Добірка наукової літератури з теми "Indian Ocean Gyre"

This paper describes a large cyclonic gyre that lasted several days in the northwest Pacific during July 1988. Cyclonic winds at 850 hPa extended beyond the 2000-km radius with a radius of maximum winds of 700–800 km. The gyre exhibited clear skies within and north of its center. Active convection extended 4000 km in longitude to its south. The Madden–Julian oscillation (MJO) was in its active phase in the Indian Ocean prior to gyre formation. Consistent with earlier studies, diabatic heating in the MJO was associated with an anomalous upper-tropospheric westerly jet over the northeast Asian coast and a jet exit region over the northwest Pacific. Repeated equatorward wave-breaking events developed downwind of the jet exit region. One such event left behind a region of lower-tropospheric cyclonic vorticity and convection in the subtropics that played a key role in the gyre formation. A second wave-breaking event produced strong subsidence north of the mature gyre that contributed to its convective asymmetry. Gyres from 1985 and 1989 were compared to the 1988 case. All three gyres developed during an active MJO in the Indian Ocean. Each gyre displayed the same strong convective asymmetry. Each developed in July or August during the climatological peak in breaking Rossby waves in the northwest Pacific. Finally, all of the gyres developed during La Niña at nearly the same location. This location and the convective structure of the gyres closely matched composite La Niña anomalies during boreal summer.

A simple reductA1 gravity wind-driven ocean circulation model is used to study the interannual variability in the upper layer of the Indian Ocean (24°S-23°N and 3S°E-IIS0E). The monthly mean wind stress for the period 1977-1986 are used as a forcing in the model. The model reproduces most of the observed features of the annual cycle of the upper layer circulation in the Indian Ocean when was forced with the ten-year average monthly mean wind. The circulation features and the model upper layer thickness show considerable interannual variability in most part of the basin; in particular, the Somali Current, the basin wide southern hemisphere gyre, the Equatorial Currents and the gyres in the Bay of Bengal. Six consecutive years starting from 1978 to 1983 which include two bad monsoon years of 1979 and 1982 are chosen to study the interannual variability. February circulation field shows stronger Equatorial Counter Currents in bad monsoon years, whereas. the cunents north of Madagascar flowing up to the African coast are found to be stronger in good monsoon years. The southward return flow from the Southern Gyre in August is strong and more to southern latitudes in the bad monsoon years. The flow circulated eastward to form another eddy east of Southern Gyre. The basin wide gyre of the southern hemisphere (SH) shows less variability in two consecutive normal years than in contrasting years.

Abstract As part of the World Ocean Circulation Experiment, 306 autonomous floats were deployed in the tropical and South Pacific Ocean and 228 were deployed in the Indian Ocean to observe the basinwide circulation near 900-m depth. Mean velocities, seasonal variability, and lateral eddy diffusivity from the resultant 2583 float-years of data are presented. Area averages, local function fits, and a novel application of objective mapping are used to estimate the mean circulation. Patterns of mean circulation resemble those at the surface in both basins. Well-developed subtropical gyres, twice as strong in the Indian Ocean as in the Pacific, feed western boundary currents. Tropical gyres are separated by eastward flow along the equator in both hemispheres of both basins, although the Indian subcontinent splits the north Indian tropical gyre. The Antarctic Circumpolar Current (ACC) and west wind drifts are prominent in both basins, generally tending slightly southward but deviating to the north behind the Del Cano, Kerguelen, and Campbell Plateaus and, of course, South America. Remarkably, the eastern boundaries of the southern subtropical gyres in all three basins apparently occur in the ocean interior, away from land. The Indian Ocean’s subtropical gyre, and perhaps part of the South Atlantic’s, reaches east to a retroflection just upstream of the Campbell Plateau south of New Zealand. Seasonal variability at 900 m is focused around the equator with weaker variability found near certain bathymetric features. There is a remarkable agreement between the observed seasonable variability and that predicted by the Jet Propulsion Laboratory (JPL)–Estimating the Circulation and Climate of the Ocean (ECCO) data-assimilating numerical model. Aside from seasonal effects, eddy variability is greatest along the equator, in tropical and subtropical western basins, and along the ACC. Integrals of velocity across regional passages (Tasman Sea, Mozambique Channel) provide useful reference for hydrographic analyses of transport. Across whole ocean basins, however, the uncertainty associated with the appropriate continuity relation for horizontal flow (e.g., geostrophy vs nondivergence) is comparable to the mean flow.

