Distribution of Phaeocystis antarctica-dominated sea ice algal communities and their potential to seed phytoplankton across the western Antarctic Peninsula in spring

The western Antarctic Peninsula has experienced extreme changes in the timing of sea ice melt and freeze up, shortening the duration of the seasonal sea ice cycle. While previous research demonstrated connections between multiple pelagic trophic levels and the physics of the sea ice, few studies have assessed the sea ice ecosystem or its linkage to the ocean ecosystem in this region. Through a field survey and shipboard experiments, our study focused on characterizing the spring ice algal bloom and elucidating its role in seeding phytoplankton communities postice melt in high and low light conditions. Field data revealed that algal communities in slush layers, often formed from the flooding of seawater (infiltration layers), dominated biomass distributions in the sea ice throughout the region, and showed distinct photophysiological characteristics from interior or bottom ice communities. Sea ice algal biomass reached 120 mg chl a m(-2) and was often dominated by Phaeocystis antarctica. Shipboard growth experiments showed that prior light history (ice or water column), rather than community composition (phytoplankton and ice algae were composed of similar taxa), primarily drove physiological responses to high and low light. P. antarctica generally dominated the community in growth experiments at the end of the 6 d incubation period. Settling column experiments suggested that P. antarctica's higher sinking rates relative to other taxa may explain its minor contributions to the summer phytoplankton community in single-cell form and its absence in colonial form, observed in the long-term ecological record of this region.