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The areal outflow of ice through Fram Strait during the period 1953–1984 is estimated on a monthly basis from the geostrophic wind and the ice concentration. Summer ice coverage in various sectors of the Arctic is then compared with the computed outflow through Fram Strait in various antecedent periods. Lag correlations indicate that interannual variations of summer ice severity in the Pacific side of the Arctic Basin are consistent with fluctuations of Fram Strait outflow during the previous 3–9 months. The findlings suggest that above-normal outflow of multiyear ice during the winter/spring months may precondition the large-scale pack ice to respond more directly to offshore flow events during the ensuing months.The areas of highest correlation with Fram Strait outflow undergo a pronounced shift in the early 1970's. Coincident changes in the large-scale circulation pattern imply that the source region of the Transpolar Drift Stream shifted westward from the Alaskan to the Siberian waters during this period. 相似文献
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In this paper the effects of four different rheologies on the evolution of a large-scale sea ice pack are determined and compared. Two rheologies are of viscous-plastic form, and two are viscous fluid relations. The initial pack domain is rectangular, and the motion is driven by wind stress and resisted by ocean drag. Two adjacent edges are rigid shore boundaries, and the other two are free boundaries at open water which move during the pack motion, so that the pack domain changes in time. Two different forms of boundary conditions at the rigid shore edges are considered, which also influence the evolution. The governing equations are solved numerically using a finite-element method, and, unlike previous numerical treatments, no artificial viscosity is incorporated to stabilise the algorithm near interfaces between converging and diverging flow. Instability arises when any tensile stress is abruptly cut-off when diverging flow is initiated, and an alternative view is offered. © 1998 John Wiley & Sons, Ltd. 相似文献
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J. Wang J. Sui P. Chen 《International Journal of Environmental Science and Technology》2009,6(1):1-12
In this paper, the k-? two-equation turbulence model has been used to simulate ice accumulation under ice cover along a river bend. A 2D depth-averaged numerical model has been developed in a nonorthogonal coordinate system with nonstaggered curvilinear grids. In this model, the contravariant velocity has been treated as an independent variable. To avoid the pressure oscillation in the nonstaggered grids, the momentum interpolation has been introduced to interpolate variables at the interface. The discretization equations have been solved by using pressure correction algorithms. An equation has been developed for describing the deformation of ice jam bottom. The thickness distribution of ice accumulation (ice jam) along the bend has been simulated. The developed model has been applied to the experimental studies under different conditions carried out at the Hefei University of Technology. Results indicate that all simulated thickness of ice accumulation agrees reasonably well with the measured thickness of ice accumulation in laboratory. 相似文献
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A method has been developed to determine ice pack rigidity and mobility using observed ice motion. Using this method, one may determine how solidly the ice pack is frozen in near real-time. In addition, spatial and temporal variations in the freezing and thawing of the ice pack can be studied. Various degrees of ice rigidity were considered using remotely-sensed ice motion off the N coast of Alaska during 1975 and 1979. Summer-time ice rigidities were detected first in late June 1975 and lasted through September 1975. However, in 1979 considerably higher rigidities were found in August while summer-like rigidities were detected into late November. Analyses of atmospheric pressure distributions suggest that less mechanical breakup occurred in the summer of 1979, resulting in the greater rigidities during August of that year. In addition, minimum ice coverage was 21% less in the Beaufort Sea in 1979 than in 1975. The result was a relatively large percent of thinner ice for November of 1979 than for 1975, the likely cause of the less rigid conditions detected during the fall of 1979.Nomenclature D
deviation in height (m) of a pressure level from the standard atmosphere (Huschke 1959).
- eT
time lag (h) at which the autocorrelation of ice speed drops to e–1
- SL
the large-scale disturbance or longwave component of a scalar field; in this study, the 500 mb circulation (Holl 1963).
