Severe flooding events in subtropical southern Africa are not uncommon and can cause damage to infrastructure, lead to huge economic losses, and fatalities. Although extreme rainfall events can have far-reaching negative consequences, they can also provide large amounts of freshwater within a short time span, which supports the rain-fed farming upon which much of the population depends. However, the mechanisms through which extreme rainfall is produced in southern Africa are still not well understood. In particular, relatively little is known about where the moisture, a key ingredient in the rainfall, is sourced and how it is transported into the region. This thesis aims to address some of the gaps in this understanding by examining the moisture sources and subsequent moisture transport moisture into one of the key river basins in southern Africa, the Limpopo River Basin (LRB). The LRB, located in eastern southern Africa and spanning four countries, has experienced a number of extreme flooding events over the last three decades. Using CHIRPS satellite merged rainfall data for 1981-2016, the thesis identified the top 200 heavy extreme rainfall events in the LRB and the associated weather systems. It was found that tropicalextratropical cloud bands account for almost half of the events and tropical lows are responsible for just over a quarter. The remaining quarter of the events are associated with mesoscale convective systems and cut-off lows, the latter more important during transition seasons. Most of the events occur in the late summer when tropical lows and cloud bands are more common. Some relationships between the frequency of heavy rainfall events over the LRB and interannual climate modes of variability such as ENSO, SIOD, and SAM were found. Having examined the annual cycle of the top 200 heavy rainfall events, the analysis then applied the Lagrangian trajectory model HYSPLIT, with NCEP II reanalysis data as input, to backtrack air parcels from the LRB to their moisture source on seasonal scales and in terms of the types of weather systems involved. The resulting trajectories show that the seasonal transport of moisture over the LRB originates from seven moisture source regions; namely, local continental, tropical southeast Atlantic Ocean, midlatitude South Atlantic Ocean, tropical Northwest Indian Ocean, tropical southwest Indian Ocean, subtropical southwest Indian Ocean, and the Agulhas Current. Important differences in moisture source regions and pathways exist between early (OctoberDecember) and late (January-April) summers, with the tropical northwestern Indian Ocean and the northern Agulhas Current sources more prominent during JFMA than OND. Generally, moisture v source regions and transport pathways for LRB tend to be influenced by both the regional summer season circulation and the synoptic systems involved. Thus, it was found that cloud band and tropical low events within the top 200 tend to have the Congo Basin as an important moisture source whereas this source is less evident for cut-off low events. To help assess the robustness of the composite synoptic approach, the final part of the thesis applied the Lagrangian analysis to the most severe case in the top 200 events over the LRB (11- 21 January 2013). It was found that this case was largely linked to three main moisture sources: (1) tropical northwest Indian Ocean, (2) the Agulhas Current / Mozambique Channel, subtropical Southwest Indian Ocean, and (3) continental sources over the Congo Basin and northern Tanzania. Generally, the moisture source regions and pathways for the January 2013 event agreed with the climatological moisture source regions over the LRB, apart from the obvious absence of the tropical southeast Atlantic source in this case. In general, the thesis has provided a better understanding of the characteristics of heavy rainfall events over the LRB in terms of their associated weather systems, seasonality, interannual variability, and moisture source regions and trajectories.

