Geomorphological controls on the coastal response under projected sea level rise: A case study at an oceanic island (Trindade, Brazil).

Sea level rise (SLR) is one of the most threatening consequences of climate change. Despite considerable attention being paid to its impact on coastal zones, the studies concerning insular ecosystems remain scarce, particularly in the South Atlantic. In addition, large uncertainties still exist regarding the SLR rates and how islands respond to them. In this study we selected Trindade Island (Brazil), which exhibits a great variety of geomorphological beach systems, to investigate how geomorphological controls (e.g., profile geometry, composition, and sediment budget) influence the coastal behavior under SLR scenarios. To quantify the contribution of the aforementioned parameters to the coastal response, a set of experiments was conducted using the Random Shoreface Translation Model. Overall, the simulation results indicated that most of the analyzed beaches experienced shoreline retreat under the projected SLR scenarios for both 2040 and 2100 (retreat values ranged from 0 to −12.5 m for 2040 and from −0.5 to −47.1 m for 2100). The shoreface slope and composition exerted a strong influence on the coastal response of Trindade, wherein smoother profiles exhibited larger shoreline displacements. When the lower shoreface primarily comprised sand rather than rock, the retreat rates declined by more than 90% under most scenarios. Moreover, we highlight from the two associated experiments, the following: 1) the hard structures in the surf zone (e.g., calcareous reefs and volcanic rock outcrops) act as natural barriers to coastal displacement; and 2) the shoreline response was particularly sensitive to different sediment budget estimates. In conclusion, the results reveal the complexity involved in the investigation of geomorphological controls, emphasizing that a accurate delineation of such parameters is critical for providing reliable forecasts when modeling the coastal responses to SLR. • Most of the simulations showed shoreline retreat under projected SLR scenarios. • Shoreface slope and composition exerted strong influence on the coastal responses. • Hard structures in the surf zone (reefs) significantly reduced shoreline retreats. • Coastal response was particularly sensitive to different sediment budget estimates. • Accurate delineation of input parameters is critical for providing reliable forecasts. [ABSTRACT FROM AUTHOR]