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The thermohaline circulation (THC) corresponds to the large time- and spatial-scales ocean circulation associated with the transport of heat and salt, and is known to be an important factor controlling the climate variability. The large scales involved in the THC make it difficult to observe, and therefore the synergy of numerical models and climate proxy reconstructions is particularly relevant to study the characteristics of this circulation in the present and past climates. In this doctoral thesis, the THC during the Last Glacial Maximum (LGM) and the Present-Day (PD) is explored using a state-of-the-art Ocean General Circulation Model in its high- and low-resolution regimes. By comparing the LGM model outputs with the paleo-proxy reconstructions, it is shown that the high-resolution simulation improves the representation of the sea surface tem- peratures in the regions where the current structures appear to be complex, i.e., the western boundary currents (Agulhas, Kuroshio, Gulf Stream) and the Antarctic Circumpolar Current, although statistical comparisons with paleo- proxy reconstructions are not significantly improved on a global scale. The THC involves a superposition of processes acting at widely different spatial and temporal scales, from the geostrophic large-scale and slowly-varying flow to the mesoscale turbulent eddies and at even smaller-scale, the mixing generated by the internal wave field. Not all these processes can be properly resolved in numerical models, and thus need to be parameterized. Analyzing the THC in an eddy-permitting numerical model, it was found that the temporal scales required for diagnosing the Southern Ocean circulation should not exceed 1 month and the spatial scales needed to be taken into account must be smaller than 1°. Important changes in the nature and intensity of the THC were observed between the LGM and PD simulations. An estimation of the turnover times (i.e., the time it takes for the water parcel to make and entire loop on the Conveyor Belt) revealed that the LGM THC could be more vigorous than under the PD conditions. As a result, the ocean transports of heat and freshwater, the oceanic uptake of CO2, the ventilation of the deep ocean and the reorganization of the passive and active tracers (e.g., temperature, salinity, greenhouse gases, nutrients) can be altered in these different regimes. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 5: Manuscript. </p>

Imunoglobulinas secretoras presentes nas superfícies mucosas representam a primeira linha de defesa do sistema imune adaptativo contra desafios infecciosos. A imunidade humoral de recém-nascidos prematuros é diminuída em comparação a recém-nascidos a termo. A identificação de antígenos de virulência de bactérias colonizadoras da cavidade oral pode ajudar na investigação dos mecanismos de estimulação antigênica e desenvolvimento da resposta imune de mucosa. No presente estudo, foram medidos os níveis de imunoglobulina A (IgA) e M (IgM) na saliva e caracterizada a especificidade de IgA contra antígenos de espécies de estreptococos da cavidade oral no início da vida. Foram estudadas as respostas de anticorpos IgA específicos para espécies bacterianas pioneiras (Streptococcus mitis , S. sanguinis , S. gordonii) e patogênicas (Streptococcus mutans) da cavidade oral em crianças a termo (AT) e pré-termo (PT) em duas visitas: ao nascimento (T0) e aos 3 meses de idade (T3). Salivas de 123 crianças (72 AT e 51 PT) foram coletadas durante as primeiras 10h após o nascimento (T0) e, novamente, aos 3 meses de idade (T3). Os níveis de anticorpos IgA e IgM nas amostras salivares foram analisados por ELISA. Um subgrupo de 26 crianças AT e 24 PT foram comparados com relação a padrões de especificidades de anticorpos contra diferentes antígenos de estreptococos, utilizando ensaios de Western blot. Não houve diferença significativa (p> 0,05) nos níveis salivares de IgA e IgM entre o grupo de crianças AT e PT ao nascimento. Em T3, os valores médios de IgA foram semelhantes entre os grupos e os níveis de IgM foram significativamente maiores em PT que AT (p < 0,05). Os ensaios Western blot identificaram resposta positiva de IgA para os estreptococos estudados na maioria das crianças, especialmente no grupo AT . Houve algumas diferenças entre os grupos com relação à frequência de crianças com resposta positiva a antígenos e intensidade da resposta IgA. Em geral, os antígenos de estreptococos orais foram mais frequentemente detectados e as bandas foram mais intensas no grupo de crianças AT quando comparados aos PT, especialmente em T3. Análise prospectiva de padrões de IgA específica para os antígenos de diferentes espécies de estreptococos revelou um aumento na complexidade da resposta de anticorpos IgA do nascimento (T0) até os 3 meses de vida (T3), tanto em PT quanto nos AT. O padrão de resposta de IgA aos antígenos dos estreptococos parece ser influenciado pela idade gestacional, o que pode refletir o grau de maturidade do sistema imune de mucosa / Secretory immunoglobulins present in mucosa surfaces represent the first line of defense of the adaptive