Ice thickness,internal layers,and surface and subglacial topography in the vicinity of Chinese Antarctic Taishan station in Princess Elizabeth Land,East Antarctica

We present the results of two ground-based radio-echo-sounding (RES) and GPS surveys performed in the vicinity of new Chinese Taishan station, Princess Elizabeth Land, East Antarctica, obtained in two austral summers during CHINARE 21 (2004/2005) and CHINARE 29 (2012/2013). The radar surveys measured ice thickness and internal layers using 60- and 150-MHz radar systems, and GPS measurements showed smooth surface slopes around the station with altitudes of 2607–2636 m above sea level (a.s.l.). Radar profiles indicate an average ice thickness of 1900 m, with a maximum of 1949 m and a minimum of 1856 m, within a square area measuring approximately 2 km × 2 km in the vicinity of the station. The ice thickness beneath the station site is 1870 m. The subglacial landscape beneath the station is quiet sharp and ranges from 662 to 770 m a.s.l., revealing part of a mountainous topography. The ice volume in the grid is estimated to be 7.6 km³. Along a 60-MHz radar profile with a length of 17.6 km at the region covering the station site, some disturbed internal layers are identified and traced; the geometry of internal layers within the englacial stratigraphy may imply a complex depositional process in the area.     

Relations between basal condition,subglacial hydrological networks and geothermal flux in Antarctica

When modelling the Antarctic ice sheet, the velocity of the ice flow is linked to its temperature. Depending on the thermal rate, the flow rate may vary between deformation and sliding. In this study, we focus on the geothermal flux because it is the least well-known component of the heat equation, and because it constrains the temperature at the bottom of the ice sheet. We used available geological data to build a map of the geothermal flux, which was found to increase from 51 mW/m² in East Antarctica to 68 mW/m² in West Antarctica. These values were integrated in the computation of a basal temperature map. The available map of hydrological networks clearly shows more melted areas in West Antarctica than in the earlier results. So we suggest that the model should be forced with higher geothermal flux values, over 85 mW/m² in this sector. This increase is in good agreement with published results which found a geothermal flux three times higher in West Antarctica. Finally, we computed the bottom melt rate over the ice sheet area which has a mean value of 3.5 mm/yr resulting in a lost of melted ice equal to 1% of the total mass balance.     

Preliminary results of the close-off depth and the stable isotopic records along a 109.91 m ice core from Dome A,Antarctica

A 109.91 m ice core was recovered from Dome A (or Dome Argus), the highest ice feature in Antarctica, during the 2004/05 austral summer by the 21st Chinese National Antarctic Research Expedition (CHINARE-21). Both methane profile along the core and firn densification model calculation suggest that the close-off depth is at about 102.0 m with an ice age about 4200 a. Stable isotopes (δ18O and δD) of the chips samples produced during each run of ice core drilling at Dome A, together with those of the other co...     

Deglacial hypsometry of Antarctica

A new and more detailed analysis of the hypsometry of the Antarctic continent, based upon 1° digital data on ice thickness and surface and subglacial elevations, shows that Antarctica, even when deglaciated according to a simple Airy-isostatic model, is an unusual continent. It is the only one with a markedly bimodal hypsometric curve, and separation of the two modes shows that they are the single modes of West Antarctica (at ?450 m a.s.1.) and East Antarctica (at 950 m a.s.1.) respectively; the two parts of the continent are probably distinct tectonic entities. The modal height of East Antarctica is 700 m higher than that of the global ensemble of continents, suggesting that hotspot epeirogeny or a less well-known mechanism has affected its recent history. The age of this modal-height anomaly has important tectonic and especially climatic implications: it is equivalent to a 4–6°C cooling of the continental surface. The area of dry land after deglaciation is 10.5 × 10⁶ km²; the volume of ice in Antarctica is estimated at 26.9 × 10⁶ km³, and of ice in the Northern Hemisphere at 2.5 × 10⁶ km³; these figures lead to a eustatic sea-level equivalent for present-day glacier ice of 68 m or somewhat less.     