Abstract A barotropic shallow-water model and continuation techniques are used to investigate steady solutions in an idealized South Indian Ocean basin containing Madagascar. The aim is to study the role of inertia in a possible connection between two subgyres in the South Indian Ocean. By increasing inertial effects in the model, two different circulation regimes are found. In the weakly nonlinear regime, the subtropical gyre presents a recirculation cell in the southwestern basin, with two boundary currents flowing westward from the southern and northern tips of Madagascar toward Africa. In the highly nonlinear regime, the inertial recirculation of the subtropical gyre is found to the east of Madagascar, while the East Madagascar Current overshoots the island’s southern boundary and connects through a southwestward jet with the current off South Africa.

Abstract. Plastic debris is the most common and exponentially increasing human pollutant in the world's ocean. The distribution and impact of plastic in the Pacific and Atlantic oceans have been the subject of many publications but not so the Indian Ocean (IO). Some of the IO rim countries have the highest population densities globally and mismanagement of plastic waste is of concern in many of these rim states. Some of the most plastic-polluted rivers empty into the IO, with all this suggesting that the IO receives a tremendous amount of plastic debris each year. However, the concentration, distribution, and impacts of plastics in the IO are poorly understood as the region is under-sampled compared to other oceans. In this review, we discuss sources and sinks, which are specific to the IO. We also discuss unique atmospheric, oceanographic, and topographic features of the IO that control plastic distribution, such as reversing wind directions due to the monsoon, fronts, and upwelling regions. We identify hotspots of possible plastic accumulation in the IO, which differ between the two hemispheres. In the southern IO, plastics accumulate in a garbage patch in the subtropical gyre. However, this garbage patch is not well defined, and plastics may leak into the southern Atlantic or the Pacific Ocean. There is no subtropical gyre and associated garbage in the northern IO due to the presence of landmasses. Instead, the majority of buoyant plastics most likely end up on coastlines. Finally, we identify the vast knowledge gaps concerning plastics in the IO and point to the most pressing topics for future investigation.

Abstract. A maximum in the strength of Agulhas Leakage has been registered at the interface between Indian and South Atlantic oceans during glacial Termination II (T II), presumably transporting the salt and heat necessary to maintain the Atlantic Meridional Overturning Circulation (AMOC) at rates similar to the present day. However, it was never shown whether these were effectively incorporated in the South Atlantic gyre, or whether they retroflected into the Indian and/or Southern Oceans. To solve this question, we investigate the presence of paleo Agulhas rings from a sediment core on the central Walvis Ridge, almost 1800 km farther into the Atlantic basin than previously studied. Analysis of a 20 yr dataset from a global ocean circulation model allows us to relate density perturbations, at the depth of the thermocline, to the passage of individual rings over the core site. Using this relation from the numerical model as the basis for a proxy, we generate a time series of δ18O variability of Globorotalia truncatulinoides single specimens, revealing high levels of pycnocline depth variability at the site, suggesting enhanced numbers of Agulhas rings moving into the South Atlantic gyre around and before T II. Our record closely follows the published quantifications of Agulhas Leakage from the east of the Cape Basin, and thus shows that Indian Ocean waters entered the South Atlantic circulation. This provides crucial support to the view of a prominent role of the Agulhas Leakage in the shift from a glacial to an interglacial mode of AMOC.

