The Antarctic climate has undergone complex changes over the last fifty years, driven largely by stratospheric ozone depletion. By the end of this century, under the current trajectory of anthropogenic emissions, the climate of Antarctica is projected to be significantly wetter, warmer and prone to the collapse of ice shelves and loss of sea ice cover. The overarching aim of this thesis is to increase our understanding of recent and projected Antarctic climate change and its drivers. We also investigate the potential global implications of these changes and show that the effects will not be limited to the southern high latitudes. In the first half, we investigate the drivers of Antarctic climate change over the observational period. Specifically, we study the influence of the stratosphere on the southern high latitude surface climate, through stratosphere-troposphere dynamic coupling as well as stratospheric ozone depletion. We examine the impact of these on the Amundsen Sea Low, a key circulation feature near West Antarctica. We demonstrate using reanalysis that stratospheric heat flux extremes are linked to high latitude tropospheric anomalies in the Amundsen Sea region. During extreme negative (positive) events there is a westward (eastward) shift of the Amundsen Sea Low, a warming (cooling) and increase (decrease) of geopotential height over the Amundsen and Bellingshausen Seas. We find that most CMIP5 models are not able to capture this relationship. Next, we demonstrate that, since 1965, stratospheric ozone depletion has acted to deepen the Amundsen Sea Low in austral summer by 1 hPa per decade. This result was consistent across two different comprehensive climate models, each with very different model physics and climate sensitivity. It must be noted that the ozone depletion signal on the Amundsen Sea Low is small compared to the internal climate variability in this region. Using ensembles of model integrations and analysing them over the full period of ozone depletion (which started a couple of decades before the satellite era) is necessary to detect a robust signal. In the second half, we investigate the effects of future Antarctic climate change, specifically the effects of projected sea ice loss over the coming century. Climate model simulations are used to isolate the effect of end-of-the-century Antarctic sea ice loss which is compared and contrasted with the effects of projected Arctic sea ice loss. We first study the effects of projected Antarctic sea ice loss used atmosphere-only simulations. As for the Arctic, results indicated that Antarctic sea ice loss will act to shift the tropospheric jet equatorward, an internal negative feedback to the poleward shift associated with increased greenhouse gases. Antarctic sea ice loss is shown to have an important effect throughout the year whereas Arctic sea ice loss will have more seasonally varying impacts. Building upon these results we the use the same climate model but in a fully coupled setup to study the effects of projected Antarctic sea ice loss on the climate system. We show that both Arctic and Antarctic sea ice loss will have important global effects, causing a ‘mini global warming’ signal. The tropical response to Antarctic sea ice loss is shown to be remarkably similar to that of Arctic sea ice loss, with enhanced warming in the Eastern Tropical Pacific and increased precipitation throughout much of the equatorial Pacific. These results highlight how intimately coupled the Antarctic climate is to the rest of the climate system.

We examine the tides in the Kitikmeot Sea using year-long time-series from moored instrumentation in Dease Strait, and a 3D barotropic numerical tidal model of the region. The in-situ data show strong tidal damping during wintertime seasonal sea ice cover, with a 50-60% reduction in M2 and K1 tidal elevation and 65% reduction in M2 and K1 tidal velocities at the sea ice maximum. We hypothesize the damping largely occurs in Victoria Strait, the eastern gateway of the Kitikmeot Sea, where tidal-induced ridging causes thick, rough ice to accumulate over its shallow sill. Using the numerical model, FVCOM, we independently vary sea ice friction and sea ice thickness, and show that the observed wintertime tidal damping likely requires both very rough ice and a partial sea ice blockage in the sill region. Analysis of the model shows different dynamics and dissipation of the dominant M2 and K1 tides. Both M2 and K1 tides are dominated by the Atlantic tides entering through Victoria Strait. Arctic tides, entering from the west, have a minor, but significant, contribution to the M2 tide. Overall, the K1 tide, after 19% dissipation in Victoria Strait and 24% in adjoining bays, propagates far into the region and behaves as a Helmholtz resonator in Dease Strait and Coronation Gulf. In contrast, 92% of the M2 tidal energy does not reach Dease Strait because, in addition to dissipation in Victoria Strait (29%), it is significantly diverted into adjoining bays and around an amphidrome in eastern Queen Maud Gulf. The K1 tide, with double the wavelength of the M2 tide, is less diverted. / Graduate / 2020-07-22

Thesis (Ocean E)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING / Includes bibliographical references. / by Carl Alzen Wales. / Ocean E

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING / Includes bibliographical references. / by Yie-Ming Chen. / M.S.

