No description available.

<p>Mars’ Polar layered Deposits (PLD) accumulated over the last few millions of years due to seasonal buildup of frost trapping atmospheric gasses and incoming sediments, thereby preserving the history of Mars' recent climate in the form of an ice-rich geologic record. The PLD includes both the North Polar Layered Deposits (NPLD) and the South Polar Layered Deposits (SPLD) which are estimated to be up to 5 Mya and 100 Mya old respectively. Characterizing the contents of these deposits is essential to understand the role of geologic and climatic processes recently active on Mars. The Mars scientific community recommends robotic exploration of these icy NPLD to sample the ice and extract recent climate records; however, linking the geologic record to the climatic history will require quantitative dating of the NPLD. The SPLD is thought to be older than the north polar deposits, so the stratigraphic records of the SPLD are a window to look deeper into the climatic history of Amazonian Mars. Deciphering the paleoenvironment at the PLD requires characterization of the ice-rich deposits, however, the origin, composition, transport histories, and alteration environment of sediments within the deposits are not well constrained.</p> <p>In this study we use orbital reflectance spectroscopy to show for the first time that dateable mafic lithics are present throughout the PLD. We find significant glass as well as diverse crystalline minerals, which suggests that surface processes like impacts and volcanism were active during the late Amazonian and transported sand-sized and finer sediments from across the planet to the poles. In situ investigation of the PLD will thus provide critical quantitative age constraint on both the recent geologic and climatic histories of Mars. Previous studies have confirmed widespread detection of sulfates at the NPLD and here we show that sulfates dominate the alteration mineralogy at the SPLD suggesting acidic, oxidizing, and evaporitic conditions. Based on this more extensive survey, previously reported rare detection of smectites and hydrated silica in the SPLD is likely due to ballistic emplacement by impacts from targets on surrounding smectite-bearing Noachian terrains.</p> <p>Detrital ice-rich sediments within the PLD are a complex mixture of mafic minerals and weathering products from multiple sources and are continuously reworked. In order to investigate the material and grain-size dependent effects of chemical and physical weathering in a cold and wet basaltic environment, a rover-based Mars analog study is conducted in the glacio-fluvial-aeolian landscapes of Iceland. A DCS-based color analysis technique is employed in tandem with VNIR spectroscopy and XRF analysis to develop a strategy for conducting sediment provenance. We observe that DCS-based color analysis is a powerful tool for identifying spectral diversity, and that it has the capability to differentiate primary minerals from alteration minerals. Because color analysis can aid in identifying diverse targets for sampling within the rover’s workspace, tactically, DCS colors can be used during operations to link detrital sediments within the rover’s vicinity to surrounding bedrock sources. DCS images enhance our ability to correlate observation of surface features from orbit, extend local mineralogical interpretation to surrounding regions, optimize rover’s traverse and select science targets. </p>

<p>Arsenic (As) is an element that is well known for its toxic capabilities. It is odorless and colorless and is known to contaminate the drinking water of populations in several parts of the world. Routine monitoring of arsenic exposure is usually performed with urine, hair or nail, where samples are collected for laboratory analysis. Arsenic’s strong affinity to keratin rich tissues make skin another possible measurement site, in addition to the latter two tissues mentioned above. In some cases, skin samples are extracted for analysis. This is painful and invasive and is not ideal for <em>in vivo</em> monitoring of arsenic. The ability to quantify elemental concentration non-destructively is the major calling card of x-ray fluorescence (XRF). To that end, work was started on development of XRF detection systems for arsenic. The technique has shown promise for other elements and dramatic improvements in As detection capabilities were previously found when going from a radioisotope-based x-ray source to an x-ray tube based approach.</p> <p>This thesis documents the comparison of three x-ray tube based detection systems intended for the measurement of arsenic in skin. Two benchtop systems were used, with a) extended development of the previously assembled system and b) the first use of a separate detection system. Two handheld x-ray analyzers (portable detection systems) were also investigated in stand mode, where they were attached to a purpose-built mounting stand, provided by the manufacturer, during all analysis. Polyester resin phantoms were used to model arsenic in skin and a nylon backing was used to represent as bulk tissue behind skin. During the course of the work, modifications were made to the laboratory setup associated with the benchtop approaches.