The first stage of sea-ice formation is often grease ice, a mixture of sea water and frazil ice crystals. Over time, grease ice typically congeals first to pancake ice floes and then to a solid sea-ice cover. Grease ice is commonly not explicitly simulated in basin-scale sea-ice ocean models, though it affects oceanic heat loss and ice growth and is expected to play a greater role in a more seasonally ice-covered Arctic Ocean. We present an approach to simulate the grease-ice layer with, as basic properties, the surface being at the freezing point, a frazil ice volume fraction of 25%, and a negligible change in the surface heat flux compared to open water. The latter governs grease-ice production, and a gradual transition to solid sea ice follows, with ∼50% of the grease ice solidifying within 24 hours. The new parameterization delays lead closing by solid ice formation, enhances oceanic heat loss in fall and winter, and produces a grease-ice layer that is variable in space and time. Results indicate a 10-30% increase in mean winter Arctic Ocean heat loss compared to a standard simulation, with instant lead closing leading to significantly enhanced ice growth.

The El Niño–Southern Oscillation (ENSO) signal in coastal Antarctic precipitation is evaluated using deuterium-excess data measured from an ice core located at Victoria Lower Glacier (VLG) Dome, McMurdo Dry Valleys. Recent studies suggest that interannual variations in the intensity and position of the Amundsen Sea low, a low-pressure centre that controls moisture flux in the West Antarctic sector, is modulated by the ENSO. Deuterium-excess values from the VLG ice core, which serve as a proxy for changes in regional moisture flux, exhibit oscillations of equivalent duration to those observed in the Southern Oscillation Index (SOI). Results of cross-spectral analyses show that temporal fluctuations in deuterium excess and the SOI covary and are coherent at ~4.9, 3.6, 3.0, 2.6, 2.4 and 2.0 year frequencies between 1950 and 2000. We ascribe this covariance to shifts in the source and transport pathway of precipitation that is deposited in coastal Victoria Land as a consequence of ENSO’s influence. High values of deuterium excess are consistent with increased meridional flow carrying warm, moist air southward across the Ross Sea when the low-pressure centre is positioned to the north of the Ross Ice Shelf (La Niña mode). Low deuterium-excess values, which reflect a more westerly to southerly flow across the West Antarctic ice sheet and Ross Ice Shelf leading to cooler and drier en-route conditions, occur when the low-pressure centre is positioned above the Amundsen Sea (El Niño mode).

Aero-measurements during the 1983–84 and 1985–86 field seasons showed that the ice in the central part of Filchner-Ronne Ice Shelf is more than 250 m thicker than has been assumed previously. In the margin area a double layering of the ice was found, with disappearing bottom reflections farther inland. High absorption of approximately 0.3 dB/m in the lower layer and a decreasing reflectivity at the ice / sea-water interface, probably caused by bottom freezing, have been estimated. Aero-measurements were used to map the surface elevation of the ice, with an accuracy of approximately 3 m. From the plot of ice thickness against surface elevation it was possible to obtain a calibration curve for isostatic conditions. Large deviations from this plot with an ice thickness which is apparently too small (they seem to be isostatic anomalies) were found in the central part of the ice shelf. The true ice thickness could easily be calculated and mapped from these anomalies and the electromagnetically measured thickness.

From the map based on flights made in 1983–84 the site for a bore hole was chosen in the central part of the ice shelf with an estimated ice thickness of about 450 m, instead of the less than 200 m deduced by an electromagnetic reflection (EMR) method. Hot-water drilling by the ground party of our group (H. Engelhardt and J. Determann) revealed an ice thickness of 465 m at this site.

