Neste trabalho a variabilidade climatica do oceano Austral e a ocorrencia da Onda Circumpolar Antartica (OCA) sao investigadas. Foram usados os dados de uma simulaçao do modelo numerico acoplado do Nacional Centre for Atmospheric Research/ Community System Model - NCAR CCSM de 150 anos, e um conjunto de dados climatologicos como base de comparaçao dos dados do modelo. estes foram obtidos da Re-analise do NCEP/NCAR (National Center for Envirommental Prediction) para o periodo de janeiro de 1948 a julho de 2002. Com o intuito de analisar o comportamento sazonal e anual foram analisadas as climatologias e utilizada a tecnica de analise harmonica das variaveis de temperatura da superficie do mar (TSM), pressao ao nivel do mar (PNM), componentes meridional (Vy) e zonal (Vx) do vento. Para analisar o comportamento interanual dessas variaveis sao utilizados diagramas Hovmoeller, espectros de potencia, alem de tecnicas estatisticas como Empirical Ortogonal Functions (EOF) e singular Value Decomposition (SVD). / In this study the climatic variability of the Southern ocean and the Antarctic Circumpolar Wave (ACW) are investigated. The National Center for Atmospheric Research/ Community System Model _ NCAR CCSM coupled model 150 years simulation data is compered with the climatology data from the Nacional Center for Envirommental Prediction - NCEP/NCAR Re-analysis, for a period from january/1948 until july/2002. Annual and seasonal climatology and harmonic analysis are used for the following variables: sea surface temperature (SST), sea level pressure (SLP), meridional and zonal wind. Hovmoeller diagrams, potencial spectra and statistics methods such as Empirical Ortogonal Functions (EOF) and Singular Value Decomposition (SVD) are used to analyze changes in interannual behavior of this variables.

O avanço da tecnologia computacional e a sofisticação da modelagem numérica nos últimos anos tornou possível a realização de diversas simulações do clima terrestre. Essas simulações buscam reproduzir a dinâmica e a variabilidade do clima global, e consequentemente prever o clima futuro. Dentro do sistema climático, o oceano é o compartimento responsável por manter estabilidade do clima. Processos oceânicos como a formação e distribuição de massas de água têm um papel chave no armazenamento e redistribuição de energia pelo sistema. Mudanças nesses fenômenos podem implicar em variações drásticas do clima atual. Considerando isso, o presente trabalho visa descrever a estrutura espaço-temporal das massas de água do Oceano Atlântico Sul e do Oceano Austral. Para isso foram utilizados dados de modelos climáticos que foram utilizados na elaboração do 4° Relatório de Avaliação do Painel Intergovernamental para as Mudanças Climáticas. Os modelos são: ECHAM5/MPI-OM, IPSL-CM4-V1, MIROC3.2 e GFDL CM2.1. Dentre as diversas simulações são comparados os experimentos para o século XX (20c3m) e o experimento que assume a concentração de CO2 aumentando a uma taxa de 1% ao ano até o valor inicial duplicar (1pctto2x). Os resultados mostraram um aumento da temperatura da Água Intermediaria Antártica (AIA) e da Água Profunda Circumpolar (CDW). As densidades delas diminuíram significativamente tanto no cenário 20c3m quanto no 1pctto2x. A Água de Fundo Antártica (AFA) sofreu um resfriamento e passou a ocupar níveis mais profundos em ambos os cenários. As variações registradas no 1pctto2x foram mais intensas do que aquelas observadas no experimento 20c3m. Já variabilidade temporal das massas de água foram bastante divergentes entre os quatro modelos. / The development and sophistication of numerical models in recent years has allowed to perform many climate system\'s simulations. Such simulations aim to reproduce the dynamics and variability of the climate and consequently predict future climate and possible climate changes. Oceanic processes such as formation and distribution of water masses have an important role in understanding the oceans as a reservoir of salt, dissolved gases and heat. Considering that changes in such processes may have great impact in global and regional climate this work aims to describe spatial and temporal variability of water masses in the South Atlantic Ocean and Southern Ocean. Data from the numerical simulations used for the preparation of the Intergovernmental Panel on Climate Change Fourth Assessment Report (4AR/IPCC) were used. Four climate models were chosen: ECHAM5/MPI-OM, IPSL-CM4-V1, MIROC3.2, NOAA / GFDL CM2.1. Results from the Climate of the 20th Century (20c3m) and the 1% per year CO2 increase (to doubling) experiment (1pctto2x) were analyzed. The four models show a positive trend of temperature and a freshening trend of the Antartic Intemediate Water (AAIW), Circumpolar Deep Water (CDW) and the Antartic Deep Water (AADW). The densities of these water masses become significantly lighter in the 20c3m scenario. In the 1pctto2x scenario in the AAIW and CDW moved to upper layers. Also in this scenario there is a cooling of the AADW, moving this water mass to deeper layers.