</p> <p>A benchtop polychromatic Mo anode x-ray tube based x-ray fluorescence (XRF) detection system was the first system used in this work. Through modifications to the existing design of the system, the lowest minimum detection limit (MDL) achievable was found to be (0.611±0.001) ppm normalized to gross scatter, where ppm is ug of arsenic per gram of dry weight (resin). The measurement time was ~1800 seconds real time. The equivalent (skin) and whole body effective doses delivered were (19±3) uSv and (163±47) uSv respectively. The corresponding direct (un-normalized) MDL was (0.499±0.002) ppm, in agreement with that found previously. Modifications to the system allowed a reduction in the localized effective dose delivered, to achieve this MDL, from (0.64±0.03) uSv previously to (0.14±0.04) uSv here.</p> <p>Next, the current work investigated two handheld x-ray analyzers provided by InnovX. A PiN diode detector based Alpha 4000S model unit (W anode x-ray tube) and a Silicon Drift Detector (SDD) based Delta model (Au anode x-ray tube). Both units were operated in benchtop mode: they were mounted in a stand and a phantom was placed on a kapton exit window. The lowest gross-scatter normalized and direct detection limit with the Alpha 4000S unit was (1.649±0.002) ppm and (1.651±0.002) ppm respectively. The equivalent and whole body effective doses delivered were found to be (9.4±2.2) mSv and (94±22) uSv respectively. The localized effective dose was (6.4±1.5) X 10^-3 uSv. By comparison, the Delta unit produced a gross-scatter and direct normalized detection limit of (0.570±0.002) ppm and (0.558±0.002) ppm respectively. The equivalent dose delivered was found to be (19.0±9.0) mSv. The corresponding localized and whole body effective doses delivered were (9.7±4.6) X 10^-3 uSv and (190±90) uSv respectively.</p> <p>The last system used in the current research was a monochromatic Ag anode x-ray tube based XRF setup. A doubly curved crystal (DCC) was used to select the Ag K-alpha line and focused the beam to a spot size of mm² at the focal length. The phantoms were placed at a farther distance where the beam had expanded to a larger area. The lowest Compton scatter normalized detection limit with the Si(Li) detector was found to be (0.696±0.002) ppm. After characterizing its performance in a range of energies, a silicon drift detector was also used on this system. It had the benefit of higher throughput capabilities and superior resolution. The housing of the detector was sufficiently small that it could be placed closer to the phantom surface than the Si(Li) detector. The lowest Compton-scatter normalized detection limit with the SDD was (0.441±0.003) ppm in 1800 seconds real time. The equivalent dose was found to be (11±2) mSv and the localized and whole body effective doses were found to be (3.92±0.87) X 10^-3 uSv and (110±23) uSv respectively. A significantly lower system dead time was observed with the SDD. Finally, Monte Carlo simulations of the system were performed to evaluate the performance of three ratios when their phantom measurement values were compared against simulations of skin. Results were found to be in agreement to withinin vivo concentration of arsenic in skin (ICRP).</p> <p>Finally, EDXRF measurements were performed on bulk cores of skin, <em>ex vivo</em>. While it was not possible to detect arsenic in the samples, due to the samples being collected from members of the public as opposed to an exposed population, a depth profile of numerous skin samples, starting from the surface and running straight down, was obtained for calcium, iron and copper.</p> / Doctor of Philosophy (PhD)

The particle size distribution of a powder plays a crucial role in the performance of bat- teries with powder-based electrodes and requires reliable and practical analysis. The aim of this project was therefore to develop a protocol for analysis of the particle size dis- tribution and composition of powders used in the electrodes of Nilar’s batteries. The analytical methods described in the protocol permits practical applications, such as com- paring the particle size distribution and composition of pristine and reclaimed powders with the manufacturer’s data as quality control.  A literature survey was initially conducted to select appropriate analysis methods for this project. After performing several practical trials, X-ray diffraction, X-ray fluorescence, laser diffraction analysis, and scanning electron microscopy were the techniques included in the protocol. X-ray diffraction showed potential in obtaining the crystallite size of the powders, but other techniques are required to confirm the results. X-ray fluorescence analysis was found to produce fairly similar values as those given by the manufacturer. Scanning electron microscopy was used to analyse the particle size distribution with the help of an image processing software. Complementary data of the smaller particle sizes was obtained using laser diffraction analysis.

