bed erosion during fast ice streaming regulated the retreat dynamics of the irish sea ice stream abstract marine terminating ice stream behaviour often defines the stability of ice sheets and is driven by a complex interplay of climatic oceanic topographic and glaciological factors here we use new integrated high resolution extensive 2100 km2 and continuous geophysical sedimentological and geotechnical data to reconstruct past glacial environments during the last glacial maximum from a well preserved palaeo landscape the data is from the axial centre of the irish sea ice stream isis which drained 17 of the former british irish ice sheet recent geochronological data of the palaeo isis show a build up and advance of ice to marine terminating maximum limits in the southern celtic sea 27 25 ka bp followed by rapid ice margin retreat into the northern irish sea basin isb by 20 8 0 7 ka bp however the flow dynamics in the central and axial bed of the isis through this timeframe are not well understood here we use our new glacial landscape reconstruction to identify the spatial and temporal patterns of flow re organisation and re activations for the marine terminating isis from this we infer how ice streaming was driven by a variety of factors through advance deglaciation and towards a temporary lift off of ice from its bed and an ultimate demise overprinted subglacial bedforms with differing ice flow directions indicate an on off behaviour to the ice streaming an increasing topographical influence and substantial realignment of ice flows subsurface geophysical data reveal the erosive capability of the ice stream through time with a first erosive component in the formation of mega scale glacial lineations leaving bedrock exposed at the ice stream bed the depositional component of msgl crest building occurred in the same ice flow phase whilst the ice stream was laterally constricted in two locations likely contributing to changes in ice margin retreat rates we also propose that changes in basal drag associated with exposed bedrock at the ice bed interface influenced the retreat dynamics particularly when this exposure was near the grounding zone the wider implications of this work are that episodic and highly erosive ice streaming during ice advance and early retreat can change ice bed conditions radically and in turn influence glacial dynamics during later retreat episode thus constituting a feedback process to be considered in modelling the dynamics of marine terminating ice streams

the subglacial thermal organisation sto of ice sheets abstract this paper examines ice sheet wide variations in subglacial thermal regime and ice dynamics using the landform record exposed on the beds of former mid latitude ice sheets the laurentide cordilleran fennoscandian and british irish ice sheets we compare the landform patterns beneath these former ice sheets to the flow organisation beneath parts of the contemporary antarctic ice sheet inferred from radarsat 1 antarctic mapping project ramp data the evidence preserved in the landform record and observed on contemporary ice masses can be grouped into four major ice dynamical components that collectively define the subglacial thermal organisation sto of ice sheets these ice dynamical components are frozen bed patches ice streams ice stream tributaries and lateral shear zones frozen bed patches appear at a wide range of spatial scales spanning four orders of magnitude in some areas frozen bed zones comprise large proportions of the bed e g near the ice divide in continental areas whilst in other areas they constitute isolated islands in areas dominated by thawed bed conditions ice streams narrow zones of fast flow in ice sheets that are otherwise dominated by slow sheet flow are also common features of quaternary ice sheets tributaries to ice streams flow at velocities intermediate between full ice stream and sheet flow and may divert ice drainage from one primary ice stream corridor to an adjacent one sharp lateral boundaries between landforms indicate sliding and non sliding conditions respectively these lateral boundaries represent important discontinuities in the glacial landscape and mark the location of shear zones between thawed bed ice streams and intervening frozen bed areas we use the landform evidence in the area around great bear lake canada to trace the evolution of an ice stream web through time demonstrating that frozen bed patches are integral components of this complex system we conclude that frozen bed patches are important for the stability of ice sheets because they laterally constrain and isolate peripheral drainage basins and their ice streams

a physically based calving model applied to marine outlet glaciers and implications for the glacier dynamics we present results from numerical ice flow models that include calving criteria based on penetration of surface and basal crevasses which in turn is a function of longitudinal strain rates near the glacier front the position of the calving front is defined as the point where either 1 surface crevasses reach the waterline model cdw or 2 surface and basal crevasses penetrate the full thickness of the glacier model cd for comparison with previous studies results are also presented for a height above buoyancy calving model qualitatively both models cdw and cd produce similar behaviour unlike previous models for calving the new calving criteria are applicable to both grounded termini and floating ice shelves and tongues the numerical ice flow model is applied to an idealized geometry characteristic of marine outlet glaciers results indicate that grounding line dynamics are less sensitive to basal topography than previously suggested stable grounding line positions can be obtained even on a reverse bed slope with or without floating termini the proposed calving criteria also allow calving losses to be linked to surface melt and therefore climate in contrast to previous studies in which calving rate or position of the terminus is linked to local water depth the new calving criterion is able to produce seasonal cycles of retreat and advance as observed for greenland marine outlet glaciers the contrasting dynamical behaviour and stability found for different calving models suggests that a realistic parameterization for the process of calving is crucial for any predictions of marine outlet glacier change

ice streams as the arteries of an ice sheet their mechanics stability and significance ice streams are corridors of fast ice flow ca 0 8 km year within an ice sheet and are responsible for discharging the majority of the ice and sediment within them consequently like the arteries in our body their behaviour and stability is essential to the well being of an ice sheet ice streams may either be constrained by topography topographic ice streams or by areas of slow moving ice pure ice streams the latter show spatial and temporal patterns of variability that may indicate a potential for instability and are therefore of particular interest today pure ice streams are largely restricted to the siple coast of antarctica and these ice streams have been extensively investigated over the last 20 years this paper provides an introduction to this substantial body of research and describes the morphology dynamics and temporal behaviour of these contemporary ice streams before exploring the basal conditions that exist beneath them and the mechanisms that drive the fast flow within them the paper concludes by reviewing the potential of ice streams as unstable elements within ice sheets that may impact on the earth s dynamic system d 2002 elsevier science b v all rights reserved

evidence for winter spring denitrification of the stratosphere in the nitrate record of antarctic firn cores a firn core from within the polar vortex in the weddell sea sector of antarctica shows nitrate peaks that occur in the spring or early summer they are far less prominent in two other cores from sites that are further north although other data are needed circumstantial evidence suggests that the peak may be due to sedimentation of polar stratospheric clouds from the stratosphere during winter and spring no change in the form of the peak is seen over the last three decades it may be possible to observe past stratospheric conditions over longer time scales from ice cores but other sources may obliterate the signal in ice from the glacial periods 34 refs 5 figs

theoretical contemporary observational and palaeo perspectives on ice sheet hydrology processes and products publisher elsevier articletitle theoretical contemporary observational and palaeo perspectives on ice sheet hydrology processes and products journaltitle earth science reviews articlelink http dx doi org 10 1016 j earscirev 2016 01 010 content type article copyright copyright 2016 elsevier b v all rights reserved

model investigations of inland migration of fast flowing outlet glaciers and ice streams recent observations of increased discharge through fast flowing outlet glaciers and ice streams motivate questions concerning the inland migration of regions of fast flow which could increase drawdown of the ice sheet interior to investigate one process that could lead to inland migration we conduct experiments with a two dimensional full stress transient ice flow model an initial steady state is perturbed by initiating a jump in sliding speed over a fraction of the model domain as a result longitudinal stress gradients increase frictional melting upstream from the slow to fast sliding transition and a positive feedback between longitudinal stress gradients basal meltwater production and basal sliding causes the sliding transition to migrate upstream over time the distance and speed of migration depend on the magnitude of the perturbation and on the degree of non linearity assumed in the link between basal stress and basal sliding larger perturbations and or higher degrees of non linearity lead to farther and faster upstream migration migration of the sliding transition causes the ice sheet to thin over time and this change in geometry limits the effects of the positive feedback ultimately serving to impede continued upstream migration

