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Evidence of glacial flour in the deepest 89 m of the Vostok ice core

par Simoes, Jefferson J.C.;Petit, Jean-Robert;Souchez, Roland ;Lipenkov, Vladimir Ya;De Angelis, Martine;Liu, Leibao;Jouzel, Jean;Duval, Paul
Référence Annals of glaciology, 35, page (340-346)
Publication Publié, 2002

Article révisé par les pairs

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Résumé :

The 3623 m long Vostok ice core is divided into two main parts: (1) from the surface to a depth of 3310 m, the ice layers are undisturbed and may be used to reconstruct the climatic record over the past 420 kyr; (2) from 3538 m to the bottom, the core is made up of accreted ice formed by freezing of the lake. In between, the glacier ice is disturbed by ice dynamics, as shown, for example, by inclined volcanic-ash layers. Microparticle concentrations and distributions as well as ionic and isotopic content were used to subdivide this third section. The identification of layers with bedrock material provides clues as to the entrainment processes at sub-freezing temperatures. Dust concentration and size distribution as well as ionic content are comparable with values found in ice of glacial and interglacial periods. Below 3450 m depth, however, the mode of the volume size distribution clearly shifts from 2.1 μm to 3.4 μm in diameter. Particles as large as 30 μm in diameter are observed and cannot have an aeolian origin. From microscopic observations, we suggest that they originate from the bedrock and represent glacial flour entrained in a shear layer up to 89 m from the glacier sole. This process most likely occurred when the ice sheet was grounded before flowing over the lake.