a revised chronology for the growth and demise of loch lomond readvance younger dryas ice lobes in the lochaber area scotland abstract we present a revised varve chronology for the duration of ice dammed lakes that formed in the lochaber district scotland during the loch lomond younger dryas stadial we analysed new varved sequences and combined them with existing varve records to develop the lochaber master varve chronology 2019 lmvc19 published here for the first time it spans an interval of 518 18 vyrs and is considered more secure than its predecessors because i it is anchored by a more robust record of the vedde ash which is dated to 12 043 43 cal yr bp and ii it provides revised estimates of the timings of key regional palaeoclimatic shifts that are fully compatible with those inferred from independently dated non varved records obtained from neighbouring sites the new results indicate that the lochaber ice dammed lakes existed between 12 135 and 11 618 61 cal yr bp but the pattern of glacier advance that led to lake formation was more complex than previously assumed with some ice fronts reaching their maximal positions 300 years before others initiation of ice retreat at 11 800 cal yr bp appears to have coincided with a rise of 2 c in mean july temperatures inferred from chironomid data obtained from the abernethy forest site in the eastern highlands this local climatic shift is thought to have been a delayed response by up to 335 years to a mid stadial northward migration of the north atlantic polar front the delay probably due to the influence of the sw highland icefield subsequent retreat that led to the formation of ice stagnation features throughout large parts of the area was initiated by a further rise in summer air temperature of 3 c at the start of the early holocene final drainage of the lake system occurred 190 years after the initiation of ice retreat while it took a further 200 years for the ice to vacate the rannoch plateau a nearby upland glacial source

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

topography and ice sheet growth this paper uses a numerical ice sheet model to investigate the role of topography in influencing ice sheet growth the model is applied to the maritime mid latitude uplands of scotland and relies on a series of assumptions about mass balance topography and ice flow it is driven by an imposed pattern of temperature change the model is able to predict effectively the extent and thickness of the loch lomond ice sheet using a palaeotemperature curve based on coleoptera assemblages a series of experiments with a stepped constant july air temperature depression suggests that in scotland a change in excess of 3 0 c is necessary to initiate ice sheet growth that steady state ice caps build up at changes of 3 to 6 5 c and that large ice sheets build up at changes of more than 6 625 c the bifurcation revealed by the last two types of behaviour is the result of topography both the vertical amplitude and the spatial distribution of bedrock basins and ridges are important in determining the pattern rate and extent of ice sheet growth the implication is that topography plays an important role in determining the dynamics of ice sheet growth

the deglaciation of eastern scotland cosmogenic 10be evidence for a lateglacial stillstand cosmogenic nuclide analysis using 10be has been used to date a lateglacial stillstand in the eastern highlands of scotland at 16 6 13 6 kyr bp the dates constrain the extent of the local cairngorm ice cap and the larger scottish ice sheet at a particular stage during deglaciation the geomorphological and sedimentological evidence suggests that the glacial stillstand persisted for around 1 kyr independent 14c dating from loch etteridge within strathspey shows that deglaciation proceeded rapidly after ca 15 kyr bp critically this study demonstrates that glaciers last occupied the valleys of the cairngorms immediately prior to the lateglacial interstadial bolling allerod contrary to previous assumptions that the last large scale glaciation of the massif took place in the loch lomond stadial younger dryas this later event in the cairngorms was therefore confined to the high corries

