NEW INSIGHTS INTO THE COUPLED INFLUENCE OF ANTECEDENT GEOLOGY AND SEA-LEVEL RISE ON BARRIER-ISLAND DYNAMICS

For at least a decade, field sedimentologists and coastal modelers have been working in parallel to better quantify the mechanisms underpinning barrier-island response to coastal change. There has been a robust exchange of insights, but inadequate integration of approaches, especially at the mesoscale and longer timeframes. Building upon past modeling and field studies, we bridge that gap by pairing a robust database of detailed field stratigraphy with morphodynamic modeling of four Holocene barrier islands along the US East Coast to explore the interplay between relative sea-level rise and antecedent geology on barrier-island behavior. Our results show antecedent substrate slope plays a central role in barrier morphodynamic behavior. Migration across a subaqueous backbarrier ridge (e.g., coastal barrier or dune deposits from earlier sea-level highstands) can cause a succession of phase changes in a modern island. For example, our case studies illustrate the steep slopes and decreased backbarrier accommodation associated with antecedent highs greater than 3 m in profile elevation can greatly reduce island migration rates, effectively “pinning” the island in place even with sea-level rise rates up to 6 mm/yr. However, once the island migrates over this antecedent high, backbarrier accommodation increases, leading to enhanced overwash fluxes, more rapid landward migration, and possible drowning. Our novel, integrated field observation and numerical modeling approach to studying barrier-island dynamics at the mesoscale yields a new conceptual model of antecedent geologic control on long-term barrier evolution.