Barrier shoreline evolution constrained by shoreface sediment reservoir and substrate control: The Miquelon-Langlade Barrier, NW Atlantic

The Saint-Pierre-et-Miquelon Archipelago (France) is located in the NW Atlantic Ocean, proximal to the Cabot Straight outlet of the Gulf of Saint-Lawrence, and 50 km south of Newfoundland (Canada). The Miquelon-Langlade Barrier is a 12-km-long, 100-2500-m-wide, north-south oriented isthmus connecting two bedrock islands (Miquelon to the north; Langlade to the south). This study aims to improve our understanding of shoreface-shoreline sediment exchange processes by comparing medium-term (1949-2011) shoreline changes, determined from aerial photographs and differential GPS data, with total shoreface sediment reservoir volumes estimated using seismic along the west coast of the Miquelon-Langlade Barrier. Spatial variability between the northern and southern sectors of the study site are seen both in the volumes of shoreface sedimentary reservoirs and in multi-decadal shifts of the shoreline position. The northern region has the lowest shoreface sediment volume and the highest rate of shoreline retrogradation. By contrast, the center and southern regions contain the largest volume of sediment in the shoreface and have demonstrated either long-term stability or progradation. This study demonstrates the primary roles of geological control and the distribution of shoreface sediments in local shoreline change at multi-decadal time scales. The sedimentary reservoir, in conjunction with shoreline-monitoring studies and knowledge of transport patterns, may provide a good alternative proxy.