scholarly journals Seasonal Variability of the South Equatorial Current Bifurcation in the Atlantic Ocean: A Numerical Study

2007 ◽  
Vol 37 (1) ◽  
pp. 16-30 ◽  
Author(s):  
Regina R. Rodrigues ◽  
Lewis M. Rothstein ◽  
Mark Wimbush
Keyword(s):  
Seasonal Variability ◽  
Numerical Study ◽  
South American ◽  
The South ◽  
Wind Stress Curl ◽  
South Equatorial Current ◽  
The North ◽  
Brazil Current ◽  
North Brazil ◽  
Equatorial Current

Abstract In this study, a reduced-gravity, primitive equation OGCM is used to investigate the seasonal variability of the bifurcation of the South Equatorial Current (SEC) into the Brazil Current (BC) to the south and the North Brazil Undercurrent/Current (NBUC/NBC) system to the north. Annual mean meridional velocity averaged within a 2° longitude band off the South American coast shows that the SEC bifurcation occurs at about 10°–14°S near the surface, shifting poleward with increasing depth, reaching 27°S at 1000 m, in both observations and model. The bifurcation latitude reaches its southernmost position in July (∼17°S in the top 200 m) and its northernmost position in November (∼13°S in the top 200 m). The model results show that most of the seasonal variability of the bifurcation latitude in the upper thermocline is associated with changes in the local wind stress curl due to the annual north–south excursion of the marine ITCZ complex. As the SEC bifurcation latitude moves south (north) the NBUC transport increases (decreases) and the BC transport decreases (increases). The remote forcing (i.e., westward propagation of anomalies) appears to have a smaller impact on the seasonal variability of the bifurcation in the upper thermocline.

scholarly journals Seasonal Variation of the Pacific South Equatorial Current Bifurcation

2015 ◽  
Vol 45 (6) ◽  
pp. 1757-1770 ◽  
Author(s):  
Zhaohui Chen ◽  
Lixin Wu
Keyword(s):  
Wave Propagation ◽  
Seasonal Variation ◽  
Rossby Wave ◽  
Wind Forcing ◽  
The South ◽  
Wind Stress Curl ◽  
South Equatorial Current ◽  
Wave Dynamics ◽  
Equatorial Current ◽  
Rossby Wave Propagation

AbstractThe seasonal variation of the South Equatorial Current (SEC) bifurcation off the Australian coast in the South Pacific (SP) is investigated with observations and a nonlinear, reduced-gravity, primitive equation model of the upper ocean. The mean SEC bifurcation latitude (SBL) integrated over the upper thermocline is around 17.5°S, almost 2° south of the position predicted by Sverdrup theory. For its seasonal variation, the SBL reaches its southernmost position in June/July and its northernmost position in November/December. The south–north migration of 2.7° is twice as large as its counterpart in the North Pacific. It is found that the large seasonal amplitude of the SBL results from the combined effect of Low-Lat-SP and Non-Low-Lat-SP processes. The Low-Lat-SP process (referred to as the Rossby wave dynamics forced by the wind stress curl over the low-latitude SP) accounts for almost ⅔ of the SBL seasonal variability, and the Non-Low-Lat-SP processes account for ⅓. Both of these processes are responsible for its south–north migration but in different ways. The Low-Lat-SP wind forcing determines the offshore upper-layer thickness (ULT) via Rossby wave propagation, while the Non-Low-Lat-SP wind forcing determines the alongshore ULT via coastal Kelvin wave propagation. A simple bifurcation model is proposed under the framework of linear Rossby wave dynamics. It is found that the seasonal bifurcation latitude is predominantly determined by the spatial pattern of the wind and baroclinic Rossby wave propagation. This model explains the roles of local/remote wind forcing and baroclinic adjustment in the south–north migration and peak seasons of the bifurcation latitude.

