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Stable isotope ratios (δ18O and δD) in Antarctic snow and ice are basic proxy indices of climate in ice core studies. The relation between the ratios has important indicative significance for moisture sources. In general, the fractionation characteristics of the two isotopes vary with different meteorological and topographical conditions. This paper presents the spatial and temporal distribution of meteoric water line (MWL) slopes along a traverse from the Zhongshan Station (ZSS) to Dome A in East Antarctica. It is found that the slopes decrease with the increasing distance inland from the coast and the lowest slope occurred at Dome A, where the long-range transported moisture dominates and clear sky snowing have an influence. The slopes in different layers of the snowpack showed a decreasing trend with depth and this is attributed to the fractionation during the interstitial sublimation and re-condensation processes of the water vapor. Frost flower development on the interior plateau surface can greatly alter the depth evolution of the MWL slope. The coastal snow pits also go through the post-depositional smoothing effect, but their influences are not so significant as the inland regions. [ABSTRACT FROM AUTHOR]

There has been extensive research on the effects of evaporation on the isotopic ratio of lacustrine and marine water bodies; however, there are limited data on how ablation or sublimation from lake or sea ice influences the isotopic ratio of the residual water body. This is a challenging problem because there remains uncertainty on the magnitude of fractionation during sublimation and because ablation can involve mixed-phase processes associated with simultaneous sublimation, melting, evaporation, and refreezing. This uncertainty limits the ability to draw quantitative inferences on changing hydrological budgets from stable isotope records in arctic, Antarctic, and alpine lakes. Here, we use in situ measurements of the isotopic ratio of water vapor along with the gradient diffusion method to constrain the isotopic ratio of the ablating ice from two lakes in the McMurdo Dry Valleys, Antarctica. We find that during austral summer, the isotopic fractionation of ablation was insignificant during periods of boundary layer instability that are typical during midday when latent heat is highest. This implies that the loss of mass during these periods did not yield any isotopic enrichment to the residual lake mass. However, fractionation increased after midday when the boundary layer stabilized and the latent heat flux was small. This diurnal pattern was mirrored on synoptic timescales, when following warm and stable conditions latent heat flux was low and dominated by higher fractionation for a few days. We hypothesize that the shifting from negligible to large isotopic fractionation reflects the development and subsequent exhaustion of liquid water on the surface. The results illustrate the complex and nonlinear controls on isotopic fractionation from icy lakes, which implies that the isotopic enrichment from ablation could vary significantly over timescales relevant for changing lake volumes. Future work using water isotope fluxes for longer periods of time and over additional perennial and seasonal ice-covered lake systems is critical for developing models of the isotopic mass balance of arctic and Antarctic lake systems. [ABSTRACT FROM AUTHOR]

Blowing snow is a frequent and widespread phenomenon over most of Antarctica. The transport and sublimation of blowing snow are important for the mass balance of the Antarctic ice sheet, and the latter is a major contributor to the hydrological cycle in high-latitude regions. Although much is known about blowing snow from surface observations, knowledge of the thermodynamic structure of deep (>50 m) blowing-snow layers is lacking. Here, dropsonde measurements are used to investigate the temperature, moisture, and wind structure of deep blowing-snow layers over Antarctica. The temperature lapse rate within the blowing-snow layer is at times close to dry adiabatic and is on average between dry and moist adiabatic. Initiation of blowing snow causes the surface temperature to increase to a degree proportional to the depth of the blowing-snow layer. The relative humidity with respect to ice is generally largest near the surface (but less than 100%) and decreases with height, reaching a minimum near the top of the layer. These findings are at odds with the generally accepted theory that blowing-snow sublimation will cool and eventually saturate the layer. The observations support the conclusion that high levels of wind-shear-induced turbulence cause mixing and entrainment of warmer air from above the blowing-snow layer, which suppresses humidity and produces the observed well-mixed temperature structure within the layer. The results may have important consequences for understanding the mass balance of the Antarctic ice sheet and the moisture budget of the atmosphere in high latitudes. [ABSTRACT FROM AUTHOR]

The article discusses whether the Antarctic continent is losing the ice sheet mass or staying the same. It mentions that ice sheet mass change can be estimated in three different ways including mass budget that keeps track of precipitation and loss in the atmosphere by sublimation, radar and laser altimetry where changes in elevation of ice sheet can be evaluated from satellite, and gravimetry in which acceleration varies for different reasons because of gravity at the earth's surface.

