Quantifying Observational Errors in Biogeochemical-Argo Oxygen, Nitrate, and Chlorophyll a Concentrations

Biogeochemical (BGC)-Argo floats observations are becoming a major data source for assimilation into and constraining of ocean biogeochemical models. An important prerequisite for a successful synthesis between models and observations is the characterization of the observational errors in BGC-Argo float data. The root-mean-square error and multiplicative and additive biases in quality-controlled data sets of oxygen, nitrate, and chlorophyll a concentrations collected with 17 BGC-Argo floats in the Mediterranean Sea between 2013 and 2017 are assessed using the triple collocation analysis. The analysis suggests that BGC-Argo float oxygen, nitrate and chlorophyll a concentrations data have an additive bias of 2.9 ± 5.5 μmol/kg, 0.46 ± 0.07 μmol/kg, and -0.06 ± 0.02 mg/m³, respectively. The root-mean-square error is evaluated at 5.1 ± 0.8 μmol/kg, 0.25 ± 0.07 μmol/kg, and 0.03 ± 0.01 mg/m³. Additional studies should determine whether these values are applicable to the global ocean.