The 2001/02 season of the long-term programme EPICA, European Project for Ice Coring in Antarctica, was a great success and resulted in the longest ice core record ever recovered. The deep drilling at Dome C reached a depth of 2 764 m below the surface. The initial results of analyses performed in the field suggest that the age of the ice at this depth is 530 000 years. The drilling operation will continue during the following seasons until the bedrock is reached about 400 m further down.

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 on a changed forcing, 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 verifies that the anthropogenic contribution of 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 Dome C will extend the existing records further back in time as well as providing a wealth of new information due to new analysis techniques developed in recent years. The ice core that has been brought to the surface at Dome C so far represents a continuous record of climate and environmental changes over half a million years. The expected time coverage of the full ice core after the drilling has reached the bedrock is more than 1 million 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˚23’E). The 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 DML drilling aims to retrieve a high-resolution record of one complete glacial-interglacial cycle 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.

Fieldwork

Mart Nyman represented Sweden in the EPICA team of 14 scientists and 8 drillers at Dome C in the season 2001/02. The crew flew in from Christchurch, New Zealand, via the Italian coastal station Terra Nova Bay. Station Concordia is located at an altitude of 3 233 m.a.s.l. The mean annual temperature is below –50˚C and the accumulation rate is less than 3 cm of water equivalent per year. The typical summer weather is blue sky, light winds and temperatures below –20˚C. The summer season at Dome C lasts about 12 weeks. The summer camp at Dome C in 2001/02 was housing about 50 people. Some of these were engaged in constructing the new French-Italian year-round station Concordia. The EPICA team was working inside the drill tent and in the 40 m long science shelter.

The electro-mechanical drill produces ice cores 98 mm in diameter, 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 aremeasured by dielectric profiling (DEP). Then the ice core passes along a processing line where the cross-section is dissected into pieces, destined for different measurements and laboratories, using a series of cuts with band saws. Changes in crystal size and orientation along the core are detected directly in the field. Also a second electrical conductivity measurement (ECM) is performed on the cut core. The remaining parts are sectioned for return to Europe for analysis of stable isotopes in the water itself (oxygen and deuterium, used as proxies for temperature variations), gases (carbon dioxide, methane etc.), dust, mechanical properties and many other parameters. At least a quarter of the ice core is packed and kept at Dome C as an archive for future analyses with new techniques and as an insurance for freeze room failures.

Analysis

The main Swedish contribution to EPICA is chemical analysis of the ice. This analysis is partly performed in the field. One section of the ice core is cut into square (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 onto a heated melt head. Only the melt water from the inner, clean part of the ice section is sucked into a warm laboratory (+20˚C), where it is analysed directly at a very high resolution for liquid conductivity, dust content, hydrogen peroxide, formaldehyde, sodium, calcium, ammonium, nitrate, chloride and sulphate. One line with melt water was not used for direct measurements in the field. Instead the melt water was collected in small bottles and later analysed by ion chromatography at five different laboratories in Europe. At Stockholm University we are analysing a fifth of these samples and we are measuring sodium, ammonium, potassium, magnesium, calcium, fluoride, methane sulphonate, chloride, nitrate and sulphate by ion chromatography. We are also developing techniques to measure S 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 information contained in the ice core on concentration changes with time in 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.