Hydrographic cruises off northwest Africa: the Canary Current and the Cape Ghir region

Pelegrí, Josep Lluís; Marrero-Díaz, Ángeles; Ratsimandresy, A. W.; Antoranz, Ana; Cisneros-Aguirre, J.; Gordo, C.; Grisolía, D.; Hernández‐Guerra, Alonso; Laiz, Irene; Martínez, Ana Cristina Lahuerta; Parrilla, Gregorio; Pérez‐Rodríguez, Paula; Rodríguez-Santana, Ángel; Sangrà, Pablo

doi:10.1016/j.jmarsys.2004.07.001

Cited by 63 publications

(51 citation statements)

References 39 publications

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“…The average width is between 10 and 20 km. The maximal velocities are on the order of 0.5 m s −1 , in agreement with the observations of Hagen et al (1996) and Pelegrí et al (2005). The shape of the filament is highly variable.…”

Section: Small Domainsupporting

confidence: 91%

“…In the studied region, filaments have typical lifetime of a few days, velocity between 0.1-1 m s −1 , a length of a few hundred kilometers, a width of a few ten kilometers and a depth of a few hundred meters (e.g. Kostianoy and Zatsepin, 1996;Barton et al, 1998;Peliz et al, 2002;Pelegrí et al, 2005). The wind stress curl is estimated from the SCOW climatology (Section 2.2).…”

Section: Analysis Of Orders Of Magnitudementioning

confidence: 99%

“…Numerous cruises also took place in the Canary Upwelling system (CUS), with the objective of examining the dynamics of the filaments and studying their effects upon primary production (e.g., Haynes et al, 1993;Hagen et al, 1996;Barton et al, 1998;Barton and Arístegui, 2004;Pelegrí et al, 2005). Remote-sensing imagery helped to identify the sites favorable to filaments (e.g, Van Camp et al, 1991;García-Weill et al, 1994;Kostianoy and Zatsepin, 1996;Hernández-Guerra and Nykjaer, 1997).…”

Section: Introductionmentioning

confidence: 99%

“…Different mechanisms have been proposed for the filament generation: interaction of the upwelling jet with the topography (Ikeda and Emery, 1984;Strub et al, 1991;Hagen et al, 1996), baroclinic instability (Ikeda and Emery, 1984), meandering of the equatorward jet (Strub et al, 1991), interaction with a field of synoptic-mesoscale eddies (Mooers and Robinson, 1984;Lutjeharms et al, 1991;Strub et al, 1991;Peliz et al, 2004), influence of the wind (e.g., Kelly, 1986;Hagen et al, 1996;Castelao and Barth, 2007). Pelegrí et al (2005) proposed that an injection of positive vorticity due to the friction of the flow with the sea floor created the offshore deflection of the jet. Most of the surveys point at coastline or topography irregularities as a responsible factor.…”

Section: Introductionmentioning

confidence: 99%

“…Indeed, along the coast of NW Africa, numerous capes ( Fig. 1) are frequently affected by filaments: Cape Ghir (Hagen et al, 1996;Pelegrí et al, 2005), Cape Jubi, Cape Bojador and Cape Blanc (Gabric et al, 1993;Karakas et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

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Generation of the Cape Ghir upwelling filament: A numerical study

et al. 2012

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Filaments are narrow, shallow structures of cool water originating from the coast. They are typical features of the four main eastern boundary upwelling systems (EBUS). In spite of their significant biological and chemical roles, through the offshore exportation of nutrient-rich waters, the physical processes that generate them are still not completely understood. This paper is a process-oriented study of filament generation mechanisms. Our goal is twofold: firstly, to obtain a numerical solution able to correctly represent the characteristics of the filament off Cape Ghir (30• 38'N, northwest Africa) in the Canary EBUS and secondly, to explain its formation by a simple mechanism based on the balance of potential vorticity.The first goal is achieved by the use of the ROMS model (Regional Ocean Modeling System) with embedded domains around Cape Ghir, with a horizontal resolution going up to 1.5 km for the finest domain. The latter gets its initial and boundary conditions from a parent solution and is forced by climatological, high-resolution atmospheric fields. The modeled filaments display spatial, temporal and physical characteristics in agreement with the available in situ and satellite observations. This model solution is used as a reference to compare the results with a set of process-oriented experiments. These experiments allow us to reach the second objective. The solutions serve to highlight the contributions of various processes to the filament generation. Since the study is focused on general processes present under climatological forcing conditions, inter-annual forcing is not necessary.The underlying idea for the filament generation is the balance of potential vorticity in the Canary EBUS: the upwelling jet is characterized by negative relative vorticity and flows southward along a narrow band of uniform potential vorticity. In the vicinity of the cape, an injection of relative vorticity induced by the wind breaks the existing vorticity balance. The upwelling jet is prevented from continuing its way southward and has to turn offshore to follow lines of equal potential vorticity.The model results highlight the essential role of wind, associated with the particular topography (coastline and bottom) around the cape. The mechanism presented here is general and thus can be applied to other EBUS.

