Seasonality estimates based on archaeological shellfish remains have been an important component of settlement pattern reconstruction. Investigations of this nature allow researchers to place prehistoric people on the landscape at points in space at different times of the year. Many of the previous seasonality studies, however, have focused on marine species from coastal sites, with little attention given to freshwater locales, especially ones in the Mississippi Delta. To address that disparity, this study examines freshwater mussel “season of capture” via analysis of stable oxygen isotope ratios in specimens recovered from two Late Woodland sites located along the Yazoo River, Mississippi. As freshwater mussel shells are composed of aragonite, a metastable form of calcium carbonate (CaCO3), they can suffer greatly from the impact of meteoric diagenesis. Because of this, samples must be evaluated for diagenesis prior to any geochemical analysis taking place. Archaeological shell samples were examined via thin-section petrography and scanning electron microscopy (SEM). Visual analysis indicated pristine aragonite microstructure and crystallography in all archaeological shell samples, and confirmed their suitability for isotope analysis. Vetted shells were then micromilled across accretionary growth bands, and analyzed for their oxygen isotope signatures. Isotope profiles were then interpreted for their individual “season of capture”, and oscillation patterns for 22 shell specimens indicated mussels were being collected in all four seasons. These data support the view that at least some portion of the human population at both sites engaged in shellfishing activities year-round, indicating sedentary populations at both locales. The shell assemblages were also investigated for the purpose of informing modern conservation efforts (i.e., “applied zooarchaeology”). Nearly 24,000 valves were analyzed taxonomically, yielding the presence of 37 species, of which 24 represented new river records for the Yazoo River. These data provide a valuable historical perspective, cataloging communities as they existed prior to extensive modern impacts, thus representing an ecological baseline to be compared with modern populations. Though modern data are extremely limited for the river, the study revealed it once supported a diverse mussel community containing numerous species currently considered rare, endangered, or extinct in Mississippi.

Sclerochronology affirms the well-established fact that banded growth increments in marine molluscs accurately record oscillations in climate and environment for the past millennia or more. This study considers how such records can enhance understanding of environmental shifts across the 18th to 20th centuries. Specifically, it investigates whether sclerochronological data are fundamentally associated with stable carbon and oxygen isotope values and if the climate phenomenon of the Little Ice Age impacts the marine radiocarbon reservoir effect. Furthermore, this study compares the North Sea and the Irish Sea to discover whether observed environmental changes are equivocal or not. Three shells of Arctica islandica were retrieved from the Dutch natural history museum "Naturalis" in Leiden, the Netherlands, to construct a chronology dating back to the 18th century from growth increments. Collection dates for the three shells vary between 1882 and 1954 in the North Sea and the Irish Sea. Shells were prepared, photographed and milled for calcium carbonate material. Digital images allowed counting of increments while the milled material was measured for stable carbon and oxygen isotopes and was radiocarbon dated. The ontogenetic bias was removed from sclerochronological data using MATLAB software to produce a purely environmental growth signal. The results agreed with the proposed hypothesis that there is a link between growth increments and the stable isotope data. However, further analysis is required to validate the presence of the Little Ice Age in the radiocarbon reservoir effect. These results indicate that the stable carbon and oxygen isotopes and growth increments are a good indicator of favourable growth conditions for Arctica islandica. Therefore, this study highlights that Arctica islandica is a suitable proxy for the North Sea and Irish Sea palaeoenvironment reconstructions. On this basis, future climate research can accurately depend on sclerochronological data to aid in understanding the patterns of anthropogenic climate change.