O avanço da tecnologia computacional e a sofisticação da modelagem numérica nos últimos anos tornou possível a realização de diversas simulações do clima terrestre. Essas simulações buscam reproduzir a dinâmica e a variabilidade do clima global, e consequentemente prever o clima futuro. Dentro do sistema climático, o oceano é o compartimento responsável por manter estabilidade do clima. Processos oceânicos como a formação e distribuição de massas de água têm um papel chave no armazenamento e redistribuição de energia pelo sistema. Mudanças nesses fenômenos podem implicar em variações drásticas do clima atual. Considerando isso, o presente trabalho visa descrever a estrutura espaço-temporal das massas de água do Oceano Atlântico Sul e do Oceano Austral. Para isso foram utilizados dados de modelos climáticos que foram utilizados na elaboração do 4° Relatório de Avaliação do Painel Intergovernamental para as Mudanças Climáticas. Os modelos são: ECHAM5/MPI-OM, IPSL-CM4-V1, MIROC3.2 e GFDL CM2.1. Dentre as diversas simulações são comparados os experimentos para o século XX (20c3m) e o experimento que assume a concentração de CO2 aumentando a uma taxa de 1% ao ano até o valor inicial duplicar (1pctto2x). Os resultados mostraram um aumento da temperatura da Água Intermediaria Antártica (AIA) e da Água Profunda Circumpolar (CDW). As densidades delas diminuíram significativamente tanto no cenário 20c3m quanto no 1pctto2x. A Água de Fundo Antártica (AFA) sofreu um resfriamento e passou a ocupar níveis mais profundos em ambos os cenários. As variações registradas no 1pctto2x foram mais intensas do que aquelas observadas no experimento 20c3m. Já variabilidade temporal das massas de água foram bastante divergentes entre os quatro modelos. / The development and sophistication of numerical models in recent years has allowed to perform many climate system\'s simulations. Such simulations aim to reproduce the dynamics and variability of the climate and consequently predict future climate and possible climate changes. Oceanic processes such as formation and distribution of water masses have an important role in understanding the oceans as a reservoir of salt, dissolved gases and heat. Considering that changes in such processes may have great impact in global and regional climate this work aims to describe spatial and temporal variability of water masses in the South Atlantic Ocean and Southern Ocean. Data from the numerical simulations used for the preparation of the Intergovernmental Panel on Climate Change Fourth Assessment Report (4AR/IPCC) were used. Four climate models were chosen: ECHAM5/MPI-OM, IPSL-CM4-V1, MIROC3.2, NOAA / GFDL CM2.1. Results from the Climate of the 20th Century (20c3m) and the 1% per year CO2 increase (to doubling) experiment (1pctto2x) were analyzed. The four models show a positive trend of temperature and a freshening trend of the Antartic Intemediate Water (AAIW), Circumpolar Deep Water (CDW) and the Antartic Deep Water (AADW). The densities of these water masses become significantly lighter in the 20c3m scenario. In the 1pctto2x scenario in the AAIW and CDW moved to upper layers. Also in this scenario there is a cooling of the AADW, moving this water mass to deeper layers.

