Submitted by Biblioteca de Pós-Graduação em Geoquímica BGQ (bgq@ndc.uff.br) on 2016-08-01T16:21:23Z No. of bitstreams: 1 Briceño-Zuluaga 2016 Tese.pdf: 9025569 bytes, checksum: 00c4eb9cee0d346d7a8681fdbb975f49 (MD5) / Made available in DSpace on 2016-08-01T16:21:23Z (GMT). No. of bitstreams: 1 Briceño-Zuluaga 2016 Tese.pdf: 9025569 bytes, checksum: 00c4eb9cee0d346d7a8681fdbb975f49 (MD5) / Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geociências - Geoquímica. Niterói, RJ / Este trabalho apresenta o registro da distribuição granulométrica de sedimentos laminados recuperados na plataforma continental de Pisco (Peru), que é caracterizada pelos aportes fluviais regionais (relacionado com aumento das precipitações) e pelo aporte eólico local (relacionado com a intensidade do vento local). Esse registro vai desde a Anomalia Climática Medieval (ACM) até o Período de Aquecimento Moderno (PAM) passando pela Pequena Idade do Gelo (PIG) numa escala secular até subdecadal. As simulações da distribuição e trajetórias atmosféricas do material eólico durante eventos registrados de erosão por tempestades de areia na região realizadas em Hysplit4 são apresentadas. Os resultados dessas simulações suportam o fato de que a origem eólica das partículas grosseiras ocorre no sedimento marinho. Os componentes granulométricos identificados são discutidos a partir do modelo matemático de fraccionamento de GOMES et al., (1990). Este modelo assume que a composição mineral dos sedimentos está composta por uma assembléia de diferentes populações de partículas minerais com distribuições granulométricas logarítmicas normais. Foi utilizada uma rotina interativa de mínimos quadrados para ajustar a distribuição granulométrica em uma expressão matemática que permite quantificar e identificar os diferentes componentes litológicos para depois inferir os mecanismos de transporte envolvidos e a variação espacial e temporal. O objetivo deste estudo foi separar os padrões de sedimentação do material terrígeno (eólico e fluvial) assim como os processos mais importantes que controlam à entrada deste material para entender como esses processos refletem a variabilidade climática e atmosférica durante o ultimo milênio. Nossos resultados mostram um ativo transporte de partículas eólicas durante a segunda metade da ACM com uma rápida diminuição da ACM para a PIG. Durante a PIG a erosão eólica exibe uma diminuição na sua atividade e assim, um enfraquecimento na intensidade do vento, ao mesmo tempo um incremento na descarga fluvial é apresentada e, isto se relaciona com um incremento na precipitação continental. Durante o PAM o transporte eólico apresenta um rápido e progressivo incremento em relação com o ACM e a PIG, enquanto que a aporte fluvial apresenta uma diminuição. Neste trabalho as simulações da distribuição e trajetórias do material eólico durante os eventos de erosão é apresentado. Comparações com outros registros paleoambientais indicam que essas mudanças estão vinculadas à mudanças no deslocamento meridional da Zona de Convergência Intertropical (ZCIT) e Alta Subtropical do Pacífico Sul (ASPS) assim como a atividade da circulação da célula de Walker em escala de tempo secular. Finalmente a deposição eólica e em consequência a intensidade do vento e sua variabilidade dos últimos 100 anos é muito mais forte que durante a ACM sob condições similares na posição do sistema ZCIT-ASPS. Esta tendência sugere uma forçante adicional na intensificação da circulação atmosférica, consistente com o atual padrão da Oscilação multidecadal do Atlantico e a tendência de aquecimento climático. / In this work are present record of laminated sediments cores retrieved in the continental shelf of Pisco (Peru) that characterize fluvial regional discharge and the wind local aeolian transport (related with the wind intensity) from Medieval Climate Anomaly (MCA) to Little Ice Age (LIA) and the current warm period (CWP) at centennial to sub-decadal resolution. The particle grain size components are discussed using a mathematical model of fractionation. This model assumes that lithological composition of the sediment is an assembled of several log-normally distributed particle population. In this way, an interactive least square fitting routine is used to fit the particle grain size collected with the mathematical expression. This allows inferring the spatial and temporal variation of particles populations and thus transport mechanisms involved. The aim of the study is unmixing and reconstructs the patters of terrigenous (aeolian and fluvial) sedimentation as well as the most important processes that control the input of this material to understand how these components reflect atmospheric climate variability during the last millennium. Our results presented in this work showed active aeolian erosion during the second half of the MCA and rapid decrease from the MCA to the LIA. During the LIA the aeolian erosion exhibit a decreased activity and them a weak in the atmospheric circulation on the same time an increase of fluvial discharge is showed this is relate with an increase of continental precipitation. During the CWP the aeolian erosion transport, display a rapid and progressive increase in relation to MCA and LIA, whereas the fluvial discharge exhibited a decrease. In this work simulation of the aeolian distribution and their trajectories during erosion events are also presented. Comparison with others records indicate that those changes are linked to change in the meridional position of the Intertropical convergence zone (ITCZ) and South Pacific Subtropical High (SPSH) at the centennial time resolution. Finally the CWP show increase in the aeolian deposition and thus in the wind intensity over the past two centuries likely represents the result of the modern position of the ITCZ–SPSH system and the associated intensification of the local and regional winds. Nevertheless, the aeolian deposition and in consequence the wind intensity and variability of the last 100 yr are stronger than the second sequence of the MCA under similar position of the ITZC-SPSH system. This trend suggests an additional forcing in the intensification of the atmospheric circulation, consistent with the current pattern of climate change.

