Utilisation du rapport (231Pa/230Th) des sédiments marins pour caractériser les changements de circulation océanique lors des variations climatiques de la dernière période glaciaire

In this thesis, I reconstruct the dynamic of the Atlantic Meridional Overturning Circulation (AMOC) during fast climate changes of the last glacial period. I find that the AMOC upper circulation cell started to slowdown 1420 ± 250 (1σ) and 690 ± 180 (1σ) years before the southward shifts of the Inter Tropical Convergence Zone associated with Heinrich Stadial 2 and Heinrich Stadial 4, respectively. I therefore confirm that an AMOC slowdown could be at the origin of the ITCZ shifts that occured during Heinrich Stadials and provide the first precise estimate of the phasing between these two climate variables. Based on these results I propose a mechanism explaining the difference between Heinrich and Dansgaard-Oeschger stadials.Using modeling results, I show that the Atlantic Ocean circulation during periods of higher Greenland temperatures (interstadials) was markedly different from that of the Holocene. Two overturning cells were likely active in the Atlantic Ocean: an upper overturning circulation cell initiated by northern-sourced deep water flowing southward above ~2500 m depth at the equator, and a lower overturning circulation cell initiated by southern sourced deep water flowing northward below ~4000 m depth at the equator. The overturning rate of the upper overturning cell was likely lower than that of present-day North Atlantic Deep Water. At the onset of Heinrich Stadials, the structure of the AMOC significantly changed, and southern-sourced deep-waters likely dominated the equatorial Atlantic Ocean below 1300 m depth.Dans cette thèse, je reconstitue la dynamique de la circulation méridienne de retournement de l’Atlantique (AMOC) au cours des changements climatiques rapides de la dernière période glaciaire. Je trouve ainsi que le ralentissement de la cellule supérieure de l’AMOC commence 1420 ± 250 (1σ) années avant le déplacement vers le sud de l’ITCZ associé au « Heinrich Stadial » 2 et 690 ± 180 (1σ) années avant celui associé au « Heinrich Stadial » 4. Mes résultats confirment donc qu’un ralentissement de l’AMOC pourrait être à l’origine des migrations de l’ITCZ associées aux « Heinrich Stadials » et fournissent une première estimation précise du décalage temporel entre ces deux variables climatiques. Sur la base de ces résultats, je propose un mécanisme expliquant les différences entre les « Heinrich Stadials » et les « Dansgaard-Oeschger Stadials ».Je montre que deux cellules de circulation étaient probablement actives dans l’océan Atlantique pendant les périodes chaudes au Groenland (« interstadials ») : une cellule supérieure initiée par l’écoulement au-dessus de 2500 m d’une masse d’eau en provenance du nord et se dirigeant vers le sud, et une cellule inférieure initiée par l’écoulement au-dessous de 4000 m d’une masse d’eau en provenance du sud et se dirigeant vers le nord. Le taux de renouvellement de la masse d’eau profonde de la cellule supérieure était probablement plus faible que celle de la masse d’eau actuellement formée dans les hautes latitudes de l’océan Atlantique Nord. Au début des « Heinrich Stadials », la structure de l’AMOC a significativement changé et des eaux en provenance du sud ont probablement dominé l’océan Atlantique en-dessous de 1300 m de profondeur

Assessing the biomineralization processes in the shell layers of modern brachiopods from oxygen isotopic composition and elemental ratios: Implications for their use as paleoenvironmental proxies

Fossil brachiopod shells are often used as valuable archives to reconstruct paleoenvironmental conditions in deep time. However, biomineralization processes can impact their fidelity as geochemical proxies. Brachiopod shells comprise an outer primary layer, a secondary fibrous layer and sometimes, a tertiary columnar layer. Therefore, it is essential to assess the potential effects of the biomineralization processes in each of the different shell microstructures of modern brachiopods. This study analyses the oxygen isotopic composition together with Li/Ca, Na/Ca Mg/Ca and Sr/Ca data at high spatial (20-50 μm) resolution in seven modern brachiopod species, focusing on differences between the primary, secondary and tertiary layers. In all studied species, δ18O values of the outer primary layer are consistently out of equilibrium with seawater. Also, this shell layer is enriched in Li, Na, Mg and Sr. Contrary to the primary layer, the innermost secondary layer is near or at oxygen isotopic and elemental equilibrium with ambient seawater. The columnar tertiary shell layer, if present, has the least variable and the heaviest oxygen isotopic composition, within the range of equilibrium values with seawater. This tertiary layer, however, is depleted in minor and trace elements relative to the other shell layers. Thus, the tertiary layer is more suitable for oxygen isotopic studies, whereas the innermost secondary layer of the most mature parts of the shell is the best target in two-layered shells. While we do not observe any clear interspecific relationships between Mg/Ca and Sr/Ca ratios, on one hand, and environmental parameters such as temperature, salinity and pH, on the other hand, there is a positive interspecific relationship between Na/Ca and salinity and a negative interspecific relationship between Li/Ca and temperature, suggesting their potential use as proxies of physicochemical parameters of seawater

