Basal and englacial debris layers have been observed to coincide distinctly with the location of glacier thrust planes or shear zones, e.g. at Shoestring Glacier (Brugman and Meier 1980) and Variegated Glacier (Kamb and others 1985). They are also evident at Findelen Glacier. Field observations strongly suggest that the mechanics of debris-laden ice can be important for understanding the flow response of certain glaciers. In this paper the material properties of basal ice at Findelen Glacier are examined, as studied with the aid of ice-core drilling techniques.

Ice cores were taken from near the center line of Findelen Glacier during the summer of 1985, for the express purpose of characterizing the basal ice in terms of observed structures, composition and rheology. Related studies were simultaneously performed on bore-hole and surface strain-rate deformation (Iken and others, unpublished) and bore-hole resistivity (Schütz and Röthlisberger 1985). The ice core, retrieved from the deepest level possible (approximately 4 m above the bed), contained only a minor amount of fine rock debris. The presence of a debris-containing basal-ice zone is strongly suggested by the evidence that further hot-water drilling in the bore holes resulted in abraded drill stems and in the irregular progress of the drill for the few remaining meters to the glacier bed. Therefore, during 1986 samples of debris-laden basal ice were taken from several locations where the basal material was clearly exposed along lateral ice cliffs in the ablation area of the glacier.

Three distinct types of ice at Findelen Glacier were compared: clean bubbly coarse-grained ice taken from above the glacier bed, clean clear coarse-grained ice taken from within a few meters of the glacier bed at center line (170 m depth), and debris-laden ice taken from the glacier bed at the lateral margin. Uniaxial compression experiments were conducted on the glacier-ice samples, using the triaxial testing apparatus of the 1GB at ETH-Höngerberg. Laboratory studies of ice deformation were carried out under the guidance of A. Hofer, P. Hertzog and Professor Huder of IGB. Sample temperature, volume and strain-rate were monitored throughout each experiment. The confining pressure of each experiment was set at 4 bars (1 bar = 100 kPa). The deviatoric stresses applied were 1, 2 and 4 bars, and testing temperatures were set at –1.5, -0.8 and –0.4°C for each type of ice sampled (clean bubbly, clean clear, and debris-laden).

Preliminary results from experiments conducted on the clean bubbly and clean clear ice indicate that the mechanical behavior of the main bulk of the glacier is well represented by a power-law creep relationship with an exponent of about 4. This value is in close agreement with independent results obtained from bore-hole–tilt studies (Iken and others, unpublished) and within the range of values cited in the published literature (Paterson 1983). The pre-exponential factor is not well represented by an Arrhenius-type relationship, and enhanced deformation is indicated for samples tested nearest the melting point. Additional laboratory and field studies on the ice-crystal fabrics and the behavior of the debris-laden ice are still in progress. In this paper the results of these investigations are discussed, with special emphasis on information gained from the ice-core drilling studies.

Ultra-clean techniques have been used to collect a series of fresh surface-snow samples on Gipps Ice Rise, Larsen Ice Shelf (68°48′S, 60°54′W) between 21 December 1984 and 12 February 1985. Aerosol samples were collected simultaneously on to pre-cleaned membrane filters to allow the direct comparison of trace-element levels in air and snow. Samples have been analysed by various techniques for cadmium, copper, lead, zinc, aluminium, calcium, potassium and sodium. For all elements, cross-sample concentration profiles have been obtained to support the data for snow samples.

The heavy-metal concentrations found in the surface snow were similar to those measured previously near Gomez Nunatak in the Antarctic Peninsula. The mean aerosol concentrations found at Gipps Ice Rise were Cd: 0.06 pg m−3, Cu: 1.0 pg m−3, Pb; 4.7 pg m−3, Zn: 6.1 pg m−3. These are the lowest concentrations measured so far in Antarctic aerosol.

The ratio of the snow concentration (pg g−1) to air concentration (ng m−3), known as the washout factor, has been calculated for each element and sampling period. The data show that, for the Antarctic Peninsula, the marine aerosol is more efficiently removed to the snow-pack than is the crustal aerosol. Heavy metals are least efficiently removed. This result suggests that the measurement of concentrations in snow and ice alone may lead to misinterpretation of atmospheric source strengths.

We are measuring 36Cl in the upper part of the 1966 Camp Century deep core, using the tandem-accelerator mass-spectrometry facility at the University of Rochester. There are two primary motivations for measuring 36Cl in ice. The first is to look for correlations between 36Cl concentrations and changes in solar activity. Previous studies of 10Be and 14C (Stuiver and Quay 1980, Raisbeck and others 1981, Beer and others 1983) have demonstrated that the production of these radio-isotopes increases during periods of low solar activity. When the sun is active, the magnetic field induced by the solar wind deflects galactic cosmic rays from the inner solar system and thereby lowers the production of radio-isotopes. Our study of 36Cl in ice dating back to A.D. 1550, from Camp Century, Greenland, shows that there was an increase in 36Cl production during the Maunder Minimum (1650–1715). However, climatic variations introduce fluctuations of a factor of 2 or more over short periods and the Maunder Minimum peak is only readily apparent when the data are smoothed mathematically.

