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1.
Ice-distal Upper Miocene marine strata from inland Antarctica   总被引：2，自引：0，他引：2  
ABSTRACT Glacimarine strata of the Battye Glacier Formation (≈ 130 m thick), Pagodroma Group, exposed in the Amery Oasis of East Antarctica, provide a record of Late Miocene palaeoenvironmental conditions in an ice‐distal setting. The formation overlies the Amery Erosion Surface (≈ 300 m to ≈ 270 m above sea level) that formed during an advance of the Lambert Glacier into Prydz Bay (ODP Site 739), at least 750 km further north than today. Two lithological members: a grey and muddier Lower Member and a brown, sand‐rich Upper Member, reflect variation in proximity to the terminus of the Lambert Glacier. Ice‐distal, glacimarine, diatom‐bearing mud (up to 12% biogenic silica) and in situ articulated molluscs occur in the Lower Member. The Battye Glacier Formation is significant because of its inland location, which indicates that ice‐distal marine conditions existed 250 km inland from the current Amery Ice Shelf edge. Similar Neogene strata are known on land only from the Pliocene Sørsdal Formation in the Vestfold Hills, near the Antarctic coast. Three stratigraphic intervals of diatom‐bearing mud are recognized from glacially reworked clasts and from in situ strata informally referred to as the McLeod Beds and ‘Bed A’. The diatom‐bearing mud also contains sponge spicules and minor silicoflagellates and ebridians. Marine diatom biostratigraphy constrains the age of the beds to between 10·7 and 9·0 Ma (late Miocene). Abundant benthic diatoms suggest deposition within shallow euphotic waters. The high abundance of intercalary valves of Eucampia antarctica from an interval of the McLeod Beds suggests that there was less winter sea‐ice than in Prydz Bay today. It is unlikely that sea‐ice was perennial because the presence of Thalassionema spp. and Stellarima stellaris (Roper) Hasle et Sims suggests that summer sea‐surface temperatures were too warm (> 0°C and > 3°C respectively). The palaeoclimate at the time of deposition appears to have been analogous to that in modern fjords of East Greenland (e.g. Kangerdlugssuaq Fjord), which is consistent with the depositional model proposed previously for the Pagodroma Group. The three diatom‐bearing mud intervals were deposited in the Amery Oasis, ≈ 250 km inland of the current Amery Ice Shelf edge, when the East Antarctic Ice Sheet was reduced in size relative to today.  相似文献   

2.
The Lambert Graben is occupied by the world’s largest fjord system, through which flows the Lambert Glacier, the Amery Ice Shelf and their tributaries. Along the western margin of the graben, in the northern Prince Charles Mountains, remnants of uplifted Miocene and Pliocene strata of the glacigenic fjordal Pagodroma Group total more than 800 m in thickness. These sediments provide evidence for a dynamic East Antarctic ice sheet during the Neogene Period. Each of the four Pagodroma Group formations defined from this region rests unconformably on either Proterozoic or Permo‐Triassic rocks. The unconformity surfaces represent parts of the walls and floors of Neogene fjords. For these surfaces to have been eroded, the ice must have been grounded out as far as the continental shelf in Prydz Bay. The Pagodroma Group was deposited by wet‐based glaciers discharging into a fjordal setting and includes lithofacies that are quite different from those produced by modern Antarctic ice masses. The principal lithofacies are massive diamicts and soulder gravels, deposited both close to a calving, grounded glacier terminus and from icebergs. The few stratified diamicts are the product of more distal iceberg sedimentation. An ice‐transported gravel lithofacies includes rockfall debris derived from palaeofjord walls and mixed with subglacially derived diamicts. Some lithofacies contain evidence of subaquatic slumping and gravity flowage. Volumetrically minor lithofacies include laminites, with some exposures exhibiting large ice‐rafted clasts. The laminites represent less proximal, mainly ice‐free fjordal sediments, resulting either from tidal‐current sorting of suspended sediment originating from subaquatic glaciofluvial discharge, or from turbidity currents derived from unstable subaquatically deposited glacigenic sediment. The Pagodroma Group provides a record of multiple glaciation by dynamic, sliding glaciers carrying large amounts of both basal and supraglacial debris. The closest modern analogues, in terms of the thermal and dynamic characteristics of the Neogene Lambert Glacier, appear to be the fast‐flowing tidewater glaciers of East Greenland. These glaciers originate from the interior ice sheet and discharge large volumes of icebergs; the resulting lithofacies are predominantly diamicts.  相似文献   

