late holocene and younger dryas glaciers in the northern cairngorm mountains scotland we present 17 cosmogenic 10be ages of glacial deposits in coire an lochain cairngorm mountains which demonstrate that glacial and nival deposits cover a longer timescale than previously recognis

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

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

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

positive degree day factors for ablation on the greenland ice sheet studied by energy balance modelling ice ablation is related to air temperature by the positive degree day factor variations of the positive degree day factor in west greenland are studied using an energy balance model to simulate ablation under different conditions degree day factors for simulated and measured ice ablation at nordbogletscher and qaman rssup sermia agree well with values around 8 mm d 1 c 1 degree day factors for snow are less than half those for ice energy balance modelling shows that degree day factors vary with summer mean temperature surface albedo and turbulence but there is only evidence of large positive degree day factors at lower temperatures and with low albedo 0 3 the greatest effect of albedo variations 0 3 0 7 is at lower temperatures while variations in turbulence have greater effect at higher temperatures current models may underestimate runoff from the greenland ice sheet by several tenths because they use a degree day factor for melting ice that is too small for the colder parts of the ice sheet i e the upper ablation area and the northerly margin

influence of sand on hydraulics and gravel transport in a braided gravel bed river measurements in a braided reach of the proglacial white river washington are used to compare the bed load capacity and competence of flow over the predominant gravel bed and over a narrow ribbon of mobile sand which extended alongside the talweg analysis of 144 velocity profiles and 222 bed load samples shows that shear stress and roughness height were significantly lower over sand than gravel but maximum bed load diameter and total gravel transport rate significantly higher as were transport rates of given size fractions at similar shear stresses these differences in competence and capacity are explained by relative size effects on the threshold shear stress for entrainment the influence on gravel transport of local variation in bed material size may explain the self sorting of bed load sheets described by other workers however in channels like that described here the continuous longitudinal ribbon of sand allows the flow to develop a lower shear stress over the smoother bed which partly offsets the relative size effects on competence and capacity

dynamic cycles ice streams and their impact on the extent chronology and deglaciation of the british irish ice sheet we present results from a suite of forward transient numerical modelling experiments of the british and irish ice sheet biis consisting of scottish welsh and irish accumulation centres spanning the last glacial period from 38 to 10 ka bp the 3d thermomechanical model employed uses higher order physics to solve longitudinal membrane stresses and to reproduce grounding line dynamics surface mass balance is derived using a distributed degree day calculation based on a reference climatology from mean 1961 1990 precipitation and temperature patterns the model is perturbed from this reference state by a scaled ngrip oxygen isotope curve and the specmap sea level reconstruction isostatic response to ice loading is computed using an elastic lithosphere relaxed asthenosphere scheme a suite of 350 simulations were designed to explore the parameter space of model uncertainties and sensitivities to yield a subset of experiments that showed close correspondence to offshore and onshore ice directional indicators broad biis chronology and the relative sea level record three of these simulations are described in further detail and indicate that the separate ice centres of the modelled biis complex are dynamically interdependent during the build up to maximum conditions but remain largely independent throughout much of the simulation the modelled biis is extremely dynamic drained mainly by a number of transient but recurrent ice streams which dynamically switch and fluctuate in extent and intensity on a centennial time scale a series of binge purge advance retreat cycles are identified which correspond to alternating periods of relatively cold based ice associated with a high aspect ratio and net growth and wet based ice with a lower aspect ratio characterised by streaming the timing and dynamics of these events are determined through a combination of basal thermomechanical switching spatially propagated and amplified through longitudinal coupling but are modulated and phase lagged to the oscillations within the ngrip record of climate forcing phases of predominant streaming activity coincide with periods of maximum ice extent and are triggered by abrupt transitions from a cold to relatively warm climate resulting in major iceberg melt discharge events into the north sea and atlantic ocean the broad chronology of the modelled biis indicates a maximum extent at 20 ka with fast flowing ice across its western and northern sectors that extended to the continental shelf edge fast flowing streams also dominate the irish sea and north sea basin sectors and impinge onto sw england and east anglia from 19 ka bp deglaciation is achieved in less than 2000 years discharging the freshwater equivalent of 2 m global sea level rise a much reduced ice sheet centred on scotland undergoes subsequent retrenchment and a series of advance retreat cycles into the north sea basin from 17 ka onwards culminating in a sustained younger dryas event from 13 to 11 5 ka bp modelled ice cover is persistent across the western and central highlands until the last remnant glaciers disappear around 10 5 ka bp

a younger dryas plateau icefield in the monadhliath scotland and implications for regional palaeoclimate a record of younger dryas glaciation in scotland is well established however the role of the monadhliath a significant plateau area extending over 840 km2 in central scotland has never been investigated systematically we present the first systematic glacial geomorphological mapping across the whole region which has led to the identification of hitherto unrecorded glacial and associated landforms the spatial distribution of these landforms indicates that the last phase of glaciation in the area was that of a local plateau icefield in addition a clear morphostratigraphical signature provides a strong indication that the icefield dates to the younger dryas 12 9 11 7 ka which is supported by numerical ages in the southeast of the study area based on the geomorphological evidence and 2d glacier surface profile modelling a 280 km2 icefield is reconstructed a novel approach is introduced to quantify plateau icefield thickness for equilibrium line altitude ela and palaeoprecipitation calculations resulting in greater overall data confidence compared to traditional reconstruction methods the ela for the whole icefield is calculated to be 714 25 m whilst the elas of individual outlet glaciers range from 560 m in the west to 816 m in the east demonstrating a significant w e precipitation gradient across the region during the younger dryas these elas compare well with those calculated for younger dryas ice masses reconstructed in neighbouring regions and are in good agreement with overall precipitation patterns suggested for scotland during this time whilst the total amount of precipitation calculated from these elas is highly dependent on the method used irrespective of this the study suggests a more arid younger dryas climate in the region compared to the present day

optimal estimation of changes in the mass of ice sheets we describe a new approach for estimating changes in ice sheet mass two methods are in common use the ice budget and geodetic methods the first makes use of separate estimates of the mass fluxes into and out of a domain differencing them to obtain the local mass balance the second estimates mass balance directly using measurements of the change in surface elevation often from aircraft or satellites here we combine ice budget and geodetic approaches to obtain an optimal estimate of mass balance we seek maximum likelihood solutions for three terms 1 the rate of change of surface elevation 2 the rate of snow accumulation and 3 the local divergence of the ice flux these estimates are constrained to obey the continuity equation we allow the location and temporal averaging interval of the estimates to be chosen arbitrarily this approach can use all relevant measurements the fidelity of any measurement is lowered by measurement error and by fluctuations in each of the three terms driven by random year to year snowfall variations we take full account of both error sources weighting the data so as to minimize the confounding effect of these influences realistic covariance between randomly forced fluctuations are provided by a linearized model of ice sheet flow we test the approach by applying the algorithm to synthetically generated measurements the method performs better than either ice budget or geodetic methods applied in isolation and has the important advantage that good estimates may still be derived when measurements appropriate to either technique are lacking or inaccurate

