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Antarctic ice cores are invaluable, direct and high-resolution archives of the past atmosphere and the evolution of Earth’s climate. These unique deposits have revealed tight interplays between dust and climate in Southern Hemisphere. We developed an algorithm (complemented with Monte Carlo simulations) using a large database of REE patterns measured in sediments/soils from well-known dust Potential Source Areas (PSAs) located in the Southern Hemisphere to determine respective contributions of these sources that best fit REE patterns measured in ice cores. We applied this methodology to Epica Dome C (EDC)[1] ice core and provide the first continuous, high-resolution record of dust provenance in Antarctica through the Last Glacial-Interglacial Transition (LGIT-2.9 to 33.7kyr BP). Our reconstructed provenance record is consistent with (i) reported isotopic signature of Antarctic dust and (ii) the climatic evolution of the various PSAs contributing to Antarctic depositions. More importantly, our results compare well with our provenance record in Epica Dronning Maud Land (EDML)[2]. Both cores show a major shift in sources between 14 and 15kyr BP when the contribution of Patagonia (main supplier of dust) fell from ̴55% and ̴70% to 35% and ̴50% in EDC and EDML, respectively. After 14kyr BP, dust from Southern Africa (and to a less extent Australia and New Zealand) became more prevalent from ̴20% and ̴8% to ̴35% and ̴23% in EDC and EDML, respectively. Intriguingly, this compositional shift occurs later than the decline in total dust flux observed between 16-18kyr BP in EDC and EDML. We ascribe this 14-15kyr BP shift in the relative contribution of dust from Patagonia and Southern Africa to (i) long-lasting changes in the hydrology of Patagonian rivers and (ii) a sudden acceleration of sea-level rise at 14.5kyr BP that submerged vast swathes of Patagonian continental shelf, triggering a decline in the supply of Patagonian dust to Antarctica and thus, letting the South Afric, info:eu-repo/semantics/published

Southern Hemisphere (SH) dust depositions recorded major changes in origin and flux intensity during the Last Glacial-Interglacial Transition (LGIT) reflecting modifications in atmospheric circulation. Dust archives from ice cores have shown compelling evidence that Southern South America (SSA) is the major dust supplier to Antarctica. However, there is yet no consensus on contributions from secondary Potential Source Areas (PSAs) such as, Australia, New Zealand, Southern Africa (SAF), and Antarctica itself. Among those, SAF is a vast PSA that has been, so far, largely understudied. With a main focus on the Namibian coast in SAF, this work presents an innovative and multi-proxy approach for the identification and quantification of the SH PSAs for Antarctica and the Southern Ocean during the LGIT. We developed a statistical algorithm (complemented with Monte Carlo simulations) combining Rare Earth Elements from well-known PSAs in SH to provide the best fit to the REE patterns measured in EPICA Dronning Maud Land (EDML) allowing for the provenance identification and quantification. Our results provide the first high-resolution and continuous record of the PSAs contribution in the South Atlantic sector of East Antarctica from 26.5kyr to 7.5kyr BP. A major shift is observed at ~14.5kyr BP where the contribution (and thus flux) from Patagonia, the main dust supplier during the Last Glacial Maximum, fell from ̴70% to ̴45%. In the Early Holocene, SAF (~25%) and to a lesser extent Australia and New Zealand became more prevalent[1]. In addition, Sr, Nd and Pb isotopic compositions from the SH PSAs were compared with the East Antarctica dust signature[2]. In agreement with our REE results, during the last glacial climatic periods, East Antarctica dust isotopic composition (EDC & Vostok ice cores) is very uniform converging to an unequivocal SSA signature. In contrast, interglacial dust depositions (in agreement with South Atlantic sediments) show more extreme negative eNd and, info:eu-repo/semantics/published

