Figure 2. Sample sites in the Baltic Sea. The contour shows averaged cold season (Feb-Apr) sea ice concentration during 2005-2015 calculated from ERA5 monthly averaged data2. The filled circles indicate sediment samples, and the numbers show Isochrysidales groups detected by environmental DNA and biomarkers from sediment samples, the asterisks show predominant alkenone-producers. The stars indicate locations where timeseries samples were collected. Note that the Group 2 Isochrysidales found in the Baltic Sea samples were exclusively 2i. In contrast, the Group 2 Isochrysidales found in the Chesapeake Bay samples were exclusively 2w species (Fig.1).