The last main project on our season list was a salt tracer experiment, all of the instruments we have put out so far will allow us to detect the presence and flow of water but tracing is really the only way of investigating connections between the different water features we see on the ice.
The idea was to release a known volume of salt water, with a known electrical conductivity, into the system and monitor conductivity at locations down glacier. From the length of time it takes for a change to happen and the size of any change in conductivity at these locations we can estimate how well connected the system is and how much water is flowing though it. Changes in conductivity would also be picked up by our self potential electrodes and the ground penetrating radar. We planned a before and after flight of the big blue box which we hoped would show us the pathway of the salt tracer through the glacier.
We chose the Channel Lake system as a focus, planning to release 2000 litres of salt water, at a constant rate, into a small stream flowing into Channel Lake. Sounds simple enough….but there were a number of both logistical and scientific issues to work around.
We thought the most challenging was going to be getting hold 2000 litres of fresh water on an Antarctic base on water restrictions so, had planned to pump water from the glacier into a large bladder and try to make salt water on the ice. This was always going to be problematic, it would take time to pump the water, be difficult to dissolve that amount of salt in glacially cold water. To make it more difficult we had to do this in a large bladder so wouldn’t know that it had all dissolved or whether we had a constant concentration through out the release. As always, with the combined help and generosity of people here, there was a much better solution. The reverse osmosis plant was about to go online, making drinking water for the station and we were told we could use this water, a drilling team were about to finish and had two large water tanks we could use and the helicopter pilots were happy to sling the tanks out onto the ice providing we kept within the weight limit. In the end it was even better, we got hot water from the tap, a pump to circulate the water and within a few hours we had two water tanks holding 2000 litres of water and 200 kg of salt fully dissolved. Finally the most challenging experiment yet was a set and ready to go. We thought it would take around 2 days but were generously given 3 days out on the ice for it….but of course this is Antarctica and you can’t control the weather. The first day we were programmed was the first of three snow days. We were still ready though and a little later were programmed again….yes more snow days. I guess we had all of our blue sky days at the beginning of the season. Despite the preparation and excitement over the experiment we had to admit that the peak melt of the season had passed and start to focus our efforts on retrieving our instrument out on the ice. At least we now have a good idea of how to set up the experiment and hopefully we can come back and do it another year.