calving processes and the dynamics of calving glaciers abstract calving of icebergs is an important component of mass loss from the polar ice sheets and glaciers in many parts of the world calving rates can increase dramatically in response to increases in velocity and or retreat of the glacier margin with important implications for sea level change despite their importance calving and related dynamic processes are poorly represented in the current generation of ice sheet models this is largely because understanding the calving problem involves several other long standing problems in glaciology combined with the difficulties and dangers of field data collection in this paper we systematically review different aspects of the calving problem and outline a new framework for representing calving processes in ice sheet models we define a hierarchy of calving processes to distinguish those that exert a fundamental control on the position of the ice margin from more localised processes responsible for individual calving events the first order control on calving is the strain rate arising from spatial variations in velocity particularly sliding speed which determines the location and depth of surface crevasses superimposed on this first order process are second order processes that can further erode the ice margin these include fracture propagation in response to local stress imbalances in the immediate vicinity of the glacier front undercutting of the glacier terminus by melting at or below the waterline and bending at the junction between grounded and buoyant parts of an ice tongue calving of projecting submerged ice feet can be regarded as a third order process because it is paced by first or second order calving above the waterline first order calving can be represented in glacier models using a calving criterion based on crevasse depth which is a function of longitudinal strain rate modelling changes in terminus position and calving rates thus reduces to the problem of determining the ice geometry and velocity distribution realistic solutions to the problem of modelling ice flow therefore depend critically on an appropriate choice of sliding law models that assume that basal velocities are controlled by basal drag can replicate much of the observed behaviour of calving glaciers with grounded termini but an important limitation is that they cannot be used to model floating glacier termini or ice shelves alternative sliding laws that parameterise drag from the glacier margins provide more flexible and robust ways of representing calving in ice sheet models such models can explain a remarkable range of observed phenomena within a simple unifying framework including downglacier increases in velocity and strain rates where basal and or lateral drag diminishes flow acceleration in response to thinning through time the tendency for glaciers to stabilise at pinning points in relatively shallow water or fjord narrowings the constraints on ice shelf stability and the contrasts in calving rates between tidewater and freshwater calving glaciers many unresolved issues remain however including the role played by the removal of backstress in the acceleration of retreating calving glaciers and the controls on melting at and below the waterline

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

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

the younger dryas cold interval as viewed from central greenland abstract greenland ice core records provide an exceptionally clear picture of many aspects of abrupt climate changes and particularly of those associated with the younger dryas event as reviewed here well preserved annual layers can be counted confidently with only 1 errors for the age of the end of the younger dryas 11 500 years before present ice flow corrections allow reconstruction of snow accumulation rates over tens of thousands of years with little additional uncertainty glaciochemical and particulate data record atmospheric loading changes with little uncertainty introduced by changes in snow accumulation confident paleothermometry is provided by site specific calibrations using ice isotopic ratios borehole temperatures and gas isotopic ratios near simultaneous changes in ice core paleoclimatic indicators of local regional and more widespread climate conditions demonstrate that much of the earth experienced abrupt climate changes synchronous with greenland within thirty years or less post younger dryas changes have not duplicated the size extent and rapidity of these paleoclimatic changes

modelling the inception of the patagonian icesheet abstract we use a coupled climate icesheet model to simulate the inception and growth of the patagonian icesheet assuming a temperature lowering of 6 c and a uniform pressure gradient driving windfields an icesheet builds up with dimensions and morphology similar to that of the last glacial maximum analysis of the stages of growth reveals the following conclusions different sectors of the 1800 km long icesheet behave differently as a result of latitudinal variations in mass balance the fastest growth occurs in latitudes 45 52 s where the north and south patagonian icefields merge and expand to the coast within 1500 model years the most favourable topography for glacier initiation is the presence of high elevation basins low elevation summits in the mountain chain take a long time to become covered by ice because of the delay in ice spreading along the main mountain axis feedback between the increasing elevation of the icesheet and increasing mass balance on its windward flank enhances the rate of migration of the icesheet towards the precipitation source there is a lee side effect whereby easterly mountains are glaciated early on but are then starved of snow as ice builds up to the windward such locations should hold an empirical record of the early stages of a glacial cycle

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

estimates of the temperature flux temperature gradient relation above a sea floor the relation between the ux of temperature or buoyancy the verti cal temperature gradient and the height above the bottom is investigatedin an oceanographic context using high resolution temperature measure ments the model for the evolution of a strati ed layer by balmforthet al 1998 is reviewed and adapted to the case of a turbulent owabove a wall model predictions are compared to the average observa tional estimates of the ux exploiting a ux estimation method proposedby winters d asaro 1996 this estimation method enables the dis entanglement of the dependence of the average ux on the height abovethe bottom and on the background temperature gradient the classicaln shaped ux gradient relation is found in the observations model andobservations show similar qualitative behaviour despite the strong sim pli cations used in the model the results shed light on the modulationof the temperature ux by the presence of the boundary and support theidea of a turbulent ux following a mixing length argument in a strati edow furthermore the results support the use of thorpe scales close to aboundary if su cient averaging is performed suggesting that the thorpescales are a ected by the boundary in a similar way as the mixing length

deglacial surface circulation changes in the northeastern atlantic temperature and salinity records off nw scotland on a century scale sea surface temperature and salinity estimates reconstructed from a core collected on the barra fan northwest scotland 56 43 n 09 19 w water depth 1320 m show a series of rapid oscillations during the last deglacial period that are very similar to those observed in the 18o records from greenland ice cores these records indicate that the transport of heat and salt toward the nordic seas was highest during the bolling period this superconveyor weakened after the bolling probably as a consequence of increased meltwater flux reducing the oceanic salt content as suggested by the barbados sea level record evidence for a phase of ice rafting during the allerod is presented for the first time from this latitude in the northeast atlantic the younger dryas stadial resolved here at a century decadal scale is characterized by very rapid oscillations in temperature and salinity indicating that warm relatively saline waters repeatedly displaced cool polar waters at this latitude these observations attest to the inherent instability of the deglacial climate system

