Ostracodes são microcrustáceos que possuem uma carapaça bivalve constituída por quitina e carbonato de cálcio, que vivem em ambientes marinhos e não-marinhos. São amplamente utilizados em estudos paleoceanográficos e paleoclimáticos, sendo bons indicadores batimétricos, de salinidade e de temperatura. Nas bacias brasileiras, os ostracodes têm larga aplicação bioestratigráfica, especialmente em intervalos não marinhos cretáceos. Por sua vez, os ostracodes marinhos têm se destacado pelos bons resultados paleoceanográficos em bacias marginais, entre elas a Bacia de Pelotas. Este trabalho propõe novas espécies eomiocênicas da família Cytherellidae e do gênero Actinocythereis. A partir do estudo taxonômico discutem-se implicações paleozoogeográficas de eventos como o estabelecimento da Corrente Circumpolar Antártica e da Corrente das Malvinas, cuja ação influenciou a dispersão dos ostracodes ora registrados na Bacia de Pelotas. A partir da análise do intervalo testemunhado 1300 m-1318 m do poço offshore 2-RSS-1 coletado pela Petrobras na década de 1970, são registradas cinco espécies da família Cytherellidae, duas das quais aqui descritas, como segue: Inversacytherella atlantica sp. nov., Cytherella pelotensis sp. nov., Cytherella sp. 1, Cytherella sp. 2 e Grammcythella? sp. É também proposta Actinocythereis imbeensis sp. nov., a qual constitui a segunda espécie descrita para o gênero no Brasil. São ainda registradas, Krithe coimbrai, Krithe gnoma e Henryhowella kempfi, atribuídas em trabalhos anteriores ao estabelecimento de massas de água frias na costa Sul-Brasileira. As ocorrências de Inversacytherella e Grammcythella, por sua vez, constituem evidências para o intercâmbio faunístico entre a América e a Oceania decorrentes de mudanças hidrológicas no Oceano Austral ao longo do Neogeno. O Apêndice 1 apresenta a lista e a documentação fotográfica das demais espécies registradas. / Ostracods are microcrustaceans with a bivalve carapace composed by chitin and calcium carbonate, living in both marine and non-marine environments. They are broadly used in paleoceanographic and paleoclimatic studies as indicators of bathymetry, salinity and temperature. In the Brazilian sedimentary basins the ostracodes have biostratigraphic importance, mainly in Cretaceous non-marine sections. The marine species, on the other hand, supply good paleoceanographyc data in marginal basins, including Pelotas Basin. In this work new Early Miocene species of the family Cytherellidae and the of genus Actinocythereis are proposed. Based on this taxonomic study some paleozoogeographic remarks are made, linking to the inception of the Antarctic Circumpolar Current and the Malvinas Current, to the dispersal of the ostracodes recorded in the Pelotas Basin. From the analysis of the core section 1300 m-1318 m of the offshore well 2-RSS-1 drilled by Petrobras in the 1970 decade, five species of cytherellids are recorded, two of them herein described, as follows: Inversacytherella atlantica sp. nov., Cytherella pelotensis sp. nov., Cytherella sp. 1, Cytherella sp. 2 and Grammcythella? sp. It is also proposed Actinocythereis imbeensis sp. nov., which constitutes the second species described for the genus in Brazil. Moreover, Krithe coimbrai, Krithe gnoma and Henryhowella kempfi, assigned in previous studies to the inception of cool water masses in Southern Brazilian coast, are recorded. The presence of Inversacytherella and Grammcythella, supply additional evidence for the faunal interchange between America and Oceania influenced by hydrological events in Southern Ocean along the Neogene. The Appendix 1 features the list and photographic documentation of other species registered.

