Comparative time series of chlorophyll a (chl a) concentration in sea ice at the Brussels site (A) and Liège site (B) using the color scale as indicated. Black dots indicate the mean sampling depths. Pie charts indicate the autotrophic biomass composition of the ice cover at selected sampling depths. The exact contribution of each microalgal group (in % and µg C L⁻¹) to the total biomass is provided in Table S1.