This multidisciplinary study describes the morphology, seismic facies, sedimentology, biology and oceanography of large deep-water coral banks and their geological setting in the Porcupine Seabight offshore Ireland. Coral banks in the Porcupine Basin are larger than most of their North Atlantic counterparts. They are about 1 km wide, can be up to 3 km long and attain heights of almost 200 m above the seafloor. The banks are mound-shaped elevations, hosting living deep-water coral and associated fauna on their upper flanks. This biological active layer covers a dead assemblage of corals, filled with terrigeneous mud similar to the surrounding seabed. The coral banks in the Porcupine Basin occur in two geographical provinces, each characterized by a typical mound shape: complex flatted topped seafloor mounds in the Hovland mound province, partly buried mounds in the Belgica mound province, and a large numbers of smaller NS elongated buried mounds of various shapes in the Magellan mound province.
All coral banks, buried or outcropping, occur in association with current-induced features such as moats, sediment tails and sediment dunes indicating their location in regions of strong currents. Only few mounds are still outcropping today, which suggests that environmental conditions were more favourable fro the mound growth in the past. The depth range of these outcropping mounds coincides with the top of the dense Mediterranean Outflow Water, where current enhancement through internal tidal waves could control coral growth. Mound growth started simultaneously, probably since the Late Pliocene and after a period of erosion and non-deposition. Various phases of mound development in the past few millions years may have occurred and be related to important fluctuations in oceanographic conditions, where the MOW can play a major role. Though the genesis and initial control of mound settings in this basin might be related to hydrocarbon seeps, it appears that the major development of the Porcupine coral banks in recent geological times has most likely been controlled by oceanic circulation and dynamics in water masses and nutrient supply. No conclusive evidence has yet been found for either hypothese.
Sediment stress, largely controlled by currents, plays an important role in the mound development. Coral banks accrete by active baffling of sediment by the biological framework and extension of the biological cap (Catch-up). Once this fragile system between sedimentation and biological growth is out of balance, the framework will progressively be filled with sediment (Keep-up) with only a few living patches. Once the sediment dominates the structure the coral banks get buried and draped by sediment (Give-up).