This thesis uses the paleoceancirculation proxy ²³¹Pa/²³⁰Th, coupled with water mass tracers δ¹³C and εNd, to reconstruct circulation histories for southern source waters masses in the South Atlantic, in addition to North Atlantic Deep Water (NADW) far from its source, for the last ~25 kyrs. Downcore ²³¹Pa/²³⁰Th records from a suite of cores along a depth transect in the Argentine Basin show distinct differences with depth, suggesting that ²³¹Pa/²³⁰Th ratios in sediments are reflective of conditions in only the bottom most waters. This indicates the importance of consideration of changes in water mass distribution when interpreting ²³¹Pa/²³⁰Th records. Opal and particle flux data from these cores show little correlation with ²³¹Pa/²³⁰Th values meaning that changes in ²³¹Pa/²³⁰Th cannot be explained by a local composition or particle flux effect and are instead likely to be reflecting changes in circulation. A core bathed by Antarctic Intermediate Water (AAIW) throughout the last 25 kyrs (GeoB 2107, 1045 m), has relatively high ²³¹Pa/²³⁰Th values (0.075) during the Holocene and distincly lower values (0.055) at the LGM suggesting faster AAIW transport during the last glacial. At greater depths, ²³¹Pa/²³⁰Th, δ¹³C and εNd data in core GeoB 2109 (2504 m) indicate a change in both circulation and water mass distribution on glacial-interglacial timescales, with moderate flow of Antarctic Bottom Water (AABW) at the LGM being replaced by more vigorous flow of NADW during the Holocene. On millenial timescales, ²³¹Pa/²³⁰Th values in deep cores GeoB 2109 and GeoB 2112 (4010 m) indicate enhanced production of AABW during northern hemisphere stadials, when variations in ²³¹Pa/²³⁰Th records are of opposite sign between hemispheres, supporting a possible bipolar seesaw relationship in deep water formation between hemispheres. These data indicate that the ²³¹Pa/²³⁰Th proxy can be used to reconstruct past flow rates of multiple water masses in the Argentine Basin and provide evidence that southern source water masses play a dynamic counterpart to NADW formation on abrupt as well as glacial-interglacial timescales.

A onipresença dos radionuclídeos naturais e artificiais nas diversas matrizes ambientais é passível de ser aproveitada como ferramenta em estudos de dinâmica sedimentar marinha, pois estes nuclídeos registram processos em escalas espaciais e temporais de acordo com seus níveis e distribuição espacial e vertical em sedimentos. Dentro deste contexto, este trabalho demonstrou o uso de radionuclídeos naturais (210Pb, 226Ra, 230,232Th, 234,238U) e artificiais (137Cs) em estudos de dinâmica sedimentar marinha com a espectrometria gama como única técnica analítica, através da apresentação de um conjunto de métodos de aplicação de radionuclídeos, modelos matemáticos e de interpretação de seus resultados. A primeira aplicação descrita foi uma avaliação quantitativa da sedimentação no Sistema Santos-São Vicente, que permitiu um estudo das variações espaciais e ao longo do tempo na sedimentação deste sistema costeiro. Outra aplicação foi o uso da ocorrência e distribuição espacial de 137Cs como uma ferramenta estratigráfica em sistemas costeiros do Oceano Atlântico Sul, com um modelo matemático cujos resultados indicaram um padrão latitudinal nos níveis de atividade deste nuclídeo consistente com observações de sua deposição atmosférica reportadas pela literatura internacional. Finalmente, um modelo de sedimentação e idade baseado nas relações entre isótopos de Th e U (validado com resultados de isótopos estáveis de oxigênio e bio/magnetoestratigrafia) foi empregado para estimar taxas de sedimentação e idades em testemunhos quaternários de duas margens continentais passivas (oeste do Oceano Atlântico Sul e Mar do Sul da China). Com os resultados deste modelo, observou-se períodos de aumento nos níveis de 230Th que podem sugerir a influência de fatores como variações na taxa de deposição de 230Th e ciclos orbitais de Milankovitch. / The occurrence of natural and artificial radionuclides in the environment can be used as a tool for studies of marine sedimentary dynamics, as these nuclides record environmental processes at both spatial and temporal scales. Within this context, this work aimed at demonstrating the use of natural (210Pb, 226Ra, 230,232Th, 234,238U) and artificial (137Cs) radionuclides in studies of sedimentary dynamics with gamma spectrometry as sole analytical technique. This was done through the application of several mathematical models and methods of radionuclides\' data interpretation. The first application was a quantitative assessment of sedimentation in the Santos-São Vicente coastal system, studying its spatial variations during the last century. Another application was the use of the occurrence and spatial distribution of 137Cs as a stratigraphical tool for age studies in coastal systems of the South Atlantic Ocean. With the results of a mathematical model it was possible to infer values of radionuclide deposition that showed a latitudinal pattern in the levels of this element, consistent with international reports of fallout atmospheric deposition. Finally, a model of sedimentation and age determination based on the relationships between Th and U isotopes was used to estimate sedimentation rates in Quaternary cores from two passive continental margins (South Atlantic western margin and South China Sea margin). The model was validated by statistical comparison with data of stable oxygen isotopes and bio/magnetostratigraphy. The results of this model showed periods with an increase on the 230Th excess activity that could be related to variations on Th deposition rate and the influence of Milankovitch orbital cycles on Th and U deposition.