L'ozone joue un rôle primordial sur l'équilibre photochimique de l'atmosphère et participe au processus d'équilibrage radiatif entre les deux hémisphères (Mecke, 1931). Dans la troposphère, l'ozone détermine la capacité oxydante de la majorité des gaz et absorbe continuellement dans la stratosphère les radiations ultraviolettes nocives (McMicheal et al., 2003). D'où l'intérêt de surveiller la variation de la couche d'ozone de façon régulière. Il a été constaté au début des années 80, une diminution inquiétante et progressive de la colonne totale de l'ozone dûe aux émissions anthropiques des substances riches en chlore, brome et fluor. Ce constat a conduit au Protocole de Montréal en 1987 dont l'objectif est de mettre en place une politique internationale visant à réduire les émissions des substances appauvrissant l'ozone. Dix ans après la signature du dit Protocole, la concentration de ces substances commence à diminuer dans l'atmosphère et la prospection d'un recouvrement progressif de la couche d'ozone demeure aujourd'hui un sujet d'actualité (UNEP/PNUE, 2009 ; OMM, 2010 et 2014). Les besoins d'aujourd'hui sont de réaliser des mesures continues et fiables de l'ozone dont leurs exploitation dans des méthodes et/ ou des modèles bien adaptés à la problématique aideront la communauté à suivre l'évolution de l'ozone et d'estimer les tendances à long terme. Dans ce travail, une variété de produits d'ozone issue de différents instruments a été combinée pour construire des bases des données fiables et homogènes afin d'étudier sa variabilité et d'estimer la tendance de l'ozone dans les régions tropicale et subtropicale sud. L'application de ces bases de données sur les ondelettes a permis d'identifier les principaux forçages qui contrôlent la variabilité de l'ozone et la période de retour associée à chaque forçage. Il s'agit des variations saisonnières du climat, les oscillations quasi-biennales, les oscillations australes El-Niño et l'activité solaire dont le cycle moyen est évalué à 11ans. Le comportement et l'influence de chacun de ces paramètres sur la viabilité de l'ozone sont étudiés. Cette étude est faite en s'appuyant sur des méthodes statistiques et sur le modèle Trend-Run. Avec ce modèle, la part de contribution et la réponse de chaque paramètre sur la variabilité de l'ozone sont quantifiées. Les résultats sur les tendances montrent une augmentation de la couche d'ozone avec un taux variant entre 0 et 2.78% par décade (selon la région et le site) sur la période 1998-2012. Cette amélioration est bien observée au-dessus de 22km, surtout aux subtropiques par rapport à la région équatoriale. / Ozone plays an important role on photochemical equilibrium of atmosphere and participate on radiative balance process between hemispheres (Mecke, 1931). In the troposphere, ozone determines the oxidizing capacity of major species and absorbs continuously in the stratosphere the harmful ultraviolet radiation (McMichael et al, 2003). Based on the above facts, it is important to monitor ozone continuously with consistency and accuracy. Global total column ozone (TCO) has depleted gradually since 1980 with an increase of chlorofluorocarbon concentrations in the stratosphere due to anthropogenic activities. In 1987, the Montreal protocol was formulated in order to regulate the emissions of substances that deplete ozone. Concentrations of these substances are observed to decrease ten years after the Montreal protocol. Thus we have been expecting an increase in ozone by now (UNEP/PNUE, 2009; WMO, 2010 and 2014). The current needs are to achieve consistent and reliable measurements in which their exploitation on adapted methods/models can help scientists to follow the ozone evolution and to estimate long term ozone trend. In this work, a variety of ozone products from different instruments was combined in order to create reliable and homogenous dataset to study the ozone variability and trend over the southern tropics and subtropics. The dataset application on wavelets method allowed to identify the dynamic parameters that control ozone variability and their periodicities. These include seasonal variations of climate, the quasi-biennial oscillations, the El-Niño Southern Oscillation and the 11-years solar cycle. The behavior of each parameter and its influence on ozone variability were analysed based on statistical method and the Trend-Run model. The contribution and response of each variable on ozone variability were quantified from the model. The obtained trends results exhibit an increase of total ozone from 1998 to 2012 with a rate varying between 0 and 2.78% par decade (depending of the site and region). The ozone increase was observed mainly above 22 km and it is more important over the subtropical region with respect to equatorial zone.