The second motivation for measuring 36Cl in ice is to test the possibility that the ratio of 36Cl to 10Be will provide a means for dating ice over 50 000 years old (Nishiizumi and others 1983). The dependence on both solar activity and climatic fluctuations mentioned above precludes dating with a single radio-isotope. If, however, the production rates of 36Cl and 10Be are each proportional to the cosmic-ray flux and are transported identically to the ice sheet, these fluctuations would cancel and the ratio of 36Cl to 10Be would provide a radiometric means of dating very old ice. The half-lives for 36Cl (3.0 × 105 years) and 10Be (1.6 × 106 years), combine to give a “half-life” for the 36Cl/10Be ratio of 3.7 × 105 years.

Unfortunately, preliminary results from Camp Century, Greenland, show that it will almost certainly not be possible to use the 10Be/36Cl ratio for dating. 10Be and 36Cl have been measured in more than 20 samples; the 10Be/36Cl ratio varied, without any obvious pattern, from below 5 to over 15. Additional evidence comes from Antarctica. We found that the 10Be/36Cl ratio changed significantly within a short depth interval within a single block of ice and that the calculated age of ice based on 10Be/36Cl differed from the age of an embedded meteorite, ALHA82102 (personal communication from K. Nishiizumi).

A variation in the 10Be/36Cl ratio may be caused by climatic effects: for example, changes in air circulation between the stratosphere and the troposphere in the polar region, in combination with chemical processes that affect aerosol chlorine and beryllium differently. Also, the 10Be/36Cl ratio is smaller than expected, indicating that there may be additional sources of 36Cl. If there is a source of 36Cl that varies independently from the galactic cosmic-ray flux, this would result in variations in the isotope ratio. Discovery of the cause of the variations may result in a new tool for understanding paleoclimate.

Two cores which had been drilled to a depth of over 200 m were recovered near Amundsen–Scott South Pole Station during the 1980–82 field seasons. A firn core drilled from 3 to 19 m depth was taken in December 1982 from a site about 5 km distant from the two others.

The cores cannot be used to study the seasonal δ18O cycle, because: (i) detailed sampling (1–2 cm increments) provides evidence of isotopic enrichment in the 1 m core sections during storage, both in the field and in the laboratory cold-room, and (ii) low accumulation (9.2 g cm−2 a−1, given by Jouzel and others 1983) led to missing years or parts thereof. Estimates of the proportion of missing years range from 1 in 10 (J.R. Petit, quoted in Mosley-Thompson and Thompson 1982) to 1 in 20 (Jouzel and others 1983).

The cores are still useful for studies on a decadal or longer time-scale. The average δ18O value of detailed measurements of the upper 40 m of the 1980 firn core differs by only 0.14±0.05‰ from the average of measurements made about 16 months earlier. Thus, although storage in the cold-room changed the isotopic composition of the outer firn layer, the bulk of the firn core was unaffected. The two measurement series of this profile show a high correlation (r2 = 0.75, P<10−6) when smoothed with a I m moving average (equivalent to 4–7 years’ accumulation) in order to reduce noise and the effect of enrichment at the ends of the 1 m sections.

In both long cores and in the short core which was taken in 1982 the δ18O–depth profile shows a long-term trend with superimposed shorter fluctuations. The seasonal signal soon disappears but variability of up to 2‰ on a 3–5 year time-scale persists at depth. Linear-correlation analysis shows a significant correlation between the 1980 firn core and the 1982 short core (r2 = 0.32, P = 0.011) for a 1 m moving average of samples 0.25 m long. Some correlation is also observed between the deeper ice parts of the 1982 core (106–227 m) and the 1981 core (100–202.4 m) (r2 = 0.087, P = 0.00043, I m moving average), if the relative depths are shifted by 3.75 m. A firm time-scale for both cores is needed to determine whether such a shift corrects for an artefact of the depth logs of the cores, or proves that no real correlation exists between the two cores.

Comparison of the long-term trend of the two South Pole cores with the 2.5 ka isotope climatic record from the 1979 Dome C core (Benoist and others 1982) and with the Law Dome core BHD record (Morgan 1985) again suggests possible correlation, but cannot prove it for lack of a firm time-scale. Collaboration with other investigators which brings together data on visible stratigraphy and density (personal communication from A.J. Gow), solid conductivity (Schwander unpublished), acid horizons (Langway and others 1988, this volume) and microparticles may solve this problem.

During the Ymer-80 expedition, a 6 m long ice core was taken on the low-lying ice cap Storøyjøkulen, Svalbard. Core samples of about 10 ml were filtered on 0.1 μm pore-size Nuclepore filters, for analysis with a soot photometer and by means of particle-induced X-ray emission, which yielded elemental carbon and about 15 metals in the insoluble microparticles. The concentrations

were comparable to Arctic snow data from other locations. Multivariate statistical analysis of the chemical results indicates two major factors affecting microparticle composition: crustal and anthropogenic. A regular seasonal concentration pattern was found which is consistent with the c. 40 cm annual accumulation deduced from mass-balance studies on the ice cap.

