Glacier and climate research on Hans Tausen Iskappe, North Greenland - 1995 glacier basin activities and preliminary results

A glaciological project was carried out between 1993 and 1995 on Hans Tausen Iskappe, a local ice cap in cen tral North Greenland (Fig. l). The project is funded by the Nordic Environmental Research Programme 1993-1997 launched by the Nordic Council of Ministers and by the European Union's third Frarnework Programme ENVI RONMENT, and is a collaboration between six institu tions from Denmark, Iceland, Norway and Sweden. The main goals of the project were to investigate the present and past climate and glacier dynamics of North Greenland by means of ice-core records, ice margin stud ies, mass balance and climate studies and glacial geologi cal studies on and around Hans Tausen Iskappe. This ice cap was chosen for the following reasons: (1) Only very limited palaeoclimatic ice core data exist for North Green land. (2) North Greenland is considered to be a region of high climatic variability and sensitivity, as indicated by Quatemary geological data and predicted by coupled atmos phere-ocean general circulation models (GCMs) (Funder et al., 1984; Bretherton et al., 1990). The three years of work have mainly comprised field activities, with planning and reconnaissance in 1993 and an increasing levelof field activities during the summers of 1994 and 1995. The activities can be divided into two main parts: ice core drilling and glacier basin investigations. most material 1995 field process ing deals with the summer 1995; described.


Hans Tausen Iskappe and locations of activities
Hans. Tausen Iskappe is a local ice cap, about 75 km from north to south and 50 km from east to west, located in western Peary Land (Fig. l). The ice cap has several dornes (outflow centres) which reach elevations of 1200 to 1300 m a.s.l. Several outflow glaciers drain the ice cap to the west, north and east, often terminating at elevations of a few hundred metres; some reach sea level with a calving front. The southem margin of the ice cap can be characterised as a 'quiet' sector, often covered by snow drifts which survive the summer melt period.
BaU. Grønlands geol. Unders. 172, 78-84 (1996) Field work was mainly undertaken at two localities: (1) the southern dorne; and (2) an outlet glacier basin including a dorne in the north-east part of the ice cap (Fig. l). The main activity in the southem dorne region was ice core drilling to bedrock with associated measurements of ice thickness, strain-rate and velocity. The work in the outlet glacier basin constituted glacier-climate and mass balance studies, collection of ice and snow samples from the surface, and measurements of ice thickness, ice velocity and englacial temperatures. In addition glacial geological investigations were made in Nordpasset and at Adolf Jensen Fjord, north and west of the ice cap, respectively (Fig. l).

Field activities 1993
A survey of surface and bedrock elevations was made in 1993 over the entire ice cap by radio-echo sounding from a Twin-Otter aircraft to identify a suitable general area for the deep drilling (Hammer, 1995). In addition, reconnaissance flights were made to locate suitable sites for the glacier basin investigations.

Field activities 1994
lee eore drilling aetivities Detailed surface and bedrock elevations were measured from the ice surface within a 6 x 6 km area centred on the intended drill site on the southem dorne, using radio-echo soundings and kinematic GPS-positioning (Fig. 1). In addition, similar data were collected along two profiles, 16 km to the south-west and 6 km to the north of the drill site. A strain net was established and measured by GPS, and a 6 m ice core drilled for 8 18 0 analysis (Hammer, 1995).

Glacier basin aetivities
A stake network for mass balance measurements and study of surface-ice velocity and deformation was established in the outlet glacier basin at the north-east part of the ice cap (Figs l & 2). The stakes were measured and positioned by GPS several times during the field season. Snow pit samples and fim cores were obtained from the accumulation area ol' the basin. as wcll as measurement ol' englacial . urface temperatures to a depth ol' 10m at selected stakes. Daily mcasurcrnents ol' ablalion in a lO-stake c1uster were made toget her with logging ol' radiation components, ice albedo and simplc c1imatc dala. including air temperature, ilumidity and wind . peed (Braithwaite el al.. 1995).
Surface-ice amples for 0 18 0 analysis wcrc collecled in the ablation area. and samples ol' snow and tim from the accumuJation area.