The surface climate response to 11-yr solar forcing during northern winter is first reestimated by applying a multiple linear regression (MLR) statistical model to Hadley Centre sea level pressure (SLP) and sea surface temperature (SST) data over the 1880–2009 period. In addition to a significant positive SLP response in the North Pacific found in previous studies, a positive SST response is obtained across the midlatitude North Pacific. Negative but insignificant SLP responses are obtained in the Arctic. The derived SLP response at zero lag therefore resembles a positive phase of the Arctic Oscillation (AO). Evaluation of the SLP and SST responses as a function of phase lag indicates that the response evolves from a negative AO-like mode a few years before solar maximum to a positive AO-like mode at and following solar maximum. For comparison, a similar MLR analysis is applied to model SLP and SST data from a series of simulations using an atmosphere–ocean general circulation model with a well-resolved stratosphere. The simulations differed only in the assumed solar cycle variation of stratospheric ozone. It is found that the simulation that assumed an ozone variation estimated from satellite data produces solar SLP and SST responses that are most consistent with the observational results, especially during a selected centennial period. In particular, a positive SLP response anomaly is obtained in the northeastern Pacific and a corresponding positive SST response anomaly extends across the midlatitude North Pacific. The model response versus phase lag also evolves from a mainly negative AO-like response before solar maximum to a mainly positive AO response at and following solar maximum.

The origin of the tropical lower-stratospheric response to 11-yr solar forcing and its possible coupling to a troposphere–ocean response is investigated using multiple linear regression (MLR) analyses of stratospheric ozone and temperature data over the 1979–2009 period and tropospheric sea level pressure (SLP) data over the 1880–2009 period. Stratospheric MLR results, comparisons with simulations from a chemistry–climate model, and analyses of decadal variations of meridional eddy heat flux indicate that the tropical lower-stratospheric response is produced mainly by a solar-induced modulation of the Brewer–Dobson circulation (BDC), with a secondary contribution from the Hadley circulation in the lowermost stratosphere. MLR analyses of long-term SLP data confirm previous results indicating a distinct positive response, on average, during the northern winter season in the North Pacific. The mean response in the Northern Hemisphere resembles a positive Arctic Oscillation mode and can also be characterized as “La Niña–like,” implying a reduction of Rossby wave forcing, a weakening of the BDC, and an increase in tropical lower-stratospheric ozone and temperature near solar maxima. However, MLR analyses of different time periods show that the Pacific SLP response is not always present during every cycle; it was most clearly detected mainly during the ~1938–93 period when 11-yr solar variability was especially strong. During the 1979–93 period, the SLP response was strongly present when the lower-stratospheric responses were large. But during the 1994–2009 period, the SLP response was much less significant and the lower-stratospheric responses were weak, supporting the hypothesis that the lower-stratospheric and surface climate responses are dynamically coupled.

No description available.