Ostracodes são microcrustáceos que possuem uma carapaça bivalve constituída por quitina e carbonato de cálcio, que vivem em ambientes marinhos e não-marinhos. São amplamente utilizados em estudos paleoceanográficos e paleoclimáticos, sendo bons indicadores batimétricos, de salinidade e de temperatura. Nas bacias brasileiras, os ostracodes têm larga aplicação bioestratigráfica, especialmente em intervalos não marinhos cretáceos. Por sua vez, os ostracodes marinhos têm se destacado pelos bons resultados paleoceanográficos em bacias marginais, entre elas a Bacia de Pelotas. Este trabalho propõe novas espécies eomiocênicas da família Cytherellidae e do gênero Actinocythereis. A partir do estudo taxonômico discutem-se implicações paleozoogeográficas de eventos como o estabelecimento da Corrente Circumpolar Antártica e da Corrente das Malvinas, cuja ação influenciou a dispersão dos ostracodes ora registrados na Bacia de Pelotas. A partir da análise do intervalo testemunhado 1300 m-1318 m do poço offshore 2-RSS-1 coletado pela Petrobras na década de 1970, são registradas cinco espécies da família Cytherellidae, duas das quais aqui descritas, como segue: Inversacytherella atlantica sp. nov., Cytherella pelotensis sp. nov., Cytherella sp. 1, Cytherella sp. 2 e Grammcythella? sp. É também proposta Actinocythereis imbeensis sp. nov., a qual constitui a segunda espécie descrita para o gênero no Brasil. São ainda registradas, Krithe coimbrai, Krithe gnoma e Henryhowella kempfi, atribuídas em trabalhos anteriores ao estabelecimento de massas de água frias na costa Sul-Brasileira. As ocorrências de Inversacytherella e Grammcythella, por sua vez, constituem evidências para o intercâmbio faunístico entre a América e a Oceania decorrentes de mudanças hidrológicas no Oceano Austral ao longo do Neogeno. O Apêndice 1 apresenta a lista e a documentação fotográfica das demais espécies registradas. / Ostracods are microcrustaceans with a bivalve carapace composed by chitin and calcium carbonate, living in both marine and non-marine environments. They are broadly used in paleoceanographic and paleoclimatic studies as indicators of bathymetry, salinity and temperature. In the Brazilian sedimentary basins the ostracodes have biostratigraphic importance, mainly in Cretaceous non-marine sections. The marine species, on the other hand, supply good paleoceanographyc data in marginal basins, including Pelotas Basin. In this work new Early Miocene species of the family Cytherellidae and the of genus Actinocythereis are proposed. Based on this taxonomic study some paleozoogeographic remarks are made, linking to the inception of the Antarctic Circumpolar Current and the Malvinas Current, to the dispersal of the ostracodes recorded in the Pelotas Basin. From the analysis of the core section 1300 m-1318 m of the offshore well 2-RSS-1 drilled by Petrobras in the 1970 decade, five species of cytherellids are recorded, two of them herein described, as follows: Inversacytherella atlantica sp. nov., Cytherella pelotensis sp. nov., Cytherella sp. 1, Cytherella sp. 2 and Grammcythella? sp. It is also proposed Actinocythereis imbeensis sp. nov., which constitutes the second species described for the genus in Brazil. Moreover, Krithe coimbrai, Krithe gnoma and Henryhowella kempfi, assigned in previous studies to the inception of cool water masses in Southern Brazilian coast, are recorded. The presence of Inversacytherella and Grammcythella, supply additional evidence for the faunal interchange between America and Oceania influenced by hydrological events in Southern Ocean along the Neogene. The Appendix 1 features the list and photographic documentation of other species registered.

