The Evolution and Demise of North Brazil Current Rings*

Fratantoni, David M.; Richardson, Philip L.

doi:10.1175/jpo2907.1

Cited by 107 publications

(158 citation statements)

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“…In Figure 11a drifter trajectories from Fratantoni and Richardson [2006] are illustrated. One of the drifters started a cyclonic loop approximately 300 km downstream of Barbados, which is near the latitude of Guadeloupe.…”

Section: Consequences Of Ring-topography Interaction and The Formatiomentioning

confidence: 99%

On the propagation and decay of North Brazil Current rings

et al. 2010

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Near the western boundary of the tropical North Atlantic, where the North Brazil Current (NBC) retroflects into the North Equatorial Countercurrent, large anticyclonic rings are shed. After separating from the retroflection region, the so‐called NBC rings travel northwestward along the Brazilian coast, until they reach the island chain of the Lesser Antilles and disintegrate. These rings contribute substantially to the upper limb return flow of the Atlantic Meridional Overturning Circulation by carrying South Atlantic Water into the northern subtropical gyre. Their relevance for the northward transport of South Atlantic Water depends on the frequency of their generation as well as on their horizontal and vertical structure. The ring shedding and propagation and the complex interaction of the rings with the Lesser Antilles are investigated in the Family of Linked Atlantic Model Experiments (FLAME) model. The ring properties simulated in FLAME reach the upper limit of the observed rings in diameter and agree with recent observations on seasonal variability, which indicates a maximum shedding during the first half of the year. When the rings reach the shallow topography of the Lesser Antilles, they are trapped by the island triangle of St. Lucia, Barbados and Tobago and interact with the island chain. The model provides a resolution that is capable of resolving the complex topographic conditions at the islands and illuminates various possible fates for the water contained in the rings. It also reproduces laboratory experiments that indicate that both cyclones and anticyclones are formed after a ring passes through a topographic gap. Trajectories of artificial floats, which were inserted into the modeled velocity field, are used to investigate the pathways of the ring cores and their fate after they encounter the Lesser Antilles. The majority of the floats entered the Caribbean, while the northward Atlantic pathway was found to be of minor importance. No prominent pathway was found east of Barbados, where a ring could avoid the interaction with the islands and migrate toward the northern Lesser Antilles undisturbed.

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Section: Consequences Of Ring-topography Interaction and The Formatiomentioning

confidence: 99%

On the propagation and decay of North Brazil Current rings

et al. 2010

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“…1). As is known from direct ship and satellite obCorrespondence to: S. N. Bulgakov (sbulgako@cencar.udg.mx) servations, the North Brazil Current sheds anticyclonic rings near approximately 6 • -8 • N, with an average frequency of 6-9 per year Johns, 2001, 2003;Jochum and Malanotte-Rizzoli, 2003;Richardson, 2005;Fratantoni and Richardson, 2006). Due to the effect of existing systems of currents (North Equatorial Current, Guyana Current), β-effect and the trade winds, these NBC rings (NBCR) travel in the NW direction, transporting water with different characteristics from the South Atlantic into the Caribbean Sea through the Lesser Antilles (LA), contributing to the exchange of mass and momentum with the surrounding waters.…”

Section: Introductionmentioning

confidence: 99%

“…The observation program consisted of hydrographic and direct-velocity ADCP measurements (Wilson et al, 2002), an array of current meter and inverted echo sounder moorings , surface drifter and subsurface float observations (Fratantoni and Richardson, 2006), satellite measurements of the sea surface height Johns, 2001, 2003), ocean color 332 R. C. Cruz Gómez and S. N. Bulgakov: Remote sensing observations in the vicinity of Lesser Antilles (Fratantoni and Glikson, 2002) and sea surface temperature (Ffield, 2005).…”

Section: Introductionmentioning

confidence: 99%

“…Vorticity of ring remnants enters through island passages and is probably amplified by the anticyclonic shear on the northern side of the Caribbean Current jets. Fratantoni and Richardson (2006) observed the evolution of 10 NBC rings through the use of near surface (15 m) drifters and deeper (250 m, 550 m and 900 m) float observations. They found out that half of the rings followed a northward path parallel to the LA with no frontal collision with the island chain, while the remaining rings propagated westward south of Barbados.…”

Section: Introductionmentioning

confidence: 99%

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Remote sensing observations of the coherent and non-coherent ring structures in the vicinity of Lesser Antilles

Gómez

Bulgakov

2007

Ann. Geophys.

