Research Spotlight: The traveling rings of the North Brazil Current

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 times. 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. However, low %-Amazon values obtained at 12° N during the same periods seem to contradict the increased delivery of Amazon sediments. We propose that reorganisations 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.

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Symmetric Instability in Cross-Equatorial Western Boundary Currents

Journal of Physical Oceanography ◽

10.1175/jpo-d-20-0273.1 ◽

2021 ◽

Vol 51 (6) ◽

pp. 2049-2067

Author(s):

Fraser W. Goldsworth ◽

David P. Marshall ◽

Helen L. Johnson

Keyword(s):

Water Mass ◽

Numerical Models ◽

Western Boundary ◽

Two Dimensional ◽

Boundary Current ◽

The North ◽

Brazil Current ◽

North Brazil ◽

North Brazil Current ◽

Symmetric Instability

AbstractThe upper limb of the Atlantic meridional overturning circulation draws waters with negative potential vorticity from the Southern Hemisphere into the Northern Hemisphere. The North Brazil Current is one of the cross-equatorial pathways in which this occurs: upon crossing the equator, fluid parcels must modify their potential vorticity to render them stable to symmetric instability and to merge smoothly with the ocean interior. In this work a linear stability analysis is performed on an idealized western boundary current, dynamically similar to the North Brazil Current, to identify features that are indicative of symmetric instability. Simple two-dimensional numerical models are used to verify the results of the stability analysis. The two-dimensional models and linear stability theory show that symmetric instability in meridional flows does not change when the nontraditional component of the Coriolis force is included, unlike in zonal flows. Idealized three-dimensional numerical models show anticyclonic barotropic eddies being spun off as the western boundary current crosses the equator. These eddies become symmetrically unstable a few degrees north of the equator, and their PV is set to zero through the action of the instability. The instability is found to have a clear fingerprint in the spatial Fourier transform of the vertical kinetic energy. An analysis of the water mass formation rates suggest that symmetric instability has a minimal effect on water mass transformation in the model calculations; however, this may be the result of unresolved dynamics, such as secondary Kelvin–Helmholtz instabilities, which are important in diabatic transformation.

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Pathways connecting the North Brazil Current and the RAPID line

10.5194/egusphere-egu21-13163 ◽

2021 ◽

Author(s):

Kimberley Drouin ◽

M Susan Lozier ◽

F Javier Beron-Vera ◽

Phillip Miron ◽

M Josefina Olascoaga

Keyword(s):

Three Dimensional ◽

Volume Transport ◽

Florida Current ◽

The North ◽

Dynamical Systems Analysis ◽

Brazil Current ◽

North Brazil ◽

North Brazil Current ◽

The Caribbean ◽

Surface Drifters

<p>The North Brazil Current is considered a bottleneck in the South Atlantic, responsible for funneling upper-ocean waters into the North Atlantic. This work explores the surface and subsurface pathways that connect the North Brazil Current to the RAPID line. To that extent, observational trajectories from surface drifters and Argo floats are used in conjunction with Markov chain theory and tools from dynamical systems analysis to compute probable pathways. More specifically, these pathways are computed as ensembles of paths transitioning directly between the North Brazil Current and the RAPID line. In addition, simulated trajectories will be used (1) to assess how representative the two-dimensional observational trajectories are of the three-dimensional circulation, and (2) to compute the associated volume transport of different pathways. Preliminary results suggest that two dominant pathways connect the North Brazil Current and the RAPID line. First, is the traditional pathway through the Caribbean Sea and Gulf of Mexico, which carries waters to the Florida Current, and second is a more direct route east of the Caribbean that supplies waters to the Antilles Current and the basin interior. &#160;</p>

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Synoptic study of warm rings in the North Brazil Current retroflection region using satellite altimetry

Interhemispheric Water Exchange in the Atlantic Ocean - Elsevier Oceanography Series ◽

10.1016/s0422-9894(03)80153-8 ◽

2003 ◽

pp. 335-356 ◽

Cited By ~ 22

Author(s):

Gustavo J. Goni ◽

William E. Johns

Keyword(s):

Satellite Altimetry ◽

The North ◽

Brazil Current ◽

North Brazil ◽

North Brazil Current

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