Historical porosity data in polar firn

Abstract

Abstract. In the 1990's, closed and open porosity volumes of firn samples have been measured by J.-M. Barnola using the technique of gas pycnometry, on firn from three different polar sites. They are the basis of a parameterization of closed porosity in polar firn, first introduced in Goujon et al. (2003) and used in several firn physics models (e.g. Buizert et al., 2012). However, these data and their processing have not been published in their own right yet. In this short article, we detail how they were processed by J.-M. Barnola, and how the closed porosity parameterization was obtained. We show that the original data processing only partially accounts for the presence of re-opened bubbles in the samples. Since the proper correction to apply for this effect is hard to estimate, we also processed the data without including a correction for re-opened bubbles. Finally, we intend to make these pycnometry data available, in order to be used by the glaciology community, notably for the study of polar ice formation and of the composition of gas records in ice cores. They are hosted on the PANGAEA database: https://doi.pangaea.de/10.1594/PANGAEA.907678 (Fourteau et al., 2019a).

Porosity dependence of elastic moduli of snow and firn

“…However, the elastic moduli only become zero in the limit ϕ → 1 in this scheme, while the elastic moduli are expected to vanish at a critical porosity ϕ c < 1, estimated by Sidler (2015) to be ϕ c = 0.8 for snow. Also, pores in firn close and trap interstitial air in airtight bubbles as porosity reduces below a value of ~0.1 referred to as pore close-off (Stauffer and others, 1985; Schaller and others, 2017; Fourteau and others, 2020). Above this value of porosity the connectivity of the pore space is important.…”