Doctora en Ciencias, Mención Geología / La costa semiárida de Chile, localizada al sur del desierto hiperárido de Atacama, es una región altamente sensible a los cambios climáticos, cuya disponibilidad de agua es limitada y fuertemente dependiente de los sistemas frontales conducidos por los Vientos del Oeste durante el invierno y la primavera austral. Estas incursiones se hacen más frecuentes e intensas durante las fases cálidas de El Niño Oscilación del Sur (ENSO: El Niño‒Southern Oscillation), producto del debilitamiento del Anticiclón Subtropical del Pacífico Suroriental y la mayor frecuencia y/o persistencia de anticiclones de bloqueo localizados al suroeste de Sudamérica producto del patrón de teleconexión trópico-extratrópico Pacífico‒América del Sur (PSA: Pacific South America) asociado a El Niño. El objetivo de esta tesis doctoral fue determinar el rol del Anticiclón Subtropical del Pacífico Suroriental y de ENSO y la variabilidad climática tipo ENSO en los cambios hidrológicos experimentados en la costa semiárida de Chile (30°-32ºS) durante los últimos 13.000 años, a través del estudio de depósitos sedimentarios costeros, continentales y marinos, asociados a la escorrentía generada a partir de la ocurrencia de lluvias torrenciales. Estos depósitos conforman un registro paleohidrológico que refleja las variaciones del clima de la región durante el Pleistoceno terminal y el Holoceno. La determinación de las principales anomalías de la circulación atmosférica que condicionaron la ocurrencia de flujos detríticos en el pasado fue evaluado a partir del análisis meteorológico de eventos aluviales históricos ocurridos durante la segunda mitad del siglo XX y su relación con las fases de ENSO en la escala interanual y tipo ENSO en escalas temporales mayores. El registro paleohidrológico permitió interpretar variaciones a escala milenial para el período comprendido entre el Pleistoceno terminal-Holoceno, basado en depósitos continentales de Los Vilos (31°50 S), y variaciones a escala centenal y multidecadal durante los siglos XIX y XX, basado en sedimentos marinos de las bahías de Tongoy y Guanaqueros (30°S). Durante el Pleistoceno terminal y el Holoceno temprano (13.000-8.600 cal años AP) la costa semiárida de Chile estuvo sujeta a una intensa influencia del Anticiclón Subtropical del Pacífico Sur, determinando una aridez extrema, regional, mayor que en la actualidad, vientos intensificados y ausencia de lluvias torrenciales. Sin embargo, la influencia del anticiclón sumado a la baja temperatura de la corriente de Humboldt durante este período, habría favorecido la mayor frecuencia e intensidad de la neblina costera, sustentando una humedad incrementada localmente en contextos geomorfológicos específicos, tal como ocurre hoy en día bajo condiciones tipo La Niña. Durante el Holoceno medio (ca. 8.600-5.700 años cal AP) la influencia del Anticiclón Subtropical del Pacífico Sur en la costa semiárida de Chile habría disminuido en relación al Holoceno temprano, aún sustentando condiciones de aridez en la región. Sin embargo, escasas lluvias intensas y esporádicas generaron flujos aluviales probablemente asociadas al desarrollo del patrón PSA bajo condiciones neutras de ENSO. A escala del Holoceno tardío, a comienzos del siglo XIX hubo un aumento secular de las lluvias torrenciales sobrepuesto a una tendencia general de aridificación, caracterizando el clima moderno hasta la actualidad. A partir de 1820 EC, lluvias intensas se desarrollaron más frecuentemente bajo condiciones El Niño a escala interanual, asociadas a un patrón de teleconexión PSA más frecuente y/o persistente, modulado por una mayor influencia de la variabilidad multi-decadal tipo ENSO. Se concluye que la intensidad del Anticiclón Subtropical del Pacífico Suroriental sobre la costa semiárida de Chile es el factor más importante para explicar la tendencia de desertificación de esta región, que continuará durante el presente siglo, determinando la mayor o menor ocurrencia de lluvias estacionales. Además, factores tales como la temperatura del océano costero y las condiciones ENSO y tipo ENSO han jugado un rol importante, condicionando la frecuencia e intensidad de la neblina costera y la ocurrencia de lluvias torrenciales en la región.

