The Agulhas Undercurrent Experiment took place in February-March 2003 off the east coast of South Africa and included 112 CTD and LADCP casts along four cross-slope sections and three offshore sections. Direct absolute velocities in the Agulhas Current show a narrow and swift current, 180 km wide and up to 2 m s-1 in speed, that deepens as it flows south, eventually detaching from the continental slope at 36ºS. Results also show the northward Agulhas Undercurrent against the continental slope, beneath the Agulhas Current with peak velocities of 10 cm s-1. Several mesoscale cyclonic eddies extending down to the intermediate layer were sampled during the survey, in particular a shear-edge eddy inshore of the Agulhas Current at 36ºS. A deep water anticyclonic eddy was found for the first time in this region centered at 2800 m in the northward flowing North Atlantic Deep Water (NADW) layer. Anomalous water properties reveal that it was formed in the Agulhas Retroflection region and may have been generated by the coupling of a deep Agulhas Ring with the NADW slope current in the SE Atlantic and later entrained into the deep flow of the Agulhas Return Current, until ejected in the Agulhas Current region by localized recirculations in the deep layers of the Agulhas Current system. An inverse model was applied to the hydrographic and LADCP data; results show that the Agulhas Current had a considerably higher transport of 103 Sv at the historical 32ºS section than earlier estimates, consistent with altimetry time series for the region. The growth of the Agulhas Current transport is given primarily by the Sverdrup transport from the supergyre connecting the southern Pacific and Indian Oceans, and the Indonesian Throughflow and Indian Ocean overturning need to be included to account for the total transport. The bulk of the Agulhas Current transport is concentrated in the thermocline layer in the cross-sections and in the intermediate layer in the offshore sections. Inshore of the Agulhas Current core, mixing is inhibited from the surface to the thermocline layers, with no transport growth downstream. Cross-stream mixing does appear to occur in the intermediate layer. The Mozambique Channel and East Madagascar Current appear to have similar contributions as sources to the Agulhas Current at the northern most section of 16 Sv each, with the Indian Ocean wind-driven sub-gyre contribution increasing as the current flows southward. In the intermediate layer, Red Sea Water is actively mixing with Antarctic Intermediate Water when eddies are present. Red Sea Water appears to advect in the form of parcels and not as a continuous flow. Results also suggest the occurrence of small localized recirculations in the deep layers. In the deepest layer of lower NADW the flow is upwelling into the overlaying layer due to the shallowing topography at the northern most section.

The laser geodetic satellites Lageos and Starlette exhibit residual orbital motion with an unexplained seasonal component. In addition, recognized polar motion excitation sources do not account for a large portion of observed polar motion. It is hypothesized that air and ocean mass redistribution is the primary source of seasonal perturbations in satellite motion, and that wind-driven ocean mass redistribution is a major source for polar motion excitation. Average monthly variations in zonal spherical harmonic geopotential coefficients are estimated from NMC air pressure for 1958 through 1973, and from variations in continental water storage predicted by a global hydrologic model. These coefficients are used to predict average monthly perturbations in the longitude of the ascending node ([Omega]) for Lageos and Starlette, and in the eccentricity vector ([Psi]) for Starlette. WMO monthly air pressures and twice-daily Navy sea level pressures are used to predict time series of [Omega] and [Psi] perturbations for Lageos during 1976 through 1985, and for Starlette during 1980 through 1983. In addition, the Hellerman and Rosenstein wind stress field for world oceans and the Gill-Niiler bottom pressure equation are used to estimate annual and semi-annual ocean mass redistribution, and to predict polar motion excitation vectors and Lageos [Omega] perturbations. Comparison of predicted [Omega] and [Psi] perturbations with observed Lageos and Starlette behavior indicate that air pressure may be responsible for much of the unmodeled seasonal variation in the Earth's geopotential. In contrast, the water storage contribution is very small. Year-to-year variability in the observed Lageos and Starlette [Omega] times series is well matched by predicted perturbations. Even after the removal of annual and semi-annual components, significant coherence remains between predicted and observed [Omega] time series for both Lageos and Starlette at periods of less than one year. Comparison of predicted polar motion with ILS observations suggest that the effect of ocean mass redistribution is significant, and second only to air pressure in magnitude. Lageos [Omega] perturbations predicted from ocean mass redistribution indicate that non-isostatic sea level fluctuations should be readily observable by satellite laser ranging. / text

No description available.

