Quantification and implications of change in organic carbon bearing coastal dune cliffs: A multiscale analysis from the Northumberland coast, UK

- Agreement in centennial, interannual and intra-annual data on change in dune cliffs
- Analysis of new UAV survey data utilising structure from motion processing
- An acceleration in dune cliff retreat and divergent profiles over the last decade
- A combination of external forcing and internal failure mechanisms govern behaviour.
- Quantification of potentially significant, readily mobilised organic carbon stores

Eroding coastlines composed of sequences of till, carbon rich peat and sand layers are characteristic of many formerly glaciated coastlines due to the interplay of relative land and sea levels. Dune cliffs cut into these materials represent one of the most sensitive systems to the processes of coastal change. Establishing appropriate scales for the quantification and analysis of change in coastal dune cliffs remains limited by the speed and nature of change, the intensity of environmental processes and the challenges of achieving adequate survey control. This paper presents the results from multi-scale analyses into the behaviour of dune cliffs on the northeast coast, UK, over a 118 year period. Repeat unmanned aerial vehicle (UAV) survey differences have been used to identify and quantify system behaviour, set in context with historic map comparisons. At the landform scale, monthly dune cliff dynamics have been analysed over the course of a year with terrestrial laser scanning (TLS) in order to gain insights into the drivers of contemporary dune cliff behaviour. Finally, pseudo three-dimensional ground-penetrating radar (GPR) data are used to trace subsurface stratigraphy from which the potential extent of stored carbon (in excess of 100 t over 50 m of monitored dune cliff) at risk of release by coastal erosion over the next 50 years can be calculated. The consideration of multi-scale changes over time periods relevant to well-constrained sea level change has revealed a complex combination of failure mechanisms that have resulted in an acceleration in dune cliff recession (particularly over the last decade) and a form change to shallower, divergent profiles. This potential acceleration in contemporary dune cliff response holds significant implications for both coastal management and the contribution of this poorly quantified input to the coastal carbon flux.