bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperate Ice Beneath the “Polar” Taylor Glacier, Victoria Land, Antarctica (Abstract only)
Authors: Robinson P.H.
Published: February 2017

Two interdependent lines of evidence contribute to an understanding of basal ice conditions within Taylor Glacier, from the thermal regime and from features of the englacial and basal debris. The thermal regime of the basal ice in Taylor Glacier suggests mechanisms for the entrainment and transportation of debris near the glacier sole.

Assuming steady-state conditions, basal temperatures over the ablation area of Taylor Glacier were calculated from the geothermal heat in flux, the nearsurface ice temperatures, ice velocities, and the ice thickness. In over 50% of the lower ablation area the basal ice may be melting.

The englacial and basal debris is incorporated by processes operating at the glacier sole. Englacial debris is incorporated by particle regelation; basal debris is incorporated by freezing block regelation. Both processes occur close to the glacier margin, where inner warm basal ice is in contact with marginal cold ice. The debris frozen to the sole here remains relatively unmodified during transport to the margin.

Both lines of evidence indicate that Taylor Glacier is, and has been, capable of erosion and entrainment of debris by temperate ice at the glacier sole. Debris deposited along the margin i s similar to drift deposited beyond the glacier, implying that any recent climatic changes have had little effect on basal ice conditions within Taylor Glacier.
Rheology of an Ice-Floe Field
Authors: Bratchie Iain
Published: February 2017

The aim of the paper is (1) to develop theory to describe sea ice as a collection of finite-sized floes and (2) to construct a rheology based on this description.

Successful sea-ice models have considered the ice to be a two-dimensional continuum with a nonlinear plastic rheology, a two-dimensional yield curve being used to determine the internal ice stresses as functions of the strain-rate (Hibler 1979). In this paper, the shape but not the size of such a yield curve is derived from an idealized picture of floes as moving discs, randomly distributed in a plane. The expected collision rate, which determines the energy loss, is calculated in terms of the average floe size, the areal floe-number density, and the strain-rate. For the case in which the ice strength is low, the dependence of the energy loss upon the strain-rate implies a lens-shaped yield curve, the curved portions being parts of a sine wave. This compares with circular, tear drop-shaped and elliptical yield curves that have been used in sea-ice models to date (Coon 1974, Colony 1976, Hibler 1979). The applicability of the derived yield curve to cases where the ice strength is not low and significant ridging takes place, such as in a continuous ice cover is discussed.
Statistical-Dynamical Model of Accumulation on the Greenland Ice Sheet
Authors: Keen Richard A.
Published: February 2017

A relatively simple, three-parameter model is used to simulate the annual precipitation (accumulation) distribution for the Greenland ice sheet and surrounding regions. The three parameters are (1) the flux of relative vorticity at the 500 mbar level (a measure of cyclonic activity), (2) atmospheric moisture content, and (3) surface terrain. The climatological (1946–79) precipitation distribution predicted by the model displays major features of the observed distribution derived from pit studies. However, the model suggests that, due to changes in storm tracks during this period of 33 a, accumulation distribution maps based on pit studies for varying periods of record may not be representative of a true mean for a uniform period of record. The model is then applied to reconstructed ice-age conditions. Compared to present conditions, accumulation reductions of 60¾ or more are indicated for much of the southern half of Greenland; only slight reductions are noted for northern Greenland.
A 1000 Year Glaciochemical Study at the South Pole
Authors: Kirchner Severine , Delmas Robert J.
Published: February 2017

Major soluble chemical impurities have been measured along a 130 m firn core from the Amundsen–Scott Station in order to assess Southern Hemisphere environmental variability over the last millennium. Particular attention is given to the possible impact of the Little Ice Age, a well-known climatic disturbance which occurred in the Northern Hemisphere between about A.D. 1500 and 1900.

Na+, K+, NH4
+, Cl+, SO4
2− and NO3
− concentrations were carefully determined in forty-two 40 cm firn sections. Stringent precautions were taken to ensure the analytical reliability of the data set obtained. The average concentrations are (in ng g−1): 11.0 ± 2.5, 0.7 ± 0.4, 0.5 ± 0.2, 31 ± 5.6, 58 ± 11.6 and 103 ± 11.6 respectively (the scatter represents the standard deviation).

