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1.
Geomorphological evidence for four former local glaciers has been mapped in the Aran and Arenig Mountains, North Wales. Former glacial extent was deduced from the distribution and assemblage of end and lateral moraines, hummocky moraine, boulder limits, drift limits and periglacial trimlines. Comparison of infilled lake sediment stratigraphies inside and outside of the former glacier limits suggests a Loch Lomond Stadial (Late Devensian) age of the former glaciers (c. 12.9–11.5 cal. ka BP ). This finding is also supported by periglacial–landform contrasts between the land inside and outside of the glacier limits. Reconstruction of the four glaciers illustrates a mean equilibrium line altitude (ELA) of c. 504 m. From the reconstructed ELAs and the combination of precipitation and snowblow input for total accumulation, by analogy with Norwegian glaciers, a mean sea‐level July temperature is calculated at 8.4°C. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

2.
Geomorphological mapping of southern Skye indicates evidence for a single readvance of locally-nourished glaciers. These comprised a major icefield that occupied c. 155 km2 of the main mountain area, a small icefield c. 10 km2 in extent in the Kyleakin hills and ten corrie glaciers with a total area of c. 16 km2. The absence of Lateglacial pollen sites, shorelines and periglacial features within the limits of local glaciation implies a Loch Lomond Readvance age for this glacial event. The area-weighted mean equilibrium line altitude (ELA) of the reconstructed Loch Lomond Readvance glaciers (319 m) conforms with a regional eastwards rise in ELAs that indicates dominant westerly airstreams during the Loch Lomond Stadial. An easterly decline in ELAs across the former icefields is interpreted in terms of easterly transfer of snow across ice-sheds by westerly winds, though the altitudes of corrie glacier ELAs suggest that the dominant snow-bearing winds were southerlies. Calculations based on the area-weighted mean ELA for the major icefield (308 m) indicate a stadial mean July sea-level temperature of c. 6 °C. The anomalously low gradients of certain former icefield outlet glaciers are attributed to deformation of subglacial sediment, an effect that may vitiate the assumption of linear ablation/accumulation gradients in the calculation of former ELAs for reconstructed glaciers.  相似文献   

3.
Geomorphological mapping in the West Drumochter Hills provides evidence of a readvance of locally nourished glaciers during the Loch Lomond (Younger Dryas) Stade, in the form of an icefield 67.7 km2 in area drained by outlet glaciers. The icefield limits accord broadly with those proposed by Sissons (1980) but all geomorphic, stratigraphic and sedimentological evidence conflicts with a recent proposal that the landforms in the area reflect southwestwards retreat of the last ice sheet. Up‐valley continuity of recessional moraines indicates that the ice remained active and close to climatic equilibrium during the earlier stages of glacier retreat, consistent with slow warming following the coldest part of the stade. The pattern of equilibrium line altitudes (ELAs) across the icefield is consistent with transfer of snow by westerly and southerly winds. The ELA of the reconstructed icefield as a whole is 622–629 m, although this figure is likely to be lower than the regional (climatic) ELA because the icefield probably received additional snow blown from adjacent plateau surfaces and slopes. Inclusion of potential snow‐blow areas in the ELA calculation yields a value of 648–656 m; the climatic ELA is therefore likely to have lain between 622 and 656 m. Mean June to August temperature at the ELA, based on chironomid assemblages at two sites, falls within the range 4.0 ± 0.7°C. Empirical relationships between temperature and precipitation at modern glacier ELAs indicate that mean annual precipitation (MAP) at the ELA was 1977 ± 464 mm, statistically indistinguishable from modern values. Comparison with precipitation values calculated for the Isle of Mull on the west coast suggest that the precipitation gradient across the Central Highlands of Scotland was steeper during the Loch Lomond Stade than at present, probably as the result of efficient scavenging of precipitation from westerly airflows by the West Highland Icefield. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

