Primary results of glaciological studies along an 1100 km transect from Zhongshan station to Dome A, East Antarctic ice sheet
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Abstract The Chinese National Antarctic Research Expedition (GHINARE) carried out three traverses from Zhongshan station to Dome A, Princess Elizabeth Land and Inaccessible Area, East Antarctic ice sheet, during the 1996/97 to 1998/99 Antarctic field seasons. The expeditions are part of the Chinese International Trans-Antarctic Scientific Expedition program. In this project, glaciological investigations of mass balance, ice temperature, ice flow, stratigraphy in snow pits and snow/firn ice cores, as well as the glaciochemical study of surface snow and shallow ice cores, have been carried out. In the 1998/99 field season, CHINARE extended the traverse route to 1128 km inland from Zhongshan station. The density profiles show that firnification over Princess Elizabeth Land and Inaccessible Area (290–1100 km along the route) is fairly slow, and the accumulation rate recovered from snow pits along the initial 460 km of the route is 4.6–21 cm (46–210 kg m–2a –1 ) water equivalent. The initial 460 km of the route can be divided into four sections based on the differences of accumulation rate. This pattern approximately coincides with the study on the Lambert Glacier basin (LGB) by Australian scientists. During the past 50 years, the trends of both air temperature and accumulation rate show a slight increase in this area, in contrast to the west side of the LGB. Data on surface accumulation rates and their spatial and temporal variability over ice-drainage areas such as the LGB are essential for precise mass-balance calculation of the whole ice sheet, and are important for driving ice-sheet models and testing atmospheric models.Keywords:
Firn
Antarctic ice sheet
Dome (geology)
Ice core
Accumulation zone
Glacier mass balance
Glacier morphology
Abstract This study uses a set of 37 firn core records over the West Antarctic Ice Sheet (WAIS) to test the performance of the twentieth century from the European Centre for Medium‐Range Weather Forecasts (ERA‐20C) reanalysis for snow accumulation and quantify temporal variability in snow accumulation since 1900. The firn cores are allocated to four geographical areas demarcated by drainage divides (i.e., Antarctic Peninsula (AP), western WAIS, central WAIS, and eastern WAIS) to calculate stacked records of regional snow accumulation. Our results show that the interannual variability in ERA‐20C precipitation minus evaporation (P − E) agrees well with the corresponding ice core snow accumulation composites in each of the four geographical regions, suggesting its skill for simulating snow accumulation changes before the modern satellite era (pre‐1979). Snow accumulation experiences significantly positive trends for the AP and eastern WAIS, a negative trend for the western WAIS, and no significant trend for the central WAIS from 1900 to 2010. The contrasting trends are associated with changes in the large‐scale moisture transport driven by a deepening of the low‐pressure systems and anomalies of sea ice in the Amundsen Sea Low region.
Firn
Ice core
Antarctic ice sheet
Peninsula
Snow field
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Long-term series of observations on the glacier of the southern slope of Elbrus manifest the change of two climatic periods in the highlands of the Caucasus. During the first one, relatively cold and snowy period of 1982–1997 with a small positive mass balance, the Garabashi Glacier accumulated a layer of 0.8 m.e. The second period (1998–2017) is characterized by rising summer air temperatures and increasing precipitation in the first decade, and catastrophic melting in 2010–2017. The mass balance of the glacier averaged −0.63 m w.e. yr−1, and in some years it reached −1.00 ÷ −1.50 m w.e. yr−1. In the last ten years, frequency of vast anticyclones covering the southern part of the European part of Russia and the North Caucasus increased. Summer temperatures in the Elbrus region rose to almost the level of the 1950s that was the hottest decade of the XX century. Duration of the summer season on the glaciers increased. Active melting resulted in elevation of the equilibrium line of the Garabashy Glacier by 200 m. In the main part of the glacier alimentation area, i.e. at heights of 3800–4000 m, the large parts of the firn area had disappeared, but open ice of the ablation zone had appeared. The former areas of the "warm" firn zone, where up to 35% of melt water retained within the 20‑meter firn thickness, were replaced by the firn-ice zone, and the ice discharge increased. The glacier alimentation is decreased, and its tongue retreats with increasing velocity. Rocks and entire lava ridges release from ice at different levels of the glacier. The inter-annual variations of the glacier mass balance are controlled by intensity of ablation. In the second period, the correlation coefficient of these values reached 0.97 compared to 0.82 in the first one. In total over 36 years of observations, reduction of the glacier mass during the second period resulted in loss of volume (0.05 km3 or 14%), area (0.51 km2 or 11.4%), and of ice layer (11.4 m).