Thesis (Ph.D.)--Flinders University, School of Chemistry, Physics and Earth Sciences. / Typescript bound. Includes bibliographical references: (leaves167-173) Also available online.

Thesis (Ph. D.)--Ohio State University, 2008.

Made available in DSpace on 2015-06-17T19:33:59Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-03-24. Added 1 bitstream(s) on 2015-06-18T12:47:40Z : No. of bitstreams: 1 000825926.pdf: 7141282 bytes, checksum: 32bb0e8b499321c636f40eef71e9f402 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Fundação para o Desenvolvimento da UNESP (FUNDUNESP) / FAPESP: 2009/54672-4 / FUNDUNESP: 1214/2010-DFP

Orientador: Adilson Fransozo / Coorientador: Fúlvio Aurélio de Morais Freire / Banca: Gustavo Monteiro Teixeira / Banca: Giovana Bertini / Banca: Valter José Gobo / Banca: Rogério Caetano da Costa / Resumo: Não disponível / Abstract: Not available / Doutor

A formação de águas profundas na Antártica afeta diretamente o clima global, uma vez que este processo conecta os ramos superior e inferior da circulação termohalina global (MOC). Avaliar os impactos das mudanças climáticas nestes processos é importante para compreensão do transporte global de calor pelos oceanos e para realização de projeções climáticas. Aplicando a forçante interanual Coordinated Ocean-Ice Reference (CORE), foi realizada uma simulação de 60 anos (1948-2007) utilizando o ROMS com módulos de gelo marinho e plataforma de gelo ativos. Uma rodada preliminar de 100 anos foi realizada com forçante do ano normal CORE, para gerar campos estáveis de inicialização da rodada interanual. Para ambos os experimentos adotou-se uma grade circumpolar periódica com resolução variável, alcançando cerca de 5 km na borda sul. Para investigar as massas de água foi aplicada a Análise Multiparamétrica Ótima - OMP. As principais massas de água do Mar de Ross foram identificadas: Água de Superfície Antártica (AASW), Água Circumpolar Profunda (CDW), Água de Fundo Antártica (AABW) e Água de Plataforma (SW), posteriormente separadas em Água da Plataforma de Gelo (ISW) e Água de Plataforma de Alta Salinidade (HSSW). Os resultados são consistentes com observações prévias (Bergamasco, 2002; Orsi & Wiederwohl, 2009; Budillon, 2011). A simulação interanual sugere que o Oceano Austral vem sofrendo um processo de aquecimento e diminuição de salinidade. Houve um aumento do calor advectado pela CDW e uma diminuição da salinidade das águas de plataforma e da AABW, consistente com as observações de Johnson & Doney (2006). A capacidade do modelo regional ROMS de reproduzir as águas de plataforma ISW, HSSW e a AABW é uma importante contribuição para estudos climáticos, visto que os modelos globais não conseguem representar tais processos. A inclusão de parametrizações explícitas dos processos de gelo marinho e plataforma de gelo capacita o ROMS para reproduzir os processos associados a criosfera, possibilitando a obtenção de projeções mais realísticas. / Dense water formation around Antarctica is recognized as a significant process that significantly impacts the global climate, since that\'s where the linkage between the upper and lower limbs of Global Thermohaline Circulation takes place. Assessing whether these processes may be affected by rapid climate changes and all the eventual feedbacks is crucial to fully understand the ocean heat transport and to provide quality future climate projections. Applying the Coordinated Ocean-Ice Reference (CORE) interannual forcing we have run a 50-year simulation (1948-2007) using ROMS with a new sea ice/ice shelf thermodynamics module. Another 100-year simulation forced with CORE normal year was previously run to provide stable starting fields. The normal year consists of single annual cycle of all the data that are representative of climatological conditions over decades and can be applied repeatedly for as many years of model integration as necessary. The 60-year forcing has interannually varying data from 1948 to 2007, which allows validation of model output with ocean observations. Both experiments employed a periodic circumpolar variable resolution grid reaching less than 5 km at the southern border. By applying the OMP water masses separating scheme, we were able to identify the main Ross Sea water masses: Antarctic Surface Water (AASW), Circumpolar Deep Water (CDW), Antarctic Bottom Water (AABW) and Shelf Water (SW), further separated into Ice Shelf Water (ISW) and High Salinity Shelf Water (HSSW). Results are consistent with previous observational studies (Bergamasco, 2002; Orsi & Wiederwohl, 2009; Budillon, 2011). The interannual simulation indicates that the Southern Ocean is becoming warmer and less salty. The CDW poleward heat transport increased while shelf waters salinity as well as the AABW salinity decreased during the simulation period, consistent with Johnson & Doney (2006), who have reported the export of less dense AABW. ROMS capability to represent ISW, HSSW and AABW is an important contribution to climate studies, since IPCC class models seem unable to provide reliable representations of such important processes, which may lead to projections of more realistic scenarios. This is significantly improved in this study by including more explicit sea ice/ice shelf parameretization. ROMS is able to reproduce cryosphere-linked mechanisms of dense water formation around Antarctica.

