Evaluation of Coastal Response to Sea-Level Rise from Holocene Stratigraphic Records: A Step Towards Coastal Forecasting

University Of Alabama Tuscaloosa, Tuscaloosa AL

Investigators

Abstract

Abstract Evaluation of Coastal Response to Sea-Level Rise from Holocene Stratigraphic Records: A Step Towards Coastal Forecasting Antonio Rodriguez and John B. Anderson The consensus of the Intergovernmental Panel on Climate Change was that the rate of sea-level rise will increase in the future as a result of global warming. An increased rate of sea-level rise will have a number of adverse impacts on world coasts, such as wetlands loss and accelerated coastal erosion, but the magnitude of these changes remains unpredictable. Predictions of coastal response to future sea-level rise rates should be improved by examining the geological record of coastal change during the Holocene, when sea level was rising at rates similar to future predictions. The best records of coastal response to rising sea level are found in incised fluvial valleys. Incised valley fill from three Gulf of Mexico bays, specifically Mobile Bay, Galveston Bay, and Corpus Christi Bay will be examined and compared. These bays are located within differing climatic belts, and are fed by morphologically distinct fluvial systems. Preliminary data from all three bays has identified an episode of rapid shoreline retreat that occurred during the Holocene. In Galveston Bay, this event resulted in the estuarine environment being shifted tens of kilometers landward and the barrier shoreline being submerged and stranded on the continental shelf as a bank (Heald Bank). The hypothesis is that variations in the rate of coastal subsidence and river discharge were not the cause of the observed coastal backstepping events. The hypothesis will by tested by collecting high-resolution seismic, sediment core (up to 30 m-long cores), and paleontologic data from each bay to identify flooding surfaces. Radiocarbon age dates obtained from plant fragments and articulated mollusks sampled at numerous locations above and below the entire dip axis of flooding surfaces within each bay will constrain the timing of the events and the rates of coastal change. Correlation of flooding surfaces between the bays, together with calculations of sedimentation and compaction rates and the generation of sea-level curves from basal peat deposits, will aid in distinguishing variations in climate and subsidence from sea-level events. This work will help quantify coastal response to forcing mechanisms, and will create data sets appropriate for testing coastal forecasting models by hindcasting.