Recent progress and future opportunities in autonomous ocean CO2 flux observing

Abstract:

Observation-based estimates of global surface ocean CO₂ flux have relied on a network of underway measurements from volunteer observing ships for several decades. Within the last decade, surface ocean pCO₂ observations from fixed surface buoys have been incorporated into the synthesis data product, the Surface Ocean CO₂ Atlas (SOCAT), supporting the generation of regional and global CO₂ flux estimates. High-frequency, surface buoy observations of seawater and air CO₂ exist in every ocean, nearly all gyre-scale biomes and biogeochemical provinces, and in coastal and coral reef ecosystems. New in the 2020 release of SOCAT is the incorporation of pCO₂ observations from Autonomous Surface Vehicles (ASVs). Like ship-based pCO₂ observations, these buoy- and ASV-based observations are of climate quality and standardized across a distributed network of investigators through the use of standard CO₂ reference gases. These new technologies provide unique opportunities. High-frequency fixed time series allow for better constraint of temporal variability in ocean CO₂ flux at given locations, and ASVs equipped with CO₂ measurements have the capability to fill persistent gaps in the existing observing network (e.g., much of the Southern Hemisphere) and the flexibility for adaptive sampling as events arise (e.g., ENSO, marine heatwaves). Here we discuss these new technologies and how their expanded use can provide better quantification of the ocean CO₂ sink and improved constraint of the global carbon budget.