-eau, montre une évolution du fractionnement isotopique de cet élément vers le fractionnement isotopique à l'équilibre d'une durée d'une année après l'atteinte de l'équilibre chimique entre la calcite et l'eau. Les vitesses de rééquilibrage des isotopes de carbone sont ainsi quatre ordres de grandeurs plus lentes que la vitesse d'équilibrage de la calcite avec la solution. Ceci suggère que l'étape limitante dans le processus de rééquilibrage des isotopes du carbone est le transport de cet élément dans le cristal après l'échange isotopique à la surface de ce dernier. Les résultats de cette thèse indiquent que la signature isotopique de Mg, Ca et C des carbonates n'est pas invariante à l'échelle des temps géologiques et qu'elle peut être altérée durant l'interaction de ces minéraux avec l'eau. Ainsi, la préservation des signatures isotopiques des carbonates requiert d'une faible perméabilité des roches ou bien quelque mécanisme inhibant les échanges des métaux et du carbone à la surface des cristauxThe isotopic signatures of carbonate minerals have been applied to illuminate a plethora of natural geochemical processes. This thesis is aimed to assess the rates and or conditions at which such isotope signatures might be altered by fluid-mineral interaction through a series of systematic experimental studies performed with dolomite (CaMg(CO3)2) magnesite (MgCO3) and calcite (Ca-CO3). Ca and Mg isotopic compositions were measured as a function of time during closed-system stoichiometric dolomite dissolution experiments at 50 to 126°C. Although identical to that of the original dolomite at low temperatures, at temperatures >120 °C, the calcium isotopic signature of fluid phase (delta(44/42)Ca fluid) became 0.6±0.1‰ higher than that of the dissolving dolomite over a 4-week period. In contrast, the delta(26/24)Mg fluid, remained equal to that of the dolo-mite both at low and high temperatures. This set of experiments evidences the two-way transfer of calcium in and out of the dolomite structure at elevated temperatures. The results suggest that the inhability of dolomite to precipitate at these conditions is due to the difficulty of Mg to be reincorporated in the dolomite structure. In a follow-up study, magnesite was dissolved at 25°C in the presence of fluids with distinct pH and CO2 pressures. The isotopic compositions of the fluid differed from that of the solid at near-to chemical equilibrium indicating the two-way transfer of magnesium into this mineral at ambient temperatures. A single fractionation mechanism cannot explain the distinct Mg isotope behaviors observed. Further work on carbon isotope exchanges in the calcite water system shows a slow by steady evolution of the carbon isotopic composition towards the accepted equilibrium fractionation factor over the course of nearly year-long experiments after the system had attained bulk chemical equilibrium. Carbon isotope reequilibration rates were found to be approximately four orders of magnitude slower than that of bulk calcite dissolution, suggesting that the rate limiting step to the carbon isotope reequilibration process is the transport of carbon into and out of the bulk mineral after it has exchanged on the surface. The results of this thesis suggest that the Mg, Ca and C isotopic signatures in carbonate minerals are not invariant over geological time-frames and can be readily altered by water-mineral interaction. Such results indicate that the preservation of carbonate mineral signatures require low permeability rock formations or some inhibitory mechanism limiting metal and carbon exchange
10
Bright, Jordon, and Jordon Bright. "Multi-Disciplinary Paleoenvironmental Context for the Integration of the Lower Colorado River Corridor, Bouse Formation, CA-AZ, USA, and Middle to Late Pleistocene Human Evolution, the Koora Plain, Southern Kenya." Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/625880.
Повний текст джерелаАнотація:
Since the seminal works of Wegener and Darwin the notion that things evolve, and the how and the why of it, has generated intense debate. The surface of the Earth, and the creatures that live on it, are not static entities. Landscapes evolve. Organisms evolve. Understanding the how and the why requires a firm understanding of a myriad of interdependent and complex variables such as (but not limited to) climate, ecology, and tectonics. Unravelling the complexities though which landscapes and ecosystems evolve requires a broad interdisciplinary approach, where multiple investigative tools are simultaneously brought to bear on a given question. The study of old lake sediments, or paleolimnology, is a marquee example of a powerful interdisciplinary methodology that has been used extensively in reconstructing the Earth's past.
This work showcases two examples where the discipline of paleolimnology advances our understanding of evolution on a landscape scale and on a human scale. In the southwestern United States, a record of the processes involved during the late Miocene and early Pliocene (~ 5 Ma) evolution of a major continental river drainage - the Colorado River – is partially preserved along the southern border of Arizona and California as the enigmatic Bouse Formation. And in southern Kenya, nearly 170 meters of lake and wetland sediments that have accumulated in the Koora Plain preserve a one-million-year long record of the environmental conditions against which our species, Homo sapiens, evolved.
My research allows me to conclude that the depositional environment of the Bouse Formation was lacustrine; a fully marine interpretation that has been previously proposed is untenable. I also demonstrate that over the past 1.0 Ma, Homo sapiens in southern Kenya evolved against a backdrop of increasing regional aridity.
11
Skinner, Luke Cameron. "Millennial climate change in the Northeast Atlantic : the role of surface- and deep hydrographic change determined by stable isotope geochemistry and MG/CA palaeothermometry." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615838.
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Court, Mélanie. "Étude des cycles du Ca et Mg dans cinq hêtraies du nord de la France et des modifications induites par un amendement calco-magnésien : utilisation combinée des approches élémentaires et isotopiques (δ26/24Mg, δ44/40Ca et 87Sr/86Sr)". Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0248/document.
Повний текст джерелаАнотація:
De nombreux écosystèmes forestiers français sont développés sur des sols acides et pauvres en éléments nutritifs. Dans de nombreux contextes, la fertilité minérale de ces sols forestiers se dégrade lentement, en lien notamment avec des pressions extérieures passées ou actuelles (e.g. diminution des apports atmosphériques de nutriments, augmentation des exportations de biomasse). Ce constat préoccupe la communauté forestière et des solutions de restauration/remédiation sont souvent envisagées. L’amendement avec un produit carbonaté est une pratique connue pour réduire l'acidité du sol, améliorer le fonctionnement global de l'écosystème et compenser les pertes de nutriments causées par la récolte de biomasse. Cependant, les effets de l’amendement sur les processus et le cycle biogéochimique du calcium et magnésium dans les écosystèmes forestiers sont peu connus à ce jour. Cette étude se focalise sur le devenir du magnésium et du calcium provenant de la dissolution des produits d’amendement dans cinq hêtraies situées dans le nord de la France sur une période allant jusqu’à 45 ans après l’apport. Pour cela, les approches élémentaires « conventionnelles » ont été combinées avec une approche multi-isotopique (26/24Mg, 44/40Ca et 87/86Sr). Les données provenant des parcelles témoins mesurées tout au long de la période d'étude suggèrent, quel que soit le site considéré, que les pools échangeables de cations nutritifs dans le sol ont diminué sur les dernières décennies et que cette tendance, associée à la faible richesse chimique du sol, se reflète dans la nutrition foliaire (Ca, Mg, K, P). En comparaison des placettes témoins, les pools échangeables de Mg et de Ca dans l’horizon 0-40 cm du sol ont augmenté dans les placettes amendées durant la première décennie après l’amendement, mais les différences s’estompent après 20 à 30 ans. Cependant, l'effet de l’amendement sur la nutrition des arbres est encore observé 40 ans après l’apport, très probablement parce que le cycle biologique de ces éléments a été dynamisé par l’amendement. La réponse des écosystèmes à l’amendement varie d'un site à l'autre, en fonction de la nature du produit (CaCO3 ou Ca-MgCO3) et du niveau de richesse chimique initial du sol, les sites les plus pauvres chimiquement enregistrant les réponses les plus marquées. Les variations naturelles des rapports isotopiques du Mg, Ca et Sr, en complément des approches conventionnelles, mettent en évidence l’importance de la composante Bio des cycles biogéochimiques du Ca et Mg dans ces hêtraies à faible fertilité minérale. Ces outils isotopiques ont également permis de démontrer l'incorporation durable de Ca et Mg issus des produits d’amendement dans leur cycle biologique respectif et de mettre en évidence des modifications de fonctionnement biogéochimique des écosystèmes suite à l’amendementIn France, many forest ecosystems grow on acidic and nutrient poor soils. In numerous cases, the chemical fertility of forest soils is slowly degrading due to increasing external pressures (e.g. decreasing atmospheric inputs, increasing biomass exportations) and is a growing concern in the international forest community. Forest management often must resort to restauration/remediation practices to ensure the sustainability of the ecosystem. Forest liming with a carbonate product is a known practice to reduce soil acidity, globally improve the ecosystem functioning and compensate nutrient losses caused by biomass harvest and exportation. However, our understanding of the effects of liming on magnesium and calcium biogeochemical processes and cycling in forest ecosystems is still incomplete. This study focuses on the fate of magnesium and calcium originating from the dissolution of liming products in the soils and trees of five beech forests located in Northern France over a period up to 45 years. In order to do so, “conventional” total-element approaches were combined with a multi-isotopic approach (26/24Mg, 44/40Ca et 87/86Sr). At all five sites, the data measured in control plots throughout the study period suggest that the exchangeable pools of nutrient cations in the soil has decreased over the last several decades and that this trend, together with the low chemical fertility level of the soil, was reflected in foliar nutrition (Ca, Mg, K, P). Compared to the control plots, soil exchangeable pools of Mg and Ca in the 0-40cm layer in the limed plots increased during the first decade after liming but differences were no longer observable in soil pools after 20 to 30 years. However, the effect of liming on tree nutrition was still observed after 40 years, most probably because the biological cycling of these elements was enhanced by the lime input. The ecosystem response to the lime input varied between sites depending on the nature of the liming product (CaCO3 or Ca-MgCO3) and the initial chemical fertility level of the soil, the poorest sites showing the strongest responses. The natural variations of Mg, Ca and Sr isotopic ratios combined with conventional approaches highlight the importance of the BIO component of the biogeochemical cycling of Mg and Ca in the studied low chemical fertility beech forests. These isotopic tools also enabled to show the long-lasting incorporation of the Mg and Ca released from the liming product in the biological cycle and highlight the changes in the biogeochemical functioning of these forest ecosystems after the liming operation
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Perretti, Adriana Rodrigues. "Avaliação da aplicação associada dos dados de δ18O e da razão Mg/Ca de foraminíferos como uma ferramenta paleoceanográfica." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/21/21133/tde-07062011-142829/.