Drywall, a popular building material made of gypsum based plaster sandwiched between two thick sheets of paper is used for building interior walls, is speedier alternative to traditional plaster, decreasing time and labor for construction. Importance of drywall increased with the demand for drywall after nine hurricanes hit Florida in 2004-05 and widespread damage caused in the Gulf Coast after Katrina in 2005. This study has two parts. First part presents an analysis of metals like strontium for the identification of Chinese drywall, and a comparison of strontium concentrations of American drywall and Chinese drywall using XRF (X-Ray Fluorescence) analysis with the Innov-X XRF analyzer. The second part presents an analysis of metal exposure during cutting and installation of drywall using 8stage Cascade impactor. The work space concentration of, different metals is analyzed using XRF analysis and particulate matter within various size ranges, were calculated and their effects are studied.

The aim of this thesis is to study 31 individuals from an early christian cemetery in Varnhem, Sweden and through the use of XRF, study the strontium concentrations and the strontium to calcium ratios in bone and use that as an indicator for diet. The material consists of femurs and teeth and through analyzing this I will compare previous dietary studies using stable carbon, nitrogene and sulphur isotope analyses to see wether quantitative strontium analysis can be used as a way to study diet in prehistoric societies. The conclusion is that XRF is not as thorough as an isotope study but it provides a general knowledge of what the population has been eating where we can determine which individuals has had diet consisting of more meat or terrestrial plants.

This thesis presents investigations on sediments from two African lakes which have been recording changes in their surrounding environmental and climate conditions since more than 200,000 years. Focus of this work is the time of the last Glacial and the Holocene (the last ~100,000 years before present [in the following 100 kyr BP]). One important precondition for this kind of research is a good understanding of the present ecosystems in and around the lakes and of the sediment formation under modern climate conditions. Both studies therefore include investigations on the modern environment (including organisms, soils, rocks, lake water and sediments). A 90 m long sediment sequence was investigated from Lake Tswaing (north-eastern South Africa) using geochemical analyses. These investigations document alternating periods of high detrital input and low (especially autochthonous) organic matter content and periods of low detrital input, carbonatic or evaporitic sedimentation and high autochthonous organic matter content. These alternations are interpreted as changes between relatively humid and arid conditions, respectively. Before c. 75 kyr BP, they seem to follow changes in local insolation whereas afterwards they appear to be acyclic and are probably caused by changes in ocean circulation and/or in the mean position of the Inter-Tropical Convergence Zone (ITCZ). Today, these factors have main influence on precipitation in this area where rainfall occurs almost exclusively during austral summer. All modern organisms were analysed for their biomarker and bulk organic and compound-specific stable carbon isotope composition. The same investigations on sediments from the modern lake floor document the mixed input of the investigated individual organisms and reveal additional influences by methanotrophic bacteria. A comparison of modern sediment characteristics with those of sediments covering the time 14 to 2 kyr BP shows changes in the productivity of the lake and the surrounding vegetation which are best explained by changes in hydrology. More humid conditions are indicated for times older than 10 kyr BP and younger than 7.5 kyr BP, whereas arid conditions prevailed in between. These observations agree with the results from sediment composition and indications from other climate archives nearby. The second lake study deals with Lake Challa, a small, deep crater lake on the foot of Mount Kilimanjaro. In this lake form mm-scale laminated sediments which were analyses with micro-XRF scanning for changes in the element composition. By comparing these results with investigations on thin sections, results from ongoing sediment trap studies, meteorological data, and investigations on the surrounding rocks and soils, I develop a model for seasonal variability in the limnology and sedimentation of Lake Challa. The lake appears to be stratified