The global Meridional Overturning Circulation (MOC) plays a significant role in the Earth\'s climate system by redistributing all over the world the excess heat gained by Earth in low latitudes. In its superficial branch, warm waters are exchanged throughout the world\'s ocean basins. The Indonesian Throughflow (ITF) and the Agulhas Leakage (AL) are the main processes responsible, respectively, for importing Pacific Ocean waters into the Indian Ocean, and for exporting Indian Ocean waters into the Atlantic Ocean. Recently, changes in both systems have been reported and can be related to global warming consequences, processes of air-sea interactions and variabilities in the ocean circulation and wind patterns. In the present work, output of a high-resolution, global implementation of HYCOM (Hybrid Coordinate Ocean Model) from different runs were used, aiming at a study of the structure and variability of the ITF, and to evaluate the use of a numerical tool for tracking virtual Lagrangian particles to correlate circulation patterns of the ITF and the AL. For the ITF, analysis of the models\' output provided a mean volume transport in the upper 700 m depth of about 13 Sv, what is in the range of values reported by observations and other numerical simulations in the region. The seasonal variability was found to be related to the monsoons wind regimes, and the ITF\'s response to the El Niño-Southern Oscillation (ENSO) was evaluated. During five La Niña events, the mean volume transport was of approximately 16 Sv, and for also five El Niño events, of approximately 12 Sv. Results show an abrupt increase in the heat transport between 2002 and 2012, what could be related to changes in the heat content within the Indian Ocean for the same period. Heat transport anomalies were analyzed in the last years of the time series and present a clear correlation with Nino3.4 index, denoting a strong response of the ITF to the 2014/16 El Niño. Numerical test-experiments simulating Lagrangian particles have been performed, to identify and quantify water masses\' origins compounding the ITF and to correlate variabilities signals of ITF in the Indian Ocean\'s basin circulation and in the Agulhas Leakage. / A Circulação de Revolvimento Meridional do oceano desempenha um papel importante no sistema climático da Terra, através da redistribuição do excesso de calor ganho pelo planeta em baixas latitudes. No seu ramo superficial, massas de águas quentes são carregadas entre as diferentes bacias oceânicas no mundo. O fluxo que ocorre através dos estreitos dos mares da Indonésia (ITF, Indonesian Throughflow), e o Vazamento das Agulhas (VA) são dois importantes processos responsáveis, respectivamente, por importar águas do Pacífico para o Oceano Índico, e por exportar águas do Índico para o Oceano Atlântico. Recentemente, mudanças em ambos sistemas têm sido reportados e podem estar relacionados a consequências do aquecimento global, a processos de interação ar-mar e a variabilidades da circulação oceânica e de padrões de vento. No presente trabalho foram usadas saídas de diferentes rodadas usando uma implementação global em alta resolução do HYCOM (Hybrid Coordinate Ocean Model), com o objetivo de estudar a estrutura e variabilidade do ITF e avaliar o uso de uma ferramenta numérica para rastrear virtualmente a trajetória de partículas Lagrangianas e correlacionar padrões de circulação do ITF e do VA. Para o ITF, análises dos resultados dos modelos forneceram um valor de transporte de volume de ≈13 Sv para os primeiros 700 m de profundidade, o qual está em acordo com valores obtidos por observações e outras simulações numéricas. A variabilidade sazonal foi demonstrada estar relacionada aos regimes de vento de monções, e a resposta do ITF para o El Niño-Oscilação Sul (ENOS) foi avaliada. Durante cinco eventos de La Niña o transporte de volume médio foi de ≈16 Sv, e para cinco eventos de El Niño, em ≈12 Sv. Os resultados mostram um aumento abrupto no transporte de calor entre 2002 e 2012, o qual pode estar relacionado a mudanças na quantidade de calor dentro do Oceano Índico para o mesmo período. Anomalias no transporte de calor foram analisadas para os últimos anos da mesma série temporal e também apresentou clara correlação com o índice Nino3.4, configurando uma forte resposta do ITF para o El Niño de 2014/16. Experimentos numéricos simulando partículas Lagrangianas foram implementados, com o objetivo de identificar origens de massas de águas que compõem o ITF e correlacionar sinais de variabilidade do ITF na bacia de circulação do Índico e do Vazamento das Agulhas.

