quaternary glaciation of the himalayan tibetan orogen glacial geological evidence from throughout the himalayan tibetan orogen is examined to determine the timing and extent of late quaternary glaciation in this region and its relation to similar changes on a global scale the evidence summarised here supports the existence of expanded ice caps and extensive valley glacier systems throughout the region during the late quaternary however it cannot yet be determined whether the timing of the extent of maximum glaciation was synchronous throughout the entire region or whether the response was more varied the lack of organic material needed for radiocarbon dating has hindered past progress in glacial reconstruction however application of optically stimulated luminescence and terrestrial cosmogenic radionuclide methods has recently expanded the number of chronologies throughout the region limits to the precision and accuracy available with these methods and more importantly geological uncertainty imposed by processes of moraine formation and alteration both conspire to limit the time resolution on which correlations can be made to milankovitch timescales several ka in order to put all studies on a common scale well dated sites have been re evaluated and all the published terrestrial cosmogenic nuclide ages for moraine boulders and glacially eroded surfaces in the himalayan tibetan orogen have been recalculated locally detailed studies indicate that there are considerable variations in the extent of glaciation from one region to the next during a glaciation glaciers throughout monsoon influenced tibet the himalaya and the transhimalaya are likely synchronous both with climate change resulting from oscillations in the south asian monsoon and with northern hemisphere cooling cycles in contrast glaciers in pamir in the far western regions of the himalayan tibet orogen advanced asynchronously relative to the other regions that are monsoon influenced regions and appear to be mainly in phase with the northern hemisphere cooling cycles broad patterns of local and regional variability based on equilibrium line altitudes have yet to be fully assessed but have the potential to help define changes in climatic gradients over time copyright 2008 john wiley sons ltd

new evidence for a grounded irish sea glaciation of the isles of scilly uk abstract new geomorphological and sedimentological data support previously published reconstructions of an irish sea glacier advance as far south as the northern shores of the isles of scilly in the celtic sea 49 58 n offshore boulder covered bars with cores of diamicton are interpreted as moraines which together with onshore moraine ridges and trimlines mark the maximal extent of the irish sea glacier at bread and cheese cove st martin s a heterogeneous sediment unit wedged between periglacial gelifluctates is interpreted as a mixture of glacitectonized and cannibalized glacilacustrine and marine deposits as well as primary subglacial tills macrofabric signatures reflect a subglacial origin but the whole unit has been subject to down slope mass movement micromorphological analysis indicates highly variable response to deformation and glacitectonism with most features relating to ductile behaviour and wet deformation the characteristics suggest deposition during a short lived advance of the irish sea glacier over pre existing marine and contemporaneous proglacial lacustrine sediments once blocks of stratified sediment and diamicton had been driven onshore they were subject to paraglacial remobilization resulting at most locations in complete disaggregation the distribution of re worked glacigenic sediments coincides with the glacial limits inferred from the geomorphological evidence

extent and spatial distribution of pleistocene glaciations in eastern tibet as a contribution to the controversial discussion regarding the nature and extent of the pleistocene glaciation on the tibetan plateau additional observations and results were obtained during several chinese german joint expeditions in the investigation area of the eastern and central tibetan plateau it will be shown that the maximum extent of the last glaciation was limited to the glaciation of isolated mountain groups or smaller plateau glaciations these glaciations are characterized by glacial erosional features such as u shaped valleys in the inner mountain massifs and cirques in the higher summit areas accumulation forms such as terminal and lateral moraines less common than basal moraines are marked by granitic and basaltic erratics using two examples from the eastern margin of the tibetan plateau nianbaoyeze shan and northern chola shan the extent of pleistocene glaciations can be mapped by the distribution of terminal and lateral moraines and erratic granite boulders on the slopes of the surrounding schists two to three main pleistocene glaciations can be separated using weathering criteria paleosols and the overlying stratum on the moraines and associated terrace sequences overlying stratum consist of aeolian sandy silt or solifluction debris the younger moraines are found to be characterized by large erratics were therefore named big boulder moraine and can be found over the investigated area the ice free areas are characterized by pleistocene terraces along the main rivers loess deposits with sand and ice wedges at higher elevations e g the basin of zoige and paleosols in the basins below 3500 m a s l e g aba basin or garze basin the hypothesis of an extensive plateau glaciation could not be verified for this region a rising snowline equilibrium line altitudes elas is revealed in two cross sections during the last glacial maximum lgm at the eastern and northern margin of the tibetan plateau snowlines migrated from about 4000 m in the east minshan to 4300 m in the nianbaoyeze and to about 4700 m in the west bayan har shan a rise was also recorded from about 3800 m in the north central qilian shan up to a range of 4300 4950 m different exposures in the kunlun shan to approximately 5200 m in the tanggula shan in the center of the tibetan plateau the general increase of modern and lgm snowlines or elas towards the plateau corresponds with a decrease of precipitation from east to west and from north to south respectively precipitation was more pronounced at the eastern margin during glacial times than compared to present

sedimentary evidence for deforming bed conditions associated with a grounded irish sea glacier southern ireland along the south coast of ireland a shelly diamict facies the irish sea till has been variously ascribed to subglacial deposition by a grounded irish sea glacier or to glacimarine sedimentation by suspension settling and iceberg rafting observations are presented here from five sites along the south coast to directly address this question at these sites sedimentary evidence is preserved for the onshore advance of a grounded irish sea glacier which glacitectonically disturbed and eroded pre existing sediments and redeposited them as deformation till recession of this irish sea glacier resulted in the damming of ice marginal lakes in embayments along the south coast into which glacilacustrine sedimentation then took place these lake sediments were subsequently glacitectonised and reworked by overriding glacier ice of inland origin which deposited deformation till on top of the succession there is no evidence for deposition of the irish sea diamicts by glacimarine sedimentation at these sites the widespread development of subglacial deforming bed conditions reflected the abundance of fine grained marine and lacustrine sediments available for subglacial erosion and reworking stratigraphical and chronological data suggest that the advance of a grounded irish sea glacier along the south coast occurred during the last glaciation and this is regionally consistent with marine geological data from the celtic sea these observations demonstrate extension of glacier ice far beyond its traditional limits in the celtic sea and on land in southern ireland during the last glaciation and remove the stratigraphical basis for chronological differentiation of surficial glacial drifts and thus the munsterian glaciation in southern ireland copyright 2001 john wiley sons ltd

review of the timing and extent of glaciers during the last glacial cycle in the bordering mountains of tibet and in east asia new accelerator mass spectrometry 14c ams14c electron spin resonance esr and thermoluminescence tl dates for glacial successions in tibetan bordering mountains and in east asia show that glacier extent during the early middle mis3 4 parts of the last glacial cycle was larger than that of the late stage mis2 in last glacial cycle glaciation was not synchronous with the north hemisphere ice sheet maxima and changes in oceanic circulation that predominately control global climate there exist three seasonal precipitation patterns that control the accumulation and ablation on glaciers in the study areas areas dominated by westerlies including the east asia coastal islands experience glacier advance mainly because of increased winter precipitation these glaciers expand during glacial stages in contrast in areas dominated by summer precipitation in the interior of mainland except in the monsoonal high precipitation zone in southeast tibet and the hengduan mountain range tend not to develop large glaciers during major glacial stages

tidal evolution of the northwest european shelf seas from the last glacial maximum to the present 1 two dimensional paleotidal simulations have been undertaken to investigate tidal and tide dependent changes tidal amplitudes tidal current velocities seasonal stratification peak bed stress vectors that have occurred in the nw european shelf seas during the last 20 ka the simulations test the effect of shelf wide isostatic changes of sea level by incorporating results from two different crustal rebound models and the effect of the ocean tide variability by setting open boundary values either fixed to the present state or variable according to the results of a global paleotidal model the use of the different crustal rebound models does not affect the overall changes in tidal patterns but the timing of the changes is sensitive to the local isostatic effects that differ between the models the incorporation of ocean tide changes greatly augments the amplitude of tides and tidal currents in the celtic and malin seas before 10 ka bp and has a large impact on the distribution of seasonally stratified conditions magnitude of peak bed stress vectors and tidal dissipation in the shelf seas the predictions on seasonal stratification are supported by well dated evidence on tidal mixing front migration in the celtic sea additional experiments using the global model suggest that the variability of offshore tides has been caused mainly by changes of eustatic sea level and ice sheet extent in particular a large decrease observed at 10 8 ka bp is attributed to the opening of hudson strait accompanied by the retreat of the laurentide ice sheet

the whittard canyon a case study of submarine canyon processes submarine canyons are large geomorphological features that incise continental shelves and slopes around the world they are often suggested to be biodiversity and biomass hotspots although there is no consensus about this in the literature nevertheless many canyons do host diverse faunal communities but owing to our lack of understanding of the processes shaping and driving this diversity appropriate management strategies have yet to be developed here we integrate all the current knowledge of one single system the whittard canyon celtic margin ne atlantic including the latest research on its geology sedimentology geomorphology oceanography ecology and biodiversity in order to address this issue the whittard canyon is an active system in terms of sediment transport the net suspended sediment transport is mainly up canyon causing sedimentary overflow in some upper canyon areas occasionally sediment gravity flow events do occur some possibly the result of anthropogenic activity however the role of these intermittent gravity flows in transferring labile organic matter to the deeper regions of the canyon appears to be limited more likely any labile organic matter flushed downslope in this way becomes strongly diluted with bulk material and is therefore of little food value for benthic fauna instead the fresh organic matter found in the whittard channel mainly arrives through vertical deposition and lateral transport of phytoplankton blooms that occur in the area during spring and summer the response of the whittard canyon fauna to these processes is different in different groups foraminiferal abundances are higher in the upper parts of the canyon and on the slope than in the lower canyon meiofaunal abundances in the upper and middle part of the canyon are higher than on adjacent slopes but lower in the deepest part mega and macrofauna abundances are higher in the canyon compared with the adjacent slope and are higher in the eastern than the western branch these faunal patterns reflect the fact that the whittard canyon encompasses considerable environmental heterogeneity related to a combination of organic matter trapping current regimes due to focused internal tides and different substrates we conclude that coordinated observations of processes driving faunal patterns are needed at a fine scale in order to understand the functioning of communities in this and other submarine canyons

esr dating studies of palaeo debris flow deposits in dongchuan yunnan province china abstract the ages of palaeo debris flow deposits in dongchuan yunnan province were determined by esr dating they are consistent with a 14 c age estimate the results suggest that the debris flow deposits were formed during humid periods of the late pleistocene simulation experiments and sem analysis show that the resetting of ge centres in quartz is most likely due to collisions of the quartz grains during the process of rapid deposition

a review of glacial sequences of the kunlun pass northern tibetan plateau abstract in the kunlun pass area of northern tibet glacial landforms and sediments provide evidence for three major quaternary glaciations esr and tl dating suggest that they date to 600 700 ka wangkun glaciation 260 ka yakou glaciation and 61 13 ka yuzhufeng glaciation the last glacial each glaciation is less extensive than its predecessor the wangkun glaciation is the largest quaternary glaciation the extent of the glaciers during the wangkun glaciation was 3 5 times larger than that of the present glaciers during the last glacial glaciers advanced several times the moraines near the modern glaciers are probably the products of neoglaciation and little ice age