Ostracodes são microcrustáceos que possuem uma carapaça bivalve constituída por quitina e carbonato de cálcio, que vivem em ambientes marinhos e não-marinhos. São amplamente utilizados em estudos paleoceanográficos e paleoclimáticos, sendo bons indicadores batimétricos, de salinidade e de temperatura. Nas bacias brasileiras, os ostracodes têm larga aplicação bioestratigráfica, especialmente em intervalos não marinhos cretáceos. Por sua vez, os ostracodes marinhos têm se destacado pelos bons resultados paleoceanográficos em bacias marginais, entre elas a Bacia de Pelotas. Este trabalho propõe novas espécies eomiocênicas da família Cytherellidae e do gênero Actinocythereis. A partir do estudo taxonômico discutem-se implicações paleozoogeográficas de eventos como o estabelecimento da Corrente Circumpolar Antártica e da Corrente das Malvinas, cuja ação influenciou a dispersão dos ostracodes ora registrados na Bacia de Pelotas. A partir da análise do intervalo testemunhado 1300 m-1318 m do poço offshore 2-RSS-1 coletado pela Petrobras na década de 1970, são registradas cinco espécies da família Cytherellidae, duas das quais aqui descritas, como segue: Inversacytherella atlantica sp. nov., Cytherella pelotensis sp. nov., Cytherella sp. 1, Cytherella sp. 2 e Grammcythella? sp. É também proposta Actinocythereis imbeensis sp. nov., a qual constitui a segunda espécie descrita para o gênero no Brasil. São ainda registradas, Krithe coimbrai, Krithe gnoma e Henryhowella kempfi, atribuídas em trabalhos anteriores ao estabelecimento de massas de água frias na costa Sul-Brasileira. As ocorrências de Inversacytherella e Grammcythella, por sua vez, constituem evidências para o intercâmbio faunístico entre a América e a Oceania decorrentes de mudanças hidrológicas no Oceano Austral ao longo do Neogeno. O Apêndice 1 apresenta a lista e a documentação fotográfica das demais espécies registradas. / Ostracods are microcrustaceans with a bivalve carapace composed by chitin and calcium carbonate, living in both marine and non-marine environments. They are broadly used in paleoceanographic and paleoclimatic studies as indicators of bathymetry, salinity and temperature. In the Brazilian sedimentary basins the ostracodes have biostratigraphic importance, mainly in Cretaceous non-marine sections. The marine species, on the other hand, supply good paleoceanographyc data in marginal basins, including Pelotas Basin. In this work new Early Miocene species of the family Cytherellidae and the of genus Actinocythereis are proposed. Based on this taxonomic study some paleozoogeographic remarks are made, linking to the inception of the Antarctic Circumpolar Current and the Malvinas Current, to the dispersal of the ostracodes recorded in the Pelotas Basin. From the analysis of the core section 1300 m-1318 m of the offshore well 2-RSS-1 drilled by Petrobras in the 1970 decade, five species of cytherellids are recorded, two of them herein described, as follows: Inversacytherella atlantica sp. nov., Cytherella pelotensis sp. nov., Cytherella sp. 1, Cytherella sp. 2 and Grammcythella? sp. It is also proposed Actinocythereis imbeensis sp. nov., which constitutes the second species described for the genus in Brazil. Moreover, Krithe coimbrai, Krithe gnoma and Henryhowella kempfi, assigned in previous studies to the inception of cool water masses in Southern Brazilian coast, are recorded. The presence of Inversacytherella and Grammcythella, supply additional evidence for the faunal interchange between America and Oceania influenced by hydrological events in Southern Ocean along the Neogene. The Appendix 1 features the list and photographic documentation of other species registered.

Trois carottes de 5 à 6 m de profondeur ont été prélevées tout au long de l’oued El Akarit (Golfe de Gabès, Sud tunisien) : deux sur la rive Nord et une à l’embouchure. L’étude sédimentologique (granulométrie), minéralogique (minéraux argileux) et micropaléontologique (ostracodes, foraminifères et charophytes) et leur étude quantitative et qualitative ainsi que le calcul des indices de diversités de Shannon et d’équitabilité nous a permis de reconstituer l’évolution des paléo-environnements succédés depuis le Pléistocène dans la région El Akarit. La carotte à l’embouchure de l’oued El Akarit (carotte AK1), nous a permis de dater avec précision les dépôts étudiés et de reconstituer la chronologie des évènements ayant contrôlé la sédimentation. La phase pléistocène (>45000 ans B.P), milieu continental estuarien évoluant vers unevaste lagune très ouverte à la mer lors de la transgression marine pléistocène (MIS5e), par la suite l’installation d’un cordon sableux isole cette lagune de l’environnement marin. Les dépôts holocènes inférieurs et moyens sont absents dans l’embouchure de l’oued El Akarit à cause d’une émersion et non dépôt et/ou d’une érosion des dépôts. La phase Holocène supérieur (derniers 3000 ans B.P), se caractérise par la succession de trois épisodes d’évènements extrêmes (crues et tempêtes). A 1 et 2 km du rivage actuel (carotte AK2 et AK3 respectivement), les dépôts généralementcontinentaux montrent des intercalations des dépôts marins et des niveaux à galets enregistrant des