The Southern Ocean plays a pivotal role in controlling the most critical greenhouse gas, carbon dioxide (CO2), in the atmosphere. However, insufficient observations, particularly in the Antarctic Sea Ice Zone (ASIZ; south of 60°S), hinders accurate estimation of the Southern Ocean sink strength of atmospheric CO2. Here, we show that Antarctic polynyas play a significant role in the CO2 budget of the Southern Ocean based on the 5-year continuous observations at the Korean Antarctic Station, Jang Bogo, in the Terra Nova Bay (TNB) polynya, Ross Sea, Antarctica and on the compilation of shipboard observations in the major Antarctic polynyas. The seasonal variation of the fugacity of dissolved CO2 (fCO2) between them shows in accordance, which was dominated by biological and physical processes in different seasons. Antarctic polynyas absorb atmospheric CO2 at a rate of 9 to 14 Tg C a-1, that is comparable to or more than the amount outgassed in the ASIZ, concentrating in the summer season from December to March. As the summer drawdown of fCO2 in the polynya is dominantly driven by phytoplankton blooms which is in turn maintained by the supply of iron from circumpolar deep water and glacier melt water, we expect this CO2 sink in the Antarctic polynyas to be enhanced in the future, resulting in a negative feedback with future climate change.