Ice flow from the ice sheets to the ocean contains the maximum potential contributing to future eustatic sea-level rise. In Antarctica most mass fluxes occur via the extended ice-shelf regions covering more than half the Antarctic coastline. The most extended ice shelves are the Filchner–Ronne and Ross Ice Shelves, which contribute ~30% to the total mass loss caused by basal melting. Basal melt rates here show small to moderate average amplitudes of <0.5ma–1. By comparison, the smaller but most vulnerable ice shelves in the Amundsen and Bellinghausen Seas show much higher melt rates (up to 30 ma–1), but overall basal mass loss is comparably small due to the small size of the ice shelves. The pivotal question for both characteristic ice-shelf regions, however, is the impact of ocean melting, and, coevally, change in ice-shelf thickness, on the flow dynamics of the hinterland ice masses. In theory, ice-shelf back-pressure acts to stabilize the ice sheet, and thus the ice volume stored above sea level. We use the three-dimensional (3-D) thermomechanical ice-flow model RIMBAY to investigate the ice flow in a regularly shaped model domain, including ice-sheet, ice-shelf and open-ocean regions. By using melting scenarios for perturbation studies, we find a hysteresis-like behaviour. The experiments show that the system regains its initial state when perturbations are switched off. Average basal melt rates of up to 2 ma–1 as well as spatially variable melting calculated by our 3-D ocean model ROMBAX act as basal boundary conditions in time-dependent model studies. Changes in ice volume and grounding-line position are monitored after 1000 years of modelling and reveal mass losses of up to 40 Gt a–1.

Snowmelt is measured over a 34 day summer period at 2440ma.s.l. on Tasman Glacier (>500m above the equilibrium-line altitude) using a tipping-bucket lysimeter and an array of ten ablation stakes. A degree-day factor for snowmelt is calculated using a linear relationship between combined measured melt and the number of degree-days. The slope of the regression line for these data points provides an estimate of the degree-day factor for use in runoff models. Average snowmelt is 17.8 mmd–1, but varies between 0 and 78 mmd–1. Melt occurs in a series of distinct cyclical events or pulses, each of which lasts 5–8 days. These correspond to the eastward passage of anticyclones, then troughs over the Southern Alps. When all days with northwest airflow across the Southern Alps are excluded, the melt factor is 3.4 mm˚C–1 d–1. Northwest days belong to a different population with a much higher average melt factor of 9.1 mm˚C–1 d–1, but more measurements are required to better understand key processes.

This paper presents a modelling study of the influence of suspended snow on turbulence in the atmospheric surface layer. Turbulence is diminished in drifting and blowing snow, since part of the turbulent energy is used to keep the particles in suspension. This decrease in turbulence directly affects the vertical turbulent fluxes of momentum and snow particles (and other scalars), and can effectively be simulated by introducing an appropriate Richardson number to account for the stability effects of the stably stratified air-snow mixture. We use a one-dimensional model of the atmospheric surface layer in which the Reynolds stress and turbulent suspended snow flux are parameterized in terms of their mean vertical gradients (first-order closure). The model calculates steady-state vertical profiles of mean wind speed, suspended snow mass in 16 size classes and stability parameters. Using the model, the influence of snowdrifting on the wind-speed profile is quantified for various values of the initial friction Velocity (which determines the steepness of the initial wind-speed profile). It will be demonstrated why the roughness length appears to increase when snowdrifting occurs. Finally, we present a parameterization of the effects of snowdrifting on atmospheric stability which can be used in data analyses as a first-order approximation.

Jakobshavns Isbra;, located at 69°10′ Ν on the west coast of Greenland, is the world’s fastest known glacier. Measurement of surface velocities at the calving front in July of 1964, 1976, 1978, 1985, and 1986 yielded a mean velocity of 20.6 m/d. Variation in mean velocity from year to year is less than 1 m/d. Velocity measurements 10 km behind the calving front indicated mean annual velocities of 17.1 m/d compared to mid-summer velocities of 17.6 m/d. The maximum possible decline in winter velocity is then 7%. Calculation of the volume flux into the fjord is 3.72 × 1010 m3 a−1 ± 10%. The surface balance of Jakobshavns Isbræ is 3.37 × 1010 m3 a−1 ± 12%. The agreement between these balance calculations, the long-term stability in glacier velocity, and the reasonably stable glacier front indicate that Jakobshavns Isbræ is in a state of near equilibrium, with probably a small negative balance.