Les variations multidécennales et saisonnières de la Mousson Ouest-Africaine (MOA) au cours des deux derniers millénaires dans la région sahélienne sont peu documentées en raison du manque d'archives paléoclimatiques. Pour cela, on se propose dans ce travail de thèse d'explorer une nouvelle archive paléoclimatique basée sur l'étude sclérochronologique des coquilles du mollusque bivalve Anadara senilis dans des amas coquilliers fossiles afin de reconstituer les variations hydrologiques multidécennales et saisonnières dans le Delta du Saloum au Sénégal de 460 à 1090 A.D. L'hydrologie de cet estuaire hypersalin est très sensible aux variations de la MOA. Les variations hydrologiques passées sont reconstituées à travers des analyses isotopiques (δ18O, δ13C) des coquilles modernes et des coquilles fossiles dans le delta. Le signal isotopique saisonnier de ces coquilles retrace fidèlement les variations hydrologiques liées au régime de la mousson. Nos résultats montrent que ces variations isotopiques, associées aux stries de croissance dont la périodicité est connue, permettent de reconstituer les durées des saisons avec une précision de 25 jours, une précision jamais atteinte dans les études paléoclimatiques antérieures dans la région sahélienne. Les variations hydrologiques multidécennales sont reconstituées à travers la composition isotopique des coquilles fossiles prélevées dans un amas coquillier massif (Dioron Boumak) dont le taux d'accumulation est très important. Les coquilles fossiles prélevées dans cet amas présentent des valeurs isotopiques moyennes en δ18O plus négatives de 1.4 ‰ par rapport à leurs analogues modernes. Ceci est une indication que les conditions hydrologiques étaient plus douces qu'aujourd'hui dans le Saloum qui n'était pas hypersalin à cette époque. Le bilan Précipitation-Evaporation était par conséquent plus positif en réponse à des pluies plus intenses et/ou plus étalées dans le temps de 460 à 1090 A.D. Il semblerait que les pluies hivernales et printanières, caractéristiques de la frange littorale sénégalo-mauritanienne, plutôt rares et insignifiantes de nos jours se produisaient plus fréquemment pendant cette période. La jonction entre ces pluies et les pluies de mousson aurait favorisé l'établissement de saisons des pluies beaucoup plus longues (~5 mois environ au lieu de 3 aujourd'hui) et une augmentation du bilan Précipitation-Evaporation. Cette étude met en lumière le potentiel considérable d'A. senilis comme archive paléoclimatique à haute résolution de la variabilité des précipitation dans la région sénégalaise. Elle montre également l'importance de la saisonnalité des précipitations dans les cycles hydrologiques passés dans cette région qui doit être prise en compte dans les études paléoclimatiques futures. / The multidecadal and seasonal variations of the West African Monsoon (WAM) in the last two millennia remain poorly documented in the Sahel region because paleoclimate archives are lacking. For this, we propose in this PhD thesis a sclerochronological study of the mollusk bivalve Anadara senilis from massive shell middens to reconstruct multidecadal and seasonal variations of hydrological conditions in the Saloum Delta (Senegal) between AD 460 and 1090. Hydrological conditions in this hypersaline estuary are highly sensitive to the WAM variations.Past hydrological variations are reconstructed by using isotopic composition (δ18O, δ13C) of modern and fossil shells in this Delta. The shells' seasonal isotopic signals reflect faithfully hydrological variations, linked to monsoonal regime. Our results show that the variations of these seasonal isotopic signals, associated to shell growth patterns with known periodicities allow the reconstruction of season durations with a precision of 25 days, a precision that has never been achieved in paleoclimate studies in the Sahel region.Multidecadal variations of hydrological conditions are reconstructed by using isotopic composition of fossil shells collected in the massive shell middens (Dioron Boumak), characterized by high accumulation rate. The averaged δ18O value of fossil shells was more negative by 1.4‰ compared to modern shells' isotopic signature. This result indicates fresher mean conditions in the Saloum Delta that was likely not hypersaline as it is today. The precipitation-evaporation budget was thus more positive in response to a more intense and/or longer rainfall season during from AD 460 to 1090. We propose that winter and early spring rainfall events, which are observed very occasionally today, were occurring frequently during this period. These rains restricted to the western Sahelian coast and followed by the monsoon would have increased the total duration of the rainy season (~ 5 months instead of 3 months today) and substantially increased the annual precipitation-evaporation budget.This study shed light on the high potential of A. senilis as a high resolution paleoclimate archive of rainfall variability in the Sahel region. It shows also the importance of rainfall seasonality in past hydrological cycles that should be taken into account in the future paleoclimate studies.

