Arctic, Antarctic, and Alpine Research

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Vol. 49, No. 1, 2017

pp. 13-27

A firn densification process in the high accumulation dome of southeastern Greenland [open access]

Yoshinori Iizuka, Atsushi Miyamoto, Akira Hori, Sumito Matoba, Ryoto Furukawa, Takeshi Saito, Shuji Fujita, Motohiro Hirabayashi, Satoru Yamaguchi, Koji Fujita, and Nozomu Takeuchi

We 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.