<strong>Constraining sea level oscillations in the Last Interglacial by modeling fossil coral reefs</strong>

Presented at the INQUA conference 2023 (Rome, Italy)    Constraining sea level oscillations in the Last Interglacial by modeling fossil coral reefs Denovan Chauveau1, Alessio Rovere1, Anne-Morwenn Pastier2 1Dipartimento di Scienze Ambientali, Informatica e Statistica Università Ca’ Foscari Venezia, Italy 2Helmholtz Centre Potsdam, German Research Centre for Geosciences (GFZ), Potsdam, Germany Understanding past sea-level (SL) oscillations is essential to gauge the future patterns of SL rise, in response to warmer climate conditions. Thanks to the good preservation and dating of fossil outcrops, the Last Interglacial (LIG; ~122 ka ago) is one of the best climate analogs to study the possibility of abrupt SL changes within an interglacial. The existence and magnitude of possible intra-LIG SL oscillations is a hotly debated topic. Indeed, some LIG coastal stratigraphic sequences, especially those stemming from coral reef terraces (CRTs), are characterized by abrupt shifts in geological facies or double/multiple stepped stratigraphies, which were hitherto interpreted as proxies for abrupt SL oscillations. To investigate whether these geological formations have an eustatic origin, we focused on modeling the processes and SL scenarios that may contribute to build such reef stratigraphies. For this purpose, we used two models:  DionisosFlow software (i.e., a forward stratigraphic model) and the code of Pastier et al. (2019; Geochemistry, Geophysics, Geosystems, 20(8); i.e., a kinematic model based on reef morphology). In our work, we first calibrated the CRT morphogenesis parameters (e.g., carbonate production/reef growth; sedimentation; marine erosion; rock foundation geometry, etc.) based on global reef observations. Then, we tested different SL scenarios (e.g., a stable SL highstand, a stable SL followed by a rapid jump, a double peak SL highstand, etc.). Finally, we compared modeled and observed stratigraphies, and investigated which parameter set, processes and SL scenario are most consistent with observations of double/multiple-stepped reef stratigraphies at different sites globally. Our results highlight that the morphology of CRT sequences provides fundamental observations to unravel past SL, including the possible intra-LIG SL oscillations. </p

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

Poster presented at EGU General Assembly 2024 (14-19 April, Vienna, Austria).Sea level oscillations within the Last Interglacial: insights from coral reef stratigraphic forward modellingDenovan Chauveaua, Nikos Georgioua, Ciro Cerronea, Silas Deana, Anne-Morwenn Pastierb, Alessio Roverea,caDepartment of Environmental Sciences, Informatics and Statistics, Ca' Foscari University of Venice, ItalybHelmholtz Centre Potsdam, German Research Centre for Geosciences (GFZ), Potsdam, GermanycMARUM, Center for Marine Environmental Sciences, University of Bremen, GermanyUnderstanding 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.</p