Dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) cell quotas variations due to sea ice shifts of salinity and temperature in the Prymnesiophyceae Phaeocystis antarctica

The Southern Ocean, including the seasonal ice zone (SIZ), is a source of large sea-air fluxes of dimethylsulfide (DMS), a climate active gas involved in Earth cooling processes. In this area, the prymnesiophyte Phaeocystis antarctica (P.antarctica) is one of the main producers of dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO), two metabolites that are precursors of DMS. These algae are also present in sea ice and could contribute substantially to the high DMSP and DMSO concentrations observed in this habitat. DMSP and DMSO production in sea ice by P.antarctica could be promoted by it living in extreme environmental conditions. We designed cell culture experiments to test that hypothesis, focusing on the impact of shifts of temperature and salinity on the DMSP and DMSO cell quotas. Our experiments show an increase in DMSP,O cell quotas following shifts in salinity (34 to 75, at 4°C), suggesting a potential osmoregulator function for both DMSP and DMSO. Stronger salinity shifts (up to 100) directly impact cell growth and induce a crash of the cultures. Combining salinity (34 to 75) and temperature (4°C to -2.3°C) shifts induces higher increases of DMSP and DMSO cell quotas also suggesting an implication of both metabolites in a cryoprotectant system. Experimental cell quotas (including diatom Fragilariopsis cylindrus quotas from a previous study) are then used to reconstruct DMSP and DMSO profiles in sea ice based on the biomass and taxonomy. Finally, the complexity of the transposition of rates obtained in the experimental domain to the real world is discussed.