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1.
Reconstruction of the Ross Ice Drainage System, Antarctica, at the Last Glacial Maximum 总被引:2,自引:0,他引:2
George H. Denton & Terence J. Hughes 《Geografiska Annaler: Series A, Physical Geography》2000,82(2-3):143-166
We present here a revised reconstruction of the Ross ice drainage system of Antarctica at the last glacial maximum (LGM) based on a recent convergence of terrestrial and marine data. The Ross drainage system includes all ice flowlines that enter the marine Ross Embayment. Today, it encompasses one-fourth of the ice-sheet surface, extending far inland into both East and West Antarctica. Grounding lines now situated in the inner Ross Embayment advanced seaward at the LGM (radiocarbon chronology in Denton and Marchant 2000 and in Hall and Denton 2000a, b), resulting in a thick grounded ice sheet across the Ross continental shelf. In response to this grounding in the Ross (and Weddell) Embayment, ice-surface elevations of the marine-based West Antarctic Ice Sheet were somewhat higher at the LGM than at present (Steig and White 1997; Borns et al. 1998; Ackert et al. 1999). At the same time, surface elevations of the East Antarctic Ice Sheet inland of the Transantarctic Mountains were slightly lower than now, except near outlet glaciers that were dammed by grounded ice in the Ross Embayment. The probable reason for this contrasting behavior is that lowered global sea level at the LGM, from growth of Northern Hemisphere ice sheets, caused widespread grounding of the marine portion of the Antarctic Ice Sheet, whereas decreased LGM accumulation led to slight surface lowering of the interior terrestrial ice sheet in East Antarctica. Rising sea level after the LGM tripped grounding-line recession in the Ross Embayment, which has probably continued to the present day (Conway et al. 1999). Hence, gravitational collapse of the grounded ice sheet from the Ross Embayment, accompanied by lowering of the interior West Antarctic ice surface and of outlet glaciers in the Transantarctic Mountains, occurred largely during the Holocene. At the same time, increased Holocene accumulation caused a slight rise of the inland East Antarctic ice surface. 相似文献
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3.
南极冰盖物质平衡最新的研究进展表明,西南极洲表现出两种变化模式,西部在增厚,而北面在更快地减薄。西南极冰盖总体可能正在减薄,其物质损失的速率可能足以使海平面每年上升近0.2mm。东南极冰盖物质不平衡可能很小,甚至其符号还不能被确定。南极半岛正在经历着快速变化。目前还不能可靠地估算南极冰盖的物质平衡状态。同时,大型冰川的停滞,一些冰川流速加快,冰盖大范围加速减薄,冰架大面积的快速崩解和支流冰川的加速,以及着地线强烈的底部融化等显示出南极冰盖存在快速变化。南极冰盖物质平衡未来的重点研究领域是开展冰盖表面高程变化的监测与模拟,确定表面物质平衡及其在各冰流盆地的分布,着地线的冰流通量,冰架底部的融化,了解冰后期冰盖退缩的动力过程,以及开发、对比和改进与冰盖物质平衡模拟和预测相关的各种模型。 相似文献
4.
Brenda L. Hall & George H. Denton 《Geografiska Annaler: Series A, Physical Geography》2000,82(2-3):305-336
More than 250 radiocarbon dates of lacustrine algae and marine shells afford a chronology for Ross Sea drift in eastern Taylor Valley. Dates of algae that lived in ice-dammed Glacial Lake Washburn show that grounded Ross Sea ice blocked the mouth of Taylor Valley between 8340 and 23,800 14 C yr bp . Ross Sea ice was at its maximum position at the Hjorth Hill moraine between 12,700 and 14,600 14 C yr bp and was within 500m distance of this position as late as 10,794 14 C yr bp . The implication is that the flow line of the Ross Sea ice sheet which extended around northern Ross Island and across McMurdo Sound to Taylor Valley must have remained intact, and hence that a grounded ice sheet must have existed east of Ross Island as late as 8340 14 C yr bp . Evidence from ice-dammed lakes in Taylor Valley and from shells from McMurdo Sound suggests grounding-line retreat from the vicinity of Ross Island between 6500 and 8340 14 C yr bp . If this is correct, then most recession to the present-day grounding line on the Siple Coast took place subsequently in the absence of significant deglacial sea-level rise. Rising sea level may have triggered internal mechanisms within the ice sheet that led to retreat, but did not in itself drive continued ice-sheet recession. Ice retreat, once set in motion, continued in the absence of sea-level forcing. If correct, this hypothesis implies that the grounding line could continue to recede into the interior reservoir of the West Antarctic Ice Sheet. 相似文献
5.