The aim of this paper is to evaluate and exemplify the potential of continuous and high-resolution ice-core analysis in atmospheric-climatic research.

At present only a few ice-core components of current interest can be measured continuously with high resolution along the cores. In this paper, the techniques of in-situ or “in the laboratory” continuous high-resolution measurement of solid-liquid electrical conductivity, pH, dust and anions will be presented and discussed. In particular, results from individual precipitation samples, seasonal changes, rare events, and the comparison of results from various Antarctic and Greenland ice cores will be discussed.

Clathrate hydrate inclusions of various shapes and sizes were first found by Shoji and Langway (1982) in ice cores from a depth greater than 1280 m at Dye 3, Greenland. Although we have assigned clathrate guest molecules to O2 and N2 by observing Raman spectra of the hydrates in a core from 1501 m depth (Nakahara and others, in press), it has not been determined whether the crystal structure of the hydrate is structure I or structure II.

Using the 4-circle diffractometer in the High Brilliance X-ray Laboratory at Hokkaido University, many reflections from the hydrate crystals were identified. Applying extinction rules for cubic crystals, the space group of the hydrate was determined as Fd3m, which corresponded to structure II. The average lattice parameter for a unit cell obtained from three samples was 17.21 A, and this also supports structure II. Structure II was also found with artificial air hydrates by the method of neutron diffraction (Davidson and others 1984).

The density of the hydrate was calculated for various combinations of the occupancy of the two types of cage by guest molecules (in a composition ratio of N2 :O2 = (1.5 2.0) : I as determined from Raman intensity). A reasonable value of the density 950 kg m”3 was obtained when only the 12-hedrons were occupied. Therefore it was concluded that the air molecules were trapped only in 12-hedrons which formed the structure II hydrate with 16-hedrons.

Oceanic studies have convincingly demonstrated that there is a link between the Pleistocene ice ages and the variations in the elements of the Earth’s orbit (Imbrie and others 1984). In contrast, the climatic conditions which prevailed over continental areas have been far less well documented and then rarely on a quantitative basis.

In this context, the 2083 m ice core recovered by the Soviet Antarctic Expeditions at Vostok (East Antarctica) is of fundamental importance because it covers fully the last glacial-interglacial cycle, back to the ice age which preceded the last interglacial (∽160 ka B.P.). Potentially it allows access to many climatic and climate-related parameters as illustrated by the oxygen-18 data we have recently published (Lorius and others 1985), from 10Be measurements (Yiou and others 1985, Raisbeck and others 1987), from aerosol concentration (De Angelis and others 1987) and from CO2 measurement (Barnola and others 1988, this volume).

Our first isotopic data set was largely discontinuous over the last 100 ka (only about 7% of the core was analyzed), but continuous beyond that time. Sampling of the ice was completed later, in the field, and we now have continuous deuterium data for the whole core (total ice recovery is about 85%), combining the data of the 2083 m core below 138 m and a complementary data set above. The core chronology was established using a two-dimensional ice-flow model and, for snow accumulation, taking into account change with time (Lorius and others 1985).

There is a general correspondence between this curve and the previously published δ18O record (Lorius and others 1985). However, there is obviously far more information in this continuous δD record, which we will examine from the deduced temperature record.

In previous work, particle analyses of fresh snow and ice cores from Camp Century, Greenland, were conducted by transmission electron-microscopy. The particles found most frequently were silicate minerals 0.05-8 μm diameter (Kumai 1977). The mean pH of snow in Ellesmere Island (81 °N, 73°W) was 5.23 for 1954-80 (Koerner and Fisher 1982). The mean pH of snow in Hanover, NH, was 4.61 for 1972-73 and 4.48 for 1980-83. The mean pH of snow in a rural area near Fairbanks, Alaska, was 5.60 for 1972-73 (Kumai 1985).

In this paper, the results of measurement of pH, electrolytic conductivity, aerosol concentration and elemental analysis of aerosols in snow and ice cores from Greenland are described and compared with those of snow from Alaska, the Canadian Arctic and New Hampshire.

The snow samples were collected at Dye 3, Greenland, from 17 to 250 cm depth; they were deposited during snowfalls from January 1980 to spring 1983. A total of 45 snow samples was examined; the samples were each about 65 g and collected at 5 cm intervals in the snow pit. The snow and ice-core samples were melted in a microwave oven for measurements of pH and electrolytic conductivity. A pH meter (Solution Analyzer, model 4505A) was calibrated by two buffer solutions of pH 4.00 and 7.00 at 25 °C. Two instruments were used for electrolytic conductivity measurements, Solution Analyzer, model 4505A, and Conductance Bridge RCM 1581, and calibrated by a standard solution of 0.005 N KC1 (720 ± 1 (μS cm−1) at 25°C. The snow and ice melt-water samples were filtered through polycarbonate membrane filters of 0.4 μm pore diameter. Particles remaining on the filters dried in a vacuum oven at 30°C, and the aerosol concentrations measured by chemical balance. The aerosols on the filters were coated by Au and Pd vapor in a vacuum chamber, for examination by scanning electron-microscopy and energy-dispersive X-ray analysis.