3.
The mode of deglaciation of the last Scottish ice sheet is assessed from evidence provided by geomorphological mapping and sedimentology. Ice-marginal deposits in the Dee valley have a distinctive morphological expression and a characteristically varied sedimentology that strongly resembles those from subpolar glaciers. The deposits tend to occur in certain topographic situations which can be accounted for by compression of ice near the margin and formation of an ice-cored supraglacial land system. A series of recessional stages of the ice-front can be mapped demonstrating that active retreat occurred. However, additional evidence shows there was probably a thin marginal zone of stagnant ice. Recessional stages are inferred to be stillstands that are considered to be topographically controlled rather than related to climate. Development of the supraglacial land system during deglaciation suggests that the ice sheet had a polythermal basal regime with a cold-based margin. This implies that deglaciation took place in northeast Scotland while the climate remained cold, probably due to a precipitation deficit, which agrees well with chronostratigraphic data.  相似文献   

4.
Key locations within an extensive area of the northeastern Tibetan Plateau, centred on Bayan Har Shan, have been mapped to distinguish glacial from non‐glacial deposits. Prior work suggests palaeo‐glaciers ranging from valley glaciers and local ice caps in the highest mountains to a regional or even plateau‐scale ice sheet. New field data show that glacial deposits are abundant in high mountain areas in association with large‐scale glacial landforms. In addition, glacial deposits are present in several locations outside areas with distinct glacial erosional landforms, indicating that the most extensive palaeo‐glaciers had little geomorphological impact on the landscape towards their margins. The glacial geological record does indicate extensive maximum glaciation, with local ice caps covering entire elevated mountain areas. However, absence of glacial traces in intervening lower‐lying plateau areas suggests that local ice caps did not merge to form a regional ice sheet on the northeastern Tibetan Plateau around Bayan Har Shan. No evidence exists for past ice sheet glaciation. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

5.
刘勇  邓晓峰 《冰川冻土》1998,20(1):79-84
希夏邦马峰－珠穆朗玛峰地区是新生代以来,在欧亚板块与印度板块碰撞的地质背景下,迅速隆升起来的极高山地区．进入第四纪以来,强烈的构造隆升,使这些山地上的冰川进退、河流发育和湖泊变迁都发生了重大变化,带来整个地貌格局的变化．倒数第二次冰期时,亦即聂聂雄拉冰期的鼎盛时期,本区发育了巨大的冰帽,覆盖了整个地区．末次冰期的冰川以长大的山谷冰川和小冰帽为主要特点．在末次间冰期,河流侵蚀能力增强,位于山地南坡的河流进行强烈的溯源侵蚀,破坏了山脉的完整性,并对北坡的河流进行劫夺,从根本上改变了本区的地貌格局．到了全新世后期、新冰期到来之际,佩枯错的水位也达到了其在地质历史上的最高水位和最大面积,高出现今湖面整整１００ｍ．此后,由于朋曲河的溯源侵蚀和劫夺作用,上游流域面积减少,水源补给逐渐丧失,水域迅速收缩,水位降低．  相似文献   

