The mean circulation of the southwestern Mediterranean Sea: Algerian Gyres

Testor, Pierre; Send, Uwe; Gascard, Jean‐Claude; Millot, Claude; Taupier‐Letage, Isabelle; Béranger, Karine

doi:10.1029/2004jc002861

Cited by 58 publications

(85 citation statements)

References 38 publications

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“…12). This first anomaly corresponds to the Eastern Algerian Gyre (EAG) already described by Testor et al, (2005). This gyre has an almost stable position during our investigation period, only moving seaward after one month and approaching the Algerian coast once again at the end of October.…”

Section: Geostrophic and Ageostrophic Velocitiessupporting

confidence: 61%

Glider and satellite high resolution monitoring of a mesoscale eddy in the algerian basin: Effects on the mixed layer depth and biochemistry

Cotroneo

Aulicino

Ruiz

et al. 2016

Journal of Marine Systems

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Despite an extensive bibliography for the circulation of the Mediterranean Sea and its sub-basins, the debate on mesoscale dynamics and their impacts on bio-chemical processes is still open because of their intrinsic time scales and of the difficulties in their sampling. In order to clarify some of these processes, the "Algerian BAsin Circulation Unmanned Survey-ABACUS" project was proposed and realized through access to the JERICO Trans National Access (TNA) infrastructure between September and December 2014. In this framework, a deep glider cruise was carried out in the area between the Balearic Islands and the Algerian coast to establish a repeat line for monitoring of the basin circulation. During the mission a mesoscale eddy, identified on satellite altimetry maps, was sampled at high-spatial horizontal resolution (4 km) along its main axes and from the surface to 1000 m depth. Data were collected by a Slocum glider equipped with a pumped CTD and biochemical sensors that collected about 100 complete casts inside the eddy. In order to describe the structure of the eddy, in situ data were merged with next generation remotely sensed data: daily synoptic sea surface temperature (SST) and chlorophyll concentration (Chl-a) images from the MODIS satellites, as well as sea surface height and geostrophic velocities from AVISO. From its origin along the Algerian coast in the eastern part of the basin, the eddy propagated northwest at a mean speed of about 4 km/day, with a mean diameter of 112-130 km, mean amplitude of 15.7 cm; the eddy was clearly distinguished from the surrounding waters thanks to its higher SST and Chl-a values. Temperature and salinity values over the water column confirm the origin of the eddy from the Algerian Current (AC) showing the presence of recent Atlantic water in the surface layer and Levantine Intermediate Water (LIW) in the deeper layer. The eddy footprint is clearly evident in the multiparametric vertical sections conducted along its main axis. Deepening of temperature, salinity and density isolines at the center of the eddy is associated with variations in Chl-a, oxygen concentration and turbidity patterns. In particular, at 50 m depth along the eddy borders, Chl-a values are higher (1.1-5.2 μg/l) in comparison with the eddy center (0.5-0.7 μg/l) with maximum values found in the southeastern sector of the eddy. Calculation of geostrophic velocities along transects and vertical quasi-geostrophic velocities (QG-w) over a regular 5 km grid from the glider data helped to describe the mechanisms and functioning of the eddy. QG-w presents an asymmetric pattern, with relatively strong downwelling in the western part of the eddy and upwelling in the southeastern part. This asymmetry in the vertical velocity pattern, which brings LIW into the euphotic layer as well as advection from the northeastern sector of the eddy, may explain the observed increases in Chl-a values.

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Section: Geostrophic and Ageostrophic Velocitiessupporting

confidence: 61%

Glider and satellite high resolution monitoring of a mesoscale eddy in the algerian basin: Effects on the mixed layer depth and biochemistry

Cotroneo

Aulicino

Ruiz

et al. 2016

Journal of Marine Systems

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“…Thus, the effect of the main advective spreading (i.e., without the eddy circulation) tends to propagate WMDW toward the Strait of Gibraltar rather than toward the Channel of Sardinia. But a part of it is trapped into the eastern Algerian gyre by closed f/H isocontours constraint [ Testor et al , 2005], where f is the planetary vorticity and H the water depth. On the contrary, we showed that the deep eddy circulation south of the Balearic Islands toward the center of the Algerian subbasin is able to transport WMDW characteristics to the east toward the Channel of Sardinia.…”