Temporal and spatial variations of the seasonal snow cover at 40 sites in Nordland county, Norway, since the last decade of the 19th century are examined. Nordland lies across the Arctic Circle. Annual maximum snow depths there have varied, reflecting the interaction of synoptic conditions, temperature and terrain. North/south and coastal/inland differences are evident, but common temporal trends are identified. Maximum snow depths are strongly related to the winter North Atlantic Oscillation index. Early in the 20th century, the index was positive and the associated stormy conditions resulted in a deep, prolonged snow cover. As the index declined in the 1920s, snow depths decreased sharply. Through much of the second half of the 20th century they increased as the index tended to become more positive. The start and duration of the period of continuous snow cover is influenced by the autumn NAO index. A decrease of duration around 1990 was particularly evident at low-lying stations and those in northern Nordland. The NAO has varied considerably over the past 120 years. Because of its influence, forecasting future trends of snow depth and snow-cover duration is not a simple task.

A local two-dimensional flow model which accounts for the anisotropic behaviour of polar ice and the evolution of its strain-induced anisotropy is briefly reviewed. Due to its complexity, it is not yet possible to use this model to simulate the flow of a whole ice sheet, and its potential applications are presently restricted to limited spatial domains around existing drilling sites. In order to calculate the local flow of ice, boundary conditions must be applied on the lateral edges of the studied domain. Since these limits correspond to fictitious sections of the ice sheet, the type of boundary condition to adopt is not obvious. In the present paper, different kinds of boundary conditions of the Dirichlet type, applied at the lateral boundary of an idealized ice sheet of simplified geometry, are discussed. This will serve as a first step towards the coupling of the local flow model with a global ice-sheet flow model.

The theoretical basis of subglacial channel dynamics can be traced back to the work of Röthlisberger (1972) and Nye (1953). Röthlisberger (1972) considered the channels’ behaviour to be governed by a mix between water friction melting back the channel walls and the viscous closure of the surrounding ice; Nye (1953) derived a viscous closure rate for the ice. While their modelling is evidently well constructed, two aspects of their work have gone undeveloped. The first is the consideration of a finite glacier depth within the viscous closure law, instead of the assumption of an infinite glacier depth. The second is the allowance of a region of open channel flow, so that a channel’s water may transition from a region of closed channel flow to one where the water is exposed to the atmosphere. This paper helps close these two gaps, showing how Nye’s equation for the rate of ice closure can be modified, and how the point of transition between closed and open channel flow may be determined.

The interpretations of relevant interfaces (i.e. the surface and bed) in radar sounding datasets over glaciers and ice sheets are primary boundary conditions in a variety of climate studies and particularly subglacial water routing models. It is therefore necessary to ensure these interpretations are consistent and not affected by cross-track clutter. For the surface interface, interferometry and a family of methods relying on digital elevation models have been used to successfully discriminate cross-track surface clutter. Here we present how interferometry can be applied to the problem of basal clutter from cross-track bed topography. Our approach is based on a comparison of the differential phases of ambiguous reflectors that may represent bed clutter and the differential phase of a reflector in an adjacent area that appears unaffected by basal clutter. The reflector yielding the smallest interferometric phase difference relative to the unambiguous bed reflector is considered to represent its consistent continuation. We successfully demonstrate our approach using 60 MHz center frequency MARFA data collected over Devon Ice Cap in the Canadian Arctic. Finally, we investigate the effects of clutter-affected and interferometry-corrected bed interpretations on ice layer thickness estimates, basal hydraulic head gradients and the potential extent of inferred subglacial water bodies.

The microwave brightness temperature of the ice sheet in Antarctica has a few narrow, elongated features of very low microwave brightness temperatures. The contrast inside and outside of these areas is at least 10 K at 37 GHz. These features are persistent throughout the year and from year to year and occur at 6.6,10.7,18 and 37 GHz. The exceptionally large frequency gradients observed in this narrow area suggest that very large snow grains exist in the snow cover. Past traverse data revealed that the entire surrounding region undergoes large temperature gradients that drive high sublimation causing very large snow grains to form and the formation of both surface and depth hoar. A detailed study of former snow pits showed that, at the place of the unique features, the snow grains from the surface down to the first 2 m are the largest observed over the region. A digital elevation model shows the surface is nearly flat, and corresponds to a subglacial depression in the underlying bed. Previously reported kilometer-scale snow dunes are observed up- and downslope of the level area, but not within the level area, where the brightness temperature is lowest. In this katabatic zone, the drift-snow redistribution and the natural wind-shadow induced by the slope depression create a protected area where the snow grains can grow into very large grains.

