forcing (Gómez et al. 2000; Echevarría et al. 2002). On the continental margin of the
NW Alboran Sea, the highest nutrient concentrations are detected during intense
coastal upwelling events (Gil and Gomis 1994; Prieto et al. 1999; Ramírez et al.
2005; Reul et al. 2005; Ramírez 2007; Macías et al. 2008; Mercado et al. 2012).
Wind-driven upwelling events normally lead to nitrate concentrations around
2.0–3.0 μM in the upper 20 m of the water column on the continental margin,
while phosphate and silicate concentrations are frequently around 0.15–0.20 μM and
1.5–2.0 μM, respectively (Ramírez et al. 2005; Reul et al. 2005; Mercado et al.
2014). Similar nutrient concentrations have also been found at the geostrophic front
associated to the path of Atlantic jet in this area (Morán and Estrada 2001; Arin et al.
2002; Reul et al. 2005; Mercado et al. 2014). Wind-driven upwelling events
frequently take place between November-March (Garcia-Gorriz and Carr 2001),
but they may sporadically occur throughout all year, thereby similarly high nutrient
concentrations in the upper layers have been occasionally reported in the NW
Alboran Sea during late spring (June) and the stratification period (e.g., Rubín
et al. 1999; Prieto et al. 1999; Ramírez 2007; Lazzari et al. 2012). Nevertheless,
during the non-bloom period, which extends from May to September (Garcia-Gorriz
and Carr 2001), coastal upwellings are less frequent and nutrient concentrations at
the surface tend to decline. However, the fertilizing effect associated to the front
persists even during the stratification period (Garcia-Gorriz and Carr 2001). Thus
nitrate concentrations in the frontal area during the stratification period are >2.0 μM,
while north and south of the jet they are <0.5 μM (Reul et al. 2005).
As a consequence of the contrasting oceanographic conditions between coastal
and offshore waters, sharp costal-offshore nutrient gradients are frequently observed
in the NW Alboran Sea (e.g., Gil and Gomis 1994; Rubín et al. 1997, 1999; Prieto
et al. 1999; Garcia-Gorriz and Carr 2001; Mercado et al. 2014) (Fig. 7.2). In addition
in the continental margin around 4.5
W there is usually a marked difference
between the waters under the influence of the front associated to the Atlantic jet
and the waters on the continental margin located north-northeast of the jet (Fig. 7.2),
out of the influence of the jet. Thus, the general circulation pattern explains the
relatively lower nutrient concentrations found in areas of the northern continental
margin of the Alboran Sea located northeast of the jet, as observed in Fig. 7.2, in
comparison with areas under the direct influence of the front associated to the
Atlantic jet (Gil and Gomis 1994; Ramírez 2007).
Nevertheless, it has to be highlighted that the presence of circulation cells
between Malaga and Motril is relatively frequent, with alternation of upwelling
and downwelling (Gil and Gomis 1994). Thus, relatively high nutrient concentrations on the continental shelf in the area off Cape Sacatrif (close to Motril) are
frequently found (Gil and Gomis 1994; García-Martínez et al. 2019), due to the
recurrence in this area of a cyclonic eddy (Parrilla and Kinder 1987; Baldacci et al.
2001). On the other hand, several studies have reported an eastward decline of
nutrients in the Alboran Sea (e.g., Denis-Karafistan et al. 1998; Karafistan et al.
2002). On the north continental margin, the lower concentrations have been
observed in Cape Gata (García-Martínez et al. 2019). Nevertheless, nutrients in the
frontal area of the Almería-Oran front are high compared to adjacent waters
7 The Biogeochemical Context of Marine Planktonic Ecosystems
217
NW Alboran Sea, the highest nutrient concentrations are detected during intense
coastal upwelling events (Gil and Gomis 1994; Prieto et al. 1999; Ramírez et al.
2005; Reul et al. 2005; Ramírez 2007; Macías et al. 2008; Mercado et al. 2012).
Wind-driven upwelling events normally lead to nitrate concentrations around
2.0–3.0 μM in the upper 20 m of the water column on the continental margin,
while phosphate and silicate concentrations are frequently around 0.15–0.20 μM and
1.5–2.0 μM, respectively (Ramírez et al. 2005; Reul et al. 2005; Mercado et al.
2014). Similar nutrient concentrations have also been found at the geostrophic front
associated to the path of Atlantic jet in this area (Morán and Estrada 2001; Arin et al.
2002; Reul et al. 2005; Mercado et al. 2014). Wind-driven upwelling events
frequently take place between November-March (Garcia-Gorriz and Carr 2001),
but they may sporadically occur throughout all year, thereby similarly high nutrient
concentrations in the upper layers have been occasionally reported in the NW
Alboran Sea during late spring (June) and the stratification period (e.g., Rubín
et al. 1999; Prieto et al. 1999; Ramírez 2007; Lazzari et al. 2012). Nevertheless,
during the non-bloom period, which extends from May to September (Garcia-Gorriz
and Carr 2001), coastal upwellings are less frequent and nutrient concentrations at
the surface tend to decline. However, the fertilizing effect associated to the front
persists even during the stratification period (Garcia-Gorriz and Carr 2001). Thus
nitrate concentrations in the frontal area during the stratification period are >2.0 μM,
while north and south of the jet they are <0.5 μM (Reul et al. 2005).
As a consequence of the contrasting oceanographic conditions between coastal
and offshore waters, sharp costal-offshore nutrient gradients are frequently observed
in the NW Alboran Sea (e.g., Gil and Gomis 1994; Rubín et al. 1997, 1999; Prieto
et al. 1999; Garcia-Gorriz and Carr 2001; Mercado et al. 2014) (Fig. 7.2). In addition
in the continental margin around 4.5
W there is usually a marked difference
between the waters under the influence of the front associated to the Atlantic jet
and the waters on the continental margin located north-northeast of the jet (Fig. 7.2),
out of the influence of the jet. Thus, the general circulation pattern explains the
relatively lower nutrient concentrations found in areas of the northern continental
margin of the Alboran Sea located northeast of the jet, as observed in Fig. 7.2, in
comparison with areas under the direct influence of the front associated to the
Atlantic jet (Gil and Gomis 1994; Ramírez 2007).
Nevertheless, it has to be highlighted that the presence of circulation cells
between Malaga and Motril is relatively frequent, with alternation of upwelling
and downwelling (Gil and Gomis 1994). Thus, relatively high nutrient concentrations on the continental shelf in the area off Cape Sacatrif (close to Motril) are
frequently found (Gil and Gomis 1994; García-Martínez et al. 2019), due to the
recurrence in this area of a cyclonic eddy (Parrilla and Kinder 1987; Baldacci et al.
2001). On the other hand, several studies have reported an eastward decline of
nutrients in the Alboran Sea (e.g., Denis-Karafistan et al. 1998; Karafistan et al.
2002). On the north continental margin, the lower concentrations have been
observed in Cape Gata (García-Martínez et al. 2019). Nevertheless, nutrients in the
frontal area of the Almería-Oran front are high compared to adjacent waters
7 The Biogeochemical Context of Marine Planktonic Ecosystems
217