Ce doctorat repose sur l'utilisation de Glycymeris glycymeris, un bivalve de la famille des Glycymerididae, pour reconstruire la variabilité environnementale en rade de Brest (France). Il vise à comparer des données géochimiques archivées dans ces coquilles avec diverses variables biologiques et écologiques. Les objectifs sont d'identifier de potentiels proxys et d'étendre notre connaissance de la variabilité environnementale avant les premières mesures instrumentales.Au total, 38 spécimens (vivants ou morts) ont été utilisés pour construire une chronologie s'étendant de 1891 à 2014.Les indices de croissance standardisés suggèrent que la croissance coquillière est principalement influencée par le débit de l'Elorn, la salinité et la matière particulaire en suspension.Des analyses isotopiques, réalisées sur les portions juvéniles de 24 spécimens, mettent en évidence que les variations de δ18Oaragonite enregistrent fidèlement la température de surface, permettant sa reconstruction sur 45 ans en rade de Brest. En terme de forçage climatique, ces variations de température en rade semblent contrôlées par le gyre subpolaire et l'East Atlantic Pattern.Cinq coquilles (3 d'âge inférieur à 10 ans et 2 âgées de 45 ans) ont ensuite été analysées pour leurs concentrations en strontium et magnésium par LA-ICP-MSLes concentrations en Mg et Sr, quant à elles, sont positivement corrélées à la température de l'eau à une échelle sub-annuelle, mais négativement à l'échelle annuelle.Cette étude met en lumière le potentiel de G. glycymeris comme archive de la variabilité climatique et environnementale en rade de Brest. Du fait du nombre important de spécimens sub-fossiles en rade, cette thèse fournit une base de travail pour l'extension de ces reconstructions dans un passé encore plus lointain. / This PhD thesis uses Glycymeris glycymeris, a temperate bivalve in the Glycymerididae family, to reconstruct environmental variability in the Bay of Brest, France. This work comprises of geochemical data archived within shells, compared with several biological and ecological variables. The aims of this study were to assess for potential proxies and expand environmental knowledge prior to local observational records.Thirty-eight live- and dead-collected specimens were used to create a chronology spanning 1891 to 2014. When the standardised growth index was correlated with local environmental factors, it showed that the predominant drivers of growth were Elorn inflow, salinity and suspended particulate matter.Isotopic analysis was undertaken on the juvenile increments of 24 shells. Our results highlight that variations in δ18Oaragonite accurately record local sea surface temperatures, leading to the creation of a 45-year SST reconstruction for the Bay of Brest. Correlations between this and climate forcings show that SSTs in this area are controlled by the subpolar gyre and the East Atlantic Pattern.Five shells (three under the age of 10 and two aged 45) were analysed using a LA-ICP-MS to determine the quantity of strontium and magnesium. Mg and Sr intensities are positively correlated with temperature sub-annually, but on an annual scale there is a negative correlation.This study conveys the potential of G. glycymeris as an archive of climatic and environmental variability in the Bay of Brest. As there are a large number of sub-fossil specimens in the area, this study also provides an anchored base for expansion further back in time.

Reef-building corals are subject to high amounts of stress, including pollution and rising sea surface temperatures due to climate change. These factors can affect the ability of corals to produce their calcium carbonate skeletons. Evaluation of the effects of climate change may be facilitated by evaluation of records of coral skeletal growth over a long period of time. The aim of this study was to evaluate skeletal growth of the coral Orbicella faveolata in La Parguera, Puerto Rico over a 32-year period. For this, 14 Orbicella faveolata core samples were collected from corals at two reefs (1.2 km apart) in southwestern Puerto Rico. Coral cores were used to obtain skeletal growth data. Average skeletal extension, density, and calcification was determined for subannual and annual periods, and compared between sites. Time series and growth master chronologies were constructed and compared between corals at the two reef sites. In addition, sea surface temperature (SST) data was obtained and summarized into time series, and correlated with coral growth chronologies for the 32-year period. Results showed that two Orbicella faveolata, growth parameters (extension and calcification) were similar between Turrumote and Pinnacles reefs, while density was non-significantly greater on Pinnacles Reef between 1973 and 2004. SST had a weak, and non-significant correlation to growth parameters over time.

