In Situ Calibration of Argo-deployed Oxygen Optodes

Abstract:

Comparison of oxygen profiles from Argo-deployed Optodes with ship-based bottle casts taken at the time of deployment shows typical low biases of approximately 0 to −40 μmol kg^-1. We describe a method to recalibrate the Optodes in situ, using reference oxygen data either from the World Ocean Database or from deployment casts. Unlike other in situ correction methods, this algorithm performs a true recalibration of the function mapping {𝜙, 𝑇} → O₂ for each Optode. Under suitable conditions, errors of less than 1 μmol kg^-1 are achievable. Oxygen profiles from 147 instruments deployed by the University of Washington between 2004 and 2015 recalibrated by these methods agreed with World Ocean Atlas 2009 climatology to within an error of about 1%. Comparison of six pairs of Optodes deployed on the same float showed relative errors after in situ recalibration of 0.1±0.6 μmol kg^-1.