interface separating the AW from the Mediterranean waters is between 150 and
200 m at the centre of the anticyclonic gyres. It is shallower than 50 m close to
3
30
0 W coinciding with the cyclonic circulation area located in front of Cape
Sacratif and to the north of the Alboran Sea frontal system. Figure 4.6b, c are northsouth transects along 4
W and 2
W. These figures also show the upward tilting of
isohalines to the north, reaching depths lower than 50 m at the position of the
Alboran Sea frontal system.
The circulation scheme described by means of Figs. 4.4, 4.5 and 4.6, and sketched
with light grey lines in Fig. 4.3, is the most frequently described in the literature.
Nevertheless, this circulation pattern is far from being stationary and it has a strong
temporal variability.
One of the first descriptions of the water masses and geostrophic circulation for
the whole Alboran Sea, was the one made by Lanoix (1974) using data from a
summer cruise in 1962. In his work, the WAG was fully developed, while the EAG
was absent and the AJ flowed in the eastern Alboran sub-basin along the African
coast. It is very likely that because of this early work, the WAG was initially
considered as a permanent feature of the Alboran Sea while the EAG was considered
a more elusive circulation pattern. The use of thermal infrared images, mainly from
the early 1980s, revealed that both the WAG and EAG could disappear and it could
be established that the disappearance of any of them had the same frequency (Heburn
and Laviolette 1990). Other works, using SST images and Empirical Orthogonal
Function decomposition showed that the dynamics of the Alboran Sea is very
complex and has a strong temporal variability on a sub-inertial scale (Baldacci
et al. 2001).
Renault et al. (2012), Flexas et al. (2006), Vélez-Belchí et al. (2005), VargasYáñez et al. (2002) observed that the circulation of the Alboran Sea could develop
more complex structures. In some situations, the AJ does not surround the WAG.
Instead of it, the AJ impinges on the WAG and then turns to the right flowing close to
the African coast. The AJ finally develops a new anticyclonic gyre that pushes and
displaces the “old” WAG. During several days or weeks, three anticyclonic gyres
can coexist within the Alboran Sea, until a new two-gyre system is re-established. In
some cases a more dramatic change can be observed. The AJ, instead of flowing in a
northeast direction after getting out of the Strait of Gibraltar, turns to the southeast,
surrounding Point Almina (black lines in Fig. 4.3), and then flows along the African
coast. In this case, the northern shore of the Alboran Sea is not affected by the AW
and its temperature/salinity takes lower/higher values. Renault et al. (2012), using
altimetry data, classified the monthly circulation patterns from 1993 to 2010. The
different situations described included the existence of one anticyclonic gyre (the
western one), two gyres, three gyres, and a coastal jet. The two-gyre circulation
situation and the coastal circulation mode are depicted in Fig. 4.3. Several hypotheses have been proposed for explaining these changes in the direction of the AJ and
the migration or disappearance of the Alboran Sea gyres. These hypotheses include
changes in the AJ velocity or blocking of the AJ caused by the size increase of the
WAG (Flexas et al. 2006; Velez-Belchi et al. 2005; Bormans and Garrett 1989). In
98
M. Vargas-Yáñez et al.
200 m at the centre of the anticyclonic gyres. It is shallower than 50 m close to
3
30
0 W coinciding with the cyclonic circulation area located in front of Cape
Sacratif and to the north of the Alboran Sea frontal system. Figure 4.6b, c are northsouth transects along 4
W and 2
W. These figures also show the upward tilting of
isohalines to the north, reaching depths lower than 50 m at the position of the
Alboran Sea frontal system.
The circulation scheme described by means of Figs. 4.4, 4.5 and 4.6, and sketched
with light grey lines in Fig. 4.3, is the most frequently described in the literature.
Nevertheless, this circulation pattern is far from being stationary and it has a strong
temporal variability.
One of the first descriptions of the water masses and geostrophic circulation for
the whole Alboran Sea, was the one made by Lanoix (1974) using data from a
summer cruise in 1962. In his work, the WAG was fully developed, while the EAG
was absent and the AJ flowed in the eastern Alboran sub-basin along the African
coast. It is very likely that because of this early work, the WAG was initially
considered as a permanent feature of the Alboran Sea while the EAG was considered
a more elusive circulation pattern. The use of thermal infrared images, mainly from
the early 1980s, revealed that both the WAG and EAG could disappear and it could
be established that the disappearance of any of them had the same frequency (Heburn
and Laviolette 1990). Other works, using SST images and Empirical Orthogonal
Function decomposition showed that the dynamics of the Alboran Sea is very
complex and has a strong temporal variability on a sub-inertial scale (Baldacci
et al. 2001).
Renault et al. (2012), Flexas et al. (2006), Vélez-Belchí et al. (2005), VargasYáñez et al. (2002) observed that the circulation of the Alboran Sea could develop
more complex structures. In some situations, the AJ does not surround the WAG.
Instead of it, the AJ impinges on the WAG and then turns to the right flowing close to
the African coast. The AJ finally develops a new anticyclonic gyre that pushes and
displaces the “old” WAG. During several days or weeks, three anticyclonic gyres
can coexist within the Alboran Sea, until a new two-gyre system is re-established. In
some cases a more dramatic change can be observed. The AJ, instead of flowing in a
northeast direction after getting out of the Strait of Gibraltar, turns to the southeast,
surrounding Point Almina (black lines in Fig. 4.3), and then flows along the African
coast. In this case, the northern shore of the Alboran Sea is not affected by the AW
and its temperature/salinity takes lower/higher values. Renault et al. (2012), using
altimetry data, classified the monthly circulation patterns from 1993 to 2010. The
different situations described included the existence of one anticyclonic gyre (the
western one), two gyres, three gyres, and a coastal jet. The two-gyre circulation
situation and the coastal circulation mode are depicted in Fig. 4.3. Several hypotheses have been proposed for explaining these changes in the direction of the AJ and
the migration or disappearance of the Alboran Sea gyres. These hypotheses include
changes in the AJ velocity or blocking of the AJ caused by the size increase of the
WAG (Flexas et al. 2006; Velez-Belchi et al. 2005; Bormans and Garrett 1989). In
98
M. Vargas-Yáñez et al.