Results of melted snow measurements from Greenland were as follows. The pH ranged from 4.57 to 5.01; the mean pH was 4.81 in 1981. For 1982 the pH ranged from 4.72 to 4.93; the mean was 4.81. For 1983, the pH ranged from 4.50 to 5.20; the mean was 4.85. The mean pH of all snow from Greenland was lower than that of snow in a rural area of the Alaskan and Canadian Arctic, but higher than that of snow in New Hampshire.

Electrolytic conductivity of snow from Greenland varied from 3.95 to 9.70 μS cm−1 for 1981, and the mean was 6.20 μS cm−1. In 1982 it ranged from 3.21 to 8.53 μS cm−1; the mean was 5.12 μS cm−1. For 1983, it ranged from 3.40 to 6.19 μS cm−1; the mean was 4.95 μS cm1. The mean electrolytic conductivity of snow from Greenland was much lower than that of snow in Hanover, New Hampshire.

Concentrations of particulate matter in snow from Greenland ranged from 0.24 to 2.40 mg kg−1; the mean was 1.37 mg kg−1. The particulate matter was examined by scanning electron-microscopy. Several kinds of silicate minerals, spherules and unidentified organic particles were found. Spherules found in the snow samples are glass, Fe-, Ti- and Ca-rich, and considered to be fly-ash particles from coal combustion.

Measurements of the chemical constituents in polar-snow deposits translate into chronological records representing a history of atmospheric composition for the periods involved. The 2037 m deep continuous and undisturbed ice core recovered at Dye 3, Greenland between 1979 and 1981 contains a temporal record of sequential snow deposits for the past 9 × 104 a B.P. (Dansgaard and others 1985). The upper 90 m of the deep core were unsuitable for chemistry studies, but stratigraphic continuity with present-day accumulation was obtained by hand-excavating a 5.4 m deep pit and augering two shallow cores to 138 and 113 m depths. The pit and shallow cores represent the last two centuries of snow precipitation.

To date, over 6000 individual samples of the pit, shallow and deep ice cores have been measured by ion chromatography for Cl−, NO3−, and SO42− in the field and laboratory (Herron and Langway 1985, Finkel and Langway 1985, Finkel and others 1986), under clean-room conditions. All pit and shallow-core samples were prepared in a continuous sequence of eight samples per year, as identified by other stable and radioactive isotope-dating methods. The deep ice-core samples were selected and prepared from core intervals spaced over the 2037 m profile from time units which showed evidence of abrupt or transitory periods in climate change or volcanic disturbances, as defined by stable isotopes (Dansgaard and others 1985), atmospheric gases (Oeschger and others 1985) and dust (Hammer and others 1985).

Approximately 1700 new measurements from the Dye 3 samples are included in this study. Variability in the chemical constituents and their concentration levels is present and meaningful on a short-term and long-term basis. The time units measured represent seasons, years, decades, centuries and longer geological periods. Particular attention is given to two new high- and low-frequency detailed chronological data sets from (1) a continuous 26 m core profile, representing 3000 years, extending from the Holocene/Wisconsin boundary back into the late Wisconsin and (2) measurements made on 106 samples spaced every 2 m over the Wisconsin-age ice from 1786 to 2008 m.

Air-hydrate inclusions have been found in deep ice cores from Dye 3, Greenland, which were taken in August 1981. Although the concentration of the air-hydrate crystals decreased with time, when the core was stored at a temperature of −50 °C, they still existed to an appreciable extent in 1985.

An ice specimen was cut out from the Dye 3 core at a depth of 1500 m, where the volume fraction of the hydrate crystals was about 10−3 by volume. Its dielectric properties were measured in September 1985, in a frequency range of 30-20 × 103 Hz and temperature range of −20° to −90°C. The activation energy obtained for the relaxation time of the Debye dispersion was about 0.2 eV, which is much smaller than that of pure ice.

The measurement was repeated once a month for about a year, and the sample was stored at a temperature of −10 °C between measurements. The time variation of the dielectric properties has been discussed in relation to the deterioration of the air-hydrate crystals.

The production of climatic-change records using glaciochemical time series has seen minimal application in the Transantarctic Mountains. This is true despite the fact that glacial geologic studies in this area are the primary basis for understanding the glacial history of East Antarctica and thus provide an excellent potential framework for the more detailed records obtainable from glaciochemical studies. Numerous sites within the Transantarctic Mountains fit the requirements necessary for the retrieval of ice cores, and pilot studies have been conducted in both southern Victoria Land (Mayewski and Lyons 1982) and northern Victoria Land (Allen and others 1985). These pilot studies have validated the hypothesis that glaciochemical records retrieved from appropriately chosen ice-core sites in the Transantarctic Mountains can be used for: (1) assessing the current stability of the East Antarctic ice sheet, (2) validating models concerning the recent glacial history of the Transantarctic Mountains, (3) searching for relatively high-frequency (1–100 year) climatic signals, (4) determining changes in the relative geography (ocean – land – ice) of a region, and (5) defining the relative importance of the chemical species source areas (i.e. volcanic, biogenic, anthropogenic, marine, crustal) that provide precipitation to the Transantarctic Mountains.

