The Holocene history of the southwestern Baltic Sea as reflected in a sediment core from the Bornholm Basin

A study of changes in siliceous microfossil assemblages and chemical analys es in a well-dated offshore sediment core from the Bornholm Basin, southwes tern Baltic Sea, is carried out with the objective of increasing knowledge of the Holocene history of the area. The core covers about 11 300 calendar years from the brackish phase of the Yoldia Sea stage to the present. The f irst weak marine influence in the Ancylus Lake stage is recorded about 10 1 00 cal. yr BP (c. 8900 C-14 BP), indicating a complex transition to the Lit orina Sea with different phases of brackish-water inflow. The lithology, or ganic carbon content and C/N and C/S ratios indicate no major changes in th e sedimentary environment during the Litorina-Post-Litorina Sea stages. A h igh productivity event recorded in the Post-Litorina Sea stage around 950 c al. yr BP correlates with the Medieval warm event. A biostratigraphical cha nge indicating a colder climate is recorded in the sediment at about 800 ca l. yr BP, which might mark the beginning of the Little Ice Age.