Oxygen Optode Sensors: Principle, Characterization, Calibration, and Application in the Ocean

Abstract

Recently, measurements of oxygen concentration in the ocean-one of the most classical parameters in chemical oceanography-are experiencing a revival. This is not surprising, given the key role of oxygen for assessing the status of the marine carbon cycle and feeling the pulse of the biological pump. The revival, however, has to a large extent been driven by the availability of robust optical oxygen sensors and their painstakingly thorough characterization. For autonomous observations, oxygen optodes are the sensors of choice: They are used abundantly on Biogeochemical-Argo floats, gliders and other autonomous oceanographic observation platforms. Still, data quality and accuracy are often suboptimal, in some part because sensor and data treatment are not always straightforward and/or sensor characteristics are not adequately taken into account. Here, we want to summarize the current knowledge about oxygen optodes, their working principle as well as their behavior with respect to oxygen, temperature, hydrostatic pressure, and response time. The focus will lie on the most widely used and accepted optodes made by Aanderaa and Sea-Bird. We revisit the essentials and caveats of in-situ in air calibration as well as of time response correction for profiling applications, and provide requirements for a successful field deployment. In addition, all required steps to post-correct oxygen optode data will be discussed. We hope this summary will serve as a comprehensive, yet concise reference to help people get started with oxygen observations, ensure successful sensor deployments and acquisition of highest quality data, and facilitate post-treatment of oxygen data. In the end, we hope that this will lead to more and higher-quality oxygen observations and help to advance our understanding of ocean biogeochemistry in a changing ocean.

The estimation of gross oxygen production and community respiration from autonomous time‐series measurements in the oligotrophic ocean

“…While optode performance is stable during glider deployments, optode storage before deployment has been documented to affect the accuracy of O 2 measurements (Bittig et al ). To correct for sensor response drift, we calibrated optode O 2 measurements by removing the offset with respect to shipboard measurements of O 2 concentrations determined by Winkler titrations.…”

Oxygen Saturation Surrounding Deep Water Formation Events in the Labrador Sea From Argo‐O2 Data

“…Our calibration of float 4900494 compares well to that of Johnson et al () for the same float using an in‐air calibration method. Many recent optode calibration studies focus on in‐air oxygen measurements (Bittig & Körtzinger, ; Bittig et al, ; Bushinsky et al, ; Johnson et al, ), which requires the optode to be located where it can sample air when at the surface. The mean surface ΔO 2 difference between the Johnson et al () calibration and our method for float 4900494 was 0.49 ± 0.36%, with much of the standard deviation arising from the drift during deployment that our method corrects (Wolf, , Appendix I).…”

“…The mean surface ΔO 2 difference between the Johnson et al () calibration and our method for float 4900494 was 0.49 ± 0.36%, with much of the standard deviation arising from the drift during deployment that our method corrects (Wolf, , Appendix I). Although the Johnson et al () calibration used a constant gain throughout the float's lifetime, the in‐air oxygen calibration method is capable of producing a time‐dependant gain for drift correction (Bittig et al, ; Bushinsky et al, ). Bittig et al () analyzed this same float including a time‐dependent gain.…”

“…Although the Johnson et al () calibration used a constant gain throughout the float's lifetime, the in‐air oxygen calibration method is capable of producing a time‐dependant gain for drift correction (Bittig et al, ; Bushinsky et al, ). Bittig et al () analyzed this same float including a time‐dependent gain. Our first profile gain value of 0.975 and subsequent average annual drift of −0.35% O 2 yr −1 compares well to the first profile gain value of 0.994 and linear trend of air O 2 observations of −0.17% yr −1 from Bittig et al ().…”

“…Bittig et al () analyzed this same float including a time‐dependent gain. Our first profile gain value of 0.975 and subsequent average annual drift of −0.35% O 2 yr −1 compares well to the first profile gain value of 0.994 and linear trend of air O 2 observations of −0.17% yr −1 from Bittig et al ().…”