A formação de águas profundas na Antártica afeta diretamente o clima global, uma vez que este processo conecta os ramos superior e inferior da circulação termohalina global (MOC). Avaliar os impactos das mudanças climáticas nestes processos é importante para compreensão do transporte global de calor pelos oceanos e para realização de projeções climáticas. Aplicando a forçante interanual Coordinated Ocean-Ice Reference (CORE), foi realizada uma simulação de 60 anos (1948-2007) utilizando o ROMS com módulos de gelo marinho e plataforma de gelo ativos. Uma rodada preliminar de 100 anos foi realizada com forçante do ano normal CORE, para gerar campos estáveis de inicialização da rodada interanual. Para ambos os experimentos adotou-se uma grade circumpolar periódica com resolução variável, alcançando cerca de 5 km na borda sul. Para investigar as massas de água foi aplicada a Análise Multiparamétrica Ótima - OMP. As principais massas de água do Mar de Ross foram identificadas: Água de Superfície Antártica (AASW), Água Circumpolar Profunda (CDW), Água de Fundo Antártica (AABW) e Água de Plataforma (SW), posteriormente separadas em Água da Plataforma de Gelo (ISW) e Água de Plataforma de Alta Salinidade (HSSW). Os resultados são consistentes com observações prévias (Bergamasco, 2002; Orsi & Wiederwohl, 2009; Budillon, 2011). A simulação interanual sugere que o Oceano Austral vem sofrendo um processo de aquecimento e diminuição de salinidade. Houve um aumento do calor advectado pela CDW e uma diminuição da salinidade das águas de plataforma e da AABW, consistente com as observações de Johnson & Doney (2006). A capacidade do modelo regional ROMS de reproduzir as águas de plataforma ISW, HSSW e a AABW é uma importante contribuição para estudos climáticos, visto que os modelos globais não conseguem representar tais processos. A inclusão de parametrizações explícitas dos processos de gelo marinho e plataforma de gelo capacita o ROMS para reproduzir os processos associados a criosfera, possibilitando a obtenção de projeções mais realísticas. / Dense water formation around Antarctica is recognized as a significant process that significantly impacts the global climate, since that\'s where the linkage between the upper and lower limbs of Global Thermohaline Circulation takes place. Assessing whether these processes may be affected by rapid climate changes and all the eventual feedbacks is crucial to fully understand the ocean heat transport and to provide quality future climate projections. Applying the Coordinated Ocean-Ice Reference (CORE) interannual forcing we have run a 50-year simulation (1948-2007) using ROMS with a new sea ice/ice shelf thermodynamics module. Another 100-year simulation forced with CORE normal year was previously run to provide stable starting fields. The normal year consists of single annual cycle of all the data that are representative of climatological conditions over decades and can be applied repeatedly for as many years of model integration as necessary. The 60-year forcing has interannually varying data from 1948 to 2007, which allows validation of model output with ocean observations. Both experiments employed a periodic circumpolar variable resolution grid reaching less than 5 km at the southern border. By applying the OMP water masses separating scheme, we were able to identify the main Ross Sea water masses: Antarctic Surface Water (AASW), Circumpolar Deep Water (CDW), Antarctic Bottom Water (AABW) and Shelf Water (SW), further separated into Ice Shelf Water (ISW) and High Salinity Shelf Water (HSSW). Results are consistent with previous observational studies (Bergamasco, 2002; Orsi & Wiederwohl, 2009; Budillon, 2011). The interannual simulation indicates that the Southern Ocean is becoming warmer and less salty. The CDW poleward heat transport increased while shelf waters salinity as well as the AABW salinity decreased during the simulation period, consistent with Johnson & Doney (2006), who have reported the export of less dense AABW. ROMS capability to represent ISW, HSSW and AABW is an important contribution to climate studies, since IPCC class models seem unable to provide reliable representations of such important processes, which may lead to projections of more realistic scenarios. This is significantly improved in this study by including more explicit sea ice/ice shelf parameretization. ROMS is able to reproduce cryosphere-linked mechanisms of dense water formation around Antarctica.