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

stress gradient coupling in glacier flow i longitudinal averaging of the influence of ice thickness and surface slope for a glacier flowing over a bed of longitudinally varying slope the influence of longitudinal stress gradients on the flow is analyzed by means of a longitudinal flow coupling equation derived from the vertically cross sectionally integrated longitudinal stress equilibrium equation by an extension of an approach originally developed by budd 1968 linearization of the flow coupling equation by treating the flow velocity u vertically averaged ice thickness h and surface slope in terms of small deviations u h and a from overall average datum values u 0 h 0 and 0 results in a differential equation that can be solved by green s function methods giving u x as a function of h x and x x being the longitudinal coordinate the result has the form of a longitudinal averaging integral of the influence of local h x and x on the flow u x u x u0 2l l 0 ln n nh n l exp x x l dx where the integration is over the length l of the glacier the operator specified deviations from the datum state and the term on which it operates which is a function of the integration variable x represents the influence of local h x x and channel shape factor x at longitudinal coordinate x on the flow u at coordinate x the influence being weighted by the influence transfer function exp x x l in the integral the quantity l that appears as the scale length in the exponential weighting function is called the longitudinal coupling length it is determined by rheological parameters via the relationship l 2h n n 3n where n is the flowlaw exponent n the effective longitudinal viscosity and n the effective shear viscosity of the ice profile n is an average of the local effective viscosity n over the ice cross section and n 1 is an average of n 1 that gives strongly increased weight to values near the base theoretically the coupling length l is generally in the range one to three times the ice thickness for valley glaciers and four to ten times for ice sheets for a glacier in surge it is even longer l 12h it is distinctly longer for non linear n 3 than for linear rheology so that the flow coupling effects of longitudinal stress gradients are markedly greater for non linear flow the averaging integral indicates that the longitudinal variations in flow that occur under the influence of sinusoidal longitudinal variations in h or with wavelength are attenuated by the factor 1 1 2 l 2 relative to what they would be without longitudinal coupling the short intermediate and long scales of glacier motion raymond 1980 over which the longitudinal flow variations are strongly partially and little attenuated are for 2l 2l 20l and 20l for practical glacier flow calculations the exponential weighting function can be approximated by a symmetrical triangular averaging window of length 4l called the longitudinal averaging length the traditional rectangular window is a poor approximation because of the exponential weighting the local surface slope has an appreciable though muted effect on the local flow which is clearly seen in field examples contrary to what would result from a rectangular averaging window tested with field data for variegated glacier alaska and blue glacier washington the longitudinal averaging theory is able to account semi quantitatively for the observed longitudinal variations in flow of these glaciers and for the representation of flow in terms of effective surface slope values exceptions occur where the flow is augmented by large contributions from basal sliding in the ice fall and terminal zone of blue glacier and in the reach of surge initiation in variegated glacier the averaging length 4l that gives the best agreement between calculated and observed flow pattern is 2 5 km for variegated glacier and 1 8 km for blue glacier corresponding to l h 2 in both cases if l varies with x but not too rapidly the exponential weighting function remains a fairly good approximation to the exact green s function of the differential equation for longitudinal flow coupling in this approximation l in the averaging integral is l x but is not a function of x effects of longitudinal variation of l are probably important near the glacier terminus and head and near ice falls the longitudinal averaging formulation can also be used to express the local basal shear stress in terms of longitudinal variations in the local stope stress with the mediation of longitudinal stress gradients

glacial deposits in great britain and ireland with the increasing awareness of environmental problems there is a growing desire for a de tailed understanding of superficial deposits in general and glacial deposits in particular this is because these sediments have a profound influence on groundwater protection waste management and nature conservation they are also of vital importance to civil engineering because they provide the foundation for as well as the materials extracted to build our roads and buildings the greater part of the british isles was glaciated at least once during the quater nary era in the regions subjected to glaciation glacial deposits underlie much of the present land surface although there have been many recent publica tions on various quaternary geological topics the present volume is the first dedicated to a detailed assessment of the glacial deposits of britain and ireland after introductory chapters presenting the glacial history the sedimentary sequences in 24 critical regions are discussed these regions include all of ireland the gla ciated area of great britain and the adjoining offshore region of the north sea the controver sial evolution of the irish sea basin during the last glaciation is discussed from various view points a collection of critical topics presented in the later part of the book range from the classification of glacigenic landforms and de posits to the results of geophysical geotechnical and geochemical analyses the book includes 368 figures 40 tables and 51 colour photographs a detailed index and a list of over 1000 references with 45 contributions by 48 scientists this volume represents a truly contemporary view of this field of research to gether with its companion volume the glacial deposits in north west europe this book pro vides an excellent textbook for the advanced student or the amateur as well as an indispen sible source and guidebook for the professional scientist