6.
Glacial drifts perched alongside outlet glaciers that drain through the Transantarctic Mountains constrain inland polar plateau ice elevations. The Taylor Glacier, which heads in the Taylor Dome (a peripheral dome of the East Antarctic Ice Sheet), drains East Antarctic ice into the Dry Valleys sector of Transantarctic Mountains and terminates in central Taylor Valley, about 24 km west of the Ross Sea. Five gravel-rich drifts (including 39 distinct moraine ridges) fringe a lateral lobe of the Taylor Glacier in the lower Arena Valley, Quartermain Mountains, southern Victoria Land. 3He and 10Be exposure age dating (from Brook et al . 1992), together with Arena Valley stratigraphy and soil morphologic data, provide chronologic control for these drifts and constrain maximum Quaternary thickening of the inland Taylor ice dome to less than 160 m. These minor Quaternary expansions of Taylor Glacier were out-of-phase with outlet glaciers that pass through the Transantarctic Mountains and terminate in the Ross Sea north and south of the Dry Valleys region. Textural analyses suggest that drift deposition occurred from cold-based ice, even though Taylor Glacier advances most likely occurred during global interglaciations. The thermal regime of former Taylor Glacier ice lobes, the character of geomorphic features superimposed on individual drifts, the chemical composition of soils developed on Taylor drifts, and the stability of in situ moraine ridges on steep valley walls suggest that the present cold-desert climate in Arena Valley has persisted for at least the last 2.2 Ma.  相似文献   

7.
This article describes distinctive lateral meltwater channels at the margins of low-elevation cold-based glaciers in the Dry Valleys. The channels significantly modify the ground surface and indicate that cold-based glaciers can be active geomorphic agents. Summer meltwater from the glacier surface flows over ice-aprons and erodes into the frozen ground creating channels up to 3 m deep and 10 m wide adjacent to unmodified ground that is protected beneath the glacier itself. Rapid fluvial excavation in the channels leads to undercutting and collapse of channel walls, which is capable of overturning large boulders. During glacial retreat, a succession of channels is incised into newly exposed ground creating a distinctive series of nested lateral channels and ridges. These represent the most obvious and persistent geomorphological signature of cold-based glacier activity in the region. Cold-based glaciers may advance and retreat over the same area many times without necessarily destroying older features, thereby creating a complex series of channels, deposits and remnant surfaces with a disordered chronology. Recognizing the role of cold-based glaciers and their meltwater channels on landscape evolution is critical for interpreting the timing and style of glacial events in the Antarctic.  相似文献   

8.
Lateral moraines constructed along west to east sloping outlet glaciers from mountain centred, pre-last glacial maximum (LGM) ice fields of limited extent remain largely preserved in the northern Swedish landscape despite overriding by continental ice sheets, most recently during the last glacial. From field evidence, including geomorphological relationships and a detailed weathering profile including a buried soil, we have identified seven such lateral moraines that were overridden by the expansion and growth of the Fennoscandian ice sheet. Cosmogenic 10Be and 26Al exposure ages of 19 boulders from the crests of these moraines, combined with the field evidence, are correlated to episodes of moraine stabilisation, Pleistocene surface weathering, and glacial overriding. The last deglaciation event dominates the exposure ages, with 10Be and 26Al data derived from 15 moraine boulders indicating regional deglaciation 9600 ± 200 yr ago. This is the most robust numerical age for the final deglaciation of the Fennoscandian ice sheet. The older apparent exposure ages of the remaining boulders (14,600-26,400 yr) can be explained by cosmogenic nuclide inheritance from previous exposure of the moraine crests during the last glacial cycle. Their potential exposure history, based on local glacial chronologies, indicates that the current moraine morphologies formed at the latest during marine oxygen isotope stage 5. Although numerous deglaciation ages were obtained, this study demonstrates that numerical ages need to be treated with caution and assessed in light of the geomorphological evidence indicating moraines are not necessarily formed by the event that dominates the cosmogenic nuclide data.  相似文献   

9.
天山托木尔峰科其喀尔巴西冰川表面运动速度特征分析   总被引：6，自引：2，他引：4  
天山托木尔峰科其喀尔巴西冰川是典型的树枝状山谷冰川,利用3组(6期)ASTER遥感影像通过COSI-corr软件反演了该冰川表面运动速度.与花杆测量数据进行对比,反演冰川表面运动速度平均绝对误差为3.1 m·a-1,相对误差为11.9%,二者在空间上的分布基本一致,表明其反演精度符合要求.在此基础上,分析冰川表面运动速...  相似文献   

