Sea-Level Change on Complex Earth Models

Abstract

This dissertation revolves around complex Earth models and a broad range of paleo sea level questions. Each problem provides a case study for whether an additional layer of complexity in theory and modeling glacial isostatic adjustment (GIA) is necessary. In Chapter 1, I investigate whether transient (i.e., time-dependent) rheology is necessary to reconcile modern day Global Navigation Satellite System (GNSS) uplift rates in Greenland with Holocene relative sea-level (RSL) records. I find that the radial resolving power of RSL data associated with the post-Last Glacial Maximum (LGM) loading history extends significantly deeper into the upper mantle than sensitivity kernels for GNSS predictions associated with modern melt. Thus, the two datasets can be reconciled with a single Maxwell rheology model by including a low viscosity zone in the upper mantle. In Chapter 2, I quantify the effect of including lateral variations in Earth structure on inferences of ice volume at the LGM, 26 000 years ago. I find that there is no consistent high-magnitude signal that may explain the systematic difference between sea level-based estimates of ice volumes and independent geological constraints on past ice sheet sizes. Nevertheless, the study demonstrates that including more realistic, three-dimensional (3-D) models of Earth viscoelastic structure is necessary in GIA analyses of post-LGM RSL records in the far field of ice sheets. In Chapter 3, I revisit estimates of global mean sea level (GMSL) rise following the collapse of the West Antarctic Ice Sheet. Specifically, I use an extended ice age sea level theory and an Earth model that captures the low viscosity beneath the region to calculate the contribution to GMSL from water expelled due to postglacial rebound as grounded, marine-based sectors of the ice sheet retreat. I conclude that previous studies have underestimated the potential GMSL rise by up to 1 m (30% of previously published values). Thus, including lateral variations in Earth viscoelastic structure is necessary for accurately retrodicting contributions of WAIS to past GMSL rise and projecting future contributions in a warming world. Finally, in Chapter 4, I present a preliminary exploration of the effect of GIA on subglacial hydrology in Antarctica from LGM to present day. This research suggests that GIA-induced changes in bedrock topography in Antarctica may have had a significant impact on evolving subglacial hydrology, and concludes that this connection warrants further study.