Impact de l'acidification et du réchauffement sur les communautés planctoniques de l'estuaire du Saint-Laurent et la production de diméthylsulfure

Les émissions anthropiques de dioxyde de carbone (CO2) ont augmenté depuis la révolution industrielle, entraînant des modifications dans les teneurs atmosphériques en CO2 et un accroissement de la pression partielle de CO2 (pCO2) océanique. L’absorption du CO2 par les océans a entraîné une baisse du pH des eaux de surface, correspondant à une augmentation de l’acidité d’environ 30 % par rapport aux valeurs préindustrielles. D’autre part, l’accumulation de CO2 anthropique dans l'atmosphère a également induit un réchauffement des eaux de surface depuis le milieu du 20e siècle. Le devenir des communautés planctoniques face à ces altérations actuelles et futures de leur environnement demeure incertain. On ignore également comment l’acidification et le réchauffement affecteront la production du diméthylsulfure (DMS), un gaz sulfuré d’origine planctonique impliqué dans la régulation du climat. Le but de cette thèse est de déterminer l’impact d’une augmentation de la pCO2 sur le développement des floraisons phytoplanctoniques de l'estuaire maritime du Saint-Laurent (EMSL) et la production de DMS, ainsi que d’évaluer dans quelle mesure le réchauffement des eaux de surface modulera l’effet de l’acidification. Deux grandes expériences ont été menées au cours de la thèse. Une première expérience en microcosmes (~20 L) a été conduite à l’été 2013 afin d’étudier les effets de la pCO2 sur la floraison printanière des diatomées dans L’EMSL, en portant une attention particulière aux processus microbiens régissant la production de DMS. Une seconde expérience de type multifactorielle en mésocosmes (~2600 L) a été conduite à l’automne 2014 afin de déterminer l’impact combiné de l’augmentation de la pCO2 et du réchauffement sur le développement de la floraison automnale de l’EMSL et la production du DMS. Les résultats de l’expérience en microcosmes montrent que les communautés phytoplanctoniques responsables de la floraison printanière dans l’EMSL sont résistantes à des augmentations de la pCO2 supérieures aux valeurs attendues pour 2100. Cette résistance reflète vraisemblablement leur adaptation au milieu estuarien, environnement connu pour ses variations de pCO2 importantes et rapides. Cette première expérience a également mis en évidence une diminution de 15 et de 40 % des concentrations moyennes de DMS chez les communautés respectivement soumises à des pCO2 de 1850 μatm et 2700 μatm par rapport au contrôle (~775 μatm). Des incubations menées en parallèle ont permis de montrer, au moyen de 35S-DMSPd, que l’effet négatif de l’acidification sur le DMS résultait en grande partie d’une diminution de l’efficacité de conversion du DMSP en DMS par les bactéries. La deuxième expérience a également mis en évidence une forte résistance de la diatomée Skeletonema costatum à une large gamme de pH (~8.0–7.2) et de pCO2 (~90–3000 μatm). Lors de cette étude, un réchauffement des eaux de 5 °C a accéléré le développement et le déclin de la floraison, mais n’a pas eu d’effet sur la production primaire intégrée pendant l’expérience. À l’instar de l’expérience en microcosmes, l’augmentation de la pCO2 a provoqué une diminution des concentrations moyennes de DMS de ~66 % dans les mésocosmes les plus acidifiés par rapport aux traitements les moins acidifiés à température in situ (10 °C). L’effet négatif d’une augmentation de la pCO2 sur la production nette de DMS pourrait cependant être annulé par le réchauffement des eaux de surface. En effet, mes résultats révèlent que la production nette de DMS était plus élevée à 15 °C par rapport à 10 °C et ce à toutes les pCO2 testées. Ces résultats inédits suggèrent que le réchauffement attendu des eaux de surface pourrait contrer en partie l’effet négatif de l’acidification sur la production nette de DMS dans l’EMSL et possiblement dans l’océan mondial.Anthropogenic carbon dioxide (CO2) emissions have increased since the industrial revolution, leading to modifications in atmospheric CO2 content and an increase in oceanic CO2 partial pressures (pCO2). The uptake of CO2 by the oceans has resulted in a lowering of surface water pH, corresponding to an increase in the acidity of the oceans by ~30 % compared with pre-industrial times. Furthermore, climate change resulting from the accumulation of anthropogenic CO2 in the atmosphere is responsible for the observed warming of sea surface temperatures since the mid 20th century. The fate of planktonic communities in the face of these changes in the marine environment over the next century remains uncertain. Even less understood are the possible interactions of acidification and warming on the production of dimethylsulfide (DMS), a sulfur-containing gas produced by planktonic communities and involved in climate regulation. The aim of this thesis is to determine the impact of heightened pCO2 on the development of the phytoplanktonic blooms in the Lower St. Lawrence Estuary (LSLE), and their production of DMS, as well as to evaluate how concomitant warming could modulate the effects of acidification. Two intricate experiments were carried out during this study. First, a microcosm experiment (~20 L) was conducted in the summer of 2013 to assess the effects of pCO2 on the development of the LSLE spring diatom bloom, paying special attention to the microbial processes governing the production of DMS. Second, a multifactorial mesocosm experiment (~2600 L) was carried out in the fall of 2014 to investigate the combined effects of pCO2 and temperature on the development of the fall bloom in the LSLE and the production of DMS. Results from our microcosm experiment show that the blooming phytoplankton community of the LSLE during spring is resistant to pCO2 increases superior to the expected values for 2100. This resistance likely reflects its adaptation to the estuarine setting, an environment known for rapid and intense fluctuations of pCO2. This first experiment has also highlighted a reduction of the average concentrations of DMS by 15 and 40 % in planktonic assemblages respectively subjected to pCO2 of ~1850 μatm and ~2700 μatm compared to the control (~775 μatm). Parallel incubations have shown, using 35S-DMSPd, that the negative effect of acidification on DMS mostly stemmed from a decrease in the conversion efficiency of DMSP to DMS by bacteria. The second experiment has also highlighted a strong resistance of the diatom Skeletonema costatum to a wide range of pH (~8.0–7.2), and corresponding pCO2 (~90–3000 μatm). In this study, a warming of 5 °C accelerated the development and decline of the bloom, but did not affect the integrated primary production over the duration of the experiment. As in the first experiment, heightened pCO2 resulted in a decrease of average concentrations of DMS of ~66 % in the most acidified mesocosms compared to the least acidified mesocosms at in situ temperature (10 °C). However, the negative effect of an increase in pCO2 on the net production of DMS could be mitigated by a warming of surface waters. Indeed, my results reveal that the net production of DMS was higher at 15 °C compared to 10 °C over the whole pCO2 gradient in our mesocosm study. These novel results suggest that warming of surface waters could mitigate, at least partly, the negative effect of acidification on DMS net production in the LSLE and perhaps in the world’s oceans