Radio‐echo layering in West Antarctica: a spreadsheet dataset

Of the various information recovered from radio‐echo sounding (RES) of polar ice sheets, internal layering is currently under‐utilized by glaciologists, due in part to a lack of available data. Here, RES layering of the West Antarctic Ice Sheet, from the 1970s RES survey of approximately 70 per cent of this ice mass, is made available in a series of spreadsheets. Three types of internal layers are evident in the dataset. The first is continuous layers that have a stratigraphic appearance and can often be traced easily for hundreds of kilometres. The second is buckled layering, which also resembles stratigraphy and can sometimes be traced over tens of kilometres (although layer identification can often be difficult). The roughness of these layers is often greater than the bed at the same wavelength. The third is highly distorted or absent layering, which is not possible to trace laterally. Despite debate concerning the origin of RES layers, they are thought by most glaciologists to represent isochronous surfaces. The pattern of internal layering is potentially of importance to glaciologists for three reasons. (1) The position of undeformed layers below the ice surface is a function of accumulation rate, ice flow and basal melting conditions. Numerical modelling (including new ‘data assimilation’ techniques) could be used to discriminate between these processes, so revealing important information about the ice sheet and its environment. (2) Buckled layers are deformed by ice flow process, and so their occurrence can be related to the flow dynamics of the ice sheet. (3) Very buckled layers are often associated with ice stream flow, which allows their location to mark the positions of past and present fast‐flowing ice. Copyright © 2005 John Wiley & Sons, Ltd.     

冰川均衡调整对南极冰质量平衡监测的影响及其不确定性

本文研究了新的全球冰川均衡调整(GIA)模型对南极冰盖质量平衡监测的影响,考虑现有冰川负荷模型和地幔黏滞度模型的差异,完整评估了结果的不确定性,最后结合GRACE和卫星测高的结果进行了对比分析.结果表明,GIA对GRACE监测的等效水柱变化有重大影响,较大的GIA影响出现在西南极,沿罗斯冰架-卡姆布冰流-罗尼冰架-南极...     

AntarcticaLC2000: The new Antarctic land cover database for the year 2000

Antarctica plays a key role in global energy balance and sea level change. It has been conventionally viewed as a whole ice body with high albedo in General Circulation Models or Regional Climate Models and the differences of land cover has usually been overlooked. Land cover in Antarctica is one of the most important drivers of changes in the Earth system. Detailed land cover information over the Antarctic region is necessary as spatial resolution improves in land process models. However, there is a lack of complete Antarctic land cover dataset derived from a consistent data source. To fill this data gap, we have produced a database named Antarctic Land Cover Database for the Year 2000 (AntarcticaLC2000) using Landsat Enhanced Thematic Mapper Plus (ETM+) data acquired around 2000 and Moderate Resolution Imaging Spectrometer (MODIS) images acquired in the austral summer of 2003/2004 according to the criteria for the 1:100000-scale. Three land cover types were included in this map, separately, ice-free rocks, blue ice, and snow/firn. This classification legend was determined based on a review of the land cover systems in Antarctica (LCCSA) and an analysis of different land surface types and the potential of satellite data. Image classification was conducted through a combined usage of computer-aided and manual interpretation methods. A total of 4067 validation sample units were collected through visual interpretation in a stratified random sampling manner. An overall accuracy of 92.3% and the Kappa coefficient of 0.836 were achieved. Results show that the areas and percentages of ice-free rocks, blue ice, and snow/firn are 73268.81 km² (0.537%), 225937.26 km² (1.656%), and 13345460.41 km² (97.807%), respectively. The comparisons with other different data proved a higher accuracy of our product and a more advantageous data quality. These indicate that AntarcticaLC2000, the new land cover dataset for Antarctica entirely derived from satellite data, is a reliable product for a broad spectrum of applications.     