No definite trend is detected which could be linked to the Little Ice Age disturbance.
Climatic Interpretation of a Continuous Deuterium Profile Obtained from the Vostok Ice Core, Antarctica (160 000 Years) (Abstract)
Authors: Jouzel J. , Lorius C. , Petit J.R. , Genthon C. , Barkov N.I. , Korotkevitch Ye.S. , Kotlyakov V.M.
Published: February 2017

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

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

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

There is a general correspondence between this curve and the previously published δ18O record (Lorius and others 1985). However, there is obviously far more information in this continuous δD record, which we will examine from the deduced temperature record.
An evaluation of scale-dependent effects of atmosphere-glacier interactions on heat supply to glaciers
Authors: Ohata Tetsuo
Published: February 2017

Scale-dependent atmosphere-glacier interactions operate over a glacier surface as the surface has different thermal and radiative characteristics from those of the surrounding ground. In order to evaluate heat supply to the glacier surface in the main ablation period, three main interaction processes are considered: advection, glacier wind, and multiple reflection of solar radiation. The amount of heat supply was calculated for the equilibrium line altitude (ELA) by assuming a simple rectangular-shaped glacier, and by applying meteorological and glaciological data for four different glaciated regions (Tien Shan, Patagonia, west Kunlun and Nepal Himalaya). The total heat supply due to the above three processes had the common tendency of being smallest for glaciers of 1 to several kilometres in length, and largest at 16 km, which was the maximum length considered in this study. Among the cases, the Tien Shan showed a daytime heat supply higher by 2.3 MJ m−2for a 16km-long glacier compared with a small glacier 2 km in length. Relating this difference directly to ELA, an ELA approximately 300 m higher might be expected for a long glacier than a short one, assuming the same amount of solid precipitation. Glacier inventory data for China support this tendency, but the calculated value is slightly larger than that observed. The results show that there is a possibility that responses in glacier variation to climate change may be modified considerably through scale-dependent atmosphere-glacier interactions.
An outline of avalanches in the southeastern Tibet Plateau, China
Authors: Yanlong Wang , Maohuan Huang
Published: February 2017

Avalanches are a widespread hazard that cause serious damage in the southeastern Tibetan Plateau. Abundant solid precipitation and high relief are favourable for avalanche occurrence. The monsoon climate brings a lot of precipitation which, however, is not well distributed. Avalanches are most common around the margins of the plateau. Wet snow avalanches occur most frequently. Based on data on precipitation and topographical relief, a map is drawn showing the areal distribution of avalanche hazards.
Identification of glaciers with surge characteristics on the Tibetan Plateau
Authors: Wenjing Zhang
Published: February 2017

Investigations of Zelunglung and Midui Glaciers in southeast Tibet, China, indicate that they have some characteristics of surge-type glaciers. There have been two extraordinary movements of Zelunglung Glacier, one in 1950 and one in 1968. A collapse of the terminus area took place in 1984. Midui Glacier experienced extraordinary movements about 55 years ago and also in 1988. During these events, the glacier termini reached moraines formed during neoglaciation and the Little Ice Age. The advances of the two glaciers are not related to climate variation. The glaciers caused serious disasters with loss of life and property, and disruption of transportation corridors.
Measurements on Air Porosity of Sea Ice
Authors: Nakawo Masayoshi
Published: February 2017

The air content of sea ice can be measured directly by melting a sample and collecting the released air, provided the air saturation ratio in the meltwater is known. The saturation ratio was found experimentally to be a function of three parameters: the time after an ice sample was melted, the average bubble size, and the air porosity of the sample. Since the last parameter is the term to be determined, an iteration method was employed in calculations of porosity. The bubble pressure was assumed to be at one atmospheric pressure. The vertical profile of air porosity was thus obtained for first-year sea ice in the Arctic. The results were in good agreement with estimations of porosity made from density values measured for the same samples. This indicates that the bubble pressure is near one atmospheric pressure.
Implications of the Time Required for Minimum and Tertiary Creep Rates for Ice Mining and Tunnel Closure (Abstract only)
Authors: Jacka T. H. , Budd W. F.
Published: February 2017

For the calculation of rates of closure of tunnels or bore holes in ice, the use of a flow law relation based on secondary or minimum creep rates necessarily underestimates closure rates, particularly for large strains where much higher tertiary creep rates develop. Long-term laboratory studies have shown that the change in strain-rate from primary to secondary or minimum and to an approximately constant tertiary stage is associated with recrystallization and the development of strong crystal-orientation fabrics which are dependent on the stress configuration, but not appreciably on crystal size. For bore holes, tunnels or cavities constructed in ice, initial rates of closure decrease, in primary creep, to a minimum value (at about 1% strain) dependent on stress and temperature. From this time, increasing strain-rates occur, analogous to the results obtained from the laboratory studies.