modelled ice sheet margins of three greenland ice sheet models compared with a geological record from ice marginal deposits in central west greenland ice sheet modelling is an essential tool for estimating the effect of climate change on the greenland ice sheet the large spatial and long term temporal scale ofice sheet models limits the amount of data which can be used to test model results the geological record is useful because it provides test material on the timescales typical for the memory of ice sheets millennia this paper compares modelled ice marginal positions with a geological scenario of ice marginpositions since the last glacial maximum to the present in west greenland morphological evidence of ice margin positions is provided by moraines moraine systems are dated by 14c dated marine shells and terrestrial peat we compared three greenland ice sheet models there are distinct differences inmodelled ice margin positions between the models and between model results and the geological record disagreement between models and the geologicalrecord in the near coastal area are explained by the insufficient treatment of marginal processes in a tidewater environment a smaller than present ice sheetaround the warm period in the holocene holocene climatic optimum only pops up when an unsmooth forcing is used this underlines the importance ofshort term variations in climatic variables in determining ice margin positions in the past but also in the future

a 2 d numerical model of snow ice energy balance and ice flow for paleoclimatic interpretation of glacial geomorphic features abstract standard methods of interpreting the paleoclimates recorded in alpine glacial geomorphic features rely on estimates of paleoglacier shape commonly assume that relationships between mass balance gradient and equilibrium line altitude of modern glaciers apply equally well to glaciers of in many cases dramatically different climates and do not account for the varying influence of topography on glacial extent while those methods may be adequate for many studies there are an increasing number of areas in which that level of analysis does not match the level of detail of the glacial chronologies being developed as an alternative we present a physically based 2 d glacier model that can be used to determine steady state glacier shapes and distributions for a wide range of climatic conditions the model requires only a modest amount of data beyond that which would be required for simpler methods and includes a relatively accurate representation of the effects of topography on the largest component of the surface energy balance shortwave radiation it calculates 2 d in the horizontal plane distribution of snow accumulation using a surface mass and energy balance approach and calculates the resultant glacier shapes with a 2 d flow model in addition to offering a potentially more accurate reconstruction of paleoclimatic conditions the model provides a means of performing detailed sensitivity analysis establishing relationships between similar deposits in basins of different shape and aspect and of predicting glacier shape terminus position in areas not yet explored

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

an ice cap landsystem for palaeoglaciological reconstructions characterizing the younger dryas in western scotland abstract this paper reviews the contrasting behaviours of ice caps and icefields defines a generic landsystem model that can effectively discriminate between them and applies the model to landform sediment assemblages in an area of western scotland such a model is necessary since many palaeoenvironmental inferences from formerly glaciated terrains are based on the geometry extent and dynamics of reconstructed ice masses the validity of these glacier reconstructions is dependent on the accurate initial interpretation of relict landforms and sediments and their inter relationships a new landsystems model is presented here in which individual geological and geomorphological elements are checked against a set of eight theoretical diagnostic criteria that characterize the style of former glaciation when applied to a 1200 km 2 area of the western scottish highlands the landsystem tool predicts 1 an extensive younger dryas ice cap with a maximum surface elevation of 900 m above sea level implying colder or wetter conditions than previously thought and 2 the survival of an independent mountain icefield in part of the area during deglaciation glaciological theory proxy palaeoenvironmental data and established glacier climate topography relationships support these predictions thereby giving credibility to the landsystem methodology as a generic tool for palaeoglaciological reconstructions

oxygen isotope and palaeotemperature records from six greenland ice core stations camp century dye 3 grip gisp2 renland and northgrip oxygen isotope variations spanning the last glacial cycle and the holocene derived from ice core records for six sites in greenland camp century dye 3 grip gisp2 renland and northgrip show strong similarities this suggests that the dominant influence on oxygen isotope variations reflected in the ice sheet records was regional climatic change differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios palaeotemperature estimates have been obtained from the records using three approaches i inferences based on the measured relationship between mean annual 18o of snow and of mean annual surface temperature over greenland ii modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile or iii by using monte carlo simulation techniques the third of these approaches was adopted to reconstruct holocene temperature variations for the dye 3 and grip temperature profiles which yields remarkably compatible results a new record of holocene isotope variations obtained from the northgrip ice core matches the grip short term isotope record and also shows similar long term trends to the dye 3 and grip inverted temperature data the northgrip isotope record reflects i a generally stronger isotopic signal than is found in the grip record ii several short lived temperature fluctuations during the first 1500 yr of the holocene iii a marked cold event at ca 8 2 ka the 8 2 ka event iv optimum temperatures for the holocene between ca 8 6 and 4 3 ka a signal that is 0 6 stronger than for the grip profile v a clear signal for the little ice age and vi a clear signal of climate warming during the last century these data suggest that the northgrip stable isotope record responded in a sensitive manner to temperature fluctuations during the holocene copyright 2001 john wiley sons ltd

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

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

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

glaciology of the british isles ice sheet during the last glacial cycle form flow streams and lobes abstract the last ice sheet over the british isles together with other mid latitude pleistocene ice sheets and in contrast to the modern ice sheets of greenland and antarctica had a relatively low profile low summit elevation and extensive elongated lobes at its margin a thermo mechanically coupled numerical ice sheet model driven by a proxy climate has been used to explore the properties that would have permitted these characteristics to develop the approach the key to quantitative palaeoglaciology is to determine the boundary conditions that permit the simulated ice sheet to mimic the evolution of the real ice sheet through the last glacial cycle simulations show how a british ice sheet may have been confluent with a scandinavian ice sheet during some parts of its history and how unforced periodic and asynchronous oscillations could occur in different parts of its margins marginal lobes are a reflection of streaming within the ice sheet such streams can be ephemeral dynamic streams located because of ice sheet properties or fixed streams whose location is determined by bed properties the simulations that best satisfy constraints of extent elevation and relative sea levels are those with major fixed streams that strongly draw down the ice sheet surface in these the core upland areas of the ice sheet were cold based at the last glacial maximum basal streaming velocities were between 500 and 1000 ma 1 compared with surface velocities of 10 50 ma 1 in inter stream zones shear stresses were as low as 15 25 kpa in streams compared with 70 110 kpa in upland areas and 60 84 of the ice flux was delivered to the margin via streams

the mathematical model of ice sheets and the calculation of the evolution of the greenland ice sheet modele d evolution des calottes polaires prenant en compte les elements climatiques et geophysiques avec parametrisation des temperatures une application au groenland montre qu il n est pas dans un etat stationnaire qui correspondrait au climat actuel

topographic controls on plateau icefield recession insights from the younger dryas monadhliath icefield scotland plateau icefields are a common form of mountain ice mass frequently found in mid latitude to high arctic regions and increasingly recognized in the quaternary record their top heavy hypsometry makes them highly sensitive to changes in climate when the equilibriaum line altitude ela lies above the plateau edge allowing ice to expand significantly as regional elas decrease and causing rapid recession as climate warms with respect to future climate warming it is important to understand the controls on plateau icefield response to climate change in order to better predict recession rates with implications for water resources and sea level rise improving knowledge of the controls on glacier recession may also enable further palaeoclimatic information to be extracted from the quaternary glacial record we use the distribution of moraines to examine topographic controls on younger dryas icefield recession in scotland we find that overall valley morphology influences the style of recession through microclimatic and geometric controls with bed gradient affecting moraine spacing ice mass reconfiguration may occur as recession progresses because ice divide migration could alter the expected response based on hypsometric distribution these results add to a growing body of research examining controls on glacier recession and offer a step towards unravelling non linear ice mass behaviour less

