AmericanChemicalSociety.com

Cold-water corals densely populate the slopes and basins of some modern carbonate platforms, and can form extensive mound structures in deep waters (mostly within 600-800m). Since most surveys of these mound fields have been at low resolution, the processes controlling cold-water coral mound distribution, morphology, and genesis are largely uncharacterized. This work uses an innovative approach that combines multiple high-resolution acoustic and oceanographic data, and applies spatial quantitative analyses to study five mound fields (130km² total area) from the Straits of Florida. The development of a reproducible approach for extracting individual mounds from acoustic data reveals that mound density in the Straits of Florida is much higher (averaging 14 mounds/km²) than previously reported (0.3 mounds/km²). Furthermore, quantitative analyses across the five surveyed sites indicate that mounds in the Straits vary significantly in their height and area, ranging from predominantly individual features to coalesced linear structures up to 100m in height with a 0.6km² footprint. The current regime is also found to be rather variable with sites dominated either by a constant south-, or northward regime, or by reversal north-south directions (tidal motion). These findings contradict previous low-resolution surveys that described streamlined mounds parallel to the dominant northerly Florida current. An example of the observed variability is the Miami Terrace site, where corals form low-relief ridges that are aligned perpendicular to the unidirectional southward current. Spatial bathymetric analyses of these ridges show statistically that dense thickets of coral colonies are preferentially positioned at the current-facing sides of ridges (i.e., northern sides) in the Miami Terrace. This suggests that colonies that face into the dominant current in these areas experience preferential growth and/or survival. In contrast, at surveyed sites on the slope of Great Bahama Bank (GBB), morphometric analyses demonstrate that mounds are capable of orienting in all directions with respect to the current, and that there is no correlation between preferential shape and size. The rather complex tidal regime observed in the GBB sites is likely to contribute to the high variability in mound orientation and shape. Seismic data depicted that mounds in areas of high sedimentation on the slope of GBB are either partially or completely buried (except for mounds atop topographic highs). This suggests that pre-existing topography is critical in order for mounds to avoid burial on some areas of the GBB slope. Furthermore, the high amplitude seismic character of mound-base reflections in these areas suggests that mound initiation at GBB occurred during lowstand periods, when the shedding of platform-derived sediments is significantly reduced (as opposed to highstand phases). Taken together, these spatial quantitative analyses of high-resolution surveys have indicated that cold-water coral mound systems in the Straits of Florida are: (1) much more diverse and abundant that previously thought, and (2) influenced in their distribution and development by a variety of oceanographic and geologic factors. This work has generated a suite of new hypotheses that can guide future research on modern cold-water coral environments and the interpretation of ancient deep-water carbonate environments, as well as ongoing exploration for hydrocarbons in off-platform carbonates.