Fusarium wilt of banana has a long and devastating history in many of the world’s banana producing countries. The most pronounced damage caused by Fusarium oxysporum f.sp. cubense (Foc), the Fusarium wilt pathogen, occurred during the 20th century in Central America, where tens of thousands of virgin forests were lost to further banana production. No control strategy is effective against Fusarium wilt other than replacement of susceptible by resistant varieties. It is, therefore, important to develop or identify resistant replacements that would not only be able to resist the pathogen, but also be acceptable to consumers. Resistance in wild banana varieties has been identified, and hybrids have been developed by breeding programmes with good resistance to Fusarium wilt. These varieties, unfortunately, appear not to be acceptable replacements for Cavendish bananas, the sweet desert banana variety that serves as the primary export banana and constitutes almost 40% of all bananas planted in the world today. A field selection, GCTCV-218, now proved to be the Cavendish plant with the most resistance to Foc ‘tropical’ race 4 (VCG 0121) has saved the Cavendish-based banana industry in Taiwan from devastation. In this thesis, GCTCV-218 has been evaluated against Foc ‘subtropical’ race 4 (VCG 0120), the primary variant of the pathogen in subtropical banana-producing countries such as South Africa, Australia and the Canary Islands. Defence-associated genes that are differentially expressed and that were up-regulated early in the defence response against the pathogen were isolated and identified. Greenhouse and field trials conducted at the research facilities of the Forestry and Agricultural Biotechnology Institute, University of Pretoria and in Kiepersol, South Africa, respectively, showed that GCTCV-218 had a significantly higher level of disease tolerance against Foc ‘subtropical’ race 4 (VCG 0120) when compared to the commercially grown Williams cultivar. Phenolic assays revealed that total phenolics and cell-wall bound phenolics were expressed at higher levels in GCTCV-218 after pathogen attack and seemed to play an important role in the tolerance of GCTCV-218. It was, therefore, proposed that GCTCV-218 could be considered a replacement for other Cavendish banana varieties planted in South Africa. The genetic basis of defence mechanisms in banana to Foc is unknown. In this investigation, Suppression Subtractive Hybridisation (SSH) was used to construct a cDNA library, containing banana genes that were up-regulated early (3&6 hours after infection), in the GCTCV-218/Foc interaction. The efficiency of the procedure was confirmed by PCR amplification of a known defence gene (endochitinase) present in the subtracted tester material, as well as analysing the reduction of a known housekeeping gene, actin, in the subtracted material compared to unsubtracted material. Southern blot data further provided confidence in the subtraction process. A cDNA library containing 736 gene fragments was constructed and then subjected to a screening procedure to remove false positives that escaped the subtraction process. The screening of a banana cDNA library for defence-related genes involved the development of a high-throughput cDNA microarray technique. This novel technique removed all false positives, such as housekeeping genes that escaped the subtraction as well as clones representing rDNAs. Seventy-nine genes differentially expressed in GCTCV-218 and not in Williams were selected, sequenced and subjected to BLASTX, BLASTN and DBest searches. Of these, several gene fragments showed homology to defence-associated genes, and 20 unique genes fragments were identified. These include two different peroxidases, response regulator 6, catalase 2, metallothionein, pectin acetylesterase (PAE), two different unknown proteins, salt stress, trypsin inhibitor, unspecific monooxygenase cytochrome P450, Bowman Birk proteinase inhibitor, root control, xylanase inhibitor, inhibitor CII, hypothetical protein, putative senescence-associated protein, pathogenesis-related protein 1 (PR1) and ribosomal protein S3a. The significance of the defence reaction to Fusarium wilt diseases in agricultural crops depends on the tempo of plant response. When a host plant is able to respond early to pathogen invasion the pathogen is successfully contained, preventing further spread throughout the plant. The expression of genes with antimicrobial activity, such as endochitinase, suggests an induced biochemical defence response against Foc. The expression of PAE and PR1 results in the deposition of lignin and callose production for cell wall strengthening. Four defence associated genes (catalase 2, pectin acetyl esterase (PAE), PR-1 and