Biological imprint dominates global mesoscale air-sea flux anomalies of carbon dioxide and oxygen

<jats:p>Abstract. Ocean mesoscale phenomena ("mesoscale eddies") are fundamental components in mediating air-sea heat and momentum fluxes through anomalies of sea surface temperatures and currents. Yet, their impacts on air-sea gas fluxes, such as carbon dioxide, CO2, and oxygen, O2, through changing solubility and biological cycling, remain underexplored. This study aims to diagnose global patterns of ocean mesoscale CO2 and O2 flux anomalies and their drivers. To this end, we use results from an ocean eddy-rich 0.1° GFDL climate model (CM2.6), namely a preindustrial control simulation and an idealized climate change simulation with a linear increase in atmospheric CO2 until CO2 doubling is reached. Mesoscale air-sea CO2 and O2 flux anomalies are isolated from large-scale signals by applying spatial filtering to monthly averaged model results. We find that globally mesoscale variability explains approximately 6–7 % of the variance in CO2 and O2 fluxes, with regional contributions exceeding 30 %. We present an analytical framework to attribute air-sea CO2 and O2 flux anomalies to thermally-driven solubility effects versus biological imprints, based on the sign of the correlation between CO2 and O2 flux anomalies. We find a clear regional imprint in the mechanisms by which mesoscale eddies influence CO2 and O2 fluxes. In subtropical and mid-latitude regions, CO2 and O2 flux anomalies are predominantly of the same sign, indicating that mesoscale eddies impact gas fluxes mainly through solubility changes. In tropical and high-latitude regions the effect of mesoscale eddies on CO2 and O2 flux is mostly of biological origin, as indicated by an opposite sign of CO2 and O2 flux anomalies, either caused by changes in biological productivity or upwelling of a respiration signal from the ocean interior. Although the regions with a biological imprint globally cover an area comparable to solubility-driven regions globally, the associated flux anomalies are larger in magnitude, causing the biological drivers to dominate the globally integrated absolute mesoscale anomalies, representing approximately two-thirds of the total signal, and account for 7–9 % to global variance (compared to 5–7 % for solubility-driven regions). Under CO2 doubling, solubility-driven regions expand and fluxes intensify, increasing their relative contribution, though the large-scale patterns of drivers remain the same. The biological contribution remains dominant for O2, while the relative importance of solubility-driven processes increases for both gases under warming. Our results highlight the spatial organization of mesoscale-driven air-sea gas fluxes into distinct regimes and demonstrate that, on a global scale, a biological imprint dominates the magnitude of mesoscale CO2 and O2 flux anomalies.</jats:p>