Ice core drilling

This page on ice core drilling was written a Peter Neff, at the time a doctoral candidate from the Antarctic Research Centre, Victoria University of Wellington and now a postdoctoral research associate at the University of Rochester, New York, USA.

Drilling through the ice

Ice core drilling in Antarctica is a pretty arduous task. To get the oldest ice, ice cores need to be drilled in the centre of the ice sheet, near the ice divide. The ice divide is far away from research bases and the ocean. It isn’t easy to deploy a large team of scientists, mechanics, engineers, cooks, field assistants and more to the middle of the Antarctic Ice Sheet! In this post, Peter Neff describes how his team went about collecting the Roosevelt Island ice core.

Introducing the Team

Ice core drilling requires a large team of people. We are twelve people from around the world: six Kiwi, three American (though two came on behalf of New Zealand and Australia), one German, one Swedish, and one Chinese. Scientists, drillers, mechanic, cook/medic, students – all of these roles are somewhat interchangeable. The ice core project is led by New Zealand scientists, with support from the United States, Denmark, United Kingdom, Germany, Australia, Italy, China, and Sweden. Our work is supported primarily by Antarctica New Zealand, with aircraft support provided by the United States Antarctic Program.

Aim of the ice core drilling team

Our goal is to drill a 760 meter-long ice core to bedrock on Roosevelt Island in the Ross Ice Shelf—the largest ice shelf in Antarctica.  This is a task that has been at least a decade in planning, and at the time of our deployment in 2012 had already involved three three-month field seasons.

Getting to the ice

To begin our field season, in mid-October we fly nearly 4000 kilometers from Christchurch, New Zealand on a U.S. Air Force C-17 cargo jet. We arrive at Scott Base, a cluster of sea-foam green buildings named after the famously-late Antarctic explorer. Between weeks preparing equipment for our own expedition, we visit Scott’s hut at Cape Evans, the home he left as he embarked on his final expedition. Everyone thanks their lucky stars that we don’t suffer now like they did back then!

Deep Field at Roosevelt Island

After two weeks of preparation and waiting for weather, we board another flight for our trip to the “deep field.” It’s only another 700 kilometer flight along the calving margin of the Ross Ice Shelf to our home for the next 3 months.

The plane lands, skipping haphazardly on its skis along the rough snow runway. Our new home (a yellow accordion-shaped RAC tent) is not 100 kilometers from Framheim, “home of the Fram,” where Roald Amundsen’s ship anchored as he trudged to and from the South Pole–one hundred years ago.

Choosing an ice-core location

Roosevelt Island is an ice dome, 550 meters high, 150 kilometers long and half as wide.  The ice here is grounded on bedrock (well, mud as it turns out) approximately 200 meters below sea-level, snow having been accumulating here for tens of thousands of years. The annual layers within the ice are very flat, easy to interpret. Older ice layers in the ice have even been brought closer to the surface, due to very stable ice flow at the island’s summit for the last 3000 years. Near bedrock, 760 meters below the surface, the ice should easily be 40,000 years old.

The West Antarctic Ice Sheet (WAIS) once extended over top of this site, but since the end of the last ice age has retreated to the southeast some 300 kilometers (1. Conway et al., 1999). Currently, our little “island” is surrounded by the Ross Ice Shelf, a mass of ice the size of France that is floating on the Ross Sea and acting as something of a bathtub plug holding back the flow of the ice sheet upstream. This is one of our primary interests:  the history of the Ross Ice Shelf and climate in the region spanning the last glacial-interglacial transition.

The WAIS has been a major focal point for Antarctic research since international programs were initiated during the 1957 International Geophysical Year, with intensified interest since the 1970s when it was hypothesized that the WAIS may be prone to collapse if support from its bounding ice shelves were removed (2. Mercer, 1978; 3. Bindshadler, 1998; 4. Joughin and Alley, 2011).  In 2012, the researchers from the United States successfully completed drilling of a 3400m ice core at a site called WAIS Divide, near the ice-flow divide that is the heart of the WAIS. This core provides a record at unprecedented resolution spanning 68,000 years (5. WAIS Divide project members, 2013).

