South Atlantic circulation in a world ocean model

1994 ◽  
Vol 12 (9) ◽  
pp. 812-825 ◽  
Author(s):  
Matthew H. England ◽  
Véronique C. Garçon
Keyword(s):  
Indian Ocean ◽  
Atlantic Ocean ◽  
North Atlantic ◽  
Drake Passage ◽  
South Atlantic ◽  
South Atlantic Ocean ◽  
Global Ocean ◽  
Intermediate Water ◽  
Agulhas Current ◽  
Benguela Current

Abstract. The circulation in the South Atlantic Ocean has been simulated within a global ocean general circulation model. Preliminary analysis of the modelled ocean circulation in the region indicates a rather close agreement of the simulated upper ocean flows with conventional notions of the large-scale geostrophic currents in the region. The modelled South Atlantic Ocean witnesses the return flow and export of North Atlantic Deep Water (NADW) at its northern boundary, the inflow of a rather barotropic Antarctic Circumpolar Current (ACC) through the Drake Passage, and the inflow of warm saline Agulhas water around the Cape of Good Hope. The Agulhas leakage amounts to 8.7 Sv, within recent estimates of the mass transport shed westward at the Agulhas retroflection. Topographic steering of the ACC dominates the structure of flow in the circumpolar ocean. The Benguela Current is seen to be fed by a mixture of saline Indian Ocean water (originating from the Agulhas Current) and fresher Subantarctic surface water (originating in the ACC). The Benguela Current is seen to modify its flow and fate with depth; near the surface it flows north-westwards bifurcating most of its transport northward into the North Atlantic Ocean (for ultimate replacement of North Atlantic surface waters lost to the NADW conveyor). Deeper in the water column, more of the Benguela Current is destined to return with the Brazil Current, though northward flows are still generated where the Benguela Current extension encounters the coast of South America. At intermediate levels, these northward currents trace the flow of Antarctic Intermediate Water (AAIW) equatorward, though even more AAIW is seen to recirculate poleward in the subtropical gyre. In spite of the model's rather coarse resolution, some subtle features of the Brazil-Malvinas Confluence are simulated rather well, including the latitude at which the two currents meet. Conceptual diagrams of the recirculation and interocean exchange of thermocline, intermediate and deep waters are constructed from an analysis of flows bound between isothermal and isobaric surfaces. This analysis shows how the return path of NADW is partitioned between a cold water route through the Drake Passage (6.5 Sv), a warm water route involving the Agulhas Current sheeding thermocline water westward (2.5 Sv), and a recirculation of intermediate water originating in the Indian Ocean (1.6 Sv).

scholarly journals THE BIFURCATION OF THE WESTERN BOUNDARY CURRENT SYSTEM OF THE SOUTH ATLANTIC OCEAN

2014 ◽  
Vol 32 (2) ◽  
pp. 241 ◽  
Author(s):  
Janini Pereira ◽  
Mariela Gabioux ◽  
Martinho Marta Almeida ◽  
Mauro Cirano ◽  
Afonso M. Paiva ◽  
...  
Keyword(s):  
High Resolution ◽  
Atlantic Ocean ◽  
Ocean Circulation ◽  
South Atlantic ◽  
Western Boundary Current ◽  
South Atlantic Ocean ◽  
Western Boundary ◽  
Intermediate Water ◽  
Boundary Current ◽  
The South

ABSTRACT. The results of two high-resolution ocean global circulation models – OGCMs (Hybrid Coordinate Ocean Model – HYCOM and Ocean Circulation andClimate Advanced Modeling Project – OCCAM) are analyzed with a focus on the Western Boundary Current (WBC) system of the South Atlantic Ocean. The volumetransports are calculated for different isopycnal ranges, which represent the most important water masses present in this region. The latitude of bifurcation of the zonalflows reaching the coast, which leads to the formation of southward or northward WBC flow at different depths (or isopycnal levels) is evaluated. For the Tropical Water,bifurcation of the South Equatorial Current occurs at 13◦-15◦S, giving rise to the Brazil Current, for the South Atlantic Central Water this process occurs at 22◦S.For the Antarctic Intermediate Water, bifurcation occurs near 28◦-30◦S, giving rise to a baroclinic unstable WBC at lower latitudes with a very strong vertical shearat mid-depths. Both models give similar results that are also consistent with previous observational studies. Observations of the South Atlantic WBC system havepreviously been sparse, consequently these two independent simulations which are based on realistic high-resolution OGCMs, add confidence to the values presentedin the literature regarding flow bifurcations at the Brazilian coast.Keywords: Southwestern Atlantic circulation, water mass, OCCAM, HYCOM. RESUMO. Resultados de dois modelos globais de alta resolução (HYCOM e OCCAM) são analisados focando o sistema de Corrente de Contorno Oeste do Oceano Atlântico Sul. Os transportes de volume são calculados para diferentes níveis isopicnais que representam as principais massas de água da região. É apresentada a avaliação da latitude de bifurcação do fluxo zonal que atinge a costa, permitindo a formação dos fluxos da Corrente de Contorno Oeste para o sul e para o norte emdiferentes níveis de profundidades (ou isopicnal). Para a Água Tropical, a bifurcação da Corrente Sul Equatorial ocorre entre 13◦-15◦S, originando a Corrente do Brasil, e para a Água Central do Atlântico Sul ocorre em 22◦S. A bifurcação daÁgua Intermediária Antártica ocorre próximo de 28◦-30◦S, dando um aumento na instabilidade baroclínica da Corrente de Contorno Oeste em baixas latitudes e com um forte cisalhamento vertical em profundidades intermediárias. Ambos os modelos apresentamresultados similares e consistentes com estudos observacionais prévios. Considerando que as observações do sistema de Corrente de Contorno Oeste do Atlântico Sul são escassas, essas duas simulações independentes com modelos globais de alta resolução adicionam confiança aos valores apresentados na literatura, relacionadosaos fluxos das bifurcações na costa do Brasil.Palavras-chave: circulação do Atlântico Sudoeste, massas de água, OCCAM, HYCOM.

