Sediment dispersion in a large ice-contact lake reconstructed from a varve record: PÄrnu bay region, Estonia

Interpretation of climate change and deglaciation events from palaeovarves requires a complete understanding of varve composition, depositional environments and the non-climatic events that may influence varve thickness record. We examined a Baltic Ice Lake varve-thickness chronology from western Estonia, eastern Baltic Sea, composed of 26 individual varve series and spanning 584 years of Late Weichselian deglaciation. The direction (azimuth) to the increasing seasonal layer thickness and correlation between the water depth and the seasonal layer thickness were calculated for each annual varve and presented as time series. The results demonstrate clear temporal changes in deposition in accordance with irregular ice recession and the topography of the lake bottom. It is found that the sedimentation in the ice-proximal environment is dominated by sediment distribution as underflows and as a result the bottom topography has a stronger effect on the sediment accumulation than the proximity to the ice margin. Lack of expected correlation between the water depth and the winter layer thickness in the ice-proximal environment is attributed to thermal water circulation. Basin-wide simultaneous shift in relation to seasonal layer thickness within a varve is explained by the trapping of coarser material in the newly opened sedimentary basin north of the study area.