binge purge oscillations of the laurentide ice sheet as a cause of the north atlantic s heinrich events ice rafted debris in sediment cores from the north atlantic suggests that the laurentide ice sheet lis periodically disgorged icebergs in brief but violent episodes which occurred approximately every 7 000 years here i propose that heinrich events i e what these episodes are called were caused by free oscillations in the flow of the laurentide ice sheet which arose because the floor of hudson bay and hudson strait is covered with soft unconsolidated sediment that forms a slippery lubricant when thawed the proposed heinrich event cycle has two phases the growth phase occurs when the sediment is frozen and the lis is stranded immobile on a rigid bed the volume of the lis slowly grows during this phase at a rate dictated by snow accumulation the purge phase occurs when the basal sediment thaws and a basally lubricated discharge pathway i e an ice stream such as those which occur in west antarctica today developes through hudson strait the volume of the lis rapidly equilibrates to the reduced basal friction during this phase by dumping icebergs into the labrador sea the periodicity t k sl2g 2 7000 years of the proposed heinrich event cycle is a function of the thermal conductivity and diffusivity of ice k and respectively the atmospheric sea level temperature sl in degrees celsius and the excess geothermal heat flux defined by g g k where is the atmospheric lapse rate and g is the geothermal heat flux agreement between the predicted t and the apparent periodicity implied by the marine record is the main virtue of the free oscillation mechanism i propose an alternative mechanism in which heinrich events are forced by periodic variations in external climate is implausible because periodic atmospheric temperature perturbations are strongly attenuated with depth in an ice sheet

frost flowers on young arctic sea ice the climatic chemical and microbial significance of an emerging ice type ongoing changes in arctic sea ice are increasing the spatial and temporal range of young sea ice types over which frost flowers can occur yet the significance of frost flowers to ocean sea ice atmosphere exchange processes remains poorly understood frost flowers form when moisture from seawater becomes available to a cold atmosphere and surface winds are low allowing for supersaturation of the near surface boundary layer ice grown in a pond cut in young ice at the mouth of young sound ne greenland in march 2012 showed that expanding frost flower clusters began forming as soon as the ice formed the new ice and frost flowers dramatically changed the radiative and thermal environment the frost flowers were about 5 c colder than the brine surface with an approximately linear temperature gradient from their base to their upper tips salinity and 18o values indicated that frost flowers primarily originated from the surface brine skim ikaite crystals were observed to form within an hour in both frost flowers and the thin pond ice average ikaite concentrations were 1013 mol kg 1 in frost flowers and 1061 mol kg 1 in the surface slush layer chamber flux measurements confirmed an efflux of co2 at the brine wetted sea ice surface in line with expectations from the brine chemistry bacteria concentrations generally increased with salinity in frost flowers and the surface slush layer bacterial densities and taxa indicated that a selective process occurred at the ice surface and confirmed the general pattern of primary oceanic origin versus negligible atmospheric deposition

the duration of the active phase on surge type glaciers contrasts between svalbard and other regions many glaciers in svalbard and in other glacierized areas of the world are known to surge however the time series of observations required to assess the duration of fast motion is very restricted data on active phase duration in svalbard come from aerial photographs satellite imagery field surveys and airborne reconnaissance evidence on surge duration is available for eight svalbard ice masses varying from 3 to 1250 km 2 worldwide active phase duration is recorded for less than 50 glaciers few observations are available on high polar ice masses the duration of the active phase is significantly longer for svalbard glaciers than for surge type glaciers in other areas from which data are available in svalbard the active phase may last from 3 to 10 years by contrast a surge duration of 1 2 years is more typical of ice masses in northwest north america iceland and the pamirs ice velocities during the protracted active phase on svalbard glaciers are considerably lower than those for many surge type glaciers in these other regions mass is transferred down glacier more slowly but over a considerably longer period svalbard surge type glaciers do not exhibit the very abrupt termination of the active phase over periods of a few days observed for several alaskan glaciers the duration of the active phase in svalbard is not dependent on parameters related to glacier size the quiescent phase is also relatively long 50 500 years for svalbard ice masses detailed field monitoring of changing basal conditions through the surge cycle is required from surge type glaciers in svalbard in order to explain the significantly longer length of the active phase for glaciers in the archipelago which may also typify other high polar ice masses the finding that surge behaviour in the form of active phase duration shows systematic differences between different regions and their environments has important implications for understanding the processes responsible for glacier surges

sustained retreat of the pine island glacier we use satellite observations to show that between 1992 and 2011 the pine island glacier hinge line retreated at a rate of 0 95 0 09 km yr 1 despite a progressive steepening and shoaling of the glacier surface and bedrock slopes respectively which ought to impede retreat the retreat has remained constant because the glacier terminus has thinned at an accelerating rate of 0 53 0 15 m yr 2 with comparable changes upstream this acceleration is consistent with an intensification of ocean driven melting in the cavity beneath the floating section of the glacier the pattern of hinge line retreat meanders and is concentrated in isolated regions until ice becomes locally buoyant because the glacier ocean system does not appear to have reached a position of relative stability the lower limit of sea level projections may be too conservative

evolution of late glacial ice marginal lakes on the northwestern canadian shield and their influence on the location of the dubawnt lake palaeo ice stream abstract during deglaciation of the north american laurentide ice sheet large proglacial lakes developed in positions where proglacial drainage was impeded by the ice margin for some of these lakes it is known that subsequent drainage had an abrupt and widespread impact on north atlantic ocean circulation and climate but less is known about the impact that the lakes exerted on ice sheet dynamics this paper reports palaeogeographic reconstructions of the evolution of proglacial lakes during deglaciation across the northwestern canadian shield covering an area in excess of 1 000 000 km2 as the ice sheet retreated some 600 km the interactions between proglacial lakes and ice sheet flow are explored with a particular emphasis on whether the disposition of lakes may have influenced the location of the dubawnt lake ice stream this ice stream falls outside the existing paradigm for ice streams in the laurentide ice sheet because it did not operate over fined grained till or lie in a topographic trough ice margin positions and a digital elevation model are utilised to predict the geometry and depth of proglacial lakes impounded at the margin at 30 km increments during deglaciation palaeogeographic reconstructions match well with previous independent estimates of lake coverage inferred from field evidence and results suggest that the development of a deep lake in the thelon drainage basin may have been influential in initiating the ice stream by inducing calving drawing down ice and triggering fast ice flow this is the only location alongside this sector of the ice sheet where large 3000 km2 deep lakes 120 m are impounded for a significant length of time and exactly matches the location of the ice stream it is speculated that the commencement of calving at the ice sheet margin may have taken the system beyond a threshold and was sufficient to trigger rapid motion but that once initiated calving processes and losses were insignificant to the functioning of the ice stream it is thus concluded that proglacial lakes are likely to have been an important control on ice sheet dynamics during deglaciation of the laurentide ice sheet

the dynamic arctic research campaigns over the last decade have yielded a growing stream of data that highlight the dynamic nature of arctic cryosphere and climate change over a range of time scales as a consequence rather than seeing the arctic as a near static environment in which large scale changes occur slowly we now view the arctic as a system that is typified by frequent large and abrupt changes the traditional focus on end members in the system glacial versus interglacial periods has been replaced by a new interest in understanding the patterns and causes of such dynamic change instead of interpreting changes almost exclusively as near linear responses to external forcing e g orbitally forced climate change research is now concentrated on the importance of strong feedback mechanisms that in our palaeo archives often border on chaotic behaviour the last decade of research has revealed the importance of on off switching of ice streams strong feedbacks between sea level and ice sheets spatial and temporal changes in ice shelves and perennial sea ice as well as alterations in ice sheet dynamics caused by shifting centres of mass in multi dome ice sheets recent advances in dating techniques and modelling have improved our understanding of leads and lags that exist in different arctic systems on their interactions and the driving mechanisms of change future arctic research challenges include further emphases on rapid transitions and untangling the feedback mechanisms as well as the time scales they operate on

