A nuclear magnetic resonance study of Antarctic sea ice brine diffusivity

Abstract

We have measured the diffusive motion of water molecules in the brine inclusions of Antarctic sea ice using a specially constructed nuclear magnetic resonance (NMR) apparatus. The method relies on the use of pulsed magnetic field 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 utilised a probehead which was inserted into the ice sheet, thus minimising any sample perturbation. The diffusive motion of water molecules in the brine inclusions is found to be strongly anisotropic, and, over short length scales, exhibits a rapidity greatly in excess of that expected for thermal equilibrium Brownian behaviour, an effect which we attribute to convective transport.