10.
Recent work in modern and ancient glacial environments has demonstrated the ability of cold-based glaciers to interact with permafrost. Geological evidence for glacier–permafrost interactions is revealed in Arctic regions where permafrost has persisted since deglaciation. Whilst similar interactions probably occurred near the margins of former ice sheets in the mid-latitudes, this interpretation is rarely applied to unfrozen glacigenic sequences. This review considers the extent to which this alternative hypothesis can explain two key aspects of the glaciotectonic sequences of North Norfolk that have traditionally been attributed to the deformation of unfrozen sediment. The substantial thickness (>10 m) of the pervasively deformed sequences and the preservation of stratified sand intraclasts within them are consistent with deformation at temperatures slightly below the pressure melting point (warm permafrost). Such deformation is also consistent with the pre-glacial environment, which was characterised by continuous permafrost. The hypothesis of deformation at sub-freezing temperatures should be considered more widely when interpreting glaciotectonically deformed, ice-marginal sequences in the mid-latitudes. The application of geological evidence to reconstruct basal thermal regimes beneath former glaciers would complement existing geomorphological inverse models and provide additional information to improve the parameterisation of subglacial processes in numerical ice-sheet models.  相似文献   

11.
Graham, A.G.C., Lonergan, L. & Stoker, M.S. 2010: Depositional environments and chronology of Late Weichselian glaciation and deglaciation in the central North Sea. Boreas, Vol. 39, pp. 471–491. 10.1111/j.1502‐3885.2010.00144.x. ISSN 0300‐9483. Geological constraints on ice‐sheet deglaciation are essential for improving the modelling of ice masses and understanding their potential for future change. Here, we present a detailed interpretation of depositional environments from a new 30‐m‐long borehole in the central North Sea, with the aim of improving constraints on the history of the marine Late Pleistocene British–Fennoscandian Ice Sheet. Seven units characterize a sequence of compacted and distorted glaciomarine diamictons, which are overlain by interbedded glaciomarine diamictons and soft, bedded to homogeneous marine muds. Through correlation of borehole and 2D/3D seismic observations, we identify three palaeoregimes. These are: a period of advance and ice‐sheet overriding; a phase of deglaciation; and a phase of postglacial glaciomarine‐to‐marine sedimentation. Deformed subglacial sediments correlate with a buried suite of streamlined subglacial bedforms, and indicate overriding by the SE–NW‐flowing Witch Ground ice stream. AMS 14C dating confirms ice‐stream activity and extensive glaciation of the North Sea during the Last Glacial Maximum, between c. 30 and 16.2 14C ka BP. Sediments overlying the ice‐compacted deposits have been reworked, but can be used to constrain initial deglaciation to no later than 16.2 14C ka BP. A re‐advance of British ice during the last deglaciation, dated at 13.9 14C ka BP, delivered ice‐proximal deposits to the core site and deposited glaciomarine sediments rapidly during the subsequent retreat. A transition to more temperate marine conditions is clear in lithostratigraphic and seismic records, marked by a regionally pervasive iceberg‐ploughmarked erosion surface. The iceberg discharges that formed this horizon are dated to between 13.9 and 12 14C ka BP, and may correspond to oscillating ice‐sheet margins during final, dynamic ice‐sheet decay.  相似文献   

12.
The study revises the maximum extent of the northwest Laurentide Ice Sheet (LIS) in the western Canadian Arctic Archipelago (CAA) during the last glaciation and documents subsequent ice sheet retreat and glacioisostatic adjustments across western Banks Island. New geomorphological mapping and maximum-limiting radiocarbon ages indicate that the northwest LIS inundated western Banks Island after ~ 31 14C ka BP and reached a terminal ice margin west of the present coastline. The onset of deglaciation and the age of the marine limit (22–40 m asl) are unresolved. Ice sheet retreat across western Banks Island was characterized by the withdrawal of a thin, cold-based ice margin that reached the central interior of the island by ~ 14 cal ka BP. The elevation of the marine limit is greater than previously recognized and consistent with greater glacioisostatic crustal unloading by a more expansive LIS. These results complement emerging bathymetric observations from the Arctic Ocean, which indicate glacial erosion during the Last Glacial Maximum (LGM) to depths of up to 450 m.  相似文献   

