The objective of this dissertation is to apply radiogenic isotopes extracted from marine sediments to investigate aspects of global climate change over the past 25 kyr, especially ocean and atmospheric circulation, continental aridity, and hydrology. By focusing on the geochemical records from marine sediments and authigenic precipitates preserved in these sediments, I aim to better understand climate forcing and feedback mechanisms, which are critical to models of climate change. Firstly, I have investigated the dynamics of the Intertropical Convergence Zone (ITCZ) over the past 25 kyr in the eastern equatorial Pacific by fingerprinting dust provenance using radiogenic isotopes (Nd, Sr, Pb) and trace elements (Fe, Si, Ba) in the detrital fraction of marine sediments along a transect across the equator at 110ºW. Results from this study suggest no glacial-Holocene difference in the mean position of the ITCZ, but a more northerly, possibly stronger, deglacial ITCZ. Secondly, I have applied Nd isotope ratios from authigenic precipitates extracted from marine sediments and those from fish debris to trace past intermediate water circulation changes on glacial-interglacial and millennial timescales. The authigenic Nd isotope record from the Florida Straits suggests a reduced circulation of Antarctic Intermediate Water (AAIW) into the tropical North Atlantic during the Younger Dryas (YD) and Heinrich 1 (H1) events, associated with a significant reduction in AMOC. However, in the Southern Caribbean, apparent deviations in the Nd isotopic compositions between the acid-reductive leachate and the fish debris suggest that the leachate method is not reliable at this location and that it needs to be tested in more detail in various oceanic settings. In the Southern Caribbean, the fish debris Nd isotope results suggest a two-step recovery of the upper North Atlantic Deep Water during the last deglaciation. Comparing our new fish debris Nd isotope data to authigenic Nd isotope data for sediments from the Florida Straits and the Demarara Rise, we propose that glacial and deglacial AAIW does not penetrate beyond the lower depth limit of modern AAIW in the tropical North Atlantic. Both studies suggest a tight connection between Atlantic intermediate water circulation variability and high-latitude North Atlantic climate change.

A Zona de Convergência Intertropical (ITCZ) marca a área de ar ascendente nos trópicos, associada com altas pluviosidades e característica chave da circulação tropical da célula de Hadley, dominando o ciclo hidrológico sazonalmente sobre os trópicos, com precipitação máxima associada ao hemisfério com as maiores temperaturas da superfície do mar. As alterações de longo prazo na posição ITCZ tem sido considerada como um importante fator de controle da paleo-precipitação na área equatorial para avaliar as alterações relativas na sua posição e intensidade em escalas de tempo orbitais e milenar. A este respeito, há uma necessidade de registros de precipitação com amplia profundida temporal, alta resolução e bem datados no norte da América do Sul para avaliar como o deslocamento da ITCZ influenciou a paleo-precipitação na região e sua relação com o Sistema da Monção Sul-Americana (SASM). Nosso registro de \'delta\' \'ANTPOT.\'18 O em espeleotema da caverna de Carracos, localizada no município de El Peñon na região centre leste da Colombia e situado na posição média atual da ITCZ no norte da América do Sul, exibiu mudanças na precipitação durante os últimos 103 ky BP até o presente, com uma curva isotópica continua para o último período deglacial. O registro de El Peñon é composto por nove espeleotemas individuais com um total de 6857 amostras de \'delta\' \'ANTPOT.\'18 O e um modelo de idade com 132 datações, precisamente datadas pelo método U/Th. Documentamos pela primeira vez como as mudanças de longo prazo na atividade da ITCZ estão associadas a mudanças na circulação do Atlântico Meridional Overturning na escala orbital. Nos eventos GI, GS e HS, há uma mudança relativa na posição e intensidade da ITCZ na região norte da América do Sul, expondo a área de El Peñon como um setor sensível a essas variações, o que gera relações de fase/antifase com registros do Caribe e a área de influência sul daITCZ. Igualmente, é sugerida uma assimetria zonal durante o LGM caracterizada pela posição da ITCZ, levando aumento do fluxo de umidade em Centro America e Colômbia, enquanto condições climáticas contrastantes são observadas do lado leste do continente o sem uma resposta forte nos outros registros de América do Sul. Apesar que as condições nas mudanças oceânicas sejam o fator climático dominante para a variabilidade da ITCZ durante o último período glacial, a forçante de insolação no verão austral