Esta tese investiga se eventos anômalos de precipitação pluviométrica (PP) na Planície Costeira do Rio Grande do Sul (PCRGS) estão relacionados a modos de variabilidade climática e como essa relação pode afetar o ambiente costeiro. A PP e suas anomalias foram estatisticamente correlacionadas aos modos de variabilidade climática, o Modo Anular do Hemisfério Sul (SAM) e El Niño - Oscilação Sul (ENOS). O índice do ENOS utilizado foi o Multivariate ENSO Index (MEI) e do SAM foi o de Nan e Li (2003). Para o cálculo das anomalias de PP foram utilizados dados do satélite Tropical Rainfall Measurement Mission, entre 1998 e 2013. As correlações foram calculadas por meio de matrizes de classificação, e suas significâncias pelo teste-t de Student. A área de estudo foi dividida em costas sul (33°44’39” – 32°09’36”S), central (32°09’36” – 30°10’12”S) e norte (30°10’12” – 29°19’34”S) e para cada uma delas foi escolhido um geoindicador (sangradouros ou lagunas), examinados em imagens de satélite. Comparouse os geoindicadores em períodos de PP anomalamente positiva e negativa. Para destacar as variações nos geoindicadores foram utilizadas composições RGB 543 dos sensores Thematic Mapper (TM) e Enhanced Thematic Mapper Plus (ETM+) do Landsat. Os resultados apontam para correlação negativa entre as anomalias de PP nas costas sul e central com o SAM e correlação positiva das anomalias de PP da costa sul com o MEI. A PP na costa norte não apresenta correlação com nenhum dos dois índices. Foram identificados 28 eventos anômalos de PP no período 1998-2013. Nas imagens de satélite todos geoindicadores apontaram para variações morfológicas e hídricas entre os períodos PP acima e abaixo da média, sendo a costa norte a que apresenta menor variação visível. A costa sul tem a menor média de PP e o maior número de eventos anômalos de PP, dos quais 67% eram de PP negativa. A maioria dos eventos são de PP negativa (78%) e podem estar relacionados simultaneamente ao SAM positivo e MEI negativo, ou somente ao MEI positivo. Todos eventos de PP positiva foram concomitantes ao MEI positivo. As costas sul e central mostram uma redução na PP média. Essa tendência pode estar relacionada as mudanças climáticas globais, pela intensificação do SAM positivo e de eventos El Niño e La Niña. As variações observadas nos geoindicadores (sangradouros ou lagunas) indicam que a redução na PP média resulta em menor volume de sedimentos transportados do pós praia para a zona de arrebentação e face praial, alterando o balanço sedimentar. As areias secas dos campos de dunas transportadas pelo vento podem assorear lagos e lagunas da área de estudo, desequilibrando o ecossistema. / This thesis investigates whether anomalous events of precipitation (PP) in the Coastal Plain of Rio Grande do Sul (RGSCP) are related to climate variability modes and how this relationship can affect the coastal environment. The PP and its anomalies were statistically correlated to climate variability modes, the Southern Annular Mode (SAM) and El Niño-Southern Oscillation (ENSO). The used ENSO index was the Multivariate ENSO Index (MEI) and SAM is the one defined by Nan and Li (2003). For the calculation of the PP anomalies, we used data from the Tropical Rainfall Measurement Mission satellite, from 1998 to 2013. Correlations were calculated using classification matrices, and their significance by the the Student t-test. The study area was divided into south (33°44'39" – 32°09'36"S), central (32°09'36"– 30°10'12"S) and north (30°10'12"– 29°19'34"S) coasts and for each one it was chosen a geoindicador (washouts or lagoons), examined on satellite images. This investigation compared the geoindicators in positive and negative anomalous PP periods. To highlight variations in the geoindicators, it was used the RGB 543 composition of the Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) Landsat sensors. The results point to a negative correlation of the PP anomalies in the southern and central coasts with the SAM and a positive correlation of PP anomalies in the south coast with the MEI. The north coast PP is not correlated with any of the two indexes. Twenty-eight anomalous PP events were found in the 1988–2013 period. In satellite images, all geoindicators pointed to morphological and hydrological variations between periods of PP above and below the mean, the northern coast has the least visible variations. The south coast has the lowest mean PP and the largest number of anomalous events, of which 67% were negative PP. The majority of events are negative PP (78%), they could be simultaneously connected to a positive SAM and a negative MEI, or only to a positive MEI. All positive PP events were concomitant to a positive MEI. The central and southern coasts show a decrease in the men PP. This trend may be related to global climate change, by the intensification of the positive SAM and of El Niño and La Niña events. The variations observed in geoindicators (washouts or lagoons) indicate that the reduction in the mean PP results in lower volume of sediments transported from the backshore to the surf zone and the shoreface, changing the sedimentary balance. The dry sands from the wind-transported dune fields could silt up lakes and lagoons of the study area, unbalancing the ecosystem.