Повний текст джерелаАнотація:
O objetivo do presente estudo é avaliar o uso associado dos proxies ?18O e Mg/Ca obtidos em testas de foraminíferos. Para alcançar tal objetivo foram realizadas análises de ?18O e Elemento/Ca em amostras de foraminíferos planctônicos (G. ruber e G. sacculifer) e bentônicos (Cibicidoides spp., C. corpulentus, Uvigerina spp. e H. elegans) de dois testemunhos do Atlântico Sul. Os resultados demonstraram que apesar dos proxies ?18O e Mg/Ca apresentarem perfis distintos em relação às espécies os mesmos se correlacionam de forma apropriada, sendo possível estimar a temperatura e os sinais de ?18OSW e ?18OLocal a partir dos mesmos. A partir dos dados de temperatura estimados com base em Mg/Ca foi possível identificar uma anomalia negativa das águas superficias entre o LGM e o HL de -1,5 ± 0,2 °C, enquanto que nas águas profundas observou-se uma anomali positiva de 1,7 ± 0,4 °C para o mesmo período. Os dados de ?18OSW estimados com base nos dados de temperatura e ?18O indicaram uma oscilação de 1,0 ± 0,1 ? e 2,0 ± 0,2 ? para as espécies planctônicas e bentônicas durante o LGM e o HL. Segundo o valor esperado para a variação do volume de gelo (~1,2 ?) há uma oscilação muito baixa da salinidade nas águas superficias da região de estudo, em contraste com uma oscilação bem marcada da salinidade nas águas de fundo. As estimativas de ?18OLocal indicaram uma oscilação entre o LGM e o HL muito pequena da salinidade (~0,1 ?) nas águas superficiais, com uma oscilação maior nas águas de fundo (1,0 ± 0,3 ?). O aumento da salinidade das águas de fundo durante o LGM corrobora a anomalia positiva da temperatura observada neste estudo, visto que, para a ocorrência da mesma, é necessário que a densidade das águas de fundo seja suficiente para manter a estratificação da coluna de água.The goal of this study is to evaluate the associated use of the proxies ?18O and Mg/Ca, both analyzed in foraminifera tests. ?18O and trace metals analyses were performed in order to achieve this purpose on samples of planktonic (G. ruber and G. sacculifer) and benthic (Cibicidoides spp., C. corpulentus, Uvigerina spp. and H. elegans) species of foraminifera from two cores from South Atlantic. Despite of the fact that the proxies used on this study present distinct fits within the species they correlate very well, being possible to estimate the values of temperature, ?18OSW and ?18OLocal. Based on the temperature estimated by Mg/Ca it was possible to identify a negative anomaly of -1,5 ± 0,2 °C between the LGM and HL, meanwhile a positive anomaly of 1,7 ± 0,4 °C was observed in the deep waters for the same period. The ?18OSW data estimated by temperature and ?18O indicate an oscilation of 1,0 ± 0,1 ? and 2,0 ± 0,2 ? for planktonic and benthic species between the LGM and the HL. Based on the literature value for the ice volume signal (~1,2 ?) the superficial waters of the study area indicated a very low salinity oscilation, opposite to the high salinity oscillation in the deep waters. The ?18OLocal estimatives exhibited a very weak salinity oscillation between LGM and HL in the superficial waters (~0,1 ?), providing a much more strong oscilation in the deep waters (1,0 ± 0,3 ?). The salinity increase during the LGM in the deep waters establish the validity of the positive temperature anomaly observed in this study, since the density of the deep water needs to be adequate to maintain the water column stratification.
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Gangloff, Sophie. "Evaluation of the mechanisms of trace elements transport (Pb, Rare Earth Elements,... ) and the elemental and isotopic fractionation (Ca and Sr) at the interface water-soil-plant." Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAH002/document.
Повний текст джерелаАнотація:
Ce travail est axé sur l’étude d’un profil de sol et des solutions de sol prélevés sur une parcelle expérimentale couvertes d’épicéas. Tous ces échantillons proviennent du Bassin Versant du Strengbach (Observatoire HydroGéochimique de l’Environnement – OHGE), ont été échantillonnés à différentes profondeurs (5, 10, 30 et 60 cm) et durant la période comprise entre 2009 et 2013.Les caractérisations des extraits des sols par spectroscopie Infra-Rouge ont permis de mettre en évidence les modifications des groupements fonctionnels organiques avec la profondeur et que ces modifications ont une forte incidence sur le comportement des cations (majeurs et traces) dans le sol. Des expérimentations d’ultra-filtration ont permis d’identifier les flux colloïdaux et dissous du carbone organique ainsi que ceux des éléments majeurs et traces présents dans les solutions de sol. L’utilisation conjointe des traceurs isotopiques (87Sr/86Sr et δ44/40Ca) et chimiques (Terres Rares) ont mis en évidence des processus ayant lieu aux interfaces eau-sol-plante, comme le prélèvement racinaire ou l’altération des solsThis work is focused on the study of a profile of soil and soil solutions collected on an experimental plot covered with spruce. All these samples come from the watershed of the Strengbach (environment - OHGE Hydrogeochimique Observatory), were sampled at different depths (5, 10, 30 and 60 cm) and during the period between 2009 and 2013. Characterizations of soil extracts by infrared spectroscopy allowed to highlight changes in the organic functional groups with depth and that these changes have a significant impact on the behaviour of the cations (major and trace) in the soil. Ultrafiltration experiments helped to identify flows of colloidal and dissolved organic carbon as well as those of the major and trace-element present in soil solutions. The joint use of isotope tracers (87Sr / 86Sr and δ44 / 40 Ca) and chemical (Rare Earth Elements) have highlighted processes taking place at the water-soil-plant interface, as the uptake by root or soil alteration
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Brazier, Jean-Michel. "Rôle des phases minérales des sols en tant que réservoirs de nutriments : approche expérimentale (abiotique), en milieu naturel et multi-isotopique (isotopes stables Ca-Sr)." Thesis, Strasbourg, 2018. http://www.theses.fr/2018STRAH005/document.
