Strong Mixing and Recirculation in the Northwestern Argentine Basin

The Atlantic component of the Meridional Overturning Circulation (AMOC) is a key contributor to the global meridional transport of volume, salt, and heat, and thus plays a central role in global climate. As part of ongoing efforts to monitor the intensity and variability of the AMOC in the South Atlantic, hydrographic sections have been regularly occupied since 2009 near the western boundary along a zonal line at 34.5°S. Here this high-quality, high-resolution data set is analyzed to establish the average hydrographic conditions of the northwestern Argentine Basin and the water mass spatial and temporal variability. The water mass analysis also reveals the pathways of the flow in this region, which are further corroborated by full-depth direct velocity measurements. The repeated hydrographic sections capture an extremely rich vertical structure, characterized by seven distinct water mass layers of northern and southern origin, each with unique property signatures. Almost all of these layers exhibit a sharp zonally banded structure, which is indicative of recirculation cells offshore from the western boundary. The circulation at intermediate levels includes a previously undetected recirculation cell confined very close to the western boundary and superimposed on the classical intermediate water pathway beneath the South Atlantic subtropical gyre. The deep level flow is characterized by the Deep Western Boundary Current (DWBC) and a northward recirculation ~500 km east from the slope.Fil: Valla, Daniel. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; ArgentinaFil: Piola, Alberto Ricardo. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; ArgentinaFil: Meinen, Christopher S.. Atlantic Oceanographic and Meteorological Laboratory; Estados UnidosFil: Campos, Edmo. Universidade de Sao Paulo; Brasi

Observed Ocean Bottom Temperature Variability at Four Sites in the Northwestern Argentine Basin: Evidence of Decadal Deep/Abyssal Warming Amidst Hourly to Interannual Variability During 2009–2019

Consecutive multiyear records of hourly ocean bottom temperature measurements are merged to produce new decade-long time series at four depths ranging from 1,360 to 4,757 m within the northwest Argentine Basin at 34.5°S. Energetic temperature variations are found at a wide range of time scales. All sites exhibit fairly linear warming trends of approximately 0.02–0.04°C per decade over the period 2009–2019, although the trends are only statistically different from zero at the two deepest sites at depths of ~4,500–4,800 m. Near-bottom temperatures from independent conductivity-temperature-depth profiles collected at these same locations every 6–24 months over the same decade show roughly consistent trends. Based on the distribution of spectral energies at the deepest sites and a Monte Carlo-style analysis, sampling at least once per year is necessary to capture the significant warming trends over this decade to within 50% error bars at a 95% confidence limit.Fil: Meinen, Christopher S.. National Ocean And Atmospheric Administration; Estados UnidosFil: Perez, Renellys C.. National Ocean And Atmospheric Administration; Estados UnidosFil: Dong, Shenfu. National Ocean And Atmospheric Administration; Estados UnidosFil: Piola, Alberto Ricardo. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; Argentina. Instituto Franco-Argentino sobre Estudios del Clima y sus Impactos; Argentina. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Campos, Edmo. Universidade de Sao Paulo; Brasil. American University Of Sharjah.; Emiratos Árabes Unido

A numerical study of the Plata River plume along the southeastern South American continental shelf

