11.3 Results
The water masses within the Bay of Biscay exhibit a coherent structure. The major
difference between sites on the Galicia Margin, on the Cantabrian Margin, and on
the Armorican Margin is the decrease in the Mediterranean Outflow Water. The
salinity minimum of the overlying Eastern North Atlantic Central Water (ENACW)
was almost identical in all sites during the METEOR cruise 84/5. We recorded
values between 35.60 psu (Cantabrian Margin) and 35.62 psu (Galicia Margin).
However, the influence of the MOW was highest in the sites on the Galicia margin,
where we observed 36.17 psu, while its effect slightly decreased gradually from
35.83 psu (Page `s Escarpment) to 35.79 psu (St. Nazaire Canyon, Amorican Margin). The core of the LSW within the NADW was only seen in the deep cast on the
Galicia Margin and on the Cantabrian margin (Fig. 11.3). Potential temperature
profiles were almost identical for all sites, except the data from the Mugia Canyon
(Galicia Margin) which showed slightly increased values between 500 and
1200 mbsl well above 11
C (Fig. 11.3).
The critical seawater density envelope of σ Θ of 27.5 Æ 0.15 kg/m
3 indicative for
the occurrence of living Lophelia pertusa (Dullo et al. 2008) occurred between
714 and 865 mbsl on the Page `s Escarpment. The existence of this density envelope
was verified by van Rooij et al. (2010b) on the Galicia Margin and by De Mol et al.
(2011) on the Armorican Margin. In addition, Hebbeln et al. (2014) demonstrated
that the amount of change in seawater density with depth is an essential hint for the
identification of a habitat of living CWCs. This gradient is calculated by subtracting
the measured seawater density in a distinct depth from the equivalent value 10 m
above resulting in Δ σ Θ 10 m. This value is shown in Fig. 11.4a, for the western
slope of the Page `s Escarpment. Since seawater density results from both temperature and salinity, we could demonstrate, that the observed density gradient is mainly
caused by salinity (Fig. 11.4b).
Single photo shot inspection of the escarpment between 700–900 mbsl revealed
coarse sediment with some rocky blocks. Epifauna was present on these hard
grounds and several dead and frequently broken colonies of stony corals, mainly
Madrepora occulata were observed. Even small-scaled CWC frameworks occurred
deeper than 800 mbsl, however, very patchy in distribution. Some sponges, sea
urchins (Cidaris), and coral rubble of Madrepora occulata and Lophelia pertusa
were recognized on muddy bottoms. All sites showed anthropogenic impact by
trash and fishing lines. The latter may have caused the damaged CWC colonies and
the coral rubble.
11.3.1 Yoyo-CTD Casts
Since we focused on the comparison of different tools measuring bottom water
dynamics, the results of the yoyo CTD are displayed in high-resolution for the
188
W.-C. Dullo et al.
The water masses within the Bay of Biscay exhibit a coherent structure. The major
difference between sites on the Galicia Margin, on the Cantabrian Margin, and on
the Armorican Margin is the decrease in the Mediterranean Outflow Water. The
salinity minimum of the overlying Eastern North Atlantic Central Water (ENACW)
was almost identical in all sites during the METEOR cruise 84/5. We recorded
values between 35.60 psu (Cantabrian Margin) and 35.62 psu (Galicia Margin).
However, the influence of the MOW was highest in the sites on the Galicia margin,
where we observed 36.17 psu, while its effect slightly decreased gradually from
35.83 psu (Page `s Escarpment) to 35.79 psu (St. Nazaire Canyon, Amorican Margin). The core of the LSW within the NADW was only seen in the deep cast on the
Galicia Margin and on the Cantabrian margin (Fig. 11.3). Potential temperature
profiles were almost identical for all sites, except the data from the Mugia Canyon
(Galicia Margin) which showed slightly increased values between 500 and
1200 mbsl well above 11
C (Fig. 11.3).
The critical seawater density envelope of σ Θ of 27.5 Æ 0.15 kg/m
3 indicative for
the occurrence of living Lophelia pertusa (Dullo et al. 2008) occurred between
714 and 865 mbsl on the Page `s Escarpment. The existence of this density envelope
was verified by van Rooij et al. (2010b) on the Galicia Margin and by De Mol et al.
(2011) on the Armorican Margin. In addition, Hebbeln et al. (2014) demonstrated
that the amount of change in seawater density with depth is an essential hint for the
identification of a habitat of living CWCs. This gradient is calculated by subtracting
the measured seawater density in a distinct depth from the equivalent value 10 m
above resulting in Δ σ Θ 10 m. This value is shown in Fig. 11.4a, for the western
slope of the Page `s Escarpment. Since seawater density results from both temperature and salinity, we could demonstrate, that the observed density gradient is mainly
caused by salinity (Fig. 11.4b).
Single photo shot inspection of the escarpment between 700–900 mbsl revealed
coarse sediment with some rocky blocks. Epifauna was present on these hard
grounds and several dead and frequently broken colonies of stony corals, mainly
Madrepora occulata were observed. Even small-scaled CWC frameworks occurred
deeper than 800 mbsl, however, very patchy in distribution. Some sponges, sea
urchins (Cidaris), and coral rubble of Madrepora occulata and Lophelia pertusa
were recognized on muddy bottoms. All sites showed anthropogenic impact by
trash and fishing lines. The latter may have caused the damaged CWC colonies and
the coral rubble.
11.3.1 Yoyo-CTD Casts
Since we focused on the comparison of different tools measuring bottom water
dynamics, the results of the yoyo CTD are displayed in high-resolution for the
188
W.-C. Dullo et al.