Wisconsinan and Holocene Climate History from an Ice Core at Taylor Dome, Western Ross Embayment, Antarctica 总被引:4,自引:0,他引:4
Eric J. Steig David L. Morse Edwin D. Waddington Minze Stuiver Pieter M. Grootes Paul A. Mayewski Mark S. Twickler & Sallie I. Whitlow 《Geografiska Annaler: Series A, Physical Geography》2000,82(2-3):213-235
Geochemical data and geophysical measurements from a 554-m ice-core from Taylor Dome, East Antarctica, provide the basis for climate reconstruction in the western Ross Embayment through the entire Wisconsinan and Holocene. In comparison with ice cores from central East and West Antarctica, Taylor Dome shows greater variance of temperature, snow accumulation, and aerosol concentrations, reflecting significant variability in atmospheric circulation and air mass moisture content. Extreme aridity during the last glacial maximum at Taylor Dome reflects both colder temperatures and a shift in atmospheric circulation patterns associated with the advance of the Ross Sea ice sheet and accounts for regional alpine glacier retreats and high lake levels in the Dry Valleys. Inferred relationships between spatial accumulation gradients and ice sheet configuration indicate that advance of the Ross Sea ice sheet began in late marine isotope stage 5 or early stage 4. Precise dating of the Taylor Dome core achieved by trace-gas correlation with central Greenland ice cores shows that abrupt deglacial warming at Taylor Dome was near-synchronous with the ∼14.6 ka warming in central Greenland and lags the general warming trend in other Antarctic ice cores by at least 3000 years. Deglacial warming was following by a warm interval and transient cooling between 14.6 and 11.7 ka, synchronous with the Bølling/Allerød warming and Younger Dryas cooling events in central Greenland, and out of phase with the Antarctic Cold Reversal recorded in the Byrd (West Antarctica) ice core. Rapid climate changes during marine isotope stages 4 and 3 at Taylor Dome are similar in character to, and may be in phase with, the Northern Hemisphere stadial–interstadial (Dansgaard–Oeschger) events. Results from Taylor Dome illustrate the importance of obtaining ice cores from multiple Antarctic sites, to provide wide spatial coverage of past climate and ice dynamics. 相似文献
6.
Predicted present-day evolution patterns of ice thickness and bedrock elevation over Greenland and Antarctica 总被引:4,自引:0,他引:4
This paper discusses predicted evolution patterns of present-day changes of ice thickness, surface elevation, and bedrock elevation over the Greenland and Antarctic continents. These were obtained from calculations with dynamic 3-D ice sheet models which were coupled to a visco-elastic solid Earth model. The experiments were initialized over the last two glacial cycles and subsequently averaged over the last 200 years to obtain the current evolution. The calculations indicate that the Antarctic Ice Sheet is still adjusting to the last glacial-interglacial transition yielding a decreasing ice volume and a rising bedrock elevation of the order of several centimetres per year. The Greenland Ice Sheet was found to be close to a stationary state with a mean thickness change of only a few millimetres per year, but the calculations revealed large spatial differences. Predicted patterns over Greenland are characterized by a small thickening over the ice sheet interior and a general thinning of the ablation area. In Antarctica, almost all of the predicted changes are concentrated in the West Antarctic Ice Sheet, which is still retreating at both the Weddell and Ross Sea margins. Over most of both ice sheets, the model indicates that the surface elevation trend is dominated by ice thickness changes rather than by bedrock elevation changes. 相似文献
7.
