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Der Einfluß eines Seherstroms auf die Ausbreitung langer barotroper Wellen wird untersucht. Der Antarktische Zirkumpolarstrom ist als eine zonale Scherströmung zu betrachten. Wir zeigen auf einer ß-Ebene, daß der Antarktische Zirkumpolarstrom für zonal sich ausbreitende Wellen als Wellenleiter wirkt. Für den linearen Fall des Scherstromes wird die analytische Lösung angegeben. Die gebundenen Wellen sind meridional modal strukturiert und bewegen sich mit einer Gruppengeschwindigkeit von rund 0.02ms·1 von West nach Ost (alle). / We study the influence of a shear current on barotropic long wave propagation. The Antarctic Circumpolar Current can be considered as a sheared zonal flow. We show tht on a ß-plane the Antarctic Circumpolar Current acts as a waveguide for zonally propagating waves. We give the analytical solution for the linear sheared case. The trapped waves are modal structured in the meridional direction and propagate from the West to the East (all) with a group velocity of nearly 0.02ms·1.

Zonal geostrophic velocity fields above 1975 dbar have been estimated for the Southern Ocean from 2004 to 2014 based on sea surface topography observed by Jason altimetry and temperature/salinity measured by Argo autonomous floats. The velocity at 1000 dbar estimated has been validated against Argo drift trajectory at the same pressure level available from the Asia Pacific Data Research Center (APDRC). Errors in mapping of dynamic ocean topography, temperature, and salinity have been quantified using the Southern Ocean State Estimate (SOSE). Analysis of errors reveals significant correlations between depth-dependent and –independent contributions to the integrated transport. Further analysis revealed optimal locations of historical ship casts to compliment the transport time series as observed by Argo. Quantifying the error associated with the historical hydrographic section indicated little benefit in combining hydrographic data obtained from ships. The anticorrelation between depth-dependent and – independent contributions was again significant in sampling by ships. The proposed explanation of the anticorrelation in error is underestimation of reference velocity by attenuation and overestimation of depth-dependent transport by attenuation of the velocity shear.

In this thesis, I describe large-scale and small-scale features of the Antarctic Circumpolar Current (ACC) by merging conductivity-temperature-depth (CTD) data obtained by novel animal-borne sensors with data obtained by more conventional means. Twenty-one CTD-Satellite Relay Data Loggers (CTD-SRDLs) were attached to Southern elephant seals (Mirounga leonina) on South Georgia in 2004 and 2005. This was part of a larger international study (Southern Elephant Seals as Oceanographic Samplers; SEaOS), in which I played a major role in developing the oceanographic approach used to integrate physical data from a range of sources, and the means to link biological findings to oceanographic parameters. The development of animal-borne oceanographic sensors and their potential place within an ocean observing system is reviewed initially. Then, I describe the Series 9000 CTD-SRDL in detail, discussing its performance in the lab and during two field experiences with Southern elephant seals and Weddell seals (Leptonychotes weddellii ). Following this, a detailed study of the ACC frontal system in the South Atlantic is presented that uses merged Argo float data and CTD-SRDL data. The structure of the frontal field revealed by this unique dataset is examined, and unprecedented insight into its variability is obtained. Amongst the important findings is that, contrary to most climate models, our in situ data suggest a northward shift of the ACC east of 40W in 2004 and 2005 compared to previous work. Next, two CTD-SRDL sections are presented to identify the locations of the ACC fronts across Drake Passage, and an empirical relationship between upper ocean temperature and baroclinic mass transport is used to determine the transport through Drake Passage at the times of the sections. This technique is a powerful complement to more conventional means of data collection in this region, especially given the ability of the seals to conduct "sections" at times when ship-based fieldwork is logistically most challenging, i.e. in the winter time. The CTD-SRDLs do not only record hydrographic data, but simultaneously record seal movements and diving behavior. This enables insight to be obtained on the behavioral and physiological responses of Southern elephant seals to spatial environmental variability throughout their circumpolar range. The resulting energetic consequences of these variations could help explain recently observed spatially varying population trends. With a stable population at South Georgia and declining populations at Kerguelen and Macquarie Island. This study also highlights the benefits to the sensorcarrying animals themselves by showing the usefulness of this approach in examining the sensitivity of top predators to global and regional-scale climate variability. More importantly, I conclude that, by implementing animal-borne sensors into ocean observing strategies, we not only gain information about global ocean circulation and enhance our understanding of climate and the corresponding heat and salt transports, but at the same time we increase our knowledge about ocean’s top predators, their life history and their sensitivity to climate change.