scholarly journals Water Mass Export from Drake Passage to the Atlantic, Indian, and Pacific Oceans: A Lagrangian Model Analysis

2005 ◽  
Vol 35 (7) ◽  
pp. 1206-1222 ◽  
Author(s):  
Yann Friocourt ◽  
Sybren Drijfhout ◽  
Bruno Blanke ◽  
Sabrina Speich
Keyword(s):  
Indian Ocean ◽  
General Circulation ◽  
Drake Passage ◽  
General Circulation Models ◽  
Lagrangian Model ◽  
Global Ocean ◽  
Western Boundary ◽  
Intermediate Water ◽  
Boundary Current ◽  
The Indian Ocean

Abstract The northward export of intermediate water from Drake Passage is investigated in two global ocean general circulation models (GCMs) by means of quantitative particle tracing diagnostics. This study shows that a total of about 23 Sv (Sv ≡ 106 m3 s−1) is exported from Drake Passage to the equator. The Atlantic and Pacific Oceans are the main catchment basins with 7 and 15 Sv, respectively. Only 1–2 Sv of the water exported to the Atlantic equator follow the direct cold route from Drake Passage without entering the Indian Ocean. The remainder loops first into the Indian Ocean subtropical gyre and flows eventually into the Atlantic Ocean by Agulhas leakage. The authors assess the robustness of a theory that relates the export from Drake Passage to the equator to the wind stress over the Southern Ocean. Our GCM results are in reasonable agreement with the theory that predicts the total export. However, the theory cannot be applied to individual basins because of interocean exchanges through the “supergyre” mechanism and other nonlinear processes such as the Agulhas rings. The export of water from Drake Passage starts mainly as an Ekman flow just northward of the latitude band of the Antarctic Circumpolar Current south of South America. Waters quickly subduct and are transferred to the ocean interior as they travel equatorward. They flow along the eastern boundaries in the Sverdrup interior and cross the southern basins northwestward to reach the equator within the western boundary current systems.

scholarly journals Freshening of Antarctic Intermediate Water in the South Atlantic Ocean in 2005–2014

2016 ◽  
Author(s):  
Wenjun Yao ◽  
Jiuxin Shi
Keyword(s):  
Atlantic Ocean ◽  
Ocean Circulation ◽  
Hydrological Cycle ◽  
World Ocean ◽  
South Atlantic ◽  
South Atlantic Ocean ◽  
Intermediate Water ◽  
Freshwater Input ◽  
The South ◽  
Antarctic Intermediate Water

Abstract. Basin-scaled freshening of Antarctic Intermediate Water (AAIW) is reported to have dominated South Atlantic Ocean during period from 2005 to 2014, as shown by the gridded monthly means Argo (Array for Real-time Geostrophic Oceanography) data. The relevant investigation was also revealed by two transatlantic occupations of repeated section along 30° S, from World Ocean Circulation Experiment Hydrographic Program. Freshening of the AAIW was compensated by the opposing salinity increase of thermocline water, indicating the contemporaneous hydrological cycle intensification. This was illustrated by the precipitation less evaporation change in the Southern Hemisphere from 2000 to 2014, with freshwater input from atmosphere to ocean surface increasing in the subpolar high-precipitation region and vice versa in the subtropical high-evaporation region. Against the background of hydrological cycle augment, the decreased transport of Agulhas Leakage (AL) was proposed to be one of the contributors for the associated freshening of AAIW. This indirectly estimated variability of AL, reflected by the weakening of wind stress over the South Indian Ocean since the beginning of 2000s, facilitates the freshwater input from source region and partly contributes to the observed freshened AAIW. Both of our mechanical analysis is qualitative, but this work would be helpful to validate and test predictably coupled sea-air model simulations.

