Water Mass Transformation and Subduction in the South Atlantic

2005 ◽  
Vol 35 (10) ◽  
pp. 1841-1860 ◽  
Author(s):  
J. Donners ◽  
S. S. Drijfhout ◽  
W. Hazeleger
Keyword(s):  
Surface Water ◽  
Indian Ocean ◽  
Mixed Layer ◽  
Water Mass ◽  
South Atlantic ◽  
Water Masses ◽  
Intermediate Water ◽  
Tropical Atlantic ◽  
The South ◽  
The Indian Ocean

Abstract The transformation of water masses induced by air–sea fluxes in the South Atlantic Ocean is calculated with a global ocean model, Ocean Circulation and Climate Advanced Modeling (OCCAM), and has been compared with several observational datasets. Air–sea interaction supplies buoyancy to the ocean at almost all density levels. The uncertainty of the estimates of water mass transformations is at least 10 Sv (Sv ≡ 106 m3 s−1), largely caused by the uncertainties in heat fluxes. Further analysis of the buoyancy budget of the mixed layer in the OCCAM model shows that diffusion extracts buoyancy from the water column at all densities. In agreement with observations, water mass formation of surface water by air–sea interaction is completely balanced by consumption from diffusion. There is a large interocean exchange with the Indian and Pacific Oceans. Intermediate water is imported from the Pacific, and light surface water is imported from the Indian Ocean. South Atlantic Central Water and denser water masses are exported to the Indian Ocean. The air–sea formation rate is only a qualitative estimate of the sum of subduction and interocean exchange. Subduction generates teleconnections between the South Atlantic and remote areas where these water masses reemerge in the mixed layer. Therefore, the subduction is analyzed with a Lagrangian trajectory analysis. Surface water obducts in the South Atlantic, while all other water masses experience net subduction. The subducted Antarctic Intermediate Water and Subantarctic Mode Water reemerge mainly in the Antarctic Circumpolar Current farther downstream. Lighter waters reemerge in the eastern tropical Atlantic. As a result, the extratropical South Atlantic has a strong link with the tropical Atlantic basin and only a weak direct link with the extratropical North Atlantic. The impact of the South Atlantic on the upper branch of the thermohaline circulation is indirect: water is significantly transformed by air–sea fluxes and mixing in the South Atlantic, but most of it reemerges and subducts again farther downstream.

Decadal Variability of Thermocline and Intermediate Waters at 24°S in the South Atlantic

2011 ◽  
Vol 41 (1) ◽  
pp. 157-165 ◽  
Author(s):  
Gerard McCarthy ◽  
Elaine McDonagh ◽  
Brian King
Keyword(s):  
Indian Ocean ◽  
Decadal Variability ◽  
Hydrological Cycle ◽  
South Atlantic ◽  
Water Masses ◽  
Intermediate Water ◽  
The South ◽  
Oxygen Utilization ◽  
Salinity Changes ◽  
Intermediate Waters

Abstract New data are presented from 24°S in the South Atlantic in an investigation of the decadal variability of the intermediate and thermocline water masses at this latitude. Variation of salinity on neutral density surfaces is investigated with three transatlantic, full-depth hydrographic sections from 1958, 1983, and 2009. The thermocline is seen to freshen by 0.05 between 1983 and 2009. The freshening is coherent, basinwide, and of a larger magnitude than any errors associated with the datasets. This freshening reverses a basinwide, coherent increase in salinity of 0.03 in the thermocline between 1958 and 1983. Changes in apparent oxygen utilization (AOU) are investigated to support the salinity changes. In the thermocline of the eastern basin, a correlated relationship exists between local AOU and salinity anomalies, which is consistent with the influence of Indian Ocean Water. This correlated relationship is utilized to estimate the magnitude of Indian Ocean influence on the salinity changes in the thermocline. Indian Ocean influence explains half of the salinity changes in the eastern thermocline from 1958 to 1983 but less of the salinity change in the eastern thermocline from 1983 to 2009. Antarctic Intermediate Water properties significantly warm from 1958 through 1983 to 2009. A significant salinification and increase in AOU is evident from 1958 to 1983. Changes in the salinity of AAIW are shown to be linked with Indian Ocean influence rather than changes in the hydrological cycle. Upper Circumpolar Deep Water is seen to be progressively more saline from 1958 through 1983 to 2009. Increased Agulhas leakage and the intensification of the hydrological cycle are conflicting influences on the salinity of thermocline and intermediate waters in the South Atlantic as the former acts to increase the salinity of these water masses and the latter acts to decrease the salinity of these water masses. The results presented here offer an interpretation of the salinity changes, which considers both of these conflicting influences.