Tee core drilling aetivitics 1995
In 1995 ice core driIling wae made on the southclll dome 1'1'0111 the surface to bedrock and a 345 111 lang iec core ol' excell Ilt qllality was rctricvcd. In addition. an extra. haJlow core wa. drilled to a depth ol' 3R m. and a pit was dug to obtain in silll samplcs for chemical . tudies in the po rous uppcr mctres af the ice cap (Hammer, 1995).

LoXislics
Field work was caITicd oUl in two period . in June and in August. In June cquipmcnl and person nel were tran. ported to and from Hans Tausen Iskappe from Station Nord with a ski-equipped Twin-Oltcr airerart. A base camp was e. tablishcd allhe easlern margin ol' the outlet glaeier (Fig. I). Due to favourable snow conditions, execpt on the lowermost pat1 or the glacier tongue where slush fjelds were dcvcloping. moving about in the area was generally eas)' using snow scooter..  In August equipment and person nel were transported to and from Hans Tausen lskappe from a Survey base eamp located at Centrum Sø in Kronprins Christian Land, eastern North Greenland, with a eombined helieopter and Twin-Oller operation. Traffie on the ice cap in August was difljeult due to the elevelopmenl ol' eXlensive deep slush fieleIs, but helicopter UppOrl was only neeeled on one oceasion.

lce-thickness measurements
Ice-thiekness measurelllents by raelio-eeho soundings were maele in June, and covered the entire glaeier basin (Fig. 2) using snow scooter to drag the radar system. The elata wil! serve as inpul for ice l10w modeIling. The system used consists 01' a control and logging module, a generator, two antennae (80 MHz high power transmitter and receiver) and connecting cables mounted on Iight-weight sledges (Jonsson. 1994).
A total ol' 70 line km ol' data were collected, including a 15 km long profilc folIowing the central flow line from the lce tongue to the northern dome ( Fig. 2) and two protile parallel to the central flow line but approximately l km to each side. In addition, several profiles perpenelieular to the central flow line were made, together with a eleose net ol' lines on the northell1 dome (Jonsson, 1995). Navigation was by Jow-resolulion hand-held GPS receivers. wilh a more aCClU'ate tracking maele by eontinuous kinematic GPS positioning. All data from the raelio-echo survey werc rccoreleel in the fielel as graphic output on a line scan recorder and on cassette tapes. The data awaits fUlther processing in combination with Lhe GPS data. However, a comparison 01' ice-thickness data from the radio-echo souneling and hot waterdrillingaround take451 (eebelow) howsthatgooel quality elata ean be expecred. Maximum ice-thicknesses of up lo 350 m occur in the glacier basin, whereas the icethickncsscs along the centre line of the glacier tongue range between 250111 and 300 m; ice-thickness at the northern dome is abollt 250 m.

Hot water drilling for ice temperature measurements
In order lo measure englacial lemperatures from lhe ice surfaee to rhe bottom ol' the ice ir was planned to install  Tausen I ·kappe. thermistor strings al the IwO Slrain-nel sites at take 13 on the norlhern dome, al slake 45 l an lhe glaeier tongue and around the equilibrium line near stake 75 (Fig. 2). The englaeial temperature data will erve as input For ice flow model studies. The holes were dlilled with a hOL waler dlill developed at the Survey (Olesen,19(9) and used in connection with glacier-hydrological studie. an the Greenland iee heet (Thom en el al., 1989). However, due to very unfavourable drilling conditions only the lhermistor tring at stake 451 was succe fully in lalled. reaching bedrock at a depth of 288 m belmv the iee surface (Fig. 3).
Temperature readings were made several limes in lhe drill hole at stake 451 from 3 to 19 August. Similar temperature readings in bat water drill holes on Wbite Glacier. Axel Heiberg Island, Canada (Blatter, 1985), bowed tbat the temperatures are close LO equilibriuITI stale arter 2 to 3 weeks. and the last readings at take 451 an Hans Tausen [skappe (on 19 August) are lhcrefore aSSUl1leello be elose to egui librium (Fig. 4). Thc englacial lemperalUre varies between -18.5°C at 10m deplh la aboul -1.5°C al tbe bOllom. Tbe relatively high temperalure at lhe bOllom was unexpceled. but indicates lhat even a moderate di matie warming at the surface might bring tbe basal temperature in the marginal zone IO lhe pressure l11elling point anel result in increased ice flow velocilies.
Thc planned drilling al stake 75 was abandoned due to the development af extensive deep 'Iush riekis al elevalions higher tb an 700 111 a.s.1. It was rberefore deeided lo dril I at stake 652 just below lhe slake 75 localion where it was po ible to mave an tbe iee surfaee. Tbe drilling went smoolbly to a e1epth af about 120 m. wben the penetration of rhe e1rill . lawed dawn. and at 220 m dlilling wa' abandoned. Tbese diffieu1ties with the driIling are assumed la be due to lhe presence af rock debri layer in the lee. as stake 652 i. loeated downflow of a large nunalak locateel in the central part af tbe iee eap seetor (Fig. 2); a medial moraine ean be followed an the iee sUIfaee down-glacier from tbe nunatak. Two further allcmplS la dril] at a loeation bel\\ieen lake 652 and 75 and between . take 55 and stake 6 wcre abancloned for the ame reason.
Thc drilling operation an the northem dome al stake 13 stllrlcd on 14 August but had to be abandon d due to breakdown af quipmenl.

