After seven field seasons on the Greenland ice sheet the goal was fulfilled. On 17 July 2003 the deep drilling at NorthGRIP reached the bedrock at a depth of 3 085 m. NorthGRIP is the latest deep ice core-drilling programme on the Greenland ice sheet. This multinational research programme is partly funded by participating institutions from Germany, Japan, Sweden, Switzerland, France, Belgium, Iceland and the U.S. The programme is co-ordinated by Denmark and the primary sponsor is the Danish Research Council. The aim of the programme is to recover a high quality ice core reaching to the bottom of the ice sheet, at a site chosen to yield the longest record ever obtained from Greenland.

Background

At the beginning of the 1990s two deep ice cores were drilled at Summit, Greenland. One ice core was drilled under the auspices of the European project GRIP on the ice divide, and the other under the auspices of the American project GISP2, at a site 30 km away. These two ice cores yielded the longest climatic records ever obtained from the Greenland ice sheet. The records matched each other perfectly throughout the last interglacial Holocene and the last glacial period, and extend back about 100,000 years. However, the records obtained from the lower part of the ice cores, which should represent the previous interglacial Eem, did not match. The Summit Eemian records showed asynchronous, abrupt changes to short, cold periods within the warm interglacial period. The NorthGRIP project was designed to retrieve Eemian ice further away from the bedrock to minimise the disturbing influence of flow over irregular bedrock.

The NorthGRIP deep-drilling camp was set up in 1996 at 75°09’N, 42°32’W, at an elevation of 2 930 m. After the drill became stuck at 1 300 m in 1997, drilling resumed from the surface in 1999 and reached a depth of 1 750 m. In 2000 drilling reached a depth of 2 930 m. In the end of the season the drilling became more and more difficult. The high ice temperature close to the bottom caused liquid water to form on the cutters and the drill to become stuck several times. Only 70 m of ice core was drilled in the following season and the quality of the ice core was no longer excellent. Each drilling run yielded only a short piece of ice core, if anything. In spite of this, measurements of stable water isotopes and the gas methane trapped in the ice convinced us that the chemical records in the ice still were undisturbed despite the high temperatures close to the bedrock and that the project was worth continuing. To solve the technical problems associated with drilling in ice at a temperature close to the pressure melting point, the field season 2002 was postponed and the field season 2003 started with many new ideas and new equipment.

Field season 2003

Field season 2003 at NorthGRIP lasted, as usual, from mid May to mid August. The participants flew in with USAF C-130s from Kangerlussuaq, located 1 000 km away on the west coast of Greenland. The NorthGRIP population varied between 8 and 27, and increased up to twice as many during short periods with visitors from different authorities and the press. Beside the main task of continuing the deep drilling, several associated projects were carried out at NorthGRIP this season. For his PhD-project, Ulf Jonsell drilled a 100 m long ice core (photo 1) for detailed studies of the last few hundred years. He also carried out a snow-pit and surface-snow sampling program for detailed snow chemistry studies. Ulf Jonsell spent the rest of his field season as a driller in the deep drilling.

Camp

The centre of the NorthGRIP camp (photo 3) is a 7 m high wooden dome with generator, kitchen, water and communication facilities. Radio contact with the outside world is established every day, if possible, via the field operation manager in Kangerlussuaq. Other permanent structures are heavy dome-shaped tents used for workshop and storage space. The participants sleep in temporary tent structures. The drilling and science trenches are located some metres under the snow surface.

Deep drilling

Drilling resumed this season from a depth of 3 000 m. The start was slow, as we were trying to find new solutions on how to drill in the warm ice. Ethanol was mixed with the drilling fluid in the borehole and a melt drill was tested. However, in the end it turned out that the only alternative was to continue just as before. In the afternoon of 17 July, the drill reached bedrock at a depth of 3 085 m when basal water entered the lower 20 m of the borehole from below. The electrical equipment of the drill shorted, and the drill was brought to the surface. A fantastic spectacle awaited the drillers: a 30 cm long structure of refrozen basal water was hanging underneath the drill. The ice had a red colour. The core segment drilled just before reaching bedrock was perfectly clean and normal, and in the next run the basal water came fast and unexpected. Within minutes of reaching bedrock the 13 scientists gathered in the drill trench to celebrate the event. The chief driller Sigfús Johnsen gave a short speech and the NorthGRIP deep drilling was officially terminated.

Science

The age of the ice in the bottom is approximately 120 000 years. The warmer conditions during the Eemian period are clearly seen in the stable water isotope record (i.e. the temperature proxy). The NorthGRIP record contains the termination of the previous interglacial Eem but not the intercept of Eem. The NorthGRIP record is longer than the GRIP and GISP2 records but it does not reach as far back as expected because of the unexpected high bottom-melting rate of 1.5 cm/year. The melt water stand in the borehole was 45 m when the camp was left in mid-August. This indicates that a large area under the Greenland ice sheet, mainly to the north of NorthGRIP drill site, is affected by bottom melting. One good thing about bottom melting is that the layers deepest down do not thin towards the bottom. This, together with the excellent quality of the NorthGRIP ice core and the development of new analytical techniques over the last few years, has led to extracted records of climate and environmental change during the entire glacial period at the highest time resolution ever. Rapid changes in temperature and precipitation rates have been revealed, together with changes in greenhouse gases and aerosols.

The NorthGRIP ice core was processed directly in the science trench during each field season. It was cut into variously sized sections with band saws. Measurements of electrical properties were made directly on the ice by dielectrical profiling (DEP) and electrical conductivity measurements (ECM). Visible structures in the ice were mapped with a line scanner. Sections of the ice core were packed and sent home for analysis of e.g. stable isotopes, gases and physical properties. Continuous flow analysis (CFA) was performed directly in the field during the field season 2000. Total particle content, particle size distributions, liquid conductivity, H₂O₂, HCHO, NH₄⁺, Na⁺, Ca²⁺, NO₃^– and SO₄^2- were analysed with the CFA set up with a final resolution of 1 cm along the entire ice core from 1 300 m down to 2 930 m depth. Melt water samples were also collected from the same depth interval at 55 cm resolution for further chemical analyses of ten different ions by ion chromatography (IC), and filter samples were collected for Tephra analyses. Several analyses have already been performed on the last part of the NorthGRIP ice core retrieved in 2003 and many more will be performed in home laboratories to extend the records to 120,000 years before present. IC and Tephra analyses are performed at Stockholm University.

Next season

We are enthusiastic about the fact that we have also retrieved basal water. We hope that the water will contain information about the biological life in Greenland 2 million years ago, before the Greenland ice sheet was formed. Although the NorthGRIP deep drilling is officially terminated, the drilling will continue next season to retrieve the 45 m of refrozen basal water. The NorthGRIP programme will continue for many more years. More ice core analyses are awaiting and the wealth of data produced will be used to reconstruct and understand past climate and environmental changes.