ainda é muito evidente durante o Holoceno, levando a um deslocamento para o sul da ITCZ em poucos graus alcançando, sua posição mais meridional no presente. / The Intertropical Convergence Zone (ITCZ) marks the area of ascending air in the tropics, which is associated with generally high rainfall and is a key feature of the tropical Hadley circulation. This ITCZ dominates the hydrological cycle seasonally over the tropics with maximum rainfall associated with warmer sea surface temperatures in each). Although long-term changes in the ITCZ position have been considered as a major factor controlling paleo-precipitation in the equatorial area to evaluate the relative changes in its position and intensity on both orbital and millennial time scales. In this regard, there is a need for long, high resolution and well-dated records of precipitation in Northern South America to evaluate how the ITCZ has influenced the paleo-precipitation over the SASM domain. Our composite speleothem \'delta\' \'ANTPOT.\'18 O record from Carracos cave inferring past precipitation changes during the last 103 ky B.P., it is located in the El Peñon municipality in the eastern Colombian Cordillera and the latitude of the study site coincides with the mean modern position of the ITCZ in northern South America. The El Peñon speleothem \'delta\' \'ANTPOT.\'18 O record is composed of nine individual speleothems with 6857 \'delta\' \'ANTPOT.\'18 O measurements and the chronology of the CAR speleothem record is based on 132 very precise U/Th dates. We document for the first time how long-term changes in ITCZ activity are associated with changes in the Atlantic Meridional Overturning circulation. In the GI and HS events, there is a relative change in the position and intensity of the ITCZ in the northern region of South America, exposing the El Peñon area as a sector sensitive to these variations, which generates phase/antiphase relationships with records from the Caribbean and the southern area of influence of the ITCZ. The El Peñon speleothem record also suggests that the ITCZ was characterized by a large zonal asymmetry during the LGM, leading to enhanced moisture influx from the Caribbean toward Colombia, intensifying the monsoon over the SASM region of western and southern Brazil and the tropical Andes, while contrasting climate conditions are observed from the eastern side of continent. Although the changing oceanic conditions are notably the dominant climate driver for ITCZ variability during the last glacial period, austral summer insolation forcing is still very evident during the Holocene, leading to a southward displacement of the ITCZ by a few degrees reaching its southernmost position at present-day.

We examine the eastern Pacific Ocean Intertropical Convergence Zone (ITCZ) both in its mean state and transient phases using a combined diagnostic, theoretical and numerical modeling approach. We note that the ITCZ is perpetually in a transient state with strong variability occurring on 4-8 day time scales. Transients, about half the amplitude of the mean ITCZ, propagate northwards from the near-equatorial southern hemisphere eventually increasing the convection in the vicinity of the mean ITCZ convection. It is argued that the mean ITCZ is continually inertially unstable with incursions of anticyclonic vorticity advected across the equator resulting in the creation of a divergence-convergence doublet. The low-level convergence generates convection and vortex tube stretching which generates cyclonic vorticity counteracting the northward advection of anticyclonic vorticity. During a cycle, the heating in the mid-troposphere near 10°N oscillated between 6 and 12 K/day at the inertial frequency of the latitude of the mean convection. The shallow meridional circulation, noted in the mean field in other studies, appears to be a result of the transient nature of the ITCZ. It is hypothesized that westward propagating equatorial waves result from the inertial oscillation of the ITCZ. To test that the waves are formed in situ in the eastern Pacific and not remnants of waves propagating from the Atlantic or promoted by the Central and South American orography, several numerical experiments are undertaken using a high-resolution regional model spanning the western Atlantic Ocean and the eastern Pacific. In the control case, the model is initialized at all boundaries with full high-frequency observations. In two additional experiments, these transients are filtered out, and a third experiment is run with the topography over a large part of Central and South America removed. In all experiments, westward propagating waves are formed in the region of high CEPG suggesting that the hypothesis of in situ development may be correct.

