Exploring the extent to which fluctuations in ice-rafted debris reflect mass changes in the source ice sheet: a model–observation comparison using the last British–Irish Ice Sheet     

David J. Wilton  Grant R. Bigg  James D. Scourse  Jeremy C. Ely  Chris D. Clark 《第四纪科学杂志》2021,36(5):934-945

The British and Irish Ice Sheet (BIIS) was highly dynamic during the Late Quaternary, with considerable regional differences in the timing and extent of its change. This was reflected in equally variable offshore ice-rafted debris (IRD) records. Here we reconcile these two records using the FRUGAL intermediate complexity iceberg–climate model, with varying BIIS catchment-level iceberg fluxes, to simulate change in IRD origin and magnitude along the western European margin at 1000-year time steps during the height of the last BIIS glaciation (31–6 ka bp ). This modelled IRD variability is compared with existing IRD records from the deep ocean at five cores along this margin. There is general agreement of the temporal and spatial IRD variability between observations and model through this period. The Porcupine Bank off northwestern Ireland was confirmed by the modelling as a major dividing line between sites possessing exclusively northern or southern source regions for offshore IRD. During Heinrich events 1 and 2, the cores show evidence of a proportion of North American IRD, more particularly to the south of the British Isles. Modelling supports this southern bias for likely Heinrich impact, but also suggests North American IRD will only reach the British margin in unusual circumstances.  相似文献   

Timing and pace of ice-sheet withdrawal across the marine–terrestrial transition west of Ireland during the last glaciation     

Colm Ó Cofaigh  S. Louise Callard  David H. Roberts  Richard C. Chiverrell  C. K. Ballantyne  David J. A. Evans  Margot Saher  Katrien J. J. Van Landeghem  Rachel Smedley  Sara Benetti  Matthew Burke  Chris D. Clark  Geoff A. T. Duller  Derek Fabel  Stephen J. Livingstone  Stephen Mccarron  Alicia Medialdea  Steven G. Moreton  Fabio Sacchetti 《第四纪科学杂志》2021,36(5):805-832

Understanding the pace and drivers of marine-based ice-sheet retreat relies upon the integration of numerical ice-sheet models with observations from contemporary polar ice sheets and well-constrained palaeo-glaciological reconstructions. This paper provides a reconstruction of the retreat of the last British–Irish Ice Sheet (BIIS) from the Atlantic shelf west of Ireland during and following the Last Glacial Maximum (LGM). It uses marine-geophysical data and sediment cores dated by radiocarbon, combined with terrestrial cosmogenic nuclide and optically stimulated luminescence dating of onshore ice-marginal landforms, to reconstruct the timing and rate of ice-sheet retreat from the continental shelf and across the adjoining coastline of Ireland, thus including the switch from a marine- to a terrestrially-based ice-sheet margin. Seafloor bathymetric data in the form of moraines and grounding-zone wedges on the continental shelf record an extensive ice sheet west of Ireland during the LGM which advanced to the outer shelf. This interpretation is supported by the presence of dated subglacial tills and overridden glacimarine sediments from across the Porcupine Bank, a westwards extension of the Irish continental shelf. The ice sheet was grounded on the outer shelf at ~26.8 ka cal bp with initial retreat underway by 25.9 ka cal bp. Retreat was not a continuous process but was punctuated by marginal oscillations until ~24.3 ka cal bp. The ice sheet thereafter retreated to the mid-shelf where it formed a large grounding-zone complex at ~23.7 ka cal bp. This retreat occurred in a glacimarine environment. The Aran Islands on the inner continental shelf were ice-free by ~19.5 ka bp and the ice sheet had become largely terrestrially based by 17.3 ka bp. This suggests that the Aran Islands acted to stabilize and slow overall ice-sheet retreat once the BIIS margin had reached the inner shelf. Our results constrain the timing of initial retreat of the BIIS from the outer shelf west of Ireland to the period of minimum global eustatic sea level. Initial retreat was driven, at least in part, by glacio-isostatically induced, high relative sea level. Net rates of ice-sheet retreat across the shelf were slow (62–19 m a⁻¹) and reduced (8 m a⁻¹) as the ice sheet vacated the inner shelf and moved onshore. A picture therefore emerges of an extensive BIIS on the Atlantic shelf west of Ireland, in which early, oscillatory retreat was followed by slow episodic retreat which decelerated further as the ice margin became terrestrially based. More broadly, this demonstrates the importance of localized controls, in particular bed topography, on modulating the retreat of marine-based sectors of ice sheets.  相似文献   