growth dynamics and deglaciation of the last british irish ice sheet the deep sea ice rafted detritus record the evolution and dynamics of the last british irish ice sheet biis have hitherto largely been reconstructed from onshore and shallow marine glacial geological and geomorphological data this reconstruction has been problematic because these sequences and data are spatially and temporally incomplete and fragmentary in order to enhance biis reconstruction we present a compilation of new and previously published ice rafted detritus ird flux and concentration data from high resolution sediment cores recovered from the ne atlantic deep sea continental slope adjacent to the last biis these cores are situated adjacent to the full latitudinal extent of the last biis and cover marine isotope stages mis 2 and 3 age models are based on radiocarbon dating and graphical tuning of abundances of the polar planktonic foraminifera neogloboquadrina pachyderma sinistral nps to the greenland gisp2 ice core record multiple ird fingerprinting techniques indicate that at the selected locations most ird are sourced from adjacent biis ice streams except in the centre of heinrich h layers in which ird shows a prominent laurentide ice sheet provenance ird flux data are interpreted with reference to a conceptual model explaining the relations between flux north atlantic hydrography and ice dynamics both positive and rapid negative mass balance can cause increases and prominent peaks in ird flux first order interpretation of the ird record indicates the timing of the presence of the biis with an actively calving marine margin the records show a coherent latitudinal but partly phased signal during mis 3 and 2 published data indicate that the last biis initiated during the mis 5 4 cooling transition renewed growth just before h5 46 ka was succeeded by very strong millennial scale variability apparently corresponding with dansgaard oeschger do cycles closely coupled to millennial scale climate variability in the north atlantic region involving latitudinal migration of the north atlantic polar front this indicates that the previously defined precursor events are not uniquely associated with h events but are part of the millennial scale variability major growth of the ice sheet occurred after 29 ka with the barra ice stream attaining a shelf edge position and generating turbiditic flows on the barra donegal fan at 27 ka the ice sheet reached its maximum extent at h2 24 ka earlier than interpreted in previous studies rapid retreat initially characterised by peak ird flux during greenland interstadial 2 23 ka was followed by readvance between 22 and 16 ka readvance during h1 was only characterised by biis ice streams draining central dome s of the ice sheet and was followed by rapid deglaciation and ice exhaustion the evidence for a calving margin and ird supply from the biis during greenland stadial 1 younger dryas event is equivocal the timing of the initiation maximum extent deglacial and readvance phases of the biis interpreted from the ird flux record is strongly supported by recent independent data from both the irish sea and north sea sectors of the ice sheet

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

ice streams in the laurentide ice sheet identification characteristics and comparison to modern ice sheets this paper presents a comprehensive review and synthesis of ice streams in the laurentide ice sheet lis based on a new mapping inventory that includes previously hypothesised ice streams and includes a concerted effort to search for others from across the entire ice sheet bed the inventory includes 117 ice streams which have been identified based on a variety of evidence including their bedform imprint large scale geomorphology topography till properties and ice rafted debris in ocean sediment records despite uncertainty in identifying ice streams in hard bedrock areas it is unlikely that any major ice streams have been missed during the last glacial maximum laurentide ice streams formed a drainage pattern that bears close resemblance to the present day velocity patterns in modern ice sheets large ice streams had extensive onset zones and were fed by multiple tributaries and where ice drained through regions of high relief the spacing of ice streams shows a degree of spatial self organisation which has hitherto not been recognised topography exerted a primary control on the location of ice streams but there were large areas along the western and southern margin of the ice sheet where the bed was composed of weaker sedimentary bedrock and where networks of ice streams switched direction repeatedly and probably over short time scales as the ice sheet retreated onto its low relief interior several ice streams show no correspondence with topography or underlying geology perhaps facilitated by localised build up of pressurised subglacial meltwater they differed from most other ice stream tracks in having much lower length to width ratios and have no modern analogues there have been very few attempts to date the initiation and cessation of ice streams but it is clear that ice streams switched on and off during deglaciation rather than maintaining the same trajectory as the ice margin retreated we provide a first order estimate of changes in ice stream activity during deglaciation and show that around 30 of the margin was drained by ice streams at the lgm similar to that for present day antarctic ice sheets but this decreases to 15 and 12 at 12 cal ka bp and 10 cal ka bp respectively the extent to which these changes in the ice stream drainage network represent a simple and predictable readjustment to a changing mass balance driven by climate or internal ice dynamical feedbacks unrelated to climate or both is largely unknown and represents a key area for future work to address

reconstruction of loch lomond stadial younger dryas glaciers on ben more coigach north west scotland and implications for reconstructing palaeoclimate using small ice masses a significant inventory of evidence exists for loch lomond stadial lls younger dryas glaciation in scotland with recent work focused on satellite icefields however studies of more marginal settings are important for assessing the influence of topoclimatic factors on glacier functioning and crucially the impact of these on glacier derived palaeoclimatic reconstructions we present systematic assessments of snowblow and avalanching contributions informed by modern analogues and test these using the first detailed palaeoglaciological reconstructions of three corrie glaciers on ben more coigach north west scotland based on morphostratigraphic principles and lithostratigraphic evidence from the region these have been attributed to the lls with the reconstructions yielding an average equilibrium line altitude ela of 328 16 m a glacier derived sea level equivalent precipitation value of 1903 178 mm a 1 is inferred for the lls suggesting wetter conditions than currently and contradicting assertions of a more arid lls climate comparison with published palaeoprecipitation estimates indicates ben more coigach does not conform to expected regional precipitation gradients we argue that these discrepancies reflect topographically enhanced snow accumulation which lowered the ela from the true climatic ela this highlights the importance of assessing the influence of topoclimatic factors when applying small glaciers in palaeoclimatic reconstructions