4.
The tongue-shaped mass of debris and associated ridges on the cirque floor below Craig Cerrig-gleisiad, Brecon Beacons National Park is important and controversial because it has been attributed to more than one glacier advance during the Late Devensian. A new origin is proposed involving landslide development from the collapse of part of the western headwall followed by a single phase of glacier development in the Loch Lomond Stadial (Younger Dryas), which reworked the landslide sediments. Evidence for this landslide, which provides useful criteria for differentiating moraines formed by small glaciers from landslides, lies in tension cracks, backward-tilted blocks and bedrock joints dipping out of the western headwall, together with lateral levées, upstanding termini and angular clasts with only occasional, indistinct striae on the tongue-shaped mass, which is interpreted as a flowslide. Glacier reworking of debris in the upper part of the Cwm Cerrig-gleisiad landslide is indicated by subparallel ridges rising to 20 m above the cirque floor containing abraded clasts (16-32% striated). This interpretation is supported by a comparison with the morphological and sedimentary characteristics of a neighbouring landslide at Fan Dringarth, where no glacier developed in the Loch Lomond Stadial. The existence of paraglacial landsliding has significant palaeoenvironmental implications leading to: (1) erroneously large estimates of equilibrium line depression ($Δ$ELA) in the Loch Lomond Stadial; (2) consequent underestimates of summer palaeotemperatures and/or overestimates of the contribution of wind-drifted snow to glacier accumulation; and (3) larger moraines than usual and overestimation of the efficacy of glacial erosion because of antecedent processes.  相似文献   

5.
Geomorphological mapping of Mull provides evidence for an icefield 143 km2 in area flanked by six corrie glaciers with a total area of ca. 13 km2. The absence of Lateglacial periglacial features, shorelines and pollen sites from the area occupied by this readvance, together with radiocarbon dating of shell fragments, confirm that it occurred during the Loch Lomond (Younger Dryas) Stade. The thickness of glacigenic deposits within the area of the readvance is attributed to reworking of paraglacial sediments. Up‐valley continuity of recessional moraines indicates that the ice remained active and near to equilibrium during retreat, consistent with slow warming following the coldest part of the stade. Reconstructed equilibrium line altitudes (ELAs) imply vigorous snow‐blowing by westerly winds, and are consistent with a general southwestwards decline in ELAs across the Scottish Highlands. An ELA of 250 m was calculated for the Mull Icefield using an ablation:accumulation balance ratio (ABR) approach. Palaeotemperature and palaeoprecipitation estimates were derived by calculating a theoretical regional ELA from meteorological data and assuming that the combination of temperature and precipitation implied by the theoretical ELA approximates conditions at 250 m on Mull during the Loch Lomond Stade. The result indicates a mean July sea‐level temperature of 5.7 ± 0.5°C and a mean annual precipitation at 250 m of ca. 2700–3800 mm (best estimate 3200 mm), indicating higher precipitation totals than at present owing to more vigorous atmospheric circulation. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

6.
There is empirical evidence of a nonlinear relation between annual precipitation, or accumulation, and summer mean temperature at the equilibrium line altitude (ELA) on glaciers around the world. The degree-day model gives a similar relation between accumulation and summer temperature, although instead of a single universal curve there is a family of curves depending upon the annual temperature range. Furthermore, the degree-day model also gives nonlinear relations between accumulation and annual mean temperature. Thus, estimations of accumulation can be made from both summer and annual temperatures at the ELA of former reconstructed glaciers, such as those in Greece. This is particularly useful since these climatic variables have major implications for biological proxies, such as vegetation history indicated in the pollen record, and for periglacial proxies, such as permafrost distributions indicated in the geomorphological record. The close relationship between glaciers and climate provides one of the most precise methods for reconstructing former climates and offers considerable potential for resolving our understanding of Pleistocene cold-stage climates.  相似文献   

