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Deep, dark and dynamic: Converted-wave seismology to explore the physical properties of Antarctic glacier ice

Dr Adam Booth (SEE), Dr Roger Clark (SEE)

Project partner(s): Alex Brisbourne (British Antarctic Survey)

Contact email: a.d.booth@leeds.ac.uk

Summary

Quantitative seismic analysis holds the key to establishing the mechanical properties of glaciers – the very properties which are required to accurately parameterise predictive models of glacier dynamics.  Global sea levels are predicted to rise by ~1 m over the next 100 years, but such estimates are uncertain and improved predictions require a comprehensive description of all aspects of the glacier system.

This project explores the scope of converted-wave seismology to quantify fundamental glaciological properties. During the project, you will acquire test data on Norway’s Hardangerjøkulen ice cap, to complement exciting Antarctic datasets, provided by the British Antarctic Survey and the Thwaites Glacier TIME project, at two priority Antarctic sites.  The successful development of converted-wave methodologies will broaden the glaciological seismic toolbox, providing novel insight at sites of international research interest.

Rationale and Motivation

Significant research effort is directed towards improving forecasts of glacier dynamics and their associated impacts on sea-level rise, particularly for ice masses on the Antarctic continent. Innovative methodologies are required to fully capture the physics of the glacier system. The study sites in this project are considered critical for the stability of two Antarctic regions: Korff Ice Rise, which influences the dynamics of the vast Filchner-Ronne Ice Shelf; and Thwaites Glacier, considered to be the vulnerable pinning-point of the West Antarctic Ice Sheet. Improved insight at these stability-critical sites will benefit all subsequent models for assessment of entire regions of Antarctic ice dynamics.

Background

Glacier flow is influenced by internal ice properties (e.g., water content, temperature) and the characteristics of the material immediately beneath the glacier bed. These properties can be quantified using seismic reflection methods: ice temperature is related to seismic attenuation, and amplitude-versus-offset (AVO) methods allow the physical properties of the subglacial environment to be diagnosed. However, these methods are typically applied only for the compressional (P-) wave component of the seismic wavefield, and other components may be overlooked. The value of mode-converted reflections (i.e., energy that impinges on an interface as a P-wave, but excites shear (S-) wave particle motion) is yet to be explored, but could offer a valuable source of constraint for quantitative assessments of physical ice properties.

In some cases, the value of the converted-wave may exceed that of its P-wave counterpart. AVO studies are a particular case in point: the theoretical reflectivity for ice overlying wet sediment can be stronger for the converted-wave than the P-wave. Glaciers accelerate when flowing over saturated sediment, therefore monitoring the distribution of subglacial water is key to predicting long-term glacier stability. Converted-wave AVO could therefore offer a sensitive new tool to studies of subglacial hydrology.

During this project, you will have the opportunity to test acquisition criteria for converted-wave compliant surveying on Norway’s Hardangerjøkulen ice cap, itself an important study area for predicting how isolated glaciers will respond to climate warming.  You will use seismic reflection data from two key study sites: Korff Ice Rise and the shear margins of Thwaites Glacier, provided respectively by the British Antarctic Survey and the NERC/NSF-funded TIME project.

Click here for a full project description.

Related undergraduate subjects:

  • Earth science
  • Geophysical science
  • Geophysics
  • Physical science
  • Physics