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Abstract. The North Brazil Current Rings (NBCR) penetration into the Caribbean Sea is being investigated by employing a merged altimeter-derived sea height anomaly (TOPEX/Poseidon, Jason-1 and ERS-1, 2), the ocean surface color data (SeaWiFS) and Global Drifter Program information. Four strategies are being applied to process the data: (1) calculations of the Okubo-Weiss parameter for NBCR identification, (2) longitude-time plots (also known as Hovmöller diagrams), (3) two-dimensional Radon transforms and (4) two-dimensional Fourier transforms.A twofold NBCR structure has been detected in the region under investigation. The results have shown that NBC rings mainly propagate into the Caribbean Sea along two principal pathways (near 12 • N and 17 • N) in the ring translation corridor. Thus, rings following the southern pathway in the fallwinter period can enter through very shallow southern straits as non-coherent structures. A different behavior is observed near the northern pathway (∼17 • N), where NBC rings are thought to have a coherent structure during their squeezing into the eastern Caribbean, i.e. conserving the principal characteristics of the incident rings. We attribute this difference in the rings' behavior to the vertical scales of the rings and to the bottom topography features in the vicinity of the Lesser Antilles.

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“…On the spring cruise (OC471), two anticyclones (A4 and A5, Figure Antilles as described by Fratantoni and Richardson (2006).…”

Section: Spring 2011: Trichodesmium Colonies In Anticyclonesmentioning

confidence: 99%

Investigating the role of trichodesmium spp. in the oceanic nitrogen cycle through observations and models

Olson¹

2014

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This work concerns the nitrogen fixation and abundance of Trichodesmium colonies in the western subtropical-tropical North Atlantic and their connections with physical processes. Data were collected in fall 2010 and spring 2011, primarily using the Video Plankton Recorder (VPR). A data processing procedure for estimating the abundance of rare taxa was devised to take advantage of the accuracy of manual classification and the effort savings of automatic classification. The procedure entails selecting a subset of the original dataset, classifying it with automated software, and then manually correcting each classification. The method was validated through comparisons with fully classified VPR data and with abundance data based on microscopic enumeration on preserved samples.Correlations of Trichodesmium colony abundance with the eddy field emerged in two subsets of the VPR observations. In fall 2010, local maxima in abundance were observed in a series of cyclones. We hypothesized Ekman transport convergence/divergence in cyclones/anticyclones as a driving mechanism. We investigated the process using idealized three-dimensional models of buoyant colonies in eddies. Elevated abundances in anticyclones in spring 2011 were correlated with anomalously fresh water, suggesting riverine input as a driver of the relationship.Finally, we evaluated the hypothesis of Davis and McGillicuddy (2006) that Trichodesmium nitrogen fixation in the North Atlantic may be underestimated by conventional sampling methods, based on their VPR observations of higher than expected colony abundances at depth in the subtropical North Atlantic. A bio-optical model was developed based on carbon-normalized nitrogen fixation rates measured in fall 2010 and spring 2011 and used to estimate nitrogen fixation over the VPR transects. Estimates of abundance and nitrogen fixation were similar in magnitude and vertical and geographical distribution to estimates compiled in a database by Luo et al. (2012). In the mean, VPR-based estimates of volume-specific nitrogen fixation 3 rates at depth in the tropical North Atlantic were not inconsistent with estimates derived from conventional sampling methods. Based on this analysis, if Trichodesmium nitrogen fixation is underestimated, it is unlikely that it is attributable to underestimation of deep colony abundances due to mechanical disturbance during net-based sampling.

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The Evolution and Demise of North Brazil Current Rings*

Cited by 107 publications

References 64 publications

On the propagation and decay of North Brazil Current rings

On the propagation and decay of North Brazil Current rings

Remote sensing observations of the coherent and non-coherent ring structures in the vicinity of Lesser Antilles

Investigating the role of trichodesmium spp. in the oceanic nitrogen cycle through observations and models

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