Technical note: Measurements and data analysis of sediment–water oxygen flux using a new dual-optode eddy covariance instrument

• Published in: Biogeosciences Vol. 17; no. 17; pp. 4459 - 4476
• Main Authors: Huettel, Markus, Berg, Peter, Merikhi, Alireza
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 07.09.2020; Copernicus Publications
• Subjects: Advection; Analysis; Benthos; Biofouling; Calibration; Carbonates; Covariance; Data; Data analysis; Data loss; Data processing; Deployment; Dissolved oxygen; Eddy covariance; Flow velocity; Fluctuations; Fluxes; Frequency variation; Information management; Instruments; Mapping; Measuring instruments; Mineralization; Ocean floor; Organic carbon; Oxygen; Oxygen probes; Sediments; Sediments (Geology); Sensors; Short-term changes; Snow; Stainless steel; Vertical velocities; Vortices; Water circulation; Water column
• ISSN: 1726-4189; 1726-4170; 1726-4189
• DOI: 10.5194/bg-17-4459-2020

Sediment–water oxygen fluxes are widely used as a proxy for organic carbon production and mineralization at the seafloor. In situ fluxes can be measured non-invasively with the aquatic eddy covariance technique, but a critical requirement is that the sensors of the instrument are able to correctly capture the high-frequency variations in dissolved oxygen concentration and vertical velocity. Even small changes in sensor characteristics during deployment as caused, e.g. by biofouling can result in erroneous flux data. Here we present a dual-optode eddy covariance instrument (2OEC) with two fast oxygen fibre sensors and document how erroneous flux interpretations and data loss can effectively be reduced by this hardware and a new data analysis approach. With deployments over a carbonate sandy sediment in the Florida Keys and comparison with parallel benthic advection chamber incubations, we demonstrate the improved data quality and data reliability facilitated by the instrument and associated data processing. Short-term changes in flux that are dubious in measurements with single oxygen sensor instruments can be confirmed or rejected with the 2OEC and in our deployments provided new insights into the temporal dynamics of benthic oxygen flux in permeable carbonate sands. Under steady conditions, representative benthic flux data can be generated with the 2OEC within a couple of hours, making this technique suitable for mapping sediment–water, intra-water column, or atmosphere–water fluxes.