During the 1984–85 austral summer, a combined University of New Hampshire – Polar Ice Coring Office effort resulted in the recovery of a 201 m long core from a 2800 m high snow massif atop the Dominion Range (85°15'S, 166°10'E), close to the confluence of the Mill and Beardmore glaciers. Chemical and physical data sets to be developed from this ice core, which is estimated to span a period of approximately 1000 years, include: a detailed 6 m snow pit, several shallow snow pits, and fresh and aged surface snow, in combination with a radio echo-sounding survey of the general area, which will be used to provide three-dimensional control. Chemical and physical analyses conducted as part of the study include: stratigraphy, density, sulfate, nitrate, fluoride, chloride, phosphate, sodium, reactive silicate, total beta activity and oxygen isotopes. The oxygen-isotope analyses are being provided by P. Grootes and M. Stuiver (University of Washington), and all other analyses are being conducted by the Glacier Research Group (University of New Hampshire).

Two cores, 302 and 132 m long, were drilled 1.5 km up-wind from Siple Station (75°55'S, 84°15'W) during the 1985–86 austral summer. These cores are expected to contain an annually resolvable 500 year record of atmospheric constituents. The entire length of these cores will be analyzed for insoluble particulate concentrations, liquid conductivity, and oxygen-isotope ratios. Anion concentrations (Cl−, SO42−) will be measured in selected sections. The extraction of a proxy climate history from these cores requires an assessment of the temporal quality and the spatial variability of the preserved record. This paper presents this assessment, which is based upon an extensive investigation of both pit and shallow-core (20 m) records.

To complement the two deeper cores, eight 20 m cores were drilled and three pits were sampled. The pits were excavated up-wind of the drill site at distances between 0.5 and 1.0 km. In the central pit, 2.8 m deep, walls A and C (each 1 m wide) were positioned parallel to the prevailing wind, with wall B (4 m wide) perpendicular to the prevailing wind. The stratigraphy of wall B was mapped and continuous vertical profiles of samples were collected for microparticle concentrations (MPC), oxygen-isotopic ratios (δ18O), anion chemistry (AC) and liquid conductivity (LC). Three 20 m cores, each associated with a vertical profile of pit samples, were drilled 0.5 m behind wall B. In addition, part of one core was sampled for beta radioactivity in order to isolate the 1965–66 horizon which resulted from atmospheric thermonuclear testing. Pits 2 and 3 were both 2 m deep and consisted of two 1 m wide perpendicular walls. Each wall was sampled for MPC, δ18O, LC and AC, and one 20 m core was drilled behind each wall. The visible stratigraphy of both walls in pit 3 was mapped. Densities were measured in each pit. The results from the pit and shallow-core analyses lead to the following conclusions.

The high frequency of storm events, often associated with winds in excess of 50 knots, leads to substantial drifting. The result is that stratigraphic features in the uppermost annual layer (e.g. crusts, mass-loss layers, hard layers, etc.) exhibit substantial vertical deviations and, on occasion, are laterally discontinuous. Substantial variation may occur over very short distances: e.g. a 2 cm thick melt feature pinched out over a distance of 10 cm. Interestingly, the stratigraphy in firn older than 1 year exhibits much less lateral variation. In fact, several distinct visible stratigraphic features can be correlated among most of the shallow cores and the two deeper cores. Examples will be presented. These features provide excellent time-stratigraphic markers for cross-core comparisons. Of special interest is the presence of a major melt feature, first reported by Swiss investigators in 1983. This feature, present at four different drill sites, allows time-stratigraphic correlation and yields nearly identical 10 year accumulation rates for all four sites. Such spatial continuity means that accumulation histories reconstructed from the two deeper cores should be representative of this area.

The MPC measurements (particles per ml of water) are the lowest that have been measured. No measurements of atmospheric particulate concentrations are available, but the low concentrations probably result from the high annual accumulation (∼0.55 m a−1, water equivalent), which dilutes the atmospheric input signal of particulates preserved in the firn. Swiss investigators reported similar results for the dilution of volcanic acids (e.g. SO42−), which muted the conductivity signals in a 201 m Siple Station core. The low concentrations make particles difficult to use for dating Siple cores. On the other hand, the low background levels of particulates may make Siple Station an excellent site for monitoring major atmospheric turbidity events (e.g. prolonged periods of desertification or volcanic activity).

The high annual accumulation leads to the excellent preservation of the δ18O annual signal. The annual δ18O signal ranges from 15‰ at the surface to 8‰ at 122 m, so it is probable that the annual δ18O signal will be preserved over the entire 500 year record, allowing nearly absolute dating of the core.

The potential of a nearly absolute time-scale, coupled with detailed particulate, liquid-conductivity and δ18O histories, should provide the first proxy climate record from this area. This 500 year history will complement similar records anticipated from the Antarctic Peninsula (∼73° S) and that recently constructed from the James Ross Island ice cap. A more global climatic picture of the last 500 years may be obtained when these high-resolution Antarctic ice-core records are integrated with non-polar records (e.g. the Quelccaya ice cap, Peru, and the Dunde ice cap, China) of similar quality.

