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

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.

Margin processes sculpting a land-detached canyon-channel system: the Gollum Channel System in the Porcupine Seabight

“…The simplest interpretation would be a direct connection with a fluvial system on the Celtic Sea Shelf. While this is not apparent in the seismic data presented here or data on the shelf investigated in other studies (Giglio et al, 2022), well data may provide some arguments for this hypothesis. At the end of the Eocene, the outer shelf was a shallow marine environment but the presence of late Eocene-early Oligocene paralic and fluvial facies on the inner Celtic Sea Shelf does suggest a narrower shelf than at present and closer proximity of terrestrial material (Merlin Energy Resources Consortium, 2020).…”

Comparison of overdeepened structures in formerly glaciated areas of the northern Alpine foreland and northern central Europe

“…Flank slopes vary between < 5 • and > 55 • (Cofaigh, 1996;Huuse and Lykke-Andersen, 2000), and van der Vegt et al ( 2012) mention examples of overhanging valley flanks. Individual valleys exhibit downstream transitions in a crosssection, for example, from a V to a U shape (Giglio et al, 2022). In both cases, overdeepenings and tunnel valleys, U-shaped morphologies with flat valley bottoms may be linked to lithological boundaries in the substratum (Gegg et al, 2021;Janszen et al, 2012) but occur also where the bedrock is seemingly rather homogeneous (e.g.…”