par Boxho, Sibylle 
Président du jury Fripiat, François
Promoteur Bonneville, Steeve
Co-Promoteur Mattielli, Nadine
Publication Non publié, 2026-09-03
Président du jury Fripiat, François
Promoteur Bonneville, Steeve
Co-Promoteur Mattielli, Nadine
Publication Non publié, 2026-09-03
Thèse de doctorat
| Résumé : | ABSTRACT: Atmospheric dust is a fundamental component of the Earth system, playing a key role in interactions between the atmosphere, oceans and continents. It originates primarily from arid and semi-arid regions, as well as from volcanic, biological, and anthropogenic sources. It is characterized by a wide diversity of sizes, compositions, and behaviors. This diversity affects both its long-distance transport and its environmental and climatic impacts. In the atmosphere, it directly affects the climate through its interaction with radiation. It can reflect some of the sun's energy, producing a cooling effect, or absorb it, leading to atmospheric warming. The balance between these two effects depends on the size and chemical composition of the particles, particularly their iron oxide content. On a global scale, its overall impact is generally considered to be slightly cooling, although this remains subject to significant uncertainty. Dust also plays an important role in cloud formation and properties. It can act as condensation or ice-forming nuclei, thereby modifying cloud microphysics, lifespan and radiation-reflecting capacity. However, these effects are complex and sometimes contradictory, making their overall impact difficult to quantify. Beyond their radiative influence, dust actively participates in biogeochemical cycles. It transports essential nutrients, such as iron and phosphorus, to distant regions. In the oceans, these nutrients stimulate the growth of phytoplankton, which absorbs carbon dioxide and stores it deep within the ocean. On land, they help to enrich nutrient-poor soils, as in the Amazon region. Therefore, although indirect, dust plays a crucial role in regulating the carbon cycle and global climate. In polar regions, dust interacts closely with the cryosphere. When it is deposited on snow and ice, it reduces albedo, increasing solar energy absorption and accelerating melting. Furthermore, it provides nutrients that promote the growth of microorganisms, particularly algae, whose pigments further darken the surface. This creates a positive feedback loop that amplifies ice melt. The distribution of dust sources is highly uneven across the globe. The vast majority originate in the Northern Hemisphere, particularly the Sahara and the Asian deserts. Carried by winds, these particles can travel thousands of kilometers and reach remote regions, including the poles. Atmospheric circulation patterns largely determine their trajectory and deposition. Consequently, Antarctica, being relatively isolated, primarily receives fine dust transported over long distances, whereas Greenland, being more connected to continental landmasses, receives a more diverse range of dust.Understanding the origin of dust, or its provenance, is essential to better grasping its effects on the climate and environment. This reconstruction relies on various methods, such as analyzing the particles' physical characteristics, studying their chemical and mineralogical composition, and using isotopic tracers. However, the mixing of particles from different sources during transport limits the effectiveness of these approaches. Recent methods, particularly the analysis of trace elements such as rare earth elements and advanced statistical modelling, provide a more accurate estimation of the relative contributions of different sources. These methods offer promising prospects for improving our understanding of the global dust cycle. In short, atmospheric dust appears to play a significant role in the climate and environmental systems. Its direct and indirect role operates at multiple scales, but remains partially uncertain due to the complexity of the processes involved and the variability of its properties and sources. This thesis aims to develop and apply quantitative tools to constrain the provenance of atmospheric dust and to assess its implications for both past climate dynamics and modern environmental processes.This research focuses on two main questions: the origin of dust, and how it is transported through the atmosphere over time and affects polar regions after deposition. To answer these questions, we used the EPICA Dome C ice core to reconstruct the origin of dust in the Southern Hemisphere, employing rare earth elements (REEs) and the DEEPOT statistical model. Our results show that, during glacial periods, dust originated in high-latitude regions such as Patagonia and New Zealand. From around 14,500 years ago, there was a significant shift towards increased contributions from low-latitude sources such as Australia, Southern Africa and the Puna-Altiplano region. This shift is linked to climatic, hydrological and sea-level changes. Comparisons with