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Atmospheric dust is a major component of the Earth System. The optical properties of dust and their roles in cloud nucleation processes have a major impact on Earth’s radiative budget and hydrological cycle. Dusts also take part in many biogeochemical cycles in surface waters of the oceans and on land through their capacity to supply key micronutrients (e.g. Fe, P) sustaining primary production. The aim of this thesis is to improve the understanding of dust cycle by creating new and innovative methods allowing to trace the source regions of dust and quantify their respective contributions. We developed a chromatographic method to isolate and analyze six isotopic systems (i.e. Pb, Nd, Sr, Zn, Cu, Fe) widely used to trace dust source areas. We optimized a new method for single, low-mass dust samples and, in doing so, we observed that the usual rock reference materials (RM) used to calibrate isotopic analysis were not representative of dust. In fact, there is little to no RM for dust and therefore, we set out to characterize precisely the isotopic signatures of two new dust reference materials, ATD and BCR-723. The latter two are representative of natural-like and urban-like dust that we propose now as new standards for atmospheric dust studies. We also investigated dust deposition, along a 250-km transect from the NE Antarctic coastline to the Princess Elisabeth Station area. Using dust samples collected from Sigma-2 passive samplers or isolated from snow samples, we determined the morphology, size distribution and chemical composition of the dust samples at the particle-scale using an automated Scanning Electron Microscope coupled to Energy Dispersive Spectroscopy (SEM-EDS). More than 5500 particles were analysed and the results showed that the grain-size distribution was <5 μm. We also observe difference in mineralogy at the coast compared to the inland section of our transect: dominance of quartz and aluminosilicates at the coast and of Fe-Mg silicates near, RésuméLes particules atmosphériques (PA) sont un composant majeur du système Terre. Leurs propriétés optiques ainsi que leur rôle au sein des processus de nucléation des nuages ont des impacts majeurs sur le budget radiatif et hydrologique de la terre. Les PA interviennent aussi dans de nombreux cycles biogéochimiques à la surface des océans ou sur terre grâce à leur capacité à fournir des nutriments clés (e.g. Fe, P) soutenant la production primaire. Le but de ce doctorat est d’améliorer la compréhension du cycle des PA en créant de nouvelles méthodes innovatrices permettant de tracer leurs origines et quantifier leurs contributions. Nous avons développé une nouvelle méthode chromatographique optimisée pour les PA afin d’analyser six systèmes isotopiques (i.e. Pb, Nd, Sr, Zn, Cu, Fe) largement utilisés pour tracer l’origine des PA. Afin de combler un manque crucial en terme de matériaux de référence (MR), nous avons quantifié deux nouveaux MR de PA, ATD et BCR-723 (représentatifs des milieux naturels et urbains) et nous les proposons pour toutes les futures études géochimiques de PA. Nous avons aussi étudié les dépositions atmosphériques le long d’un ‘transect’ de 250 km depuis la côte Antarctique jusqu’à la station Belge Princesse Elisabeth. Premièrement, nous avons réalisé des analyses morphologiques et chimiques à l’échelle de la particule à l’aide d’un Microscope Electronique à Balayage à dispersion d’énergie (MEB-EDS). Les analyses ont montré une distribution granulométrique <5 μm ainsi qu’une variation de composition chimique (i.e. minéralogie) depuis la côte jusqu’aux Sør Rondane. Deuxièmement, afin de mieux identifier l’origine de ces PA, nous avons analysé les terres rares (REE) et développé dans son intégralité une nouvelle approche statistique permettant d’identifier les sources ainsi que leurs contributions relatives. Grâce à cela, nous avons déterminé que les échantillons à la côte proviennent du Puna-Altiplano, de Patagonie et du Sud de l’Afrique (SAF, Doctorat en Sciences, info:eu-repo/semantics/nonPublished