2013和2012年夏季格陵兰岛冰盖表面融化对比及可能的影响机理分析     

陈志强  刘骥平  范广洲  胡永云 《大气科学》2015,39(4):757-766

本文重点分析了2013年夏季格陵兰冰盖表面的融化特征, 并将2013年与2012年融化极值年的异常进行对比, 探讨二者之间存在的动力和热力差异及其对冰盖表面融化的影响和机制。结果表明:2013年夏季格陵兰冰盖表面最大融化范围仅为44%, 远小于2012年的97%, 持续的时间也比2012年短20天左右, 平均的融化面积和持续时间都接近气候平均态。2013年夏季大气环流异常与2012年近乎完全相反, 格陵兰及附近海域为低压异常, 500 hPa位势高度场为负异常, 大气环流和2012年相比更具有纬向型。格陵兰岛的北部和南部出现气旋异常, 有利于输送北极的冷空气到格陵兰岛, 不仅降低了夏季格陵兰冰盖表面的平均温度, 而且也减少了格陵兰高温事件发生的频率。同时, 2013年夏季格陵兰表面向下的辐射通量异常分布大体上呈西南—东北走向, 不同于 2012年的南北分布。尽管从分布上看, 总的向下辐射通量以正的短波分量为主, 但是长短波分量相互抵消使得 2013年夏季总的向下辐射通量接近气候平均态, 这使得辐射对冰盖表面温度的影响不明显。大气环流的动力和表面辐射收支的热力共同作用导致2013年夏季格陵兰冰盖表面融化经历了相对缓和的一年。  相似文献   

Dome A冰川学研究进展及深冰芯计划展望   总被引：3，自引：0，他引：3       下载免费PDF全文

唐学远  孙波  李院生  崔祥斌  李鑫 《极地研究》2012,24(1):77-86

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   

10Be and 26Al exposure‐age dating of bedrock surfaces on the Aran ridge,Wales: evidence for a thick Welsh Ice Cap at the Last Glacial Maximum     

Neil F. Glasser  Philip D. Hughes  Cassandra Fenton  Christoph Schnabel  Henrik Rother 《第四纪科学杂志》2012,27(1):97-104

This paper presents results of the analysis of paired cosmogenic isotopes (¹⁰Be and ²⁶Al) from eight quartz‐rich samples collected from ice‐moulded bedrock on the Aran ridge, the highest land in the British Isles south of Snowdon. On the Aran ridge, comprising the summits of Aran Fawddwy (905 m a.s.l.) and Aran Benllyn (885 m a.s.l.), ²⁶Al and ¹⁰Be ages indicate complete ice coverage and glacial erosion at the global Last Glacial Maximum (LGM). Six samples from the summit ridge above 750–800 m a.s.l. yielded paired ¹⁰Be and ²⁶Al ages ranging from 17.2 to 34.4 ka, respectively. Four of these samples are very close in age (¹⁰Be ages of 17.5 ± 0.6, 17.5 ± 0.7, 19.7 ± 0.8 and 20.0 ± 0.7 ka) and are interpreted as representing the exposure age of the summit ridge. Two other summit samples are much older (¹⁰Be ages of 27.5 ± 1.0 and 33.9 ± 1.2 ka) and these results may indicate nuclide inheritance. The ²⁶Al/¹⁰Be ratios for all samples are indistinguishable within one‐sigma uncertainty from the production rate ratio line, indicating that there is no evidence for a complex exposure history. These results indicate that the last Welsh Ice Cap was thick enough to completely cover the Aran ridge and achieve glacial erosion at the LGM. However, between c. 20 and 17 ka ridge summits were exposed as nunataks at a time when glacial erosion at lower elevations (below 750–800 m a.s.l.) was achieved by large outlet glaciers in the valleys surrounding the mountains. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Resistance to flow in rough supercritical sheet flow     