基于GRACE RL06数据监测和分析南极冰盖27个流域质量变化

本文基于CSR最新公布的GRACE RL06版本数据,采用Slepian空域反演法估算了南极冰盖27个流域的质量变化.Slepian空域反演法结合了Slepian空间谱集中法和空域反演法的技术优势,能够有效降低GRACE在小区域反演时信号出现的严重泄漏和衰减,进而精确获得南极冰盖在每个流域的质量变化.相对于GRACE RL05版本数据,RL06在条带误差的控制上要更加优化,获得的南极冰盖质量变化时间序列也更加平滑,但在趋势估算上差别并不明显(小于10Gt/a).本文的估算结果显示:在2002年4月至2016年8月期间,整个南极冰盖质量变化速率为-118.6±16.3Gt/a,其中西南极为-142.4±10.5Gt/a,南极半岛为-29.2±2.1Gt/a,东南极则为52.9±8.6Gt/a.南极冰盖损失最大的区域集中在西南极Amundsen Sea Embayment(流域20-23),该地区质量变化速率为-203.5±4.1Gt/a,其次为南极半岛(流域24-27)以及东南极Victoria-Wilkes Land (流域13-15),质量变化速率分别为-29.2±2.1Gt/a和-19.0±4.7Gt/a,其中Amundsen Sea Embayment和南极半岛南部两个地区的冰排放呈现加速状态.南极冰盖质量显著增加的区域主要有西南极的Ellsworth Land(流域1)和Siple Coast(流域18和19)以及东南极的Coats-Queen Maud-Enderby Land (流域3-8),三个地区质量变化速率分别为17.2±2.4Gt/a、43.9±1.9Gt/a和62.7±3.8Gt/a,质量增加大多来自降雪累积,比如:Coats-Queen Maud-Enderby Land在2009年和2011年发生的大规模降雪事件,但也有来自冰川的增厚,如:Siple Coast地区Kamb冰流的持续加厚.此外,对GRACE估算的南极冰盖质量变化年际信号进行初步分析发现,GRACE年际信号与气候模型估算的冰盖表面质量平衡年际信号存在显著的线性相关关系,但与主要影响南极气候年际变化的气候事件之间却不存在线性相关关系,这说明南极冰盖质量变化的年际信号主要受冰盖表面质量平衡的支配,而气候事件对冰盖表面质量平衡的影响可能是复杂的非线性耦合过程.     

利用ICESat数据解算南极冰盖冰雪质量变化

南极冰盖冰雪质量变化反映了全球气候变化,并且直接影响着全球海平面变化.ICESat测高卫星的主要任务之一就是要确定南北两极冰盖的质量变化情况并评估其对全球海平面变化的影响.本文利用2003年10月至2008年12月的ICESat测高数据,针对南极DEM分辨率有限的特殊性,通过求解坡度改正值,解决重复轨道地面脚点不重合的问题,计算了南极大陆(86°S以北区域,后文所述南极冰盖均不包括86°S以南区域)在这5年里的冰雪质量变化情况,得到东南极冰盖的质量变化为-18±20Gt/a,西南极-26±6Gt/a,南极冰盖的冰雪质量变化为-44±21Gt/a,对全球海平面上升的影响约为0.12mm·a~(-1).解算结果表明,南极冰盖质量亏损主要集中在西南极阿蒙森海岸附近冰川以及东南极波因塞特角区域.     

多极化冰雷达所揭示的DOME A区域冰盖内部冰晶组构特征

The ice exceeding one million years old has significant meaning for verifying and interpreting the middle Pleistocene transition （MPT） and the relationship between greenhouse gas and climate change. The region near Dome A in Antarctica satisfies the conditions for obtaining million-years-old ice since it has low temperatures and low accumulation rates. We analyze the corresponding relation between radar wave features and the crystal orientation fabric （COF） types based on the results of multi-polarization plane radio echo sounding （RES）. The results show that, even in the summit of the ice sheet, the COF type is not perfect, but is an elongated single-pole COF. Principal-axis-orientation differences of the COF among the different periods exist and reveal that the ice flow orientations are not constant but deviate clockwise with the increasing depth. This may be related to the adjacent basal valley or both height and position changes of the summit during the glacial-interglacial periods.     

