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An O18/O16 study of water flow in natural snow

University of British Columbia

One of the most successful applications of oxygen isotope variations in nature has been their use in glaciology. Yearly isotopic variations in snowfall provide a means of determining past climatological trends from deep ice cores. The most notable example of this type of application would be the Greenland Ice Core discussed by Dansgaard et al. (1969). When utilizing variations in stable isotope ratios as an indication of past climates two fundamental assumptions must be made. First, it is assumed that the isotopic ratio of precipitation falling in the area varies in some regular manner with a period of one year. The second assumption is that the isotopic composition of the snow does not change after it accumulates on the ground. This thesis project was an attempt to study the interaction between the liquid and solid phases of water inside naturally occurring snow. One of the most reasonable methods of studying this interaction is by studying isotopic changes inside the snowpack when liquid water with an 018/0** ratio much greater than the snowpack is uniformly distributed on top of the snow. It was found that water flow in several different types of sub-zero snow could be described quite satisfactorily in terms of isotopic, density and temperature variations. It was further concluded that accurate qualitative descriptions of flow would be extremely difficult without the isotopic information. The most unique result of this thesis project was the discovery that isotopic patterns in cold snow seemed to be manifestations of earlier water movement. That is to say, movement of the tracer through the snow tended to enhance the original isotopic pattern of the snow. The positions of the isotopic maxima and minima could usually be explained in terms of density variations. The above result has definite implications for the use of oxygen isotope variations for the determination of past climates from ice cores. If liquid water, either from rain or surface melting, is present in the snowpack at any time we must conclude that isotopic variations may be introduced into the snowpack that are not related to climatological factors. Isotopic dating of such cores would obviously be in error. The conclusion reached by many researchers that liquid water movement inside a snowpack will tend to homogenize the snow isotopically does not seem to apply to sub-zero snowpacks. In addition to the field project discussed above, this thesis presents a comprehensive description of the instrumentation and techniques used to measure the isotopic compositions of water samples with a precision of fourteen parts in one hundred thousand9 & complete analysis of the exchange of oxygen isotopes between water and carbon dioxide is presented. A determination of factors that can introduce errors into the analysis of water samples is also given. It is somewhat surprising that the non-zero voltage coefficients of resistance for the Victoreen Hi-meg resistors can be a major source of error in the analyses.

Text

2010-02-01

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http://hdl.handle.net/2429/19472

Geophysics

University of British Columbia

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