évènements extrêmes. Les dépôts de ̴ 8000ans B.P de la poche à « Cardium » à 9 m d’altitude de la mer actuelle, montrent une influence marine (abondance des foraminifères planctoniques), il s’agit évidemment d’un évènement extrême exceptionnel qui provoquerait le transport des foraminifères planctoniques à l’intérieur de la lagune El Akarit. / Three cores varying from 5 to 6 m of depth were taken throughout in the El Akarit River (Gulf of Gabes, south of Tunisia): two on the left river bank and the last at the mouth. The study of the sedimentology (particle size), mineral (clay minerals) and micropaleontology (quantitative and qualitative study of ostracods, foraminifera, charophytes and the calculation of the Shannon / equitability diversity index) deposits content allowed us to reconstruct the paleoenvironments evolution since the Pleistocene in this region. The mouth core (AK1), permitted us to date precisely the studied deposits and reconstruct the events chronology controlling the sedimentation. The Pleistocene phase (> 45 000 years BP) shows a continental estuarine environment evolving toward a vast open lagoon during the Pleistocene marine transgression (MIS5e). Then, the formation of a sand bar isolates the lagoon from the marine environment. The lower and middle Holocene deposits are absent in the mouth deposits. This could be interpreted by the emersion of the zone or by the erosion of deposits. The late Holocene (last 3000 years B.P) phase is characterized by the succession of three extreme events (floods and storms) episodes. At 1 and 2 km from the current shoreline (AK2 and AK3 cores respectively), the continental deposits show an intercalation of marine deposits and pebble levels suggestive of an extreme events occurrence. The existence of the 8000 yr BP deposits "Cardium pocket” at 9 m of the current sea, show a marine influence (planktonic foraminifera abundance). It is apparently an exceptional event that would cause extreme transport of planktonic foraminifera inside the El Akarit lagoon

Re-creation and building new small freshwater habitats belong among the important management activities within the Protected Landscape Area Kokořínsko - Máchův kraj (Czech Republic) for almost two decades. These pools keep the water within the landscape and serve as the habitats for vulnerable species of amphibians and invertebrates, which I have studied within this thesis. Most studies focusing on studying metacommunities of small water bodies have been based on the data from one or two seasons, and thus completely neglect the development of composition of these metacommunities over longer periods of time. This thesis builds on previous research on the species composition of small ponds in the Kokořínsko Protected Landscape Area, which had been done in 2005 and 2006. In 2009 and 2017, sampling in the same ponds continued. I investigated the influence of spatial and environmental variables of individual ponds on the species composition of ostracods, copepods and molluscs in specific years and how has the representation of individual species changed among those years. With one exception, I have not observed any new incoming species of copepods and ostracods since 2006; the number of species had in fact decreased. In the case of molluscs, there was a significant exchange of species between individual...

Sexual dimorphism is the phenotypic difference between males and females of the same species, but how these phenotypic differences arise is largely unstudied at the molecular level. It is understood that sexual selection, or competition for mates, drives sexual dimorphism, but more recently it has been suggested that resource partitioning, or niche pressure, may exert evolutionary pressure, leading to sexual dimorphism. Many members of the sarseilloid family of ostracods exhibit sexual dimorphism of their lateral eyes with males having an image forming eye, while females have a rudimentary eye limited to sensing light and dark. Ostracods progress through five instar stages of development before becoming an adult, and by studying expression levels of selected developmental genes at instar IV, V adult stages and embryos, the underlying expression pattern change that leads to phenotypic differences can be seen. By comparing the differences in expression between two sarseilloid species, Euphilomedes carcharodonta and Euphilomedes morini , we can see how these species develop their specific phenotypes. In E. carcharodonta and E. morini , the genes Sine oculis, Dachshund, Seven in absentia, Chaoptic, Protein Kinase C and Opsin show different expression patterns between groups. The highest expression levels of Sine oculis are in developing embryos when compared to other stages of development. Dachshund, Seven in absentia, Chaoptic, Protein Kinase C and Opsin show significantly different patterns in males or noticeable male trends, demonstrating that these genes are important in the development and function of the sexually dimorphic lateral eye. E. carcharodonta and E. morini show similar gene expression patterns suggesting that these patterns have been conserved over evolutionary time to produce the observed dimorphic morphology.

