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Abstract:
Global mean sea level during the mid-Pliocene Epoch, when CO2 and temperatures were above those of the present day, was significantly higher as a result of reduced global ice sheet coverage. However, the extent to which ice sheets responded to Pliocene warmth remains in question, owing to high levels of uncertainty in proxy-based sea-level reconstructions and solid Earth dynamic models that have been compared with only a limited set of data constraints. Here, we present a global dataset of 11 wavecut scarps that formed over successive Pliocene sea-level oscillations and occur today at elevations varying from ~6 to 109 m above sea level. The present-day elevations of these features have been identified using a combination of high-resolution digital elevation models and field mapping. Using the MATLAB interface, TerraceM, we project the cliff and platform surfaces to determine the elevation of the scarp toe, which often is buried under meters of talus. We correct the scarp elevations for glacial isostatic adjustment and find that this process alone cannot explain observed differences in paleoshoreline elevations. We next calculate the signal associated with mantle dynamic topography by back-advecting the present-day three-dimensional buoyancy structure of the mantle and calculating the difference in radial surface stresses over the last 3 Myr using the convection code ASPECT. We include a wide range of present-day mantle structures (temperature and viscosity) constrained by seismic tomography models, geodynamic observations, and laboratory experiments. Finally, we explore to what extent models can reproduce the different shoreline observations and deformation along them.