On the seasonal variability and eddies in the North Brazil Current: insights from model intercomparison experiments

2001 ◽  
Vol 48 (2-3) ◽  
pp. 195-230 ◽  
Author(s):  
Bernard Barnier ◽  
Thierry Reynaud ◽  
Aike Beckmann ◽  
Claus Böning ◽  
Jean-Marc Molines ◽  
...  
Keyword(s):  
Seasonal Variability ◽  
Model Intercomparison ◽  
The North ◽  
Brazil Current ◽  
North Brazil ◽  
North Brazil Current

A Lagrangian view of the transfer of Southern waters to the South Atlantic Ocean

2021 ◽  
Author(s):  
Anna Olivé Abelló ◽  
Josep L. Pelegrí ◽  
Ignasi Vallès-Casanova
Keyword(s):  
South Africa ◽  
Surface Water ◽  
Drake Passage ◽  
South Atlantic ◽  
Subtropical Gyre ◽  
The South ◽  
The North ◽  
Brazil Current ◽  
North Brazil ◽  
North Brazil Current

<p>The Atlantic Meridional Overturning Circulation (AMOC), a key component of the Earth's climate system, is sustained through the northward transport of Southern Ocean waters to high latitudes. This returning limb of the AMOC consists largely of relatively cold waters entering from the Pacific Ocean through the Drake Passage, what is commonly referred to as cold-water route. Here, we explore the pathways and transit times of these Antarctic waters that are incorporated to the South Atlantic, with special attention to their recirculation in the subtropical gyre and their escape northward through the North Brazil Current. For this purpose, we use daily values of the climatological GLORYS12v1 velocity field, as obtained using data for 2002-2018 and track the trajectories with the help of the OceanParcels software. We trace the particles transiting through four sections in the Southern and South Atlantic Oceans: 64°W and 27°E, crossing entire Antarctic Circumpolar Current (ACC) through the Drake Passage and off South Africa, respectively; 32°S, from the African coast out to 5°S, sampling the eastern boundary current system; and 21°S, from the American coast out to 30°W, sampling the North Brazil Current.</p><p>Particles are released daily in the Drake Passage down to 1800 m during one full year, its spatial distribution and number being proportional to the transport crossing each vertical portion of the section. This represents an annual-mean of 116.3 Sv entering the Atlantic sector through the Drake Passage, split into 13.3 Sv for surface (Subantarctic Surface Water, SASW, and Subantarctic Mode Water, SAMW), 40.2 Sv for intermediate (Antarctic Surface Water, AASW, and Antarctic Intermediate Water, AAIW) and 62.8 Sv for deep (Upper Circumpolar Deep Water, UCDW) water masses. The particles are then tracked forward, with a one-day resolution, during 20 years. The simulation shows that about 83% of the SASW/SAMW transport follow the ACC past South Africa while the remaining 17% are incorporated to the subtropical gyre. Among the latter, only 13% veer northward and cross the 21°S section. Regarding the intermediate waters, AASW/AAIW, 93% of transport follows the ACC, and 7% join the subtropical gyre. Finally, for the UCDW transport, which remains part of ACC, about 97% follow eastward as the ACC and only 3% drift cross the 32°S section, and only 4% of the latter reach through the 21°S section. The median times for the Drake Passage water particles to get to the 27°E, 32°S and 21°S sections are: 1.7, 2.1 and 5.7 yr for the SASW/SAMW; 2.3, 5.3 and 6.5 yr for the AASW/AAIW; and 3.3, 6.0 and 11.7 yr for the UCDW, respectively. Long tails in the age distributions reflect a high degree of recirculation, being remarkable the high presence of mesoscale eddies around 32°S over Cape Basin.</p>

scholarly journals Bifurcation of the Subtropical South Equatorial Current against New Caledonia in December 2004 from a Hydrographic Inverse Box Model*

2008 ◽  
Vol 38 (9) ◽  
pp. 2072-2084 ◽  
Author(s):  
Alexandre Ganachaud ◽  
Lionel Gourdeau ◽  
William Kessler
Keyword(s):  
Pacific Islands ◽  
New Caledonia ◽  
South Pacific ◽  
Ocean Dynamics ◽  
Box Model ◽  
Boundary Current ◽  
The South ◽  
South Equatorial Current ◽  
The North ◽  
Equatorial Current

