Evolution décennale des zones côtières (forçages climatiques, forçages anthropiques)

Ne couvrant que 8% de l océan mondial mais offrant 85% des ressources marines exploitées, les systèmes côtiers sont d importantes plaques tournantes d échanges de matières et d énergie, jouant un rôle capital dans les cycles biogéochimiques. De plus, ces milieux sont marqués par une forte hétérogénéité spatio-temporelle des facteurs environnementaux, contribuant ainsi à leur complexité. Au cours des dernières décennies, les changements globaux s'exerçant sur ces systèmes sont devenus si intenses, que la mise en place de réseaux d'observation à long-terme est devenue cruciale afin d'extraire les grandes tendances et de prédire les changements potentiels. La question de l'identification de la réponse spécifique de ces zones d'interfaces littorales reste cependant posée. En France, le suivi des paramètres physiques et chimiques des eaux côtières est assuré depuis 1997 par le programme SOMLIT (Service d Observation en Milieu LIToral). L'objectif de cette thèse est de donc caractériser l'évolution physico-chimique, à l'échelle décennale, des systèmes côtiers français et d'estimer les parts respectives de la variabilité naturelle et de l'influence anthropique. Dans un premier temps, l'analyse de ces séries chronologiques montre que les systèmes côtiers français présentent une variabilité temporelle importante, liée en partie aux fluctuations hydro-climatiques à méso-échelle, mais également à des échelles plus régionales. Dans un deuxième temps, le développement d'une nouvelle procédure multivariée non paramétrique, aboutissant à la construction d'états de référence relatifs et à la détection rapide des changements, permet de quantifier le phénomène de fertilisation en nutriments. Il est montré que la fertilisation peut être fortement influencée par le forçage climatique. Dans un troisième temps, après soustraction de la part de variabilité climatique naturelle, des indicateurs de fertilisation anthropique sont proposés, permettant la quantification de l'impact des activités humaines sur les systèmes côtiers français. Ce travail propose une nouvelle approche qui permet de détecter dès que les données deviennent accessibles les perturbations potentielles dans tous types de systèmes, avec plus particulièrement pour objectif de répondre aux attentes, scientifiques et sociétales, d'une gestion adaptée des milieux côtiers.Covering only 8% of the World Ocean but with 85% of exploited marine resources, coastal systems are important areas for the exchange of materials and energy, playing a crucial role in biogeochemical cycles. Moreover, these environments are marked by strong spatial and temporal heterogeneity of environmental factors, contributing to their complexity. In recent decades, global change exerted on these systems has become so intense that the implementation of long-term monitoring programmes has become essential to extract major trends and predict potential changes. However, the identification of the specific response of these coastal systems remains posed. In France, monitoring of physical and chemical parameters of coastal waters is provided since 1997 by the programme SOMLIT (Service d'Observation en Milieu LITtoral). The aim of this PhD Thesis is therefore to characterize year-to-year variability in physic-chemical properties of the surface layer, at a decadal scale, of the French coastal systems, and to evaluate the respective influence of natural and anthropogenic variability. Firstly, the analysis of these time series shows that the French coastal systems exhibit significant temporal variability, due to hydro-climatic fluctuations at meso and regional scales. Secondly, the development of a new nonparametric multivariate procedure, resulting in the constitution of relative reference states for the rapid detection of changes, allows quantifying the fertilization in nutrient concentrations. Moreover, it is shown that fertilization can be strongly influenced by climate forcing. Thirdly, after the removal of natural climate variability, indicators of human fertilisation are proposed, allowing the quantification of the impact of human activities on French coastal systems. This study proposes a new approach to detect as soon as data become available, potential alterations in all types of systems, with the aim of meeting the scientific and societal assumptions and allowing the adaptive management of coastal environments.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

Insight into the PrPC -> PrPSc conversion from the structures of antibody-bound ovine prion scrapie-susceptibility variants

