10.3.4 Mound Morphometrics
Morphometrics (e.g., height, shape, orientation, etc.) of the 854 mounds analyzed
from the high-resolution map of the GBB site (47 km
2 total area) show that
mounds range from 81 to *268,000 m
2 in footprint area and from 1 to 83 m in
height. Mounds in this site are mostly located on a series of topographic highs that
are up to 5 m in relief, 500–1500 m wide and extend along a divergent pattern in
an east–west direction (Fig. 10.8). The nature of these highs are unknown but are
commonly observed on the slope of carbonate platforms (e.g., Mullins et al. 1984).
The highest mounds at the GBB site are located on these topographic highs
(Figs. 10.1c and 10.7), but large mounds up to 60 m in relief are also present
within lows (Fig. 10.7). The largest mound was ground-truthed by submersible
and was found to contain dense coral colonies of predominantly Lophelia pertusa
and Enallopsammia profunda (Fig. 10.1c–d).
The footprint shape of each mound was quantified in terms of the ratio between its
longest and shortest diameters (i.e., principle axes ratio). For this parameter, a
mound with a ratio of 1 is circular, while an elongated ellipsoidal mound has a ratio
approaching 0.5, and a long linear mound has a ratio close to 0.1 (e.g., Purkis et al.
2007; Correa et al. 2011). For the mounds that have a ratio\1, the azimuth of their
longest axis is calculated (i.e., footprint orientation). Analyses of the mound footprint shape and orientation show that no correlation exists between area and shape
(Fig. 10.8a). This indicates that mounds do not become streamlined as their area
increases. A predominant mound orientation is also not documented (Fig. 10.8b).
The AUV measured bottom current data depict a north–south (N–S) flowing
current that reverses approximately every 6 h over 45 h (Fig. 10.8c). Grasmueck
et al. (2006), using the same current data, show that the changes in bottom current
direction correlate with the modeled curve for the nearby North Bimini tidal
gauge. This indicates that a diurnal tide is the dominant current regime along on
the GBB slope. The current data therefore show that there is no preferred alignment of the mounds along the dominant N–S bottom current directions (Fig. 10.8).
The mound footprint shapes also show no correlation with the N–S current regime.
These findings therefore contradict the previous studies that interpreted mounds in
the Straits of Florida as teardrop-shaped and aligned parallel to the northward
current (Neumann et al. 1977; Messing et al. 1990).
10.3.5 Habitat Classification Map
The Miami Terrace site lies on the eastern side of the Florida Peninsula at water
depths from *630 to 870 m (Fig. 10.9a). The AUV high-resolution DEM reveals
that the slope of the lower Miami Terrace is covered with a series of linear ridges
that extend downslope for up to 2,000 m and are as much as 20 m in relief
(Fig. 10.9b). The ridges are oriented perpendicularly to the terrace break and have
10 Deep Acoustic Applications
269
Morphometrics (e.g., height, shape, orientation, etc.) of the 854 mounds analyzed
from the high-resolution map of the GBB site (47 km
2 total area) show that
mounds range from 81 to *268,000 m
2 in footprint area and from 1 to 83 m in
height. Mounds in this site are mostly located on a series of topographic highs that
are up to 5 m in relief, 500–1500 m wide and extend along a divergent pattern in
an east–west direction (Fig. 10.8). The nature of these highs are unknown but are
commonly observed on the slope of carbonate platforms (e.g., Mullins et al. 1984).
The highest mounds at the GBB site are located on these topographic highs
(Figs. 10.1c and 10.7), but large mounds up to 60 m in relief are also present
within lows (Fig. 10.7). The largest mound was ground-truthed by submersible
and was found to contain dense coral colonies of predominantly Lophelia pertusa
and Enallopsammia profunda (Fig. 10.1c–d).
The footprint shape of each mound was quantified in terms of the ratio between its
longest and shortest diameters (i.e., principle axes ratio). For this parameter, a
mound with a ratio of 1 is circular, while an elongated ellipsoidal mound has a ratio
approaching 0.5, and a long linear mound has a ratio close to 0.1 (e.g., Purkis et al.
2007; Correa et al. 2011). For the mounds that have a ratio\1, the azimuth of their
longest axis is calculated (i.e., footprint orientation). Analyses of the mound footprint shape and orientation show that no correlation exists between area and shape
(Fig. 10.8a). This indicates that mounds do not become streamlined as their area
increases. A predominant mound orientation is also not documented (Fig. 10.8b).
The AUV measured bottom current data depict a north–south (N–S) flowing
current that reverses approximately every 6 h over 45 h (Fig. 10.8c). Grasmueck
et al. (2006), using the same current data, show that the changes in bottom current
direction correlate with the modeled curve for the nearby North Bimini tidal
gauge. This indicates that a diurnal tide is the dominant current regime along on
the GBB slope. The current data therefore show that there is no preferred alignment of the mounds along the dominant N–S bottom current directions (Fig. 10.8).
The mound footprint shapes also show no correlation with the N–S current regime.
These findings therefore contradict the previous studies that interpreted mounds in
the Straits of Florida as teardrop-shaped and aligned parallel to the northward
current (Neumann et al. 1977; Messing et al. 1990).
10.3.5 Habitat Classification Map
The Miami Terrace site lies on the eastern side of the Florida Peninsula at water
depths from *630 to 870 m (Fig. 10.9a). The AUV high-resolution DEM reveals
that the slope of the lower Miami Terrace is covered with a series of linear ridges
that extend downslope for up to 2,000 m and are as much as 20 m in relief
(Fig. 10.9b). The ridges are oriented perpendicularly to the terrace break and have
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