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Drilling and logging an ice core is dirty business

Posted August 13th, 2009 by celene.carillo@oregonstate.edu

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I just returned from my second night logging shift, where we cleaned and documented the 3.5 m piece of ice that pushed our drilling depth past 1700 meters (more than 1 mile) below the surface. This is an amazing feat, since just last week the drillers were celebrating the considerable success of reaching 1600 m during the first season. Even with the usual complications and hurdles, we have been recovering 28 m per day on average for the last few weeks, bringing back ice far older than anyone dared to hope for this year. In fact, there is talk of breaking the deep drilling record for a single season, currently held by the first year of drilling at North GRIP, an ice core from central Greenland.

However, drilling and logging an ice core is dirty business. Because ice sheets are giant glaciers, and by definition, glaciers must flow, it is necessary to fill the borehole with a drill fluid of the same density as ice. This prevents the drill hole from being squeezed closed by the constantly deforming ice, and allows us to raise and lower the drill through a 10 cm hole without complication and to return the following year and more or less pick up where we left off.

After the first futile minutes of trying to stay clean while logging the core, you resign yourself to the muck. Then, the process engenders a strange type of messy satisfaction, like finger painting or building sand castles. And as drill fluids go, the one we use is fairly benign. Even though its principal ingredient is just coconut oil, it still has some pernicious qualities. Mainly, it aggressively dissolves any plastic or rubber it meets. The poor computer that aids the drillers looks as though one of those psychedelic screen savers was permanently seared into its monitor, and it is necessary to have a working knowledge of the layout of a qwerty keyboard to input any information.

Tonight, I solved a particular bothersome mystery involving drilling fluid. Since I arrived, I had been wondering how, when we live and work on snow, in a place with no soil or dust, everything was so dirty. The snow on the floor of the trenches is black, and little dark tracks mark the commonly trod paths on the plywood floors of the dome. I conceded that the wood might generate some dirt, and maybe the squished remains of food that fell on the floor, but I could not conceive of a source of filth significant enough to account for these ubiquitous stains.

As I was waiting to log the core this evening, I was sliding around the coconut-slick floor of the driller’s shack in my giant Sorel boots. I looked down to see little black ribbons tracing the path of my feet, exactly in the shape of my boot treads. It occurred to me that all this grime was actually the disintegration of 34 pairs of rubber-soled boots, slowly eroding under the oily caress of estisol. I felt extremely satisfied at discovering the answer, a little embarrassed that it had not occurred to me before, and more than a little bit disturbed. If it can dissolve my boots, what is it doing to my hands, which invariably become drenched in drill fluid by my oily gloves?

The ECM is getting a little more exciting these days as well. We just passed through the cold, relatively uneventful period of the Last Glacial Maximum, when conditions remained fairly constant for about 10 thousand years prior to deglaciation. Now, we are getting deeper into the last glacial period, a time marked by a series of abrupt Northern Hemisphere climate changes known as Dansgaard-Oeschger events. Temperature reconstructions from previously drilled Greenland ice cores show changes of over 10 degrees Celsius (nearly 20 F) occurring in a matter of decades. These are evident in the ECM as huge spikes in the conductivity of the ice, and the ice appears clearer in the line scanner. These events are still poorly understood, but their imprint is found in paleoclimate records around the world, suggesting that the global climate system reorganized itself drastically and rapidly numerous times during the last glacial period. One of the biggest questions about the Eemian was whether the same types of rapid Northern Hemisphere changes occurred during the last interglacial, when the background conditions were much more similar to today’s.

Answering these big questions, however, requires us to drill, log, process, and ship 2500 m of ice, and that is a big job. Luckily, the NEEM sauna was completed a few days ago, and is perfect for relaxing sore muscles, unclogging estisol-plugged pores, and being really, truly warm for a few short minutes a day. Its existence is another mind-boggling aspect of life on top of the Greenland ice sheet. Inside one of the red garage tents, there is an inconspicuous plywood room. When you open the door, the cloud of 80 C (176 F) air that spills out is the first indication that something very weird is going on. There are two rows of benches made of sanded cedar and a gas-powered furnace that heats a heaping pile of black rocks. By pouring snow (which quickly melts into water) onto the rocks, it is possible to increase the humidity to almost 40%. Although this is an arid day by Oregon standards, it is a significant improvement over the skin-cracking dryness of the conditions here.

Unfortunately, the sauna will only operate for a few more days until it is time to start packing up camp. This is a momentous task that will require everyone’s help for the days leading up to the next flight period on Tuesday. Everything that is going must be packed and palletized, and everything that stays has to be packed and stored in a safe over-wintering location. Although it will be strenuous, it is all part of what is necessary to facilitate this extraordinary effort and is more than compensated for by the luxurious living conditions here and the state of the art laboratory we work in every day on top of a few miles of polar ice.

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