Prion diseases are associated with the conversion of the_-helix rich prion protein (PrPC) into a _-structure-rich insoluble conformer (PrPSc) that is thought to be infectious. The mechanism for the PrPC 3 PrPSc conversion and its relationship with the pathological effects of prion diseases are poorly understood, partly because of our limited knowledge of the structure of PrPSc. In particular, the way in which mutations in the PRNP gene yield variants that confer different susceptibilities to disease needs to be clarified. We report here the 2.5-Å-resolution crystal structures of three scrapie-susceptibility ovine PrP variants complexed with an antibody that binds to PrPC and to PrPSc; they identify two important features of the PrPC 3 PrPSc conversion. First, the epitope of the antibody mainly consists of the last two turns of ovine PrP second _-helix. We show that this is a structural invariant in the PrPC 3 PrPSc conversion; taken together with biochemical data, this leads to a model of the conformational change in which the two PrPC Cterminal _-helices are conserved in PrPSc, whereas secondary structure changes are located in the N-terminal _-helix. Second, comparison of the structures of scrapie-sensitivity variants defines local changes in distant parts of the protein that account for the observed differences of PrPC stability, resistant variants being destabilized compared with sensitive ones. Additive contributions of these sensitivity-modulating mutations to resistance suggest a possible causal relationship between scrapie resistance and lowered stability of the PrP protein

Glycan-Controlled Epitopes of Prion Protein Include a Major Determinant of Susceptibility to Sheep Scrapie

A key feature of prion encephalopathies is the accumulation of a misfolded form of the host glycoprotein PrP. Cell-free and cell culture studies have shown that the efficiency of conversion of PrP into the disease-associated form is influenced by its amino acid sequence and also by its carbohydrate moiety. Here, we characterize four novel glycoform-dependent monoclonal antibodies raised against prokaryotic recombinant sheep PrP. We demonstrate that these antibodies discriminate the PrP monoglycosylated species, since two of them recognize molecules that have the first Asn glycosylation site occupied (mono1) while the other two recognize molecules glycosylated at the second site (mono2). Remarkably, the recognition of PrP by the anti-mono2 antibodies was strongly influenced by the amino acid present at position 171, i.e., either Gln or Arg. This polymorphism is known to be the main determinant of susceptibility and resistance to scrapie in sheep. Altogether, our findings lead us to propose that each glycan chain controls the accessibility of PrP determinants located close upstream from their attachment site. The monoglycoform-assigned and the allotype-restricted antibodies described here, the first to date, should provide further opportunities to investigate the involvement of each glycan chain in PrP conversion in relation to prion strain diversity and the basis of the resistance conferred by the Arg-171 amino acid

Large and local-scale influences on physical and chemical characteristics of coastal waters of Western Europe during winter

There is now a strong scientific consensus that coastal marine systems of Western Europe are highly sensitive to the combined effects of natural climate variability and anthropogenic climate change. However, it still remains challenging to assess the spatial and temporal scales at which climate influence operates. While large-scale hydro-climatic indices, such as the North Atlantic Oscillation (NAO) or the East Atlantic Pattern (EAP) and the weather regimes such as the Atlantic Ridge (AR), are known to be relevant predictors of physical processes, changes in coastal waters can also be related to local hydro-meteorological and geochemical forcing. Here, we study the temporal variability of physical and chemical characteristics of coastal waters located at about 48°N over the period 1998-2013 using (1) sea surface temperature, (2) sea surface salinity and (3) nutrient concentration observations for two coastal sites located at the outlet of the Bay of Brest and off Roscoff, (4) river discharges of the major tributaries close to these two sites and (5) regional and local precipitation data over the region of interest. Focusing on the winter months, we characterize the physical and chemical variability of these coastal waters and document changes in both precipitation and river runoffs. Our study reveals that variability in coastal waters is connected to the large-scale North Atlantic atmospheric circulation but is also partly explained by local river influences. Indeed, while the NAO is strongly related to changes in sea surface temperature at the Brest and Roscoff sites, the EAP and the AR have a major influence on precipitations, which in turn modulate river discharges that impact sea surface salinity at the scale of the two coastal stations

