EPICA Dome C and EPICA DML: Two parallel deep ice core drillings in Antarctica1 December 2002 - 28 February 2003
The 2002/03 season of the long-term programme EPICA (European Project for Ice Coring in Antarctica) was a great success. The EPICA Dome C drilling reached a depth of 3 200 m and resulted in the longest ice core record ever recovered. The EPICA Dome C ice core represents, so far, a continuous record of past climate and environmental changes covering eight glacial cycles. About 100 m of drilling remains before reaching the bedrock, where the age of the ice is estimated to be 1 million years. The EPICA DML drilling reached a depth of 1 550 m. The depth to the bedrock, at this site, is approximately 2 760 m and the age of the ice at the bedrock is estimated to be 300 000 years.
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 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 confirm that the anthropogenic contribution to greenhouse gases has increased the global concentrations far beyond any natural variations seen the last 420,000 years. The present European ice core drilling effort at EPICA Dome C has extended the length of the existing records by a factor of two. It has also provided a wealth of new information due to new analysis techniques developed during the last years.
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 EPICA 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 area in the search for the optimal drill site.
EPICA DML Fieldwork
Kerstin Hörnby represented Sweden and worked as a driller in the EPICA DML team at the German base Kohnen Station in the season 2002/03. In the beginning of December, the crew flew with an Ilyushin 76 ML aircraft from Cape Town in South Africa to the Russian base Novolazarevskaya close to the coast. The EPICA team was the first team to arrive this season and they were warmly greeted by the Russian over-wintering team. German Polar aircrafts (Dornier 228), stationed at the Neumayer base, took the team to the Kohnen Station on the Antarctic Plateau. Constant bad weather conditions at either Novolazarevskaya, Kohnen Station or Neumayer (but only at one site at a time), delayed the put-in. The team was complete at Kohnen Station just in time for the Christmas celebrations. The pull-out was in early-to-mid February. The EPICA team went to Novolazarevskaya again and met the Swedish team going out from Wasa on the joint flight to Cape Town.
The Kohnen Station is situated at an elevation of 2 892 m.a.s.l. The mean annual temperature is -44.6°C, about ten degrees warmer that at Dome C, and the mean annual accumulation rate is above 6 cm 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 some metres under the snow surface. The temperature in the drill trench never exceeded -25°C during the field season. Kerstin Hörnby was one out of 10 drillers in three shifts that kept the drilling operation running for 24 hours per day. The field season is short and the work has to be done in the most efficient way. A deep drilling to the bedrock takes several seasons to complete and it is a race against time. The snow is constantly accumulating on top of the drill trench, which can only survive for a few years, and the borehole is also deformed by the movement of the ice. The drilling in 2002/03 resumed from the depth of 450 m and reached the depth of 1 550 m. The EPICA DML drilling will continue for at least two more seasons before reaching the bedrock.
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 gathers 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. 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.
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 into 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. 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 knowledge of aerosol impact on the radiation balance of the atmosphere by studying natural variations of aerosols and climate over glacial cycles. We use the ice core information of 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 the future climate development.