Weichselian history of the Fennoscandian Ice Sheet centre, Kvarken archipelago, western Finland—flow shifts, thermal regime and deglaciation

Rapid thaw of the Earth's cryosphere in response to anthropogenic warming highlights the need to identify and understand the contrasting signatures of past ice‐sheet stability and collapse. The Kvarken archipelago, western Finland, at the centre of the former Fennoscandian Ice Sheet (FIS), has been designated a UNESCO World Heritage site in recognition of the exceptional preservation of glacial landforms exposed by rapid (10 mm a −1 ) postglacial isostatic uplift. Detailed mapping of hard and soft glacial bedforms allows reconstruction of ice sheet dynamics over the last glacial cycle. Striation orientation measurements ( n ~ 1100) were made at 700 sites on Precambrian gneiss and granite bedrock surfaces around the present shorelines. The striation data are classified into relative age categories and broader striation arrays to identify ice‐flow paths and then integrated with other directional indicators from overlying glacial sediments and landforms. The full data set reveals a sequence of six ice‐flow stages, which are then placed in a revised event and chronostratigraphic model for the wider Ostrobothnia region. After a major glacial erosion phase in Kvarken in late MIS 6, ice sheets returned in MIS 4 and MIS 3. During brief sliding phases, till sheets were deformed and eroded, but cross‐striations indicate that bedrock erosion was locally weak (