Master of Science (M.Sc.)
Virginia Institute of Marine Science
A sediment transport model within the Regional Ocean Modeling System (ROMS) was used to examine how repeated cycles of deposition, erosion, and bioturbation influence flood and storm event bed character offshore of a significant fluvial source. Short-lived radioisotopes Beryllium-7 (7Be) and Thorium-234 (234Th) can be used as tracers of deposition and reworking on the continental shelf, and modeled profiles of these radioisotopes, along with simulated profiles of sediment bed grain size distributions, were analyzed for various model runs.The presence of an atmospherically derived radionuclide,7Be, in seafloor sedimentindicates terrestrial (riverine derived) sediment deposition offshore of a fluvial source.In contrast,234Th naturally occurs in seawater through the decay of its generally conservative parent, 238U, and its presence in the seabed indicates the recent suspension of sediment in oceanographic water. Simulated profiles of 7Be and 234Th weredirectly related to the flood and storm sequences used as model input.The model results showedthat the radioisotopic profiles are sensitive to the timing of 7Be input, phasing of wave and current energy, and intensity of bioturbation; complicating the relationship between simulated profiles andmodel input of flood and hydrodynamic forcing. Sediment grain size and geochronological tracers were used as markers of event beds for flood and storm deposition scenarios.
© The Author
Birchler, Justin J., "Sediment Deposition and Reworking: A Modeling Study using Isotopically Tagged Sediment Classes" (2014). Dissertations, Theses, and Masters Projects. Paper 1539617950.