Ice Core Paleoclimatology : How

How are ice cores obtained?
How does the team get ready?
How are the ice cores obtained?
How are ice cores stored?
How are the samples handled?
How are the samples analyzed?


How are ice cores obtained?
Ice cores can be extracted using a variety of methods and technologies that are chosen for the unique circumstances of each project. The planning that is required for such an expedition includes the cost and timing of preparing and transporting equipment and supplies up the mountains to the ice fields; living at high altitudes while drilling the ice cores; carefully describing, protecting, and storing the ice cores at the drill site; and transporting them (and the team, equipment, and waste) down off the mountain.

All the materials that will be needed by the team are loaded on a truck and taken as close to the drilling site as possible. In many instances, there are no roads to these regions, so there are unusual circumstances and unavoidable delays in getting there. From there, the equipment and supplies are carried by humans (in fitted backpacks) or hauled up the mountains on the backs of pack animals to a base camp. Local people are often hired, along with the pack animals they typically use, to carry the approximately 6 tons of camping and drilling equipment and supplies up the mountain. Weeks later, approximately 10 tons of equipment, waste, and ice cores are also carried down from the drilling site by the same group of porters.

How does the team get ready?
The team spends a few days at base camp, which allows them to adjust to the change in air pressure and to make more red blood cells, which enables them to work at that altitude without an oxygen tank. Once the team has become accustomed to the air pressure at base camp, they then move higher on the mountain, and within a week or so, up to the elevation where they will drill for ice. Once there, they have to set up the drilling station, and also set up the tents they will live in for the next couple weeks.

How are the ice cores obtained?
Ice cores are obtained by drilling a vertical hole into the ice with a drill. The smallest of the drills is a hand auger, which can be used to drill approximately 30.5 meters (or about 100 feet) into the ice. Some type of power source is required to drill deeper than that. The type of power that is used often depends on the nature of the ice.

An electro-mechanical drill is used to retrieve cores in very cold places, such as Greenland and Antarctica where the ice is hard. This hollow drill, which is 100 mm in diameter (approximately 4 inches), has a grinding bit that chews its way through the ice. As the drill works its way down into the ice, the central part of the drill is filled with ice. This piece of ice is the “ice core” that the scientists describe and analyze. The mechanical drills are very efficient at retrieving cores to about 200 meters (roughly 650 feet) in depth.

To extract cores in “warmer” ice caps and glaciers, where temperatures may be only slightly below freezing, a thermal electric drill may be used. This drill has a metal coil, similar to the heating element in a toaster, which melts its way down into the ice. Again, the ice core is the cylinder of ice that is inside the hollow drill bit when it’s pulled up. A new, lightweight, thermal electric drill has been developed for ice coring in cold glaciers. It is capable of recovering a 100 mm diameter (about 4 inches wide) ice core to a depth of 1,000 meters (3280 feet) over a period of a couple weeks.

Ice core drills may be powered by various sources, but the two most common power sources used are fuel-powered generators and solar panels (photovoltaics), which convert sunlight directly to electricity. Solar powered drills were first used in the early 1980s for ice core recovery. Since then, special portable drills that can be powered by solar panels have been developed and used by BPRC researchers. The solar-powered drill and solar panels are only taken on an expedition when the drilling conditions are predicted to warrant using them.

Once everything is operating, the team works as many hours each day as they can. The drilling stops when the team reaches a point where they can’t get a good sample anymore. Hopefully, this means they have reached the bedrock beneath the ice!

How are ice cores stored?
The ice cores are put into a clear plastic sleeve, labeled, and lowered into a pit in the ice cap for temporary storage, until the drilling is finished. Then the ice cores are packed into special cardboard tubes, which are marked. Six cores can be placed into an insulated box. Then specially designed cold packs (“cryopacks”) are placed on the ice core tubes and a layer of foam is added before the box is sealed. (see picture). With this level of insulation and packaging, the cores are safe for 3-5 days of travel without danger of thawing. It is critically important that the ice does not melt while being transported.

The boxes of ice cores are hauled down the mountain to a waiting freezer truck, which hauls them to the nearest airport. They are brought back as frozen cargo, and delivered by another freezer truck to the cold storage facility at BPRC. Two large freezer compartments inside the cold storage area can hold approximately 3,000 meters (sections) of ice cores at temperatures of approximately -30 to -40 degrees Celsius. Attached to the cold storage unit are two cutting rooms that are kept at -10 degrees Celsius (about 21 degree Fahrenheit). This is where the cores are analyzed (on a light table) to note the thickness of the ice accumulation, any visible dust or ash layers or insects, and the sizes and shapes of air bubbles. The thickness of the layers are an indication of whether or not it was a snowy year, and the presence of volcanic ash or a distinct dust layer provides information about other conditions throughout the year as well.

Once they have been described, the ice cores are cut into samples for lab analysis. The samples are kept in sample cups at 21 degreees F. until they are ready to be carried to the “clean room” where the samples are filtered and analyzed chemically.

How are the samples handled?
The samples are covered and carried to the Class 100 clean room, a state-of-the-art lab where there are less than 100 particles, greater than 0.5 um (micrometer or micron) in diameter, per cubic foot of air. The room is maintained with a “positive air pressure” so that when the door is opened, no outside air comes into the lab. The scientists must wear a lab gown with a hood, and special booties to cover their shoes, to minimize any other particles being brought into the room on their clothing or in their hair. The samples are rinsed with ultra-pure water (de-ionized) and allowed to melt.

How are the samples analyzed?
The liquid sample is analyzed for both organic and inorganic particulates (pollen, bacteria, dust, ash, and other solids), which are measured and identified. Microparticle concentrations in the melted samples are determined in 16 size ranges using equipment known as Model TA-II Coulter Counters and in 256 size ranges using another device called the Coulter Multisizer. The scientists also analyze the chemicals dissolved within each melted sample to determine the concentration of specific ions that were in solution in the cloud, such as: chlorides, sulfates, nitrates, etc. These ions (and other chemical markers) provide a measure of other types of activity (such as wind storms, forest fires, and testing or detonation of atomic bombs) at the time the snow fell. Radioactivity of particulates filtered from melt water samples is also measured.

A specific piece of lab equipment, a mass spectrometer, is used to determine the ratios of oxygen and hydrogen in the water molecules of each sample. This analysis offers evidence of the temperature of the sea surface, from which the water evaporated to form the clouds that delivered the snow to the mountaintops. Dr. Lin analyzes the samples using the mass spec. He processes up to 200 samples per week in the mass-spec lab.

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