A 25-year record of closure of a tunnel at about 30 in depth at site S2 on Law Dome, Antarctica, illustrates the application of the laboratory-derived relations. Comparison between the results of deformation from bore holes, tunnels and laboratory tests, comprising various stress configurations, under similar conditions of stress and temperature, indicates that the strain-rates are compatible when considered as a function of total strain.
Dielectric Variability of a 130 m Antarctic Ice Core: Implications for Radar Sounding
Authors: Moore J. C.
Published: February 2017

A 130 m long ice core has been dielectrically profiled. From an analysis of the measurements, we obtain a profile of the high-frequency (radio-echo) conductivity. This profile has been represented by a simplified 700 layer model. The model has layers of differing conductivities, permittivities and thicknesses. A reflection-coefficient log can be calculated, assuming that permittivity is a smooth function of depth. Variations in conductivity are shown to be more likely sources of internal reflections from depths greater than a few hundred metres than changes in permittivity caused by density changes. The log is convoluted with input pulses of various frequencies and pulse lengths in order to produce synthetic radargrams. These show features that correspond to the internal reflections typically seen when radio echo-sounding polar ice sheets.
Growth Rate of Crystals Within the Surface-Snow/Firn Layer in Wilkes Land, East Antarctica
Authors: Dahe Qin , Young Neal W. , Thwaites Richard J.
Published: February 2017

Measurements of crystal size have been made on seven firn cores drilled at sites covering a range of mean annual temperature from –12.6° to –52.5°C and a range of accumulation rate from 52 to 315 kg m−2 a−1. The sorting coefficient, which gives a measure of the dispersion of crystal sizes within a sample, shows an overall pattern when data from all cores are grouped together as a function of depth. The values are generally small near the surface, increasing to a maximum around 8 m depth, then decreasing but becoming more diffuse at greater depths. Below about 5 m depth, the crystal size increases at an essentially constant rate, which depends on temperature, but in the upper 5 or 7 m the size increases at 1.5 to 2 times this rate. The seasonal variation in temperature enhances the effective mean growth rate of crystals in the near-surface layers compared to conditions with a constant mean temperature and accounts for a part of that increase. But it is likely that vapour diffusion along strong vertical temperature gradients causes the greater part of the observed increase in growth rate. The dependence of crystal-growth rate on temperature is consistent with the Arrhenius-type relation found by other studies.
Crary Ice Rise, Antarctica: Formed in Response to a Surging Ice Stream? (Abstract)
Authors: MacAyeal D. R. , Bindschadler R. A.
Published: February 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.
Interpretation of the Temperature Profile Measured at Vostok, East Antarctica
Authors: Ritz Catherine
Published: February 2017

The temperature profile measured in the Vostok bore hole is analysed. The temperature distribution in polar ice sheets depends mainly on past surface temperature, geothermal flux, and accumulation rate. In the present work, the heat equation is solved both for ice and for the underlying bedrock. The Vostok ice core offers a 160 000 year climatic record which is used to define the past surface temperature, while accumulation-rate variations are assumed to be governed by the saturation vapour pressure. The model is run for a number of different sets of parameters in order to find the parameter associations giving a good fit between the observed and the computed temperature profiles. With this model, it is possible to simulate the measured temperature profile within 0.1°C. To obtain this good fit, geothermal flux has to be higher than 50 mW/m2 and present-day accumulation rate must be lower than 2.6 cm/year. Sensitivity of these results both to the amplitude of surface-temperature change and to the velocity profile with depth is also investigated. Finally, it is shown that ice is at the melting point at the base of the ice sheet, which is in agreement with the presence of a subglacial lake near Vostok Station.
Basin-Scale Ice Motion and Deformation in the Weddell Sea During Winter
Authors: Wadhams P. , Sear C.B. , Crane D.R. , Rowe M.A. , Morrison S.J. , Limbert D.W.S.
Published: February 2017

Ice motion in the Weddell Sea is examined for the period 19 August (Day 232) to 12 October (Day 286) 1986 using the tracks of four Argos buoys deployed during the Winter Weddell Sea Project 1986 (WWSP 86). Two were SPRI/BAS buoys, launched in December 1985 and March 1986 in the south-east and north-west Weddell Sea. The others were part of a mesoscale array deployed in the Maud Rise area by H. Hoeber of the Meteorologisches Institut der Universität Hamburg, during the WWSP 86 cruise of FS Polarstern. The four buoys operated together for 44 d, comprising a basin-scale quadrilateral from which the differential kinematic parameters of divergence, vorticity, shear, and stretch were extracted, as well as the large-scale pattern of motion. It is found that most deformation episodes were associated with atmospheric forcing events.
The Storage of Water in, and Hydraulic Characteristics of, the Firn of South Cascade Glacier, Washington State, U.S.A.
Authors: Fountain Andrew G.
Published: February 2017