13.
Late-Pleistocene deposits in north County Mayo were deposited in three main glacigenic environments. 1. Drumlins and basal tills were formed when ice moved from the Irish lowlands and local mountain catchments into Donegal Bay. 2. Gilbert-type deltas accumulated up to 80m I.O.D. on the lowlands and subaqueous moraines formed across minor valleys when marine-based ice grounded inland. 3. A thick drape of fossiliferous glaciomarine mud along the coastal fringe was deposited from meltwater plumes and by ice-rafting immediately outside of these ice limits. The muds contain an Elphidium clavatum-dominated, low-diversity microfauna which is characteristic of cold-water conditions adjacent to glacier termini. Valves of Macoma calcarea from the mud have been 14C dated at 16940 ± 120 and 17300 ± 100 BP. The high-level delta complex was deposited from tidewater glaciers in a peripheral depression adjacent to the drumlin ice limits of north County Mayo. Although the field evidence cannot be used to determine former sea level history with any accuracy, it poses general problems for sea level history and isostatic effects of the last major ice sheet in the west of Ireland. Raised glaciomarine sequences commonly occur in close association with drumlin ice limits elsewhere in Ireland and represent marine transgressions prior to glacial unloading. It is suggested that the magnitudes and patterns of crustal depression are greater and geometrically more complex at the margins of ice sheets in Ireland than hitherto realised.  相似文献   

14.
Three localities with marginal moraines deposited by former cirque glaciers are investigated in east-central southern Norway. The wet-based (erosive) cirque glaciers with aspects towards S-SW and N-NE are mapped at altitudes above 1100 m, and have a mean equilibrium-line altitude of 1275 m. With a suggested mean annual winter precipitation close to the average for the modern accumulation season (1 October-30 April) when the cirque glaciers existed, the mean air-temperature depression during the ablation season (1 May-30 September) is calculated to be 6–7°C lower than at present. The high-altitude cirques of central Rondane were still covered by ice when the low-altitude cirque glaciers developed in distal position for this massif in eastern Rondane and on isolated mountains. Hence, the cirque glaciers are suggested to have existed during the deglaciation after the Late Weichselian maximum, and most likely during the Younger Dryas (11000–10000 BP). The cirque glaciers indicate a downwasting ice-sheet surface well below an altitude of 1100 m prior to the Younger Dryas, and this supports a limited (small) vertical extent for the Late Weichselian ice sheet in this region. With the contemporaneous level for instantaneous glacierization (glaciation threshold) just below the highest elevated peaks in east-central southern Norway, this fits with the idea of a continuous downwasting of the Late Weichselian ice sheet since the 'first' nunataks appeared. The occurrence of the cirque glaciers indicates a multidomed Scandinavian ice-sheet geometry during the Late Weichselian.  相似文献   

