quaternary glaciations in the southern hemisphere an overview abstract large glacier systems in antarctica have existed at least since the early miocene glaciers in the patagonian andes advanced in the late miocene and fluctuated several times during the pliocene as did ice masses elsewhere in the southern hemisphere sedimentological evidence of glaciation during the early and middle quarternary is best preserved in volcanic regions patagonia new guinea africa but is poorly constrained by dating there is evidence of glaciation during oxygen isotope stages 10 8 and 6 in several parts of the southern hemisphere but the only well dated advance of the middle quarternary is that of stage 6 in the transantarctic mountains during the last glaciation montane glaciers in parts of the southern hemisphere were as large during isotope stage 4 as during isotope stage 2 the last glaciation maximum stage 2 is well dated in tasmania new zealand and patagonia culminating as 21 18 ka bp following slight recession from the lgm limits late glacial advances peaked at 15 14 ka bp and at 12 10 ka bp major holocene advances occurred on at least three occasions during the last 5 ka in areas presently glacier covered

reconstructing the environmental history of the last glacial interglacial transition evidence from the isle of skye inner hebrides scotland abstract a new interpretation is presented of the late devensian late weichselian wisconsinan lateglacial and early flandrian holocene environmental history of the isle of skye inner hebrides scotland this reconstruction based on pollen percentage pollen concentration pollen preservation and chemical data differs in a number of respects from previous explanations of the lateglacial environmental history of the island the evidence suggests that throughout the lateglacial and early flandrian variation in degree of exposure to prevailing westerly winds was the dominant factor influencing the development of regional vegetation patterns the data provide a proxy climatic record for western scotland during the last glacial interglacial transition and this is discussed in the context of both onshore and offshore evidence the results from skye demonstrate the importance of pollen preservation studies in the interpretation of pollen taphonomy and in the evaluation of lateglacial and early flandrian radiocarbon dates

little ice age glaciers in britain glacier climate modelling in the cairngorm mountains it is widely believed that the last glaciers in the british isles disappeared at the end of the younger dryas stadial 12 9 11 7 cal kyr bp here we use a glacier climate model driven by data from local weather stations to show for the first time that glaciers developed during the little ice age lia in the cairngorm mountains our model is forced from contemporary conditions by a realistic difference in mean annual air temperature of 1 5 c and an increase in annual precipitation of 10 and confirmed by sensitivity analyses these results are supported by the presence of small boulder moraines well within younger dryas ice limits and by a dating programme on a moraine in one cirque as a result we argue that the last glaciers in the cairngorm mountains and perhaps elsewhere in upland britain existed in the lia within the last few hundred years rather than during the younger dryas

the recognition of glacial retreat from palynological data a review of recent work in the british isles recent publications have presented palynological data from the early postglacial period in the british isles which have been interpreted as reflecting sequential glacial retreat following the loch lomond stadial the methodologies and results of these studies were examined and were concluded to be insufficient to demonstrate glacial retreat a more cautious methodology was adopted and tested at several pollen sites in the awe valley scotland the results differed from previous studies in not demonstrating the sequence of palynological changes predicted from the hypothesis these results need to be replicated at other localities however before the deglacial chronology hypothesis can be dismissed proposals to test the hypothesis further are suggested

periglacial trimlines former nunataks and the altitude of the last ice sheet in wester ross northwest scotland high level weathering limits separating ice scoured topography from frost weathered detritus were identified on 28 mountains in wester ross at altitudes of 700 960 m and a further 22 peaks support evidence of ice scouring to summit level weathering limits are defined most clearly on sandstone and gneiss which have resisted frost shattering during the late devensian lateglacial but can also be distinguished on schists and quartzite schmidt hammer measurements and analyses of clay mineral assemblages indicate significantly more advanced rock and soil weathering above the weathering limits the persistence of gibbsite above weathering limits indicates that they represent the upper limit of late devensian glacial erosion the regular decline of weathering limit altitudes along former flowlines eliminates the possibility that the weathering limits represent former thermal boundaries between protective cold based and erosive warm based ice the weathering limits are therefore interpreted as periglacial trimlines that define the maximum surface altitude of the last ice sheet calculated basal shear stresses of 50 95 kpa are consistent with this interpretation reconstruction of ice sheet configuration indicates that the former ice shed lay above 900 m along the present watershed and that the ice surface descended northwestwards with broad depressions along major troughs and localised domes around independent centres of ice dispersal extrapolation of the ice surface gradient and altitude suggests that the ice sheet did not overrun the outer hebrides but was confluent with the independent outer hebrides ice cap in the north minch basin erratics located up to 140 m above the reconstructed ice surface are inferred to have been emplaced by a pre late devensian ice sheet or ice sheets of unknown age 1997 john wiley sons ltd

mass balance flow and subglacial processes of a modelled younger dryas ice cap in scotland we use an empirically validated high resolution three dimensional ice sheet model to investigate the mass balance regime flow mechanisms and subglacial characteristics of a simulated younger dryas stadial ice cap in scotland and compare the resulting model forecasts with geological evidence input data for the model are basal topography a temperature forcing derived from grip 18 o fluctuations and a precipitation distribution interpolated from modern data the model employs a positive degree day scheme to calculate net mass balance within a domain of 112 500 km 2 which under the imposed climate gives rise to an elongate ice cap along the axis of the western scottish highlands at its maximum the ice cap is dynamically and thermally zoned reflecting topographic and climatic con trols respectively in order to link these palaeoglaciological conditions to geological interpretations we calculate the relative balance between sliding and creep within the simulated ice cap forecast areas of the ice cap with the greatest capacity for basal erosion and predict the likely pattern of subglacial drain age we conclude that ice flow in central areas of the ice cap is largely due to internal deformation and is associated with geological evidence of landscape preservation conversely the distribution of stream lined landforms is linked to faster flowing ice whose velocity is predominantly the result of basal sliding the geometry of the main ice mass focuses subglacial erosion in the mid sections of topographic troughs and produces glaciohydraulic gradients that favour subglacial drainage through low order arterial routes