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Many glacial deposits in the Quartermain Mountains, Antarctica present two apparent contradictions regarding the degradation of unconsolidated deposits. The glacial deposits are up to millions of years old, yet they have maintained their meter-scale morphology despite the fact that bedrock and regolith erosion rates in the Quartermain Mountains have been measured at 0·1-4·0 m Ma. Additionally, ground ice persists in some Miocene-aged soils in the Quartermain Mountains even though modeled and measured sublimation rates of ice in Antarctic soils suggest that without any recharge mechanisms ground ice should sublimate in the upper few meters of soil on the order of 10 to 10 years. This paper presents results from using the concentration of cosmogenic nuclides beryllium-10 (Be) and aluminum-26 (Al) in bulk sediment samples from depth profiles of three glacial deposits in the Quartermain Mountains. The measured nuclide concentrations are lower than expected for the known ages of the deposits, erosion alone does not always explain these concentrations, and deflation of the tills by the sublimation of ice coupled with erosion of the overlying till can explain some of the nuclide concentration profiles. The degradation rates that best match the data range 0·7-12 m Ma for sublimation of ice with initial debris concentrations ranging 12-45% and erosion of the overlying till at rates of 0·4-1·2 m Ma. Overturning of the tills by cryoturbation, vertical mixing, or soil creep is not indicated by the cosmogenic nuclide profiles, and degradation appears to be limited to within a few centimeters of the surface. Erosion of these tills without vertical mixing may partially explain how some glacial deposits in the Quartermain Mountains maintain their morphology and contain ground ice close to the surface for millions of years. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: To date, studies of the stability of subsurface ice in the McMurdo Dry Valleys of Antarctica have been mainly based on climate-based vapor diffusion models. In University Valley (1800m), a small glacier is found at the base of the head of the valley, and adjacent to the glacier, a buried body of massive ice was uncovered beneath 20–40cm of loose cryotic sediments and sandstone boulders. This study assesses the origin and stability of the buried body of massive ice by measuring the geochemistry and stable O–H isotope composition of the ice and applies a sublimation and molecular diffusion model that accounts for the observed trends. The results indicate that the buried massive ice body represents an extension of the adjacent glacier that was buried by a rock avalanche during a cold climate period. The contrasting δ18O profiles and regression slope values between the uppermost 6cm of the buried massive ice (upward convex δ18O profile and S D-18O =5.1) and that below it (progressive increase in δ18O and S D-18O =6.4) suggest independent post-depositional processes affected the isotope composition of the ice. The upward convex δ18O profile in the uppermost 6cm is consistent with the ice undergoing sublimation. Using a sublimation and molecular diffusion model, and assuming that diffusion occurred through solid ice, the sublimation rate needed to fit the measured δ18O profile is 0.2 ⋅ 10−3 mm yr−1, a value that is more similar to net ice removal rates derived from 3He data from cobbles in Beacon Valley till (7.0 ⋅ 10−3 mm yr−1) than sublimation rates computed based on current climate (0.1–0.2mm yr−1). We suggest that the climate-based sublimation rates are offset due to potential ice recharge mechanisms or to missing parameters, particularly the nature and thermo-physical properties of the overlying sediments (i.e., temperature, humidity, pore structure and ice content, grain size). [Copyright &y& Elsevier]

A surface energy balance model is forced by 13 years of high-quality hourly observations from the Antarctic coastal station Neumayer. The model accurately reproduces observed surface temperatures. Surface sublimation is significant in summer, when absorbed solar radiation heats the surface. Including a first order estimate of snowdrift sublimation in the calculation more than triples the total sublimation, removing 19% of the solid precipitation, indicating that snowdrift sublimation is potentially important for the mass balance of Antarctic ice shelves. Surface melt occurs at Neumayer in all summers, but all the meltwater refreezes. In two-thirds of the cases, the refreezing is quasi-instantaneous (within the model timestep of 6 min), so that no liquid water remains in the snow. For all other events, the occurrence of liquid water in the snowpack at Neumayer agrees well with satellite-based liquid water detection. [ABSTRACT FROM AUTHOR]

Abstract: Soils in the McMurdo Dry Valleys, Antarctica contain ice and considerable amounts of salt. Ice often occurs at shallow depth throughout the Dry Valleys and other areas of hyperarid permafrost, notably on Mars. This common occurrence of shallow ice is enigmatic; however, since according to published sublimation models it should disappear relatively quickly (at rates of order 0.1mma−1) due to vapor loss to the atmosphere. This loss may be offset by recharge from snowmelt infiltrating and freezing in the soil. Herein, we present a first quantitative estimate of this recharge based on measured vertical profiles of δD and δ18O that reveal considerable detail about the sources and sinks of ice. We model these profiles, taking into account the salt content and a soil temperature record along a 1.6m depth profile of ∼10ka old ice-cemented soils in Victoria Valley, Antarctica. The stable isotopes of ice are enriched in heavy isotopes at the top of the ice cement (20cm depth); both δD and δ18O values plotted against depth exhibit a concave upward curve. At depth, the isotope composition is similar to that of Lake Victoria and modern meteoric water. The concave shape of the isotope profile is suggestive of downward advection–dispersion of snowmelt water enriched in heavy isotopes into the ice cement. Our advection–dispersion model, coupled with field data, enables us to quantify the advective flux and dispersion of melt water into the ice. The advective velocity and dispersion coefficient depend on the time since advection began and the ice-to-brine ratio; they are, respectively, of the order of 10−11–10−10 ms−1 and 10−12–10−11 m2 s−1. These values suggest that over the ∼10ka time period, a total of 190mm water infiltrated into the ice-cemented ground. The isotope composition and deuterium excess values of the uppermost ice cement can be modeled from snowmelt water enriched in salts using open system-Rayleigh fractionation. To develop the isotopic signature of the upper ice cement requires evaporation of ∼95% of the snowmelt water. Based on 190mm brine infiltrating into the soil requires an initial total of ∼4m of snowmelt water. This corresponds to ∼0.4mma−1 suggesting that, under the current climate condition, water from snowmelt is sufficient to compensate modeled sublimation rates, and therefore conserve ground ice in Victoria Valley. [Copyright &y& Elsevier]