A onipresença dos radionuclídeos naturais e artificiais nas diversas matrizes ambientais é passível de ser aproveitada como ferramenta em estudos de dinâmica sedimentar marinha, pois estes nuclídeos registram processos em escalas espaciais e temporais de acordo com seus níveis e distribuição espacial e vertical em sedimentos. Dentro deste contexto, este trabalho demonstrou o uso de radionuclídeos naturais (210Pb, 226Ra, 230,232Th, 234,238U) e artificiais (137Cs) em estudos de dinâmica sedimentar marinha com a espectrometria gama como única técnica analítica, através da apresentação de um conjunto de métodos de aplicação de radionuclídeos, modelos matemáticos e de interpretação de seus resultados. A primeira aplicação descrita foi uma avaliação quantitativa da sedimentação no Sistema Santos-São Vicente, que permitiu um estudo das variações espaciais e ao longo do tempo na sedimentação deste sistema costeiro. Outra aplicação foi o uso da ocorrência e distribuição espacial de 137Cs como uma ferramenta estratigráfica em sistemas costeiros do Oceano Atlântico Sul, com um modelo matemático cujos resultados indicaram um padrão latitudinal nos níveis de atividade deste nuclídeo consistente com observações de sua deposição atmosférica reportadas pela literatura internacional. Finalmente, um modelo de sedimentação e idade baseado nas relações entre isótopos de Th e U (validado com resultados de isótopos estáveis de oxigênio e bio/magnetoestratigrafia) foi empregado para estimar taxas de sedimentação e idades em testemunhos quaternários de duas margens continentais passivas (oeste do Oceano Atlântico Sul e Mar do Sul da China). Com os resultados deste modelo, observou-se períodos de aumento nos níveis de 230Th que podem sugerir a influência de fatores como variações na taxa de deposição de 230Th e ciclos orbitais de Milankovitch. / The occurrence of natural and artificial radionuclides in the environment can be used as a tool for studies of marine sedimentary dynamics, as these nuclides record environmental processes at both spatial and temporal scales. Within this context, this work aimed at demonstrating the use of natural (210Pb, 226Ra, 230,232Th, 234,238U) and artificial (137Cs) radionuclides in studies of sedimentary dynamics with gamma spectrometry as sole analytical technique. This was done through the application of several mathematical models and methods of radionuclides\' data interpretation. The first application was a quantitative assessment of sedimentation in the Santos-São Vicente coastal system, studying its spatial variations during the last century. Another application was the use of the occurrence and spatial distribution of 137Cs as a stratigraphical tool for age studies in coastal systems of the South Atlantic Ocean. With the results of a mathematical model it was possible to infer values of radionuclide deposition that showed a latitudinal pattern in the levels of this element, consistent with international reports of fallout atmospheric deposition. Finally, a model of sedimentation and age determination based on the relationships between Th and U isotopes was used to estimate sedimentation rates in Quaternary cores from two passive continental margins (South Atlantic western margin and South China Sea margin). The model was validated by statistical comparison with data of stable oxygen isotopes and bio/magnetostratigraphy. The results of this model showed periods with an increase on the 230Th excess activity that could be related to variations on Th deposition rate and the influence of Milankovitch orbital cycles on Th and U deposition.