La banquise, qui couvre de larges étendues de l’océan près des pôles, est une composante majeure du climat. Le réchauffement de la planète entraîne sa fonte massive, en particulier en Arctique.Là où l’extension de la banquise diminue, l’augmentation du fetch est associée à une élévation de la hauteur des vagues, laissant penser que les effets liés aux interactions vagues-glace pourraient s’accroître dans le futur. L’évolution rapide de la banquise associée à l’intensification des activités humaines dans les régions polaires pressent à améliorer notre connaissance de ces interactions.La banquise atténue les vagues. Elles peuvent néanmoins s’y propager et briser la glace sur de longues distances. L’atténuation dépend des propriétés de la glace comme l’épaisseur, la taille des plaques... Les plaques de glace une fois cassées sont plus susceptibles de dériver et de fondre. En outre, lors de l’atténuation, les plaques sont poussées dans la direction de propagation des vagues.Une représentation simple de la banquise dans un modèle de vagues intégrant une distribution de la taille des plaques nous a permis de montrer l’importance des mécanismes dissipatifs dans l’atténuation, notamment ceux induits par la flexion de la glace.Après avoir été validé, ce modèle a été couplé à un modèle de glace. La taille des plaques est échangée et utilisée dans le calcul de la fonte latérale. La force exercée par les vagues sur la banquise est également envoyée depuis le modèle de vagues. En été, cette force compacte la glace et tend à diminuer la fonte, augmentant significativement la température et la salinité des eaux de surface au bord de la banquise. / Sea ice, which covers most of the ocean near the poles, is a key component of the climate system. Global warming is driving its massive melting, especially in the Arctic. Where sea ice cover decreases, fetch increases leading to more energetic sea states. This means potentially enhanced wavesice interactions effects in the future. The quick evolution of sea ice extent and volume combined with the intensification of human activities in polar regions urge us to improve our understanding of waves-ice interactions.Sea ice attenuates waves. They can however propagate through it and break it far into the ice cover. Attenuation depends on ice properties such as floe size, thickness, etc. Once broken, resulting floes are more likely to drift and melt. In addition, wave attenuation yields a force which pushes the floes in the direction of wave propagation.A simplified representation of sea ice, including a floe size distribution, has been incorporated in a wave model.It allows us to show the important contribution of dissipative mechanisms in the wave attenuation, especially those induced by the bending of the ice plates. After validation, the modified wave model is coupled to an ice model. The floe size distribution is exchanged in the coupled framework and used in ice lateral melt computation. The force exerted by the waves on the ice floes is sent from the wave model and is shown to compact sea ice in summer. This reduces the melting and significantly increases the temperature and salinity in the surface ocean close to the ice edge.