O Rio da Prata, um dos maiores rios da Terra, descarrega no oceano águas de uma bacia de drenagem que cobre uma ampla área da América do Sul. Sua pluma extende-se ao longo do norte da Argentina, Uruguay e sul do Brasil influenciando amplamente os ecossistemas costeiros. A despeito disso, pouco se sabe a respeito dos mecanismos que a controlam. Relatamos aqui simulações conduzidas com o modelo POM na investigação do papel dos ventos e da descarga fluvial na dinâmica da pluma do Prata. Descargas com valores médios climatológicos e magnitudes representativas de El Niño e La Niña foram explorados. Somente sob descarga fluvial, a velocidade média de penetração da pluma ao longo da costa foi diretamente relacionada à vazão. Sua extensão variou entre 850 e 1550 km e no caso da vazão média uma banda de baixa salinidade formou-se desde o estuário até 30ºN na plataforma continental sul brasileira. O efeito de ventos de sudoeste, que causam subsidência, e de nordeste, que promovem a ressurgência costeira, foram investigados após 130 dias de descarga fluvial. Os resultados sugerem que a distribuição de baixa salinidade é muito mais sensível à direção dos ventos do que à descarga fluvial. Ventos de sudoeste são capazes de advectar o sinal de baixa salinidade ao longo da costa. Já os ventos de nordeste demonstram ser eficientes na erosão da pluma, que é destacada da costa por deriva de Ekman. Uma intrusão anormal da pluma de baixa salinidade em direção a baixas latitudes pode ser o resultado da posição original da pluma acoplada a eventos persistentes de fortes ventos de sudoeste.The Rio de la Plata, one of the largest rivers on Earth, discharges into the ocean waters from basin that covers a large area of South America. Its plume extends along northern Argentina, Uruguay, and southern Brazil shelves strongly influencing the ecosystems. In spite of this, little is known about the mechanisms that control it. Here we report results of simulations with POM carried out to investigate the roles of wind and river discharge in Plata plume dynamics. Different outflows were explored, including an average climatological value and magnitudes representative of La Niña and El Niño. Forcing the model with river discharge the average plume speed was directly related to the outflow intensity. The Plata northward extension varied from 850 to 1550 km and for average discharge a band of low salinity waters formed from the estuary up to 30ºN of South Brazilian Shelf. Upwelling and downwelling winds were applied after 130 days. The distribution of low salinity waters over the shelf was more sensitive to the wind direction than to the river outflow variability. Downwelling winds were very capable of advecting the low salinity signal downshelf. Upwelling winds were efficient in eroding the plume, which was basically detached from the coast by Ekman drift. Abnormal plume intrusions toward low latitudes may be a result of the original plume position coupled with events of persistent strong downwelling favorable winds

Physical Oceanography of the Southwest Atlantic Ocean

First Paragraph: From its littoral margin to the open ocean, the western South Atlantic (Fig. 1) is marked at all depths by circulation patterns and exchange processes that are centrally important to the regional marine resources and local economies, and to the global flux of heat and dissolved substances. Among other important characteristics, the Southwest Atlantic (SWA) is characterized by the presence of the Brazil Current (BC), a warm western boundary current that, while weaker than the Gulf Stream in terms of mass transport, is energetically comparable to its North Atlantic counterpart, particularly in the region of confluence with the northward-flowing Malvinas Current (MC) at approximately 38°S. Because of the wide range of issues needed to be understood in terms of the physical oceanography, this oceanic region has been addressed by several important scientific programs, a few of which are listed in Table 1 and indicated on Fig. 2. Results from these and other programs are summarized here and recommendations for future efforts are offered

Dominant Modes of Variability in the South Atlantic: A Study with a Hierarchy of Ocean-Atmosphere Models.

Abstract Using an atmosphere model of intermediate complexity and a hierarchy of ocean models, the dominant modes of interannual and decadal variability in the South Atlantic Ocean are studied. The atmosphere Simplified Parameterizations Primitive Equation Dynamics (SPEEDY) model has T30L7 resolution. The physical package consists of a set of simplified physical parameterization schemes, based on the same principles adopted in the schemes of state-of-the-art AGCMs. It is at least an order of magnitude faster, whereas the quality of the simulated climate compares well with those models. The hierarchy of ocean models consists of simple mixed layer models with an increasing number of physical processes involved such as Ekman transport, wind-induced mixing, and wind-driven barotropic transport. Finally, the atmosphere model is coupled to a regional version of the Miami Isopycnal Coordinate Ocean Model (MICOM) covering the South Atlantic with a horizontal resolution of 1° and 16 vertical layers. The coupled modes of mean sea level pressure and sea surface temperature simulated by SPEEDY–MICOM strongly resemble the modes as analyzed from the NCEP–NCAR reanalysis, indicating that this model configuration possesses the required physical mechanisms for generating these modes of variability. Using the ocean model hierarchy the authors were able to show that turbulent heat fluxes, Ekman transport, and wind-induced mixing contribute to the generation of the dominant modes of coupled SST variability. The different roles of these terms in generating these modes are analyzed. Variations in the wind-driven barotropic transport mainly seem to affect the SST variability in the Brazil–Malvinas confluence zone. The spectra of the mixed layer models appeared to be too red in comparison with the fully coupled SPEEDY–MICOM model due to the too strong coupling between SST and surface air temperatures (SATs), resulting from the inability to advect and subduct SST anomalies by the mixed layer models. In SPEEDY–MICOM anomalies in the southeastern corner of the South Atlantic are subducted and advected toward the north Brazilian coast on a time scale of about 6 yr

