Capacitance measurements of bulk salinity and brine movement in first-year sea ice

Backstrom, Lars G. E.

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Abstract

Sea ice is an important component of the global climate system, as it changes the properties of the ocean-atmosphere interface. Understanding sea ice requires detailed knowledge of its temperature and bulk salinity. To measure these attributes using non-destructive in-situ techniques, instruments were frozen into first-year sea ice, and analysed jointly with ice-core, mass balance and climate data. The bulk salinity of the ice is calculated from measurements of temperature and complex dielectric permittivity at 50 MHz in landfast ice in McMurdo Sound, Antarctica, the Chukchi Sea, Alaska, and in an outdoor tank experiment in Fairbanks, Alaska. A simple relation for estimating brine volume fraction and bulk salinity in columnar, bubble-free ice from the real part of the complex dielectric permittivity was derived. For relative brine volumes below 50-70 % the error in the derived bulk salinity was below 15%. The observed brine movement events are analyzed. The data clearly indicate the extent and impact of brine movement on ice temperature and salinity. The analysis of a drainage event recorded by both the temperature and dielectric permittivity probe provided insight into gravity drainage of brine driven by a large brine reservoir in the freeboard layer.

Description

Thesis (M.S.) University of Alaska Fairbanks, 2007

1. Capacitance probe measurements of brine volume and bulk salinity in first-year sea ice -- 1.1. Abstract -- 1.2. Introduction -- 1.3. Methodology -- 1.3.1. Complex dialectric permittivity of sea ice -- 1.3.2. Instrumentation -- 1.3.3. Laboratory and field experiments -- 1.3.3.1. Measurements in Landfast sea ice in McMurdo Sound, Antarctica, July 10 -- November 11, 2002 -- 1.3.3.2. Measurements in landfast sea ice off Barrow, Alaska, February 2 -- June 4, 2003 -- 1.3.3.3. Outdoor ice tank experiment, Fairbanks, Alaska, February 8-April 20, 2003 -- 1.4. Results and analysis -- 1.4.1. Field data -- 1.4.1.1. McMurdo Sound -- 1.4.1.2. Barrow -- 1.4.1.3. Ice tank experiment -- 1.4.2. Deriving the bulk salinity of the ice from complex dielectric permittivity measurements -- 1.4.2.1. Apparent aspect ratio of brine inclusions in sea ice -- 1.4.2.2. Establishing the relation between the real part of the complex dielectric permittivity and bulk salinity of sea ice -- 1.4.2.3. Salinity change in the landfast sea ice at Barrow, Alaska, 2003 -- 1.4.2.4. Sources of error -- 1.5. Conclusions -- 1.6. Figures -- 1.7. Tables -- 1.8. References -- 2. Analysis of brine movement in first-year sea ice based on a case study of temperature and dielectric permittivity data -- 2.1. Abstract -- 2.2. Introduction -- 2.2.1. Aims -- 2.2.2. Theory -- 2.3. Study area and instrumentation -- 2.4. Results and analysis -- 2.4.1. Analysis of individual events -- 2.4.2. Analysis of heat flow -- 2.5. Discussion and conclusion -- 2.6. Figures -- 2.7. Tables -- 2.8. References -- General conclusions -- References.

Date

2007-05

Type

Thesis

Collections

Geosciences