Submitted by Lucienne Costa (lucienneferreira@ufcg.edu.br) on 2018-08-28T16:57:40Z No. of bitstreams: 1 MAISSA LUDYMILLA CARVALHO PONTES – DISSERTAÇÃO (PPGMET) 2018.pdf: 4820642 bytes, checksum: e320b4696bcf114846cc43a6004d16a1 (MD5) / Made available in DSpace on 2018-08-28T16:57:40Z (GMT). No. of bitstreams: 1 MAISSA LUDYMILLA CARVALHO PONTES – DISSERTAÇÃO (PPGMET) 2018.pdf: 4820642 bytes, checksum: e320b4696bcf114846cc43a6004d16a1 (MD5) Previous issue date: 2017-06-05 / Capes / A qualidade da estação chuvosa no Nordeste pode ser relacionada com a variabilidade que surge em decorrência do fenômeno El Niño-Oscilação Sul (ENOS) que influencia a estação chuvosa tanto pela alteração na célula de Walker quanto, por padrões de teleconexões, sendo este último responsáveis por causar variabilidades na Temperatura da superfície do Mar (TSM) no Atlântico Norte, através de padrões de trem de onda, que pode influenciar no deslocamento e tempo da permanecia da Zona de Convergência Intertropical (ZCIT) nestas latitudes. O deslocamento mais para norte da ZCIT pode ocasionar a formação de uma célula termalmente direta com seu ramo de subsidência ao sul do equador. A precipitação na estação chuvosa no Nordeste ainda pode ser influenciada pela variabilidade da TSM, pressão ao nível do mar (PNM) e vento sobre a bacia do Atlântico, influenciando também o posicionamento da ZCIT, tanto por influenciar o gradiente inter-hemisférico de TSM quanto pelo posicionamento da convergência dos alísios. Neste trabalhou buscou-se melhorar a compreensão da forma como estes mecanismos se combinam, e se há predominância entre eles. Numa etapa inicial foram analisados compostos de um conjunto de variáveis para situações de El Niño, La Niña e neutralidade no Pacífico, com o intuito de investigar os principais mecanismos controlador da variabilidade do Atlântico nesses diferentes casos. Mostrando assim, que nas fases positiva e negativa do ENOS a grande variabilidade nos extratrópicos se sobressai sobre as pequenas variações na região tropical e que as anomalias de fluxo de calor são influenciadas pelo o mecanismo de retroalimentação positiva, para condições de neutralidade a variabilidade nos trópicos parece ser mais notada e a variação do fluxo de calor ocorre pela variação da temperatura na interface oceano-atmosfera. Tais resultados foram seguidos por analises de alguns estudos de casos, para isto, foram analisados anos específicos com relação às anomalias nas células de Hadley, Walker, fluxos de calor, TSM, pressão ao nível (PNM), vento e precipitação mostrando que os efeitos das teleconexões do ENOS são influenciados de maneiras diferentes dependendo da intensidade do fenômeno. Para os anos estudados um dos principais mecanismos de variabilidade para a TSM na região tropical foi o mecanismo de retroalimentação positiva. Todavia, para o ano em que o gradiente inter-hemisférico foi bem defino, a variação da temperatura na interface oceano-atmosfera foi o principal forçante para as anomalias de fluxo de calor. Mostrando que o mecanismo de variabilidade mudará de ano para ano a depender das anomalias da TSM. As bacias do Atlântico Tropical Norte e Sul tendem a responderem a variabilidade com mecanismos diferentes de um ano para outro. / The quality of the rainy season in the Northeast can be related to the variability that arises in from of the phenomenon El Niño-Southern Oscillation (ENSO). That influences the rainy season by both the change in Walker's cell and by teleconnection patterns. The latter are responsible for causing variability in the sea surface temperature (SST) in the North Atlantic, by means of wave train patterns, which may influence the displacement and time of permanence of the Intertropical Convergence Zone (ITCZ) in these latitudes. This further northward shift of the ITCZ may lead to the formation of a thermally direct cell with its branch of subsidence south of the equator. Precipitation in the rainy season in the Northeast can still be influenced by the variability of SST, sea level pressure (PNM) and wind over the Atlantic basin. This variability also affects the positioning of the ZCIT, both because it influences the inter - hemispheric SST gradient and the positioning of the trade-offs. In this work was sought to improve the understanding of how these mechanisms combine, and whether there is predominance between them. In an initial stage we analyzed compounds of a set of variables for situations of El Niño, La Niña and neutral Pacific. The aim was to investigate the main mechanisms controlling the Atlantic variability in these different cases. It is possible to observe that in the positive and negative phases of the ENSO the great variability in the extratropics stands out for the small variations in the tropical region and that the anomalies of the heat flow were influenced by the positive feedback mechanism. For the neutral Pacific the variability in the tropics seemed to be more noticeable and the variation of the heat flow occurred by the temperature variation at the ocean-atmosphere interface. Some case studies were then made. That is, we analyzed specific years with respect to the anomalies in the cells of Hadley, Walker, heat flows, SST, geopotential, wind and precipitation. Thus, the effects of ENSO teleconnections are influenced in different ways depending on the intensity of the phenomenon. For the years studied, one of the main mechanisms of variability for SST in the tropical region was the positive feedback mechanism. However, for the year in which the inter-hemispher ic gradient was well defined, the temperature variation at the ocean-atmosphere interface was the main force for the heat flow anomalies. Showing that the variability mechanism will change from year to year depending on the SST anomalies. The results show that the North Atlantic and Southern Tropical Atlantic basins tend to respond to variability with different mechanisms from year to year.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Meteorology and Physical Oceanography, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN. / Bibliography: leaves 118-120. / by Randall J. Patton. / M.S.