Age-model derived sediment mass accumulation rates (MARs) are consistently higher than 230Th-normalized MARs in the Equatorial Pacific Ocean during the past 25 ka. The offset, being highest in the Panama Basin, suggests sediment redistribution in this region is prominent. I test the hypothesis that downslope transport of sediments from topographically highs that surround the Panama Basin is the cause of higher-than-expected xs230Th inventories in the deeper parts of the basin. There is little difference in xs230Th inventories between the highest and lowest reaches of the basin suggesting that the topographic highs did not serve as a source of xs230Th. A spatial analysis suggests that there may be an enhanced scavenging of xs230Th closest to the equator in productive waters. To examine whether lateral mixing of productive equatorial waters with adjacent waters delivers xs230Th to the Panama Basin, I measured dissolved 230Th in eight deep-water casts within the Guatemala, Panama, and Peru Basins along a meridional transect at ~86°W. Below 1000 m, the Panama Basin shows the highest deficit (~50%) of 230Th in deep waters assuming a reversible exchange of 230Th between dissolved and sinking particulate matter. Peru Basin waters have a larger range of dissolved 230Th concentrations (7.9-16.5 fg/kg) than that within Panama Basin waters (5.7-7.1 fg/kg). There is a progressive decrease, suggesting advection, in average dissolved deep-water (>1000 m) 230Th concentrations from the southernmost sites in the Peru Basin toward the Panama Basin. My calculations suggest that advected 230Th is between 15-30% of the total 230Th being produced within waters of the Panama Basin itself. In the Panama Basin, the averaged biogenic barium and opal MARs suggest that productivity was greater during the Holocene (0-13000 years) than that during the last glacial (13000-25000 years) suggesting higher productivity during the Holocene. Uauth, however, is higher in sediments deposited during the last glacial than in those deposited during the Holocene, suggesting that low bottom water oxygen contents rather than respiration of organic matter drives Uauth enrichment. This oxygen depletion during the last glacial suggests that bottom waters were enriched in respired carbon, which, in turn, could be a driver of lower glacial atmosphere pCO2 values.

In der Arbeit werden nach einer detaillierten Beschreibung der eingesetzten Böden mit erhöhter Konzentration an den Radionukliden 210Pb, 226Ra, 227Ac, 230Th und 238U und der angewandten Analysenverfahren eine umfangreiche Übersicht über die Transferfaktoren Boden - Pflanze für die einzelnen Pflanzenteile der in der menschlichen Ernährung genutzten Gemüse und in Futterpflanzen vorgestellt. Die gammaspektrometrischen Bestimmungen von geringen Radioaktivitäten wurden einem Untertagemesslabor durchgeführt. Die Unterschiede in den Transferfaktoren für die Pflanzen und deren Teile und Böden und die Beziehungen zwischen Transferfaktoren und eluierbaren Anteilen der Böden, Pflanzenteile; sowie zwischen den radioaktiven Elementen Radium und Actinium und den Elementen Barium und Lanthan wurden dargestellt. Es wurde bei den Pflanzen eine Abnahme der Radioaktivität von der Wurzel über Stängel und Blatt zur Frucht festgestellt. Die Transferfaktoren für das bisher kaum bestimmten 227Ac ist relativ hoch und liegt in der Größenordnung der sehr konservativ angesetzten Richtwerte des Strahlenschutzes, während sie für die anderen Radionuklide weit unter den Richtwerten liegen. / The used soils with enhanced activity of the radionuclides 210Pb, 226Ra, 227Ac, 230Th, and 238U and the analytical methods for the determination of soil-plant transfer factors are described and a survey of the obtained values for parts of plants used for human nutrition are presented. Gamma spectrometric determination of low radioactivities has been performed in an underground laboratory. For comparison the factors are determined for the plants of similar elements Ba for Ra and La for Ac. In all cases the values decreases from the roots over the leaves to the fruits. The values for 227Ac are relatively high and are in the magnitude of the „Richtwerte“ for radiation protection, in spite of the other radionuclides, which are lower than the „Richtwerte“.

In der Arbeit werden nach einer detaillierten Beschreibung der eingesetzten Böden mit erhöhter Konzentration an den Radionukliden 210Pb, 226Ra, 227Ac, 230Th und 238U und der angewandten Analysenverfahren eine umfangreiche Übersicht über die Transferfaktoren Boden - Pflanze für die einzelnen Pflanzenteile der in der menschlichen Ernährung genutzten Gemüse und in Futterpflanzen vorgestellt. Die gammaspektrometrischen Bestimmungen von geringen Radioaktivitäten wurden einem Untertagemesslabor durchgeführt. Die Unterschiede in den Transferfaktoren für die Pflanzen und deren Teile und Böden und die Beziehungen zwischen Transferfaktoren und eluierbaren Anteilen der Böden, Pflanzenteile; sowie zwischen den radioaktiven Elementen Radium und Actinium und den Elementen Barium und Lanthan wurden dargestellt. Es wurde bei den Pflanzen eine Abnahme der Radioaktivität von der Wurzel über Stängel und Blatt zur Frucht festgestellt. Die Transferfaktoren für das bisher kaum bestimmten 227Ac ist relativ hoch und liegt in der Größenordnung der sehr konservativ angesetzten Richtwerte des Strahlenschutzes, während sie für die anderen Radionuklide weit unter den Richtwerten liegen. / The used soils with enhanced activity of the radionuclides 210Pb, 226Ra, 227Ac, 230Th, and 238U and the analytical methods for the determination of soil-plant transfer factors are described and a survey of the obtained values for parts of plants used for human nutrition are presented. Gamma spectrometric determination of low radioactivities has been performed in an underground laboratory. For comparison the factors are determined for the plants of similar elements Ba for Ra and La for Ac. In all cases the values decreases from the roots over the leaves to the fruits. The values for 227Ac are relatively high and are in the magnitude of the „Richtwerte“ for radiation protection, in spite of the other radionuclides, which are lower than the „Richtwerte“.