external controls on turbidite sedimentation on the glacially influenced armorican margin bay of biscay western european margin abstract sequence stratigraphic models predict increased sediment delivery to deep water areas during sea level lowstand the armorican margin bay of biscay western european margin is an interesting area to test this hypothesis because the margin has a wide continental shelf still partly flooded during sea level lowstand and the armorican turbidite system has experienced fluctuating sediment fluxes since the last glacial period the stratigraphic response of the armorican turbidite system to sea level oscillations and climate changes was assessed for the last 35 000 years through the study of the guilcher crozon and audierne levees millennial timescale resolution chronostratigraphy allowed us to reconstruct the sediment accumulation and turbidite frequency thickness and grain size over this period of time we found that the armorican turbidite system was sediment starved during highstand conditions ca 8 0 ka and that glacial conditions favoured sediment delivery to the deep bay of biscay however contrary to what would be expected from sequence stratigraphic models the turbidite flux did not reach a maximum during the lgm lowstand ca 26 20 ka but at the onset of termination i between ca 20 and 17 ka this makes the armorican turbidite system a transgression dominated one this sediment pulse can be interpreted as a huge increase in the meltwater discharge of the fleuve manche palaeoriver in response to the decay of the british and fennoscandian ice sheets at that time despite the rising sea level a large deltaic system had to have developed on the outer shelf leading to the delivery of the fleuve manche sediment load into the canyon heads on the other hand our dataset suggest that the delivery of sediment into canyons was mainly forced by the winnowing and reworking of the sediment stored on the wide drowned shelf during the last glacial period between ca 35 and 20 ka and between 17 and 8 ka these findings illustrate the competing influences of accommodation and sediment supply on the armorican margin over the last 35 000 years with a shelf acting as a buffer for the sediment supply signal for most of the period except during the last deglaciation at that time the western european sediment routing system was reactive the climatic signal rapidly propagated from the southern limb of the european ice sheet to the armorican turbidite system finally our study demonstrates that precise reconstruction of turbidite flux in deep water areas added to knowledge about the morphology of the margin and the palaeoenvironmental changes fluvial system shoreline position etc are crucial for determining the response of turbidite systems to external forcing

evidence for late pleistocene ice stream activity in the witch ground basin central north sea from 3d seismic reflection data abstract buried submarine landforms mapped on 3d reflection seismic data sets provide the first glacial geomorphic evidence for glacial occupation of the central north sea by two palaeo ice streams between 58 59 n and 0 1 e streamlined subglacial bedforms mega scale glacial lineations and iceberg plough marks within the top 80 m of the quaternary sequence record the presence and subsequent break up of fast flowing grounded ice sheets in the region during the late pleistocene the lengths of individual mega scale glacial lineations vary from 5 to 20 km and the distance between lineations typically ranges from 100 to 1000 m the lineations incise to a depth of 10 12 m with trough widths of 100 m the most extensive and best preserved set of lineations is attributed to the action of a late weichselian ice stream which either drained the ne sector of the british irish ice sheet or was sourced from the sw within the fennoscandian ice sheet the 30 50 km wide palaeo ice stream is imaged along its flow direction for 90 km trending nw se an older set of less well preserved lineations is interpreted as an earlier weichselian or saalian ice stream and records ice flow in an sw ne orientation cored sedimentary records tied to 3d seismic observations support grounded ice sheet coverage in the central north sea during the last glaciation and indicate that ice flowed over a muddy substrate that is interpreted as a deformation till the identification of a late weichselian ice stream in the witch ground area of the north sea basin provides independent geomorphic evidence in support of ice sheet reconstructions that favour complete ice coverage of the north sea between scotland and norway during the last glacial maximum

water load definition in the glacio hydro isostatic sea level equation abstract models of glacio hydro isostatic rebound and the concomitant sea level change have been progressively improved over the past three decades recently the procedures used by the group at the australian national university anu for the hydro isostatic component of the theory have been questioned quat sci rev 21 2002 409 although the details of the anu group s procedures have not been published because they are mainly computational in nature rather than representing significant conceptual advances because of this criticism we set out here in detail the procedures that have been used for the treatment of the migration of shorelines as sea levels rise and fall the effect of retreat and advancing grounded ice on shelves and shallow seas and the transitions from grounded to floating ice and vice versa we conclude that there is no basis for the criticism that these formulations and their implementation provide a high resolution and complete description of both sea level change and of the estimates of volumes of ice exchanged with the oceans the results from this formulation are confirmed by the entirely independent analyses of milne et al quat sci rev 21 2002 361 and mitrovica and milne geophys j int 2002 submitted for publication who conclude that our formulation is significantly more accurate than the procedure advocated by peltier science 265 1994 195 rev geophys 36 1998a 603 geophys res lett 25 1998b 3955

the shallow marine architecture knowledge store a database for the characterization of shallow marine and paralic depositional systems abstract the shallow marine architecture knowledge store smaks is a relational database devised for the storage of hard and soft data on the sedimentary architecture of ancient shallow marine and paralic siliciclastic successions and on the geomorphological organization of corresponding modern environments the database allows incorporation of data from the published literature which are uploaded to a common standard to ensure consistency in data definition the database incorporates data on geological entities of varied nature and scale i e surfaces depositional tracts architectural elements sequence stratigraphic units facies units geomorphic elements including attributes that characterize their type geometry spatial relations hierarchical relations and temporal significance furthermore geological entities are assigned to depositional systems or to parts thereof that can be classified on multiple parameters e g shelf width delta catchment area tied to metadata e g data types data sources the smaks permits the quantitative characterization of modern and ancient shallow marine and paralic clastic depositional systems it aims to serve as a repository of analogue information for hydrocarbon bearing successions and as a research tool that can be applied to aid the development of facies models or to assess the sensitivity of depositional systems to particular controlling factors for example to demonstrate the wide applicability of the database in fields of both fundamental and applied research example database output is presented that i includes data from wave tide and fluvial dominated shallow seas and sedimentary successions and ii covers a wide depositional spectrum from backshore to shelf edge settings the examples include information on the facies organization of different types of paralic sub environments on the hierarchical arrangement of architectural elements that form deltaic constructional units in quaternary deltas on the morphometry of modern and quaternary tidal sand ridges and on the geometry of parasequence scale nearshore sandstone belts from the upper cretaceous of the western interior seaway in utah usa

ice sheet extension to the celtic sea shelf edge at the last glacial maximum previous reconstructions of the british irish ice sheet biis envisage ice streaming from the irish sea to the celtic sea at the last glacial maximum to a limit on the mid shelf of the irish uk sectors we present evidence from sediment cores and geophysical profiles that the biis extended 150 km farther seaward to reach the continental shelf edge three cores recently acquired from the flank of outer cockburn bank a shelf crossing sediment ridge terminated in an eroded glacigenic layer including two facies overconsolidated stratified diamicts and finely bedded muddy sand containing micro and macrofossil species of cold water affinities we interpret these facies to result from subglacial deformation and glacimarine deposition from turbid meltwater plumes a date of 24 265 195 cal bp on a chipped but unabraded mollusc valve in the glacimarine sediments indicates withdrawal of a tidewater ice sheet margin from the shelf edge by this time consistent with evidence from deep sea cores for ice rafted debris peaks of celtic sea provenance between 25 5 and 23 4 ka bp together with terrestrial evidence this supports rapid ca 2 ka purging of the biis by an ice stream that advanced from the irish sea to the shelf edge and collapsed back during heinrich event 2

quaternary glacial chronology of the ateaoyinake river valley tianshan mountains china abstract the ateaoyinake river originates on the southern slope of the tumur peak the largest center of modern glaciation in the central tianshan mountains in china six sets of moraines and associated glacial sediments are well preserved in the ateaoyinake river drainage recording a complex history of quaternary glacial cycles and landscape evolution dating the landforms allow the temporal and spatial shifts of past cryosphere and climate to be determined dating of the tills and outwashes was undertaken with electron spin resonance esr and optically stimulated luminescence osl two osl ages date outwash and till to 7 3 0 8 ka and 12 3 1 2 ka respectively the esr ages date six sets of moraines to 3 4 ka 14 27 ka 40 54 ka 55 62 ka 134 4 12 6 ka and 219 7 20 5 ka 440 6 41 7 ka if these are correct ages of deposition they suggest that glaciers advanced during the neoglacial and during marine oxygen isotope stages mis 2 3b 4 6 and 12 the mis 3b moraine was created by a glacier nearly as large as or possibly larger than those of the global last glacial maximum of mis 2 the oldest till belongs to the qingshantou glacial stage its single age is consistent with two published esr ages 459 7 46 and 471 1 ka from the gaowangfeng till near the headwaters of the urumqi river in the eastern tianshan mountains these dates suggest that the central and the eastern segments of the tianshan mountains were high enough to be glaciated by mis 12 the geochronology of the glacial landforms in this valley is the first step towards understanding glacial and landscape evolution in this region furthermore this geochronology and previously published geochronology near the headwaters of the urumqi river provide a temporal framework for examining the rates of landscape evolution in the glaciated regions of the tianshan mountains

changes in wave climate over the northwest european shelf seas during the last 12 000 years 1 because of the depth attenuation of wave orbital velocity wave induced bed shear stress is much more sensitive to changes in total water depth than tidal induced bed shear stress the ratio between wave and tidal induced bed shear stress in many shelf sea regions has varied considerably over the recent geological past because of combined eustatic changes in sea level and isostatic adjustment in order to capture the high frequency nature of wind events a two dimensional spectral wave model is here applied at high temporal resolution to time slices from 12 ka bp to present using paleobathymetries of the nw european shelf seas by contrasting paleowave climates and bed shear stress distributions with present day conditions the model results demonstrate that in regions of the shelf seas that remained wet continuously over the last 12 000 years annual root mean square rms and peak wave heights increased from 12 ka bp to present this increase in wave height was accompanied by a large reduction in the annual rms wave induced bed shear stress primarily caused by a reduction in the magnitude of wave orbital velocity penetrating to the bed for increasing relative sea level in regions of the shelf seas which remained wet over the last 12 000 years the annual mean ratio of wave to m2 tidal induced bed shear stress decreased from 1 at 12 ka bp to its present day value of 0 5 therefore compared to present day conditions waves had a more important contribution to large scale sediment transport processes in the celtic sea and the northwestern north sea at 12 ka bp

landscape analysis of the huang he headwaters ne tibetan plateau patterns of glacial and fluvial erosion the large scale geomorphology of the huang he yellow river headwaters centered around the bayan har shan 5267 m asl in the northeastern part of the tibetan plateau is dominated by an uplifted

