The Histories Beneath Our Feet

What’s cooler: snow pits or soil pits? Among the IGERT group, that could be a bit of a loaded question. I may be just a tad biased, so I will diplomatically bow out of answering that question directly, and instead present the facts that I’ve gathered about snow and soil and what we can learn from them.

Creating the pit

Digging is digging is digging. If you want a hole in the ground, you’ve found the right group! We love it so much that we have even created a dance move to celebrate digging.

Whether in the tundra or on the ice, the IGERT crew can conquer any digging challenge.

Layers and Horizons

One feature shared between both soils and snow is their tendency to form stratigraphic layers. In snow, these layers can be seasonal or from particular storm events. As more snow accumulates every year, and the layers remain frozen even through the summer, the layers continuously build on top of one another. In soils, the layers are referred to as “horizons.”   The uppermost horizon is known as the O-horizon, which is an organic rich layer, followed by the A, B and C horizons. Proceeding downwards, the horizons become decreasingly organic and increasingly mineral rich until you reach the parent material beneath the soil.

Stratigraphy in the snow and firn at Summit (left) and in the Sandflugtdalen of Kangerlussuaq (right).

Dating

In both soil and snow pits, isotopes can be used to estimate the age of the horizon. In high snow accumulation areas, the snow layers show seasonal trends in oxygen isotopes. Counting back from the surface allows researchers to determine the age of layers. In soils, any remaining organic material in the soils can be dated by analyzing the isotopes of carbon. Histories can be unraveled in both snow and soil by tying the age of the horizons to other properties. In soils, this could be an investigation of what types of plants were growing at a time in the past. In snow, this could be a study of how carbon dioxide in the atmosphere has changed over time. In either case, the story needs a timeline and isotopes provide the tick marks for us.

Though I was skeptical at first, Ross’s module on soil horizons won me over!

Density

In seems that across many disciplines, density measurements are used as a simple way to characterize a material. We found ourselves measuring density along snow pit walls at Summit and in deflation zone scarps in Kangerlussuaq.  Not surprisingly, the least dense loess sample in our soil studies was far denser than even the ice samples that we measured at Summit.

Ruth and Kristin measure snow density at Summit (left), and Zak measures loess density in a deflation zone scarp (right).

Little known perks

We’ve also managed to explore some of the lesser known perks of soil and snow pits. We have found that covered snow pits create a perfect venue for puppet shows. And though it’s a bit of an acquired taste, Zak has found sandy soils to be quite a delicacy!

Zak tests the grit of the soil against his teeth.

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JSEP and IGERT at Summit: the meeting of the acronyms

While up at Summit camp, we were fortunate to overlap with students from the Joint Science Education Project (JSEP). The program provides high school students from Denmark, Greenland and the United States with the opportunity to travel to Summit Station and learn about the scientific research that occurs there. The ladies of Cohort 4 were eager to share our polar knowledge with the JSEP students, so we set up four different activities that revolved around snow and ice.

Summit flies flags from all of the participating countries in the Joint Science Education Project.

The first activity took the students out around camp to investigate snow albedo. We searched for snow that somehow looked different. For example, these differences could be due to compaction from heavy equipment, exhaust from LC-130 planes, or frost flower growth on the surface. We made measurements of albedo and used hand lenses to take a closer look at the snow grains and see how they differed from place to place.

Looking at snow grains through a hand lens.

One afternoon took us down to the beautiful backlit snow pit, where we discussed snow layering from different storm events and different seasons. We analyzed the snow stratigraphy, made density measurements and talked about implications for ice core studies, like the research done on GISP2 right at Summit!

Measuring density in the backlit snow pit.

Kristin led a hands-on exercise to teach the JSEP participants about glacial flow. The students made their own flubber from glue, water and borax, and they ran experiments to determine how their flubber “glaciers” would flow under various “bedrock” conditions. A wee bit messy, but worth the clean up!

Kristin explains the physics of glacial flow using flubber!

Our last afternoon at Summit fell on a beautiful, warm, sunny-sky day. The JSEP students broke into teams and set out on a scavenger hunt! Using GPS coordinates or clues about things around camp, the students were led place to place until they reached a final clue that could only be solved with input from all three groups. At last, they found the long sought-after buried treasure of Summit Camp!