immune system against infectious challenges. Preterm neonates humoral immunity is diminished compared to fullterm newborns. The identification of important antigens of virulence of oral species may help in the investigation of the mechanisms of antigenic stimulation and the development of the mucosal immune response. In the present study we measured saliva levels of immunoglobulin A (IgA) and M (IgM) and characterized the specificity of IgA against antigens of several streptococcal species found early in life. Salivary IgA antibody responses to bacterial species that are prototypes of pioneer (Streptococcus mitis, S. sanguinis, S. gordonii) and pathogenic (Streptococcus mutans) microorganisms of the oral cavity were studied in fullterm (FT) and preterm (PT) children in two visits: at birth (T0) and at 3 months of age (T3). Salivas from 123 infants (72 FT and 51 PT) were collected during the first 10h after birth (T0) and again at 3 months of age (T3). Salivary levels of IgA and IgM antibodies were analyzed by ELISA. A subgroup of 26 FT and 24 PT children were compared with respect to patterns of antibody specificities against different streptococci antigens using Western blot assays. No significant differences (P>0.05) in salivary levels of IgA and IgM between FT and PT babies were found at birth. At T3, mean sIgA values were similar between groups and salivary IgM levels were significantly higher in PT than FT (p<0.05). Western blot assays identified positive IgA response to streptococci in the majority of children, especially in the FT group. There were some differences between groups in relation to the frequency of children with positive response to antigens and intensity of IgA response. In general, oral streptococci antigens were more frequently detected and bands were more intense in FT than in PT, especially in T3. Prospective analysis of patterns of saliva IgA against Ags of different streptococcal species revealed an increase in complexity of the salivary IgA antibody response from the first day of birth (T0) to T3 in PT and FT. The patterns of salivary IgA response to streptococci antigens appear to be influenced by the gestational age, which might reflect the level of immunological maturity of the mucosal immune system

Imunoglobulinas secretoras presentes nas superfícies mucosas representam a primeira linha de defesa do sistema imune adaptativo contra desafios infecciosos. A imunidade humoral de recém-nascidos prematuros é diminuída em comparação a recém-nascidos a termo. A identificação de antígenos de virulência de bactérias colonizadoras da cavidade oral pode ajudar na investigação dos mecanismos de estimulação antigênica e desenvolvimento da resposta imune de mucosa. No presente estudo, foram medidos os níveis de imunoglobulina A (IgA) e M (IgM) na saliva e caracterizada a especificidade de IgA contra antígenos de espécies de estreptococos da cavidade oral no início da vida. Foram estudadas as respostas de anticorpos IgA específicos para espécies bacterianas pioneiras (Streptococcus mitis , S. sanguinis , S. gordonii) e patogênicas (Streptococcus mutans) da cavidade oral em crianças a termo (AT) e pré-termo (PT) em duas visitas: ao nascimento (T0) e aos 3 meses de idade (T3). Salivas de 123 crianças (72 AT e 51 PT) foram coletadas durante as primeiras 10h após o nascimento (T0) e, novamente, aos 3 meses de idade (T3). Os níveis de anticorpos IgA e IgM nas amostras salivares foram analisados por ELISA. Um subgrupo de 26 crianças AT e 24 PT foram comparados com relação a padrões de especificidades de anticorpos contra diferentes antígenos de estreptococos, utilizando ensaios de Western blot. Não houve diferença significativa (p> 0,05) nos níveis salivares de IgA e IgM entre o grupo de crianças AT e PT ao nascimento. Em T3, os valores médios de IgA foram semelhantes entre os grupos e os níveis de IgM foram significativamente maiores em PT que AT (p < 0,05). Os ensaios Western blot identificaram resposta positiva de IgA para os estreptococos estudados na maioria das crianças, especialmente no grupo AT . Houve algumas diferenças entre os grupos com relação à frequência de crianças com resposta positiva a antígenos e intensidade da resposta IgA. Em geral, os antígenos de estreptococos orais foram mais frequentemente detectados e as bandas foram mais intensas no grupo de crianças AT quando comparados aos PT, especialmente em T3. Análise prospectiva de padrões de IgA específica para os antígenos de diferentes espécies de estreptococos revelou um aumento na complexidade da resposta de anticorpos IgA do nascimento (T0) até os 3 meses de vida (T3), tanto em PT quanto nos AT. O padrão de resposta de IgA aos antígenos dos estreptococos parece ser influenciado pela idade gestacional, o que pode refletir o grau de maturidade do sistema imune de mucosa / Secretory immunoglobulins present in mucosa surfaces represent the first line of defense of the adaptive immune system against infectious challenges. Preterm neonates humoral immunity is diminished compared to fullterm newborns. The identification of important antigens of virulence of oral species may help in the investigation of the mechanisms