late devensian and holocene shorelines of the british isles and north sea from models of glacio hydro isostatic rebound sea level change around the british isles since the time of the last glacial maximum is largely due to of the crustal rebound from the glacial unloading of northern britain and the concomitant melt water loading of the adjacent seas and atlantic ocean minor but not insignificant contributions also result from the rebound caused by the unloading of the distant ice sheets including fennoscandia and north america observations of sea level change for this period constrain the glacio hydro isostatic rebound model parameters describing the effective lithospheric thickness or rigidity and the effective mantle viscosity as well as certain ice sheet characteristics such as the ice thickness at the time of the last glacial maximum the models permit palaeobathymetry and palaeoshorelines to be predicted for the british isles region including the north sea the resulting evolution of the coastlines exhibits a complex behaviour through time one that is quite different from the usual models in which sea level change is assumed to be a function of time only in part this is because of the delayed response of the mantle to the spatially variable and time dependent ice and water loads and in part because the unloading history of the british ice sheet is different from those of the major global ice sheets thus maximum emergence of the north sea occurred after deglaciation had started and lasted for an extended period from about 15 000 to 12 000 radiocarbon years bp during this relative sea level still stand shoreline features could have formed for example along the western edge of the norwegian trough when access to the firths of eastern scotland would have been via a long and shallow marine inlet shoreline retreat across the north sea became relatively rapid after about 10000 years the model predictions for the irish and celtic seas also suggest a complex behaviour with the formation of a wide land bridge between about 20000 and 13 000 years ago the model also suggests that as long as the scottish ice extended across the northern irish sea until about 14 000 years ago there would have been a large freshwater periglacial lake located further south both the predicted sea level height age relations and the shoreline positions are consistent with a large body of observational evidence but some discrepancies occur particularly in northern scotland and ireland where the ice heights may have been somewhat greater than assumed in the model

classifying seabed sediment type using simulated tidal induced bed shear stress abstract an ability to estimate the large scale spatial variability of seabed sediment type in the absence of extensive observational data is valuable for many applications in some physical e g morphodynamic models knowledge of seabed sediment type is important for inputting spatially varying bed roughness and in biological studies an ability to estimate the distribution of seabed sediment benefits habitat mapping e g scallop dredging although shelf sea sediment motion is complex driven by a combination of tidal currents waves and wind driven currents in many tidally energetic seas such as the irish sea long term seabed sediment transport is dominated by tidal currents we compare observations of seabed sediment grain size from 242 irish sea seabed samples with simulated tidal induced bed shear stress from a three dimensional tidal model roms to quantitatively define the relationship between observed grain size and simulated bed shear stress with focus on the median grain size of well sorted seabed sediment samples we present predictive maps of the distribution of seabed sediment classes in the irish sea ranging from mud to gravel when compared with the distribution of well sorted sediment classifications mud sand and gravel from the british geological survey digital seabed sediment map of irish sea sediments digsbs250 this grain size tidal current proxy gstcp correctly estimates the observed seabed sediment classification in over 73 of the area

catastrophic flooding origin of shelf valley systems in the english channel britain became geographically isolated from continental europe when high interglacial seas flooded the shallow english channel and north sea shelf areas but a tenuous link remained the weald artois chalk ridge between southeast england and northwest france just how this isthmus was breached making britain an island has been a matter of conjecture a new bathymetric map of the sea floor may solve the mystery it reveals a large bedrock floored valley containing landforms including grooves and streamlined islands consistent with a megaflood event caused when a rock dam at the dover strait breached draining a large pro glacial lake in the north sea basin a hypothesis for the permanent isolation of britain from mainland europe during interglacial high sea levels has been confirmed gupta et al analysed a new regional bathymetric map of part of the area finding a valley with landforms indicating large scale subaerial erosion by high magnitude water discharges they suggest breaching of a rock dam at the dover strait instigated drainage of a large lake in the north sea basin megaflood events involving sudden discharges of exceptionally large volumes of water are rare but can significantly affect landscape evolution continental scale drainage patterns and climate change1 it has been proposed that a significant flood event eroded a network of large ancient valleys on the floor of the english channel the narrow seaway between england and france2 3 4 this hypothesis has remained untested through lack of direct evidence and alternative non catastrophist ideas have been entertained for valley formation5 6 here we analyse a new regional bathymetric map of part of the english channel derived from high resolution sonar data which shows the morphology of the valley in unprecedented detail we observe a large bedrock floored valley that contains a distinct assemblage of landforms including streamlined islands and longitudinal erosional grooves which are indicative of large scale subaerial erosion by high magnitude water discharges our observations support the megaflood model in which breaching of a rock dam at the dover strait instigated catastrophic drainage of a large pro glacial lake in the southern north sea basin2 we suggest that megaflooding provides an explanation for the permanent isolation of britain from mainland europe during interglacial high sea level stands7 and consequently for patterns of early human colonisation of britain together with the large scale reorganization of palaeodrainage in northwest europe4

effect of sea level rise and tidal current variation on the long term evolution of offshore tidal sand ridges abstract tidal sand ridges are large scale bedforms that occur in the offshore area of shelf seas they evolve on a time scale of centuries due to tide topography interactions while being further shaped by wind waves during their evolution ridges are also affected by changes in sea level strength and direction of the tidal current according to their present day behavior ridges are classified as active sand transport everywhere quasi active sand transport only on parts of the ridges and inactive no sand transport anywhere using a nonlinear morphodynamic model the present study extends earlier work by investigating the effect of sea level rise and changes in the amplitude and principal direction of the tidal current on the growth time and height of active tidal sand ridges besides the role of sea level rise and tidal current variation in the presence of quasi active inactive ridges is explored two specific settings are considered which are characteristic for the dutch banks in the north sea and for sand ridges in the celtic sea the time range considered here is less than 20 000 years roughly the period from the last glacial maximum to the present generally active tidal sand ridges occur if the tidal current amplitude is larger than 0 5 m s for these ridges with increasing rates of sea level rise their growth time becomes longer and the root mean square height keeps on increasing a smaller initial tidal current amplitude gives rise to a larger growth time while changes in the principal current direction have a minor effect on the characteristics of the ridges on the considered time scale assuming a constant wave climate quasi active tidal sand ridges occur mainly as a result of a decreasing tidal current amplitude such that the effective velocity in the sense of stirring sand becomes smaller than the critical velocity for sand erosion the ridges further become inactive on a time scale that depends inversely on the rate of sea level rise modeled ridges are compared with observed ridges similarities are found and quantitative differences are explained

the origin of heinrich layers evidence from h2 for european precursor events recent well dated isotopic sr nd fingerprinting of heinrich layer ice rafted detritus ird on the european margin indicates supply from european ice sheets as precursors to laurentide ice sheet lis supply f e grousset et al geology 28 2000 123 126 h snoeckx et al mar geol 158 1999 197 208 these precursorevents lead lis input by up to 1 5 ka f e grousset et al geology 28 2000 123 126 and have been interpreted to indicate lis collapse during heinrichevents stimulated by events originating on the european side of the atlantic f e grousset et al geology 28 2000 123 126 such phasing of ird supply from different sources within heinrich layers therefore has implications for the origin and mechanics of heinrichevents we present evidence here that the ird comprising heinrich layer 2 h2 20 21 14c ka bp on the european continental margin contains detrital campanian upper chalk deriving from bedrock sources eroded on the celtic shelf by the british ice sheet bis in addition to lithic material sourced from the lis high resolution radiocarbon chronology indicates chalk grain deposition as discrete pulses both before and coincident with supply of lis sourced detritus the specificity of the chalk fingerprint to the bis enables a 700 1000 yr lag between the bis and lis events to be identified this phasing indicates a more rapid response of the outlet lobes draining the smaller bis than those draining the lis and implicates external climatic forcing of heinrichevents it is unlikely that this precursorevent represents ird event 18 the recently identified 1 2 ka ird cycle event which immediately precedes h2 because the lag between precursor and main event is here less than 1 5 ka and because such pervasive periodicity is not apparent in european continental margin ird records the later synchroneity between the bis and lis input in h2 identifies glacio eustatic sea level rise associated with lis discharges as a possible feedback mechanism causing destabilisation of ice streams elsewhere during heinrichevents

relative dating of quaternary moraines rongbuk valley mount everest tibet implications for an ice sheet on the tibetan plateau abstract relative dating studies applied to high altitude moraines 5000 5500 m in the rongbuk valley on the northern flank of mt everest reveal strong contrasts in the weathering characteristics of the boulders exposed along moraine crests these differences serve to define three intervals of major pleistocene glaciation that on the basis of the degree of weathering are interpreted to extend back to at least the penultimate glaciation and probably encompass at least one still older glaciation either interpretation indicates that some of these moraines are considerably older than their previously assigned ages the magnitude of equilibrium line lowering during neoglacial and late pleistocene times is calculated to be ca 50 100 and 350 450 m respectively the data described here are incompatible with the recently proposed model kuhle 1987 for large scale ice sheet development on the tibetan plateau the reconstructed equilibrium line lowering in the everest region is only 30 of that cited in the ice sheet model moreover the flow patterns and geometry of the former rongbuk glaciers are in opposition to those proposed by the model based on the data from the everest region it appears that valley glaciation rather than ice sheet growth characterized the southern margin of the tibetan plateau during the middle and late pleistocene glaciations

the quaternary history of the central and southwestern celtic sea abstract the british sector of the celtic sea south of the isles of scilly has recently been investigated by the institute of geological sciences igs using several types of bottom sampler and several types of acoustic device by this means the bathymetry has been improved a surface sediment chart constructed and the stratigraphy established by comparison of boreholes with seismic sections a great deal of new information has emerged regarding the late pliocene quaternary history of the area the celtic sea shelf is very wide with a low general gradient and a relatively deep shelf edge the inner shelf is topographically almost featureless whereas the middle and outer shelf are diversified by a series of large tidal sand ridges tsr running approximately normal to the shelf edge the late pliocene quaternary sediments in the area consist of two main formations the late pliocene early pleistocene upper part of the little sole formation and the late devensian early flandrian melville formation both formations appear to be composed predominantly of sand with subordinate gravel and a minor proportion of mud the upper little sole probably consists mainly of fluvial deposits accompanied by subordinate shallow marine deposits in its upper part whereas the melville consists essentially of tidal deposits which have been fashioned probably by the huthnance mechanism into the tidal sand ridges later erosion has developed a gravelly lag pavement layer b across the top of the melville formation and across exposures of upper little sole or older formations between the ridges above this comes a layer of mobile sandy sediment layer a never more than a few metres thick but fashioned in most places into bedforms appropriate to the local current regime these include ripples megaripples sand waves and sand ribbons ice rafting has evidently been responsible for depositing 1 occasional small mounds of material revealed by side scan sonar which are found on the sea bed between the tsr 2 scattered boulders which occur in the normally pebbly lag pavement and 3 scattered outcrops of till revealed by sampling some of which may represent mounds massive marine planation has occurred in the celtic sea shelf area prior to the upper little sole following the deposition of that formation and probably many times during the pleistocene depths of deposition of samples from the upper little sole together with similar data from the almost coeval st erth beds on the cornish mainland indicate that the area has been tilted oceanwards subsidence of the outer shelf area is confirmed by the relatively deep shell edge the most likely mechanism for these displacements appears to be the resolution of large scale gravity anomalies in the asthenosphere