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Glacier mass balance
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Glacier morphology
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<p>With a maximum in glaciated area below 450 m elevation (peak in the hypsometry), most Svalbard glaciers currently experience summer melt that consistently exceeds winter snowfall. Consequently, these glaciers can only exist through efficient meltwater refreezing in their porous firn layers. Before the mid-1980s, refreezing retained 54% of the meltwater in firn above 350 m. In 1985-2018, atmospheric warming migrated the firn line upward by 100 m, close to the hypsometry peak, which triggered a rapid ablation zone expansion (+62%). The resulting melt increase in the accumulation zones reduced the firn refreezing capacity by 25%, enhancing runoff at all elevations. In this dry climate, the loss of refreezing capacity is quasipermanent: a temporary return to pre-1985 climate conditions between 2005 and 2012 could not recover the meltwater buffer mechanism, causing strongly amplified mass loss in subsequent warm years (e.g. 2013), when ablation zones extend beyond the hypsometry peak.</p>
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Meltwater
Ablation zone
Accumulation zone
Glacier mass balance
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Elevation (ballistics)
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In recent decades, several large ice shelves in the Antarctic Peninsula region have experienced significant ice loss, likely driven by a combination of oceanic, atmospheric and hydrological processes. All three areas need further research, however, in the case of the role of liquid water the first concern is to address the paucity of field measurements. Despite this shortage of field observations, several authors have proposed the existence of firn aquifers on Antarctic ice shelves, however little is known about their distribution, formation, extension and role in ice shelf mechanics. In this study we present the discovery of saturated firn at three drill sites on the Müller Ice Shelf (67°14′ S; 66°52′ W), which leads us to conclude that either a large contiguous or several disconnected smaller firn aquifers exist on this ice shelf. From the stratigraphic analysis of three short firn cores extracted during February 2019 we describe a new classification system to identify the structures and morphological signatures of refrozen meltwater, identify evidence of superficial meltwater percolation, and use this information to propose a conceptual model of firn aquifer development on the Müller Ice Shelf. The detailed stratigraphic analysis of the sampled cores will provide an invaluable baseline for modelling studies.
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Iceberg
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Vertical distributions of 210Pb in surface firn were obtained at five locations in east Dronning Maud Land, Antarctica. The distributions obtained in the inland high-plateau region are well described by the theoretical radioactive decay curve. On the other hand, the distributions obtained in the katabatic wind region have significant fluctuations including intervals where higher activity is found below layers with lower activity. We examined the relationship between the fluctuation of the 210Pb profile and the temporal variation of the snow accumulation rate obtained by the snow stake method, and found a clear negative correlation between them. This result suggests that the fluctuation of the 210Pb profile in the firn layer is closely related to the environment in the ice sheet surface, i.e. the extent of erosion—redistribution of snow. The measurement of the 210Pb distribution in the ice sheet will be useful as an indicator of the surface stability in the Antarctic ice sheet.
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Antarctic ice sheet
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Based on the measured surface temperature data on the Qiumianleiketage Glacier in the Kunlun Mountains,Tibetan Plateau,in the spring of 2013,it was found that:1)the glacier surface(covered by firn)temperature was lower in the clear day than in the cloudy or overcast day,which might be caused by that some parts of energy absorbed by the glacier surface were consumed for the firn surface melting rather than for the firn surface temperature increasing in the clear day;2)the glacier surface temperature decreased with increasing altitude with a lapse rate of 0.58 ℃·(100m)-1 in the clear day,which is slightly lower than the local free-air lapse rate;3)the depth of firn on the glacier surface could exert an important influence on the surface temperature in the clear day,and there was a significant positive relationship between them,which showed that the firn surface temperature increased by 0.46℃ while the depth of firn increased by 10cm.By comprehensive analysis of the surface temperature data from the glaciers over the Tibetan Plateau,it was revealed that the diurnal amplitude of glacier surface temperature was small,only about several degrees,under the condition that the melting occurred on the glacier surface.