the amphi atlantic distribution of the younger dryas paleoclimatic oscillation abstract interest in significant climatic fluctuations affecting large geographic areas but having a time range that is too brief to adduce the milankovitch radiation cycles has focused on the allerod younger dryas event which is a well established phenomenon of western europe manifested by glacial and vegetational reconstructions it is also shown by the foraminiferal evidence for shifts in the polar front in the north atlantic recent pollen and lithostratigraphic investigations in the maritime provinces of eastern canada and in the till plains of west central ohio on opposite sides of the late glacial spruce forest indicate that the event also left a record in eastern north america experiments with an atmospheric general circulation model with the temperature of north atlantic surface waters depressed to full glacial levels lowered summer temperatures in upwind periglacial eastern north america by 2 c just as far inland as they did downwind in western europe where the paleoecological record of cooling is clear a leading hypothesis for the cause for the younger dryas cooling appeals to the influx of tabular icebergs released from arctic ice shelves around the wasting scandinavian and siberian ice sheets during the allerod warming the resulting cooling of the north atlantic waters during the younger dryas could be facilitated or precipitated by the abrupt influx of glacial meltwater derived from almost the entire southern margin of the laurentide ice sheet and emerging from the gulf of st lawrence as brought about by a major shift in drainage direction from the mississippi river to the st lawrence river about 10 8 ka bp a supplemental influx of fresh water may have come from the contemporaneous drainage of the baltic ice lake the diversion of laurentide meltwater to the atlantic was caused by retreat of an ice lobe in northwestern ontario north of minnesota allowing the huge glacial lake agassiz in saskatchewan and manitoba to drain into the great lakes and more than double the inflow of meltwaters in the north atlantic thereby diverting the gulf stream and permitting the influx of icebergs from the north to cool the ocean surface minor readvance of the ice lobe about 10 ka bp temporarily diverted the lake agassiz drainage to the south with the final retreat of the ice the drainage again went to the east but by this time the ice sheets were much diminished and the regional climate had warmed enough so that the effects of the meltwater flux on the gulf stream were muted and the ice sheets bordering the north atlantic had retreated onto the land and no longer delivered enough icebergs to cool the surface waters the younger dryas interval thus was terminated and the warming manifested in the allerod was renewed

ice caps existed throughout the lateglacial interstadial in northern scotland we constrain in detail fluctuations of two former ice caps in nw scotland with multibeam seabed surveys geomorphological mapping and cosmogenic 10 be isotope analyses we map a continuous sequence of 40 recessional moraines stretching from 10 km offshore to the wester ross mountains surface exposure ages from boulders on moraine ridges in assynt and the summer isles region show that substantial dynamic ice caps existed in nw scotland between 13 and 14 ka bp we interpret this as strong evidence that large active glaciers probably survived throughout the lateglacial interstadial and that during the older dryas period ca 14 ka bp ice caps in nw scotland were thicker and considerably more extensive than in the subsequent younger dryas stadial by inference we suggest that lateglacial ice cap oscillations in scotland reflect the complex interplay between changing temperature and precipitation regimes during this climatically unstable period ca 15 11 ka bp natural environment research council nerc copyright 2008 reproduced with the permission of nerc published by john wiley sons ltd

the loch lomond readvance on north arran scotland glacier reconstruction and palaeoclimatic implications 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

push moraines and glacier contact fans in marine and terrestrial environments the local climatic regime and the mass balance state are important determinants of the dynamics of terrestrial and marine glacier fronts which in turn determine the sediments and landforms produced at the glacier front many modern glaciers undergoing overall retreat in areas of maritime climate produce winter push moraines during a late winter readvance followed by a summer retreat whilst in more continental regions no significant winter readvance occurs and annual push moraines are absent the frontal dynamics which lead to these changes are analysed and the form structure sequence and field relations of both terrestrial and marine push moraines are described from iceland spitsbergen and baffin island long term changes in mass balance leading to major glacier advances or readvances also generate large push moraines in terrestrial environments push moraine formation is accompanied by uplift rejuvenation and down cutting of outwash systems whose sediments become closely associated with glaciotectonic structures which permit pre syn and post tectonic sequences to be identified the development of ice marginal fan moraine complexes is modelled as a function of the relative magnitude of two parameters the velocity of ice movement and the calving rate a high ice velocity just exceeded by the calving rate gives closely spaced push moraines and confluent ice marginal fans a high velocity far exceeded by the calving rate produces closely spaced moraines but separate ice marginal fans a low ice velocity in combination with a high calving rate results in well separated and feebly developed push moraines while a low ice velocity and a low calving rate produces feeble push moraines and coalescent fans

high energy sedimentation creag aoil spean bridge scotland implications for meltwater movement and storage during loch lomond stadial younger dryas ice retreat this paper examines the origin and significance of loch lomond stadial younger dryas gravel deposits at creag aoil spean bridge scotland sedimentation into ice dammed lakes in glen roy and glen spean associated with shorelines at 260 m 325 m and 350 m is well documented yet little is known about later lower level lakes near spean bridge excavations on the northern flanks of the lundy channel revealed exposures into a 35 40 m thickness of sand and gravel these sediments reflect deposition in a subaqueous environment experiencing repeated short lived periods of high energy subaerial deposition deformation structures within subaqueous deposits are associated with at least two ice push events this study presents new evidence for the existence of ice dammed lakes at elevations between 260 m and 113 m and for periodic jokulhlaups draining southwest via the lundy channel active glacier ice associated with the deposits flowed northwest to southeast driving meltwater across the great glen to the lundy channel glacier retreat was punctuated by periodic minor readvances progressive ice retreat was accompanied by ice thinning and changes in ice flow direction and subglacial meltwater routing these findings add to knowledge of loch lomond stadial deglaciation around spean bridge and have implications for our understanding of lacustrine glacier margins during deglaciation copyright 2003 john wiley sons ltd keywords ice dammed lake subaqueous outwash jokulhlaups ice push structures scotland

younger dryas glacial landsystems in north west scotland an assessment of modern analogues and palaeoclimatic implications abstract by explicitly linking process to form landsystem models developed in modern environments provide powerful tools for the reconstruction of past environments from the sedimentological and geomorphological record some landform characteristics however may originate by more than one process equifinality so although a particular depositional model may fit the data it is not necessarily the correct one here we critically examine the use of modern analogues to interpret glacial landforms focusing on hummocky moraine a distinctive landform association consisting of numerous sharp crested moraine mounds and ridge fragments which occurs on many valley floors in upland britain detailed studies of examples of younger dryas age in the north west highlands of scotland show that they represent ice contact fans which have been affected to varying degrees by ice push and subglacial deformation and that they formed at active oscillating ice margins the sedimentological data are inconsistent with an origin by englacial thrusting as has been proposed for similar moraines elsewhere in upland britain on the basis of morphological criteria comparison with modern glacial landsystems shows that although aspects of hummocky moraines in the study area have close modern counterparts none provides an exact analogue in all respects this may reflect the distinctive climate of western scotland during the younger dryas estimates of mean july temperatures in the younger dryas in scotland based on chironomid assemblages are c 8 c at sea level when combined with reconstructed equilibrium line altitudes for contemporaneous glaciers these estimates indicate mean annual precipitation totals in the range of 2358 337 mm yr 1 at sea level in nw scotland c 26 higher than present day values the implied heavy snowfall suggests that glaciers in western scotland during the younger dryas were of high activity type unlike modern glaciers in svalbard for example high glacier velocities and high winter precipitation would suppress permafrost development despite low mean annual temperatures the climatic environment also favoured rapid oscillations of glacier margins during both glacier build up and retreat phases climatic factors combined with the availability of large quantities of subglacial debris led to the development of distinctive glacial landsystems which may have no direct modern analogue