The shape of the thermocline and the depth of the lysoline in the western tropical Pacific are both influenced by the overlying atmosphere, and both the shape of thermocline and the depth of the lysocline can be reconstructed from foraminifera-based paleo-proxies. Paleoclimate proxy evidence suggests a southward shift of the Intertropical Convergence Zone (ITCZ) during times of Northern Hemisphere cooling, including the Last Glacial Maximum (LGM), 19-23 ka before present. However, evidence for movement over the Pacific has mainly been limited to precipitation reconstructions near the continents, and the position of the Pacific marine ITCZ is less well constrained. In this study, I address this problem by taking advantage of the fact that the upper ocean density structure reflects the overlying wind field. I reconstruct changes in the upper ocean density structure during the LGM using oxygen isotope measurements on the planktonic foraminifera G. ruber and G. tumida in a transect of sediment cores from the Western Tropical Pacific. The data suggest a ridge in the thermocline just north of the present-day ITCZ persists for at least part of the LGM, and a structure in the Southern Hemisphere that differs from today. The reconstructed structure is consistent with that produced in a General Circulation Model with both a Northern and Southern Hemisphere ITCZ. I also attempt to reconstruct the upper ocean density structure for Marine Isotope Stages 5e and 6, the interglacial and glacial periods, respectively, previous to the LGM. The data show a Northern Hemisphere thermocline ridge for both of these periods. There is insufficient data to draw any conclusions about the Southern Hemisphere thermocline. Using the same set of sediment cores, I also attempt to reconstruct lysocline depth over the last 23,000 years using benthic foraminiferal carbon isotope ratios, planktonic foraminiferal masses, and sediment coarse fraction percentage. Paleoclimate proxy evidence and modeling studies suggest that the deglaciation following the LGM is associated with a deepening of the lysocline and an increase in sedimentary calcite preservation. Although my data lack the resolution to constrain the depth of the lysocline, they do show an increase in calcite preservation during the last deglaciation, consistent with lysocline deepening as carbon moves from the deep ocean to the atmosphere.

Satellite data have shown that east-west oriented cloud bands, known as Intertropical convergence zone (ITCZ), propagate eastwards along the equator throughout the year and northwards during boreal summer on intraseasonal time scales. The northward propagations over Bay of Bengal have important connection with onset of south Asian monsoon and active-break cycles of the Indian monsoon. Some studies on mean structure of ITCZ have concluded that preferred location of ITCZ is governed by meridional variation of sea surface temperature (SST) while other studies have stressed the importance of heating in the free atmosphere. Studies on the migration of ITCZ have shown that northward migration of maximum convergence zone is due to generation of positive barotropic vorticity north of the convection in the boundary layer due to internal dynamics of the atmosphere. In the present study mean and transient structure of northward migration of ITCZ over Bay of Bengal is simulated with the help of a general circulation model (GCM). The mean ITCZ is found not to occur at SST maximum or SST gradient maxima. A new simple model for the mean state of ITCZ based on moisture budget, linear friction and hydrostatic assumption is proposed. It highlights the relative importance of SST and atmospheric effects in generation of maximum convergence. The large cancellation between the effect of SST on boundary layer and thermodynamic effects in free troposphere is shown to control convergence. The model also shows that latitude and time independent linear friction parameterization in a simple model is able to predict monthly mean location of ITCZ in a GCM. The results give a quantitative understanding about the relative role of surface effects and atmospheric effects in determining location of the mean ITCZ. A simple linear model for understanding the mechanism of instability that governs the northward migration of ITCZ is proposed. Vertical shear in mean winds couples the barotrpic and baroclinic modes in free troposphere in this model. The model is able to predict the correct scale with standard values of friction and diffusion parameters. The mechanism of instability is found to be due to internal dynamics of troposphere. It is shown that direction of propagation is decided by vertical shear in zonal as well as meridional mean winds. This is contrary to the previous studies which conclude that either vertical shear in zonal winds or vertical shear in meridional winds control the direction of propagation.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Meteorology and Physical Oceanography, 1981. / Microfiche copy available in Archives and Science. / Bibliography: leaves 53-54. / by James Che-Ming Chung. / M.S.