Structurally Simple Osmium(II) Polypyridyl Complexes as Photosensitizers for Photodynamic Therapy in the Near Infrared**

Five osmium(II) polypyridyl complexes of the general formula [Os(4,7‐diphenyl‐1,10‐phenanthroline)$_{2}$L]$^{2+}$ were synthesized as photosensitizers for photodynamic therapy by varying the nature of the ligand L. Thanks to the pronounced π‐extended structure of the ligands and the heavy atom effect provided by the osmium center, these complexes exhibit a high absorption in the near‐infrared (NIR) region (up to 740 nm), unlike related ruthenium complexes. This led to a promising phototoxicity in vitro against cancer cells cultured as 2D cell layers but also in multicellular tumor spheroids upon irradiation at 740 nm. The complex [Os(4,7‐diphenyl‐1,10‐phenanthroline)$_{2}$(2,2′‐bipyridine)]$^{2+}$ was found to be the most efficient against various cancer cell lines, with high phototoxicity indexes. Experiments on CT26 tumor‐bearing BALB/c mice also indicate that the Os$^{II}$ complexes could significantly reduce tumor growth following 740 nm laser irradiation. The high phototoxicity in the biological window of this structurally simple complex makes it a promising photosensitizer for cancer treatment

Clinically Translatable Transcrocetin Delivery Platform for Correction of Tumor Hypoxia and Enhancement of Radiation Therapy Effects

Improving the tumor reoxygenation to sensitize the tumor to radiation therapy is a cornerstone in radiation oncology. Here, the pre‐clinical development of a clinically transferable liposomal formulation encapsulating trans sodium crocetinate (NP TSC) is reported to improve oxygen diffusion through the tumor environment. Early pharmacokinetic analysis of the clinical trial of this molecule performed on 37 patients orient to define the optimal fixed dosage to use in a triple‐negative breast cancer model to validate the therapeutic combination of radiation therapy and NP TSC. Notably, it is reported that this formulation is non‐toxic in both humans and mice at the defined fixed concentration, provides a normalization of the tumor vasculature within 72 h window after systemic injection, leads to a transient increase (50% improvement) in the tumor oxygenation, and significantly improves the efficacy of both mono‐fractionated and fractionated radiation therapy treatment. Together, these findings support the introduction of a first‐in‐class therapeutic construct capable of tumor‐specific reoxygenation without associated toxicities

Reconstructing last glacial changes in Atlantic meridional overturning rate using marine sediment (231Pa/230Th)

Dans cette thèse, je reconstitue la dynamique de la circulation méridienne de retournement de l’Atlantique (AMOC) au cours des changements climatiques rapides de la dernière période glaciaire. Je trouve ainsi que le ralentissement de la cellule supérieure de l’AMOC commence 1420 ± 250 (1σ) années avant le déplacement vers le sud de l’ITCZ associé au « Heinrich Stadial » 2 et 690 ± 180 (1σ) années avant celui associé au « Heinrich Stadial » 4. Mes résultats confirment donc qu’un ralentissement de l’AMOC pourrait être à l’origine des migrations de l’ITCZ associées aux « Heinrich Stadials » et fournissent une première estimation précise du décalage temporel entre ces deux variables climatiques. Sur la base de ces résultats, je propose un mécanisme expliquant les différences entre les « Heinrich Stadials » et les « Dansgaard-Oeschger Stadials ».Je montre que deux cellules de circulation étaient probablement actives dans l’océan Atlantique pendant les périodes chaudes au Groenland (« interstadials ») : une cellule supérieure initiée par l’écoulement au-dessus de 2500 m d’une masse d’eau en provenance du nord et se dirigeant vers le sud, et une cellule inférieure initiée par l’écoulement au-dessous de 4000 m d’une masse d’eau en provenance du sud et se dirigeant vers le nord. Le taux de renouvellement de la masse d’eau profonde de la cellule supérieure était probablement plus faible que celle de la masse d’eau actuellement formée dans les hautes latitudes de l’océan Atlantique Nord. Au début des « Heinrich Stadials », la structure de l’AMOC a significativement changé et des eaux en provenance du sud ont probablement dominé l’océan Atlantique en-dessous de 1300 m de profondeur.In this thesis, I reconstruct the dynamic of the Atlantic Meridional Overturning Circulation (AMOC) during fast climate changes of the last glacial period. I find that the AMOC upper circulation cell started to slowdown 1420 ± 250 (1σ) and 690 ± 180 (1σ) years before the southward shifts of the Inter Tropical Convergence Zone associated with Heinrich Stadial 2 and Heinrich Stadial 4, respectively. I therefore confirm that an AMOC slowdown could be at the origin of the ITCZ shifts that occured during Heinrich Stadials and provide the first precise estimate of the phasing between these two climate variables. Based on these results I propose a mechanism explaining the difference between Heinrich and Dansgaard-Oeschger stadials.Using modeling results, I show that the Atlantic Ocean circulation during periods of higher Greenland temperatures (interstadials) was markedly different from that of the Holocene. Two overturning cells were likely active in the Atlantic Ocean: an upper overturning circulation cell initiated by northern-sourced deep water flowing southward above ~2500 m depth at the equator, and a lower overturning circulation cell initiated by southern sourced deep water flowing northward below ~4000 m depth at the equator. The overturning rate of the upper overturning cell was likely lower than that of present-day North Atlantic Deep Water. At the onset of Heinrich Stadials, the structure of the AMOC significantly changed, and southern-sourced deep-waters likely dominated the equatorial Atlantic Ocean below 1300 m depth

