Investigating surface-ocean oxygen dynamics using MIMS-based O₂/Ar measurements

Air–sea gas exchange exerts a critical control on marine biogeochemistry, yet quantifying biologically driven oxygen fluxes in dynamic sea conditions remains challenging. Here, we use membrane inlet mass spectrometry (MIMS) measurements of dissolved gases to estimate net community production (NCP) from biologically driven oxygen anomalies across the Irish Exclusive Economic Zone (EEZ). High-precision dissolved O₂ and Ar measurements were obtained using a Hiden Analytical MIMS system, enabling calculation of O₂/Ar ratios that isolate the biological oxygen signal by normalisation to inert argon and reference to air–sea equilibrium.

 

Seawater samples collected during multiple research cruises were analysed under controlled temperature conditions. Raw ion currents were corrected using solubility based relative sensitivity factors, and O₂/Ar ratios were converted to biological supersaturation (ΔO₂/Ar) from the temperature and salinity of the sea water sample, providing a robust tracer of biologically driven O₂ fluxes independent of temperature and solubility effects. Data quality was assessed through comparison of flow through cell and dip-probe measurements and analysis of poisoned samples to constrain non-biological influences.

 

The collected ΔO₂/Ar dataset covers a diverse oceanic condition from coastal to open ocean, from the Irish Exclusive Economic Zone (EEZ) to the North and South Atlantic. Samples were collected in various seasons in 2024, and in 2025, they were collected along the latitudinal transect. The purpose of these observations is to examine the variations in surface-ocean oxygen levels across different regions, seasons, and latitudes, and to analyse the impacts of biological production, stratification, and air-sea gas exchange on different oceanographic conditions. This method will demonstrate how MIMS-based O₂/Ar measurements may assist in identifying short-term air-sea oxygen fluxes and provide more precise constraints on the productivity and carbon cycling of the ocean.