An empirical firn-densification model comprising ice-lences

In the past, several empirical firn-densification models have been developed fitted to measured density-depth profiles from Greenland and Antarctica. These models do not specifically deal with refreezing of meltwater in the firn. Ice lenses are usually indirectly taken into account by choosing a suitable value of the surface snow density.

In the present study, a simple densification model is developed that specifically accounts for the content of ice lenses in the snowpack. An annual layer is considered to be composed of an ice fraction and a firn fraction. It is assumed that all meltwater formed at the surface in one year will refreeze in the corresponding annual layer, and that no additional melting or refreezing occurs in deeper layers.

With this assumption, further densification is solely controlled by compaction of the firn fraction of the annual layer. Comparison of modelled and observed depth-density profiles from Canadian Arctic ice-core sites with large melting-refreezing percentages shows good agreement. The model is also used to estimate the long-term surface elevation change in interior Greenland that will result from temperature-driven changes of density-depth profiles.

These surface elevation changes reflect a volume change of the ice sheet with no corresponding change of mass, i.e. a volume change that does not influence global sea level.