knowledge of a no motion reference level which is usually considered as the 200 or
300 dbar level. Bryden and Stommel (1982) considered that the anticyclonic circulation of the upper layer extended to the intermediate and deep layers below, and the
sea bottom should be used as the reference layer for geostrophic calculations.
Nevertheless, the velocity of the currents at the deep layers is of the order of a few
centimetres per second, while the AW velocities can reach 1 m/s. Therefore, the error
induced by the selection of the no motion reference level does not affect the
description of the main features of the upper layer circulation. In the case of the
LIW, WMDW and TDW circulation, the low-velocity values make it difficult to
extract conclusions from geostrophic calculations. Our knowledge about the pathways followed by these water masses is inferred from their θS values and from direct
measurements using current meters or drifters.
Lanoix (1974) considered that the LIW is divided into three branches within the
Alboran Sea. One of them would flow to the north because of the Coriolis force. The
other two branches flow to the north and south of the Alboran Island. Auffret et al.
(1974) concluded that the intermediate and deep waters flow close to the Spanish
coast. These authors, once again, invoked the Coriolis force as the responsible
mechanism. Bryden and Stommel (1982) deployed a current meter at the Moroccan
continental slope close to the Strait of Gibraltar (between 4
and 5
W). The
instrument depth was 500 m and the average speed was 4.6 cm/s, directed to the
Strait of Gibraltar, along the direction of the isobaths. According to these results and
using hydrographic measurements, these authors considered that the WMDW flows
along the African slope, uplifting as it approaches the Strait of Gibraltar. The
presence of the LIW was also stronger at the central and southern parts of the
Alboran Sea. The results concerning the behaviour of the WMDW were confirmed
by Gascard and Richez (1985) using free drifters deployed between 600 and 800 m
depth at the Moroccan continental slope. The average speeds found in this work were
around 4 cm/s with peaks that could reach 12 cm/s. Kinder (1984) and Parrilla et al.
(1986) analyzed time series from several current meters deployed in the central and
northern sectors of the Western Alboran Sea. At 540 m, the currents were directed
towards the Strait of Gibraltar with average speeds between 1 and 3 cm/s. According
to these results, the authors concluded that the LIW does not follow an anticyclonic
circuit, but flows as a slow current (1–2 cm/s) across the central and northern parts of
the Alboran Sea, not being so clear the LIW behaviour in the southern sector.
Concerning the deep water circulation, results in Parrilla et al. (1986) coincide
with previous ones and show that the WMDW flows in an SW direction to the
north of the Alboran Island because of bathymetric constrictions. Then it flows along
the Moroccan slope uplifting to 400–500 m as it approaches the Strait of Gibraltar.
According to these authors, it is not clear if the WMDW partially recirculates
anticyclonically in the northern sector of the Alboran Sea. More recently it has
been accepted that the deep currents in the Alboran Sea that finally outflow through
the Strait of Gibraltar because of Bernoulli’s aspiration (Kinder and Bryden 1990;
Kinder and Parrilla 1987), are not formed just by WMDW, but they also have an
important contribution from TDW (Naranjo et al. 2015; Millot 2009).
100
M. Vargas-Yáñez et al.
300 dbar level. Bryden and Stommel (1982) considered that the anticyclonic circulation of the upper layer extended to the intermediate and deep layers below, and the
sea bottom should be used as the reference layer for geostrophic calculations.
Nevertheless, the velocity of the currents at the deep layers is of the order of a few
centimetres per second, while the AW velocities can reach 1 m/s. Therefore, the error
induced by the selection of the no motion reference level does not affect the
description of the main features of the upper layer circulation. In the case of the
LIW, WMDW and TDW circulation, the low-velocity values make it difficult to
extract conclusions from geostrophic calculations. Our knowledge about the pathways followed by these water masses is inferred from their θS values and from direct
measurements using current meters or drifters.
Lanoix (1974) considered that the LIW is divided into three branches within the
Alboran Sea. One of them would flow to the north because of the Coriolis force. The
other two branches flow to the north and south of the Alboran Island. Auffret et al.
(1974) concluded that the intermediate and deep waters flow close to the Spanish
coast. These authors, once again, invoked the Coriolis force as the responsible
mechanism. Bryden and Stommel (1982) deployed a current meter at the Moroccan
continental slope close to the Strait of Gibraltar (between 4
and 5
W). The
instrument depth was 500 m and the average speed was 4.6 cm/s, directed to the
Strait of Gibraltar, along the direction of the isobaths. According to these results and
using hydrographic measurements, these authors considered that the WMDW flows
along the African slope, uplifting as it approaches the Strait of Gibraltar. The
presence of the LIW was also stronger at the central and southern parts of the
Alboran Sea. The results concerning the behaviour of the WMDW were confirmed
by Gascard and Richez (1985) using free drifters deployed between 600 and 800 m
depth at the Moroccan continental slope. The average speeds found in this work were
around 4 cm/s with peaks that could reach 12 cm/s. Kinder (1984) and Parrilla et al.
(1986) analyzed time series from several current meters deployed in the central and
northern sectors of the Western Alboran Sea. At 540 m, the currents were directed
towards the Strait of Gibraltar with average speeds between 1 and 3 cm/s. According
to these results, the authors concluded that the LIW does not follow an anticyclonic
circuit, but flows as a slow current (1–2 cm/s) across the central and northern parts of
the Alboran Sea, not being so clear the LIW behaviour in the southern sector.
Concerning the deep water circulation, results in Parrilla et al. (1986) coincide
with previous ones and show that the WMDW flows in an SW direction to the
north of the Alboran Island because of bathymetric constrictions. Then it flows along
the Moroccan slope uplifting to 400–500 m as it approaches the Strait of Gibraltar.
According to these authors, it is not clear if the WMDW partially recirculates
anticyclonically in the northern sector of the Alboran Sea. More recently it has
been accepted that the deep currents in the Alboran Sea that finally outflow through
the Strait of Gibraltar because of Bernoulli’s aspiration (Kinder and Bryden 1990;
Kinder and Parrilla 1987), are not formed just by WMDW, but they also have an
important contribution from TDW (Naranjo et al. 2015; Millot 2009).
100
M. Vargas-Yáñez et al.