For this last blog post of the season, we summarize our work with numbers and photos to give you an idea of our field camp and the life/work on the ice sheet.
This summer fieldwork can be summarized as:
Weather and camping:
- 18 days spent on the ice including 16 sunny days and 2 overcast days
- Daily air temperature near 0°C in average with our coldest nights at -15°C
- Only 2 inches of snowfall (compared to 60 inches gotten last spring!)
- 200 dehydrated meals were eaten, about one per person and per day – favorite flavors: chicken teriyaki and lasagna.
- ~30 liters of water melted from snow every day for cooking and drinking
- 1 hot water bottle per team member to warm up the sleeping bag at night
- 1 refreshing hair wash per team member in 18 days, using 0°C aquifer water!
- A total of 200 km driven with the snowmobile to commute between sites and do radar surveys
- 3 slings load transported by BlueWest helicopters which contained ~5,000lbs of equipment (science gear + camping equipment) from Kulusuk onto the ice sheet
- ~100 km of GPR data total was collected to image the water table
- ~1850 hammer swings, used as seismic source, were performed, spread out over 18 seismic lines. It was enough to bend the metal plate!
- A stack of 30 hammer swings at the same location allowed us to get a return from the bedrock about 2,600 feet (~800 m) below the snow surface!
- A 55-m firn/ice core successfully extracted using a new lightweight (50lbs) thermal drill developed by Jay Kyne
- Water samples collection and hydraulic conductivity measurements were made at 2 different locations
- 21 liters of water including aquifer water and melted firn samples, which were collected for dating and understanding the timing of the aquifer formation and evolution
- ~8 magnetic resonance soundings (MRS) were performed along an elevation gradient to calibrate the GPR signal
- 6 liters of water per minute were pumped out of the aquifer during 3 hours to make a significant lowering of the water table level. This represents a total of 1300L of water brought up at the surface.
- Simultaneous seismic, MRS, GPS and GPR data were collected, allowing direct comparison between the different geophysical approaches
- The iWS station from Univ. of Utrecht was relocated next to one of the logging station
- 2 logging stations were installed to monitor 4 variables: water table height, firn and ice temperature, air temperature, firn compaction…
And that is about it for the 2015 fieldwork! Our team will spend fall working on the data at their labs, and we will be back into the field next year in the spring (May/June).
We hope you are enjoying the blog posts and we would like to thank you all very much for following this work! See you all next year!
Sling load containing the snowmobile is lowered by the helicopter.
Anatoly, Lynn and Nick taking a picture break in the cook tent.
Olivia and I taking turns operating the thermal drill.
Nick showing a beautiful clear ice layer found below the firn aquifer.
Anatoly posing next to the iWS from the University of Utrecht before and after backfilling the 2-feet deep snow pit.
The complex path of water infiltrating in the SE Greenland firn.
During the 18 days of fieldwork we got the chance to witness great moonrise.
Field team! From left to right: Clem, Nick, Lynn, Anatoly and Olivia.
A nice glacier with a dark tongue that we saw on the East side of the Sermilik Fjord.
Left: Lynn and I posing at the front of the container after putting the snowmobile inside. Right: gear in the container, ready to over winter.
Greenlandic puppies napping peacefully at the village of Kulusuk.
Last sunset in Kulusuk, Greenland before heading back to the U.S.
Our entire team left Greenland in the last week or so and I am writing this blog post from a warm place. In this post, I will describe the additional measurements taken by the team and show a few photos to illustrate how these data were taken. As reminder, the seismic data collection was explained by Lynn here, and hydrologic measurements described by Olivia in the previous post. Here, we will present the ground-penetrating radar collection, the magnetic resonance soundings, the intelligent weather station set up, and the monitoring of the firn temperature and water-table level.
The ground-penetrating radar (GPR) was used first to decide where to extract the firn cores, do the hydrological tests, and set up magnetic soundings and seismic surveys. During the first days of the fieldwork, we did not have the snowmobile on site, so we made a small sled with a piece of foam that we could drag. It had the advantage on being light and fast to set up.
Initial GPR setup with a light sled.
The GPR profile allows us to derive the depth of the water table below the snow surface. The water table corresponds to the top of the firn aquifer and is represented in the GPR data by a bright internal horizon (see GPR profile on photo 2, bottom part). In the summer time, we expected the wet firn above the aquifer to prevent the electromagnetic signal from penetrating to the water table but we were still able to image the water table. However, the correction from two-way-travel time to depth will need to take into account the presence of near surface water as it slows down the electromagnetic signal. To determine the water-table depth and adjust our dielectrical model, the magnetic resonance soundings will be important as it provide a direct measurement of the water volume.
GPR survey on the snowmobile with the mountains at the background (Photo Credit: Nick Schmerr). At the bottom, example of GPR profile collected above the water table (Miège et al., 2015, JGR in review). The bright reflector represents the water table.
Magnetic resonance sounding (MRS) is a non-invasive technique which captures the magnetic resonance signal generated only by water molecules in the subsurface. Anatoly, a researcher from LTHE in Grenoble (FR), accepted our invitation to use his instrument over the Greenland firn aquifer. After successful initial testing in the spring, we performed several additional soundings this summer. The setup consists in a square loop about 80m long, made of wire. At one corner of the loop, all the instruments are hooked up, powered with 12V batteries.
Anatoly is laying on a tarp finishing connecting the wires to the instruments. The bamboo stick marks one corner of the loop.
Anatoly is configuring a magnetic resonance sounding using the field computer.
One MRS takes about 1 hour to setup including walking the wire for installing the square loop. The measurement takes between 2 and 3 hours, it is always a good idea to go back to the tent for a hot drink in the meantime.
The last part of this fieldwork was to set up sensors to monitor the surface conditions on the ice sheet as well as the shallow subsurface (snow and firn) throughout the year, when we are not in the field. First, we moved the intelligent weather station (iWS) to a new location, about 20 km north. This iWS was initially installed in the spring of 2014 and we decided to move it at the new fieldwork location located directly upstream of Helheim Glacier.
iWS developed by our colleagues from the University of Utrecht in the Netherlands. On the left, iWS at the old location and on the right, the iWS left at its new location.
To look at the firn and water thermal properties we also installed a string of 50 temperature sensors from the surface to the top of the aquifer, within the aquifer, and beyond in the ice. We also dropped a pressure sensor to measure the vertical fluctuations of the water table from the snow surface. Finally, we had the chance to use one of the compaction devices designed by our colleagues from the University of Colorado. The Colorado team is setting up the largest snow/firn compaction network on the Greenland ice sheet. If you are interested to know more about their work, follow this link. The compaction device consists of a wire with one end anchored at depth in the firn. The other end of the wire, located at the surface, reels back on a spool as the surface is lowering with snow being compacted.
iWS standing next to the firn and water level logging station with our snowmobile in between for scale.
One of the logging stations was set up in April this year, and surprise, we got some visitors! They left us a note in the logging station case. It was a fun and unexpected moment as visitors are very rare on the ice sheet. Also it would be difficult to spot such a tiny station unless you go right by it, due to the surface undulations. These visitors are researchers from the University of Berlin, Germany. They are crossing the ice sheet between Tasiilaq and Ilulissat, repeating a route that a Swiss explorer, Alfred de Quervain, took in 1912.
Hi to them, and best of luck in their crossing! If you are interested to know more of their adventure, they left us their website link.
That is all for this blog post, stay tuned because we’ll send one last post for this summer season to wrap up and show more photos.