Enhanced Southern Ocean O ₂ Uptake Due To Bubble‐Mediated Gas Exchange Revealed by Climate Model Simulations

Abstract

Despite advances in understanding the ocean oxygen cycle, climate models continue to show regionally varying discrepancies from O ₂ distributions, reflecting incomplete representation of the biological and physical processes controlling ocean oxygen. Air‐sea O ₂ flux—a key driver of oceanic oxygen variability—remains underconstrained in climate models, with bubble‐mediated exchange emerging as a potential missing mechanism. Here we integrate a novel bubble‐mediated parameterization into the Community Earth System Model and assess its impact on Southern Ocean O ₂ exchange. Including bubble injection increases annual Southern Ocean O ₂ uptake by 13%–19%, depending on the prescribed bubble strength. The moderately scaled configuration (BUB‐0.3) reduces the near‐surface model‐observation RMSE in three of the four Southern Ocean regions, with the largest improvement, approximately 34%, occurring in the Subantarctic Zone. In Pacific Subantarctic Mode Water, BUB‐0.3 reduces the distributional mismatch with BGC‐Argo+ observations by 73%, whereas BUB‐1.0 increases the mismatch by 41%. Machine‐learning attribution indicates that mixed‐layer depth remains the leading predictor of nonthermal O ₂ flux variability, while the relative importance and nonlinear influence of wind speed increase when bubble pathways are represented. Our results highlight the importance of bubble‐mediated transfer in refining climate models and elucidating the Southern Ocean's capacity as a dynamic oxygen sink, offering a mechanistic advance toward resolving longstanding discrepancies in global marine oxygen cycling.