The porosity and water saturation of the firn of South Cascade Glacier were measured in order to determine both the volume of water stored in it and the significance of this water content for the water volume stored in the glacier. The distance to water below the firn surface was found never to be greater than 4 m, and the average thickness of the water-saturated layer was estimated to be 1.25 m. The average firn porosity was 0.15, the water saturation was 0.61, and the total volume of water stored in the firn was approximately 1.78 × 105m3representing about 12% of the total spring storage. The water table was found to exhibit a pattern of diurnal fluctuation which starts in late June or early July, indicating that melt water from the accumulation zone may pressurize the bed at diurnal frequencies. The depth-averaged permeability was found to be 1.5 × 10−5m/s, a value which compares favorably with those from other studies.
A Mathematical Model for Instability in Snow Gliding Motion
Authors: Nohguchi Yasuaki
Published: February 2017

In this paper a fundamental model is proposed to describe the time-dependent behaviour of uniform snow glide on an infinite slope. This model is composed both of a mechanical balance equation relating a driving force and a resistant force, and of a rate equation for a real contact area at the boundary. In the model, a steady motion of glide is described as a stable equilibrium of glide motion, and a non-steady motion is considered as a transient one not in equilibrium. Finally, the model is applied to a full-depth avalanche release caused by acceleration of snow glide. By comparing the model predictions with glide-velocity field data, a proper model of acceleration prior to full-depth avalanche release is determined. As a result, we can obtain the safety standards to be applied in the event of full-depth avalanches in terms of a glide velocity.
Snow-Collection Mechanisms and the Capacities of Snow Fences
Authors: Takeuchi Masao
Published: February 2017

The shapes of equilibrium lee drifts formed by snow fences are scaled in proportion to height of snow fences independent of the snow and weather conditions, even in small-scale models, but those of up-wind drifts are not.

Field studies have been made of the snow-collection mechanisms of a snow fence. It has been observed that particles of saltated snow piled up to windward, and that it was the previously suspended particles that were heaped up in the lee drift. It can be shown that the shapes of up-wind drifts vary in different snow and weather conditions because threshold shear stress and drift-snow saltation depend on the physical properties of the surface snow.

Equilibrium lee drifts are scaled in proportion to fence height, because snow and weather conditions have less effect on threshold wind speed for suspension, and the sheltering effect of a fence is scaled in proportion to the height of the fence.

The dimensions of the equilibrium drifts at snow fences were measured, and maximum snow-retention capacity and lee-drift length presented as a function of fence height, fence density, and depth of snow cover.
Modeling Onset of Glaciation
Authors: Crowley Thomas J. , North Gerald R.
Published: February 2017

Numerous studies have shown that climate has varied between ice-free and glaciated states, with transitions often marked by abrupt steps. We summarize some modeling studies that have attempted to explain elements of the long-term trend and discuss a particular model for abrupt transitions that involves instabilities due to albedo discontinuities at the snow/ice edge.
Thinning of the Ice Sheet Estimated from Total Gas Content of Ice Cores in Mizuho Plateau, East Antarctica
Authors: Kameda Takao , Nakawo Masayoshi , Mae Shinji , Watanabe Okitsugu , Naruse Renji
Published: February 2017

A linear relation between total gas content in ice and the elevation of ice formation (i.e. pore close-off) was obtained from seven shallow ice cores in Mizuho Plateau, Antarctica. The derived relation was applied to the vertical profile of total gas content in a 700 m long ice core at Mizuho Station. A general trend of gradual increase in total gas content was observed from 600 to 200 m in depth, from which toward the upper layer it showed a steep increase. After eliminating the effect of down-slope flow of ice around Mizuho Station, it was estimated that the thickness of the ice sheet decreased by about 350 m at maximum during the last 2000 years. This tendency also appears in the δ18O profile of the same ice core.
Topographic and Glaciological Controls on Holocene Ice-Sheet Margin Dynamics. Central West Greenland
Authors: Warren C.R. , Hulton N.R.J.
Published: February 2017

The retreat of the West Greenland ice sheet from its Sisimiut (Wisconsinan) glacial maximum, was punctuated by a series of Stillstands or small readvances that formed numerous moraines. These landforms have been interpreted in the past as the result of short-term, regional falls in ablation-season temperatures. However, mapping of the geomorphological evidence south of Ilulissat (Jakobshavn) suggests that retreat behaviour was not primarily governed by climate, and therefore that the former ice margins are not palaeoclimatically significant. During warm climate ice-sheet wastage, the successive quasi-stable positions adopted by the ice margin were largely governed by topography. The retreat of the inherently unstable calving glaciers was arrested only at topographically-determined locations where stability could be achieved.
Changes In Glacier Length Induced By Climate Changes
Authors: Raymond C.F. , Waddington E.D. , Jøhannesson Tómas
Published: February 2017

