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L’objectif principal de cette thèse était de comprendre comment la variabilité temporelle et spatiale de l’oxygénation de l’eau de fond est enregistrée dans le test des foraminifères benthiques, à travers le rapport Mn/Ca et les paramètres des pores. Pour atteindre cet objectif, Ammonia tepida, un groupe d’espèces pseudocryptiques, du Grevelingenmeer (Pays-Bas) a été principalement étudié. A ce site, le gradient bathymétrique est accompagné par une augmentation de la durée et de l’intensité de l’hypoxie/anoxie saisonnière qui influence indirectement le rapport Mn/Ca et directement la porosité d’A. tepida. Notre étude de la Zone à Oxygène Minimum de la Mer d’Arabie suggère la présence d’un important biais diagénétique dans le signal Mn/Ca lors de la transition d’un foraminifère vivant vers un test fossile. En conclusion de cette thèse, la composition Mn/Ca d’un test des foraminifères benthiques dans notre zone d’étude semble être influencée par trois facteurs temporelles 1) l’oxygénation du milieu benthique et la position de la zone redox enrichie en Mn2+ dans l’eau interstitielle, 2) l’activité des bactéries câblées et 3) la période de calcification, ainsi que par trois facteurs spatiaux qui déterminent la position du foraminifère par rapport à la zone de Mn2+ lors de la calcification 4) le microhabitat, 5) la migration verticale des foraminifères et 6) la bioturbation de la macrofaune. Dans le Grevelingenmeer, la porosité d’A. tepida montre une relation avec l’oxygénation. Le couplage entre porosité et oxygénation semble être direct, une plus grande porosité permettant des échanges de gaz plus intensifs. Au contraire, la relation entre le rapport Mn/Ca et l’oxygénation serait plus indirecte, puisque celle-ci est également influencée par l’activité microbienne. L’utilisation simultanée de ces deux proxies totalement indépendants nous semble prometteuse, spécialement parce que ces proxies réagissent à différentes échelles de temps. / The main objective of this thesis was to investigate how the temporal and spatial variability of bottom water oxygenation is recorded in the benthic foraminiferal test, by the Mn/Ca ratio, and by the pore parameters. To achieve this objective, Ammonia tepida, a group of pseudocryptic species, of the Lake Grevelingen (Netherlands) was mainly studied. At this site, the depth gradient is accompanied by an increase in duration and intensity of seasonal hypoxia/anoxia which indirectly influences the Mn/Ca ratio and directly the porosity of A. tepida. Our study of the Oxygen Minimum Zone in the Arabian Sea suggests the presence of a significant diagenetic effect during the transition of a Mn/Ca signal from a living foraminifer to a fossil signal. In conclusion of this PhD research, the Mn/Ca signal of a benthic foraminiferal test seems to be influenced by three temporal factors: 1) the oxygenation of the benthic ecosystem and the position of the Mn2+ zone in the interstitial water, 2) the cable bacteria activity, and 3) the period of calcification, as well as by three spatial factors which determine the position of the foraminifer with respect to the Mn2+ zone during calcification 4) the microhabitat, 5) the vertical migration of the foraminifer and 6) the bioturbation of macrofauna. In the Lake Grevelingen, the porosity of A. tepida shows a relationship with oxygenation of the benthic ecosystem. The coupling between porosity and oxygenation could be rather direct, a greater porosity allowing more intensive gas exchanges. In contrast, the relationship between the Mn/Ca ratio and the oxygenation would be more indirect, being influenced in particular by the microbial activity. The simultaneous use of these two totally independent proxies seems promising, especially because these proxies react at different time scales.

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Determination of metal in milk powder and soil by slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry

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In this research, electrochemical methods are used to synthesize the inorganic fraction of bone, hydroxyapatite, for application in biological implants and as a calibration material for elemental analysis in human bone. Optimal conditions of electrochemically deposited uniform apatite coatings on stainless steel were investigated. Apatite is a ceramic with many different phases and compositions that have beneficial characteristics for biomedical applications. Of those phases hydroxyapatite (HA) is the most biocompatible and is the primary constituent of the inorganic material in bones. HA coatings on metals and metal alloys have the ability to bridge the growth between human tissues and implant interface, where the metal provides the strength and HA provides the needed bioactivity. The calcium apatites were electrochemically deposited using a modified simulated body fluid adjusted to pH 4-10, for 1-3 hours at varying temperature of 25-65°C while maintaining cathodic potentials of -1.0 to -1.5V. It was observed that the composition and morphology of HA coatings change during deposition by the concentration of counter ions in solution, pH, temperature, applied potential, and post-sintering. The coatings were characterized by powder x-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. The precipitated powders from the experiment were also characterized, with results showing similarities to biological apatite. There is a need for quantitative elemental analysis of calcified biological matrices such as bone and teeth; however there are no suitable calibration materials commercially available for quantitative analysis. Matrix-matched standards are electrochemically synthesized for LA-ICP-MS analysis of human bone. The synthetic bioapatite is produced via a hydrothermal electrochemical process using a simulated body fluid solution to form hydroxyapatite. Additional bioapatite standards are synthesized containing trace amounts of metals. The x-ray diffraction of the synthesized standards shows an increase in cell volume for the crystal structure from 0.534 to 0.542 nm3 with the substitution of metals into the crystal structure. The analyte concentration and recoveries for the synthesized standards and reference materials were determined by ICP-MS with % RSD below 6.3% and limits of detection below 1.2 ng/mL for trace metals. The electrochemically synthesized bioapatite was also compared to standard reference materials with X-ray diffraction, FTIR, and Raman spectroscopy. Optimum laser ablation parameters were determined for the standards and human bone. The synthesized standards were homogeneous and the reproducibility for the isotope concentrations determined by LA-ICP-MS was between 3-10 % compared to 10-35% for SRM 1486 Bone Meal and SRM 1486 Bone Ash. A quantitative method has been developed for 2D mapping using LA-ICP-MS and the matrix-matched standards of metal-doped biopaptite to characterize metal concentrations in human bone. Laser ablation parameters for the method are refined resulting in concentration (ug/g) contour map measurements for each isotope measured in the human bone. Essential and non-essential metals, Al, Ca, Cu, Fe, Pb, and Zn are quantitatively mapped using these parameters. Limit of detection for the metals in the bone range from 0.001 to 0.08 ug/g. The LA-ICP-MS analysis method developed proves to be a straightforward and simple method for quantitative analysis of human bone.