Seabed morphology and the bottom-current pathways around Rosemary Bank seamount, northern Rockall Trough, North Atlantic

Abstract

Rosemary Bank is a broadly domed and elongate seamount with a diameter of 70 km, occurring in water depths of between 300 and 2300 m, 120 km west of the UK mainland in the northern Rockall Trough. Recent multibeam bathymetry and sub-bottom profiles, together with pre-existing current meter and CTD data, seismic reflection profiles and seabed core samples were examined in order to evaluate past and present bottom-current pathways and processes. The multibeam data image volcanic parasitic cones, concave slide scars and the terraced slopes of the bank. Bottom-current sedimentation is interpreted as producing a drift–moat complex surrounding the entire seamount and including two sediment wave-fields, developed to the west and east of the bank in water depths of 1500–2000 m. The western drift covers an area of over 1000 km 2. Sediment waves to the west of the bank are up to 150 m high with wave lengths of 1.5–2 km. Four 100 m deep, 3 km wide, linear depressions, bisect the waves and are interpreted as 25–30 km long extensions of the moat. Seismic reflection profiles show the main phase of drift construction was during the mid-Miocene to Pliocene with the Pliocene to Holocene being an interval of drift maintenance. Cores from sediments draping over and adjacent to the seamount contain sandy and gravelly contourites interbedded with hemipelagites of late Pleistocene to Holocene age. Current meter and CTD data from the western moat indicate Labrador Sea Water flowing northwest, in contrast to the previously assumed anticlockwise circulation pattern around the seamount.