bluuebunny/crossref_metadata_2025 huggingface dataset:
Airborne Precipitation and Cloud Sampling Techniques (Abstract)
Authors: Joe P.I. , Schemenauer R.S. , Strapp J.W. , Daum P.
Published: September 2017

Techniques have been developed for the airborne bulk sampling of cloud and precipitation, including snow, for later chemical analysis. The techniques include the use of cyclones, meshes, riming rods, scoops and slotted collectors. The role of sampling location on the aircraft, flying attitude, collection efficiency, and sampling procedures for clean samples and mixed clouds with respect to the design and performance of the collectors will be discussed. The polyethylene meshes, with thread diameters of 545 and 345 microns, and the riming rods, with diameter of 1.0 cm, collect supercooled droplets with different efficiencies and can be used to examine the dependence of chemistry on the droplet size. Airborne snow samples were collected for the first time, with the cyclone being the most effective collector.
Distribution of Grain Sizes and Internal Surface Area and their Role in Snow Chemistry in A Sub-Arctic Snow Cover
Authors: Granberg H.B.
Published: September 2017

The variations in grain size and internal surface area in a seasonal snow cover have been studied near Schefferville, Quebec. Sieve analysis was applied to snow in very cold conditions and gave closely reproducible results.

The studies show that grain-size distributions vary greatly with depth but show a pattern that is closely repeatable between sites in similar environments and which is also closely repeatable from one year to the next. Different environments produce variations on the general pattern.

The measurements enable estimation of the internal surface area and its variations with depth in different snow covers. The effects of this variation in surface area on contaminants of the snow cover are discussed.
Hydrometeorological Interpretation of Isotopic Data On Atmospheric Moisture and Precipitation
Authors: Saxena R.K. , Eriksson E.
Published: September 2017

The influence of advective and eddy transport of atmospheric moisture on the 18O content of atmospheric vapour and precipitation is discussed. Measurements of the 18O content of atmospheric vapour and precipitation have been carried out since July 1981 in Uppsala, Sweden. The removal of water from atmospheric vapour is accomplished by freezing it out of a stream of air passed at the rate of 60 1 h−1 through cooling traps maintained at a temperature of −60°C. The method is practically non-fractionating. The observed slopes of the regression equations defining the linear relationship between weighted monthly δ18O of precipitation and mean monthly temperatures at the ground level agree fairly well with the predicted slopes assuming that the transport of atmospheric moisture is due to eddy motion. Similarly the slope of the linear relationship between δ18O in atmospheric vapour and vapour density at ground level is also closely predicted by the eddy transport model. However, if it is assumed that the transport of atmospheric moisture is advective, the predicted slopes are nearly double those observed.

It was also observed that precipitation and atmospheric vapour are in isotopic equilibrium during summer, but not during winter. Results obtained confirm the strong large-scale eddy diffusive nature of the transport of atmospheric moisture.
Spatial and Temporal Variability of Surface Snowfall and Snowpack Chemistry in Central Ontario
Authors: Schemenauer R.S. , Summers P.W. , Wiebe H.A. , Anlauf K.G.
Published: September 2017

The physical and chemical structure of the snowpack near North Bay, Ontario was examined during the winter of 1984. precipitation chemistry measurements were also made. A marked areal uniformity was noted in the layered structure of the snowpack and in the vertical variation of the chemical composition. In late January, pH values of the snowpack varied from ∼4.1 at the surface to ∼4.8 near the ground. After rain and a major thaw in February the pH was near 4.8 throughout. Nitrate concentrations exceeded those of sulfate in the snowpack. The molar concentration ratio of / was typically 0.5.

Samples of precipitation from six sites had pH values ranging from 3.4 to 5.2. to equivalent ratios were <1 in snow and near 1 or >1 in rain. The chemical composition of the precipitation was closely related to the airmass trajectory. Southerly trajectories yielded the lowest pH values and highest pollutant concentrations. The one-month period from 20 January to 21 February had a deposition of 0.2 g m−2 and a deposition of 0.35 g m−2. For , this deposition would be about one-twelfth the expected annual deposition and for about one-fifth.
A Study of Atmospheric Deposition onto the Snowpack in Northern Saskatchewan
Authors: Shewchuk S.R.
Published: September 2017

The purpose of this study is to use the snowpack of the Saskatchewan portion of the Precambrian Shield as a passive collector of atmospheric total deposition. Although the focus is on the anions of sulphate and nitrate, the hydrogen ion and various metals are also considered.

Twenty-six small lakes on the Precambrian Shield area of northern Saskatchewan were used as sites. The lakes were all approximately 1 square km in area and serviced by aircraft. The study was conducted in late March 1982 and 1983 just before the major snowmelt period.

Concentrations of sulphate ranged from 0.26 to 7.3 mg 1−1. The concentrations were typical of large areas in northern Saskatchewan with sharp transitions in composition occurring as the treeline boundary was encountered. Typical sulphate deposition was approximately 30 mg m−2 in the Precambrian areas and 150 mg m−2 in the other areas. The distribution of conductivity in the snow cores ranged from 6 to 13 μS cm−1. Most of the snow on the Precambrian Shield areas can be described as acidic, with pH values of the meltwater being below 5.6.