The zooplankton community of Marguerite Bay, western Antarctic Peninsula, was investigated in relation to variability in chlorophyll concentrations and sea ice dynamics, using a combination of satellite remote sensing techniques and plankton net data. SeaWiFS chlorophyll data were validated with concurrent in situ data measured by HPLC and fluoromentric methods, and results indicate that SeaWiFS chlorophyll is an accurate measure of in situ values when HPLC data are used as ground truth. Climatology data of SeaWiFS chlorophyll west of the Antarctic Peninsula showed that the Bellingshausen Sea and Marguerite Bay usually had higher and more persistent chlorophyll concentrations compared with northern regions. These predictable phytoplankton blooms could provide the Antarctic krill, Euphausia superba, with the food required for successful reproduction and larval survival. Unusually high krill reproduction in 2000/2001 was coincident with above-average chlorophyll concentrations throughout the study area and was followed by the largest juvenile recruitment since 1981. High larval densities at the shelf break along the Antarctic Peninsula may have resulted, in part, from krill spawning in the Bellingshausen Sea. Interannual differences in sea ice also probably contributed to the variability in larval krill abundances. Interannual differences were observed in the species composition of the zooplankton of Marguerite Bay during fall, and these were linked to variability in the environmental conditions. Thysanoessa macrura was the most abundant euphausiid in 2001, while Euphausia crystallorophias dominated in 2002, and E. superba had intermediate densities during both years. Copepods were more abundant in 2001 by a factor of 2.6. Copepods and T. macrura showed a rapid population response to unusually high chlorophyll concentrations in the Bellingshausen Sea and Marguerite Bay during spring-summer 2000/2001, whereas E. superba and E. crystallorophias had a longer term response and showed increased recruitment in fall 2002. There were no clear associations between the distribution of zooplankton and environmental conditions in fall; however there was a significant relationship between chlorophyll concentrations in the Bellingshausen Sea during the preceding spring and zooplankton patterns during fall.

The distribution, abundance, chemical composition, metabolism, and feeding ecology of the tentaculate ctenophore, Callianira antarctica (Chun 1897), were investigated during austral winter 2001and autumn & winter 2002, in the vicinity of Marguerite Bay west of the Antarctic Peninsula. Callianira antarctica had a widespread distribution during autumn and winter, and variable abundance (0.02 to 2.6 ind. m-2) during winter 2001 associated with specific circulation features. Size frequency distributions for autumn and winter suggest that more than half of the C. antarctica population may have experienced 'degrowth' during winter due to low food availability. Callianira antarctica is a fairly robust ctenophore with geometric mean (geomean) carbon (C) and nitrogen (N) values of 8.41 and 1.83% dry weight (DW), respectively. Winter oxygen consumption and ammonium excretion rates ranged from 0.059 to 0.410 micro l O2 [mg DW]-1 h-1 and 0.60 to 31.1 µg-at N [g DW]-1 h-1, respectively, at 0oC. Daily minimum maintenance rations based on respiration experiments were 2.7% to 3.6% of the total body carbon (TBC) for small ctenophores, and 1.4% to 1.9% TBC for larger ctenophores. Calanoid copepods and larval and juvenile Antarctic krill were offered to ctenophores in incubation experiments. Digestion times were variable, lasting 8 to 20 h, and were independent of ctenophore size and dependent on number and type of prey. Gut content analysis from one autumn and two winter seasons indicated C. antarctica preyed on both copepods and krill in situ, with an increased dependence on larval krill during winter. Lipid biomarker analysis on C. antarctica and their potential prey confirmed these results. Divers observed aggregations of C. antarctica passively drifting with tentacles extended near dense concentrations of larval Euphausia superba during winter. These observations along with gut content and lipid biomarker analysis suggest that larval krill is an important prey item for C. antarctica during winter.

