The European Project for Ice Coring in Antarctica (EPICA)

March 17, 2010 by jason

This article is a broad description of the European Project for Ice Coring In Antarctica (EPICA), a multinational (European) deep ice core drilling project in Antarctica. The purpose of the project is comprehensively document the state of the atmosphere throughout recent earth history. Accurate data about atmospheric composition obtained from EPICA dates back almost 1,000,000 years.

Drilling was performed at 2 separate sites:

• Concordia Base (Dome C) - 75°S 123°E 3233 m altitude
• Kohnen Station, Dronning Maud Land - 75°S 00°E 2892 m altitude

Concordia Base (Dome C)

Having realized the importance of the continental antarctic plateau, the National Program for Research in Antarctica (PNRA) and the French Polar Institute (IPEV) signed a cooperative agreement for the erection of the Concordia station in the vicinity of Dome C. The Concordia site was chosen as it was able to provide the longest undisturbed information about the atmosphere. This means that researchers were able to dig the farthest without hitting disturbed or polluted samples. The 2nd drilling project at Dome C was completed in December 2004, reaching a depth of 3270 m (only 5 m above the bedrock) (source: EPICA). The depths and drilling points of the two drill-sites at EPICA Dome C are shown in the image below:

Depths and drilling times of the two EPICA Dome C drilling sites (source: Laurent Augustin, LGGE, Grenoble)

Kohnen Station, Dronning Maud Land

Information on this base is somewhat more limited, suffice to say that it was selected based on its higher rainfall levels, as well as its sensitivity to conditions in the south Atlantic. This made it suitable for testing any connections between changes in Atlantic Ocean circulations and the changes in climate in Greenland.

Picture of the Kohnen Station EPICA drilling site (source: Close coupling of climate with green house gases in the past)

How the Samples are Obtained

This is one of those things that are much harder to do than they sound. In principle, drilling for ice cores is simple enough; each ice core sample is obtained by passing a hollow tube into the ground. This is done simply by inserting the tube into the ground when the ice is sufficiently soft and the sampling is being performed at low depths. For deeper samples or where the ice is increasingly dense and hard, the process becomes more difficult, requiring hollow drill-tips to be used. In the case of sampling deeper than about 300 m, the hole is filled with a fluid to stop it closing.

When ice core samples are taken from great depths, they undergo a process of decompression when they are brought to the surface. This process, called relaxation, can take months. During relaxation, the sample needs to be stored at subzero temperatures to avoid cracking (and release of air) from the samples (Ommanney, 2002). Contamination of the ice core samples does occur, an ice core sample will typically have 2 to 3 times as much bacterial density and organic carbon on the edges of the sample than the center (Brent, 2003). This is normal, and has of course been accounted for.

Obtaining the cores themselves is the first step, the next is to obtain useful information from them. Each sample is chemically analyzed for composition, and by identifying what its composition would have to have been in order for it to have the composition it has today (based on its age) we can determine what the atmospheric conditions were when this sample was taken.

Identifying the Age of the Ice Core Samples

The first logical step in analyzing each sample, is to identify its age. For the shallower samples, this is done more or less the same way we analyze the age of a tree; by looking at annual stripes in the samples. The stripes are either visual visible (related to the pace at which the ice froze), isotopic (related to temperature), or chemical (reflecting different mechanisms by which the ice is transported during different parts of the year). Because of this, dating younger cores is both accurate and relatively simple (although laborious). Older cores require more complex methods, outline in more detail at the Vostok Ice Core Timescales section of the NOAA Paleoclimatology website.

Ice core sample taken from the GISP 2 drilling project in Greenland (source: Ice Cores)

Data Obtained from the Samples

Once the age of each sample is identified, the chemical and isotopic compositions are measured. Chemical analyses give us information about the atmospheric composition at the time, such as CO2, NO2 and CH4 concentrations. Isotopic analysis is used to obtain other information, of those most notable and important to climate science are the isotope Beryllium-10 (commonly referred to as Be10), and Delta-O-18 (commonly written δ¹⁸O or D18O). Be10 is important because it is related to cosmic ray intensity (the limited importance of which is discussed in my article on cosmic ray levels). When D18O is analyzed in combination with the concentrations of normal Oxygen atoms, the temperature at time of solidification of the surrounding water can be identified. This information can be used to predict atmospheric temperature at the time.

Temperature and CO2 concentrations for the past 400,000 years, as obtained from the EPICA Dome C Ice Cores (source: Petit et. al, 1999)

The extraction of information about atmospheric compositions from ice cores is a vastly complex subject, and methods vary for each atmospheric constituent. For those interested in learning more about the details of obtaining information about ice cores, I would refer you to the NOAA Paleoclimatology website, where more or less all available data on ice core records is kept. For an interpretation of the data obtained from EPICA, you might like to read my article on EPICA Ice Core Data and temperature/CO2 relationships.