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Atmospheric dust is an integral component of the Earth system with major implications for the climate, biosphere and public health. In this context, identifying and quantifying the provenance and the processes generating the various types of dust found in the atmosphere is paramount. Isotopic signatures of Pb, Nd, Sr, Zn, Cu and Fe are commonly used as sensitive geochemical tracers. However, their combined use is limited by the lack of (a) a dedicated chromatographic protocol to separate the six elements of interest for low-mass samples and (b) specific reference materials for dust. Indeed, our work shows that USGS rock reference materials BHVO-2, AGV-2 and G-2 are not applicable as substitute reference materials for dust. We characterised the isotopic signatures of these six elements in dust reference materials ATD and BCR-723, representatives of natural and urban environments, respectively. To achieve this, we developed a specific procedure for dust, applicable in the 4–25 mg mass range, to separate the six elements using a multi-column ion-exchange chromatographic method and MC-ICP-MS measurements., SCOPUS: ar.j, info:eu-repo/semantics/published

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Mineral dust is a major source of micronutrients (e.g. Fe) in open oceans and HNLC zones. In the Southern Ocean in particular, the properties and impacts of current dust deposition are not well constrained. Here, several dust-bearing snow samples collected in the NE Antarctica coast are investigated in order to :(i) characterize the mineralogy, size, and morphology of dust by single particle analyses (automated-FEG-SEM-EDS and TEM-SAED), (ii) trace the origin and the relative contribution of natural and anthropogenic particles in dusts through elemental and multi-isotopic analyses (HR-ICP-MS and MC-ICP-MS) and (iii) quantify the Fe bioavailability in dusts (via extractions). Our first results show a fine size distribution (98% of particles < 5 µm, n=1550). A large fraction exhibits a Fe contribution, either from mineralogy or coating. While the mineralogy suggest a substantial contribution of proximal rocks, a high Pb enrichment factor (x7 relative to upper continental crust - UCC) indicates an anthropogenic contribution to the dust deposition. Overall, this study will improve our understanding of dust reaching the coast of NE-Antarctica, which may represent a proxy for the dust material supplied to the Southern Ocean, by far the largest HNLC., info:eu-repo/semantics/nonPublished

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Ce mémoire présente l’analyse géochimique et isotopique d’une section de tourbe sondée à Karukinka (Terre de Feu, Chili) entre 350 et 450 cm de profondeur correspondant à un intervalle de temps compris entre 4300 et 8450 cal. BP. Le but de cette étude est d’identifier les sources des apports atmosphériques en Terre de feu et leurs variations au cours du temps par le biais d’une caractérisation géochimique (REE) et isotopique (Nd et Pb) du sondage de tourbe. Par ailleurs, les outils géochimiques ont été complétés par un nouveau traceur, les isotopes de l’Hf, dont il convenait d’évaluer son potentiel appliqué pour la première fois dans une archive de tourbe et en Patagonie. Les variations isotopiques du sondage (εNd de -1,22 à +2,20 ;206Pb/204Pb de 18,55 à 18,74 ;207Pb/204Pb de 15,61 à 15,64 ;εHf de 3,38 à 7,15) indiquent que tout au long du profil étudié, les apports atmosphériques proviennent de la Patagonie et vont donc permettre d’identifier des sources au sein de cette dernière. Les isotopes du Pb et du Nd couplés aux REE ont mis en évidence, au sein de nos échantillons, le dépôt de deux téphras (H1, 7300 cal. BP et MB2, 4300 cal. BP) ainsi que différentes sources de poussières dominantes. De manière globale 3 intervalles de temps distincts ont été identifiés. La première période allant de la base du sondage jusqu’à 6200 cal. BP et dominée par les apports de poussières en provenance du batholite Patagonien. Les deux périodes suivantes indiquent un signal dominé, cette fois-ci, par les pampas. Une dominée par le « Main & post Plateau » entre 6200 et 5200 cal. BP, l’autre par la région de « Glencross » et/ou « Pali Aike » à partir 5200 cal. BP et jusqu’au sommet de la section de tourbe étudiée (4200 cal. BP). Pour la première fois, il a été montré que le batholite Patagonien peut constituer une source majeure de poussières en Patagonie. De plus, ce dernier présente une dynamique érosive différente contrôlée par les glaciers et elle-même principalement liée aux vari, info:eu-repo/semantics/nonPublished

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