early holocene history of the west greenland ice sheet and the gh 8 2 event abstract the margin of the greenland ice sheet retreated rapidly during the first few thousand years of the holocene during this period of relative warmth known as the holocene thermal maximum ice core records identify a significant short lived cooling event at approximately 8 4 8 0 ka cal yr bp the gh 8 2 event associated with a 5 7 c fall in mean annual air temperature over the centre of the ice sheet in this paper we constrain the history of the ice sheet margin in disko bugt west greenland and that of a major ice stream jakobshavns isbrae during the early holocene which incorporates the interval of the gh 8 2 event our work is based on a new relative sea level curve and minimum age estimates for the timing of deglaciation from two field sites combined with a review of previously published research from the study area we identify important differences in the chronology of ice margin recession during the early holocene most noticeably the margin of jakobshavns isbrae retreated well inland of the adjacent ice sheet at this time we conclude that the early holocene fjord stade moraines in disko bugt do not record a uniform ice sheet margin response to the gh 8 2 event rather these moraines are diachronous and formed between c 10 8 ka cal yr bp their age varying as a function of the interplay between topography and ice sheet ice stream dynamics we hypothesise that one cause for the lack of an identifiable response to the gh 8 2 event is because topographic controls dominated ice sheet behaviour at this time in lowland areas any increase in ice sheet mass balance was probably associated with an increase in calving rather than any major advance of a grounded ice sheet margin

the genesis and significance of hummocky moraine evidence from the isle of skye scotland abstract the range of genetic and climatic interpretations of scottish hummocky moraine is reviewed and new data are presented from the isle of skye western scotland which are used as the basis of a genetic classification hummocky moraine on skye is shown to consist of three principal sediment landform associations 1 recessional moraines 2 chaotic ice stagnation moraines and 3 drumlins and fluted moraines the recessional moraines consist of transverse moraine ridges and chains of mounds and were formed by a combination of glaciotectonics and debris accumulation at active ice margins second chaotic moraines consist of randomly distributed hummocks mounds and rim ridges and record deposition in contact with inactive ice finally drumlins and fluted moraines are longitudinally oriented subglacial bedforms formed by a combination of lodgement and sediment deformation individual occurrences of hummocky moraine may comprise one two or all of these associations the detailed study and differentiation of scottish hummocky moraine provides a valuable source of information on former glacier dynamics and landscape change

chironomid inferred air temperatures from lateglacial and holocene sites in north west europe progress and problems abstract non biting midges insecta diptera chironomidae are now widely recognised as powerful biological proxies for inferring past climatic change in this paper the response of chironomid assemblages to lateglacial and holocene climatic change from sites in scotland and norway is discussed analyses have shown that midge assemblages have responded to major and minor climatic fluctuations during the last 15 000 yr such as the aegelsee oscillation gerzensee oscillation and younger dryas in the lateglacial and the thermal optimum little ice age and cooling events at 8 2 and 2 0 cal ka bp in the holocene in an attempt to quantify these and other climatic fluctuations a chironomid mean july air temperature inference model based on a modern calibration set of 109 lakes in norway and svalbard has been developed the 3 component weighted averaging partial least squares inference model performs well with a root mean squared error of prediction of 0 90 c and a maximum bias of 0 59 c both based on leave one out cross validation which is lower than chironomid temperature inference models developed in canada switzerland and finland however while temperature inference models perform well in the lateglacial the more subtle climatic changes of the holocene are more difficult to reconstruct because the likely temperature changes are close to the limits of the prediction errors of the existing models to address this problem future work is required to refine and develop the calibration set by further improving taxonomic resolution by adding more lakes to the calibration set and by investigating the influence of other environmental variables on chironomid distributions and abundances

chironomid inferred late glacial air temperatures at whitrig bog southeast scotland this paper presents the first chironomid inferred mean july air temperature reconstruction for the late glacial in britain the reconstruction suggests that the thermal maximum occurred early in the interstadial with temperatures reaching about 12 degreesc there was then a gradual downward trend to about 11 degreesc punctuated by four distinct cold oscillations of varying intensity at the beginning of the younger dryas mean july temperatures fell to about 7 5 degreesc but gradually increased to about 9 degreesc before a rapid rise at the onset of the holocene the chironomid inferred temperature curve agrees closely both in general trends and in detail with the grip ice core oxygen isotope curve the reconstructed temperatures are 2 4 degreesc lower than coleopteran inferred temperatures but are closer to those inferred from plant macrofossils and glacial equilibrium line altitudes during the younger dryas copyright c 2000 john wiley sons ltd