This study focuses on how the construction of a paleoclimate time series influences the interpretation in the frequency domain. Three time series are examined: a New Caledonian coral (Amedee Island), a Chinese speleothem (Dongge Cave), and New Mexican trees (El Malpais). This study presents a monthly resolved coral Sr/Ca time series from New Caledonia that reconstructs sea surface temperature (SST; 1648-1999). The chronology is based on density-band counting, cross-correlating Sr/Ca, and ²³°Th dating. The intracolony coral Sr/Ca variations are coherent on interannual to centennial time scales and are reproducible for >300 years. The SST reconstruction reveals estimated cooling trend (~0.4°C) from 1741-1815, a colder nineteenth century (~0.6°C), and a warming trend (~0.6°C) in the twentieth century. Spectral and wavelet analysis reveals significant inter-decadal periodicities (~14-21 years/cycle) that modulate with time, and nearly persistent multi-decadal periodicities (~25-33 years/cycle) that do not exhibit coherence with the Inter-decadal Pacific Oscillation. The multi-decadal periodicities may be a harmonic of the inter-decadal periodicities or may represent an independent mode not previously recognized. The Dongge Cave time series is based on uneven time intervals between data points (∆t) requiring interpolation to a constant ∆t for analysis with traditional spectral methods. A comparison of the even and uneven ∆t spectra using the Lomb-Scargle transform reveals the interpolated spectrum contains suppressed periodicities (<20 years/cycle), in contrast to the uninterpolated spectrum, resulting in a steeper slope in the red noise model thus influencing significance testing. The El Malpais time series is an average of tree-ring width series. Spectral analysis of the entire time series identified significant periodicities. However, significance varies between three temporal subsets, in which the number of series varies; therefore, these periodicities may be a function of the number of series or may represent a real temporal variability. Cross-spectral analysis of the El Malpais and Dongge Cave time series reveals significant coherence; however, cross-wavelet analysis, which examines localized frequencies in the time domain, reveals a lack of correlation; therefore, coherence in the frequency domain does not indicate correlation in the time domain.

Stable isotope values of ostracod calcite provide a record of variation in ¥ä18O(H2O) values and water temperature from the late glacial to mid-Holocene in Western Ireland. Lough Monreagh, located in County Clare, Western Ireland, contains marl sediment that includes pristine ostracod calcite whose ¥ä18O and ¥ä13C values were evaluated. These values were used relative to modern ecological requirements to derive a paleoenvironmental record for Lough Monreagh that includes water temperature, eutrophication, water depth, as well as terrestrial vegetation and weathering within the lake¡¯s watershed. ¥ä13C values of ostracod calcite presented herein suggest a significant increase in terrestrial vegetation beginning during the Aller©ªd (13,600 cal year B.P.) and extending through to the mid-Holocene (6,997 cal year B.P.). Marl and ostracod ¥ä18O values record variability in temperature and precipitation ¥ä18O(H2O) values that are in turn forced by variation in atmospheric and oceanic circulation. Water temperatures presented herein were calculated from ¥ä18O values of ostracod calcite and marl, constrained by temperature preference and tolerance ranges of ostracod species, yielding the highest resolution temperature record covering this period to date. Over 4,700 ostracods representing all three freshwater superfamilies were counted and identified to evaluate the trophic stage of the lake. The lake was characterized as a clear-, cold-water (~8¨¬C summer water temperature), low-nutrient environment during the Aller©ªd, then freezes abruptly during the Younger Dryas as evidenced by black clay deposits aged 12,800 to 11,300 cal yr B.P. Following the Younger Dryas, transitional warming and increasing terrestrial vegetation are evidenced by decreasing ¥ä13C values of ostracoda and faunal transition to phytophyllic species. Summer water temperatures warm to >16¨¬C, with ostracod species suggesting a shallow-water, fen- and macrophyte-rich environment with abundant plant life in and around the lake by ~8,000 cal yr B.P.

