Quaternary sedimentation and Norwegian Sea overflow pathways around Bill Bailey Bank, northeastern Atlantic

Abstract

Using high-resolution multi-channel sleeve gun seismics and TOBI side-scan sonar and subbottom profiler acoustic data, as well as sediment cores and published hydrographic measurements, a study has been made of Quaternary sedimentation patterns and depositional processes around Bill Bailey Bank (BBB) in the northeastern Atlantic. From the western outlet of the Faeroe Bank (FB) Channel, which is the main conduit of Norwegian Sea Overflow Water (NSOW), there is a complex pattern of NSOW-controlled sediment transport pathways extending to areas north of Lousy Bank (LB). The acoustic data and sediment cores reveal the existence of a contour current at water depths exceeding 1000 m flowing from the Wyville–Thomson Ridge via the southern rise of FB and BBB into the valley between BBB and LB and further northward towards the area north of BBB. We conclude that this contour current is related to intermittent NSOW overflow of the Wyville–Thomson Ridge. The maximum bottom flow speed along this secondary NSOW flow pathway is inferred to reach about 0.50 m/s. Bedforms observed in the northeastern part of the study area, north of BBB, suggest a maximum bottom flow speed of locally at least 1.0 m/s. The maximum thickness (0.5 s TWT) of the Pliocene–Quaternary seismic sequence, at water depths in excess of 1000 m, south of BBB is nearly twice that found north of BBB. On average, higher accumulation rates in the former area can be ascribed to a hydrographic setting favouring sediment accumulation which, especially under glacial conditions, markedly differed from conditions north of BBB. This applies to both bottom and surface circulation. Linear bulk sedimentation rates north of BBB were largest during deglacial warming when the rates were about three times higher than the average Holocene rate (4.5 cm/ka). Increased fluxes during deglaciation reflect transport and depositional conditions associated with reactivation of the NSOW current system. South of BBB, average linear bulk accumulation rates were persistently higher, i.e. in the range 15–23 cm/ka, during various Late Pleistocene stages between 30 and 10 ka.