Bias Evaluation for Sensor-Based Dissolved Oxygen from CTD and Profiling Floats in the World Ocean Database
Year: 2025
Type: article
Abstract: Sensor-based oxygen (O 2 ) measurements in the ocean have become the dominant data source for in situ O 2 since 2010. We examine the overall quality of the shipborne conductivity–temperature–depth (CTD)- and Argo-measured O 2 in the World Ocean Database (WOD) and evaluate biases by comparing them to independently measured reference bottle-sampled profiles. No significant O 2 difference is found between CTD and bottle data for the global ocean, suggesting high quality of CTD O 2 observations generally. A negative residual bias is found in both postcorrected delayed-mode (−1.69 ± 5.15 μ mol kg −1 , fitted mean ± standard deviation) and real-time-adjusted (−4.68 ± 6.99 μ mol kg −1 ) Argo O 2 . Residual biases have both spatial (basin scale and vertical) and temporal variations, indicating the complexity of residual biases. We also examine Argo O 2 biases based on the type of calibration methods. The Argo delayed-mode O 2 profiles calibrated using the World Ocean Atlas ( WOA ), on average, are offset by −1.60 ± 5.30 μ mol kg −1 , while a larger bias (−3.29 ± 4.86 μ mol kg −1 ) is found for profiles calibrated using in-air measurements for the global ocean. The Argo delayed-mode data calibrated with O 2 profiles from the WOD have a slight positive bias (0.33 ± 4.16 μ mol kg −1 ). Further analysis demonstrates that the O 2 profiles without matched reference profiles also have negative bias similar to those with matched reference profiles when they are compared to WOA . This analysis suggests the negative residual biases in Argo postcorrected O 2 should be carefully considered when using Argo O 2 data to draw conclusive inferences about anthropogenic impacts on ocean oxygen concentrations and/or derived quantities in a changing ocean. Significance Statement This study evaluates the quality of dissolved oxygen (O 2 ) measurements from CTD and Argo profiling floats in the World Ocean Database, comparing them to reference bottle data. Results show that CTD measurements are highly accurate and serve as a reliable reference for Argo O 2 evaluations. Argo data reveal negative residual biases, both in real-time-adjusted and delayed-mode measurements, with variations across spatial, vertical, and temporal scales. Biases are also influenced by calibration methods, with larger discrepancies found in profiles calibrated using in-air measurements compared to those calibrated with the World Ocean Atlas . These findings suggest the presence of global negative biases in Argo O 2 data, highlighting the need for further corrections to improve the calibration methods of Argo O 2 .
Institutions: NOAA National Environmental Satellite Data and Information Service, NOAA National Centers for Environmental Information, Monterey Bay Aquarium Research Institute, Georgia Institute of Technology, University of Washington, NOAA Pacific Marine Environmental Laboratory, Cooperative Institute for Climate, Ocean, & Ecosystem Studies, National Oceanic and Atmospheric Administration, Stennis Space Center
Language: English
Subfield: Oceanography
Field: Earth and Planetary Sciences
Domain: Physical Sciences
SDG: Life below water
Open Access status: green
Awards: Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM2), Mid-scale RI-2 Consortium: Biogeochemical-Argo: A global robotic network to observe changing ocean chemistry and biology, SOCCOM3: Science to Predict the Future of the Southern Ocean and its Global Impacts, Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM)
OpenAlex ID: W4413197351