Historic and Geologic Sea Level Change in Winyah Bay, SC

Madison Fink, Coastal Carolina University, Coastal and Marine Systems Science, Conway, SC, United States, Till Jens Joerg Hanebuth, Geological Survey of Canada, Sidney, BC, Canada, Stefan A Talke, California State Polytechnic University, San Luis Obispo, Civil and Environmental Engineering, San Luis Obispo, SC, United States and Andrea Hawkes, University of North Carolina at Wilmington, Earth and Ocean Sciences, Wilmington, NC, United States
Abstract:
The study of historic regional sea level variability has important implications for understanding ongoing and future changes in sea level. This knowledge is essential in regards to multiple potential impacts on coastal areas that rely heavily on waterfront activities – socio-economically, culturally, and ecologically. The site of this project, Georgetown County, South Carolina is widely exposed to these issues, but the regional sea level dynamics are widely unknown.

This research project follows a two-line approach with the aim of producing the first robust sea level record for the Georgetown region. Hand-written historic tide gauge data from Georgetown Lighthouse were documented for the years 1899 to 1904. These documents were recovered from the US National Archives, digitized and referred to the original benchmark used as its vertical reference. We also installed a water-level logger at the lighthouse dock in October 2018 to monitor the modern water level variations. The historic and the current gauge data will be vertically related and compared in detail in order to calculate the overall change in sea level over the past 120 years.

Sea level history is contemporaneously reconstructed using intertidal marsh foraminifera assemblages in sediment cores from local marshes. Three cores were taken in vicinity to the Winyah Bay mouth where historic maps and aerial photos documented the exact timing of marsh progradation over the past 120 years, particularly in the second half of the 20th century. These cores are analyzed using foraminiferal assemblage identification and statistics in combination with Pb/Cs dating and regional traces metal stratigraphy.

The preliminary results will describe how relative sea level has changed from 1899 until today as well as compare tidal statistics and annual sea level variations between the historic and modern records. The data currently suggests a rate of sea level rise at least comparable if not exceeding that of Charleston, SC.