A Firn Densification Process in the High Accumulation Dome of Southeastern Greenland

Abstract

ABSTRACTWe examine a firn core from a dome in southeast Greenland that exhibits distinct firn densification. The ice was −20.9 °C at 20 m depth, and the core gives an average accumulation rate of 1.0 m w.e. yr−1 in water equivalent. However, the close-off density of 830 kg m−3 occurs at 83.4–86.8 m depth, which is about 20-m shallower than that obtained from two empirical models. Where the density ρ > 750 kg m−3, the densification appears faster than that from the empirical models. As a result, compared to the empirical coefficient, the actual compactive viscosity coefficient is nonlinear and decreases at ρ > 750 kg m−3, indicating that the firn with a higher density is softer than that from the empirical result. We argue here that the high accumulation rate creates a high overburden pressure in a short time. Thus, the relative softness of the firn may arise from (1) there being not enough time to form bonds between grains as strong as those in a lower accumulation-rate area, and similarly, (2) the dislocation density in the firn being relatively high.