Electrical resistivity sounding using the four-electrode Schlumberger array was carried out at station UpB on Ice Stream B to an electrode spacing of 3 km. Measured apparent resistivities were compared with theoretical models based on known relations between resistivity, density and temperature. Densities were measured in a pit and two coreholes; temperatures were measured in the upper 200 m of the ice stream and have been calculated for greater depth from an ice-stream temperature model. The resistivity, after correction for density and temperature, increases with depth down to 650-700 m. Below that is a marked decrease over the next 100m or so that we correlate with the Holocene-Wisconsin transition zone. Still deeper there is an orders-of-magnitude increase to a value, in the basal ice, of 30 MΩ m or more. This extremely high resistivity is similar to that reported for temperate glaciers and deep in the Antarctic ice sheet elsewhere. We attribute it to the destruction, by extensive metamorphism, of impurity-conduction paths at two-grain boundaries

The precision of satellite-radar altimetry over the Antarctic ice sheet can be improved by using a physically based retracking algorithm on the altimeter returns ("wave forms"). Ridley and Partington (1988) have shown that both surface and volume-scattering affect the shape of the return. Here, we develop a model that is based on a variable combination of surface- and volume-scattering and determine the model parameters through least-square fitting to the observed wave forms. The model parameters include surface roughness, proportion of volume-scattering, extinction coefficient and an amplitude coefficient. Geosat data collected over a test sector of the East Antarctic ice sheet have been analyzed to find quantitative estimates of seasonal and geographic variations of the several parameters. Our results show that the effect of volume-scattering can change the elevation measurement over the inland part of the East Antarctic ice sheet by more than I m and that there are both spatial and temporal variations; temporal variations are less significant than spatial variations.

Experimental investigations on the formation and growth processes of air-hydrate crystals were carried out to determine the transformation process of air bubbles into air-hydrate crystals in deep ice sheets. The microscopic observations revealed that the transformation began at the boundary between a bubble and ice. Faster transformation occurred along the boundary and, subsequently, the transformation progressed towards the center of the bubble at a lower rate. Each transformation rate increased with pressure and also with temperature. The activation energy of the transformation was about 0.52 eV for the primary transformation process and about 0.90 eV for subsequent processes. These results indicate that the rate determining the process of transformation is mainly supplementation of water molecules to the transformation site. An estimation of the transformation period of an air bubble into an air-hydrate crystal in a deep ice sheet reveals that it is about one thousandth of the time period of the transition zone, where both air-hydrates and air bubbles exist

Radar profiling in the area around Upstream B camp (82.5° S, 128.7° W) was performed during the austral 1991−92 summer. About 150 km of lines covering 80 km2 along The Ohio State University strain grid were profiled. The high density of data along the profiling lines allowed us to use median filtering schemes to remove or decrease interference from near-surface diffractors. Bed and surface elevations are poorly correlated. Hydraulic-head gradients suggest ponding of water in some places and drainage from others. Reflection amplitudes vary over a range of about 24 dB, partly because of scattering by crevasses, but partly also because of real differences in bed reflection.

Two types of experiments were performed near Upstream B Camp on Ice Stream B2 using a high-resolution ground-penetrating radar system. In the first type of experiment, tracking a metal drill tip through the upper 85 m of the ice column indicated an approximately linear decrease of wave speed with depth down to 50 m, with a constant speed of 170 ± 4 m µs−1 below. We believe the (unexpected) linearity may have been caused by one or more buried crevasses. In the second experiment, a survey of a 250 km2 grid showed a population of buried crevasses at about 30 m depth that have an estimated burial age of 210 ± 25 years, which is taken to indicate that this ice has been exhibiting streaming behavior for at least that length of time. One 3 km segment along the edge of the survey area nearest the center of the stream showed virtually flat, undisrupted stratigraphy down to the maximum depth of our measurements. The fact that this ice was accelerated from near-zero speed to its present 440 m a−1 without cracking or folding suggests that this ice may have been incorporated into the ice stream as a solid block.

Results of measurements performed on and around an Antarctic blue-ice field are presented in this paper. The measurements were carried out in a valley of Heimefrontfjella, Dronning Maud Land, during a 2 month field season in the austral summer of 1992–93. A simple model is used to evaluate the surface-energy balance from measured meteorological quantities. The large differences in the surface-energy-balance values between snow and blue ice are mainly caused by differences inalbedo, surface roughness, thermal conductivity and short-wave radiation extinction coefficient. Taking into account uncertainties in the calculations, it appears that the calculated sublimation rates over ice and snow do not differ much.