Stable isotope values of ostracod calcite provide a record of variation in ¥ä18O(H2O) values and water temperature from the late glacial to mid-Holocene in Western Ireland. Lough Monreagh, located in County Clare, Western Ireland, contains marl sediment that includes pristine ostracod calcite whose ¥ä18O and ¥ä13C values were evaluated. These values were used relative to modern ecological requirements to derive a paleoenvironmental record for Lough Monreagh that includes water temperature, eutrophication, water depth, as well as terrestrial vegetation and weathering within the lake¡¯s watershed. ¥ä13C values of ostracod calcite presented herein suggest a significant increase in terrestrial vegetation beginning during the Aller©ªd (13,600 cal year B.P.) and extending through to the mid-Holocene (6,997 cal year B.P.). Marl and ostracod ¥ä18O values record variability in temperature and precipitation ¥ä18O(H2O) values that are in turn forced by variation in atmospheric and oceanic circulation. Water temperatures presented herein were calculated from ¥ä18O values of ostracod calcite and marl, constrained by temperature preference and tolerance ranges of ostracod species, yielding the highest resolution temperature record covering this period to date. Over 4,700 ostracods representing all three freshwater superfamilies were counted and identified to evaluate the trophic stage of the lake. The lake was characterized as a clear-, cold-water (~8¨¬C summer water temperature), low-nutrient environment during the Aller©ªd, then freezes abruptly during the Younger Dryas as evidenced by black clay deposits aged 12,800 to 11,300 cal yr B.P. Following the Younger Dryas, transitional warming and increasing terrestrial vegetation are evidenced by decreasing ¥ä13C values of ostracoda and faunal transition to phytophyllic species. Summer water temperatures warm to >16¨¬C, with ostracod species suggesting a shallow-water, fen- and macrophyte-rich environment with abundant plant life in and around the lake by ~8,000 cal yr B.P.

Using ERA40 and independent observations, I assess how well Amazon surface water budget is estimated. ERA40 basin wide annual precipitation (P) agrees with observations showing an underestimation of 10%, whereas runoff (R) is underestimated by a larger margin (~25%). Observed residual of precipitation and runoff (P-R) is better estimated by ERA40 P-R than actual ET which includes soil moisture nudging. Nudging is necessary during the dry season to produce realistic ET and compensate for low soil moisture recharge during the wet season. Insufficient recharge may be caused by: underestimation of rainfall amount and intensity; a shallow root layer in the model that does not represent the deep soil water reservoir of the Amazonian forest. The physical links between changes in wet season onset and synoptic scale systems are investigated in the second part of my work. A delayed wet season onset is consistent with a decreasing number of cold air incursion (CAI) days in southern Amazon during 1979-2001. CAI variability in southern Amazon is related to SST in the tropical Pacific and Indian Oceans. The first mode of co-variability shows that during El Nio (La Nia) a strong (weak) subtropical jet stream over South America is related to decreased (increased) CAI days during SON. The second mode shows warm western Indian Ocean also related to strong subtropical jet stream. The absence a well defined subpolar jet stream, favors the northward displacement of transient waves into central South America, but shows little response in southern Amazon. CAI days reconstructed from the first and second modes do not present any significant trend in southern Amazon. CAI days reconstructed from the third mode of co-variability reproduces SON observed trend. This mode describes negative (positive) anomalies in CAI days associated with cold (warm) SST anomalies, anomalous wavetrain in the tropical Pacific and Walker Cell displacement that are unfavorable (favorable) to the incursion of CAI into southern Amazon. This mode's temporal evolution correlates with the Pacific Decadal Oscillation (PDO), suggesting that its recent gradual signal shift reflected on the interannual response of southern Pacific atmospheric patterns, hence on the behavior of transients propagation.

