The multinational NorthGRIP research programme has partly been funded by participating institutions from Germany, Japan, Sweden, Switzerland, France, Belgium, Iceland and the U.S. The programme has been coordinated by Denmark and the primary sponsor has been the Danish Research Council. The aim of the programme was 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. This goal was fulfilled beyond expectations.

The eighth and last field season of the NorthGRIP project on the Greenland ice sheet gave new exciting surprises. The main purpose was to drill the 45 m long column of refrozen basal water that entered the drill hole when the ”bedrock” was reached the previous season. The reddish refrozen basal water was recovered but a slight difference in inclination forced the drill more and more to the side into the old original ice. The surprise was great when the drilling passed by the termination depth of previous season, 3 085 m, and continued for six more meters. This time crustal material was scraped off from the bedrock and no melt water entered the borehole.

Background

At the beginning of 1990s two deep ice cores were drilled at Summit, Greenland. One ice core was drilled on the ice divide under the auspices of the European project GRIP and the other at a site 30 km away under the auspices of the American project GISP2. 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 farther 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 1300 m in 1997, drilling resumed from the surface in 1999 and reached a depth of 1750 m. In 2000 drilling reached a depth of 2 930 m. At 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 ice core piece, if anything. 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 thus that the project was worthwhile 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 starred with many new ideas and new equipment.

The drill reached ”bedrock” in 2003 at a depth of 3 085 m when basal water entered the borehole from below. The electrical equipment of the drill shorted, and the drill was brought to the surface. A 30 cm long structure of refrozen basal water was hanging underneath the drill. This ice had a red colour. The core segment drilled just before was perfectly clean and normal and in the next run the basal water came rapidly and unexpectedly. The deep drilling had reached the bedrock and it was declared terminated. However the basal water was refreezing in the bore hole and the decision was taken to return next season to drill the 45 m high column of refrozen basal water.

Field season 2004

The field season 2004 was shorter than usual and lasted from mid-June to mid-August. The participants flew in with USAF C-130s from Kangerlussuaq, located 1000 km away on the west coast of Greenland. The NorthGRIP population varied between 10 and 23, with visitors from the press for shorter periods. Beside the main task of drilling the refrozen basal water several associated projects were carried out at NorthGRIP. Ulf Jonsell carried out a snow-pit sampling program for detailed snow chemistry studies. Ulf Jonsell was also leader of one of the deep drilling teams.

Camp

The centre of the NorthGRIP camp was a 7 m high wooden dome with generator, kitchen, water and communication facilities. Radio contact with the outside world was established every day, if possible, via the field operation manager in Kangerlussuaq. Other permanent structures were heavy dome-shaped tents used for workshop and storage space. The participants slept in temporary tent structures. The drilling and science trenches were located some meters under the snow surface. All temporary and permanent structures except the wooden main dome were taken down in the end of this season and the drilling and science trenches were filled with snow. The bore hole casing was extended to 2.5 m above the surface to make it possible to return and perform bore hole measurements in coming years.

Drilling

To start with the drilling produced red-coloured ice cores of refrozen basal water. Since the drilling did not exactly follow the bore hole of last year a half-moon shaped piece of old original ice became soon visible. A clear difference is seen in the crystal structure between small crystals in the refrozen basal water and large crystals in the old original ice. With depth the piece of original ice became larger and larger and the piece of red refrozen basal water smaller and smaller, to eventually disappear. About 50 kg of refrozen basal water was retrieved in total. The drilling in the original ice continued below the termination depth of last season. Six meters further down, at a depth of 3 091 m, red mud was found at the bottom of the last core. The cutters were damaged and replaced by hardened cutter but we also failed to achieve further penetration this time. No melt water entered the bore hole. The Drillers mounted a conical scraper, which produced big amounts of reddish slush with 1-2 cm mud and  ice lumps in. Organic material, a needle, was also found in the slush. This needle may tell us about the vegetation on Greenland before glaciation started some million years ago.

Science

The warmer conditions during the Eemian period are clearly seen in the stable water isotope record (i.e. the temperature proxy) . The 123 000 year long NorthGRIP record (North Greenland Ice Core Project members, 2004) starts with the warm Eemian period shows the transition into the glacial period. The record from the last six metre> of ice from this season, extending the record beyond 123,000 years, shows an increasing temperature trend, possibly the end of the intercept of Eem. The layers deepest down are not thinning towards the bottom due to an exceptionally high bottom-melting rate at NorthGRIP. 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 at the highest time resolution ever du ring the entire glacial period. Rapid changes in temperature and precipitation rates have been revealed, together with changes in greenhouse gases and aerosols.

The NorthGRIP ice core has been processed directly in the field in the science trench during each field season. It has been cut into various-sized sections with band saws. Measurements of electrical properties have been made directly on the ice by dielectrical profiling (DEP) and electrical conductivity measurements (ECM). Visible structures in the ice have been mapped with a line scanner. Sections of the ice core have been packed and sent home for analysis of, for example, 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 SO42- 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 a 55 cm resolution for further chemical analyses of ten ion 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 2004. Many more will now be performed in home laboratories. The chemical records will be extended from depth 2 930 m to 3 091 m. IC and Tephra analyses are performed at Stockholm University.

The red refrozen basal water, the red mud at the bottom and the needle found in the slush at the bottom, will all be examined with methods new in ice core research, e.g. DNA analysis, together with experts in biology, hydrology and geology.

Future

Although the NorthGRIP deep drilling has been terminated the NorthGRIP programme will continue for many more years. More ice core analyses await and the wealth of data produced will be used to reconstruct and understand past climate and environmental changes. The last six metres of original ice retrieved this season, showing an increasing temperature trend in the Eemian period, convinced us that it is possible to find a drill site on Greenland that can provide a full record of the Eemian period. For all climate research, both with regard to predicting the future and understanding the past, it is essential to have a record over a full glacial cycle from the northern hemisphere for comparison with the information we have retrieved from the Antarctic ice sheet. Therefore the search has already started for the optimal drill site to retrieve ice containing the transition into the Eemian period. Hopefully we will see a new international deep drilling effort on the Greenland ice sheet in the near future.