endochitinase) were selected for expression profile analysis using Real-time reverse transcriptase PCR, with TaqMan® and Light Cycler technology. All four genes were shown to be differentially expressed in GCTCV-218 at 3 and 6 hrs after infection, confirming SSH results. PR-1 and PAE were induced very early (3 hrs after infection) in the GCTCV-218, while PR3 and catalase 2 followed with a significant induction at 6 hrs after infection. This study concludes that GCTCV-218 is able to respond rapidly in response to Foc infection by activating both a biochemical and structural defence mechanism. / Thesis (PhD (Plant Pathology))--University of Pretoria, 2006. / Microbiology and Plant Pathology / unrestricted

Gullies are significant contributors of sediment to streams in the southeastern USA. This study investigated gully erosion in the clay-rich soils of east Tennessee under a humid subtropical climate. The aims of this study were to (1) estimate long-term erosion rates for different gully geomorphic settings, (2) compare patterns of erosion for the different settings, and (3) model the response of gully erosion to freeze-thaw events. Erosion was measured weekly from June 2012 to August 2018 using 105 erosion pins distributed in gully channels, interfluves, and sidewalls. Erosion rates were estimated from average slopes of lines of best fit of pin lengths versus time. Maximum and minimum temperature was calculated daily using an on-site weather station and freeze-thaw events were identified. Gully erosion was modeled using antecedent freeze-thaw activity for the three geomorphic settings. Long-term erosion rates in channels, interfluves, and sidewalls were 2.5 mm/year, 20 mm/year, and 21 mm/year, respectively; however, week-by-week erosion was statistically different between the three settings, indicating different erosive drivers. Models of erosion with lagged freeze-thaw variables explained up to 34.8% of the variability in erosion variables; sidewall erosion was most highly related to freeze-thaw activity. Freeze-thaw in prior weeks was an important variable in all erosion models.

Streams have been impacted by human activities in a variety of ways. Over time, these ecosystems become dominated by the most resilient species, with significant losses in the natural components that provide valuable ecosystem services to people. In impacted streams, the loss of ecosystem services often is not recognized until the stream has already been dramatically altered. In this study, I provide data on the natural distribution of freshwater decapods and the status of decapod communities in streams with different land use histories. I reviewed the decapod distribution for the Caribbean to provide an update of the species that inhabit the freshwater systems. I determined the presence of 18 species of decapods in Puerto Rico and concluded that these decapods follow the island-species relationship in the Caribbean. Also, I present data associated with decapod community dynamics in watersheds with different urban development. As, expected the highly urban watershed had lower diversity and density of decapods than the medium and low urban watersheds. The variations in decapod communities among watersheds correlated with the degradation of the physical-chemical environments and clearing of the riparian zones. I compare the food webs among streams with different human impacts. Specific influences of point/nonpoint sources of N could be distinguished in food web components. This shows to an effect of human activities on the stream and watershed. In addition, I determined the effect of abiotic and biotic factors on the growth of A.lanipes (0.27 mm) and X.elongata (0.1 mm) over the 10-year period of study. The results showed that these species transform a wide range of organic materials into their biomass. Finally, I developed a series of education projects which promote the understanding and knowledge of freshwater ecosystems; interactions and the organisms that inhabit these systems. The results showed an increasing interest about freshwater fauna and ecosystems. I concluded that: a) the distribution of freshwater decapods in the Caribbean islands follows the area-species relationship; b) urbanization represents one of the many distinct land uses that affect habitat structure, energy sources and biotic interactions; and c) it’s necessary to present the results of our research to the general public in ways that are easily understood.

Human settlement displaces and fragments natural habitats. Design choices in the landscape directly affect both local diversity and extinction rates. This study seeks to understand how avifauna are responding to this new technology in Mississippi.

No description available.

