Oxygen production and consumption of permeable carbonate reef sands measured with a new dual-optode eddy covariance instrument

Abstract:

Sediment-water oxygen fluxes are widely used as a proxy for organic carbon production and mineralization at the seafloor. In nearshore and shelf environments, light penetration to the seafloor and strong bottom currents can significantly modulate these fluxes through benthic photosynthesis and by driving advective pore water exchange in permeable sand sediments. Carbonate sands are an integral part of coral reef ecosystems but their role in the cycles of matter in the reef is poorly quantified. We deployed a non-invasive aquatic dual-optode eddy covariance instrument in a backreef sand flat in the Florida Keys Reef Tract. The measurements of the instrument took the effects of light, bottom flows and patchiness of interfacial exchange into account, and thereby produced oxygen flux data that can be used to estimate realistic organic carbon production and mineralization rates for this dynamic environment. The deployments revealed high primary production, prompt responses of interfacial fluxes to changes in the bottom currents, and substantial mineralization activity in the carbonate sands at 10 m water depth.