High-resolution stable isotope records from southwest Sweden: The drainage of the Baltic Ice Lake and Younger Dryas ice margin oscillations

Benthic foraminifera in two shallow marine sediment cores from southwest Sweden were analyzed for oxygen isotopes. Several deglaciation events, previously recognized in terrestrial and lake sediments throughout the Baltic region, are identified and radiocarbon dated. An initial Baltic Ice Lake (BIL) drainage at the Mount Billingen threshold is inferred from a distinct 2.4 parts per thousand delta(18)O oscillation in one of the investigated cores. The estimated radiocarbon age for this event is approximately 10,900 C-14 years. The final drainage, which ended BIL history, occurred in two steps during the younger part of the radiocarbon plateau at 10,000 C-14 years. Biostratigraphy suggests that the final drainage took place in the climatically warm early Preboreal. At approximately 11,150 C-14 years, the deglacial trend toward lighter isotopic composition was interrupted and slightly reversed and is interpreted to represent the onset of the cold Younger Dryas period. For a few hundred years prior to the Younger Dryas, melting of the Fennoscandian ice sheet appears to have been rapid. Besides the dramatic drainage events and reduced melting during the Younger Dryas, the records display several other salinity variations. These variations may reflect ice margin oscillations during the Younger Dryas, previously identified throughout Scandinavia as ice marginal deposits. The isotopic records suggest approximately 10 climatically induced ice margin recession/readvances of the southeastern Fennoscandian ice sheet during the Younger Dryas.