Furthermore, typical circulation patterns are described. The large continental-scale katabatic flow is forced by radiative cooling of the surface (night-time) and the mesoscale horizontal temperature gradient (daytime). The latter penetrates to the surface due to enhanced mixing in an unstable stratified boundary layer. At night, shallow katabatic layers form along local fall lines. On some occasions the large-scale katabatic winds decrease through the presence of a high-pressure system in the weddell Sea and a local circulation can develop inside the valley.

Thirty-nine 50 MHz radar polarization experiments were performedin 1991–92 near Upstream B Camp, Antarctica, along two lines perpendicular to flow,1.4 and 2 km long and 900 m apart. For each of the experiments, which were at 100m intervals, the receiving antenna was held fixed, alternately parallel and perpendicular to flow, while the transmitting antenna was rotated in 15° increments through a full circle twice, once for each orientation of the receiving antenna. The data consist ofecho-amplitude measurements from the bottom of the ice. Assuming a model of the ice sheet as a crystalline medium with axial symmetry, the azimuths of the symmetry axis and the cosines of the phase shifts between extraordinary and ordinary waves can beestimated from the variations in amplitude with orientation of the transmitting antenna. The results from bottom echoes show an abrupt change in the axis of symmetry in a distance of only 100m. This suggests that the experimental lines crossthe boundary between two blocks of ice with different stress histories.

Phases of seismic P-wave reflections from the bed of Ice Stream B ata site on its ice plain have been examined. The survey comprised a 36 km line at ashallow angle (18°) to ice movement and four 3.6 km cross lines. Reversed-phase and unreversed-phase reflections each characterize about half the bed. The corresponding zones can be correlated in stripes quasi-parallel to ice movement. We take this as support for a model previously developed that relates the zones to different types of subglacial sediment dragged along by the ice. There is also evidence for patches of pooled water.

Microearthquakes at the base of slow-moving Ice Stream C occur many times more frequently than at the base of fast-moving Ice Stream B. We suggest that the microearthquake source sites are so-called “sticky spots”, defined as limited zones of stronger Subglacial material interspersed within a weaker matrix. The fault-plane area of the microearthquakes (O (102m2)) is therefore a measure of the size of the sticky spots. The spatial density of the microearthquakes (O (10 km-2)) is a measure of the distribution of sticky spots.

The average stress drop associated with these microearthquakes is consistent with an ice-stream bed model of weak subglacial till interspersed with stronger zones that support much or all of the basal shear stress. We infer a weak inter-sticky-spot material by the large distances (O (103 m)), relative to fault radius, to which the microearthquake stress change is transmitted.

Water piracy by Ice Stream B, West Antarctica, may have caused neighboring Ice Stream C to stop. The modern hydrologic potentials near the upstream end of the main trunk of Ice Stream C are directing water from the C catchment into Ice Stream B. Interruption of water supply from the catchment would have reduced water lubrication on bedrock regions projecting through lubricating basal till and stopped the ice stream in a few years or decades, short enough to appear almost instantaneous. This hypothesis explains several new data sets from Ice Stream C and makes predictions that might be testable.

Data on Antarctic sea‐ice characteristics, and their spatial and temporal variability, are presented from cruises between 1986 and 1993 for the region spanning 60°−150° E between October and May. In spring, the sea‐ice zone is a variable mixture of different thicknesses of ice plus open water and in some regions only 30−40% of the area is covered with ice >0.3 m thick. The thin‐ice and open‐water areas are important for air‐sea heat exchange. Crystallographic analyses of ice cores, supported by salinity and stable‐isotope measurements, show that approximately 50% of the ice mass is composed of small frazil crystals. These are formed by rapid ice growth in leads and polynyas and indicate the presence of open water throughout the growth season. The area‐averaged thickness of undeformed ice west of 120° E is typically less than 0.3 m and tends to‐increase with distance south of the ice edge. Ice growth by congelation freezing rarely exceeds 0.4 m, with increases in ice thickness beyond this mostly attributable to rafting and ridging. While most of the total area is thin ice or open water, in the central pack much of the total ice mass is contained in ridges. Taking account of the extent of ridging, the total area‐averaged ice thickness is estimated to be about 1m for the region 60°−90° E and 2 m for the region 120°−150° E. By December, new ice formation has ceased in all areas of the pack and only floes >0.3 m remain. In most regions these melt completely over the summer and the new season's ice formation starts in late February. By March, the thin ice has reached a thickness of 0.15 0.30 m, with nilas formation being an important mechanism for ice growth within the ice edge