Le château de Neuville-sur-Ailette (Aisne) : état des recherches

International audienceLe site du château de Neuville a fait l’objet de deux diagnostics complétés par des recherches documentaires et des observations de surface en dehors de l’emprise des deux opérations archéologiques.Les vestiges imposants d’un bâtiment médiéval ont été dégagés. Cette construction aux caractéristiques monumentales appartient au château de Neuville. Réoccupé pendant la Première Guerre mondiale par l’armée allemande, ce bâtiment a fait l’objet d’un réaménagement intérieur et un dessin y a été peint. Pilonné pendant ce conflit, il a ensuite en grande partie été remblayé.Une restitution du tracé de l’enceinte castrale a été proposée. La confrontation des différents résultats nous a également amené à réfléchir à l’implantation du château construit au lendemain des guerres de Religion en remplacement de l’ancienne forteresse médiévale.L’emprise du cimetière qui s’étendait dans l’espace situé entre l’église et le château a enfin été partiellement circonscrite. L’une des tombes fouillées indique une occupation relativement précoce de cet espace funéraire dans les années 1170-1268

Brackish water carbonate chemistry and concentrations of dimethyl sulfide (DMS) and dimethylsulfoniopropionate (DMSP)

The objective of this study was to assess experimentally the potential impact of anthropogenic pH perturbation (ApHP) on concentrations of dimethyl sulfide (DMS) and dimethylsulfoniopropionate (DMSP), as well as processes governing the microbial cycling of sulfur compounds. A summer planktonic community from surface waters of the Lower St. Lawrence Estuary was monitored in microcosms over 12 days under three pCO2 targets: 1 * pCO2 (775 µatm), 2 * pCO2 (1,850 µatm), and 3 * pCO2 (2,700 µatm). A mixed phytoplankton bloom comprised of diatoms and unidentified flagellates developed over the course of the experiment. The magnitude and timing of biomass buildup, measured by chlorophyll a concentration, changed in the 3 * pCO2 treatment, reaching about half the peak chlorophyll a concentration measured in the 1 * pCO2 treatment, with a 2-day lag. Doubling and tripling the pCO2 resulted in a 15% and 40% decline in average concentrations of DMS compared to the control. Results from 35S-DMSPd uptake assays indicated that neither concentrations nor microbial scavenging efficiency of dissolved DMSP was affected by increased pCO2. However, our results show a reduction of the mean microbial yield of DMS by 34% and 61% in the 2 * pCO2 and 3 * pCO2 treatments, respectively. DMS concentrations correlated positively with microbial yields of DMS (Spearman's ρ = 0.65; P < 0.001), suggesting that the impact of ApHP on concentrations of DMS in diatom-dominated systems may be strongly linked with alterations of the microbial breakdown of dissolved DMSP. Findings from this study provide further empirical evidence of the sensitivity of the microbial DMSP switch under ApHP. Because even small modifications in microbial regulatory mechanisms of DMSP can elicit changes in atmospheric chemistry via dampened efflux of DMS, results from this study may contribute to a better comprehension of Earth's future climate