The Late Rhaetian (Late Triassic) extinction event is characterised by shelled species showing a reduction in size, and thickness, which together with changed mineralogy is thought to be as a result of increased atmospheric pCO2 levels. Similar morphological changes have been demonstrated for extant species exposed experimentally to high CO2 leading to the hypothesis that Late Triassic extinctions were linked with global ocean acidification and increased oceanic palaeotemperatures. Consequently, the aim of this present work was to test this ocean acidification hypothesis by investigating morphological changes in selected shelled fossil species across this extinction event, and attempt to correlate them with changes in environmental temperature and pCO2. The abundance, size, shell thickness and mineralogy was determined for three common species, the bivalves Liostrea hisingeri and Plagiostoma gigantea and the ostracod Ogmoconchella aspinata collected from Triassic and Jurassic rocks from two locations in southwest England. Palaeotemperature was reconstructed from examination of these fossils and from the literature and atmospheric pCO2 estimated from published accounts. The shell size of bivalves increased during periods of high pCO2 and high palaeotemperature at both locations. Ostracod carapace sizes increased at St Audrie’s Bay but decreased at Lyme Regis during periods of high pCO2, while ostracod carapace size decreased during periods of high palaeotemperature at St Audrie’s Bay. However, ostracod shell thickness increased and decreased as pCO2 increased but shows no relationship with palaeotemperature at either location. Laboratory experiments on the effect of elevated pCO2 and elevated temperature on three modern species of ostracod was carried out. Modern species Leptocythere sp. and L. castanea subjected to either elevated pCO2 or elevated temperature showed increased dissolution, however size and thickness did not significantly change. In the same experimental conditions L. lacertosa showed increased dissolution however size continued to increase, while thickness was maintained. Comparison of fossil bivalve and ostracod data to modern high pCO2 and high temperature experiments illustrates some correlations to the modern experiments results indicating high pCO2 and high palaeotemperature conditions could have been occurring during the Triassic-Jurassic boundary interval. From the evidence presented, combined with an appropriate trigger (CAMP volcanism), it can be concluded that both ocean acidification and palaeotemperature were contributing to the species adaptations identified across the Triassic-Jurassic boundary interval.

Examination of an important new 319m core of lake sediment recovered from Ioannina in NW Greece has attempted to relate changes in the lake to variations in the regional climate of south-central Europe over the last 600,000 years. The site is known to have been extremely sensitive to past climatic change for three reasons: (i) temperate vegetation persisted throughout glacial stages (albeit at low frequencies), so the vegetational response to climatic change would therefore have been almost immediate; (ii) the extreme thickness of the sediments suggests that accumulation rates were high (at times, > 1m per thousand years), which has enabled high-resolution palaeoclimatic reconstructions; and (iii) precipitation of authigenic carbonate has preserved a remarkably sensitive proxy record of productivity variations for most of the lake's history. Well-defined shifts from glacial - interglacial mode have been correlated with vegetational changes identified in a core previously analysed from the same basin (using magnetic susceptibility profiles), enabling tentative correlations to be suggested with other European terrestrial sequences and with the marine oxygen isotope record, back to marine isotope stage 16. Twelve AMS radiocarbon determinations from the upper part of the core, together with the identification of a series of reversed palaeomagnetic events within the Brunhes chron, support the proposed age model for the sequence. The sediments at Ioannina, unlike most of the other long terrestrial European sequences, are calcareous and contain mollusc and ostracod assemblages. Part of this project has involved a comprehensive review of Quaternary and modem aquatic faunas from the lake, as well as the description, illustration and critical assessment of several poorly-known endemic taxa. Faunal assemblage data have been used to provide valuable information concerning the variable response of lake-level to climatic change over time. Convincing new mollusc an evidence indicates low lake-levels at the Last Glacial Maximum, agreeing with regional pollen data, but conflicting with geomorphological evidence derived from Kastritsa, a well-documented nearby Palaeolithic cave site. It is suggested that this discrepancy may be a result of subsequent tectonic uplift of the rockshelter. In addition, stable isotopic analyses of both the ostracods and the bulk carbonate within the sediments have contributed towards deriving a comprehensive palaeoenvironmental history for the site. Although the study analysed physical, biological and geochemical aspects of the entire core, two distinct parts of the record were selected for more detailed investigation. High-resolution analysis over the last interglacial (the Eemian) has revealed evidence for a clear, two-step deglaciation at the beginning of the period, known from elsewhere as the Zeifen-Kattegat Oscillation. Climatic instability has also been detected within the full interglacial. Comparisons are drawn with a range of other Eemian records from across Europe, as well as the Greenland ice cores. High-resolution analysis of the period from the end of the last glacial to the present day has also revealed evidence for climatic instability. A cool and arid oscillation is demonstrated by several climatic proxies that may constitute the first recognition of the Younger Dryas stadial from Greece. A shorter, but more subdued cooling event has also been detected during the first half of the Holocene, which may correspond with a widespread climatic oscillation from high-resolution terrestrial, marine and ice core records that has been dated to between 7,500 and 8,000 years BP.