Numerical simulations of the temperature regime of the ice shelf Fimbulisen, Antarctica, are presented. A vertical temperature profile (S1) of Fimbulisen has been measured at the extension of Jutulstraumen, in which the temperature decreases with depth. The three-dimensional steady-state temperature field was computed by a finite-element technique. Horizontal flow velocities and surface accumulation rates were derived from observations. The basal melt rate distribution arose from an assumption of balance in the mass continuity equation. The computed basal melt rate distribution (ab) indicates that the highest basal melt rates, up to 15 m a 1 occur at the inflow gate of Jutulstraumen, and low basal melt rates (<0.6ma 1) occur in the slower moving parts. Where the ice shelf overhangs the continental shelf, ab ~1.2ma−1 . The resulting temperature field indicates that Fimbulisen consists of a cold middle part, built up by the extension of Jutulstraumen, and warmer ice masses in slow-moving areas to the west and east. Furthermore, model runs were set up in which the atmospheric temperatures increased in +1 K steps. The results suggest that the warming effectively increases the temperatures throughout the ice column in the slower-moving parts, therefore enhancing shear at the margins of the extension of Jutulstraumen.

Simulations of the Northern Hemisphere ice sheet at the Last Glacial Maximum (LGM; 21 kyr BP) are performed using a high-resolution atmospheric general circulation model (AGCM) in order to re-evaluate the conventional surface temperature- or elevation-based parameterization. The influence of precipitation change on the steady-state topography of the Laurentide ice sheet at the LGM is estimated using an AGCM with a horizontal resolution of ∼1° and a three-dimensional thermomechanically coupled ice-sheet model. The ice volume estimated by the AGCM simulation is much larger than that indicated by the conventional parameterization. Through sensitivity analysis of the AGCM and ice-sheet model, it is found that the rate of precipitation change depends on the location of the ice sheet, and that the rate of precipitation change due to surface elevation change is higher than the rate unrelated to surface elevation change on the Laurentide ice sheet. The rate of precipitation is also shown to exhibit seasonality and regionality due to effects such as interior desertification and the concentration of storm tracks.

The surface velocity of Thwaites Glacier (TG), West Antarctica, during the period 1992–2000 is measured with synthetic aperture radar feature-tracking techniques. We find no indication of interannual velocity variations of the grounded ice further than about 20 km inland of the grounding line. The velocity of the floating TG Tongue shows cyclicalvariations with an amplitude of 10%; a minimum around 1997 is bracketed by similarly sized maxima in 1995 and 2000. The observed velocity variations can be explained by time-dependent rotation and deformation superimposed on the steady flow of TG Tongue. The orientation of the rotation is clockwise during the entire observation period; the mean center of the rotation is close to a small ice rise, situated at the east side of the tongue about 20 km past the grounding line. The recent calving of TG Tongue in February 2002 is consistent with continued clockwise rotation that eventually led to cracking from west to east across the tongue. The rotation and deformation of TG Tongue is caused by forces unrelated to glacier dynamics. Analysis of European Centre for Medium-Range Weather Forecasts wind data suggests a synoptic-scale origin for the external forcing that causes the rotation.

As part of the pre-site survey in Dronning Maud Land for the European Project for Ice Goring in Antarctica (EPICA), the spatial variability of snow-layer thickness and snow chemistry was studied at two geographically different ice-core drill sites. The study aimed to quantify error bars on accumulation rates derived from firn and ice cores. One site is located on the polar plateau at Amundsenisen (76° S, 8° W) and the other in the coastal area at Maudheimvidda (73° S, 13° W). Medium-deep ice cores (100 m) and shallow firn cores (10-20 m) were drilled and snow pits (0.5-2 5 m) were dug at each site. At Amundsenisen a large (16 m x 6 m x 2.5 m deep) snow pit was dug. Snow structure in this large snow pit was mapped using optical surveying equipment, and photographically documented. Samples for analysis of nine ions and oxygen isotopes were collected along one depth profile. Density and in situ electrical conductivity measurements were made along three depth profiles! Snow-layer variability was studied in two different areas and at two different scales. At a regional scale, measured by snow-radar soundings, the variability was 8% on the polar plateau and 45% in the coastal area. The variability at a micro-scale in the large snow pit was 9%. The results indicate that ice cores from the polar plateau are more representative for a larger area than ice cores drilled in the coastal area There is no doubt that there are significant error bars on high-resolution accumulation data received from firn and ice cores, especially from the coastal area, but averaging over tens of years reduces the error in accumulation estimates.