Over extensive areas of the Arctic and Antarctic, the c-axes of the grains in a sea-ice sheet develop a preferred orientation in a particular direction in the Horizontal plane, causing the physical and electromagnetic properties of the material to be anisotropic. A number of mechanisms have been proposed for this alignment, the more likely including the tilting of floes, horizontal temperature gradient, horizontal deviatone stresses, and oceanic currents. Laboratory experiments have been performed at the Scott Polar Research Institute to distinguish the effects of these mechanisms on the fabric of sea ice. Ho correlation was found between the development of the preferred orientation of c-axes and any of the first three mechanisms. However, in the presence of a current, the strength of the alignment increases rapidly with depth in the ice, the mean c-axis direction coinciding with the current direction. A significant reduction in alignment was produced when the flow was reduced to zero. In addition, upstream deflection of the columnar axis was observed in flowing brine. These results indicate the importance of fluid motion in controlling the rate of transport of solute from the interface and hence the relative growth rates of grains of different orientations.

Velocity measurements carried out on Hintereisferner, Central Alps, Austria, provide the unique opportunity to study 100 years of ice dynamics of this glacier. During this time, three periods of accelerated flow occurred, around 1920, in 1940 and in the 1970s; but only around 1920 did the acceleration actually lead to an advance of about 60 m. The velocity increased from 30 m year−1 in 1914 to more than 120 m year−1 in 1919, and doubled during the accelerations of 1940 and 1980. In the course of the third event, the velocity increase spread over a period of more than a decade (1965–79) with a comparatively low maximum. These velocity changes cannot be explained by increased deformation velocity due to increased ice thickness alone.

Time series of the velocities at various locations along the glacier are given for the entire period, and an attempt was made to construct a time series of the velocity at a point 2 km from the strongly retreating front. The flow divergence was about 0.1 per year in the lowest 2 km, and emergence velocities reached 5 myear−1.

The response of the Antarctic ice sheet to climate change over the next 500 years is calculated using the output of a transient-coupled ocean-atmosphere simulation assuming the atmospheric CO2 value increases up to three times present levels. The main effects on the ice sheet on this time-scale include increasing rates of accumulation, minimal surface melting, and basal melting of ice shelves. A semi-Lagrangian transport scheme for moisture was used to improve the model’s ability to represent realistic rates of accumulation under present-day conditions, and thereby increase confidence in the anomalies calculated under a warmer climate. The response of the Antarctic ice sheet to the warming is increased accumulation inland, offset by loss from basal melting from the floating ice, and increased ice flow near the grounding line. The preliminary results of this study show that the change to the ice-sheet balance for the transient-coupled model forcing amounted to a minimal sea-level contribution in the next century, but a net positive sea-level rise of 0.21 m by 500 years. This new result supercedes earlier results that showed the Antarctic ice sheet made a net negative contribution to sea-level rise over the next century. However, the amplitude of the sea-level rise is still dominated In the much larger contributions expected from thermal expansion of the ocean of 0.25 m for 100 years and 1.00 m for 500 years.

The classical theory of jökulhlaups used Röthlisberger’s earlier theory of ice-channel drainage to describe the development of the flood hydrograph. This theory has some drawbacks: the mechanism of initiation (breaking the seal) is opaque, the Manning roughness coefficient is too large and the hydrographs can reveal a sudden switching from channel opening to channel closure which is not simulated by the model. In this paper, we examine these features by exploring a more detailed model, which takes into account the physics of sediment erosion and its effect on channel morphology. We propose a theory in which channels need not be semicircular, but have shapes determined by a local balance between closure and melting, and in which erosion of the tunnel margins is taken into account; in particular, we derive theoretical predictions for sediment discharge, and we also propose a mechanism whereby the pressure seal over the caldera rim at Grímsvötn in Vatnajökull, Iceland, can be broken when the lake-level water pressure is still some 6 bar below the maximum overburden ice pressure.

The North and South Klawatti glaciers are adjacent glaciers in the North Cascade Mountains of Washington state. During 1947–61 North Klawatti Glacier lost volume, equivalent to a mean decrease in thickness of 8.3 m over the glacier area, whereas South Klawatti Glacier gained volume, equivalent to an increase in thickness of 5.8 m. Although the glaciers are in the same climate, they have different distributions of area with altitude, resulting in different responses to climatic variations.

A quadratic equation is assumed to approximate the relation of mass balance to altitude for both Klawatti glaciers. The coefficients of the equation are derived by comparing the calculated mass change to the mass change for each glacier estimated from topographic maps. The resultant relation of mass balance to altitude is the mean for the time period between maps (1947–61).

