Air mixing in firn and the age of the air at pore close-off ...

The air trapped in the bubbles of natural ice is not the same age as the surrounding ice. This is due to the fact that the air is enclosed in isolated bubbles only at the depth of the firn–ice transition. Within the overlying porous firn layer the air is able to mix and to exchange to a certain degr...

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Bibliographic Details
Main Authors: Schwander, J., Stauffer, B., Sigg, A.
Format: Text
Language:unknown
Published: International Glaciological Society 1988
Subjects:
Online Access:https://dx.doi.org/10.48350/158757
https://boris.unibe.ch/158757/
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Summary:The air trapped in the bubbles of natural ice is not the same age as the surrounding ice. This is due to the fact that the air is enclosed in isolated bubbles only at the depth of the firn–ice transition. Within the overlying porous firn layer the air is able to mix and to exchange to a certain degree with the atmosphere. The age difference between ice and air is given by the age of the ice at pore close-off, less the mixing delay. Also, there is an age distribution due to diffusive smoothing and due to the gradual enclosure of the air at the firn–ice transition. Knowledge of this age relation is necessary for the interpretation of climatic parameters measured on ice cores. This work concentrates on the effect of diffusive mixing. We report on measurements of the diffusivity of CO2 and O2 (in N2) in firn samples from Siple Station, Antarctica. It is shown that the dominant mixing process is molecular diffusion. The diffusion coefficient depends approximately linearly on the porosity. A one-dimensional ...