Between May 1983 and July 1984 glaciological parties of the 24th and 25th Japanese Antarctic Research Expeditions (JARE–24 and 25) carried out ice-core drilling using a thermal drill, down to 700.5 m depth at Mizuho Station (70°41'53"S, 44°19'54"E), as a part of the Glaciological Research Program in east Dronning Maud Land, Antarctica.

The thermal drill, 3.9 m long and capable of taking a core 1.5 m long and 130 mm in diameter, is an improved version of a drill used by JARE–15 in 1975. The most important improvement was the monitoring system during drilling, for which a micro-computer was fitted in the drill. By using this system, such accidents as heater burn-out, tank overflow and failure of water suction would immediately be brought to our attention. The drilling speed was about 1.6 m/h, when the optimum output was 3.6 kW. The core recovery rate was above 99%.

The core quality was good down to a depth of 80 m. Between 80 and 120 m, cracks were found at intervals of 0.15–0.5 m, and horizontal cracks were found continuously at intervals of 0.01 m or less.

Immediately after the core was pulled, the stratigraphy was observed and bulk density was measured. A dust band, presumably volcanic particles, was seen at only 500.2 m depth during stratigraphic observation. The following analyses were carried out at Mizuho Station within a month of recovery:

• (1) Density determination by the hydrostatic method.

• (2) Measurement of total gas content.

• (3) Thin-section analyses, including observation of cracking around air bubbles and the crystalline texture, and ice-fabric studies.

The 700.5 m core has been brought to Japan, and the following analyses are now under way:

• (1) Oxygen-isotope ratio.

• (2) Concentration of microparticles.

• (3) Electric conductivity.

• (4) Chemistry of soluble impurities.

The evolution of gas content from clathrated ice is very sensitive to pressure and to storage temperature. As such substances are likely to be found in deep Antarctic ice and the Greenland ice sheet (Miller 1969, Shoji and Langway 1982), the influence of clathrate formation and incomplete back-diffusion on the measured air composition was investigated.

We have undertaken laboratory studies on the kinetics of formation and decomposition of clathrate hydrates of air and carbon dioxide. The kinetics were found to be controlled mainly by the self-diffusion of water molecules. The clathrate structure being of type II (Davidson and others 1984), the diffusion of guest molecules and the role of auxiliary gases was studied.

A bubble-relaxation model is presented for air-hydrate inclusions in fresh ice cores. It takes into account the diffusion constant for desorption of clathrates and the mechanical relaxation of the bulk ice. The increasing pressure and the initially low bubble surface are factors which limit the rate of decomposition. The rate of decomposition was compared with the natural bubble relaxation measured in deep ice cores (Gow and Williamson 1975).

Fractionation was also observed through the formation and decomposition of mixed hydrates. The diffusion control of the recrystallization process affects this fractionation.

On the basis of this study we make some recommendations for the analysis of deep ice-core samples.

In 1979 ice-core drilling was carried out in the accumulation area of the temperate Alpine glacier Vernagtferner (Ötztaler Alpen, Austria). The cores are among the few cores from temperate glaciers in the eastern Alps. Encouraged by the results of the isotope analysis (2H, 18O, 3H) of this core, which proved that it was possible to detect the annual layering in the firn, a second drilling operation was undertaken in 1983. One core (IV) was drilled near the 1979 drilling site, in order to check the results from the first core. A second one (VI) was drilled near the equilibrium line, in order to obtain information on the isotope content of the ice body near the ablation area. In addition, the electrical conductivity was also measured. The paper presents the measurements of the 80 m core VI of 1983: 18O and 2H profile, together with the calculated deuterium excess d, as well as the 3H profile, which gives evidence of the 1952-63 nuclear-bomb tests already at a depth of between approximately 4.5 and 7 m below the surface. There is a discrepancy of about 0.5 m between the maximum 3H peak and the peak of an in-situ gamma-ray log. The latter would coincide better with the 18O layering, so that there remains an uncertainty of 3 years in dating the upper 20 years of accumulation. The annual variations in the isotope content remain recognizable, especially with the aid of the deuterium excess. Thus it is possible to compare the thickness of the annual layers of the earlier core I (in the accumulation area) with that of the later core VI (which is located at a lower elevation) and see how the layers become thinner. Comparing cores I and IV, possible sources of changes in the isotope content, such as melt-water flow, are discussed.

Stauffer and others (1984) observed in the Greenland ice core from Dye 3 CO2 variations between low values in the range of 180-200 ppm volume and higher values in the range of 240-260 ppm volume, over a period tentatively dated to 30 000-40 000 years B.P. The low values are observed in samples with low δ18O, high particle and chemical impurity contents, representing precipitation from periods of cold climate; the higher CO2 concentrations are measured in samples which reflect warm climatic conditions because of their high δ18O and low impurity contents. The change from one climatic state to the other seems to occur within less than a century. This unexpected observation has received considerable attention from the scientific community. First, the question was posed whether the rapid CO2 variations do indeed reflect atmospheric CO2-concentration changes or whether they are caused by the interaction of gases with chemical constituents in the ice matrix. Secondly, carbon-cycle modellers searched for a mechanism in the carbon system which could produce such rapid changes in atmospheric CO2. Here we try to answer the first question.