Mass balance 1994/1995
The stakes established in June 1994 between tbe nOltbem dome at an elevation of about 1320111 anel tbe terminus of the outlet glacier tongue at an elevalion ol' aboul 220 111 were visiled an several oeeasions in June and August 1995, to measure tbe transit balance for the winler pcriod 1994/95 and lhe SUl11mer period 1995. respectively. Ablation reaelings anel snow soundings were made. fn the accumulation ar a stake readings were made to record snow accurnulation and mel l. In addilion, den itY profi les were made in the top few metres af the snow and tirn in .lune and Augusl to compare the protiles and delect lhe elTeets af ummer melting and r free7.ing. Snow and fim samples for 8 1s O analysis were elected to investigate possiblc fractionalion in the aecumulation area in eonneetion with rcfreezing anel formalion af uperimpo ed ie . Tbe nmv and fim densitie. were measUI'ed in .Iune anel Augusl to a reference level of2 111 deptb. wbieh was assumed to be below the depth of maXimlllTI percolalion; experienee from tile Devon fsland iee eap in Arctic Canada ba: 'hown that the depth of maximum percolation lhere i less than 2 m (Koerner. 1970). The density measurements were made in snow pit and samples were taken from the wall af the pit. Samples below lee veloeity and deformation measurements Ice flow velocities were measured by repeated relative GPS surveys at all stakes in the north-east glacier basin (Fig. 2). This data will serve as input for ice dynamic modelling. The stakes established and positioned in 1994 were re-positioned twice in 1995, in June and August. Strain rates were detennined in three strain nets, one at the northem dorne, one just below the equilibrium line at about 706 m a.s.l. and one at a location on the central part of the glacier tongue at an elevation of about 500 m a.s.l. All data have been processed to give preliminary summer, winter and annual values of vertical and horizontal velocities, as well as flow directions. The data show that horizontal surface ice velocities on the glacier tongue range from about 5 rn/yr near the terminus to about 50 rn/yr near the equilibrium line at about 750 m a.s.l. (Fig. 6) In the accumulation area, velocities are typically a few metres per year.