The Antarctic Circumpolar Current (ACC) is well known for its multiple bands with large meridional property gradients in the upper waters, each associated with a deep-reaching current core. A revised nineteen-year time series (1992?2011) of altimeter data from the CNES/CLS AVISO is analyzed to identify and trace the spatial distribution of ACC fronts. Specific contours of sea surface height (SSH) are selected within narrow continuous bands of relative maxima SSH slope in the Southwest Atlantic Ocean sector, where they closely follow the distribution of ACC fronts derived from inspection of concurrent high-resolution profile data at hydrographic stations. When applied to the full circumpolar belt, the frontal distribution derived from these new altimeter-based indicators also agrees well with the traces of current jets and in-situ dynamic height fields calculated from concurrent Argo profile data. The temporal variability of ACC fronts is analyzed in relation to dominant modes of atmospheric forcing variability in the Southern Ocean. All three ACC fronts have experienced large seasonal to decadal variability throughout the satellite altimetry era. The general seasonal tendency for each of these jets, with respect to long-term mean positions, is to be located farther to the south during the austral summer and to north in the winter. Circumpolar-mean annual frontal locations show a consistent linear trend of southward migration. However, the estimated decadal variability of the frontal distributions is highly localized, and due to selective response mechanisms to atmospheric variability. A persistent poleward drift of ACC fronts is observed in the Indian sector consistent with increasing sea surface temperature trends. In contrast, a vacillation in the meridional location of ACC fronts is observed in the Pacific sector in association to minor sea surface cooling trends. Therefore, unlike in the Indian sector, the regional Pacific Ocean response is significantly sensitive to dominant atmospheric forcing indices. Mesoscale eddies derived from instabilities at strong current cores are successfully identified with specific SSH gradient criteria. The new estimates of rings population in the Southern Ocean are tightly linked to interannual to decadal atmospheric variability. Increased number of mesoscale eddies correlate with positive SAM forcing about two years earlier, or negative ENSO forcing two to three months earlier. These cross-correlations might explain a prominent peak in rings abundance estimated during 2000 and 2001, and the short-lived maximum that appeared in 2010. There are no persistent trends in the estimated sea surface slope across Drake Passage, and therefore neither in the transport of the ACC. High cross-correlation between the abundance of mesoscale eddies and atmospheric forcing suggests that the overall ACC system is in an eddy-saturated state. However, Drake Passage positive sea level slope anomalies were two-year lagged with negative SAM forcing and with positive ENSO events. These regional responses are characteristic of eastward-propagating signals from a buoyancy-dominated Pacific sector of the Southern Ocean.

Observations of Antarctic sea ice thickness are sporadic in space and time, hindering knowledge of its variability. A proxy based on stage of development data from the National Ice Center (NIC) weekly operational charts is used to create a high-resolution time series of sea ice concentration, thickness and volume for 2000-2009. Record-length mean thickness and volume of Antarctic sea ice are 66.7 cm and 7.7 x10^3 km^3. The mean growth and decay seasons in the Southern Ocean and in the Ross sector are 210 days and 155 days, but at least at least one week shorter (growth) and longer (decay) in the Amundsen/Bellingshausen sector. Over 90% of the Antarctic continental shelf is covered with sea ice for 3-5 months, and for 2 to 4 months longer periods in the Amundsen/Bellingshausen and Ross sectors. Yearly mean sea ice area (extent) in the Southern Ocean increased at a rate of 0.71 x 10^6 km^2/decade (0.70 x 10^6 km^2/decade), equivalent to a 7.7 %/decade (6.3 %/decade) rise. A comparable trend of 9.1 %/decade (8.5 %/decade) is estimated in the Ross sector, at 0.21 x 10^6 km2/decade (0.23 x 10^6 km2/decade). The opposite trend is found in the Amundsen/Bellingshausen sector: a -0.15 x 10^6 km^2/decade (-0.17 x 10^6 km^2/decade) decline, or -14.6 %/decade (-13.4 %/decade). The estimated annual increase of Antarctic sea ice thickness is 22.6 cm/decade (49.2 %/decade) and of volume is 3.78 x 10^3 km^3/decade (68.3 %/decade). The Ross sector showed similar trends for thickness, at 23.8 cm/decade (47.0 %/decade), and volume, at 1.11 x 10^3 km^3/decade (75.8 %/decade). Thickness has increased in the Amundsen/Bellingshausen sector, 20.7 cm/decade (44.8 %/decade), but with a less pronounced volume rise of 0.17 x10^3 km^3/decade (26.0 %/decade). Monthly sea ice thickness anomalies show a weak response to the El Nino Southern Oscillation (ENSO) index. A strong positive response is observed in 2008 when a negative a negative ENSO index compounded to a positive Southern Annular Mode (SAM) index. Therefore the estimated increase of sea ice thickness in the Southern Ocean could be attributed to the prevailing atmospheric conditions with a positive SAM phase over the past decade.