Can in-situ cosmogenic 14C be used to assess the influence of clast recycling on exposure dating of ice retreat in Antarctica?

Cosmogenic nuclide exposure dating of glacial clasts is becoming a common and robust method for reconstructing the history of glaciers and ice sheets. In Antarctica, however, many samples exhibit cosmogenic nuclide ‘inheritance’ as a result of sediment recycling and exposure to cosmic radiation during previous ice free periods. In-situ cosmogenic ¹⁴C, in combination with longer lived nuclides such as ¹⁰Be, can be used to detect inheritance because the relatively short half-life of ¹⁴C means that in-situ ¹⁴C acquired in exposure during previous interglacials decays away while the sample locality is covered by ice during the subsequent glacial. Measurements of in-situ ¹⁴C in clasts from the last deglaciation of the Framnes Mountains in East Antarctica provide deglaciation ages that are concordant with existing ²⁶Al and ¹⁰Be ages, suggesting that in this area, the younger population of erratics contain limited inheritance.     

Dissolved major ions,Sr and 87Sr/86Sr of coastal lakes from Larsemann hills,East Antarctica: Solute sources and chemical weathering in a polar environment

Dissolved major ions, Sr concentrations and ⁸⁷Sr/⁸⁶Sr ratios of 10 coastal lakes from the Larsemann Hills, East Antarctica have been studied to constrain their solute sources, transport and glacial weathering patterns in their catchments. In absence of perennial river/streams, lakes serve as only reliable archive to study land surface processes in these low-temperature regions. The lake water chemistry is mostly Na-Cl type and it does not show any significant depth variations. Sr isotope compositions of these lakes vary from 0.7110 to 0.7211 with an average value of 0.7145, which is higher than modern seawater value. In addition to oceanic sources, major ions and Sr isotopic data show appreciable amount of solute supply from chemical weathering of silicate rocks in lake catchments and dissolution of Ca-Mg rich salts produced during the freezing of seawaters. The role of sulphide oxidation and carbonate weathering are found to be minimal on lake hydro-chemistry in this part of Antarctica. Inverse model calculations using this chemical dataset provide first-order estimates of dissolved cations and Sr; they are mostly derived from oceanic (seawater + snow) sources (cations approximately 76%) and (Sr approximately 92%) with minimal supplies from weathering of silicates (cations approximately 15%); (Sr approximately 2%) and Ca-rich minerals (cations approximately 9%); (Sr approximately 7%). The silicate weathering rate and its corresponding atmospheric CO₂ consumption rate estimates for Scandrett lake catchment (3.6 ± 0.3 tons/km²/year and 0.5 × 10⁵ moles/km²/year), are lower than that of reported values for the average global river basins (5.4 tons/km²/year and 0.9 × 10⁵ tons/km²/year) respectively. The present study provides a comprehensive report of chemical weathering intensity and its role in atmospheric CO₂ consumption in low-temperature pristine environment of Antarctica. These estimates underscore the importance of Antarctica weathering on atmospheric CO₂ budget, particularly during the past warmer periods when the large area was exposed and available for intense chemical weathering.     

High-accuracy topographical information extraction based on fusion of ASTER stereo-data and ICESat/GLAS data in Antarctica