the configuration sensitivity and rapid retreat of the late weichselian icelandic ice sheet abstract the fragmentary glacial geological record across the icelandic continental shelf has hampered reconstruction of the volume extent and chronology of the late weichselian ice sheet particularly in key offshore zones marine geophysical data collected over the last two decades reveal that the ice sheet likely attained a continental shelf break position in all sectors during the last glacial maximum though its precise timing and configuration remains largely unknown within this context we review the available empirical evidence and use a well constrained three dimensional thermomechanical model to investigate the drivers of an extensive late weichselian icelandic ice sheet its sensitivity to environmental forcing and phases of deglaciation our reconstruction attains the continental shelf break across all sectors with a total ice volume of 5 96 105 km3 with high precipitation rates being critical to forcing extensive ice sheet flow offshore due to its location astride an active mantle plume a relatively fast and dynamic ice sheet with a low aspect ratio is maintained our results reveal that once initial ice sheet retreat was triggered through climate warming at 21 8 ka bp marine deglaciation was rapid and accomplished in all sectors within c 5 ka at a mean rate of 71 gt of mass loss per year this rate of ice wastage is comparable to contemporary rates observed for the west antarctic ice sheet the ice sheet subsequently stabilised on shallow pinning points across the near shelf for two millennia but abrupt atmospheric warming during the bolling interstadial forced a second dramatic collapse of the ice sheet onshore with a net wastage of 221 gt a 1 over 750 years analogous to contemporary greenland rates of mass loss geothermal conditions impart a significant control on the ice sheet s transient response particularly during phases of rapid retreat insights from this study suggests that large sectors of contemporary ice sheets overlying geothermally active regions such as siple coast antarctica and ne greenland have the potential to experience rapid phases of mass loss and deglaciation once initial retreat is initiated

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

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

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

reconstructing climate from glaciers glaciers offer the potential to reconstruct past climate over timescales from decades to millennia they are found on nearly every continent and at the last glacial maximum glaciers were larger in all regions on earth the physics of glacier climate interaction are relatively well understood and glacier models can be used to reconstruct past climate from geological evidence of past glacier extent this can lead to significant insights regarding past present and future climate for example glacier modeling has demonstrated that the near ubiquitous global pattern of glacier retreat during the last few centuries resulted from a global scale climate warming of 1 c consistent with instrumental data and climate proxy records climate reconstructions from glaciers have also demonstrated that the tropics were colder at the last glacial maximum than was originally inferred from sea surface temperature reconstructions future efforts to reconstruct climate from glaciers may provide new constraints on climat

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

towards a gis assessment of numerical ice sheet model performance using geomorphological data a major difficulty in assimilating geomorphological information with ice sheet models is the lack of a consistent methodology to systematically compare model output and field data as an initial step in establishing a quantitative comparison methodology automated proximity and conformity analysis apca and automated flow direction analysis afda have been developed to assess the level of correspondence between modelled ice extent and ice marginal features such as end moraines as well as between modelled basal flow directions and palaeo flow direction indicators such as glacial lineations to illustrate the potential of such an approach an ensemble suite of 40 numerical simulations of the fennoscandian ice sheet were compared to end moraines of the last glacial maximum and the younger dryas and to glacial lineations in northern sweden using apca and afda model experiments evaluated in this manner were ranked according to level of correspondence such an approach holds considerable promise for optimizing the parameter space and coherence of ice flow models by automated quantitative assessment of multiple ensemble experiments against a database of geological or glaciological evidence

