Wednesday 3rd July 2024

How the ice stream generates heat in its margins

Martin, Kyra and Sepp are digging out the double pit with a thin snow wall between them

Today, Sepp, Kyra and Martin went out to the SE shear margin to do a temperature logging of shallow bore hole ExS5-02. One of the purposes of temperature logging the shallow boreholes over the last week is to investigate to what degree the temperature of the ice sheet is influenced by the movement of the ice stream. At the S3 site close to camp and in the middle of the ice stream, the ice is moving as a block and the ice temperature is driven by the mean annual temperature of the snow as it deposits. The main warming trend in all temperature profiles towards the surface is thus mainly caused by global warming. The ExS5-01 and 02 sites, however, are in the ice stream shear zone, so in the zone between the ‘fast’ moving ice stream (moving some 50m per year) and the almost stagnant ice outside the ice stream. The shear occurring in this zone due to the different velocities of ice is known to release heat in the ice, but the question has been how much heat and how that is reflected in the ice temperature. The borehole measurements from about 100 m depth now quantify the effect to about 0.25 deg.°C warmer temperatures in the shear zone compared the that of the central ice stream where no shear is occurring. The borehole logger team also dug a beautiful double snow pit in which the firn stratigraphy can be studied.

What we did today:

1. Backfilling inclined trench in white tent with snow
2. Packing and documenting boxes in carpenters’ garage
3. Temperature logging of shallow borehole ExS5-02
4. Digging a double wall snow pit
5. Made flag line radar survey S of camp

Weather today: Overcast most of the day and some snowfall. Temperatures from -21 °C to -6 °C. Wind 0-7 kt Starting in S and turning first E and then N.

FL, Anders Svensson

When one pit is covered it allows to see the light traversing the snow wall and thereby revealing the firn stratigraphy

Same but different light setting

In the white tent the inclined trench was filled with show using the snow blower. Quite a lot faster than digging it out.

Soon the white tent is back to pre-drilling conditions

The temperature profiles for the S3 borehole in the ice stream and the S51 (alias ExS5-01) borehole in the shear margin.