Bio-optical properties of algal communities in Antarctic pack ice during spring

Microalgae use Antarctic sea ice as habitat and accumulate in spring, leading to significant early-season production in Southern Ocean ecosystems. As key contributors to the marine food web and carbon fixation within the Antarctic pack-ice zone, ice algae depend on the light environment and their adaptability to irradiance extremes. This study examines spectral ice algal and non-algal particulate absorption coefficients, pigments, and community composition in pack-ice cores sampled off East Antarctica and in the Weddell Sea during the winter-spring transitions in 2012 and 2013, respectively. Our results show that ice algae dominated particulate absorption in pack ice in both regions. From high- to low-light exposure in both East Antarctica and Weddell Sea, biomass-specific absorption decreased, suggesting strong pigment packaging with depth towards the ice-water interface. Ice algae also showed increased production of photoprotective pigments in the surface in comparison to the bottom of the sea ice, with flagellates being more dominant in the surface ice sections. Our results indicate species-specific light-acclimation and photoprotection through the ice profiles, and highlight the role of light conditions in influencing pigment production and shifts in community composition.