Controls on the distribution of cosmogenic ¹⁰Be across shore platforms

Abstract. Quantifying rates of erosion on cliffed coasts across a range of timescales is vital for understanding the drivers and processes of coastal change and for assessing risks posed by future cliff retreat. Historical records cover at best the last 150 years; cosmogenic isotopes, such as ¹⁰Be could allow us to look further into the past to assess coastal change on millennial timescales. Cosmogenic isotopes accumulate in situ near the Earth surface and have been used extensively to quantify erosion rates, burial dates and surface exposure ages in terrestrial landscapes over the last 3 decades. More recently, applications in rocky coast settings have quantified the timing of mass wasting events, determined long-term averaged rates of cliff retreat and revealed the exposure history of shore platforms. In this contribution, we develop and explore a numerical model for the accumulation of ¹⁰Be on eroding shore platforms. In a series of numerical experiments, we investigated the influence of topographic and water shielding, dynamic platform erosion processes, the presence and variation in beach cover, and heterogeneous distribution of erosion on the distribution of ¹⁰Be across shore platforms. Results demonstrate that, taking into account relative sea level change and tides, the concentration of ¹⁰Be is sensitive to rates of cliff retreat. Factors such as topographic shielding and beach cover act to reduce ¹⁰Be concentrations on the platform and may result in overestimation of cliff retreat rates if not accounted for. The shape of the distribution of ¹⁰Be across a shore platform can potentially reveal whether cliff retreat rates are declining or accelerating through time. Measurement of ¹⁰Be in shore platforms has great potential to allow us to quantify long-term rates of cliff retreat and platform erosion.