Modelling Ice Sheets and Sea Level During the Penultimate Deglaciation and the Last Interglacial: Uncertainty, Sensitivity, and Calibration

Antarctica's contribution to future global mean sea level rise is likely to be significant, and yet the rate, magnitude, and timing of this contribution beyond 2300 is poorly understood as predicted future melt scenarios are outside the window of modern observations. The Last Interglacial period was the last time in Earth's history that the global mean sea level was higher than today, driven, in part, by a smaller than present-day Antarctic ice sheet and could, therefore, provide constraints on scenarios and mechanisms of future ice-sheet melt. The Last Interglacial evolution of Antarctic ice-sheet geometry resulted in a particular global pattern, or fingerprint, of Antarctic-driven sea-level change, subsequently recorded in records of Last Interglacial relative sea levels. Records from certain Eurasia regions may be sensitive to this fingerprint and could be used to help uncover Last Interglacial Antarctic ice-sheet evolution. However, for this analysis, the complex contribution of glacial isostatic adjustment to Eurasian Last Interglacial relative sea-level records must be quantified.

This thesis explores uncertainty in the Penultimate Glacial Maximum and subsequent Penultimate Deglaciation of the Eurasian ice sheet, the predominant driver of Eurasian glacial isostatic adjustment during the Last Interglacial, using a simple, calibrated ice-sheet model, resulting in a Penultimate Glacial Maximum volume of 48 ± 8 m SLE. The sensitivity of Eurasian Last Interglacial relative sea level is quantified with respect to ice-sheet and Earth model uncertainty in which the latter is found to be dominant. A suite of Last Interglacial Antarctic ice-sheet scenarios are developed to determine regional sensitivity to Antarctic ice-sheet changes, revealing a particularly strong influence in Wales, Atlantic, and English Channel regions. Finally, Bayesian history matching is applied to compare a relative sea-level ensemble against a Last Interglacial sea-level database, suggesting an Antarctic ice-sheet melt contribution of 3.2 - 9.3 m (likely, 66th percentile). However, when compared against relative sea-level data, none of the modelled scenarios are found to be implausible. More work is needed to constrain the large model-data uncertainties before rates, timings and East vs West contributions of the Antarctic ice sheet during the Last Interglacial can be identified.