glacial geomorphological mapping a review of approaches and frameworks for best practice geomorphological mapping is a well established method for examining earth surface processes and landscape evolution in a range of environmental contexts in glacial research it provides crucial data for a wide range of process oriented studies and palaeoglaciological reconstructions in the latter case providing an essential geomorphological framework for establishing glacial chronologies in recent decades there have been significant developments in remote sensing and geographical information systems gis with a plethora of high quality remotely sensed datasets now often freely available most recently the emergence of unmanned aerial vehicle uav technology has allowed sub decimetre scale aerial images and digital elevation models dems to be obtained traditional field mapping methods still have an important role in glacial geomorphology particularly in cirque glacier valley glacier and icefield ice cap outlet settings field mapping is also used in ice sheet settings but often takes the form of necessarily highly selective ground truthing of remote mapping given the increasing abundance of datasets and methods available for mapping effective approaches are necessary to enable assimilation of data and ensure robustness this paper provides a review and assessment of the various glacial geomorphological methods and datasets currently available with a focus on their applicability in particular glacial settings we distinguish two overarching work streams that recognise the different approaches typically used in mapping landforms produced by ice masses of different sizes i mapping of ice sheet geomorphological imprints using a combined remote sensing approach with some field checking where feasible and ii mapping of alpine and plateau style ice mass cirque glacier valley glacier icefield and ice cap geomorphological imprints using remote sensing and considerable field mapping key challenges to accurate and robust geomorphological mapping are highlighted often necessitating compromises and pragmatic solutions the importance of combining multiple datasets and or mapping approaches is emphasised akin to multi proxy approaches used in many earth science disciplines based on our review we provide idealised frameworks and general recommendations to ensure best practice in future studies and aid in accuracy assessment comparison and integration of geomorphological data these will be of particular value where geomorphological data are incorporated in large compilations and subsequently used for palaeoglaciological reconstructions finally we stress that robust interpretations of glacial landforms and landscapes invariably requires additional chronological and or sedimentological evidence and that such data should ideally be collected as part of a holistic assessment of the overall glacier system

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

geophysical surveys of the sediments of loch ness scotland implications for the deglaciation of the moray firth ice stream british irish ice sheet we present results from three geophysical campaigns using high resolution sub bottom profiling to image sediments deposited in loch ness scotland sonar profiles show distinct packages of sediment providing insight into the loch s deglacial history a recessional moraine complex in the north of the loch indicates initial punctuated retreat subsequent retreat was rapid before stabilisation at foyers rise formed a large stillstand moraine here the calving margin produced significant volumes of laminated sediments in a proglacial fjord like environment subsequent to this ice retreated rapidly to the southern end of the loch where it again deposited a sequence of proglacial laminated sediments sediment sequences were then disturbed by the deposition of a thick gravel layer and a large turbidite deposit as a result of a jo kulhlaup from the spean roy ice dammed lake these sediments are overlain by a holocene sheet drape data indicate i a former tributary of the moray firth ice stream migrated back into loch ness as a major outlet glacier with a calving margin in a fjord like setting ii there was significant sediment supply to the terminus of this outlet glacier in loch ness and iii that jo kulhlaups are important for sediment supply into proglacial fjord lake environments and may compose 20 of proglacial sedimentary sequences

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

rock slope failure following late pleistocene deglaciation on tectonically stable mountainous terrain the ages of 31 postglacial rock slope failures rsfs in scotland and nw ireland derived from 89 cosmogenic isotope exposure ages are employed to analyse the temporal pattern of failure and its relationship to the timing of deglaciation rates of glacio isostatic crustal uplift and periods of rapid climate change rsf ages span almost the whole period since ice sheet retreat from 18 2 1 2 ka to 1 7 0 2 ka or from 17 1 1 0 ka to 1 5 0 1 ka depending on the production rate used in 10 be age calculation but catastrophic failure of rock slopes was w4 6 times more frequent prior to w11 7 ka than during the holocene 95 of dated rsfs at sites deglaciated during retreat of the last ice sheet occurred within w5400 years after deglaciation with peak rsf activity 1600e1700 years after deglaciation this time lag is inferred to represent 1 stress release initiated by deglacial unloading leading to 2 time dependent rock mass strength degradation through progressive failure plane development and ultimately 3 to either spontaneous kinematic release or failure triggered by some extrinsic mechanism by contrast 11 dated rsfs at sites reoccupied by glacier ice during the younger dryas stade yds of w12 9e11 7 ka exhibit no clear temporal pattern suggesting that glacial reoccupance during the yds was ineffective in preconditioning a renewed cycle of enhanced rsf activity comparison of timing of individual rsfs with that of deglaciation and rapid warming events at w14 7 ka and w11 7 ka suggests that glacial debuttressing enhanced joint waterpressuresduringdeglaciationandthawofpermafrosticeinrockjointscouldhavetriggeredfailurein only a small number of cases conversely the timing of maximum rsf activity following ice sheet deglaciation corresponds broadly with maximum rates of glacio isostatic crustal uplift suggesting that the two are linked by enhanced seismic activity a seismic failure trigger is consistent with full slope failure at all sites where failure planes are clearly defined our results indicate that numerous rsfs must have occurred in areas that were reoccupied by glacier ice during the yds but have not been identified because runout debris was removed by yds glaciers more generally they provide the first reliably dated body of evidence to support the view that retreat of the last ice sheets in tectonically stable mountainous terrain initiated a period of enhanced rock slope failure due to deglacial unloading and probably lateglacial seismic activity implying that most undated rsfs in such areas are probably of lateglacial or veryearly holocene age they also demonstrate however that a low frequency of rsf activity extended throughout the holocene

application of a degree day model to reconstruct pleistocene glacial climates there is empirical evidence of a nonlinear relation between annual precipitation or accumulation and summer mean temperature at the equilibrium line altitude ela on glaciers around the world the degree day model gives a similar relation between accumulation and summer temperature although instead of a single universal curve there is a family of curves depending upon the annual temperature range furthermore the degree day model also gives nonlinear relations between accumulation and annual mean temperature thus estimations of accumulation can be made from both summer and annual temperatures at the ela of former reconstructed glaciers such as those in greece this is particularly useful since these climatic variables have major implications for biological proxies such as vegetation history indicated in the pollen record and for periglacial proxies such as permafrost distributions indicated in the geomorphological record the close relationship between glaciers and climate provides one of the most precise methods for reconstructing former climates and offers considerable potential for resolving our understanding of pleistocene cold stage climates

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

degree day glacier mass balance modelling with applications to glaciers in iceland norway and greenland a degree day glacier mass balance model is applied to three glaciers in iceland norway and greenland for which detailed mass balance measurements are available over a period of several years model results are in good agreement with measured variations in the mass balance with elevation over the time periods considered for each glacier in addition the model explains 60 80 of the year to year variance in the elevation averaged summer season mass balance measurements on the glaciers using a single parameter set for each glacier the increase in ablation on the glaciers due to a warming of 2 c is predicted to range from about 1 m w e year 1 at the highest elevations to about 2 5 m w e year 1 at the lowest elevations predicted changes in the winter balance measured between fixed date are relatively small except at the lowest elevations on the icelandic and norwegian glaciers where the winter balance is significantly reduced equilibrium line altitudes are raised by 200 300 m on the icelandic and norwegian glaciers except at the highest elevations the winter balance of the icelandic and norwegian glaciers is predicted to decrease even if the warming is accompanied by a 10 increase in the precipitation no firm evidence of a climate related variation in the degree day factors or in the temperature lapse rate on the same glacier could be found the model furthermore reproduces large variations in the mass balance with elevation and from year to year on each glacier using the same parameter set we assume therefore that these parameters will not change significantly for the climate scenarios considered here