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 location of fronts has a direct influence on both the physical and biological processes in the Southern Ocean. However, until recently fronts have been poorly resolved by available data and climate models. In this thesis we utilise a combination of high resolution satellite data, model output and ARGO data to improve our basic understanding of fronts. A method is derived whereby fronts are identified as local maxima in sea surface height gradients. In this way fronts are defined locally as jets, rather than continuous-circumpolar water mass boundaries. A new climatology of Southern Ocean fronts is presented. This climatology reveals a new interpretation of the Subtropical Front. The currents associated with the Subtropical Front correspond to the western boundary current extensions from each basin, and we name these the Dynamical Subtropical Front. Previous studies have instead suggested that the Subtropical Front is a continuous feature across the Southern Ocean associated with the super gyre boundary. A comprehensive assessment of the relationship between front locations and wind stress is conducted. Firstly, the response of fronts to a southward shift in the westerly winds is tested using output from a 100 year climate change simulation on a high resolution coupled model. It is shown that there was no change in the location of fronts within the Antarctic Circumpolar Current as a result of a 1.3° southward shift in the westerly winds. Secondly, it is shown that the climatological position of the Subtropical Front is 5-10° north of the zero wind stress curl line, despite many studies assuming that the location of the Subtropical Front is determined by the zero wind stress curl. Finally, we show that the nutrient supply at ocean fronts is primarily due to horizontal advection and not upwelling. Nutrients from coastal regions are entrained into western boundary currents and advected into the Southern Ocean along the Dynamical Subtropical Front. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Submitted.</p>

Der Einfluß eines Seherstroms auf die Ausbreitung langer barotroper Wellen wird untersucht. Der Antarktische Zirkumpolarstrom ist als eine zonale Scherströmung zu betrachten. Wir zeigen auf einer ß-Ebene, daß der Antarktische Zirkumpolarstrom für zonal sich ausbreitende Wellen als Wellenleiter wirkt. Für den linearen Fall des Scherstromes wird die analytische Lösung angegeben. Die gebundenen Wellen sind meridional modal strukturiert und bewegen sich mit einer Gruppengeschwindigkeit von rund 0.02ms·1 von West nach Ost (alle). / We study the influence of a shear current on barotropic long wave propagation. The Antarctic Circumpolar Current can be considered as a sheared zonal flow. We show tht on a ß-plane the Antarctic Circumpolar Current acts as a waveguide for zonally propagating waves. We give the analytical solution for the linear sheared case. The trapped waves are modal structured in the meridional direction and propagate from the West to the East (all) with a group velocity of nearly 0.02ms·1.

No description available.

