A nuclear magnetic resonance study of Antarctic sea ice brine diffusivity

We have measured the diffusive motion of water molecules in the brine inclu sions of Antarctic sea ice using a specially constructed nuclear magnetic r esonance (NMR) apparatus. The method relies on the use of pulsed magnetic f ield gradients in precise analogy to well established laboratory procedures . One version of the apparatus utilised core samples extracted from the ice sheet which were subsequently analysed on site while a later version utili sed a probehead which was inserted into the ice sheet, thus minimising any sample perturbation. The diffusive motion of water molecules in the brine i nclusions is found to be strongly anisotropic, and, over short length scale s, exhibits a rapidity greatly in excess of that expected for thermal equil ibrium Brownian behaviour, an effect which we attribute to convective trans port. (C) 1999 Elsevier Science B.V. All rights reserved.