The spatial pattern of accumulation rate for eastern Kemp Land in the elevation range 1850-2700 m is presented together with observations of the physical parameters of snow temperature, average microwave emissivity (19 GHz, H polarization), distribution of depth hoar and firn-crystal diameter. The broad accumulation pattern in the region was found to be significantly low when compared to other coastal areas of East Antarctica such as Wilkes Land. The low accumulation regime is attributed to low atmospheric moisture transport and low penetration of synoptic cyclonic systems on to the coastal slopes. In the absence of high coastal precipitation, the accumulation rate is determined predominantly by surface snow redistribution processes. Attempts to determine accumulation-rate time series using visible layer, δ18O isotope and electrical conductivity stratigraphies were unsuccessful due to the relatively low coastal accumulation rates (less than 280 kg m-2a-1) and the complex modification of precipitation by redistribution processes.δ18O variations of seemingly cyclic nature observed throughout the cores were interpreted as a product of the snow-dune building and erosion processes, together with general redistribution of snows by the surface wind field, under the influence of mesoscale topographic roughness

Several sets of temperature measurements were carried out in 1972- 88 in the Vostok boreholes. They have provided the ice-sheet temperature profile down to a depth of 2000 m. The accuracy of the profile is sufficient to analyze perturbations induced by the surface-temperature variations over the last climatic cycle. The mathematical model developed for the ice-temperature computation is applied to solve an inverse problem. The amplitudes and phase lags of the main harmonic components in the surface-temperature variations are reconstructed on the basis of fitting the calculated ice-temperature profile to the experimental one with the assumption that Milankovich's cycles (100, 41, 23 and 19 kyear) are dominant in the climate oscillations. The paleotemperature record simulated with the inverse procedure is revealed to be insensitive to the model parameters varied within the range of their uncertainty. Minimal standard deviation between calculated and measured temperature profiles is found of the same order as the reproducibility of the temperature measurements (0.005-0.01°C). Although the simulated temperature-time curve obtained in this study does not contain short-term variations, all the main climate events predicted from the ice-core isotope analysis can be recognized. Thus, the age of the events can be verified independently of the ice-sheet dynamics dating. The resultant time-scale for the Vostok record appears to be in good agreement with the dating of climate events recorded in deep-sea sediments.

The brine infiltration zone of Mc Murdo Ice Shelf, Antarctica, has been extensively studied by previous authors. Brine percolates inland laterally from the ice front, opposite to the direction of ice-shelf motion. Inland propagation of brine pulses following ice-shelf break-outs appears to be the primary brine-infiltration mechanism. During the 1992-93 field season, we used radio-echo sounding to resurvey the inland limit of the brine-infiltration zone. The boundary had been similarly mapped in 1977. We observed that since the earlier survey, one 7km section his retreated seaward by approximately 800 m while another 5 km section is unchanged. These displacements are consistent with the earlier hypothesis that brine infiltration occurs by the influx of brine pulses

10m firn temperatures are commonly used on the Antarctic plateau to estimate mean annual air temperatures. 10m firn temperatures measured at Taylor Dome (also referred to as McMurdo Dome in the literature), Antarctica, are influenced by a factor other than altitude and latitude that varies systematically across Taylor Dome. Some inter-related factors possibly contributing to the modern temperature variability are differences in sensible heat from warm or cold air masses, differences in wind strength and source region, differences in temperature inversion strength and differences in cloudiness. Our preliminary data are compatible with spatially variable katabatic winds that could control the winter temperature inversion strength to provide a large part of the signal. This has implications for paleoclimate studies.(1) Variations of the stable isotopes δ18O and δD from ice cores are a proxy for paleotemperature. The isotope thermometer is calibrated by comparing local isotope ratios with corresponding measured temperatures. In order to derive a useful isotope-temperature calibration, we must understand the processes that control the modern spatial variability of temperature. (2) In order to quantify past changes in local climate, we must understand processes that influence local spatial variability. If those processes differed in the past, ice-core climate reconstruction would be affected in two ways: through alteration of the geochemical record and through alteration of deep ice and firn temperatures.

