The process of calcification of shellfish produces CO₂. However, there are large differences in carbonate system compositions among different aquaculture areas. Thus, more rigorous carbonate chemistry modeling, including concurrent changes in seawater carbonate systems, is needed to quantify the CO₂ released into the atmosphere during calcification. In this study, the ratio between the CO₂ emitted into the atmosphere during various biogeochemical processes and the CO₂ produced by these processes is defined as Φ. Therefore, in the calcification process, the Φ_cal value represents the amount of CO₂ emitted from the seawater to the atmosphere when 1 mol of CaCO₃ is formed during shell growth. Results showed that Φ_cal value varied among seasons. The Φ_cal value was lowest during summer in Jiaozhou Bay, Sanggou Bay, and Shenao Bay. Regional differences in the carbonate system in the aquaculture sea area could change the Φ_cal value. In Jiaozhou Bay, 0.79 mol CO₂ was released into the atmosphere for every 1 mol CaCO₃ deposited during shell growth. In Sanggou Bay and Shenao Bay, this value was 0.72. In Jiaozhou Bay, the Φ_cal value decreased in the shellfish's main growing season (from March to July). The result of polynomial fitting further suggested that the Φ_cal value decreased with the temperature rise during this season. The Φ_cal value decreased faster when the water temperature exceeded 18 ℃. Finally, the annual production of 3.2×10⁵ tons of Philippine clams in Jiaozhou Bay was expected to emit about 1.084×10⁵ tons of CO₂ into the atmosphere due to shell growth. This study preliminarily confirmed that Φ_cal, including concurrent changes in the seawater carbonate system in the aquaculture area, could better quantify the CO₂ release caused by shellfish calcification. This study could provide some references for future studies on the topic of the carbon source/sink process of shellfish.