La circulation méridienne de retournement (MOC) de l’Atlantique Nord est une composante clé du système climatique global, via son rôle dans la redistribution de chaleur, d’eau douce et de propriétés chimiques entre hautes et basses latitudes. Aux moyennes et hautes latitudes, le Courant Nord-Atlantique(NAC) forme la branche haute de la MOC. Il s’écoule vers le nord-est à la frontière des gyres subpolaire et subtropical, et se divise en deux branches principales dans l’est du gyre subpolaire : une branche nord qui recircule vers l’ouest dans le gyre subpolaire et une branche sud qui alimente les mers Nordiques.Une simulation réaliste haute résolution (ORCA025-G70, 1/4°) est combinée à un outil d’analyse Lagrangienne pour étudier la variabilité de la MOC (1965-2004) à travers la section A25-Ovide qui joint le Portugal au Groenland. Deux cellules de retournement vertical sont identifiées : une cellule subtropicale connectant les hautes et basses latitudes et une cellule interne aux régions subpolaires. La variabilité décennale de la MOC est associée à des changements synchronisés des apports subtropical et subpolaire dans la NAC. Ce dernier subit d’importantes restructurations horizontales caractérisées par la variabilité opposée de ses deux branches. Ces modifications de la distribution horizontale du transport sont principalement régies par la variabilité de l’afflux subtropical.Les variations du transport de chaleur à travers A25-Ovide sont la cause principale de la variabilité du contenu de chaleur observée dans l’est du gyre subpolaire (1965-2004). La variabilité du transport de chaleur résulte d’un déséquilibre entre des changements opposés de ses composantes « vitesse » et « température ». Les anomalies de vitesse et température sont en partie reflétées dans des déplacements verticaux d’isopycnes, potentiellement associés à la proportion changeante de masses d’eau subtropicales et subpolaires transportées par la branche nord du NAC.Enfin, une circulation surface-fond moyenne calculée depuis des mesures hydrographiques répétées et des mesures altimétriques indique une contribution mineure de la mer du Labrador pour la MOC global. Cependant, l’intensité du retournement diapycnal à AR7W a presque diminué de moitié entres les 1990’s et les 2000’s, confirmant l’importance de la région pour la variabilité basse-fréquence de la MOC. / The meridional Overturning Circulation (MOC) of the North Atlantic ocean is a key component of the global climate system, through its role in redistributing heat, freshwater end chemical properties between low and high latitude regions. In mid-high latitude regions, the North Atlantic Current (NAC) forms the upper limb of the MOC. It flows northeastward at the subtropical/subpolar boundary, and splits into two main branches in the eastern subpolar gyre: a northern branch that recirculates within the subpolar region and a southern branch that feed the Nordic Seas.A realistic eddy-permitting simulation (ORCA025-G70, 1/4°) is combined with a Lagrangian analysis tool (ARIANE) to investigate the MOC variability (1965-2004) across the A25-Ovide line, which joins Greenland to Portugal. Two vertical overturning cells are identified: a subtropical cell connecting low and high latitudes (12Sv) and a cell internal to the subpolar gyre (4Sv). The decadal MOC variability is associated with synchronized transport changes of the subtropical and subpolar inflow within the NAC. The latter undergoes important horizontal restructuring with opposed transport changes of its northern and southern branches. Those horizontal transport changes are largely induced by the horizontal variability of the subtropical inflow.Changes in oceanic heat transport across A25-Ovide are largely responsible for the observed heat content changes in the eastern subpolar gyre (1965-2004). Heat transport variability at A25-Ovide results from an imbalance between opposed changes in its velocity and temperature components. Both temperature and velocity anomalies are partly reflected in large scale heaves of isopycnals, and potentially relate to the varying proportion of warm subtropical waters and cold subpolar waters advected within the northern NAC branch.A 2000’s mean full-depth circulation computed along the merged AR7W/A25-Ovide line from repeated hydrographic profile and altimetry data indicates a minor contribution of the Labrador Sea to the basin wide mean MOC. However, the strength of the diapycnal overturning at AR7W has almost halved between the 1990’s and the 2000’s, confirming the importance of the region for the low-frequency MOC Variability.