steep reverse bed slope at the grounding line of the weddell sea sector in west antarctica the bed of the west antarctic ice sheet is in places more than 1 5 km below sea level1 2 it has been suggested that a positive ice loss feedback may occur when an ice sheet s grounding line retreats across a deepening bed1 2 3 applied to the west antarctic ice sheet this process could potentially raise global sea level4 by more than 3 m hitherto attention has focussed on changes at the siple coast5 6 7 and amundsen sea embayment8 9 10 sectors of west antarctica here we present radio echo sounding information from the ice sheet s third sector the weddell sea embayment that reveals a large subglacial basin immediately upstream of the grounding line the reverse bed slope is steep with about 400 m of decline over 40 km the basin floor is smooth and flat with little small scale topography that would delay retreat indicating that it has been covered with marine sediment5 11 and was previously deglaciated upstream of the basin well defined glacially carved fjords with bars at their mouths testify to the position of a former ice margin about 200 km inland from the present margin evidence so far suggests that the weddell sea sector of the west antarctic ice sheet has been stable but in the light of our data we propose that the region could be near a physical threshold of substantial change

the distribution and flow characteristics of surge type glaciers in the canadian high arctic a systematic review of 1959 60 aerial photography and 1999 2000 landsat 7 imagery has identified 51 surge type polythermal glaciers in the canadian high arctic these were identified from the presence of features such as looped medial moraines intense folding visible at the surface rapid terminus advance heavy surface crevassing and high surface velocities these observations suggest that surging glaciers are much more common than previously believed in the canadian high arctic where only six surge type glaciers have previously been described of the 51 surge type glaciers identified in this study 15 were observed in the active phase in the 1959 60 and or 1999 2000 imagery the most dramatic advances have occurred on western axel heiberg island where iceberg good friday bay and airdrop glaciers have all advanced by 4 7 km between1959 and 1999 for glaciers with repeat landsat 7 coverage from 1999 and 2000 image correlation software was used to determine the magnitude and spatial distribution of surge velocities for example mittie glacier on manson icefield was moving at a rate of up to 1 kma over a distance of at least 25 km back from its terminus the terminus of this glacier has advanced by at least 4 km since 1959 and the glacier was observed to be heavily crevassed during overflights in april 2000 with clear signs of surface lowering of 10 25 m indicated by a strandline

modeled glacial north atlantic ice rafted debris pattern and its sensitivity to various boundary conditions an iceberg drift and decay model is used to compute the ice rafted debris ird flux to the glacial north atlantic under steady iceberg discharge from the greenland and laurentide ice sheets i investigate the sensitivity of modeled ird distribution pattern to formulation of glacial iceberg decay meltwater drainage of laurentide ice sheet at its southern margin and the choice of ocean current and wind fields used as model boundary conditions modeled ird patterns are compared with the observed basic glacial mode ird pattern ruddiman 1977 and the last five heinrich layer patterns grousset et al 1993 model results show that the first order control on ird deposition pattern is the prevailing ocean currents and the choice of current fields is critical in determining the results winds can have significant effect when they exert drag in concert with ocean currents formulation of glacial iceberg decay directly affects its survival and the expanse of ird distribution but the formulation is perhaps one of the largest uncertainties in the model drainage of the southern margin of the laurentide ice sheet through the laurentian channel by meltwater instead of glaciers predicts no significant ird deposition in the open north atlantic in contrast to observations suggesting that glacier i e iceberg drainage through the laurentian channel was significant during the times of observed ird deposition in most experiments the model predicts a high ird deposition band that roughly coincides with the latitudinal band of high heinrich layer deposition but are measurably south of the basic glacial mode high ird deposition band this discordance suggests either that the flow fields used as model boundary conditions are inaccurate or that much of the basic glacial mode ird was not delivered by icebergs but perhaps sea ice

bedrock mega grooves in glaciated terrain a review abstract bedrock mega grooves are assemblages of straight and parallel troughs eroded in bedrock typically over 1000 m in length most sites occur within the limits of the last glacial maximum both on and off shore in this paper we review the current understanding of these important yet enigmatic landforms and propose a framework for their future research mega grooves are important to our understanding of ice sheet dynamics ice bedrock interactions and bedrock landscape evolution in glaciated areas the overall straightness of mega grooves across the landscape their parallel alignment to palaeo ice flow direction and occurrence below the general land surface level has led to their unanimous interpretation as landforms of subglacial erosion scenarios proposed for mega groove formation focus on either glacier ice or subglacial meltwater as the principal agent of erosion yet none offers a comprehensive explanation at locations where mega grooves occur along lines of structural geology their location formation and morphology were largely controlled by the bedrock characteristics where no underlying structural control is apparent mega grooves were likely initiated through glacial abrasion and subsequently modified through a range of erosional processes potentially involving multiple morphogenetic agencies and feedbacks operating between bedrock topography and basal ice flow in the absence of absolute dates morphostratigraphic analyses suggest mega groove survival through multiple glacial cycles no specific ice flow characteristics have been identified as a condition for bedrock grooving but it has been suggested that some bedrock mega grooves are related to ice streaming which deserves further study an initial analysis of bedrock grooves with seemingly similar morphology at a range of scales hints at a bedrock groove landform size continuum which could be a useful framework for exploring process landform relationships future research could usefully focus on quantitative analysis of mega groove morphology augmented with detailed field analysis of landform relationships to bedrock structure and lithology and thereby potentially provide further insight into the age and glaciological significance of these landforms

reconstructing the retreat dynamics of the bjornoyrenna ice stream based on new 3d seismic data from the central barents sea the stability of contemporary ice sheets is influenced by the discharge from ice streams corridors of fast flowing ice bounded by ice flowing an order of magnitude slower reconstructions of palaeo ice stream dynamics contribute to our understanding of ice stream sensitivity to the ocean climate system and can aid in the numerical modelling and prediction of future changes in contemporary ice sheets here we use 3d seismic data covering 13 000 km2 in the central bjornoyrenna bear island trough barents sea to investigate the record of ice streaming preserved on the seafloor and on a buried palaeo seafloor surface the unusually broad coverage and high resolution of the dataset as well as its location in the central area of the trough enables improved reconstruction of dynamics of the former bjornoyrenna ice stream in terms of number of streaming events their trajectory and their relative age sequence during deglaciation our results reveal major changes in the configuration and flow dynamics of the ice stream with up to 10 flow switching events identified for the first time we also document ice streaming sourced from the eastern barents sea around the time of the lgm this high degree of flow variability is suggested to have resulted from climate driven changes in ice sheet geometry and ice divide migration and variations in topography that influenced calving at the ice stream terminus

a year long record of size segregated aerosol composition at halley antarctica 1 size segregated aerosol samples were collected with a cascade impactor at 2 week intervals for a year at the research station halley situated near the coast in the weddell sea region of antarctica sea salt is a major component of aerosol throughout the year and we estimate that at least 60 of the total sea salt arriving at halley is from brine and frost flowers on the sea ice surface rather than open water chloride in sea salt particles is depleted relative to sodium in summer consistent with loss of hcl as sea salt particles react with gaseous acidic species but is enhanced in large particles in winter because of fractionation occurring during the production of new sea ice non sea salt sulphate peaks in the summer with the majority being in small particles indicative of a gas phase origin the distribution of methane sulphonic acid closely follows that of non sea salt sulphate in the winter non sea salt sulphate is frequently negative especially on stages collecting large particle sizes consistent with the source of sea salt during the winter being predominantly the sea ice surface rather than open water nitrate peaks in the spring and summer and shows some association with sea salt particles