Brazil Current volume transport variability during 2009-2015 from a longterm moored array at 34.5°S

The Brazil Current, the western limb of the subtropical gyre of the South Atlantic Ocean, is one of the major Western Boundary Currents of the global ocean. Here, we present the first multiyear continuous daily time series of Brazil Current absolute volume transport obtained using 6+ years of observations from a line of four pressure-recording inverted echo sounders (PIES) deployed at 34.5°S. The array was augmented in December 2012 with two current meter-equipped PIES and in December 2013 with a moored Acoustic Doppler Current Profiler on the upper continental slope. The Brazil Current is bounded by the sea surface and the neutral density interface separating South Atlantic Central Water and Antarctic Intermediate Water, which is on average at a reference pressure of 628 ± 46 dbar, and it is confined west of 49.5°W. The Brazil Current has a mean strength of −14.0 ± 2.8 Sv (1 Sv ≡ 106 m3 s−1; negative indicates southward flow) with a temporal standard deviation of 8.8 Sv and peak-to-peak range from −41.7 to +20 Sv. About 80% of the absolute transport variance is concentrated at periods shorter than 150 days with a prominent peak at 100 days. The baroclinic component accounts for 85% of the absolute transport variance, but the barotropic variance is not negligible. The baroclinic and barotropic transports are uncorrelated, demonstrating the need to measure both transport components independently. Given the energetic high frequency transport variations, statistically significant seasonal to interannual variability and trends have yet to be detected.Fil: Chidichimo, María Paz. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval. Departamento Oceanografía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Franco-Argentino sobre Estudios del Clima y sus Impactos; Argentina. Centre National de la Recherche Scientifique. Institut de Recherche pour le Developpement. Département Ecologie, Biodiversité et Fonctionnement des Ecosystèmes Continentaux; FranciaFil: Piola, Alberto Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; Argentina. Instituto Franco-Argentino sobre Estudios del Clima y sus Impactos; Argentina. Centre National de la Recherche Scientifique. Institut de Recherche pour le Developpement. Département Ecologie, Biodiversité et Fonctionnement des Ecosystèmes Continentaux; FranciaFil: Meinen, Christopher S.. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval. Departamento Oceanografía; Argentina. National Ocean And Atmospheric Administration; Estados UnidosFil: Perez, Renellys. National Ocean And Atmospheric Administration; Estados UnidosFil: Campos, Edmo. Universidade de Sao Paulo; Brasil. American University Of Sharjah.; Emiratos Árabes UnidosFil: Dong, Shenfu. National Ocean And Atmospheric Administration; Estados UnidosFil: Lumpkin, Rick. National Ocean And Atmospheric Administration; Estados UnidosFil: Garzoli, S. L.. National Ocean And Atmospheric Administration; Estados Unido

Registro do gradiente latitudinal, de descargas de rios e de massas de água ao longo da costa subtropical da América do Sul, utilizando-se associações de foraminíferos bentônicos

