Both areas are characterized by the presence of waters upwelled by westerlies and/or
cyclonic circulation cells (Baldacci et al. 2001), but they differ in their upwelling
patterns throughout the year. Although the upwelling occurs simultaneously in both
areas in spring and early autumn (October), higher Chl-a concentrations are found in
area B in late autumn. In contrast in winter (January to March) and in summer higher
Chl-a are found in area A.
In addition, the upwelling associated to the frontal area of the Atlantic jet is also a
distinctive feature from Chl-a satellite data. The periphery of the WAG becomes
richer in Chl-a as the jet travels through the Alboran Sea, due to the in situ growth of
phytoplankton and also due to advection of Chl-a patches from nearby areas (Ruiz
et al. 2001; Garcia-Gorriz and Carr 2001; Arin et al. 2002; Macías et al. 2007). On
the other hand, according to Garcia-Gorriz and Carr (2001) the Chl-a annual cycle in
the Alboran is in general characterized by a bloom period (November to March) and
a non-bloom period (May to September), with transition periods between these two
regimes. Other studies in the NW Alboran Sea based on satellite data have reported
an intense bloom in March-April (Macías et al. 2007), declining the Chl-a values
from June to September and increasing again from September to December. Lazzari
et al. (2012), based on a 6 years study of satellite data for the whole Alboran basin,
found the lower Chl-a values from June to September and higher values from
November to May. Nevertheless, the interannual variability of Chl-a in the Alboran
Sea is very high (Bosc et al. 2004) and its seasonal cycle, as derived from satellite
data, is the most chaotic of the Mediterranean Sea (Bosc et al. 2004), with a
minimum in summer (~0.20–0.25 μg Chl-aÁl
À1
).
While satellite images are limited to surface waters, 3D models allow integration
of Chl-a and other variables in the water column (Lazzari et al. 2012). Figure 7.6
shows comparatively the mean integrated Chl-a values (1999–2016) during the
month of May, one of the most productive months in the Alboran Sea according
to the results of Lazzari et al. (2012), for the whole Mediterranean Sea and the
Alboran Sea. Figure 7.6b shows a marked eastward gradient of Chl-a in the Alboran
Sea with large differences between the western and the eastern basin. According to
this Figure, in the western basin very high Chl-a concentrations are observed in
spring in the NW sector off Malaga Bay, while very low values are found at the Strait
of Gibraltar and in the westernmost part of the Alboran Sea. These low Chl-a values
could be due to a time lag in the response of phytoplankton to the injection of
nutrient into the euphotic layer. Some authors have argued that due to the high
velocity of the Atlantic jet in the vicinities of the Strait, nutrients would have a quasiconservative behavior (Minas et al. 1991). Thus the combined effect of the speed of
the Atlantic jet and the time lapse for building phytoplankton biomass may result in
low integrated Chl-a values at the vicinities of the Strait. Figure 7.6b also shows high
Chl-a concentrations covering the entire eastern Alboran basin, probably due to
the effect of wind-driven upwelling at this time of the year and the advection towards
the center of the basin, although the values are slightly lower than those observed off
the Malaga Bay. The higher variability is found between Marbella and Malaga due to
intermittent upwelling processes (Fig. 7.6c).
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T. Ramírez et al.
cyclonic circulation cells (Baldacci et al. 2001), but they differ in their upwelling
patterns throughout the year. Although the upwelling occurs simultaneously in both
areas in spring and early autumn (October), higher Chl-a concentrations are found in
area B in late autumn. In contrast in winter (January to March) and in summer higher
Chl-a are found in area A.
In addition, the upwelling associated to the frontal area of the Atlantic jet is also a
distinctive feature from Chl-a satellite data. The periphery of the WAG becomes
richer in Chl-a as the jet travels through the Alboran Sea, due to the in situ growth of
phytoplankton and also due to advection of Chl-a patches from nearby areas (Ruiz
et al. 2001; Garcia-Gorriz and Carr 2001; Arin et al. 2002; Macías et al. 2007). On
the other hand, according to Garcia-Gorriz and Carr (2001) the Chl-a annual cycle in
the Alboran is in general characterized by a bloom period (November to March) and
a non-bloom period (May to September), with transition periods between these two
regimes. Other studies in the NW Alboran Sea based on satellite data have reported
an intense bloom in March-April (Macías et al. 2007), declining the Chl-a values
from June to September and increasing again from September to December. Lazzari
et al. (2012), based on a 6 years study of satellite data for the whole Alboran basin,
found the lower Chl-a values from June to September and higher values from
November to May. Nevertheless, the interannual variability of Chl-a in the Alboran
Sea is very high (Bosc et al. 2004) and its seasonal cycle, as derived from satellite
data, is the most chaotic of the Mediterranean Sea (Bosc et al. 2004), with a
minimum in summer (~0.20–0.25 μg Chl-aÁl
À1
).
While satellite images are limited to surface waters, 3D models allow integration
of Chl-a and other variables in the water column (Lazzari et al. 2012). Figure 7.6
shows comparatively the mean integrated Chl-a values (1999–2016) during the
month of May, one of the most productive months in the Alboran Sea according
to the results of Lazzari et al. (2012), for the whole Mediterranean Sea and the
Alboran Sea. Figure 7.6b shows a marked eastward gradient of Chl-a in the Alboran
Sea with large differences between the western and the eastern basin. According to
this Figure, in the western basin very high Chl-a concentrations are observed in
spring in the NW sector off Malaga Bay, while very low values are found at the Strait
of Gibraltar and in the westernmost part of the Alboran Sea. These low Chl-a values
could be due to a time lag in the response of phytoplankton to the injection of
nutrient into the euphotic layer. Some authors have argued that due to the high
velocity of the Atlantic jet in the vicinities of the Strait, nutrients would have a quasiconservative behavior (Minas et al. 1991). Thus the combined effect of the speed of
the Atlantic jet and the time lapse for building phytoplankton biomass may result in
low integrated Chl-a values at the vicinities of the Strait. Figure 7.6b also shows high
Chl-a concentrations covering the entire eastern Alboran basin, probably due to
the effect of wind-driven upwelling at this time of the year and the advection towards
the center of the basin, although the values are slightly lower than those observed off
the Malaga Bay. The higher variability is found between Marbella and Malaga due to
intermittent upwelling processes (Fig. 7.6c).
230
T. Ramírez et al.