The origin and characteristics of the Algerian Current

Abstract

Satellite and ship data collected between May 1 and 22, 1986, show that the Algerian Current originates in the Almeria‐Oran Front and remains within 30 km of the Algerian coast for over 300 km, between Oran and Algiers. The differences between the water masses of the current and the resident regional waters are clearly observed in the chlorophyll concentrations and optical characteristics, thus permitting the resulting patterns to be used as tracers of the circulation. During this field period, the Algerian Current begins as an extension of the Almeria‐Oran Front, which is found at the western periphery of the Eastern Alboran Gyre. This major oceanographic salinity front (ΔS > 1/km) delineates the boundary of the Algerian Current, which has average surface velocities of 40 cm/s and maximum speeds reaching 80 cm/s. The current, which has a volume transport between 0.4 and 0.5 Sv, is confined to the upper 150 m and is in geostrophic balance. A sequence of coastal zone color scanner (CZCS) and advanced very high resolution radiometer (AVHRR) satellite imagery showing the rapidly evolving surface circulation features is augmented with in situ ship data of current and water mass characteristics. Rapid undulations and frontal movements of the current were observed during the study period; however, the flow remained unbroken between 1° and 3°E. Current instability increased eastward as the undulations were sharper and the current appeared to depart from the coast near Algiers.

Mesoscale subduction at the Almeria–Oran front

“…Diatom and nanoplankton abundance, chlorophyll content and primary production have been observed to be higher in the jet, either from satellite data (Arnone and La Violette, 1986;Lohrenz et al, 1988;Arnone et al, 1990) or in-situ shipboard data (Prieur et al, 1993;Videau et al, 1994;Fiala et al, 1994). This suggests that the frontal-jet system exhibits a fertilising effect on the otherwise oligotrophic waters of the Alboran Sea.…”

Mesoscale subduction at the Almeria–Oran front

“…Mediterranean Surface Waters (MSW) (Arnone et al 1990), salinity >37.5 temperature >15.5 °C, were found in the N. E. corner of the LSS2 area. This water appeared to be flowing slowly south westward along the Spanish coast but had not reached the area that was to be covered by the later fine scale surveys.…”

“…The lowest salinity waters, ~36.63, are surface waters of recent Atlantic origin and are referred to as Modified Atlantic Water (MAW) (Arnone et al, 1990;Sparnocchia et al, 1994).…”

The seasonal cycle of the Atlantic Jet dynamics in the Alboran Sea: direct atmospheric forcing versus Mediterranean thermohaline circulation

“…The entrance of the Atlantic Jet (AJ) through the strait drives the main circulation of the Alboran Sea, with two anticyclonic gyres: the more permanent Western Anticyclonic Gyre (WAG) and the more elusive Eastern Anticyclonic Gyre (EAG) in the open-sea regions (e.g., Lacombe 1971;Lanoix 1974;Arnone et al 1990;La Violette 1984) and smaller cyclones along the northern and southern shores (e.g., Peliz et al 2013). The presence of the AJ close to the northern shore of the Alboran Sea favors the onset of upwelling conditions ) that increase primary production in the region (García-Gorriz and Carr 1999;Macías et al 2007b) and favors the spawning and recruitment of small pelagic fish (Catalán et al 2013) that sustains an economically important fishing activity in the region (Macías et al 2014a).…”