Повний текст джерелаАнотація:
Ce travail de thèse a appréhendé les mécanismes de stockage/libération, d’un point de vue élémentaire et isotopique, du calcium (Ca) et du strontium (Sr) sur ou dans des phases minérales communes des sols (minéraux primaires, minéraux argileux, oxy-hydroxydes, carbonate pédogénétiques). Une méthode de mesure robuste du δ88Sr a dû être développée et validée par la mesure de matériaux de références internationaux, pour la plupart jamais mesuré dans la littérature. Les résultats montrent que l’adsorption du Ca sur des minéraux phyllosilicatés génère un fractionnement isotopique par prélèvement préférentiel de l’isotope léger (40Ca) dans nos conditions expérimentales lorsque les minéraux possèdent une charge structurale et une surface spécifique importante et/ou un espace interfoliaire ouvert à l’adsorption de cations hydratés. Une étude sur des rhizolithes en milieu naturel a mis en avant que l’utilisation des isotopes du Ca et du Sr permet un traçage de source et de mécanismes efficaces dans les thématiques touchant au stockage de ces deux éléments dans les solsThis PhD thesis examined the mechanisms of storage and release, from and elementary and isotopically point of view, of calcium (Ca) and strontium (Sr) onto or into mineral phases commonly encountered within soils (primary minerals, clay minerals, oxy-hydroxides, pedogenic carbonate). A robust δ88Sr measurements method had to be developed in the laboratory and validated by the measurement of international reference materials, mostly never measured in the literature. The results of this work show that Ca adsorption onto phyllosilicate minerals generates a quantifiable isotopic fractionation by preferential uptake of the light isotope (40Ca) under our experimental conditions when the minerals have a significant structural charge and specific surface area and/or an interlayer space open to hydrated cations adsorption. A study on rhizoliths in natural environment has also highlighted that the combination of Ca and Sr isotopes allows an effective tracing of sources and mechanisms in the problematic related to the storage of these two elements within soils
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Einloth, Sharon L. "Intrinsic Isotopic Tracers as Independent Evaluators for China Lake Basin, CA." Thesis, The University of Arizona, 2000. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu_etd_hy0204_sip1_w.pdf&type=application/pdf.
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Heuser, Alexander. "Variations of calcium isotopes (d44Ca) [delta 44 Ca] in foraminifers over the past 24 Ma." [S.l.] : [s.n.], 2002. http://e-diss.uni-kiel.de/diss_713/d713.pdf.
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Montanari, D. "Reaction dynamics of neutron rich nuclei in Ca isotopes with heavy ions and gamma spectroscopy." Doctoral thesis, Università degli Studi di Milano, 2010. http://hdl.handle.net/2434/152526.
Повний текст джерелаАнотація:
The thesis work concerns the experimental study of the population and gamma-decay of n-rich nuclei around 48Ca using deep-inelastic collisions (DIC) on 64Ni, at energies ~2.5 times above the Coulomb barrier. The experiment has been performed at the INFN Laboratori Nazionali di Legnaro (Padova), with an experimental setup consisting of the CLARA Ge array coupled to the PRISMA magnetic spectrometer. DIC are proved to be a powerful tool to study nuclear properties far from stability, while the study of the reaction dynamics is a starting point for extracting nuclear structure information.
A large fraction of the work consists in a careful evaluation of the response of the PRISMA magnetic spectrometer, which is here done for the first time. The response is calculated on basis of a Monte Carlo simulation of the transport of the ions into the spectrometer, making use of a ray tracing code procedure which uses numerical integrators to determine the trajectories into the magnetic fields.
The experimental results concern in a detailed investigation of the reaction properties, such as total cross sections and angular distributions of the most relevant transfer channels. In particular, angular distributions are extracted both energy integrated and in coincidence to specific nuclear states, such as transitions to the ground state and the first excited states.
The results are compared with predictions from the semiclassical multi-nucleon transfer model, which is found to reproduce well the data corresponding to 0p, -1p and +1p channels. In addition, in the case of the 0 p, +/- 1p and +/- 1n channels, angular distributions of the first excited states are interpreted in terms of DWBA calculations, providing information on spectroscopic factors and particle-vibration coupling.
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DeLong, Kristine L. "Reconstructing 20th century SST variability in the southwest pacific : a replication study using multiple coral Sr/Ca records from New Caledonia." [Tampa, Fla] : University of South Florida, 2006. http://purl.fcla.edu/usf/dc/et/SFE0001734.
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Denk, Eberhard. "Evaluation of ⁴¹Ca as a novel isotopic tool to assess the impact of diet on bone health /." Zürich : ETH, 2006. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=16416.
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Sans-Jofre, Pierre. "L' environnement post-marinoen (ca. 635 ma) : une étude multi-proxy de la plateforme carbonatée du Groupe d'Araras (Mato Grosso, Brésil)." Paris 7, 2011. http://www.theses.fr/2011PA077166.
Повний текст джерелаАнотація:
De nombreux sédiments glaciaires déposés à basses latitudes durant le Néoprotérozoïque ont mené à l'hypothèse d'un englacement complet du globe terrestre. La sortie de cet état climatique extrême aurait été engendrée par un effet de serre intense. Ce travail repose sur le croisement d'études sédimentologique, géochimique, magnétique et isotopique sur des sédiments de la plateforme carbonatée d'Araras contemporaine de la transgression postglaciaire Marinoenne. Les résultats révèlent une régression du niveau marin qui atteint son maximum à la fin du dépôt des cap-dolomies, qui est suivit par une période transgressive. Une étude des conditions redox de dépôt basée sur des analyses de concentrations en éléments traces, de minéralogie magnétique et de spéciation du fer, indique des conditions de dépôt oxydantes au sein du sédiment, qui deviennent progressivement réductrices quand la profondeur de dépôt augmente. Les compositions isotopiques en carbone et multi-isotopique du soufre suggèrent que la transgression postglaciaire s'accompagne d'un épuisement de la colonne d'eau en sulfate, du à une augmentation conjointe de la productivité primaire et de la sulfato-réduction bactérienne. Pour l'atmosphère post-Marinoenne, des analyses de compositions isotopiques du carbone des carbonates et de la matière organique qui y est associée ont permis d'estimer une concentration en CO2 maximale de 3200 ppmv. Cette concentration est bien inférieure à celle prédite par les modèles pour permettre la fonte des glaces mais est plus cohérente avec la pO2 atmosphérique attendue pour le Néoprotérozoïque et les conditions de pH des océans favorables à la précipitation des carbonatesThe occurrence of low latitude glacial deposits in the Neoproterozoic is the basis of the Snowball Earth hypothesis, which postulates the planet had been completely covered by ice. The recovery from such an extreme climatic state would occur through an extreme greenhouse event. In this thesis we have combined sedimentological studies, geochemistry, magnetic methods and isotopic studies to investigate the Neoproterozoic carbonate platform of Araras, which is correlated to the Marinoan post-glacial successions. Five sections were sampled across the platform. Our results show that the dolomitic succession in the inner shelf sections is deposited in a progressive context, being then covered by transgressive limestones. Redox conditions were deduced from an integrated study, combining trace elements, magnetic mineralogy and iron speciation, which indicate oxic conditions in the shallower facies and relatively more reduced conditions at deeper facies. Multi-isotopic analyses of sulfur and carbon suggest that the end of the glacial event and the post-glacial transgression is accompanied by depletion in the sulfur reservoir, due to the increase in both primary productivity and bacterial sulfate reduction. Carbon isotopic composition of carbonate and associated organic matter in the cap carbonates indicate a maximum CO2 atmospheric concentration of 3200 ppmv. This concentration is coherent with Oa concentrations for the Neoproterozoic and with the ocean pH necessary for the widespread deposition of carbonate successions by that time. Yet, it is significantly lower than that predicted by numerical models of deglaciation
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Stephans, Christie L. "Assessing the Reproducibility of Coral-based Climate Records: A Multi-proxy Replication Test using Three Porites lutea Coral Heads from New Caledonia." [Tampa, Fla.] : University of South Florida, 2003. http://purl.fcla.edu/fcla/etd/SFE0000165.
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Schimmelpfennig, Irene. "Cosmogenic [36]Cl in Ca and K rich minerals : analytical developments, production rate calibrations and cross calibration with [3]He and [21]Ne." Aix-Marseille 3, 2009. https://tel.archives-ouvertes.fr/tel-00468337.
