Ice Core Science

In this section you can learn more about the science conducted at EastGRIP.

Watch a short movie about the science at EastGRIP
Read about drilling of the main ice core
The EastGRIP associated projects (2019)
Or immerse yourself in popular science papers

Ice cores - Revealing secrets of past climate

Video from UiB - Universitetet i Bergen.

Ice core drilling

Ice core drilling in Greenland was initiated in 1955 and since then numerous of short ice cores and several deep ice cores have been retrieved from the Greenland Ice Sheet. At EastGRIP we aim to drill an ice core through more than 2550m of ice.

The ice core can provide us with a range of information both on the dynamics of the ice (how the ice 'behaves') and on past climate (temperature, greenhouse gas concentration, vulcanic eruptions etc.).

Below you can click on the interactive map to learn more about how we drill the ice core, the following (laboratory) analyzes and the knowledge that can be derived from the measurements.

In addition to drilling the main ice core through an ice sheet measuring more than 2500m, a range of other projects and measurements are also conducted at the site, this including drilling of short ice cores (shallow drilling), a range of measurements on the surface of the snow (e.g. snow accumulation, vapour and gas content and radiation), drone measurements, radar measurements and much more.

Drilling

The drilling of the main ice core began late in the 2016 field season, so the borehole casing could be installed in the beginning of the 2017 season before the main drilling could start.

To drill the ice core a special ice core drill has been developed by a group at the Centre for Ice and Climate. The ice core drill is mounted to a cable and contains all necessary electronics and a motor.

Schematic draving of drill with 2.2 m core barrel used in 2017 at EGRIP. Notice that the drawing is shortened at several points marked by white 'lines'.

The drill head rotates and cuts its way through the ice using knives. The core barrel consists of an inner and an outer part. The inner barrel is covered with spirals (see picture below). The ice core is pushed into the inner core barrel, while excess ice in the form of ice chips is transported between the inner and outer core barrels using the thick spirals. The ice chips are then pumped into the chips champer.

Fresly drilled ice core still in the ice core barrel

Once the drill is filled with ice the rotation stops and the process of raising the drill using a winch starts. "Core-catchers", small spring-loaded knives, cut into the ice core and prevents it from gliding out of the drill while it is being pulled towards the surface.

Once the drill reaches the surface the tiltable drill tower makes it possible to transport the core in the core barrel to the extraction freezer where the core is pushed into a tray for further processing.

Drillers Dennis and Sune push the core barrel containing ice core into the extraction freezer (left), where Lydia and Emilie wait to receive it. The bottom of the ice core is visible in the barrel (middle). Sune is then pushing the core out of the core barrel into a tray (right). – Or is he baking a pizza?

Visit the EGRIP trenches, including the drilling trench, in this 360° film by By Susanne Buchardt, DIS

Even though the actual drilling takes about a quarter of an hour it can take up to three hours from drilling to the point where the ice core reaches the surface. The time is used to transport the drill up and down in the borehole and servicing the drill section at the surface

The conditions are not alike throughout the ice. Thus, the drilling setup has to be changed at certain depths.

For example, the length of the ice cores drilled changes. At the top part of the ice, cores of about 2m are drilled. This is especially important in a certain section of the ice called the ‘brittle zone’. In this section the ice is fragile. Once the drilling passes this zone longer ice cores of about 3.5 meters are drilled.

Another condition that changes with depth is pressure. At the bottom of the ice sheet the pressure is approx. 280 atmospheres because of the enormous weight of the ice above. Due to the high pressure a borehole will quickly close. To prevent this from happening borehole fluid of approximately the same density as the surrounding ice is used.

On the Centre for Ice and Climates website you can find further information on drilling techniques and development of the drills.

Measurements in the field

Some measurements are conducted in the field, while others are done in the labs back at the laboratories at the participating universities. Before the measurements can be performed, the ice core is cut into different pieces (see previous section). Below you can see a schematic drawing showing which part of the ice core is assigned to the different measurements. In this section you can read more about the measurements performed in the field.

Cutting Scheme from EastGRIP showing which parts of the ice core that is assigned for different measurements

Measurements in warm laboratories

Inside the science trench there are two warm laboratories. In one, continuous measurements of stable water isotopes on sticks of ice core are performed and in the other measurements on physical properties are conducted.