Esta dissertação revisa as mudanças ambientais que ocorreram no Ártico ao longo das últimas décadas e analisa as suas consequências geopolíticas. O interesse na região por parte das nações árticas (Canadá, Dinamarca - Groenlândia, EUA, Finlândia, Islândia, Noruega, Rússia e Suécia) aumentou, principalmente devido ao volume de hidrocarbonetos disponível na região, estimado em 13% do petróleo e 30% do gás natural ainda não descobertos. Durante os últimos 50 anos, o Ártico mostrou a mais rápida tendência de aquecimento no mundo, duas vezes mais que a média mundial, isso tem causado rápidas mudanças ambientais, como a redução do volume das geleiras, o que contribuiu para o aumento do nível médio dos mares; o degelo do permafrost, que libera grandes quantidades de CO2 e CH4 na atmosfera, intensificando o efeito estufa; a migração da vegetação em direção ao Norte, alterando a disponibilidade de alimentos e os padrões de migração dos animais; o aumento da temperatura da superfície do mar, o que pode causar a migração de cardumes de peixes para áreas mais frias. No entanto, a mudança mais rápida naquele ambiente, e a que mais chama a atenção, é a redução da área coberta por gelo marinho no verão. Essa redução favorece a exploração de recursos naturais e também abre o Oceano Ártico à navegação no verão (ou seja, a abertura das passagens do Nordeste e do Noroeste). Os países do Ártico desenvolveram estratégias para lidar com novos desafios decorrentes dessas mudanças, todos se comprometeram a trabalhar pela paz e cooperação, mas, na verdade, é evidente um aumento em exercícios militares na região para exercer a soberania regional. Os países com uma costa no Oceano Ártico (Canadá, Dinamarca, EUA, Noruega e Rússia) planejam expandir suas ZEEs (Zonas Económicas Exclusivas) e algumas reivindicações territoriais se sobrepõem, o que pode ser um novo foco de conflito. Além disso, existe um interesse emergente de nações não-árticas (por exemplo, China, Índia e Singapura) que desejam utilizar as novas rotas marítimas e também participar em consórcios para exploração de recursos naturais. O cenário geopolítico é ainda incerto, Canadá e os EUA ainda não chegaram a um acordo sobre a soberania da Passagem do Noroeste, consideradas águas internacionais por este último, e só a Noruega e a Rússia chegaram a um acordo diplomático sobre suas fronteiras marítimas. Considerando que o Ártico está passando por essas rápidas mudanças ambientais e geopolíticas, é aconselhável que o Brasil atue na região, pelo menos para observar os cenários resultantes de tais modificações. Como uma das primeiras ações, sugere-se a assinatura do Tratado de Svalbard, o que daria ao país o acesso a este arquipélago ártico, tanto para a realização de pesquisa científica como para a possível exploração de recursos naturais. / This dissertation reviews the Arctic environmental changes in recent decades and examines their geopolitical consequences. The interest in the region by the Arctic nations (Canada, Denmark - Greenland, Finland, Iceland, Norway, Russia, Sweden and USA) have increased, mainly due to the volume of hydrocarbons available in the region, estimated at 13% of the oil and 30% of the natural gas yet to be discovered. For the last 50 years, the Arctic has shown the fastest warming trend in the world, twice as much as the worldwide mean, this has caused rapid environmental changes such as the shrinkage of glaciers, which contributed to the mean sea level rise; the permafrost thaw, which releases large amounts of CO2 and CH4 in the atmosphere, intensifying the greenhouse effect; the migration of the vegetation towards the North, changing food availability and the migration patterns of animals; the increase of the ocean surface temperature, which may cause the migration of fish shoals to colder areas. However, the most rapid environmental change, which draws the most attention, is the reduction of the sea ice cover area in the summer. Such reduction favours the exploitation of natural resources in the ocean and also opens the Arctic Ocean to navigation in the summer (i.e., opening of the Northeast and the Northwest passages). The Arctic countries have developed strategies to deal with the new challenges arising from these changes, all have promised to work for peace and cooperation, but, in fact, it is apparent an increase in military exercises in the region to exercise regional sovereignty. Countries with an Arctic Ocean coast (Canada, Denmark, Norway, Russia and USA) plan to expand their EEZs (Exclusive Economic Zones) and some claims overlap, which can be a new focus of conflict. Also, there is an emergent interest of non-Arctic nations (e.g., China, India and Singapore) that want to use the new sea routes and also participate in consortia for natural resources exploitation. The geopolitical scenario is still uncertain, Canada and the US have not yet reached an agreement on the sovereignty of the Northwest Passage, considered international waters by the latter, and only Norway and Russia reached a diplomatic agreement on their maritime boundaries. Considering that the Arctic is undergoing these rapid environmental and geopolitical changes, it is advisable that Brazil acts in the region, at least to observe the scenarios resulting from such modifications. As one of the first actions, it is suggested the signing of the Svalbard Treaty, which would give to the country access to this Arctic archipelago, both for conducting scientific research as for possible exploitation of natural resources.

In this thesis, the development and methodology of a new, consolidated BYU/NIC Antarctic Iceberg Tracking Database is presented. The new database combines data from the original BYU daily iceberg tracking database derived from scatterometers, and the National Ice Center's weekly Antarctic iceberg tracking database derived from mostly optical and infrared sensors. Using this data, interpolation methods and statistical analyses of iceberg locations are discussed. The intent of this database is to consolidate iceberg location data in order to increase accessibility to users.Active microwave remote sensing instruments are used to track tabular icebergs and provide a daily estimate of their positions and sizes. A consolidated data set of these positions from several different instruments is valuable to ensure accurate positional data. The scatterometer iceberg positional record began with the Seasat-A Satellite Scatterometer (SASS) and is continued with the Quick Scatterometer (QuikSCAT) and Advanced Scatterometer (ASCAT) data sets.A reliable method of automatically estimating Antarctic iceberg contours and sizes from satellite data is desirable to help better understand patterns in iceberg formation and behavior. Starting from scatterometer images, this thesis develops a method of using the relatively constant backscatter values across the surface of an iceberg to derive a contour of its shape. Contours are then used to find an angle of rotation between images taken on successive days. This method produces size estimates that are within 10% of the area given by the National Ice Center (NIC). The size estimates and rotation angles are included in the new consolidated database.

