and the Alboran Sea. The processed data correspond to the month of May, one of the
most productive months in the Alboran Sea (Lazzari et al. 2012).
On the other hand, the data on the nutrient distribution at 50 m depth in the
Alboran Sea during the IctioAlboran 0793 survey (July 1993) were provided by
Dr. Juan Pérez de Rubín (Instituto Español de Oceanografía, IEO).
7.2 Nutrients Dynamics: Coupling with Physical Processes
7.2.1 Nutrients and Water Masses in the Alboran Sea
Surface layers in the Alboran Sea are occupied by Surface Atlantic Water (SAW),
known also as Modified Surface Atlantic Water (MSAW), which has its origin in the
Gulf of Cadiz (see Chap. 5 of this book). Many studies have reported that the SAW
entering the Alboran Sea is nutrient poor or even nutrient depleted (Minas et al.
1991; Béthoux et al. 1992; Turley 1999) due to the consumption by phytoplankton in
the Gulf of Cadiz and the Strait of Gibraltar. However, the question of whether the
Atlantic water entering into the Alboran Sea is depleted or not in nutrients has been
matter of debate during the last decades (Béthoux et al. 1992; Dafner et al. 2003;
Huertas et al. 2012). Much of these discrepancies could be due to the fact that in
many studies nutrient concentrations have been reported for the Atlantic inflow
entering into the Alboran Sea rather than for the SAW. At the Strait of Gibraltar,
and due to intense mixing processes, the upwelling of subsurface rich nutrient
Mediterranean waters into the Atlantic surface layer takes place. Other processes
like incursions of NACW also occur (see below), thereby the nutrient load in the
Atlantic inflow largely depends on these processes and also on the biological activity
(Gómez et al. 2000). Moreover, mixing at the Strait is largely controlled by different
physical factors (see Sect. 7.2.2). Therefore, nutrient levels in the Atlantic inflow can
be rather variable. Nevertheless, the nutrient signatures of the SAW at the Strait have
been obtained from the analysis of water masses (Minas et al. 1991; Gómez et al.
2000), where SAW is characterized by nitrate <2 μM, phosphate <0.01 μM, and
silicate <1 μM (Gómez et al. 2000).
NACW has been detected by several studies in the upper layer of the Strait of
Gibraltar and also in the Alboran Sea (Gascard and Richez 1985; Minas et al. 1991;
Gómez et al. 2000; Ramírez et al. 2005; Ramírez-Romero et al. 2014). The entrance
of this water mass into the Alboran Sea is strongly modulated by the tidal cycles at
the Strait (see Sect. 7.2.2). NACW is a water mass rich in nutrients, with nitrate
~5–7 μM, phosphate ~0.35–0.45 μM, and silicate ~2–3 μM (Gómez et al. 2000).
Although other studies have found lower phosphate concentrations (0.09 μM) associated to this water mass at the Strait of Gibraltar (Ramírez-Romero et al. 2014).
On the other hand, the intermediate and deep water masses found in the Alboran
Sea are Winter Intermediate Water (WIW), Levantine Intermediate Water (LIW),
and Western Mediterranean Deep Water (WMDW) (see Chap. 5 of this book). These
water masses are characterized by different biogeochemical signatures due to their
7 The Biogeochemical Context of Marine Planktonic Ecosystems
209
most productive months in the Alboran Sea (Lazzari et al. 2012).
On the other hand, the data on the nutrient distribution at 50 m depth in the
Alboran Sea during the IctioAlboran 0793 survey (July 1993) were provided by
Dr. Juan Pérez de Rubín (Instituto Español de Oceanografía, IEO).
7.2 Nutrients Dynamics: Coupling with Physical Processes
7.2.1 Nutrients and Water Masses in the Alboran Sea
Surface layers in the Alboran Sea are occupied by Surface Atlantic Water (SAW),
known also as Modified Surface Atlantic Water (MSAW), which has its origin in the
Gulf of Cadiz (see Chap. 5 of this book). Many studies have reported that the SAW
entering the Alboran Sea is nutrient poor or even nutrient depleted (Minas et al.
1991; Béthoux et al. 1992; Turley 1999) due to the consumption by phytoplankton in
the Gulf of Cadiz and the Strait of Gibraltar. However, the question of whether the
Atlantic water entering into the Alboran Sea is depleted or not in nutrients has been
matter of debate during the last decades (Béthoux et al. 1992; Dafner et al. 2003;
Huertas et al. 2012). Much of these discrepancies could be due to the fact that in
many studies nutrient concentrations have been reported for the Atlantic inflow
entering into the Alboran Sea rather than for the SAW. At the Strait of Gibraltar,
and due to intense mixing processes, the upwelling of subsurface rich nutrient
Mediterranean waters into the Atlantic surface layer takes place. Other processes
like incursions of NACW also occur (see below), thereby the nutrient load in the
Atlantic inflow largely depends on these processes and also on the biological activity
(Gómez et al. 2000). Moreover, mixing at the Strait is largely controlled by different
physical factors (see Sect. 7.2.2). Therefore, nutrient levels in the Atlantic inflow can
be rather variable. Nevertheless, the nutrient signatures of the SAW at the Strait have
been obtained from the analysis of water masses (Minas et al. 1991; Gómez et al.
2000), where SAW is characterized by nitrate <2 μM, phosphate <0.01 μM, and
silicate <1 μM (Gómez et al. 2000).
NACW has been detected by several studies in the upper layer of the Strait of
Gibraltar and also in the Alboran Sea (Gascard and Richez 1985; Minas et al. 1991;
Gómez et al. 2000; Ramírez et al. 2005; Ramírez-Romero et al. 2014). The entrance
of this water mass into the Alboran Sea is strongly modulated by the tidal cycles at
the Strait (see Sect. 7.2.2). NACW is a water mass rich in nutrients, with nitrate
~5–7 μM, phosphate ~0.35–0.45 μM, and silicate ~2–3 μM (Gómez et al. 2000).
Although other studies have found lower phosphate concentrations (0.09 μM) associated to this water mass at the Strait of Gibraltar (Ramírez-Romero et al. 2014).
On the other hand, the intermediate and deep water masses found in the Alboran
Sea are Winter Intermediate Water (WIW), Levantine Intermediate Water (LIW),
and Western Mediterranean Deep Water (WMDW) (see Chap. 5 of this book). These
water masses are characterized by different biogeochemical signatures due to their
7 The Biogeochemical Context of Marine Planktonic Ecosystems
209