Earth's polar regions are extreme ecosystems, marked by perennial darkness and seasonal mosaics of sea ice that modify the salinity, temperature, and incoming light of subsurface waters. Recent work in the Arctic has shown that phytoplankton can thrive underneath sea ice, dwarfing previous estimates for phytoplankton productivity across the annual cycle (Arrigo et al., 2012(Arrigo et al., , 2014Assmy et al., 2017), and raising questions of how sea ice influences under ice phytoplankton.The effects of sea ice on phytoplankton in the Southern Ocean remains largely unknown as much research has focused on the Arctic Ocean, although more recent studies have expressed the possibility of widespread microbial life under Antarctic sea ice from observations (Arteaga et al., 2020;Cimoli et al., 2020;Hague & Vichi, 2021). Phytoplankton in the Southern Ocean are primarily limited by light and iron, and massive blooms under ice sea are generally not suspected in this region. However, nutrient replenishment from deeper Winter mixed layer depths combined with light at the onset of Spring may enable phytoplankton growth under ice. Still needed are assessments of how ice characteristics affect the under ice environment. On one hand, the thicker snow cover of Southern Ocean sea ice compared to the Arctic may prohibit the transmission of light to the waters below because the snow has a higher albedo than sea ice. On the other hand, most Antarctic sea ice melts in the Austral Spring and Summer (Pfirman et al., 1990), which may create a stable mixed layer and enhance growth of an already active under ice phytoplankton population previously living in deeper mixed layers (Hague & Vichi, 2021;Petty et al., 2014).