Depositional environment of Sirius Group sediments, Table Mountain, Dry Valleys area, Antarctica 总被引:1,自引:0,他引:1
James R. Goff Ian W. Jennings & Warren W. Dickinson 《Geografiska Annaler: Series A, Physical Geography》2002,84(1):11-24
Outcrops and cores of the Sirius Group sediments were studied at Table Mountain, Dry Valleys area, Antarctica. These sediments form a surficial veneer at least 9.5 m thick. Three facies — a gravelly sandstone, a sandstone, and a sandy conglomerate — are mapped and described from 13 outcrops and three cores. The gravelly sandstone, constituting 13%of all cored material, is bimodal with matrix-supported clasts comprising 5–33%of the facies. Fabric analysis indicates that it was deposited primarily by lodgment from glacial ice but with minor elements of meltout and flow. The sandstone facies, constituting 77%of all cored material, is a well-sorted, fine- to medium-grained sand, which commonly has laminated bedding. It is predominantly a glaciofluvial deposit but has some glaciolacustrine elements. The sandy conglomerate, constituting 10%of all cored material, is a minor facies. It is massive and clast-supported. It was deposited in a high-energy environment suggestive of subglacial meltwater channels.
Sirius Group sediments at Table Mountain are the result of wet-based ice advancing and retreating over waterlain deposits. This is consistent with an advancing ice mass in climatic conditions that were warmer than present. The majority of the sediments were deposited by alpine ice following a similar pathway to the present-day Ferrar Glacier and as such the depositional environment is one that concurs with evidence of a stable East Antarctic Ice Sheet approach. At Table Mountain, the predominantly glaciofluvial and glaciolacustrine facies is inferred to represent a more distal part of the Sirius Group environment than that seen at other outcrops in the Dry Valleys. 相似文献
Sirius Group sediments at Table Mountain are the result of wet-based ice advancing and retreating over waterlain deposits. This is consistent with an advancing ice mass in climatic conditions that were warmer than present. The majority of the sediments were deposited by alpine ice following a similar pathway to the present-day Ferrar Glacier and as such the depositional environment is one that concurs with evidence of a stable East Antarctic Ice Sheet approach. At Table Mountain, the predominantly glaciofluvial and glaciolacustrine facies is inferred to represent a more distal part of the Sirius Group environment than that seen at other outcrops in the Dry Valleys. 相似文献
8.
Extent and Chronology of the Ross Sea Ice Sheet and the Wilson Piedmont Glacier along the Scott Coast at and Since the Last Glacial Maximum 总被引:1,自引:0,他引:1
Brenda L. Hall & George H. Denton 《Geografiska Annaler: Series A, Physical Geography》2000,82(2-3):337-363
During the last glacial maximum, a coalescent ice mass consisting of the grounded Ross Sea ice sheet and an expanded Wilson Piedmont Glacier covered the southern Scott Coast. This coalescent ice mass was part of a larger grounded ice sheet that occupied the Ross Sea Embayment during the last glacial maximum. Deglaciation of the western Ross Sea Embayment adjacent to the southern Scott Coast was delayed until shortly before 6500 14 C yr bp , aconclusion based on ages of marine shells from McMurdo Sound, a relative sea-level curve, and algae that lived in ice-dammed lakes. Therefore, most recession of grounded ice in the Ross Sea Embayment occurred in mid to late Holocene time, after deglacial sea-level rise due to melting of Northern Hemisphere ice sheets essentially was accomplished. Rising sea level alone could not have driven grounding-line retreat back to the present-day Siple Coast. 相似文献
9.
MELTWATER FEATURES THAT SUGGEST MIOCENE ICE-SHEET OVERRIDING OF THE TRANSANTARCTIC MOUNTAINS IN VICTORIA LAND, ANTARCTICA 总被引:2,自引:0,他引:2
GEORGE H. DENTON DAVID E. SUGDEN 《Geografiska Annaler: Series A, Physical Geography》2005,87(1):67-85
ABSTRACT. We illustrate here spectacular meltwater features associated with outburst floods beneath an ice sheet that overrode the Transantarctic Mountains in southern Victoria Land. Because of long-term hyperarid polar climate, these features are part of an ancient landscape preserved for about 14 million years. Some channels are associated with areal scouring of basement rocks extending from sea level to as much as 1200–2100 m elevation in coastal regions. Scablands with scallops, potholes and plunge pools are cut in Beacon Super group sandstones and Ferrar Dolerite and cover wide areas of high western plateaus near the mountain crest. Subglacial channel systems commonly originate near divides and converge downhill toward the northeast. We argue that the landforms were created beneath a major Antarctic Ice Sheet that submerged the whole area, with the possible exception of the high peaks of the Royal Society Range, as it flowed northeastward toward the outer Antarctic continental shelf. Areal scouring, associated with warm-based regimes, is restricted to the lower slopes close to the coast. In the higher terra in, meltwater channels and scabland alongside preserved patches of regolith are best explained by the breaching of cold-based ice on the mountain rim by subglacial melt water outbursts. Melt from warm-based ice, along with subglacial lakes trapped upstream of the mountain rim, are possible sources of the meltwater necessary to form the channel systems and scablands. 相似文献
10.
