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2. The geomorphology of Ireland’s continental shelf

Author

Arosio, Riccardo, primary, Wheeler, Andrew J., additional, Sacchetti, Fabio, additional, Guinan, Janine, additional, Benetti, Sara, additional, O’Keeffe, Eimear, additional, van Landeghem, Katrien J. J., additional, Conti, Luis A., additional, Furey, Thomas, additional, and Lim, Aaron, additional

Published
2023
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3. Late Quaternary sedimentation associated with the British-Irish Ice Sheet on the NW Irish continental slope: a marine geological and geophysical investigation

Author

Sacchetti, Fabio

Subjects
551.41
Abstract

This research demonstrates the impact that glaciations had on the geomorphology and sediment deposition of the NW Irish continental margin, including both sides of the Rockall Trough and the Rockall Bank. A modern hydrographic, geophysical and sedimentological approach is used to analyse and interpret new and historical datasets, including multi beam, sidescan sonar, seismic and core data. New methodologies such as CUBE and Geocoder algorithms for multi beam bathymetry and backscatter data processing, 3D visualisations, ArcGIS Spatial and Hydrological Analysis and digital X-Ray scanning are used to deliver an accurate geomorphological and sedimentological interpretation and to understand the changes that occurred in the sedimentary processes from shelf edge to basin floor since the last glaciation, through deglaciation and in the Holocene. This research demonstrates a number of correlations between glacial geomorphology observed on the continental shelf and the various geomorphological and sedimentary features observed along the NW Irish continental slope and trough. It also provides extensive evidence that the Rockall Bank was scoured by several generations of icebergs and acted as a natural barrier against which icebergs coming from the western Atlantic Ocean grounded. Near seabed geophysical investigation throughout the Irish Rockall Trough is used to classify the area into six sedimentary provinces, each characterised by different depositional processes. This also provides new evidence of previously undetected mass transport deposits and extensive fluid-migration on a wide area of the trough. Finally, the study of sediment cores along two major canyons and across the trough provides a regional perspective on the sedimentary processes that took place since the last glaciation on the north-eastern margin of the Rockall Trough. The study reveals that margin physiography, distance from the ice sheet grounding zone, style of glaciation on the shelf and strength of deep sea circulation are the main controlling factors over the depositional processes.

Published
2012

5. Timing and pace of ice‐sheet withdrawal across the marine–terrestrial transition west of Ireland during the last glaciation

Author

Ó Cofaigh, Colm, Callard, S. Louise, Roberts, David H., Chiverrell, Richard C., Ballantyne, C. K., Evans, David J. A., Saher, Margot, Van Landeghem, Katrien J. J., Smedley, Rachel, Benetti, Sara, Burke, Matthew, Clark, Chris D., Duller, Geoff A. T., Fabel, Derek, Livingstone, Stephen J., Mccarron, Stephen, Medialdea, Alicia, Moreton, Steven G., Sacchetti, Fabio, Ó Cofaigh, Colm, Callard, S. Louise, Roberts, David H., Chiverrell, Richard C., Ballantyne, C. K., Evans, David J. A., Saher, Margot, Van Landeghem, Katrien J. J., Smedley, Rachel, Benetti, Sara, Burke, Matthew, Clark, Chris D., Duller, Geoff A. T., Fabel, Derek, Livingstone, Stephen J., Mccarron, Stephen, Medialdea, Alicia, Moreton, Steven G., and Sacchetti, Fabio

Abstract

Understanding the pace and drivers of marine‐based ice‐sheet retreat relies upon the integration of numerical ice‐sheet models with observations from contemporary polar ice sheets and well‐constrained palaeo‐ glaciological reconstructions. This paper provides a reconstruction of the retreat of the last British–Irish Ice Sheet (BIIS) from the Atlantic shelf west of Ireland during and following the Last Glacial Maximum (LGM). It uses marine‐ geophysical data and sediment cores dated by radiocarbon, combined with terrestrial cosmogenic nuclide and optically stimulated luminescence dating of onshore ice‐marginal landforms, to reconstruct the timing and rate of ice‐sheet retreat from the continental shelf and across the adjoining coastline of Ireland, thus including the switch from a marine‐ to a terrestrially‐based ice‐sheet margin. Seafloor bathymetric data in the form of moraines and grounding‐zone wedges on the continental shelf record an extensive ice sheet west of Ireland during the LGM which advanced to the outer shelf. This interpretation is supported by the presence of dated subglacial tills and overridden glacimarine sediments from across the Porcupine Bank, a westwards extension of the Irish continental shelf. The ice sheet was grounded on the outer shelf at ~26.8 ka cal BP with initial retreat underway by 25.9 ka cal BP. Retreat was not a continuous process but was punctuated by marginal oscillations until ~24.3 ka cal BP. The ice sheet thereafter retreated to the mid‐shelf where it formed a large grounding‐zone complex at ~23.7 ka cal BP. This retreat occurred in a glacimarine environment. The Aran Islands on the inner continental shelf were ice‐free by ~19.5 ka BP and the ice sheet had become largely terrestrially based by 17.3 ka BP. This suggests that the Aran Islands acted to stabilize and slow overall ice‐sheet retreat once the BIIS margin had reached the inner shelf. Our results constrain the timing of initial retreat of the BIIS from the outer shelf w