La présente recherche souligne l'importance de la pêche chez les chasseurs cueilleurs marins de la région centrale du détroit de Magellan et des mers adjacentes. L'approche méthodologique prend en compte l'analyse ichthyoarchéologique de 13 sites archéologiques couvrant une chronologie de 6000 à 1000 ans BP. La méthode de la sclérochronologie est appliquée aux vertèbres de l'espèce la plus importante (Salilota aust alis) afin d'évaluer la saisonnalité des activités de pêche. Les techniques de pêche sont abordées à partir des éléments de technologie découverts dans les gisements étudiés (poids lithiques, pointes en os, murets de pêcherie) et de l'information ethnographique. Les résultats permettent de discuter et de réévaluer le rôle de la pêche par rapport à la chasse aux mammifères marins, généralement estimée (avec les mollusques) comme l'axe principal de subsistance de ces sociétés nomades. Des changements radicaux sont observés dans le modèle d'exploitation des poissons à travers le temps. On observe à l'époque ancienne et moyenne (de 6000 à 2000 ans BP) une grande spécialisation dans des espèces démersales exploitées à différents moments de l'année, et l'emploi de technologies spécialisées standardisées. Au cours des derniers 2000 ans et jusqu'à la période ethnographique, la pêche est concentrée sur les bords de côte ; son rôle dans la subsistance est variable et on observe des stratégies opportunistes permises par l'usage de techniques de pêche variées. Le modèle d'exploitation observé tout au long de la séquence chronologique est différent de celui qui avait été suggéré par D. Zangrando pour les nomades marins du canal Beagle, où est observée une intensification progressive de la pêche à travers le temps. Finalement on remarque le haut niveau de spécialisation de la pêche chez les premiers indiens canoeros qui ont peuplé la région de Magellan, il y a 6000 ans, ce qui permet de discuter du degré d'adaptation de ces populations aux milieux marins. Cette observation renforce l'hypothèse, de plus en plus documentée, d'un peuplement maritime venu du nord, le long de la côte pacifique. / This research highlights the importance of fishing in marine hunter-gatherers of the central region of the Magellan Strait and adjacent seas. The methodological approach takes into account the ichthyoarchaeological analysis of 13 archaeological sites covering a chronology from 6000 to 1000 years BP. The Sclerochronology method is applied to the vertebrae of the most important species (Salilota australis) to estimate the seasonality of fishing activities. Fishing techniques are discussed from technology elements discovered in the studied deposits (weight lithic, bone points, fishing weirs) and ethnographic information. The results allow to discuss and reassess the role of fisheries in respect to the hunting of marine mammals, generally estimated to be (along with shellfish) the main source of subsistence nomadic societies. Radical changes are observed on fishing strategies over time. We observe in the Early and Middle Periods (6000 to 2000 years BP) a specialization in demersals species exploited at different moments of the year, and the use of standardized and specialized technologies. ln the last 2000 years until the ethnographic period, fishing is concentrated on the seashore; the role in subsistence is variable and opportunistic strategies enabled by the use of various fishing technics can be observed. The fishing strategies observed throughout the chronological sequence is different from the one suggested by F. Zangrando for the marine nomads of the Beagle Channel, where a progressive intensification of fishing through time is detected. Finally this research emphasizes the high level of the fishing specialization of the first canoeros Indians who populated the region of Magallanes, 6000 years ago, which allows us to discuss the degree of adaptation of these populations to marine environments. This observation strengthens the hypothesis, increasingly documented, of the existence of a maritime population from the Northern regions, along the Pacific Coast.