of antigenic stimulation and the development of the mucosal immune response. In the present study we measured saliva levels of immunoglobulin A (IgA) and M (IgM) and characterized the specificity of IgA against antigens of several streptococcal species found early in life. Salivary IgA antibody responses to bacterial species that are prototypes of pioneer (Streptococcus mitis, S. sanguinis, S. gordonii) and pathogenic (Streptococcus mutans) microorganisms of the oral cavity were studied in fullterm (FT) and preterm (PT) children in two visits: at birth (T0) and at 3 months of age (T3). Salivas from 123 infants (72 FT and 51 PT) were collected during the first 10h after birth (T0) and again at 3 months of age (T3). Salivary levels of IgA and IgM antibodies were analyzed by ELISA. A subgroup of 26 FT and 24 PT children were compared with respect to patterns of antibody specificities against different streptococci antigens using Western blot assays. No significant differences (P>0.05) in salivary levels of IgA and IgM between FT and PT babies were found at birth. At T3, mean sIgA values were similar between groups and salivary IgM levels were significantly higher in PT than FT (p<0.05). Western blot assays identified positive IgA response to streptococci in the majority of children, especially in the FT group. There were some differences between groups in relation to the frequency of children with positive response to antigens and intensity of IgA response. In general, oral streptococci antigens were more frequently detected and bands were more intense in FT than in PT, especially in T3. Prospective analysis of patterns of saliva IgA against Ags of different streptococcal species revealed an increase in complexity of the salivary IgA antibody response from the first day of birth (T0) to T3 in PT and FT. The patterns of salivary IgA response to streptococci antigens appear to be influenced by the gestational age, which might reflect the level of immunological maturity of the mucosal immune system

The global climate has experienced four glacial cycles in the last 420,000 years, with each cycle characterised by a prolonged period of cooling culminating in maximal glaciation followed by a brief warm period. The most recent period of maximal glaciation is termed the Last Glacial Maximum (LGM) and occurred about 21,000 years ago. We currently live in one of the warm periods. The global climate is changing, and it is becoming more important to understand the extremes of the climate system and how well our modelling capability can capture those extremes. / There has been a modelling intercomparison project established to examine how global general circulation models compare in simulating past climates, including the LGM. Analysis and comparison of these model results has been presented for many parts of the globe, but there has not been a comparison of the different model results over the Australian region. This thesis aims to fill that gap and explore the simulated LGM weather and climate of Australia and its drivers in more detail. Comparison with proxy evidence is also undertaken, and inconsistencies seen in the literature addressed. / The Australian climate at the LGM was believed to be generally cooler, drier and possibly windier from proxy evidence in the literature. In the comparison done here the mean temperature and precipitation fields from most models show cooler and drier conditions, with some seasonal variability, but there are some strong outliers. It was found that the differences were not dependent on model resolution, but that the surface parameterisations were highly important for these fields. / The shifts in the circulation were examined both in the model results and with a study of the non-linear link between the wind, surface moisture and dunes, which are a proxy for past winds. All the models simulate a southward shift in the westerlies in the Australian region. This is strongly driven byte prescribed sea-surface temperatures. Australia's current wind regime is conducive to dune building. However, the binding effect of soil moisture (or vegetation) is strong enough to limit present day movement, whereas in the drier climate at the LGM there was a capacity for sand movement. The analysis of dune orientations did not produce conclusive evidence for how the westerlies might have shifted at the LGM. / An apparent enigma in the proxy evidence at the LGM is the high lake levels in Australia’s south east, while most inland lakes were dry. Previous authors believed that the precipitation was still low, but the high lake levels were driven by lowered potential evaporation. The hydrological cycle was generally depressed in the LGM simulations, but the potential for evaporation remained high. Thus an alternative hypothesis is posed based on increased run off due to a known shift in the vegetation types and a lag in the timing of the run off due to snowmelt. / The analysis here shows that our capacity to simulate climates quite different from the present is still developing, but that model results can help explain apparent inconsistencies in the reconstruction of past climates from proxies.