Roosevelt Island is at the terminal end of the WAIS system, and an ice core from this site will provide new spatial information about climate in West Antarctica.

Building this camp, selecting a drill site, and installing the drill has taken three years (planning and equipment development spanned nearly a decade).  The deep borehole was initiated during the 2011-2012 austral summer, using a newly-built electromechanical ice coring drill manufactured in New Zealand.

Drilling an ice core is not unlike drilling a hole to install a doorknob, though there are a few complications (after all, the door in this metaphor is hundreds to thousands of meters thick).  Since we want to retrieve core samples and not just destructively bore our way through the ice sheet, our drill has to be hollow.  Also, as we’re carving our ice cores with a hollow drill-head, we have to collect the ice cuttings we make in order to keep the borehole open.  Additionally, to lubricate the drilling process and fill the void left by our coring, we use an ester-based drilling fluid that makes our ice cuttings look a lot like shave-ice, or a piña colada (the drill fluid does not taste so good, but does smell of coconut).

Storing the ice core

But what to do with all that ice?

It turns out that, especially at a low-elevation site like Roosevelt Island, keeping the ice cores cold is a big challenge! Although the average yearly temperature is -23°C, during the summer the temperature comes right up to 0°C.

Yes, an ice core will remain frozen right up to 0°C, but the gases in the air bubbles within the ice will start to diffuse when the cores get warmer than -18°C.  Since this is one of the primary interests in ice cores—measuring ancient samples of atmospheric gases like carbon dioxide and methane—we have to store and ship the ice cores at low temperatures.

The solution to this problem is an ironic one—we bring a freezer with us to Antarctica! The ice cores are stored in a snow cave dug about 2-3 meters below the surface, and ducts are plumbed into the cave to circulate air through the freezer unit. This way, we’re able to keep the cores at around -23°C.

Getting the ice core safely home

The next step in the process is to get an airplane to come out and pick up the ice cores! When the weather is cooperative enough for this to happen (we once waited three weeks), the plane is loaded up and takes off with a heavy load of ice. They can’t cool the cabin of the plane, so they turn off all heating and fly higher than normal, about 10,000 feet, where the air is nice and cold.

A few hours later, the ice cores are unloaded from the plane and put into a mobile freezer on a big sled, to be towed back to Scott Base where yet another freezer container sits. This is the final container that eventually will be shipped by oceangoing vessel back to New Zealand!

In January, after nearly another month of cleanup, taking things apart, and packing equipment into boxes for shipment home or for storage over the winter, we hitch a ride off the island and follow our ice cores home to New Zealand.

Then begins the real work of analyzing the ice core samples…. But that’s another story!

References

1. Conway, H., Hall, B.L., Denton, G.H., Gades, A.M., and Waddington, E.D., 1999. Past and future grounding-line retreat of the West Antarctic Ice Sheet. Science, 286(5438), 280-283.

2. Mercer, J.H., 1978. West Antarctic ice sheet and CO2 greenhouse effect: a threat of disaster. Nature, 271, 321-325.

3. Bindschadler, R., 1998. Future of the West Antarctic Ice Sheet. Science, 282(5388), 428-429.

4. Joughin, I., and Alley, R.B., 2011. Stability of the West Antarctic ice sheet in a warming world. Nature Geoscience, 4, 506-513.

5. WAIS Divide Project Members, 2013. Onset of deglacial warming in West Antarctica driven by local orbital forcing. Nature, 500, 440-444.

About the author

Peter Neff is a PhD Candidate at Victoria University of Wellington, New Zealand, studying the trace element chemistry of ice core samples from Roosevelt Island. He has participated in ice coring and other glaciological projects on the Greenland and West Antarctic ice sheets, as well as in the mountains of British Columbia, Canada. He is a native of the Pacific Northwest region of the United States.