15.
《Quaternary Science Reviews》2007,26(7-8):1149-1191
Quaternary glacial stratigraphy and relative sea-level changes reveal at least four expansions of the Kara Sea ice sheet over the Severnaya Zemlya Archipelago at 79°N in the Russian Arctic, as indicated from tills interbedded with marine sediments, exposed in stratigraphic superposition, and from raised-beach sequences that occur at altitudes up to 140 m a.s.l. Chronologic control is provided by AMS 14C, electron-spin resonance, green-stimulated luminescence, and aspartic-acid geochronology. Major glaciations followed by deglaciation and marine inundation occurred during MIS 10-9, MIS 8-7, MIS 6-5e and MIS 5d-3. The MIS 6-5e event, associated with the high marine limit, implies ice-sheet thickness of >2000 m only 200 km from the deep Arctic Ocean, consistent with published evidence of ice grounding at ∼1000 m water depth in the central Arctic Ocean. Till fabrics and glacial tectonics record repeated expansions of local ice caps exclusively, suggesting wet-based ice cap advance followed by cold-based regional ice-sheet expansion. Local ice caps over highland sites along the perimeter of the shallow Kara Sea, including the Byrranga Mountains, appear to have repeatedly fostered initiation of a large Kara Sea ice sheet, with exception of the Last Glacial Maximum (MIS 2), when Kara Sea ice did not impact Severnaya Zemlya and barely graced northernmost Taymyr Peninsula.  相似文献   

16.
Despite a wealth of research on the patterns and timing of glaciation in Glen Roy over the last 150 years, glacial events within Glen Turret remain heavily debated. These debates centre on the extent and source of Loch Lomond Stadial (Younger Dryas) ice in Glen Turret, and the implications for the age and genesis of the Turret Fan. Here we present details of recent systematic geomorphological mapping of Glen Turret and the neighbouring valleys to the north and east. The geomorphological evidence recorded indicates a plateau icefield style of glaciation centred on the Carn Dearg plateau, of which the Turret Glacier was an outlet. A morphostratigraphical approach is used to identify a relative chronology of glacial events, and suggests that the Turret Fan may have formed prior to the Loch Lomond Stadial. A reconstruction of the Carn Dearg plateau icefield is presented, which was connected to the larger Monadhliath Icefield to the east. Equilibrium line altitudes for the outlet glaciers range from 560 ± 20 m to 646 ± 20 m and are comparable with those calculated for surrounding regions. This research suggests that the Turret Fan is predominantly an older feature that was deposited by a more extensive plateau ice-sourced Turret Glacier prior to the Loch Lomond Stadial, most likely during or immediately after deglaciation of the last ice sheet.  相似文献   

17.
The Late Devensian (<20 ka BP) glacial geology of the Irish Sea Basin (4000 km2) is an event stratigraphy recording the entry of marine waters into a glacio-isostatically-depressed basin, and the rapid retreat of the Irish Sea Glacier as a tidewater ice margin. Marine limits occur up to 140 m O.D. Across much of the central basin, the ice margin was uncoupled from its bed exposing a subglacially-scoured topography to glaciomarine processes. The Irish Sea Glacier was a major drainage conduit of the last British Ice Sheet; calving of the marine ice margin resulted in fast flow (surging) of ice streams recorded by drumlin fields around the northern basin margin and tunnel valleys. Rapid evacuation of the basin may have stranded large areas of dead ice in peripheral zones (e.g. Cheshire/Shropshire Lowlands) and initiated the collapse of the ice sheet.Thick wedges of ice-contact glaciomarine sediments were deposited during ice retreat as morainal bank complexes by successive tidewater ice margins stabilized at pinning points around the Irish Sea coast. Where morainal banks occur on the seaward side of drumlin swarms there is a clear sequential relationship between rapid ice loss from calving ice margins, the development of fast flowing ice streams, drumlinization and the pumping of subglacial sediment to tidewater. Raised delta complexes are locally associated with marine limits along the high relief coastal margins of Wales, east central Ireland, and the Lake District. Associated valley infill complexes record downslope resedimentation of heterogenous sediments into the marine environment during ice retreat. Co-eval offshore deposits are represented by well-stratified glaciomarine complexes that infill a subglacially-scoured topography that shows networks of tunnel valleys. Glaciomarine mud drapes occur well to the south of the maximum limit of grounded ice in the basin (e.g. North Devon, Scilly Islands, Southern Ireland). The age of these distal sediments, previously mapped as pre-Devensian tills, is constrained by amino acid ratios.Basin rebound following deglaciation was rapid, with over 100 m recovery in 3 ka, and was followed by a low marine still stand. Peat, accumulating in offshore areas now as much as 55 m below sea level has been drowned by the postglacial eustatic rise in sea level.The glacio-sedimentary model identified in this paper, involving rapid ice retreat and related sedimentation triggered by rising relative sea level, suggests that isotatic downwarping is an important mechanism for deglaciating continental shelves.  相似文献   