deglaciation of fennoscandia abstract to provide a new reconstruction of the deglaciation of the fennoscandian ice sheet in the form of calendar year time slices which are particularly useful for ice sheet modelling we have compiled and synthesized published geomorphological data for eskers ice marginal formations lineations marginal meltwater channels striae ice dammed lakes and geochronological data from radiocarbon varve optically stimulated luminescence and cosmogenic nuclide dating this is summarized as a deglaciation map of the fennoscandian ice sheet with isochrons marking every 1000 years between 22 and 13 cal kyr bp and every hundred years between 11 6 and final ice decay after 9 7 cal kyr bp deglaciation patterns vary across the fennoscandian ice sheet domain reflecting differences in climatic and geomorphic settings as well as ice sheet basal thermal conditions and terrestrial versus marine margins for example the ice sheet margin in the high precipitation coastal setting of the western sector responded sensitively to climatic variations leaving a detailed record of prominent moraines and other ice marginal deposits in many fjords and coastal valleys retreat rates across the southern sector differed between slow retreat of the terrestrial margin in western and southern sweden and rapid retreat of the calving ice margin in the baltic basin our reconstruction is consistent with much of the published research however the synthesis of a large amount of existing and new data support refined reconstructions in some areas for example the lgm extent of the ice sheet in northwestern russia was located far east and it occurred at a later time than the rest of the ice sheet at around 17 15 cal kyr bp we also propose a slightly different chronology of moraine formation over southern sweden based on improved correlations of moraine segments using new lidar data and tying the timing of moraine formation to greenland ice core cold stages retreat rates vary by as much as an order of magnitude in different sectors of the ice sheet with the lowest rates on the high elevation and maritime norwegian margin retreat rates compared to the climatic information provided by the greenland ice core record show a general correspondence between retreat rate and climatic forcing although a close match between retreat rate and climate is unlikely because of other controls such as topography and marine versus terrestrial margins overall the time slice reconstructions of fennoscandian ice sheet deglaciation from 22 to 9 7 cal kyr bp provide an important dataset for understanding the contexts that underpin spatial and temporal patterns in retreat of the fennoscandian ice sheet and are an important resource for testing and refining ice sheet models

hintereisferner austria mass balance reconstruction and numerical modelling of the historical length variations in this study an attempt is made to simulate the historical length variations of hintereisferner austria key elements in the model are 1 reconstruction of the local climate vent 2 multiple linear regression analysis between measured climate and mass balance variations 3 reconstruction of the mass balance with 1 and 2 4 a one dimensional numerical ice flow model forced by the mass balance history

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

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

stress gradient coupling in glacier flow iii exact longitudinal equilibrium equation the vertically integrated exact longitudinal stress equilibrium equation of budd 1970 is developed further in such a way as to yield an equation that gives explicitly and exactly the contributions to the basal shear stress made by surface and bed slope surface curvature longitudinal stress deviators and longitudinal stress gradients in a glacier flowing in plane strain over a bed of longitudinally varying slope with this exact equation questions raised by various approximate forms of the longitudinal equilibrium equation can be answered decisively and the magnitude of errors in the approximations can be estimated to first order in the angle that describes fluctuations in the surface slope from its mean value the exact equilibrium equation reduces to 1 2sin 2 b pghsin 2g t b k where g and t are the well known stress deviator gradient and variational stress terms k is a longitudinal curvature term and b is a basal drag term that contributes a resistance to sliding across basal hills and valleys except for t these terms are expressed in simple form and evaluated for practical situations the bed slope relative to the mean slope is not assumed to be small which allows the effects of bedrock topography to be determined particularly through their appearance in the b term

initial results from a distributed physically based model of glacier hydrology this paper describes the development and testing of a distributed physically based model of glacier hydrology the model is used to investigate the behaviour of the hydrological system of haut glacier d arolla valais switzerland the model has an hourly time step and three main components a surface energy balance submodel a surface flow routing submodel and a subglacial hydrology submodel the energy balance submodel is used to calculate meltwater production over the entire glacier surface the surface routing submodel routes meltwater over the glacier surface from where it is produced to where it either enters the subglacial hydrological system via moulins or runs off the glacier surface the subglacial hydrology submodel calculates water flow in a network of conduits which can evolve over the course of a melt season simulation in response to changing meltwater inputs the main model inputs are a digital elevation model of the glacier surface and its surrounding topography start of season snow depth distribution data and meteorological data model performance is evaluated by comparing predictions with field measurements of proglacial stream discharge subglacial water pressure measured in a borehole drilled to the glacier bed and water velocities inferred from dye tracer tests the model performs best in comparison with the measured proglacial stream discharges but some of the substantial features of the other two records are also reproduced in particular the model results show the high amplitude water pressure cycles observed in the borehole in the mid melt season and the complex velocity discharge hysteresis cycles observed in dye tracer tests the results show that to model outflow hydrographs from glacierized catchments effectively it is necessary to simulate spatial and temporal variations in surface melt rates the delaying effect of the surface snowpack and the configuration of the subglacial drainage system itself the model s ability to predict detailed spatial and temporal patterns of subglacial water pressures and velocities should make it a valuable tool for aiding the understanding of glacier dynamics and hydrochemistry 1998 john wiley sons ltd