Le paysage littoral de la basse vallée de l’Aude est composé d’une mosaïque de milieux laguno-deltaïques mobiles à l’échelle des derniers millénaires. Du fait de cette mobilité et de l’ancienneté de l’occupation humaine, continue depuis le Néolithique, la compréhension des dynamiques environnementales passées constitue une problématique incontournable de la recherche archéologique narbonnaise. Le travail que nous présentons vise à identifier et expliquer les transformations de ce paysage fluvio-lagunaire à l’Holocène, à partir de l’analyse sédimentologique et micropaléontologique des enregistrements sédimentaires datés au radiocarbone. Dans un premier temps, une étude de la répartition spatiale actuelle des ostracodes des lagunes et embouchures fluviales modernes est proposée en vue d’utiliser cette microfaune comme bioindicateur privilégié des conditions environnementales passées dans la zone d’étude. Elle repose sur le prélèvement d’une soixantaine d’échantillons de sédiments de surface provenant de différents complexes paraliques de Méditerranée nord-occidentale. Les assemblages d’ostracodes actuels permettent de caractériser différents stades d’isolement des bassins, des lagunes complètement fermées jusqu’aux baies largement ouvertes sur la mer, ainsi que la variabilité intra-lagunaire des milieux en relation avec la proximité des embouchures et des graus. La base de données présentée peut être utilisée, à titre comparatif, pour reconstituer les dynamiques géomorphologiques littorales holocènes, telles que la mobilité deltaïque et l’évolution des systèmes barrières-lagunes, dans le golfe du Lion. Dans un second temps, l’étude des enregistrements sédimentaires a permis d’appréhender l’évolution du littoral narbonnais à l’Holocène. Elle repose sur neuf sondages carottés répartis sur les deux branches deltaïques, méridionale et orientale, de l’Aude. Les résultats obtenus permettent de proposer un scénario paléogéographique reconstituant la dynamique des environnements de la basse vallée depuis 9500 ans cal. BP, en même temps qu’ils renseignent le contexte local de la remontée du niveau marin holocène dans l’intervalle 9500-6000 ans cal. BP. Plusieurs problématiques sous-jacentes à l’évolution des paléoenvironnements littoraux narbonnais sont discutées. Elles concernent les modalités de la transgression holocène dans les lagunes du golfe du Lion, l’enregistrement d’un événement marin extrême en fond de ria vers 5200-5000 ans cal. BP, et le rythme de progradation accéléré du delta de l’Aude durant le dernier millénaire. L’identification de deux périodes d’enrichissement en plomb cohérentes avec les principaux pics d’exploitation minière connus en Languedoc à la charnière du changement d’ère et au début du Moyen-âge classique suggère un enregistrement de la fluctuation historique des activités métallurgiques. / The present day Aude valley’s coastal landscape is the result of unstable lagoonal and deltaic environments during the last millennia. The understanding of past environmental dynamics is a key issue of the local ar-chaeological research, because since the Neolithic period human beings have settled in this area. This work aims to identify and explain the fluvio-lagoonal landscape’s evolution in the Narbonne region during the Holocene by using sedimentology, micropalaeontology and radiocarbon sediment datations. First, we analysed the present ostracods spatial distribution in modern lagoons and river mouths in order to use this microfauna as a bioindicator of past environmental conditions in the study area. Various aquatic envi-ronments (60) from the NW Mediterranean coastline were studied. The present ostracod assemblages characterize different stages of isolation, from completely closed lagoons to widely open marine bays, as well as intra-lagoonal environmental variability in relation to the inlets and river mouth proximities. The proposed database can be used to reconstruct coastal geomorphologies and dynamics, such as the holocene evolution of delta and barrier-lagoon systems in the Gulf of Lion. Second, sedimentary recording studies have been used to analyse the Narbonne’s coastal evolution. This study is based on nine cores distributed over the southern and eastern deltaic branches of the Aude river. With theses results, it is possible to propose a palaeogeographic scenario associated with the environmental dynamics of the lower valley since 9500 years cal. BP. This same data informs us about the local context of the Holocene sea level rise during the 9500-6000 years cal. BP. Several issues are discussed such as : the Holocene’s transgressions of the Gulf of Lion’s lagoons, the extreme marine event near the bay head delta around 5200-5000 years cal. BP, and the Aude delta’s rapid progradation during the last millennium. Additionally, we identified two periods of lead enrichment; which are consistent with the major mining peaks known in Languedoc (beginning of the first century AD - beginning of the classical Middle ages) and suggest a record of fluctuating metallurgical activity.