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Accumulation zone
Glacier mass balance
Overcast
Glacier ice accumulation
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Firn is the transitional product between fresh snow and glacier ice and acts as a boundary between the atmosphere and the glacier ice of the Antarctic Ice Sheet (AIS). Spatiotemporal variations in firn layer characteristics are therefore important to consider when assessing the mass balance of the AIS. In this thesis, a firn densification model, forced with a realistic climate, is used to examine contemporary (1979-2012) and future (2000-2200) variations in the Antarctic firn layer. Currently, 99% of the AIS is covered with a firn layer of 50-150 m thick. The thickest firn layers occur in the cold interior of the AIS, while thinner firn layers appear along the coastal margins, where regular melt occurs. On the remaining 1-2% of the AIS no firn layer exist; a so-called blue-ice area. Here, annual ablation, by either sublimation or melt, is larger than the annual accumulation, resulting in no long-term firn layer. The presence of a blue-ice area depends on a favorable combination of 1) ice velocity, 2) net surface ablation and 3) the mass of the existing firn layer. Next to the spatial variations, also temporal variations in firn layer characteristics exist. Due to the seasonal cycle in temperature and accumulation, the air content of the Antarctic firn layer grows in winter and shrinks in summer. As a consequence, the surface elevation of the AIS also shows cyclic behavior with a seasonal amplitude of 2.6 cm. In order to simulate the reaction of the current Antarctic firn layer on a warmer and wetter future climate, four simulations with the regional atmospheric climate model RACMO2 are performed. By forcing RACMO2 with two different global climate models (HAdCM3 and ECHAM5) and two different emission scenarios (A1B and E1), the possible spread in future climate is mimicked. The temperature increase over the AIS is similar to the global average; +1.8-3.0 K in 2100 and +2.4-5.3 K in 2200. This warmer climate leads to increased accumulation, as warmer air has a larger water vapor holding capacity. This accumulation increase outweighs the increases in both sublimation and melt, leading to a positive surface mass balance sensitivity: +98 Gt yr-1 K-1. In combination with the simulated temperature increase, this would result to a sea level drop of 73-163 mm by 2200. This is however without taking any ice dynamical response into account. Due to the future increase in snowfall, the air content of the Antarctic firn layer will increase. Roughly half of this effect is counteracted by both enhanced firn densification and a faster firn-to-ice transition at the bottom of the firn layer. Along the coast, firn air content will decrease significantly due to increasing melt. On several ice shelves at the Antarctic Peninsula, this will lead to depleted firn layers and enhanced runoff of meltwater. Averaged over the ice sheet, this decrease in firn air content is however small, resulting in an increase of the total AIS air content with 120-150 km3 yr-1, or +2.1 cm surface elevation per year.
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Ablation zone
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1. Introduction ( a ) The transition of firn into glacier ice; glacier structure Glaciers are divided into two main parts: the accumulation area, firn region or névé where the annual accumulation in the form of snow exceeds the loss by melting, evaporation and wind erosion, and the ablation area or glacier tongue. The dividing line between the two regions is called the Firn Line. Granular, compacted snow called firn covers the accumulation area. Its crystals are rarely larger than 2 mm. in diameter and are mixed with a considerable volume of air, so that the specific gravity is much lower than that of ice. The surface of the tongue consists of blue or glassy ice, more or less covered with rock debris; here the diameter of the ice crystals varies between 1 and 10 cm. or even more; the specific gravity of the ice is never far below 0.90. In summer the tongue has a bluish or grey appearance, while the firn region retains its white or whitish hue.
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Accumulation zone
Glacier ice accumulation
Glacier morphology
Dome (geology)
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Abstract. Observed changes in the surface elevation of the Greenland Ice Sheet are caused by ice dynamics, basal elevation change, basal melt, surface mass balance (SMB) variability, and by compaction of the overlying firn. The last two contributions are quantified here using a firn model that includes compaction, meltwater percolation, and refreezing. The model is forced with surface mass fluxes and temperature from a regional climate model for the period 1960–2014. The model results agree with observations of surface density, density profiles from 62 firn cores, and altimetric observations from regions where ice-dynamical surface height changes are likely small. In areas with strong surface melt, the firn model overestimates density. We find that the firn layer in the high interior is generally thickening slowly (1–5 cm yr−1). In the percolation and ablation areas, firn and SMB processes account for a surface elevation lowering of up to 20–50 cm yr−1. Most of this firn-induced marginal thinning is caused by an increase in melt since the mid-1990s and partly compensated by an increase in the accumulation of fresh snow around most of the ice sheet. The total firn and ice volume change between 1980 and 2014 is estimated at −3295 ± 1030 km3 due to firn and SMB changes, corresponding to an ice-sheet average thinning of 1.96 ± 0.61 m. Most of this volume decrease occurred after 1995. The computed changes in surface elevation can be used to partition altimetrically observed volume change into surface mass balance and ice-dynamically related mass changes.
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Greenland ice sheet
Accumulation zone
Meltwater
Glacier mass balance
Ice core
Elevation (ballistics)
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