Aeolian dust is an important but poorly understood component of the climate system, which both responds to and drives global climate. Recently, dust produced at the high latitudes is also gaining attention as a possible contributor to the atmospheric dust load. However, little is known about its past dynamics and well­ dated records close to the former ice margins at the higher latitudes are scarce. Loess in Brittany region, France, is, therefore a valuable archive of the past dustiness, climate and landscape dynamics close to the former margins of the British–Irish and Fennoscandian ice sheets. However, knowledge of the timing of its deposition and accumulation dynamics, based on a detailed and independent chronology, is mostly lacking. Here, loess stratigraphy at the newly established site Primel Trégastel (Brittany, France) is presented. Loess deposits are dated in detail by optically stimulated luminescence of quartz. Moreover, to account for a variable past dust activity, loess sedimentation and dust mass accumulation rates are derived from a continuous Bayesian age model. Furthermore, this thesis tests the hypothesis of whether the same wind and dust accumulation patterns from the north of the Channel system can also be traced south the English Channel. Luminescence ages and Bayesian age modelling results show a phase of enhanced dust accumulation between 22.5–25.5 ka, coinciding with the Heinrich event 2 and Greenlandstadial 3. Although the proposed model with two phases of the enhanced dust accumulation between 25–19 ka does not exactly match the record at Primel Trégastel, the hypothesis of the glacial dynamics, associate glacial lake drainage and linked atmospheric circulation reorganisation controlling the loess accumulation in western France cannot be rejected with certainty. / Eoliskt damm är en viktig, men illa förstådd komponent av klimatsystemet som både reagerar på, såväl som driver, det globala klimatet. Nyligen har damm som producerats vid höga latituder också fått uppmärksamhet som ett möjligt bidrag till den atmosfäriska dammbelastningen. Kunskapen är dock liten gällande dess föregående dynamik och väl daterade uppgifter om tidigare isgränser vid höga latituder är fortfarande undermåliga. Loess i regionen Bretagne i Frankrike är därför ett värdefullt arkiv av tidigare dammhalter, klimat och landskapets dynamik nära de tidigare gränserna av de Brittiskt­-Irländska och Fennoskandiska istäckena. Men kunskap om timingen mellan dess deposition och ackumuleringsdynamik, baserad på en detaljerad och självständig kronologi, saknas till stor del. Här kan loess stratigrafi, vid den nyligen etablerade utgrävningsplatsen Primel Trégastel (Bretagne, Frankrike), presenteras. Loess avlagringar är daterade i detalj genom optiskt stimulerad luminescens av kvarts. Ytterligare, för att tamed variationen av dammets aktivitet i beräkningarna, är loess sedimentering och ackumuleringstakt av dammets massa härledda från en kontinuerlig Bayesiansk åldersmodell. Vidare så testar detta arbete hypotesen om huruvida samma vindar och ackumuleringsmönster av damm, som ses norr on kanalsystemet, även kan ses söder om den engelska kanalen. Resultat från luminescensåldrar och Bayesiansk åldersmodellering visar en fas av ökad dammackumulering mellan 22.5–25.5 ka, något som sammanfaller med Heinrich händelse 2 och Grönland stadial 3. Även om den föreslagna modellen med två faser av den ökade dammackumuleringen mellan 25–19 ka inte exakt överensstämmer med uppgifterna från Primel Trégastel, så kan inte hypotesen rörande den glaciala dynamiken med tillhörande dränering av glaciärsjöar och den sammankopplade atmosfäriska cirkulativa omorganisationen som kontrollerar loess ackumulering i västra Frankrike avvisas med säkerhet.

