Fig. 1.

Syndiniales group I OTU (SG1-OTU) dominates samples near sea-ice edge. a The concentric circles show the relative abundance of SG1-OTU in three surface plankton size fractions (0.45–5, 5–20, and >20 µm) south of the Kerguelen Plateau region of the Southern Ocean. b Surface chlorophyll a in the same region. Both SG1-OTU relative abundance and surface chlorophyll were highest in the easternmost transect. Upper and lower blue lines are sea ice in November and January, respectively. Historical positions of southern Antarctic Circumpolar Current (ACC) front and Southern Boundary of the ACC are shown as dotted lines. c Relative abundance of SG1-OTU in each size fraction in relation to days since sea-ice melt. Only the period following 50 days since melt is shown to highlight the greater relative abundance in the pico-nanoplankton compared to the other size fractions following 80 days since melt