Section: Discussionmentioning

confidence: 99%

Spreading of the Western Mediterranean Deep Water after winter 2005: Time scales and deep cyclone transport

Beuvier¹,

Béranger²,

Brossier³

et al. 2012

J. Geophys. Res.

Self Cite

104

186

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[1] This work is dedicated to the study of the propagation of the Western Mediterranean Deep Water (WMDW) formed in the Gulf of Lions during the exceptional winter 2005. A simulation of the 1998-2008 period has been carried out with an eddy-resolving Ocean General Circulation Model of the Mediterranean Sea, driven by interannual high-resolution air-sea fluxes. This study first presents a validation of the recently improved model configuration against satellite observations. Then, we assess the ability of the model to reproduce the particularly intense deep convection event of winter 2005 in the Gulf of Lions. A huge volume of very dense water is formed in the simulation at that time (annual formation rate higher than 3 Sv). The thermohaline characteristics of the new WMDW allow a monitoring of its deep propagation. We identify several deep cyclones as mainly responsible of the fast spreading of the WMDW southwards in the Western Mediterranean. By comparing Eulerian and Lagrangian approaches, we estimate different transport times of the WMDW by these cyclonic eddies and compare them to those deduced from several observations. Finally, we argue that these cyclones favor the propagation of the WMDW thermohaline characteristics toward the Channel of Sardinia and decrease the volume of WMDW which can reach the Strait of Gibraltar.

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“…The Atlantic Water enters the Mediterranean at the Strait of Gibraltar in the surface layer and flows around the sea in a cyclonic path of more or less stable boundary currents, producing meanders and eddies [64]. The general surface circulation in the Mediterranean is strongly constrained by the wind [65] and by the complex bathymetry [66].…”

Section: Methodsmentioning

confidence: 99%

Low Connectivity between Mediterranean Marine Protected Areas: A Biophysical Modeling Approach for the Dusky Grouper Epinephelus marginatus

et al. 2013

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Marine protected areas (MPAs) are major tools to protect biodiversity and sustain fisheries. For species with a sedentary adult phase and a dispersive larval phase, the effectiveness of MPA networks for population persistence depends on connectivity through larval dispersal. However, connectivity patterns between MPAs remain largely unknown at large spatial scales. Here, we used a biophysical model to evaluate connectivity between MPAs in the Mediterranean Sea, a region of extremely rich biodiversity that is currently protected by a system of approximately a hundred MPAs. The model was parameterized according to the dispersal capacity of the dusky grouper Epinephelus marginatus, an archetypal conservation-dependent species, with high economic importance and emblematic in the Mediterranean. Using various connectivity metrics and graph theory, we showed that Mediterranean MPAs are far from constituting a true, well-connected network. On average, each MPA was directly connected to four others and MPAs were clustered into several groups. Two MPAs (one in the Balearic Islands and one in Sardinia) emerged as crucial nodes for ensuring multi-generational connectivity. The high heterogeneity of MPA distribution, with low density in the South-Eastern Mediterranean, coupled with a mean dispersal distance of 120 km, leaves about 20% of the continental shelf without any larval supply. This low connectivity, here demonstrated for a major Mediterranean species, poses new challenges for the creation of a future Mediterranean network of well-connected MPAs providing recruitment to the whole continental shelf. This issue is even more critical given that the expected reduction of pelagic larval duration following sea temperature rise will likely decrease connectivity even more.

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The mean circulation of the southwestern Mediterranean Sea: Algerian Gyres

Cited by 58 publications

References 38 publications

Glider and satellite high resolution monitoring of a mesoscale eddy in the algerian basin: Effects on the mixed layer depth and biochemistry

Glider and satellite high resolution monitoring of a mesoscale eddy in the algerian basin: Effects on the mixed layer depth and biochemistry

Spreading of the Western Mediterranean Deep Water after winter 2005: Time scales and deep cyclone transport

Low Connectivity between Mediterranean Marine Protected Areas: A Biophysical Modeling Approach for the Dusky Grouper Epinephelus marginatus

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