Arguments in favour of an atmospheric origin of the CO2 variations are: CO2 measurements on an ice core from Siple Station, Antarctica, show a monotonous increase over the past 250 years, from values around 280 ppm volume to values overlapping closely with the direct atmospheric data which have been obtained since 1958 (Neftel and others 1985). Thus a consistent picture of the anthropogenic CO2 increase has been obtained which is compatible with estimates of the man-made CO2 emissions and with the carbon-cycle calculations of the airborne fraction of these emissions.

In addition, convincing CO2-concentration data have been obtained, from two ice cores from Greenland and four ice cores from Antarctica, for the transition from low (180-200 ppm volume) late-Wisconsin values to the higher (260-300 ppm volume) Holocene values. In spite of considerable differences in temperature, fabrics and chemical properties, the Wisconsin CO2-concentration values for ice cores from different locations lie in a narrow band. The Holocene values show a greater scatter; in particular, the values obtained for the Dye 3 core are significantly higher than those for the other cores. This can be explained by a relatively high temperature, which leads to melting in summer. In refrozen melt layers, CO2 is enriched in comparison with the other air gases. On the basis of these observations we conclude that melt layers are the main factor which can lead to considerable deviations in the CO2 concentration of the air occluded in ice cores from that of the atmosphere at ice formation.

To test if the melt-layer effect was the cause of the rapid changes in CO2 concentration which were observed in the Dye 3 core, increments of the Camp Century core from north Greenland were measured for CO2; they show similarly rapid Wisconsin δ18O and CO2 changes, though they are less abrupt than in the Dye 3 core. At Camp Century the present mean annual temperature is 4.5 °C lower than at Dye 3, and during the Wisconsin the temperature difference was even greater, as indicated by the δ18O values. Because even for Holocene ice in the Camp Century core the melt-layer effect on the CO2 concentration is relatively small, we exclude any similar significant effect on the Wisconsin ice. On the basis of the Greenland ice-core information alone, therefore, we have no indication that the rapid Wisconsin CO2 variations do not represent an atmospheric phenomenon.

Arguments against an atmospheric origin for the rapid CO2 variations stem from detailed analyses of the ice core from Byrd Station, Antarctica. Observation of the increase in anthropogenic atmospheric CO2 in both hemispheres indicates that within a few years CO2 becomes well mixed throughout the atmosphere. Thus the CO2 variations observed in the Greenland core should also appear in the Antarctic core increments which represent corresponding periods. A thorough CO2 study was performed on a Byrd Station core fraction which, according to a tentative time-scale (personal communication from C.U. Hammer, 1987), corresponds to the time interval 5000-55 000 years B.P. (Fig. 1). In what follows, we briefly discuss the data in the 25 000–55 000 years B.P. time interval. A first look reveals that all the data lie in a band between 180 and 220 ppm volume; no values are observed in the 240 and 260 ppm volume band. There are periods showing trends, e.g. from c. 210 ppm volume around 40 000 years B.P. to c. 185 ppm volume around 32 000 years B.P., and periods of strong scattering of the data, e.g. between 41 000 and 44 000 years B.P., with values in the 185-215 ppm volume band. At Byrd Station the annual accumulation is 0.16 m of water equivalent, compared to 0.50 m of water equivalent at Dye 3. This means that at Byrd Station, both the difference between the age of the surrounding ice and the mean age of the air, and the width of the age distribution of the gases, are larger than at Dye 3. In addition, the Byrd Station core does not show the rapid δ18O changes which indicate warm periods with relatively high accumulation. Thus one might argue that in the Byrd Station core the CO2 changes are dampened, due to a significantly wider age distribution of the gases in the ice.

This effect was modelled by Neftel and others (in press). They applied a deconvolution procedure in order to reinstall the range of possible atmospheric CO2 concentrations (see Fig. 2). This procedure results in a somewhat wider band of possible CO2 concentrations; in some periods it is 170-230 ppm volume. But it does not produce the possible high values in the range observed in the Greenland ice cores. All this new information leads to the following ambiguous conclusions:

The new CO2 data for the Camp Century ice core show rapid Wisconsin CO2 changes similar to those in the Dye 3 data, in spite of the differences in the temperatures and the physical and chemical properties of the two ice cores. However, similar CO2 changes do not appear in the Byrd Station ice core (from Antarctica) in the core fraction thought to represent the corresponding time interval.

There are three possible ways to resolve the apparent discrepancy:

(1) In the Wisconsin warm-period ice, CO2 is artificially enriched, due to a process which has not yet been identified.

(2) In the Byrd Station core, the CO2 changes during the Wisconsin are attenuated to a much higher degree than was assumed in the model calculations by Neftel and others (in press).

(3) The increments in both the Greenland and Byrd Station cores which have been investigated do not represent overlapping time intervals, perhaps due to rheological irregularities in the Greenland ice sheet close to bedrock (Staffelbach and others 1988, this volume).

With the existing core material it is difficult to resolve this important problem. The dilemma of the rapid Wisconsin CO2, variations is one of the many important arguments for the recovery of new deep cores both in Greenland and in Antarctica.

