The role of bottom boundary turbulence for the transport of tracers in marine basins (ROBOTRACE)

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The main objective of this proposal is to identify, analyse, and quantify the physical processes contributing to the exchange of dissolved substances between the sediment-water interface, the turbulent BBL (bottom boundary layer), and the weakly turbulent interior of stratified basins. The focus will be on the effect of sloping topography, where the exchange is complicated by the interplay between BBL restratification, BBL turbulence, and sub-mesoscale processes that are assumed to determine the lateral exchange of fluid between the BBL and the interior. These processes will be investigated here with a combined experimental and numerical modelling approach. More specifically, the project will focus on the sediment-water exchange processes of oxygen and sulphide, which will be measured in situ by an eddy-correlation and a microprofiling system. These measurements will be accompanied by a set of standard oceanographic instrumentation as well as ship- and mooring-based turbulent measurements, creating a novel dataset of (A) sediment-water fluxes of oxygen/sulphide with (B) turbulence measurements within the BBL and the interior water column. In addition to the in situ measurements a numerical investigation will be based on an implementation of a simplified sediment model in combination with a parameterisation of the transport processes across the sediment-water interface. This model will be used in idealised one-dimensional parameter studies as well as in a two-dimensional BBL exchange setup at a sloping topography. Also a fully three-dimensional realistic model of the central Baltic Sea will be setup and used to investigate the role of three-dimensional features as eddies on the transport of oxygen/sulphide.