Truncated drumlins and their implication for past sea level reconstructions

Coastal erosion of glacigenic sediments, particularly in the form of retreating drumlin bluffs, is a key process in paraglacial landscape evolution during periods of relative sea‐level (RSL) rise. As marine transgression reworks formerly subaerial glacial terrains, drumlins act as discrete sediment sources generating characteristic erosional and depositional drowned landforms. In this study, we identify extensive fields of submerged truncated sediment drumlins across several locations in the Irish Sea and along the western Scottish seaboard. The drumlins were formed during maximum and retreat phases of the last British‐Irish Ice Sheet (BIIS). They now exhibit flat‐topped morphologies often associated with gravel tails, tombolos and coalesced platforms, closely resembling previously described examples of eroding drumlin coasts from the west coast of Ireland and North America. The geomorphic assemblages are consistent with wave‐driven erosion of drumlin bluffs during lower sea‐level stands, and we interpret the truncated drumlins as terrestrial‐limiting indicators of past RSL. Comparison with existing RSL reconstructions and glacio‐isostatic adjustment (GIA) models reveals discrepancies between observed truncation depths and predicted sea‐level minima, suggesting that current models may underestimate lowstand magnitudes in parts of Britain and Ireland. These findings highlight the potential of submarine geomorphological records to refine regional sea‐level reconstructions and improve understanding of post‐glacial coastal evolution.