The Moira Mounds, small cold-water coral mounds in the Porcupine Seabight, NE Atlantic: Part B Evaluating the impact of sediment dynamics through high-resolution ROV-borne bathymetric mapping

Large cold-water coral carbonate mounds are well-known from several locations along the north-east Atlantic continental margin. With these mound structures, which can measure up to 350 m in height, often smaller mounds are found in the same hydrodynamic settings. This paper illustrates the importance of local sediment dynamics on the morphology and development of small-sized mounds, the Moira Mounds, in the Belgica Mound Province (Porcupine Seabight, SW of Ireland) through ROV-borne microbathymetry and video data. The data set illustrates the sedimentary setting of small mounds in the Porcupine Seabight, gives new insights in the sedimentary processes acting around the small mounds and sheds more light on the interaction between hydrodynamics, sedimentation and erosion, cold-water coral mound initiation and mound growth. The high-resolution bathymetry over the Moira Mounds reveals the presence of several well-delineated zones, each characterized by typical sedimentary structures bearing witness of active sediment transport. The most important ones are: (1) regular E-W directed sediment waves, (2) irregular overgrown sediment waves, and (3) furrows and ridges associated with straight-crested sediment waves. The Moira Mounds appear as small-mounded features, subcircular in shape, measuring 30-50 m across and up to similar to 5 m tall. The evolution of the Moira Mounds can be explained by the interaction between cold-water coral growth and sediment baffling through a positive feedback mechanism. However, it is suggested that the small mound build-ups represent nowadays rather a way of mound formation under stressed conditions due to high sediment fluxes, than an initial phase of extensive mound growth. (C) 2011 Elsevier B.V. All rights reserved.