Повний текст джерелаАнотація:
Les taux de production du nucléide cosmogénique [36]Cl par spoliation du Ca et du K (SLHL) proposés actuellement dans la littérature montrent des divergences allant jusqu'à 50% (e. G. Gosse and Phillips, 2001). Nous avons pu montrer que des fortes teneurs en Cl dans les roches utilisées pour les calibrations précédentes entraînent une surestimation de ces taux de production, lié à la production de [36]Cl à partir du [35]Cl qui est peu contrainte. Nous avons entrepris une nouvelle calibration à partir de laves datées indépendamment entre 0. 4 et 32 ka situées au Mt Etna (38°N, Italie) et au Payun Matru (36°S, Argentine). Le [36]Cl a été mesuré dans des feldspaths riches en Ca et en K, mais faibles en Cl. A partir d'une approche bayesienne incluant toutes les incertitudes, les taux de production obtenus sont de 42. 2 ± 4. 8 atomes [36]Cl (g Ca) / an pour la spallation du Ca et de 124. 9 ± 8. 1 atomes [36]Cl (g K) / an pour la spallation du K, avec les facteurs d'échelle calculés selon Stone (2000). Quatre autres modèles de facteurs d'échelle sont également proposés avec des résultats très semblables. Ces nouveaux taux de production sont en accord avec les valeurs précédemment obtenues par d'autres auteurs avec des échantillons faibles en Cl. Finalement, les concentrations en [36]Cl, [3]He et [21]Ne ont été mesurées dans des pyroxènes prélevés entre 1000 et 4300 m dans des laves du Kilimandjaro (3°S). Les rapports entre ces nucléides ne montrent pas de dépendance altitudinale, ce qui suggère que les taux de production ne varient pas d'un nucléide à l'autre avec l'altitudePublished cosmogenic [36]Cl SLHL production rates from Ca and K spallation differ by almost 50% (Gosse and Phillips, 2001). The main difficulty in calibrating [36]Cl production rates is to constrain the relative contribution of the various production pathways, which depend on the chemical composition of the rock, particularly on the Cl content. Whole rock [36]Cl exposure ages were compared with [36]Cl exposure ages evaluated in Ca-rich plagioclases in the same independently dated 10 ± 3 ka lava sample taken from Mt. Etna (Sicily, 38° N). Sequential dissolution experiments showed that high Cl concentrations in plagioclase-grains could be significantly reduced after 16% dissolution yielding [36]Cl exposure ages in agreement with the independent age. Stepwise dissolution of whole rock grains, on the other hand, is not as effective in reducing high Cl concentrations as it is for the plagioclase. 330 ppm Cl still remains after 85% dissolution. The [36]Cl exposure ages are systematically about 30% higher than the ages calculated from the plagioclase. We could exclude contamination by atmospheric or magmatic [36]Cl as an explanation for this overestimate. High Cl contents in the calibration samples used for several previous production rate studies are most probably the reason for overestimated spallation production rates from Ca and K. This is due to a poorly constrained nature of [36]Cl production from low-energy neutrons. We used separated minerals, very low in Cl, to calibrate the production rates from Ca and K. [36]Cl was measured in Ca-plagioclases collected from 4 lava flows at Mt. Etna (38° N, Italy, altitudes between 500 and 2000 m), and in K-feldspars from one flow at Payun Matru volcano (36° S, Argentina, altitudes 2300 and 2500 m). The flows were independently dated between 0. 4 and 32 ka. Scaling factors were calculated using five different published scaling models resulting in five calibration data sets. Using a Bayesian statistical model allowed including the major inherent uncertainties. The inferred SLHL spallation production rates from Ca and K are 42. 2 ± 4. 8 atoms [36]Cl (g Ca)-1 a-1 and 124. 9 ± 8. 1 atoms [36]Cl (g K)-1 a-1 scaled with Stone (2000). Using the other scaling methods results in very similar values. These results are in agreement with previous production rate estimations both for Ca and K calibrated with low Cl samples. Moreover, although the exposure durations of our samples are very different and the altitude range is large, the ages recalculated with our production rates are mostly in agreement, within uncertainties, with the independent ages no matter which scaling method is used. However, scaling factors derived from the various scaling methods differ significantly. Cosmic ray flux is sensitive to elevation and its energy spectrum increases considerably with increasing altitude and latitude. To evaluate whether various TCN production rates change differently with altitude and latitude and if nuclide-specific or even target-element-specific scaling factors are required, cosmogenic [36]Cl, [3]He and [21]Ne concentration were determined in pyroxenes over an altitude transect between 1000 and 4300 m at Kilimanjaro volcano (3° S). No altitude-dependency of the nuclide ratios could be observed, suggesting that no nuclide-specific scaling factors be needed for the studied nuclides
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Yurco, Lyanne Nadine. "A Multi-Proxy Investigation of the Late Glacial "Mystery Interval" (17.5-14.5 ka)in the Cariaco Basin, Venezuela." Scholarly Repository, 2010. http://scholarlyrepository.miami.edu/oa_theses/26.
Повний текст джерелаАнотація:
The "Mystery Interval" (17.5-14.5 ka) is an unusual time period of abrupt global climate change during the late glacial between Heinrich event 1 and the Bølling-Allerød warm period (~17.5-14.5 ka). This period was characterized by extreme cooling in the North Atlantic region, warming in Antarctica, the rise of atmospheric greenhouse gases, and a variety of hydrologic changes around the globe, all of which may have stemmed from Heinrich event 1 and the possible collapse of the Atlantic?s meridional overturning circulation. A distinctive and unique gray clay layer was deposited in Cariaco Basin, Venezuela, within this time period, which has no apparent counterpart in the basin?s sediment record for at least the last full glacial-interglacial cycle. One hypothesis for the origin of the gray layer is that the initial pulse of deglacial sea level rise over the shallow Unare Platform, south of the basin, caused remobilization and rapid emplacement of previously deposited shelf sediments. However, analysis of the timing and extent of sea level rise as well as evidence from radiocarbon ages and a comparison of the organic content of gray layer sediments and known turbidites in the basin does not support this hypothesis. The alternative hypothesis, that the gray layer is related to increased fluvial discharge from local rivers as a result of elevated regional rainfall, is supported by a number of lines of evidence. The bulk sediment elemental content measured by scanning X-ray fluorescence (XRF) (this study) and clay mineralogy (Yu, 1996) support input of local river sediments. Coccolith abundances (Mertens et al., 2009), sea surface salinity (SSS) estimates and foraminiferal Ba/Ca analysis (this study) are also consistent with freshening of surface waters caused by elevated river runoff. This implies increased rainfall in the region which is corroborated by elemental and mineralogical ratios that point to increased precipitation and chemical weathering. Average terrigenous grain size and terrigenous fluxes are also in line with modern rainy season data. Despite prior suggestions that the Cariaco Basin region should be dry due to a southward-shifted Inter-tropical Convergence Zone (ITCZ) during cool periods in the North Atlantic, such as the Mystery Interval, data presented in this thesis suggest elevated rainfall and fluvial input related to deposition of the gray layer. Multiple lines of proxy evidence indicate that Cariaco Basin may have been characterized by a drier climate in the first part of the Mystery Interval but then shifted to a wetter climate in the second part, after ~16.5 ka, which might resolve this apparent conflict. The change to wetter conditions is most likely due to a northward shift in the position of the ITCZ, possibly due to warming tropical North Atlantic sea surface temperatures (SSTs) and/or extreme North Atlantic seasonality. Comparison of the Cariaco Basin climate records to climate observations from around the globe reveal a similar shift in climatic conditions around the same time, suggesting that the Mystery Interval may actually have been a two-phase event. Although many of the climatic observations from around the world can be explained by a shift from a southerly position of the ITCZ within the first part of the Mystery Interval to a more northerly position during the later part of the interval, many regions are not directly affected by the ITCZ and other complicating factors may play a role in the rapid climate changes observed globally.
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Stair, Kristine L. "Assessing the reproducibility of skeletal geochemistry records in Atlantic corals using Montastraea annularis coral heads from the Dry Tortugas, Florida." [Tampa, Fla.] : University of South Florida, 2007. http://purl.fcla.edu/usf/dc/et/SFE0001966.
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Maupin, Christopher Robert. "Extracting a Climate Signal from the Skeletal Geochemistry of the Caribbean Coral Siderastrea siderea." [Tampa, Fla] : University of South Florida, 2008. http://purl.fcla.edu/usf/dc/et/SFE0002433.
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Perrot, Frédéric. "Etude spectroscopique des isotopes $^{51, 52, 53}$Ca par décroissance $\beta$ des noyaux riches en neutrons $^{51, 52, 52}$K et interaction effective dans la couche fp." Phd thesis, Université Louis Pasteur - Strasbourg I, 2004. http://tel.archives-ouvertes.fr/tel-00385423.
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Amsellem, Elsa. "Le fractionnement isotopique du Ca et du Sr à haute température : apport sur la formation et l’évolution de la Terre." Thesis, Université de Paris (2019-....), 2019. https://wo.app.u-paris.fr/cgi-bin/WebObjects/TheseWeb.woa/wa/show?t=3979&f=25544.