7.
近50年来北极斯瓦尔巴地区冰川物质平衡变化特征   总被引：3，自引：2，他引：1  
利用长时间序列的冰川物质平衡资料,详细分析了北极斯瓦尔巴地区冰川的物质平衡变化特征以及气候因子对物质平衡的影响。结果表明：近50年来斯瓦尔巴地区冰川物质平衡变化主要呈负平衡、零平衡/略微增长两种状态。冰川净平衡一般为负值,年际变化波动幅度较大且呈负平衡趋势,累积物质平衡表现出长期稳定的负平衡增长态势。除Kongsvegen冰川外,其他冰川不存在短期内的平衡波动。季节变化表现为夏季消融、冬季积累,且夏季消融比冬季积累波动更大,冰川净平衡与夏季消融保持同步变化趋势。冰川净平衡与平衡线高度（ELA）呈负相关（平均相关系数为-0.89）,与积累区面积比率（AAR）呈正相关（平均相关系数为0.84）,该地区大多数冰川AAR减小,说明冰川物质补给处于劣势,冰川物质平衡向负平衡发展。夏季气温升高是斯瓦尔巴地区冰川表面物质加速亏损的直接原因。  相似文献   

8.
Geomorphological mapping of northern Arran provides evidence for two advances of locally nourished glaciers, the younger being attributable to the Loch Lomond Stade (LLS) of ca. 12.9–11.5 k yr BP, primarily through the mutually exclusive relationship between glacial limits and Lateglacial periglacial features. The age of the earlier advance is unknown. Inferred LLS glacier cover comprised two small icefields and eight small corrie or valley glaciers and totalled 11.1 km2. ELAs reconstructed using area–altitude balance ratio methods range from 268 m to 631 m for individual glaciers, with an area‐weighted mean ELA of 371 m. ELAs of individual glaciers are strongly related to snow‐contributing areas. The area‐weighted mean ELA is consistent with a north–south decline in LLS ELAs along the west coast of Great Britain. This decline has an average latitudinal gradient of 70 m 100 km?1, equivalent to a mean southwards ablation‐season temperature increase of ca. 0.42°C 100 km?1. Mean June–August temperatures at the regional climatic ELA, estimated from chironomid assemblages in SE Scotland, lay between 5.7 ± 0.1°C and 4.1 ± 0.2°C. Empirical relationships between temperature and precipitation at modern glacier ELAs indicate equivalent mean annual precipitation at the ELA lay between 2002 ± 490 mm and 2615 ± 449 mm. These figures suggest that stadial precipitation on Arran fell within a range between +8% and ?33% of present mean annual precipitation. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

9.
Geomorphological mapping has identified the former existence of five cirque glaciers that formed during the Loch Lomond Stadial in the western Pennines, northern England. Landforms in Mallerstang, which previously have been interpreted as moraine ridges, are shown to be better explained as large complex landslides. Reconstruction of these former glaciers has allowed the calculation of the former equilibrium line altitudes (ELA) by a number of different methods. Values for the ELA show a range across the area from 311 m to 608 m OD, but with low values (311 m and 428 m) for the two western glaciers. These are explained by the existence of large plateau areas adjacent to the former glaciers, which contributed additional mass to the glaciers by snowblow on to the glacier surfaces. Delimitation of the potential snowblow area for each glacier shows that it has a distinct orientation, with the western sector (225–315°) being statistically significant with the ELA indicating the importance of winds from this direction in determining the existence of these palaeoglaciers. The significance of snowblow for the generation of small glaciers in marginal areas means that such local factors must be investigated before regional firn line trends are determined in former glaciated areas.  相似文献   

10.
Geomorphological mapping of North Harris provides evidence for the former existence of 10 glaciers with a total area of ca 35 km2. A Loch Lomond (Younger Dryas) Stadial age (ca 12.9–11.5 kyr BP) for this glacial episode is inferred from glacier configuration, landsystems dominated by hummocky recessional moraines, and relationships with Lateglacial periglacial phenomena. Equilibrium line altitudes (ELAs) of 150–289 m were calculated for individual glaciers. ELA variability mainly reflects differences in snow-contributing area. The area-weighted mean ELA (204 m) is consistent with a northwards decline in ELAs along the western seaboard of the British Isles of 69.5 m (100 km)−1, equivalent to a northwards ablation-season temperature decrease of 0.42 °C (100 km)−1. This latitudinal temperature gradient implies a mean July sea-level temperature of ca 7.2 °C for the coldest part of the stade, roughly 6 °C lower than at present. Sea-level precipitation at the time of the LLS glacial maximum is inferred to have been between ca 1970±200 and 2350±200 mm yr−1, implying that LLS precipitation was up to 25% greater than now. Patterns of recessional moraines indicate that the glaciers remained close to climatic equilibrium as they retreated to their sources, though moraine belts implying near-stationary or readvancing ice margins on flat valley floors are separated by moraine-free zones indicating uninterrupted retreat. Calculation of ELAs for ‘residual’ glaciers in former source areas suggests that summer warming of 1.0 °C would have resulted in shrinkage of the glaciers to their sources.  相似文献   

