Collapse of the Last Eurasian Ice Sheet in the North Sea Modulated by Combined Processes of Ice Flow, Surface Melt, and Marine Ice Sheet Instabilities

Niall Gandy,Christopher D Clark,Stephen L Cornford,Lauren J Gregoire,David M Hodgson,Jeremy C Ely

doi:10.1029/2020jf005755

Abstract

AbstractThe record of the confluence and collapse of the British‐Irish Ice Sheet and the Fennoscandian Ice Sheet is obscured by the North Sea, hindering reconstructions of the glacial dynamics of this sector of the Eurasian Ice Sheet complex during the last glacial cycle. Previous numerical simulations of the deglaciation of the North Sea have also struggled to capture the confluence and separation of the British‐Irish and Fennoscandian Ice Sheets. We ran an ensemble of 70 experiments simulating the deglaciation of the North Sea between 23 and 18 ka BP using the BISICLES ice sheet model. A novel suite of quantitative model‐data comparison tools was used to identify plausible simulations of deglaciation that match empirical data for ice flow, margin position, and retreat ages, allowing comparisons to large amounts of empirical data. In ensemble members that best match the empirical data, the North Sea deglaciates through the collapse of the marine‐based Norwegian Channel Ice Stream, unzipping the confluence between the British‐Irish Ice Sheet and the Fennoscandian Ice Sheet. Thinning of the Norwegian Channel Ice Stream causes surface temperature feedbacks, rapid grounding line retreat, and ice stream acceleration, further driving separation of the British‐Irish and the Fennoscandian Ice Sheets. These simulations of the North Sea deglaciation conform with the majority of empirical evidence, and therefore provide physically plausible insights that are consistent with reconstructions based on the empirical evidence, and permit a quantitative comparison between model and data.

Highlights

At the Last Glacial Maximum (LGM), the North Sea sector of the Eurasian Ice Sheet complex was at the confluence of two ice sheets, the British-Irish Ice Sheet (BIIS) to the west, and the Fennoscandian Ice Sheet to the east (Clark et al, 2012; Hughes et al, 2016; Sejrup et al, 2015)
Beginning with full confluence of the BIIS and Fennoscandian Ice Sheet (Figures 3a and 3b), there is an initial retreat of the Norwegian Channel Ice Stream (NCIS), with ice remaining to the east and west of the Norwegian Channel
We completed an ensemble of simulations of the deglaciation of the North Sea sector of the Eurasian Ice Sheet complex, using the BISICLES ice sheet model, simulating deglaciation in a manner that conforms with the majority of empirical evidence for the first time

Summary

Introduction

At the Last Glacial Maximum (LGM), the North Sea sector of the Eurasian Ice Sheet complex was at the confluence of two ice sheets, the British-Irish Ice Sheet (BIIS) to the west, and the Fennoscandian Ice Sheet to the east (Clark et al, 2012; Hughes et al, 2016; Sejrup et al, 2015). The North Sea sector hosts an archive of palaeo ice sheet dynamics with marine, lacustrine, and terrestrial margins. The northern marine margin may have been vulnerable to similar marine processes that are in effect in contemporary West Antarctica (Favier et al, 2014; Joughin et al, 2014; Shepherd et al, 2001) These marine sectors are prone to instabilities of retreat, which represent the largest source of uncertainty for future sea level projections (Edwards et al, 2019). The requirement to better understand the deglaciation of the North Sea sector of the Eurasian Ice Sheet complex has motivated several previous empirical and modeling studies (e.g., Boulton & Hagdorn, 2006; Dove et al, 2017; Patton et al, 2016; Roberts et al, 2018; Sejrup et al, 2016)

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Conclusion