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.

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

Ocean Science ◽  
2017 ◽  
Vol 13 (4) ◽  
pp. 521-530 ◽  
Author(s):  
Wenjun Yao ◽  
Jiuxin Shi ◽  
Xiaolong Zhao
Keyword(s):  
Atlantic Ocean ◽  
Hydrological Cycle ◽  
World Ocean ◽  
South Atlantic ◽  
South Atlantic Ocean ◽  
Intermediate Water ◽  
Freshwater Input ◽  
The South ◽  
Antarctic Intermediate Water ◽  
Basin Scale

Abstract. Basin-scale freshening of Antarctic Intermediate Water (AAIW) is reported to have occurred in the South Atlantic Ocean during the period from 2005 to 2014, as shown by the gridded monthly means of the Array for Real-time Geostrophic Oceanography (Argo) data. This phenomenon was also revealed by two repeated transects along a section at 30° S, performed during the World Ocean Circulation Experiment Hydrographic Program. Freshening of the AAIW was compensated for by a salinity increase of thermocline water, indicating a hydrological cycle intensification. This was supported by the precipitation-minus-evaporation change in the Southern Hemisphere from 2000 to 2014. Freshwater input from atmosphere to ocean surface increased in the subpolar high-precipitation region and vice versa in the subtropical high-evaporation region. Against the background of hydrological cycle changes, a decrease in the transport of Agulhas Leakage (AL), which was revealed by the simulated velocity field, was proposed to be a contributor to the associated freshening of AAIW. Further calculation showed that such a decrease could account for approximately 53 % of the observed freshening (mean salinity reduction of about 0.012 over the AAIW layer). The estimated variability of AL was inferred from a weakening of wind stress over the South Indian Ocean since the beginning of the 2000s, which would facilitate freshwater input from the source region. The mechanical analysis of wind data here was qualitative, but it is contended that this study would be helpful to validate and test predictably coupled sea–air model simulations.

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 Oceanic Fluxes in the South Atlantic

2005 ◽  
Vol 35 (1) ◽  
pp. 109-122 ◽  
Author(s):  
Elaine L. McDonagh ◽  
Brian A. King
Keyword(s):  
Heat Flux ◽  
Ocean Circulation ◽  
World Ocean ◽  
South Atlantic ◽  
Freshwater Flux ◽  
Intermediate Water ◽  
The South ◽  
Cape Basin ◽  
Small Gain ◽  
The Difference

Abstract A box inverse of the World Ocean Circulation Experiment A10 (30°S) and A11 (nominally 45°S) sections in the South Atlantic Ocean was undertaken. The authors find a heat flux across A10 of 0.22 ± 0.08 PW, consistent with previous studies, and a heat flux of 0.43 ± 0.08 PW across A11. The A11 heat flux is lower than some previous analyses of this section but implies a plausible oceanic heat convergence (heat loss to the atmosphere) of 0.21 ± 0.10 PW. The difference is principally due to adding a cyclonic component to the circulation in the Cape Basin. As compared with the solution of other studies, the anticyclonic circulation in the surface and intermediate water of the subtropical gyre is weakened. The circulation of the deep water is cyclonic rather than anticyclonic; this is in better agreement with previously published circulation schemes based on examination of water properties. A southward freshwater flux of 0.7 Sv (1 Sv ≡ 106 m3 s−1) at A11, consistent with previous inverse studies, is still inconsistent with the net Atlantic evaporation inferred from integrated surface climatologies. Results suggest a small gain of freshwater (0.2 ± 0.1 Sv) between the sections.

scholarly journals Simulation of the South Atlantic Ocean circulation and its seasonal variability

1998 ◽  
Vol 103 (C5) ◽  
pp. 10241-10251 ◽  
Author(s):  
Jianping Gan ◽  
Lawrence A. Mysak ◽  
David N. Straub
Keyword(s):  
Atlantic Ocean ◽  
Ocean Circulation ◽  
Seasonal Variability ◽  
South Atlantic ◽  
South Atlantic Ocean ◽  
The South
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