Metals such as Ca, Mn, Mg, Zn and As were measured across the region. The metals Ca and Mg show a direct correlation with high sulphate levels south of the treeline. Metals such as Zn and As show anthropogenic influence particularly within 100 km of industrial sources. Large areas of the study region show uniform and low deposition to the snowpack. It is suggested that natural atmospheric processes are dominating deposition in this area of Canada.
Ice-Core Analysis on the Siple Coast of West Antarctica
Authors: Alley Richard B. , Bentley Charles R.
Published: September 2017

Pit and core studies at the Upstream Β camp (UpB) and ridge BC (BC) on the Siple Coast, West Antarctica, have revealed a number of interesting results. Both sites have 10 m temperatures near −26.5°C and accumulation rates near 0.09 m a−1 of ice. At both sites, the low densities of annual depth-hoar layers arise in the first year following snow deposition. Densification rates at UpB are accelerated compared to BC and to other sites, probably owing to stress enhancement of power-law-creep densification caused by the large longitudinal deviatoric stresses at UpB. The connectivity of firn, measured by the number of bonds per grain and by the fraction of total surface area per grain involved in bonds, correlates well with density and shows no significant dependence on grain-size. The longitudinal stresses at UpB cause the ice to develop a fabric of horizontally elongated bubbles and grains, interpenetrating grains, and strain shadows between about 30–70 m. Ice at BC below about 95 m shows rapid grain growth and development of a bimodal grain-size distribution, but no preferred orientation of grains or pores. The temperature-depth profile to 100 m at BC suggests a basal heat flux near 1.9 heat-flow units (HFU), typical of a region of active rifting. Surface-melt events occur about once every 50 years, and correlate well between UpB and BC.
Ice Thickness and Sea Depth Derived from Reflection-Seismic Measurements on the Central Part of Filchner-Ronne Ice Shelf, Antarctica
Authors: Determann J. , Thyssen F. , Engelhardt H.
Published: September 2017

In January 1986, reflection-seismic measurements were made in the central part of Filchner-Ronne Ice Shelf, north of Henry and Korff ice rises, by a German oversnow traverse. With the help of a newly developed “ice streamer”, two people were able to obtain seismic records nearly every 5km over a distance of 150km within 3d. Processing of digitally recorded seismograms yielded profiles of ice thickness and sea depth. The ice thickness varies from 400 to 500 m and is in good agreement with the thickness of 465 m at a drill hole. The reflection-seismic results are comparable with those obtained from aerogeophysical measurements.
Relative Importance of Lateral and Vertical Shear on Rutford Ice Stream, Antarctica
Authors: Frolich R. M. , Doake C. S. M.
Published: September 2017

Survey data from three transverse profiles across Rutford Ice Stream show that most of the shear deformation occurs in boundary layers about 10 km wide on both sides of the glacier. There is a central part, also about 10 km wide, where lateral shear-stress gradients are not significantly different from zero. This implies that friction from the side walls does not impede the flow in the middle of the glacier. Instead, a basal shear stress of around 40 kPa is required in order to provide the necessary restraint. Even then, only a small proportion of the forward movement will be caused by internal deformation of the ice and the remainder must arise from sliding or rapid deformation at or near the base of the glacier. Although the present analysis does not consider in detail the variation with depth in stresses and strain-rates, the formulation of the problem suggests that a self-consistent solution can be found for the distribution of basal and vertical shear stresses.
Accumulation and Ice-Core Studies on Filchner-Ronne Ice Shelf, Antarctica
Authors: Graf W. , Moser H. , Oerter H. , Reinwarth O. , Stichler W.
Published: September 2017

Accumulation rates in the eastern part of Ronne Ice Shelf were determined by isotopic stratigraphy (18O). The samples were taken from snow-pits dug during the Filchner I and II operations in 1984 and 1986. In general, the accumulation rate decreases towards the south; the greatest decrease, from 21.3 to 13.3 g cm−2 a−1, was observed between Filchner Station and measuring point 341, sited 270 km up-stream of the ice edge. The δ18O values of the near-surface layers vary between −25 and -29‰. The 18O content in the more southerly part is progressively depleted in the direction of Möllereisstrom, paralleling a decrease in the accumulation rate. Near the ice edge the 18O content decreases to the west. A 100 m ice core drilled in 1984 at point 340, 220 km from the ice edge, probably goes back to A.D. 1460; it has been dated by isotopic stratigraphy.

The accumulation rate up-stream of the drilling site was deduced from the sequence of annual layers, using a simple ice-flow model. The accumulation shows strong variations over the last 200 years, which may be caused in part by local variations in the accumulation on Ronne Ice Shelf.
Formation of the West Antarctic Ice Sheet
Authors: Lindstrom D. R.
Published: September 2017