the last ice sheet in north west scotland reconstruction and implications recent models of the last scottish ice sheet suggest that nunataks remained above the ice surface in areas peripheral to the main centres of accumulation this proposition has been investigated on 140 mountains over an area of 10 000 km2 in nw scotland outside the limits of the later loch lomond readvance in this area there is evidence for a single high level weathering limit that separates glacially eroded terrain from higher areas of in situ frost debris this limit occurs at altitudes ranging from 425 to 450 m in the outer hebrides to 950 m on the mainland and is best developed on lithologies that resisted breakdown after ice sheet downwastage interpretation of this weathering limit as a periglacial trimline cut by the last ice sheet at its maximum thickness is supported by 1 joint depth and schmidt hammer measurements that indicate significantly more advanced rock breakdown above the weathering limit 2 a much greater representation of gibbsite a pre late devensian weathering product in the clay fraction of soils above the limit 3 cosmogenic isotope dating of the exposure ages of rock outcrops above and below the limit 4 the sharpness of the limit at some sites and its regular decline along former ice flowlines and 5 shear stress calculations based on the inferred altitude and gradient of the former ice surface reconstruction of the ice surface based on trimline evidence indicates that the mainland ice shed lay near or slightly east of the present watershed and descended northwards from 900 m to ca 550 m at the north coast independent dispersion centres fed broad ice streams that occupied major troughs on skye an ice dome 800 m deflected the northwestwards movement of mainland ice but the mountains of rum were over ridden by mainland ice up to an altitude of ca 700 m the outer hebrides supported an independent ice cap that was confluent with mainland ice in the minches extrapolation of the trimline evidence indicates that most reconstructions of ice extent are too conservative and suggests that low gradient ice streams extended across the hebridean shelf offshore wider implications of this research are 1 that blockfields and other periglacial weathering covers are not all of the same age or significance depending on the resistance of different lithologies to frost weathering 2 that the contrasting degree of glacial modification in the western and eastern highlands of scotland may reflect a former cover of predominantly warm based ice in the former and predominantly cold based ice in the latter and 3 that the approach and techniques developed in this study have potential application for constraining ice sheet models not only in areas peripheral to the main centres of ice accumulation in britain and ireland but also in other mountain areas where nunataks protruded through warm based late pleistocene ice masses

cosmogenic 10be insights into the extent and chronology of the last deglaciation in wester ross northwest scotland cosmogenic 10be surface exposure ages for bedrock sites around torridon and the applecross peninsula in wester ross northwest scotland provide new insights into the lateglacial transition accounting for postglacial weathering six statistically comparable exposure ages give a late younger dryas g 1 exposure age of 11 8 1 1 ka two further outliers are tentative pre younger dryas exposure ages of 13 4 0 5 ka in torridon and 17 5 1 2 ka in applecross the younger dryas exposure ages have compelling implications for the deglaciation of marginal loch lomond stadial ice fields in torridon and applecross firstly they conflict with predictions of restricted ice cover and rapid retreat based on modelling experiments and climate proxies instead fitting a model of vertically extensive and prolonged ice coverage in wester ross secondly they indicate that 2 m of erosion took place in the upper valleys of torridon and applecross during the younger dryas implying a dominantly warm based glacial regime finally the exposure ages have clarified that corrie cirque glaciers did not readvance in wester ross following final deglaciation copyright 2011 john wiley sons ltd

relict rock glaciers and protalus lobes in the british isles implications for late pleistocene mountain geomorphology and palaeoclimate many relict rock glaciers and protalus lobes have been described in mountainous areas of the british isles this paper reviews their distribution chronology supposed origin and development and places the research within current investigations and knowledge rock glaciers and protalus lobes are located in a number of different topographic locations and settings they developed at the base of steep cliffs following the catastrophic failure of rock faces at the base of scree slopes following the gradual accumulation of rock debris and in association with glaciers protalus lobes probably developed in response to the permafrost creep of talus material while rock glaciers formed through the deformation and sliding of large bodies of buried ice rock glaciers probably developed or were last active during the younger dryas although the possibility exists that some of these landforms are dimlington stadial in age the development of protalus lobes during the younger dryas suggests that precipitation levels were low and permafrost was widespread during this time the lack of rock glaciers sensu stricto in the british isles compared with other mountain areas is believed to be a consequence of the rock type and relative scarcity of weathered debris for their formation rather than a lack of suitable sites or appropriate environmental conditions copyright 2007 john wiley sons ltd

a spatially restricted younger dryas plateau icefield in the gaick scotland reconstruction and palaeoclimatic implications considerable research has been conducted in scotland to reconstruct younger dryas glaciers and palaeoclimatic conditions but our understanding remains incomplete in this contribution we examine the gaick a dissected plateau that extends over 520 km 2 in the central grampians scotland the extent and style of younger dryas glaciation in the gaick has been repeatedly contested although a model of extensive plateau icefield glaciation has become generally accepted this is despite well documented issues with key elements of the plateau icefield reconstruction we synthesise the results of recent geomorphological mapping in the gaick and recognise a distinct morphostratigraphic signature in the upper parts of the western catchments this differs markedly from sediment landform associations in other parts of the area and we argue this provides a strong indication of spatially restricted younger dryas 12 9 11 7 ka glaciation in the gaick our interpretation is independently supported by glacierisation threshold analysis which implies that the eastern gaick was unable to nourish younger dryas ice we therefore contest the accepted paradigm of extensive younger dryas glaciation in this area based on the geomorphological evidence and glacier surface profile modelling we reconstruct a 42 km 2 plateau icefield that yields an equilibrium line altitude of 751 46 m using this value a sea level precipitation value of 826 331 mm a 1 is inferred for the younger dryas which suggests considerably drier conditions than at present using recalculated glacier derived precipitation estimates from scotland we present regional climate analysis that corroborates arguments for a strong west east precipitation gradient across scotland

routing of meltwater from the laurentide ice sheet during the younger dryas cold episode rooth1 proposed that the younger dryas cold episode which chilled the north atlantic region from 11 000 to 10 000 yr bp was initiated by a diversion of meltwater from the mississippi drainage to the st lawrence drainage system the link between these events is postulated to be a turnoff during the younger dryas cold episode of the north atlantic s conveyor belt circulation system which currently supplies an enormous amount of heat to the atmosphere over the north atlantic region2 this turnoff is attributed to a reduction in surface water salinity and hence also in density of the waters in the region where north atlantic deep water nadw now forms here we present oxygen isotope and accelerator radiocarbon measurements on planktonic foraminifera from orca basin core en32 pc4 which reveal a significant reduction in meltwater flow through the mississippi river to the gulf of mexico from about 11 200 to 10 000 radiocarbon years ago this finding is consistent with the record for lake agassiz which indicates that the meltwater from the southwestern margin of the laurentide ice sheet was diverted to the northern atlantic ocean through the st lawrence valley during the interval from 11 000 to 10 000 years before present yr bp

