Complex palaeo-ice sheet dynamics in northeast Ireland during the retreat and reorganisation of the central British-Irish Ice Sheet

Improving our understanding of the marine- to terrestrial-based transition of the last British-Irish Ice Sheet (BIIS) is crucial for assessing future ice sheet loss in analogous regions of contemporary ice sheets. Current palaeo-ice sheet reconstructions constrain the nature of BIIS wastage from its maximum extents well from c. 27 ka BP during a period of sea level rise and ice sheet instability. However, the drivers and influences of deglaciation from c. 20 ka BP as the BIIS separated into separate, terrestrial-based ice domes amid rapid, high-magnitude climate change remain a challenge to unravel. This study investigates palaeo-ice sheet dynamics in northeast Ireland pertaining to the reorganisation of the central BIIS to constrain and untangle these drivers. A 0.4 m horizontal resolution digital surface model was employed to map 12,979 glacial landforms over a 3905 km 2 study area in Northern Ireland. New sedimentological analyses are combined to interrogate palaeo-ice sheet dynamics through a relative chronological framework of six ‘flow stages’ that unravel the deglaciation of the central BIIS c. 20-15 ka. Intrinsic drivers such as meltwater drainage, ice sheet thinning, and ice divide migration heavily influenced the collapse of a major ice divide over northeast Ireland, as well as the initiation of an ephemeral ice stream at its margins. Irish ice dispersing from lowland and upland centres decayed during full stadial conditions as Scottish ice readvanced from a better nourished source, stabilising along the Irish coast. However, more absolute ages are required to better understand these complex, contrasting dynamical behaviours.