Abstract. East of Madagascar, the shallow “South Indian Ocean Counter Current (SICC)” flows from west to east across the Indian Ocean against the direction of the wind-driven circulation. The SICC impinges on west Australia and enhances the sea level slope, strengthening the alongshore coastal jet: the Leeuwin Current (LC), which flows poleward along Australia. An observed transport maximum of the LC around 22° S can likely be attributed to this impingement of the SICC. The LC is often described as a regional coastal current that is forced by an offshore meridional density gradient or sea surface slope. However, little is known about the controls of these open-ocean gradients. The regional circulation system is embedded in the subtropical “super gyre” that connects the Indo-Pacific via the Tasman Gateway and the Indonesian passages. The Indonesian Throughflow (ITF) circulates through the Indian Ocean back into the Pacific south of Australia. This return pathway appears to be partly trapped in the upper layer north of an outcrop line. It is redirected along this outcrop line and joins the eastward flow of the SICC. To study the connection of the basin-scale and the inter-ocean-scale dynamics, we apply both an ocean general circulation model and a conceptual two-layer model. Shutdown of the ITF in the models leads to a large decrease in Leeuwin Current transport. Most of the SICC was found to then reconnect to the internal gyre circulation in the Indian Ocean. ITF, SICC and LC thus appear to be dynamically connected.

AbstractThe Kerguelen Plateau is a major topographic feature in the Southern Ocean. Located in the Indian sector and spanning nearly 2000 km in the meridional direction from the polar to the subantarctic region, it deflects the eastward-flowing Antarctic Circumpolar Current and influences the physical circulation and biogeochemistry of the Southern Ocean. The Kerguelen Plateau is known to govern the local dynamics, but its impact on the large-scale ocean circulation has not been explored. By comparing global ocean numerical simulations with and without the Kerguelen Plateau, this study identifies two major Kerguelen Plateau effects: 1) The plateau supports a local pressure field that pushes the Antarctic Circumpolar Current northward. This process reduces the warm-water transport from the Indian to the Atlantic Ocean. 2) The plateau-generated pressure field shields the Weddell Gyre from the influence of the warmer subantarctic and subtropical waters. The first effect influences the strength of the Antarctic Circumpolar Current and the Agulhas leakage, both of which are important elements in the global thermohaline circulation. The second effect results in a zonally asymmetric response of the subpolar gyres to Southern Hemisphere wind forcing.