L’analyse de sédiments totaux et de fractions granulométriques de la rivière Gandak (Himalaya) a montré que la variabilité des séries de l’uranium observée pour les sédiments himalayens est contrôlée par leur évolution minéralogique et granulométrique plutôt que par le mécanisme d’altération. Cette conclusion questionne les travaux antérieurs et souligne la nécessité d’étudier la mobilité des radionucléides à échelle minérale. A cette fin, une approche sur fractions minérales a mis en évidence des processus d’échange entre les minéraux, avec une mobilité significative de 230Th, fortement appauvri dans les zircons, et 226Ra, enrichis en particulier dans la fraction argileuse. Les déséquilibres observés semblent induits par un processus d’altération récent, de quelque ka.Ces résultats sont confirmés par l’analyse des déséquilibres 238U-234U-230Th dans des minéraux par SIMS, qui montre un enrichissement en 230Th à la surface des monazites et une perte de Th (232, 230) dans les zircons. / The analysis of total sediments and grain-size fractions from the Gandak river (Himalaya) showed that the Uranium series variability observed for the Himalayan sediments is controlled by their mineralogical and grain-size evolution, rather than by the weathering process.This conclusion called into question the transfer timescale in Himalayan plains estimated by previous works and highlighted the need to explore radionuclide mobility at the mineral scale. For this purpose, an approach on pure mineral fractions pointed out exchange processes between the mineral phases, with a significant mobility of 230Th, strongly depleted in zircon, and 226Ra, particularly enriched in the clay fraction. The observed disequilibria are attributed to a recent weathering process of a few ky. Those observations are confirmed by the SIMS analysis of 238U-234U-230Th disequilibria on mineral grains, which show a 230Th enrichment at the grain surface in monazites and a loss of Th, 230 and 232, in zircons.