A numerical ice-shelf model is employed to observe the inception of the West Antarctic ice sheet (WAIS) from a thin (20 m thick) floating ice cover under the following conditions: (i) a lower sea-level than at present, due to ice-sheet formation in the Northern Hemisphere, (ii) surface and basal temperature and accumulation rates approximately equal to those of present Antarctic ice shelves, and (iii) ice flow from East Antarctica into West Antarctica is neglected. The model determines the flow and thickness of floating ice and assumes that grounded ice is stagnant. Under these constraints, all regions except the Ross Sea, the Filchner region (east of Berkner Island), and up-stream of Thwaites Glacier ground within 4000 years. Ice readily grounds in the Ronne region (west of Berkner Island), forcing ice from Ellsworth Land to flow east toward the Filchner region. It is suggested that grounding over the Ross Sea, the Filchner region, and up-stream of Thwaites Glacier occurs only after grounded-ice flow is established. Grounded-ice flow is also a prerequisite of bed erosion and sediment deposition, which leave historical records of the actual ice-sheet formation. It is suggested that erosion and sediment deposition is minimal over the Ronne region and considerable along the path from Ellsworth Land to the Filchner region, because more ice flows toward the Filchner region than the Ronne region. It is probably difficult for ice to ground over the Ross region, so this region should have a high proportion of glacial marine sediments.
Can Relict Crevasse Plumes on Antarctic Ice Shelves Reveal a History of Ice-Stream Fluctuation?
Authors: MacAyeal D. R. , Bindschadler R. A. , Jezek K. C. , Shabtaie S.
Published: September 2017

Configurations of relict surface-crevasse bands and medial moraines that emanate from the shear margins of ice streams are simulated, using a numerical model of an ideal rectangular ice shelf to determine their potential for recording a past ice-stream discharge chronology.
Glacial Geodetic Contributions to the Mass Balance and Dynamics of Ice Shelves
Authors: Möller D. , Ritter B.
Published: September 2017

The glacial geodetic contribution to the mass balance and dynamics of ice shelves includes repeated determinations of the absolute position (ϕ,λ,Η) of selected points (using satellite methods), the establishment of relative positions (y,x,Δh) in deformation figures, and height measurements. The results are used to establish ice-flow velocities and directions, strain and rotation rates, and changes in height. Modelling of deformation parameters at a few points over a large ice shelf is made possible by the collocation method. Results of these observations and analysis of Ekström Ice Shelf for the period 1979–87 are reported.
Numerical Analysis of Landsat Thematic Mapper Images of Antarctica: Surface Temperatures and Physical Properties
Authors: Orheim Olav , Lucchitta Baerbel K.
Published: September 2017

Landsat-5 Thematic Mapper (TM) data from Dronning [Queen] Maud Land, Antarctica, have been analysed to provide insights into physical properties of the ice sheet. Brightness (at-satellite) temperatures calculated from digital numbers of the thermal band (TM band 6), using state-of-the-art equations and constants (Markham and Barker 1986), are 8° to 20°C lower than temperatures measured on the surface. Such differences cannot be ascribed to atmospheric absorption or to emissivity variations; instead, they suggest errors in either the sensor or instrument calibration for the temperature range 0° to −20°C. The results indicate an excess gain factor of about 1.63. The TM band 6 data seem to reproduce faithfully the relative temperature variations across the surface.

Principal components (PCs) calculated for TM bands 2, 3, 4, 5, and 7 are presented for a region of the interior ice sheet. PCs are superior to individual bands or combinations of bands for analysing the main characteristics of an image, such as rendition of surface topography (mostly given in PCl), and for distinguishing between different surface materials (mostly given in PCs 2 and 3). Band ratioing was most useful for enhancing subtle albedo variations, such as those caused by changes in surface properties due to melting.

TM data of the region, collected 18 d apart, show large changes on the snow surface; strong patterns shown in PC2 and TM bands 5 and 7 of the earlier image were nearly faded 18 d later. These strong patterns are not present at visual wavelengths or in the thermal band, and we believe they reflect wind-related variations in the physical properties of the snow.
Ice-Thickness Map of the West Antarctic Ice Streams by Radar Sounding
Authors: Shabtaie S. , Bentley C. R.
Published: September 2017

Extensive radar ice-thickness sounding of ice streams A, B, and C, and the ridges between them, has been carried out. Closely spaced flight lines, as well as ties to numerous ground stations, have enabled us to compile a detailed ice-thickness map of the area. The map reveals a highly complex pattern of ice-thickness variations, which, because they are much larger than the surface relief, largely reflect the subglacial topography. Several cross-sectional profiles across the ice streams and ridges are shown, and a new configuration for Ice Stream A is presented.

Ice Stream A is connected to Reedy Glacier and Horlick Ice Stream by subglacial troughs that converge down-stream. The single trough continues, at a depth of more than 1000 m below sea-level, beneath the entire length of the ice stream and adjacent part of Ross Ice Shelf. Ridge AB (part of which may be a remanent ice stream) overlies a deep bed with pronounced troughs at its headward end; the bed shoals rapidly down-stream to a height more than 500 m above the beds of the adjacent ice streams. Ice stream B1 overlies a subglacial trough that is deep inland and also shoals markedly toward the grounding line. Near its head. Ice Stream B2 is as much as 1000 m thinner than Ice Stream Bl, but then remains much more nearly constant in thickness along its length. Ridge BC is characterized by a smoother bed and less variation in bed depth than ridge AB. Ice Stream C, which is inactive, is particularly marked by uncorrelated maxima and minima in surface and bed topography.

