Accession Number:

ADA021765

Title:

Brine Drainage and Initial Salt Entrapment in Sodium Chloride Ice.

Descriptive Note:

Research rept.,

Corporate Author:

COLD REGIONS RESEARCH AND ENGINEERING LAB HANOVER N H

Personal Author(s):

Report Date:

1975-12-01

Pagination or Media Count:

88.0

Abstract:

To obtain a better understanding of the desalination of natural sea ice, an experimental technique was developed to measure sequential salinity profiles of a growing sodium chloride ice sheet. Using radioactive Na22 as a tracer, it was possible to determine both the concentration and movement of the brine within the ice without destroying the sample. A detailed temperature and growth history of the ice was maintained so that the variation of the salinity profiles could be properly interpreted. Since the experimental salinity profile represented a smoothed, rather than a true salinity distribution, a deconvolution method was devised to restore the true salinity profile. In all respects, the salinity profiles are similar to those of natural sea ice. They have a characteristic C-shape, and clearly exhibit the effects of brine drainage. To determine the relative importance of the desalination mechanisms, a theoretical brine expulsion model was derived and compared to the experimental data. As input for the model, equations describing the variation of some properties of NaCl brine with temperature were derived. A simplified form of the model, when compared to the experimental results, indicated that brine expulsion was only important during the first several hours of ice growth, and later became a minor desalination process relative to gravity drainage which continued to be the dominant mechanism for the remainder of the study period up to 6 weeks. The rate of gravity drainage was found to be dependent on the brine volume and the temperature gradient of the ice. As either the brine volume or temperature gradient was increased, the rate of change of salinity due to gravity drainage increased.

Subject Categories:

  • Snow, Ice and Permafrost

Distribution Statement:

APPROVED FOR PUBLIC RELEASE