Ice and Fire: Investigating Links between Mantle Dynamics and Ice Sheet Stability

The West Antarctic and Greenland ice sheets are losing mass at increasingly rapid rates and are projected to contribute between 0.5 and 1.8 m of sea-level rise by 2100 if greenhouse gas emissions continue unabated. These forecasts have huge economic and humanitarian implications for coastal populations with ~1 billion people living in regions expected to be permanently inundated or regularly flooded by storm surges. However, the rate, magnitude and spatial distribution of future sea-level change remains highly uncertain due, in large part, to poor constraint on the interaction between polar ice mass changes and solid Earth deformation on both human and geological timescales. This project aims to address this knowledge gap by combining advanced numerical modelling techniques with new geophysical and geological datasets to quantify the contribution of evolving mantle dynamics to past, present and future ice sheet stability.

Mantle dynamics can influence ice sheet stability in several important ways: mantle convection-driven uplift and subsidence of the Earth's surface can alter the grounding line position of major glaciers ); upwelling mantle plumes can increase heat flow into the base an ice sheet, triggering melting and increasing ice flow velocities ; and elevated temperatures can reduce mantle viscosity, accelerating glacial isostatic adjustment in response to ice mass changes. Accurate quantification of these different effects remains challenging but is now possible thanks to recent advances. First, improvements in seismic imaging have greatly enhanced our knowledge of the threedimensional velocity structure of the mantle. Secondly, modern rock mechanics experiments have made it possible to map seismic velocities into key physical properties, like temperature, density and viscosity. Thirdly, sophisticated software that can accurately model mantle convection and glacial isostatic adjustment in an Earth with significant lateral viscosity variations has recently been developed. Finally, the rapid growth of geophysical and geological datasets, especially in the polar regions, allows numerical model outputs to be benchmarked far more stringently than was previously possible.

This project aims to leverage these breakthroughs from across the geosciences, with major objectives including, but not limited to: i) creation of accurate three-dimensional models of Earth's internal temperature, density and viscosity structure; ii) quantification of convectivelysupported vertical motions and glacial isostatic adjustment with these revised Earth models to evaluate sea-levels during past warm periods (e.g. Mid-Pliocene Warm Period and Last Interglacial) and their implications for modern sea-level rise; iii) determination of the impact of updated viscosity structure on existing measurements of ice mass loss from the poles.