palaeo ice streams in the northern keewatin sector of the laurentide ice sheet evidence for ice streams in the laurentide ice sheet is widespread in the region of northern keewatin and the boothia peninsula nunavut canada palaeo ice streams have been recognized but their location size and potential role in ice sheet dynamics are poorly constrained based on the interpretation of satellite imagery we produce a palaeo ice stream map of this region glacial directional landforms eskers and moraines were mapped and integrated into landform assemblages using a glacial geological inversion model palaeo frozen bed areas were also identified relative age of the geomorphic swarms was assessed by cross cutting relationships and radiocarbon ages where available using this information we obtained a glaciologically plausible picture of ice stream evolution within the northernmost laurentide ice sheet on the m clintock channel corridor three generations of pure ice streams are found on baffin island and the gulf of boothia glaciation was dominated by frozen bed zones located on high plateaus and ice streams running along the troughs i e topographic ice streams a massive convergent pattern at the head of committee bay drained ice from both the keewatin and foxe sectors and was probably one of the main deglaciation channels of the laurentide ice sheet finally our results indicate that streaming flow was present in the deep interior of the laurentide ice sheet as recently shown for the greenland and antarctic ice sheets

climate related variations in atmospheric sb and tl in the epica dome c ice east antarctica during the past 800 000 years 1 a record of antimony sb and thallium tl from the european project for ice coring in antarctica epica dome c antarctic ice core provides the characteristics of climate related natural changes in concentrations and fluxes of these toxic elements over the time period back to marine isotope stage 20 2 800 kyr b p a strong variability in concentrations and fluxes are observed for both elements with considerably higher values during glacial maxima and lower values during intermediate and warm periods rock and soil dust accounts for on average 58 of sb and 76 of tl in ice during glacial maxima this contribution remains significant during warm periods accounting for 21 for sb and 27 for tl the contribution from volcanoes appears to be very important particularly for tl when climatic conditions become warmer with an estimated volcanic contribution of 72 for tl during interglacials the sea salt contribution is significant for sb particularly during intermediate climatic periods with an average contribution of 17 this sea salt contribution is most likely caused by greater production of sea salt from highly saline frost flowers and relatively more efficient transport of sb enriched sea ice salt from source areas on the east antarctic plateau our ice core data along with snow data recently reported from the antarctic snow layers at dome fuji shows that the present day sb flux 6 6 ng m2 yr is approximately double the highest natural level 2 8 ng m2 yr during glacial maxima throughout the last successive eight glacial interglacial cycles this result indicates that human activity has induced the greatest perturbation of the atmospheric cycle of sb ever experienced over a period of 800 kyr in the most remote area on earth

elevation changes 1949 1995 of black rapids glacier alaska derived from a multi baseline insar dem and historical maps we have constructed a new digital elevation model dem of the 1995 surface of black rapids glacier a surge type glacier in the central alaska range using ers 1 2 repeat pass interferometry we isolated the topographic phase from three interferograms with contrasting perpendicular baselines numerous phase unwrapping errors caused by areas of poor coherence were corrected in all three interferograms using a novel iterative semi automated approach that capitalizes on the multi baseline nature of the dataset comparison of our dem with a 1949 us geological survey dem and with 1973 95 ground survey data shows the gradual return of black rapids glacier to a pre surge hypsometry following a surge in 1936 37 maximum elevation changes along the glacier center line in the ablation and accumulation areas are respectively 249 and 63 m 5 4 and 1 4 m a 1 maximum elevation changes of survey points at nearby locations are 4 9 m a 1 1975 84 and 0 5 ma 1 1975 85 center line thickening of 62 m between 1949 and 1995 1 4 m a 1 just above the loket tributary in the upper part of the ablation zone indicates dynamic thickening following the 1936 37 surge

the vestfjorden traenadjupet palaeo ice stream drainage system mid norwegian continental shelf abstract an ice stream in the vestfjorden traenadjupet depressions off northern norway transported glacial debris to the shelf edge and into the deep sea during the last glaciation our interpretation is based mainly on regional and detailed bathymetry and 2d and 3d seismic data this palaeo ice stream was approximately 400 km long and covered an area of 20 000 km 2 including a complex system of tributary fjords and valleys in nordland county the drainage basin had an area of ca 150 000 km 2 within the fennoscandian ice sheet fis during the last glacial maximum lgm the location of the palaeo ice stream prevented large ice masses from reaching the montainous areas of lofoten and vesteralen a local ice dome was established in these areas the palaeo ice stream eroded extensively into both mesozoic and cenozoic sedimentary rocks and quaternary sediments a pattern of well developed subglacial sedimentary bedforms was produced e g mega scale lineations drumlins ice stream shear margin moraines are located on both sides of traenadjupet defining the width of the palaeo ice stream 90 km at the shelf edge these moraines are commonly 10 20 m high a few kilometres wide and reach several tens of kilometres in length a large recessional moraine the tennholmen ridge has been mapped in vestfjorden it is 80 m high 20 km wide and 60 km long we have interpreted this ridge as a grounding line moraine formed during a halt or a readvance of the ice stream during the last deglaciation the large transport of glacial debris towards the grounding line occurred during this stage northeast of the tennholmen ridge several smaller moraine ridges were developed at still stands during deglaciation

a case study in the new york drumlin field an investigation using microsedimentology resulting in the refinement of a theory of drumlin formation abstract the formation of drumlins remains a major enigma it is accepted that drumlins form under active temperate ice most likely within a soft sediment deforming bed at ephemeral sticky points these sticky points likely lead to the causative mechanism around which sediment nucleation occurs the critical question is under what conditions and where and how do sticky spots form a comparative investigation of a drumlin and mega flute in the new york drumlin field as a case study demonstrates that rheological and sedimentological tills from these different forms are similar it is not therefore rheological change alone that must account for drumlin shape and form but likely the advective subglacial basal sediment flux rate at the ice bed the rate of sediment motion between the upper interface at the ice sediment bed boundary and the lower immobile sediment at depth is crucial at the lower decollement between the mobile and immobile sediment units within the deforming sediment package proto drumlin nucleation is likely to occur and develop into a streamlined form the trigger mechanism for such a perturbation is a derivative of sediment rheology and sediment flux rate driven by the overlying ice stresses recent evidence from antarctica lends credence to this new hypothesis that can be related to all drumlins formed under temperate soft sediment deforming bed conditions

sea level as a stabilizing factor for marine ice sheet grounding lines climate change could potentially destabilize marine ice sheets which would affect projections of future sea level rise1 2 3 4 specifically an instability mechanism5 6 7 8 has been predicted for marine ice sheets such as the west antarctic ice sheet that rest on reversed bed slopes whereby ice sheet thinning or rising sea level leads to irreversible retreat of the grounding line however existing analyses of this instability mechanism have not accounted for deformational and gravitational effects that lead to a sea level fall at the margin of a rapidly shrinking ice sheet9 10 11 here we present a suite of predictions of gravitationally self consistent sea level change following grounding line migration our predictions vary the initial ice sheet size and also consider the contribution to sea level change from various subregions of the simulated ice sheet using these results we revisit a canonical analysis of marine ice sheet stability5 and demonstrate that gravity and deformation induced sea level changes local to the grounding line contribute a stabilizing influence on ice sheets grounded on reversed bed slopes we conclude that accurate treatments of sea level change should be incorporated into analyses of past and future marine ice sheet dynamics

