An Overview of Microphysical Processes in Ice Sheets: Toward Nanoglaciology

Abstract: In recent years, substantia! efforts among icc core researchers have been directed IOward understanding microphysical processes occuning in icc sheets, because they could affect significantly the paleoclimatic and paleoatmospheric signals recorded in icc cores. For example, a very large fractionation of N2 and O2 found in the transition zone from air bubbles to air hydrates was successfully explained in terms of molecular diffusion in icc [1-4]. More recently, we found very many water-soluble micropartic1cs, of which distributions and behavior must be a key to understand the chemical processes in ice sheets [5-9]. In the present poper behaviors of gas molecules and chemical species in ice sheets arc summarized and discussed in the light of recent studies. Moreovcr, thc anisotropic defonllation of icc crystals is taken into consideration in recent rescarch on ice sheet flow dynamics (1 0-13]. Although a very large anisotropy in plasticity of icc was well established in the 1960 's by labomlOry experiments, almost all icc sheet flow models developed so far have assumed isotropic ice because of difficulty in modeling the anisotropic deformation. As you wil! sec in this vol ume, this difficulty can be surmounted by the new models [12, 13]. In the present paper, I wil! discuss the fundamental dislocation processes in icc to bener understand why and how icc defonns in di ITcrent orientations. In order to emphasize Ihe importance of integration of microphysical processes more closely with macroscopic phenomena, I will propose a new phase of glaciological research, designated as nanoglaciology, for further development of the icc core research. Key words: Dislocation, stacking fa ult, plasticity of icc, clathrate hydrate, transition zone, eutectic depth, water-soluble microparticle, ti rn, gas fractionation, ice core, icc sheet, nanoglaciology