Controls on the distribution of cosmogenic &amp;lt;sup&amp;gt;10&amp;lt;/sup&amp;gt;Be across shore platforms

Michael A Ellis,Martin D Hurst,Dylan H Rood

doi:10.5194/esurf-5-67-2017

Controls on the distribution of cosmogenic &lt;sup&gt;10&lt;/sup&gt;Be across shore platforms

Michael A Ellis, Martin D Hurst + Show 1 more

Open Access

https://doi.org/10.5194/esurf-5-67-2017

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Abstract

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.

Highlights

There is societal need to assess the rates, and the change of rates, at which cliffed coastlines will erode in the face of changing sea levels and wave climates that may result in more energetic coasts (Bray and Hooke, 1997; Trenhaile, 2010; Ashton et al, 2011; Barkwith et al, 2014)
We only considered the development of shore platforms during the Holocene, over the timescale during which eustatic sea level has been relatively stable (7 ka to present)
The values calculated from the digital elevation model (DEM) are in good agreement with Eq (11) as demonstrated by three example transects, each with different cliff heights (Fig. 4c)

Summary

Introduction

There is societal need to assess the rates, and the change of rates, at which cliffed coastlines will erode in the face of changing sea levels and wave climates that may result in more energetic coasts (Bray and Hooke, 1997; Trenhaile, 2010; Ashton et al, 2011; Barkwith et al, 2014). An emerging tool to assess past rates of cliff retreat comes from the accumulation of cosmogenic isotopes such as 10Be across active marine platforms that are generated via cliff retreat (Regard et al, 2012; Choi et al, 2012). These isotopes have the potential to yield rates of cliff recession and shore-platform erosion over millennial timescales (Hurst et al, 2016). The production of cosmogenic isotopes in the shore platform is in turn influenced by these processes and the resultant mor-

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