Nas últimas décadas, particularmente desde a década de 1970, testemunhou-se um rápido recuo das geleiras em várias partes dos Andes tropicais. Uma tendência de aquecimento foi observada na região durante o mesmo período, com um hiato recente desde no início de 2010. No entanto, este hiato pode não ser o principal fator a influenciar as observações de aquecimento e recuo das geleiras em altitudes elevadas nos Andes tropicais. Com o surgimento de imagens de alta resolução espacial e espectral, e de modelos digitais de elevação (MDE) de alta resolução, agora é possível compreender as mudanças multitemporais das geleiras, o que era difícil de realizar utilizando as técnicas tradicionais e os dados de baixa resolução. Neste trabalho foram calculadas as variações da linha de neve das geleiras selecionadas ao longo dos Andes tropicais desde o início de 1980. A linha de neve máxima observada durante a estação seca (inverno austral) nos trópicos pode ser considerada como equivalente à linha de equilíbrio que separa a zona de acumulação da zona de ablação. A fim de reduzir o erro na estimativa da linha de neve foram consideradas somente as geleiras com declividades menores que 20o. Dependendo da região estudada e da presença de cobertura de nuvens, foram selecionadas imagens de várias fontes. As imagens da série Landsat (MSS, TM, ETM+ e OLI), EO1 OLI, ASTER e IRS LISS III foram usadas junto com MDE do ASTER GDEM-v2. Três bandas espectrais (TM5 - infravermelho médio, TM4- infravermelho próximo e TM2 - verde) foram utilizadas para calcular a linha de neve durante a estação seca, aplicando limiares adequados para TM4 e TM2. Os conjuntos de dados meteorológicos de várias fontes também foram analisados para observar as mudanças na precipitação, na temperatura e na umidade que influenciam os parâmetros glaciológicos como: o balanço de massa e a linha de equilíbrio. Geleiras representativas nos trópicos internos e trópicos externos foram consideradas separadamente dentro de um novo quadro, que foi baseado na precipitação, umidade e condições de temperatura ao longo da América do Sul. Neste âmbito, os Andes tropicais são classificados em trópicos internos, trópicos externos úmidos do norte, trópicos externos úmidos do sul e os trópicos externos secos. O Vulcão Cotopaxi no Equador (trópicos internos), o Nevado Caullaraju-Pastoruri que é uma geleira na Cordilheira Branca no Peru (trópicos externos úmidos do norte), o Nevado Cololo na Cordilheira Apolobamba na Bolívia (trópicos externos úmidos do sul), o Nevado Coropuna na Cordilheira Ampato no Peru e o Nevado Sajama na Cordilheira Ocidental da Bolívia (trópicos externos secos) são as geleiras representativas de cada grupo consideradas neste estudo. As geleiras tropicais nos trópicos internos, especialmente as situadas perto da Zona de Convergência Intertropicais (ZCIT), são mais vulneráveis a aumentos na temperatura e menos sensíveis a variações na precipitação. Em contraste, as geleiras nos trópicos externos respondem à variabilidade de precipitação muito rapidamente em comparação com a variação de temperatura, particularmente quando se deslocam para as regiões subtropicais. A dependência do balanço de massa sobre as características de sublimação também aumenta a partir dos trópicos internos para os trópicos externos. As condições de aquecimento, com maior umidade, tendem a aumentar a perda de massa por causa do derretimento em vez da sublimação. A elevação da umidade nos trópicos externos pode alterar as geleiras dominadas pela sublimação (nos trópicos externos e subtrópicos) e para as geleiras dominadas por derretimento. Observa-se que as geleiras próximas da ZCIT (trópicos internos e trópicosexternos úmidos do sul) estão recuando mais rapidamente como uma resposta ao aquecimento global, enquanto que as geleiras nos trópicos externos úmidos do norte e trópicos externos secos mostraram recuo relativamente mais lento. Possivelmente isso pode ser devido à ocorrência de fases frias do El Niño - Oscilação Sul (ENOS) conjuntamente com a Oscilação Decenal do Pacífico (ODP). As anomalias observadas nas variáveis meteorológicas seguem os padrões de ODP e as variações anuais de linha de neve seguem eventos de El Niño particularmente na fase ODP quente. No entanto, uma forte correlação entre as variações da linha de neve e dos fenômenos ENOS (e ODP) não está estabelecida. As geleiras do Equador mostram menos retração em resposta à tendência de aquecimento se comparadas às observações feitas por outros pesquisadores na Colômbia e na Venezuela, provavelmente devido à grande altitude das geleiras equatorianas. Em poucas palavras, as geleiras menores e em baixas altitudes nos trópicos internos e trópicos externos úmidos do sul estão desaparecendo mais rapidamente do que outras geleiras nos Andes tropicais. Também se observou neste estudo a existência de uma propriedade direcional no recuo das geleiras, o que não se observou em quaisquer outros