Browsing by Author "Piggott, MD"

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    Multi-objective optimisation of a rock coast evolution model with cosmogenic 10Be analysis for the quantification of long-term cliff retreat rates
    (American Geophysical Union (AGU), 2021-12-15) Shadrick, J; Hurst, MD; Rood, DH; Piggott, MD; Wilcken, KM; Seal, A; Hebditch, BG
    Understanding the antecedent trajectory of rock coast evolution is central to the development of predictive models of cliff retreat that account for a changing climate. Moreover, the unison between high-precision, measured datasets and coastal evolution modelling is essential in order to understand long-term behaviours of real-world coastal sites. We present a methodology that uses site-specific topographic and cosmogenic 10Be data to perform multi-objective model optimisation of a coupled rock coast evolution and cosmogenic radionuclide production model. This new capability allows for a time-series of cliff retreat rates to be quantified for rock coast sites over millennial timescales. This is the first study that has 1) applied a process-based coastal evolution model to quantify long-term cliff retreat rates for real, rock coast sites, and 2) coupled cosmogenic radionuclide analysis with a process-based model. Process-based coastal evolution models simplify erosional processes and, as a result, often have equifinality properties, for example, that similar topography develops via different evolutionary trajectories. Here, we show that coupling modelled topography with modelled 10Be concentrations can reduce equifinality in model outputs. Furthermore, these results reveal that multi-objective optimisation is essential in limiting model equifinality caused by parameter correlation to constrain best-fit model results for real-world sites. Our results show that in order for modelled platform morphology and 10Be concentrations to match both measured datasets simultaneously, the model requires negligible weathering and lowering of the shore platform, suggesting that erosion of these rock coasts is wave-dominated. Furthermore, results from two UK sites indicate that the rates of cliff retreat over millennial timescales are primarily driven by the rates of relative sea level rise. This implies that future increases in the rate of relative sea level rise could accelerate cliff retreat, even at these rock coast sites that currently exhibit minimal erosion. These findings provide strong motivation for further studies that investigate the effect of past and future relative sea level rise on cliff retreat at other rock coast sites globally. Plain-language Summary Here we use topographic and 10Be concentration data to optimise a coastal evolution model. Model results strongly suggest the erosion at the coast sites investigated are wave-dominated, as minimal weathering rates are needed to match model results to the measured datasets. Cliff retreat rates are calculated for two UK sites for the past 8000 years, and for the first time, highlight a strong link between the rate of sea level rise and long-term cliff retreat rates. This method enables us to study past cliff response to sea level rise, and so, to greatly improve forecasts of future responses to accelerations in sea level rise that will result from climate change.