It has been suggested that the freshwater flux due to the recent melting of the Antarctic ice-sheet/shelf will suppress ventilation in the Southern Ocean. In this study, we performed idealized  earth  system  simulations  to  examine  the  impacts  of  Antarctic  meltwater  on surface phytoplankton biomass in the Antarctic Ocean. The enhanced stratification due to the meltwater leads to a decrease in the surface nitrate concentration but an increase in the surface  dissolved iron  concentration.  These  changes  are  associated  with  the  reduced upwelling  of  nitrate-rich  deep  water  and  the  trapped  iron  exported  from  the  terrestrial sediment.  Because of the limited iron availability in the Southern Ocean, the trapped iron in surface water enhances the chlorophyll concentration in the open ocean. However, in the marginal sea along the Antarctic coastline where the iron is relatively sufficient, a nitrate reduction induces a chlorophyll decrease, indicating a regime shift from iron-limited to nitrate-limited conditions.