This dataset provides counts of diatom valves for the MIS-5a sediment sequence retrieved from Sokli (Finland) in 2010. Counts per taxon are presented against depth (m); total sums for classes of diatoms (e.g. Sum Benthic Taxa) are presented as well. The diatom dataset provides information on MIS 5a lake ecosystem dynamics (Helmens et al., 2021). A total of 22 samples were selected for diatom analysis. Diatoms were extracted from the sediment following the protocol presented by Battarbee et al. (2003). First, organic matter was oxidized in H2O2 in a water bath (at c. 100 °C). Subsequently, carbonates were removed by 10% HCl treatment (no visible reaction). Clay particles were decanted from 100 ml beakers after sedimentation overnight. Sand grains were removed after five seconds of sedimentation. The residue was mounted in Naphrax® and analysed under a light microscope with X1000 magnification using immersion oil. Flora used for species identification and information on ecological preferences are presented in Helmens et al. (2009). A minimum of 500 diatom valves were identified from each of the samples (average count = 1322, range = 531-2264 valves). All analyses were performed in the laboratories Stockholm University, Sweden.

Further funding was provided by SKB (Swedish Nuclear Fuel and Waste Management Company) and the Bolin Centre for Climate Research.