The Holocene glacial and climatic development in Antarctica differed considerably from that in the Northern Hemisphere. Initial deglaciation of inner shelf and adjacent land areas in Antarctica dates back to between 10-8 Kya, when most Northern Hemisphere ice sheets had already disappeared or diminished considerably. The continued deglaciation of currently ice-free land in Antarctica occurred gradually between ca. 8-5 Kya. A large southern portion of the marine-based Ross Ice Sheet disintegrated during this late deglaciation phase. Some currently ice-free areas were deglaciated as late as 3 Kya. Between 8-5 Kya, global glacio-eustatically driven sea level rose by 10-17m, with 4-8 m of this increase occurring after 7 Kya. Since the Northern Hemisphere ice sheets had practically disappeared by 8-7 Kya, we suggest that Antarctic deglaciation caused a considerable part of the global sea level rise between 8-7 Kya, and most of it between 7-5 Kya. The global mid-Holocene sea level high stand, broadly dated to between 8-4 Kya, and the Littorina-Tapes transgressions in Scandinavia and simultaneous transgressions recorded from sites e.g. in Svalbard and Greenland, dated to 7-5 Kya, probably reflect input of meltwater from the Antarctic deglaciation. 相似文献
11.
Proglacial Lake-ice Conveyors: A New Mechanism for Deposition of Drift in Polar Environments 总被引:2,自引:0,他引:2
C.H. Hendy A.J. Sadler G.H. Denton & B.L. Hall 《Geografiska Annaler: Series A, Physical Geography》2000,82(2-3):249-270
Interpretation of sediments in the floors of valleys opening into western McMurdo Sound has been so problematic that it has hindered understanding of the late Quaternary history of the Antarctic Ice Sheet. Lateral moraines and enclosed drift sheets so clearly exposed on the headlands are generally absent within the valleys themselves. Instead, valley-floor sediments and landforms consist of hummocky, stratified fine sediment generally capped by coarser, poorly sorted material, small cross-valley and longitudinal ridges, and lateral ridges that superficially resemble shorelines. One clue as to the origin of these deposits is that at least some of the valleys were occupied by large proglacial lakes during the last glacial maximum (e.g. Glacial Lakes Trowbridge and Washburn in Miers and Taylor Valleys, respectively). This paper describes a new mechanism observed in a modern perennially ice-covered proglacial lake that documents the movement of glacial debris beyond the grounding line across the surface of the lake. This mechanism accounts for the absence of moraines and other ice-contact features on the valley floors, as well as for the presence of the other deposits and landforms mentioned above. 相似文献
12.
The Bunger Hills in East Antarctica occupy a land area of approximately 400 km2. They have been exposed by Holocene retreat of the Antarctic ice sheet and its outlet glaciers. The accompanying sea level rise flooded the marine inlets that now separate the northern islands and peninsulas from the major part of the hills. During deglaciation the continental ice sheet margin retreated south‐eastwards with several temporary halts, during which ice‐dammed lakes were formed in some valleys. These lakes were maintained long enough to permit formation of beaches of sand and gravel, and for the erosion of shore platforms and low cliffs in bedrock. Around the western end of Fish Tail Bay impressive shoreline features 20 m above sea level define a former ice‐dammed lake that was 5.5 km long. A similar 7 km long former ice‐dammed lake was formed at Lake Dolgoe. The more extensive and deeper glacial lake is revealed by well‐developed and preserved shoreline features cut at 29 m which is 16 m above present lake level. In addition, several small ice‐dammed lakes existed temporarily near Lake Shchel and in the valley to the west. Lake Fish Tail existed more than 6,900 14C years ago and Lake Shchel probably more than 6,680 14C years ago. It is inferred that the shore platforms and beaches were formed by lake ice and wave action over considerable periods when the lakes were impounded by steep cold ice margins. There appears to have been a balance between meltwater input and evaporative loss from the lakes in the cold dry continental climate. There is no evidence for rapid lake level fluctuations, and there was very little input of clastic sediment. This resulted in poor development of deltaic and rhythmically laminated lake floor deposits. It is suggested that such deposits are more characteristic of ice‐dammed lakes formed in association with wet‐based temperate ice than those associated with dry‐based polar ice. 相似文献
13.