The buried treasure of Summit Camp is found!

Coveted penguin stickers in the scavenger hunt prize!

When we weren’t sharing our love of science, the IGERT and JSEP teams enjoyed other activities around camp, such as singing songs together in the Big House or playing board games in the Recport. It was a fantastic opportunity for the IGERT students to share our science, to learn about science education in other countries, and to have a great time while doing it!

JSEP and IGERT groups after a successful scavenger hunt!

Learn more about the JSEP program at their website: http://www.polartrec.com/expeditions/joint-science-education-project-2013

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Diggin’ out fingers

The Greenland Ice Sheet holds many stories of past climate. Summit Camp, in fact, was established for scientists to drill two miles down into the ice and pull out an ice core that tells a story of warming and cooling events from the past 100,000 years.

Ten years and 1 week after the completion of this GISP2 drilling operation, the IGERT C4 gals made our way up to Summit and uncovered a new story held in recent ice.

Alden, Kristin, Christine, and Ruth at the site of GISP2

In July of last year, as you may recall, 97% of the Greenland icesheet experienced surface melting.

While much of this melt refroze on the surface,  some melted snow flowed below the surface to form frozen fingers poking down through layers of previously fallen snow. The frozen fingers, which we call vertical flow channels, are like icicles that are suspended in snow rather than air.

A trip to a backlit snowpit introduced us to the melt layer and one vertical flow channel. These features were buried 75 cm below the surface by a year’s worth of snow.

Unlike surrounding layers, the melt layer and the vertical flow channels were icy, clear, and hard; easily distinguishable with the naked eye or the touch of a finger running down the snow pit wall. It is important for scientists to study these icy features to better understand the physics of water flow through snow and to understand how their  properties may affect the information that satellites and radar collect about the ice sheet.

Alden showing us the snow pit. The green arrow points to the melt layer, the white arrow points to a vertical flow channel (i.e., finger).

Our mission was to dig under the frozen melt layer and excavate any ice fingers we could find.  We were like archeologists, hoping to discover arctic artifacts.

We first uncovered the snow pit that Alden had dug earlier in the season.

Removing the snow from plywood that covers the snow pit.

Revealing the snow pit.

Then Alden and Kristin graphed the stratigraphy of the snow pit layers to document the depths of the melt layer, winter and summer snow, and wind crusts.

Kristin’s lovely stratigraphy diagram

With our hands protected by waterproof mittens and zipbloc bags, we swept away the snow under the melt layer, feeling for any icy vertical flow channels. Kristin and I found several frozen fingers right away and started excavating by delicately brushing out the snow around them until we reached their icy bottom tips.  It took me 2 hours to excavate a beautiful flow channel that was one-half meter long.  We measured the fingers, recorded their position, and made notes about their form.

Carefully excavating a finger, which I nicknamed ‘Precious’.

Alden and Ruth worked on a side of a snow pit that seemed to have a different flow pattern. They diligently dug back through 1 meter of snow but didn’t uncover any frozen fingers.

While Kristin and I chip away at our excavations, Ruth and Alden continue to dig back, looking for vertical flow channels…the snow pit is getting larger!

As we reached the corner of our site, Mary found a behemoth vertical flow channel. We named him Hector II. Tired and cold, Ruth and Alden quickly sawed, shoveled, and pried Hector II out of the snow so that we could return back to camp.

After dinner, Mary, Ruth, and I excavated Hector II ex-situ and loaded him and our other frozen fingers into an insulated ice core box. We covered the fingers with cardboard, snow, and icepacks to make sure that they would stay frozen on their trip back to Dartmouth College.

Ruth carrying Hector II – all wrapped up – to the ice core box.

We made one last trip to the snow pit…this time on a snow mobile. I was particularly excited about this arrangement. We blazed across the ice sheet at a whopping 5 miles per hour, filled in our digging site, and recovered our tools.  Although the work was difficult, we were grateful to be at Summit a year after the surface melt, when the ice fingers were still within reach of a shovel and the hands of four motivated IGERTs.

Celebrating a job well done

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