during the warm rain seasons (October – December and March – May) during which detrital material is delivered to the lake and carbonates precipitate. On the lake floor forms a dark lamina with high contents of Fe and Ti and high Ca/Al and low Mn/Fe ratios. Diatoms bloom during the cool and windy season (June – September) when mixing down to c. 60 m depth provides easily bio-available nutrients. Contemporaneously, Fe and Mn-oxides are precipitating which cause high Mn/Fe ratios in the light diatom-rich laminae of the sediments. Trends in the Mn/Fe ratio of the sediments are interpreted to reflect changes in the intensity or duration of seasonal mixing in Lake Challa. This interpretation is supported by parallel changes in the organic matter and biogenic silica content observed in the 22 m long profile recovered from Lake Challa. This covers the time of the last 25 kyr BP. It documents a transition around 16 kyr BP from relatively well-mixed conditions with high detrital input during glacial times to stronger stratified conditions which are probably related to increasing lake levels in Challa and generally more humid conditions in East Africa. Intensified mixing is recorded for the time of the Younger Dryas and the period between 11.4 and 10.7 kyr BP. For these periods, reduced intensity of the SW monsoon and intensified NE monsoon are reported from archives of the Indian-Asian Monsoon region, arguing for the latter as a probable source for wind mixing in Lake Challa. This connection is probably also responsible for contemporaneous events in the Mn/Fe ratios of the Lake Challa sediments and in other records of northern hemisphere monsoon intensity during the Holocene and underlines the close interaction of global low latitude atmospheric circulation. / In dieser Arbeit werden Ergebnisse von Untersuchungen an den Sedimenten zweier afrikanischer Seen vorgestellt, die ein Archiv für Klimaveränderungen über einen Zeitraum von mehr als 200.000 Jahren darstellen. Der Schwerpunkt liegt in dieser Arbeit auf dem letzten Glazial und dem Holozän (ca. 100.000 Jahre vor heute [nachfolgend als 100 kyr BP bezeichnet] bis heute). Grundlegende Voraussetzung für solche Studien ist ein gutes Verständnis der Ökosysteme in und um den See, sowie des gegenwärtigen Sedimentationsgeschehens. Deswegen beinhalten beide Seestudien Untersuchungen der heutigen Organismen, Böden, Gesteine, Wasserchemie und Sedimentablagerungen. Im Tswaing-See im nordöstlichen Südafrika wurden anhand eines 90 m langen Sedimentprofils Studien zur Sedimentzusammensetzung und Untersuchungen der Zusammensetzung und Qualität des organischen Materials durchgeführt. Sie zeigen einen Wechsel zwischen Phasen hohen detritischen Eintrags, während derer v.a. kaum autochthones organisches Material im See erhalten blieb, mit Phasen geringen Eintrags und dafür karbonatischer oder evaporitischer Sedimentation, die hohe Gehalte v.a. autochthonen organischen Materials aufweisen. Diese Phasen werden als relativ feuchte bzw. trockene Perioden interpretiert und folgen bis vor ca. 75 kyr BP Schwankungen der lokalen solaren Einstrahlung. Dieser Einfluss nimmt nach 75 kyr BP ab und azyklische feuchte Phasen werden beobachtet. Mögliche Ursachen sind Veränderungen in der ozeanischen Zirkulation und Verschiebungen in der Lage der Innertropischen Konvergenzzone (ITCZ); beides sind auch heute Haupteinflussfaktoren auf die Niederschläge in der Region. Die heute lebenden Organismen des Tswaing-Kraters wurden mittels Analysen der Biomarkerzusammensetzung und der Kohlenstoffisotopie charakterisiert und ihr Einfluss auf die heutigen Seeablagerungen untersucht. Dabei konnten zusätzlich Indikatoren für die Aktivität methanotropher Bakterien nachgewiesen werden. Der Vergleich heutiger Sedimente mit denen des Zeitraumes 14 bis 2 kyr BP zeigt deutliche Veränderungen sowohl in der Zusammensetzung, als auch in der Kohlenstoffisotopie der Biomarker, die mit Veränderungen in der Hydrologie erklärt werden können. Die gefundenen Hinweise auf feuchtere Bedingungen im Zeitraum älter als 10 kyr BP, für trockenere Verhältnissen zwischen 10 und 7.5 kyr BP und für die nachfolgende Wiederzunahme an Feuchtigkeit werden durch die sedimentologischen Ergebnisse unterstützt. Objekt der zweiten Seestudie ist der Challa-See am Fuß des Kilimanjaro. Hier werden heute im mm-Maßstab laminierte Sedimente gebildet, die mit Mikro-XRF-scanning auf Veränderungen in der Elementzusammensetzung untersucht wurden. Zusammen mit Untersuchungen der Mikrofazies und im Vergleich mit ersten Ergebnissen noch laufender Sedimentfallenstudien, mit meteorologischen Daten und Analysen des Umgebungsgesteins