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

influence of seasonality on glacier mass balance and implications for palaeoclimate reconstructions climates inferred from former glacier geometries in some areas exhibit discrepancies with regional palaeoclimates predicted by general circulation models gcms and modelling of palaeoecological data possibly as a consequence of their differing treatments of climatic seasonality since glacier based climate reconstructions potentially offer an important tool in the calibration of gcms which themselves need validation if used to predict future climate scenarios we attempt to resolve mismatches between these techniques by 1 investigating the influence of seasonality on glacier mass balance and 2 refining the methodology used for the derivation of glacier based palaeoclimates focussing on the younger dryas stadial glaciation of scotland northeast atlantic we show that sea ice amplified seasonality led to a significantly drier climate than has been suggested by glacier based interpretations this was characterised by a relatively short ablation season and the survival of a more substantial winter snowpack we suggest that if palaeoglaciological studies were to account for changes in seasonal temperature and precipitation variability their results would agree more closely with the cold arid northeast atlantic palaeoenvironment predicted by atmospheric modelling and northwest european pollen studies and would therefore provide more accurate constraints for gcm calibration

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

numerical reconstruction of a soft bedded laurentide ice sheet during the last glacial maximum we used a numerical ice sheet model to reconstruct the north american laurentide ice sheet during the last glacial maximum our model simulates ice sheet conditions that can be specified experimentally as either a rigid substrate hard bed or a wet deformable till soft bed basal sliding is excluded we use geologic records of former basal ice sheet processes to prescribe the distribution of hard and soft beds our reconstruction of the laurentide ice sheet is significantly lower in ice surface height and contains less ice volume than the climap maximum reconstruction in contrast our reconstruction agrees well with the ice 4g reconstruction both in height and volume because the ice 4g reconstruction is based on the inversion of relative sea level data whereas our reconstruction is based on glacial geology and ice mechanics this agreement suggests that soft beds provide a glaciological mechanism to explain the shape and volume of the laurentide ice sheet that is most consistent with observations of relative sea level change and other geodynamic considerations

climate at the equilibrium line of glaciers the relationships between temperature precipitation and radiation on glacier equilibrium lines are investigated using 70 glaciers for which the mass balance and meteorological observations have been carried out for sufficiently long periods it is found that the characteristic climate at glacier equilibrium lines can be described using the summer 3 months temperature in a free atmosphere annual total precipitation and the sum of global and long wave net radiation all of these are measured at or very near the equilibrium line altitudes then it is shown how the shift of the equilibriumline will occur as a result of a climatic change finally the effect of the shift of the equilibrium line on the annualmean specific mass balance is analytically derived and compared with observations the present results make it possible to identify the altitudes in climate models where glacierization should begin and to evaluate the mass balance changes as a result of possible future changes in the climate

numerical reconstructions of the eurasian ice sheet and climate during the late weichselian abstract geological investigations undertaken through the quaternary environments of the eurasian north programme established ice sheet limits for the eurasian arctic at the last glacial maximum lgm sedimentary records of palaeo ice streams and uplift information relating to ice sheet configuration and the pattern of deglaciation ice sheet numerical modelling was used to reconstruct a history of the eurasian ice sheet compatible with these geological datasets the result was a quantitative assessment of the time dependent behaviour of the ice sheet its mass balance and climate and predictions of glaciological products including sediments icebergs and meltwater at the lgm ice cover was continuous from scandinavia to the arctic ocean margin of the barents sea to the north and the kara sea to the east in the west along the continental margin between the norwegian channel and svalbard the ice sheet was characterised by fast flowing ice streams occupying bathymetric troughs which fed large volumes of sediment to the continental margin that were deposited as a series of trough mouth fans ice streams may also have been present in bathymetric troughs to the north between svalbard and franz josef land further east however the ice sheet was thinner across the kara sea the ice thickness was predicted to be less than 300 m while on severnaya zemlya the ice cover may have been thinner at the lgm than at present it is likely that the taymyr peninsula was mainly free of ice at the lgm in the south the ice margin was located close to the shoreline of the russian mainland the climate associated with this ice sheet is maritime to the west and in stark contrast desert like in the east atmospheric general circulation modelling has revealed that such a contrast is possible under relatively warm north atlantic conditions because a circulation system develops across the kara sea isolating it from the moisture laden westerlies which are diverted to the south ice sheet decay began through enhanced iceberg calving in the deepest regions of the barents sea which caused a significant ice embayment within the bear island trough by about 12 000 years ago further iceberg calving reduced ice extent to the northern archipelagos and their surrounding shallow seas ice decay was complete by about 10 000 years ago

calving laws sliding laws and the stability of tidewater glaciers a new calving criterion is introduced which predicts calving where the depth of surface crevasses equals ice height above sea level crevasse depth is calculated from strain rates and terminus position and calving rate are therefore functions of ice velocity strain rate ice thickness and water depth we couple the calving criterion with three sliding laws in which velocity is controlled by 1 basal drag 2 lateral drag and 3 a combination of the two in model 1 velocities and strain rates are dependent on effective pressure and hence ice thickness relative to water depth imposed thinning can lead to acceleration and terminus retreat and ice shelves cannot form in model 2 ice velocity is independent of changes in ice thickness unless accompanied by changes in surface gradient velocities are strongly dependent on channel width and calving margins tend to stabilize at flow unit widenings model 3 exhibits the combined characteristics of the other two models and suggests that calving glaciers are sensitive to imposed thickness changes if basal drag provides most resistance to flow but stable if most resistance is from lateral drag ice shelves can form if reduction of basal drag occurs over a sufficiently long spatial scale in combination the new calving criterion and the basal lateral drag sliding function model 3 can be used to simulate much of the observed spectrum of behaviour of calving glaciers and present new opportunities to model ice sheet response to climate change

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

climate variations in britain during the last glacial holocene transition 15 0 11 5 cal ka bp comparison with the grip ice core record stratigraphic records from four sequences in britain that span the last glacial holocene transition c 15 0 11 5 cal ka bp are summarized and compared using a calibrated timescale palaeoclimatic changes are defined using temperature estimates based on coleopteran data at two of the sites and chironomid assemblages at the other sites an attempt is made to distingish between the timing of a climate shifts and b ecosystem responses at all four sites the british data are compared with the grip ice core record recently advocated by bjorck et al as the type sequence for the last termination in the north atlantic region there is a degree of compatibility between the british and grip palaeoclimatic records the clearest climatic signals in the british lake records are a a period of warm conditions a thermal maximum between 15 0 and 14 5 cal ka bp which equates approximately with grip zone gi le b the onset of climatic cooling which appears to have commenced during grip zone gi le at c 14 5 cal ka bp c a period of marked climatic instability from 14 4 to 12 7 cal ka bp the regional effects of which are difficult to resolve using the evidence presently available d further climatic cooling which commenced at around 13 0 cal ka bp after which the lake biota catchment soils and vegetation cover at least in some parts of britain did not recover until the onset of the holocene e continued climatic cooling with the most severe impact on lake ecosystems occurring during the period c 12 6 to 11 5 cal ka bp