quaternary glaciation of the tashkurgan valley southeast pamir the quaternary glacial history of tashkurgan valley in the transition between the pamir and karakoram in xinjiang province china was examined using remote sensing field mapping geomorphic analysis of landforms and sediments and 10be terrestrial cosmogenic nuclide dating moraines were assigned to four glacial stages 1 the dabudaer glacial stage that dates to the penultimate glacial cycle and or earlier and may represent one or more glaciations 2 the tashkurgan glacial stage that dates to early last glacial most likely marine oxygen isotope stage mis 4 3 the hangdi glacial stage that dates to mis 2 possibly early mis 2 and 4 the kuzigun glacial stage that dates to the mis 2 possibly the global last glacial maximum and is younger than the hangdi glacial stage younger moraines and rock glaciers are present at the heads of tributary valleys but these were inaccessible because they are located close to politically sensitive borders with pakistan afghanistan and tajikistan glaciers during the dabudaer glacial stage advanced into the central part of the tashkurgan valley during the tashkurgan glacial stages glaciers advanced several kilometers beyond the mouths of the tributary valleys into the tashkurgan valley glaciers during the hangdi and kuzigun glacial stages advanced just beyond the mouths of the tributary valleys glaciation in this part of the himalayan tibetan orogen is likely strongly controlled by northern hemisphere climate oscillations although a monsoonal influence on glaciation cannot be ruled out entirely

reconstruction of the 2 4 million km2 late pleistocene ice sheet on the tibetan plateau and its impact on the global climate during 20 expeditions new data were obtained on the maximum extent of glaciation in tibet and the surrounding mountains evidence was found of moraines at altitudes as low as 460 m on the southern flank of the himalayas and 2300 m on the northern slope of the tibetan plateau in the qilian shan on the northern slopes of the karakorum aghil and kuen lun moraines occurred as far down as 1900 m in southern tibet radiographic analyses of erratics document former ice thicknesses of at least 1200 m glacial polishing and knobs in the himalayas and karakorum are proof of glaciers as thick as 1200 2000 m on the basis of this evidence a 1100 1600 m lower equilibrium ela line was reconstructed for the ice age which would mean 2 2 4 million km2 of ice covering almost all of tibet since the equilibrium ela line was far below the average altitude of tibet on mount everest and k2 radiation was measured up to 6650 m yielding values of 1200 1300 w m2 because of the subtropical latitude and the high altitude solar radiation in tibet is 3 4 times greater than the energy intercepted between 60 and 70 n or s with an area of 2 2 4 million km2 and an albedo of 90 the tibetan ice sheet caused the same heat loss on the earth as a 6 9 6 million km2 sized ice sheet at 60 70 n because of its proximity to the present day equilibrium ela line tibet must have undergone large scale glaciation earlier than other areas being subject to intensive radiation the tibetan ice must have performed an amplifying function during the onset of the ice age

timing and style of late quaternary glaciation in northeastern tibet glacial successions in the anyemaqen and nianbaoyeze mountains of northeastern tibet are reassessed and new glacial chronologies are presented for these regions cosmogenic radionuclide and optically stimulated luminescence dating indicates that two glacial advances occurred in marine isotope stage mis 3 and mis 2 in the anyemaqen mountains a third advance occurred in the early holocene we suggest that glaciation was synchronous in the anyemaqen and nianbaoyeze mountains as well as in other glaciated areas of tibet and the himalaya that are influenced by the asian monsoon the maximum extent of glaciation occurred early in the last glacial cycle mis 3 during a time of increased insolation when the monsoon intensified and supplied abundant precipitation as snow at high altitude to feed high altitude glaciers this suggests that precipitation as snow is fundamental in controlling glaciation in these regions however the occurrence of glacial advances during the insolation minimum of mis 2 suggests that despite reduced precipitation at this time the annual temperatures were cold enough to maintain positive glacier mass balances the numerically defined chronologies for the anyemaqen and nianbaoyeze mountains presented here provide a framework for comparing glacial advances in other parts of high asia

late quaternary architecture of trough mouth fans debris flows and suspended sediments on the norwegian margin abstract trough mouth fans are the main marine depocentres for glacier derived sediments in the polar north atlantic but their growth through the late quaternary is complex glacigenic debris flows gdfs are sourced from a common and homogeneous part of the upper fan and only develop as coherent individual flows after downslope transport their genesis and mode of deposition mean that gdfs are confined to particular areas of trough mouth fans accumulation of these subglacial sediments is controlled by a combination of margin glaciology and fan morphology although most of the fan sediment is deposited as gdfs during glacials considerable areas of trough mouth fans are dominated by sedimentation of suspension deposits associated with extensive meltwater release from a warm based ice sheet and probable contour current activity the depositional sequence of these two sediment types may be important in generating the long run out distances of gdfs which are initiated and sustained over low gradients furthermore emplacement of gdfs is interpreted to be a relatively low frequency event and temporally at least fans are not dominated by this mode of sediment emplacement whilst ice sheets are at the shelf break large scale trough mouth fan development is therefore asynchronous and non uniform a result of the interaction between glaciology morphology and oceanography

glacimarine slope sedimentation contourite drifts and bottom current pathways on the barra fan uk north atlantic margin the sedimentary record of a 30 m core md95 2006 from the barra fan in the eastern rockall trough has been correlated with high resolution seismic profiles obtained across sediment drifts and large mass flow deposits a series of sediment drifts featuring upslope migrating wavy bedforms has been identified with deposition focussed along topographic steps created by glacigenic debrite lobes the most extensive drift accumulation termed the barra fan drift is observed on the distal fringe of the fan where an 80 m thick sequence of aggrading to migrating sediment waves onlap a mega debrite scarp prior to 26 ka 14c yr and during the late glacial to holocene transition silty muddy contourites were deposited by the northward flowing deep northern boundary current between 26 and 18 ka and around 14 ka contourite deposition was replaced by distal glacimarine sedimentation featuring thin bedded sandy turbidites that were triggered during shelf edge advances of the british ice sheet during the last glacial period sediments accumulated at rates of more than 40 cm ka as a consequence of the high flux of sediments from the shelf margin and winnowing of exposed mass flow deposits by along slope currents in contrast the holocene is represented by a condensed interval of silty sandy mud due to vigorous bottom circulation and a low terrigenous sediment supply seismic seafloor signatures suggest that the present morphology of the barra fan is shaped by two pathways of bottom currents probably both related to the deep northern boundary current one branch of this water mass follows the lower slope causing pronounced erosion on the distal part of the barra fan drift while the other is directed across the debrite topography of the fan bulge

celtic sea linear tidal sand ridges the irish sea ice stream and the fleuve manche palaeotidal modelling of a transitional passive margin depositional system abstract the linear tidal sand ridges ltsr of the celtic sea constitute the largest examples of their bedform type on earth previous sedimentological and seismic stratigraphic interpretation suggests that the ltsr are moribund tidally remobilised sediments representing the transgressive systems tract this interpretation is supported by two dimensional finite difference model reconstructions of the m 2 tide forced using the output from a glacial isostatic adjustment model to derive palaeotopography and a global ocean model to derive the tides on the ocean boundary used here to reconstruct peak bed stress vectors for the celtic sea for timesteps covering the transgression since the last glacial maximum last 21 ka these data are coupled with interpretation of recent published observations on the outer shelf depocentres of the fleuve manche and the irish sea ice stream isis to confirm that the ltsr distribution is consistent with modelled sand transport paths during transgression the main phase of ltsr growth was between 20 cal ka and 12 cal ka ridge axis orientations reflect the final phase of ltsr construction around 12 cal ka with some later growth of the most southerly ltsr as late as 10 cal ka ltsr growth was from the sw across the shelf towards the ne strong tidal pumping of sediments into slope canyon heads on the outer shelf occurred between 20 cal ka and 12 cal ka contributing to turbidite activity and the growth of the celtic and armorican deep sea fans it is proposed that 1 the fleuve manche shelfal estuary delta and the irish sea ice stream isis shelf fan were the main sediment depocentres supplying the growing ltsr 2 the lack of sediments available in the western channel limited ltsr growth in this area and that the easterly termination of the ltsr in this sector results from sediment starvation and 3 the northeasterly termination in the celtic sea sector is a function of declining peak bed stresses rather than sediment starvation the celtic sea margin represents a passive margin depositional system transitional between true glacial ice stream trough mouth fan systems to the north and the fluvial canyon systems characteristic of the margin to the south this interpretation therefore complements studies of macroscale sedimentation linked to glaciation on the continental margins of the north atlantic

summer temperature reconstruction on the central tibetan plateau during 1860 2002 derived from annually resolved ice core pollen 1 we present a 140 year ice core pollen record with annual time resolution from the puruogangri ice field in the central tibetan plateau a linear regression model between the sum of the steppe and meadow pollen taxa and summer temperature at naqu accounts for 66 of the summer temperature variance for the period 1955 2002 on the basis of this model we reconstructed summer temperature history for the central tibetan plateau from 1860 to 2002 three marked warm periods during the 1870s 1890s and 1990s and five cold periods during the 1860s 1880s 1900s 1950s and 1960 1970s were identified within the last 100 years late 20th century warming is distinctive and may have had a major role in the present retreat of most glaciers on the tibetan plateau the pollen record is also significantly correlated with average annual temperatures over the whole tibetan plateau suggesting that these proxy data have the potential for reflecting large scale regional temperature change the statistically significant similarity between the puruogangri ice core pollen record and the 18o time series indicates that both are reliable indicators of temperature change at annual to multiyear timescales in this region

extent and timing of the last glacial maximum lgm in britain and ireland a review the last glacial maximum lgm of marine isotope stage mis 2 is defined here as the period either of maximum global ice volume or in which major ice sheets reached their maximum extent both definitions lack clarity as there is no reason to suppose that maximum volumes or limits were reached simultaneously at either all ice sheets or around the margins of individual ice sheets here we review the traditional terrestrial limits of the biis british irish ice sheet examine developments in understanding the offshore record and attempt a redefinition of the extent and timing of the mis 2 maximum as a working chronological model the build up of the biis is assigned to after 35 32 ka the maximum to the period 27 21 ka and a more limited readvance after 19 ka as marginal oscillations driven by ice sheet dynamics appear to have characterised much of the advance and especially the retreat of the biis caution should be exercised in assigning climatic significance to the many identified ice limits or still stands while much of the terrestrial limit in britain remains relatively unaltered significant revision is required offshore around britain and ireland to portray an extensive ice advance to the shelf edge and a period when the biis was conjoined with the adjacent fenno scandinavian ice sheet although there appears to be a broad synchrony between the biis and other major ice sheets local controls have produced some variation in the timing of advance to and retreat from maximum limits for particular ice streams or lobes but much of the offshore limit remains very poorly age constrained consequently a key objective in future research should be to improve and refine the chronological control for all portions of the maximum margin of the biis and its subsequent retreat stages copyright 2010 john wiley sons ltd