St. Lawrence Estuary phytoplankton spring bloom and associated dimehtylsulfide cycling sensitivity to acidification in a microcosm experiment

The potential impact of ocean acidification (OA) on the concentrations of dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP), as well as the processes governing the cycling of sulfur compounds by microbial organisms were investigated in a microcosm experiment during summer 2013. A natural planktonic community sourced from the surface waters of the Lower St. Lawrence Estuary (LSLE) was monitored over 12 days under three pCO2 targets: 1 × pCO2 (775 µatm), 2 × pCO2 (1850 µatm), and 3 × pCO2 (2700 µatm). The effects of heightened pCO2 were assessed on phytoplankton biomass, taxonomy and productivity, as well as on DMSP and DMS concentrations and microbial cycling via 35S-DMSPd radioisotope uptake assays. A mixed phytoplankton bloom comprised of the diatoms Chaetoceros spp., Skeletonema costatum, and Thalassiosira spp., as well as unidentified flagellates (2-20 µm) developed over the course of the study period. Concentrations of chlorophyll a (Chl a) peaked on day 6 from an initial 1.26 µg L-1 to 20 ± 4 µg L-1 and 17 ± 1 µg L-1, at 1 × pCO2 and 2 × pCO2, respectively. However, the timing and the magnitude of the biomass build-up were altered in the 3 × pCO2 treatment reaching only 11 ± 4 µg L-1 by day 8 of the experiment. Variations in the concentrations of total DMSP (DMSPt) were largely related to variations in Chl a (Spearman's rho correlation (rs) = 0.77; p < 0.001; n = 61) and peak values of DMSPt were reached consecutively on day 8 in the 1 × pCO2 treatment (264 nmol L-1), on day 10 in the 2 × pCO2 (245 nmol L-1), and on day 12 in the 3 × pCO2 (192 nmol L-1). Concentrations of dissolved DMSP (DMSPd) increased irregularly from 2 ± 1 nmol L-1 to an overall average of 5.2 ± 0.8 nmol L-1 by the end of the experiment; the fluctuations being broadly associated with those observed in DMSPt (rs  = 0.70; p < 0.001; n = 61). Neither concentrations of DMSPd nor the microbial scavenging efficiency of DMSPd (kDMSPd) seemed to be strongly affected by increasing pCO2 suggesting that acidification did not alter the availability and the bacterial uptake of this substrate. However, our results show a reduction of the mean microbial yield of DMS by 34 % and 61 % in the 2 × pCO2 and 3 × pCO2 treatments. Doubling and tripling the pCO2 respectively resulted in a 15 % and 40 % decline in average concentrations of DMS compared to the control. DMS concentrations were positively correlated with microbial yields of DMS (rs = 0.65; p < 0.001; n = 45), suggesting that in diatom-dominated systems, the impact of OA on concentrations of DMS may be strongly linked with alterations of the microbial breakdown of DMSPd. Findings from this study provide the first empirical evidence of the sensitivity of the microbial DMSP switch under OA

Letermovir for Secondary Prophylaxis of Cytomegalovirus Infection and Disease after Allogeneic Hematopoietic Cell Transplantation: Results from the French Compassionate Program

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Transcatheter edge-to-edge repair following surgical valve repair with ring implantation: Results from the multicentre &quot;Clip-in-Ring&quot; registry

International audienceBACKGROUND: Management of mitral regurgitation recurrence after failed surgical valve repair with ring implantation is controversial. AIM: To describe the French experience regarding midterm safety and efficacy of transcatheter edge-to-edge mitral valve repair (TEER) in patients with failed surgical valve repair with ring implantation. METHODS: The &quot;Clip-in-Ring&quot; registry is a multicentre registry conducted in 11 centres in France, approved by local institutional review boards, of consecutive TEER following surgical valve repair with ring implantation. Outcomes were Mitral Valve Academic Research Consortium (MVARC) technical success, modified 30-day device and procedural success (where 10mmHg is considered as a cut-off for significant mitral stenosis) and MVARC complications. RESULTS: Twenty-three patients were studied: mean age, 69±10years; male sex, 74%; EuroSCORE II, 16±17; left ventricular ejection fraction, 53±12%; mitral regurgitation grade 3+/4+, 17%/78%; New York Heart Association class III/IV, 47%/22%; median surgery to TEER delay, 23 (6-94) months. Technical success was 100%. At discharge, residual mitral regurgitation grade was≤2+ in 87% and median transmitral gradient was 4 (3-5) mmHg. Thirty-day modified MVARC device and procedural success was 82%: four patients (17%) had residual mitral regurgitation grade&gt;2+, including two patients who needed complementary surgery. No patient had a 30-day transmitral gradient&gt;7mmHg. No patient died or had a stroke or any life-threatening complications. One patient presented a vascular access complication requiring transfusion. No other MVARC-2 adverse event was reported. CONCLUSIONS: TEER in patients with failed mitral ring is feasible and safe. Further studies shoulddelineate its exact role in the therapeutic armamentarium for this medical issue