Abstract The South Equatorial Current (SEC), the westward branch of the South Pacific subtropical gyre, extends from the equator to 30°S at depth. Linear ocean dynamics predict that the SEC forms boundary currents on the eastern coasts of the South Pacific islands it encounters. Those currents would then detach at the northern and southern tips of the islands, and cross the Coral Sea in the form of jets. The Fiji Islands, the Vanuatu archipelago, and New Caledonia are the major topographic obstacles on the SEC pathway to the Australian coast. Large-scale numerical studies, as well as climatologies, suggest the formation of three jets in their lee: the north Vanuatu jet (NVJ), the north Caledonian jet (NCJ), and the south Caledonian jet (SCJ), implying a bifurcation against the east coast of each island. The flow observed during the SECALIS-2 cruise in December 2004 between Vanuatu and New Caledonia is presented herein. An inverse box model is used to provide quantitative transport estimates with uncertainties and to infer the pathways and boundary current formation. For that particular month, the 0–2000-m SEC inflow was found to be 20 ± 4 Sv (1 Sv ≡ 106 m3 s−1) between Vanuatu and New Caledonia. Of that, 6 ± 2 Sv bifurcated to the south in a boundary current against the New Caledonia coast (the Vauban Current), and the remainder exited north of New Caledonia, feeding the NCJ. The flow is comparable both above and below the thermocline, while complex topography, associated with oceanic eddy generation, introduces several recirculation features. To the north, the NCJ, which extends down to 1500 m, was fed not only by the SEC inflow, but also by waters coming from the north, which have possibly been recirculated. To the south, a westward current rounds the tip of New Caledonia. A numerical simulation suggests a partial continuity with the deep extension of the Vauban Current (this current would then be the SCJ) while the hydrographic sections are too distant to confirm such continuity.

scholarly journals Surface Circulation and Vertical Structure of Upper Ocean Variability Around Fernando de Noronha Archipelago and Rocas Atoll During Spring 2015 and Fall 2017

2021 ◽  
Vol 8 ◽  
Author(s):  
Alex Costa da Silva ◽  
Alexis Chaigneau ◽  
Alina N. Dossa ◽  
Gerard Eldin ◽  
Moacyr Araujo ◽  
...  
Keyword(s):  
Mixed Layer ◽  
The South ◽  
South Equatorial Current ◽  
Equatorial Undercurrent ◽  
Study Region ◽  
Near Surface ◽  
North Brazil ◽  
Fernando De Noronha ◽  
Equatorial Current ◽  
Central South

Using current, hydrographic and satellite observations collected off Northeast Brazil around the Fernando de Noronha Archipelago and Rocas Atoll during two oceanographic cruises (spring 2015 and fall 2017), we investigated the general oceanic circulation and its modifications induced by the islands. In spring 2015, the area was characterized by lower SST (26.6°C) and deep mixed-layer (∼90 m). At this depth, a strong current shear was observed between the central branch of the eastward flowing near-surface South Equatorial Current and the westward flowing South Equatorial Undercurrent. In contrast, in fall 2017, SST was higher (∼28.8°C) and the mixed-layer shallower (∼50 m). The shear between the central South Equatorial Current and the South Equatorial Undercurrent was weaker during this period. Interestingly, no oxygen-rich water from the south (retroflection of the North Brazil undercurrent) was observed in the region in fall 2017. In contrast, we revealed the presence of an oxygen-rich water entrained by the South Equatorial Undercurrent reaching Rocas Atoll in spring 2015. Beside these global patterns, island wake effects were noted. The presence of islands, in particular Fernando de Noronha, strongly perturbs central South Equatorial Current and South Equatorial Undercurrent features, with an upstream core splitting and a reorganization of single current core structures downstream of the islands. Near islands, flow disturbances impact the thermohaline structure and biogeochemistry, with a negative anomaly in temperature (−1.3°C) and salinity (−0.15) between 200 and 400 m depth in the southeast side of Fernando Noronha (station 5), where the fluorescence peak (>1.0 mg m–3) was shallower than at other stations located around Fernando de Noronha, reinforcing the influence of flow-topography. Satellite maps of sea-surface temperature and chlorophyll-a confirmed the presence of several submesoscale features in the study region. Altimetry data suggested the presence of a cyclonic mesoscale eddy around Rocas Atoll in spring 2015. A cyclonic vortex (radius of 28 km) was actually observed in subsurface (150–350 m depth) southeast of Rocas Atoll. This vortex was associated with topographically induced South Equatorial Undercurrent flow separation. These features are likely key processes providing an enrichment from the subsurface to the euphotic layer near islands, supplying local productivity.