glaciation of scotland during the younger dryas stadial a review considerable research effort in recent years has refined our knowledge of the landforms and sedimentary sequences generated by glaciers of the last cold episode in scotland the younger dryas and the chronology of their formation these recent advances have benefited from new technologies such as high resolution digital terrain models numerical ice sheet simulations and cosmic ray surface exposure dating this review presents a summary of recent younger dryas research in scotland particularly focusing on studies from the last two decades the findings of these investigations are compared with those of earlier workers and critically are appraised in terms of their relevance to five key aspects of younger dryas glaciation growth of the ice cap its geometry dynamics mode of decay and likely stadial climate minor differences aside the consensus view appears to favour a relatively thick but areally restricted central ice cap surrounded by satellite ice fields at its centre the ice cap was probably thickest during the first 500 years of the stadial after which it most likely thinned as the climate became increasingly arid outlet glaciers were dynamic only in marginal areas where they produced abundant moraine sequences during deglaciation but throughout much of the stadial central areas of the ice cap effected only minimal landscape modification deglaciation took place by active retreat under a rapidly warming climate overall the stadial was dominated by much colder and drier conditions than present and probably experi enced greater intra annual temperature ranges copyright 2009 john wiley sons ltd

modelling the younger dryas abstract an energy balance climate model ebcm having land sea surface air and latitudinal resolution and which simulates the seasonal growth and decay of sea ice in terms of a number of explicit physical processes is used to test the following hypotheses for the cause of the younger dryas cold episode 1 a low salinity meltwater lens from ablation of continental ice sheets which would have increased the freezing point and stability of the oceanic mixed layer thereby allowing more extensive sea ice 2 a flood of icebergs into the north atlantic from collapse of continental ice sheets or of a hypothetical arctic ocean ice shelf 3 a reduction or cessation in the rate of formation of north atlantic deep water nadw which would have led to a reduction in the northward oceanic heat flux in the north atlantic ocean and 4 a reduction in atmospheric co 2 concentration a low salinity meltwater lens leads to zonally averaged atmospheric cooling over land of up to 2 5 c in winter but warming of up to 1 5 c in summer temperature effects outside the latitudes of hypothesized low salinity meltwater are negligible an iceberg flood covering 30 of the ocean between latitudes 45 and 70 n causes a winter atmospheric cooling over land of up to 8 c and a summer cooling of up to 4 c in the northern hemisphere but maximum winter cooling at high southern hemisphere latitudes of only 1 3 c if the icebergs are initially 100 m thick and allowed to ablate without replenishment then the icebergs completely disappear in only 20 50 years and negligible temperature response occurs in the southern hemisphere a reduction in the northward meridional oceanic heat flux by 0 6 10 15 w at 45 n leads to maximum winter and summer atmospheric coolings over land of 5 6 c and 1 2 c respectively at high latitudes in the northern hemisphere but a warming at low latitudes and in the southern hemisphere however a reduction in the rate of nadw formation would also lead to a reduction in the upward heat flux at the base of the mixed layer at high latitudes in the southern hemisphere this is a parameter of the model used here and reducing its value by 20 causes a mean annual temperature cooling of up to 3 3 c in the southern hemisphere a co 2 decrease from 300 ppmv to 250 ppmv causes a global mean cooling of about 0 7 c and maximum mean annual atmospheric temperature responses of about 1 c in both hemispheres with greater response in winter this study identifies a number of specific types of paleoclimatic data which can help in discriminating among different hypothesized causes of the younger dryas in particular a seasonal patterns of temperature change b differences between high and low latitude and between northern hemisphere and southern hemisphere temperature changes as well as regional patterns of climatic change c phase lags of temperature change between different regions and d a more precise determination of the duration of the younger dryas in various localities

the loch lomond readvance on the isle of mull scotland glacier reconstruction and palaeoclimatic implications 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

first cosmogenic 10be age constraint on the timing of younger dryas glaciation and ice cap thickness western scottish highlands we use cosmogenic 10 be surface exposure age techniques at a locality close to rannoch moor western scottish highlands in order to establish the age and chronology of its most recent glaciation glacial erratics and an in situ bedrock quartz vein sampled from this site the summit of beinn inverveigh have yielded zero erosion exposure ages of 12 9 1 5 ka to 11 6 1 0 ka implying complete ice cover of the mountain during the younger dryas or loch lomond stadial these results fit closely with published 14 c dates that bracket the maximum lateral extent of ice cap outlet glaciers and are the first internally consistent ages to specifically address this period of glaciation in scotland furthermore the dates imply that previous palaeoglaciological reconstructions for this area may have underestimated both the thickness of the former ice cap and by implication its volume british geological survey natural environment research council copyright 2007 reproduced with the permission of bgs nerc published by john wiley sons ltd

deglaciation of the younger dryas or loch lomond stadial ice field in the northern highlands scotland when viewed from the air scottish hummocky moraine can be resolved into a series of linear ridges that resemble those found at the margins of actively retreating glaciers today recent work has supported the interpretation of these linear ridges as ice marginal landforms and the authors believe that the majority of hummocky moraine deposits can be interpreted in this way consequently the pattern of deglaciation can be established fairly precisely from the pattern of linear ridges this approach is applied to the landforms of the northern part of the loch lomond stadial ice field in order to reconstruct the regional pattern of deglaciation this leads to important inferences about the significance of topographic control during deglaciation and more importantly it provides fresh insight into the environment of the british isles during the loch lomond stadial

the abrupt termination of the younger dryas climate event previous studies on two deep greenland ice cores have shown that a long series of climate oscillations characterized the late weichselian glaciation in the north atlantic region1 and that the last glacial cold period the younger dryas ended abruptly 10 700 years ago2 here we further focus on this epoch defining event and present detailed heavy isotope and dust concentration profiles which suggest that in less than 20 years the climate in the north atlantic region turned into a milder and less stormy regime as a consequence of a rapid retreat of the sea ice cover a warming of 7 c in south greenland was completed in about 50 years

reconstruction of a lateglacial younger dryas mountain ice field in sutherland northwestern scotland and its palaeoclimatic implications quaternary geomorphological and geological mapping of a large area 1800 km2 in the northwestern scottish highlands has led to the reconstruction of a coherent mountain ice field approximately 45 km long and 30 km wide at its maximum extent this west sutherland ice field covered an area of 350 km2 and had a mean equilibrium line altitude of 334 m assuming that the outlet glaciers all reached their maxima simultaneously numerical dating strongly suggests a younger dryas 12 9 11 7 ka age of the mapped limits of this mountain ice field this study also shows that the area of northwestern scotland covered by younger dryas glaciers was five times larger than previously thought palaeo temperature estimates obtained from chironomid and beetle assemblages elsewhere have been used to reconstruct palaeo precipitation during the younger dryas for west sutherland using a previously published global empirical dataset annual precipitation of 2344 248 mm a 1 at sea level is inferred from our new palaeo glacier reconstruction suggesting slightly wetter conditions compared to the present day these figures are in good agreement with those reconstructed for other parts of the scottish highlands and islands and this may indicate a marked w e palaeo precipitation gradient during the younger dryas this paper goes on to discuss the wider validity of palaeo climatic reconstructions from inferred palaeo glacier geometries and presents a number of possible scottish lateglacial climate scenarios which warrant further testing copyright 2010 john wiley sons ltd

