Dating of recent sediments from Lago Maggiore and Lago di Lugano (Switzerland/Italy) using 137Cs and 210Pb

This paper presents the results of Cs-137 and Pb-210 dating of sediments from the northern and western basins of Lago Maggiore and the southern basin of Lago di Lugano. Vertical distributions of Cs-137 in sediment cores taken in 2017/18 were compared to those of the sediment cores taken almost two decades ago at the same positions. This comparison showed that Cs-137 peaks do not alter their shape significantly over time and Cs-137 remains a reliable time-marker for many decades. Pb-210 dating using for the first time the piecewise "constant rate supply" (CRSPW) model constrained with Cs-137 time-markers is performed for sediment cores of Lago Maggiore and Lago di Lugano. "Event-linked" mass accumulation rates (MARs) were derived from the CRSPW model. In combination with the dry bulk density, organic matter content, K-40 and Pb-210 activity concentrations, these "event-linked" MARs were used for the identification of one or more event layers (turbidites, detrital layers) in 1-cm thick sediment samples. "Continuous" mean MARs which are independent of the event layers were estimated: in Lago Maggiore sediment cores they are 0.066-0.090 g cm(-2) yr(-1); in Lago di Lugano they vary in the range of 0.032-0.057 g cm(-2) yr(-1) with higher values in the time interval 1963-1986 as compared to 1986-present.