O presente estudo avalia como a estrutura e a produção da comunidade de copépodes pelágicos da plataforma interna ao largo de Ubatuba (SP, Brasil) responderam às variações ambientais durante o período de julho de 2005 a junho de 2008. Durante estes três anos, a produção secundária dos copépodes foi estudada por meio da aplicação de modelos empíricos de crescimento e de estimativas de crescimento peso-específico obtidas através de experimentos de produção de ovos. Aspectos reprodutivos de 16 espécies de copépodes (9 calanóides, 3 ciclopóides e 4 harpacticóides) foram analisados neste período, através de experimentos de incubação e de métodos indiretos de obtenção de taxas de produção e viabilidade dos ovos. A comunidade de copépodes esteve representada por 70 espécies e foi caracterizada por altos valores de riqueza, diversidade e eqüitabilidade. Os copépodes apresentaram grande variabilidade nos valores médios de densidade (4726 ± 3711 ind. m-3) e de biomassa (7,42 ± 5,64 mg C m-3) e foram dominados por espécies de pequeno porte (< 1000 µm), destacando-se as fêmeas adultas de Oncaea waldemari e os copepoditos imaturos de paracalanídeos e clausocalanídeos. Quando comparada com outros ambientes tropicais e subtropicais, a região estudada apresentou valores elevados de densidade e biomassa. Da mesma maneira, a produção secundária média apresentou variabilidade temporal elevada (1,13 ± 1,11 mg C m-3 dia-1), com uma importante contribuição dos copepoditos imaturos de espécies dispersoras de ovos. No geral, os valores médios registrados foram considerados altos quando comparado com outros ambientes tropicais e subtropicais, embora a razão Produção/Biomassa média tenha sido similar às registradas nestes locais. A intrusão periódica da ACAS parece ter sido a principal responsável pelas alterações observadas na estrutura e produção da comunidade. A maioria dos meses não influenciados pela ACAS apresentou valores de densidade, biomassa e produção inferiores às respectivas médias. Entretanto, os resultados observados sugerem que as flutuações da comunidade de copépodes podem responder não apenas à intrusão da ACAS, mas também a uma complexa conjunção de fatores, incluindo as próprias relações inter e intra-específicas. Com relação à reprodução, as espécies dispersoras de ovos apresentaram taxas médias de produção de ovos similares às obtidas em outras regiões tropicais e subtropicais, enquanto que as retentoras apresentaram valores levemente inferiores. Entretanto, foram registrados picos ocasionais de produção destas últimas espécies, sugerindo que estes copépodes possuem estratégias que compensam os meses de baixa produtividade. A reprodução de algumas espécies analisadas parece ser associada a fatores intra-específicos, tais como o tamanho dos ovos e a razão entre machos e fêmeas. Além disso, as espécies dispersoras analisadas são provavelmente influenciadas pela temperatura e pelo alimento. A relação entre os tamanhos e pesos de fêmeas e ovos de 32 espécies de copépodes pelágicos mostrou que a variabilidade interespecífica observada nessas proporções é similar à tendência observada para espécies de altas latitudes. Comparando as taxas de produção estimadas a partir das equações empíricas com as obtidas experimentalmente, observa-se diferenças expressivas nas estimativas de produção secundária, o que sugere a influência de outras variáveis além daquelas consideradas pelos modelos. / The present study evaluates how the pelagic copepod community structure and production from the inner shelf off Ubatuba (SP, Brazil) responded to environmental variability from July 2005 to June 2008. During these three years copepod secondary production was studied by the application of growth empirical models and weight-specific growth estimates obtained through egg production experiments. Reproductive aspects of 17 copepod species (10 calanoid, 3 cyclopoid and 4 harpacticoid) were analyzed through incubation experiments and indirect methods to obtain production and egg hatching success rates. Copepod community was represented by 70 species and was characterized by high values of richness, diversity and evenness. Copepods had great variability in mean abundance values (4,726 ± 3,711 ind. m-3) and biomass (7.42 ± 5.64 mg C m-3) and were dominated by small size species (< 1,000 µm), especially Oncaea waldemari adult females and immature copepodites of paracalanids and clausocalanids. When compared to other tropical and subtropical environments, the