LARGE-SCALE COASTAL BEHAVIOR OF A BARRIER FRONTED COASTLINE IN RESPONSE TO HOLOCENE SEA-LEVEL RISE AND STORM IMPACTS

An NSF-funded investigation designated CHaNGE (Coastal Hydrodynamics and Natural Geologic Evolution) is defining the Holocene evolution of the Pamlico Sound estuarine region and Outer Banks barrier islands in response to storm impacts, sea-level rise, and geomorphic changes. The investigation lays the foundation for understanding future changes to the system, and other similar coastal systems, as sea-level rise accelerates and hurricane intensity increases. Working hypotheses include 1) that the system records rapid changes related to regional climate and sea-level changes, and 2) the hydrodynamics (tides and currents) may change rapidly in response to barrier segmentation associated with periods of rapid sea-level rise or major storm impacts. Data being used to test hypotheses include geophysical data (seismic and ground penetrating radar), lithofacies and sedimentological data, micropaleontological data, organic and inorganic (including stable isotopes) geochemical data, and radiocarbon data. The hypothesis that tidal amplitude may increase in response to barrier segmentation is supported by the occurrence and distribution of normal marine salinity foraminiferal assemblages within the Sound dating to ca. 4.1-3.7 ka, and 1.2-0.5 ka, as outlined in previous studies. New cores and seismic data show that tidalite deposits occur in tidal channels embedded within the Holocene section of the Pamlico Sound. These tidalite units are characterized by oblique clinoform deposits filling tidal channels and consisting of laminated muds and sands. Data further show that channels occur in regions of previously proposed barrier collapse, and are scoured to a maximum depth of 20 m below sea-level. These data corroborate the hypothesis of increased tidal range and current activity linked to barrier island geomorphology and estuarine paleobathymetry. Radiocarbon ages of these tidalites are pending and will be compared to the record of barrier island change and regional to global climate patterns. Hydrodynamic models of tidal water level elevations and currents using paleobathymetric and geomorphic reconstructions as input, are consistent with the geological findings. Models suggest high energy currents in excess of 0.5 m/s in regions of proposed barrier collapse and newly found tidal channel locations.