The article presents a study that aims to present statistical data on high-resolution microstructures from the samples of the European Project for Ice Coring in Antarctica Dronning Maud Land (EDML) deep ice core in East Antarctica. The study revealed that subgrain boundaries were found to have shallow sublimation grooves on ice sample terrain and they showed intracystalline deformation and recrystallization. The data from the EDML failed to detect a portion of increased subgrain-boundary formation but grain-boundary structures demonstrated an influence of internal strain energy on the microstructure. Microscopic analysis provides a way to classify several subgrain-boundary types.

We have determined the flux of calcium, chloride and nitrate to the McMurdo Dry Valleys region by analysing snow pits for their chemical composition and their snow accumulation using multiple records spanning up to 48 years. The fluxes demonstrate patterns related to elevation and proximity to the ocean. In general, there is a strong relationship between the nitrate flux and snow accumulation, indicating that precipitation rates may have a great influence over the nitrogen concentrations in the soils of the valleys. Aeolian dust transport plays an important role in the deposition of some elements (e.g. Ca2+) into the McMurdo Dry Valleys' soils. Because of the antiquity of some of the soil surfaces in the McMurdo Dry Valleys regions, the accumulated atmospheric flux of salts to the soils has important ecological consequences. Although precipitation may be an important mechanism of salt deposition to the McMurdo Dry Valley surfaces, it is poorly understood because of difficulties in measurement and high losses from sublimation. [ABSTRACT FROM AUTHOR]

A remnant of Taylor Glacier ice rests beneath a 40–80 cm thick layer of sublimation till in central Beacon Valley, Antarctica. A vapour diffusion model was developed to track summertime vapour flow within this till. As input, we used meteorological data from installed HOBO data loggers that captured changes in solar radiance, atmospheric temperature, relative humidity, soil temperature, and soil moisture from 18 November 2004–29 December 2004. Model results show that vapour flows into and out of the sublimation till at rates dependent on the non-linear variation of soil temperature with depth. Although measured meteorological conditions during the study interval favoured a net loss of buried glacier ice (∼0.017 mm), we show that ice preservation is extremely sensitive to minor perturbations in temperature and relative humidity. Net loss of buried glacier ice is reduced to zero (during summer months) if air temperature (measured 2 cm above the till surface) decreases by 5.5°C (from -7°C to -12°C); or average relative humidity increases by 22% (from ∼36% to 58%); or infiltration of minor snowmelt equals ∼0.002 mm day-1. Our model results are consistent with the potential for long-term survival of buried glacier ice in the hyper-arid stable upland zone of the western Dry Valleys. [ABSTRACT FROM AUTHOR]

We map polygonally patterned ground formed in sublimation tills that overlie debris-covered glaciers in Mullins Valley and central Beacon Valley, in southern Victoria Land, Antarctica, and distinguish five morphological zones. Where the Mullins Valley debris-covered glacier debouches into Beacon Valley, polygonal patterning transitions from radial (orthogonal) intersections to non-oriented (hexagonal) intersections, providing a time-series of polygon evolution within a single microclimate. We offer the following model for polygon formation and evolution in the Mullins Valley system. Near-vertical cracks that ultimately outline polygons are produced by thermal contraction in the glacier ice. Some of these cracks may initially be oriented radial to maximum surface velocities by pre-existing structural stresses and material weaknesses in the glacier ice. In areas of relatively rapid flow, polygons are oriented down-valley forming an overall fan pattern radial to maximum ice velocity. As glacier flow moves the cracks down-valley, minor variations in flow rate deform polygons, giving rise to deformed radial polygons. Non-oriented (largely hexagonal) polygons commonly form in regions of stagnant and/or near-stagnant ice. We propose that orientation and morphology of contraction-crack polygons in sublimation tills can thus be used as an indicator of rates of subsurface ice flow. [ABSTRACT FROM AUTHOR]

The time-dependent physics of ice sublimation through thin layers of till is considered, to determine whether sublimation could be sufficiently slow to permit the preservation of ice for 8 Ma in the Dry Valleys, Antarctica. This could only happen if the ice had been very thick, but other evidence (crystal size, dating of other ice-cored moraines) is not consistent with this possibility. Steady-state models suggest that sublimation is rate-controlled by vapor transport. A time-dependent model coupling vapor concentration, air pressure, temperature and ice concentration is formulated, and the resulting equations solved non-linearly. No transient coupling between vapor concentration, air temperature and pressure that substantially slows down sublimation was found in the numerical experiments. This means either that vapor transport is being slowed down by some unconsidered physical process or that the ice is much younger than 8 Ma. [ABSTRACT FROM AUTHOR]