| Summary: | Sea-level projections depend on models calibrated with constraints of ice sheet sensitivity to past warm climate conditions. The early Pliocene Epoch is one important target for sea-level reconstructions since interglacial global mean temperatures were around 4 ˚C warmer than today. Paleoshorelines serve as measures of ancient sea level and ice volume but are deformed due to processes such as glacial isostatic adjustment (GIA) and mantle dynamic topography (DT). Along the southeastern passive margin of Argentina, three paleoshorelines date to early Pliocene times (4.8 to 5.5 Ma), and their variable present-day elevations (36 to 180 m) reflect a unique topographic deformation signature. We use a mantle convection model to back-advect present-day buoyancy variations, including those that correspond to the Patagonian slab window. Varying the viscosity and initial mantle buoyancy structures allows us to compute a suite of predictions of DT change that, when compared to GIA-corrected shoreline elevations, makes it possible to identify the most likely DT change. Our simulations illuminate an interplay of upwelling asthenosphere through the Patagonian slab window and coincident downwelling of the subducted Nazca slab in the mantle transition zone. This flow leads to upwarping of the southern Patagonian foreland since early Pliocene times, in line with the observations. Our preferred model of DT change leads to an estimate of global mean sea level of 17.5 ± 6.4 m (1σ) in the early Pliocene Epoch. This result confirms that sea level was significantly higher than present and provides important constraint for ice sheet model calibration.
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