Estimating long-term coastal cliff retreat using cosmogenic nuclides: Development of a user-friendly inversion tool

Cosmogenic isotope dating of rock samples taken from shore platforms is the only dating method for reconstructing the long-term evolution (centuries to millennia) of fully erosional rock coasts. Two techniques can be used: the first is based on the collection of samples on the platform and the distribution of their cosmogenic isotope concentrations over a transect perpendicular to the shoreline (e.g. Regard et al., 2012; Hurst et al., 2016; Swirad et al., 2020); the second, which is limited to low rates of recession, is implemented by measuring cosmogenic isotope concentrations in the colluvium at the foot of the cliff (Bossis et al., 2024). Here we focus on the first technique which involves fitting the distribution of observed concentrations to a model. This model allows the cliff retreat rate to be constant or variable over the Holocene, and shore platform either to erode in concert with the cliff retreat (steady state model) or to widen through time. The simple inversion model is as widely usable as possible and allows a quick, easy, robust and standardised calculation of exposure ages based on information such as cosmogenic isotope concentrations, present topography and relative sea level change.

 

References

Bossis, R., Regard, V., Carretier, S., and Choy, S., 2024, Evidence of slow millennial cliff retreat rates using cosmogenic nuclides in coastal colluvium: EGUsphere, p. 1–15, doi:10.5194/egusphere-2023-3020.

Hurst, M.D., Rood, D.H., Ellis, M.A., Anderson, R.S., and Dornbusch, U., 2016, Recent acceleration in coastal cliff retreat rates on the south coast of Great Britain: Proceedings of the National Academy of Sciences, v. 113, p. 13336–13341, doi:10.1073/pnas.1613044113.

Regard, V., Dewez, T., Bourlès, D.L., Anderson, R.S., Duperret, A., Costa, S., Leanni, L., Lasseur, E., Pedoja, K., and Maillet, G.M., 2012, Late Holocene seacliff retreat recorded by 10Be profiles across a coastal platform: Theory and example from the English Channel: Quaternary Geochronology, v. 11, p. 87–97, doi:10.1016/j.quageo.2012.02.027.

Swirad, Z.M., Rosser, N.J., Brain, M.J., Rood, D.H., Hurst, M.D., Wilcken, K.M., and Barlow, J., 2020, Cosmogenic exposure dating reveals limited long-term variability in erosion of a rocky coastline: Nature Communications, v. 11, p. 3804, doi:10.1038/s41467-020-17611-9.