《Geomorphology》2005,64(1-2):25-65
Surficial deposits in eastern and central Wright Valley, Antarctica, record multiple inland incursions of grounded ice from the Ross Sea Embayment. Glacial geologic mapping, coupled with 42 AMS 14C dates of lacustrine algae and 10 40Ar/39Ar dates of basalt erratics, indicate westward ice expansion at least eight times during the Pliocene and Quaternary. The most extensive westward incursion resulted in an advance of at least 21 km beyond the margin of present-day Wright Lower Glacier, accompanied by ice thickening of ≥500 m at the location of the present-day Wilson Piedmont Glacier in the eastern valley mouth. Large proglacial lakes and glaciolacustrine sedimentation coincide with at least some of these advances. 相似文献
14.
目前,位于东南极冰盖分冰岭中心的冰穹-Dome A已成为深入理解南极冰盖演化、稳定性和找寻地球气候久远记录的研究热点。通过整理总结在Dome A获得的冰川学研究进展,结合国际冰芯科学研究计划(International Partnerships in Ice Core Sciences,简称IPICS)有关寻找最古老冰芯的相关资料,对Dome A的气象要素、地貌、冰厚、冰下地形、冰体流速、冰盖内部结构等环境特征进行归纳分析,讨论Dome A冰川学的最新发展及其对深冰芯钻探计划的影响,并分析概述Dome A深冰芯钻探需考虑的问题和未来发展动向。 相似文献
15.
本文介绍了近期南极冰架-海洋相互作用的研究进展。冰架底部融化速率大于前缘崩解通量,成为南极冰盖质量损失的首要途径。冰架下的海洋按照底部融化驱动因素的不同,可以分为由高密度陆架水驱动的冷冰腔和由变性绕极深层水驱动的暖冰腔。威德尔海的菲尔希纳-龙尼冰架和罗斯海的罗斯冰架属于冷冰腔,占南极冰架总面积的2/3,却只贡献了15%的净融化;东南太平洋扇区阿蒙森海和别林斯高晋海等若干属于暖冰腔的小型冰架,虽然只占南极冰架总面积的8%,却贡献了超过一半的冰架融水。以往看做冷冰腔的东南极托滕冰架和埃默里冰架,也相继发现有变性绕极深层水进入冰腔并造成底部融化。冰架对海洋有冷却和淡化的作用。冷冰腔输出的冰架水具有海洋中最低的温度,对南极陆架水性质乃至南极底层水的形成都有影响。冰架融化加剧,可能是近期观测到的南极底层水淡化的原因。 相似文献
16.
Christine Elliott 《New Zealand geographer》2005,61(1):68-76
Abstract: The landscape in the vicinity of Scott Base is one of the most singular of landscapes in the already unique environment of the Ross Sea Region of Antarctica. A rich history of human endeavour together with a broad range of physical features such as volcanoes, various glacial landforms, polar beaches and the Dry Valleys with their own glaciers, sand dunes and patterned ground must make it one of the most fascinating areas on earth. This paper highlights some of the more notable of these landscape features. 相似文献
17.
《Polar Science》2009,3(4):262-271
We investigated the vertical structure of physicochemical properties in 27 lakes at Skarvsnes and Langhovde, Syowa Oasis, East Antarctica, from December 2003 to February 2004. The lakes were classified into three types based on their origin and geographical characteristics: non-marine relic lakes, marine relic and lotic lakes, and marine relic and lentic lakes. We describe the physicochemical characteristics of each lake type. When the non-marine relic lakes were partly covered with ice, the water column was stratified beneath the ice. In the non-marine relic lakes, during the season with no ice cover, physicochemical parameters were uniform throughout the water column, probably due to frequent vertical mixing induced by wind force and thermal convection within the shallow basins. Similarly, in marine relic and lotic lakes, lake waters appeared to be completely mixed because of a large inflow of meltwater from glaciers and outflow to other lakes and the coastal sea. In the marine relic and lentic lakes, except for Lake Himebati-ike, the lake water was vertically stratified with a strong halocline. In Lakes Suribati-ike and Hunazoko-ike, salinity was very high (up to 20%) due to evapoconcentration. Lake Suribati-ike is a meromictic lake, with a monimolimnion developed below 10 m water depth. 相似文献
18.