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

timing and periodicity of paraglacial rock slope failures in the scottish highlands abstract many formerly glaciated mountains exhibit a high density of postglacial rock slope failures rsfs in the form of rockslides rock avalanches or deep seated gravitational slope deformations such rsfs are often termed paraglacial as they reflect pre conditioning by glaciation and deglaciation the temporal pattern of paraglacial rsfs is unknown we employ 47 cosmogenic isotope exposure ages obtained for 17 catastrophic rsfs in the scottish highlands to test models of changes in rsf frequency since deglaciation our results show that rsf activity spans almost the entire postglacial period from 17 ka until 1 5 ka and that the periodicity of sampled postglacial rsfs is statistically indistinguishable from a pattern of uniform periodicity 1 ka 1 our data do not conform to proposed models of declining rsf frequency with time elapsed since deglaciation but suggest that the temporal distribution of postglacial rsfs is best described by a combination of rapid response enhanced rsf frequency during or immediately after deglaciation followed by approximately constant periodicity our findings are consistent with near surface fracturing of rock when glacially induced confining stresses are removed causing some failures during or immediately after deglaciation and reducing other slopes to critical conditional stability so that failure is triggered by progressive rock mass weakening or by transient triggering mechanisms neither permafrost degradation thaw of ice in joints nor seismic activity offers a general explanation for triggering scottish rsfs but could be contributory in some cases the quasi constant periodicity inferred for holocene rsfs implies that the probability of rsfs in this seismically quiescent intraplate area has not changed in the past 10 ka and that further though infrequent catastrophic rsfs are likely to occur in the future

pattern and timing of retreat of the last british irish ice sheet during the last glacial the ice sheet that subsumed most of britain ireland and the north sea attained its maximum extent by 27 ka bp and with an ice volume sufficient to raise global sea level by ca 2 5 m when it melted we reconstruct the demise of this british irish ice sheet biis and present palaeo glaciological maps of retreat stages between 27 and 15 ka bp the whole land area was investigated using remote sensing data and we present maps of moraines meltwater channels eskers and drumlins and a methodology of how to interpret and bring them together for the continental shelf numerous large moraines were discovered recording an extensive pattern of retreat stretching from sw ireland to the shetland isles from an integration of this new mapping of glacial geomorphology 26 000 landforms with previously published evidence compiled in the britice database we derive a pattern of retreat for the whole biis we review and compile relevant dates 881 examples that constrain the timing of retreat all data are held within a geographic information system gis and are deciphered to produce a best estimate of the combined pattern and timing of retreat pattern information reveals an ice sheet mainly comprised of a shelf parallel configuration from sw ireland to ne scotland but it spread far enough to the south to incorporate outlying ice domes over wales the lake district and kerry final disintegration was into a number of separate ice caps rather than reduction as a single mass and paradoxically retreat was not always back to high ground by 23 ka bp ice withdrew along its northern boundaries at the same time as the southern margins were expanding including transient ice streaming down the irish sea and advances of lobes in the cheshire basin vale of york and east coast of england ice divides migrated south by 19 ka the ice sheet was in crisis with widespread marine based ice losses particularly in the northern north sea and the irish sea considerable dynamic thinning occurred during this phase final collapse of all marine sectors occurred by 17 ka bp and with most margins beginning to back step onshore disintegration of the north sea ice bridge between britain and norway remains loosely constrained in time but the possibility of catastrophic collapse of this sector is highlighted the north channel and irish sea ice streams had finally cleaved the ice sheet into separate irish and scottish ice sheets by 16 ka bp rates of ice loss were found to vary widely over space and time e g 65 260 km3 per year the role of ice streams and calving losses of marine based sectors are examined retreat rates of up to ca 150 ma 1 were found for some ice stream margins that large parts 2 3 of the biis were marine based drained by ice streams and possibly with fringing ice shelves in places makes it a useful analogue for the west antarctic ice sheet wais this is especially so because the biis deglaciated in response to rising temperatures and a rising sea level driven by melting of other ice masses which are the current forcings that might cause collapse of the wais our reconstruction when viewed from the opposite perspective documents when fresh land became exposed for exploitation by plants animals and man and records for how long such land has been available for soil and geochemical development and ecological succession

the validation and sensitivity of a model of the icelandic ice sheet abstract the derivation and implementation of a three dimensional model used to investigate the last glacial maximum ice sheet across iceland by hubbard et al 2006 a modelling insight into the icelandic last glacial maximum ice sheet quaternary science reviews is described it is applied at 2 km resolution and requires boundary distributions of topography geothermal heat flux surface air temperature and mass balance calculated using a temperature index approach based on reference distributions of annual temperature and precipitation the model enables the variables of ice thickness stress strain and temperature to evolve freely through time and caters for the coupling of thermally triggered basal sliding with non local dynamics through the computation of longitudinal stresses it is driven through perturbations in sea level and annual precipitation and temperature a series of contemporary experiments are initiated to validate the model against the present ice cover across iceland forcing the model from ice free conditions with the 1961 1990 reference climatology yields a good simulation of all the ice masses except for vatnajokull where the model falls well short of its present margins however an experiment forced from ice free conditions for 1000 years with a 2 c cooling perturbation followed by 100 years of reference climatology yields a good simulation of vatnajokull in addition to other ice masses implying that it is a remnant icecap inherited from the little ice age and perpetuated through strong ice elevation mass balance coupling an ensemble of experiments are initiated to investigate the sensitivity of the optimum lgm model isolated in hubbard et al 2006 ice sheet volume and aspect ratio but not area are found to be sensitive to basal boundary conditions in particular to the choice of sliding parameter and the applied geothermal conditions due to strong topographic control in particular the configuration of offshore bathymetry and shelf break ice sheet volume and area is sensitive to the calving parameter and sea level change however an asymmetrical response indicates that the ice sheet is effectively decoupled from further climatic deterioration once it advances to the continental shelf break these experiments imply that there is little latitude in the selection of model parameters which yields an ice sheet compatible with the available evidence and that the optimum lgm experiment represents a sound result by inference at least 63 of the optimum lgm ice sheet was grounded below sea level implying potential instability with the onset of deglaciation

