32Si dating of sediments from Lake Baikal

We applied the Si-32 dating technique to a sediment core from Lake Baikal to obtain the sediment chronology for the last millennium. The core was recovered about 4 km offshore from the north slope of the South Basin in 1,366 m water depth. The sediment material consisted of continuously accumulated diatom-rich geogenic-terrigenous mud, intercalated with a number of dark olive-grey turbidite layers. The sediment layers containing the turbidites were excluded from Si-32 sampling to obtain the chronology that is representative of the continuous sedimentation. The initial Si-32 activity of 31.3 dpm kg(-1) SiO2, measured in sediment trap samples, confirms the trend of Si-32 specific activities of biogenic silica found in other Northern Hemisphere lakes. The four sediment core samples from depth 0-48 cm have Si-32 specific activities between 23.5 and 0.5 dpm kg(-1) SiO2, with corresponding ages between 60 and 860 years and constant sedimentation rate of 0.036 +/- A 0.004 cm year(-1) over the most recent 800 years. Si-32 allowed us for the first time to date the uppermost turbidites in the South Basin of Lake Baikal, to 1030, 1310 and 1670 ad. Given these dates, the last long-distance turbidity current triggered by slope instabilities had occurred 330 years before 2000 ad, and the intervals between the 1310 and 1670 ad event and between the 1030 and 1310 ad event were 360 and 280 years, respectively. The Si-32 ages allow unprecedented time resolution for reconstruction of the former environmental and climatic conditions during the past millennium.