Seabed mapping and seafloor processes in the Kish, Burford, Bray and Fraser Banks area, South‐Western Irish Sea

Abstract

Mapping of the seabed and sub-seabed strata in an area comprising offshore banks and intervening sediments in outer Dublin Bay is presented. Bathymetric comparisons suggest that the offshore banks are quasi-stable over time probably maintaining their position due to the interaction between wave and current regimes. Seven acoustic seabed facies are defined on the basis of side-scan sonar characteristics reflecting differences in bedforms and bottom types. Sediment waves indicative of a mobile substrate are common both on and between banks. Maximum sediment wave development occurs on bank flanks and outer limits. The effects of wave action on seabed morphology are clearly discernible in the structure and appearance of the bank crests. Grain-size data and bedform interpretations suggest a northerly sediment transport system with gravel dominant in the south of the area (Bray Bank) grading to sands in the north (Kish and Burford Banks). Sub-bottom profiling reveals a consistent upper unit overlying a hard reflector allowing unit thickness (isopachs) to be defined. No internal structures or 'hard' cores were revealed within banks. Two shipwrecks were also imaged. Relationships are drawn with models of offshore bank evolution suggesting that the Irish examples are quasi-stable dependent on a relatively consistent input of sediment and metocean variables. Banks genesis, however, may relate more to former conditions of post-glacial rapid sea-level rise and high sediment input.