LAUSR

Abstract The rapid retreat of the Baltic Ice Stream and the development of the Baltic Ice Lake is assessed using data from sediment cores retrieved from three sub-basins in the southern Baltic Sea. Hydraulic piston coring by the International Ocean Discovery Program (IODP) recovered for the first time intact glacial lake sequences overlying diamictons and other ice-contact deposits at Sites M0063, M0064 and M0065. Based on the particle size and bulk sediment chemical composition the glacial lake sediments were subdivided into a proximal and a distal varve sequence. The origin of a dark, lithologically distinct horizon between the proximal and distal varves is attributed to a lake drainage event following the opening of a spillway in central Sweden. Available age constraints suggest that the Baltic Ice Lake developed during the Bolling-Allerod interstadial and reached its maximum size at ∼13 ka. Ice retreat was forced by surface melt, and amplified by calving in the upstream deepening lake environment. Furthermore, rapid ice retreat and glacio-isostatic processes allowed for the storage of substantial amounts of meltwater in the Baltic Ice Lake during the Allerod warm period. Subsequent lake drainage into the North Atlantic took place through a conduit at higher latitude than previous drainage pathways. The pronounced changes in meltwater storage and routing caused by the rapid retreat of the Baltic Ice Stream may have contributed to abrupt climate change through the effects of changing freshwater supply on Atlantic overturning circulation.