Jan Savat 《地球表面变化过程与地形》1980,5(2):103-122

Shallow water depths on steep slopes of as much as fifty per cent can be measured easily by weighing a light flume and the water it contains. Because water accelerates along the flume, a good approximation of the steady state depth is obtained when the recording balance is fixed to its bottom end. From the unit discharge and the depth, and not from measurements of the surface velocity, the Darcy-Weisbach friction coefficient can be calculated. The present results show that this friction coefficient is larger in thin sheet flows than that calculated from the equation for rough turbulent flow. This latter could fit at a Reynolds Number of 50,000. When the regime is laminar (Re < 2,440) the Darcy-Weisbach friction coefficient always exceeds the theoretical value of 96/Re. The great relative depth of standing and travelling waves could account for this discrepancy together with turbulence and wake formation around bottom grains. Herein it is assumed that a regime can prevail where a laminar superlayer glides over a turbulent sublayer in the vicinity of bottom grains, because the ratio of the surface velocity to the mean velocity can greatly exceed 1.5, especially on steep slopes. Until photographs of the streamlines are taken, no statement about flow regimes in supercritical sheet flow can be made.  相似文献   

The last British Ice Sheet: A review of the evidence utilised in the compilation of the Glacial Map of Britain     

David J.A.  Chris D.  Wishart A. 《Earth》2005,70(3-4):253-312

This paper reviews the evidence presently available (as at December 2003) for the compilation of the Glacial Map of Britain (see [Clark C.D., Evans D.J.A., Khatwa A., Bradwell T., Jordan C.J., Marsh S.H., Mitchell W.A., Bateman, M.D. , 2004. Map and GIS database of glacial landforms and features related to the last British Ice Sheet. Boreas 33, 359–375] and http://www.shef.ac.uk/geography/staff/clark_chris/britice.html) in an effort to stimulate further research on the last British Ice Sheet and promote a reconstruction of ice sheet behaviour based on glacial geology and geomorphology. The wide range of evidence that has been scrutinized for inclusion on the glacial map is assessed with respect to the variability of its quality and quantity and the existing controversies in ice sheet reconstructions. Landforms interpreted as being of unequivocal ice-marginal origin (moraines, ice-contact glacifluvial landforms and lateral meltwater channels) and till sheet margins are used in conjunction with available chronological control to locate former glacier and ice-sheet margins throughout the last glacial cycle. Subglacial landforms (drumlins, flutings and eskers) have been used to demarcate former flow patterns within the ice sheet. The compilation of evidence in a regional map is crucial to any future reconstructions of palaeo-ice sheet dynamics and will provide a clearer understanding of ice sheet configuration, ice divide migration and ice thickness and coverage for the British Ice Sheet as it evolved through the last glacial cycle.  相似文献   

地形图分幅编号解析法优化研究   总被引：3，自引：0，他引：3  

马永立 《测绘学院学报》1998,(2)

依据地形图分幅编号的规律 ,应用测算地面点坐标和语言学的原理 ,从建立解算地形图分幅编号数学模式的坐标系和使数学模式的参数符号概念化两个方面 ,对国家基本比例尺地形图分幅编号的解析法进行优化研究 ,以提高其科学性  相似文献   

青藏高原更新世晚期冰川的均衡效应     

汪汉胜  许厚泽 《测绘学报》1997,26(2):148-154

本文基于Ｋｕｈｌｅ关于青藏更新世晚期存在统一大冰盖的假说，构制冰负荷史模型，利用Ｐｅｌｔｉｅｒ（１９７４，１９７６）粘弹地球表面负荷形变理论，计算出冰盖负荷引起的地表垂直位移和重力变化，并将其作为该区冰种均衡效应的最大估计，数值计算结果表明，冰盖负荷的均衡作用对高原隆升有一定的影响。  相似文献   

Ice-distal Upper Miocene marine strata from inland Antarctica   总被引：2，自引：0，他引：2  

Jason M. Whitehead†  David M. Harwood†  Andrew McMinn 《Sedimentology》2003,50(3):531-552

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