An intermediate-depth (1751 m) ice core was drilled at the South Pole between 2014 and 2016 using the newly designed US Intermediate Depth Drill. The South Pole ice core is the highest-resolution interior East Antarctic ice core record that extends into the glacial period. The methods used at the South Pole to handle and log the drilled ice, the procedures used to safely retrograde the ice back to the National Science Foundation Ice Core Facility (NSF-ICF), and the methods used to process and sample the ice at the NSF-ICF are described. The South Pole ice core exhibited minimal brittle ice, which was likely due to site characteristics and, to a lesser extent, to drill technology and core handling procedures.

The determination of catchment boundaries is a major source of uncertainty in net balance studies on large ice sheets. Here, a method for defining a catchment boundary is developed using new measurements of ice-surface velocity and elevation near the Ice Stream B/C boundary in West Antarctica. An objective method for estimating confidence in the catchment boundary is proposed. Using elevation data, the resulting mean standard deviation in boundary location is 13 km in position or 6000 km2 in area. Applying a similar uncertainty to both sides of the Ice Stream Β catchment results in a catchment-area uncertainty of 9%. Much larger uncertainties arise when the method is applied to velocity data. The uncertainty in both cases is primarily determined by the density of field measurements and is proportionally similar for larger catchment basins. Differences in the position of the velocity-determined boundary and the elevation-determined boundary probably result from data sampling. The boundary positions determined here do not support the hypothesis that Ice Stream Β captured parts of the Ice Stream C catchment.

Daily A ntarrtir sea-ice concentration, wind and temperature data for the years 1988-94 were analyzed using Fourier techniques to determine their temporal spectra for three equal-length “seasons". The percentage of the total variance explained (VE) by each individual wave (i.e. frequency] was calculated, and spatial averages made over six latitudinal hands surrounding Antarctica. Comparisons of trie sea-ice concentration, wind stress and surface air-temperature spectra showed sea-ice concentration VE has smallest, and wind-stress VE greatest, value in the synoptic time-scales. Conversely, in the 20-25 day window the wind-stress VE is smallest, and sea-ice concentration VE greatest. This “red shift” of the sea-ice concentration suggests it has inertia to the wind slress and temperature Forcing. Resulls show the magnitude of the red shift varies with not only time of year, but also distance from the coast, and is dependent upon the position of the Antarctic circumpolar trough.

Supraglacial streams are a significant part of the glacial hydrological system and important for understanding the connection between glacial hydrology and glacier dynamics. Here we determine the factors that influence the development of step-pool formation and pulsating flow in a supraglacial stream on Bylot Island, Nunavut. Results show that during the second week of a 2-week study, multiple successive rainfall events occurred, stream temperature increased and ablation decreased; which also caused stream discharge to decrease. In addition, the stream, which flowed over a 13 m high waterfall off the front of Fountain Glacier, rapidly formed 21 step-pools and began to pulsate. The pulsating phenomenon involved the complete stoppage of flow over the waterfall and the subsequent restart between 8 and 20 s later. Pulsating flow resulted from rapid changes in the streambed morphology. In particular, the formation of the step-pool sequence was caused by helical flow around meander bends and hydrologically induced slippage along transverse shear planes, evidenced by observations of high-pressure artesian flow from transverse fractures. Contrary to previous literature, this study shows that high discharge is not necessarily the cause of step-pool formation and pulsating flow within supraglacial streams.

The microwave emissivity of two snow covers was measured in Alaska in March, 1990. Observations were made on taiga snow near Fairbanks that was 0.83 m thick with a 0.55 m thick basal layer of depth hoar. Other measurements were made on the tundra snow cover at Imnaviat Creek north of the Brooks Range which was 0.27 to 0.64 m thick and consisted of two or more wind slabs overlying a depth hoar layer 0.14 to 0.26 m thick. Density, crystal structure, and grain size were similar in tundra and taiga depth hoar layers.