werden die saisonalen Veränderungen in der Temperaturverteilung, der Durchmischungstiefe, dem detritischen Eintrag und der Bioproduktivität des Sees in den Sedimenten nachvollziehbar. Der See ist in den feucht-warmen Perioden von Oktober bis Dezember und von März bis Mai stratifiziert. Während dieser Zeit erfolgt der Eintrag detritischen Materials und Kalziumkarbonat fällt aus; eine dunkle Lage mit hohen Gehalten an Fe und Ti und mit hohen Ca/Al- und niedrigen Mn/Fe-Verhältnissen bildet sich am Boden des Sees. Diatomeen blühen während der kühlen, windigen Periode von Juni bis September, wenn die Durchmischung bis auf etwa 60 m Tiefe Nährstoffe verfügbar macht. Die Ausfällung von Fe- und Mn-oxiden sorgt für hohe Mn/Fe-Verhältnisse; es bildet sich eine helle Lage auf dem Sediment. Trends im Mn/Fe-Verhältnis werden als Signal für Veränderungen in der Intensität oder Dauer der saisonalen Durchmischung interpretiert. Dies wird unterstützt durch parallele Trends im Gehalt an organischem Material und an biogenem Silizium, wie durch Analysen an einem 22 m langen Bohrkern gezeigt werden kann. Nach gut durchmischten und von erhöhtem Eintrag von außen geprägten Verhältnissen während des letzten Glazials erfolgt gegen 16 kyr BP ein Übergang zu stärker stratifizierten Bedingungen. Diese korrespondieren mit einem steigenden Seespiegel und verbreiteten Hinweisen auf feuchte Bedingungen im tropischen Ostafrika. Stärkere Durchmischung herrschte während der Jüngeren Dryas und von 11.4 bis 10.7 kyr BP. Diese Perioden entsprechen Zeiten verringerter Südwest- und vermutlich verstärkter Nordostmonsunintensität im Bereich des Indisch-Asiatischen Monsuns und spiegeln eine global beobachtete südliche Verschiebung der ITCZ wider. Nach einer kurzen stabilen, feuchten Phase im frühen Holozän nimmt die Durchmischung des Sees im Verlauf des Holozän wieder zu. Abrupte Ereignisse während des Holozän scheinen im Challa-See zeitgleich mit Veränderungen der Monsunintensität der Nordhemisphäre aufzutreten und bezeugen die starke klimatische Kopplung der niederen Breiten in globalem Maßstab.

L’attività di ricerca ha previsto il confronto fra due siti inquinati da metalli pesanti e due siti controllo naturali. Contrariamente ai parametri chimico-fisici e ai contenuti in metallo dei suoli, le analisi vegetazionali non hanno evidenziato differenze significative tra i siti. E’ stata necessaria la messa a punto strumentale di tecniche ICP-OES, ED(P)XRF per la calibrazione empirica di un XRF portatile, per le osservazioni puntiformi in situ di suoli e flora ed è stata modificata la metodica ufficiale per le stime della biodisponibilità dei metalli pesanti nei suoli inquinati. 6 specie comuni ai 4 siti sono state valutate per i loro TF e BAF. Viene confermata la specie-specificità del TF e del BAF per il quale è stato elaborato un inedito algoritmo per un corretto confronto tra le specie. Tra le sei specie, Silene Alba ha i migliori TF e BAF. Successivamente, sono state valutate alcune caratteristiche del Pennisetum clandestinum, candidato per la fitodepurazione: tollera le concentrazioni di arseniato tipiche dei suoli inquinati, l’arseniato è un inibitore competitivo del trasporto del fosfato, possiede un’elevata velocità di assorbimento dell’arseniato che accumula nella radice, ma non lo trasloca nella frazione epigea, parte dell’As(V) viene ridotto ad As(III) che viene efflusso dalla radice / The research has provided a comparison between two heavy metals polluted sites and two natural control sites. Unlike physical-chemical parameters and metal content in the soils, vegetation analysis showed no significant differences between sites. The development and optimization of instrumental techniques ICP-OES and ED(P)XRF was necessary to calibrate empirically a portable XRF for soil and flora point observations in situ and the official method for estimation of bioavailability of heavy metals in polluted soil was changed. Six species, common to the four sites, were evaluated for their TF and BAF. Were confirmed the TF and the BAF species-specificity for which it was developed a novel algorithm to obtain a correct comparison among species. Among the six species, Silene Alba has the best TF and BAF. In the second stage, some characteristics of Pennisetum clandestinum, candidate for the phytoremediation, were assessed: it tolerates arsenate concentrations typical of polluted soil, arsenate is a competitive inhibitor of phosphate transport, it has a high uptake rate of arsenic that accumulates in the root, but it doesn’t move in the aboveground fraction and part of As(V) is reduced to As(III), which is efflux from roots.