velocity and stress fields in grounded glaciers a simple algorithm for including deviatoric stress gradients a new and efficient algorithm for computing the three dimensional stress and velocity fields in grounded glaciers includes the role of deviatoric stress gradients a consistent approximation of first order in the aspect of ratio of the ice mass gives a set of eight field equations for the five stress and three velocity components and the corresponding boundary conditions a coordinate transformation mapping the local ice thickness on to unity and approximating the derivatives in the horizontal direction by centred finite differences yields five ordinary differential and three algebraic equations this allows use of the method of lines starting the integration with prescribed stress and velocity components at the base and a simple iteration procedure converges rapidly the algorithm can lie used for a wide range of stress strain rate relations as long as strain only depends on deviatoric and shear stresses and on temperature sensitivity tests using synthetic and realistic ice geometries show the relevance of normal deviatoric stresses in the solutions for the velocity components even for ice sheets stress and velocity fields may deviate substantially from the widely used shallow ice approximation

glacial isostatic adjustment associated with the barents sea ice sheet a modelling inter comparison the 3d geometrical evolution of the barents sea ice sheet bsis particularly during its late glacial retreat phase remains largely ambiguous due to the paucity of direct marine and terrestrial based evidence constraining its horizontal and vertical extent and chronology one way of validating the numerous bsis reconstructions previously proposed is to collate and apply them under a wide range of earth models and to compare prognostic isostatic output through time with known relative sea level rsl data here we compare six contrasting bsis load scenarios via a spherical earth system model and derive a best fit 2 parameter using rsl data from the four main terrestrial regions within the domain svalbard franz josef land novaya zemlya and northern norway poor 2 values allow two load scenarios to be dismissed leaving four that agree well with rsl observations the remaining four scenarios optimally fit the rsl data when combined with earth models that have an upper mantle viscosity of 0 2 2 1021 pa s while there is less sensitivity to the lithosphere thickness ranging from 71 to 120 km and lower mantle viscosity spanning 1 50 1021 pa s gps observations are also compared with predictions of present day uplift across the barents sea key locations where relative sea level and gps data would prove critical in constraining future ice sheet modelling efforts are also identified

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

several location methods for underwater shots in the gulf of genoa western mediterranean structural implications abstract during the egt survey 50 underwater shots were detonated on a n s section through the gulf of genoa running from the northern margin 44 12 n towards corsica 42 90 n along the 9 e meridian the aim of this work is in a first stage to establish the propagation model of regional phases in this region and consequently to improve the location of epicentres and afterwards to refine our structural knowledge of this complex crustal area the relocation of these shots was carried out with arrival times of seismic signals recorded at land stations we have used different location methods all of which led to similar crustal models they reveal a low p n velocity area in the northern ligurian sea and in the gulf of genoa with a 20 km thick crust in the southern part approximately south of latitude 43 7n a 4 km thick oceanic crust covered by 8 km of sediments is clearly confirmed using these models a significant improvement of epicentre locations was obtained these improvements to propagation models lead to the two main structural conclusions 1 1 in the southern part of the investigated area the spread of an oceanic type domain as far as the foot of the continental margin 2 2 a sharp transition between the two domains of different stretching rate the northern one with a moho depth of about 20 km and the southern one with an average moho depth of about 14 km these observations substantiate the presence of a transform margin between the rifted gulf of genoa and the oceanic type ligurian basin

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

palaeoglaciology of bayan har shan ne tibetan plateau exposure ages reveal a missing lgm expansion the bayan har shan a prominent upland area in the northeastern sector of the tibetan plateau hosts an extensive glacial geological record to reconstruct its palaeoglaciology we have determined

topography climate and ice masses a review topography acts as a filter between regional climate and the consequent response of a glacier or ice sheet it influences the mass and energy inputs and modifies the ice dynamics the evolution of the ice sheet surface and over longer time scales of the bed topography modulates the climatic forcing until we have a better understanding of these topographic linkages the use of geophysical signals from former ice masses to determine palaeoclimates must be regarded as fundamentally flawed