The representation of the South Tropical Atlantic teleconnection to the Indian Ocean in the AR4 coupled models

2011 ◽  
Vol 38 (5-6) ◽  
pp. 1147-1166 ◽  
Author(s):  
Rondrotiana Barimalala ◽  
Annalisa Bracco ◽  
Fred Kucharski
Keyword(s):  
Indian Ocean ◽  
Tropical Atlantic ◽  
The South ◽  
Coupled Models ◽  
The Indian Ocean

Hydrology of the Indian Ocean. III. Water masses of the upper 500 metres of the South-east Indian Ocean

1964 ◽  
Vol 15 (1) ◽  
pp. 25 ◽  
Author(s):  
DJ Rochford
Keyword(s):  
Indian Ocean ◽  
Persian Gulf ◽  
Water Mass ◽  
Sea Water ◽  
Core Layer ◽  
Water Masses ◽  
Intermediate Water ◽  
Surface Currents ◽  
North West ◽  
East Indian

The following seven water masses have been identified, and their distribution traced during several seasons of the year: Red Sea mass, with the same distribution and properties in 1962 as the north-west Indian Intermediate described in 1959-60; Persian Gulf mass, which is confined to the region south of Indonesia and is limited in extent of easterly flow by the opposing flow of Banda Intermediate water; upper salinity minimum mass, entering via Lombok Strait and moving zonally in the direction of the prevailing surface currents, a secondary movement of this water mass towards north-west Australia is limited by the northern boundary of a south-east Indian high salinity water mass. This latter water mass occurs as three separate core layers north of 22-23� S. The deep core layer mixes with waters of the oxygen maximum below it, the mid-depth core layer mixes with Persian Gulf and upper salinity minimum water masses, and the upper core layer mixes with the Arabian Sea water mass. The latter water mass spreads eastwards to about 120� E. and southwards to north-west Australia, in conformity with surface currents. A sixth water mass enters with the counter-current and is found as a salinity maximum within the thermocline to about 20� S. A seventh water mass characterized by a salinity maximum around temperatures of 28-29�C has a limited distribution and an unknown origin. Both of these water masses move in the direction of surface currents.

scholarly journals The Role of Interocean Exchanges on Decadal Variations of the Meridional Heat Transport in the South Atlantic

2011 ◽  
Vol 41 (8) ◽  
pp. 1498-1511 ◽  
Author(s):  
Shenfu Dong ◽  
Silvia Garzoli ◽  
Molly Baringer
Keyword(s):  
Indian Ocean ◽  
Heat Transport ◽  
South Atlantic ◽  
Similar Response ◽  
The South ◽  
Meridional Heat Transport ◽  
Interior Region ◽  
The Pacific ◽  
The Indian Ocean

Abstract The interocean exchange of water from the South Atlantic with the Pacific and Indian Oceans is examined using the output from the ocean general circulation model for the Earth Simulator (OFES) during the period 1980–2006. The main objective of this paper is to investigate the role of the interocean exchanges in the variability of the Atlantic meridional overturning circulation (AMOC) and its associated meridional heat transport (MHT) in the South Atlantic. The meridional heat transport from OFES shows a similar response to AMOC variations to that derived from observations: a 1 Sv (1 Sv ≡ 106 m3 s−1) increase in the AMOC strength would cause a 0.054 ± 0.003 PW increase in MHT at approximately 34°S. The main feature in the AMOC and MHT across 34°S is their increasing trends during the period 1980–93. Separating the transports into boundary currents and ocean interior regions indicates that the increase in transport comes from the ocean interior region, suggesting that it is important to monitor the ocean interior region to capture changes in the AMOC and MHT on decadal to longer time scales. The linear increase in the MHT from 1980 to 1993 is due to the increase in advective heat converged into the South Atlantic from the Pacific and Indian Oceans. Of the total increase in the heat convergence, about two-thirds is contributed by the Indian Ocean through the Agulhas Current system, suggesting that the warm-water route from the Indian Ocean plays a more important role in the northward-flowing water in the upper branch of the AMOC at 34°S during the study period.

Mixing Trajectories of Intermediate Depth Waters of the South-East Indian Ocean as Determined by a Salinity Frequency Method

1963 ◽  
Vol 14 (1) ◽  
pp. 1 ◽  
Author(s):  
DJ Rochford
Keyword(s):  
Indian Ocean ◽  
Water Masses ◽  
Intermediate Water ◽  
The South ◽  
Intermediate Depth ◽  
East Indian ◽  
The Core ◽  
Deep Mixing ◽  
Core Method ◽  
East Indian Ocean

A new method for the detection of water masses and for the tracing of their mixing paths is described. Histograms of the salinity frequency distribution on 0.10 σt intervals from σt 26.90 to 27.70 contain modes which indicate the salinity characteristics of the intermediate water masses of the south-east Indian Ocean. These salinity characteristics are used to trace the extent of spreading of the water masses on these σt intervals and to determine trajectories of shallow and deep mixing. Comparison is made of the results obtained by the new method with those by the core method for the water masses and circulation in intermediate depth of the south-east Indian Ocean. The core method in this region has not been able to show the large extent of deep mixing associated with the spreading of the Banda and Antarctic Intermediate water masses. The core method has also failed to show the widespread distribution of patches of Banda water at about 400-500 m throughout the whole south-east Indian Ocean.

