Preservation Potential of Hurricane Signatures in Mississippi Bight: Observations and Model Hindcasts

The consequences of multiple event bed deposition are being studied using radiometric estimates of bioturbation and accumulation from cores and a three-dimensional numerical sediment resuspension and transport model. The focus area is near Ship Island, Mississippi. Two historical hurricanes are being evaluated: an unnamed category 4 hurricane in 1947 and Hurricane Camille from 1969 (category 5). In cores collected from the region, fine-scale stratigraphy was evaluated using Pb-210/Cs-137 geochronology, X-radiography, granulometry, and a multi-sensor core logger. The most widespread preserved event layer was probably produced by Hurricane Camille (Category 5) in 1969, although multiple event layers (four other major storms in the past century) are locally preserved. There were no major storms between 1947 and 1969, however, so any modification of the 1947 event bed probably resulted from bioturbation and Hurricane Camille. The preserved event layers (3-10 cm thick) represent only the basal portions of beds that were significantly thicker when created. The estimated initial thickness (10-17cm) of preserved layers implies that hurricanes represent a source of new sediment to the depositional system in addition to reworking the bottom. Physical and biological post-depositional processes produced regional discontinuity and localized truncation of event layers, thus resulting in an imperfect and biased record of sedimentary processes. The storm wind field is computed using a parametric cyclone model. The storm waves are calculated using the SWAN third-generation wave model. Storm currents are simulated using the ADCIRC 2D finite-element model and the Princeton Ocean Model. Sediment resuspension is calculated using a stratified wave-current bottom boundary layer model on a 1 km grid. The sedimentation model calculates resuspension and advection of sediment. The results from both storms show an event bed that is locally more than 0.5 m thick on the Gulf side of the barrier islands where storm waves were largest. The predicted storm beds for the two storms are stacked using the maximum resuspension depth and final bed elevation for each. Inter-storm deposition of fine sediment and biogenic bed destruction are simulated using rates and depths estimated from radiometric and sedimentological data. The resulting synthetic stratigraphy is similar in profile to the cores but shows horizontal variability that was not sampled by the limited number of observations.