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

geomorphological signature and flow dynamics of the minch palaeo ice stream northwest scotland large scale streamlined glacial landforms are identified in 11 areas of northwest scotland from the isle of skye in the south to the butt of lewis in the north these ice directional features occur in bedrock and superficial deposits generally below 350 m above sea level and where best developed have elongation ratios of 20 1 sidescan sonar and multibeam echo sounding data from the minch show elongate streamlined ridges and grooves on the seabed with elongation ratios of up to 70 1 these bedforms are interpreted as mega scale glacial lineations all the features identified formed beneath the minch palaeo ice stream which was ca 200 km long up to 50 km wide and drained ca 15 000 km2 of the northwest sector of the last british irish ice sheet late devensian glaciation nine ice stream tributaries and palaeo onset zones are also identified on the basis of geomorphological evidence the spatial distribution and pattern of streamlined bedforms around the minch has enabled the catchment flow paths and basal shear stresses of the palaeo ice stream and its tributaries to be tentatively reconstructed british geological survey natural environment research council copyright 2007 reproduced with the permission of bgs nerc published by john wiley sons ltd

radiocarbon constraints on the age of the maximum advance of the british irish ice sheet in the celtic sea reconstructions of the british irish ice sheet biis during the last glacial maximum lgm in the celtic sea and southern ireland have been hampered by a paucity of well dated stratigraphic records as a result the timing of the last advance of the largest outlet of the biis the irish sea ice stream to its maximum limit in the celtic sea has been variously proposed as being pre last glaciation early devensian and lgm the irish sea till was deposited by the irish sea ice stream during its last advance into the celtic sea we present 26 stratigraphically well constrained new ams radiocarbon dates on glacially transported marine shells from the irish sea till in southern ireland which constrain the maximum age of this advance the youngest of these dates indicate that the biis advanced to its overall maximum limit in the celtic sea after 26 000 20 000 14c yr bp thus during the last glaciation the most extensive phase of biis growth therefore appears to have occurred during the lgm at least along the celtic sea and irish margins these data further demonstrate that the uppermost inland glacial tills from the area of supposed older drift in southern ireland a region previously regarded as having been unglaciated during the lgm also date from the last glaciation thus most of southern ireland was ice covered at the lgm advance of the biis to its maximum southern limit in the celtic sea may have been a short lived glaciodynamic response facilitated by subglacial bed conditions rather than a steady state response to climate forcing alone

glacier mass loss induced the rapid growth of linggo co on the central tibetan plateau remote sensing and gis techniques in conjunction with field investigations show how glacier mass loss has led to the rapid growth of linggo co a glacier fed lake on the central tibetan plateau which has expanded by 21 3 in area between 1974 and 2010 with a lake level rise of 11 2 m the lake volume of linggo co increased at a rate of 0 02 10 6 42 67 10 6 and 65 8 10 6 m 3 a 1 during the periods 1974 92 1992 99 and 1999 2010 respectively other non glacier fed lakes in the vicinity i e longwei co amur co and darngo co ngion shrank considerably from the early 1970s to 1992 and then expanded from 1992 to 2010 despite being in the same climate region linggo co and the non glacier fed lakes have differed in response to climate change the glaciers in the catchment of linggo co retreated by 2 4 in area between 1974 and 2007 and their mean thickness decreased by 6 19 1 91 m between 1974 and 2000 with an associated glacier meltwater runoff of 7 52 2 32 10 8 m 3 the results indicate that glacier mass loss had a significant impact on the growth of linggo co over the past 40 years

tide induced bedload transport pathways in a multiple sand ridge system offshore of hainan island in the beibu gulf northwest south china sea modern sand transport pathways in a multiple sand ridge system are elusive and have rarely been studied in recent years we report herein a field with four en echelon linear sand ridges offshore of hainan island in the beibu gulf and describe the distribution and morphology of these sand ridges in detail for the first time dune crest comparisons and seismic profiles are also interpreted to assess sand transport over the dunes based on a delft 3d model regional tidal currents and tide induced bedload transport in the multiple sand ridge system were simulated to provide insights into the related bedload transport paths the results show that bedload transport and residual flows are mostly directed to the south on the east side of the sand ridges and to the north on the west side and these differences coincide with dune asymmetries and migrations cross ridge transport is weak and mostly converges on the crests of sand ridges from the two flanks the bedload transport is unbalanced on either flank of the sand ridges thus leading to the asymmetry and crest kinks of the sand ridges a distinct correlation is not observed between the net cross ridge sand transport and sand ridge asymmetry in this system cross swale transport is significant between the neighboring sand ridges and helps construct the bedload transport circulation in the swales sand accretion also occurs in the swales and benefits from the southwestward bedload transport from the north end of sand ridge 3 distinct evidence has not been found for closed bedload transport circulation around sand ridges in this multiple sand ridge system although limited clockwise current vortices develop on several sand ridges additional field observations and simulations are required to characterize the suspended load transport in a multiple sand ridge system and the effects of local sand supply conditions on sand transport also need further evaluation copyright c 2018 john wiley sons ltd

cosmogenic radionuclide evidence for the limited extent of last glacial maximum glaciers in the tanggula shan of the central tibetan plateau abstract cosmogenic radionuclide crn exposure ages provide evidence for the limited extent of last glacial maximum glaciers in the tanggula shan central tibetan plateau the most extensive advances occurred during or before marine oxygen isotope stage 6 mis 6 based on previous crn exposure ages the second most extensive advance occurred during or before mis 4 based on previous ages and new ages of 41 400 4300 and 66 800 7100 10 be yr a mis 2 advance of less than 3 km occurred between 31 900 3400 and 16 000 1700 10 be yr

low sea level tidal origin of celtic sea sand banks evidence from numerical modelling of m2 tidal streams abstract numerical modelling of m 2 tidal streams in the celtic sea with a sea level lowered by 100 m indicates tidal currents about twice as strong as those at present such currents would have been sufficient to generate and maintain the linear tidal sand banks now found in that region as moribund bedforms furthermore an indicated clockwise rotation of the major axes of the tidal ellipses at a sea level lowered by 100 m with respect to the present day is in the correct sense to further the comparison with modern examples of actively maintained linear tidal sand banks

quaternary glaciation of tibet the geological evidence the question of the number and extent of pleistocene glaciations on the qinghai xizang tibet plateau remains contentious there has been considerable research activity in tibet by chinese scientists since the late 1950s and their principal findings including data on glacial and periglacial geomorphology sedimentology tectonics stratigraphy and lake history have been used to reconstruct ice margins and palaeosnowlines three and in places four distinct glaciations have been recognised the most extensive occurring in the later middle pleistocene valley and piedmont glacial systems with some mountain ice caps and a small ice sheet on the upper reaches of the huang he have been recognised but there is no evidence of a single tibetan ice sheet as the plateau and the himalaya karakoram underwent accelerating uplift through the quaternary there occurred progressive desiccation in the interior as the influx of indian ocean moisture was constrained equilibrium line elevations in the last glacial maximum were 4000 m in the south east and northeast plateau margins rising to 5500 m in the northwest interior the heat island provided by the plateau the progressive reduction in precipitation most marked during the glacials and the strong southeast to northwest precipitation gradients produced a glacier distribution pattern dominated by the trans tibetan mountain ranges tectonics and periglacial including aeolian processes have played an equal role with glaciation in generating the plateau s quaternary sedimentary succession

formation of proglacial dunes in front of the puruogangri icefield in the central qinghai tibet plateau implications for reconstructing paleoenvironmental changes since the lateglacial there are sand dunes and stony desert surfaces gobi on the piedmont along the western side of the puruogangri icefield in central qinghai tibet plateau the dunes formed on the gobi probably after 16 ka their sediment derived from the underling till deflated by mid latitude westerly winds and the qiangtang high pressure system the gobi contains granitic moraine boulders ventifacts of limestone and secondary caco3 precipitates at subsurface occasional humus layers are present within the sand dunes a total of 13 humus layers were collected for radiocarbon dating and 20 samples for particle size analysis the dune particle size distribution is generally negatively skewed the radiocarbon ages range from 12 709 to 922 calendar years bp it is likely that the humus layers correspond to warm times and can be correlated to the results from oxygen isotopic data in the ice cores from guliya in the western kunlun mountains and dunde in the qilian mountains these results initially provide an outline of lateglacial climate history for the ice field area

quaternary glaciation of puruogangri the largest modern ice field in tibet abstract the puruogangri the largest modern ice field in the tibetan plateau with an area of over 400 km2 in total is in the inner plateau although it is very difficult to reach the scale of the ice field makes it important to study the quaternary glaciation in this inland area to determine whether there was a unified ice sheet in the tibetan plateau during the quaternary field observation showed that five moraine groups termed moraine i v of terminal moraines and lateral moraines are present located from the snouts of modern glaciers to the piedmont based on geomorphic locations stratigraphic correlation relative weathering reworked degrees by wind action and the esr ages of the sands covering the gobi with erratics as well as through comparison with the quaternary glaciations with numerical ages in western chinese mountains these moraine groups represent the modern moraine the little ice age neoglacial the late stage of the last glaciation and the early stage of the last glaciation respectively the granite boulders of moraine v are scattered for 6 km from the mountain front on an extensive peneplain this suggests that the ancient glaciers in the west slope of the ice field advanced to the piedmont during the late pleistocene but did not integrate with the ice in the mountains nearby to form a unified ice sheet

activity of the turbidite levees of the celtic armorican margin bay of biscay during the last 30 000 years imprints of the last european deglaciation and heinrich events abstract high resolution sedimentological and micropaleontological studies of several deep sea cores retrieved from the levees of the celtic and armorican turbidite systems bay of biscay north atlantic ocean allow the detection of the major oscillations of the british irish ice sheet biis and fleuve manche palaeoriver discharges over the last 30 000 years which were mainly triggered by climate changes between 30 and 20 cal ka the turbiditic activity on the celtic armorican margin was weak contrasting with previous stratigraphic models which predicted a substantial increase of sediment supply during low sea level stands this low turbidite deposit frequency was most likely the result of a weak activity of the fleuve manche palaeoriver and or of a reduced seaward transfer of sediments from the shelf to the margin however two episodes of turbiditic activity increase were detected in the celtic armorican margin during heinrich events he 3 and 2 this strengthening of the turbiditic activity was triggered by the meltwater releases from european ice sheets and glaciers favouring the seaward transfer of subglacial material at least via fleuve manche palaeoriver at around 20 cal ka a significant increase of turbidite deposit frequency occurred as a response to the onset of the last deglaciation the retreat of the european ice sheets and glaciers induced a substantial increase of the fleuve manche palaeoriver discharges and seaward transfer of continentally derived material into the armorican turbidite system the intensification of the turbiditic activity on the celtic system was directly sustained by the widespread transport of subglacial sediments from the british irish ice sheet biis to the celtic sea via the irish sea basin a sudden reduction of turbiditic activity in the armorican system between ca 19 and 18 3 cal ka could have been triggered by the first well known abrupt sea level rise meltwater pulse at around 19 cal ka favouring the trapping of sediment in the fleuve manche palaeoriver valleys and the decrease of the seaward transfer of continentally derived material the maximum of turbiditic activity strengthening in the celtic armorican margin between ca 18 3 and 17 cal ka was induced by the decay of european ice sheets and glaciers producing the most extreme episode of the fleuve manche palaeoriver runoff and a great seaward transfer of subglacial material into the bay of biscay between ca 17 5 and 16 cal ka the turbiditic activity significantly decreased in both celtic and armorican turbidite systems in response to a global re advance of glaciers and ice sheets in europe the last episode of ice sheet retreat between ca 16 and 14 cal ka is well expressed in the celtic system by a new increase of the turbiditic activity the major episode of sea level rise at around 14 cal ka meltwater pulse 1a precluding the seaward transfer of sediments induced the end of turbiditic activity in both the celtic and the armorican system although two main phases of global sea level rise seem to have had an effect on the celtic armorican margin this work proposes the biis retreat and associated riverine discharges as the main trigger mechanisms of the turbiditic activity in this region during the last 30 000 years