Stable isotope studies
In 1994 surface ice, snow and fim samples for ol8Q analysis were collected along the stakes in the glacier basin for comparison with the ol8Q record from the ice core at the southem dorne. Preliminary analysis of the glacier basin samples showed unexpected large variations and trends (Fig. 6). In order to make a meaningful comparison of the ol8Q record from the surface of the ablation area with the deep drilling record, the surface ol8Q record needs to be corrected for variations in the ol8Q content of the ice in the accumulation area of the glacier basin. Samples from snow pits and SIPRE corings in the accumulation area of the glacier basin reveal a pronounced 'reverse' relationship of ol8Q with elevation; Fig. 6 illustrates a 4.5%0 increase of ol8Q in the accumulation area for a 550 m increase of elevation.
In order to shed light on the cause of these variations in ol8Q a more detailed sampling programme was carried out in August 1995; samples were taken at all stakes from stake 25 to 652, as well as at locations between the stakes. A total of 290 ice samples were taken from the glacier tongue area with 10 samples collected at each location; a further 60 samples of snow and fim were taken from the accumulation area during pit work and SIPRE coring.
The new repeated sampling confirmed the results from the 1994 sampling programme.
A similar 'reverse' ol8Q trend was found in the ice core the snow pit were taken using a SIPRE corer. Mass change measurements in the accumulation area show that all melting refreezes in the snow and fim, together with any small amounts of summer precipitation. The exact values of the area mass change are uncertain, because the measurements only represent one point at each location. However, the general trend for all measured locations in the accumulation area shows that the transient balance for the summer period is close to zero. The mass balance study also showed that slush, several decimetres thick, develops late in the melt season over extensive areas of the glacier basin. Measurements indicate that most slush refreezes to fonn ice layers in the snow and fim or superimposed ice. This process releases energy (latent heat) causing local warming of the surface-near layers of the glacier, which is confinned by measurements of ice temperatures in the top 10 m of the glacier at severallocations.
To explain the melting and refreezing processes, further work is needed, including modelling of the temperature in the snow and fim based on the recorded near surface temperature data. This also includes the analysis of snow and fim ol8Q values to study possibie seep-away of summer snow with high ol8Q values and fractionation in connec- Surfaee ice samples collected in 1994 near the terminus of the glacier tongue and on a glacier tongue south-east of the ice core drilling location on the southem dorne ( Fig. 1) indicated that ice from the last ice age was not present at the margin ofHans Tausen Iskappe. To confirm this observation 300 additional ice samples were collected in 1995 near the ice core drilling location along a two kilometre profile covering the outermost part of the ice tongue; the sampling interval was 5 m for the outermost kilometre, and 10 m for the remainder of the profile. This additional sampling confirmed the observation that ice from the last ice age is not present, suggesting that the ice cap may have melted away complete1y during the Holocene climatic optimum. The 8 18 0 record from the ice core drilled to bedrock at the southem dorne ofHans Tausen Iskappe in spring 1995 supports this hypothesis; Holocene 8 18 0 values are present throughout (Hammer, 1995).

Discovery of biogenic material in the ice
During a foot traverse onAugust 19 a musk-ox carcass was found on the ice surface 500 m east of stake 400 on the glacier tongue (Fig. 2). Individual body parts were more or less intact, but distributed over a 10 m long stretch parallel with the direction of ice movement. Excavations in the ice upstream of the carcass revealed musk-ox meat and fur continuing down into the ice, indicating that the musk-ox had been transported within and melted out of the ice. Selected body parts were brought home for biological investigations and 14C dating.
The discovery of the musk-ox may serve as an interesting natural tracer for dating the ice. However, this will depend on how the musk-ox was originally incorporated into the ice. Preliminary ca1culations of the age of the ice at the location of the discovery indicate an age of 500-1000 years.

Preliminary conc1usions
The 8 18 0 surface ice sampling programme indicates that ice from the last ice age is not present at the margin of Hans Tausen Iskappe, a conc1usion supported by the ice core drilled at the southem dorne (Hammer, 1995). The ice cap must thus have melted away complete1y during the Holocene c1imatic optimum. Glacial geological studies to the north of the ice cap carried out in 1994 (Landvik & Hansen, 1994), and earlier investigations south and west of the ice cap (A. Weidick, personal communication, 1995), show that areas adjacent to the present ice cap margin became ice-free after the last ice age about 6000-7000 years ago. It is thus 1ikely, that anyearlier ice cap became extinct some time after 6000 BP, and that the present Hans Tausen Iskappe started to build up in the mid-Holocene. By contrast, the Canadian Arctic ice caps at similar high northem latitudes can be shown to have survived the Holocene c1imatic optimum, which might indicate that eastem North Greenland is highly sensitive to c1imate change.
Resu1ts of the mass balance and eng1acial temperature studies, and studies of 0 18 0 variations, indicate the existence of an efficient warming mechanism probably due to development and refreezing of extensive slush fie1ds. The heat produced may propagate to the bottom of the ice and raise the temperature of the basa11ayers with the effect of increasing ice flow velocities and enhancing the tendency for ice cap deterioration. Similar, but more pronounced, conditions are likely to have occurred during the Holocene c1imatic optimum leading to disintegration of the ice capo To quantify this conc1usion in terms of modelling the varied processes involved, will require a major effort of data analysis, compilation and interpretation, as well as developing and running models for glacier mass balance and thermodynamics.