10 Shoreline variability along the 3.6-km long Narrabeen Beach embayment in SE Australia is 11 investigated over a 5-year period. We apply the one-line shoreline change model LX-Shore, 12 which couples longshore and cross-shore processes and can handle complex shoreline 13 planforms, non-erodible emerged headlands and submerged rocky features. The model 14 skilfully reproduces the three dominant modes of shoreline variability, which are by 15 decreasing order of variance: cross-shore migration, rotation, and a third mode possibly 16 related to breathing. Model results confirm previous observations that longshore processes 17 primarily contribute to the rotation and third modes on the timescales of months to seasons, 18 while cross-shore processes control the shoreline migration on shorter timescales from hours 19 (storms) to months. Additional simulations simplifying progressively the bathymetry show 20 how the inherent geology strongly modulates the spatial modes of shoreline variability. The 21 offshore central rocky outcrop is found to limit the rotation. In contrast, the submerged rocky 22 platforms that extend from the headlands enhance the shoreline rotation mode and increase 23 alongshore variability of the cross-shore migration mode, owing to increased alongshore 24 variability in wave exposure. Offshore wave transformation across large-scale submerged 25 rocky features and headland shape are therefore critical to contemporary shoreline dynamics. 26 2< Réduire