Nuclear magnetic resonance study of sea-water freezing mechanisms: 1. Temperature dependence of relative brine content in sea ice

Abstract

The results of measuring relative brine content (Qlm) in the liquid phase of frozen sea water at temperatures between -2°C and -43°C with variable rate and direction of temperature change are presented. Various pulsed and steady-state nuclear magnetic resonance (NMR) methods are used and the results are compared with data in the literature. Temperature dependences of Qlm in sea water with dry NaCl added are given. Quasi-hysteresis corresponding to the crystallization range of certain seawater salts, mainly NaCl, which partially precipitates as the crystalline hydrate NaCl-2H 2O at temperatures below -23°C, is detected in the temperature dependence of Qlm. The reasons why Qlm values, under various experimental conditions, differ from data in the literature are explained. Brine salinity (S) is calculated from the relative intensity of NMR signals of Ql, and agrees well with previously published data over a wide temperature range. It is shown that determining Qlm from base measurements of Ql in ice does not require information about brine salinity. Empirical equations for calculating brine content at different sea-water temperatures and salinity are given.