- U
mean ice speed over a given time interval
- V
variance of ice speed over a given time interval 相似文献
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空气反循环钻进技术具有钻速快、能耗低、可不提钻连续取心取样、能有效避免积雪层漏失等优点,在冰层钻探中极具应用潜力。本文针对冰层钻探技术特点,提出了双壁钻杆式、双通道高压胶管式和寄生高压胶管式等三种空气反循环冰层钻探技术,分别介绍了其工作原理及特点。基于气力输送和气体钻井基本理论,对冰屑颗粒气体介质中的悬浮速度进行了分析,建立了单颗粒冰屑悬浮、运移方程和冰屑颗粒群悬浮方程,并设计了冰屑悬浮实验台,对冰屑悬浮所需的风速进行了实验测试。理论计算值与实验实测值吻合较好,最大误差约10.91%,可用本文建立的冰屑运动方程来计算实际钻进时携带冰屑所需的风量,为后续在极地实施冰层空气反循环钻进技术提供了依据。 相似文献
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DAVID H. ROBERTS ANTONY J. LONG 《Boreas: An International Journal of Quaternary Research》2005,34(1):25-42
This study investigates the marginal subglacial bedrock bedforms of Jakobshavns Isbrae, West Greenland, in order to examine the processes governing bedform evolution in ice stream and ice sheet areas, and to reconstruct the interplay between ice stream and ice sheet dynamics. Differences in bedform morphology (roche moutonnee or whaleback) are used to explore contrasts in basal conditions between fast and slow ice flow. Bedform density is higher in ice stream areas and whalebacks are common. We interpret that this is related to higher ice velocities and thicker ice which suppress bed separation. However, modification of whalebacks by plucking occurs during deglaciation due to ice thinning, flow deceleration, crevassing and fluctuations in basal water pressure. The bedform evidence points to widespread basal sliding during past advances of Jakobshavns Isbrae. This was encouraged by increased basal temperatures and melting at depth, as well as the steep marginal gradients of Jakobshavns Isfjord which allowed rapid downslope evacuation of meltwater leading to strong ice/bedrock coupling and scouring. In contrast to soft-bedded ice stream bedforms, the occurrence of fixed basal perturbations and higher bed roughness in rigid bed settings prevents the basal ice subsole from maintaining a stable form which, coupled with secondary plucking, counteracts the development of bedforms with high elongation ratios. Cross-cutting striae and double-plucked, rectilinear bedforms suggest that Jakobshavns Isbrae became partially unconfined during growth phases, causing localised diffluent flow and changes in ice sheet dynamics around Disko Bugt. It is likely that Disko Bugt harboured a convergent ice flow system during repeated glacial cycles, resulting in the formation of a large coalesced ice stream which reached the continental shelf edge. 相似文献
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The basal ice of many glaciers contains debris structures that reflect subglacial processes. Presented here is an unusually clear photograph of ice and debris in the lowest 2 m of the basal layer at the margin of the Greenland ice sheet. The photograph shows ice-debris relationships and deformation structures that reflect entrainment processes and flow history. 相似文献
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MIKKO PUNKARI 《Boreas: An International Journal of Quaternary Research》1980,9(4):307-310
On the basis of glacial landforms interpreted by means of Landsat satellite imagery and ice-flow data obtained by other methods, the Scandinavian ice sheet has been observed to have divided at the deglaciation stage into several ice lobes. The ice lobes were more active parts of the uniform ice sheet. They represent parts that had bordered on each other in different directions or on more passive portions of the ice. The reasons for the appearance of separate ice lobes were evidently the Fennoscandian topography, the location of accumulation areas, and regional differences in the amounts of ice generated. In the boundary zones of the different ice lobes, there occur exceptionally large glaciofluvial forms and moraines (interlobate complexes). An area of passive ice was often between ice lobes, and in such areas there occur no noteworthy eskers, marginal formations or streamlined forms. In the part of Finland located on the southern side of the Arctic Circle, six different ice lobes and four major areas of passive ice are interpreted to have existed. 相似文献
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Sarah Aciego Bernard Bourdon Jakob Schwander Heinrich Baur Alessandro Forieri 《Quaternary Science Reviews》2011,30(19-20):2389-2397
Ice sheets and deep ice cores have yielded a wealth of paleoclimate information based on continuous dating methods while independent radiometric ages of ice have remained elusive. Here we demonstrate the application of (234U/238U) measurements to dating the EPICA Dome C ice core based on the accumulation of 234U in the ice matrix from recoil during 238U decay out of dust bound within the ice. Measured (234U/238U) activity ratios within the ice generally increase with depth while the surface areas of the dust grains are relatively constant. Using a newly designed device for measuring surface area for small samples, we were able to estimate reliably the recoil efficiency of nuclides from dust to ice. The resulting calculated radiometric ages range between 80 ka and 870 ka. Measured samples in the upper 3100 m fall on the previously published age-depth profile. Samples in the 3200–3255 m section show a marked change from 723–870 ka to 85 ka indicating homogenization of the deep ice prior to resetting of the (234U/238U) age in the basal layers. The mechanism for homogenization is likely enhanced lateral ice flow due to high basal melting and geothermal heat flux. 相似文献
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Diandong Ren Rong Fu David J. Karoly Lance M. Leslie Jianli Chen Clark R. Wilson 《Central European Journal of Geosciences》2010,2(4):501-513