La haute montagne est un terrain particulièrement sensible aux variations climatiques. La hausse de température depuis plusieurs décennies a un fort impact sur les parois du massif du Mont Blanc : la dégradation du permafrost s’y traduit par une activité gravitaire majeure. Une augmentation du nombre d'écroulements (>100 m3) liés à des périodes chaudes a en effet été mis en évidence à plusieurs échelles de temps, lors des étés particulièrement chauds de 2003 et 2015 comme au cours des trois dernières décennies. La fréquence des écroulements dans le massif devrait continuer à s’accroitre avec l’augmentation de la température au 21e siècle.En revanche, la fréquence des écroulements dans le massif antérieurement à la fin du Petit Âge Glaciaire (PAG) est très largement inconnue. Pendant l'Holocène voire le Tardiglaciaire, les écroulements dans le massif du Mont Blanc ont-ils également été favorisés par les hausses de température ? Pour répondre à cette question, cette thèse poursuit quatre objectifs :i. Dater un grand nombre d'écroulements dans la partie centrale du massif pour comprendre leur distribution pendant l'Holocène et le Tardiglaciaire. L'âge des niches d’arrachement est obtenu par datation cosmogénique.ii. Vérifier les possibles corrélations entre périodes à forte occurrence d’écroulements et périodes climatiques post-glaciaires.iii. Quantifier le volume des écroulements par reconstruction 3D de la forme des blocs écroulés, et étudier la relation entre volumes écroulés et périodes climatiques.iv. Etudier la relation entre âge d'exposition et couleur des niches d’arrachement quantifiée avec la spectroscopie de réflectance.Un total de 70 surfaces a été échantillonné dans les parois du massif au cours de trois campagnes de terrain en 2006, 2011, et 2015-2016. Les âges d'exposition de 63 surfaces ont été obtenus, compris entre 30 ± 20 ans et 100.50 ± 8.50 ka. Trois groupes d’âges peuvent être corrélés aux périodes climatiques chaudes que sont : les Périodes Chaudes de l'Holocène moyen (7.50 – 5.70 ka), l'Optimum de l'âge de Bronze (3.35 – 2.80 ka) et le Période Chaude Romaine (2.35 – 1.75 ka) ; un quatrième groupe d'âges est daté entre 4.91 et 4.32 ka. Le groupe d'âges le plus nombreux, entre 1.09 ka et l'Actuel, aux volumes généralement réduits, est interprété comme représentatif de l'activité gravitaire annuelle du massif avec le climat actuel.Les données spectrales des échantillons datés ont permis de développer un index de la couleur du granite (GRIGRI) par combinaison des valeurs de réflectivité de deux longueurs d'onde différentes. Cet index est corrélé avec l'âge d'exposition (R=0.861) ; il a permis de proposer la datation de 10 échantillons d'âge inconnu à partir de leurs caractéristiques spectrales. / High mountain is particularly sensitive to climate variations. The raising temperature that is currently taking place due to climate change has a strong impact on the Mont Blanc massif rock walls: a higher rockfall (>100 m3) occurrence has been noticed, caused by permafrost thawing. The raising in number of rockfalls has been successfully correlated to warm periods at different timescales, e.g., during extreme warm episodes like the 2003 and 2015 heat waves, and during the last 30 years. According to the expected raising temperatures, during the 21st century rockfall occurrence should continue to rise.Rockfall frequency in the Mont Blanc massif before the Little Ice Age is still largely unknown. During Lateglacial and Holocene, high occurrence has been related to warm periods as well? In order to answer this question, this PhD thesis has four aims:i. To date several rockfalls having taken place in the central part of the Mont Blanc massif, in order to understand their frequency during Lateglacial and Holocene. Exposure age of rockfall scars is obtained using Terrestrial Cosmogenic Nuclide dating.ii. To verify possible relationships between high rockfall occurrence periods and post-glacial climate periods.iii. To quantify rockfall volumes by means of 3D reconstruction of the rockfall shapes, to explore the possible relationship between cumulate volumes and climate periods.iv. To study the relationship between exposure ages and colours of rock surfaces. Colours are quantified by reflectance spectroscopy.A total of 70 rock surfaces have been sampled during three field campaigns that took place in 2006, 2011 and 2015-2016. 63 exposure ages were obtained, ranging 30 ± 20 a to 100.50 ± 8.50 ka. Three age clusters can be correlated to warm periods, corresponding to: two Holocene Warm Periods (7.50 – 5.70 ka), the Bronze Age Optimum (3.35 – 2.80 ka) and the Roman Warm Period (2.35 – 1.75 ka). A fourth age cluster has been detected with ages ranging 4.91 – 4.32 ka. The biggest cluster, ranging 1.09 ka – recent, shows rather small volumes. This is interpreted as the normal erosion activity corresponding to the current climate.The samples reflectance spectra allowed to develop a granite colour index (GRIGRI) by combining the values of two different wavelengths. This index is correlated to the samples exposure age (R = 0.861), and has been used to date the exposure age of 10 samples where Terrestrial Cosmogenic Nuclide dating failed

