that, at least since the beginning of the 1980s, the surface temperature of the WMED
has warmed with linear trends higher than 1
C/100 year (Skliris et al. 2011; Nikjaer
2009).
Figure 4.8 shows the evolution of the temperature and salinity for the upper
(0–150 m), intermediate (150–600 m) and deep (600 m bottom) layers for the
Alboran Sea. These time series have been constructed using data from MEDAR/
MEDATLAS (MEDAR 2002) database and from the monitoring program
RADMED, operated by the Spanish Institute for Oceanography (Lopez-Jurado
et al. 2015).
The intermediate layer of the Alboran Sea (Fig. 4.8c, d) has increased its
temperature and salinity at rates of 0.22 Æ 0.05
C/100 year and 0.24 Æ 0.04/100
year. The linear trends estimated for the deep layer of the Alboran Sea are
0.30 Æ 0.04
C/100 year and 0.13 Æ 0.01/100 year for the temperature and salinity,
respectively. The salinity of the upper layer has increased at a rate of 0.81 Æ 0.11/
100 year. Nevertheless, no warming is observed for the upper layer from in situ data.
This latter result seems to be the consequence of the data scarcity and the strong
variability of the surface layer. If satellite data from 1982 to 2017 are considered,
there is a clear positive trend of 2.1 Æ 0.7
C/100 year which is coincident with the
results obtained in other areas of the Mediterranean Sea (Nikjaer 2009) and with the
upper layer warming of the world ocean (Levitus et al. 2012).
4.9 Summary and Conclusions
The main water masses and their circulation within the Alboran Sea are the results of
the exchange between the Mediterranean Sea and the Atlantic Ocean through
the Strait of Gibraltar. This exchange is the consequence of the freshwater deficit
and the heat losses to the atmosphere in the Mediterranean Sea, but is also conditioned by the geometry and the intense mixing within the Strait, associated to
internal tides.
The intermediate and deep layers of the Alboran Sea are occupied by intermediate
waters of both Eastern (LIW) and Western (WIW) origin, and by deep waters:
WMDW and TDW. These water masses have a slow circulation within the Alboran
Sea with velocities around a few cm/s. Their pathways are not very clear, but it
seems that the LIW flows preferentially to the north of the basin, forced by the
Coriolis force, whereas WMDW and TDW flow close to the African coast at the
Western Alboran Sea, because of topographic restrictions, and then they are uplifted
by Bernoulli’s aspiration to finally outflow through the Strait of Gibraltar.
The upper layer of the Alboran Sea is filled by waters of Atlantic origin: SAW and
NACW. This layer occupies the upper 150–200 m and has a very energetic dynamics. A frontal thermohaline system is associated with the fast Atlantic Jet (AJ), which
describes anticyclonic and cyclonic structures. The circulation scheme of this upper
layer can present different situations: two anticyclonic gyres at the western and
eastern Alboran Sea sub-basins, only one anticyclonic gyre at the western sub-basin,
104
M. Vargas-Yáñez et al.
has warmed with linear trends higher than 1
C/100 year (Skliris et al. 2011; Nikjaer
2009).
Figure 4.8 shows the evolution of the temperature and salinity for the upper
(0–150 m), intermediate (150–600 m) and deep (600 m bottom) layers for the
Alboran Sea. These time series have been constructed using data from MEDAR/
MEDATLAS (MEDAR 2002) database and from the monitoring program
RADMED, operated by the Spanish Institute for Oceanography (Lopez-Jurado
et al. 2015).
The intermediate layer of the Alboran Sea (Fig. 4.8c, d) has increased its
temperature and salinity at rates of 0.22 Æ 0.05
C/100 year and 0.24 Æ 0.04/100
year. The linear trends estimated for the deep layer of the Alboran Sea are
0.30 Æ 0.04
C/100 year and 0.13 Æ 0.01/100 year for the temperature and salinity,
respectively. The salinity of the upper layer has increased at a rate of 0.81 Æ 0.11/
100 year. Nevertheless, no warming is observed for the upper layer from in situ data.
This latter result seems to be the consequence of the data scarcity and the strong
variability of the surface layer. If satellite data from 1982 to 2017 are considered,
there is a clear positive trend of 2.1 Æ 0.7
C/100 year which is coincident with the
results obtained in other areas of the Mediterranean Sea (Nikjaer 2009) and with the
upper layer warming of the world ocean (Levitus et al. 2012).
4.9 Summary and Conclusions
The main water masses and their circulation within the Alboran Sea are the results of
the exchange between the Mediterranean Sea and the Atlantic Ocean through
the Strait of Gibraltar. This exchange is the consequence of the freshwater deficit
and the heat losses to the atmosphere in the Mediterranean Sea, but is also conditioned by the geometry and the intense mixing within the Strait, associated to
internal tides.
The intermediate and deep layers of the Alboran Sea are occupied by intermediate
waters of both Eastern (LIW) and Western (WIW) origin, and by deep waters:
WMDW and TDW. These water masses have a slow circulation within the Alboran
Sea with velocities around a few cm/s. Their pathways are not very clear, but it
seems that the LIW flows preferentially to the north of the basin, forced by the
Coriolis force, whereas WMDW and TDW flow close to the African coast at the
Western Alboran Sea, because of topographic restrictions, and then they are uplifted
by Bernoulli’s aspiration to finally outflow through the Strait of Gibraltar.
The upper layer of the Alboran Sea is filled by waters of Atlantic origin: SAW and
NACW. This layer occupies the upper 150–200 m and has a very energetic dynamics. A frontal thermohaline system is associated with the fast Atlantic Jet (AJ), which
describes anticyclonic and cyclonic structures. The circulation scheme of this upper
layer can present different situations: two anticyclonic gyres at the western and
eastern Alboran Sea sub-basins, only one anticyclonic gyre at the western sub-basin,
104
M. Vargas-Yáñez et al.