Vertical profile of snow-firn density in the vicinity of Vostok station, Central Antarctica

Abstract

The density of the snow and firn thickness is one of the fundamental and most important physical properties of the polar ice sheets. The data on density is used for reconstructing the past snow accumulation rate variability based on firn core studies, for correcting the results of the instrumental surface mass balance measurements and for verification of empirical and physical densification models. In this work we present a unique dataset on the snow and firn density in the upper 70 m of Antarctic glacier in the vicinity of Vostok Station based on data from 32 snow pits and firn cores. This newly obtained stacked density profile reveals different stages of the densification process. In the upper 27 cm a fast growth of the density is observed from 0.320 to 0.365 g cm^-3 as a result of the initial snow grain metamorphism. Below 0.3 m much slower densification rates are observed. At the depth of 22.5 m the transition from snow to firn can be seen at the density of 0.526 g cm^-3. The vertical density distribution can be approximated with a polynomial function with the accuracy of 0.01 g cm^-3 along the whole profile except for the upper 0.3 m. In order to investigate the glacio-climatic conditions under which the snow-firn density has evolved, we applied a semi-empirical model by Herron and Langway (1980). In first approximation, the density distribution can be explained with the initial snow density equal to 0.35 g cm^-3, surface glacier temperature equal to -57 C, and snow accumulation rate of 1.8–2.1 g cm^-2 yr-1. The discrepancy between the data and model can be, to our opinion, explained by the recent increase of the snow accumulation rate as evidenced from the firn core studies. However, the non-stationary physical densification model failed to reproduced the density data with sufficient accuracy, which calls for revisiting the model configuration and tuning.