Geomorphology of the Irish Rockall Trough, North Atlantic Ocean, mapped from multibeam bathymetric and backscatter Data

Abstract

Multibeam echosounder data collected by the Irish National Seabed Survey (INSS) between 2000 and 2001 in the Rockall Trough have been used by many projects to analyze the geomorphology and the sedimentary processes of the margins of the Trough. However, due to the low spatial resolution of 150-250 m and the amount of artefacts still embedded in the publicly available data, many geomorphological features have been overlooked. This paper shows that the same multibeam dataset can provide more detailed information on seabed processes when the latest hydrographic and backscatter post-processing techniques are used to reduce data artefacts and improve data quality and spatial resolution.The resulting map, presented here at a scale of 1:450,000, is based on a semi-automatic and manual interpretation of geomorphological features highlighted using a new and improved 30 m bathymetric grid and a multibeam backscatter mosaic obtained using the GEOCODER post-processing algorithm.Overall, the map shows a complex sedimentological scenario where the Rockall Bank Mass Flow failure, the Donegal-Barra trough-mouth fan, along slope structures such as the Feni Contourite Drift and the Porcupine moat dominate the Rockall Trough flanks and basin floor. Smaller features such as canyon and gully systems, escarpments, coral mounds, volcanic mounds and iceberg scours have also been mapped in detail. In addition, the interpretation of the backscatter mosaic allows for the first time the identification of depositional lobes generated by downslope mass transport and canyon drainage systems, particularly where these features completely lose their bathymetric expression.

Processing and performance of topobathymetric lidar data for geomorphometric and morphological classification in a high-energy tidal environment

“…for geomorphological mapping. Previous studies classifying morphology in either terrestrial or marine environments have been performed numerous times (Al-Hamdani et al, 2008;Cavalli and Marchi, 2008;Hogg et al, 2016;Höfle and Rutzinger, 2011;Ismail et al, 2015;Kaskela et al, 2012;Lecours et al, 2016;Sacchetti et al, 2011). These classification studies generally focus on either the marine or the terrestrial environment and do not cover the fine-scale morphology in the shallow water, due to the challenging environmental conditions.…”

Geophysical evidence of deep-keeled icebergs on the Rockall Bank, Northeast Atlantic Ocean

“…Within the north-eastern Atlantic, iceberg scours have been previously recorded on the western Irish continental shelf and slope (Belderson et al, 1973;Benetti et al, 2010;Sacchetti et al, 2011;Ó Cofaigh et al, in press), on the Rockall Bank in UK waters (Kenyon et al, 2003), and on the Porcupine Bank where iceberg furrows, 50-500 m wide and hundreds of meters to over 20 km long, have been reported (O'Toole and Monteys, 2010). Between 2000 and 2004, the Irish portion of the Rockall Bank was fully surveyed using multibeam swath bathymetry under the auspices of the Irish National Seabed Survey (INSS) (Fig.…”

Seabed geomorphology of the Porcupine Bank, West of Ireland

“…It is characterised by water depths between 300 and 400 m and an approximate width of 100 km. To the north and to the west the Porcupine Bank displays a shelf break at c. 500 m water depth; the slope is steep and narrow towards the Rockall Trough (Sacchetti, Benetti, Georgiopoulou, Dunlop, & Quinn, 2011). To the south and southeast, the bank opens with a gentle slope to the deep embayment of the Porcupine Seabight.…”

“…These were recognised mainly on the northern edges of the study area at the top of the steep slopes running to the Rockall Trough (Sacchetti et al, 2011) and to the edge of the cluster of identified bedrock outcrops to the southeast of the bedrock plateau. Another two long escarpments (30 and 40 km long) were identified in the southern Porcupine Bank at 350-370 m water depth.…”

“…The band pass filtering techniques of Hiller and Smith (2008) were applied to de-trend (remove regional slope) and remove azimuthally biased interpretation from landform morphology and pattern analysis. Morphometric analysis was performed predominantly through visual interpretation of raster grids in QPS Fledermaus v 7.4.0 and Esri ArcGIS TM v10.1 (similar to the procedures adopted by Dolan, Grehan, Guinan, & Brown, 2008;Sacchetti et al, 2011;. This initial interpretation was completed using bathymetry, shaded relief (false illumination at right angles) and slope gradient (in degrees).…”