Previous studies have suggested that ocean bottom pressure (OBP) can be used to measure the transport variability of the Antarctic Circumpolar Current (ACC). The OBP observations from the Gravity Recovery and Climate Experiment (GRACE) are used to calculate transport along the choke point between Antarctica and Australia. Statistical analysis will be conducted to determine the uncertainty of the GRACE observations using a simulated data set. There has been some evidence to suggest that Southern Hemisphere winds and the Southern Annular Mode (SAM) or the Antarctic Oscillation (AAO) play a significant role in accelerating/decelerating ACC transport, along with some contribution from buoyancy forcing. We will examine whether average zonal wind stress, wind stress curl, local zonal winds, or the SAM are representative of the low frequency zonal mass transport variability. Preliminary studies suggest that seasonal variation in transport across the Australia-Antarctica choke point is driven by winds along and north of the northern front of the ACC, the Sub Tropical front (STF). It also appears that interannual variations in transport are related to wind variations centered south of the Sub Antarctic Front (SAF). We have observed a strong negative correlation/positive correlation across the STF of the ACC in the Indian Ocean, which suggests wind stress curl may also be responsible for transport variations.

The western Antarctic Peninsula (WAP) is a hotspot of climatic and oceanographic change, with a 6°C rise in winter atmospheric temperatures and >1°C warming of the surface ocean since the 1950s. These trends are having a profound impact on the physical environment at the WAP, with widespread glacial retreat, a 40% decline in sea ice coverage and intensification of deep water upwelling. The main objective of this study is to assess the response of phytoplankton productivity to these changes, and implications for the marine carbon and nitrogen cycles in the WAP coastal zone. An extensive suite of biogeochemical and physical oceanographic data was collected over five austral summer growing seasons in northern Marguerite Bay between 2004 and 2010. Concentrations and isotopic compositions ( 15N, 13C, 14C) of dissolved nitrate, dissolved inorganic carbon species, particulate nitrogen, organic carbon and chlorophyll a are used in the context of a substantial ancillary dataset to investigate nutrient supply, phytoplankton productivity and nutrient uptake, export flux and the fate of organic material, and the factors underpinning pronounced seasonal and interannual variability. High-resolution biogeochemical time-series data for surface and underlying seawater, sea ice brine, sediment trap material and coretop sediments allow detailed examination of carbon and nitrogen cycle processes under contrasting oceanographic conditions and the interaction between these marine processes and air-sea exchange of climate-relevant CO2. This study shows that the WAP marine environment is currently a summertime sink for atmospheric CO2 in most years due to high productivity and biological carbon uptake sufficient to offset the CO2 supply from circumpolar deep waters, which act as a persistent source of heat, nutrients and CO2 across the shelf. For the first time, CO2 sink/source behaviour is parameterised in terms of nitrate utilisation, by exploiting the relationship between CO2 and nitrate concentrations, and deriving the nitrate depletion at which surface ocean CO2 is undersaturated relative to atmosphere and carbon sink behaviour is achieved. This could have vast utility in examining CO2 sink/source dynamics over greater spatial and temporal scales than by direct CO2 measurements, of which availability is more limited. This study documents abrupt changes in phytoplankton productivity, nitrate utilisation and biological CO2 uptake during a period of rapid sea ice decline. In fact, nitrate utilisation, particulate organic matter production and biological CO2 uptake all decrease by at least 50 % between a sea ice-influenced, high productivity season and one of low sea ice and low productivity. The key driver of interannual variability in production and export of organic material is found to be upper ocean stratification and its regulation of light availability to phytoplankton. Productivity, CO2 uptake and export are maximal when stratification is sufficient to provide a stable well-lit surface environment for phytoplankton growth, but with some degree of mixing to promote export of suspended organic