NEW PERSPECTIVES ON THE HOLOCENE EVOLUTION OF THE NORTH CAROLINA OUTER BANKS BARRIER ISLAND AND ESTUARINE/LAGOON SYSTEM

The NSF-funded Coastal Hydrodynamics and Natural Geologic Evolution (CHaNGE) Program has produced a multi-disciplinary dataset that is used to reconstruct the mid- to late-Holocene evolution of the North Carolina Outer Banks barrier islands and associated estuaries (e.g., Pamlico Sound). Data used to develop this new understanding include geophysics (seismic and ground-penetrating radar), sedimentology and lithostratigraphy, micropaleontology, magnetic susceptibility, hydrodynamic modeling, and organic, isotopic, and elemental geochemistry. These data illustrate the dynamic nature of this system, and responses to relative sea-level (RSL) rise, geomorphic change, and North Atlantic basin-wide meteorological and oceanographic processes. In summary, the coastal system evolved via rapid flooding of incised valleys during Termination 1, with sea level overtopping the most seaward Pleistocene interfluves by ca. 5000 cal y BP. Initial rapid transgression and ravinement occurred, producing a shoreline several km west of the modern oceanic shoreline by ca. 4000 cal y BP, followed by progradation during a period of very slow sea-level rise or still-stand. Eroded remnants of a normal regressive systems tract are now buried beneath the modern Outer Banks in some locations, but are exposed at Kitty Hawk as a ridge and swale morphology. The estuaries experienced periods of rapid change to salinity structure, tides and currents, and sedimentation patterns in response to geomorphic changes to the barrier islands, driven by sea-level change and storm conditions. Normal marine salinity conditions occurred locally in Pamlico Sound during rapid flooding at ca. 4000 cal yBP, and again, but more widespread, between ca. 1200 to 550 cal yBP likely in response to intense hurricane activity and accelerated RSL rise during the Medieval Climate Anomaly (MCA). MCA conditions created very wide shoals and inlets with increased fluxes between the estuary and ocean compared to the present day system. The modern transgressive system has developed over the last several hundred years, and is now approaching a threshold where hurricane impacts and recently accelerated sea-level rise may cause extensive geomorphic changes to the barrier islands, impacting the estuaries, and resulting in conditions similar to those during the MCA.