11.
The deglaciation of Skye at the close of the Loch Lomond Stadial is assessed on the basis of detailed geomorphological mapping and pollen-stratigraphic correlations. It is concluded that deglaciation proceeded in two distinct stages. The first was marked by numerous glacier stillstands and readvances, while uninterrupted retreat and local glacier stagnation occurred during the second and final stage. The pollen evidence indicates that the first stage was well advanced before the marked thermal improvement at the start of the Flandrian, and it is inferred that initial glacier retreat occurred in response to a decline in precipitation in the later part of the Loch Lomond Stadial. The first stage of glacier retreat continued into the early Flandrian, during which climatic amelioration was interrupted briefly. Final deglaciation appears to have occurred rapidly in response to sustained temperature increases. The collective evidence also indicates spatial variations in the timing of deglaciation, which appear to reflect differences in glacier morphology.  相似文献   

12.
Glacial geomorphology relating to the Loch Lomond Stadial (Younger Dryas) in Britain is used to construct five glacial landsystem models. These landsystems lie on a continuum of increasing ice thickness and decreasing topographic control and typify the principal styles of glaciation during the stadial. The landsystems comprise: the cirque/niche glacier landsystem, the alpine icefield landsystem, the lowland piedmont lobe landsystem, the plateau icefield landsystem and the icecap landsystem. Geomorphological features representing the icecap landsystem are present only at the centre of the West Highland Glacier Complex, which was flanked primarily by satellite alpine and plateau icefields. The cirque/niche glacier landsystem was present predominantly in areas that experienced conditions only marginally favourable for glacier development at peripheral sites. Three styles of glacier retreat are recorded by the geomorphology: active, two‐phase and uninterrupted retreat. Of these, active retreat appears to be most widespread within the Loch Lomond Stadial limits. These retreat styles reflect a combination of climatic and topographic conditions, coupled with local factors influencing the preservation of landforms from which retreat dynamics can be inferred. Likewise, the distribution of landsystems was influenced by an interplay between topography and climate, with glacier formation being facilitated in locations where topographical conditions aided in the accumulation of snow. The pattern also supports the existence of previously recognized northward and eastward precipitation gradients across Britain during the stadial.  相似文献   

13.
北极Svalbard地区冰川物质平衡研究进展   总被引：6，自引：1，他引：5  
回顾了Svalbard地区冰川物质平衡观测研究的历史,总结了该区域自1950年代以来冰川物质平衡的主要特征.结果表明:1)冰川净平衡、冬季积累和夏季消融没有明显长期变化趋势,净平衡一般为负值,导致冰体不断地缩减;2)冰川冬季积累年际波动较小,基本保持稳定状态;夏季消融年际波动较大,但没有融化增加的迹象;3)面积/海拔高度分布的不同导致了各冰川物质平衡的差异,面积较小(<10 km2)、海拔较低(<500 m)的冰川持续退缩;而具有更高海拔高度、更大面积的冰川则处于平衡或略微增长状态;4)净平衡与冰川平衡线高度(ELA)具有良好的负相关性,平均物质平衡梯度无明显变化,物质平衡对平衡线高度变化(气候变化)的敏感性保持稳定;5)Svalbard地区冰川物质平衡与该区夏季各月正积温和冬季降水具有密切的相关性.最后提出了加强Svalbard地区冰川物质平衡内补给过程研究以及与我国天山冰川物质平衡的对比研究,以求更加准确地认识Svalbard地区冰川物质平衡特征.  相似文献   