estudos recentes. As geleiras nas cordilheiras leste do Peru e da Bolívia, que alimentam muitos rios nos lados leste das cordilheiras orientais, estão recuando do que aquelas geleiras situadas nas encostas ocidentais dos Andes tropicais. / Recent decades, particularly since the late 1970s, witnessed a rapid retreat of glaciers in many parts of the tropical Andes. A warming trend is observed in this region during the same period, with a recent hiatus since the early 2010s. However, this hiatus is observed to have not influenced the retreat of high elevation glaciers in the tropical Andes. Due to the emergence of high spatial and spectral resolution images and high quality digital elevation models (DEM), it is now possible to understand the multi-temporal glacier changes compared with the techniques that existed a few decades before. We calculated the snowline variations of selected glaciers along the tropical Andes since the early 1980s. The maximum snowline observed during the dry season (austral winter) in the tropics can be considered as nearly equivalent to the equilibrium line that separates the accumulation zone from the ablation zone. In order to reduce the error in the estimated snowline, glaciers with slopes < 20o only were considered in this research. Depending on the study region and the presence of cloud cover, images from multiple sources were selected. Landsat series (MSS, TM, ETM+, and OLI), EO1 OLI, ASTER, and IRS LISS III images were used along with digital elevation models (DEM) from ASTER GDEM-v2. Three wavebands (TM5 - Middle Infrared, TM4 - Near Infrared, and TM2 - Green) were used to calculate the dry season snowline, after applying suitable threshold values to TM4 and TM2. Meteorological datasets from multiple sources were also analysed to observe the changes in precipitation, temperature, and humidity that influence key glaciological parameters such as the mass balance and the equilibrium line. Representative glaciers in the inner and the outer tropical Andes were considered separately within a new framework, which is based on the precipitation, humidity, and temperature conditions along the South America. In this framework, tropical Andes are classified in to inner tropics, northern wet outer tropics, southern wet outer tropics, and dry outer tropics. Cotopaxi ice-covered volcano, Ecuador (inner tropics), Nevado Caullaraju-Pastoruri Glacier, Cordillera Blanca, Peru (northern wet outer tropics), Nevado Cololo, Cordillera Apolobamba, Bolivia (southern wet outer tropics), and Nevado Coropuna, Cordillera Ampato Peru and Nevado Sajama, Cordillera Occidental, Bolivia (dry outer tropics) are the representative glaciers in each group considered in this study. Inner tropical glaciers, particularly those situated near the January Intertropical Convergence Zone (ITCZ), are more vulnerable to increases in temperature and these glaciers are less sensitive to variations in precipitation. In contrast, outer tropical glaciers respond to precipitation variability very rapidly in comparison with the temperature variability, particularly when moving towards the subtropics. Mass balance dependency on sublimation characteristics also increases from the inner tropics to the outer tropics. Warming conditions with higher humidity tends to enhance mass loss due to melting rather than sublimation. Increased humidity observed in the outer tropics may change the sublimation dominated glaciers in the outer tropics and subtropics to melting dominated ones in the future. It is observed that the glaciers above and near the January ITCZ (inner tropics and southern wet outer tropics) are retreating faster as a response to global warming, whereas the glaciers in the northern wet outer tropics and dry outer tropics show relatively slower retreat. This can be possibly due to the occurrence of cold phases of El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) together. The observed anomalies in the meteorological variables slightly follow PDO patterns and the variations in annual snowlines follows El Niño events, particularly when in phase with warm PDO. However, a strong correlation between snowline variations and ENSO (and PDO) is not established. Mountain glaciers in Ecuador show less retreat in response to the warming trend compared with observations done by other researchers in Colombia and Venezuela, probably due to very high altitude of the Ecuadorean glaciers. In a nutshell, smaller glaciers at lower altitudes in the inner tropics and the southern wet outer tropics are disappearing faster than other glaciers in the tropical Andes. Another observation made in this study is the directional property of glacier retreat, which was not covered in any other recent studies. Those glaciers on the eastern cordilleras of Peru and Bolivia, which feed many rivers on the eastern sides of the eastern cordilleras, are retreating faster than those glaciers situated on the western sides.