Published
2021

7. A Late Pleistocene channelized subglacial meltwater system on the Atlantic continental shelf south of Ireland.

Author

Giglio, Cristiana, Benetti, Sara, Sacchetti, Fabio, Lockhart, Edward, Hughes Clarke, John, Plets, Ruth, Van Landeghem, Katrien, Ó Cofaigh, Colm, Scourse, James, and Dunlop, Paul

Subjects
MELTWATER, CONTINENTAL shelf, GLACIAL landforms, ICE sheets, ICE streams, SEA ice, PLEISTOCENE Epoch
Abstract

The study of palaeo‐glacial landforms and sediments can give insights into the nature and dynamics of ice sheets. This is particularly the case with regards to the subglacial record, which is challenging to observe in contemporary glaciated settings and hence remains only partially understood. The subglacial hydrological system is an essential component of ice dynamics, where increased water pressure enhances ice motion and sediment deformation, thus reducing ice‐bed contact. Tunnel valleys are large, sinuous, steep‐sided incisions that, together with smaller scale meltwater channels, indicate subglacial meltwater discharge beneath large ice sheets. Through the use of high‐resolution marine geophysical data, a system of buried and exposed tunnel valleys, possible subglacial or proglacial meltwater channels and palaeo‐fluvial valleys have been identified across the shelf of the Celtic Sea between Ireland and Britain. The presence of steep‐sided and overdeepened tunnel valleys is indicative of a large channelized meltwater drainage system beneath the former Irish Sea Ice Stream, the most extensive ice stream to drain the last British–Irish Ice Sheet. After the rapid ice expansion across the Celtic Sea shelf around 28–26 ka, the tunnel valleys were carved into both bedrock and glacigenic sediments and are associated with rapid ice stream retreat northwards into the Irish Sea Basin between 25.6 and 24.3 ka. The presence of a major subglacial meltwater system on the relatively shallow shelf suggests that significant erosive meltwater discharge occurred during the last deglaciation and highlights the important contribution of meltwater to the retreat of the British–Irish Ice Sheet on the continental shelf. [ABSTRACT FROM AUTHOR]

Published
2022
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9. Geomorphology and substrate of Galway Bay, Western Ireland

Author

McCullagh, Denise, Benetti, Sara, Plets, Ruth, Sacchetti, Fabio, O’Keeffe, Eimear, and Lyons, Kieran

Subjects
14. Life underwater
Abstract

A combination of multibeam bathymetry and backscatter, LiDAR altimetry and bathymetry, satellite images, and hydrodynamic model outputs were used to map the seafloor and coastline of Galway Bay (western Ireland). This is the first time these multiple datasets have been integrated into a single combined geomorphological and substrate map. The substrate of the bay is predominantly mud and sand with bedrock outcropping extensively around the coastline. The main depositional features are dunes, while the main erosional features are scours and outcropping bedrock. Hydrodynamic model outputs show good correlation between the direction and intensity of prevailing currents and the location and shape of the features in the bay. This indicates that although Galway Bay was shaped glacially through the passage of the British-Irish Ice Sheet across the bay and ensuing glacial and marine sediment deposition, many of the mapped seafloor landforms are modern and current-induced.

10. Geomorphology and substrate of Galway Bay, Western Ireland

Author

McCullagh, Denise, Benetti, Sara, Plets, Ruth, Sacchetti, Fabio, O’Keeffe, Eimear, and Lyons, Kieran

Subjects
14. Life underwater
Abstract

A combination of multibeam bathymetry and backscatter, LiDAR altimetry and bathymetry, satellite images, and hydrodynamic model outputs were used to map the seafloor and coastline of Galway Bay (western Ireland). This is the first time these multiple datasets have been integrated into a single combined geomorphological and substrate map. The substrate of the bay is predominantly mud and sand with bedrock outcropping extensively around the coastline. The main depositional features are dunes, while the main erosional features are scours and outcropping bedrock. Hydrodynamic model outputs show good correlation between the direction and intensity of prevailing currents and the location and shape of the features in the bay. This indicates that although Galway Bay was shaped glacially through the passage of the British-Irish Ice Sheet across the bay and ensuing glacial and marine sediment deposition, many of the mapped seafloor landforms are modern and current-induced.

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