14.
丁永建  谢自楚 《冰川冻土》1991,13(3):213-218
  相似文献   

15.
A wide variety of Late Devensian periglacial landforms developed on Scottish mountains both before ca. 13,000 BP and during the Loch Lomond Stadial of ca. 11,000-10,000 BP. Nearly all such features are now inactive. Late Devensian periglacial weathering produced three types of regolith mantle (openwork block deposits, sandy diamicts and silt-rich frost-susceptible diamicts), each of which supports a characteristic assemblage of relict landforms. On upper slopes these include large-scale sorted circles and stripes, earth hummocks and nonsorted relief stripes, sorted and nonsorted solifluction features, massive boulder sheets and lobes, and nivation benches. Talus, protalus ramparts, rock glaciers and alluvial fans also developed at the base of mountain slopes.The distribution of Late Devensian periglacial features on Scottish mountains is locally controlled by topography, the response of underlying rocks to periglacial weathering and the limits of former glaciers. Regional variations in the altitude of certain forms of Loch Lomond Stadial age (particularly protalus ramparts and rock glaciers) indicate a decrease in former snowfall eastwards across the Scottish Highlands and northwards from the Highland Boundary Fault. Several upland periglacial features are also diagnostic of former permafrost, and complement palaeotemperature reconstructions based on ice-wedge casts and the equilibrium firn line altitudes of stadial glaciers. These suggest that under stadial conditions mean January temperatures at 600 m and 1000 m on mountains in the Western Grampians must have been no higher than −20°C and −23°C respectively, and possibly several degrees lower.  相似文献   

16.
聂宁  张智杰  张万昌  邓财 《冰川冻土》2013,35(3):541-552
综合运用RS和GIS手段, 利用卫星遥感影像, 结合中国第一次冰川编目数据及数字高程模型(DEM), 获取了雅鲁藏布江流域不同朝向上冰川面积分布、 冰川面积随高度带分布状况统计结果, 及3个冰川聚集区21条大型海洋性冰川在1976、 1988、 2005年的冰川面积、 厚度、 冰储量及物质平衡线等基本参数, 丰富了该研究区相关冰川信息, 并统计分析了21条大型冰川面积变化状况及与气候变化的响应关系. 研究表明: 3个区域冰川在1976-1988年和1988-2005年时间段内随着气温、 降水的变化出现了相应的波动, 但总的来说在1976-2005年间, 这21条大型海洋性冰川并没有出现明显的前进或退缩现象, 这可能是由于降水的增加抵消了气温升高给冰川积累带来的不利影响, 也可能是由于大型冰川在高海拔地区有较大的积累区补给造成的, 进一步的研究亦在进展中.  相似文献   

17.
Considerable uncertainty surrounds the timing of glacier advance and retreat during the Younger Dryas or Loch Lomond Stade (LLS) in the Scottish Highlands. Some studies favour ice advance until near the end of the stade (c. 11.7 ka), whereas others support the culmination of glacier advance in mid‐stade (c. 12.6–12.4 ka). Most published 10 Be exposure ages reported for boulders on moraines or deglacial sites post‐date the end of the LLS, and thus appear to favour the former view, but recalibration of 33 10 Be ages using a locally derived 10 Be production rate and assuming rock surface erosion rates of zero to 1 mm ka?1 produces exposure ages 130–980 years older than those originally reported. The recalibrated ages are filtered to exclude anomalous data, and then employed to generate aggregate probability density distributions for the timing of moraine deposition and deglaciation. The results suggest that the most probable age for the timing of the deposition of the sampled outermost moraines lies in the interval 12.4–12.1 ka or earlier. Deglacial ages obtained for sites inside Loch Lomond Stadial glacier limits imply that glaciers at some or all of the sampled sites were retreating prior to 12.1 ka. Use of aggregated data does not exclude the possibility of asynchronous glacier behaviour at different sites, but confirms that some glaciers reached their maximum limits and began to retreat several centuries before the rapid warming that terminated the LLS at 11.7–11.6 ka, consistent with the retrodictions of recent numerical modelling experiments and with geomorphological evidence for gradual oscillatory ice‐margin retreat under stadial conditions.  相似文献   

