The deep ice core drilling project at the German Kohnen Station in Dronning Maud Land (DML) is part of the European Project for Ice Coring in Antarctica (EPICA) which started one decade ago. The drilling at Kohnen Station reached the bedrock in the season 2005/06 after four seasons of drilling. The final depth was recorded as 2 774 m.

Aims of the project

Advanced simulations of our future climate call for increased understanding of the complex climate system. Only records of climate variations in the past can provide us with information about the total response of the climate system when influencing factors are changed with all the various feedback mechanisms in action. The knowledge achieved from analyses of ice cores from Antarctica and Greenland has been revolutionary in the field of climate research. The Vostok ice core, drilled one decade ago in Antarctica by a Russian-French team, revealed the variations in atmospheric greenhouse gas concentrations over several glacial cycles. The ice core data verify that the anthropogenic contribution of greenhouse gases has increased the global concentrations far beyond any natural variations seen the last 420,000 years.

The EPICA ice core drilling effort at Dome C extended the length of the existing records by a factor of two. It also provided a wealth of new information due to new analysis techniques developed during the last few years. The EPICA-Dome C ice core thus far represents a continuous record of past climate and environmental changes over eight glacial cycles (EPICA community members 2004). The records of greenhouse gases have been extended to the last 650,000 years (Siegenthaler et al., 2005, Spahni et al., 2005). The EPICA-DML ice core together with the NGRIP (North Greenland Icecore Project) ice core have for the first time revealed a one-to-one interhemispheric coupling for the shorter climate variations during the glacial period, the so called Dansgaard-Oeschger events (EPICA community members 2006). EPICA has been funded by the EU and by national contributions from Belgium, Denmark, France, Germany, Italy, the Netherlands, Norway, Sweden, Switzerland and the United Kingdom.

The programme consisted of two deep drillings in Antarctica at sites with different characteristics. The first drilling started in the season 1996/97 at Concordia Station, Dome C, in the Indian Ocean sector of Antarctica (75°06’S, 123°21’E). The aim of the EPICA-Dome C drilling was to recover an ice core reaching as far back in time as possible. The second drilling started a few years later, in 2001/02, at Kohnen Station in Dronning Maud Land (75°00’S, 00°04’E). The EPICA-DML drilling aimed to retrieve a high-resolution record of a few complete glacial–interglacial cycles at a site facing the Atlantic Ocean.

EPICA-DML fieldwork

During the season 2005/06 PhD student Torbjörn Karlin represented Sweden in the EPICA-DML drilling team at Kohnen Station. EPICA personnel and part of the cargo were flown in and out within the framework of DROMLAN (Dronning Maud Land Air Network), using an Ilyushin 76 TD (picture 1) aircraft. The feeder flights from Novolazarevskaya airbase to Kohnen Station were carried out using a Basler Turbo 67 (picture 3). The first group (logistics) landed at Novolazarevskaya airbase on 3^rd November and the second group (drilling and science) landed on 11^th November. Feeder flights started immediately to Kohnen Station. The days following arrival were used for acclimatization to cold conditions and altitude.

Meanwhile light work was performed, such as preparing the drill tower, setting up logging systems, communication systems and installing science facilities. Preparatory work – such as logging and reshaping of the borehole and maintenance of the drill winch – took another three weeks, and the drilling started at a depth of 2 565 meters on 7^th December. The drilling reached bedrock on 17^th January at a depth of 2 774 meters. The station was occupied for a period of 98 days until 8^th February 2006. Altogether 26 people (ten drillers, six scientists, ten logistics) worked at the station. One traverse from the German station Neumayer supplied Kohnen Station with fuel, drill liquid, heavy equipment and food.

At the end of the season the scientific group left Kohnen Station for Novolazarevskaya airbase with a Basler Turbo 67 and arrived in Cape Town on 5^th February 2006. On 9^th January a group of five Germans, nine Norwegians and one Swede visited Kohnen Station as part of a presentation tour of Dronning Maud Land research stations for representatives from the German Government and the Norwegian ministries of Education and Research, Environment and Foreign Affairs. The group came by Basler aircraft from the Norwegian station Troll and returned there afterwards. The Swedish visitor was Ann-Sofie Rickby from the Swedish Polar Research Secretariat.