Time scales for adjustment in the length of a glacier to changing climate may be described in terms of a relatively short time scale, T
S and a longer memory time, T
m. The memory Tm
represents the time scale needed for asymptotic approach of the glacier to a steady state following a climate change event. Tm is determined by simple continuity considerations concerning the total volume change that must occur to reach steady state and the balance rate that drives the change. We show that T
m is relatively independent of the size of the climate change or to details of how ice flow is related to the geometry of the glacier. The time scale T
S represents the time between a climate event and the occurrence of substantial changes in the glacier length. We show that, in contrast to T
m, T
s is highly dependent on the size of the climate change and on details of ice dynamics. This dependence is investigated by several ice-flow models including a simple one in which ice transport is determined by local thickness and slope, as in the analysis of kinematic waves, and a finite element representation that fully includes longitudinal stress gradients. The ice-flow models are subjected to mass-balance perturbations of varying size — from small, for which linearization approximations are valid, to large, for which linearization breaks down.

The following behavior may be identified. Increasing the size of a mass-balance rate change causes a more rapid initial response of a glacier terminus, which tends to shorten T
s. Longitudinal stress gradients damp local variations in velocity and thereby slow the propagation and diffusion of kinematic waves and retard the response of the terminus, which tends to lengthen T
s. Longitudinal stress gradients transmit forces to the terminus region and influence the terminus motion without the necessity of redistributing mass from the glacier length into the terminus zone, which tends to shorten T
s. These various results indicate that accurate modeling of the short term responses of glaciers to climate change requires fairly sophisticated ice-flow models, However, for purposes of tracking glacier lengths (or areas) over time scales considerably great than T
s, fairly simple ice-flow models may suffice.
Annual Salt and Energy Budget Beneath an Antarctic Fast Ice Cover
Authors: Allison Ian , Tivendale C. M. , Copson G. R.
Published: February 2017

Water temperature and salinity profiles were measured to a depth of 300 m below a fast ice cover near Mawson, Antarctica over a full annual cycle. Together with measurements of ice thickness and salinity, they are used to determine the heat and salt balance of the ice/ocean system at this site. The energy balance of the ocean is related to measured energy fluxes at the surface.

Throughout the winter there is a net advection of salty water to the site which enhances the salinity increase in the water due to brine ejected from ice. After the ice reaches its maximum thickness there is considerable advection of warmer water which both raises the water temperature at the site and provides heat for the large oceanic heat flux previously reported for Mawson. The rate of this heat advection increases as the ice extent around Antarctica decreases. The ice partially meltsin situand breaks out in mid January. This effective removal of fresh water is balanced by a large influx of melt water from the continental ice sheet. The fresh water, initially near the surface, becomes well mixed to depths of greater than 200 m by strong storms in the ice free period from mid January to early April.
Actively surging West Antarctic ice streams and their response characteristics
Authors: Bindschadler Robert
Published: February 2017

Ice Streams B, D and E, West Antarctica, all show a longitudinal pattern of ice thickness change that is consistent with ongoing surge behavior modeled for glaciers. The measured pattern is not consistent with model response of any other scenario such as accumulation-rate change or changes on the ice shelf. Inland migration of the ice-stream onset is a requirement of this behavior pattern. If such a surge is presently taking place, the remaining lifetime of the West Antarctic ice sheet is 1200–6000 years. A complete surge period lasting 50 000–120 000 years is hypothesized, with a relatively brief surge phase (lasting 16000–21 000 years) required to completely remove the West Antarctic ice sheet from its maximum extent. Applying classic glacier response theory demonstrates that the diffusive component of response is much faster for ice streams than for glaciers, making the identification of either kinematic waves or localized responses on ice streams unlikely.
Relation between ice sheet internal radio-echo reflections and ice fabric at Mizuho Station, Antarctica
Authors: Fujita Shuji , Mae Shinji
Published: February 2017

The relationship between ice fabric and the internal radio-echo reflections was investigated using observation data collected at Mizuho Station, Antarctica. The data were obtained by 179 MHz radio-echo sounding and the ice fabric was measured from 700 m Mizuho ice core. The dielectric permittivity tensor at given depths in the ice sheet was calculated from the ice fabric.

The calculated dielectric permittivity tensor showed that the ice sheet at Mizuho Station is a uniaxially birefringent medium. The symmetrical axis of rotation was the same as the flow line. In such a medium, theory predicts that the electric field vectors are allowed only in the two directions parallel and perpendicular to the flow line. The prediction coincided well with the observation: a strong signal was observed only when the transmitting antenna and the receiving antenna, kept parallel to one another, were oriented parallel or perpendicular to the flow line. However, the observed signal strength in these two directions differed from one another at each depth.