Emissivity was measured at 18.7 and 37 GHz using radiometers mounted on a 1.5 m tall bipod. Measurements were made on undisturbed snow, and then several snow layers were removed and additional measurements were made. This sequence was repeated until all snow had been removed. Effective emissivity values for the full snow depth ranged from 0.6 (37 GHz, H-pol) to 0.95 (18.7 GHz, V-pol) and were similar for both taiga and tundra snow covers. For both snow covers, there was a marked reduction in the effective emissivity (eeff) from that of the underlying ground with a maximum reduction of about 30%. All of the reduction was found to occur within the depth hoar layer. Maximum reduction in eeff could be caused by a depth hoar layer 0.3 m thick. Overlying wind slab or new snow were nearly “invisible”, increasing the effective emissivity only by a small amount due to self-emittance. Thus, it was difficult to distinguish the two different snow covers on the basis of their emissivity, since both contained 0.3 m of depth hoar or more.

Ice-core chemistry data from Victoria Lower Glacier, Antarctica, suggest, at least for the last 50 years, a direct influence of solar activity variations on the McMurdo Dry Valleys (MDV) climate system via controls on air-mass input from two competing environments: the East Antarctic ice sheet and the Ross Sea. During periods of increased solar activity, when total solar irradiance is relatively high, the MDV climate system appears to be dominated by air masses originating from the Ross Sea, leading to higher aerosol deposition. During reduced solar activity, the Antarctic interior seems to be the dominant air-mass source, leading to lower aerosol concentration in the ice-core record. We propose that the sensitivity of the MDV to variations in solar irradiance is caused by strong albedo differences between the ice-free MDV and the ice sheet.

Wind plays an important role in determining accumulation and δ(18O) on some ice caps. Three surface-to-bed cores spaced about 1 km apart have been taken on a flow line of the Agassiz Ice Cap, Ellesmere Island. The A84 core comes from the top of a local dome. The A79 core is 1200 m down the flow line, but very close to the ridge through the local dome. The A77 core is 1100m from A79 and well away from the ridge. The ridge causes wind turbulence, which removes or scours the soft winter snow from the A84 and A79 sites. No snow is scoured from the A77 site. Because of scour the retained accumulation and average δ(l8O) are different. The accumulations are 17.5, 11.5, 9.7 cm/a (ice equivalent) at A77, A79 and A84 respectively and the corresponding surface δs are –30.40, -27.90 and –27.05‰. The core records were dated by annual layer thicknesses and by identification of electrical conductivity measurement (ECM) acid peaks. With the three cores accurately aligned we examine the (δA84-δA77) and (δA84-δA79) time series. Significant variations in these difference series are interpreted as being caused by changes in the seasonal δ amplitude, which is then explained by changes in sea-ice cover. A seasonal δ amplitude series independently obtained from the Devon Island ice cap δ noise record is consistent with that from the Agassiz Ice Cap sites.

Thermodynamics of a seasonal supraglacial lake were examined based on field data from three summers. At maximum, the lake body consisted of an upper layer with thin ice on top, and a lower layer with slush, hard ice and sediment at the bottom. Sublimation from the upper ice surface averaged to 0.7 mm d−1, and melting in the ice interior averaged to 9.1 mm d−1 during summer. Albedo was on average 0.6 and light attenuation coefficient was ~1 m−1. Averaged over December and January, and over 3 different years, we found that the net solar heating was 137 W m−2, while the losses averaged to 62 W m−2 for the longwave radiation, 16 W m−2 for the sensible heat flux, 24 W m−2 for the latent heat flux and 3 W m−2 for the bottom flux. The depth scale is determined by the light attenuation distance and thermal diffusion coefficient, and the net liquid water volume ranged from 0.5 to 1.0 m in different years. The potential winter growth is more than summer melting, and thus the lake freezes up completely in winter in the present climate.

The avalanche-hazard index is a numerical expression of damage and loss as the result of an interaction between snow avalanches and vehicles on a road. The index is determined by multiplying the frequencies of moving and waiting vehicles being hit by various types of avalanches by a weighting which indicates the severity of the consequences. The avalanche-hazard index has proved to be a useful decision-making tool for identification of those avalanche paths where control would be most beneficial, for evaluation of options for control measures, and for comparison of the risks for different roads.

