Dating of sediments from four Swiss prealpine lakes with 210Pb determined by gamma-spectrometry: progress and problems

• State-of-the-art aspects of gamma-spectrometry of unsupported 210Pb are summarized.
• Reduction of 222Rn loss by sealing sediment samples was experimentally quantified.
• 210Pb models (CF-CSR, CRS, SIT) are applied on long sediment cores from 4 lakes.
• Results for profiles, depth–age relations and sedimentation rates are compared.
• 210Pb dating is supported by independent time-markers (7Be, 137Cs, 241Am, 239Pu).

In this paper the most important problems in dating lake sediments with unsupported 210Pb are summarized and the progress in gamma-spectrometry of the unsupported 210Pb is discussed. The main topics of these studies concern sediment samples preparation for gamma-spectrometry, measurement techniques and data analysis, as well as understanding of accumulation and sedimentation processes in lakes. The vertical distributions of artificial (137Cs, 241Am, 239Pu) and natural radionuclides (40K, 210,214Pb, 214Bi) as well as stable trace elements (Fe, Mn, Pb) in sediment cores from four Swiss lakes were used as examples for the interpretation, inter-comparison and validation of depth–age relations established by three 210Pb-based models (CF-CSR, CRS and SIT). The identification of turbidite layers and the influence of the turbidity flows on the accuracy of sediment dating is demonstrated. Time-dependent mass sedimentation rates in lakes Brienz, Thun, Biel and Lucerne are discussed and compared with published data.