Use of cold waters geochemistry as a geothermal prospecting tool for hidden hydrothermal systems in Réunion Island

International audienceMost untapped high-enthalpy geothermal resources are blind, meaning lacking surface evidence of their existence. The first step in their discovery is to find evidence of hydrothermal activity. Here we apply an approach based on the geochemistry of cold waters, which allowed us to identify evidence of the existence of a hydrothermal system at Piton de la Fournaise volcano (Réunion Island), and constrain its location. This approach uses the concentrations in B, Li, SO 4 , F, Mo, P, V, As and HCO 3 and the isotopic ratios δ 13 C and δ 11 B as geochemical markers of hydrothermal activity that can be used even in waters with extremely low ion content (Electrical conductivity <80 µS/cm), and even when their geochemical composition is mainly controlled by other processes. This noninvasive approach is easy to implement and can be applied wherever the presence of a blind geothermal system is suspected

Ruthenium(II) Polypyridyl Complexes Containing Simple Dioxo Ligands: a Structure‐Activity Relationship Study Shows the Importance of the Charge

International audienceCancer is one of the main causes of death worldwide. Platinum complexes (i.e., cisplatin, carboplatin, and others) are currently heavily used for the treatment of different types of cancer, but unwanted effects occur. Ruthenium complexes have been shown to be potential promising alternatives to these metal-based drugs. In this work, we performed a structure-activity relationship (SAR) study on two small series of Ru(II) polypyridyl complexes of the type [Ru(L1)2(O^O)]Cln (3-8), where L1 is 4,7-diphenyl-1,10-phenantroline (DIP) or 1,10phenantroline (phen), and O^O is a symmetrical anionic dioxo ligand: oxalate (ox, n = 0), malonate (mal, n = 0), or acetylacetonate (acac, n = 1). These two self-consistent series of compounds allowed us to perform a systematic investigation for establishing how the nature of the ligands and the charge affect the anticancer properties of the complexes. Cytotoxicity tests on different cell lines demonstrated that some of the six compounds 3-8 have a promising anticancer activity. More specifically, the cationic complex [Ru(DIP)2(η 2-acac)]Cl (4) has IC50 values in the mid-nanomolar concentration range, lower than those of cisplatin on the same cell lines. Interestingly, [Ru(DIP)2(η 2-acac)]Cl was found to localize mainly in the mitochondria, whereas a smaller fraction was detected in the nucleus. Overall, our SAR investigation demonstrates the importance of combining the positive charge of the complex with the highly lipophilic diimine ligand DIP

Efficient release of bromine by super-eruptions

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Waelkens, C. M., Stix, J., Monteleone, B., & Burckel, P. Efficient release of bromine by super-eruptions. Geology, 49(12), (2021): 1416–1420, https://doi.org/10.1130/G49114.1.Bromine is a key halogen element in the quantification of volcanic volatiles, but analytical difficulties in measuring its very low abundances have prevented progress in understanding its behavior and its role in volcanic emissions. We present a new data set of bromine, chlorine, and fluorine concentrations in melt inclusions and matrix glasses for two rhyolitic super-eruptions from the Toledo and Valles calderas, New Mexico, USA. We show that before eruption, Br and Cl were efficiently partitioned from the gas-saturated magma into a separate fluid phase, and we calculate the mass of halogens in the fluid phase. We further demonstrate that syn-eruptive magma degassing was negligible during the super-eruptions, so that the main source of halogen emissions must have been the fluid phase. If the fluid phase were erupted, the large mass of Br and Cl could have severely impacted the atmospheric chemistry upon eruption.This research was supported by a Geological Society of America grant (C. Waelkens), Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery and CREATE grants (J. Stix), and Institut de Physique du Globe de Paris multidisciplinary program PARI and Paris–IdF region SESAME grant 12015908 (P. Burckel). The Northeast National Ion Microprobe Facility is subsidized by U.S. National Science Foundation (NSF) facility support grant NSF-EAR-1664308