Sedimentary Coastal Cliff Erosion in Greenland

Climate change will increase the duration of annual sea-ice-free periods and shift precipitation patterns across the Arctic. Those factors are likely to increase erosion rates along its coasts. Large parts of the Arctic coast consist of hard rock. However, glacial, deltaic, and coastal sedimentary deposits occur in deglaciated areas and isostatic uplift following glaciations has created beach ridge plains and pocket beaches with coarse soft-sediment cliffs. Hitherto, very little was known about the spatial distribution, erosion rates, and morphodynamics of soft sediment cliffs along the coast of Greenland. Here, we investigate a 3-km sedimentary cliff section on the south coast of Qeqertarsuaq (Disko Island). We measured 2D cliff top erosion over 50 years between 1964 and 2014 as well as 3D cliff profile change over 2 years between 2019 and 2021. Morphometric indices of the gravel beach and cliff were calculated based on a series of cross-shore elevation profiles. Wave run-up at the beach fronting the cliff was modeled with XBeach-G for a series of storm events under present day sea-ice conditions and for a reduced sea-ice scenario. Cliff top erosion rates varied along the cliff with maximum rates of 0.3 m y(-1). The investigated coastal cliff erodes by two coupled processes: (a) precipitation-driven surface runoff downslope the cliff and (b) wave-driven erosion at the cliff toe. In a continuously warming climate, this study shows that erosion of soft coastal cliffs in Greenland thus can accelerate due to increased storminess and prolonging open water periods.