Abstract
Abstract. 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.
Highlights
The significant role of sediments in the marine cycles of matter (Walsh, 1988; Johnson et al, 1999; Jahnke, 2010; Bauer et al, 2013) emphasizes the need for reliable benthic flux data
Where currents and benthic photosynthesis influence interfacial flux at the seafloor, the aquatic eddy covariance technique is a preferred tool for determining benthic oxygen fluxes, as it permits flux measurements with minimal disturbance of bottom flow and light
The goals of this study were (1) to develop an eddy covariance instrument with dual optodes that through parallel oxygen measurements allows improved quality control of the oxygen data and thereby more reliable oxygen fluxes, (2) to develop a data evaluation procedure for the dual optode eddy covariance data sets that helps in identifying compromised optode signals, and (3) to demonstrate the performance of this instrument through deployment in an inner shelf environment with dynamic changes in sediment–water flux
Summary
The significant role of sediments in the marine cycles of matter (Walsh, 1988; Johnson et al, 1999; Jahnke, 2010; Bauer et al, 2013) emphasizes the need for reliable benthic flux data. Where currents and benthic photosynthesis influence interfacial flux at the seafloor, the aquatic eddy covariance technique is a preferred tool for determining benthic oxygen fluxes, as it permits flux measurements with minimal disturbance of bottom flow and light. This technique derives vertical oxygen flux from time series of rapid simultaneous measurements of vertical flow velocity changes and associated oxygen changes at a fixed point above the sediment surface. The microelectrodes typically used for these measurements (sensor tip
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