There are no distinct topographical steps that demarcate the transition from sheet to streaming flow at the head of the ice streams, and the ice streams are placed asymmetrically in some places with respect to their subglacial troughs. This may reflect a relative impermanence or transient behavior of the “Ross” ice streams.
Thinning and Grounding-Line Retreat on Ross Ice Shelf, Antarctica
Authors: Thomas R. H. , Stephenson S. N. , Bindschadler R. A. , Shabtaie S. , Bentley C. R.
Published: September 2017

Detailed measurements of surface topography, ice motion, snow accumulation, and ice thickness were made in January 1974 and again in December 1984, along an 8 km stake network extending from the ice sheet, across the grounding line, and on to floating ice shelf in the mouth of slow-moving Ice Stream C, which flows into the eastern side of Ross Ice Shelf, Antarctica. During the 11 years between surveys, the grounding line retreated by approximately 300 m. This was caused by net thinning of the ice shelf, which we believe to be a response to the comparatively recent, major decrease in ice discharge from Ice Stream C. Farther inland, snow accumulation is not balanced by ice discharge, and the ice stream is growing progressively thicker.

There is evidence that the adjacent Ice Stream B has slowed significantly over the last decade, and this may be an early indication that this fast-moving ice stream is about to enter a period of stagnation similar to that of Ice Stream C. Indeed, these large ice streams flowing from West Antarctica into Ross Ice Shelf may oscillate between periods of relative stagnation and major activity. During active periods, large areas of ice shelf thicken and run aground on seabed to form extensive “ice plains” in the mouth of the ice stream. Ultimately, these become too large to be pushed seaward by the ice stream, which then slows down and enters a period of stagnation. During this period, the grounding line of the ice plain retreats, as we observe today in the mouth of Ice Stream C, because nearby ice shelf, no longer compressed by ice-stream motion, progressively thins. At the same time, water within the deformable till beneath the ice starts to freeze on to the base of the ice stream, and snow accumulation progressively increases the ice thickness. A new phase of activity would be initiated when the increasing gravity potential of the ice stream exceeds the total resistance of the shrinking ice plain and the thinning layer of deformable till at the bed. This could occur rapidly if the effects of the shrinking ice plain outweigh those of the thinning (and therefore stiffening) till. Otherwise, the till layer would finally become completely frozen, and the ice stream would have to thicken sufficiently to initiate significant heating by internal deformation, followed by basal melting and finally saturation of an adequate thickness of till; this could take some thousands of years.
Absorption of Solar Radiation at the Antarctic Snow Surface (Abstract)
Authors: Grenfell Thomas C. , Warren Stephen G. , Mullen Peter C.
Published: September 2017

Solar radiation incident on, and reflected by, the snow surface was measured near the South Pole as a function of wavelength, angle, and distance from the station. The objectives of the study were: (1) to observe spectral albedos of snow across the solar spectrum, (2) to obtain depth profiles of snow-grain radius in order to construct theoretical models of spectral albedo for pure snow, (3) to document the extent and degree of soot pollution due to station activities and to assess whether it could invalidate solar-radiation measurements made close to large stations, and (4) to obtain the spectral distribution of incident solar radiation at the Antarctic surface for various cloud conditions, in order to test radiation models of the Antarctic atmosphere.

Spectral albedo, measured under diffuse lighting conditions (overcast cloud) on many days, repeatedly agreed with the results of theoretical models which predicted values approaching unity in the visible and found grain-size to be the most important variable controlling snow albedo in the near-infra-red. A representative albedo curve is shown in Figure 1.The visible albedo values were found to be 98–99% and were relatively insensitive to grain-size. (These results disagree with the only previous measurements of Antarctic snow albedo which had good spectral resolution: those of Kuhn and Siogas. Their maximum albedo was only about 90% in the visible.) The near-infra-red albedo, however, varied substantially among the experiments, due to day-to-day variations in snow grain-size, caused by precipitation and wind drifting. The experimental points in the figure match theoretical calculations for grain radius less than 50 μm at wavelengths beyond 1.5 μm, and 50–100 μm for shorter wavelengths. At the shorter wavelengths the light penetrates more deeply into the snow, so the albedo is sensitive to grains beneath the surface, whereas at the longer wavelengths the albedo is influenced only by the grains very close to the surface. The observed albedos can thus be explained by an increase in grain-size with depth.

In order that our measurements would be representative of large areas, we were concerned to avoid possible effects of pollution from the station. We collected samples from the top 20 cm of snow, melted and filtered them, and analyzed the filters. The conclusion is that the pollution is very minor. Just 500 m up-wind of the station there is normally less than 1 ng of carbon per gram of snow (1 ppb). Even down-wind of the station the carbon content did not exceed 3 ppb. For snow grain-sizes typical of Antarctica, our models predict that 15 ppb carbon would reduce snow albedo by only 1% at the most sensitive wavelength. Thus we reject our earlier suggestion that the low visible albedos of Kuhn and Siogas were due to impurities in the snow and now favor other explanations.
Crary Ice Rise, Antarctica: Formed in Response to a Surging Ice Stream? (Abstract)
Authors: MacAyeal D. R. , Bindschadler R. A.
Published: September 2017

