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.
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.
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.
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.
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.
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.
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.
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.