A quantitative interpretation of oxygen-isotope data in ice cores in terms of climate has so far been hampered by the lack of a quantitative understanding of the processes which determine the isotopic composition of precipitation. Dansgaard (1964) has demonstrated that observed relations between 18O/16O and temperature can be explained reasonably well by the Rayleigh condensation model. This model is re-interpreted by noting that it predicts a dependence of the 18O/16O ratio on the water-vapour mixing ratio in the atmosphere. The relationship between the monthly data from different European stations and the water-vapour mixing ratio agrees remarkably well with the Rayleigh model. Data from Greenland snow show good correlation with the following parameters: mean annual temperature Ta, the water-vapour mixing ratio corresponding to Ta, and the accumulation rate. These correlations will be discussed in terms of the Rayleigh model and of the underlying physical processes. The correlation between 18O/16O ratios and the accumulation rate allows us to estimate the latter during the ice age. The change in the accumulation rate between the ice age and postglacial time can also be estimated from the chemical composition or the 10Be concentration. The different results will be compared.

Since 1977, we have been studying the weather and climate of a mountain area, and particularly the winter snow-pack.

The area is situated in the French Alps, at an altitude of 1450-2500 m. Since winter 1982-83, we have been studying the snow-pack each week and every time we collected snow cores. We collected them at different test sites (area 1: 1850 m NW; area 2: 1800 m SE; area 3: 1600 m NW; area 4: 2000 m).

The following parameters were collected at the test sites on a continuous basis throughout the winter: new and total snow depth, wind direction and precipitation (solid and liquid), snow-water equivalent (precipitation and total snow depth), standard snow profiles, and structure of the snow-pack.

After data analysis, many different questions were investigated, in two respects:

(1) Analytical techniques: problems of sampling snow cores (transport, conservation, evolution), and analysis of the micro-structure of the different snow layers in correlation with the macro-structure of the snow-pack.

(2) Results and interpretations: do changes in the structure (macro- and micro-structure) of the snow cores take place during their conservation? Can we consider snow cores as preserving the record of the winter climate (precipitation, chemical pollution)?

(3) Data archive: Constitution of snow-core data archive, in relation to the climatology of the area.

A procedure has been developed to extract and measure the relative concentrations of O2, and 15N14N, as well as the isotopic abundance of these occluded gases, in ice cores. A wet-extraction procedure is used to extract 99.995% of the gas from the ice. The gas is removed from the extraction vessel by helium cryogenic trapping of all its constituents in a stainless-steel sample tube immersed in liquid helium. The elemental O2/N2 ratio is determined by measuring the ratio of masses 16O16O (O2) and 15N14N (N2) simultaneously, using a Finnigan MAT 251 isotope-ratio mass spectrometer. Mass 29 is used because the instrument cannot be configured to measure masses 28 and 32 simultaneously. The δ18O of O2 and δ15N of N2 are also measured on the same ice sample. The bubble composition is compared to a dry-air standard admitted to the reference side of the inlet system. The notation used to report the O2/N2 ratio is the delta notation:

where

Applying these methods both to shallow and to deep ice cores will help us to understand global carbon cycling during the period covered by the ice cores. Changes in the distribution of carbon within the biosphere, atmosphere, oceans, and sediments will produce changes in the O2/N2 ratio of the recent atmosphere. Thus measurements of the O2/N2 ratio in ice will increase our understanding of the distribution of carbon within various reservoirs.

The δ18O of O2 in the atmosphere has been shown to be coupled with the δl8O of the water used during photosynthesis. The δ18Owater of the whole ocean was 1.3‰ heavier during the last glacial maximum, which has been shown to correspond to a 1.3‰ enrichment in the δ180 of atmospheric O2 (Bender and others 1985). Thus the measurements of the δ18O of O2 in ice will give an insight into the coupling between biological and hydrological cycles. Measurements of the δ15N of N2 serve as a fractionation indicator. Any change in the δ15N must be due to some fractionation process, as δ15N cannot have changed over the time-scales in question.

To date, we have analyzed recent (approximately 200 years B.P.) bubble samples from Crête, D10 and Byrd Station ice cores. For the δ(O2/N2) analysis, the range of averaged values from each core was from –0.051 to –7.5‰ relative to present-day air. We believe that the large range is due to separation of O2 relative to N2, either during bubble close-off or during storage of the collected cores. For δ18O of the O2, the average values ranged from +0.37 to +0.71‰. The δ15N results ranged from +0.18 to +0.33‰. The results indicate that there has been some fractionation of the gases, based on the δ15N of the N2 in the bubbles. There is a striking covariance between δ18O and δ15N. The correlation coefficient r = 0.96. The slope of δ15O versus δ15N is 2.2, which is slightly greater than the slope which would be expected if the two isotopes were fractionated in a mass-dependent fashion. Possible explanations for the isotopic fractionation are: (1) the gases were fractionated during close-off in the firn, or (2) the composition of the bubbles has been changed since coring by diffusion through small cracks in the core. Radial sampling of gases in the core is in progress in order to investigate possible gas diffusion from the core during post-coring relaxation of the ice.