Martin's Antarctic Visit  
January 2004  

We make thin sections of the ice cores so that we can examine the inclusions in the ice and the ice crystal texture.

To examine the inclusions we need only look at the ice in plain transmitted light, in this case from a light table or slide shorter below. The small dark grey objects in the left hand panel are mostly brine inclusions. Note how many inclusions are aligned in roughly vertically oriented rows, while others are oriented at an angle. This gives us some preliminary information about the type and orientation of the ice crystals.

The ice crystals are revealed by placing the thin section between polarizing filters that are oriented perpendicular to each other. Thus, the right hand panel is the same section as that in the left hand panel but now illuminated between crossed polarizers. The diagonally oriented crystals are known as ice platelets.

Platelet ice is not very common. It is occasionally observed in Arctic sea ice, but Antarctica is the best place to find it. Even in Antarctica, platelet ice is not widespread, but you are guaranteed to find it in the landfast ice in McMurdo Sound.

The thin sections that we have made so far are about 2 mm thick. In due course we will make sections that are less than 1 mm thick, which will make it easier to count the number of inclusions per unit area, and to measure their dimensions. The very thin sections are also much more colourful than the thicker sections. I hope to send some examples of those before we leave.

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