La dorsale de Reykjanes est une structure topographique majeure de l’océan Atlantique Nord qui s’étend de l’Islande à la zone de fracture de Charlie Gibbs. Située entre le bassin d’Islande et la mer d’Irminger, la dorsale de Reykjanes influence fortement la circulation du gyre subpolaire et est une porte d’entrée vers les zones de convection profondes. Cependant, la circulation et la répartition des masses d’eau à travers la dorsale de Reykjanes n’ont jamais été directement quantifiées, de sorte que la caractérisation de la connexion entre le bassin d’Islande et la mer d’Irminger est encore incomplète. Dans le cadre du projet « Reykjanes Ridge Experiment », nous avons été capables d’analyser la circulation autour, au-dessus et à travers la dorsale de Reykjanes. Essentiellement à partir de sections hydrographiques perpendiculaires et le long de l’axe de la dorsale, l’objectif de cette thèse a été de quantifier et caractériser la circulation 3-D et les propriétés des courants qui longent et traversent la dorsale de Reykjanes. Nous avons commencé par quantifier précisément le transport géostrophique à travers les sections, ce qui a permis d’améliorer le traitement des données S-ADCP. A travers la dorsale de Reykjanes, l’intensité de la branche du gyre subpolaire qui rejoint la mer d’Irminger a été estimée à 21.9 + 2.5 Sv en Juin – Juillet, avec des intensifications dans la zone de fracture Bight (BFZ) et à 59 – 62°N. Dans la BFZ, les masses d’eau profondes sont influencées par la bathymétrie, de sorte que leurs propriétés hydrologiques se modifient lorsqu’elles traversent la dorsale de Reykjanes. Enfin, la bathymétrie et la circulation horizontale cyclonique du bassin d’Islande contrôlent les courants qui longent la dorsale en bloquant certaines masses d’eau, et donc sont à l’origine de la répartition de ces masses d’eau le long de la dorsale. En plus des masses d’eau du Bassin d’Islande, le Courant d’Irminger comprend également des masses d’eau qui proviennent de la mer d’Irminger. / The Reykjanes Ridge is a major topographic feature of the North-Atlantic Ocean that extends from Iceland to the Charlie Gibbs Fracture Zone. Located between the Iceland Basin and the Irminger Sea, the Reykjanes Ridge strongly influences the subpolar gyre circulation and is a gate toward the deep convection areas. However, the circulation and distribution across the Reykjanes Ridge has never been directly quantified such that the characterization of the connection between the Iceland Basin and the Irminger Sea is still incomplete. As part of the Reykjanes Ridge Experiment project, we were able to analyze the circulation around, above and across the Reykjanes Ridge. Mainly based on hydrographic sections along and perpendicular to the ridge axis, the aim of this PhD thesis was thus to characterize the 3-D circulation and properties of the flow along and across the Reykjanes Ridge.We started by accurately quantifying geostrophic transports across the sections, which led to improvements in the treatment of S-ADCP data. Across the Reykjanes Ridge, the intensity of the wesward branch of the subpolar gyre was estimated at21.9 + 2.5 Sv in June – July 2015 with intensifications at the Bight Fracture Zone (BFZ) and at 59 – 62°N. At the BFZ, overflow waters are influenced by the bathymetry such as their hydrological properties evolve as they cross the Reykjanes Ridge. Finally, both the bathymetry and the cyclonic horizontal circulation of the Iceland Basin regulate the evoluton of the along-ridge flows by blocking water masses, and thus shaping the water mass distribution over the Reykjanes Ridge. In addition to waters from the crossridge flow, the Irminger Current incorporates waters from the center of the Irminger Sea.