Crucial Role of Bacterial Processes in the Net Community Production of the Amundsen Sea Polynya Disclosed by a Modeling Study

Abstract

We investigated seasonal net community production (NCP) variations in the productive Amundsen Sea Polynya, integrating observational data and ecosystem modeling. NCP estimates (NCPO2/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 NCPO2/Ar values ranging from 115 to 139 mmol O(2 )m(-2) d(-1) among observations. Over the summer, NCPO2/Ar gradually decreased, reaching 40 mmol O-2 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 degrees C in January to -1.33 degrees C in late February. Refining NCPO2/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&apos;s remarkable sensitivity to minor temperature fluctuations (<1 degrees 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. Plain Language Summary Our study delved into the seasonal changes in productivity in the Amundsen Sea Polynya, a bustling region near Antarctica. We combined real-world observations with computer modeling to unravel these patterns. In early January, this area was super productive, generating lots of oxygen. As summer progressed, productivity slowly declined, but it remained positive even in late summer, despite a significant drop in ocean temperature. This suggested that the ecosystem continued to thrive. To refine our model, we adjusted how bacteria interacted in the ecosystem. The results were fascinating. When we made bacteria more reliant on a specific algae, Phaeocystis, and more sensitive to temperature, our model better matched real-world conditions. This revealed that even minor water temperature changes, less than 1 degrees C, could significantly impact this ecosystem. Furthermore, altering bacterial dynamics led to a 2-week delay in the peak period of ocean plant growth, highlighting the crucial role of the interaction between tiny plants called phytoplankton and bacteria in the ocean&apos;s carbon cycle. Our study provides valuable insights into polar regions, emphasizing the need for comprehensive observations that include bacterial activities. Understanding these intricate interactions is vital for grasping the bigger picture of life in these remote and extreme environments.