The presence of annual density banding in certain long-lived reef-building corals provides a record of the coral’s growth rate over time in response to changing environmental conditions. Coral growth is best described by three parameters: linear extension, bulk density, and calcification. Coral growth is generally controlled by the combined influences of light, temperature, and water quality; however, corals are highly responsive to their surrounding conditions and thus record environmental variations through their rates and patterns of skeletal accretion. Because coral growth rates reflect environmental conditions over time, they allow testing of hypotheses regarding the effects of climate change, more specifically global warming which affects sea surface temperatures and rising atmospheric carbon dioxide which affect the aragonite saturation state of seawater. Influences on coral growth include local changes in sea surface temperature and rainfall as well as large scale climatic indices such as the Atlantic Multidecadal Oscillation (AMO), the North Atlantic Oscillation (NAO), and the Southern Oscillation Index (SOI). Chapter 1, Background, reviews the current state of knowledge in three primary areas: 1) coral biology, growth, density band formation, and measurement of extension, density, and calcification, 2) potential climate change impacts on coral growth, and 3) long-term coral growth records. This section is broadly intended to review the literature, identify possible information gaps, and recognize current debate within coral and climate change research. Chapter 2, Sample Size for Coral Sclerochronology, presents data of sample size correlations based on statistical analyses of annual extension rates. A standardized period (1970-1985) of annual extension rates from the largest number of Montastraea faveolata samples available from southeast Florida (136 corals) was used to test correlation on varying spatial scales and to determine sample size requirements for desired levels of correlation based on objective criteria. The results provide basic information on masterchronology construction for sclerochronological growth rate studies and provide a framework from which further growth rate variability can be assessed. Extension and bulk density can be measured from X-ray films of coral skeletal slabs and can be used to calculate calcification. Chapter 3, Relative Optical Densitometry, describes the techniques and associated errors through the process of coral coring, sectioning, X-raying, developing, digitizing, calibrating and analyzing. The principles of relative optical densitometry and the calculation of mass absorption coefficient ratios for aragonite and aluminum standards are explained. Calculated and measured errors are quantified to define the accuracy and precision of these techniques necessary to detect potentially subtle changes in coral growth caused by climate change. Coral cores from the Florida Key, USA, were used to construct growth records over a 60-yr period from 1973-1996. Chapter 4, Coral Growth Records and Climate Change, uses linear extension rate, bulk-density, and calcification rate from annual and sub-annual bands in order to assess: 1) growth averages, variability, and relationships between growth parameters, 2) long term trends with respect to rising carbon dioxide levels and sea surface temperature, 3) correlation with local environmental variables of temperature and rainfall, and 4) correlation with major climate indices of Atlantic Multidecadal Oscillation, North Atlantic Oscillation, and the Southern Oscillation.

Le climat asiatique est aujourd'hui caractérisé par une forte dualité entre un climat de moussons au Sud-Est et un climat aride en Asie centrale. Ces climats sont tous les deux définis par une saisonnalité marquée, que ce soit en terme de précipitations pour le premier ou de températures pour le second. Si l'intensification des moussons asiatiques au Néogène, liée à l'influence du soulèvement final du plateau tibétain sur les climats asiatiques, semble faire consensus dans la communauté scientifique, la caractérisation des climats paléogènes est encore peu établie. Ainsi la question de savoir quand cette dualité climatique s'est installée en Asie reste encore ouverte. Au Paléogène, les reliefs liés à la collision entre les plaques indienne et eurasiatique étaient encore naissant et la distribution entre les terres et les mers très différente de l'actuelle. Notablement, une vaste mer épicontinentale et peu profonde (la Proto-Paratethys) s'étendait à travers l'Europe et l'Asie Centrale. À la fin du Paléogène, la Proto-Parathetys se retire de l'Asie Centrale, et les hautes topographies asiatiques se mettent en place. Dans ce contexte géodynamique, cette thèse cherche à caractériser les fluctuations à haute fréquence du climat en Asie Centrale afin de comprendre l'évolution de la saisonnalité au cours du Paléogène, et plus précisément pendant la période de l'Éocène (-55 à -34 Ma). Pour cela une approche originale utilisant une méthode géochimique multi- proxy sur des coquilles d'huîtres a été établie. Grâce à l'apport de l'analyse incrémentielle de marqueurs élémentaires et isotopiques sur les coquilles nous accédons aux variations saisonnières de la température et de la