A 600-year sedimentary record of flood events from two sub-alpine lakes (Schwendiseen, Northeastern Switzerland)

Short sediment cores from two small interconnected sub-alpine lakes (Vorderer and Hinterer Schwendisee) in northeastern Switzerland contain a continuous record of environmental changes, which occurred during the last 600 years. Several light-colored layers within predominantly organic carbon-rich sediments display elevated density values and a high amount of detrital material. This composition points towards an allochthonous origin, which we interpret as material brought into the lake by unusually strong rainfall events. Based on this interpretation, four event horizons were identified in the sedimentary record. These horizons were dated combining a 137Cs and 210Pb-based chronology with meteorological and historical data. They occurred mostly within the 19th and at the beginning of the 20th century, whereas only one event occurred prior to 1800. The well-documented strong rainfall event that occurred on June 14, 1910 is observed in the sedimentary record as the thickest detrital horizon. These short-lived climatic events archived in the sediments of both lakes are superimposed on a longer-term environmental trend characterized by fluctuating conditions in organic productivity. The formation and preservation of authigenic minerals, such as siderite and vivianite, are most likely related to intervals of different primary productivity in the water column.