modern glacier characteristics as a basis for inferring former climates with particular reference to the loch lomond stadial abstract studies of the mass balance of modern glaciers have indicated that the equilibrium line altitude ela is the most critical parameter in the link between glaciers and climate average accumulation on a glacier includes components derived from direct precipitation on the glacier surface as well as wind drifting and avalanching of snow and approximates closely to accumulation at the equilibrium line ablation is most usefully predicted by mean summer temperature and there is a close non linear relationship between accumulation and mean summer temperature at the equilibrium line following discussion of methods of reconstructing former glaciers and calculating their equilibrium line altitudes the application of the above relationships to the loch lomond readvance glaciers of highland britain is considered and an outline of the precipitation pattern and the mean summer temperature of the loch lomond stadial is given

the formation of a geometrical ridge network by the surge type glacier kongsvegen svalbard traditionally geometrical ridge networks are interpreted as the product of the flow of subglacial sediment into open basal crevasses at the cessation of a glacier surge crevasse fill ridges they are widely regarded as a characteristic landform of glacier surges understanding the range of processes by which these ridge networks form is therefore of importance in the recognition of palaeosurges within the landform record the geometrical ridge network at the surge type glacier kongsvegen in svalbard does not form by crevasse filling the networks consist of transverse and longitudinal ridges that can be seen forming at the current ice margin the transverse ridges form as a result of the incorporation of basal debris along thrust planes within the ice the thrusts were apparently formed during a glacier surge in 1948 longitudinal ridges form through the meltout of elongated pods of debris which on the glacier surface are subparallel to the ice foliation and pre date the surge this work adds to the range of landforms associated with glacier surges

a chronostratigraphy of mid and late holocene slope evolution creagan a chaorainn northern highlands scotland unusual exposure of the drift stratigraphy of a typical vegetated hillslope in the northern highlands of scotland has allowed reconstruction of its holocene history graphic logging of palaeogully fill sediment analysis radiocarbon dating and microscopic investigation of horizon boundaries link periodic slope instability to changes in hydrology and vegetation cover the oldest preserved organic matter dates from about 7 5 cal ka bp several millennia of subsequent stability were followed at about 4 3 cal ka bp by destabilization whose magnitude and frequency markedly increased after about 2 7 cal ka bp precipitation driven weathering and erosion offer the best explanation for late holocene slope rejuvenation at this site with change effected through long lasting shifts in system equilibria as well as high magnitude inputs anthropogenic impacts on slope stability are apparently restricted to the last few hundred years the timing and episodicity of slope evolution suggests climate forcing resu

the quaternary geomorphology of scotland the research contribution of j b sissons abstract between 1958 and his retirement in 1982 j b sissons published some 80 articles and two books the majority of these were devoted to aspects of the quaternary geomorphology of scotland but many of his findings have much wider application this paper reviews the six main areas in which sissons made an outstanding research contribution in approximate chronological order these were as follows i reassessment of the significance of meltwater channels and related fluvioglacial landforms 1958 1963 ii the deciphering of an extremely complex sequence of raised and buried shorelines and associated sea level changes in eastern scotland 1962 1972 together with reinterpretation of the age and origin of marine rock cut platforms in western scotland 1974 1982 iii work on the data banking of borehole records and the relevance of certain aspects of drift stratigraphy to engineering operations 1969 1971 iv research on the extent and chronology of the last scottish ice sheet and associated readvances 1961 1982 v the reconstruction of the extent and palaeoclimatic implications of loch lomond stadial glaciers 1972 1982 and vi investigation into aspects of landscape evolution in the glen roy area including the formation of former lake shorelines the catastrophic drainage of former ice dammed lakes and its effects the interpretation of complex terrace sequences and the discovery of links between deglaciation unloading faulting earthquakes and landslides 1978 1982 this paper also includes a complete list of sissons publications

high resolution modeling of the advance of the younger dryas ice sheet and its climate in scotland abstract ice sheet modeling tightly constrained by empirical studies provides an effective framework to reconstruct past climatic and environmental conditions scotland was severely affected by the abrupt climate change associated with the younger dryas stade during which an extensive ice sheet formed across the west highlands after a period of ice free conditions here a quasi three dimensional time dependent ice flow mass balance model is developed and applied to scotland at 1 km resolution the flow model is based on the driving stress approximation with an additional longitudinal correction term essential at this scale of operation surface mass balance is driven by temperature and precipitation changes and further mass wastage is achieved through an empirically defined calving term the ice dynamics and mass balance components are coupled through the equation for mass continuity which is integrated through time over a finite difference grid which yields the geometric evolution of the ice sheet initial experiments reveal the model to be relatively insensitive to internal parameters but highly sensitive to mass balance furthermore these experiments indicate that scotland is readily susceptible to glaciation with large glaciers building up on the flanks of ben nevis after a temperature depression of 2 5 c under present day precipitation the younger dryas is modeled using a grip temperature series locally adjusted for amplitude and a systematic series of runs enables the isolation of the climate which best matches mapped ice limits this optimum fit configuration requires an annual temperature cooling of 8 c and the introduction of substantial west east and south north precipitation gradients of 40 and 50 respectively to the present day regime under these conditions a series of substantial independent regional ice centers develop in agreement with trimline studies and after 550 years the modeled ice sheet closely resembles the maximum limits as indicated by field mapping however modeled ice continues to expand beyond 550 yr in conflict with the mapped ice limits which suggest a prolonged period of stability this discrepancy may be explained by the onset of extreme aridity ca 400 yr into the stade associated with a southern migration of the polar front leading to a reduction in atmospheric circulation which effectively starved the ice sheet of its moisture source preventing further expansion introduction of an additional 20 reduction in precipitation to the optimum fit regime after 350 yr brings the modeled ice sheet to equilibrium substantiating this conclusion

an integrated approach to the study of glaciolacustrine landforms and sediments a case study from hagavatn iceland abstract this paper describes the landform assemblage associated with the neoglacial fluctuation of hagafellsjokull eystri into proglacial hagavatn iceland this landform assemblage is dominated by three components firstly a series of moraines formed both by thrusting within the glacier margin and by proglacial subglacial deformation the internal sedimentary architecture of these moraines ranges from stacked sediment slabs separated by listric thrusts to complexly folded and faulted sequences all in glaciolacustrine sediments the second component is a morainal bank and associated ice contact delta the morainal bank consists of a series of low amplitude ridges composed of laminated silts and clays which have been deformed proglacially during the neoglacial ice advance 1890 this morainal bank helped stabilise the 1890 ice limit within the proglacial lake and was the focus for subaqueous outwash first in the form of a subaqueous out wash fan and subsequently as an ice contact delta the third component is a series of lake bed kame terraces formed by rapid sedimentation in a canal like lake formed as the ice retreated away from the push moraines a range of glaciolacustrine facies is present within the lake bed kame terraces and the sedimentary architecture records a complex pattern of ice marginal oscillations and changes in lake level this detailed case study provides an important analogue for the interpretation of both glaciolacustrine and glaciomarine landform sediment assemblages of pleistocene age and illustrates a range of styles of glaciolacustrine sedimentation and glaciotectonic deformation

