Submarine sediment and landform record of a palaeo‐ice stream within the British− Irish Ice Sheet

• Published in: Boreas
• Main Authors: Bradwell, Tom, Stoker, Martyn S.
• Other Authors: Natural Environment Research Council
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2015
• Subjects: Ice Sheet
• Online Access: http://dx.doi.org/10.1111/bor.12111; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fbor.12111; https://onlinelibrary.wiley.com/doi/pdf/10.1111/bor.12111

This paper examines marine geophysical and geological data, and new multibeam bathymetry data to describe the P leistocene sediment and landform record of a large ice‐stream system that drained ∼3% of the entire B ritish− I rish I ce S heet at its maximum extent. Starting on the outer continental shelf NW of S cotland we describe: the ice‐stream terminus environment and depocentre on the outer shelf and continental slope; sediment architecture and subglacial landforms on the mid‐shelf and in a large marine embayment (the M inch); moraines and grounding line features on the inner shelf and in the fjordic zone. We identify new soft‐bed (sediment) and hard‐bed (bedrock) subglacial landform assemblages in the central and inner parts of the M inch that confirm the spatial distribution, coherence and trajectory of a grounded fast‐flowing ice‐sheet corridor. These include strongly streamlined bedrock forms and megagrooves indicating a high degree of ice‐bed coupling in a zone of flow convergence associated with ice‐stream onset; and a downstream bedform evolution (short drumlins to km‐scale glacial lineations) suggesting an ice‐flow velocity transition associated with a bed substrate and roughness change in the ice‐stream trunk. Chronology is still lacking for the timing of ice‐stream demise; however, the seismic stratigraphy, absence of moraines or grounding‐line features, and presence of well‐preserved subglacial bedforms and iceberg scours, combined with the landward deepening bathymetry, all suggest that frontal retreat in the M inch was probably rapid, via widespread calving, before stabilization in the nearshore zone. Large moraine complexes recording a coherent, apparently long‐lived, ice‐sheet margin position only 5–15 km offshore strongly support this model. Reconstructed ice‐discharge values for the M inch ice stream (12–20 G t a −1 ) are comparable to high mass‐flux ice streams today, underlining it as an excellent palaeo‐analogue for recent rapid change at the margins of the G reenland and W est A ntarctic ...