Award: OPP-1744645

Sea-ice algae provide a vital but poorly understood link in polar marine ecosystems and carbon sequestration. Our research quantified the roles of sea-ice algae along coastal waters of the Western Antarctic Peninsula, a region experiencing rapid warming and loss of sea ice. Our research found in laboratory cultures that sea-ice algae possessed unique metabolic profiles compared to other algae containing some of the highest intracellular concentrations of protective osmolytes found in marine microorganisms to date. Under high salinity, these protective osmolytes can rescue growth rates and reduce the production of exopolymers. Under freshening conditions, algae rapidly release many of these compounds to the environment, providing a significant source of labile dissolved organic nitrogen and carbon. Future work is quantifying the role sea-ice algae play in partitioning particulate and organic matter during ice melt. Shifts in temperature and salinity did not need to be extreme for the algae to drastically alter their intracellular metabolism. This response was also observed in natural communities of microorganisms, collected from surface coastal seawater near the Western Antarctic Peninsula. Unexpectedly, we found that under freshening conditions, algae reduced the concentration of their total metabolome and increased fatty acid degradation. As a freshening environment is likely to become more prevalent due to sea ice loss and glacial melt, it is likely that algae will be reduced in nutritional value, which may have serious impacts to polar marine food webs as sea-ice algae are a vital food source for juvenile krill, a keystone species. We also explored how sea-ice algae acclimate their photosynthetic machinery during the spring melt of sea ice. Sampling ice-algae inhabiting sea ice in various stages of melt along coastal waters of the western Antarctic Peninsula found sea-ice algae adjust their photosynthetic machinery to harness increasing light levels. We explored different methods to estimate rates of primary production in sea-ice algae, which is notoriously difficult by traditional methods due to their location within the ice, hidden from satellites. We also provided some of the first measurements of sea-ice algae production near Palmer Station, despite over 40 years of phytoplankton measurements as part of the Palmer LTER. Finally, our work explored how sea-ice algae will respond to ocean acidification and rising temperatures by modeling their carbon uptake kinetics and physiology. We found that sea-ice algae can adjust the mechanisms by which they take up inorganic carbon in a way that is energetically proportional to the rate at which they fix carbon. This suggests that sea-ice algae will be remarkably robust as surface seawater warms and acidifies. Last Modified: 12/04/2023 Submitted by: JodiNYoung