<p> Speleothems are calcium carbonate deposits, such as stalagmites, stalactites and flowstones, formed in a cave environment by loss of carbon dioxide from saturated groundwaters. Variations in the 18o/16o ratio of calcite are related to changes in depositional temperature provided that the speleothem formed in isotopic equilibrium with its seepage water (conditions characterised by slow coloss and no evaporation of seepage water). Variations in 18o/16o of the seepage water will also be reproduced in the calcite but allowance for this effect can be made if 18o/16o ratio of the source (ocean water) can be estimated (from deep sea sediment cores) and if the influence of temperature on 18o/16o ratio of precipitation at the site can be determined. Because cave temperatures closely approximate mean annual surface temperature, the axial 18o/16o record of a speleothem is therefore an indication of paleoclimate and of temperature change over the period of its growth. </p> <p> The frequency distribution of age measurements for several speleothems from an area may also be used as a paleoclimatic indicator because cold or glacial conditions above the cave will inhibit speleothem growth by freezing water at the surface and removing vegetation and soil cover, the main source of CO2 for the limestone dissolution-reprecipitation process. </p> <p> Pure, non-porous calcite speleothems from several limestone regions have been dated in this study by the 230Th/234U method, and in cases of uranium-rich speleothems, by the 231Pa/230Th method also. For ten such cases, examined, good agreement of ages determined by both dating methods was found. </p> <p> Relatively few deposits however, have shown deposition under isotopic equilibriwn conditions, due probably to the well-ventilated nature of the caves studied. </p> <p> The age distribution for speleothem from Cascade Cave on Vancouver Island, B.C., indicates growth during the mid-Wisconsin interstadial dated as 65 -30,000 yrs. B.P. Stable isotope profiles for two speleothems which grew over this period both show values of 18o/16o ratios of calcite which are significantly lower than calcite growing in the cave today. This is the first clearly-defined record of such an occurence (in previous work, 18o/16o of fossil speleothem was generally greater than modern). Using estimates of the change in 18o/16o of ocean water from a Pacific deep sea core, and the value determined by Dansgaard (1964) for the temperature dependence of 18o/16o of precipitation for oceanic sites, a realistic paleotemperature record is derived. The results indicate that temperatures at the Cascade Cave site were about 4.0°C , 64,000 yrs. ago· and gradually declined to 0°c by 35,000 yrs. ago. These data are consistent with the findings of Canadian workers from 14c and palynological studies of fossil organic matter in the area, and do not support the proposal by some American workers of a major glaciation occurring between 35 - 40,000 yrs. B.P. </p> <p> The age distribution for 140 analyses of 82 speleothems collected from caves in north-west England show abundant deposition during the periods 130 -90,000 yrs. B.P. and 13,000 yrs. B.P. to present, with limited growth over the periods > 350 -170,000 yrs. B.P. and 70 -35,000 yrs. B.P. No ages were found to lie within the periods 170 -140,000 yrs. B.P. and 35-15,000 yrs. B.P. These intervals are correlated to the Wolstonian and Devensian glaciations respectively. </p> <p> Only four speleothems were found to have grown in isotopic equilibrium with their seepage waters, and one of these showed periods of non-equilibrium deposition. In contrast to the Vancouver Island results, 18o/16o all ratios were found to be greater than or equal to modern, indicating that the apparent oceanic location of this site is not expressed in the on the value for temperature dependence of 18o/16o precipitation. </p> <p> An oxygen isotope profile for a flowstone dated between 126,000 and 109, 000 yrs. B.P. shows 18o/16o ratios commencing at values slightly lower than for modern calcite and shifting to still lower values at about 112, 000 yrs. B.P. This shift may indicate a cooling event perhaps carrelative with the isotope stage 5e-5d transition seen in the deep sea core record. A profile for a flowstone over the period 290 -190,000 yrs. B.P. shows excellent correlation to interglacial stages 9e and 7c seen in the deep sea core record, and a pronounced growth hiatus dated at about 250 210,000 yrs. B.P. correlates with glacial stage 8. These are the first speleothem results to show a climatic record beyond 200,000 yrs. B.P. </p> <p> The differences in 18o/16o behaviour for speleothems from the two locations (N .E. Pacific and ..E. Atlantic) are interpreted in terms of their relative proximity to the ocean, potential for exchange of water vapour and 'rainout' by airmasses moving towards the cave sites, and possibility of change in meteorological conditions (principally storm track) over the periods studied. </p> <p> In a subsidiary study, evidence for major sea level lowering during the Illinoian glaciation is recognised by age determinations on the calcite core of speleothems collected at 45m below present sea level from a 'blue hole' near Andros Island in the Bahamas. </p> <p> The possibility of applying the 234U/238U dating method to speleothem is also investigated in this work, by the analysis of modern calci tes and their seepage waters, using a new method for uranium extraction from groundwater. However the variations in 234U/238U ratios observed over short distances in the same cave demonstrate that estimation of initial fossil 234U/238U in the speleothem cannot simply be made by averaging modern ratios for the cave. </p> <p> Consideration is also given to the temperature dependent distribution of trace elements in calcite, particularly magnesium and strontium. Analyses of modern calcites and waters show that Mg incorporation is strongly temperature dependent whereas Sr is not. The possibility of using Mg variations in fossil speleothem as indication of temperature change is briefly examined but the results for one sample are found to be inconclusive. </p> / Thesis / Doctor of Philosophy (PhD)

This thesis is focused on prominent uranium deposits in Czech Republic and their secondary uranium mineralization. Main goal of this thesis is to analyze collected minerals and to determine their ages. Next step is to prove or disprove hypothesis that this secondary uranium minerals are products of Quaternary glacier weathering. As a suitable analytical method, an alpha spectrometry was used and the age was calculated by 230 Th/234 U ratio. Firstly, chosen methodology was verified with admixture of reference material PU1 (Přibram uraninite) in secular equilibrium and internal standard, both with known activity. Analyzed spectra confirmed that some of the samples lay on the very edge of datability, especially in case of PL1 and GF1, both samples are very young, so they easily could be products of anthropogenic activity (changed environment due to mining works). On the other hand, in case of sample GF3, the age was successfully determined, although it is also quite young phase. In case of samples ME3, ME4 and ME6 was used threshold dating method, because they were considered to be too old for age calculation. The rest of the samples chosen for age determination was analyzed without further complications. Based on the age and geological setting, samples GF3 (3 725 ± 845 years), JE1 (10 655 ± 1 795...

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