the minch palaeo ice stream nw sector of the british irish ice sheet geophysical data from the uk continental shelf off nw scotland reveal strongly parallel subglacial bedforms on the sea bed field mapping on the adjacent landmass has identified closely spaced bedrock megagrooves and highly elongate drumlinoid forms all these mega scale glacial lineations probably formed beneath the same fast flowing zone of the last british irish ice sheet the minch palaeo ice stream this ice stream drained the nw sector of the british irish ice sheet during the late devensian glaciation marine isotope stage 2 and terminated near the edge of the continental shelf the size of the adjacent trough mouth sula sgeir fan and the presence of buried mega scale glacial lineations within the quaternary stratigraphic record imply that fast ice sheet flow in the minch has been a feature of several mid to late pleistocene glaciations

latest pleistocene and holocene glacier fluctuations in the himalaya and tibet abstract the timing and extent of latest pleistocene and holocene alpine glacier fluctuations in the himalaya and tibet are poorly defined due to the logistical and political inaccessibility of the region and the general lack of modern studies of the glacial successions nevertheless renewed interest in the region and the aid of newly developing numerical dating techniques have provided new insights into the nature of latest pleistocene and holocene glacier oscillations these studies provide abundant evidence for significant glacial advances throughout the last glacial cycle in most high himalayan and tibetan regions glaciers reached their maximum extent early in the last glacial cycle however true last glacial maximum glacier advances were significantly less extensive notable glacier advances occurred during the lateglacial and the early holocene with minor advances in some regions during the mid holocene there is abundant evidence for multiple glacial advances throughout the latter part of the holocene although these are generally very poorly defined and were less extensive than the early holocene glacier advances the poor chronological control on latest pleistocene and holocene glacial successions makes it difficult to construct correlations across the region and with other glaciated regions in the world which in turn makes it hard to assess the relative importance of the different climatic mechanisms that force glaciation in this region the lateglacial and holocene glacial record however is particularly well preserved in several regions notably in muztag ata and kongur and the khumbu himal these successions have the potential to be examined in detail using newly developing numerical dating methods to derive a high resolution record of glaciation to help in paleoclimatic reconstruction and understanding the dynamics of climate and glaciation in the himalaya and tibet

on the problem of quaternary glaciations and the extent and patterns of pleistocene ice cover in the qinghai xizang tibet plateau abstract data accumulated during investigations since the 1960s indicate that up to four pleistocene glaciations can be recognized in the qinghai xizang tibet plateau and the adjacent himalaya mountains in order of decreasing age these are the xixabangma nyanyaxungla guxiang and baiyu glacial episodes the history of pleistocene glacial evolution in various areas throughout the plateau differs and the pattern is very complex throughout the early pleistocene the elevation of the qinghai xizang plateau was approximately 2000 m above sea level during the xixabangma glacial episode recorded at higher elevations the climate and topographical conditions on the plateau were largely unfavourable for the development of glaciers present investigations have revealed that the oldest till is only found at isolated localities on the plateau glaciofluvial or alluvial deposits such as the gongba conglomerate dating from 2 4 to 0 73 ma bp and the fluvial lacustrine deposits of the qiantang group dating from 2 4 to 1 7 ma bp are present rather than glacial till therefore the postulate of a large early pleistocene ice sheet proposed previously has been disproves during the most recent glaciation uplift of the plateau and the himalayas continued the majority of the qinghai xizang plateau reached 4000 m a s l and the great himalaya were approximately 6000 m a s l the mountains formed a barrier against the incursion of the indian monsoon so that precipitation decreased sharply on the northern flank of the himalayas and the climate to the north became cold and dry all of the glaciers on the qinghai xizang plateau underwent extensive retreat thus during the pleistocene no unified glacial cover existed over the qinghai xizang plateau similarly the source area of the hwang he yellow river did not support a local ice sheet

the first estimation of fleuve manche palaeoriver discharge during the last deglaciation evidence for fennoscandian ice sheet meltwater flow in the english channel ca 20 18 ka ago the fleuve manche english channel palaeoriver represents the largest river system that drained the european continent during pleistocene lowstands particularly during the elsterian marine isotope stage 12 and saalian drenthe mis 6 glaciations when extensive ice advances into the north sea area forced the central european rivers to flow southwards to the bay of biscay ne atlantic numerous long piston cores and high resolution acoustic data from the northern bay of biscay have been correlated using a well constrained chronostratigraphical framework and for the first time allow the estimation of the discharge of the fleuve manche palaeoriver at the end of the last glacial period i e weichselian our results discussed in the light of relationships between river loads and drainage area characteristics strongly suggest that the bay of biscay collected sediment laden meltwater from the northern european lowlands and the southern part of the fennoscandian ice sheet at the end of the last glacial period and particularly during the paroxysmal phase of the european deglaciation ca 20 18 ka ago this demonstrates that the fleuve manche drainage area at that time was equivalent to those dating from the major elsterian and saalian drenthe glaciations based on our data we propose a revision of the palaeogeographical and palaeoglaciological evolution of the north sea area while showing that the british and fennoscandian ice sheets entered the north sea basin until ca 18 ka initiating isostatic adjustment of the basin this allowed the north sea fluvial system to flow southwards through the dover strait finally we discuss the fleuve manche freshwater discharge during the maximum european ice sheet retreat ca 18 ka the estimated discharge at this time appears important and sufficiently sustained to possibly contribute to the profound destabilisation of the thermohaline circulation recognised in the north atlantic from ca 18 to 16 ka

quaternary glacial chronology of the kanas river valley altai mountains china the kanas river originates on the southern slope of youyi peak the largest center of modern glaciation in the altai mountains in central asia glaciers advanced and retreated repeatedly during quaternary glacialeinterglacial cycles in the kanas river valley and four moraine complexes and associated glaciofluvial deposits are preserved in the valley optically stimulated luminescence osl dating has been used to determine ages of glaciofluvial deposits sand lenses sandwiched between tills in moraines using a single aliquot regenerative dose sar protocol based on dating results from this and previous studies including 14 c electron spin resonance esr and osl dates and geomorphic relationships the innermost moraine complex was concluded to deposit during the little ice age lia the second akekule moraine complex was deposited during the neoglacial the third kanas moraine complex was deposited during the last glacial cycle marine oxygen isotope stage mis 2e4 and the outermost set of moraines is mis 6 in ages penultimate glaciation the kanas moraine complex could be divided into three subsets iii1 iii2 and iii3 with inferred ages of mis 2 mid mis 3 and mis 4 respectively which is consistent with moraine records from other areas in central asia and climate reconstructions from the guliya ice core the glaciers in the kanas valley at their maximum extents during the lia neoglacial last glaciation and penultimate glaciation were 13 8 km 32 km w100 km and w120 km long respectively

osl dating of glacier extent during the last glacial and the kanas lake basin formation in kanas river valley altai mountains china the kanas river originates on the southern slope of youyi peak the largest center of modern glaciers in altai mountains china three sets of moraines and associated glacial sediments are well preserved near the kanas lake outlet recording a complex history and landscape evolution during the last glacial dating the moraines allows the temporal and spatial glacier shift and climate during the last glacial to be determined and then constrains when and how the kanas lake basin was formed dating of the glacial tills was undertaken by utilizing the optically stimulated luminescence osl method results date four samples from the three sets of moraines to 28 0 34 4 38 1 and 49 9 ka and one sample from outwash sediment to 6 8 ka the kanas lake basin is a downfaulted basin and was eroded by glacier before 28 0 ka and the glacial moraines blocked the glacier melt water after the glacier retreat which made the present day kanas lake eventually form at least before 6 8 ka bp in altai mountains the glacier advance was more extensive in marine isotope stage mis 3 than mis 2 probably because the mid latitude westerlies shifted northward and or intensified during the mis 3 resulting in a more positive glacier mass balance nevertheless the siberian high dominated the altai mountains in mis 2 resulting in a relative decrease in precipitation

tide and wave dynamics on a sand bank from the deep shelf of the western channel approaches abstract the sedimentary response of deep shelf sediments to the interplay of tides and waves based on the example of the celtic sea sand banks is described grab samples and 1500 km of multibeam and side scan data have been collected from the 300 km2 densely surveyed kaiser bank area the bank is 140 170 m deep 30 m high and 60 km long oriented perpendicular to the shelf edge and nearly parallel to the major axis of the tidal ellipse surficial sediments of the bank consist of medium to gravely biolithoclastic sands they are swept by tidal currents that reach 0 9 m s 1 m above the seabed and under the occasional influence of waves the mobile sands are commonly bedformed and rest on a highly backscattering lag the flanks below 140 m mainly exhibit transverse tidal dunes and sand ribbons whereas the top of the bank mostly displays discontinuous sand patches and wave ripples the sand patches are interpreted as the remnants of tidal bedforms reworked by waves calculations of the threshold of motion of four modal grain sizes under various conditions at the seabed show that tidal bedforms are active during spring tides sometimes associated with waves whereas only the largest annual waves may explain the observed wave ripples as in active tidal banks there is a reversal of tidal bedload transport from one bank side to the other the sedimentation rate is very low on the kaiser bank in addition there is a loss of sediment at both bank extremities and the tidal bedload cross bank transfer is very small probably controlled by shelf residual currents and long term drift of sediment resuspended by waves however the present day action of waves at the bank top is less intense than it was at lower sea levels during the holocene as evidenced by seismic studies

some characteristics of thunderstorms over bathurst and melville islands near darwin australia a study defining the occurrence structure and evolution of maritime continent island thunderstorms over bathurst and melville islands near darwin australia is presented satellite data for the november december pre monsoon transition season show unambiguous records of island thunderstorms on at least 65 of days over the period 1978 1986 storms develop most commonly between 1230lst and 1530lst and radar data indicate a mean lifetime of 2 5 h non occurrence was found on only 7 of the days examined and was associated with a return to dry flow typical of the early transition season with middle level subsidence or suppressed conditions in the wake of previous convective activity environmental sounding data indicated that these maritime continent thunderstorms develop in a regime with moderate cape low to moderate shear and high moisture the dynamic regime is characteristic of multicellular storms examination of the evolution of the storms indicates the existence of a typical lifecycle but with considerable variability in detail initially the lifecycle is consistent with the multicellular storm concept but the developing storms tend to aggregate to form one or more mesoscale systems which in turn may develop into propagating squall lines in the mature stage the developing storms have preferred geographic regions of genesis and intensification over the islands and while motion of the storms is variable it is generally consistent with the mean surface to 700mb pressure weighted flow

influence of climate change on saline lakes of the tibet plateau 1973 2010 abstract levels and surface areas of saline lakes are indicators of climate change and climate variability the surface extents of 93 saline lakes with areas larger than 20 km2 excluding dry saline lakes on the tibet plateau were delineated from landsat images obtained in 1973 1977 1989 1992 1999 2001 and 2008 2010 based on remote sensing spatial analysis techniques and gis the dynamic changes of the saline lake surface areas from 1973 to 2010 were analyzed the total surface area of these saline lakes increased especially since around 2000 and the total surface area increased by 47 during 1973 1977 to 2008 2010 during 1973 1977 to 1989 1992 saline lakes with decreased areas were mainly distributed in the northern and middle parts of the tibet plateau whereas those in other places tended to expand since around 2000 nearly all the saline lakes expanded mean annual temperature mean annual maximum temperature mean annual minimum temperature annual precipitation and evaporation on the tibet plateau were analyzed over the past four decades the climate has become warmer and wetter rising temperature and dropping evaporation are two dominant factors responsible for saline lake expansion the salinity of many saline lakes decreased during this climate warming new analyses included factors responsible for the changes i e tectonics climate lake basin shape glaciers catchments open or closed systems and human activities