hummocky moraine landscape on jaeren sw norway implications for glacier dynamics during the last deglaciation abstract the jaeren area sw norway can topographically be divided in two regions lagjaeren and hogjaeren hogjaeren is a plateau 120 m a s l covered by quaternary sediments the stratigraphically youngest deposit is a sandy diamicton which accumulated in ridges and hummocks during the last deglaciation this hummocky moraine landscape has previously been interpreted as the record of a stagnant glacier detailed morphological mapping and sedimentological investigations have revealed that various glacigenic elements exist and dominate different areas of the hogjaeren plateau glacigenic elements formed by an active wet based glacier characterize the southern central hummocky area and include marginal moraine ridges and drumlins while circular moraine ridges and glaciofluvial features formed in a stagnant glacial regime dominate the northern central hummocky area the distribution of glacigenic elements within the hummocky moraine landscape shows that active and stagnant ice coexisted on hogjaeren during the last deglaciation and that actively flowing ice was focused through eastward extending valleys it is not possible to determine whether ice flow was kept active in the southern area throughout the deglaciation or if the glacier was reactivated a possible readvance is suggested to have happened simultaneous to a readvance previously suggested based on the morphology on lagjaeren

high resolution numerical simulation of younger dryas glaciation in scotland golledge n r hubbard a sugden d e 2008 high resolution numerical simulation of younger dryas glaciation in scotland quaternary science reviews 27 9 10 888 904 sponsorship nerc

trimlines blockfields mountain top erratics and the vertical dimensions of the last british irish ice sheet in nw scotland periglacial trimlines separating glacially eroded lower slopes from blockfield covered plateaus on british and irish mountains have been interpreted either 1 in terms of representing the maximum altitude of the last ice sheet during the last glacial maximum lgm or 2 as a thermal boundary separating wet based ice at pressure melting point from cold based ice on summit plateaus we test these competing hypotheses through 10be exposure dating of high level erratic boulders above trimlines on five mountains in nw scotland nine out of 14 erratics yielded post lgm exposure ages ranging from 14 0 0 7 ka to 16 5 0 9 ka or from 14 9 0 9 ka to 17 6 1 1 ka depending on the 10be production rate employed in exposure age calculation these ages refute hypothesis 1 as they imply that the last ice sheet overtopped the mountains preservation of apparently intact blockfields on the summits implies cold based ice cover supporting hypothesis 2 as altitudinally consistent high level trimlines extend from our sampled sites across much of nw scotland and the hebrides our conclusions apply to all trimlines in this broader area and probably to all high level trimlines elsewhere in the british isles preservation of blockfields under cold based ice is consistent with blockfield evolution on plateaus throughout much or all of the quaternary averaged exposure ages of 15 16 ka for plateau top erratics implies nunatak emergence from the downwasting ice sheet prior to a regional readvance of the ice margin the wester ross readvance and before rapid warming at 14 7 ka at the onset of the lateglacial interstade but after the timing of ice sheet thinning as retrodicted by recent proxy climate driven thermo mechanical coupled models our findings provide an additional constraint on the future development of such models by implying that high level trimlines represent the altitude of a former transition zone between ice at pressure melting point and ice below pressure melting point

periglacial trimlines in the scottish highlands abstract two periglacial weathering limits have been identified on mountains in the highlands of scotland the lower has been interpreted as a periglacial trimline marking the upper limits of loch lomond younger dryas stade glaciers and has been employed to reconstruct the dimensions of parts of the main west highland icefield and certain smaller glaciers and icefields interpretation of the upper weathering limit has been more contentious but recent research has demonstrated 1 significant contrasts in the degree of bedrock weathering above and below this limit 2 that gibbsite a pre devensian weathering product is abundant above the limit but rare in soils farther downslope 3 that the isotopic 26al age of bedrock exposures above the limit greatly exceeds that at lower altitudes and 4 that the altitude of the weathering limit descends regularly along former ice sheet flowlines collectively these attributes suggest that the upper weathering limit is a periglacial trimline defining the maximum altitude of the last ice sheet calculated basal shear stress values are consistent with this interpretation which implies that the mainland ice shed lay at ca 900 m in wester ross and descended gently northwards whilst harris and lewis in the outer hebrides supported an independent ice cap that achieved a maximum altitude of ca 700 m wider implications of this interpretation and the future potential for ice sheet reconstruction are explored

controlled moraines origins characteristics and palaeoglaciological implications abstract controlled moraines are supraglacial debris concentrations that become hummocky moraine upon de icing and possess clear linearity due to the inheritance of the former pattern of debris rich folia in the parent ice linearity is most striking wherever glacier ice cores still exist but it increasingly deteriorates with progressive melt out as a result moraine linearity has a low preservation potential in deglaciated terrains but hummocky moraine tracts previously interpreted as evidence of areal stagnation may instead record receding polythermal glacier margins in which debris rich ice was concentrated in frozen toe zones recent applications of modern glaciological analogues to palaeoglaciological reconstructions have implied that a controlled moraine development can be ascribed to a specific process e g englacial thrusting or supercooling and b controlled moraine preservation potential is good enough to imply the occurrence of the specific process in former glacier snouts e g ancient polythermal or supercooled snouts these assumptions are tested using case studies of controlled moraine construction in which a wide range of debris entrainment and debris rich ice thickening mechanisms are seen to produce the same geomorphic features polythermal conditions are crucial to the concentration of supraglacial debris and controlled moraines in glacier snouts via processes that are most effective at the glacier permafrost interface end moraines lie on a process form continuum constrained by basal thermal regime the morphological expression of englacial structures in controlled moraine ridges is most striking while the moraines retain ice cores but the final deposits landforms tend to consist of discontinuous transverse ridges with intervening hummocks preserving only a weak impression of the former englacial structure these are arranged in arcuate zones of hummocky moraine up to 2 km wide containing ice walled lake plains and lying down flow of streamlined landforms produced by warm based ice a variety of debris entrainment mechanisms can produce the same geomorphic signature spatial and temporal variability in process form relationships will lead to the sequential development of different types of end moraines during the recession of a glacier or ice sheet margin

the quaternary deposits and landforms of scotland and the neighbouring shelves a review abstract a thick sequence of quaternary sediments up to 1000 m has been deposited in the north sea basin and perhaps five major glacial episodes the first occurring prior to ca 1 8 2 1 ma bp and the last during the late devensian can be recognised between the glacial events periods of low salinity arctic marine or glacio marine sedimentation have been dominant although episodes of ameliorated climate when north atlantic drift waters had access to the north sea have been identified a number of horizons in separate boreholes have been correlated with the last interglacial oxygen isotope stage 5e and a sequence of water mass movements around the scottish coasts can be reconstructed for the last ca 125 ka on land sequences of quaternary deposits relating to several glacial and non glacial terrestrial and marine events occur in different areas but due to poor dating correlation between these sequences cannot yet be achieved in particular north east scotland has a complex glacial history with evidence for ice sheet glaciation on at least four occasions evidence from the outer hebrides north east scotland and the north sea basin indicates that the late devensian scottish ice sheet had a rather restricted extent only reaching a short distance offshore along much of the east and west coasts at this time ice free areas existed in north east scotland on the isle of lewis and probably in caithness and orkney whilst part of the outer shelf around st kilda was dry land a marine embayment extended down the east coast of scotland between the scottish and scandinavian ice sheets and independent ice caps existed on the outer hebrides and probably on shetland deglaciation of the greater part of the country took place prior to ca 13 ka bp whilst the climate was still very cold the ice retreat appears to have been orderly with stagnant ice masses being trapped only in topographically suitable locations a number of retreat stages or minor readvances occurred during the general deglaciation the firth of clyde was one of the last areas outside the highlands to be deglaciated and this occurred in a rapid possibly catastrophic fashion shortly prior to ca 13 ka bp despite the mild climate at the start of the lateglacial interstadial it is not known if there was complete deglaciation prior to the loch lomond readvance the readvance glaciers however may have started to advance during the latter part of the interstadial when declining terrestrial temperatures coincided with a period of mild marine conditions the loch lomond readvance maximum can only be dated to some time after ca 10 9 ka bp and it is likely that final ice free conditions were not achieved until the earliest holocene

