Diatom distribution in sediment core PG2208

A total of 37 samples from sediment core PG2208 were analyses for diatoms, of which we found valves in 32 samples. For species analysis we prepared diatom slides for light microscopy following the common procedure developed by Battarbee et al. (2001). About 0.1 g of freeze-dried sample material was treated with hydrogen peroxide (30%) for several hours and washed before adding 5 × 106 microspheres to estimate diatom valve concentration (DVC). Diatom valves were identified using a Zeiss AXIO Scope.A1 light microscope with a Plan-Apochromat 100x/1.4 Oil Ph3 objective at 1,000× magnification. A minimum of 300 diatom valves (Wolfe, 1997) were counted (mean 316) in each sample. Only 23 valves were found in the deepest sample at 310.5 cm. In parallel to diatom analysis, Chrysophyte cysts and Mallomonas scales were counted but not further identified. Diatom species identification was supported by images from a scanning electron microscope (SEM) at GeoForschungZentrum Potsdam. The diatom species identification was carried to lowest possible taxonomic level. To guarantee correct identification literature was used including Hofmann et al. (2011) and Krammer and Lange-Bertalot (1986–1991) as well as online databases (i.e., http://www.algaebase.org).