Measurement of Oxygen Uptake from Marine Sediments by Eddy Correlation

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ABSTRACTOCE-0221259Oxygen transport into sediments in natural marine environments is mediated by the turbulent transport scales of motion of the bulk overlying solution, molecular diffusion being orders of magnitude slower and a virtually insignificant term. The oxygen consumption by sediments, conventionally quantified by either laboratory measurements on recovered cores or by the artifice of an in-situ enclosure experiment, is a key parameter in assessing organic matter decomposition rates and also controls the oxidation of sediment reductants such as NH4+, Mn2+, Fe2+, HS-, FeS etc produced during anaerobic respiration. Ventilation and irrigation of sedimentary layers either by wave induced pumping or bioturbation activity are also processes that could potentially be quantified by more reliable measurements of sediment O2 uptake.This proposal will extend and explore a recently suggested approach being jointly developed by the PI together with colleagues at the Max Planck Institute for Marine Microbiology (Bremen). The technique involves correlating the time varying concentration of dissolved oxygen, measured by fast response microelectrodes, in the sediment boundary layer within a few cm of that surface with locally sensed vertical velocity components also sampled at high frequency by acoustic Doppler velocimetry (ADV). An eddy correlation approach has direct analogues with similar techniques that are used by atmospheric scientists measuring scalar (e.g. heat, moisture (momentum) and trace gas) fluxes in the planetary boundary layer. Theoretical and practical considerations for the adaptation of the basic approach into aquatic systems are discussed and will be explored at shallow coastal field sites in Denmark (Aarhus Bay).