Evaluation of present-day hydrodynamic processes associated to the Belgica Mound contourite drift, offshore Ireland

The Belgica Mound Drift is a contourite drift located in the Porcupine Seabight, offshore Ireland, formed in association with cold-water coral mounds. ROV imagery and bathymetry provided a close-up view of the drift seafloor, identifying multiple bedforms, including sinuous, linguoid and washed-out ripples as well as sediment waves. Three moorings equipped with current meters were deployed to better understand the spatial and temporal variations of the present-day hydrodynamic conditions over the drift moats and crest. Several velocity flows, ranging from 20 to 100 cm/s, were deduced from the interpretation of the bedforms and compared with the mooring-recorded flow values and character to evaluate the representativeness of the bedforms as a tool in the assessment of the strength and direction of bottom currents in deep environments. Both the tidally forced flows up to 50 cm/s, and the observed flow directions are consistent with the bedform estimation. While bedforms which require weaker bottom currents are currently formed during every tidal flow, the ripples created under stronger flows may be relic features formed during unrecorded peak flow events. This suggests that the drift and its moats are still being influenced by a strong hydrodynamic regime. The spatial distribution of the bedforms suggests that the bottom current flow velocities are extremely variable, partly supported by the measured currents. This is likely related to the local topography which may have a very small spatial scale impact on the bottom flows. Highlights • Steering of bottom currents due to local topography, including sediment waves. • Not yet recorded peak flow events responsible for the formation of sediment waves. • Small-scale bedforms can be translated into current velocities and directions. • Matching between bedforms and current meter data.