matter. Strong stratification causes intense initial production, but retention of suspended organic particles in the surface ocean induces a self-shading effect, and overall productivity, CO2 uptake and export fluxes are low. When stratification is weak, mixing of phytoplankton over a larger depth range exposes cells to a wider range of light levels and reduces photosynthetic efficiency, thus total productivity and CO2 uptake. A conceptual model is developed here, which attempts to describe the mechanism by which sea ice dynamics exert the principal control on stratification and therefore productivity and CO2 uptake at the WAP, with potential application to other regions of the Antarctic continental shelf. Although meteoric waters (glacial melt and precipitation) are more prevalent in surface waters throughout the study, sea ice meltwater variability is driven by large and rapid spring/early summer pulses, which stabilise the upper ocean and initiate phytoplankton growth. The timing and magnitude of these sea ice melt pulses then exert the key control on stratification and seasonal productivity. In a low sea ice year of this study, the sea ice trigger mechanism was absent and productivity was low. This strongly suggests that ongoing sea ice decline at the WAP and greater frequency of such low sea ice years is likely to drive a dramatic reduction in productivity and export, which would substantially reduce the capacity of the summertime CO2 sink in this region. Ongoing warming and ecosystem change are thus likely to have severe impacts on net CO2 sink/source behaviour at the WAP over the annual cycle, and the role of the Southern Ocean in regulating atmospheric CO2 and global climate. Finally, factors influencing the stable isotopic signature of particulate organic carbon ( 13CPOC), a common paleo-proxy, are assessed. 13CPOC is greatly influenced by seasonal shifts in diatom assemblages and isotopically heavy sea ice material, so cannot be used as a robust proxy for ambient CO2 in the coastal Southern Ocean.

Microbes fulfill important ecosystem functions by contributing as drivers of global nutrient cycles. Their distribution patterns are mainly controlled by environmental heterogeneities. So far, little is known about the mode of action of particular environmental drivers on the microbiota, particularly in low productivity habitats. The aim of this thesis was to investigate the relationships between local environmental drivers and the microbial responses at the level of communities, individuals and realized function, using three structurally different model habitats sharing the feature of overall low productivity. Using a hypothesis-based approach and extensive 16S rRNA amplicon mapping of bacterioplankton colonizing the polar Southern Ocean, I identified how the seasonal formation of open-water polynyas and coupled phytoplankton production affected the diversity of surface bacterial communities and resulted in a cascading effect influencing the underlying dark polar water masses. Additional laboratory experiments, with cultures exposed to light, resulted in reduction in alpha diversity and promoted opportunistic populations with most bacterial populations thriving in the cultures typically reflected the dominants in situ. Furthermore it was experimentally tested how induced cyclic water table fluctuations shaping environmental heterogeneity in a constructed wetland on temporal scale, by directly affecting redox conditions. Twelve months of water table fluctuations resulted in enhanced microbial biomass, however a shift in community composition did not lead to a significant increase in pollutant removal efficiency when compared to a static control wetland. I detected phyla that have previously been proposed as key players in anaerobic benzene break-down using a protocol that was developed for single cell activity screening using isotope-substrate uptake and microautoradiography combined with taxonomic identification based on fluorescent in situ hybridization targeting the 16S rRNA. Eventually, I provide an example of how anthropogenic pollution with polyaromatic hydrocarbons induced a strong environmental filtering on intrinsic microbial communities in lake sediments. In conclusion, my studies reveal that microorganisms residing in low productivity habitats are greatly influenced by environmental heterogeneity across both spatial and temporal scales. However, such variation in community composition or overall abundance does not always translate to altered community function.