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

ice stream stability on a reverse bed slope marine ice streams whose beds deepen inland are thought to be inherently unstable numerical modelling of the maguerite bay ice stream retreat in west antarctica since the last glacial maximum suggests that an ice stream can stabilize on an inland sloping bed owing to increased lateral drag where the ice stream narrows marine based ice streams whose beds deepen inland are thought to be inherently unstable1 2 3 this instability is of particular concern because significant portions of the marine based west antarctic and greenland ice sheets are losing mass and their retreat could contribute significantly to future sea level rise4 5 6 7 however the present understanding of ice stream stability is limited by observational records that are too short to resolve multi decadal to millennial scale behaviour or to validate numerical models8 here we present a dynamic numerical simulation of antarctic ice stream retreat since the last glacial maximum lgm constrained by geophysical data whose behaviour is consistent with the geomorphological record we find that retreat of marguerite bay ice stream following the lgm was highly nonlinear and was interrupted by stabilizations on a reverse sloping bed where theory predicts rapid unstable retreat we demonstrate that these transient stabilizations were caused by enhanced lateral drag as the ice stream narrowed we conclude that as well as bed topography ice stream width and long term retreat history are crucial for understanding decadal to centennial scale ice stream behaviour and marine ice sheet vulnerability

nitrate in greenland and antarctic ice cores a detailed description of post depositional processes a compilation of nitrate no 3 data from greenland has shown that recent no 3 concentrations reveal a temperature dependence similar to that seen in antarctica except for sites with very low accumulation rates lower temperatures tend to lead to higher no 3 concentrations preserved in the ice accumulation rate which is closely linked to temperature might influence the concentrations preserved in snow as well but its effect cannot be separated from the temperature imprint processes involved in no 3 deposition are discussed and shown to be temperature and or accumulation rate dependent apart from scavenging of nitric acid hno 3 during formation of precipitation uptake of hno 3 onto the ice crystal s surface during and after precipitation seems to contribute further to the no 3 concentrations found in surface snow post depositional loss of no 3 from the top snow layers is caused by release of hno 3 and by photolysis of no 3 it is suggested that photolysis accounts for considerable losses at sites with very low accumulation rates depending on the site characteristic and given that the temperature and accumulation rate dependence is quantified it should be possible to infer changes in atmospheric hno 3 concentrations

the last glacial termination a major puzzle of paleoclimatology is why after a long interval of cooling climate each late quaternary ice age ended with a relatively short warming leg called a termination we here offer a comprehensive hypothesis of how earth emerged from the last global ice age a prerequisite was the growth of very large northern hemisphere ice sheets whose subsequent collapse created stadial conditions that disrupted global patterns of ocean and atmospheric circulation the southern hemisphere westerlies shifted poleward during each northern stadial producing pulses of ocean upwelling and warming that together accounted for much of the termination in the southern ocean and antarctica rising atmospheric co2 during southern upwelling pulses augmented warming during the last termination in both polar hemispheres

abrupt early holocene 9 9 9 6 ka ice stream advance at the mouth of hudson strait arctic canada radiocarbon dated glacial geologic evidence documents an abrupt advance of the northern margin of the labrador sector of the laurentide ice sheet during the last deglaciation ice flow directional indicators together with ice marginal features found onshore and offshore delimit an ice stream that advanced north northeast 300 km crossed the mouth of hudson strait and outer frobisher bay and overran summits 400 m above sea level on outer hall peninsula southeast baffin island fifty eight 14 c ages including 27 accelerator mass spectrometry ages on single shells indicate that the advance was extremely rapid the entire advance retreat cycle took place in an 300 yr 14 c interval 9 9 9 6 ka at its maximum extent the ice stream supported a calving margin 200 km long terminating in open water 500 m deep implying a massive iceberg release marine evidence for the outflow is preserved along the labrador sea shelf as thick carbonate rich glacial marine drift but has not been recognized farther east in the north atlantic either the discharge of icebergs was insufficient to produce a trans north atlantic carbonate rich heinrich layer or the icebergs tracked southward where they encountered warming sea surface temperatures although the advance seems to have been coincident with a brief interval of minor regional cooling it failed to trigger a significant climate perturbation suggesting that the ocean atmosphere system had attained its stable interglacial condition by that time

capabilities and limitations of numerical ice sheet models a discussion for earth scientists and modelers the simulation of dynamically coupled ice sheet ice stream and ice shelf systems poses a challenge to most numerical ice sheet models here we review present ice sheet model limitations targeting

characteristics of water soluble inorganic and organic ions in aerosols over the southern ocean and coastal east antarctica during austral summer 1 to characterize the concentrations and size distributions of water soluble organic and inorganic aerosol species including na non sea salt sulfate nss so42 methane sulfonate msa oxalate and succinate over the southern ocean so and coastal east antarctica cea bulk and size segregated aerosols were collected from 40 s 100 e to 69 s 76 e and between 69 s 76 e and 66 s 110 e during a cruise from november 2010 to march 2011 results show that sea salt was the major component of the total aerosol mass accounting for 72 over the so and 56 over cea the average concentrations of nss so42 varied from 420 ng m 3 over the so to 480 ng m 3 over cea the concentrations of msa ranged from 63 to 87 ng m 3 over the so and from 46 to 170 ng m 3 in cea the average concentrations of oxalate were 3 8 ng m 3 over the so and 2 2 ng m 3 over cea the concentrations of formate acetate and succinate were lower than those of oxalate a bimodal size distribution of aerosol mass existed over cea peaking at 0 32 0 56 m and 3 2 5 6 m msa was accumulated in particles of 0 32 0 56 m over cea high chloride depletion was associated with fine mode particles enriched with nss so42 msa and oxalate higher cation to anion and nh4 nss so42 ratios in aerosols over cea compared to that over the so imply the higher neutralization capacity of the marine atmosphere over cea

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

reconciling records of ice streaming and ice margin retreat to produce a palaeogeographic reconstruction of the deglaciation of the laurentide ice sheet abstract this paper reconstructs the deglaciation of the laurentide ice sheet lis including the innuitian ice sheet from the last glacial maximum lgm with a particular focus on the spatial and temporal variations in ice streaming and the associated changes in flow patterns and ice divides we build on a recent inventory of laurentide ice streams and use an existing ice margin chronology to produce the first detailed transient reconstruction of the ice stream drainage network in the lis which we depict in a series of palaeogeographic maps results show that the drainage network at the lgm was similar to modern day antarctica the majority of the ice streams were marine terminating and topographically controlled and many of these continued to function late into the deglaciation until the ice sheet lost its marine margin ice streams with a terrestrial ice margin in the west and south were more transient and ice flow directions changed with the build up peak phase and collapse of the cordilleran laurentide ice saddle the south eastern marine margin in atlantic canada started to retreat relatively early and some of the ice streams in this region switched off at or shortly after the lgm in contrast the ice streams draining towards the north western and north eastern marine margins in the beaufort sea and in baffin bay appear to have remained stable throughout most of the late glacial and some of them continued to function until after the younger dryas yd the yd influenced the dynamics of the deglaciation but there remains uncertainty about the response of the ice sheet in several sectors we tentatively ascribe the switching on of some major ice streams during this period e g m clintock channel ice stream at the north west margin but for other large ice streams whose timing partially overlaps with the yd the drivers are less clear and ice dynamical processes rather than effects of climate and surface mass balance are viewed as more likely drivers retreat rates markedly increased after the yd and the ice sheet became limited to the canadian shield this hard bed substrate brought a change in the character of ice streaming which became less frequent but generated much broader terrestrial ice streams the final collapse of the ice sheet saw a series of small ephemeral ice streams that resulted from the rapidly changing ice sheet geometry in and around hudson bay our reconstruction indicates that the lis underwent a transition from a topographically controlled ice drainage network at the lgm to an ice drainage network characterised by less frequent broad ice streams during the later stages of deglaciation these deglacial ice streams are mostly interpreted as a reaction to localised ice dynamical forcing flotation and calving of the ice front in glacial lakes and transgressing sea basal de coupling due to large amount of meltwater reaching the bed debuttressing due to rapid changes in ice sheet geometry rather than as conveyors of excess mass from the accumulation area of the ice sheet at an ice sheet scale the ice stream drainage network became less widespread and less efficient with the decreasing size of the deglaciating ice sheet the final elimination of which was mostly driven by surface melt

