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

The aquatic eddy covariance technique is increasingly used to determine oxygen (O-2) fluxes over benthic ecosystems. The technique uses O-2 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 O-2 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 O-2 sensor's response time was significantly faster in O-2-undersaturated water compared to in O-2-supersaturated water (0.087 vs. 0.12 s), but still sufficiently fast for aquatic eddy covariance measurements. The O-2 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 similar to 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 O-2 flux data. Overall, the new meter is a powerful option for collecting robust aquatic eddy covariance data.

Automated summary

This study evaluates a new optical submersible O-2 meter equipped with an ultra-high-speed optical fiber sensor for aquatic eddy covariance measurements. The meter, paired with an acoustic Doppler velocimeter, has a fast response time and can measure in both O-2-undersaturated and O-2-supersaturated water, recording high-quality, low-noise O-2 flux data.