fast tidewater glaciers some iceberg calving outlet glaciers flow continuously at speeds normally associated with surging glaciers arid exhibit dramatic instability scenarios related to those suggested for marine ice sheets no temperate tidewater glaciers are known to have floating termini but many polar and subpolar tidewater glaciers do the fast flow of temperate calving glaciers is almost entirely due to basal sliding and appears to be a function of the effective pressure on the bed which may approach zero and the longitudinal back stress on the terminus the terminus boundary condition the calving relation is imperfectly known yet is vital to the dynamics of these glaciers calving relations for grounded tidewater glaciers have been suggested on empirical grounds but have not been rigorously tested the calving relations for floating termini are virtually unknown this together with the imperfect understanding of basal sliding inhibits confidence in our understanding of the stability of these glaciers columbia glacier alaska is an instructive example because observations have been made on the major changes in its geometry calving rate and dynamics that have occurred in less than 10 years the calving flux has increased more rapidly than the glacier flux causing thinning and retreat as a result the ice velocity has increased markedly the short term velocity changes relate to changes in back pressure ice recession tidal changes and the flux of water injected to the bed these results have relevance to the mechanisms of basal sliding glacier surges and the stability of marine ice streams

cosmogenic 10be and 26al exposure ages of tors and erratics cairngorm mountains scotland timescales for the development of a classic landscape of selective linear glacial erosion abstract the occurrence of tors within glaciated regions has been widely cited as evidence for the preservation of relic pre quaternary landscapes beneath protective covers of non erosive dry based ice here we test for the preservation of pre quaternary landscapes with cosmogenic surface exposure dating of tors numerous granite tors are present on summit plateaus in the cairngorm mountains of scotland where they were covered by local ice caps many times during the pleistocene cosmogenic 10be and 26al data together with geomorphic relationships reveal that these landforms are more dynamic and younger than previously suspected many cairngorm tors have been bulldozed and toppled along horizontal joints by ice motion leaving event surfaces on tor remnants and erratics that can be dated with cosmogenic nuclides as the surfaces have been subject to episodic burial by ice an exposure model based upon ice and marine sediment core proxies for local glacial cover is necessary to interpret the cosmogenic nuclide data exposure ages and weathering characteristics of tors are closely correlated glacially modified tors and boulder erratics with slightly weathered surfaces have 10be exposure ages of about 15 to 43 ka nuclide inheritance is present in many of these surfaces correction for inheritance indicates that the eastern cairngorms were deglaciated at 15 6 0 9 ka glacially modified tors with moderate to advanced weathering features have 10be exposure ages of 19 to 92 ka these surfaces were only slightly modified during the last glacial cycle and gained much of their exposure during the interstadial of marine oxygen isotope stage 5 or earlier tors lacking evidence of glacial modification and exhibiting advanced weathering have 10be exposure ages between 52 and 297 ka nuclide concentrations in these surfaces are probably controlled by bedrock erosion rates instead of discrete glacial events maximum erosion rates estimated from 10be range from 2 8 to 12 0 mm ka with an error weighted mean of 4 1 0 2 mm ka three of these surfaces yield model exposure plus burial ages of 295 71 84 520 141 178 and 626 85 102 ka a vertical cosmogenic nuclide profile across the oldest sampled tor indicates a long term emergence rate of 31 2 mm ka these findings show that dry based ice caps are capable of substantially eroding tors by entraining blocks previously detached by weathering processes bedrock surfaces and erratic boulders in such settings are likely to have nuclide inheritance and may yield erroneous too old exposure ages while many cairngorm tors have survived multiple glacial cycles rates of regolith stripping and bedrock erosion are too high to permit the widespread preservation of pre quaternary rock surfaces

glacier modeling and the climate of patagonia during the last glacial maximum ice cap modeling constrained by empirical studies provides an effective way of reconstructing past climates the former patagonian ice sheet is in a climatically significant location since it lies athwart the southern hemisphere westerlies and responds to the latitudinal migration of climatic belts during glacial cycles a numerical model of the patagonian ice cap for the last glacial maximum lgm is developed which is time dependent and driven by changing the mass balance altitude relationship it relies on a vertically integrated continuity model of ice mass solved over a finite difference grid the model is relatively insensitive to ice flow parameters but highly sensitive to mass balance the climatic input is adjusted to produce the best fit with the known limits of the ice cap at the lgm the ice cap extends 1800 km along the andes and has a volume of 440 000 km3 during the lgm the equilibrium line altitude ela was lower than at present by at least 560 m near latitude 40 s 160 m near latitude 50 s and 360 m near latitude 56 s the latitudinal variation in ela depression can be explained by an overall fall in temperature of about 3 0 c and the northward migration of precipitation belts by about 5 latitude annual precipitation totals may have decreased by about 0 7 m at latitude 50 s and increased by about 0 7 m at latitude 40 s the ela rises steeply by up to 4 m per kilometer from west to east as the westerlies cross the andes and this prevents ice growth to the east the limited decrease in temperature during the lgm could be related to the modest migration of the antarctic convergence between south america and the antarctic peninsula