Seasonal Variation of the South Equatorial Current Bifurcation off Madagascar

2014 ◽  
Vol 44 (2) ◽  
pp. 618-631 ◽  
Author(s):  
Zhaohui Chen ◽  
Lixin Wu ◽  
Bo Qiu ◽  
Shantong Sun ◽  
Fan Jia
Keyword(s):  
Seasonal Variation ◽  
Time Dependent ◽  
North Equatorial Current ◽  
Island Rule ◽  
The South ◽  
South Equatorial Current ◽  
Dynamic Framework ◽  
The North ◽  
Equatorial Current ◽  
The Mean

Abstract In this paper, seasonal variation of the South Equatorial Current (SEC) bifurcation off the Madagascar coast in the upper south Indian Ocean (SIO) is investigated based on a new climatology derived from the World Ocean Database and 19-year satellite altimeter observations. The mean bifurcation integrated over the upper thermocline is around 18°S and reaches the southernmost position in June/July and the northernmost position in November/December, with a north–south amplitude of about 1°. It is demonstrated that the linear, reduced gravity, long Rossby model, which works well for the North Equatorial Current (NEC) bifurcation in the North Pacific, is insufficient to reproduce the seasonal cycle and the mean position of the SEC bifurcation off the Madagascar coast. This suggests the importance of Madagascar in regulating the SEC bifurcation. Application of Godfrey’s island rule reveals that compared to the zero Sverdrup transport latitude, the mean SEC bifurcation is shifted poleward by over 0.8° because of the meridional transport of about 5 Sverdrups (Sv; 1 Sv ≡ 106 m3 s−1) between Madagascar and Australia. A time-dependent linear model that extends the Godfrey’s island rule is adopted to examine the seasonal variation of the SEC bifurcation. This time-dependent island rule model simulates the seasonal SEC bifurcation well both in terms of its mean position and peak seasons. It provides a dynamic framework to clarify the baroclinic adjustment processes involved in the presence of an island.

scholarly journals Seasonal and interannual variability of the southern south Equatorial Current bifurcation and meridional transport along the eastern brazilian edge.

2011 ◽  
Vol 39 (1) ◽  
Author(s):  
Dóris R A VELEDA ◽  
Moacyr ARAÚJO ◽  
Marcus SILVA ◽  
Raul MONTAGNE ◽  
Rodolfo ARAÚJO
Keyword(s):  
Field Measurements ◽  
Ocean Model ◽  
Numerical Results ◽  
Seasonal Migration ◽  
Meridional Transport ◽  
South Equatorial Current ◽  
The North ◽  
North Brazil ◽  
Terrain Following ◽  
Equatorial Current

The dynamics of the southern band of the South Equatorial Current (sSEC) near to Brazilian shelf is investigated using recent field observations and a regional numerical modeling approach. The field measurements were obtained from five moorings deployed by German CLIVAR (Climate Variability and Predictability Program) cruises (March 2000- August 2004) along a crossshore line at 11oS. The Regional Ocean Model (ROMS) is used to simulate the circulation and thermohaline structures within the ocean area comprised between 5°S-25°S and 20°W-47°W. This integration domain was covered by an isotropic 1/12o horizontal grid and 40 terrain-following layers. The numerical results confirm a seasonal migration of the sSEC divergence along the Brazilian edge, as well as its depth dependence with a maximum southward shift in July at 200 m depth, while a maximum northward displacement occurs in November at this same depth. This intrannual variability coincides with the North Brazil Undercurrent (NBUC) seasonality at 11oS from moorings measurements. Empirical Orthogonal Function (EOF) and numerical results show a minimum NBUC strength during November and a maximum northward transport in July. The mean transport from field measurements is 25Sv while this from numerical simulations is 24.5Sv. The SODA reanalysis with 47 years of monthly mean indicates that the sSEC has not only a seasonal variability as well as quasi-biannual variability.