Field data is presented to support the hypothesis that Crary Ice Rise (on Ross Ice Shelf, Fig. 1) has substantially increased in area over the last 500 years, in response to ice advection through the mouth of Ice Stream B. The up-stream end of the ice rise is now surrounded by ice shelf that is currently thickening at 0.44 0.06 m/year (under an assumed zero basal melting rate). This rate of thickening suggests that the ice rise's contribution to back-stress resistance of Ice Stream B's flow, presently calculated to be 50% of the total back stress, is growing in the course of time. We speculate that this current development of the ice rise is the precursor to the possible future stagnation of Ice Stream B. It is convenient to conceptualize a possible see-saw oscillation between ice-stream surging and ice-rise build-up.
Vostok, Antarctica, Ice Core: The Dust Record Over The Last Climatic Cycle (∼160 ka) (Abstract)
Authors: Mounier L. , Petit J. R. , Jouzel J. , Lorius C. , Korotkevich Ye. S. , Barkov N. I.
Published: September 2017

The 2083 m Vostok Antarctic ice core provides a unique opportunity for access to many paleoclimatic and paleo-environmental proxy data. This core, which has been dated by using a glaciological model, fully covers the last glacial-interglacial cycle, and goes back to the ice age which preceded the last interglaciai (−160 ka B P ).

A continuous deuterium record is now available and we have interpreted it in terms of local temperature changes. This record is dominated by the large 100 ka glacial-inter-glacial oscillation, with a maximum temperature amplitude of about 11°C; the long Last Glacial period is very well documented and it is confirmed that the warmest part of the Last Interglaciai period was about 2°C warmer than the Holocene. Comparison with the ice-volume marine record shows that the Vostok climate record is of relatively large geographical significance, which makes it possible to establish, over the last 160 ka, the link between worldwide climatic changes and the Vostok dust record that we present here.

This dust content corresponds to the non-soluble microparticles. It was obtained on a discontinuous basis (1 sample = about ∼10 m). Due to the very low concentration of some samples (down to 20 x 10−9gg−1) and cracks in the ice from the first 1000 m depth, we used stringent decontamination procedures. Size distribution and total concentration were measured, using a Coulter counter and an optical microscope; the results were tested against chemical measurements (aluminium concentration). In previous studies, it has been shown that the main proportion of insoluble microparticles is of terrigenous origin and represents the small-sized (radius <2 μm) dust produced on the continents.

The Vostok record displays an increase in dust concentration of up to 20 times during the coldest climatic periods, coupled with the presence of larger particles. It confirms, on a much longer time-scale, a characteristic previously noted in Antarctic and Greenland ice cores over the Last Glacial Maximum. This large increase is attributed to a greater areal extent of global tropical aridity during the cold periods, coupled with higher efficiency of atmospheric circulation in respect of dust production and transport. Beyond this, the relationship between the dust input and the successive stages during the Last Glacial is now very well documented and will be discussed with a view to correlating the Vostok climatic record with other marine and terrestrial paleodata.
Thermal Regime of George VI Ice Shelf, Antarctic Peninsula (Abstract)
Authors: Paren J. G. , Cooper S.
Published: September 2017

New data on the thermal regime of George VI Ice Shelf have been obtained by thermistor chains installed through the use of a hot-water drill. Twenty thermistors are used at each site, spaced close together at sea-level and at the base of the ice shelf, and farther apart elsewhere in the ice shelf and in the sea beneath. Based on earlier observations (Bishop and Walton 1981, fig. 7) that the 10 m temperature warms from around −10°C in the central melt-lake area of the ice shelf (from 70°45′ to 71°45′S) to around −2°C near the northern ice front (70°00′S), the thermistor chains were deployed at three sites (70°00′, 70°15′ and 70°30′S) along a presumed flow line.

The observations show that as ice flows towards the northern ice front of George VI Ice Shelf, it becomes more temperate in character. Heat from the sea and from the percolation of melt water at the upper surface progressively warms the ice shelf. At mid-depth (the coldest level in the ice shelf) the recorded temperatures were −6°C off Moore Point (70°30′S), −4°C off Carse Point (70°15′S) and, near the northern ice front (70°00′S), between −1.6° and −1.8°C depending on the time of year.

The ice-shelf temperatures near the ice front, warmer in mid-summer than the freezing point of fully saline sea-water, are most unusual. The only explanation of the high, fluctuating temperatures found 1 year after drilling is that the hole through the ice shelf was open, allowing unimpeded water movement. This implies that the ice shelf is also warmed by the percolation of sea-water, whose presence was confirmed by ice-core drilling to below sea-level. Confirmation of the presence of brine below sea-level in the ice shelf comes from geo-electrical investigations. A Schlumberger georesistivity array modelled the ice shelf as a simple two-layer structure, with ordinary glacier overlying highly conductive ice. This is consistent with the fact that no radio echoes have been received from the bottom of George VI Ice Shelf to the north of 70°09′S.

