Coastal-Cosmo-Model (CCMv1): a cosmogenic nuclide model for rocky coastlines

Abstract. Understanding the long-term evolution of rocky coasts requires models that can account for complex interactions between exposure, erosion and sea level, constrained by empirical observations. This paper introduces Coastal-Cosmo-Model version 1 (CCMv1), a modular forward modelling framework designed to reconstruct coastal histories from in situ cosmogenic nuclide concentrations. CCMv1 integrates community-standard production rate calculations and allows flexible inversion of platform histories using discrete erosion and exposure parameters. The model includes four sub-models – inheritance, zero erosion, down-wearing only, and cliff retreat with down-wearing – enabling users to test hypotheses of increasing complexity. Crucially, CCMv1 can be applied to both eroding and non-eroding coastlines, offering a means to investigate the dominant controls on rocky shore histories for different settings. A demonstration using a published dataset from shore platform shows that CCMv1 effectively reproduces measured nuclide concentrations and supports a history of Holocene cliff retreat. CCMv1 provides an adaptable and hypothesis-driven framework for exploring rocky shore histories, with potential for future development to incorporate probabilistic optimisation and additional nuclide systems, and implementation for testing complex (multi-stage) erosion histories or relative sea-level histories.