scholarly journals Terrigenous input off northern South America driven by changes in Amazonian climate and the North Brazil Current retroflection during the last 250 ka

2014 ◽  
Vol 10 (2) ◽  
pp. 843-862 ◽  
Author(s):  
A. Govin ◽  
C. M. Chiessi ◽  
M. Zabel ◽  
A. O. Sawakuchi ◽  
D. Heslop ◽  
...  
Keyword(s):  
Sediment Cores ◽  
Austral Summer ◽  
Suspended Sediments ◽  
Sole Source ◽  
South American ◽  
The North ◽  
Brazil Current ◽  
North Brazil ◽  
North Brazil Current ◽  
Freshwater Plume

Abstract. We investigate changes in the delivery and oceanic transport of Amazon sediments related to terrestrial climate variations over the last 250 ka. We present high-resolution geochemical records from four marine sediment cores located between 5 and 12° N along the northern South American margin. The Amazon River is the sole source of terrigenous material for sites at 5 and 9° N, while the core at 12° N receives a mixture of Amazon and Orinoco detrital particles. Using an endmember unmixing model, we estimated the relative proportions of Amazon Andean material ("%-Andes", at 5 and 9° N) and of Amazon material ("%-Amazon", at 12° N) within the terrigenous fraction. The %-Andes and %-Amazon records exhibit significant precessional variations over the last 250 ka that are more pronounced during interglacials in comparison to glacial periods. High %-Andes values observed during periods of high austral summer insolation reflect the increased delivery of suspended sediments by Andean tributaries and enhanced Amazonian precipitation, in agreement with western Amazonian speleothem records. Increased Amazonian rainfall reflects the intensification of the South American monsoon in response to enhanced land–ocean thermal gradient and moisture convergence. However, low %-Amazon values obtained at 12° N during the same periods seem to contradict the increased delivery of Amazon sediments. We propose that reorganizations in surface ocean currents modulate the northwestward transport of Amazon material. In agreement with published records, the seasonal North Brazil Current retroflection is intensified (or prolonged in duration) during cold substages of the last 250 ka (which correspond to intervals of high DJF or low JJA insolation) and deflects eastward the Amazon sediment and freshwater plume.

Seasonal variability of the bifurcation of the North Equatorial Current

2013 ◽  
Vol 25 (4) ◽  
pp. 550-555 ◽  
Author(s):  
Qiang-chang Ju ◽  
Song Jiang ◽  
Ji-wei Tian ◽  
Ling-hai Kong ◽  
Guo-xi Ni
Keyword(s):  
Seasonal Variability ◽  
North Equatorial Current ◽  
The North ◽  
Equatorial Current

Impact of mesoscale eddies on salinity and CO2 ocean parameters in the western tropical Atlantic in February 2020

2021 ◽  
Author(s):  
Léa Olivier ◽  
Jacqueline Boutin ◽  
Nathalie Lefèvre ◽  
Gilles Reverdin ◽  
Peter Landschützer ◽  
...  
Keyword(s):  
Dissolved Inorganic Carbon ◽  
Salinity Gradient ◽  
Sea Surface Salinity ◽  
Amazon River ◽  
Tropical Atlantic ◽  
Surface Salinity ◽  
The North ◽  
Brazil Current ◽  
North Brazil

<p>Large oceanic eddies are formed by the retroflection of the North Brazil Current (NBC) near 8°N in the western tropical Atlantic. The EUREC<sup>4</sup>A-OA/Atomic cruise took place in January - February 2020, and extensively documented two NBC rings. The NBC flows northward across the Equator and pass the mouth of the Amazon River, entraining fresh and nutrient-rich water along its nearshore edge. From December to March, the Amazon river discharge is low but a freshwater filament stirred by a NBC ring was nevertheless observed. The strong salinity gradient can be used to delineate the NBC ring during its initial phase and its westward propagation. Using satellite sea surface salinity and ocean color associated to in-situ measurements of salinity, temperature, dissolved inorganic carbon, alkalinity and fugacity of CO<sub>2</sub> we characterize the salinity and biogeochemical signature of NBC rings.</p>

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