This dissertation aims to identify the main changes in monsoon activity observed over the American monsoon and Amazonian regions during the last decades and the possible links between such changes. To address this, several observational and reanalysis datasets were used. The results suggest the occurrence of two regime types of the North American monsoon during 1948-2009: two dry regimes during 1948-1959 and 1990-2009 and one wet regime during 1960-1989. The occurrence of such regimes is modulated by the Atlantic Multidecadal Oscillation. However, the two dry regimes have different causes. In particular, the more recent dry regime is mainly due to both an anomalous westward expansion of the North Atlantic Subtropical High and a northward displacement of the subtropical jet stream over the United States. The former enhances the low-level flow from the Gulf of Mexico to the Great Plains and weakens moisture transport to Mexico and the southwestern US. In addition to such a weakening of the North American monsoon during the last two decades, this research shows that the American monsoon systems have shortened after 1978 due to a trend toward earlier retreats of the North American monsoon and delayed onsets of the southern Amazon wet season. These changes produce a longer transition season between both monsoon systems. Whether these changes are caused by a common factor or they are the consequence of independent and unrelated causes was not clear previously. The results discussed here indicate that the observed changes in the American monsoons are partially a consequence of the westward expansion of the North Atlantic surface high observed since 1978. Such a westward expansion enhances the activity of easterly waves over the southern Caribbean Sea and northern South America, producing a dominant easterly flow over the region, which in turn prevents the reversal of the cross-equatorial flow necessary to transport moisture to the southern Amazon and the South American monsoon domain and contributes to its delayed onset. This investigation provides evidence that the shortening and weakening of the American monsoons and the lengthening of the transition season between them are associated with the same large-scale forcing, which may be caused by anthropogenic influence. / text

This thesis contributes increased knowledge about climate variability during the late Quaternary in the eastern Mediterranean. Results from a paleoclimate review reveal that regional wetter conditions from 6000 to 5400 years BP were replaced by a less wet period from 5400 to 4600 years BP and to fully arid conditions around 4600 years BP. The data available, however, show that there is not enough evidence to support the notion of a widespread climate event with rapidly drying conditions in the region around 4200 years ago. The review further highlights the lack of paleoclimate data from the archaeologically rich Peloponnese Peninsula. This gap is addressed in this thesis by the provision of new paleoclimate records from the Peloponnese. One stalagmite from Kapsia Cave and two stalagmites from Glyfada Cave were dated and analyzed for stable oxygen (δ18O) and carbon (δ13C) isotopes. The Glyfada record covers a period from ~78 ka to ~37 ka and shows that the climate in this region responded rapidly to changes in temperatures over Greenland. During Greenland stadial (interstadial) conditions colder (warmer) and drier (wetter) conditions are reflected by depleted (enriched) δ13C-values in the speleothems. The Kapsia record covers a period from ~2900 to ~1100 years BP. A comparison between the modern stalagmite top isotopes and meteorological data shows that a main control on stalagmite δ18O is wet season precipitation amount. The δ18O record from Kapsia indicates cyclical humidity changes of close to 500 years, with rapid shifts toward wetter conditions followed by slowly developing aridity. Superimposed on this signal is a centennial signal of precipitation variability. A second speleothem from Kapsia with multiple horizons of fine sediments from past flood events intercalated with the calcite is used to develop a new, quick and non-destructive method for tracing flood events in speleothems by analyzing a thick section with an XRF core scanner. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Accepted.</p>

The role of weather and climate variability on the health of Aboriginal people in Fort Albany and Toronto, Ontario, Canada is explored through four complementary research studies. The first study examined past temperature trends of Fort Albany (using climate records of Moosonee) and Toronto. Temperature variability was found to be greater in Moosonee than in Toronto, and day to day temperature minimum (Tmin) threshold exceedances of 5 degrees Celsius was found to have significantly declined in both Toronto and Fort Albany. The second study explored the effects of climate change on a rural First Nation group in Fort Albany. Observed environmental changes include changes in the timing of seasons, spring melt and ice freeze-up; warmer seasons, an increase in extreme and unpredictable weather, and changes in animal patterns. These changes have affected subsistence harvesting activities and community infrastructure, which have lead to increased health risks, though many community members have exhibited resiliency and adaptation. The third study compared current health status between an urban Aboriginal and non-Aboriginal group. Urban Aboriginal participants were found to be at greater risk to psychological distress and seasonal affective disorder (SAD) than non-Aboriginal participants. Moreover, those who self-rated their health as poor/fair were more likely to exhibit psychological distress than those who self-rated their health as good/very good/excellent. The fourth study compared the effects of weather and seasonal change among a rural First Nation group, an urban Aboriginal group and an urban non-Aboriginal group. Urban Aboriginal participants were most affected by weather while rural Aboriginal (i.e. First Nation) participants were least affected by weather. These studies demonstrate that both urban and rural Aboriginal groups may be at risk to climate change and weather-related changes; though specific implications may differ due to different lifestyles and capacities to adapt to environmental conditions.

