Seminar: Dr. Antonio Rodriguez, UNC Institute of Marine Sciences

UNC Marine Sciences’ is proud to host a seminar by Antonio Rodriguez, Ph.D.

Presenter Affiliation: University of North Carolina, Institute of Marine Sciences

Title: Impacts of Accelerated Sea-Level Rise, Storms, and Development on Barrier-Island Landscapes and Carbon Reservoirs

Abstract: Barrier islands migrate landward with rising sea level primarily through overwash transport of sand from the beach across the barrier where it is deposited as ephemeral flood-tidal deltas and washover fans (barrier rollover).  Salt marsh subsequently colonizes back-barrier sandflats, accumulating carbon in their rapidly-accreting sediment.  Storminess, the rate of sea-level rise, barrier-island setting, and development impact rates of barrier rollover and the function of the barrier as a carbon sink.  We present a carbon-budget model for transgressive barrier islands that includes a dynamic carbon-storage term, driven by back-barrier-marsh width, and a carbon-export term, driven by ocean and back-barrier shoreline erosion.  Shoreline erosion and burial of back-barrier marsh from washover deposition and development can temporarily transition a barrier into a net exporter (source) of carbon.  At the end of the 19^th century, there was a three-fold increase in the rate of sea-level rise and the geologic record from Onslow Beach, NC, a transgressive barrier island, shows that the number and landward extent of washover deposits increased abruptly.  The change in washover deposition was likely caused by an increase in the rate of island transgression associated with island narrowing through landward movement of the ocean shoreline and decreased elevation of the island through dune erosion, not increased storminess.  Washover deposits are commonly interpreted as event beds, representing discrete storm events; however, our data show that washover deposition can be a continual process, especially when initiated across narrow transgressive barrier islands.  With progressive narrowing of the back-barrier marsh, barriers will begin to function more persistently as carbon sources until the reservoir is depleted at the point where the barrier welds with the mainland.  Undeveloped barrier islands with wide lagoons are carbon sources briefly during erosive periods; however, at century time scales are net carbon importers (sinks) because new marsh habitat can form during barrier rollover. Human development on backbarrier saltmarsh serves to reduce the carbon storage capacity and can hasten the transition of an island from a sink to a source.

Rodriguez Lab Website Link