Este trabalho elaborou séries temporais de eventos extremos de precipitação, de 1901 a 2000 para o Estado do Rio Grande do Sul (RS). Utilizou-se reanálises da Universidade de Delaware (EUA), registros históricos de jornais, registros oficiais, e dados de 17 estações meteorológicas do INMET no RS. Identificou-se anomalias climáticas (positivas e negativas) de precipitação ao longo do século XX em diferentes pontos do RS. Adotou-se como evento extremo anomalias superiores (inferiores) a 50 mm (-50 mm). As séries foram aplicadas a um zoneamento da precipitação do RS visando avaliar a variabilidade e a distribuição, assim como a influência do El Niño – Oscilação Sul (ENOS). O zoneamento escolhido foi: Campanha, Litoral e Planalto. Por fim, foi gerada uma classificação da variabilidade da precipitação durante eventos ENOS para o RS, no século XX, com base na classificação do ENOS na região do Niño 3.4. Identificou-se que as zonas Campanha e Planalto são mais suscetíveis à variabilidade do ENOS com média de 75 mm em eventos positivos e -67 mm em eventos negativos de precipitação, e o Litoral apresenta menor influência aparente, indicando uma subdivisão desta zona em dois setores devido ao seu contraste latitudinal. A maior anomalia mensal para os meses neutros foi de 428,90 mm (abril de 1959), 224,51 (abril de 1941) mm em anos de El Niño e 174,55 mm (janeiro de 1938) em La Niña. Por fim, observouse que o zoneamento não se mostrou adequado para esta análise, pois o Planalto, maior zona em área, apresenta uma amplitude de 1200 m na altimetria, e o Litoral apresenta um comportamento diferenciado devido ao contraste latitudinal e a escarpa do planalto no litoral norte. Identificou-se que os primeiros 50 anos do século XX apresentam equivalência entre a região do Niño 3.4 e o RS. A partir de 1950, os eventos no RS passaram a ter uma classe maior do que no Niño 3.4, ou seja, houve um aumento (diminuição) médio de 50 mm (-25 mm) nas anomalias positivas (negativas) de precipitação no RS. Assim, nos últimos 50 anos, um evento de uma determinada classe na região Niño 3.4 pode gerar anomalias de precipitação maiores no Rio Grande do Sul. / This work elaborated time series of precipitation extreme events (1901-2000) for the Rio Grande do Sul State (RS). Reanalysis from University of Delaware, newspapers historical records, official records and data from 17 INMET meteorological stations were used. Precipitation climatic anomalies (positive and negative) were identified at different points of RS during the 20th century. It was found that positive (negative) anomalies were above (below) of 50 mm (-50 mm). The time series were applied to a RS precipitation zoning to spatialize the variability and distribution, as well the influence of El Niño – South Oscillation (ENSO). The zoning was: Campanha, Litoral and Planalto. Afterwards, a classification of RS precipitation variability during ENSO events was generated based on Niño 3.4 region classification. It was identified that Campanha and Planalto zones are more susceptible to ENSO variability, pointing a mean of 75 (-67) mm in positive (negative) precipitation events, and the Litoral showed less apparent influence, indicating a subdivision of this zone into two sectors due it’s latitudinal contrast. The highest monthly anomaly in neutral months was 428,90 mm (April 1959), 224,51 mm (April 1941) in El Niño events and 174,55 mm (January 1938) in La Niña events. Finally, it was observed that the zoning was not adequate for this analysis, since the Planalto, largest zone, presents 1200 m of amplitude in altimetry and the Litoral presents differentiated behavior due the latitudinal contrast and the escarpment of the Plateau on the north coast. It was identified that the first 50 years of the 20th century presented equivalence between Niño 3.4 region and the RS classifications. After 1950, the events in RS started to show a higher class than in Niño 3.4. There was an average increase (decrease) of 50 mm (-25 mm) in positive (negative) precipitation anomalies in RS. Then, in the last 50 years, an event of a certain category may generate higher precipitation anomalies at the Rio Grande do Sul.