La plupart des déchets plastiques mal gérés pénètrent dans l'environnement marin. Une fois dans les océans, ces plastiques dérivent jusqu'à atteindre des zones de convergence subtropicales, où ils s'accumulent pour former des « Garbage Patch ». Cinq de ces zones ont été découvertes,dont l’une dans le sud de l'océan Indien. Cette dernière a fait l'objet de peu d'études d'observation en surface, et plusieurs modèles de dispersion indiquent une localisation différente, la plaçant soit à l’ouest ou à l’est du bassin. Supposée être la deuxième « Garbage Patch » la plus polluée après celle du Pacifique Nord, il est crucial de l'identifier correctement pour intervenir efficacement. C'est dans ce contexte que s'inscrit le projet doctoral, visant à déterminer la composition, la concentration et l'origine des débris plastiques accumulés dans le sud-ouest de l'océan Indien. Depuis le début du projet, 19 campagnes océanographiques ont été déployées pour effectuer des suivis visuels des macrodéchets (> 2,5 cm) et collecter des microplastiques (500 μm – 5 mm). Des collectes des déchets marins (macro et méso : 5 mm – 2,5 cm) échoués sur des plages inhabitées ont également été réalisées pour évaluer la proportion qui ne reste pas en surface. De plus, une étude à long terme de cette pollution plastique a été entreprise en recherchant des espèces bio-indicatrices de la pollution dans la région. Toutes les observations ont été comparées ou complétées par des modèles de dispersion de particules dans l'océan Indien. Sur l'ensemble des déchets marins collectés ou observés, 95 % étaient constitués de plastiques. Parmi les plastiques, la sous-catégorie prédominante était celle des plastiques durs déjà fragmentés, retrouvés en surface de l'océan, échoués sur des îles inhabitées et ingérés par les espèces bio-indicatrices. La composition principale de ces polymères était le polyéthylène et le polypropylène, et elle ne différait pas entre la surface de l'océan et les plages. Un gradient de concentration de microplastiques a également été identifié, allant de 10^3 items.km^-2 à 40°E à 10^5 items.km^-2 à 65°E sur les latitudes 30/33°S. Ce gradient a été confirmé par les modèles de dispersion, bien que sous-estimé par ces derniers. Certains macroplastiques échoués sur des îles venaient d'emballages alimentaires d'Asie du Sud-Est. Afin de poursuivre l'étude de la pollution plastique dans la région, trois espèces ont été identifiées répondant aux critères de sélection : les tortues caouannes (Caretta caretta), les pétrels de Barau (Pterodroma baraui) et les puffins tropicaux (Puffinus baillonni). Pour les futures études, il serait intéressant d'accroître les collectes dans la partie centrale et orientale du bassin de l'Océan Indien à différentes saisons, d'étudier également l'impact de ces déchets plastiques sur les écosystèmes associés et d’établir des solutions de gestions adaptées
The majority of mismanaged plastic waste enters the marine environment. Once in the oceans, these plastics drift until reaching subtropical convergence zones, where they accumulate to form “Garbage Patches”. Five zones have been discovered, including one in the southern Indian Ocean. This latter patch has undergone limited surface observation studies, and several predicted models indicate a different location, placing it either west or east of the basin. Supposedly the second most polluted “Garbage Patch” after the North Pacific, it is crucial to identify it for effective intervention accurately. Within this context, the doctoral project aimed to determine the composition, concentration, and origin of plastic debris accumulated in the Southwest Indian Ocean. Since the project's inception, 19 oceanographic campaigns have been conducted to visually monitor macro-debris (> 2.5 cm) and collect microplastics by manta trawl deployment (500 μm – 5 mm). Surveys of marine debris (macro-meso (5 mm – 2.5 cm) beached on uninhabited, remote islands have also been carried out to assess the concentration that does not remain on the surface. Furthermore, a long-term study of plastic pollution was initiated by identifying bio-indicator species in the region. All observations have been compared or complemented with plastic dispersion predictive models in the Indian Ocean. Of all the marine debris collected or observed, 95% consisted of plastics. Among plastics, the predominant subcategory was pre-existing fragmented hard plastics found on the ocean surface, beached on uninhabited islands, and ingested by bio-indicator species. The primary composition of these polymers was polyethylene and polypropylene, and it did not differ between the ocean surface and beaches. A concentration gradient of microplastics was also identified, ranging from 10^3 items.km^-2 at 40°E to 10^5 items.km^-2 at 65°E on latitudes 30/33°S. This gradient has been confirmed by plastic dispersion predicted models, although they tend to underestimate it. In addition, some of the macroplastics stranded on the islands originated mainly from Southeast Asian food packaging. Three species have been identified for long-term monitoring of plastic pollution in the region: loggerhead turtles (Caretta caretta), Barau's petrels (Pterodroma baraui), and tropical shearwaters (Puffinus baillonni). Future studies should include increasing sampling in the central and eastern parts of the Indian Ocean basin during different seasons, studying the impact of plastic debris on associated ecosystems, and developing tailored management solutions