salinité de l'eau de mer. Ceci nous permet de mieux cerner les bilans hydriques et thermiques à l'échelle de l'année et ainsi de caractériser le climat d'Asie Centrale à très haute résolution. Combinant cette approche géochimique avec une étude sédimentologique et une étude numérique à plus grande échelle, cette thèse cherche à mieux établir les causes de l'évolution du climat régional au cours du Paléogène. / The modern Asian climate is mainly characterized by a monsoonal duality between humid summers in southern and eastern Asia and arid winters in Central Asia resulting in a strong seasonality in terms of precipitation and temperature in these respective regions. Although Neogene monsoonal intensification - mainly attributed to Tibetan plateau uplift - is well established, Paleogene Asian climate is still poorly understood such that the question of how and when this climate duality was established remains open. During Paleogene times, paleoreliefs due to the ongoing Indo-Asia collision and the land-sea distribution were very different compared to modern. Notably, a shallow epicontinental sea (the Proto-Paratethys) covered part of Europe and Central Asia. During the Eocene (-55 to -34 Ma), the Proto-Paratethys retreated westward while high Asian topographies formed. In this peculiar context, this PhD thesis aims to characterize the evolution of high-frequency climatic fluctuations in Central Asia in order to better constrain the seasonality changes associated with sea retreat, topographic uplift or nascent monsoons. We develop a novel approach using a geochemical multi-proxy methodology on oyster shells. Thanks to incremental analyses of elements and isotopes on bivalve shells, we estimate seasonal variations of temperature and salinity in seawater at high resolution. This enables to constrain precisely the annual-scale water and thermal balances and, by applying this technique to successive oyster bearing deposits widely distributed over Central Asia, aims to characterize Central Asian climate evolution. Combining this geochemical approach with a sedimentological and a numerical studies at larger time- and geographic- scale, this PhD thesis is aiming at better understanding the causes of the Eocene regional climate evolution.

<p>In many interpretations of hunter-gatherer settlement systems, archaeologists have assumed implicitly or explicitly that a pattern of mobilitybased on seasonally-scheduled movements between different site locations waspracticed. This pattern of mobility is often characterized as a seasonal round, where different locations are used during specific times of the year for different purposes. An implication of this pattern of mobility is that short-term occupation sites are visited annually, approximately at the same time each year and longer-term residential sites can span multiple seasons. To interpret seasonality, indirect indicators are often used but the high-resolution methods presented in this study provide direct evidence of seasonal site occupation. The Pacific Northwest Coast provides an ideal landscape to examine seasonality since many of the staple resources, particularly salmon, were available on a seasonal basis. Contrary to longstanding assumptions of regular seasonal movement between sites, the analysis of shell samples from multiple archaeological sites from distinct regions in British Columbia show complex patterns of multi-seasonal occupation at smaller campsites and specific seasonal or multi-seasonal emphasis in occupation and/or shellfish harvest at longer-term residential sites.</p> <p>To identify patterns of shellfish harvest, stable oxygen isotope analysis and high-resolution sclerochronology were applied to the bivalve <em>Saxidomus gigantea</em> (butter clam). Combined with shell growth increment analysis to examine relative levels of harvest pressure, local rates of shellfish collecting are also interpreted. To examine regional variability in seasonality and resource use in British Columbia, three environmentally and historically distinct areas were selected spanning approximately 6000 years of history. These regions include the central coast in the tradition territory of the Heiltsuk, and two areas on the northern coast, specifically the Dundas Islands Group and Prince Rupert Harbour in the traditional territory of the Tsimshian. The results of the analysis show site-specific trends in shellfish harvesting on the central coast; a pattern which is not as clear on the northern coast. Sites on the Dundas Islands show multi-seasonal collection and a stronger emphasis on winter shellfish harvesting. The results also show that shellfish were harvested more intensively in the Dundas Islands area relative to the central coast. The pattern of seasonal shellfish harvesting on the mainland coast at village sites in Prince Rupert Harbour is similar to the pattern found at long-term residential sites on the central coast. With respect to the dietary importance of clams, another longstanding issue in Northwest Coast archaeology, the results show a mix of patterns including casual resource use at most campsites, intensive multi-season harvest in some regions and strategic multi-season harvest and spring consumption at some residential sites.</p> / Doctor of Philosophy (PhD)