Stable water isotope measurements

An atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and typically a similar number of neutrons. However, the number of neutrons can vary and the different variants of the same atom is thus called isotopes. Below three different water molecules formed from 2 hydrogen atoms and different oxygen isotopes (similar, but with different number of neutrons in the nucleus) are depicted. The most common form is H₂¹⁶O. For each 10,000 water molecules in nature, only 3 are H₂¹⁷O and 20 are H₂¹⁸O. A water molecule consists of one oxygen atom and two hydrogen atoms. However, the atoms can vary with respect to the number of neutrons (see picture to the right). This means that some of the water molecules will be heavier than others. The maximum amount of moisture that air can hold drops with decreasing temperatures. When humid air cools, at some point the water molecules will condensate to form precipitation. As the heavier isotopes have a slightly larger tendency to condensate, the humid air mass will gradually lose relatively more and more of the water molecules containing heavy isotopes (¹⁸O and Deuterium; D or ²H). Every time precipitation forms, the air mass will become more depleted in heavy isotopes. In the language of physics, fractionation takes place. During cold conditions (e.g. during winter or in a cold climatic period), the air masses arriving in Greenland have cooled more on the way, thereby having formed more precipitation and the remaining vapor is therefore more depleted in heavy isotopes (corresponding to lower δ¹⁸O vales). Thus, the isotope values in the snow falling at the Greenland ice sheet reflects the level of rain-out from the air mass, which correlates with temperature. Therefore, by measuring the isotope composition in the ice core it is possible to reconstruct the annual temperature variations year by year.
For the active days, approx. 13-15 meters of ice core can be processed per day in camp using a method called Continous Flow Analyses (CFA). You can read more about the method in the 'measurements in labs' section.

Measurements of physical properties

Ice crystals in different types of polarized light. The squares are 1 cm on each side. The phrase "Physical Properties" covers a range of different measurements. Many of these measurements are conducted in laboratories at the universities participationg in the projects (e.g. the Alfred-Wegener-Institute in Germany). However, for the analyses that require fresh ice, systems will be set up in the science trench and in the before mentioned designated warm lab. Here, the physical properties of the ice, e.g. the crystal structure, is measured.

Measurements in the lab

Gas Analysis

Gas bubbles trapped in the ice when an ice core can be analysed in order to determine the composition of the atmosphere hundreds of thousand years back in time. This is done either by by melting content (e.g. for analysis of the CH₄ or N₂O) or crushing the ice (for anlysis of the CO₂ content), thus releasing the samples of past atmospheric air from the ice and analysed.
Concentration measurements can be performed using a gas chromatograph (GC), where isotope ratios are determined using mass spectrometry.
You can read more about sampling and analysing the gas here .

CFA

CFA is short for 'Continous Flow Analysis' - a method used to prevent contamination of samples thereby enableing measurements of impurities of very low concentration in the ice.

In short the ice is melted in a way so only the clean inner part is used for the analysis:

A part of the drilled ice core is melted continuously at a speed of approx. 3 cm/min on a gold coated plate which is located in a cold lab (–20°C). Only the inner part which was never in contact with ambient air is used and is pumped into a warm lab, whereas the possibly contaminated water from the outer part is rejected. The melt water stream still contains air bubbles (approx. 10% of the total volume) from the enclosed air in the ice.

The air is removed in a so-called debubbler, before the sample stream is split and passed into a number of analysis systems, in which the following records are obtained:

The amount of insoluble dust, and the size distribution of the particles.

The concentration of NH₄⁺, Ca²⁺, NO₃^–, Na⁺, SO₄^2–, HCHO, and H₂O₂.

The conductivity of the melt water (which is tightly connected with the ion content)

The impurities come from different sources and thus yield different information about the climate system. Some of the impurities have an annual cycle, and these records can therefore be used for identification of the annual layers in the ice. One example is Ca2+, which comes mainly from dust and has highest concentration in spring.

Tephra samples

A visible volcanic ash layer in the ice core at 1078 m depth (drillers’ depth). Possibly the well-known 10,400 yr old Saksunarvatn tephra layer. When large volcanic eruptions occur, huge quantities of acids are introduced into the atmosphere and distributed over vast areas. In ice cores, volcanic layers can sometimes be identified by volcanic ash particles (tephra), but more often the layers only contain elevated concentrations of acids seen in the ice cores as mainly sulphate and sometimes fluoride. In Greenland the nearby Icelandic and Alaskan volcanoes have a strong imprint in the ice cores. However, if the volcanic eruptions are strong enough to inject acids into the stratosphere, also volcanoes from the tropics or even the southern hemisphere can be identified in Greenland. Examples of well-known historic volcanoes that have left a clear fingerprint in all Greenland ice cores are Tambora, Indonesia (1815), Krakatau, Indonesia (1883), Katmai, Alaska (1912), El Chichón, Mexico (1982), and Mount Pinatubo, Philippines (1991). The largest volcanic events are also impacting global climate by injecting large amounts of small particles (so-called aerosols) into the stratosphere thereby partially shielding the Earth from solar radiation and reducing temperatures. The impact of volcanoes on past climate is constrained from the long records of past volcanism reconstructed from Greenland and Antarctic ice cores. Acid and tephras from volcanic eruptions are also used for dating purposes and for linking ice cores with other climate archive.