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Section: Small Domainsupporting

confidence: 91%

Section: Analysis Of Orders Of Magnitudementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Generation of the Cape Ghir upwelling filament: A numerical study

et al. 2012

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On the temporal memory of coastal upwelling off NW Africa

et al. 2014

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We use a combination of satellite, in situ, and numerical data to provide a comprehensive view of the seasonal coastal upwelling cycle off NW Africa in terms of both wind forcing and sea surface temperature (SST) response. Wind forcing is expressed in terms of both instantaneous (local) and time-integrated (nonlocal) indices, and the ocean response is expressed as the SST difference between coastal and offshore waters. The classical local index, the cross-shore Ekman transport, reproduces reasonably well the time-latitude distribution of SST differences but with significant time lags at latitudes higher than Cape Blanc. Two nonlocal indices are examined. One of them, a cumulative index calculated as the backward averaged Ekman transport that provides the highest correlation with SST differences, reproduces well the timing of the SST differences at all latitudes (except near Cape Blanc). The corresponding time lags are close to zero south of Cape Blanc and range between 2 and 4 months at latitudes between Cape Blanc and the southern Gulf of Cadiz. The results are interpreted based on calculations of spatial and temporal auto and cross correlations for wind forcing and SST differences. At temporal scales of 2-3 weeks, the alongshore advection of alongshore momentum compensates for interfacial friction, allowing the upwelling jet and associated frontal system to remain active. We conclude that the coastal jet plays a key role in maintaining the structure of coastal upwelling, even at times of relaxed winds, by introducing a seasonal memory to the system in accordance with the atmospheric-forcing annual cycle.

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The Cape Ghir filament system in August 2009 (NW Africa)

et al. 2015

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In the framework of the Canaries-Iberian marine ecosystem Exchanges (CAIBEX) experiment, an interdisciplinary high-resolution survey was conducted in the NW African region of Cape Ghir (30838 0 N) during August 2009. The anatomy of a major filament is investigated on scales down to the submesoscale using in situ and remotely sensed data. The filament may be viewed as a system composed of three intimately connected structures: a small, shallow, and cold filament embedded within a larger, deeper, and cool filament and an intrathermocline anticyclonic eddy (ITE). The cold filament, which stretches 110 km offshore, is a shallow feature 60 m deep and 25 km wide, identified by minimal surface temperatures and rich in chlorophyll a. This structure comprises two asymmetrical submesoscale (18 km) fronts with jets flowing in opposite directions. The cold filament is embedded near the equatorward boundary of a much broader region of approximately 120 km width and 150 m depth that forms the cool filament and stretches at least 200 km offshore. This cool region, partly resulting from the influence of cold filament, is limited by two asymmetrical mesoscale (50 km) frontal boundaries. At the ITE, located north of the cold filament, we observe evidence of downwelling as indicated by a relatively high concentration of particles extending from the surface to more than 200 m depth. We hypothesize that this ITE may act as a sink of carbon and thus the filament system may serve dual roles of offshore carbon export and carbon sink.

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Hydrographic cruises off northwest Africa: the Canary Current and the Cape Ghir region

Cited by 63 publications

References 39 publications

Generation of the Cape Ghir upwelling filament: A numerical study

Generation of the Cape Ghir upwelling filament: A numerical study

On the temporal memory of coastal upwelling off NW Africa

The Cape Ghir filament system in August 2009 (NW Africa)

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