Mais de 30% de dominância de Buccella peruviana, Globocassidulina crassa porrecta, Cibicides mackannai e C. refulgens indica a presença de água fria da Corrente Subantártica de plataforma no inverno entre 33,5-38,3° S, principalmente no setor sul da area estudada. No verão, no entanto, nas estações mais profundas do que 100 m, a abundância dessa\ud associação diminui para menos de 15% em torno de 37,5-38,9° S, onde duas espécies (Globocassidulina subglobosa e Uvigerina peregrina) dominam. G. subglobosa, U. peregrina e Hanzawaia boueana são encontradas principalmente em menos de 55 m de profundidade na parte norte da área (27-33° S), tanto no inverno como no verão, e estão relacionadas\ud com águas mais quentes de Plataforma Subtropical e de Água Tropical. Em quatro áreas da plataforma continental, foi observada a influência de aporte continental com alta concentração de silicato no sedimento. Essa influência é detectada pela presença de Pseudononion atlanticum, Bolivina striatula, Buliminella elegantissima, Bulimina elongata,\ud Elphidium excavatum, E. poeyanum, Ammobaculites exiguus, Arenoparrella mexicana, Gaudryina exillis, Textularia earlandi e tecamebas. A presença de Bulimina marginata entre 34,1-32,8° S no inverno e 34,2-32,7° S no verão indica que a influência da Frente Subtropical Plataforma sobre os sedimentos não muda azonalmente; mas, por outro lado, a presença de Angulogerina angulosa no inverno, apenas na estação mais profunda de Mar del Plata (38,9° S), mostra que as correntes das Malvinas não estão influenciando o sedimento dessa região no verão

Highly variable upper and abyssal overturning cells in the South Atlantic

The Meridional Overturning Circulation (MOC) is a primary mechanism driving oceanic heat redistribution on Earth, thereby affecting Earth’s climate and weather. However, the full-depth structure and variability of the MOC are still poorly understood, particularly in the South Atlantic. This study presents unique multiyear records of the oceanic volume transport of both the upper (~3100 meters) overturning cells based on daily moored measurements in the South Atlantic at 34.5°S. The vertical structure of the time-mean flows is consistent with the limited historical observations. Both the upper and abyssal cells exhibit a high degree of variability relative to the temporal means at time scales, ranging from a few days to a few weeks. Observed variations in the abyssal flow appear to be largely independent of the flow in the overlying upper cell. No meaningful trends are detected in either cell.Fil: Kersalé, Marion. National Ocean And Atmospheric Administration; Estados Unidos. University of Miami; Estados UnidosFil: Meinen, Christopher S.. National Ocean And Atmospheric Administration; Estados UnidosFil: Perez, Renellys C.. National Ocean And Atmospheric Administration; Estados UnidosFil: Le Hénaff, Matthieu. National Ocean And Atmospheric Administration; Estados Unidos. University of Miami; Estados UnidosFil: Valla, Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval. Departamento Oceanografía; ArgentinaFil: Lamont, Tarron. University of Cape Town; SudáfricaFil: Sato, Olga T.. Universidade de Sao Paulo; BrasilFil: Dong, Shenfu. National Ocean And Atmospheric Administration; Estados UnidosFil: Terre, T.. University of Brest; Francia. Centre National de la Recherche Scientifique; FranciaFil: van Caspel, M.. Universidade de Sao Paulo; BrasilFil: Chidichimo, María Paz. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval. Departamento Oceanografía; ArgentinaFil: van den Berg, Marcel Alexander. Department of Environmental Affairs; SudáfricaFil: Speich, Sabrina. University Of Cape Town; SudáfricaFil: Piola, Alberto Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Ecole Normale Superieure. Laboratoire de Meteorologie Dynamique; Francia. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval. Departamento Oceanografía; Argentina. Instituto Franco-Argentino sobre Estudios del Clima y sus Impactos; Argentina. Universidad de Buenos Aires; ArgentinaFil: Campos, Edmo. Universidade de Sao Paulo; Brasil. American University Of Sharjah.; Emiratos Árabes UnidosFil: Ansorge, Isabelle. University of Cape Town; SudáfricaFil: Volkov, Denis L.. University of Miami; Estados Unidos. National Ocean And Atmospheric Administration; Estados UnidosFil: Lumpkin, Rick. National Ocean And Atmospheric Administration; Estados UnidosFil: Garzoli, S. L.. University of Miami; Estados Unidos. National Ocean And Atmospheric Administration; Estados Unido