during the southward shift of the jet, and its intensity is low compared to upwelling
by westerlies (Sarhan et al. 2000).
Lateral advection of surface nutrient-rich waters by the main Atlantic current has
also been described as an important fertilization mechanism in the Western Alboran
Sea, as well as for other areas located at the center of the basin (Minas et al. 1991:
Garcia-Gorriz and Carr 2001; Ruiz et al. 2001). These surface nutrients rich waters
have their origin in upwelling events at the Strait of Gibraltar as well as in coastal
upwelling occurring between Europa Point and Marbella (Minas et al. 1991; GarciaGorriz and Carr 2001; Baldacci et al. 2001; Oguz et al. 2014). Other studies have
also pointed to the advection of phytoplankton rich waters from the Gulf of Cadiz
towards the Alboran Sea as a source of phytoplankton biomass (Navarro et al. 2011;
Ramírez-Romero et al. 2014). In the Alboran Sea, the surface waters are advected
further east by the Atlantic jet following the main circulation pattern (Baldacci et al.
2001; Ruiz et al. 2001; Garcia-Gorriz and Carr 2001; Sánchez-Vidal et al. 2004),
being an important source of nutrients and phytoplankton to the central and eastern
part of the basin.
The upwelling Mediterranean waters at the Strait of Gibraltar is caused by
different processes (Minas et al. 1991; Gómez et al. 2000; Echevarría et al. 2002)
involving intense mixing and entrainment between nutrient-rich Mediterranean
waters and Atlantic waters. These mixing processes are governed by the exchange
of water masses at the Strait, which largely depend on the tidal cycles and the bottom
topography (Echevarría et al. 2002). Dafner et al. (2003) calculated that ~16% of
Mediterranean water outflow entrains with the Atlantic inflow and recirculates back
into the Alboran Sea. Other studies have estimated that the mixing process during
spring tides, alongside with injection of waters from coastal areas in the Gulf of
Cadiz, would account for 31% of the total nitrate supply to the Alboran Sea through
the Strait, while upwelling due to internal waves would account for 74% of the total
entry of phosphate in the Alboran Sea (Ramírez-Romero et al. 2014). The upwelled
waters at the Strait are advected towards the Alboran Sea by the Atlantic inflow. As
indicated above, internal waves generated at the Camarinal Sill play a major role in
the mixing processes at the Strait particularly during spring tides (Gascard and
Richez 1985; Echevarría et al. 2002; Vázquez et al. 2008). In addition, it has been
suggested that the trapping of internal waves at the Camarinal Sill could increase the
mixing (Bruno et al. 2002). Once the train of waves enters into the Alboran Sea their
path produces the intermittent lifting of subsurface waters (Vázquez et al. 2009; Van
Haren 2014) leading to the pulsed injection of nutrients into the upper layer.
The nutrient enrichment of surface waters in the Western Alboran Sea is also
caused by incursions of nutrient-rich NACW in the Atlantic inflow at the Strait of
Gibraltar (Minas et al. 1991; Gómez et al. 2000, 2001; Ramírez-Romero et al. 2014),
which are controlled by tidal cycles. The incursions of large amounts of NACW
occur at spring tides, while at neap tides the incursions of NACW are discontinuous
(Gómez et al. 2004; Ramírez-Romero et al. 2014). Once these incursions of NACW
have reached the upper layers they are advected by the Atlantic inflow into the
Alboran Sea and mixed with the surface waters (Minas et al. 1991; Echevarría et al.
2002), contributing to the fertilization of the euphotic layer in the western sector of
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T. Ramírez et al.
by westerlies (Sarhan et al. 2000).
Lateral advection of surface nutrient-rich waters by the main Atlantic current has
also been described as an important fertilization mechanism in the Western Alboran
Sea, as well as for other areas located at the center of the basin (Minas et al. 1991:
Garcia-Gorriz and Carr 2001; Ruiz et al. 2001). These surface nutrients rich waters
have their origin in upwelling events at the Strait of Gibraltar as well as in coastal
upwelling occurring between Europa Point and Marbella (Minas et al. 1991; GarciaGorriz and Carr 2001; Baldacci et al. 2001; Oguz et al. 2014). Other studies have
also pointed to the advection of phytoplankton rich waters from the Gulf of Cadiz
towards the Alboran Sea as a source of phytoplankton biomass (Navarro et al. 2011;
Ramírez-Romero et al. 2014). In the Alboran Sea, the surface waters are advected
further east by the Atlantic jet following the main circulation pattern (Baldacci et al.
2001; Ruiz et al. 2001; Garcia-Gorriz and Carr 2001; Sánchez-Vidal et al. 2004),
being an important source of nutrients and phytoplankton to the central and eastern
part of the basin.
The upwelling Mediterranean waters at the Strait of Gibraltar is caused by
different processes (Minas et al. 1991; Gómez et al. 2000; Echevarría et al. 2002)
involving intense mixing and entrainment between nutrient-rich Mediterranean
waters and Atlantic waters. These mixing processes are governed by the exchange
of water masses at the Strait, which largely depend on the tidal cycles and the bottom
topography (Echevarría et al. 2002). Dafner et al. (2003) calculated that ~16% of
Mediterranean water outflow entrains with the Atlantic inflow and recirculates back
into the Alboran Sea. Other studies have estimated that the mixing process during
spring tides, alongside with injection of waters from coastal areas in the Gulf of
Cadiz, would account for 31% of the total nitrate supply to the Alboran Sea through
the Strait, while upwelling due to internal waves would account for 74% of the total
entry of phosphate in the Alboran Sea (Ramírez-Romero et al. 2014). The upwelled
waters at the Strait are advected towards the Alboran Sea by the Atlantic inflow. As
indicated above, internal waves generated at the Camarinal Sill play a major role in
the mixing processes at the Strait particularly during spring tides (Gascard and
Richez 1985; Echevarría et al. 2002; Vázquez et al. 2008). In addition, it has been
suggested that the trapping of internal waves at the Camarinal Sill could increase the
mixing (Bruno et al. 2002). Once the train of waves enters into the Alboran Sea their
path produces the intermittent lifting of subsurface waters (Vázquez et al. 2009; Van
Haren 2014) leading to the pulsed injection of nutrients into the upper layer.
The nutrient enrichment of surface waters in the Western Alboran Sea is also
caused by incursions of nutrient-rich NACW in the Atlantic inflow at the Strait of
Gibraltar (Minas et al. 1991; Gómez et al. 2000, 2001; Ramírez-Romero et al. 2014),
which are controlled by tidal cycles. The incursions of large amounts of NACW
occur at spring tides, while at neap tides the incursions of NACW are discontinuous
(Gómez et al. 2004; Ramírez-Romero et al. 2014). Once these incursions of NACW
have reached the upper layers they are advected by the Atlantic inflow into the
Alboran Sea and mixed with the surface waters (Minas et al. 1991; Echevarría et al.
2002), contributing to the fertilization of the euphotic layer in the western sector of
214
T. Ramírez et al.