azimuthal anisotropy of velocity in the mantle lid beneath the basin and range province the basin and range province in western north america is one of the largest and best studied regions of cenozoic continental extension1 2 yet there is still considerable debate surrounding the geological history of the province and the cause of the observed widespread rifting although recent geological and crustal geophysical observations2 constrain crustal scale processes within the basin and range more information is needed on the structure and rheology of the mantle part of the lithosphere the mantle lid to distinguish between competing geodynamic models1 2 here we present seismic data showing an azimuthal variation of 3 2 in the p wave velocity in the shallowest mantle beneath the basin and range the direction of maximum seismic velocity coincides with the nw se direction of neogene and present day tectonic extension suggesting that penetrative deformation associated with this extension has induced a preferred orientation of the minerals in the mantle lid our results thus imply that deformation associated with present day surface rifting extends at least 30 km into the underlying mantle

the palaeoglaciology of the central sector of the british and irish ice sheet reconciling glacial geomorphology and preliminary ice sheet modelling digital elevation models of the area around the solway lowlands reveal complex subglacial bedform imprints relating the central sector of the lgm british and irish ice sheet drumlin and lineation mapping in four case studies show that glacier flow directions switched significantly through time these are summarised in four major flow phases in the region phase i flow was from a dominant scottish dispersal centre which transported criffel granite erratics to the eden valley and forced lake district ice eastwards over the pennines at stainmore phase ii involved easterly flow of lake district and scottish ice through the tyne gap and stainmore gap with an ice divide located over the solway firth phase iii was a dominant westerly flow from upland dispersal centres into the solway lowlands and along the solway firth due to draw down of ice into the irish sea basin phase iv was characterised by unconstrained advance of scottish ice across the solway firth forcing of a numerical model of ice sheet inception and decay by the greenland ice core record facilitates an assessment of the potential for rapid ice flow directional switching during one glacial cycle the model indicates that after fluctuations of smaller radially flowing ice caps prior to 30 ka bp the ice sheet grows to produce an elongate triangular shaped dome over nw england and sw scotland at the lgm at 19 5 ka bp recession after 18 5 ka bp displays a complex pattern of significant ice flow directional switches over relatively short timescales complementing the geomorphologically based assessments of palaeo ice dynamics the palaeoglaciological implications of this combined geomorphic and modelling approach are that a the central sector of the biis was as a major dispersal centre for only ca 2 5 ka after the lgm b the ice sheet had no real steady state and comprised constantly migrating dispersal centres and ice divides c subglacial streamlining of flow sets was completed over short phases of fast flow activity with some flow reversals taking place in less than 300 years

glacial geomorphology and geographic information systems recent developments in the field of glacial geomorphology have dramatically increased the need to acquire maintain manipulate and analyze large amounts of landform landscape and sediment data the use of geographic information systems gis has provided new platforms and tools for analysis and visualization of geomorphic data glacial geomorphologists have used gis to integrate multi source data manage multi scale studies identify previously unrecognized spatial and temporal relationships and patterns in geomorphic data and to link landform data with numerical models as part of model calibration and verification gis based analyses associated with numerical modeling are improving our understanding of glacial landscape evolution and are allowing new quantitative and systematic examinations of spatial and temporal patterns of glacial landforms and processes this has allowed for the development of insights and concepts that would be unlikely to arise using traditional methods alone key recommendations for future research and applications in glacial geomorphology include enhanced gis education and dissemination the development of standards and conventions for glacial geomorphic data community projects to collect data into readily accessible databases and enhanced use of linked gis model frameworks to address major issues in glacial geomorphology

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