| Abstract | A total of 800 km2 of multibeam echosounder coverage, about 800 km of chirp-sonar data and 18 16
km of side scan sonar profiles (100/500 kHz), were acquired several km offshore Santa Maria di 17
Leuca (south-eastern Italy) from 200 m down to 1300 m water depth, along the upper slope of the 18
gently south-eastward dipping Apulian continental margin (northern Ionian sea). These acoustic 19
data set were collected by three different oceanographic expeditions, where evidence of living cold 20
water coral (CWC) colonies was documented by previous surveys and samples. 21
The high-resolution multibeam bathymetry shows an extensive rough seafloor with an irregular 22
faulted upper surface to the west (reflecting the large-scale tectonic control on the margin) and a 23
highly disrupted upper slope formed by prominent downslope mass-movements. A broad eastern 24
area has affected by mass-transport deposition, which results in a very complex hummocky 25
seafloor, mainly shaped by detached block-like features and failure related bedforms (i.e. low 26
scarps, downslope lineations, compressional ridges). From the shallow seismic-stratigraphic data, 27
failure events appear to be multiple and recurrent, and chaotic reflectors, both buried and exposed at 28
the seafloor, affect most of the investigated area. Drift sedimentation is also recognized along a 29
central large ridge, resulting in an interplay between contour currents and downslope turbidity 30
31 currents.
The spatial distribution of the CWC reefs has been inferred from the acoustic facies interpretation 32
based on video images and ground-truthed by sediment samples. It appears that: 1) within the 33
investigated area, living coral frameworks are located along large topographic highs facing the main
flow of the bottom currents, where hard and firm substrata and/or failure-related sediment bedforms 35
occur; 2) CWC mainly settled on clustered (and isolated) mound-like features, tens to a few 36
hundreds of meters long and no more than 25 m high. They are located between 600 and 900 m 37
water depth, within the broad area affected by down-slope mass transport deposits. Such mound- 38
like morphologies could thus be interpreted as a result of sediment accreted by coral growth, with 39
the consequent sediment trapping on small-scale positive seafloor irregularities; these are formed by 40
different types of Pleistocene exposed mass transport deposits, their burial prevented by bottom 41
42 currents.
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