May 23: Snow pit – Air and Ice : Firn air sampling and ice core drilling on Müller ice cap, Axel Heiberg Island

A snow pit is a (large) pit dug in the snow. Over the last few days, we (well, mostly Tessa and Rebecca, with the help of many others) dug a backlit snow pit. This is my favourite type of snow pits. It’s actually two snow-pits separated by a 50cm thick wall. One of the pits is covered (we used a tarp, but plywood is nicer, it makes it darker), so that the only light we have inside is through the wall. This makes the wall a beautiful ice blue color, and makes the layers of the pit much more visible than if we were staring at just a wall of snow.

We like to dig snow pits to have a closer look at layers of snow. Each snowfall leaves a layer, and by looking at the shape of the grains, we can tell many things about when, how, how much snow fell. Here, on Mueller ice cap, it seems like we can learn more about how snow melts rather than how it falls. There are traces of melt almost everywhere in the snowpit. It’s a bit surprising, but when snow melts, it doesn’t just stay at the surface: it percolates down the snowpack, until it looses all of its heat and re-freezes into an ice lens. We can tell that snow has been coated in melt by looking at the snow grains: fresh snow grains have sharp edges, but melted ones are smooth and rounded. And refrozen melt is quite hard, very different from fluffy fresh snow.

By looking at this snow-pit, we get an idea about how far down the meltwater travels before it refreezes, and also how many melt events we have in a year, although just like that, it’s hard to tell years apart. Chemistry samples will help with that..

It was the first time that Bluee and Popi saw a backlit snowpit, and they were very impressed. Bluee took the spatula and used it to shave the wall to make it very smooth and beautiful. Popi, on the other hand, was more interested in building himself a little staircase on the side so that he could climb to the top of the pit, and see the layers up-close.. His favorite are the very shiny melt layers. My favorite layers are usually the depth hoar, but here, they’re a bit strange..