Developing a low-cost device for estimating air–water ΔpCO₂ in coastal environments

Abstract. The ocean is one of the world’s largest anthropogenic carbon dioxide (CO₂) sinks, but closing the carbon budget is logistically difficult and expensive, and uncertainties in carbon fluxes and reservoirs remain. Specifically, measuring the CO₂ flux at the air–sea interface usually requires costly sensors or analyzers (>30,000 USD), which can limit what a group is able to monitor. Our group has developed and validated a low-cost ΔpCO₂ system for ~1,400 USD with Internet of Things (IoT) capabilities to combat this limitation using a ~100 USD pCO₂ K30 sensor at its core. Our Sensor for the Exchange of Atmospheric CO₂ with Water (SEACOW) may be placed in an observational network with traditional pCO₂ sensors to extend the spatial coverage and resolution of monitoring systems. After calibration, the SEACOW reports atmospheric pCO₂ measurements within 2–3 % of measurements made by a calibrated LI-COR LI-850. We also demonstrate the SEACOW’s ability to capture diel pCO₂ cycling in seagrass, provide recommendations for SEACOW field deployments, and provide additional technical specifications for the SEACOW and for the K30 itself (e.g., air and water-side 99.3 % response time; 5.7 and 29.6 minutes, respectively).