Steady-state longitudinal profiles of both glaciers were obtained by shifting the existing mass-balance versus altitude curve by a magnitude equal to the measured mean annual mass balance. To produce steady-state conditions, the equilibrium-line altitudes of both glaciers would need to move less than 90 m (85 m higher for South Klawatti Glacier and 88 m lower for North Klawatti Glacier).

Improved knowledge of geometrical boundary conditions, such as bedrock geometry and surface topography, can contribute significantly to glaciological studies including ice-sheet-flow modelling. Precise thickness and altimetric data allow an estimation of ice-flow direction, the balance velocity and the basal shear stress. These parameters are calculated along a 1160 km profile in East Antarctica using a relationship between shear stress, basal temperature, the Glen flow exponent and a parameter related to strain rate. Strong variations of the flow-law parameters and basal conditions are found to play a major role in the ice-flow pattern. Sliding, anisotropy and longitudinal stress strongly perturb the validity of the law, but their signature can be identified.

35 mm still and television techniques are shown to be of great value in following changes at the bedrock/ice interface and along borehole walls during closure over one or more years in polar or sub-polar ice caps. We have found no evidence of basal slip over a one year period in a 137 m hole at the top of the flow line on an ice cap in northern Ellesmere Island, However, the bore hole has deformed to an elliptical cross-section near the bed and some pronounced extrusion-like layers have developed within 3 m of the bed in dirty ice in the year since drilling.

A compact, operational prototype for automatic seismic detection of natural avalanches, named SARA, is proposed as a means to improve real-time estimation of natural avalanche activity. A software combining multi-component signal analysis and fuzzy logic has been set up to reject spurious signals automatically. The average success rate of our system, estimated from a set of previously identified signals, is somewhat over 90%. Two prototypes have been installed in the French Alps dur ing the winter of 1996–97. The SARA system enables the user to follow up the evolution of natural avalanche activity with a high time resolution. Results obtained in 1997 are presented and compared with other data related to avalanche activity.

Mass changes of polar ice sheets have an important societal impact, because they affect global sea level. Estimating the current mass budget of ice sheets is equivalent to determining the balance between surface mass gain through precipitation and outflow across the grounding line. For the Antarctic ice sheet, grounding line outflow is governed by oceanic processes and outlet glacier dynamics. In this study, we compute the mass budget of major outlet glaciers in the eastern Dronning Maud Land sector of the Antarctic ice sheet using the input/output method. Input is given by recent surface accumulation estimates (SMB) of the whole drainage basin. The outflow at the grounding line is determined from the radar data of a recent airborne survey and satellite-based velocities using a flow model of combined plug flow and simple shear. This approach is an improvement on previous studies, as the ice thickness is measured, rather than being estimated from hydrostatic equilibrium. In line with the general thickening of the ice sheet over this sector, we estimate the regional mass balance in this area at 3.15 ± 8.23 Gt a−1 according to the most recent SMB model results.

Long-term observatinns of precipitating clouds were carried out by a vertical pointing radar and plan-position indicator PPI) radar at Syowa station (69.0°S, 40.5°E), Antarctica, in 1989. The observations revealed that there were three abundant snowfall seasons at Syowa station and the amount of snowfall was uniform in all seasons except summer. The amounts of precipitation in autumn, winter and spring were 74, 74 and 53 mm (liquid water equivalent), respectively. The amounts of precipitation in autumn and winter were large at Syowa station in 1989. However, the amount of precipitation on the inland ice is expected to be small in winter, indicated by the distributions of precipitation measured by the PPI radar.

The occurrence frequencies of cloud vortices which brought snowfall to Syowa station increased in the autumn and spring seasons, corresponding to the activity of the circumpolar trough. However, the activities ofcloud systems that bring precipitation weaken in Spring when the sea-ice area expands to low latitudes, because of a lower supply of heat and vapor. Thus the activities of cloud vortices are also weakened above the sea ice.

After completion of the drilling by the US Army Cold Regions Research and Engineering Laboratory (USA-CRREL) at Camp Century, Greenland, in July 1966, the operation was moved to Byrd Station, Antarctica, during the 1966/67 austral summer. The drill employed was an electromechanical cable-suspended drill that used ethylene glycol to dissolve the chips formed, producing a core with an average diameter of 114 mm. A mixture of diesel oil and trichlorethylene was used as a borehole fluid. Ice-core drilling at Byrd Station occurred from 2 to 18 February 1967 and from 12 October 1967 to 2 February 1968 when the ice sheet was penetrated at a depth of 2164 m. During the ensuing 1968/69 season the drill was lost, and ultimately the cable was severed in early 1969/70 at a depth of 1545 m. This brief report reviews the drilling operation and some of the problems encountered primarily during the 1967/68 season, with a focus on the last few days of drilling.