the celtic sea banks an example of sand body analysis from very high resolution seismic data very high resolution seismic data from the kaiser i hind sand bank southern celtic sea recently highlighted the internal structure of the enigmatic celtic banks which are among the deepest and largest shelf sand ridges the main body of the bank is made up of 4 seismic depositional units which reflect a transgressive evolution new data on the detailed architecture of two of these units allow discussion of bank growth in terms of either 1 a channel levee system preserved both by lateral migration and aggradation of the channels or 2 a package of large offshore tidal sediment bodies bar chains and or giant dunes careful geometrical observations of seismic discontinuities make the second hypothesis more likely the unit architecture is analysed in terms of long to short term processes of build up long term processes are evinced by the landward stacking of erosive sub units in response of the last post glacial sea level rise whereas short term processes control the seaward progradation of sand bodies and fills due to the ebb predominance of the western channel approaches

ongoing evolution of submarine canyon rockwalls examples from the whittard canyon celtic margin ne atlantic abstract during the codemap 2015 research expedition to the whittard canyon celtic margin ne atlantic a remotely operated vehicle rov gathered high definition video footage of the canyon rockwalls at depths of approximately 412 4184 m below sea level this dataset was supplemented by predominantly carbonate rock samples collected during the dives which were subsequently tested for key physical property characteristics in a geotechnical laboratory the high resolution video footage revealed small scale rockwall slope processes that would not have been visible if shipboard geophysical equipment was solely relied upon during the survey of particular interest was the apparent spalling failure of mudstone and chalk rockwalls with fresh superficial flaking scars and an absence of sessile fauna possibly suggesting relatively recent mass wasting activity extensive talus slopes often consisting of coarse gravel cobble and occasionally boulder sized clasts were observed at the foot of slopes impacted by spalling failures this debris was rarely colonised by biological communities which could be an indicator of frequent rockfall events bio erosion was also noted on many of the walls prone to this form of rock slope failure rsf as in subaerial equivalents internal fracture networks appear to control the prevalence of rsf and the geometries of blocks often resulting in cubic and tabular blocks 0 2 1 0 m scale of bedrock toppling or sliding out of the cliff face tensile strength parameters of carbonate rock samples were determined and these may affect the mass wasting processes observed within the canyon it was found that carbonate samples which appeared to have a higher mud content and reduced porosity produced significantly higher tensile strength values it is proposed that these stronger muddy carbonate units form the overhanging ledges that often provide an ideal setting for sessile species such as acesta excavata clams to colonise whereas the weaker pure carbonate units are more easily eroded and therefore form the undercutting receding sections of the rockwall by combining the rov observations basic discontinuity assessments estimation of fracture orientations and laboratory testing results an understanding of the geomechanical properties of the bedrock can be obtained and linked with past and ongoing rock slope processes within the whittard canyon these conclusions will have a wider implication for ongoing geomechanical processes within submarine canyons on a global scale

widespread complex flow in the interior of the antarctic ice sheet it has been suggested that as much as 90 of the discharge from the antarctic ice sheet is drained through a small number of fast moving ice streams and outlet glaciers fed by relatively stable and inactive catchment areas here evidence obtained from balance velocity estimates suggests that each major drainage basin is fed by complex systems of tributaries that penetrate up to 1000 kilometers from the grounding line into the interior of the ice sheet this finding has important consequences for the modeled or estimated dynamic response time of past and present ice sheets to climate forcing

accelerated glacier mass loss 2011 2016 over the puruogangri ice field in the inner tibetan plateau revealed by bistatic insar measurements abstract the temporal variation of glacier mass balance during recent years remains poorly known for the mountain glaciers in the inner tibetan plateau itp due to the lack of field measurements in this study we retrieved the annual glacier mass balance of the puruogangri ice field which is the largest modern ice mass in the itp by differencing multi temporal digital elevation models dems generated with five pairs of tandem x bistatic interferometric synthetic aperture radar insar images acquired between april 2011 and january 2016 we compared the tandem x dems in january and april 2012 to estimate the x band radar penetration depth difference 0 61 0 06 m which enabled systematic bias correction in the estimation of annual glacier mass balance the observed mass balance reveals a glacier mass gain of 0 44 0 10 m w e yr 1 in 2011 12 which was followed by accelerated glacier mass loss in 2012 16 glacier mass balances of 0 13 0 03 0 34 0 06 and 0 52 0 10 m w e yr 1 were estimated for the periods of 2012 13 2013 14 and 2014 16 respectively this accelerating trend of glacier mass loss is likely caused by the continuous decrease in annual precipitation according to the climate data recorded by adjacent meteorological stations this study demonstrates that repeated bistatic insar measurement is a promising method for monitoring glacier elevation change and mass balance at regular intervals

holocene evolution of seasonal stratification in the celtic sea refined age model mixing depths and foraminiferal stratigraphy published stable isotopic oxygen carbon and preliminary foraminiferal data from a holocene vibrocore from the celtic sea northwest european continental shelf have been interpreted in terms of the progressive replacement of tidally mixed by seasonally stratified water the first study of the long term dynamics of seasonal stratification this study was hampered by poor age control and the foraminiferal data were based on processing with a 125 m sieve which has been shown not to recover critical small taxa we present here a new age model for this vibrocore bgs 51 07 199 based on 12 accelerator mass spectrometry 14c dates on foraminifera and molluscs radionuclide 137cs 40k profiles from the vibrocore and juxtaposed multicores and a complete foraminiferal stratigraphy based on sieving at 63 m together the three datasets enable a mixing model to be proposed which clarifies the resolution of the record which is confirmed as extending from the late glacial to the late holocene correction for autocompaction reveals an increase in sedimentation rate and mixing depth from the early to the late holocene a temporary increase in sedimentation rate at 6650 yr cal bp is attributed to migration of the productive frontal zone across the core site some time after 3000 yr cal bp sedimentation either slowed abruptly or ceased completely giving the modern mixed layer an apparent age of 3000 yr cal bp the mixed layer depth indicates strongly that the apparent transition to stratification during the early holocene is primarily a threshold change attenuated by bioturbation secondary attentuation is related to reworking the mixed layer model adopted suggests that this isotopic transition occured between 8990 and 8440 yr cal bp 8720 2 the foraminiferal analyses in the light of modern foraminiferal distributional data support the inference that the succession can be interpreted as a response to the progressive seasonal stratification of the celtic sea during the holocene the data highlight the value of key taxa as indicators of shelf palaeostratification in the geological record notably of textularia bocki and stainforthia fusiformis as mixed frontal and frontal stratified indicators respectively the critical change to this frontal assemblage occurs at the same depth as the isotopic threshold based on the mixing model these data affirm the earlier interpretation of the isotopic record as registering bottom water temperature and water column productivity changes driven by the evolution of seasonal stratification the clear association between grain size and sedimentation as well as these isotopic and faunal data indicates that the shelf record of highstand sedimentation is preferentially biased towards the preservation of sequences deposited under seasonally stratified rather than mixed water masses

the dangeard and explorer canyons south western approaches uk geology sedimentology and newly discovered cold water coral mini mounds the celtic margin is a complex area in terms of sedimentary dynamics and evolution with a number of submarine canyons dissecting the continental slope and outer continental shelf the complex terrain and diverse range of sea bed sediments play a part in submarine canyons being described as areas of high habitat heterogeneity this study has concentrated on the heads of two canyons dangeard also known as dangaard and explorer first named here located in uk territorial waters in water depths between 138 and 1165 m multibeam echosounder 2d reflection seismic and photographic ground truthing data have been combined to map the sea bed geomorphology sedimentary features and canyon megafauna of these canyons in addition two previously unknown provinces of cold water coral cwc mini mounds were discovered on the interfluves of the dangeard and explorer canyons the study area comprises a dendritic network of gullies feeding into the canyon thalwegs amphitheatre rims where slope angles are commonly in excess of 20 occur along the margins and heads of both canyons and are interpreted as drainage basins indicative of retrogressive mass wasting in a shelfward direction the cwc mini mounds occur in water depths between 250 m and 410 m with more than 400 mounds identified they are up to 3 m in height and 50 150 m in diameter with no sub surface expression suggesting these mounds are in geological terms relatively young and possibly holocene in age biological analyses revealed that the mounds form a habitat for ophiuroids and munida associated with lophelia pertusa coral rubble suggesting these mini mounds are not present day living features

quaternary glaciations and glacial landform evolution in the tailan river valley tianshan range china abstract the tailan river originates on the southern slope of tumur peak the largest center of modern glaciation in the tianshan range five moraine complexes and associated fluvioglacial deposits in this valley record a complex history of quaternary glacial cycles and landform evolution electron spin resonance esr dating of glacial sediments was carried out using germanium ge centers in quartz grains which are sensitive to both sunlight and grinding based on the dating results as well as geomorphic and stratigraphic data the piyazilike end moraines the second moraine complex were deposited during neoglaciation the largest glacial advances during the last 3 4 ka in western china and an early holocene glacial advance the third set of moraines was deposited in marine isotope stage mis 2 4 and the glacial landforms of the tailan glaciation the fourth moraine complex which include hummocky moraines on the piedmont were formed in mis 6 penultimate glaciation the end moraines of the innermost moraine complex the first moraine complex are inferred to have been deposited during the little ice age lia thus the landforms and dates indicate compound valley glaciers from the lia to mis 2 4 and piedmont glaciers during mis 6 the oldest tills studied belong to the kokdepsang glacial stage and occur on a high plateau based on similar glacial landforms glacial deposits on a high plateau and a high glacial terrace and their esr ages in adjacent valleys on the southern slope of tumur peak the kokdepsang glacial stage is assigned to mis 12

the offshore quaternary sediment bodies of the english channel and its western approaches after a short review of present day surficial sediments on the sea floor of the english channel and its western approaches this paper summarises recent results on the present quaternary sandy accumulations tidal bank systems based on sea floor imaging very high resolution seismic surveys and a few piston cores the english channel a typical funnel shaped tidal shelf is presently starved of terrigenous sediments most of mobile sediments at the sea floor are autochthonous either skeletal carbonates or siliciclastic sands reworked from old littoral deposits or incised valley fills three zones are considered 1 the central and western central channel which is a bedload parting zone characterised by a pebbly lag making up the sole of the quaternary sediments throughout the shelf area 2 the eastern channel a flood dominated area characterised by medium to fine siliciclastic sands mainly of aeolian periglacial origin 3 the western approaches an ebb dominated area with a polygenic sediment cover characterised by coarse carbonate rich gravelly to muddy sands of marine to glaciomarine origin with a diachronous faunal content these sediments are sourced by reworking of a former littoral barrier or incised valley fills the seismic stratigraphy of quaternary sediment accumulations 10 50 m points to the predominant control of tidal dynamics together with the general interplay between the channel morphology and the sea level story the thickest deposits in the eastern channel and western approaches are built up into bank systems whereas the interpretation of the active eastern channel banks finds a general agreement the moribund banks in the western approaches i e the southern celtic banks remains under debate owing to the lack of long cores in our hypothesis both systems were built up during the last post glacial sea level rise the celtic banks would represent the tidal transgressive systems tract whereas the eastern channel banks correspond to the highstand systems tract the architecture of both bank systems is studied from two examples the bassure de baas bank in the eastern channel and the kaiser bank in the western approaches both examples show transgressive features the bassure de baas exhibits from base to top an estuarine mouth barrier a wave erosion surface a shoreface bank and finally a classic tidal bank by contrast the kaiser bank consists of the offshore reworking of fully marine deposits its base would correspond to the amalgamation of the last glacial sea level fall with a strong tidal ravinement surface from base to top the bank underwent tidal bar accretion very large dune field aggradation perched channels incision storm erosion and deposition