The Kohnen Station (picture 2) is situated at an elevation of 2 892 m a.s.l. The mean annual temperature is -44.6ºC and the mean annual accumulation rate is above 6 cm (water equivalent) per year. The drill trench is located a few metres under the snow surface. The temperature in the drill trench never exceeds -25ºC during the field season. The ten drillers in three shifts kept the drilling operation running for 24 hours per day since the field season is short and work has to be done in the most efficient way.

The weekly production decreased towards the end of the season due to the increasingly difficult penetration. This was due to the higher temperature of the ice and the pressure melting of the ice. At 2 550 m depth the recorded temperature of the ice is as high as -7.5°C, which can be compared to temperatures of -44.5°C close to the surface of the ice sheet. With increasing temperature the ice cuttings contain more water and tend to stick together. The ice itself gets tougher, less brittle and thus harder to break. By the end of the drilling, at the depth of 2 774 m, the ice temperature was at the pressure-melting point and the bore hole was partly refilled with water (picture 4. 5).

The electro-mechanical drill produces 98 mm diameter ice cores, typically in unbroken lengths of 0.5 m–1 m for each run. Each run takes about 2.5 hours to complete. After the newly retrieved ice core has been physically measured and marked, its electrical properties are measured by dielectric profiling (DEP). Next the ice core is packed for transport to the freeze room facilities at Alfred Wegener Institute (AWI) in Bremerhaven. After each field season a large group of European scientists gather for several weeks in the freeze rooms at AWI in a post-field sample preparation campaign. A processing line is built up where the ice core cross-section is dissected into pieces for different measurements in various laboratories by a series of cuts with band saws. Changes in crystal size and orientation along the core are detected. A second electrical conductivity measurement (ECM) is also performed on the cut core. The remaining parts are sectioned for transport to different European laboratories for analysis of stable isotopes in the water itself (oxygen and deuterium used as proxies for temperature variations), gases (carbon dioxide, methane etc.), dust, ions, mechanical properties and many other parameters. At least a quarter of the ice core is packed and kept at AWI as an archive for future analyses with new techniques.

Analysis at Stockholm University

We perform chemical analysis of the two deep ice cores drilled within EPICA. The analysis of the EPICA-DML ice core has partly been performed during the post-field sample preparation campaigns at AWI. One section of the ice core was cut into squared (3 × 3 cm) 100 cm long pieces and used for continuous flow analysis (CFA). The 100 cm long ice bar was mounted in a tray and lowered down on a heated melt head. Only the melt water from the inner, clean part of the ice section was sucked into a warm laboratory where it was analysed directly at very high resolution for liquid conductivity, dust content, hydrogen peroxide, formaldehyde and six ions. One line with melt water was not used for direct measurements. Instead the melt water was collected in small bottles and later analysed by ion-chromatography at four different laboratories in Europe. At Stockholm University we are analysing one quarter of these samples and we are measuring ten different ions by means of ion-chromatography (eg. Wolff et al., 2006).

We aim to increase knowledge on the impact of aerosols on the radiation balance of the atmosphere by studying the natural variations of aerosols and climate over glacial cycles. We use the information contained in the ice cores on concentration changes with time in model simulations of the past. We test which processes are most important in yielding the record present in the ice. We learn how these processes have changed with climate change and how the chain of different climate feedbacks has acted. The different sources of sulphate aerosols and their potential to provide climate feedback mechanisms are in focus. This knowledge will enable an assessment of the role of anthropogenic sulphate aerosols in future climate development.

Latest results

Palaeoclimate records from Antarctic and Greenland ice cores showed different temperature patterns during the last glacial period. The latest results from the EPICADML ice core show that these changes are not independent. We have been able to synchronize precisely climate records from Antarctica and Greenland using the common information on global changes in methane concentrations archived in air bubbles in the ice. Even shorter and smaller temperature variations in the south were directly linked to the rapid temperature variations in the north via changes in the ocean circulation in the Atlantic. The results show that, for any period in the time between 55,000 to 20,000 years BP, Antarctica gradually warmed when the North was cold and warm water export from the Southern Ocean to the North Atlantic was reduced. In contrast the Antarctic started to cool every time more warm water started to flow into the North Atlantic during warm events in the north. Data shows that the degree of warming in the south is linearly related to the duration of cold periods in the North Atlantic. This result suggests a general linkage between long-term climate changes in both hemispheres via a “Bipolar Seesaw” when the overturning circulation of the Atlantic changes (EPICA community members 2006).