A detailed analysis of the ice-shelf / ocean-temperature profiles was undertaken. This included an analysis of the fluctuation observed in mid-summer at the warmest site and the subsequent transition to a stable isothermal profile through the submerged part of the ice shelf.
Glacier Fluctuations in the Antarctic Peninsula: The Last Decade (Abstract)
Authors: Paren J. G. , Richardson N. A.
Published: September 2017

Following international recommendations (UNESCO / IASH 1969), the decision was made to determine the surface profile of a number of glaciers in Palmer Land and Alexander Island. By comparison with the ice sheet elsewhere on the continent, the chosen glaciers were small and hence more sensitive to the effect of climate over the last few decades. Six profiles were established between 1972 and 1976 and they were re-levelled in the 1985-86 summer. The profiles are between 0.5 and 4.5 km long and are terminated, at one end at least, by a bench mark established on rock. The profiles were re-measured close to the calendar date of the original survey so that recent trends would not be masked by the annual cycle of accumulation, densification and ablation. Five of the six profiles show that the ice sheet has thickened in the last 10-15 years, albeit at a slow rate. Changes in four profiles on Alexander Island within 300 m of sea-level range from a thickening of 66 mm a−1 to a thinning of 83 mm a−1; on average the sites show a thickening of just 6 mm a year. This is similar to the thickening rate of 5 mm a−1 which was found for a cold site on the spine of the Antarctic Peninsula at 1600 m above sea-level. The greatest change was found at an intermediate elevation (500 m). In a snow-field between two parallel mountain groups in the Batterbee Mountains of Palmer Land, thickening averaged 165 mm a−1. To put these values into perspective, in the absence of glacier flow and summer melting, the glaciers would thicken by up to about 500 mm each year as a result of the accumulation of snow.

Except in the Batterbee Mountains, we find that glacier flow is in close balance with present climate, despite the general warming trend that has occurred in the Antarctic Peninsula region over the past 30 years.
Air Temperature and Snow Accumulation in the Antarctic Peninsula During the Past 50 Years (Abstract)
Authors: Peel David A. , Mulvaney Robert
Published: September 2017

Trends in climate affecting the West Antarctic ice sheet may be detected first in the Antarctic Peninsula region. Although the area contains the most comprehensive weather records for any part of Antarctica, reliable snow-accumulation data are lacking.

Mainly as a result of the large snow-accumulation rate in the region (typically in the range 4.0–10.0 kg m−2 a−1), stratigraphie evidence of climate derived from ice cores can be resolved in much greater detail than is possible over most of the continent. Ice cores have been drilled at two sites, representing the extremes of climate type encountered in the region. A 133 m core has been obtained from Dolleman Island (70°35.2′S, 60°55.5′W) to represent the continental-type climate of the Weddell coast region, and an 87 m core has been obtained from the Palmer Land plateau (74°01′S, 70°38′W) to represent the more maritime regime of the west coast and central areas. Replicated cores were obtained at both sites in order to assess the contribution of local noise factors to the climatic signal preserved in the cores. Climatic trends during the period 1938–86 have been assessed on the basis of stable-isotope analysis of the top 47 m of the Palmer Land core and of the top 32 m of the Dolleman Island core.

A statistical analysis of derived profiles of mean annual δ18O and accumulation rate indicates that the local noise factors at these sites are sufficiently small that data averaged over periods as short as 5 years should reveal climatic shifts at the level of 0.2% and 5% respectively. These changes are much smaller than trends that have actually occurred during the past 50 years.

The most notable trend over the past 30 years is an increase of more than 30% in the snow-accumulation rate that has occurred in parallel with an overall temperature increase of 0.06°C/a during the same period. Increases of similar magnitude can be inferred from studies in East Antarctica, and may be related to a significant increase in precipitation rate that has been documented recently at mid-to high-latitude stations in the Northern Hemisphere. The finding may have relevance to studies of the possible consequences of a CO2-induced climate change. More extensive accumulation time series are now required from Antarctica, if satisfactory models of the long-term balance of the ice sheet are to be derived.
δD And δ18O In South Pole Snow: Further Comparison With Meteorological Data and The Record From the Last Millennium (Abstract)
Authors: Petit J. R. , Jouzel J. , White J. C. , Qiu-yu Qian , Legrand M. , Pourchet M.
Published: September 2017

The stable-isotope content of precipitation (δD and δ18O) is governed by the successive fractionation processes which occur during the atmospheric water cycle. As a result there is, in polar areas, a well-obeyed and theoretically well-understood linear relationship between the mean istopic content of snow and its mean temperature of formation. This relationship is well documented on a spatial scale but poorly known for a given site on a temporal basis, the main reason being that relatively long-term and sufficiently detailed meteorological data are only available for a few polar sites. The South Pole appears to be a suitable place for such a study because: (i) snow accumulation is high enough (∼20 cm of snow per year), thus reducing the possibility that annual layers will be lost as a result of wind; (ii) seasonal variation in isotope content is still preserved in snow up to 50 years old; (iii) meteorological data are available from the time the station was opened in 1957.

