Position of Churchill on a map of Canada

At the end of November I flew to Churchill (on the Hudson Bay, Canada) to participate in a two week sea ice campaign. We planned to spend two weeks conducting radar and snow-science experiments on the sea ice, staying on land and commuting to the ice each day. But at the time of flying out, the region was experiencing a record late freeze-up and it looked a lot like the ice would be dangerously thin, making research impossible.

Despite the bad start, a miraculous cold spell meant that we could access the ice after waiting a few days for it to thicken. We spent these days testing out our instrument (a sled-mounted radar) on nearby frozen lakes. Because lakes are filled with fresh water which has a higher freezing point than salty sea water, they freeze earlier and easier.

Our foray into lake-ice-science turned out to be a fascinating experience: we found that our radar waves penetrated considerably deeper into the ice, revealing the top surface as well as the bottom. This allowed the estimation of ice thickness. By contrast, radar waves are rapidly extinguished by salty sea ice, making the bottom of the ice invisible to our instrument. The bottom surface of the lake ice was so visible and well imaged that we were able to guess about whether it was stuck to the lake bed (“grounded” ice), or whether it had water below it. Later in our campaign we attempted to identify a lake that would be entirely frozen to the bottom using satellite imagery; we then scanned it comprehensively with the radar. We hope that this will produce a map of the lake depth.

John Yackel rides the (switched-off) radar as we traverse a frozen lake.

Once the sea ice had thickened enough to be safe, we began doing science on it. After an exploratory visit, we took our radar and started to scan it. Immediately we noticed that the ice surface was extremely rough, as tidal forces and shallow water had broken and turned the ice floes over before they joined together. For every visit we travelled several kilometres to the sea ice over tundra and frozen lakes - an awe inspiring experience when your goggles aren’t frozen over!

The main science goal was to take radar measurements of the snow on the sea ice, while simultaneously measuring the depth and physical properties of the same snow with other instruments. Doing this on recently formed ice fills a knowledge gap, as the radar instrument has only previously been deployed on older ice during the MOSAiC expedition. Newly formed ice is saltier than older ice, so much so that it makes the snow above salty as well. Salty snow is theoretically less penetrable by radar waves - but how much less?

Vishnu Nandan and John Yackel dig a snow pit.

To answer our questions about how radar waves interact with snow on young ice, we dug “snow pits” throughout the campaign. This involves cutting a cross section through the snow with a shovel, and sampling the snow’s density, salinity and temperature vertically. The first is measured with a “density cutter”, which removes a known volume of snow that can then be bagged, melted, and later weighed. To measure the salinity of the snow sample, we measure the conductivity of the melted snow. Saliter snow is a better conductor of electricity, so when a higher current flows, we infer saliter snow. Finally, we measure the snow temperature in the field with a temperature probe (a bit like a kitchen meat thermometer). We hope that all these measurements will tell us about what drives greater and smaller radar reflection from the snow.

Rosie Willatt about to sample some very dense snow over lake ice.

Overall the fieldwork was a big success, not least due to our palatial field station and excellent guide, Brian Gulick. Brian is a Churchill local and seemed to have the solution to every problem, regularly fixing snowmobiles and even our science equipment in the field, in tough conditions with few tools. He combined his technical knowhow with a professionalism that made us always feel safe and empowered to do science. As for our field station itself, it was equipped with twenty rooms, each with four beds. But our nine person team was the only booking, so we had lots of space to both work and relax. As well as having a lab, garage, kitchen and two classrooms, the station also had a gym, rec room, and “aurora dome”. This was a large perspex dome-shaped room on the roof of the station: it allowed three or four people panoramic and cozy views of the Northern lights. We took full advantage of the dome when it was too cold to use the balconies.

Having a comfortable base was really important because we were limited in our ability to leave the station. Daylight temperatures often dropped below -20, getting down to -29 on our coldest working day. To add to this, the risk of polar bears was always present: we carried a gun whenever we left on foot. Now the hard yards begin at the desk, analysing and collating the data we gathered. While that’s considerably less glamorous, it can mercifully be done with a warm coffee in hand.