extent and deglacial chronology of the last british irish ice sheet implications of exposure dating using cosmogenic isotopes over 160 10be and 36cl exposure ages pertaining to the extent and chronology of the last british irish ice sheet biis are critically reviewed despite uncertainties inherent in the use of exposure ages this approach has demonstrated that at the last glacial maximum lgm ca 26 21 ka the biis extended over all low ground in scotland and all or almost all of ireland consistent with recent models depicting extension of the last biis to the atlantic shelf edge all exposure ages obtained for high level sites above trimlines on the mountains of northwestern scotland and ireland pre date the lgm this finding confirms that high plateaux in these areas escaped significant glacial erosion probably under a protective cover of cold based glacier ice that remained frozen to the underlying substrate in terms of deglaciation chronology the southern irish sea basin was probably deglaciated by 19 18 ka with extensive deglaciation of low ground in ireland and northeastern scotland prior to ca 14 5 ka ice cover on low ground in northwestern scotland apparently persisted after 14 0 ka suggesting survival of ice in favourable locations during the lateglacial interstade ca 14 5 12 9 ka attempts to date readvances have had mixed success the wester ross readvance in northwestern scotland was initially dated to ca 16 3 ka but more recent research implies a much younger age ca 14 0 13 5 ka exposure ages indicating a prolonged stillstand during ice sheet retreat in the cairngorms at ca 14 5 14 0 ka conflict with ages obtained on postglacial rockslides and basal radiocarbon dates which indicate deglaciation before ca 15 5 15 0 ka exposure dating has been successfully employed to confirm a loch lomond stadial ca 12 9 11 5 ka age for moraines in several mountain areas and to constrain the minimum altitude of the ice cap that extended over the western grampians at that time copyright 2009 john wiley sons ltd

the relation between surface rock fragment cover and semiarid hillslope profile morphology abstract rock fragment covers veneer hillslopes in many parts of the world and influence the operation of hydrologic and geomorphic processes on those surfaces the purpose of this investigation was the examine the spatial variability of rock fragment cover on morphological units of hillslopes in southeastern arizona u s a simple statistical models based upon hillslope gradient as well as a soil slope factor ssf were developed and validated for the estimation of percent rock fragment covers rfc on these units although reasonably accurate estimates were made using either hillslope gradient or the ssf it appears more efficient to utilize hillslope gradient alone likewise reasonably accurate estimates of rfc can be made using either a composite model for the entire hillslope or unit specific models however it appears more efficient to utilize the gradient composite model

the role of inversion tectonics in the structure of the cordillera oriental nw argentinean andes the salta basin of cretaceous age in the andes of nw argentina was inverted during the development of the cordillera oriental between the neogene and recent the different orientations of the extensional faults of the salta rift system and the subsequent w e shortening resulted in a great variety of inversion structures extensional faults dipping ne to ese were preferentially reactivated as contractional faults the initial stepped geometry of these faults gave rise to a distinctive sigmoidal pattern of basement involved thrusts and related folds these contractional structures tended to run parallel to the extensional faults and acquired a n s trend across the previous accommodation zones resulting in folding interference patterns other interference patterns are attributed to the superposition of contractional folds on previous rollovers and to the constrictional deformation imposed by the reactivation of adjacent extensional faults with different orientations the nnw to wsw dipping extensional faults show no evidence of reactivation despite the fact that some of them are folded the inversion at crustal scale is limited owing to the presence of the cretaceous salta rift across the different andean structural units and foreland

lateglacial surface exposure dating in the monadhliath mountains central highlands scotland we constrain the deglaciation history of the monadhliath mountains since the last glacial maximum using glacial geomorphology and surface exposure dating collectively these data clarify the glacial history of the monadhliath mountains at the close of the devensian cold period 10be exposure ages indicate deglaciation of the last devensian ice sheet at 15 1 1 4 ka at ca 640 m od the exposure ages are consistent with basal radiocarbon ages from nearby loch etteridge 5 km to the south east 15 3 0 2 kcal bp1 boulders from moraines in three monadhliath corries yielded exposure ages between 11 8 ka and 9 8 ka 470 600 m od suggesting that a lateglacial advance occurred during the younger dryas stadial the limited extent of these younger dryas glaciers in the monadhliath mountains results from the combined effect of a drier climate experienced in the eastern part of the central highlands ice cap and topographical factors our reconstruction largely supports the deglaciation model of golledge et al 2008 and confirms that a sw to ne precipitation gradient dominated scotland during the younger dryas

deglaciation of the eurasian ice sheet complex the eurasian ice sheet complex eisc was the third largest ice mass during the last glacial maximum with a span of over 4500 km and responsible for around 20 m of eustatic sea level lowering whilst recent terrestrial and marine empirical insights have improved understanding of the chronology pattern and rates of retreat of this vast ice sheet a concerted attempt to model the deglaciation of the eisc honouring these new constraints is conspicuously lacking here we apply a first order thermomechanical ice sheet model validated against a diverse suite of empirical data to investigate the retreat of the eisc after 23 ka bp directly extending the work of patton et al 2016 who modelled the build up to its maximum extent retreat of the ice sheet complex was highly asynchronous reflecting contrasting regional sensitivities to climate forcing oceanic influence and internal dynamics most rapid retreat was experienced across the barents sea sector after 17 8 ka bp when this marine based ice sheet disintegrated at a rate of 670 gigatonnes per year gt a 1 through enhanced calving and interior dynamic thinning driven by oceanic atmospheric warming and exacerbated by eustatic sea level rise from 14 9 to 12 9 ka bp the eisc lost on average 750 gt a 1 peaking at rates 3000 gt a 1 roughly equally partitioned between surface melt and dynamic losses and potentially contributing up to 2 5 m to global sea level rise during meltwater pulse 1a independent glacio isostatic modelling constrained by an extensive inventory of relative sea level change corroborates our ice sheet loading history of the barents sea sector subglacial conditions were predominately temperate during deglaciation with over 6000 subglacial lakes predicted along with an extensive subglacial drainage network moreover the maximum eisc and its isostatic footprint had a profound impact on the proglacial hydrological network forming the fleuve manche mega catchment which had an area of 2 5 106 km2 and drained the present day vistula elbe rhine and thames rivers through the seine estuary during the bolling allerod oscillation after c 14 6 ka bp two major proglacial lakes formed in the baltic and white seas buffering meltwater pulses from eastern fennoscandia through to the younger dryas when these massive proglacial freshwater lakes flooded into the north atlantic ocean deglaciation temporarily abated during the younger dryas stadial at 12 9 ka bp when remnant ice across svalbard franz josef land novaya zemlya fennoscandia and scotland experienced a short lived but dynamic re advance the final stage of deglaciation converged on present day ice cover around the scandes mountains and the barents sea by 8 7 ka bp although the phase lagged isostatic recovery still continues today