other Antarctic ice cores reveal consistent global trends, as well as regional variations. Building on this, we developed a harmonized database of REE signatures for the main dust sources in the Northern Hemisphere, alongside an enhanced DEEPOT model. This approach enables the robust, quantitative identification of sources by incorporating uncertainties through statistical simulations. The results demonstrate that this method effectively complements classical isotopic approaches, allowing for a clearer resolution of complex source mixtures. Finally, in the Northern Hemisphere, our focus was on the Greenland polar region, where we analyzed the relative contributions of local and distant dust sources to algal growth on the ice, and their role in supplying the necessary nutrients. The results show that the dust originates from a mixture of local and distal sources, particularly in Asia. Phosphorus-rich particles are predominantly local and could promote the expansion of the 'Dark Zone' by enhancing biological activity and ice melt. However, the extent of this expansion depends primarily on environmental conditions, such as temperature and precipitation, rather than solely on the origin of the dust. This thesis highlights the importance of understanding the origin of dust in order to: (i) past atmospheric circulations, (ii) biogeochemical cycles and (iii) polar climatic processes. It also demonstrates that, while dust does contribute to phenomena such as ice darkening, its impact is heavily influenced by other environmental factors. |
| RÉSUMÉ: Les poussières atmosphériques jouent un rôle central dans les interactions entre l'atmosphère, les océans et les continents, ce qui en fait un élément essentiel du système Terre. Les sources de ces particules sont variées ce qui influent à la fois sur leur transport atmosphérique longue distance, ainsi que sur leurs impacts environnementaux et climatiques lors de leur dépôt. Dans l'atmosphère, elles interagissent directement sur le climat avec le rayonnement solaire, exerçant un forçage radiatif global communément considéré comme refroidissant l’atmosphère, bien que cette affirmation demeure entachée d’incertitudes. Par ailleurs, les poussières jouent un rôle majeur dans les cycles biogéochimiques en transportant des nutriments essentiels tels que le fer et le phosphore. En milieu polaire, leur dépôt sur la neige et la glace réduit l'albédo, accélérant ainsi la fonte et favorisant le développement d'organismes, comme des algues, dont la présence assombrit davantage la surface, amplifiant ainsi ce phénomène de fonte par rétroaction positive. L’objectif de cette thèse vise à mieux identifier et quantifier la provenance des poussières et leurs impacts biogéochimiques dans les régions polaires. Cette thèse propose une analyse approfondie de la carotte de glace EPICA Dome C (chapitre II), une archive unique permettant de reconstituer avec précision les sources de poussières dans l'Hémisphère Sud sur le dernier cycle glaciaire-interglaciaire. Grâce au modèle DEEPOT (Dust rare Earth Element Patterns Over Time) basé sur les profils des terres rares, cette étude montre que, durant les périodes glaciaires, les apports en poussière proviennent majoritairement de régions de hautes latitudes (Patagonie et Nouvelle-Zélande), tandis qu’à partir d'environ 14.5 ka, une augmentation des contributions en provenance de basses latitudes (Australie, Plateau Puna-Altiplano, et Afrique australe) est observée, corrélée à des changements climatiques et environnementaux majeurs des régions sources (e.g., submersion de la plateforme continentale argentine). Cette capacité de reconstruction de la provenance des poussières minérales a ensuite été étendue à l’Hémisphère Nord, où une nouvelle base de données harmonisée de signatures en terres rares des régions sources de poussières a été développée et associée à une version améliorée du modèle DEEPOT (chapitre III). Cette approche couplée a permis une reconstruction plus robuste et quantitative des sources de poussières arrivant dans les précipitations neigeuses au Groenland qui ont été échantillonnées lors d’un transect ouest-est réalisé lors de l’expédition « Nanok » (chapitre IV). Les résultats indiquent que ces sources sont à la fois locales et lointaines (e.g., Asie Centrale), contribuant à l’apport de nutriments qui favorisent la croissance des algues sur la glace. Les particules riches en phosphore, majoritairement locales, pourraient être l’un des acteurs clefs de l’expansion de la « Dark Zone », amplifiant ainsi la fonte de la calotte groenlandaise. Toutefois, cette expansion dépend surtout des conditions environnementales comme la température et les précipitations. En conclusion, cette thèse a développé un outil de traçage de la provenance des poussières atmosphériques et a permis de mettre en évidence l’importance de la provenance des poussières pour mieux comprendre la circulation atmosphérique passée, et les impacts de la déposition atmosphérique dans l’environnement polaire. |
