• Glacial isostasy and the viscosity structure of the Earth

    • The waxing and waning of Pleistocene ice sheets imposed large loads on the surface of the surface of the lithosphere which responds over broad regions by flexure. By comparing the predictions of spherical viscoelastic models to observations of post-glacial sea-level changes at near-and far-field sites, it has been possible to constrain the radial viscosity structure of the sub-lithospheric mantle. While most studies agree on the viscosity structure through the upper mantle and transition zone, there is considerable current controversy about the average viscosity structure of the lower mantle. In the British Isles, for example, the sea-level data been interpreted by Lambeck and co-workers in terms of a lower mantle viscosity of 1022 Pa s while Peltier and co-workers prefer a value that is a factor of 5 smaller. This essay explores the role that the viscosity structure, together with other factors such as the elastic lithosphere, the ice loading and melting history, and the continent/ocean boundary, may play in determining the pattern of glacial isostatic adjustment.

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