The work presented in this Thesis concerns the large-scale circulation of the Indian Ocean and follows three lines of investigation: (i) decadal variability of the subtropical gyre circulation; (ii) decadal variability of the deep meridional overturning circulation (MOC); and (iii) the influence of diapycnal diffusivity on quasi-steady MOC states. The decadal variability of the subtropical gyre transport over the ocean interior (away from boundary currents) is investigated using hydrographic data from 32°S. Estimates of the relative gyre transports are: 41 ± 5.1 Sv (1 Sv = 106 m3s-1) for 1987, 42 ± 7.0 Sv for 1995 and 58 ± 7.0 Sv for 2002. This represents a 40% increase from 1987 to 2002. The main areas of change in the geostrophic transports are just east of Madagascar Ridge and around Broken Plateau, which is consistent with differences observed in the isopycnal depths in these areas. Maps of contoured velocity suggest that most of the change happened between 1995 and 2002, which supports the transport estimates. The 1987 and 2002 hydrographic data are then combined with a regional model of the Indian Ocean to investigate the impact that changes in conditions near 32°S might have on the deep MOC. The model has lateral open boundaries at 35°S for the Southern Ocean and 122°E for the Indonesian Throughflow. The meridional velocity field dominates over density at the southern boundary (SB) in determining the basin-wide deep circulation on decadal timescales. The initial adjustment of the deep MOC to the first 5-6 years of model integration and shows a large sensitivity to the SB conditions. With ‘best’ estimates of the flow field near 32°S the model shows a 6 Sv and 16 Sv deep MOC for 1987 and 2002, respectively. There are also changes in the zonal structure of the deep circulation. The results suggest that the Indian Ocean exhibits decadal variability in the size and structure of the deep MOC. Furthermore, the apparent inconsistency between previous non-GCM and regional GCM studies may be a result of the lateral boundary conditions, rather than a conflict in the model dynamics. 200-year model integrations suggest that quasi-steady MOC states in the Indian Ocean are reached on century time scales. The size, structure and adjustment time of the quasi-steady deep MOC are controlled by the distribution of diapycnal diffusivity (Kd). The zonal mean distribution of Kd required to support the prescribed deep inflow at the model SB can be estimated using a one-dimensional (1-D) advective-diffusive balance in isopycnal layers. The 18 Sv overturning circulation put forward by Ferron and Marotzke [2003] (FM) collapses when their model configuration is integrated to quasi-steady state under a number of different Kd regimes. With a diagnosed Kd field only 70% of the FM circulation can be supported in quasi-steady state, and the Kd values are an order of magnitude larger than recent observations suggest. The results imply that one can get a good a priori estimate of the Kd-field required to support a quasi-steady model MOC by applying a 1-D advective-diffusive balance in isopycnal layers to the SB conditions. Overall, the research highlights the need to implement improved estimates of (nonuniform) Kd in ocean GCMs when investigating quasi-equilibrium model states.