In order to better support Antarctic inland ice sheet expedition from Zhongshan Station to Dome A, the topographic data are necessary. At present, although the entire Antarctic DEM provided by RAMP (Radarsat Antarctic Mapping Project) was estimated at the highest horizontal (spatial) resolution of about 200 m, the real horizontal resolution of the DEM varies from place to place depending on the density and scale of the original source data. For ice shelves and the inland ice sheet, the horizontal resolution is about 5 km; the vertical accuracy is estimated to be ±50 m in interior East Antarctic ice sheet and away from the mountain ranges. Therefore, more accurate topographic data are unavailable in Antarctica. In order to meet the requirements of high-accuracy topographic information for further researches, this paper mainly addresses a fusion study of ASTER stereo pairs and ICESat/GLAS altimetry data for extraction of high-accuracy DEM in East Antarctica, based on the high horizontal resolution (15 m) of ASTER and vertical accuracy (13.8 cm) of ICESat/GLAS. First, some altimetry data were selected as vertical control points to reduce errors of image correlation matching during the extraction of ASTER-based DEM. Second, ice sheet altimetry data derived from ICESat were used to generate DEM ranging from 75° to 81°S because existing ASTER data do not cover this area and high density of the coverage of ICESat altimetry data. Finally, the DEM in coverage of the expedition route was produced. The analysis of result reveals that the DEM accuracy is improved significantly. The absolute vertical accuracy of DEM is higher than 15 m in some cases and higher than 30 m for all the areas along the expedition route except from the 009-001 scene; the interior accuracy is higher than 15 m and higher than 7 m in some cases. It can meet the requirements of topographic map at 1:50000 scale, which is an economic and advantageous method to produce the topographic products. Supported by National Natural Science Foundation (Grant No. 40606002), Surveying and Mapping in Chinese Antarctic Expedition Area (Grant No. 1469990711109-1), National Key Technology R & D Program (Grant No. 2006BAD18B01), and GLA12 dataset of ICESat/GLAS in National Snow and Ice Data Center (NSIDC)     

Greenland and Antarctica Ice Sheet Mass Changes and Effects on Global Sea Level

Thirteen years of GRACE data provide an excellent picture of the current mass changes of Greenland and Antarctica, with mass loss in the GRACE period 2002–2015 amounting to 265 ± 25 GT/year for Greenland (including peripheral ice caps), and 95 ± 50 GT/year for Antarctica, corresponding to 0.72 and 0.26 mm/year average global sea level change. A significant acceleration in mass loss rate is found, especially for Antarctica, while Greenland mass loss, after a corresponding acceleration period, and a record mass loss in the summer of 2012, has seen a slight decrease in short-term mass loss trend. The yearly mass balance estimates, based on point mass inversion methods, have relatively large errors, both due to uncertainties in the glacial isostatic adjustment processes, especially for Antarctica, leakage from unmodelled ocean mass changes, and (for Greenland) difficulties in separating mass signals from the Greenland ice sheet and the adjacent Canadian ice caps. The limited resolution of GRACE affects the uncertainty of total mass loss to a smaller degree; we illustrate the “real” sources of mass changes by including satellite altimetry elevation change results in a joint inversion with GRACE, showing that mass change occurs primarily associated with major outlet glaciers, as well as a narrow coastal band. For Antarctica, the primary changes are associated with the major outlet glaciers in West Antarctica (Pine Island and Thwaites Glacier systems), as well as on the Antarctic Peninsula, where major glacier accelerations have been observed after the 2002 collapse of the Larsen B Ice Shelf.     

DMSP and DMS in coastal fast ice and under-ice water of Lützow-Holm Bay, eastern Antarctica

The combined concentration of total dimethylsulfoniopropionate and dimethylsulfide (DMSP+DMS) were measured in Antarctic fast ice on the coast of Lützow-Holm Bay, eastern Antarctica. High bulk-ice DMSP+DMS and chlorophyll a concentrations were found at the bottom of the sea ice, and these concentrations were higher than those in the under-ice water. The bulk-ice DMSP+DMS and chlorophyll a concentrations were highly correlated (r²=0.68, P<0.001), suggesting that the high bulk-ice DMSP+DMS concentrations were caused mainly by the presence of algae assemblages in the ice. The calculated brine DMSP+DMS concentrations were as high as 1100 nM in the bottom ice layer, and the vertical profile patterns of brine DMSP+DMS concentrations were almost the same as for the bulk ice, mainly because of the small amount of variability in the vertical brine volume fraction. DMSP+DMS and chlorophyll a concentrations in the under-ice water increased, whereas the salinity of the under-ice water decreased, during the sampling period. These results reflect the supply of freshwater containing high levels of DMSP+DMS to the water just under the ice as the ice melted. These results suggest that sea-ice melting could be important to sulfur cycling in coastal ice-covered regions of the polar oceans.     