Ce travail de thèse a permis de reconstituer la dynamique à long terme de deux écosystèmes lacustres alpins dans les Alpes du sud grâce à l’étude (1) de la variabilité tardi-holocène des paramètres physico-chimiques de l’eau, des niveaux lacustres et des dynamiques de communautés aquatiques, et (2) des types de réponse de ces environnements à des perturbations externes en lien avec les changements du bassin versant et du climat. Les deux séquences sédimentaires prélevées par carottage au lac d’Allos et au lac Petit (Massif du Mercantour, 2200 m) ont permis de reconstituer en détail l’évolution des écosystèmes lacustres depuis les derniers 13,500 cal. BP grâce à trois grands volets : (1) l’étude de fossiles d’espèces aquatiques indicatrices des conditions de vie dans le milieu lacustre (les diatomées et les ostracodes) ; (2) l’analyse des isotopes de l’oxygène contenus dans ces mêmes fossiles afin de reconstituer un signal paléohydrologique ; (3) une comparaison multi-proxy permettant de mettre en lien les changements de l’écosystème lacustre avec les dynamiques du bassin versant. Les résultats obtenus et leur confrontation à un cadre multidisciplinaire très documenté ont permis d’évaluer l’importance première des processus érosifs et des modifications du couvert végétal sur la dynamique lacustre, au travers de changements majeurs dans les communautés aquatiques et les niveaux trophiques. Enfin, les données isotopiques mesurées sur les fossiles de diatomées et d’ostracodes ont mis en évidence des variations paléohydrologiques inédites pour la région : cette approche, novatrice ouvre la perspective d’une reconstitution paléoclimatique de référence pour les Alpes du sud. / The thesis is devoted to the reconstruction of long-term changes in two lacustrine ecosystems in the Southern Alps. This study aims at assessing (1) the lateglacial-holocene variability of water physico-chemistry, lake levels and aquatic species dynamics; and (2) the environmental responses of the lacustrine ecosystem to external forcing (watershed and climate changes), with the study of Lake Allos and the Lake Petit (Mercantour National Park, 2200 m a.s.l). The two sedimentary cored profiles provided a detailed record of the past lacustrine dynamics since 13.500 cal. BP. An integrative approach was carried out including (1) the study of fossils of aquatic bioindicators species (diatoms and ostracods) informing about changes in lacustrine living conditions ; (2) the analysis of oxygen isotopes recorded by these aquatic fossils tracing a palaeohydrological signal ; (3) a multiproxy comparison linking the aquatic environment with changes in watershed dynamics. These results integrated into a rich multidisciplinary framework evidenced the major role of erosion processes and changes in vegetation cover as factors triggering lake responses to disturbance, with concomitant changes in aquatic communities and trophic levels at several timescales. The different geological settings and lake morphologies have also played a significant role, modulating changes in benthic and planktonic aquatic communities over long time periods. Finally, oxygen isotopes records allow to trace for the first time palaeohydrological changes in the region: this innovative approach represents an original outcome for reconstructing a reference past climate for the Southern Alps.