Повний текст джерелаАнотація:
La formation du Système Solaire et son évolution restent peu connues aujourd’hui malgré le grand nombre de missions d’exploration spatiale mises en place depuis la deuxième moitié du 20ème siècle. Pour obtenir des informations sur les premières phases de la formation de la Terre et l’évolution du manteau terrestre, les météorites et les roches ignées sont de bons objets d’étude: les premières sont des témoins des conditions de la formation du Système Solaire et sont formées avant les planètes, les secondes nous renseignent sur la composition du manteau terrestre. Ces travaux de thèse se consacrent à l’analyse isotopique du calcium (Ca), du strontium (Sr) et du rubidium (Rb) d’une grande variété de roches terrestres et extra-terrestres en utilisant le MC-ICP- MS. Les isotopes stables du Ca et Sr permettent de tracer des processus physico-chimiques liés à la formation des roches. Le système Rb-Sr permet quant à lui de dater des évènements liés à l’histoire de ces roches. Les chondres, composants majoritaires des chondrites, ont été étudiés par analyse isotopique du Ca pour tes- ter et confirmer un modèle récent d’accrétion planétaire, le pebble accretion model. D’autres phénomènes peuvent affecter les corps qui peuplent notre système solaire. Notamment les chondrites peuvent subir des épisodes de chauffage et donc subir un métamorphisme thermique. La chronologie Rb-Sr permet de dater ces évènements de chauffage et d’en révéler l’origine qu’on estime alors liée à des impacts dans la ceinture d’astéroïdes. Les échantillons terrestres, des komatiites, MORBs et OIBs sont analysés pour estimer la composition isotopique du manteau en Ca et Sr ainsi que son évolution. La composition des isotopes stables du Sr dans le manteau semble homogène dans le temps alors que les isotopes du Ca révèlent la préservation d’hétérogénéités datant du début de l’histoire de la Terre. Les carbonatites, roches magmatiques contenant au moins 50% de minéraux carbonatés, sont étudiées en isotopie du Ca dans l’optique de révéler leur origine. L’enrichissement en isotopes légers du Ca des carbonatites comparé à la valeur moyenne du manteau reflète une contribution de matériel recyclé dans leur source mantellique. Ces travaux de recherche visent à explorer les grandes applications du fractionnement isotopique du Ca et du Sr à haute températureThe formation of the Solar System and its evolution remain poorly known despite the explosion of space exploration in the mid 20th century. Meteorites and terrestrial igneous rocks are particularly useful objects of study for gaining insights into the formation and evolution of the Earth: the former existed before the planets and the latter reflect the composition of the terrestrial mantle. For this thesis, we performed Ca, Sr and Rb isotopic analyses using MC-ICP-MS technique on a variety of terrestrial and extra-terrestrial rocks. The fractionation of Ca and Sr stable isotopes allows for tracing processes and source effects and Rb-Sr system enables us to date primordial events. Chondrules, a major component of chondrites, are analysed for Ca isotopic composition to test and confirm the pebble accretion model for the formation of the Earth. The timing of the heating event of thermally metamorphosed carbonaceous chondrites is estimated using Rb-Sr chronology and reveals the process of the event as impacts in the asteroid belt. From Earth, komatiites, OIBs and MORBs samples are analysed to estimate the Ca and Sr isotopic composition and evolution of the mantle. The stable isotopic composition of Sr in the mantle is homogenous through the evolution of the mantle while Ca isotopes reveal preservation of early heterogeneities. Carbonatites, rare igneous rocks containing 50 % of carbonate minerals, are studied for Ca isotopic composition in order to indicate their origin. We suggest that the enrichment in lighter Ca isotopes of the carbonatites compared to the bulk silicate Earth’s value derives from a contribution of recycled components through subduction in their mantle source. This thesis explores the wide applications of Ca and Sr isotopic fractionation in high temperature geochemistry
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Hetzinger, Steffen [Verfasser]. "Stable oxygen isotopes and Sr-Ca-ratios in modern Diploria strigosa corals from different sites in the Caribbean Sea : evaluation of a new climate archive for the tropical Atlantic = Stabile Sauerstoffisotope und Sr-Ca-Elementverteilung in rezenten Diploria-strigosa-Korallen von verschiedenen Lokationen in der Karibik / Steffen Hetzinger." Kiel : Universitätsbibliothek Kiel, 2010. http://d-nb.info/1019952245/34.
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Bowles, Rachel E. "The Use of the Ostracode Cyprideis Americana (Sharpe) as a Proxy for Salinity in Bahamian Lake Systems." TopSCHOLAR®, 2013. http://digitalcommons.wku.edu/theses/1272.
Повний текст джерелаАнотація:
Ostracodes, bi-valved crustaceans, are potentially excellent proxies for salinity.They are abundant, react to changes in salinity, and secrete low-magnesium calcite shells that preserve information about their host water chemistry. Changes in valve trace element concentration, stable isotope composition, and sieve pore shape values have been linked to changes in salinity. This study analyzed the response of the euryhaline ostracode, Cyprideis americana, to salinity in six lakes from two Bahamian islands across two seasons. The purpose of this work was to determine which compositional and morphological variables in C. americana are the most useful for paleosalinity reconstructions.Ostracode and water samples were collected from lakes of varying water chemistry on San Salvador Island (winter and summer seasons), and Exuma (winter season). Dissolved oxygen, pH, salinity, and temperature measurements were taken for each lake. The best-preserved valves from each lake were analyzed for sieve pore circularity, Mg and Ca concentrations, and δ18 O isotopic composition. Mg/Ca ratios and Kd[Mg] values were calculated for each lake. Each parameter was plotted against salinity for all of the lakes and for lakes from each season and island. Only the samples collected during the summer followed expected trends: with increases in lake water salinity, Mg/Ca ratio decreased, δ18 O composition increased, and sieve pore circularity decreased. Samples collected from the winter field sessions did not follow expected trends, potentially due to the breeding and moulting habits of C. americana. Temperature was more correlative with valve composition than a previous study of C. americana suggests, but is supportive of similar correlations of Cyprideis species in continental and other island settings. The valve Mg/Ca ratio and mean sieve pore circularity showed the best correlation with salinity and are the variables that will be most useful in paleosalinity studies from sediment cores. Future work should further investigate the relationship between mean sieve pore circularity and lake salinity as well as the breeding and moulting habits of C. americana. Such work may allow for past salinity ranges to be reconstructed from fossil C. americana samples.
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Hollstein, Martina Verfasser], Mahyar [Akademischer Betreuer] [Mohtadi, Dierk [Gutachter] Hebbeln, and Gerhard [Gutachter] Schmiedl. "Variations in surface and thermocline conditions of the Western Pacific Warm Pool : Insights from Mg/Ca and stable isotopes in foraminifera tests / Martina Hollstein ; Gutachter: Dierk Hebbeln, Gerhard Schmiedl ; Betreuer: Mahyar Mohtadi." Bremen : Staats- und Universitätsbibliothek Bremen, 2018. http://d-nb.info/1156710405/34.
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Campos, Marília de Carvalho. "Variabilidade milenar da Corrente do Brasil e do clima da América do Sul durante o último período glacial." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/100/100136/tde-27072016-113954/.
