Enhancing air–sea CO ₂ exchange and modulating seawater carbonate–pH dynamics: the role of wave effect mechanisms in the POP2–waves coupled model

In this study, a wave module is online-coupled into the Parallel Ocean Program version 2 (POP2) within the CESM1.2.2 framework (hereafter POP2–waves). Unlike empirical data analyses of observation-based products and offline-forced ocean models that treat wave-induced gas transfer velocity and the air–sea difference in partial pressure of CO2 (ΔpCO2) as decoupled variables, the online-coupled POP2–waves model captures their interactive, ΔpCO2-mediated negative feedbacks. This setup enables wave properties to dynamically modulate gas transfer velocity and physical mixing through sequential processes. POP2–waves is evaluated alongside a control simulation (B–CTL) against the National Oceanic and Atmospheric Administration (NOAA) CarbonTracker (CT2022) inversion product. The spatial air–sea CO2 flux in POP2–waves simulation shows generally closer structural agreement with NOAA CT2022 than the control B–CTL, thereby improving performance in most selected regions. Specifically, bubble-mediated transfer accounts for up to 41.3 % of the total flux, consistent with the ∼40 % contribution reported in recent research. Although the inclusion of waves (POP2–waves) enhances regional oceanic CO2 uptake by 11.8 % and outgassing by 41.6 %, these two processes largely offset each other. Consequently, this dual enhancement results in only a slight 1.8 % increase in the global net ocean CO2 sink compared to the B–CTL simulation. Globally, air–sea ΔpCO2 and pH exhibit the strongest positive and negative regression coefficients with the air–sea CO2 flux, respectively. Regionally, the gas transfer velocity shows a positive (negative) regression coefficient within oceanic CO2 outgassing (uptake) regions, whereas SST displays the opposite trend.