copepod community in the study area had high average abundance and biomass. Mean secondary production rates had high temporal variability (1.13 ± 1.11 mg C m-3 day-1), with an important contribution from immature copepodites of broadcast spawner species. Production values were also high but mean Production/Biomass ratios were similar when compared to other tropical and subtropical environments. The periodic SACW (South Atlantic Central Water) intrusions seem to be the main responsible for the variability in community structure and production. Most months non-influenced by SACW had abundance, biomass and production values lower than the annual average. However, copepod community fluctuations may not have responded only to SACW intrusions, but also to inter- and intra-specific relations. Broadcast spawner species had mean egg production rates similar to the ones obtained in other tropical and subtropical regions, while sac spawners showed slightly lower values. Nevertheless, occasional production peaks were recorded for the latter, suggesting that these copepods have reproductive strategies to compensate for low productivity periods. Some species reproduction traits seem to be related to intra-specific factors, such as egg size and the male/female ratio. Besides, broadcast spawners were probably influenced by temperature and food. The relationship between female and egg size and weight from 32 pelagic copepod species showed that inter-specific variability observed in these proportions was similar to those observed for high-latitude species. When reproduction rates estimated from empirical equations with those obtained experimentally are compared, expressive differences in secondary production estimates emerge, which suggests the influence of other variables in addition to those accounted for by empirical models.

As interações tróficas de 31 espécies de peixes e 2 de lulas da Baía do Araçá, São Sebastião (SP), foram investigadas por meio dos isótopos estáveis de carbono (&#948;13C) e nitrogênio (&#948;15N). Os valores de &#948;13C das espécies variaram entre -17,2&#8240; e -12,1&#8240;, e os de &#948;15N, entre 10,0&#8240; e 14,5&#8240;. Os valores de &#948;13C dos produtores e consumidores permitiram indicar que as espécies analisadas participam das teias tróficas, pelágica e bentônica, e têm como base da cadeia alimentar o fitoplâncton, os microfitobentos e a matéria orgânica dos sedimentos. Maiores valores de &#948;13C nos peixes e lulas foram registrados no verão, associados a valores mais altos na base. As posições tróficas das espécies variaram entre 3,18 e 4,72, indicando que atuam como consumidores secundários e terciários. A composição da dieta dos peixes, avaliada pelo modelo de mistura isotópica, apontou elevada contribuição de presas como Polychaeta, Tanaidacea e Ophiuroidea, grupos com alta abundância na Baía do Araçá e no Canal de São Sebastião. A ingestão de presas disponíveis no interior da baía e no canal evidenciou a importância desses peixes e lulas como carreadores de nutrientes, realizando tanto acoplamento pelágico-bentônico, como entre as regiões sublitoral e entremarés da Baía do Araçá. / The trophic interactions of 31 fish species and 2 squid species of the Araçá Bay, São Sebastião (São Paulo, Brazil), were investigated through carbon (&#948;13C) and nitrogen (&#948;15N) stable isotopes. The &#948;13C of the species ranged from -17.2&#8240; to -12.1&#8240;, and the &#948;15N, from 10.0&#8240; to 14.5&#8240;. The &#948;13C data of the producers and consumers indicated that the species analysed are part of the pelagic and benthic trophic webs, and have phytoplankton, microphytobenthos and organic matter from the sediment as the base of the food web. Higher values of &#948;13C were registered in the summer, linked to the higher values at the base. The trophic positions of the species varied between 3.18 e 4.72, an indication that they act as secondary and tertiary-quaternary consumers. The diet composition of fish, evaluated trough the isotope mixing model, showed high contribution of prey, such as Polychaeta, Tanaidacea and Ophiuroidea, groups highly abundant in the Bay and the adjacent São Sebastião Channel. The intake of available prey in the intertidal region and in the Channel revealed the importance of the fish and squid as nutrient pathway links, coupling the pelagic-benthic systems and the sublittoral and intertidal regions of the Araçá Bay.

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.