It is also shown that the power reflection coefficient due to the variation of ice fabric with depth is of approximately the same order as that due to the density change and is large enough to produce the predominant internal radio-echo reflections.
Discrimination of a wet snow cover using passive microwave satellite data
Authors: Walker A.E. , Goodison B.E.
Published: February 2017

Snow-cover monitoring using passive microwave remote sensing methods has been shown to be seriously limited under melt conditions when the snowpack becomes wet. A wet snow indicator has been developed using DMSP SSM/I 37 GHz dual-polarization data for the open prairie region of western Canada. The indicator is used to identify areas of wet snow and discriminate them from areas of snow-free land. Validation and testing efforts have illustrated that the addition of the indicator to the current SSM/I snow water equivalent algorithm provides a more accurate representation of spatial snow coverage throughout the winter season for the open prairie region. The improved spatial and temporal information resulting from the use of the indicator enhances both climatological and hydrological analyses of snow-cover conditions using passive microwave data. Although the wet snow indicator has only been validated for the open prairie region of western Canada, it may also be applicable to other regions of similar terrain and vegetative characteristics. However, in areas of dense vegetation, such as the boreal forest, the performance of the indicator is poor due to the generally low 37 GHz polarization differences of the vegetation cover.
The calculation of surface temperature and albedo of Arctic sea ice from AVHRR
Authors: Lindsay R. , Rothrock D.
Published: February 2017

The temperature and albedo distributions of Arctic sea ice are calculated from images obtained from the AVHRR satellite sensor. The temperature estimate uses a split window correction incorporating regression coefficients appropriate for the arctic atmosphere. The albedo estimate is found assuming a clear and dry atmosphere. Both estimates are made with published correction techniques. Inherent errors due to the uncertainty of the atmospheric interference produced by humidity, aerosols, and diamond dust are judged to be 2–5°C in surface temperature and 0.10–0.20 in surface albedo. Cloudy regions are masked out manually using data from all five channels. The relationship between temperature and albedo is shown for a sample scene. A simple model of a surface composed of only cold, bright ice and warm, dark water is inadequate. Model calculations based on the surface energy balance allow us to relate albedo and temperature to ice thickness and snow-cover thickness and to further assess the accuracy of the surface estimates.
Ice-sheets’ surface mass-balance evaluation in the UGAMP GCM: the climate of Antarctica
Authors: Marsiat I.
Published: February 2017

General Circulation Models (GCMs) will be more and more used for coupled climatic simulations involving ice sheets. It is therefore of prime importance to evaluate the performance of these models in simulating the mass balance and climate over ice sheets. The Antarctic climate simulated with the U.K. Universities Global Atmospheric Modelling Programme General Circulation Model (UGAMP GCM, hereafter referred to as the UGCM) is in good agreement with the available observations. In particular, the accumulation pattern appears fairly reasonable. Some imperfections are related to the surface temperature and energy budget but without severe consequences for the atmosphere behaviour. Refining the snow-related parameterizations could improve the results of the model in high latitudes.
Models for strain localization in Law Dome, Antarctica
Authors: Rowden-Rich R. J. M. , Wilson C. J. L.
Published: February 2017

A finite-element model was implemented that relates the computed flow to some field and fabric observations recorded on the Law Dome ice cap, East Antarctica. The results of the model suggest that the general ice flow is markedly affected by the bedrock topography. The zones of measured anomalous flow correlate with significant changes in the modelled stress within the ice mass. Stress increases of up to 50% above the reduced model shear stress were obtained in the models where the ice moved over a bedrock rise. Stress relaxation also occurs in the ice mass as the ice moves downward to a lee depression. There is a marked oscillation in the direction of principal stress and this is responsible for the progressive development of a set of high stress zones that are superimposed on the down-slope ice movement.
Impact of transient increases in atmospheric CO2 on the accumulation and mass balance of the Antarctic ice sheet
Authors: O’Farrell Siobhan P. , McGregor John L. , Rotstayn Leon D. , Budd William F. , Zweck Christopher , Roland Warner
Published: February 2017

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 CO2value 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.
Impact of sea-ice formation on the properties of Antarctic bottom water
Authors: Goosse H. , Campin J. M. , Fichefet T. , Deleersnijder E.
Published: February 2017

It is generally accepted that fresh-water fluxes due to ice accretion or melting profoundly influence the formation of Antarctic bottom water (AABW). This is investigated by means of a global, three-dimensional ice-ocean model. Two model runs were conducted. At the high southern latitudes, the control experiment exhibits positive (i.e. towards the ocean) fresh-water fluxes over the deep ocean, and large negative fluxes over the Antarctic continental shelf, because of the intense ice-production taking place in this region. The salinity of shelf water can increase in such a way that deep-water formation is facilitated. The simulated net fresh-water flux over the shelf has an annual mean value of −1 m a−1. This flux induces a transport of salt to bottom waters, which corresponds to an increase of their salinity estimated to be around 0.05 psu. In the second model run, the fresh-water fluxes due to ice melting or freezing are neglected, leading to a rearrangement of the water masses. In particular, the AABW-formation rate decreases, which allows the influence of North Atlantic deep water (NADW) to increase. As NADW is warmer and saltier than AABW. the bottom-water salinity and temperature become higher.
Physical modelling of avalanches using an aerosol cloud of powder materials
Authors: Bozhinskiy A.N. , Sukhanov L. A.
Published: February 2017

