Dissolved strontium (Sr) concentrations in the Southern Ocean water samples and Sr export fluxes from sediment trap moorings at 1000 m were used to assess particulate organic carbon (POC) export associated with Acantharia for 2010, 2018 and 2020. The dissolved Sr data revealed a prominent vertical gradient with lower surface Sr concentrations depleted up to 1.4% relative to deep waters. A strong latitudinal surface gradient was observed, ranging from 87.3 near the northern end to 88.5 near the southern end of a transect through the Australian sector of the Southern Ocean. These findings highlight the significant role that Acantharia, which precipitate celestite (SrSO4), play in marine Sr cycling. Seasonal variability in Sr export fluxes can be large, particularly during intense events in summer, and reaches a maximum of 2.8 , contributing up to 7% of the POC export flux. The coincidence of Sr flux with the second peak of POC export flux implies a potential association of Acantharia biomass with summertime productivity.
