Every snowflake that falls on an ice sheet is slowly squeezed into glacier ice. In between lies firn: a porous, compressible layer, often around 100 metres thick, that covers most of the ice sheets. How firn deforms is surprisingly poorly understood, yet it matters for everything from measuring ice-sheet mass loss from space to dating the air bubbles in ice cores.

Firn densification is usually modelled as a 1D column that compacts under its own weight. But firn is also carried along by the flowing ice, stretched and sheared on its way. This deformation leaves fingerprints in the density profile. In ice-stream shear margins, for example, firn densifies much faster than in calm interior regions. By comparing places where the firn has experienced different deformation histories, we can learn how firn actually flows, which is what my current research is about.

Projects in this area combine continuum mechanics, numerical modelling, inverse methods and field data from Greenland and Antarctica. Possible directions include:

  • Inferring firn rheology from density profiles in contrasting flow regimes, such as ice divides, ice rises and shear margins.
  • Estimating strain rates and accumulation histories from firn density and age data.
  • Inverse modelling of firn temperatures at Antarctic ice rises.
  • Testing and comparing firn densification models against observations under different climates.

Depending on your interests, the project can lean towards modelling, data analysis or theory, and can be shaped around your own ideas.

Curious? Look up: firn densification, Community Firn Model, SUMup, strain softening, close-off depth.

Interesting places to start:

Students:

  • PUK pre-study: Nikolaj Munk Kjærsgård