A high‐resolution submersible oxygen optode system for aquatic eddy covariance

Abstract

AbstractThe aquatic eddy covariance technique is increasingly used to determine oxygen (O2) fluxes over benthic ecosystems. The technique uses O2 measuring systems that have a high temporal and numerical resolution. In this study, we performed a series of lab and field tests to assess a new optical submersible O2 meter designed for aquatic eddy covariance measurements and equipped with an existing ultra‐high speed optical fiber sensor. The meter has a 16‐bit digital‐to‐analog‐signal conversion that produces a 0–5 V output at a rate up to 40 Hz. The device was paired with an acoustic Doppler velocimeter. The combined meter and fiber‐optic O2 sensor's response time was significantly faster in O2‐undersaturated water compared to in O2‐supersaturated water (0.087 vs. 0.12 s), but still sufficiently fast for aquatic eddy covariance measurements. The O2 optode signal was not sensitive to variations in water flow or light exposure. However, the response time was affected by the direction of the flow. When the sensor tip was exposed to a flow from the back rather than the front, the response time increased by 37%. The meter's internal signal processing time was determined to be ~ 0.05 s, a delay that can be corrected for during postprocessing. In order for the built‐in temperature correction to be accurate, the meter should always be submerged with the fiber‐optic sensor. In multiple 21–47 h field tests, the system recorded consistently high‐quality, low‐noise O2 flux data. Overall, the new meter is a powerful option for collecting robust aquatic eddy covariance data.