Exploring past and present ice-sheet dynamics with geophysically-derived temperature and crystal orientation fabric

Abstract

The greatest physical uncertainty for projections of future sea-level rise is in ice-sheet flow dynamics and the potential realization of theorized instabilities. While knowledge on the precise fate of Earth’s ice sheets is still out of reach, looking to past states provides insight on their potential evolution. Past ice-sheet states, and particularly their flow dynamics, are preserved in present-day ice temperature (Robin, 1955) and preferred crystal orientation fabric (COF); moreover, the future ice dynamics are governed by those same properties through the ice viscosity and the tendency to slide over a temperate bed. Theoretically, ice temperature and COF can both be inferred using ice-penetrating radar measurements, but prior work shows that it is difficult to disentangle these intrinsic properties of the ice column from each other or even from interface properties, such as reflectivity between layers and at the ice-sheet bed. Here, I contribute to the development of methods for ice-penetrating radar power and phase interpretation. I use those methods alongside mathematical models to infer both present-day and historical ice-sheet dynamics for three areas of the Antarctic Ice Sheet: Siple Coast, South Pole Lake, and Hercules Dome. Each of the three regional studies is formulated around a separate scientific problem, and the results for each drive physical interpretation of ice-sheet processes. At the Siple Coast I calculate spatial variations in radar attenuation and use them to show that ice-stream temperatures are colder than previously thought because of their upstream sourcing. At South Pole Lake, I calculate spatial variations in ice-bed reflectivity, depth variations in radar attenuation, and develop a novel ice-temperature model to show that the ice-bed interface is regionally thawed and has been stable at least since the last glacial period, in contradiction to prior studies. At Hercules Dome, I use measurements of the present-day ice dynamics, both surface and englacial velocities, to constrain a model of COF evolution. I then compare the modeled COF against measurements from radar polarimetry to infer stability in the regional ice dynamics since the last glacial period. Together, these three studies demonstrate novel and innovative radar analysis used to theorize dynamic evolution of the Antarctic Ice Sheet. Looking forward, these types of radar measurements will be incorporated into continent-wide modeling studies to constrain ice-sheet dynamics and projections of future sea-level rise.