A multiple-step deformation history of basal ice from the Dye 3 (Greenland) core: new insights from the CO₂ and CH₄ content 

Annals of Glaciology, 35, p. 231-236, 2002 

V. Verbeke, R. Lorrain, J.-L. Tison
Laboratoire de Glaciologie, Département des Sciences de la Terre et de l'Environnement, Faculté des Sciences, CP 160/03, Université Libre de Bruxelles, 50 av. F.D. Roosevelt, B-1050 Brussels, Belgium.
S.J. Johnsen
Geofysisk Afdeling, Niels Bohr Instituttet for Astronomi, Fysik og Geofysik, Københavns Universitet

ABSTRACT.
The ice depth-age relationship used for the Dye 3 (Greenland) core implies strong deformation of the silty ice present at the bottom. This paper focuses on the study of the relationship between carbon dioxide and methane concentration in the silty ice. In a CO₂-CH₄ diagram, sample points are well aligned along different straight lines with striking differences in slopes and concentration ranges, depending on their spatial location in the core. These slopes are interpreted as resulting from distinct mixing events between ice-sheet ice flowing from upstream and ice of local origin. Occurrence of these various events suggests a complex deformation history for the basal part of the ice sheet. It involves a progressive build-up of the high-deformation layer along the basal flowline up-glacier from Dye 3, reaching >25 m thickness at the site