Meltwater storage, Greenland Icesheet
Location: Greenland Ice Sheet Lat & Long: 67°04'N, 49°23'W
Members: Tom Gribbin (University of Bristol) with Joseph Cook (University of Sheffield), Andrew Tedstone (Bristol University)
Objectives: In 2016 researchers from Bristol, Sheffield, Leeds, Potsdam, Aberystwyth and NASA JPL camped on the Greenland Ice Sheet through the summer melt season. Tom joined them in 2017 to see if meltwater storage is related to the physical properties of the weathering crust.
Website and Expedition Timeline: https://blackandbloom.org/
Dates: 7 July to 30 July 2017
Aug 3: Tom Gribbin returns home with lots of melt data: https://twitter.com/Arctic_Club_UK
Watch Tom's video: Greenland 2017: Research trip to the Greenland Ice Sheet
Tom reports: It has been a very unusual season in Greenland. Before leaving, our team had been watching the weather reports from the nearby S6 weather station, located on the SW margin of the Greenland Ice Sheet. It appeared that snowfall events had deposited significant quantities of the white stuff much later than in a typical season. A team on the ground at our soon-to-be camp location corroborated the story - as much as 30cm was deposited in one event in June - and it was sticking around! By this point in the year the winter’s snowfall would normally have slowly melted away to leave a bare ice surface that melts at a faster rate. It was this ice surface that I wanted to study. The ice surface isn’t usually ice-cube smooth because once the sun’s rays start penetrating, water actually fills the upper couple of centimetres as in a sponge. This porous layer is known as the weathering crust and may act to transport meltwater downhill towards a developing stream system. However, when a blanket of highly reflective fresh snow lies on the surface of the ice, there isn't enough radiation penetrating through the snow to create this porous weathering crust, and neither is there much meltwater! If the snow did not melt quickly, the weathering crust I wanted to study would not develop before we had to leave for home.
It was with an anxious feeling I jetted out to Kangerlussuaq, Greenland to begin the work; with the equipment I had, could I adapt my science to the conditions I would find? Because once on the ice sheet, alternative equipment or expertise, was a prohibitively expensive helicopter ride back to Kangerlussuaq, and more than likely another plane ride from there. We spent a few days in Kangerlussuaq, checking and rechecking our kit ready to fly into camp, but we still had time to visit the magnificent Russell Glacier. A periodic grumbling thunder signalled we were close before we saw it. Rounding the corner, an ice cliff towers hundreds of feet tall above the viewer and the cause of the thunder soon becomes apparent as we watched huge chunks of ice fall from the cliff as if in slow motion to the river below. The tundra which covers hundreds of square km around Kangerlussaq ends abruptly at the disintegrating glacier front, marking the edge of the ice sheet. But from space the tundra might as well be just a thin elastic band encircling the huge white mass of the ice sheet in Greenland’s interior. The icy interior has enough water locked up in frozen form to raise sea-level by 7 m the world over; high enough to displace major international cities. But the force that the Greenland Ice Sheet is facing is not a giant tundra elastic band. Human-induced climate change will cause the Greenland Ice Sheet to melt and shrink over the coming centuries – that is if we don’t do something about it.
We were joined by the BBC as we flew onto the icesheet. Camp setup was a little more involved because we had to cater for the additional members to our original 4-man team. The first few days were a mixture of putting up tents, cooking, washing up, setting up the toilet (watch the BBC video How do you go to the toilet?), setting up the solar array and other camp maintenance. Once the BBC had left, I started trying out the methods I had planned. By this point snow cover was patchy which meant the weathering crust was starting to develop beneath the snow. Very little work has been done on the weathering crust so some of the methods I was trying were new and ‘teething’ problems abounded! In particular, the weathering crust was very crumbly which made obtaining a known volume by coring very difficult. This made density, porosity and water content measurement unreliable. Using a larger corer improved the method, but greatly slowed me down because it was arduous work in cold conditions, and as such the number of measurements I could make was reduced. Drone footage was useful in defining a water catchment. This meant I had an area within which I could estimate all the water inputs (melt) and all the outputs (stream flow at the catchment boundary). Analysing the timings of these water inputs and outputs alongside the aforementioned weathering crust characteristics will inform me about the surface hydrology of the area.
However, like the rest of the season, conditions did not remain as expected. We experienced snowfall which left a covering for several days. Water movement through my catchment almost completely shut down as a result of the reduced melt rates, and there was very little water in the stream. My surface hydrology research suddenly became much easier – because there wasn’t much going on! But one final weather event left us feeling like we’d experienced all 4 seasons in one week. Another low-pressure system with very strong winds moved through one night at the start of our second week. We spent the evening preparing for the worst by packing science equipment inside the tents into storage boxes. At 1 am the tent collapsed under the battery of the winds and rain and we were forced to move to our personal tents. An unpleasant next day followed as we waited out what remained of the storm and ate a few easy meals consisting of emergency rations. However, whilst a disaster for the tent (see below), the science may yet yield interesting results. The rain event almost completely stripped the weathering crust to the bare ice surface, giving a nice end-member data point to my weathering crust observations.