Hydrological extreme event occurrences and impacts linked with climate variations in coastal waters of western Europe

The dynamics of physico-chemical processes in the bay of Brest are studied to better understand the impact of local events on the coastal ocean. We are analyzing long-term in situ data (since 2000), high and low frequencies, from the COAST-HF (buoy Marel Iroise) and SOMLIT sites, located at the entrance to the bay of Brest. This study is divided into two main stages: the detection and characterization of extreme events, followed by a numerical simulation of these events to understand the underlying oceanic processes. The focus is on desalination events during the winter months (December, January, February and March), considering the season with the greatest number of extreme events. We show the relationship between local extreme events and variability at larger scales, considering climate indices such as the North Atlantic Oscillation (NAO). A comparison between the low frequency data of the SOMLIT program and the high frequency data of the Marel buoy is carried out, highlighting the interest of high frequency measurements for the detection of extreme events. A comparison between in situ data and two numerical simulations of different resolutions is also performed over salinity time series. This study also show an interannual variability of extreme events interesting in a context of climate change. We make the link between these extreme desalination and the nitrate level in the bay of Brest. To finally study the relationship between nutrients and chlorophyll in order to look at the correlation that it can exists between extreme events and biology in the coastal environment.

Unraveling Salinity Extreme Events in Coastal Environments: A Winter Focus on the Bay of Brest

Extreme weather events affect coastal marine ecosystems. The increase in intensity and occurrence of such events drive modifications in coastal hydrology and hydrodynamics. Here, focusing on the winter period (from December to March), we investigated multi-decade (2000–2018) changes in the hydrological properties of the Bay of Brest (French Atlantic coast) as an example of the response of a semi-enclosed bay to extreme weather episodes and large-scale atmospheric circulation patterns. The relationships between extreme weather events and severe low salinity conditions (as a proxy for changes in water density) were investigated using high-frequency in situ observations and high-resolution numerical simulations. The identification of intense episodes was based on the timing, duration, and annual occurrence of extreme events. By examining the interannual variability of extreme low salinity events, we detect a patent influence of local and regional weather conditions on atmospheric and oceanic circulation patterns, precipitation, and river runoff. We revealed that low salinity events in Brittany were controlled by large-scale forcings: they prevailed during the positive phase of the North Atlantic Oscillation and periods of low occurrences of the Atlantic Ridge weather regime. The increase in severe storms observed in western France since 2010 has led to a doubling of the occurrence and duration of extreme low salinity events in Brittany

Extreme coastal events linked with climate variation. Understanding low salinity episodes in the Bay of Brest, north-eastern Atlantic

Aims - To detect and characterise extreme events in a coastal ecosystem by combining in situ high-frequency observations and high-resolution numerical simulations -To describe the interannual variability of extreme events in a context of climate change  -To quantify the links between extreme low salinity episodes and both large and local scale processes, using weather regimes, precipitations and river runoffs as proxies of hydro-climate forcin

A Scheme for Detecting Every Single Target Molecule with Surface-Enhanced Raman Spectroscopy

Surface-enhanced Raman spectroscopy (SERS) is now a well-established technique for the detection, under appropriate conditions, of single molecules (SM) adsorbed on metallic nanostructures. However, because of the large variations of the SERS enhancement factor on the surface, only molecules located at the positions of highest enhancement, so-called hot-spots, can be detected at the single-molecule level. As a result, in all SM-SERS studies so far only a small fraction, typically less than 1%, of molecules are actually observed. This complicates the analysis of such experiments and means that trace detection via SERS can in principle still be vastly improved. Here we propose a simple scheme, based on selective adsorption of the target analyte at the SERS hot-spots only, that allows in principle detection of <i>every</i> single target molecule in solution. We moreover provide a general experimental methodology, based on the comparison between average and maximum (single molecule) SERS enhancement factors, to verify the efficiency of our approach. The concepts and tools introduced in this work can readily be applied to other SERS systems aiming for detection of every single target molecule