Cann 1996; Pollard and Pu 1985). According to Le Boyer et al. (2013) this
condition creates unstable slope currents and eddies in the interior of the Bay of
Biscay (Fig. 11.1).
Surface water down to a depth of 450–600 mbsl consists of Eastern North
Atlantic Central Water (ENACW) which moves in a cyclonic gyre with an average
velocity of 4 cm/s (Pingree and Le Cann 1989) exhibiting a salinity of more than
35.62 psu (Pollard et al. 1996). The lower part of the ENACW reaching down to
600 mbsl seems to be laterally influenced by the Subarctic Intermediate Water
(SAIW) indicated by very little to almost no change in density and a salinity
minimum around 35.59 psu. Below salinity increases rapidly indicating the influence of Mediterranean Outflow Water (MOW), which extends down to a depth of
around 1500 mbsl. Salinity maxima around 35.79 psu occur around 900 mbsl. The
MOW forms a contour current along the continental margin, which is controlled by
the Coriolis force and seafloor morphology. Therefore salinities are slightly lower
on the Armorican margin in contrast to the Galicia margin. Pingree and Le Cann
(1989) observed current velocities between 2 and 3 cm/s. Most of the living corals
observed in the Bay of Biscay during photo surveys, thrive in a depth interval
between 700–850 mbsl and are therefore bathed by the upper portion of the MOW
representing the intermediate water salinity maximum
The North Atlantic Deep Water (NADW) underlies the MOW in water depths
between 1500 and 3000 mbsl. A small but pronounced salinity decrease around
1800 mbsl is indicative for the influence of the Labrador Sea Water (LSW)
according to Gonza ´lez-Pola et al. (2006). Over the abyssal plain a cyclonic
recirculation cell with poleward velocities of 1.2 Æ 1.0 cm/s near the continental
margin can be observed (Dickson et al. 1985; Paillet and Mercier 1997).
The continental slope of the Bay of Biscay is considered as one of the most high
energy areas of the world (Je ´ze ´quel et al. 2002) favouring the formation of internal
tides in combination with water mass stratification and steep topography (Holligan
et al. 1985; Huthnance 1995; Pingree and Griffiths 1982; Pingree and Le Cann
1989, 1990). Strong barotropic tidal currents are channelled and locally increase
flow within the numerous canyons cutting the slope reaching local currents of
14 cm/s or higher (Pingree and Le Cann 1989, 1990). These internal tides, in
particular on the upper slope, are a possible explanation for enhanced levels of
surface phytoplankton abundance (Van Rooij et al. 2010b).
Canyons and irregularly shaped escarpments usually lack significant covers of
draping sediment, because of the strong current regime and low sediment deposition rates (Van Rooij et al. 2010b). Therefore hard substrata in such settings are
ideal sites for CWCs to settle. Several studies show that the occurrence of deepwater corals in the Northeast Atlantic correlates well to nutrient supply, high energy
current regime, little to very little sedimentation, and hard substratum (Frederiksen
et al. 1992; Freiwald et al. 1999; Mortensen et al. 1995). Seawater temperature and
salinity in combination yield seawater density which is another controlling factor
for living CWC reef growth. Dullo et al. (2008) demonstrated that living CWC reef
ecosystems on the Celtic and Norwegian Margin thrive within a density range of
sigma-theta (σΘ) ¼ 27.35–27.65 kg/m
3 . This has been confirmed for the Bay of
184
W.-C. Dullo et al.
condition creates unstable slope currents and eddies in the interior of the Bay of
Biscay (Fig. 11.1).
Surface water down to a depth of 450–600 mbsl consists of Eastern North
Atlantic Central Water (ENACW) which moves in a cyclonic gyre with an average
velocity of 4 cm/s (Pingree and Le Cann 1989) exhibiting a salinity of more than
35.62 psu (Pollard et al. 1996). The lower part of the ENACW reaching down to
600 mbsl seems to be laterally influenced by the Subarctic Intermediate Water
(SAIW) indicated by very little to almost no change in density and a salinity
minimum around 35.59 psu. Below salinity increases rapidly indicating the influence of Mediterranean Outflow Water (MOW), which extends down to a depth of
around 1500 mbsl. Salinity maxima around 35.79 psu occur around 900 mbsl. The
MOW forms a contour current along the continental margin, which is controlled by
the Coriolis force and seafloor morphology. Therefore salinities are slightly lower
on the Armorican margin in contrast to the Galicia margin. Pingree and Le Cann
(1989) observed current velocities between 2 and 3 cm/s. Most of the living corals
observed in the Bay of Biscay during photo surveys, thrive in a depth interval
between 700–850 mbsl and are therefore bathed by the upper portion of the MOW
representing the intermediate water salinity maximum
The North Atlantic Deep Water (NADW) underlies the MOW in water depths
between 1500 and 3000 mbsl. A small but pronounced salinity decrease around
1800 mbsl is indicative for the influence of the Labrador Sea Water (LSW)
according to Gonza ´lez-Pola et al. (2006). Over the abyssal plain a cyclonic
recirculation cell with poleward velocities of 1.2 Æ 1.0 cm/s near the continental
margin can be observed (Dickson et al. 1985; Paillet and Mercier 1997).
The continental slope of the Bay of Biscay is considered as one of the most high
energy areas of the world (Je ´ze ´quel et al. 2002) favouring the formation of internal
tides in combination with water mass stratification and steep topography (Holligan
et al. 1985; Huthnance 1995; Pingree and Griffiths 1982; Pingree and Le Cann
1989, 1990). Strong barotropic tidal currents are channelled and locally increase
flow within the numerous canyons cutting the slope reaching local currents of
14 cm/s or higher (Pingree and Le Cann 1989, 1990). These internal tides, in
particular on the upper slope, are a possible explanation for enhanced levels of
surface phytoplankton abundance (Van Rooij et al. 2010b).
Canyons and irregularly shaped escarpments usually lack significant covers of
draping sediment, because of the strong current regime and low sediment deposition rates (Van Rooij et al. 2010b). Therefore hard substrata in such settings are
ideal sites for CWCs to settle. Several studies show that the occurrence of deepwater corals in the Northeast Atlantic correlates well to nutrient supply, high energy
current regime, little to very little sedimentation, and hard substratum (Frederiksen
et al. 1992; Freiwald et al. 1999; Mortensen et al. 1995). Seawater temperature and
salinity in combination yield seawater density which is another controlling factor
for living CWC reef growth. Dullo et al. (2008) demonstrated that living CWC reef
ecosystems on the Celtic and Norwegian Margin thrive within a density range of
sigma-theta (σΘ) ¼ 27.35–27.65 kg/m
3 . This has been confirmed for the Bay of
184
W.-C. Dullo et al.