ICE-NADI-1: A new deglacial ice sheet thickness history (25–1 ka) for North America using empirically-constrained ice margins with implications for global sea-level contributions, relative sea level, and vertical land motion

Abstract. We generate three new empirically-based deglacial ice sheet histories (ice sheet thickness reconstructions) of the North American Ice Sheet Complex (ICE-NADI-1, ICE-NADI-1_min, and ICE-NADI-1_max) from 25 ka to 1 ka in 500-year intervals using a simple, steady-state numerical ice sheet model. To build the ice sheet histories, we adopt the North America Deglaciation Isochrones (NADI-1; Dalton et al., 2023). Our new ICE-NADI-1 ice sheet thickness reconstruction contains a peak North American sea-level equivalent (SLE) ice volume of 64 m of at the Last Glacial Maximum, 25 % smaller than the North American ice volume contained within ICE-7G (Roy & Peltier, 2017). North American ice saddle merging contributes 13 m SLE to global sea-level fall leading into the Last Glacial Maximum. Across Meltwater Pulse 1a (14.5–14 ka), our ICE-NADI-1 ice sheet thickness reconstruction contributes 6.3 m SLE, and the peak ice loss rate (13 mm SLE/year) is less than half the rate of ice loss in ICE-7G.

Glacial isostatic adjustment simulations show that our new ICE-NADI-1 ice sheet thickness reconstruction fits relative sea-level observations across North America as well or better than previous reconstructions. Predicted present-day vertical land motion with ICE-NADI-1 differs from previous predictions by up to 9 mm per year. Because NADI-1 ice margins capture geologic uncertainty in ice margin, we are able to quantitatively assess the sensitivity of glacial isostatic adjustment predictions (relative sea level, paleotopography, and present-day vertical land motion) to ice geometry, which previously has not been possible. We find this uncertainty comparable in magnitude to that associated with unknowns in Earth structure. Ultimately, our ice sheet thickness reconstructions illustrate how 2-D ice margins inform the history of ice volume evolution, granting new insight into North American Ice Sheet Complex dynamics and the associated changes in global sea level, relative sea level, and vertical land motion.