L’océan joue un rôle important dans le système climatique du fait des importants échanges de gaz carbonique avec l’atmosphère et du déplacement de ses échanges vers un puits océanique lors de l’Anthropocène. Les océans Atlantique Nord et Austral sont reconnus comme étant des acteurs majeurs de cette séquestration du carbone anthropique (Cant). En effet, ~25% du Cant pénètre dans les eaux de surface de l’Atlantique Nord et ~40% résident dans les eaux modales et intermédiaires de l’océan Austral. Il est clairement établi que le puits de carbone présente des variations dans le temps mais mal connues, rendant les prévisions climatiques difficiles. Il est donc recommandé de concentrer les efforts d’observations dans les régions où l’absorption de CO2 est élevée : les océans Atlantique Nord et Austral. Dans ce contexte, l’étude de la variabilité saisonnière, interannuelle à décennale des paramètres du système des carbonates dans ces deux régions est requise pour appréhender l’impact des changements actuels sur le cycle du carbone océanique. Basée sur des observations acquises dès le milieu des années 1990 et jusqu’en 2021 dans le cadre des programmes français SURATLANT et OISO, ces travaux de thèse visent à décrire l’évolution spatiale et temporelle des paramètres du système des carbonates (AT, CT, fCO2, pH et δ13CDIC) dans le gyre subpolaire nord Atlantique (NASPG) et le secteur Indien de l’océan Austral. Les processus physiques et biogéochimiques contrôlant l’évolution de la fCO2, de l’acidification des eaux et de l’effet Suess océanique, ont été étudiés en séparant le signal anthropique des signaux naturels. L’évolution de la fCO2 et du pH, sur l’ensemble de la période et dans ces deux régions, est en accord avec l’augmentation de CO2 atmosphérique et les tendances moyennes pour l’océan global. Toutefois, selon la saison, la zone sélectionnée ou sur de plus courtes périodes, les résultats peuvent être différents. L’augmentation du Cant a été identifié comme le driver contrôlant majoritairement les changements de fCO2 et pH observés, mais d’autres processus peuvent moduler ces tendances. Ainsi, le réchauffement (refroidissement) des eaux de surface accélère (limite) l’augmentation de la fCO2 et la diminution du pH. De plus, des tendances à l’augmentation de AT ont également été observées dans chacune des deux régions, ce qui a limité en partie l’acidification des eaux par rapport à l’augmentation du Cant. Cependant, les résultats suggèrent une certaine stabilité, voir une inversion de la tendance à l’augmentation de la fCO2 et de l’acidification autour de 2010, tant dans le NASPG que dans la zone antarctique de l’océan Indien Austral. Les observations de 13CDIC semblent confirmer cette analyse et permettent de mettre en avant un effet Suess différent entre les deux régions. Ce paramètre complémentaire a cependant été moins échantillonné et ne permet pas encore de valider les changements observés autour de 2010. Mon travail met en avant l’importance de maintenir des observations à long terme dans ces régions où l’absorption de CO2 atmosphérique est importante, afin de suivre l’évolution du carbone anthropique, de l’effet Suess océanique et de l’acidification des eaux de surface au cours des prochaines décennies
The ocean plays a very large role in the climate system due to the large exchange of carbon dioxide with the atmosphere and the recent shift of the exchanges towards a large oceanic sink of CO2 in the Anthropocene era. The North Atlantic and the Southern oceans are acknowledged to be major repositories of this anthropogenic carbon (Cant). Indeed, ~25% of the Cant penetrates through the surface waters of the North Atlantic and ~40% reside in the intermediate and mode waters of the Southern ocean. It has been established that this oceanic carbon sink presents a large time variability of seasonal to multidecadal times scales, but that is poorly known, resulting in large uncertainties in long term climate predictions. It has thus been recommended to focus observing efforts in the regions where the absorption of CO2 is large: the North Atlantic and the Southern oceans. In this frame, the study of the seasonal to decadal variability of the oceanic carbonate system is required to better understand the effects of current changes on the oceanic carbon cycle. I use data collected since the mid-1990s until 2021 within the framework of the two French surveys SURATLANT and OISO, in order to describe the spatial and temporal variability of parameters of the carbonate system (AT, CT, fCO2, pH and δ13CDIC) in the North Atlantic subpolar gyre (NASPG) as well as in the Indian sector of the Southern Ocean. I studied the physical and biogeochemical processes that control the evolution of fCO2, water acidification and the oceanic Suess effect, separating the anthropogenic induced changes from natural variability. The long-term evolution of fCO2 and pH during the period samples has a similar magnitude to the atmospheric CO2 increase and the overall surface ocean trends. Nonetheless, results can differ from this average view, depending on season, the particular region or specific periods. Cant increase has been identified as the prime driver controlling the observed changes in fCO2 and pH, but other processes modulate these tendencies. For instance, the warming (cooling) of the surface waters will increase (restrain) the increase of fCO2 and the decrease of pH. Furthermore, an increase of AT has been identified in both regions, which partially limit the increase of ocean acidification induced by Cant increase. Also, the data suggest that changes have been smaller since 2010, with even some reversal in the increase in fCO2 and ocean acidification, both in the NASPG than in the Antarctic region of the Southern Indian ocean. 13CDIC data seem to reinforce these conclusions and to identify a different Suess effect in the two regions. This additional parameter has nonetheless been less sampled and the current data do not allow to clearly identify the change since 2010. My work supports the need to continue the long-term observations in these key regions for anthropogenic CO2 export to the deep ocean, in order to better characterize the changes in anthropogenic carbon, the oceanic Suess effect, and the acidification of surface waters for the next decades

