The long-term programme EPICA, European Project for Ice Coring in Antarctica, continued during season 2003/04 with deep drilling at Kohnen Station in Dronning Maud Land (EPICA-DML). The driller Kerstin Hörnby represented Sweden in field. The drilling reached 2565 m depth which corresponds to an approximately age of 190 000 years. The depth to the bedrock is approximately 2 760 m. Borehole measurements were performed at Dome C (EPICA-Dome C) this season but no drilling was carried out. The EPICA-Dome C ice core, at present 3 190 m long, already covers 740 000 years. (EPICA community members, 2004). Only 120 m of ice above the bedrock remain to be drilled during the coming season, but these are the most difficult ones. The drilling at Kohnen Station will continue the following season.

Aims of the project

Advanced simulations of 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 to a changed forcing, with all the various feedback mechanism in action. The knowledge obtained from analyses of ice cores from Antarctica and Greenland has been revolutionary for the field of climate research. The Vostok ice core drilled one decade ago in Antarctica by Russian-French team revealed the variations in atmospheric greenhouse gas concentrations over several glacial cycles. The ice core data verify the anthropogenic contribution to greenhouse gas has increased the global concentrations far beyond any natural variations seen the last 420 000 years. The present European ice core drilling effort at Dome C has extended the length of the existing records by a factor of two. It has al so provided a wealth of new information due to new an analysis techniques developed during the last few years. The EPICA-Dome C ice core so far represents a continuous record of past climate and environmental changes over eight glacial cycles (EPICA community members, 2004).

EPICA is 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 consists 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 (75°06’S, 123°21’E). The EPICA-Dome C drilling aims to recover an ice core reaching as far back in time as possible. The second drilling started a few years later at Kohnen Station, Dronning Maud Land (DML) (75°00’S, 00°04’E). The EOICA-DML drilling aims to retrieve a high-resolution record of a few complete glacial-interglacial cycles at a site facing the Atlantic Ocean. Sweden has previously contributed to EPICA by pre-site surveys in the DML are in the search for the optimal drill site.

EPICA-DML fieldwork

The driller Kerstin Hörnby represented Sweden in the EPICA-DML team at Kohnen Station in the season 2003/04, as in the previous season. EPICA personnel and part of the cargo were flown in and out in the frame of DROMLAN. The feeder flight from Novolazarevskaya airbase to Kohnen Station were carried out with Dornier Do228 and Twin Otter aircraft. The first group (logistics) landed at Novolazarevskaya airbase on 27 November and the second group (drilling and science) landed on 3 December.  Feeder flights started immediately to Kohnen Station. The drilling could start after a few days of acclimatisation to the height and unpacking of the equipment. The station was occupied for a period of 77 days until 12 February, 2004. Altogether 27 people (11 drillers, 6 scientists, 10 logistics) worked at the station. Two traverses starting at Neumayer Station supplied Kohnen Station with fuel, drill liquid, heavy equipment and food. At the end of season the scientific group left Kohnen Station with Dornier aircraft for Novolazarevskaya airbase and arrived at Cape Town on 15 February, 2004.

The Kohnen Station is situated at an elevation of 2 892 masl. The mean annual temperature is -44.6°C, about ten degrees warmer than at Dome C, and the mean annual accumulation rate is above 6 cm w.e. per year. The higher accumulation rate compared to Dome C leads to a higher resolution in the records extracted from the EPICA- DML ice core. The drill trench is located a few metres under the snow surface. The temperature in the drill trench never exceeds -25°C during the field season. The 11 drillers kept the drilling operation running for 24 hours per day in three shifts. The field season is short and the work has to be done in the most efficient way. The drilling in 2003/04 resumed from a depth of 1 550 m and reached 2 565 m, which corresponds to an approximate age of 190 000 years. The weekly production decreased towards the end of the season due to the more and more difficult penetration. This was due to the higher temperature 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. According to radio echo sounding measurements the present drilling depth is approximately 200m above bedrock. The EPICA-DML drilling will continue in the season 2005/06.

The electro-mechanical drill produces 98 mm diameter ice cores, typically in unbroken lengths of 3 m for each run. After the newly retrieved ice core has been physically measured and marked, its electrical properties are measured by dielectric profiling (DEP). Then the EPICA-DML 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 build up where the ice core cross-section is dissected into pieces for different measurements and laboratories by a series of cuts with bandsaws. Changes in crystal size and orientation along the core are detected. Also a second electrical conductivity measurement (ECM) is 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

The main Swedish contribution to EPICA is chemical analysis of the two ice cores from EPICA-Dome C and EPICA-DML. The analysis of the EPICA-DML ice core is partly performed during the post-field sample preparation campaigns at AWI. One section of the ice core is cut in to squared (3 x 3 cm) 110 cm long pieces and used for continuous flow analysis (CFA). The 110 cm long ice bar is 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 is sucked into a warm laboratory where it is analysed directly at very high resolution for liquid conductivity, dust content, hydrogen peroxide, formaldehyde, sodium, calcium, ammonium, nitrate, chloride and sulphate. One line with melt water is not used for direct measurements. Instead the melt water is 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 sodium, ammonium, potassium, magnesium, calcium, fluoride, methane sulfonate, chloride, nitrate and sulphate by ion chromatography (Castellano and others, in press; Udisti and others, in press; Röthlisberger and others, 2003; Littor and others, 2002). We are also measuring sulphur isotopes in low volume samples and Sr and Nd isotopes in the insoluble fraction of the samples.

We aim to increase the knowledge of aerosol impact on the radiation balance of the atmosphere by studying natural variations in aerosols and climate over glacial cycles. We use the information in the ice core on concentration changes with time as input into model simulations of the past. We test which processes are most important to yield 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.