genesis of hummocky moraines by thrusting in glacier ice evidence from svalbard and britain irregular mounds of glacial debris commonly referred to as 9hummocky moraine9 until recently were linked to ice stagnation during rapid climatic amelioration however recent work in scotland has demonstrated that some hummocky moraine dating from the younger dryas event c 10 000 years bp was the product of deposition at active ice margins observations at modern high arctic glacier margins in svalbard 76 80 n indicate that some moraines of this type form under a dynamic glaciological regime mainly by thrusting in active polythermal ice undergoing strong longitudinal compression this situation is particularly common where there is a transition from warm based ice in the interior of a glacier to cold based ice at the margins or snout from their morphological similarity rectilinear slopes facing up glacier and irregular downglacier faces and apparent stacking of slabs of sediment of subglacial derivation it is concluded that some assemblages of british moraines are also the product of thrusting this process appears to be most dominant in polythermal glaciers rather than in temperate glaciers on this basis it is tentatively suggested that the younger dryas in britain was characterized by a climatic regime similar to that in svalbard today mean annual temperature 5 c 400 1000 mm precipitation and that the associated glaciers may have been of polythermal character

a reinterpretation of scottish hummocky moraine and its significance for the deglaciation of the scottish highlands during the younger dryas or loch lomond stadial the aim of this paper is to demonstrate that much of the hummocky moraine present within the northern part of the lochlomond readvance ice cap formerly situated in the north west scottish highlands may be interpreted as suites of ice front moraines deposited during active decay these landforms can be used to reconstruct ice cap decay whichleads to important insights into the shrinking form of the ice cap and associated environmental conditions evidence has been collected from 10803 airphotographs and from detailed field survey it is presented at three spatial scales

sedimentary facies and landform genesis at a temperate outlet glacier soler glacier north patagonian icefield glasser n f hambrey m j 2002 sedimentary facies and landform genesis at a temperate outlet glacier soler glacier north patagonian icefield 49 1 43 64

the chronology of the last deglaciation implications to the cause of the younger dryas event it has long been recognized that the transition from the last glacial to the present interglacial was punctuated by a brief and intense return to cold conditions this extraordinary event referred to by european palynologists as the younger dryas was centered in the northern atlantic basin evidence is accumulating that it may have been initiated and terminated by changes in the mode of operation of the northern atlantic ocean further it appears that these mode changes may have been triggered by diversions of glacial meltwater between the mississippi river and the st lawrence river drainage systems we report here accelerator mass spectrometry ams radiocarbon results on two strategically located deep sea cores one provides a chronology for surface water temperatures in the northern atlantic and the other for the meltwater discharge from the mississippi river our objective in obtaining these results was to strengthen our ability to correlate the air temperature history for the northern atlantic basin with the meltwater history for the laurentian ice sheet

lateglacial ice cap dynamics in nw scotland evidence from the fjords of the summer isles region abstract the seaboard of western scotland is a classic fjord landscape formed by glaciation over at least the last 0 5 ma we examine the glacial geology preserved in the fjords or sea lochs of the summer isles region of nw scotland using high resolution seismic data multibeam swath bathymetry seabed sediment cores digital terrain models aerial photographs and field investigations detailed analyses include seismic facies and lithofacies interpretations sedimentological and palaeoenvironmental analyses and radiocarbon dating of selected microfauna our results indicate that the pleistocene sediments of the summer isles region on and offshore can be subdivided into several lithostratigraphic formations on the basis of seismic character geomorphology and sedimentology these are subglacial tills ice distal and glacimarine facies ice proximal and ice contact facies moraine assemblages and holocene basin fill the submarine landscape is also notable for its large scale mass movement events the result of glaciodynamic paraglacial or seismotectonic processes radiocarbon dating of marine shells indicate that deglaciation of this part of nw scotland was ongoing between 14 and 13 ka bp during the lateglacial interstadial greenland interstadial 1 consistent with cosmogenic surface exposure ages from previous studies a sequence of numerous seafloor moraine ridges charts oscillatory retreat of the last ice sheet from a buoyant calving margin in the minch to a firmly grounded margin amongst the summer isles in the early part of lateglacial interstadial gi 1 pre 14 ka bp subsequent punctuated frontal retreat of the ice mass occurred in the following 1000 years during which time ice cap outlet glaciers became topographically confined and restricted to the fjords a late stage readvance of glaciers into the inner fjords occurred soon after 13 ka bp which calls into question the accepted limits of ice extent during the younger dryas stadial greenland stadial 1 we examine the wider implications of our chronostratigraphic model discussing the implications for british ice sheet deglaciation lateglacial climate change and the style and rates of fjord sedimentation

palaeoclimatic reconstruction from loch lomond readvance glaciers in the west drumochter hills scotland 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

glacier response to climatic change during the loch lomond stadial and early flandrian geomorphological and palynological evidence from the isle of skye scotland 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

did large ice caps persist on low ground in north west scotland during the lateglacial interstade recent research based primarily on exposure ages of boulders on moraines has suggested that extensive ice masses persisted in fjords and across low ground in north west scotland throughout the lateglacial interstade greenland interstade 1 ca 14 7 12 9 ka and that glacier ice was much more extensive in this area during the older dryas chronozone ca 14 0 ka than during the younger dryas stade ca 12 9 11 7 ka we have recalibrated the same exposure age data using locally derived 10be production rates this increases the original mean ages by 6 5 12 implying moraine deposition between ca 14 3 and ca 15 1 ka and we infer a most probable age of ca 14 7 ka based on palaeoclimatic considerations the internal consistency of the ages implies that the dated moraines represent a single readvance of the ice margin the wester ross readvance pollen stratigraphic evidence from a lateglacial site at loch droma on the present drainage divide demonstrates deglaciation before ca 14 0 ka and therefore implies extensive deglaciation of all low ground and fjords in this area during the first half of the interstade ca 14 7 14 0 ka this inference appears consistent with lateglacial radiocarbon dates for shells recovered from glacimarine sediments and a dated tephra layer our revised chronology conflicts with earlier proposals that substantial dynamic ice caps persisted in scotland between 14 and 13 ka that large active glaciers probably survived throughout the lateglacial interstade and that ice extent was greater during the older dryas period than during the younger dryas stade copyright 2011 john wiley sons ltd