The problem of physically modelling snow avalanches with an aerosol cloud is considered. Using the simplest model of avalanche-body motion, the criteria of similarity for transit and deposit zones are written. The transit relations between model and natural scales for dynamic parameters of the avalanche body are established. On the basis of the similarity criteria, an approximate physical model of avalanches with an aerosol cloud is made using a mixture of ferromagnetic sawdust and aluminium dust. The setup allows us to start and stop the model avalanche during any stage of its motion and to model actual avalanches. A series of experiments was completed. It is shown that the basic mechanism of aerosol cloud generation for model avalanches is related to the hydraulic jump of fluid when a stormy flow changes to a calm one. A comparison of parameters for model and “home” avalanches (the vicinity of Elbrus) showed that the ratios of the sizes of dense and aerosol components and deposition zones of those avalanches are close to the geometric scale factor and the ratios of velocities, and durations of processes are close to the square root of this coefficient. The latter corresponds to modelling the process by Froude number.
Lumped-element model for subglacial transport of solute and suspended sediment
Authors: Clarke Garry K. C.
Published: February 2017

Present understanding of the subglacial water system and its role in transporting solute and sediment is largely based on subglacial observations of water pressure, turbidity and electrical conductivity and on portal measurements. Such data reveal a wealth of intriguing phenomena, but convincing interpretations can be elusive. Although a proper mathematical description of the subglacial water system would unquestionably lead to a coupled system of non-linear partial differential equations, it is not fruitful to introduce this level of complexity until the important physical processes have been identified and quantified. Lumped-element models offer an efficient approach to examining the complex but dimly perceived physics of the subglacial water system. Water volume, hydraulic head, discharge and flow resistance have the respective electrical analogues of charge, voltage, current and ohmic resistance. Thus, subglacial hydraulic circuits can be approximated by electrical circuits. Mathematically, this circuit description commonly leads to a coupled system of algebraic and differential equations which can be solved numerically. It is straightforward to enrich this representation by adding sources and sinks of solute and sediment. To demonstrate the method, model results are compared to records of subglacial pressure, electrical conductivity and turbidity measured beneath Trapridge Glacier, Yukon Territory, Canada.
Surface energy exchange at the equilibrium line on the Greenland ice sheet during onset of melt
Authors: Steffen Konrad
Published: February 2017

The energy balance was measured at the ETH/CU research camp, located at the equilibrium-line altitude of the Greenland ice sheet (69°34′N, 49°17′W), in spring 1993. Prior to the onset of melt the latent energy flux is the only energy sink, with an average value of 1.18 MJ m−2d−1. This turbulent transfer of moisture is responsible for an average daily snow sublimation of 5 × 10−4 m. The sensible heat flux (0.91 MJ m−2d−1) is the major energy source, and the net radiation only a minor contributor with a positive balance of 0.12 MJ m−2d−1. The residual of the turbulent fluxes and the net radiation is about 0.14 MJ m−2d−1, which agrees surprisingly well with the in situ ground-heat flux measurements of 0.15 MJ m−2d−1 made at the same location. Assuming a 3°C temperature increase in a global-change scenario, and using the information gained from the energy-balance measurements, a simple calculation showed that 5.4 × 10−2 m w.e. of snow would be lost by sublimation for an area of approximately 400 000 km2. The increased sublimation is due to an increase in the net radiation balance caused by an albedo reduction. This would lead to a total annual mass reduction of 22 km3 w.e. of snow for the entire Greenland ice sheet, which is 4.2% of today’s annual accumulation.
Constraints on holocene ice-thickness changes in central Greenland from the GISP2 ice-core data
Authors: Bolzan J. F. , Waddington E. D. , Alley R.B. , Meese D.A.
Published: February 2017

The depth–age relation observed in the GISP2 ice core is the result of the integrated effects of ice-sheet changes over time, as well as the accumulation-rate history. Here, we construct a forward model to compute ages at various depths in the core. In the model, these ages are functions of parameters that describe the ice thickness as a function of time. Using the maximum-likelihood inverse method, these parameters are iteratively adjusted until measured and computed ages agree satisfactorily. The results suggest that the thickness along the flowline connecting the GISP2 and GRIP drill sites has not changed significantly since the onset of the Holocene. We also derive bounds on the likely thickness changes. Because these bounds are independent of assumptions concerning the processes driving the ice-sheet evolution, they can provide useful constraints for other ice-sheet modeling efforts.
Ages and ablation and accumulation rates from 14C measurements on Antarctic ice
Authors: Roijen J.J. Van , der Borg K. van , De Jong A.F.M. , Oerlemans J.
Published: February 2017