Submitted by Biblioteca de Pós-Graduação em Geoquímica BGQ (bgq@ndc.uff.br) on 2017-09-11T18:18:13Z No. of bitstreams: 1 diss-Raphael-Logato-de-Oliveira-PPGA.pdf: 25249109 bytes, checksum: bebdeef5c344d7c319f3fd7481af2cce (MD5) / Made available in DSpace on 2017-09-11T18:18:13Z (GMT). No. of bitstreams: 1 diss-Raphael-Logato-de-Oliveira-PPGA.pdf: 25249109 bytes, checksum: bebdeef5c344d7c319f3fd7481af2cce (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geoquímica, Niterói, RJ / A taxa de crescimento de uma colônia do coral endêmico brasileiro Siderastrea stellata, proveniente da Reserva Biológica do Atol das Rocas (3° 45’ S / 33° 40’ O – 3° 55’ S / 33° 50’ O), baseada em conta gem de bandas de crescimento e datação absoluta pelo método U-Th, seguidas de analises geoquímicas e isotópicas, revelaram uma variablidade das Temperaturas de Superfície do Mar (TSM) durante os últimos 39 anos. Os resultados demonstram uma forte correlação entre o crescimento do coral e a razão Sr/Ca, como também entre o Sr/Ca e U/Ca. O crescimento, Sr/Ca e U/Ca indicaram um forte sinal com frequência decadal, que é correspondente a um dos principais regimes de variabilidade do Atlântico Tropical Sul. Além disto, pode ser dito que o sinal do δ18O apresentou uma boa coerência com a ZCIT, indicando um potencial para futuros estudos sobre flutuações de salinidade. Porém, a falta de correlação entre os parametros geoquimicos com a TSM pode ser atribuída à limitação dos registros instrumentais de TSM disponíveis para a área de estudo (PIRATA), que são provenientes de bóias oceanográficas espaçadamente distribuídas. Assim, este estudo destaca alguns importantes fatores: a necessidade de se obter os registros de TSM in situ, para que seja possível estabelecer boas correlações entre esta e os traçadores; a clara relação entre o crescimento e Sr/Ca, sugerindo que este traçador pode não ser regulado somente pela TSM no caso de S. stellata; e a predominância de influências de variabilidades decadais e semi-decadais para esta região / One colony growth rate of an endemic Brazilian coral Sideratrea stellata from Atol das Rocas Biological reserve (3° 45’ S / 33° 4 0’ O – 3° 55’ S / 33° 50’ O), based on growth band counting and U-Th dating method, followed by geochemical analysis, revealed Sea Surface Temperature (SST) variability for the last 39 years. Results show a strong correlation between coral growth and Sr/Ca ratio, and also strong correlation between Sr/Ca and U/Ca. Growth, Sr/Ca and U/Ca indicate strong signal at decadal frequencies, corresponding to one of major South Tropical Atlantic variability. Moreover, it can be said that δ18O signal has showed good coherence with respect to ITCZ, pointing out to potential future studies about salinity fluctuations. However, the lack of correlation between SST and geochemical tracers can be attributed to instrumental SST data restriction for the study site, which comes from sparsely distributed oceanographic buyos (PIRATA). Insofar, this study highlights some important factors: the need for in situ SST registry in order to establish good correlations for SST and geochemical data; the clear relationship between coral growth and Sr/Ca, suggesting that this ratio may not be regulated by SST only for S. stellata; and the predominance decadal and semi-decadal variabilities at this region.