AbstractWe investigated seasonal net community production (NCP) variations in the productive Amundsen Sea Polynya, integrating observational data and ecosystem modeling. NCP estimates (NCP_O2/Ar) from in situ O₂/Ar data during the austral summer (January‐March) from 2011 to 2018 were compared with those from a one‐dimensional ecosystem model. Early January saw the highest NCP_O2/Ar values ranging from 115 to 139 mmol O₂ m⁻² d⁻¹ among observations. Over the summer, NCP_O2/Ar gradually decreased, reaching 40 mmol O₂ m⁻² d⁻¹ by late February. Late summer values, though one‐third of early January, remained notably positive, indicating net autotrophy. This persisted despite sea surface temperature dropping from >−0.4°C in January to −1.33°C in late February. Refining NCP_O2/Ar, we modified bacterial dynamics in our ecosystem model. Significantly improved model performance resulted from two key modifications. First, we introduced bacterial uptake dependency on Phaeocystis primary production. Second, we heightened temperature‐dependent bacterial respiration and production approximately fifteenfold. These changes revealed NCP's remarkable sensitivity to minor temperature fluctuations (<1°C). Furthermore, modified bacterial dynamics delayed the net primary production peak by 2 weeks, underlining the importance of phytoplankton‐bacteria interaction in the ocean carbon cycle. Model results estimated annual NCP in the Amundsen Sea Polynya at 4.04 mol C m⁻², aligning with summer NCP estimates (0.2–5.9 mol C m⁻²) in observational study. Our study advances NCP understanding in polar regions, emphasizing comprehensive observations, including bacterial processes, for understanding intricate biotic interactions. These findings align with past observations on bacterial metabolism and Phaeocystis ecological properties in the Antarctic oceans.