Firn aquifer observations on Lomonosovfonna Svalbard (Nbreen)

The project "Firn aquifer observations on Lomonosovfonna  Svalbard (Nbreen)" received funding from the SIOS Access Programme to conduct fieldwork in April 2019. This is their report from the field.

Field work was done in a group of five people including four researchers from Uppsala University and one from Utrecht University. Preparations for the field work were done in Longyearbyen at the UNIS/NPI garage. From there we left on April 6 with snow scooters pulling sleds for a 5-6 hour drive to the glacier. We built a camp at the top of the glacier (~1200 m above sea level), including a mess tent and four sleeping tents. During the nights we made shifts to have a permanent polar bear watch.

The actual field work was performed between April 6 and 10 after which we broke down the camp and returned to Longyearbyen. Our activities in the field included:
• Measuring mass balance using stakes drilled into the snow/ice
• Servicing and installing automatic weather stations measuring atmospheric conditions
• Installing GPS units, measuring ice flow velocity
• Performing ground-penetrating radar profiling to map firn aquifer extent
• Installing pressure sensors in two deep boreholes drilled into the firn


Figure 1: Water table depth recorded with ground-penetrating radar (left). A focused view of water table depth in the region in the gray box is shown in the right panel. The inset photo shows the weather station 
installed at the firn aquifer site.

The mass balance measurements, automatic weather station observations and GPS data collection are all part of long-term monitoring programs dating back to 2006 (mass balance & GPS data) and 2009 (automatic weather station). The firn aquifer was first discovered in April 2015 and further mapped in 2016-2019. Firn aquifers are large water bodies stored in deep snow packs at high elevations on Arctic glaciers. As firn aquifers may substantially reduce and delay runoff of melt water into the oceans, better constraints on firn aquifer development are of high relevance for estimating the ongoing and future glacier contribution to sea level rise. A firn aquifer cannot be seen at the surface, but can be detected by using ground-penetrating radar to look in the snowpack (Figure 1). Due to a difference of permittivity the radar signal in water and snow the top of the water table will show up as a clear reflector in the radar image. Pulling the radar with a snow scooter we performed a detailed grid survey covering tens of kilometers of tracks to map water 
table presence and corresponding depths. The data reveals that the firn aquifer is most pronounced (i.e. closest to the surface) in flat terrain, which confirms that a firn aquifer is behaving like a slow flowing river in the snow and firn pack (Figure 1). Since 2018, we have installed two pressure sensors in 25-m boreholes drilled in the firn aquifer zone. These pressure sensors continuously measure water pressure and thereby record water table depth fluctuations. During the most recent field campaign we have downloaded the 2018-2019 pressure data, which showed some very promising first results. The sensors have been reinstalled in newly drilled boreholes and the site will be visited again in April 2020. 


Figure 2: Digging a 3 meter pit to recover a weather
station installed a year earlier.

The collected data will be highly valuable for assessing the dynamics (e.g. hydraulic conductivity) of the water reservoir, which in turn is needed for calibrating numerical models simulating firn aquifer evolution. Finally, in collaboration with Andy Hodson, we have in April 2019 taken water samples from the firn aquifer and brought them back to UNIS for further analysis by the cryobiology community.

The SIOS funding has been acknowledged in our most recent paper entitled "A long-term dataset of climatic mass balance, snow conditions and runoff in Svalbard (1957–2018)", which is published in The Cryosphere. The paper can be accessed here: https://www.the-cryosphere.net/13/2259/2019/