Barachois Evolution in the Bras d’Or Lakes Under Past, Present and Future Sea-Level Rise

English Abstract:

Barrier beaches enclosing small ponds and lagoons (known locally as ‘barachois’) comprise ~12% of the Bras d’Or Lakes (BDL) shoreline in Cape Breton, Nova Scotia. Many of these barriers have been developed into harbours, roads and recreational areas. Well-preserved, drowned coastal landforms observed up to 25 m below mean sea level in the BDL that date to the early/mid Holocene may be an indication of things to come for the modern barriers, especially given the forecasted acceleration in relative sea-level rise for this region over the next 100 years. Any increase in storm frequency and/or intensity combined with the ongoing decrease in sea ice will accelerate this process. Likewise, if shoreline development that results in hardening persists, sediment supply to coastal barriers may be cut off in some areas, increasing the likelihood of barrier erosion and drowning. A basic understanding of the age of the barachois, including the nature of the sediments underlying them and the geodynamics of the barriers (i.e., how quickly they evolve from growing or stable phases to landward-migrating or submerging phases) is required to provide baseline data with which modern and future coastal dynamics may be compared. Results of sea floor mapping (shallow seismic and side-scan sonar) and preliminary analyses of six sediment cores extracted from three ponds in the BDL, including micro- and macro-fossils, grain-size and radiocarbon dated organic matter, will be presented.