Les échanges indo-atlantiques d’eau subtropicale jouent un rôle essentiel dans le contrôle du climat global. L’intense activité de mésoechelle au sud de l’Afrique contribue fortement à ces échanges, mais reste mal connue. Un schéma de circulation de ces eaux veut que les gyres subtropicaux des océans voisins soient reliés en un super-gyre. A partir d’une série temporelle altimétrique de hauteur de mer de plus de douze ans, nous étudions les échanges par la « branche nord » du super-gyre (Indien vers Atlantique), et par la « branche sud » (sens inverse). Concernant la branche nord, une première étude de la rétrotiection du Courant des Aiguilles apporte une description statistique fine de son comportement, et met en évidence le rôle perturbateur de la bathymétrie locale. Puis, un suivi exhaustif des trajectoires d’anneaux des Aiguilles libérés par la rétroflection fait apparaître trois chemins types, en lien avec la bathymétrie régionale, dont les contributions aux échanges indo-atlantiques sont évaluées. Une application de ces études à des simulations régionales met en lumière une représentation imparfaite de la rétroflection et des trajectoires d’anneaux. Les échanges par la branche sud du super-gyre pourraient reposer sur l’écoulement associé au Front Subtropical, la continuité de ce front étant alors essentielle. Si celle-ci apparaît en vision moyenne, l’application d’une méthode développée pour positionner le front sur les champs de hauteur de mer hebdomadaires montre une forte perturbation du front par les structures de mésochelle à l’ouest de la rétroflection, et un tracé discontinu. Les mécanismes d’échanges par cette branche sont donc probablement plus complexes
Indo-Atlantic exchanges of subtropical water play a crucial role in controlling global climate. The intense mesoscale activity south of Africa contributes to these exchanges, yet remains poorly described. A commonly accepted circulation scheme of those waters assmues that the subtropical gyres of the neighbouring oceans are partially connected, forming a super-gyre. Using an altimeter-derived sea-level time series spanning over 12 years, we study the exchanges through the “northern branch” of the super-gyre (Indian to Atlantic ocean), and through the “southern branch” (opposite direction). Regarding the northern branch, an initial study of the Agulhas Current Retroflection yields a statistical description of its behaviour, and shows the disrupting role of local bathymetry. Then, a thorough tracking of all Agulhas Rings trajectories shed by the Retroflection yields 3 typical paths, linked to regional bathymetry, whose contributions to inter-ocean exchanges are evaluated. Applying the same methods to regional simulations shows inadequate behaviour of the Retroflection and ring trajectories. Exchanges through the southern branch of the super-gyre could be associated with the a jet-like flow of the Subtropical Front, the question of its continuity thus being crucial. If the front seems continuous in the mean sea level field, applying the method developed to locate the mean front to weekly SSH fields shows that mesoscale features west of the retroflection strongly disturb its path, making it discontinuous. Exchanges mechanisms through this branch are thus probably more complex

The Global Ocean constitutes about 97 per cent of all the water that exists on our planet. It is divided into five regional oceans: the Pacific, Atlantic, Indian, Arctic, and Southern oceans. ‘The oceanic environment’ looks at the structural features of the oceans, the composition of the water, the temperature, the light sources, water pressure, gases, and the living environment they contain. It also discusses the movement of the water throughout the oceans: at the surface in a series of five enormous, roughly circular, wind-driven current systems, or gyres, and at deeper levels, which transports oxygen, nutrients, and heat throughout the oceans, moderating the global climate.

This chapter censoriously appraises the comprehensive theories that specify that more concepts are needed to bridge the gap found between the dynamic of the Southern Indian Ocean and the actual MH370 vanishing mechanism. Thus, this chapter is devoted to the Rossby waves, which could attribute to the fact that the MH370 flaperon got to Réunion Island. In this view, Rossby waves generate growth of energy in the west of the ocean gyres and create the strengthening currents on the western side of the ocean basins. Pareto optimization algorithm of the impact power of Rossby waves proves that the flaperon could not drift across the Southern Indian Ocean and be positioned on Réunion Island.