Os sistemas eólicos na região dos Lençóis Maranhenses no Maranhão, da costa oriental do Rio Grande do Norte e do médio Rio Branco, norte da Amazônia em Roraima, estão sob ação direta da zona de convergência intertropical (ZCIT) As variações da ZCIT controlam a intensidade dos ventos e chuvas nessas regiões, importantes forçantes na dinâmica desses sistemas eólicos, os quais são representados principalmente por campos de dunas Nos campos de dunas do Maranhão e Rio Grande do Norte, adiciona-se a ação das variações do nível relativo do mar (NRM), que afetam a disponibilidade de sedimentos e o nível freático da planície costeira, que por sua vez influenciam a construção e estabilização dunar Depósitos eólicos dunares dessas três áreas foram selecionados para investigar a ação de forçantes climáticas e do NRM na sedimentação eólica durante o Pleistoceno tardio e Holoceno Para tanto, foi utilizada datação por luminescência oticamente estimulada (optically stimulated luminescence, OSL) associada a análises sedimentológicas e geoquímicas de alta resolução em perfis de sucessão de paleodunas Isto permitiu a identificação de períodos de atividade e estabilização do sistema eólico O registro dos Lençóis Maranhenses abrange o último ciclo glacial, com sedimentos eólicos depositados de 132,20 ± 7,00 ka mil anos atrás) até 12,90 ± 0,60 ka Nele, se detecta períodos de formação de dunas durante NRM decrescente e baixo A preservação desses registros entre aproximadamente 71 a 13 ka está relacionada a períodos de maior precipitação durante os eventos Heinrich, quando houve migração persistente da ZCIT para o sul Já o registro do Rio Grande do Norte abrange o período de 78,98 ± 8,30 ka até 0,06 ± 0,01 ka e indica a formação de campos de dunas também em condições de NRM decrescente e baixo, além de campo de dunas formado sob linha de costa transgressiva e clima predominantemente úmido favorecido pela última fase de subida do NRM, entre o último máximo glacial e o Holoceno médio O estudo no Rio Grande do Norte destaca também a influência dos campos de dunas na fisiografia costeira, onde a interação fluvio-eólica proporcionou a formação de lagoas (Lagoa do Boqueirão) no Holoceno Médio Por sua vez, os depósitos eólicos de Roraima abrangem o período de 21,9 ± 1,00 ka até 1,10 ± 0,10 ka e registram o desenvolvimento de campo de dunas a partir de areias do médio Rio Branco, com maior taxa de construção dunar entre o último máximo glacial (23 ka) e o evento climático Heinrich 1 (15 ka), quando a incidência de ventos fortes e pluviosidade reduzida nas baixas latitudes do hemisfério norte estão relacionadas a persistente migração ao sul da ZCIT Os registros dos campos de dunas do MA e RN e RR produzem assim um notável arquivo do efeito das variações da ZCIT e do NRM nos sistemas eólicos das regiões nordeste e norte do Brasil durante o Pleistoceno tardio e Holoceno / Eolian sand deposits in the region of the Lençóis Maranhenses in Maranhão, the eastern coast of Rio Grande do Norte, and the Middle Branco River, north of the Amazon in Roraima, are under direct influence of the intertropical convergence zone (ITCZ) . ITCZ fluctuations control wind intensity and rains in these regions, important forcings controlling the dynamics of eolian systems, that are mainly represented by dunefields In the coastal dunefields of Maranhão and Rio Grande do Norte, an additional forcing is the relative sea level (RSL), that affects the availability of sediments and controls the water table level of the coastal plain, that in turn influence the construction and stabilization of dunes Eolian sand deposits in these three areas were selected to investigate the effects of climate and RSL forcings on construction and stabilization of dunes during the late Pleistocene and Holocene using optically stimulated luminescence dating (OSL) associated with sedimentological and geochemical analysis from high-resolution sampling of paleodune succession profiles. The Lençóis Maranhenses record encompasses the last glacial cycle, with eolian sand accumulation from 132.20 ± 7.00 ka (thousand years ago) to 12. 90 ± 0. 