a review of topographic controls on moraine distribution ice marginal moraines are often used to reconstruct the dimensions of former ice masses which are then used as proxies for palaeoclimate this approach relies on the assumption that the distribution of moraines in the modern landscape is an accurate reflection of former ice margin positions during climatically controlled periods of ice margin stability however the validity of this assumption is open to question as a number of additional nonclimatic factors are known to influence moraine distribution this review considers the role played by topography in this process with specific focus on moraine formation preservation and ease of identification topoclimatic controls are not considered published literature indicates that the importance of topography in regulating moraine distribution varies spatially temporally and as a function of the ice mass type responsible for moraine deposition in particular in the case of ice sheets and ice caps 1000 km2 one potentially important topographic control on where in a landscape moraines are deposited is erosional feedback whereby subglacial erosion causes ice masses to become less extensive over successive glacial cycles for the marine terminating outlets of such ice masses fjord geometry also exerts a strong control on where moraines are deposited promoting their deposition in proximity to valley narrowings bends bifurcations where basins are shallow and or in the vicinity of topographic bumps moraines formed at the margins of ice sheets and ice caps are likely to be large and readily identifiable in the modern landscape in the case of icefields and valley glaciers 10 1000 km2 erosional feedback may well play some role in regulating where moraines are deposited but other factors including variations in accumulation area topography and the propensity for moraines to form at topographic pinning points are also likely to be important this is particularly relevant where land terminating glaciers extend into piedmont zones unconfined plains adjacent to mountain ranges where large and readily identifiable moraines can be deposited in the case of cirque glaciers 10 km2 erosional feedback is less important but factors such as topographic controls on the accumulation of redistributed snow and ice and the availability of surface debris regulate glacier dimensions and thereby determine where moraines are deposited in such cases moraines are likely to be small and particularly susceptible to post depositional modification sometimes making them difficult to identify in the modern landscape based on this review we suggest that despite often being difficult to identify quantify and mitigate topographic controls on moraine distribution should be explicitly considered when reconstructing the dimensions of palaeoglaciers and that moraines should be judiciously chosen before being used as indirect proxies for palaeoclimate i e palaeoclimatic inferences should only be drawn from moraines when topographic controls on moraine distribution are considered insignificant

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

the role of seasonality in abrupt climate change abstract a case is made that seasonality switches dominated by wintertime were instrumental in abrupt climate changes in the north atlantic region during the last glaciation and into the holocene the primary evidence comes from mismatches between mean annual temperatures from greenland ice cores in comparison with snowline changes in east greenland northern europe and north america the most likely explanation is a shutdown or reduction in strength of the conveyor this allows the spread of winter sea ice across the north atlantic thus causing the northern region to experience much colder winters because they mimic the greenland temperature rather than the snowline signal changes in the atlantic intertropical convergence zone and the asian monsoon may also share a winter linkage with greenland thus the paleoclimate record is consistent with the notion that a huge continental sector of the northern hemisphere stretching from greenland to asia was close to an extreme winter threshold during much of the last glaciation winter climate crossed this threshold repeatedly with marked changes in seasonality that may well have amplified and propagated a signal of abrupt change throughout the hemisphere and into the tropics

retreat velocity of the north atlantic polar front during the last deglaciation determined by 14 c accelerator mass spectrometry the glacial oscillations which dominate the quaternary global climate are closely related to changes in incoming solar radiation but the details of palaeoclimatic spectra suggest that other parameters usually referred to as feedback have significantly increased the climatic response to extraterrestrial forcing1 the last deglaciation appears to be one of the more characteristic examples of nonlinearity because its abruptness strongly contrasts with the smooth shape of the associated solar radiation maximum dated at 11 000 yr bp in addition the presence of the younger dryas cold event concomitant with the solar radiation maximum could be interpreted as a transitory phenomenon caused by the rapid meltwater influx linked to the first phase of the ice sheet s disintegration2 3 here using accelerator mass spectrometry we date precisely the movements of the polar front during the whole period of glacial retreat 15 000 8 000 yr bp our results show that the polar front has moved between 35 n and 55 n in 1 000 yr for the earliest retreat 12 500 12 000 bp and moved almost instantaneously that is 400 yr during the two abrupt climatic changes associated with the younger dry as cold event

using the surface profiles of modern ice masses to inform palaeo glacier reconstructions abstract morphometric study of modern ice masses is useful because many reconstructions of glaciers traditionally draw on their shape for guidance here we analyse data derived from the surface profiles of 200 modern ice masses valley glaciers icefields ice caps and ice sheets with length scales from 100 to 103 km from different parts of the world four profile attributes are investigated relief span and two parameters c and c that result from using nye s 1952 theoretical parabola as a profile descriptor c and c respectively measure each profile s aspect ratio and steepness and are found to decrease in size and variability with span this dependence quantifies the competing influences of unconstrained spreading behaviour of ice flow and bed topography on the profile shape of ice masses which becomes more parabolic as span increases with c and c tending to low values of 2 5 3 3 m1 2 the same data reveal coherent minimum bounds in c and c for modern ice masses that we develop into two new methods of palaeo glacier reconstruction in the first method glacial limits are known from moraines and the bounds are used to constrain the lowest palaeo ice surface consistent with modern profiles we give an example of applying this method over a three dimensional glacial landscape in kamchatka in the second method we test the plausibility of existing reconstructions by comparing their c and c against the modern minimum bounds of the 86 published palaeo ice masses that we put to this test 88 are found to be plausible the search for other morphometric constraints will help us formalise glacier reconstructions and reduce their uncertainty and subjectiveness

regression coefficients of thermal gradients in northwestern europe during the last glacial holocene transition using beetle mcr data palaeotemperature estimates obtained from 74 sites in northern europe and collectively spanning approximately the last 45 000 yr radiocarbon time scale have been compiled as a major component o

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

climate patterns during former periods of mountain glaciation in britain and ireland inferences from the cirque record we map glacial cirques and analyse spatial variability in their altitude and aspect to derive a long term time integrated perspective on climate patterns during former periods of mountain glaciation likely spanning multiple quaternary glaciations in britain and ireland the data reveal that although air temperatures were important exposure to moisture bearing air masses was the key factor in regulating sites of former mountain glacier formation and indicate that during such periods moisture supply was largely controlled by north atlantic westerlies with notable inland precipitation gradients precipitation decreasing inland similar to present day in places trends in cirque altitude may also reflect regional differences in the extent of cirque deepening controlled by the dimensions and dynamics of the glaciers that came to occupy them specifically comparatively deep cirques in coastal locations may reflect the former presence of dynamic fed by moisture from the north atlantic but comparatively small glaciers largely confined to their cirques by contrast decreasing cirque depth further inland may reflect the former presence of larger and or less dynamic ice masses occupying comparatively continental climatic conditions

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