Oceanic Gyres are the most conspicuous features in the Earth\'s ocean. They are ubiquitous to each basin and hemisphere. In the Atlantic Ocean, there is an uncanny symmetry between the North and South Atlantic Subtropical Gyres. Focusing on their poleward limits, we can think of them as virtually perfect analogues. However, while the North Atlantic Current has been extensively studied, the South Atlantic Current (SAC) still has been very little investigated and its knowledge presents crucial gaps on understanding it ocean\'s mesoscale variability and climate. Very little studies attempted so far to describe the SAC characteristics in terms of water mass properties and volume transports. In addition, there is the presence of recently described Saint Helen Current (StHC), which can be considered as the South Atlantic analogue of the Azores Current. The StHC has its formation tied with the Brazil Current (BC) retroflection. The SAC, on the other hand, is originated at the Brazil-Malvinas Confluence (BMC), and flows crossing zonally the Atlantic Basin. However, the presence of the northern branch of Antarctic Circumpolar Current (ACCn) (without an analogue in the northern hemisphere) brought a few additional challenges to studying the SAC. The ACCn can be thought as the Malvinas Current (MC) Extension, which exits the BMC region via the southern flank of the Zapíola Rise. In this work, we revisit the descriptive oceanography of the SAC system with newly developed climatologies (WOA13 and ARMOR3D) and seek to unravel the pattern associated with the current in the Southern limb of the region. Recent literature mentions that there is an important interplay between this three zonal jets as the cross the South Atlantic. However, only kinematics arguments were used to pinpoint this interplay so far. Hence, we opted to employ a statistical correlation method involving temperature, salinity and density vertical profiles (and consequently, T-S curves as well). We also computed volume transport values for the whole zonal domain across the South Atlantic Subtropical Gyre southern limb. In particular, at the longitude that it reaches the Mid-Atlantic Ridge, the major portion of the SAC veers south and merge almost completely with the ACCn. Its smaller northern the StHC. Near the eastern ocean border of the South Atlantic Ocean, the SAC-ACCn as well as a portion of the StHC traverse into the Indian Ocean. The combined analysis of geostrophic streamfunction fields and the temperature-density correlation diagrams do not show sufficient evidence for the StHC being an independent current, and not a branch of the SAC. Since there is also no study regarding the dynamics of the SAC we also constructed a linear QG instability model aiming to evaluate the current system mesoscale activity. We then analyzed the mesoscale activity of the SAC, and discovered that SAC is unstable throughout the whole path domain towards Africa. This instabilities, however, are found to be not as vigorous as the ACC. We also identify a shift in mesoscale vorticity wave regime as the SAC crosses the Mid-Atlantic Ridge. We found it to be less unstable than at the western side. We, however, could not identify the type of instabilities associated with the current. Therefore, we propose as sequential future work to further pursue investigation on the mesoscale dynamics of the ACCn-SAC-StHC system. / Os Giros Oceânicos são os aspectos mais notáveis dos oceano. Eles são ubíquos em todos os hemisférios e bacias oceânicas. No Atlântico, por exemplo, existe uma clara simetria entre os giros subtropicais do Atlântico norte e sul. Nos seus limites mais polar, podemos pensar neles como análogos perfeitos. Entretanto, enquanto a Corrente do Atlântico Norte foi extensamente estudado, a Corrente do Atlântico Sul ainda tem sido muito pouco investigada deixando lacunas cruciais no conhecimento no entendimento do clima e variabilidade de mesoscala nos oceanos. Pouquíssimos estudos foram realizados até agora a fim de descrever a CAS e suas características nos tópicos relacionados às propriedades das massas de água transporte de voluma. Ademais, há a presença de um corrente recentemente descrita, cunhada de Corrente de Santa Helena (CStH) que pode considerada, tal qual a Corrente do Atlântico Sul, uma análoga da Corrente dos Açores. A CStH possui sua formação atrelada à Corrente do Brasil (CB). A CAS, por sua vez, origina-se na confluência Brasil-Malvinas e escoa atravessando zonalmente a bacia do Atlântico. Entretanto, a presença do ramo norte da Corrente Circumpolar Antártica (CCAn) (sem um análogo no hemisfério norte) trouxe desafios adicionais ao estudo da CAS. A CCAn pode ser pensada como uma extensão da Corrente das Malvinas (CM), a qual sai da região da confluência via o flanco sul da Elevação de Zapiola. Nesse trabalho, revisitamo a oceanografia descritiva do sistema CAS com novas climatologias desenvolvidas (WOA13 e ARMOR3D) e procuramos desvendar o padrão associado à corrente no membro sul da região. Estudos recentes apontam uma importante interação entre os três jatos zonais enquanto atravessam o Atlântico Sul. Somente argumentos cinemáticos, entretanto, foram utilizados para identificar essa interação. Consequentemente, optamos em empregar um método de correlação estatística envolvendo perfis verticais de temperatura, salinidade e densidade(e, logo, curvas T-S). Nós também calculamos o transporte de volume para todo o domínio zonal através do ramo sul do Giro Subtropical do Atlântico Norte. Em particular, na longitude que alcança a Cadeia Meso-Atlântica, a maior porção da CAS desvia-se para o sul e dilui-se quanse que por completo à CCAn. Próxima à borda este do Oceano Atlântico Sul, tanto a CAS-CCAn como uma parte da CStH atravessam em direção ao Oceano Índico. A análise combinada dos campos de função de corrente geostróficos e pelos diagramas de correlação de temperatura-densidade não mostra evidências suficientes para que a CStH seja considerada uma corrente independente e não um ramo da CAS. Além disso, já que não há estudos relacionados a dinâmica da CAS, nós tambémconstruímos um modelo de instabilidade QG a fim de avaliar a atividade de mesoscala do sistema de correntes. Analisamos essa atividade da CAS e descobrimos que ela é instável durante todo o seu percurso em direção à África. Essas instabilidades, entretanto, não são tão vigorosas quanto aquelas da CCA. Também identidicamos mudanças no regime de ondas das vorticidades de mesoscala no cruzamento da CAS com a cadeia meso-oceânica. Descobrimos que a corrente é menos instável ao lado leste da cadeia. Não podemos, contudo, identificar os tipos de instabilidades associada à corrente. Por conseguinte, propomos trabalhos futuros que irão auxiliar à investigação da dinâmica de mesoscala do sistema CCAn-CAS-CstH.