60 ka This paleoenvironmental archive shows periods of dune construction during falling and low RSL. The preservation of these records between approximately 71-13 ka is related to periods of greater precipitation during Heinrich events, when there were persistent southbound shifts of the ITCZ The record of the Rio Grande do Norte dunefield from 78.98 ± 8.30 to 0.06 ± 0.01 ka also indicates the formation of dunefields under falling and low RSL in addition to transgressive dunefields formed under rising RSL and wetter climate during the last phase of the deglaciation in the late Holocene. The study in Rio Grande do Norte also highlights fluvialOeolian interplay that affected coastal physiography and promoted the formation of the Boqueirão Lake in the middle Holocene In turn, the eolian sand deposits of Roraima record accumulation from 21.9 ± 1.00 to 1.10 ± 0.10 ka from Branco River reworked sands In Roraima, the highest rate of dune construction was between the last glacial maximum (23 ka) and the Heinrich 1 climate event (15 ka), at times of high winds and low rainfall at low latitudes of the northern hemisphere related to persistent southward migration the ITCZ. The dunefield record from Maranhão, Rio Grande do Norte and Roraima thus provide a remarkable archive of the effects of the variations of the ITCZ and RSL in eolian deposits in the northeast and north regions of Brazil during the late Pleistocene and Holocene

This dissertation investigated the optimal strategy for the model specification search in the latent growth modeling. Although developing an initial model based on the theory from prior research is favored, sometimes researchers may need to specify the starting model in the absence of theory. In this simulation study, the effectiveness of the start models in searching for the true population model was examined. The four possible start models adopted in this study were: the simplest mean and covariance structure model, the simplest mean and the most complex covariance structure model, the most complex mean and the simplest covariance structure model, and the most complex mean and covariance structure model. Six model selection criteria were used to determine the recovery of the true model: Likelihood ratio test (LRT), DeltaCFI, DeltaRMSEA, DeltaSRMR, DeltaAIC, and DeltaBIC. The results showed that specifying the most complex covariance structure (UN) with the most complex mean structure recovered the true mean trajectory most successfully with the average hit rate above 90% using the DeltaCFI, DeltaBIC, DeltaAIC, and DeltaSRMR. In searching for the true covariance structure, LRT, DeltaCFI, DeltaAIC, and DeltaBIC performed successfully regardless of the searching method with different start models.

Hourly winter weather conditions of the Last Glacial Maximum (LGM) are simulated using the Community Climate Model version 3 (CCM3) on a globally resolved T170 (~75 km) grid. This simulation has been run in-tandem with a lower temporally resolved six-year climatological run. The purpose of the study is to determine: (1) whether examination of higher-resolution simulations, on both spatial and temporal scales, can enhance paleometeorological inferences based previously on monthly statistics of model output and (2) whether certain synoptic-scale events, which may have only a modest impact on seasonal statistics, might exert a disproportionate impact on geological climate records. Analysis is focused on changes in wind flow, no analogue climate “states”, synoptic scale events including Northern Hemisphere cyclogenesis, and gust events over glacial dust source regions. Results show a decrease in North Atlantic and increase in North Pacific cyclogenesis during the LGM. Storm trajectories react to the mechanical forcing of the Laurentide Ice Sheet, with Pacific storms tracking over middle Alaska and northern Canada and terminate in the Labrador Sea. The latter result supports observations and other model runs showing a significant reduction in Greenland winter precipitation. The modified Pacific track results in increased precipitation and the delivery of warmer air along the west coast of North America. This could explain “early” glacial warming inferred in this region from proxy climate records, potentially representing instead a natural regional response to ice age boundary conditions. Results also indicate a low variability, “no analogue” region just south of the Laurentide Ice Sheet margin which has appropriate conditions to harbour temperature-sensitive trees west of the Appalachian Mountains. Combined with pollen data, this lends valuable insight into the known disagreement between modern seed dispersal experiments and calculated migration rates. Finally, hourly-scale gust events over dust source regions during the LGM are two to five times greater than the modern, providing a mechanism to help explain the increased glacial dust load seen in the ice cores. Backwards air-parcel trajectories from Antarctic ice core locations show air sources over Patagonia and the Altiplano with some inputs from South Africa agreeing with recent isotopic tracer analyses. Results demonstrate that high temporal and spatial resolution simulations can provide valuable insight to add to the cornucopia of information already available from lower-resolution runs. They can also enhance our interpretation of geological records, which have been previously assumed to record longer time-scale climatological mean-states and thus ignoring any extreme synoptic events which may actually have had a disproportionate impact on their preservation.