Monthly δ18O and Sr/Ca records generated from modern and fossil corals from Southwestern Pacific Ocean sites in the Republic of Vanuatu are used to assess the differences in mean climate state, seasonality, and interannual variability between a glacial and interglacial period. The modern coral contains a well-defined annual signal in δ18O and Sr/Ca. The top 40 cm of the coral used in this study has a mean δ18O value of -4.99+/-0.13%VPDB (2σ) and a mean Sr/Ca value of 8.691+/-0.015mmol/mol (2σ). El Nino-Southern Oscillation (ENSO) events are characterized by positive δ18O and Sr/Ca anomalies, consistent with cooler temperatures and reduced rainfall that typifies ENSO at Vanuatu. The ~12cm long fossil coral is dated to 346 ka + 25, - 9, based on uranium-series analysis and stratigraphic forward modeling, indicating that the fossil coral grew during MIS10 - a glacial period. X-ray diffraction, petrographic inspection, SEM analysis, and geochemical considerations indicate excellent preservation. The mean δ18O value is enriched by 0.74%, and the mean Sr/Ca value is equivalent, compared to the modern coral. Mathematical modeling of Pleistocene mean SST and SSS results in temperature estimates up to ~2˚C warmer and salinity up to ~2 psu saltier than present-day conditions, if seawater Sr/Ca were 1-2% higher in MIS10. Our fossil coral data and modeling results preclude colder SST and lower SSS at Vanuatu during MIS10. Accurate estimates of past values of seawater Sr/Ca remain the largest obstacle to accurately reconstructing past tropical SST using pristine fossil corals. The fossil coral Sr/Ca annual range is similar to the modern range, indicating that seasonal SST ranges were similar, whereas the δ18O annual range is about half that of the modern coral, indicating weaker past seasonal salinity variations. The reduced seasonal SSS variations and increased SSTs near Vanuatu are interpreted as evidence that the SPCZ was displaced from its present location while the fossil coral lived. The geochemical response to El Niño events in the modern coral is observed twice in the fossil coral record, indicating that ENSO-like processes are not unique to interglacial time periods, but characterize the tropical Pacific at least back to MIS 10.

Nonlinear dynamical systems theory has inspired a new set of useful tools to be applied in climate studies. In this work we presented specific examples where information has been gained by the application of methods from nonlinear dynamical systems theory. The main goal is to understand the relative importance of stochastic forcing versus deterministic coupling within the context of Coupled General Circulation Models. This work address this important subject by approaching this goal through the development of a hierarchy of models with increasing complexity that we assert contain the essential dynamics of ENSO. We examined the effect of noise in a low order model and found that it is not restricted to blurring the attractor trajectories in phase space, but includes important changes in the dynamics of the system. The main results indicate that the presence of noise in a nonlinear system has two different effects. The presence of noise acts to increase the maximum Lyapunov exponent and can result in noise induced chaos if the system was originally stable. However, the same arguments are not valid if the original system is already in the chaotic regime, where the noise inclusion acts to decrease the maximum Lyapunov exponent, therefore increasing the system stability. The system of interest includes coupled ocean-atmosphere interactions and here we mimic this interaction by coupling two low order models with very different dominant time scales. These subsystems interact in a complex, nonlinear way and the behavior of the whole system cannot be explained by a linear summation of dynamics of the system parts. We used information theory concepts to detect the influence of the slow system dynamics in synchronizing the fast system in coupled models. We introduced a fast-slow coupled system, where both the slowness of the ocean model and the intensity of the boundary forcing anomalies contribute to the asymmetry and phase locking of both subsystems. The mechanisms controlling the fast modelspread were uncovered revealing uncertainty dynamics depending on the location of ensemble members in the model’s phase space. As an intermediate step between low order models and CGCMs we study the effect of noise on an intermediate complexity model. The addition of gaussian noise to the Zebiak-Cane model in order to understand the effects of noise on its attractor led to a way of estimating the noise level based on the effects of noise on the correlation dimension curves. We investigate the intrinsic predictability of the coupled models used here, and the different time scales associated with fast and slow modes were detected using the Finite Size Lyapunov Exponents. We found new estimates for the prediction horizon of ENSO for the Zebiak-Cane model as well as for the NCAR CCSM3 model and observations. The whole analysis of observations and CCSM3 was possible after applying noise reduction techniques. We also improved our understanding of three different noise reduction techniques by comparing the Local Projective Noise Reduction, the Interactive Ensemble strategy, and a Random Interactive Ensemble applied to CCSM3. The main difference between these two noise reduction techniques is when the process is applied. The Local Projective Noise Reduction can be applied to both model and observations, and it is done a posteriori in phase space, therefore the trajectories to be adjusted already posses the physical mechanisms embedded in them. The Interactive Ensemble approach can only be applied to model simulations and has shown to be a very useful technique for noise reduction since its done a priori while the system evolves instead of a posteriori, besides the fact that it allows to retrieve the spatial distribution of the noise level in physical space.