Abstracts of GRIP papers on basal (silty) ice

This file contains abstracts of GRIP papers whose primary content concerns basal ice studies. Papers are listed alphabetically by first author. You can go straight to the abstract you want.

Souchez et al. 1994
Souchez et al. 1995a
Souchez et al. 1995b
Souchez 1997
Tison et al. 1994
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Souchez, R., Tison, J.-L., Lorrain, R., Lemmens, M., Janssens, L., Stievenard, M., Jouzel, J., Sveinbjornsdottir, A. & Johnsen, S.J. 1994. Stable isotopes in the basal silty ice preserved in the Greenland Ice Sheet at Summit; environmental implications. Geophysical Research Letters, 21, 693-696.

Corresponding author: R. Souchez, Departement des Sciences de la Terre et de l'Environnement, Universite Libre de Bruxelles CP160/03, 50, avenue F.D. Roosevelt, B-1050 Bruxelles, Belgium.
E-mail: glaciol@ulb.ac.be

Modelling ice sheet behaviour in the context of climatic changes depends on initial and boundary conditions which can be better defined by studying the composition of basal ice. This study deals with basal ice reached by deep drilling at Summit in Central Greenland (GRIP core). The isotopic composition of this ice indicates that ice formed at the ground surface in the absence of the ice sheet largely contributed to its formation. The basal silty ice is a remnant of a growing stage of the ice sheet, possibly the original build up.

Souchez, R., Janssens, L., Lemmens, M. & Stauffer, B. 1995. Very low oxygen concentration in basal ice from Summit, Central Greenland. Geophysical Research Letters, 22, 2001-2004.

Oxygen concentration as low as 3% has been detected in the basal silty ice of the GRIP core. Such values were never observed in ice from ice sheets. They are most probably the consequence of organic matter oxidation in ice developed in a peaty deposit when the Greenland Ice Sheet was not present at the site. Flow-induced mixing has further incorporated this ice into glacier ice during the ice sheet build up. The part of the local ice component in the mixing process diminishes with the distance from the bed. This is the process which explains the oxygen profile.

Souchez, R., Lemmens, M. & Chappellaz, J. 1995. Flow-induced mixing in the GRIP basal ice deduced from the CO{-2} and CH{-4} records. Geophysical Research Letters, 22, 41-44.

This paper documents a larger degree of mixing in ice near the bottom of an ice sheet than described, or suspected, previously. It shows, thanks to favourable circumstances due to CO2 and CH4 production underneath the ice, that flow-induced mixing within the basal ice has taken place at the scale of a few centimeters in the GRIP core. Such a mechanism must be considered when interpreting the ice properties in the bottom part of ice sheets and must be taken into account as a potential process of layer disruption in the low levels of the Central Greenland ice cores.

Souchez, R. 1997. The buildup of the ice sheet in central Greenland. Journal of Geophysical Research, 102, 26317-26323.

A study of the isotopic and gas composition of the basal silty ice recovered by the Greenland Ice Core Project (GRIP) core indicates that local ice formed in the absence of the Greenland Ice Sheet is still preserved at Summit. Such ice developed most probably within a peat deposit in a permafrost environment. This local ice was subsequently intimately mixed with glacier ice from an advancing ice sheet progressing on the site. This is in agreement with the ''highland origin and windward growth'' hypothesis for ice sheet development, not for an in situ or regional growth from snowbanks. The basal ice from the GRIP core possibly dates back to the original buildup of the Greenland Ice Sheet 2.4 million years ago.

Tison, J.-L., Thorsteinsson, T., Lorrain, R. & Kipfstuhl, J. 1994. Origin and development of textures and fabrics in basal ice at Summit, Central Greenland. Earth and Planetary Science Letters, 125, 421-437.

Corresponding author: J.-L. Tison, Departement des Sciences de la Terre et de l'Environnement, Universite Libre de Bruxelles CP160/03, 50, avenue F.D. Roosevelt, B-1050 Bruxelles, Belgium.
E-mail: glaciol@ulb.ac.be

Detailed textural and crystallographic characteristics of the bottom 6 meters of the GRIP core (Summit, Central Greenland) are presented. Results are discussed in the light of present-day fabric analogues. Ice fabrics are shown to retain the mark from the entrainment of locally formed ice by the growing ice-sheet. This mark is only partly overprinted by the present-day stress configuration at the ice divide. These results corroborate the model put forward by Souchez et al. [1] on stable isotopes and gas composition grounds, in which the basal silty ice appears as a remnant of a growing stage of the ice sheet. During this stage, which is probably the original build-up, ice of local origin formed at the ground surface was overridden by the main ice sheet and incorporated into its base. Preservation of remnants of ancient fabric patterns and occurrence of annealing recrystallization fabrics just above the first layer of silty ice are used, amongst other arguments, to demonstrate that this basal ice is not presently submitted to large cumulative strains. Implications for flow and dating models are discussed.