The seabed appearance of different coral bank provinces in the Porcupine Seabight, NE Atlantic: results from sidescan sonar and ROV seabed mapping

摘要

Carbonate mounds, identified as deep-water coral banks, have been reported recently from three provinces in the Porcupine Seabight, SW of Ireland. As yet, the mechanisms behind their formation and development are only partly understood. This contribution discusses their seabed appearance and present-day sedimentary environment, based on a large-scale TOBI sidescan sonar mapping carried out in 2002, and on detailed ROV video records from specific sites within the three mound provinces, collected in 2001. The study of the present-day characteristics and variability of these mounds can help to understand their development history in the past. The imagery clearly shows that the sedimentary environment in the Magellan and Hovland Mound provinces in the northern Porcupine Seabight is much quieter than in the current-swept Belgica Mound province on the eastern flank of the basin. In the latter area, for example, gravel lags and coarse sediments are found, together with patches of sorted sands, striations, barchan dunes and sediment waves. The difference in environment results in different mound appearances. The richest coral communities with the most abundant live coral occurrences are found in the Belgica province, while for example on the Magellan Mounds only a few live coral colonies are left. The present-day situation of the coral banks in the Porcupine Seabight thus illustrates the influence of the interplay between current and sediment dynamics on coral growth and mound development.