Ice cores

The Norwegian Polar Institute studies the mass and distribution of glaciers, and how climate change affects them from year to year. Old layers of ice in glaciers can also be used as a climate archive, and can show the prevalence of hazardous substances.

Climate archive in the deep freeze

A slice from an ice core

A slice from an ice core. The ice contains air bubbles and particles with climatically active gases such as CO2. Photo: Ola Brandt / Norwegian Polar Institute

Chemist with ice core

Chemist Anja Eichler logs an ice core taken from Lomonosovfonna, Svalbard. The ice cores are drilled and packed inside a tent to avoid wind and sun. Photo: Gerit Rotschky / Norwegian Polar Institute

Researchers retrieving an ice core on Lomonosovfonna, Svalbard

Researchers from the Norwegian Polar Institute and the Paul Scherrer Institute (Switzerland) doing field work on Lomonosovfonna, Svalbard. A 149-metre long ice core was retrieved. Photo: Gerit Rotschky / Norwegian Polar Institute

The ice sheets in Antarctica and Greenland contain huge amounts of frozen information about past climate. The snow that once fell there provides important information about what characterized the climate eons ago.

We can access this archive by drilling ice cores, and in Antarctica they can go as deep as 3 000 metres. Ice cores can show us how temperatures have varied and ice ages have come and gone hundreds of thousands of years back in time. This information gives us perspective on our own time. Tiny air bubbles in the ice tell us how the composition of the atmosphere varied according to the temperature 700 000 years ago. Ice cores from Antarctica have revealed that the atmospheric concentrations of greenhouse gases (including CO2) are much higher now than they were before.

Sixty percent of the land in Svalbard is covered by glaciers, but they are not equally easy to use as climate archives. The main problem with Svalbard’s glaciers is that they melt so much in the summer that some information disappears when the meltwater flows down through the ice. But if we choose to study glaciers at high elevations, where less ice is lost to melting, Svalbard’s glaciers are also valuable climate archives.
Our ice cores from Svalbard cover the past 1000 years. 

Dating ice cores from glaciers

Whenever natural climate archives are being studied, accurate dating is crucial. Many different methods can be used to date ice cores, and scientists usually use several methods in parallel. Distinct layers laid down during historical events – layers termed “horizons” – are important in this context. For example, nuclear test explosions such as those done in Siberia between 1954 and 1974 created a horizon with high concentrations of the radioactive isotope of cesium (137Cs) in ice in Svalbard. The highest concentrations of radioactive isotopes from nuclear explosions were laid down in the period 1962-1963. Measurements related to the Chernobyl accident in 1986 can also be used to date the snow in several places in Svalbard, but the signal is not as distinct as that from the nuclear testing in Siberia.

Historic volcanic eruptions provide another way to date ice. All our ice cores from Svalbard show clear signs of the eruption of the Icelandic volcano Laki in 1783. The eruption is detectable not only in the form of high levels of sulfate, but also as a few fragments of volcanic ash. 

How do we extract information from the ice cores?

Glaciologist Jack Kohler drilling an ice core at Midtre Lovénbreen

Glaciologist Jack Kohler drilling an ice core at Midtre Lovénbreen. Photo: Elvar Ørn Kjartansson

Glaciological fieldwork on Fimbulisen, Antarctica

Glaciological fieldwork on Fimbulisen (the Fimbul Ice Shelf) in Antarctica, during the research project ICE-Fimbulisen. Photo: Helgard Anschütz / Norwegian Polar Institute

Ice cores are a wonderful archive from which to reconstruct climate history. For example, they can tell us much more than the relatively short series of air temperature data that have been collected in Svalbard, where systematic measurement only started in 1911.

In contrast, the 1000-year time series of climate information from Svalbard stretches back to the end of the Viking Era, when the climate was mild. It was actually the mild climate that enabled the Vikings to sail around in the northern seas.

It appears that hot summers similar to those we have experienced in the past decade have not occurred on Lomonosovfonna since the 1200s. There was also a time span with higher temperatures around 1750. At that time there was a lot of whaling north of Nordaustlandet, but the rest of the climate record in ice cores is dominated by the cold period known as the "Little Ice Age".

Results from ice cores agree very well with temperature trends showing that the most recent years are also the warmest recorded in Svalbard since temperature measurement with modern instruments began in 1911.

What is hidden under the ice?

Drill hole in the ice

Drill hole in the ice. Photo: Helgard Anschütz / Norwegian Polar Institute

Radar data play a crucial role in glaciological research. The radar can reveal otherwise invisible structures in snow and ice, and provide information about topography and conditions beneath ice several kilometres thick.

Water is easy to recognize in radar images, and in many places, lakes have been found under Antarctic ice between 2 000 and 4 000 metres thick. These lakes have attracted much attention because some believe that they may be habitats for unknown life forms. Researchers are working to develop a reliable drilling technique that will not contaminate the lakes, so they can drill down and examine what is in them.