HR: 0800h
AN: OS41D-0514    [Abstracts]
TI: Sedimentary Particle Transport During an Upwelling Event - A Case Study from the Namibian Passive Margin
AU: * Seyferth, M
EM: mseyferth@uni-bremen.de
AF: RCOM, University of Bremen, PO Box 330440, Bremen, 28334 Germany
AU: Huhn, K
EM: khuhn@uni-bremen.de
AF: RCOM, University of Bremen, PO Box 330440, Bremen, 28334 Germany
AU: Paul, A
EM: apau@palmod.uni-bremen.de
AF: RCOM, University of Bremen, PO Box 330440, Bremen, 28334 Germany
AB: Upwelling events are accompanied by a complex interplay of erosion, transport, and deposition of sedimentary particles. The characteristics of individual transport paths are controlled by the physical properties of the respective particle (grain size, shape, and density), the location and time of its release and the water velocity field, which is, in turn, dependent on the seafloor topography and the oceanographic boundary conditions. In this study, we combine velocity data provided by ROMS circulation models with lagrangian particle tracing techniques to detect key parameters controlling the respective transport patterns. The model geometry mimics a two-dimensional bathymetric profile from the passive continental margin offshore Namibia. Each model run describes a five day upwelling event driven by increased surface wind stress and the subsequent period of relaxation under mean wind stress conditions. Background circulation is roughly re-established 10 days after the drop of driving wind forces. Based on the calculated velocity fields transport paths of a large number of lagrangian tracers are calculated, which are released at variable times and positions relative to the shoreline either at the sea surface or bottom. Since water currents are directed offshore at the surface and landwards near the bottom, particles inserted a the surface typically traverse different currents during their gravitational settling. Thereby, rapidly sinking or early released tracers experience a net landward transport, whereas slowly sinking or lately relased particles undergo an overall offshore transport. In addition, there are prominent lateral variations in the shape of particle paths. Surface source tracers from the shelf area tend to show an overall landward offset, while those emitted outside the shelf break are uniformly transported offshore. Near the coast, clay and fine silt particles mobilized from the bottom sources are transported onshore and to some extent backwards into the open ocean driven by the surface current. Modified model runs simulating the situation at the LGM with a significantly diminished shelf indicate transport of particles from the continental slope landwards onto the shelf.
DE: 4255 Numerical modeling
DE: 4279 Upwelling and convergences
DE: 4532 General circulation
DE: 4558 Sediment transport
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting