Now we are in ze pit

Written by Chris Polashenski

Just keeping ourselves warm, cozy, and fed does take up a pretty big part of the day, but science – not simply survival – is the goal of our trip. Things are going pretty well on that front. Four sampling stations are done now and we’ve begun to develop our routine, which is something like we envision a rockstar roadshow life. The day starts at the crack of 9 when we have to do our sat phone call in to our ‘agent’, the Kangerlussuaq logistics office, to assure everyone we’ve not driven off the edge of the ice sheet. We get a weather report and are questioned sufficiently for the logistics staff to determine if we’ve totally lost it yet.  Then we sort of slothfully get breakfast together and stare blankly into our mugs of warm cereal and/or coffee until they disappear. The pace picks up about then as one of us writes the blog post while the others pack up camp around them – the longer you take writing the colder it gets. A good incentive for quick writing.

Around 11am the rockstar lifestyle roars into life as we start up the machines, warm the belts, break the tracks free , and roar off  across the ice sheet feeling like masters of the universe. 2-2.5 hrs of blaring along at top speed, cooking fast food (lunchitos) on the mufflers, all the while running a ground penetrating radar, puts us at our next site where the next show (science) can begin. First on the docket is the “ASD” measurements – which need to be taken around solar noon (~130 local time). The ASD is an instrument that measures light, wavelength by wavelength, across the solar spectrum from ultraviolet thru visible, to near infrared. Taking a measurement of the incoming sunlight with the instrument, then another of the light reflected from the surface allows us to calculate what percentage of each color of light is being reflected by the ice sheet – the “albedo”. Since different types of impurities or changes in the snow create changes in sunlight reflectance at different colors of light, this can help us to understand what processes are controlling light reflection from the ice sheet.

ASD measurements of surface albedo

Digging the pit

Examining and noting pit stratigraphy

Mike makes much needed water

Sampling for density

Sampling for ions

Setting the tent fly

Those measurements complete, it is time for us to dig in and start sampling to figure out why the albedo was what we just measured. While Mike sets up
camp and starts batteries charging, Nate starts digging the pit, and I start building a snow-block retaining wall to keep drifting snows from immediately refilling Nate’s handiwork. As I join Nate, we dig down a set of stairs to
about 2 meters (7 feet) below the surface and clean up a wall to display the stratigraphy of the snow – a perfect record of everything that’s happened here at the site for about the past 3 and  a half years.  The top 10-20 cm of the snow is what’s driving the current albedo, so we’ll sample that snow heavily for black carbon, trace elements, and snow grain size right away. Deeper down, the snow properties have no effect on the current surface albedo, but lots of interesting history is recorded. Looking at the layers in the snow we can see individual snow storms and wind events in the past,
tracing storm deposition from one site to the next.  About 60 cm down, we find last summer’s surface – a layer of particular interest to us here. According to satellite observations, last summer almost the entire ice sheet
experienced melting conditions on the surface – and some pretty substantial melt conditions at that. This is rare. High on the ice sheet where we are, it typically remains below freezing year round and the snow stays dry. The last recorded widespread melt (observed from ice cores) is from about 1889, and prior to that the next one is in medieval times. With climate warming, more and more of the ice sheet has been experiencing melt over the past few decades, up to about 50 % of the ice sheet. Last summer was a big shift though and certainly more of a change than we’d expect from the gradual march of climate change.

There are many theories for why this extra-ordinary melt occurred and many questions about how likely it is to happen more frequently in a warming climate. A particularly strong warm front could have brought an oddly warm air mass over Greenland, low clouds could have acted like a blanket keeping heat in, snow grain size may have increased at the surface or black carbon may have been deposited on the surface, reducing sunlight reflection. All are likely true to an extent. Low, blanket-like clouds, for example are very important to the energy balance of the ice sheet and they’ve accompanied us most of our trip so far. A nice warm front is greeting us today (Temps about -10F this morning). The key to understanding the melt, however, is to understand those processes that are not just important, but which were
likely different last year. We think that the one thing that may have been quite different last year, was how much black carbon was deposited on the surface, thanks to emissions from raging forest fires in Siberia as well as North America. And so we dig down to and through the (irritatingly hard) melt layer for sampling.  We sample not just the snow that had been at the surface, but also the re-frozen melt water that percolated down into the snow, potentially carrying some of the surface contaminants with it. We’ve
been quite impressed with the shear amount of meltwater that had been produced last summer. High on the ice sheet, we’d expected to find a nice layer of refrozen melt grains, and some refrozen melt water perhaps 20-40 cm below what had been the surface last summer. Instead we’re finding huge lenses of ice, percolation tubes as big in diameter as my leg, and evidence that meltwater penetrated over 2 meters below last year’s surface. – a lot
of melting occurred!

When sampling for black carbon and a series of trace elements and ions that will help us understand where any impurities came from (i.e. forest fires vs internal combustion engines) is complete, we move on to sampling the snow grain size as the midnight sun begins to rise again. We have three methods along for this. The first is to put a few grains on a piece of gridded cardstock and estimate their size – moderately unreliable. The second is to take a snow sample and preserve it in a caste of a plastic-like substance
called dimethyl phthalate for analysis back in the lab – a cumbersome and unwieldy, but accurate, process. The third is to use an instrument developed by Florent Domine from the Universite Laval in Quebec dubbed the DUFISSS (DUal Frequency Integrating Sphere for Snow SSA measurement) , which measures snow grain size using an optical technique right in the pit, convenient and quick, more on this in a future post.

Completing our pit sampling, we finale by drilling a 10 meter deep hole into the ice and lower in a temperature measurement string before heading in to a dinner that Mike’s been working on for us. The rock star schedule ends around 2 or 3 am, and we all crash hard until we have to groggily check in at 9 again tomorrow.

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