COASTAL HYDRODYNAMICS AND NATURAL GEOLOGICAL EVOLUTION (CHANGE) PART 1: GEOLOGICAL INDICATORS OF RAPID CLIMATE CHANGE IN ESTUARINE SYSTEMS DURING THE HOLOCENE

The NSF-funded CHaNGE project is contributing to an understanding of barrier island and estuarine dynamics associated with periods of rapid climate change. The project is utilizing geological data from sediments of Pamlico Sound, North Carolina, to define signatures associated with major episodes of barrier-island segmentation thought to occur during the Medieval Climate Anomaly (MCA, 950–1250 CE), the Little Ice Age (LIA, 1400–1700 CE), and other periods of rapid climate change. Data include: sediment grain-size, C and O isotopes of foraminifera, foraminiferal biofacies, bulk magnetic susceptibility, high-resolution chirp seismic, inorganic (elemental) and organic (total organic carbon (TOC), total nitrogen (TN), and their isotopic signatures) geochemistry, and radiocarbon ages. Geomorphic reconstructions based on geological evidence are also being used to define bathymetric grids and numerically model the hydrodynamics of the system during specific time intervals. Modern analogues are used to interpret geological and geochemical data and reconstruct paleoenvironments. The geological data indicate greater marine influence at ca. 4000, 2500, and 1200 Cal BP. For instance, during the MCA, an abrupt depositional change occurred in Pamlico Sound. This event is marked by more marine biofacies, a negative magnetic susceptibility excursion, a drop in Al content, a prominent seismic reflection, and a positive C isotope shift (both carbonates and TOC). These data can be correlated along a SW to NE transect in the Sound which indicate a high degree of barrier island segmentation and increased marine influence, with higher tidal and/or wave energy within the system. The hydrodynamic model results are consistent with the geologic interpretation, suggesting an increase in tidal range and stronger currents. A similar approach is used to identify the events at ca. 4000, 2500 Cal BP, and LIA, providing a greater understanding of coastal evolution due to climatic changes.