this basin. During neap tides and in absence of internal waves the Atlantic inflow
accounts for 69% of nitrate inputs to the Mediterranean from the Atlantic, mostly due
to the contribution of NACW (Ramírez-Romero et al. 2014).
The presence of submesoscale cyclonic eddies in the North Alboran Sea (from
Estepona to Cape Gata) has also been reported by a number of papers as a relevant
source of new nutrients to the photic layer (Sarhan et al. 2000; Reul et al. 2005;
Ramírez et al. 2005; García-Martínez et al. 2019). These eddies are formed from
filaments detached from the main Atlantic current and they can persist for several
days (Parrilla and Kinder 1987; Ramírez et al. 2005; Reul et al. 2005; GarcíaMartínez et al. 2019). One of the most recurrent cyclonic cell is found off Estepona
(e.g., Parrilla and Kinder 1987; Perkins et al. 1990; Cano and García Lafuente 1991;
Baldacci et al. 2001) whose formation seems to be linked to the southward shift of
the jet (Sarhan et al. 2000).
In the eastern sector of the Alboran Sea, the ageostrophic cross-frontal circulation
associated to the presence of an almost permanent geostrophic front, caused by the
path of the Atlantic jet, is one of the main fertilization mechanisms in this eastern
sector. The front is known as the “Almeria-Oran front” and it separates the less saline
and colder SAW in the Alboran basin from saltier and warmer Surface Mediterranean Waters (SMW) found in the Algero-Balear Basin (Tintoré et al. 1991; Prieur
and Sournia 1994). The front exhibits a high variability linked to the high mesoscale
instabilities in the general circulation pattern in the eastern basin compared to the
western one (Millot 1999; Prieur and Sournia 1994; Renault et al. 2012). When the
Eastern Anticyclonic Gyre (EAG) is well developed, usually in summer and autumn,
the front is found at the easternmost boundary of this gyre (Prieur and Sournia 1994).
However in winter the EAG is usually absent (Viúdez et al. 1996; Vargas-Yañez
et al. 2002; Snaith et al. 2003) and the Atlantic jet shifts southwards and flows closer
to the African coast (Claustre et al. 1994; Prieur and Sournia 1994; Renault et al.
2012).
7.2.3 Distribution Patterns of Inorganic Nutrients (N, P,
and Si)
The dynamics of inorganic nutrients in the Alboran Sea presents a high spatial and
temporal variability as a result of the high hydrodynamic variability and to the
intense biological productivity in this basin. As a result, steeped nutrient gradients
are observed both in the vertical and horizontal distribution (Figs. 7.1 and 7.2). The
lowest nutrient concentrations in the Alboran Sea are usually found and the center of
the WAG and the EAG (Fig. 7.2). Both gyres are downwelling zones where SAW,
impoverished in nutrient due to the previous consumption by phytoplankton, converges, and sinks (Parrilla and Kinder 1987). Consequently, nutrient concentrations
in the Alboran Sea central areas are particularly low during the stratification period,
being frequently <0.25 μM for nitrate, <0.06 μM for phosphate, and <0.70 μM for
7 The Biogeochemical Context of Marine Planktonic Ecosystems
215
accounts for 69% of nitrate inputs to the Mediterranean from the Atlantic, mostly due
to the contribution of NACW (Ramírez-Romero et al. 2014).
The presence of submesoscale cyclonic eddies in the North Alboran Sea (from
Estepona to Cape Gata) has also been reported by a number of papers as a relevant
source of new nutrients to the photic layer (Sarhan et al. 2000; Reul et al. 2005;
Ramírez et al. 2005; García-Martínez et al. 2019). These eddies are formed from
filaments detached from the main Atlantic current and they can persist for several
days (Parrilla and Kinder 1987; Ramírez et al. 2005; Reul et al. 2005; GarcíaMartínez et al. 2019). One of the most recurrent cyclonic cell is found off Estepona
(e.g., Parrilla and Kinder 1987; Perkins et al. 1990; Cano and García Lafuente 1991;
Baldacci et al. 2001) whose formation seems to be linked to the southward shift of
the jet (Sarhan et al. 2000).
In the eastern sector of the Alboran Sea, the ageostrophic cross-frontal circulation
associated to the presence of an almost permanent geostrophic front, caused by the
path of the Atlantic jet, is one of the main fertilization mechanisms in this eastern
sector. The front is known as the “Almeria-Oran front” and it separates the less saline
and colder SAW in the Alboran basin from saltier and warmer Surface Mediterranean Waters (SMW) found in the Algero-Balear Basin (Tintoré et al. 1991; Prieur
and Sournia 1994). The front exhibits a high variability linked to the high mesoscale
instabilities in the general circulation pattern in the eastern basin compared to the
western one (Millot 1999; Prieur and Sournia 1994; Renault et al. 2012). When the
Eastern Anticyclonic Gyre (EAG) is well developed, usually in summer and autumn,
the front is found at the easternmost boundary of this gyre (Prieur and Sournia 1994).
However in winter the EAG is usually absent (Viúdez et al. 1996; Vargas-Yañez
et al. 2002; Snaith et al. 2003) and the Atlantic jet shifts southwards and flows closer
to the African coast (Claustre et al. 1994; Prieur and Sournia 1994; Renault et al.
2012).
7.2.3 Distribution Patterns of Inorganic Nutrients (N, P,
and Si)
The dynamics of inorganic nutrients in the Alboran Sea presents a high spatial and
temporal variability as a result of the high hydrodynamic variability and to the
intense biological productivity in this basin. As a result, steeped nutrient gradients
are observed both in the vertical and horizontal distribution (Figs. 7.1 and 7.2). The
lowest nutrient concentrations in the Alboran Sea are usually found and the center of
the WAG and the EAG (Fig. 7.2). Both gyres are downwelling zones where SAW,
impoverished in nutrient due to the previous consumption by phytoplankton, converges, and sinks (Parrilla and Kinder 1987). Consequently, nutrient concentrations
in the Alboran Sea central areas are particularly low during the stratification period,
being frequently <0.25 μM for nitrate, <0.06 μM for phosphate, and <0.70 μM for
7 The Biogeochemical Context of Marine Planktonic Ecosystems
215