La investigació que es presenta en aquesta tesi es centra en l'aplicació i millora de metodologies analítiques existents i el desenvolupament de nous procediments que poden ser utilitzats per a l'estudi dels efectes ambientals de la dispersió dels metalls entorn a les zones mineres abandonades.En primer lloc, es van aplicar diferents procediments d'extracció simple i seqüencial per a estudiar la mobilitat, perillositat i bio-disponibilitat dels metalls continguts en residus miners de característiques diferents. Per altra banda, per a estudiar les fonts potencials de Pb en la vegetació de les zones mineres d'estudi, una metodologia basada en la utilització de les relacions isotòpiques de Pb determinades mitjançant ICP-MS va ser avaluada. Finalment, tenint en compte l'elevat nombre de mostres analitzades per a avaluar l'impacte de les activitats mineres, es va considerar apropiat el desenvolupament de mètodes analítics d'elevada productivitat. En aquest sentit la implementació d'estratègies quantitatives així com l'aplicació de les millores instrumentals en els equips de XRF han estat avaluades per a aconseguir resultats analítics fiables en l'anàlisi de plantes. A més, alguns paràmetres de qualitat com la precisió, l'exactitud i els límits de detecció han estat curosament determinats en les diverses configuracions de espectròmetres de XRF utilitzats en el decurs d'aquest treball (EDXRF, WDXRF i EDPXRF) per a establir la capacitat de la tècnica de XRF com a tècnica alternativa a les clàssiques comunament aplicades en la determinació d'elements en mostres vegetals. / The research presented in this thesis is based on the application and improvement of analytical existing methodologies and the development of novel procedures that can be used to assess the environmental effects on metal dispersal around abandoned mining activities. On the one hand, single and sequential extraction procedures were properly applied in order to study the potential mobility, risk and bioavailability of the metals contained in several mining wastes of different features. On the other hand, in an attempt to study the potential sources of the anomalous lead content in vegetation specimens growing on the waste and soils of abandoned mining areas, a methodology based on the use of stable lead isotope ratios using ICP-MS instrumentation was evaluated.Finally, in view of the considerable number of vegetation specimen analysis necessary to assess the impact of mining activities, the study of high productivity analytical methods for metal determination in this kind of matrices was considered appropriate. In this sense, the implementation of suitable quantitative strategies and the recent improvements in the XRF instrumentation have been evaluated to achieve reliable analytical results for plant analysis. Besides, analytical figures of merit such as precision, accuracy and limits of detection have been carefully determined in the diverse configurations of XRF spectrometers employed in the course of this work (EDXRF, WDXRF, EDPXRF) using different excitation sources in order to assess the capability of XRF as an alternative analytical tool to classical destructive methodologies, commonly applied for the determination of elements in vegetation matrices.

Cette thèse a pour objectifs de documenter les variations spatiotemporelles de la zone de minimum d’oxygène (OMZ) du Pacifique Nord-Est, et d’identifier les mécanismes qui ont causé ces variations. L’étude est fondée sur l’analyse géochimique des composants majeurs, mineurs et traces de sédiments prélevés dans le Pacifique Nord-Est, en combinant des mesures par ICP-MS et scanneur XRF. Ces mesures ont permis de distinguer l’effet de la productivité biologique de celui de la ventilation océanique sur l’oxygénation du sédiment. J’ai pu mettre en évidence le rôle prépondérant de la productivité au niveau de la Basse Californie (23°N), qui varie en phase avec les températures en Atlantique Nord durant les 120.000 dernières années. Par ailleurs, la ventilation océanique a probablement joué un rôle important au niveau du golfe de Papagayo (12°N), par l’advection de masses d’eau provenant des hautes latitudes nord et sud. L’intensité de l’OMZ du Pacifique Nord-Est serait donc influencée par des modifications des circulations océaniques et atmosphériques, liées aux climats des hautes latitudes des deux hémisphères. / This thesis aims at documenting the spatiotemporal variations of the Oxygen Minimum Zone (OMZ) of the northeastern Pacific, and identifying the mechanisms that caused theses variations. The study is based on the geochemical analyses of major, minor, and trace elements of sediments from the northeastern Pacific, by combining ICP-MS and XRF scans measurements. These measurements allowed distinguishing the effect of biologic productivity and oceanic ventilation on sediment oxygenation. I was able to highlight the predominant impact of the productivity off the Baja California Margin (23°N), which varied in phase with the high northern Atlantic temperature across the past 120,000 years. Moreover, oceanic ventilation did play an important role off the Papagayo Gulf (12°N), because of the advection of water mass coming from the high northern and southern latitudes. OMS intensity in the northeastern Pacific could thus be influenced by changes in the atmospheric and oceanic circulation, in relation to high northern and southern latitudes climates.