Our previous studies of surface and recently deposited snow at the South Pole were very encouraging in this respect; they have been extended with a two-fold purpose: (i) to test the geographical representativity of the isotope record by comparing results from various cores taken within a 10 km radius of the station. The cores are dated by various techniques, such as stratigraphy, seasonal variation in isotopic content, beta-radioactivity fall-out layers, and detection by solid conductivity measurements of the high “spike” which is thought to correspond to the 1815 Tambora eruption; (ii) to discuss the South Pole isotope record over the last 1000 years as recovered from a 127 m deep ice core.
Ice-Sheet Topography From Geosat Radar Altimetry (Abstract)
Authors: Jay Zwally H. , Bindschadler R. A.
Published: September 2017

Ice-sheet surface topography is the principal ice parameter obtainable from satellite radar altimetry. Surface-elevation maps of the East Antarctic ice sheet north of 72°S from Seasat data, collected between July and October 1978, and preliminary maps from Geosat data, collected between March 1985 and September 1986, are described. The Geosat data, obtained from the U.S. Navy as an unclassified data set, have greatly increased the density of elevation measurements. A principal correction to the altimeter measurements is obtained by applying a computer curve-fitting procedure to each radar waveform to correct for errors in the automatic range-tracking circuitry of the altimeter. The errors are caused by slow response to range variations due to undulations of the ice surface between successive measurements made at intervals of 662 m along track. The retracking correction for Geosat data has a standard deviation of 2.4 m and a mean value of 1.1m, values which are about 20% smaller than the corresponding values for Seasat. The positive mean correction indicates a common tendency of the altimeters' automatic tracking to give an excessive range to the surface. The precision of the measurements, given by the standard deviation of the range differences at cross-over points, is about 1.6 m before adjustment for errors in the radial position of the satellite orbit. The preliminary surface-elevation maps from Geosat data are improved over those produced from Seasat, mainly due to optimal spacing of successive ground tracks. The locations of ice divides and drainage basins along the East Antarctic coast are delineated by several methods, including vector plots of surface slope.
Hot-Water Drilling in the Antarctic Peninsula (Abstract)
Authors: Cooper S.
Published: September 2017

The British Antarctic Survey has developed a hot-water drilling system used chiefly for installing temperature sensors through ice shelves and for retrieving oceanographic equipment tethered through thick fast ice. The specification, design and operation of the drill for these two activities will be discussed and practical field problems will be highlighted.

A novel aspect of the design is the use of reaming nozzles to enlarge a pilot hole. These nozzles eject water upwards along the surface of the nozzle cone, and drill most efficiently when they hang free and unsupported by the sides of the pilot hole. The nozzles incorporate a nozzle-mounted valve, activated when the nozzle cone contacts the ice, thus increasing the back pressure of the water flow. The pressure increase is monitored at the surface and the winch speed is reduced accordingly in order to ensure an efficient drilling operation.
Stable Water-Isotope Studies for Deciphering the Recent Structure and Holocene Evolution of the East Antarctic Ice-Sheet Margin Near 12° E (Abstract)
Authors: Hermichen W. -D. , Strauch G. , Vaikmäe R.
Published: September 2017

Since 1978 scientists from the German Democratic Republic, in collaboration with members of Soviet Antarctic Expeditions, have been studying the isotopic composition of ice and snow, as well as the trapped gas content of glacier ice from northern Queen Maud Land near 12 °E, in order to decipher recent structures and Holocene evolution of this part of the margin of the East Antarctic ice sheet.

Along a 180 km north-south profile three large bodies could be distinguished: (1) Novolazarevskaya Ice Shelf (100 km wide, ≲700 m thick); (2) the ice cover (30 km wide, ≲300 m thick) of the Skaly Instituta Geologii Arktiki nunataks [“Skaly IGA”], with a scarp to the Schirmacher oasis; and (3) a firn glacier (50 km wide, c. 1000 m thick), filling the depression between “lskaly IGA” and the Wohlthat massif.

The ice-flow conditions of the surface layer are known. On the basis of isotope profiles from Soviet drilling sites on the ice shelf (447 m core) and on the firn glacier (809 m core), from the scarp and slope of the inland ice to the south of the Schirmacher oasis (ablation zone), and from numerous pits through the surface layer, a preliminary stratigraphic model has been developed.

On the basis of recent flow conditions, the basal layer of Novolazarevskaya Ice Shelf and that of the inland ice of the “Skaly IGA” region were identified as relics of late Pleistocene ice cover by their mean deuterium content of −390 and −330% respectively. The old ice is covered by Holocene layers of regional origin (δD = −230 to −150%); in the ice shelf there are also layers derived from the interior of Antarctica (δD = −350 to −280%).

The isotope profile of the firn glacier (range of δ18O variations −32.3 to −18.1%, identifiable annual layers of about 20 cm of ice to a depth of 500 m) represents a unique record of the last 7–8 ka for this region. It is also supported by measurements of the total air content trapped in ice samples (V = 107–127 cm3/kg) taken from the 809 m core. Details will be published elsewhere.

More information is expected to be provided by isotope studies of extended blue-ice fields and ice-cored moraines.
The Variation in the Ice Sheet of Mizuho Plateau, East Antarctica (Abstract)
Authors: Mae Shinji , Nishio Fumihiko , Ohmae Hirokazu , Takahashi Shuhei , Nakawo Masayoshi , Kawada Kunio
Published: September 2017

The Japanese Antarctic Research Expedition (JARE) has conducted glaciological studies on Mizuho Plateau since 1981. We have already reported that the ice sheet flowing from Mizuho Plateau into Shirase Glacier is thinning at a rate of about 70 cm/year and that the profile of the distribution of basal shear stress is similar to that of surging glaciers.