Drifting-snow samples were collected at Mizuho Station (74°42' S, 44°20' E, 2230 m a.s.1.) from February to October 1986 and along traverse routes in east Dronning Maud Land (1800-3000 m a.s.1.), East Antarctica, from October 1986 to January 1987. The typical sampling interval was about once a week but two sets of intensive sampling were made at the end of February and November at between 2 h and 1 d intervals

Measurements for CI-, NO3,SO42and Na+ were made on the drifting-snow samples by ion chromatography. Oxygen-isotope ratios were .also measured .on the samples. Concentrations levels ofNO3-and SO4-show distinctive seasonal variations: high in summer (4.6 neq g-1 for NO3 and 3.3 neq g1 for SO42) and low in winter during mid-March to mid-November(1.0 neq g1 for NO3 and 0.5 neq g1 for SO42). Results obtained at Mizuho Station show that the transition from the summer high values to winter low values takes about 20 d for NO3 and SO42-.The variations in Cl and Na+ concentration levels are small in both autumn and spring (averages are about 1 neq g-l) with greater variability throughout the rest of the year. The intensive sampling data set shows that there is considerable variability within a day with NO3 and SO42- concentration levels up to about a factor of 4 associated with a 10%0 change in 3180 ratios.

Cores of highly strained ice recovered from depths of 1200–1800 m at Byrd Station in 1967–68 have been found to have recrystallized while in storage in the United States. Such recrystallization, inferred to have occurred when temperatures in the storage facility rose above about – 14°C, would not have been discovered if thin sections of the cores had not been prepared and photographed at the drill site within hours of pulling the cores to the surface. It was only after new sections of the long stored cores were compared with the original sections that the full extent of recrystallization was revealed. The recrystallized structure emulates in both texture and fabric those observed in naturally annealed ice in the bottom 350 m at Byrd Station. It is concluded that polar ice cores should be stored at temperatures of –20°C or colder in order to inhibit or minimize post-drilling recrystallization.

A survey of ice-front changes since 1910–13 shows that the Koettlitz Ice Tongue, located along the western shore of McMurdo Sound, Antarctica, has undergone significant retreat during the past 80 years. The ice front in 1910–13 was located 5 km in front of the Dailey Islands. Today, only two of the six Dailey Islands remain connected to the Koettlitz Ice Tongue. The most recent break-out of ice is believed to have occurred in 1979 or 1980, resulting in an estimated loss of 80 km2 of ice. Based on the current position of the ice front, it is estimated that a minimum of 300 km of ice has called off the Koettlitz Ice Tongue during the 80 year period that has elapsed since the ice front was first mapped in 1910–13.

The surface mass balance in east Dronning Maud Land has been observed mainlvbv means of the snow-stake method. The surface mass balance generallv decreased with distance from the coast; from more than 250 mm a−1 in the coastal region to less than 50 mm a−1 in the inland region higher than 3500 m in altitude. At Mizuho Station (2230 m a.s.l.). the sublimation was about 50 mm a−1. precipitation was between 140 and 260 mm a−1, and the loss from the surface by theredistribution was estimated to be about 100 mm a−1, which agrees with the surface mass balance estimated as 70 mm a−1 from the grain-growth rate. Around the mountainous area, the balance was small or in some cases negative, where a bare-ice field has developed. In the inland area, 3000– 3200 m a.s.l..the surface mass balance was less than 50 mm a−1, i.e. lower than in the surrounding areas. This low mass-balance area can be explained bv redistribution by the drifting snow. The whole mass input in five drainage basins with a total area of 620 × 103 km2 is 61.2Gton a−1 and the mean surface mass balance is 99 mm a−1.

The time decay of surface undulations is modeled analytically. The particular application is the decay of flow stripes on the Ross Ice Shelf that emanate from Byrd Glacier. The model predicts two extreme undulation types. One extreme, which we term the buckle solution, has a decay time of only 13 years. The other, the pinch-and-swell case, can persist much longer (700 years), because each surface ridge is underlain by deep roots. Flow stripes may originate as a combination of both the buckle and pinch-and-swell extremes, but only the pinch-and-swell aspect is predicted to survive in the ice shelf The predicted decay time and that measured from satellite imagery are in close agreement.