12.3 The Zonal (East-to-West) Connectivity
The main circulation pattern favors the zonal connectivity, which includes the interbasin connection Gulf of Cadiz—Alboran Sea through the Strait. Their feasibility
and accomplishment depend on the stability of the flow patterns, which suggests two
different breakdowns of the topic: the aforementioned inter-basin connectivity that
involves a rather permanent flow structure, the AJ, and intra-basin connectivity
between different areas of the Alboran Sea, which implies more variable mesoscale
scenarios.
12.3.1 Interbasin Connectivity: Gulf of Cadiz-Alboran Sea
The ultimate origin of the Atlantic inflow is the hydric deficit of the Mediterranean
Sea and, therefore, the east-going AJ is a rather permanent feature. It enables an
intuitive west-to-east surface connectivity between the Gulf of Cadiz and the
Alboran Sea, which makes the former basin a potential source of biological material
for the Alboran Sea. This material, among which spawning products are particularly
relevant for establishing one-direction connected fish stocks, can be displaced
downstream with few obstacles. And it happens in a very steady manner due to
the permanence of the AJ. Such surface layer connectivity was pointed out by
Muñoz et al. (2015), who used geostrophic currents deduced from altimetry in
order to track corridors for connectivity in terms of time. Surface connectivity in
the opposite direction from the Alboran Sea to the Gulf of Cadiz, is highly improbable as it implies transport against the east-going AJ. Exceptionally, however, under
strong meteorological forcing the AJ can be halted or, even, temporarily reversed
(Garcia-Lafuente et al. 2002), which gives a little chance for this otherwise highly
improbable surface connectivity. According to these authors, the north shore of the
Strait is the suitable place for this process to happen since the AJ starts reversing at
this shore and then the reversal progresses southwards. If the meteorological forcing
is strong enough, the reversal reaches the south coast and the inflow interruption is
fully achieved. If it is not, the AJ still keeps on flowing eastwards as a weak narrow
stream attached to the African shore. Tides may increase the chances of the shortlasting reversal if the peak of meteorological forcing coincides with the flood (rising
tide) tidal current, a realization suggested by trajectories of drifting buoys under the
rarely achieved simultaneity of these conditions that have been further confirmed by
numerical simulation (Sanchez-Garrido et al. 2014).
Although the surface east-to-west connection is feasible, yet exceptional, biological connectivity would be even more exceptional, as it requires the presence of
spawning events at the time of the flow reversal. Such connection, however, is
achievable in intermediate and deep layers (i.e., below 150–200 m depth) where the
prevailing motion of the Mediterranean waters is to the west. The genuine hydrodynamic connectivity within this depth range is from the Alboran Sea to the Gulf of
Cadiz, although a successful biological connectivity depends again on the
464
J. Garcia-Lafuente et al.
The main circulation pattern favors the zonal connectivity, which includes the interbasin connection Gulf of Cadiz—Alboran Sea through the Strait. Their feasibility
and accomplishment depend on the stability of the flow patterns, which suggests two
different breakdowns of the topic: the aforementioned inter-basin connectivity that
involves a rather permanent flow structure, the AJ, and intra-basin connectivity
between different areas of the Alboran Sea, which implies more variable mesoscale
scenarios.
12.3.1 Interbasin Connectivity: Gulf of Cadiz-Alboran Sea
The ultimate origin of the Atlantic inflow is the hydric deficit of the Mediterranean
Sea and, therefore, the east-going AJ is a rather permanent feature. It enables an
intuitive west-to-east surface connectivity between the Gulf of Cadiz and the
Alboran Sea, which makes the former basin a potential source of biological material
for the Alboran Sea. This material, among which spawning products are particularly
relevant for establishing one-direction connected fish stocks, can be displaced
downstream with few obstacles. And it happens in a very steady manner due to
the permanence of the AJ. Such surface layer connectivity was pointed out by
Muñoz et al. (2015), who used geostrophic currents deduced from altimetry in
order to track corridors for connectivity in terms of time. Surface connectivity in
the opposite direction from the Alboran Sea to the Gulf of Cadiz, is highly improbable as it implies transport against the east-going AJ. Exceptionally, however, under
strong meteorological forcing the AJ can be halted or, even, temporarily reversed
(Garcia-Lafuente et al. 2002), which gives a little chance for this otherwise highly
improbable surface connectivity. According to these authors, the north shore of the
Strait is the suitable place for this process to happen since the AJ starts reversing at
this shore and then the reversal progresses southwards. If the meteorological forcing
is strong enough, the reversal reaches the south coast and the inflow interruption is
fully achieved. If it is not, the AJ still keeps on flowing eastwards as a weak narrow
stream attached to the African shore. Tides may increase the chances of the shortlasting reversal if the peak of meteorological forcing coincides with the flood (rising
tide) tidal current, a realization suggested by trajectories of drifting buoys under the
rarely achieved simultaneity of these conditions that have been further confirmed by
numerical simulation (Sanchez-Garrido et al. 2014).
Although the surface east-to-west connection is feasible, yet exceptional, biological connectivity would be even more exceptional, as it requires the presence of
spawning events at the time of the flow reversal. Such connection, however, is
achievable in intermediate and deep layers (i.e., below 150–200 m depth) where the
prevailing motion of the Mediterranean waters is to the west. The genuine hydrodynamic connectivity within this depth range is from the Alboran Sea to the Gulf of
Cadiz, although a successful biological connectivity depends again on the
464
J. Garcia-Lafuente et al.