As promised: more descriptions from field day #1.
The first thing that I helped with when we got out into the field was digging and examining a snow pit. There were about 20cm of snow on top of the sea ice. We created a flat wall and examined the layers. It was a lot like when geologists look at sediments, except that the grains we are examining melt as we look at them and describe them. We also took temperature and density profiles of the snow layers.
A thin wind-blown layer covered another not-too-dense layer. Below that was some snow that was metamorphosed. Maybe it was exposed to rain. The crystals under the magnifying lens were more developed than the round grains in the layer above. Below that was a much denser layer that might even have seen some refreezing. The weight of the snow pushes the sea ice below sea level. Water seaps up and may help refreeze the lower layers of snow. There was a good centimeter of ambiguity about where the snow ended and the sea ice slush began.
A narrow hole was bored throught the ice to measure its thickness: about 70cm. Albedo measurements were made. I didn’t help with that the first day out, but maybe another day. Albedo is the fraction of incoming light that is reflected by the surface. Lots of properties effect the albedo, including the amount of soot or other light-absorbing foreign matter in the snow or ice.
We are also estimating those concentrations. I took snow samples from the two thicker layers of snow. We also took an ice core that was sectioned into 10cm chunks to be melted and filtered. Thus we should have a dataset that includes albedos, light-absorbing material concentrations, and also transmittance.
Transmittance is what it sounds like: you could also call it transmission. It’s the amount of incoming light that makes it through to the water below, or whatever was neither reflected nor absorbed. To measure transmittance we are using two different instruments to compare. Both involve sticking an arm down through a hole in the ice. Ours, from the UW, bends when it gets below the ice because there is buoyant floaty material wrapped around the bottom part. Then there are instruments attached to the end that measure visual light in a few different ways.
It takes a while to get through making all of these measurements, especially the first day out, and especially when the field assistants (e.g. me) don’t know what they are doing at all. The first day was understood to be a bit of a trial run though. More on field day two coming!