Therefore the index of this chapter is as follows:
• Climate forcing, water mass formation processes and thermohaline circulation in
the Mediterranean Sea.
• Water masses in the Alboran Sea.
• Currents and circulation in the Alboran Sea.
– Tidal currents.
– The upper layer circulation.
– Intermediate and deep water circulation.
• Long-term variability.
• Summary and conclusions.
4.2 Climatic Forcing, Water Mass Formation Processes
and Thermohaline Circulation
in the Mediterranean Sea
The Mediterranean Sea is a concentration basin. When averaging over the whole
basin and for a long period of time, the evaporation exceeds the freshwater supplies.
Different works (Skliris et al. 2018; Jordà et al. 2017; Criado-Aldeanueva et al.
2012; Schroeder et al. 2012; Sánchez-Gómez et al. 2011; Ludwig et al. 2009;
Struglia et al. 2004; Boukthir and Barnier 2000) have attempted to estimate the
terms involved in the freshwater budget of the Mediterranean Sea: Evaporation (E),
Precipitation (P) and river runoff (R). Although there is a large dispersion between
the different estimations (Jordà et al. 2017), for the purposes of the present review it
could be stated that, if the Mediterranean was not connected to the Atlantic Ocean,
the freshwater deficit would produce a decrease in the Mediterranean Sea level of
between 0.5 and 1 m/year.
If the heat fluxes between the sea surface and the atmosphere are averaged for the
whole Mediterranean surface, the result is a net heat flux from the Mediterranean to
the atmosphere. In other words, the Mediterranean Sea losses heat through its
surface. Once again it is not an easy task to estimate the average fluxes (Jordà
et al. 2017; Criado-Aldeanueva et al. 2012; Ruiz et al. 2008; Bunker et al. 1982) but
they can be reasonably considered to be between 5 and 7 W/m
2 .
The Mediterranean water deficit and the net heat loss through its surface are
compensated by the entrance of AW through the Strait of Gibraltar. The AW
compensates for the net evaporation and it also produces a salt flux into the
Mediterranean Sea. This is compensated by an Outflow of Mediterranean Water
(MOW) as a deep current below the AW. The AW inflow is larger than the MOW to
compensate for the net evaporation. At the same time, the net salt transport through
Gibraltar must be zero in a theoretical equilibrium state. This balance is usually
described by means of the Knudsen equations:
4 The Oceanographic and Climatic Context
87
• Climate forcing, water mass formation processes and thermohaline circulation in
the Mediterranean Sea.
• Water masses in the Alboran Sea.
• Currents and circulation in the Alboran Sea.
– Tidal currents.
– The upper layer circulation.
– Intermediate and deep water circulation.
• Long-term variability.
• Summary and conclusions.
4.2 Climatic Forcing, Water Mass Formation Processes
and Thermohaline Circulation
in the Mediterranean Sea
The Mediterranean Sea is a concentration basin. When averaging over the whole
basin and for a long period of time, the evaporation exceeds the freshwater supplies.
Different works (Skliris et al. 2018; Jordà et al. 2017; Criado-Aldeanueva et al.
2012; Schroeder et al. 2012; Sánchez-Gómez et al. 2011; Ludwig et al. 2009;
Struglia et al. 2004; Boukthir and Barnier 2000) have attempted to estimate the
terms involved in the freshwater budget of the Mediterranean Sea: Evaporation (E),
Precipitation (P) and river runoff (R). Although there is a large dispersion between
the different estimations (Jordà et al. 2017), for the purposes of the present review it
could be stated that, if the Mediterranean was not connected to the Atlantic Ocean,
the freshwater deficit would produce a decrease in the Mediterranean Sea level of
between 0.5 and 1 m/year.
If the heat fluxes between the sea surface and the atmosphere are averaged for the
whole Mediterranean surface, the result is a net heat flux from the Mediterranean to
the atmosphere. In other words, the Mediterranean Sea losses heat through its
surface. Once again it is not an easy task to estimate the average fluxes (Jordà
et al. 2017; Criado-Aldeanueva et al. 2012; Ruiz et al. 2008; Bunker et al. 1982) but
they can be reasonably considered to be between 5 and 7 W/m
2 .
The Mediterranean water deficit and the net heat loss through its surface are
compensated by the entrance of AW through the Strait of Gibraltar. The AW
compensates for the net evaporation and it also produces a salt flux into the
Mediterranean Sea. This is compensated by an Outflow of Mediterranean Water
(MOW) as a deep current below the AW. The AW inflow is larger than the MOW to
compensate for the net evaporation. At the same time, the net salt transport through
Gibraltar must be zero in a theoretical equilibrium state. This balance is usually
described by means of the Knudsen equations:
4 The Oceanographic and Climatic Context
87