Fire and ice: investigating links between mantle dynamics and ice sheet stability
File(s)
Author(s)
Hazzard, James
Type
Thesis
Abstract
Oceanic and atmospheric warming threaten melting and collapse of Earth's ice sheets. Global mean sea level rise disrupts coastal ecosystems and communities by increasing destructive potential of coastal inundation events, and disturbing ocean circulation patterns. Therefore, robust projections of spatiotemporal patterns of sea level change are critically important. To construct them, improved understanding of solid Earth structure is required, due to physical couplings between mantle dynamics and ice sheet stability. Poor constraint on Earth's interior structure has obfuscated reliable estimation of future sea level change. Here, a Bayesian inverse framework for self-consistent conversion of seismic velocity into estimates of mantle thermomechanical structure is applied to Antarctica. Low viscosity anomalies are inferred in West Antarctica, such as western Marie Byrd Land, where viscosity is 10^(19.5 +/- 0.3) Pa s at 150 km depth. Thick lithosphere, high viscosity, and low geothermal heat flow is inferred in East Antarctica, consistent with cratonic lithosphere. By consideration of time-dependent viscosity perturbations (1 order of magnitude), seemingly disparate inferences of West Antarctic mantle viscosity derived from GPS data are reconciled. Variations in Antarctic geothermal heat flow from 20-130 mW/m^2 are inferred, based on a novel method incorporating crustal composition. Modifying the framework developed for estimating mantle structure, to incorporate use of xenolith-derived palaeogeotherm constraints, Australian lithospheric structure is mapped. It is demonstrated that 97% of mass mined from Australian base metal deposits is located within 200 km of the 195 km LAB depth contour. Finally, the impact of transient rheology on ice sheet stability is explored, and applied to a simple model of Antarctic glacial isostatic adjustment. For short melting timescales, significantly more near-field deformation is caused by a novel rheological model (exhibiting transient behaviour), as compared to a Maxwell model. When melting occurs over 25 years, a 52% increase in Earth surface displacement is observed.
Date Issued
2024-06-27
Date Awarded
01/03/2025
License URL
Advisor
Richards, Fred
Roberts, Gareth
Sponsor
Natural Environment Research Council
Grant Number
NE/S007415/1
Publisher Department
Department of Earth Science & Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)