Evaluation of the glacial isostatic adjustment (GIA) models for Antarctica based on GPS vertical velocities

Due to the scarcity of data, modeling the glacial isostatic adjustment(GIA) for Antarctica is more difficult than it is for the ancient ice sheet area in North America and Northern Europe. Large uncertainties are observed in existing GIA models for Antarctica. Modern space-based geodetic measurements provide checks and constraints for GIA models. The present-day uplift velocities of global positioning system(GPS) stations at 73 stations in Antarctica and adjacent regions from 1996 to 2014 have been estimated using GAMIT/GLOBK version 10.5 with a colored noise model. To easily analyze the effect of difference sources on the vertical velocities, and for easy comparison with both GIA model predictions and GPS results from Argus et al.(2014) and Thomas et al.(2011), seven sub-regions are divided. They are the northern Antarctic Peninsula, the Filchner-Ronne Ice Shelf, the Amundsen Sea coast, the Ross Ice Shelf, Mount Erebus, inland Southwest Antarctica and the East Antarctic coast,respectively. The results show that the fast uplift in the north Antarctic Peninsula and Pine Island Bay regions may be caused by the elastic response to snow and ice mass loss. The fast subsidence near Mount Erebus may be related to the activity of a magma body. The uplift or subsidence near the East Antarctic coast is very slow while the uplift for the rest regions is mainly caused by GIA. By analyzing the correlation and the associated weighted root mean square(WRMS) between the GIA predictions and the GPS velocities, we found that the ICE-6G_C(VM5a) model and the Geruo 13 model show the most consistency with our GPS results, while the W12a and IJ05_R2 series models show poor consistency with our GPS results. Although improved greatly in recent years, the GIA modeling in Antarctica still lags behind the modeling of the North American. Some GPS stations, for example the Bennett Nunatak station(BENN), have observed large discrepancies between GIA predictions and GPS velocities.Because of the large uncertainties in calculating elastic responses due to the significant variations of ice and snow loads, the GPS velocities still cannot be used as a precise constraint on GIA models.     

Degradation of glacial deposits quantified with cosmogenic nuclides,Quartermain Mountains,Antarctica

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^?1. 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 10³ to 10⁵ years. This paper presents results from using the concentration of cosmogenic nuclides beryllium‐10 (¹⁰Be) and aluminum‐26 (²⁶Al) 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^?1 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^?1. 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.     

Large-Scale Surface Mass Balance of Ice Sheets from a Comprehensive Atmospheric Model

The surface mass balance for Greenland and Antarctica has been calculated using model data from an AMIP-type experiment for the period 1979?C2001 using the ECHAM5 spectral transform model at different triangular truncations. There is a significant reduction in the calculated ablation for the highest model resolution, T319 with an equivalent grid distance of ca 40?km. As a consequence the T319 model has a positive surface mass balance for both ice sheets during the period. For Greenland, the models at lower resolution, T106 and T63, on the other hand, have a much stronger ablation leading to a negative surface mass balance. Calculations have also been undertaken for a climate change experiment using the IPCC scenario A1B, with a T213 resolution (corresponding to a grid distance of some 60?km) and comparing two 30-year periods from the end of the twentieth century and the end of the twenty-first century, respectively. For Greenland there is change of 495?km³/year, going from a positive to a negative surface mass balance corresponding to a sea level rise of 1.4?mm/year. For Antarctica there is an increase in the positive surface mass balance of 285?km³/year corresponding to a sea level fall by 0.8?mm/year. The surface mass balance changes of the two ice sheets lead to a sea level rise of 7?cm at the end of this century compared to end of the twentieth century. Other possible mass losses such as due to changes in the calving of icebergs are not considered. It appears that such changes must increase significantly, and several times more than the surface mass balance changes, if the ice sheets are to make a major contribution to sea level rise this century. The model calculations indicate large inter-annual variations in all relevant parameters making it impossible to identify robust trends from the examined periods at the end of the twentieth century. The calculated inter-annual variations are similar in magnitude to observations. The 30-year trend in SMB at the end of the twenty-first century is significant. The increase in precipitation on the ice sheets follows closely the Clausius-Clapeyron relation and is the main reason for the increase in the surface mass balance of Antarctica. On Greenland precipitation in the form of snow is gradually starting to decrease and cannot compensate for the increase in ablation. Another factor is the proportionally higher temperature increase on Greenland leading to a larger ablation. It follows that a modest increase in temperature will not be sufficient to compensate for the increase in accumulation, but this will change when temperature increases go beyond any critical limit. Calculations show that such a limit for Greenland might well be passed during this century. For Antarctica this will take much longer and probably well into following centuries.     