18.
Major and trace element chemical analyses of the Plio‐Pleistocene Bardin Bluffs Formation, on the margin of a major ice‐stream of the East Antarctic Ice Sheet, yield an anomalous chemically altered sediment composition. The Bardin Bluffs Formation of the Pagodroma Group is one of the key deposits on the Antarctic continent recording glaciomarine sedimentation under open marine fjord conditions as recently as the Plio‐Pleistocene. In modern fjords occupied by outlet glaciers of ice sheets, the composition of fine‐grained terrigenous sediments approaches that of unweathered rock types exposed upstream. In the Bardin Bluffs Formation, average abundances of stable elements (Ti, Al, Zr) approach average upper crustal compositions and the element ratios are consistent with sediments with a cratonic source, implying glacial dispersal from a large shield area through the Lambert Glacier drainage system. Interestingly, the chemical index of alteration (CIA) of these sediments has values similar to those of average shales formed under conditions of chemical weathering. The sediments are particularly depleted in silicate Ca, which has been observed elsewhere in glacial muds sourced from pre‐glacial saprolites. The anomalous chemistry of the Bardin Bluffs Formation can be explained by a sequence of events, involving chemical weathering prior to glacial expansion and erosion. The presence of a remnant 1·5 m deep late Neogene weathering profile at the base of the Bardin Bluffs sequence corroborates this conclusion. Supply of large quantities of chemically weathered materials to Antarctic marginal basins requires at least partial deglaciation of the continent and was previously regarded as uncharacteristic for late Neogene Antarctica.  相似文献   

19.
In this paper we present geological evidence from the Larsemann Hills (Lambert Glacier – Amery Ice Shelf region, East Antarctica) of marine sediments at an altitude of c. 8 m a.s.l., as revealed by diatom, pigment and geochemical proxies in a lake sediment core. The sediments yielded radiocarbon dates between c. 26 650 and 28 750 14C yr BP (31 366–33 228 cal yr BP). This information can be used to constrain relative sea level adjacent to the Lambert Glacier at the end of Marine Isotope Stage 3. These data are compared with the age and altitude of Marine Isotope Stage 3 marine deposits elsewhere in East Antarctica and discussed with reference to late Quaternary ice sheet history and eustatic sea-level change.  相似文献   

20.
The Antarctic Ice Sheet plays a major role in the global system, and the large ice streams discharging into the circumpolar sea represent its gateways to the world's oceans. Satellite radar altimeter data provide an opportunity for mapping surface elevation at kilometer-resolution with meter-accuracy. Geostatistical methods have been developed for the analysis of these data. Applications to Seasat data and data from the Geosat Exact Repeat Mission indicate that the grounding line of Lambert Glacier/Amery Ice Shelf, the largest ice stream in East Antarctica, has advanced 10–12 km between 1978 and 1987–89. The objectives of this paper are to explore possibilities and limitations of satellite-altimetry-based mapping to capture changes for shorter time windows and for smaller areas, and to investigate some methodological aspects of the data analysis. We establish that one season of radar altimeter data is sufficient for constructing a map. This allows study of interannual variation and is the key for a time-series analysis approach to study changes in ice streams. Maps of the lower Lambert Glacier and the entire Amery Ice Shelf are presented for austral winters 1978, 1987, 1988, and 1989. As a first step toward understanding the dynamics of the ice-stream/ice-shelf system, elevation changes are calculated for grounded ice, the grounding zone, and floating ice. In the absence of (sufficient) surface gravity control for the Lambert Glacier/Amery Ice Shelf area, altimetry-based maps may facilitate improvement of geoid models as they provide constraints on the terrain correction in the inverse gravimetric problem.  相似文献   

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