Sea level oscillations within the Last Interglacial: insights from coral reef stratigraphic forward modelling

Understanding past sea-level variations is essential to constrain future patterns of sea-level rise in response to warmer climate conditions. Due to good preservation and the possibility to use various geochemical methods to date fossil sea-level index points, the Last Interglacial (Marine Isotope Stage (MIS) 5e; 130-116 ka ago) is often regarded as one of the best climate analogs for a future slightly warmer climate. Some MIS 5e coastal stratigraphic sequences, especially fossil coral reefs in tectonically stable areas, are characterized by abrupt shifts in their geological facies or steps within the reef topography, which have been often interpreted as proxies for abrupt sea-level fluctuations within the interglacial. However, the observational evidence and magnitude of such abrupt changes are controversial. Here, we run nearly 50 thousand simulations of a 2D kinematic reef model that can reproduce reef growth and demise through time. Our aim is to investigate the parameter space, the sea-level scenarios, and the processes by which double-stepped MIS 5e fossil reefs can form. Our results show that the only sea-level history that could explain the generation of an emerged MIS 5e backstepped reef is an abrupt rise in sea level, followed by a short-term peak. Any other multiple-stepped stratigraphy can be explained by the interplay between accommodation space, marine erosion, and bedrock slope, rather than by abrupt changes in sea level.