CENTENNIAL-SCALE IMPACTS OF MELTWATER PULSES ON PERIODICALLY RETREATING BARRIER ISLANDS

In many locations around the world, continental shelves preserve evidence of ancient barrier islands in the form of ‘overstepped’ deposits, or portions of the lower shoreface and/or backbarrier platform stranded on the seabed during transgression. Until recently, it was assumed that such deposits were entirely allogenic in origin, recording the response of barriers to rapid increases in rates of sea-level rise associated with glacial meltwater pulses during the early Holocene. Modeling using a cross-shore morphodynamic framework has shown that these deposits can also be created by barriers experiencing alternating periods of aggradation and transgression in response to lags between shoreface and overwash fluxes. In this investigation, we model the interaction of a centennial-scale, variable-magnitude sea-level pulse with a periodically retreating barrier to demonstrate novel depositional and retreat responses. Our results show the pulse magnitude and its timing as it interacts with the barrier’s autogenic periodicity can lead to either amplification or suppression of overstepped deposits, with corresponding episodes of enhanced aggradation or rapid migration. In some cases, the barrier’s geometry and balance of fluxes can predispose the system to complete drowning (loss of subaerial barrier profile), including for rates of rise similar to observed in modern coastal systems. While we do not model specific real-world examples, insights from this investigation may be a first step towards interpreting autogenic periodicity and retreat state in ancient barriers subjected to past sea-level pulses. This could prove invaluable to studies of modern systems, which lack historical context to infer the centennial-scale impacts of enhanced sea-level rise.