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 coordinated 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 1990s two deep ice cores were drilled at Summit, Greenland. The European project GRIP drilled one ice core on the ice divide, and the American project GISP2 drilled another one, 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 back to about 100,000 years ago. 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 off low over irregular bedrock.

The NorthGRIP deep-drilling camp was set up in 1996 at 75°06’N 42°20’W, at an elevation of 2920 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 field season 2000 drilling reached a depth of 2930 m. Only 150 m of ice remains between the final depth of the drilling and the bedrock which lies at a depth of 3080 m.

Field season 2000

Field season 2000 started in mid-May with the landing of a smaller crew of 16. The participants flew in from Kangerlussuaq, located 1000 km away on the west coast of Greenland. A week later the NorthGRIP population increased to 28, which was about the size of the camp for most of the season. The camp was abandoned for the year in mid-August. Mid-May on the Greenland ice sheet is the beginning of spring, with minimum temperatures approaching -40°C at night, and rising 10 to 20 degrees during the day. Most of the time the weather was excellent with blue skies and light winds, except on the flight days every third week. On the flight days low-level clouds reduced visibility until all contrast disappeared between snow surface and air. The ground temperature also increased, which is a great disadvantage for the large ski-mounted USAF C-130s attempting to take off in to the thin air at this high altitude. However, with take offs scheduled for the coldest hours of the night and by using ATO (i. e., by firing rockets mounted on the planes) all planes got airborne. Once, six attempts were needed for a plane to take off. The day after a flight the sun would again be shining in a blue sky.

Camp

The centre of the NorthGRIP camp 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 five 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.

Drilling

Drilling resumed this season from a depth of 1750 m. The production was around 150 m a week and the quality of the NorthGRIP ice core was excellent. On the 23rd of July the drill again got stuck, this time at a depth of 2930 m. The temperature at this depth (-6°C) was close to the pressure melting point, causing water to form on the cutters and the drill to become stuck. Frozen glycol was dropped in to the drill hole, which was filled with drilling liquid (a diesel mixture), and the drill became free again. The rest of the season was spent cleaning the glycol slush from the hole. Glycol is still present in the hole and has to be removed before drilling can resume next season.

Science

The NorthGRIP ice core will provide records of climate and environmental change at the highest time resolution ever. This is possible due to the excellent quality of the ice core and the development of new analytical techniques over the last few years. Rapid changes in temperature and precipitation rates will be revealed, together with changes in greenhouse gases, aerosol concentrations and composition.

The ice core was processed directly in the field in the science trench, and was cut in to various-sized sections with band saws. Measurements of electrical properties were made directly on the ice by dielectrical profiling and electrical conductivity measurements. Visible structures in the ice were mapped with a line scanner. The sections of the ice core were packed for later analysis back home. Fifty-five-cm pieces were packed for the analysis of, for example, gases and physical properties; 2.5 cm pieces were cut and packed for high resolution stable isotope analyses. One section was cut in to squared (3 x 3 cm) 165 cm-long pieces and used for continuous flow analysis directly in the field. The 165 cm-long ice bar was mounted in a tray and lowered on to a heated melt head. Only the melt water from the inner part of the ice section was sucked in to the continuous flow analysis system and distributed into ten different lines. Total particle content, particle size distributions, liquid conductivity, H2O2, HCHO, NH4+, Na+, Ca2+, NO3– and SO42- were analysed with the continuous flow analysis set up with a resolution of 1 cm along the entire ice core from 1300 m down to 2930 m depth. Melt water samples were also collected from the same depth interval at a 55 cm resolution for further chemical analyses at home by ion chromatography (IC), and filter samples were collected for electron microscopy.

Results

The most striking result was that although, based on present knowledge of the Greenland ice sheet and the most developed ice flow models, we expected to encounter Eemian ice at a depth of 2600 m at this site, we never reached Eemian ice this year. According to the pattern of the stable oxygen isotope profile the age of the ice at 2930 m depth is about 100,000 years. The reason for this unexpected result is yet not understood. Next field season we will make a great effort to obtain a core from the last 150 m of ice lying over the bedrock.

The unexpectedly young age of the ice close to bedrock also means that a greater length of the ice core than expected represents the last glacial period, and that various analyses will reveal records with a high time resolution throughout the entire glacial period. The high-resolution profiles from the continuous flow analysis will reveal seasonal variations reaching far back in to the glacial period.