本文在简要介绍冰盖物质平衡及其对海平面影响的基础上,从整体法和分量法两个方面总结了南极冰盖物质平衡研究的最新进展,并分析了影响其物质平衡的不确定因素。研究表明,整个南极冰盖物质平衡呈现负增长的趋势,其中西南极Amundsen海湾附近的冰盖物质流失最为明显。另外,南极冰盖边缘的大部分地区还呈现变薄的趋势。南极冰盖物质流失是引起海平面上升的最大潜在因素之一,其冰架的缓冲作用、冰盖的不稳定性和冰盖底部融水的作用等不确定因素对南极冰盖物质平衡具有重要的影响。未来随着观测技术和数据处理技术的不断提高,南极冰盖物质平衡的估算及其不确定因素有望得到进一步的认识,从而为预测海平面的上升范围提供更多的理论和技术支撑。 相似文献
19.
Andy Breckenridge Thomas V. Lowell Timothy G. Fisher Shiyong Yu 《Journal of Paleolimnology》2012,47(3):313-326
The evolution of the early Great Lakes was driven by changing ice sheet geometry, meltwater influx, variable climate, and
isostatic rebound. Unfortunately none of these factors are fully understood. Sediment cores from Fenton Lake and other sites
in the Lake Superior basin have been used to document constantly falling water levels in glacial Lake Minong between 9,000
and 10,600 cal (8.1–9.5 ka) BP. Over three meters of previously unrecovered sediment from Fenton Lake detail a more complex
lake level history than formerly realized, and consists of an early regression, transgression, and final regression. The initial
regression is documented by a transition from gray, clayey silt to black sapropelic silt. The transgression is recorded by
an abrupt return to gray sand and silt, and dates between 9,000 and 9,500 cal (8.1–8.6 ka) BP. The transgression could be
the result of increased discharge from Lake Agassiz overflow or the Laurentide Ice Sheet, and hydraulic damming at the Lake
Minong outlet. Alternatively ice advance in northern Ontario may have blocked an unrecognized low level northern outlet to
glacial Lake Ojibway, which switched Lake Minong overflow back to the Lake Huron basin and raised lake levels. Multiple sites
in the Lake Huron and Michigan basins suggest increased meltwater discharges occurred around the time of the transgression
in Lake Minong, suggesting a possible linkage. The final regression in Fenton Lake is documented by a return to black sapropelic
silt, which coincides with varve cessation in the Superior basin when Lake Agassiz overflow and glacial meltwater was diverted
to glacial Lake Ojibway in northern Ontario. 相似文献
20.
Takanobu Sawagaki & Kazuomi Hirakawa 《Geografiska Annaler: Series A, Physical Geography》1997,79(4):223-238
The formation of the glacial erosional bedforms at the Soya Coast of Lützow-Holm Bay, East Antarctica is discussed. The streamlined bedforms in the studied area are classified into crescentic transverse ridges and tadpole rocks, and these bedforms are accompanied by small erosional marks (s-forms) which suport the interpretation of subglacial meltwater erosion. Some tadpole rocks are superimposed on a large roche moutonnée, and these two kinds of landform are interpreted to have different modes of formation. Observations and interpretations of these bedforms are used to reconstruct the historical development of the glacial erosional bedforms, and to draw attention to the significance and implications of subglacial meltwater erosion on the marginal area of the Antarctic Ice Sheet in the past. An initial episode of glacial plucking and abrasion produced roches moutonnées and basic large-scale landforms. Subglacial meltwater flowing peiodically into the Lützow-Holm Bay sculptured s-forms and streamlined bedforms in bedrock over much of the area. During this period, except for water-flowing phases, ice again came in contact with the bedrock to form striations superimposed on the s-forms and the hillocks. 相似文献