Повний текст джерелаАнотація:
A Corrente do Brasil (CB) representa o ramo sul da bifurcação da Corrente Sul Equatorial que interage com a margem continental sudeste do Brasil. A temperatura da superfície do mar na região da CB exerce um importante papel no controle da intensidade e posição da Zona de Convergência do Atlântico Sul, um dos principais componentes do Sistema de Monção da América do Sul (SMAS). Tal sistema atmosférico é responsável pela precipitação de verão em grande parte do continente sul-americano, sendo, portanto, uma feição natural de grande importância para o contexto político-econômico nacional e internacional. Além disto, a CB é marcantemente influenciada pela Atlantic Meridional Overturnig Circulation (AMOC), cujas oscilações pretéritas foram responsáveis por mudanças abruptas no clima global. Atualmente, os poucos registros paleoceanográficos disponíveis no sudoeste do Atlântico Sul não permitem uma reconstituição detalhada das mudanças ocorridas na CB durante o último período glacial. Esta Dissertação de Mestrado visou reconstituir a variabilidade da CB ao redor de 32°S durante os eventos Heinrich Stadial (HS) 3 e 2, bem como seus impactos no clima da porção sudeste da América do Sul. Para tanto, foi investigado um testemunho sedimentar marinho coletado na margem continental sul do Brasil sob a influência da CB. Para este testemunho foram produzidos modelo de idades baseado em datações 14C, análises de isótopos estáveis de carbono e oxigênio, bem como análises de Mg/Ca, ambas em testas de foraminíferos planctônicos e análises de fluorescência de raios-X em amostras de sedimento total. Os resultados mostram que durante os eventos HS (notadamente durante o HS2) ocorreu marcante aumento na taxa de sedimentação bem como nas razões ln(Ti/Ca) e ln(Fe/Ca), e diminuição na composição dos isótopos estáveis de carbono bem como na temperatura e salinidade da superfície do mar. Tais alterações foram relacionadas à desintensificação da AMOC, à intensificação da ressurgência do Oceano Austral e ao fortalecimento do SMAS. A ocorrência de uma estrutura em w nos registros dos HSs apresentados aqui, bem como em registros do Atlântico Norte e da América do Sul, sugere que esta estrutura é uma característica do HS2, e possivelmente também do HS3The Brazil Current (BC) represents the southern branch of the bifurcation of the South Equatorial Current that interacts with the southeastern Brazilian continental margin. Sea surface temperature at BC region plays an important role in controlling the intensity and position of the South Atlantic Convergence Zone, which represents one of the main componets of the South American Monsoon System (SAMS). This atmospheric system is responsible for summer precipitation in a large sector of South America, and, therefore, it is a natural feature of great importance for the national and international political-economic context. Moreover, the BC is markedly influenced by the Atlantic Meridional Overturning Circulation (AMOC) whose past oscillations generated marked global abrupt climatic changes. Presently, the few paleoceanographic records available from the western South Atlantic do not allow a detailed reconstruction of the changes that happened in the BC during the last glacial cycle. This MSc. dissertation aimed at reconstructing the variability of the BC around 32°S during the events Heinrich Stadial (HS) 3 and 2, as well as its impacts on the climate of southeastern South America. Therefore, we investigated one marine sediment core collected in the southern Brazilian continental margin, under the influence of the BC. For this core we produced an age model based on 14C ages, downcore records of carbon and oxygen stable isotopes and Mg/Ca, both in tests of planktonic foraminifera, and X-ray fluorescence in bulk sediment samples. During HSs (notably during HS2), the records show marked increases in sedimentation rate as well as in ln(Ti/Ca) and ln(Fe/Ca), and decrease in the stable carbon isotopic composition as well as sea surface temperature and salinity. Such changes were releted to the weakening of the AMOC, the intensification of the Southern Ocean upwelling, and the strengthening of the SAMS. The occurrence a w-structure in our HS records as well as in North Atlantic and South American records, suggest that such structure is a pervasive feature of HS2, and possibly also HS3
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Romahn, Sarah [Verfasser], Andreas [Akademischer Betreuer] Mackensen, and Gerold [Akademischer Betreuer] Wefer. "Western Indian Ocean circulation and climate variability on different time scales : a study based on stable oxygen and carbon isotopes, benthic foraminiferal assemblages and Mg/Ca paleothermometry / Sarah Romahn. Gutachter: Andreas Mackensen ; Gerold Wefer. Betreuer: Andreas Mackensen." Bremen : Staats- und Universitätsbibliothek Bremen, 2014. http://d-nb.info/1072226677/34.
Повний текст джерела
34
Santarosa, Ana Claudia Aoki. "Respostas dos foraminíferos planctônicos às variações da Célula de Revolvimento Meridional do Atlântico (AMOC) desde o Último Máximo Glacial na Bacia de Campos." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/21/21136/tde-17012019-180044/.
Повний текст джерелаАнотація:
O objetivo do presente estudo foi investigar a resposta da assembleia de foraminíferos planctônicos frente às variações paleoceanográficas superficiais na porção oeste do Atlântico Sul, o qual desempenha um papel fundamental na Célula de Revolvimento Meridional do Atlântico (AMOC, Meridional Overturning Circulation). Para esta finalidade, foi analisado um registro sedimentar marinho contínuo desde o Último Máximo Glacial até o presente, com base na assembleia de foraminíferos planctônicos, isótopos de oxigênio e na razão Mg/Ca. Adicionalmente, foram avaliadas as variações na ocorrência e na geoquímica dos dois morfotipos de G. ruber (branca), principal espécie utilizada em estudos paleoceanográficos de regiões tropicais e subtropicais. Os resultados mostraram que as diferenças geoquímicas e de abundância relativa dos morfotipos de G. ruber branca evidenciam dois grupos de espécimes ecologicamente distintos, confirmando que o morfotipo sensu stricto calcifica em menores profundidades com relação ao morfotipo sensu lato e que reconstituições paleoceanográficas baseadas no uso não-seletivo dos morfotipos poderiam ser tendenciosas. A Análise Fatorial realizada nos dados de abundância relativa dos foraminíferos planctônicos identificou 4 fatores principais: o Fator 1, representado pelas espécies G. tenella, G. calida, e G. rubescens e relacionado com a temperatura subsuperficial; o Fator 2, representado pelas espécies N. incompta, N. dutertrei e G. truncatulinoides, relacionado com a profundidade da termoclina; o Fator 3, representado pela espécie G. bulloides, associado com o processo de ressurgência e o Fator 4, representado pelas espécies G. ruber e G. glutinata, associado com a intensidade da Corrente do Brasil. As variações mais expressivas de paleotemperatura e paleosalinidade da superfície do mar e da fauna de foraminíferos planctônicos estão relacionadas com os eventos climáticos abruptos do Hemisfério Norte ocorridos durante a deglaciação, tendo sido moduladas pelas variações de arranjo e intensidade da AMOC. Durante os eventos frios Heinrich 1 e Younger Dryas, relacionados a um enfraquecimento da AMOC, foi observado um aumento das paleotemperatura e paleosalinidade e da intensidade da Corrente do Brasil (Fator 4). Contrariamente, durante o evento quente Bolling-Allerod, a paleotemperatura e a paleosalinidade diminuíram expressivamente, como resposta à retomada da AMOC, e houve aumento da produtividade e presença de uma termoclina mais rasa (Fatores 2 e 3). Sugere-se ainda, que entre 26 e 15 ka houve um deslocamento para norte da Confluência Brasil-Malvinas, possivelmente alcançando a latitude da área de estudo (∼23°S), inferido pela presença da espécie G. inflata. Durante o Holoceno, também foi registrada variação significativa na intensidade da Corrente do Brasil, indicada pelos valores máximos do Fator 4 em torno de 7 ka. O reaparecimento das espécies do plexo G. menardii se deu em 8 ka, assim como o aumento das espécies de foraminíferos planctônicos subsuperficiais, indicado pelo Fator 1. Essas mudanças no Holoceno foram atribuídas à entrada efetiva das águas quentes e salinas do Oceano Índico via vazamento das Agulhas, as quais foram essenciais para o restabelecimento da AMOC moderna.The objective of the present study was to investigate the response of the planktonic foraminiferaassemblage to the superficial paleoceanographic variations in the western South Atlantic, which plays a key role in the AMOC. For this purpose, a continuous marine sedimentary record was analyzed from the Late Glacial Maximum to the present, based on the planktonic foraminifera assemblage, oxygen isotopes and the Mg/Ca ratio. In addition, variations in the occurrence and geochemistry of the two morphotypes of G. ruber (white) were evaluated. This is the main species used in paleoceanographic studies of tropical and subtropical regions. The results showed that the geochemical and relative abundance differences between the G. ruber morphotypes show two ecologically distinct groups of specimens, confirming that the morphotype sensu stricto calcifies at lower depths with respect to the morphotype and sensu lato, and paleoceanographic and paleoceanographic reconstructions using non-selective mixture of morphotypescould potentially be biased. The Factorial Analysis identified four factors: Factor 1, represented by G. tenella, G. calida, and G. rubescens, is related to the subsurface temperature; Factor 2, represented by N. incompta, N. dutertrei and G. truncatulinoides is related to the depth of the thermocline; Factor 3, represented by G. bulloides, is related toupwelling; and Factor 4, represented by G. ruber and G. glutinata, is related to the intensity of the Brazil Current. The results showed that the most significant variations of paleotemperature and paleosalinity and the planktonic foraminifera assemblage are related to the abrupt climatic events of the Northern Hemisphere occurred during deglaciation and were modulated by variations in AMOC arrangement and intensity. During the cold events Heinrich 1 and Younger Dryas, related to a weakening of the AMOC, an increase of paleotemperature and paleosalinity and intensity of the Brazil Current (Factor 4) in the western portion of the South Atlantic was observed. Conversely, during the hot event Bolli-Allerod, paleotemperature and paleosalinity decreased expressively, as a response to AMOC resumption, with increased productivity and presence of a shallower thermocline (Factors 2 and 3). It is also suggested that between 26 and 15 ka there was a displacement to the north of the Brazil-Malvinas Confluence, possibly reaching the latitude of the study area (∼23°S), inferred by the presence of the G. inflata. Along the Holocene, there was also a significant variation in the intensity of the Brazil Current, indicated by the maximum values of Factor 4 around 7ka. The reappearance of G. menardii plexus occurred in 8ka, as well as the increase of the species of subsurface planktonic foraminifera, indicated by Factor 1. These changes in the Holocene were attributed to the effective entrance of the hot and saline waters from the Indian Ocean via the Agulhas Leakage, which were essential for the reestablishment of the modern AMOC.
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Schimmelpfennig, Irene. "L'isotope cosmogénique Cl-36 dans les minéraux riches en Ca et en K : développements analytiques, calibrations des taux de production et inter-calibration avec le He-3 et le Ne-21." Phd thesis, Université Paul Cézanne - Aix-Marseille III, 2009. http://tel.archives-ouvertes.fr/tel-00468337.
