Since 2012 we run a comprehensive lake sediment monitoring at Lake Tiefer See in the NE German lowlands within the TERENO (Terrestrial Environmental Observatories) initiative of the Helmholtz Association and the BaltRap project. The goals of this project are twofold:
Decoding of sedimentation processes is essential for the interpretation of proxy data from long sediment records for reliably reconstructions of past climate changes.
We have selected Tiefer See for the monitoring because it presently forms annually laminated sediments (varves) allowing us to decipher seasonal sedimentation at great detail.
Tiefer See is located in the northeastern corner of the Natural Park Nossentiner-Schwinzer Heide. With ca 62.5 m maximum depth it is the deepest lake of the Klocksin lake chain that formed as subglacial channel during the last glaciation. Tiefer See is located close to the Pomeranian Ice margin (W2 moraine) and the catchment is formed by glacial till. After melting of the ice sheet in this region the lake basin was filled with dead ice for several thousand years until the lake formed in the late Allerød ca 13 000 years ago. Organic-dominated sedimentation abruptly commenced with the warming at the onset of the Holocene 11 600 years ago.
Tiefer See specifications
Coordinates: 53° 36' N / 12° 32' E
Elevation above sea level: 63 m
Maximum depth: 62.5 m
Lake area: 75 ha
Lake volume: 14 x 106 m3
Catchment area: 5.5 km2
Our monitoring setup includes (1) a permanent weather station on the lake, (2) lake water observation, (3) sediment trapping, and, (4) regular sampling of short sediment cores from different parts of the lake basin.
(1) The weather station is mounted on a floating platform which is permanently anchored in the deepest part of the lake basin. We measure air temperature and pressure, precipitation global radiation, photosynthetically active radiation (PAR), wind direction and speed, all at 10 min time resolution. In addition, we collect rain water and dust mounted on the platform. Rain water is analysed in monthly intervals for δD und δ18O isotopes.
(2) Lake water monitoring: with two parallel automatic water probes we measure at 12-hour resolution water temperature, pH, conductivity, turbidity, oxygen content, redox potential and chlorophyll every meter down to 55 m water depth. In addition, permanent loggers are installed for temperature measurements every 6 hours with 1 m-spacing down to 12 m water depth and 5 m-spacing down to 55 m. In monthly intervals, we manually measure secchi depth and take water samples at 1, 3, 5, 7, 20, und 50 m for δD and δ18O analyses. Lake water samples are filtered for solid particles at 1, 3, 5, 7, 10, 20, and 50 m water depth.
(3)Sediment trapping: We have installed three different types of sediment traps at different water depths and time resolution. A sequential trap at 50 m water depths samples sediments in 15-day intervals. A parallel double-cylinder trap at the same water depths as backup integrates sediment samples over 6 months. Two additional 4-cylinder traps at 12 and 50 m water depth collect sediment samples in monthly intervals. From sediment samples in all traps we determine total carbon (TC), total organic carbon (TOC), total nitrogen (TN), calcium carbonate (CaCO3), and δ13Corg, δ15N, δ13Ccarb und δ18Ocarb isotopes. The 4-cyclinder trap at 50 m water depth is additionally analysed for sedimentary DNA from cyanobacteria.