Accurate prediction of future sea level rise requires models that accurately reproduce and explain the recent observed dramatic ice sheet behaviours. This study presents a new multi-phase, multiple-rheology, scalable and extensible geofluid model of the Greenland ice sheet that shows the credential of successfully reproducing the mass loss rate derived from the Gravity Recovery and Climate Experiment (GRACE), and the microwave remote sensed surface melt area over the past decade. Model simulated early 21st century surface ice flow compares satisfactorily with InSAR measurements. Accurate simulation of the three metrics simultaneously cannot be explained by fortunate model tuning and give us confidence in using this modelling system for projection of the future fate of Greenland Ice Sheet (GrIS). Based on this fully adaptable three dimensional, thermo-mechanically coupled prognostic ice model, we examined the flow sensitivity to granular basal sliding, and further identified that this leads to a positive feedback contributing to enhanced mass loss in a future warming climate. The rheological properties of ice depend sensitively on its temperature, thus we further verified modelâ?s temperature solver against in situ observations. Driven by the NCEP/NCAR reanalysis atmospheric parameters, the ice model simulated GrIS mass loss rate compares favourably with that derived from the GRACE measurements, or about ?147 km3/yr over the 2002–2008 period. Increase of the summer maximum melt area extent (SME) is indicative of expansion of the ablation zone. The modeled SME from year 1979 to 2006 compares well with the cross-polarized gradient ratio method (XPGR) observed melt area in terms of annual variabilities. A high correlation of 0.88 is found between the two time series. In the 30-year model simulation series, the surface melt exhibited large inter-annual and decadal variability, years 2002, 2005 and 2007 being three significant recent melt episodes. 相似文献
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V. I. Solomatin 《Doklady Earth Sciences》2017,477(2):1426-1429
New results of experimental studies into ice deformation and structural changes are presented. A sequence of structural mechanisms of deformation from polygonization to formation of cracks, cavities and shattering of crystals that replace each other primarily relatively to the load value and the deformation rate is developed. The principal mechanism of creep deformation is crack formation and crystal shattering. A brittleness index for ice deformation is proposed. It is shown that the vesicular texture of ice can be the result of the regeneration of open cracks during deformation. 相似文献
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基于浅层探冰雷达的东南极内陆地区冰盖内部等时层提取 总被引：2，自引：1，他引：1
中国第32次南极考察内陆队首次使用雪地车载浅层探冰雷达取得了中山站至昆仑站全程1 300 km 的浅层冰盖数据,通过MATLAB对数据进行FFT转换、背景滤波、改变叠加次数去噪和基于曲波变换的图像处理,使用Reflexw对MATLAB处理后数据进行地形校正、二次背景滤波和平滑滤波等处理,成功提取了冰盖浅层等时层并得出了等时层的平均深度、最大深度和波动情况。最后进行了数据的连接,展示了LGB69冰芯处等时层的分布并与冰芯数据结合大体对应了相应等时层的年代和事件。给出了Dome A附近的等时层分布情况。为东南极中山站至昆仑站沿途的物质积累率计算提供重要的数据支撑。 相似文献
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基于海冰分析图获取北极固定冰分布的方法研究 总被引：2，自引：2，他引：0
对北极沿岸地区固定冰的分析研究,将有助于更全面认识北极海冰的变化趋势,并为进一步探索北极航道的开发利用提供数据支撑。基于美国国家冰中心发布的2008-2018年逐周/逐两周海冰分析图发展了一个数据转化处理方法,准确提取了全北极逐周的固定冰分布格点数据。分析该时间序列发现,北极平均固定冰范围为（9.0±6.3）×105 km2,呈现出（-1.0±3.9）×103 km2·a-1的减小趋势;4月份固定冰范围最大,多年平均值为1.6×106 km2,处于北极冬季的1-6月份的范围均高于百万平方公里,而7-10月份为北半球夏季,几乎无固定冰存在。将MODIS图像作为基准数据对不同月份的七组结果进行对比验证,结果显示：结冰末期和融冰前期的平均偏差较小,如2012年3月12日的固定冰外缘线平均偏差为-0.8 km;而融冰末期的偏差较大,如2009年9月14日的固定冰外缘线平均偏差为-9.4 km;但所有月份的验证误差都小于格点网格的大小（25 km）,因此认为该方法是可行的,得到的格点数据可以代表固定冰的真实分布情况。 相似文献
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Understanding the flow of ice in glaciers and polar ice sheets is of increasing relevance in a time of potentially significant climate change. The flow of ice has hitherto received relatively little attention from the structural geological community. This paper aims to provide an overview of methods and results of ice deformation modeling from the single crystal to the polycrystal scale, and beyond to the scale of polar ice sheets. All through these scales, various models have been developed to understand, describe and predict the processes that operate during deformation of ice, with the aim to correctly represent ice rheology and self-induced anisotropy. Most of the modeling tools presented in this paper originate from the material science community, and are currently used and further developed for other materials and environments. We will show that this community has deeply integrated ice as a very useful “model” material to develop and validate approaches in conditions of a highly anisotropic behavior. This review, by no means exhaustive, aims at providing an overview of methods at different scales and levels of complexity. 相似文献
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In Snowdonia there is a marked contrast between weathered summits, often with well‐developed blockfields or tors, and lower ice‐moulded terrain. The boundary is interpreted as a trimline marking the upper surface of the last ice sheet. This interpretation is supported by the presence of gibbsite, an end‐product of prolonged weathering, at the base of soils above but not below the trimline. The reconstructed ice surface reaches about 850 m above present sea‐level along an ice divide running NE–SW through the massif. There is no evidence to support the popular view that ice centred further south extended over Snowdonia, and breaching to form the major glacial troughs can be explained by the action of local ice. The field evidence presented here demonstrates that most models of the southern British and Irish Sea ice sheets are significantly flawed, the earliest being far too thick and the most recent far too thin. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献