A 5 year glaciological programme on Mizuho Plateau and in east Queen Maud Land is now being carried out and we have obtained the following new results:

(1) The ice sheet in the down-stream region (where ice elevation is lower than about 2400 m) is thinning, based on measurements of horizontal and vertical flow velocity, strain-rate, the slope of the ice surface, the accumulation rate and densification of snow.

(2) δ18O analysis of deep ice cores obtained at Mizuho Station (2240 m a.s.l.) and point G2 (1730 m a.s.l.) shows that δ18O increased about 200 years ago at Mizuho Station and about 400 years ago at point G2. If we can assume that the increase in δ18O is caused by the thinning of the ice sheet, then this result means that this thinning propagates to up-stream areas.

(3) Radio-echo-sounding measurements on Mizuho Plateau show that the ice base in the down-stream region is wet. This supports the result described in (1), since the basal sliding due to a wet base causes ice-sheet thinning, as proposed in our previous studies.

In summary, a possible explanation of ice-sheet variation on Mizuho Plateau is as follows: the thinning of the ice sheet, caused by the basal sliding due to basal ice melting, started at Shirase Glacier and has been propagating up-stream to reach its present position. A simple calculation, using flow velocities, shows that the thinning started at Shirase Glacier about 1500–2000 years ago.
Snow Accumulation and Oxygen-Isotope Records at the Law Dome Summit, Antarctica (Abstract)
Authors: Morgan V. I.
Published: September 2017

At the summit of Law Dome (66°44′S, 112°50′E) the annual snow accumulation is equivalent to 0.7 m of water, and seasonal cycles of oxygen-isotope ratio are preserved clearly in the firn. Isotope-ratio measurements on three 28 m deep ice cores taken 15 m apart near the summit show that although annual layer thicknesses are well correlated between the cores, the actual isotope values (even when averaged over several years’ accumulation) are poorly correlated.

Since the three sites must obviously receive the same precipitation, the differences in isotope ratio imply that the amounts of the precipitation retained as accumulation from individual snow-falls throughout the year must vary. The large seasonal variation in isotope ratio then easily accounts for the offsets.

In the Law Dome region, precipitation occurs mainly as a result of cyclonic activity in spring, winter and autumn. The stronger winds experienced at these times cause the snow to be formed into large dunes, which are the stable (although moving) surface configuration under these conditions. The movement of dunes by erosion on one face and deposition on the other causes the snow in them to be well mixed. Isotope measurements on a 0.7 m high dune on the inland ice cap showed that it was composed of “winter” snow, with an average isotope value of −28.2% and a range of only 1%. The harder underlying snow had values which varied between −24.2 and −27.4%.

During periods of relatively calm or warm conditions the dunes become consolidated and their movement is greatly reduced. Further snow-falls then do not add accumulation to the top and up-wind side of the dunes but tend to fill them in on the down-wind side. In particular it is observed that for Law Dome the surface profile is quite rough in winter and spring, but the more gentle winds and light snow-falls experienced in summer produce a very smooth surface at the beginning of autumn, with all the surface hollows filled in.

The ice-core isotope profiles confirm the evenness of the summer accumulation, compared to that of winter. Correlation coefficients are typically 0.26 for the winter minima and 0.65 for the summer peak in isotope ratio. This means that somewhat shorter averaging times can be used when compiling “climatic” records from isotope profiles if only the “summer” isotope values are used. This is useful in comparison of isotopic and meteorological data when only a limited time span is available.

Apart from the short-term effects, which can be reduced as desired by longer averaging periods, these core studies also demonstrate how any process which can modulate the precipitation or accumulation will also affect the isotopic composition of the accumulated snow.
Tiltmeter Observations From Doake Ice Rumples, Ronne Ice Shelf, Antarctica (Abstract)
Authors: Smith A. M.
Published: September 2017

New tiltmeter data from Doake Ice Rumples on Ronne Ice Shelf are presented. The tiltmeters detected flexing of the ice shelf close to the grounding line, due to tidal forces. In earlier studies on Rutford Ice Stream, flow was from grounded ice into the floating ice shelf. In contrast, the area studied on Ronne Ice Shelf exhibits flow from the ice shelf on to grounded ice rumples.

The data span 5 km of the up-stream ice shelf and much of the grounded ice. Approximately 30 d of continuous tilt data are available for one site on the ice shelf. Analysis of this record can determine the dominant tidal frequencies present.

A number of shorter records cover periods normally of a few days. These were obtained from sites both up-stream and down-stream of the long-term site. They have been used to investigate the variation in tilt amplitude with distance from the grounding line.

The approximate position of the grounding line was located from the position of strand cracks and by using surface-elevation and ice-thickness data. The tiltmeters helped to confirm this position. Over grounded ice, tidal flexing is clearly present up to about 2 km from the grounding line. Beyond this it appears to be absent. The signal recorded by tiltmeters on grounded ice farther than 2 km from the grounding line is attributed, at present, to a temperature dependency of the tiltmeters.

The flexing of ice shelves at tidal frequencies has previously been treated as an elastic problem. Available models which use beam theory require the use of a time-dependent function and a reduced “effective” ice thickness in the elastic modulus. On preliminary analysis, data from the ice shelf and grounding line of Doake Ice Rumples appear to be consistent with these theories. More detailed analysis and interpretation is required in order to confirm the level of agreement and to determine possible variations due to the “reversed” nature of the flow direction.