Southern by Degrees

2017 ◽  
Author(s):  
Isabel Hofmeyr
Keyword(s):  
Indian Ocean ◽  
South Atlantic ◽  
Literary Representations ◽  
The South ◽  
Anglophone Literature ◽  
Subantarctic Islands ◽  
Imperial Expansion ◽  
The Indian Ocean ◽  
The Antarctic

From the perspective of Anglophone literature, the South Atlantic has been something of a blank—in colonial maritime fiction, a prefatory space leading up to the Cape of Storms or on the journey home, a fast-forward space as the ship hurries to the metropole. This article suggests that one way to fill this blank is to focus on the subantarctic islands of the South Atlantic and the Indian Ocean. This insular world played a key role in the scramble for the Antarctic and reproduces the role of islands in imperial expansion elsewhere. The article examines two contrasting literary representations of these island worlds: H. Rider Haggard’s novel Mary of Marion Isle and Yvette Christiansë’s collection of poetry Imprendehora.

scholarly journals Revisiting remote drivers of the 2014 drought in South-Eastern Brazil

2020 ◽  
Vol 55 (11-12) ◽  
pp. 3197-3211
Author(s):  
Kathrin Finke ◽  
Bernat Jiménez-Esteve ◽  
Andréa S. Taschetto ◽  
Caroline C. Ummenhofer ◽  
Karl Bumke ◽  
...  
Keyword(s):  
Indian Ocean ◽  
General Circulation ◽  
Circulation Model ◽  
Tropical Pacific ◽  
South Atlantic ◽  
The South ◽  
South Eastern ◽  
Eastern Brazil ◽  
The Indian Ocean ◽  
Sst Anomalies

Abstract South-Eastern Brazil experienced a devastating drought associated with significant agricultural losses in austral summer 2014. The drought was linked to the development of a quasi-stationary anticyclone in the South Atlantic in early 2014 that affected local precipitation patterns over South-East Brazil. Previous studies have suggested that the unusual blocking was triggered by tropical Pacific sea surface temperature (SST) anomalies and, more recently, by convection over the Indian Ocean related to the Madden–Julian Oscillation. Further investigation of the proposed teleconnections appears crucial for anticipating future economic impacts. In this study, we use numerical experiments with an idealized atmospheric general circulation model forced with the observed 2013/2014 SST anomalies in different ocean basins to understand the dominant mechanism that initiated the 2014 South Atlantic anticyclonic anomaly. We show that a forcing with global 2013/2014 SST anomalies enhances the chance for the occurrence of positive geopotential height anomalies in the South Atlantic. However, further sensitivity experiments with SST forcings in separate ocean basins suggest that neither the Indian Ocean nor tropical Pacific SST anomalies alone have contributed significantly to the anomalous atmospheric circulation that led to the 2014 South-East Brazil drought. The model study rather points to an important role of remote forcing from the South Pacific, local South Atlantic SSTs, and internal atmospheric variability in driving the persistent blocking over the South Atlantic.

scholarly journals A ÁFRICA DO SUL, O ATLÂNTICO SUL E A EQUAÇÃO IBAS-BRICS: O ESPAÇO TRANSATLÂNTICO EM TRANSIÇÃO

2013 ◽  
Vol 2 (3) ◽  
pp. 77-106 ◽  
Author(s):  
Francis Kornegay
Keyword(s):  
South Africa ◽  
Developing Countries ◽  
Indian Ocean ◽  
South Atlantic ◽  
Great Powers ◽  
African Continent ◽  
The South ◽  
The Indian Ocean

In a context of increasing South-South cooperation, the members of an important trilateral dialogue forum that represent the emergent powers – IBSA –, have been incorporated into another organization, BRICS. It resulted from an overlap of the Southern developing countries into the domain of the Euro-Asiatic great powers. Bearing in mind that both alliances are centered on the geostrategic space of the Indian Ocean and the South Atlantic, South Africa´s South Atlantic strategic potential in tandem with Brazil is of extreme importance. It is possible to differentiate two steams in the transatlantic ties: the Afro-Latin and the trans-Mediterranean.  It is also relevant to place the role of Angola in the African continent as a possible influence in South Atlantic´s dynamics, given due importance to the Lusophone ties which are represented by CPLP.

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