13 nmolÁl
À1
Áh
À1 (L’Helguen et al. 2002). The low new PP and nitrate uptake rates in
the Almeria-Oran front could be caused by the low nitrate concentration in the photic
layer and the relatively deep location of the nitracline (L’Helguen et al. 2002). In the
NW Alboran Sea, the recurrence of intense upwelling events would temporarily
overcome the limitation by nitrate, promoting phytoplankton blooms and a phytoplankton community dominated by diatoms (Gómez et al. 2000; Reul et al. 2005;
Arin et al. 2002; Mercado et al. 2008, 2014). The rapid depletion of nitrate after the
cessation of westerlies suggests that under the absence of upwelling, phytoplankton
biomass and PP could be largely supported by regenerated forms of N. This is
consistent with the findings of L’Helguen et al. (2002) who observed that PP in the
Almeria-Oran front was initially nitrate-based, while regenerated production became
gradually more important as nitrate was progressively consumed. In addition,
average seasonal nitrate uptake rates in the upper layers of the NW Alboran Sea
ranged from ~2 to ~70 nmol N l
À1
Áh
À1 , although most values were
<11 nmol NÁl
À1
Áh
À1 (Mercado et al. 2008), which are close those reported by
L’Helguen et al. (2002) in the Almeria-Oran front. In contrast, ammonium uptake
rates ranged between ~5 and 86 nmolÁN l
À1
Áh
À1 throughout the year (Mercado et al.
2008), with most of the mean seasonal values <30.6 nmol NÁl
À1
Áh
À1 . Higher uptake
rates of both nitrate and ammonium were observed at the Chl-a maximum (Mercado
et al. 2008).
However, most in situ measurements of Chla-a and PP have been carried out in
particular areas of the Alboran Sea and did not cover either the whole Alboran basin
or all the seasons. Over the last decades, several studies based on remote sensing data
have analyzed the Chl-a and PP data in the whole Alboran Sea or in large parts of this
basin, providing more comprehensive and synoptic information on the variability of
phytoplankton biomass and PP in the Alboran Sea. This approach is discussed in the
next section.
7.3.2 Distribution Patterns of Chlorophyll-a and Primary
Production from Satellite Derived Data Models
7.3.2.1 Sea Surface Chlorophyll-a Concentration from Satellite Data
Surface Chl-a concentration as derived from satellite measurements allows detecting
the main spatial and temporal patterns in the Mediterranean and the Alboran Sea
(Morel and Andre 1991; Garcia-Gorriz and Carr 1999, 2001; Bosc et al. 2004;
Macías et al. 2007). Based on Sea Surface Temperature (SST) and Chl-a concentration, Baldacci et al. (2001) defined two upwelling areas along the Spanish coast in
the Alboran Sea: the first one is located between 5.5
W and 4.5
W, and the second
one is located between 4.5
W and 2
W. The first area (A) is associated to the NW
Alboran upwelling area and it stretches from the Strait of Gibraltar to Cape Pino
(Malaga). The second upwelling area (B) extends from Cape Pino to Cape Gata
(Almeria), the named Atlantic-Mediterranean Transition zone (Muñoz et al. 2017).
7 The Biogeochemical Context of Marine Planktonic Ecosystems
229
À1
Áh
À1 (L’Helguen et al. 2002). The low new PP and nitrate uptake rates in
the Almeria-Oran front could be caused by the low nitrate concentration in the photic
layer and the relatively deep location of the nitracline (L’Helguen et al. 2002). In the
NW Alboran Sea, the recurrence of intense upwelling events would temporarily
overcome the limitation by nitrate, promoting phytoplankton blooms and a phytoplankton community dominated by diatoms (Gómez et al. 2000; Reul et al. 2005;
Arin et al. 2002; Mercado et al. 2008, 2014). The rapid depletion of nitrate after the
cessation of westerlies suggests that under the absence of upwelling, phytoplankton
biomass and PP could be largely supported by regenerated forms of N. This is
consistent with the findings of L’Helguen et al. (2002) who observed that PP in the
Almeria-Oran front was initially nitrate-based, while regenerated production became
gradually more important as nitrate was progressively consumed. In addition,
average seasonal nitrate uptake rates in the upper layers of the NW Alboran Sea
ranged from ~2 to ~70 nmol N l
À1
Áh
À1 , although most values were
<11 nmol NÁl
À1
Áh
À1 (Mercado et al. 2008), which are close those reported by
L’Helguen et al. (2002) in the Almeria-Oran front. In contrast, ammonium uptake
rates ranged between ~5 and 86 nmolÁN l
À1
Áh
À1 throughout the year (Mercado et al.
2008), with most of the mean seasonal values <30.6 nmol NÁl
À1
Áh
À1 . Higher uptake
rates of both nitrate and ammonium were observed at the Chl-a maximum (Mercado
et al. 2008).
However, most in situ measurements of Chla-a and PP have been carried out in
particular areas of the Alboran Sea and did not cover either the whole Alboran basin
or all the seasons. Over the last decades, several studies based on remote sensing data
have analyzed the Chl-a and PP data in the whole Alboran Sea or in large parts of this
basin, providing more comprehensive and synoptic information on the variability of
phytoplankton biomass and PP in the Alboran Sea. This approach is discussed in the
next section.
7.3.2 Distribution Patterns of Chlorophyll-a and Primary
Production from Satellite Derived Data Models
7.3.2.1 Sea Surface Chlorophyll-a Concentration from Satellite Data
Surface Chl-a concentration as derived from satellite measurements allows detecting
the main spatial and temporal patterns in the Mediterranean and the Alboran Sea
(Morel and Andre 1991; Garcia-Gorriz and Carr 1999, 2001; Bosc et al. 2004;
Macías et al. 2007). Based on Sea Surface Temperature (SST) and Chl-a concentration, Baldacci et al. (2001) defined two upwelling areas along the Spanish coast in
the Alboran Sea: the first one is located between 5.5
W and 4.5
W, and the second
one is located between 4.5
W and 2
W. The first area (A) is associated to the NW
Alboran upwelling area and it stretches from the Strait of Gibraltar to Cape Pino
(Malaga). The second upwelling area (B) extends from Cape Pino to Cape Gata
(Almeria), the named Atlantic-Mediterranean Transition zone (Muñoz et al. 2017).
7 The Biogeochemical Context of Marine Planktonic Ecosystems
229