Abstract
Impacts from a changing climate, in particular sea-level rise, will be most acutely felt on small oceanic islands. A common configuration of mid-latitude islands is the sandy barrier island. Sable Island, Nova Scotia, Canada is a vegetated sand island near the shelf edge, 160 km from the nearest point of land, that is morphologically similar to a barrier island. This study uses 60 years of airphoto records to analyse changes in coastline position through digitized shore and vegetation (foredune proxy) lines. Rates of coastal movement are analysed to model the future (2039) coastal configuration. The analyses suggest that the majority of the coastline on Sable Island is in retreat, with net retreat on the south side of the island only partially offset by modest net advance on the north side. The different morphologies of the beach–dune systems of South Beach and North Beach, driven by incident wind and waves, yield these different coastline responses. Projected loss of 10 ha by 2039 of the climax heath vegetative community to shoreline retreat suggests a trend toward island instability due to coastline migration. Island-wide data set trends show support for two different but complementary hypotheses about whole-island evolution: (1) the island is mobile via bank migration driving southern coastline changes and experiencing sediment transport toward the east, or (2) the island is generally immobile and losing subaerial sediments (and thus shrinking) likely due to ongoing (and accelerating) sea-level rise.
Highlights
Small oceanic islands are important scaled-down indicators of coastal change driven by changing ocean dynamics
This dynamic stability can be influenced by a broad range of factors, including geologic, ecologic, climatic/oceanographic, and anthropogenic(Moore et al 2014; Walters et al 2014; Vinent and Moore 2015; Fruergaard and Kroon 2016; Miselis and Lorenzo-Trueba 2017; Houser et al 2018; Shim and Kim 2018; Wernette et al 2018; Zinnert et al 2018; Nienhuis and Lorenzo-Trueba 2019)
Coastlines have been highly dynamic along Sable Island since 1959
Summary
Small oceanic islands are important scaled-down indicators of coastal change driven by changing ocean dynamics. With adequate sediment supply and accommodation room, barrier islands can persist through large changes in sea level over thousands of years (Raff et al 2018). This dynamic stability can be influenced by a broad range of factors, including geologic (e.g., underlying bedrock geology, foredune connectivity, and surrounding substrate), ecologic (e.g., vegetation assemblage and backbarrier marsh/island interaction), climatic/oceanographic (e.g., tidal range and inlet configuration, storms, and SLR), and anthropogenic (e.g., urbanization and dredging)(Moore et al 2014; Walters et al 2014; Vinent and Moore 2015; Fruergaard and Kroon 2016; Miselis and Lorenzo-
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