The dynamics of a surge is manifested in the crevasse patterns: literally, deformation state frozen in ice. This basic observation is utilized as the concept of an automated approach to map and analyze deformation stages and progression of surge kinematics. The classification method allows imagery to be used as geophysical data and is applied to aerial observations (photographic and video imagery, GPS data) collected in September 2011 during the surge of the Bering Glacier–Bagley Ice Valley system, Alaska, USA. As the third dimension that complements two-dimensional imagery, ice-surface elevation is observed using aerial laser altimetry. The classification method builds on concepts from signal processing, geostatistical data analysis and neural networks. Steps include calculation of generalized directional vario functions from image data and composition into feature vectors. The vario function operates as an information filter that retains spatial characteristics at an intermediate scale that captures crevasse spacing, anisotropy and other generalized roughness properties. Association of feature vectors to crevasse classes and hence deformation types employs a connectionist algorithm. In general, the connectionist–geostatistical classification allows the mapping of kinematic changes in crevassed glaciers.

Dedicated to the memory of Austin Post

The potential of satellite radar altimetry for high-resolution mapping of Antarctic ice streams is evaluated, using retracked and slope-corrected data from the Lambert Glacier and Amery Ice Shelf area, East Antarctica, acquired by Geosat during the Exact Repeat Mission (ERM), 1986–89. The map area includes lower Lambert Glacier north of 72.18°S, the southern Amery Ice Shelf, and the grounded inland ice sheet on both sides. The Geosat ERM altimetry is found to provide substantially more complete coverage than the 1978 Seasat altimetry, due to improved tracking. Variogram methods are used to estimate the noise levels in the data as a function of position throughout the map area. The spatial structure in the data is quantified by constructing experimental variograms using altimetry from the area of the grounding zone of Lambert Glacier, which is the area chiefly of interest in this topographically complex region. Kriging is employed to invert the along-track height measurements onto a fine-scale 3 km grid. The unsmoothed along-track Geosat ERM altimetry yields spatially continuous maps showing the main topographic features of lower Lambert Glacier, upper Amery Ice Shelf and the adjacent inland ice sheet. The probable position of the grounding line of Lambert Glacier is identified from a break in slope at the grounded ice/floating ice transition. The approximate standard error of the kriged map is inferred from the data noise levels.

The Antarctic ice sheet has almost no net annual ablation on its surface, so most mass losses are by iceberg calving along its perimeter, which may be either grounded in shallow water or floating in deep water. An ice cliff forms along the perimeter in both cases. Wave action undercuts ice margins in the tide-water zone along beaches, and causes coastal calving if the rate of undercutting compares with the forward ice velocity. If the ice velocity is sufficiently greater, the ice sheet advances into deeper water and becomes a float at depths of 200 to 300 m (Robin 1979). A floating ice shelf then forms and icebergs calve along the ice front. Iceberg calving along this ice front may be due to several causes (Holdsworth 1977,Robin 1979). Since iceberg calving, either from ice shelves or in the tidewater zone of beaches between ice shelves, is the principal ablation mechanism of the Antarctic ice sheet, it is important to understand calving dynamics quantitatively. This paper presents the results of a finite-element examination of calving along floating margins of the ice sheet.

The advance of Hubbard Glacier, near Yakutat, Alaska, U.S.A., in spring 1986 blocked the entrance to Russell Fiord with an ice-and-sediment dam, behind which a lake formed. The water level in Russell Lake rose to 25.5 m a.s.l. The dam catastrophically failed in October 1986, releasing 5.4 km3 of water into Disenchantment Bay. High-resolution seismic-reflection profiles show a 7.5 km long channel system cut into and buried by glacimarine sediment, represented by continuous, parallel reflections. The chaotic seismic facies filling the channel is interpreted to be debris flow deposits. A gravity core from channel-overbank deposits contained sandy diamicton with mud clasts. Above the channel a 1–2 m thick sediment drape extends across the bay. Laminated mud, fining-upward sand beds and diamicton were recovered from this unit. The sediment-drape deposits were produced by suspension settling from turbid plumes and non-channelized turbidity currents generated by the outburst flood.