Повний текст джерелаАнотація:
Les taux de production du nucléide cosmogénique 36Cl par spallation du Ca et du K (SLHL) proposés actuellement dans la littérature montrent des divergences allant jusqu'à 50% (Gosse and Phillips, 2001). Nous avons pu montrer que des fortes teneurs en Cl dans les roches utilisées pour les calibrations précédentes entraînent une surestimation de ces taux de production, lié à la production de 36Cl à partir du 35Cl qui est peu contrainte. Nous avons entrepris une nouvelle calibration à partir de laves datées indépendamment entre 0.4 et 32 ka situées au Mt. Etna (38°N, Italie) et au Payun Matru (36°S, Argentine). Le 36Cl a été mesuré dans des feldspaths riches en Ca et en K, mais faibles en Cl. A partir d'une approche bayesienne incluant toutes les incertitudes, les taux de production obtenus sont de 42.2 ± 4.8 atomes 36Cl (g Ca)-1 an-1 pour la spallation du Ca et de 124.9 ± 8.1 atomes 36Cl (g K)-1 an-1 pour la spallation du K, avec les facteurs d'échelle calculés selon Stone (2000). Quatre autres modèles de facteurs d'échelle sont également proposés avec des résultats très semblables. Ces nouveaux taux de production sont en accord avec les valeurs précédemment obtenues par d'autres auteurs avec des échantillons faibles en Cl. Finalement, les concentrations en 36Cl, 3He et 21Ne ont été mesurées dans des pyroxènes prélevés entre 1000 et 4300 m dans des laves du Kilimandjaro (3°S). Les rapports entre ces nucléides ne montrent pas de dépendance altitudinale, ce qui suggère que les taux de production ne varient pas d'un nucléide à l'autre avec l'altitude.
36
Chiang, Hong-Wei, and 姜宏偉. "Oxygen Isotope and Ba/Ca Ratio Records in Coral Skeletons and their Environmental Explanations from Southern Taiwan." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/17373667981244403999.
Повний текст джерелаАнотація:
博士國立臺灣大學
地質科學研究所
99
Coral has been one of the best marine archives to study climate change from weekly to decadal timescales. The abundant trace elements and stable oxygen isotopes in massive coral skeletons are affected by the environment condition prevailing at the time of skeleton deposition. In this study two coral heads were collected from the Nanwan Bay, southern Taiwan to test the capabilities of traditional d18O values and recent-developed Ba/Ca ratios, with seasonal to sub-decadal timescales. Firstly, during El Niño episodes the skeletal d18O–SST correlation showed a gentler slope of -0.12 ± 0.04‰ °C-1 rather than the value of -0.21 ± 0.04‰ °C-1 during normal year. The difference was likely caused by enhanced penetration of Kuroshio Current waters into the South China Sea during El Niño summers. Secondly, an annually distinct double-peak feature of Ba/Ca ratios in coral was identified. The earlier peak is not concordant with the time of major precipitation but regularly occurred before the Sr/Ca value reached the minimum. It was resulted from a biotic source and possibly related to Cyanophyta bloom in the early-spring. The later peak happened at the time of raining seasons. Two different linear correlations are presented between skeletal Ba/Ca and accumulated precipitation in July-October. Before 1999, the relationship was given by Ba/Ca=3.02+0.0024*P; while after 1999, the relationship is given by Ba/Ca=2.26+0.0011*P. The decreased Ba/Ca baseline from the end of 1999 to 2001 is believed to relate to the operating of two sewage treatment plants since 1999 and 2000. It also can explain the gentler slope value of Ba/Ca-precipitation regression and the decreased amplitude of Ba/Ca maxima after 1999. Thus, the skeletal Ba/Ca ratios can be applied as a quantitative proxy of the paleo-precipitation in southern Taiwan.
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"Scarlet Macaws, Long-Distance Exchange, and Placemaking in the U.S. Southwest and Mexican Northwest, ca 900-1450 CE." Doctoral diss., 2020. http://hdl.handle.net/2286/R.I.57275.
Повний текст джерелаАнотація:
abstract: Exchange is fundamental to the establishment and maintenance of social institutions and political economies in all scales of societies. While today people rapidly exchange goods and information over great distances, in the past, long-distance exchange necessitated the mobilization of vast networks of interaction with substantial transport costs. Objects traded over long distances were often valuable and challenging to obtain, granting them multifaceted significance that is difficult to understand using traditional archaeological approaches.
This research examines human interactions with scarlet macaws (Ara macao) in the United States (U.S.) Southwest and Mexican Northwest (SW/NW) between 900 and 1450 CE. This period saw large-scale cultural change in the form of migrations, rapid population aggregation, and an expansion of long-distance exchange relations in regional centers at Pueblo Bonito (900-1150 CE) in northwestern New Mexico, Wupatki (1085-1220 CE) in north-central Arizona, and Paquimé (1200-1450 CE) in northern Chihuahua. Despite the distant natural habitat of scarlet macaws, their importation, exchange, and sacrifice appear to have played integral roles in the process of placemaking at these three regional centers. Here, I use an Archaeology of the Human Experience approach and combine radiogenic strontium isotope analysis with detailed contextual analyses using a Material Histories theoretical framework to (1) discern whether macaws discovered in the SW/NW were imported or raised locally, (2) characterize the acquisition, treatment and deposition of macaws at Pueblo Bonito, Wupatki, and Paquimé, and (3) identify patterns of continuity or change in acquisition and deposition of macaws over time and across space in the SW/NW.
Findings from radiogenic strontium isotope analysis indicate that scarlet macaws from all case studies were primarily raised locally in the SW/NW, though at Paquimé, macaws were procured from sites in the Casas Grandes region and extra-regionally. Variation in the treatment and deposition of scarlet macaws suggests that despite their prevalence, macaws were interpreted and interacted with in distinctly local ways. Examination of the human experience of transporting and raising macaws reveals previously unconsidered challenges for keeping macaws. Overall, variation in the acquisition and deposition of scarlet macaws indicates changing strategies for placemaking in the SW/NW between 900 and 1450 CE.Dissertation/Thesis
Doctoral Dissertation Anthropology 2020
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Chen, Jang-Chung, and 陳建璋. "Surprising Ca isotopic anomalies in the early solar system." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/50491210936538337869.
Повний текст джерелаАнотація:
碩士臺灣大學
天文物理研究所
98
We have achieved higher precision for the measurement of Ca isotopic ratio by increasing the beam intensity to around 1.2nA. 42Ca/44Ca was normalized in order to correct the remaining ratios for fractionation. The two standard deviations in reproducibility for 40Ca/44Ca, 43Ca/44Ca, 46Ca/44Ca and 48Ca/44Ca were 1.5, 0.3, 7.5 and 0.7ε (ε ≡ 0.01%) respectively. The improved precision enabled us to not only confirm 48Ca anomalies up to 5.1ε in ordinary CAIs (Ca-Al-Inclusions) in meteorites but also search for Ca isotopic variation in bulk meteorites. Prior to this, 48Ca anomalies were only endemic to CAIs in carbonaceous chondrites. Surprisingly, our experiment revealed 48Ca deficit up to －2.3ε in achondrites relative to terrestrial samples. Because achondrites were presumably solidified from large scale melting on planetary bodies hundreds of km in size, they were not expected to present any detectable heterogeneities. On the other hand, the widespread 48Ca anomalies that correlate with 50Ti and 54Cr without large effects on the tiny 46Ca indicate that these nuclides originated from the rare neutron rich nuclear statistic equilibrium (n-rich NSE), not neutron capture. However, it remains unclear. As to how to keep this nucleosynthetic component made only in rare subset of type Ia supernovae from completely mixed in the solar system after the achondrites being solidified, it lends some support to the speculation that the solar system received some injected material from a nearby supernova that happened to explode after the solidification of achondrites but before the formation of terrestrial planets.
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Camaiani, Alberto, Giovanni Casini, and Andrea Stefanini. "Complete isotopic characterization of projectile fragments in Ca+Ca reactions at Fermi energies with the FAZIA array." Doctoral thesis, 2020. http://hdl.handle.net/2158/1204443.
Повний текст джерелаАнотація:
This thesis is part of the studies that the international FAZIA collaboration is performing
on heavy-ion collision experiments using the new setup of telescopes developed in the last
decade, capable of excellent capabilities in terms of ion identification. In this thesis, we analyzed
the data of Ca+Ca reactions, collected in one of the first experiments using the new FAZIA
telescopes. The beams were accelerated at 35 MeV/u, well within the so-called Fermi energy
range. The main goal of the experiment was an accurate study of the semi-peripheral collisions,
in particular from the point of view of the mechanisms that intervene in the neutron-to-proton
equilibration, accessing for the first time to the neutron content of the quasi-projectile remnant.
