Refining Estimates of Pliocene Sea-Level Change and Geographic Source of Ice Melt: An Ice Sheet-Solid Earth-Sea Level Model Approach

Predictions for future sea-level change and ice sheet stability rely on accurate reconstructions of sea level during past warm epochs, such as the mid-Pliocene Warm Period (MPWP; 3.264-3.025 Ma). While MPWP global mean annual surface temperatures are agreed to be ~2-3°C higher than preindustrial values (Haywood et al., 2013), uncertainty in the scale and source of Pliocene ice volume melt leads to sea-level reconstructions that vary by 5-35 m between studies (Dowsett and Cronin, 1990; Naish and Wilson, 2009; Miller et al., 2012; Grant et al., 2019). Simplified assumptions of glacial isostatic adjustment (GIA) likely misestimate the spatial variability of sea level through glacial-interglacial cycles (Peltier, 2004; Milne and Mitrovica, 2008; Lambeck et al., 2014). Here we aim to constrain the magnitude, timing, and source of MPWP ice melt and, with this, contextualize ice sheet sensitivity for future change. We perform GIA modeling to systematically capture the sensitivity of global sea-level to individual ice sheet collapse by testing different MPWP ice melt sources and amplitudes. We adopt GCM-determined snapshots of Pliocene ice geometries (Berends et al., 2019) and vary the volumes of individual ice sheets at 100, 75, 50, and 25% of the following maximum eustatic sea level equivalents: WAIS (5 m), marine-based EAIS (14 m), Greenland (6 m), Eurasia (5 m), and North America (35 m). Ice volume fluctuations within the model time period (3.61-2.95 Ma) are scaled according to the LR04 benthic δ18O stack (Lisiecki and Raymo, 2004). To calculate a time-history of sea-level change, and local peak sea level, for globally distributed sites we pair these ice histories with 1-D earth models (varying lithospheric thickness and upper and lower mantle viscosity) within the consensus range of models inferred from studies of GIA data sets (Mitrovica and Forte, 2004; Lambeck et al., 2014). These initial model runs establish the relationship between a geographic location's perceived sea-level amplitude with the actual amplitude of ice sheet melt under a variety of scenarios, improving insight into which locations can provide accurate information about the source and magnitude of Pliocene ice volume change.