the average profile of Chl-a in summer for the whole Alboran Sea presents also a
shallower peak (Fig. 7.5), resembling the vertical profile in other areas of the
Mediterranean (Lavigne et al. 2015). This shallower peak can be due to upwellings
and advection of Chl-a patches. During the mixing period (late autumn to winter) the
DCM is shallower or even disappear, with the higher Chl-a concentrations in the
upper 20 m (Fig. 7.5) (Ramírez 2007; García-Martínez et al. 2019). In most of these
cases, the Chl-a maximum is not properly a DCM, but a surface or subsurface
maximum. In general, Chl-a concentration at the DCM in the Alboran Sea is
commonly >0.5 μgÁl
À1 , although values >1.0 μgÁl
À1 are often found in the NW
margin, where values close to ~8 μgÁl
À1 can occasionally be found (Rodríguez et al.
1998; Ramírez et al. 2005; García-Martínez et al. 2019).
In the Alboran Sea PP decreases in general eastward, from the Strait of Gibraltar
to Cape Gata. Although the existing in situ measurements of PP (
14 C) in the NW
Alboran Sea reveal that there is also a decrease of the integrated PP (PPint) following
a coast-offshore gradient, with the highest average values in the frontal area
(632 Æ 184 mgÁC m
À2
Áday
À1 ) and the lowest average values in the center of the
WAG (330 Æ 149 mgÁC m
À2
Áday
À1 ) (Morán and Estrada 2001). On the other hand,
Macías et al. (2009) found that PPint varied between 644 mgÁC m
À2
Áday
À1 at the
frontal area and 6 mgÁC m
À2
Áday
À1 at the western side of the Strait of Gibraltar (off
Europa Point). In the Almeria-Oran front (Eastern Alboran Sea), Semperé et al.
(2003) estimated that the average PPint was around 242 mgÁC m
À2
Áday
À1 in the
modified Atlantic jet area and the gyre, while it declined to 117 mgÁC m
À2
Áday
À1 in
Mediterranean waters. Also in the Almería-Oran front and the Algerian Current the
PP values at the frontal area ranged from 500 to 1300 mgÁC m
À2
Áday
À1 (with a mean
value of 880 mgÁC m
À2
Áday
À1 ) (Lohrenz et al. 1988).
It has been hypothesized that in the absence of upwelling, the relatively low
nitrate concentration found in the upper layers together with the low N:P and N:Si
ratios, could favor the growth of a phytoplankton community of smaller cell size in
NW Alboran Sea (Ramírez 2007), which are better adapted to grow in nutrientdeficient environments (Chisholm 1992) in comparison with other phytoplankton
groups of larger cell size, such a diatoms. In fact several studies have reported that
picoplankton and nanoplankton dominate the phytoplankton community in the
surface layers of the Alboran Sea (Rodríguez et al. 1998; Arin et al. 2002; Reul
et al. 2005). Moreover, temporal changes in the phytoplankton community at the
continental margin of the NW Alboran Sea have been observed (Mercado et al.
2005, 2007). These changes, involving the shift of a phytoplankton community
dominated by diatoms to a community dominated by coccolithophorids and small
flagellates, were associated to changes in nitrate and the N:P the molar ratio.
Moreover, taking into account that during great part of the year nitrate concentrations are low and that the N:P ratio is <16:1, it has been suggested that regenerated
PP could be important in the NW Alboran Sea (Ramírez 2007). This is consistent
with the low new PP values measured at the Almeria-Oran front (mean value
2.5 mmolÁ m
À2
Áday
À1 ) compared to other oceanic and coastal areas (L’Helguen
et al. 2002). Low nitrate uptake rates (up to 6.4 nmolÁl
À1
Áh
À1 ) have been obtained in
the frontal area, while maximum ammonium uptake rates were about
228
T. Ramírez et al.
shallower peak (Fig. 7.5), resembling the vertical profile in other areas of the
Mediterranean (Lavigne et al. 2015). This shallower peak can be due to upwellings
and advection of Chl-a patches. During the mixing period (late autumn to winter) the
DCM is shallower or even disappear, with the higher Chl-a concentrations in the
upper 20 m (Fig. 7.5) (Ramírez 2007; García-Martínez et al. 2019). In most of these
cases, the Chl-a maximum is not properly a DCM, but a surface or subsurface
maximum. In general, Chl-a concentration at the DCM in the Alboran Sea is
commonly >0.5 μgÁl
À1 , although values >1.0 μgÁl
À1 are often found in the NW
margin, where values close to ~8 μgÁl
À1 can occasionally be found (Rodríguez et al.
1998; Ramírez et al. 2005; García-Martínez et al. 2019).
In the Alboran Sea PP decreases in general eastward, from the Strait of Gibraltar
to Cape Gata. Although the existing in situ measurements of PP (
14 C) in the NW
Alboran Sea reveal that there is also a decrease of the integrated PP (PPint) following
a coast-offshore gradient, with the highest average values in the frontal area
(632 Æ 184 mgÁC m
À2
Áday
À1 ) and the lowest average values in the center of the
WAG (330 Æ 149 mgÁC m
À2
Áday
À1 ) (Morán and Estrada 2001). On the other hand,
Macías et al. (2009) found that PPint varied between 644 mgÁC m
À2
Áday
À1 at the
frontal area and 6 mgÁC m
À2
Áday
À1 at the western side of the Strait of Gibraltar (off
Europa Point). In the Almeria-Oran front (Eastern Alboran Sea), Semperé et al.
(2003) estimated that the average PPint was around 242 mgÁC m
À2
Áday
À1 in the
modified Atlantic jet area and the gyre, while it declined to 117 mgÁC m
À2
Áday
À1 in
Mediterranean waters. Also in the Almería-Oran front and the Algerian Current the
PP values at the frontal area ranged from 500 to 1300 mgÁC m
À2
Áday
À1 (with a mean
value of 880 mgÁC m
À2
Áday
À1 ) (Lohrenz et al. 1988).
It has been hypothesized that in the absence of upwelling, the relatively low
nitrate concentration found in the upper layers together with the low N:P and N:Si
ratios, could favor the growth of a phytoplankton community of smaller cell size in
NW Alboran Sea (Ramírez 2007), which are better adapted to grow in nutrientdeficient environments (Chisholm 1992) in comparison with other phytoplankton
groups of larger cell size, such a diatoms. In fact several studies have reported that
picoplankton and nanoplankton dominate the phytoplankton community in the
surface layers of the Alboran Sea (Rodríguez et al. 1998; Arin et al. 2002; Reul
et al. 2005). Moreover, temporal changes in the phytoplankton community at the
continental margin of the NW Alboran Sea have been observed (Mercado et al.
2005, 2007). These changes, involving the shift of a phytoplankton community
dominated by diatoms to a community dominated by coccolithophorids and small
flagellates, were associated to changes in nitrate and the N:P the molar ratio.
Moreover, taking into account that during great part of the year nitrate concentrations are low and that the N:P ratio is <16:1, it has been suggested that regenerated
PP could be important in the NW Alboran Sea (Ramírez 2007). This is consistent
with the low new PP values measured at the Almeria-Oran front (mean value
2.5 mmolÁ m
À2
Áday
À1 ) compared to other oceanic and coastal areas (L’Helguen
et al. 2002). Low nitrate uptake rates (up to 6.4 nmolÁl
À1
Áh
À1 ) have been obtained in
the frontal area, while maximum ammonium uptake rates were about
228
T. Ramírez et al.