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Liu, Hou-Chun, and 劉厚均. "Precise Determination of Ca Isotopic Composition in Carbonate and Seawater." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/63224611853735991669.
Повний текст джерелаАнотація:
碩士國立成功大學
地球科學系碩博士班
97
The Ca isotope composition of synthetic carbonates and corals have been measured in order to evaluate the Ca isotope fractionation during the carbonate formation; and the δ44/42Ca of a seawater profile in South China Sea (SCS) has been performed as well to realize the oceanic Ca cycle in preliminary. A fast and high-precision analytical technique for the Ca isotopes has been developed using high-resolution multi-collector ICP-MS (Neptune, Thermo-Fisher) coupled with a desolvation system (APEX-IR, ESI). Two-steps separation technique has been successfully applied to separate matrix component from the analyzed compound to avoid potential spectral interferences. The external reproducibility for δ44/42Ca analysis is better than 0.11‰ (2σ) using a standard-sample-standard bracketing method. Calcium carbonates obtained from controlled inorganic precipitation were used for evaluating the Ca isotope fractionation during precipitation and display a rather small temperature-dependent fractionation at 5-40°C (0.002 and 0.001‰/°C for aragonite and calcite, respectively). The Ca isotope fractionation factor (α) in synthetic carbonates reveals a significant difference compared with previous studies, which was attributed to the difference in growth rate under various precipitation techniques. Furthermore, Ca isotopes in cultured and field corals, Porites sp., show also only minor temperature-dependent fractionation. Kinetic rather than the temperature effects would strongly affect the Ca isotope fractionation in carbonates. On the other hand, seawaters collected from SCS displays a small but significant δ44/42Ca vertical variation. The lowest value of δ44/42Ca in the SCS is detected in the bottom water which could be partly attributed to the intense partial dissolution on marine carbonates. Further studies are necessary to improve analytical precision and to understand the main controlling factors on seawater Ca isotopes.
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Bürger, Alexander [Verfasser]. "Nuclear structure of light Ca and heavy Cr isotopes / vorgelegt von Alexander Bürger." 2007. http://d-nb.info/987153021/34.
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Proulx, Alexandre. "L'effet des amendements cationiques sur la photosynthèse : le cas des érables à sucre (Acer Saccharum)." Thèse, 2020. http://depot-e.uqtr.ca/id/eprint/9737/1/eprint9737.pdf.
Повний текст джерела
43
Heuser, Alexander [Verfasser]. "Variations of calcium isotopes (δ44Ca) [delta 44 Ca] in foraminifers over the past 24 Ma / vorgelegt von Alexander Heuser". 2002. http://d-nb.info/971995583/34.
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44
Teh, Ee-Ee, and 鄭郁豫. "Reconstruction of paleotemperature and paleosalinity of the South China Sea for the past 170kyrs using planktonic foraminiferal Mg/Ca ratio and oxygen isotopes." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/14866613111877671126.
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Hennissen, Jan. "Late Pliocene–Early Pleistocene North Atlantic Circulation: Integrating Dinocyst Assemblages and Foraminiferal Geochemistry." Thesis, 2013. http://hdl.handle.net/1807/35845.
Повний текст джерелаАнотація:
During the Late Pliocene, between 3.3 Ma and 2.6 Ma, tectonic events changed ocean basin interactions against a background of shifting orbital forcing mechanisms and a global cooling trend. A climate system that had been locked in a stable, warm state gradually transformed into one typified by the high-amplitude glacial–interglacial fluctuations characteristic of the later Quaternary. The onset of Northern Hemisphere glaciations in the Late Pliocene marks an important step in this transition, due to the role of feedback mechanisms including ice albedo. A crucial factor in this Northern Hemisphere ice sheet expansion is the North Atlantic surface ocean circulation. To evaluate how they are linked, a ca. 200-kyr time slab spanning 2782-2520 ka (Late Pliocene–Early Pleistocene) was analyzed at millennial scale resolution from eastern North Atlantic Deep Sea Drilling Project (DSDP) Site 610 and Integrated Ocean Drilling Program (IODP) Site U1313. The causes of the Plio-Pleistocene climatic turnover are compared to that of the well-documented Marine Isotope Stage (MIS) M2 occurring in the Late Pliocene (3.3 Ma). MIS M2, a severe glacial event seen as a precursor to later Quaternary-style glaciations, was investigated from western North Atlantic DSDP Site 603.
Utilizing a same-sample methodology, two paleoceanographic proxies were used: (1) dinocyst assemblages, and (2) foraminiferal geochemistry (δ18O and Mg/Ca). Dinocysts are proven tracers of sea-surface temperature (SST), salinity, nutrient supply, and sea ice cover, and are analyzed here to characterize the overlying water masses at the studied sites. Strong dinocyst assemblage fluctuations attest to variations in the influence of the North Atlantic Current (NAC). Using Mg/Ca ratios for the planktonic foraminifer Globigerina bulloides to determine absolute SSTs allows salinity changes to be reconstructed when combined with stable oxygen isotopes. This study shows a persistent Gulf Stream–NAC in the western North Atlantic during MIS M2, favoring a southern shift of the NAC over a shutdown of the thermohaline circulation. At the newly established Plio-Pleistocene boundary, a profound turnover in dinoflagellate cyst assemblages reveals a shift in ocean mode during MIS 104 (2.6 Ma). Three distinct dinocyst ecozones demonstrate this fundamental reorganization of the North Atlantic circulation.
46
Knott, Diane Clemens. "Geologic and isotopic investigations of the early Cretaceous Sierra Nevada Batholith, Tulare Co., CA, and the Ivrea Zone, NW Italian Alps: examples of interaction between mantle-derived magma and continental crust." Thesis, 1992. https://thesis.library.caltech.edu/6347/2/Knott_dc_1992.pdf.
Повний текст джерелаАнотація:
Two igneous suites containing layered ultramafic-mafic cumulates were investigated with the intent to characterize the parental magma and to identify processes significant to the petrogenesis of these rocks. In both study areas, the early Cretaceous Sierra Nevada batholith and the Ivrea Zone, isotopic systematics of the cumulates were found to preserve the characteristics of the mantle-derived parental magma and to record the effects of fractional crystallization and assimilation. Modeling the relative importance of these processes and characterization of the material derived from the mantle are necessary to understanding the growth of the continental crust.
Geologic mapping of 110 mi2 of the 125 to 110 Ma Stokes Mountain region reveals the presence of layered cumulate megaxenoliths and two coeval ring dike complexes. Petrographic analysis and geochemical modeling of 125 dominantly mafic and intermediate samples demonstrate the comagmatic nature of this suite. Combined oxygen, strontium and neodymium analysis of 22 samples indicates, however, that each ring complex was fed by an isotopically distinct parental magma (εNd(115) = +6.1, Sri = 0.70338, δ18O = 6.6‰ ; (εNd(115) = +5.7, Sri = 0.70372, δ18O = 6.7‰) both of which were derived from a variably contaminated, depleted mantle source. Minor assimilation of continentally-derived metasediments and mafic-ultramafic material of the Kings-Kaweah ophiolite further affected the isotopic evolution of the two subsuites. Hydrothermal alteration in the subvolcanic environment is recorded only by rare stoped xenoliths of 120 Ma hypabyssal intrusives.
Late Hercynian (≈300 - 270 Ma) magmatism produced the 10 km thick Mafic Complex lying at the base of the Ivrea-Strona-Ceneri crustal cross section. δ18O analysis of 237 whole rock samples and 26 mineral separates reveals that presumably early intrusions into the cool crust preserve the depleted mantle signature of the modeled parental magma (εNd(115) = +7, Sri = 0.703, δ18O = 6.5‰) while later intrusions assimilated significant amounts of the 10 - 12‰ metapelite. Subsequent intrusion of voluminous basaltic magma fonned a large, convecting magma chamber in which assimilation was concentrated within boundary layers. Such lower crustal production of high-18O (δ18O = 8 - 10‰) mafic magmas is suggested as contributing to the petrogenesis of upper crustal Permian granites.
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Zarrieß, Michelle [Verfasser]. "Primary productivity and ocean circulation changes on orbital and millennial timescales off Northwest Africa during the last glacial, interglacial cycle : evidence from benthic foraminiferal assemblages, stable carbon and oxygen isotopes and Mg, Ca paleothermometry / vorgelegt von Michelle Zarrieß." 2010. http://d-nb.info/1010641425/34.
Повний текст джерела