automated drumlin shape and volume estimation using high resolution lidar imagery curvature based relief separation a test from the wadena drumlin field minnesota abstract resolving the origin s of drumlins and related megaridges in areas of megascale glacial lineations msgl left by paleo ice sheets is critical to understanding how ancient ice sheets interacted with their sediment beds msgl is now linked with fast flowing ice streams but there is a broad range of erosional and depositional models further progress is reliant on constraining fluxes of subglacial sediment at the ice sheet base which in turn is dependent on morphological data such as landform shape and elongation and most importantly landform volume past practice in determining shape has employed a broad range of geomorphological methods from strictly visualisation techniques to more complex semi automated and automated drumlin extraction methods this paper reviews and builds on currently available visualisation semi automated and automated extraction methods and presents a new curvature based relief separation cbrs technique for drumlin mapping this uses curvature analysis to generate a base level from which topography can be normalized and drumlin volume can be derived this methodology is tested using a high resolution 3 m lidar elevation dataset from the wadena drumlin field minnesota usa which was constructed by the wadena lobe of the laurentide ice sheet ca 20 000 years ago and which as a whole contains 2000 drumlins across an area of 7500 km 2 this analysis demonstrates that cbrs provides an objective and robust procedure for automated drumlin extraction there is strong agreement with manually selected landforms but the method is also capable of resolving features that were not detectable manually thereby considerably expanding the known population of streamlined landforms cbrs provides an effective automatic method for visualisation of large areas of the streamlined beds of former ice sheets and for modelling sediment fluxes below ice sheets

basal conditions beneath a soft bedded polythermal surge type glacier bakaninbreen svalbard original article can be found at http www sciencedirect com science journal 10406182 copyright elsevier ltd and the international union for quaternary research inqua doi 10 1016 s1040 6182 01 00053 2 full text of this article is not available in the uhra

the late weichselian glacial record in northern poland a new look at debris transport routes by the fennoscandian ice sheet abstract the area of the kashubian coastland and areas adjacent to the northern part of the lower vistula valley northern poland were involved in the major transgressive phases distinguished in poland during the late weichselian due to the small scale of the regressions between the different phases of the late weichselian the ice sheet usually deposited only one till but with a complex vertical profile based on the studies of the directional properties petrographic composition of the fine gravel fraction and the analysis of indicator erratics the dichotomy of the till bed was demonstrated the petrographic composition of the gravel fraction in tills together with the analysis of the indicator erratics and delimitation of the theoretical boulder centres were used to determine the direction of the influx of ice masses this allowed speculation on the reasons for the different dynamics of the fennoscandian ice sheet fis as well as the operation and time variability of the baltic ice stream bis it was emphasised that the delivery system of debris by the ice sheet might have been complex and multidirectional more than one route it has been suggested that changes in the petrographic composition of the gravel fraction of the glacial sediments did not have to be associated only with shifting the centre of glaciation but may have resulted from a change in the thermal regime of the ice sheet s bed in the source area especially with the spread of the cold regime zone and depended on the dynamics of the ice sheet stream or sheet flow as well as the spatial and temporal conditions of its development in the deposition area

coastal antarctic aerosol and snowfall chemistry aerosol samples have been collected at three stations on the coast of antarctica at dumont d urville station samples have been collected for 4 years at halley station for 2 years and at neumayer station for 12 years fresh snow samples have also been collected at the three sites at halley daily surface snow samples were taken as well as firn cores covering the sampling period meteorological including upper air data are available at the three sites in the subsequent papers of this special section the data from the three stations have been combined in order to make general statements about the chemistry of aerosol in coastal antarctica about the differences between sectors of antarctica and about the relationship between air concentrations and the chemistry that is eventually seen in ice cores this paper summarizes the samples collected and the sampling methods used at the three sites it also highlights the main role of each paper in this special section

frost flowers implications for tropospheric chemistry and ice core interpretation 1 this paper discusses the chemical composition of frost flowers and their accompanying slush layers and the evidence for their role as a salt source in processes important to atmospheric chemistry and ice core interpretation analysis of antarctic frost flowers shows that they are highly saline and fractionated in sea salt ions with sulfate being depleted strongly relative to sodium because frost flowers give a bright return on satellite scatterometer images the times and places of their formation can be identified when winds blow towards an aerosol sampling station from areas identified by the scatterometer as covered with flowers the collected aerosol is also depleted in sulfate because the flowers have a large salinity bromide concentrations are elevated in frost flowers relative to seawater with their high surface area it is possible that bromine is released to the atmosphere from frost flowers with consequent implications for tropospheric ozone depletion the finding that quantities of fractionated sea salt are available at the sea ice interface in the winter months and may be transported inland as aerosol also has implications for the interpretation of ice core records analysis of one near coastal core shows that the majority of the sodium comes from a fractionated source rather than from open water hitherto strong sea salt signals in ice cores have been attributed to increased open water and more efficient transport inland perhaps due to stormier weather at least in coastal regions however these signals may be related instead to the increased formation of sea ice and frost flowers

glacial geological studies of surge type glaciers in iceland research status and future challenges abstract surging glaciers are potential analogues for land terminating palaeo ice streams and surging ice sheet lobes and research on surge type glaciers is important for understanding the causal mechanisms of modern and past ice sheet instabilities the geomorphic signatures left by the icelandic surge type glaciers vary and range from glaciotectonic end moraines formed by folding and thrusting crevasse squeeze ridges concertina eskers drumlins and fluted forefields to extensive dead ice fields and even drift sheets where fast ice flow indicators are largely missing we outline some outstanding research questions and review case studies from the surge type outlets of bruarjokull eyjabakkajokull and tungnaarjokull vatnajokull ice cap mulajokull and satujokull hofsjokull ice cap hagafellsjokull and su urjokull langjokull ice cap kaldalonsjokull leirufjar arjokull and reykjarfjar arjokull drangajokull ice cap as well as the surge type cirque glaciers in northern iceland we review the current understanding of how rapid ice flow is sustained throughout the surge the processes that control the development of the surge type glacier landsystem and the geological evidence of surges found in sediments and landforms we also examine if it is possible to reconstruct past surge flow rates from glacial landforms and sediments and scale up present day surge processes landforms and landsystems as modern analogues to past ice streams finally we also examine if there is a climate mass balance control on surge initiation duration and frequency

power law extreme flood frequency conventional flood frequency analysis ffa has been criticized both for its questionable theoretical basis and for its failure in extreme event prediction an important research issue for ffa is the exploration of models that have theoretical explanatory value as the first step towards more accurate predictive attempts self similar approaches offer one such alternative with a plausible theoretical basis in complexity theory that has demonstrable wide applicability across the geophysical sciences this paper explores a simple self similar approach to the prediction of extreme floods fifty river gauging records from the usa exhibiting an outlier event were studied fitting a simple power law pl relation to events with return period of 10 years or greater resulted in more accurate discharge and return period estimates for outlier events relative to the log pearson iii model similar success in predicting record events is reported for 12 long term rainfall records from the uk this empirical success is interpreted as evidence that self similarity may well represent the underlying physical processes generating hydrological variables these findings have important consequences for the prediction of extreme flood events the pl model produces return period estimates that are far more conservative than conventional distributions

the international bathymetric chart of the southern ocean ibcso version 1 0 a new bathymetric compilation covering circum antarctic waters the international bathymetric chart of the southern ocean ibcso version 1 0 is a new digital bathymetric model dbm portraying the seafloor of the circum antarctic waters south of 60 degrees s

