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 behaviour 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.
Highlights
The dissolved oxygen concentration of seawater was among the suite of parameters measured during the famous H.M.S
Float 4900883 was excluded because (1) in air data reflected to almost 90 % in water samples and (2) suspected optode malfunctioning started 1.5 years after deployment. This leaves a total of 67 floats, FIGURE 7 | Oxygen sensitivity change for all optodes: The pressure of O2 (pO2) slope factor of a linear oxygen domain correction is shown against the time elapsed since the first calibration
O2-T-response near saturation is only valid at 10 ◦C and that we have a linear offset in pO2 the farther we diverge from 10 ◦C, we can approximate that offset with a pO2-T-slope a according to: pO2 = m · pOo2bs + a · (θ − 10◦C)
Summary
The dissolved oxygen concentration of seawater was among the suite of parameters measured during the famous H.M.S. A major prerequisite for this, was the invention of an elegant and precise wet-chemical method by Winkler (1888), which amazingly, albeit with various improvements (e.g., Carpenter, 1965), has remained the standard method to this day This favorable situation has allowed oceanographers to draw a most detailed picture of the distribution of oxygen in the ocean and to detect the subtle ongoing change that has established itself as the phenomenon of “ocean deoxygenation” (Keeling et al, 2010). Following promising early results (e.g., Körtzinger et al, 2004, 2005) the ocean biogeochemistry community has invested significant time and effort to fully characterize the major commercially available optode-based oceanographic oxygen sensors in view of their readiness for use on novel observation platforms such as floats and gliders. The purpose of the present article is to bring all this knowledge together in a comprehensive, yet concise manner making it a one-stop-shop for users that need information and guidance on how to use oxygen optodes in an optimal way
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