Diaphus hudsoni (Pisces: Myctophidae), a new lanternfish from the South Atlantic Ocean

1976 ◽  
Vol 54 (9) ◽  
pp. 1538-1541
Author(s):  
R. E. Zurbrigg ◽  
W. B. Scott
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
South Atlantic ◽  
South Atlantic Ocean ◽  
The South ◽  
Gill Rakers ◽  
Royal Ontario Museum ◽  
The North ◽  
The North Atlantic

A new myctophid species, Diaphus hudsoni, was captured in the South Atlantic Ocean, and is described. It is similar to Diaphus subtilis Nafpaktitis, which occurs in the North Atlantic Ocean, but is definitely distinct with its slender, more numerous gill rakers (total 23–25), and non-continuous AOp–Prc series. The AO series numbers 5 + 5–6. The holotype is deposited in the Royal Ontario Museum, ROM 27569.

scholarly journals Derivation of seawater pCO<sub>2</sub> from net community production identifies the South Atlantic Ocean as a CO<sub>2</sub> source

2021 ◽  
Author(s):  
Daniel Ford ◽  
Gavin H. Tilstone ◽  
Jamie D. Shutler ◽  
Vassilis Kitidis
Keyword(s):  
Atlantic Ocean ◽  
Carbon Budget ◽  
South Atlantic ◽  
South Atlantic Ocean ◽  
Global Ocean ◽  
Biological Parameters ◽  
The South ◽  
Net Community Production ◽  
Chl A ◽  
Community Production

Abstract. A key step in assessing the global carbon budget is the determination of the partial pressure of CO2 in seawater (pCO2 (sw)). Spatially complete observational fields of pCO2 (sw)  are routinely produced for regional and global ocean carbon budget assessments by extrapolating sparse in situ measurements of pCO2 (sw) using satellite observations. Within these schemes, satellite chlorophyll a (Chl a) is often used as a proxy for the biological drawdown or release of CO2. Chl a does not however quantify carbon fixed through photosynthesis and then respired, which is determined by net community production (NCP). In this study, pCO2 (sw) over the South Atlantic Ocean is estimated using a feed forward neural network (FNN) scheme and either satellite derived NCP, net primary production (NPP) or Chl a to compare which biological proxy is the most accurate. Estimates of pCO2 (sw)  using NCP, NPP or Chl a were similar, but NCP was more accurate for the Amazon Plume and upwelling regions, which were not fully reproduced when using Chl a or NPP. Reducing the uncertainties in the satellite biological parameters to estimate pCO2 (sw), illustrated further improvement and greater differences for NCP compared to NPP or Chl a. Using NCP to estimate pCO2 (sw) showed that the South Atlantic Ocean is a CO2 source, whereas if no biological parameters are used in the FNN (following existing annual carbon assessments), this region becomes a sink for CO2. These results highlight that using NCP improved the accuracy of estimating pCO2 (sw), and changes the South Atlantic Ocean from a CO2 sink to a source. Reducing the uncertainties in NCP derived from satellite parameters will further improve our ability to quantify the global ocean CO2 sink.

scholarly journals Characteristics of Water Masses in the Atlantic Ocean based on GLODAPv2 data

2019 ◽  
Author(s):  
Mian Liu ◽  
Toste Tanhua
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
Deep Water ◽  
Bottom Water ◽  
South Atlantic ◽  
Weddell Sea ◽  
Water Masses ◽  
Intermediate Water ◽  
South Atlantic Central Water ◽  
The North

Abstract. The characteristics of the main water masses in the Atlantic Ocean are investigated and defined as Source Water Types (SWTs) from their formation area by six key properties based on the GLODAPv2 observational data. These include both conservative (potential temperature and salinity) and non-conservative (oxygen, silicate, phosphate and nitrate) variables. For this we divided the Atlantic Ocean into four vertical layers by distinct potential densities in the shallow and intermediate water column, and additionally by concentration of silicate in the deep waters. The SWTs in the upper/central water layer originates from subduction during winter and are defined as central waters, formed in four distinct areas; East North Atlantic Central water (ENACW), West North Atlantic Central Water (WNACW), East South Atlantic Central Water (ESACW) and West South Atlantic Central Water (WSACW). Below the upper/central layer the intermediate layer consist of three main SWTs; Antarctic Intermediate Water (AAIW), Subarctic Intermediate Water (SAIW) and Mediterranean Overflow Water (MOW). The North Atlantic Deep Water (NADW) is the dominating SWT in the deep and overflow layer, and is divided into upper and lower NADW based on the different origins and properties. The origin of both the upper and lower NADW is the Labrador Sea Water (LSW), the Iceland–Scotland Overflow Water (ISOW) and Denmark Strait Overflow Water (DSOW). Antarctic Bottom Water (AABW) is the only natural SWT in the bottom layer and this SWT is redefined as North East Atlantic Bottom Water (NEABW) in the north of equator due to the change of key properties, especial silicate. Similar with NADW, two additional SWTS, Circumpolar Deep Water (CDW) and Weddell Sea Bottom Water (WSBW), are defined in the Weddell Sea in order to understand the origin of AABW. The definition of water masses in biogeochemical space is useful for, in particular, chemical and biological oceanography to understand the origin and mixing history of water samples.

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