glacial interglacial changes in mineral dust and sea salt records in polar ice cores sources transport and deposition 1 sea salt and mineral dust records as represented by na and ca2 concentrations respectively in greenland and antarctic ice cores show pronounced glacial interglacial variations for the last glacial maximum lgm mineral dust sea salt concentrations in greenland show an increase of a factor of approximately 80 15 compared to the holocene and significant shifts by a factor of 15 5 during dansgaard oeschger events in antarctica the dust sea salt flux is enhanced by a factor of 15 3 during the lgm compared to the holocene and variations by approximately a factor of 8 1 2 exist in parallel to antarctic warm events primary glacial dust sources are the asian deserts for greenland and patagonia for antarctica ice core evidence and model results show that both changes in source strength as well as atmospheric transport and lifetime contributed to the observed changes in greenland ice cores in antarctica changes in ice core fluxes are in large parts related to source variations both for sea salt and dust where the formation of sea salt aerosol from sea ice may play a pivotal role summarizing our latest estimates on changes in sources transport and deposition these processes are roughly able to explain the glacial increase in sea salt in both polar regions while they fall short by at least a factor of 4 7 for mineral dust future improvements in model resolution and in the formulation of source and transport processes together with new ice core records e g on dust size distributions will eventually allow convergence of models and observations

reconstruction of palaeo ice sheets the use of geomorphological data the article discusses the nature of the glacial inversion problem which is defined as the extraction of time slice ice sheet flow patterns from the patchy and partly overprinted landform record present in former ice sheet areas a coherent inversion model for derivation of flow patterns and interior ice sheet configuration from geomorphological data is presented glacial landscapes are classified according to the three criteria of internal age gradients presence or absence of meltwater traces aligned to flow traces and basal condition frozen bed thawed bed inferred from morphology the inversion model uses landscapes classified accordingly spatially delineated into fans as input data relative chronologies at fan intersections are used to sort fans in a relative age stack that can be linked to stratigraphic dating information

ice streaming in the laurentide ice sheet a first comparison between data calibrated numerical model output and geological evidence 1 despite the importance of rapidly flowing ice streams to ice sheet mass balance their incorporation into numerical ice sheet models is a major scientific challenge this introduces large uncertainties in model output and inhibits a more complete understanding of the role of ice streams in overall ice sheet stability recent computational advances have enabled more realistic representations of ice streaming but few studies have attempted to compare model output against known locations of ice streams this paper compares predictions of ice streaming derived from a large ensemble analysis of a glacial systems model of the laurentide ice sheet against independent geological evidence compiled from previously published studies although the precise dating of paleo ice stream locations is problematic our analysis includes comparisons at six different time steps 18 to 10 cal ka bp during deglaciation results indicate that the model is successful in predicting all of the major marine terminating ice streams but there is mixed success in simulating terrestrial ice streams in the right place and at the right time which is vital in guiding future model development the model also reveals that whilst some ice streams persist throughout deglaciation the focus of mass loss associated with ice streaming switches through time with dynamic changes in ice stream catchments and tributaries this implies that major changes in ice stream activity are to be expected in a deglaciating ice sheet with important implications for contemporary ice sheet dynamics

durations and propagation patterns of ice sheet instability events continued atmospheric and ocean warming places parts of the west antarctic ice sheet at risk for collapse through accelerated ice flow and grounding line retreat over reversed bed slopes however

frost flowers as a source of fractionated sea salt aerosol in the polar regions frost flowers collected from the surface of new sea ice near the brunt ice shelf antarctica show depletion in sulphate and sodium relative to other sea water ions this is consistent with loss of mirabilite na2so4 during formation of the brine from which the frost flowers grow aerosol generated from frost flowers would have higher sodium sulphate ratios than aerosol generated from sea water this would explain low values of non sea salt sulphate encountered in winter aerosol and winter layers in ice cores at coastal antarctic sites calculations confirm that the frost flower source should be significant compared to an open water source for coastal regions

fennoscandian palaeoglaciology reconstructed using a glacial geological inversion model the evolution of ice sheet configuration and flow pattern in fennoscandia through the last glacial cycle was reconstructed using a glacial geological inversion model i e a theoretical model that formalises the procedure of using the landform record to reconstruct ice sheets the model uses mapped flow traces and deglacial melt water landforms as well as relative chronologies derived from cross cutting striae and till lineations as input data flow trace systems were classified into four types i time transgressive wet bed deglacial fans ii time transgressive frozen bed deglacial fans iii surge fans and iv synchronous non deglacial event fans using relative chronologies and aggregation of fans into glaciologically plausible patterns a series of ice sheet configurations at different time slices was erected a chronology was constructed through correlation with dated stratigraphical records and proxy data reflecting global ice volume geological evidence exists for several discrete ice sheet configurations centred over the scandinavian mountain range during the early weichselian the build up of the main weichselian fennoscandian ice sheet started at approximately 70 ka and our results indicate that it was characterised by an ice sheet with a centre of mass located over southern norway this configuration had a flow pattern which is poorly reproduced by current numerical models of the fennoscandian ice sheet at the last glacial maximum the main ice divide was located overthe gulf of bothnia a major bend in the ice divide was caused by outflow of ice to the northwest over the lowest part of the scandinavian mountain chain widespread areas of preserved pre late weichselian landscapes indicate that the ice sheet had a frozen bed core area which was only partly diminished in size by inward transgressive wet bed zones during the decay phase

initial effects of oceanic warming on a coupled ocean ice shelf ice stream system abstract the initial retreat of ice shelf grounding lines stabilized on seaward sloping beds is influenced by the rheology of these beds according to new model results we apply a fully coupled process model to investigate how the response of an ice stream to increased ocean temperature beneath its ice shelf depends on the assumed form of its basal flow law for the same applied oceanic warming the increase in grounding line flux can be twice as great for an effectively plastic bed as for a linear viscous bed suggesting that improved knowledge of the basal flow law of ice streams is necessary for predicting ice sheet response to climatic forcing

major changes in ice stream dynamics during deglaciation of the north western margin of the laurentide ice sheet abstract victoria island lies at the north western limit of the former north american laurentide ice sheet in the canadian arctic archipelago and displays numerous cross cutting glacial lineations previous work suggests that several ice streams operated in this region during the last wisconsinan glaciation and played a major role in ice sheet dynamics and the delivery of icebergs into the arctic ocean this paper produces the first detailed synthesis of their behaviour from the last glacial maximum through to deglaciation 21 9 5 cal ka bp based on new mapping and a previously published radiocarbon constrained ice sheet margin chronology over 70 discrete ice flow events flow sets are fitted to the ice margin configuration to allow identification of several ice streams ranging in size from large and long lived thousands of years to much smaller and short lived hundreds of years the reconstruction depicts major ice streams in m clure strait and amundsen gulf which underwent relatively rapid retreat from the continental shelf edge at some time between 15 2 and 14 1 cal ka bp a period which encompasses climatic warming and rapid sea level rise meltwater pulse 1a following this overall retreat was slower and the ice streams exhibited asynchronous behaviour the amundsen gulf ice stream continued to operate during ice margin retreat whereas the m clure strait ice stream ceased operating and was replaced by an ice divide within 1000 years this ice divide was subsequently obliterated by another short lived phase of ice streaming in m clintock channel 13 cal ka bp the timing of this large ice discharge event coincides with the onset of the younger dryas subsequently a minor ice divide developed once again in m clintock channel before final deglaciation of the island shortly after 9 5 cal ka bp it is concluded that large ice streams at the nw margin of the laurentide ice sheet equivalent in size to the hudson strait ice stream underwent major changes during deglaciation resulting in punctuated delivery of icebergs into the arctic ocean published radiocarbon dates constrain this punctuated delivery as far as is possible within the limits imposed by their precision and we note their coincidence with pulses of meltwater delivery inferred from numerical modelling and ocean sediment cores