Spaceborne microwave sensors are capable of estimating various properties of many geophysical phenomena, including the age and extent of Arctic sea ice and the relative soil moisture over land. The measurement and classification of such geophysical phenomena are used to refine climate models, localize and predict drought, and better understand the water cycle. Data from the active Ku-band scatterometers, the Quick Scatterometer (QuikSCAT), and the Oceansat-2 Scatterometer (OSCAT), are here used to classify areas of first-year and multiyear Arctic sea ice using a temporally adaptive threshold on reported radar backscatter values. The result is a 15-year data record of daily ice classification images. An additional ice age data record is produced using the C-band Advanced Scatterometer (ASCAT) and the Special Sensor Microwave Imager Sounder (SSMIS) with an alternate classification methodology based on Bayesian decision theory. The ASCAT/SSMIS classification methodology results in a record which is generally consistent with the QuikSCAT and OSCAT classifications, which conclude in 2014. With multiple ASCAT and SSMIS sensors still operational, the ASCAT/SSMIS ice classifications can continue to be produced into the future. In addition to ice classification, ASCAT is used to estimate the relative surface soil moisture at high-resolution (4.45 — 4.45 km per pixel). The soil moisture estimates are obtained using enhanced resolution image reconstruction techniques and an altered version of the Water Retrieval Package (WARP) algorithm. The high-resolution soil moisture estimates are shown to agree well with the existing lower resolution WARP products while also revealing finer details.

Loss of sea ice due to global warming may affect the phenology and distribution of polar bear (Ursus maritimus) denning by altering access to denning habitats. We examined trends in the selection of maternal denning substrate (land versus sea-ice denning) in the southern Beaufort Sea (SB), addressing the potential influence of summer land-use and fall sea-ice conditions on substrate selection. We developed an algorithm based on statistical process control methods to remotely identify denning bears and estimate denning phenology from temperature sensor data collected on collars deployed 1985–2013 in the SB and Chukchi Sea (CS). We evaluated cub survival relative to den entrance, emergence, and duration, and examined differences in the phenology of land and sea-ice dens. Land denning in the SB was more common during years when ice retreated farther from the coast and off of the continental shelf in September. All SB bears that occupied land prior to denning subsequently denned on land; however, only 29% of denning bears that summered on sea ice denned on land. Den entrance and duration in the SB and CS were similar, although CS bears emerged later. Land dens were occupied longer than those on ice. Bears later observed with cubs remained in dens 23 days longer and emerged from denning 17 days later on average than bears that denned but were subsequently observed without cubs, suggesting that den exit dates are related to cub survival. The increase in land-based denning in the SB when sea ice retreated farther from shore, along with the positive correlation between fall land-use and land denning, suggest that further sea-ice declines may result in continued increases of onshore denning. Growing numbers of denning females along the coast may increase the potential for human-bear interactions.

Measuring hormonal changes is vital for understanding how the social and physical environment influences behaviour, reproduction and survival. Various methods of hormone measurement exist, potentially explaining variation in results across studies; methods should be cross validated to ensure they correlate. I directly compare faecal and plasma hormone measurements (Chapter 2), and use the most suitable endocrine measure to test the Darling hypothesis (Chapter 3) - that breeding is hastened and synchronized in larger colonies due to increased social stimulation (mediated by the endocrine system). Blood and faecal samples were simultaneously collected from individual Adelie penguins (Pygoscelis adeliae) for comparison, and assayed for testosterone and corticosterone (or their metabolites). Sex differences and variability within each measure, and correlation of values across measures were compared. For both hormones, plasma samples showed greater variation than faecal samples. Males had higher corticosterone levels than females, but the difference was only significant in faecal samples. Plasma testosterone, but not faecal testosterone, was significantly higher in males than females. Correlation between sample types was poor overall, and weaker in females than in males; perhaps because measures from plasma represent hormones that are both free and bound to globulins, whereas measures from faeces represent only the free portion. Faecal samples also represent a cumulative measure of hormones over time, as opposed to a plasma 'snapshot' concentration. Faecal sampling appears more suitable for assessing baseline hormone levels. In the second study I examined, over two seasons, whether the timing of breeding varied with colony size; larger colonies present occupants with higher levels of social stimulation and are predicted to show earlier, more synchronous breeding. Baseline faecal hormone levels throughout the breeding season, and survival, were measured to investigate possible proximate and ultimate mechanisms for the results. The influence of environmental variability was examined, by relating the timing of breeding, survival, and endocrine changes to sea ice conditions. Colony size did not influence the timing or synchrony of breeding, survival, or hormone levels within years; perhaps because colonies in an Adelie rookery are not independent from the 'social environment' of adjacent colonies. Across years, synchrony in the smaller rookery was higher than in the larger rookery. The scale of these comparisons may exceed the applicability of the Darling hypothesis. Therefore, no support was found for the Darling hypothesis, at the colony or rookery level, in this species. Higher corticosterone metabolite and lower sex hormone levels in the first season correlated to later breeding and lower survival compared to the second season. This is likely due to the persistence of extensive sea ice conditions late into the first season. Researchers should take care in selecting the most appropriate method of hormone measurement for their question. Future studies testing the Darling hypothesis must carefully select their definition of a colony (i.e. a truly isolated social unit) and the scale at which the hypothesis is tested. Combining endocrine measurements with behavioural, survival, and environmental information allows for a more comprehensive interpretation of animal ecology.