18.
Northern Folgefonna (c. 23 km2), is a nearly circular maritime ice cap located on the Folgefonna Peninsula in Hardanger, western Norway. By combining the position of marginal moraines with AMS radiocarbon dated glacier‐meltwater induced sediments in proglacial lakes draining northern Folgefonna, a continuous high‐resolution record of variations in glacier size and equilibrium‐line altitudes (ELAs) during the Lateglacial and early Holocene has been obtained. After the termination of the Younger Dryas (c. 11 500 cal. yr BP), a short‐lived (100–150 years) climatically induced glacier readvance termed the ‘Jondal Event 1’ occurred within the ‘Preboreal Oscillation’ (PBO) c. 11 100 cal. yr BP. Bracketed to 10 550–10 450 cal. yr BP, a second glacier readvance is named the ‘Jondal Event 2’. A third readvance occurred about 10 000 cal. yr BP and corresponds with the ‘Erdalen Event 1’ recorded at Jostedalsbreen. An exponential relationship between mean solid winter precipitation and ablation‐season temperature at the ELA of Norwegian glaciers is used to reconstruct former variations in winter precipitation based on the corresponding ELA and an independent proxy for summer temperature. Compared to the present, the Younger Dryas was much colder and drier, the ‘Jondal Event 1’/PBO was colder and somewhat drier, and the ‘Jondal Event 2’ was much wetter. The ‘Erdalen Event 1’ started as rather dry and terminated as somewhat wetter. Variations in glacier magnitude/ELAs and corresponding palaeoclimatic reconstructions at northern Folgefonna suggest that low‐altitude cirque glaciers (lowest altitude of marginal moraines 290 m) in the area existed for the last time during the Younger Dryas. These low‐altitude cirque glaciers of suggested Younger Dryas age do not fit into the previous reconstructions of the Younger Dryas ice sheet in Hardanger. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

19.
中国冰川变化对气候变化的响应程度研究   总被引：3，自引：2，他引：1  
理清冰川变化对气候变化的响应程度、揭示响应度的空间变化规律,是开展冰川变化预估及其对社会经济影响程度量化研究的基础。使用1958-2010年西部地区150个气象站点的夏季平均气温和年降水量资料、中国第一、二次冰川编目数据,通过夏季平均气温和年降水量变化趋势值定量反映气候变化,以冰川面积变化率表征冰川变化,借助GIS技术平台,采用参照对比方法,从宏观层面研究了中国西部冰川变化对气候变化的响应程度。依据等分分类法（Equal Interval）,将响应程度分为极低度响应、低度响应、中度响应、高度响应、极高度响应5级。结果表明：中国冰川变化对气候变化的响应方式与程度不同,对夏季平均气温变化表现为正响应,而对年降水量变化主要表现为负响应,冰川分布区年降水量增加带来的冰川积累量增多不足以抵消因温度升高而增加的消融量,升温是中国西部冰川快速退缩的主导性因素。就整体而言,冰川变化对夏季平均气温变化的响应程度相对较低,但局部地区冰川变化对温度变化高度敏感,响应程度高与极高。不同类型冰川的变化对夏季平均气温变化的响应程度亦不同,海洋型冰川的变化以中高度响应为主,极大陆型冰川的变化主要呈现极低、低响应程度,而大陆型冰川变化的响应程度呈两级化。  相似文献   

20.
山地冰川对气候变化的响应最为敏感, 在全球变暖的大背景下山地冰川和极地冰盖正在发生显著的变化。冰川运动速度的变化是气候变化的结果之一。乌鲁木齐河源1号冰川是中国西部山地冰川的代表, 本文以1981-2007年27a的运动速度资料与1982年以来的季节运动速度资料为基础, 结合冰川物质平衡、气温、降水等资料分析冰川运动速度对气候变化的响应。研究发现, 27a来1号冰川运动速度下降趋势明显, 冬、夏季节运动速度波动较大, 但夏季运动速度较大。气候变化通过冰川物质平衡的改变作用于冰川运动速度, 物质平衡的持续亏损最终导致了冰川运动速度的持续降低。夏季的高温与降水对冰川运动速度具有加速的作用。  相似文献   

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