atmospheric methane sulfonate and non sea salt sulfate records at the european project for ice coring in antarctica epica deep drilling site in dronning maud land antarctica abstract during three summer campaigns in january february 2000 2001 and 2002 the ionic compo sition of the aerosol at the epica deep drilling site at kohnen station was measured in daily resolution in 2000 and 2002 we observed mean std non sea salt sulfate nss so42 con centrations of 353 100 ng m 3 and 320 250 ng m 3 as well as methane sulfonate ms con centrations of 59 36 ng m 3 and 74 80 ng m 3 respectively for the summer campaign in 2001 significantly lower nss so42 and ms levels of 164 150 ng m 3 and 19 12 ng m 3 respectively were typical the mean ms nss so42 ratio ranged from about 0 1 to 0 2 ms and nss so42 concentrations and their variability were roughly comparable to coastal stations at summer supported by air mass back trajectory analyses this finding documented an effi cient long range transport to kohnen via the free troposphere ms nss so42 ratios exhibited a strong dependence on the ms concentration with systematically higher ratios at higher ms concentrations a peculiarity which is also evident in a firn core drilled at this site

northern hemisphere ice sheet responses to past climate warming during periods of glaciation the northern hemisphere was swathed by large ice sheets a review of ice sheet retreat during the last two deglaciations shows that land based ice sheets responded rapidly to rising summer insolation whereas marine based ice sheets underwent a delayed but more abrupt response

basal conditions for pine island and thwaites glaciers west antarctica determined using satellite and airborne data we use models constrained by remotely sensed data from pine island and thwaites glaciers west antarctica to infer basal properties that are difficult to observe directly the results indicate strong basal melting in areas upstream of the grounding lines of both glaciers where the ice flow is fast and the basal shear stress is large farther inland we find that both glaciers have mixed bed conditions with extensive areas of both bedrock and weak till in particular there are weak areas along much of pine island glacier s main trunk that could prove unstable if it retreats past the band of strong bed just above its current grounding line in agreement with earlier studies our forward ice stream model shows a strong sensitivity to small perturbations in the grounding line position these results also reveal a large sensitivity to the assumed bed sliding or deforming model with non linear sliding laws producing substantially greater dynamic response than earlier simulations that assume a linear viscous till rheology finally comparison indicates that our results using a plastic bed are compatible with the limited observational constraints and theoretical work that suggests an upper bound exists on maximum basal shear stress

the role of southern ocean processes in orbital and millennial co2 variations a synthesis abstract recent progress in the reconstruction of atmospheric co 2 records from antarctic ice cores has allowed for the documentation of natural co 2 variations on orbital time scales over the last up to 800 000 years and for the resolution of millennial co 2 variations during the last glacial cycle in unprecedented detail this has shown that atmospheric co 2 varied within natural bounds of approximately 170 300 ppmv but never reached recent co 2 concentrations caused by anthropogenic co 2 emissions in addition the natural atmospheric co 2 concentrations show an extraordinary correlation with southern ocean climate changes pointing to a significant direct or indirect influence of climatic and environmental changes in the southern ocean region on atmospheric co 2 concentrations here we compile recent ice core and marine sediment records of atmospheric co 2 temperature and environmental changes in the southern ocean region as well as carbon cycle model experiments in order to quantify the effect of potential southern ocean processes on atmospheric co 2 related to these orbital and millennial changes this shows that physical and biological changes in the so are able to explain substantial parts of the glacial interglacial co 2 change but that none of the single processes is able to explain this change by itself in particular changes in the southern ocean related to changes in the surface buoyancy flux which in return is controlled by the waxing and waning of sea ice may favorably explain the high correlation of co 2 and antarctic temperature on orbital and millennial time scales in contrast the changes of the position and strength of the westerly wind field were most likely too small to explain the observed changes in atmospheric co 2 or may even have increased atmospheric co 2 in the glacial also iron fertilization of the marine biota in the southern ocean contributes to a glacial drawdown of co 2 but turns out to be limited by other factors than the total dust input such as bioavailability of iron or macronutrient supply

drainage pathways beneath ice sheets and their implications for ice sheet form and flow the example of the british ice sheet during the last glacial maximum the drainage system beneath ice sheets is poorly understood even though it is a major determinant of their basal boundary condition with implications for their form flow and stability and particularly of the ice streams that are crucial dynamic components understanding can be enhanced by evidence from the beds of former ice sheets glaciological principles are applied to geological evidence in the vale of york that demonstrate occupancy by a major ice stream of the british ice sheet with deduced gravitational shear stresses in the range 4 24 kpa compared with a typical glacier shear stress of about 80 100 kpa and horizontal velocities in the terminal zone in the range of 400 950 ma 1 it is shown that the ice stream was in an almost buoyant state with effective pressures in the range 50 100 kpa forarange of ice pressures between 2000and 5000kpa similar deductions are madefor other ice streams on the southern flank of the british ice sheet the esker system in the area of the ice stream represents locations of subglacial drainage tunnels that are suggested to be the key drainage elements in ice sheets where excess surface water penetrates to the bed a theory of channel groundwater coupling which self organises in response to the rate of water recharge and the transmissivity of the subglacial bed is applied to the sub ice stream esker system when matched to local geological evidence the theory predicts the distribution of basal water pressures the rate of recharge of surface water to the glacier bed local shear stresses the areal pattern of sedimentary processes including bed deformation and their seasonal fluctuations predictions of the annual recharge rate of 950 mm are consistent with the modern values of modern mean annual rainfall in the ouse vale of york catchment of 906mm the calculated mean annual discharge of the four major subglacial rivers in 55 m 3 s 1 compared with a mean flow of the modern ouse of 49 m 3 s 1 a transient analysis shows the response time of water pressures in the underlying aquifer to changes in surface recharge to be of the order 10 100 days suggesting the possibility of instabilities at the ice bed interface it is not possible however to determine whether the vale of york ice stream was characterized by stable or instable surging flow copyright 2010 john wiley sons ltd

stability of the west antarctic ice sheet in a warming world equivalent to 0 28 to 0 56 mm yr 1 sea level rise with the rate growing over at least the past two decades 1 4 these observations intensify concerns about the ice sheet s stability that were first raised more than four decades ago 5

reassessment of the potential sea level rise from a collapse of the west antarctic ice sheet theory has suggested that the west antarctic ice sheet may be inherently unstable recent observations lend weight to this hypothesis we reassess the potential contribution to eustatic and regional sea level from a rapid collapse of the ice sheet and find that previous assessments have substantially overestimated its likely primary contribution we obtain a value for the global eustatic sea level rise contribution of about 3 3 meters with important regional variations the maximum increase is concentrated along the pacific and atlantic seaboard of the united states where the value is about 25 greater than the global mean even for the case of a partial collapse

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

century scale discharge stagnation and reactivation of the ross ice streams west antarctica 1 flow features on the surface of the ross ice shelf west antarctica record two episodes of ice stream stagnation and reactivation within the last 1000 years we document these events using maps of streaklines emerging from individual ice streams made using visible band imagery together with numerical models of ice shelf flow forward model experiments demonstrate that only a limited set of discharge scenarios could have produced the current streakline configuration according to our analysis whillans ice stream ceased rapid flow about 850 calendar years ago and restarted about 400 years later and macayeal ice stream either stopped or slowed significantly between 800 and 700 years ago restarting about 150 years later until now ice stream scenarios emphasized runaway retreat or stagnation on millennial timescales here we identify a new scenario century scale stagnation and reactivation cycles as well as lateral communication with adjacent ice streams through thickness changes on lightly grounded ice plains this introduces uncertainty into predictions for future sea level withdrawals by the west antarctic ice sheet which are based in part on recent slowing of whillans ice stream and the stagnant condition of kamb ice stream