Ice margin oscillations during deglaciation of the northern Irish Sea Basin

R C Chiverrell,G S P Thomas,K Van Landeghem,D H Roberts,C K Ballantyne,G A T Duller,S L Callard,S Livingstone,C Ó Cofaigh,D J A Evans,M J Burke,J D Scourse,P Wilson,D Fabel,R K Smedley,D Small,M Saher,C D Clark

doi:10.1002/jqs.3057

Abstract

ABSTRACTWe present a new chronology to constrain ice‐margin retreat in the northern Irish Sea Basin. Estimates on the timing of ice thinning derived from surface exposure ages for boulders from the summits of the Isle of Man and south‐west Cumbria suggest that ice thinning was commensurate with the rapid retreat that followed the short‐lived advance of the Irish Sea Ice Stream (ISIS) to maximum limits in the Celtic Sea. This ice retreat in the northern Irish Sea Basin was fastest at 20 ka in response to a wider calving margin, but slowed as ice stabilized and oscillated against the Isle of Man. We provide the first age constraints for the Scottish Readvance (19.2–18.2 ka) and demonstrate that it was a potentially regional event across the Isle of Man and Cumbrian lowlands not linked with Heinrich Event 1. After the Scottish Readvance, the ice front retreated northwards towards the Southern Uplands of Scotland at the same time as climate north of ∼45°N warmed in response to summer insolation. This sequence demonstrates the importance of internal dynamics in controlling ice retreat rates in the Irish Sea, but also that deglaciation of the northern Irish Sea Basin was a response to climate warming.

Highlights

During the Late Devensian (Marine Isotope Stage 2), ice flowed into the northern Irish Sea Basin (NISB) from Ireland, south-west Scotland and the English Lake District (Fig. 1)
Estimates on the timing of ice thinning derived from surface exposure ages for boulders from the summits of the Isle of Man and south-west Cumbria suggest that ice thinning was commensurate with the rapid retreat that followed the short-lived advance of the Irish Sea Ice Stream (ISIS) to maximum limits in the Celtic Sea
Surface exposure ages obtained for high ground on the Isle of Man (18.9 Æ 1.0 ka) and western Cumbrian Mountains (21.5 Æ 0.8 ka) overlap with the rapid retreat of ice from maximum limits in the Celtic Sea (Praeg et al, 2015; Smedley et al, 2017b) with ice margins retreating across the Ll^yn Peninsula from 23.9 Æ 1.6 to 21.1 Æ 0.6 ka (Smedley et al, 2017a) and the Isle of Man from 20.8 Æ 0.7 to 18.3 ka

Summary

Introduction

During the Late Devensian (Marine Isotope Stage 2), ice flowed into the northern Irish Sea Basin (NISB) from Ireland, south-west Scotland and the English Lake District (Fig. 1). The extensive subglacial bedforms of Phase II indicate north-eastwards migration of an ice divide across the Carlisle lowlands, and the development of convergent ice flows west and south-west into the NISB during draw-down of the Irish Sea Ice Stream (ISIS) (Livingstone et al, 2012). This pattern conforms with evidence on the Isle of Man (Roberts et al, 2007) and from the central Irish Sea (Van Landeghem et al, 2009). The bedforms attributed to Phase III indicate that unconfined southerly flow of ice from southwest Scotland reached the Carlisle lowlands and deposited ice-marginal landforms (Livingstone et al, 2010c) that have been attributed to the Scottish Readvance originally proposed by Trotter et al (1937)

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Discussion

Conclusion