This dissertation reports on studies on the role of the mean state in modulating climate variability at interannual and decadal time scales. In the atmosphere, the nonlinear superposition of mean flow and anomalous flow has important implications for many phenomena associated with variables that are nonlinear by definition, such as the vertical wind shear and surface wind speed. In the first part of this dissertation, the influence of mean flow and anomalous flow on vertical wind shear variability is studied in observations and numerical model simulations. At interannual timescales, the ENSO-shear relationship is compared between observations and numerical model simulations. It is shown that there is strong influence of mean flow on the ENSO-shear relationship. For same anomalous flow, different mean flows could give rise to a different ENSO-shear relationship. The nonlinear superposition of mean flow and anomalous flow also helps explains the dipole mode of tropical Atlantic vertical wind shear variability seen in observations and models, which implies opposite variation of vertical wind shear over the two sides of the tropical Atlantic. This has important implications for predicting phenomena such as Atlantic hurricanes, whose variations are modulated by vertical shear variability. The dissertation also addresses the role of the mean surface wind in decadal variability and predictability, as manifested through the Wind-Evaporation-SST (WES) feedback. The nonlinear superposition of anomalous surface wind on the mean trade wind can give rise to a positive WES feedback, which can amplify tropical climate variability. To study this feedback, we carried out ensembles of decadal climate predictions using the CAM3 atmospheric model coupled to a slab ocean model (CAM3- SOM) with prescribed ocean transport and simple extrapolative prescriptions of future external forcings. Mechansitic sensitivity runs using the CAM3-SOM were also carried out, where the WES feedback was switched off by prescribing climatological surface wind. Results suggest that switching off the WES feedback enhances the prediction skill over some regions, especially over the eastern tropical Pacific, by increasing the signal- to-noise ratio. To address the issue of cold bias noted in the decadal prediction experiments, we carried out additional sensitivity experiments where we used an adaptive formulation for the prescribed oceanic heat transport (Q-flux) in the slab ocean. The results from these experiments demonstrate that the mean oceanic heat transport plays a crucial role in influencing decadal predictability, by helping improve predictions of the trend component of decadal variations.

The role of weather and climate variability on the health of Aboriginal people in Fort Albany and Toronto, Ontario, Canada is explored through four complementary research studies. The first study examined past temperature trends of Fort Albany (using climate records of Moosonee) and Toronto. Temperature variability was found to be greater in Moosonee than in Toronto, and day to day temperature minimum (Tmin) threshold exceedances of 5 degrees Celsius was found to have significantly declined in both Toronto and Fort Albany. The second study explored the effects of climate change on a rural First Nation group in Fort Albany. Observed environmental changes include changes in the timing of seasons, spring melt and ice freeze-up; warmer seasons, an increase in extreme and unpredictable weather, and changes in animal patterns. These changes have affected subsistence harvesting activities and community infrastructure, which have lead to increased health risks, though many community members have exhibited resiliency and adaptation. The third study compared current health status between an urban Aboriginal and non-Aboriginal group. Urban Aboriginal participants were found to be at greater risk to psychological distress and seasonal affective disorder (SAD) than non-Aboriginal participants. Moreover, those who self-rated their health as poor/fair were more likely to exhibit psychological distress than those who self-rated their health as good/very good/excellent. The fourth study compared the effects of weather and seasonal change among a rural First Nation group, an urban Aboriginal group and an urban non-Aboriginal group. Urban Aboriginal participants were most affected by weather while rural Aboriginal (i.e. First Nation) participants were least affected by weather. These studies demonstrate that both urban and rural Aboriginal groups may be at risk to climate change and weather-related changes; though specific implications may differ due to different lifestyles and capacities to adapt to environmental conditions.