The role of the global surface ocean as a source and sink for atmospheric carbon dioxide and the flux strengths between the ocean and the atmosphere can be quantified by measuring the fugacity of CO₂ (ƒCO₂) as well as the dissolved inorganic carbon (DIC) concentration and its isotopic composition in surface seawater. In this work, the potential of continuous wave cavity ringdown spectroscopy (cw-CRDS) for autonomous underway measurements of ƒCO₂ and the stable carbon isotope ratio of DIC [δ¹³C(DIC)] is explored. For the first time, by using a conventional air-sea equilibrator setup, both quantities were continuously and simultaneously recorded during a field deployment on two research cruises following meridional transects across the Atlantic Ocean (Bremerhaven, Germany–Punta Arenas, Chile). Data are compared against reference measurements by an established underway CO2 monitoring system and isotope ratio mass spectrometric analysis of individual water samples. Agreement within ΔƒCO₂ = 0.35 μatm for atmospheric and ΔƒCO₂ = 2.5 μatm and Δδ¹³C(DIC) = 0.33‰ for seawater measurements have been achieved. Whereas “calibration-free” ƒCO₂ monitoring is feasible, the measurement of accurate isotope ratios relies on running reference standards on a daily basis. Overall, the installed CRDS/equilibrator system was shown to be capable of reliable online monitoring of ƒCO₂, equilibrium δ¹³C(CO₂), δ₁₃C(DIC), and pO₂ aboard moving research vessels, thus making possible corresponding measurements with high spatial and temporal resolution.