Reconnaissance Survey of the Irish Continental Shelf/Shelf Edge - Atlantic Irish Regional Survey (AIRS) 1996: A GLORIA Survey of the Irish Continental Margin

Abstract

The Atlantic Irish Regional Survey (AIRS96) sidescan sonar survey was carried out in August 1996. Covering an area of 200,000 sq.km it represented the largest reconnaissance seabed survey of the Irish Continental Shelf region. It covered both margins, together with much of the basin floor, of the Irish sector of the Rockall Trough and extended into the northern part of the Porcupine Seabight. The objectives of this project were two fold: 1. Strategic: •to undertake, for the first time a preliminary reconnaissance survey of the Irish Continental Shelf/Shelf Edge, •to establish a strategic database on Shelf/Slope Edge conditions, •to provide training and experience to Irish researchers in state of the art marine surveying equipment (GLORIA) and data processing. 2. Scientific: •to document slope stability and mass wasting features on the margins of the Rockall Trough, •to map, where possible, occurrences of deep water carbonate mounds, •to investigate the sediment erosional, transport and depositional mechanisms that have shaped the present morphology of the region. The survey revealed a range of sedimentary features across the steep (i.e. >6º slope) margins and the basin floor in the Rockall Trough. Four classes of sedimentary feature are recognised: (1) mass failure, (2) canyon systems, (3) sediment fans, and (4) sediment drifts. The western margin is characterised by large-scale downslope mass movement features. The western and central parts of the basin floor in the Rockall Trough contain the Feni Sediment Ridge, a large Miocene-Recent contourite sediment accumulation draped by large sediment waves trending sub-parallel to the dominant modern current pattern. A large-scale downslope mass failure feature is recognised across 14,000 sq.km of the northeastern margin of the Rockall Trough. Smaller slides and slumps occur along the eastern margin in association with more prevalent canyon, channel and fan systems. A cluster of carbonate mounds was imaged in the northern part of the Porcupine Seabight. These represent part of one of the most extensive suites of deep-water carbonate mounds in the Atlantic Margin and are currently the subject of a number of new EU-funded research projects. Strong northward-directed bottom currents along the eastern margin are suggested to erode, circulate and re-deposit sediment on the basin floor and on the western margin of the Rockall Trough. The main terrigenous sedimentary input was from the Irish Mainland Shelf. A broad interplay of alongslope and downslope sediment transport processes shaped the morphology of the Rockall Trough, while tectonically-driven basin subsidence, Quaternary glaciations and glacio-eustatic sea-level fluctuations also influenced the overall sedimentation pattern in the Rockall Trough.Funder: Marine Institut