Thermal, pressure and wind fields at ground level in the area of the Italian base at Terra Nova Bay, Victoria Land, Antarctica, as observed by a network of automatic weather stations

Ground temperature, pressure and wind speed monthly averages in the area of the Italian Station at Terra Nova Bay, Antarctica, were analyzed for the period 1987–1991 by means of a network of nine AWS (automatic weather stations). Spatial configurations of temperature show a well-defined, relatively warm island in the area of Terra Nova Bay, between Drygalsky and Campbell ice tongues, throughout the year. A second warm island is present to the north along the coast, between Aviator and Mariner ice tongues, for most of the year. From February to March a rapid drop in temperature is observed at all stations. A strong thermal gradient develops during February, March, April and October, November, December, between the coastal region and inner highlands. The baric configuration follows the elevation of the area. Annual average pressure and temperature as functions of stations altitude show linear trends. Severe katabatic wind episodes are recorded at all stations, with wind speed exceeding 25 ms^–1 and direction following the orographic features of the inner areas. Co-occurrences of these episodes were observed for stations located along stream lines of cold air drainage. The autocorrelation function of maximum wind speed time series shows wind persistence of 2–3 days and wind periodicity of about one week.     

Ice storms,tree throw,and hillslope sediment transport in northern hardwood forests

In December 2008, 694 trees uprooted within a 108 ha (1·08 km²) watershed in central Massachusetts due to a severe ice storm, resulting in the displacement of ~1300 m³ of root material, unconsolidated sediment, and fractured bedrock. Overall, we find that uprooting and tree throw is often grouped in clusters and cascades; conifers displace more material than deciduous trees; areas with abundant mature hemlock and steep slopes are more susceptible to tree throw, with clusters as dense as 125 per hectare; and failure is predominantly downhill, suggesting that ice storms promote efficient downslope hillslope sediment transport in northern hardwood forests. Combining the recurrence interval of severe storms in New England (20–75 years) with the forest response presented here, we calculate a sediment transport rate of 2–5 × 10^?5 m³ m^?1 a^?1 averaged over the entire watershed. Forest susceptibility to tree throw differed based on location in the watershed; some areas experienced up to ~30× higher than average sediment transport rates, while others experienced no tree throw. Two severe storms following the 2008 ice storm (hurricane in 2011; snow storm in October 2012) did not result in significant tree throw within the study area, highlighting that the coupling of storm severity and forest susceptibility controls the amount of tree throw during a given forest disturbance. In addition to recent tree throw from the 2008 ice storm, widespread pit and mound microtopography in the study area indicates that tree throw is a recurrent process in this landscape. Two factors emerge that will influence future ice storms related hillslope sediment transport in the steep forested hillslopes of New England: regional climate gradients and changing climate determine the size, intensity and recurrence of ice storms; forest management practices and health control the tree age and type. Copyright © 2015 John Wiley & Sons, Ltd.