Shallow ice cores from an Antarctic blue-ice area at Scharffenbergbotnen werel4C-analyzed using a dry-extraction technique and accelerator mass spectrometry. The in situ production was determined from the14CO component and used to deduce the natural14CO2component. The ages were measured at 10 000 ± 3000 BP. The accumulation and ablation rates determined from the in situ production are 7–20 and 10 cm a−1. respectively, showing agreement with field observations. The derived ages and air-yield data show a nearby origin for the surface ice.
Sensitivity experiments to sea surface temperatures, sea-ice extent and ice-sheet reconstruction, for the Last Glacial Maximum
Authors: Ramstein G. , Joussaume S.
Published: February 2017

For the Last Glacial Maximum, (LGM; 21 000 BP), simulations using atmospheric general-circulation models (AGCMs) are very sensitive to the prescribed boundary conditions. Most of the recent numerical experiments have used the CLIMAP (1981) data set for ice-sheet topography, sea-ice extent and sea surface temperatures (SSTs). To demonstrate the impact of ice-sheet reconstruction on the LGM climate, we performed two simulations: one using CLIMAP (1981) ice-sheet topography, the other using the new reconstruction provided by Peltier. We show that, although the geographical structure of the annually averaged temperature is not modified, there are important seasonal and regional impacts on the temperature distribution. In a second step, to analyze the effects of cooler SSTs and sea-ice extent, we performed a simulation using CLIMAP (1981) for the ice-sheet topography, but with present SSTs. We find that the cooling due to ice sheets for the LGM climate is one-third of the global annually averaged cooling, and dial the southward shift of the North Atlantic low in winter is not due to sea-ice extent, but is an orographic effect due to the Laurenride ice sheet. This set of sensitivity experiments allows us also to discriminate between thermal and orographic forcings and to show the impact of the ice-sheet topography and cooler SSTs on the pattern of planetary waves during the LGM climate.
On the effect of sea-ice dynamics on oceanic thermohaline circulation
Authors: Hibler W. D. , Zhang Jinlun
Published: February 2017

An idealized planetary flat-bottom geostrophic ice–ocean model is constructed with boundaries at latitudes 5° and 65° N and longitudes 50° W and 10° E in order to approximate the North Atlantic. The model is driven by fixed zonally averaged wind, surface air temperatures and surface ocean salinity. A dynamic thermodynamic sea-ice model is coupled to the ocean model. Only the thermodynamic insulating effects of the sea ice are considered, and no salt fluxes due to melting and freezing are included. Four equilibrium simulations of about 5000 years each are performed: two with interactive sea ice with and without ice dynamics, and two control simulations with either a fixed or no ice cover.

In the two simulations including interactive sea ice, characteristic oscillations in the ice thickness and ocean temperature are found to occur. The oscillations are smaller when sea-ice dynamics are included. The dominant oscillation occurs at about a 5 year period, with the key feature being that the presence of sea ice tends to insulate the ocean and hence allows an oceanic warming. This warming in turn eventually causes a melt-back of the ice and a subsequent cool-down of the ocean. Oscillations at longer periods of about 20 years in the thermohaline circulation are also observed. These longer-period oscillations are particularly pronounced in the northward surface water transport.
Simulation of past variability in seasonal snow in the Southern Alps, New Zealand
Authors: Fitzharris B.B. , Garr C.E.
Published: February 2017

There are no systematic measurements of seasonal snow in the Southern Alps, New Zealand, so little information is available as to its past variability. To rectify this, a conceptual model is developed that calculates seasonal snow deposition, ablation and accumulation. The model is based on daily temperature and precipitation data from long-established climate stations about the Southern Alps. Output is given as daily specific net balance of snow at five elevation bands from 1000 to 2200 m and as total water stored as seasonal snow over several major river catchments. Model output is in general agreement when tested against the few historical observations of snow and is tuned to the long-term water balance. A chronology of seasonal snow is reconstructed from 1931 to 1993. Area-averaged annual maxima average 366 mm. They show no trend, but large inter-annual variability from less than 200 to over 650 mm w.e. Seasonal snow can peak at any time between September and January.
Reading the garden in Byzantium: nature and sexuality
Authors: Barber Charles
Published: February 2017

The subject of the Byzantine garden is primarily to be tackled from texts, and is very much a subject of its texts. My research on the Byzantine garden began from an art historian’s point of view, I wanted to examine the possibilities of interpreting the garden as an example of visual culture. How was the garden represented? What did the garden look like? But the information demanded by such questions proved to be thin.