Abstract: The latest hypothesis on the mechanism of glacial/interglacial variation in atmospheric partial pressure of carbon dioxide (pCO_2-atm) in the Southern Ocean suggests that the decrease of pCO_2-atm during glaciation can be satisfactorily explained by CO₂ sequestration via the reduced deep ventilation indicated by the decrease in the Antarctic zone productivity, and the CO₂ fixation by the increase in the subantarctic zone productivity. Obviously, verifying the mirror-image relation between productivity evolution in the Antarctic zone and the subantarctic zone in glacial cycles is the key to examine this hypothesis. The productivity evolution in the Weddell Sea (in Antarctic Zone) since MIS 5 was reconstructed based on the biogenic opal content from sediment cores. The results indicate that the productivity in the Weddell Sea showed glacial-interglacial variations, with high productivity during warm periods (MIS 5 and 3) and low productivity during cold periods (MIS 4 and 2), and a long-term decreasing trend was also observed. By combining our productivity records with those of other areas in the Southern Ocean, the mirror-image model of productivity evolution in the Antarctic and subantarctic zones was confirmed. Furthermore, comparison between the productivity records and potential environmental influence factors indicated that the meridional movement of Westerlies as well as the expansion and retreat of sea ice controlled the nutrient availability from deep water into surface by affecting deep convection, and ultimately drove glacial-interglacial and long-term variations of productivity in the Weddell Sea since MIS 5. The sequestration and release of CO₂ due to variation of deep convection in the Weddell Sea probably contributed to the long-term trend and glacial-interglacial cycles of pCO_2-atm since MIS 5. This research confirms that the above hypothesis about the mechanism for glacial-interglacial pCO_2-atm cycles in the Southern Ocean is reasonable, indicating that the Southern Ocean plays an important role in global climate evolution.