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

eustatic and hydrodynamic controls on the architecture of a deep shelf sand bank celtic sea the architecture of a tidal sand bank in the south eastern celtic sea was examined using very high resolution seismic surveys the bank comprises four depositional units the lowest unit 1 is characterized by gently dipping 1 8 strata that strike parallel to the length of the bank unit 1 is erosionally overlain by unit 2 which forms the bulk of the bank this unit consists of stacked sets of downcurrent dipping 7 12 master bedding formed by climbing sinuouscrested tidal dunes that are up to 20 m high these deposits are locally incised by an anastomosed channel network unit 3 that may represent a buried swatchway system the upper part of the bank comprises wave related deposits that are mainly preserved on the bank flanks unit 4 the outer bank surface is erosional the bank is believed to have formed during the last postglacial sea level rise the facies evolution from unit 1 to unit 3 indicates an upward increase in tidal energy mainly characterized by the thickening of dune cross bed sets in unit 2 the majority of bank growth is inferred to have occurred in water depths of the order of 60 m this evolution was controlled by relative sea level rise which is likely to have caused an episode of tidal resonance with associated strong tidal currents that were responsible for the incision of the deep cross cutting channels of unit 3 the transition to wavedominated sedimentation in unit 4 is related to the decay of resonance with continued sea level rise

far flung moraines exploring the feedback of glacial erosion on the evolution of glacier length abstract over many glacial cycles the glacial erosion of alpine valleys can be sufficient to reduce the length of glaciers in the most recent cycles we document field cases illustrative of this erosional feedback and model the long term evolution of glacier lengths analytically and numerically the general feature we target is a moraine deposited well beyond the last glacial maximum lgm limit which we refer to as a far flung moraine firstly we assemble published observations to illustrate that far flung moraines are documented around the world the observations suggest that the downvalley distance to such far flung moraines can exceed the distance to lgm moraines by up to twofold secondly we address the problem analytically making several simplifying assumptions to demonstrate that glacier length scales linearly with erosion depth finally we employ a numerical model to test the analytical solution this 1d depth integrated flowline model includes i a depth averaged longitudinal coupling stress approximation ii prescribed winter and summer surface mass balance profiles iii evolving ice temperature calculated via the conventional heat equation and iv glacier sliding velocity parameterized as a function of basal ice temperature and spatially and temporally variable prescribed flotation fraction the simulated alpine landscape is modified through the competing processes of glacier erosion which is dependent on glacier sliding velocity and prescribed bedrock erodibility and prescribed uplift rate the climate controlling surface mass balance is prescribed by time series of air temperature and snowfall approximated by the sum of two sinusoidal cycles the recurrence statistics of these prescribed climate drivers closely match those of the marine isotopic record hence the prescribed climate drivers faithfully mimic observed long term climate drivers consistent with earlier landscape evolution studies we find that the primary effect of repeated glaciations is to flatten a valley floor and steepen its headwall effectively cutting a longitudinal notch in a fluvial valley profile analytical and numerical model results also demonstrate that far flung moraines are an inevitable consequence of repeated glaciations glaciers in tectonically inactive regions can sufficiently erode their valleys so that the earliest glaciations leave moraines many kilometers down valley from moraines left by the latest glaciations despite similar climates this suggests that a different landscape rather than a different climate is capable of explaining the early glacier extents as a corollary the long term drift toward reduced glacier length favors the survival of early moraines in the face of later glacial advances finally rock uplift can defeat this erosional feedback while rock subsidence enhances the feedback

late quaternary evolution and sea level history of a glaciated marine embayment bantry bay sw ireland ireland experienced a spatially complex pattern of relative sea level rsl changes and shoreline development caused by the interplay of isostatic and eustatic ice equivalent sea level processes since the last glacial maximum lgm using a combination of high resolution marine geophysical data vibrocores foraminiferal analysis and 10 ams radiocarbon dates we reconstruct the late quaternary evolution and rsl history of bantry bay a large 40 km long 5 10 km wide embayment in sw ireland the data indicate two infill phases one before and one after the lgm separated by glacial and lowstand sediments the pre lgm history is not dated and the depositional history is inferred a large sediment lobe formed at the outer edge of bantry bay as a lowstand ice proximal glacimarine outwash system as the ice retreated after the lgm at a sea level ca 80 m lower than present iceberg scour immediately west of this location likely relate to the break up of the local kerry cork ice cap long curvilinear ridges seen both offshore and on top of the sediment lobe probably formed as shoreface ridges under stronger than present tidal currents during a period of rsl stability pre 14 6 ka cal bp a subsequent infill phase is characterised by a basin wide erosional ravinement surface and the deposition of inter and sub tidal estuarine sediments although our data support the general trends our stratigraphic and radiocarbon data suggest a higher sea level between 11 and 13 5 ka cal bp than predicted by existing glacial isostatic adjustment models

pleistocene glacial history of the nw european continental margin abstract in this paper new and previously published data on the pleistocene glacial impact on the nw european margin from ireland to svalbard between c 48 n 80 n are compiled the morphology of the glaciated part of the european margin strongly reflects repeated occurrence of fast moving ice streams creating numerous glacial troughs channels that are separated by shallow bank areas end moraines have been identified at several locations on the shelf suggesting shelf edge glaciation along the major part of the margin during the last glacial maximum deposition of stacked units of glacigenic debris flows on the continental slope form fans at a number of locations from 55 n and northwards whereas the margin to the south of this is characterised by the presence of submarine canyons glaciation curves based primarily on information from the glacial fed fan systems that depict the pleistocene trends in extent of glaciations along the margin have been compiled these curves suggest that extensive shelf glaciations started around svalbard at 1 6 1 3 ma while repeated periods of shelf edge glaciations on the uk margin started with mis 12 c 0 45 ma the available evidence for mis 2 suggest that shelf edge glaciation for the whole margin was reached between c 28 and 22 14 c ka bp and maximum positions after this were more limited in some regions north sea and lofoten the last glacial advance on the margin has been dated to 15 13 5 14 c ka bp and by c 13 14 c ka bp the shelf areas were completely deglaciated the younger dryas loch lomond advance reached the coastal areas in only a few regions

climatic and topographic controls on the style and timing of late quaternary glaciation throughout tibet and the himalaya defined by 10be cosmogenic radionuclide surface exposure dating abstract temporal and spatial changes in glacier cover throughout the late quaternary in tibet and the bordering mountains are poorly defined because of the inaccessibility and vastness of the region and the lack of numerical dating to help reconstruct the timing and extent of glaciation throughout tibet and the bordering mountains we use geomorphic mapping and 10 be cosmogenic radionuclide crn surface dating in study areas in southeastern gonga shan southern karola pass and central western nyainqentanggulha shan and tanggula shan tibet and we compare these with recently determined numerical chronologies in other parts of the plateau and its borderlands each of the study regions receives its precipitation mainly during the south asian summer monsoon when it falls as snow at high altitudes gonga shan receives the most precipitation 2000 mm a 1 while near the margins of monsoon influence the karola pass receives moderate amounts of precipitation 500 600 mm a 1 and in the interior of the plateau little precipitation falls on the western nyainqentanggulha shan 300 mm a 1 and the tanggula shan 400 700 mm a 1 the higher precipitation values for the tanggula shan are due to strong orographic effects in each region at least three sets of moraines and associated landforms are preserved providing evidence for multiple glaciations the 10 be crn surface exposure dating shows that the formation of moraines in gonga shan occurred during the early mid holocene neoglacial and little ice age on the karola pass during the lateglacial early holocene and neoglacial in the nyainqentanggulha shan date during the early part of the last glacial cycle global last glacial maximum and lateglacial and on the tanggula shan during the penultimate glacial cycle and the early part of the last glacial cycle the oldest moraine succession in each of these regions varies from the early holocene gonga shan lateglacial karola pass early last glacial western nyainqentanggulha shan and penultimate glacial cycle tanggula shan we believe that the regional patterns and timing of glaciation reflect temporal and spatial variability in the south asian monsoon and in particular in regional precipitation gradients in zones of greater aridity the extent of glaciation has become increasingly restricted throughout the late quaternary leading to the preservation of old 100 ka glacial landforms in contrast in regions that are very strongly influenced by the monsoon 1600 mm a 1 the preservation potential of pre lateglacial moraine successions is generally extremely poor this is possibly because lateglacial and holocene glacial advances may have been more extensive than early glaciations and hence may have destroyed any landform or sedimentary evidence of earlier glaciations furthermore the intense denudation mainly by fluvial and mass movement processes which characterize these wetter environments results in rapid erosion and re sedimentation of glacial and associated landforms which also contributes to their poor preservation potential

the quaternary channel river seismic stratigraphy of its palaeo valleys and deeps based on the interpretation of geophysical data very high resolution seismic data combined with em1000 swath bathymetry this paper reviews the history of the channel river throughout the late cenozoic new evidence does illustrate how the interplay of tectonics eustacy and climate have influenced this northwest european drainage system the concepts of sequence stratigraphy allow the subdivision of the sedimentary record into depositional sequences bounded by unconformities resulting from globally synchronous sea level changes however the recognition of eustatic sea level changes in a cold climate environment is very difficult because of the interplay of additional phenomena such as glacio isostatic sea level changes with glacio eustatic changes for our interpretation it was necessary to adjust these concepts with the relative importance of geomorphological processes determining the behaviour of rivers and steering their evolution the foundations of the modern drainage system were laid after the oligocene channel inversion in general these early rivers occupied shallow valleys the pleistocene cold climates resulted in fluvial incision through time the channel river has adopted a drainage system that can be divided into three parts i the drainage basin comprising the southern bight the eastern channel and the london and paris basins ii the river zone itself which begins at the cotentin peninsula and passes through the hurd deep before reaching the continental shelf break in the celtic sea iii the depositional basin represented by the celtic banks complex and by the deep sea fans located at the foot of shamrock and black mud canyons during important lowstands marine oxygen isotope stages 22 16 10 6 and 2 the channel river seems to have reached the shelf break as indicated by the internal structure of the banks copyright 2003 john wiley sons ltd

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

advance and retreat of the marine terminating irish sea ice stream into the celtic sea during the last glacial timing and maximum extent abstract the dynamics of the british irish ice sheet biis during the last glacial were conditioned by marine based ice streams the largest of which by far was the irish sea ice stream isis which drained southwest across the celtic shelf the maximum extent and timing of the isis have been constrained by onshore evidence from the uk and ireland and by glacigenic sediments encountered in a small suite of vibrocores from the uk irish continental shelf from which a single radiocarbon date is available these data have long supported ice advance to at least the mid shelf while recent results suggest the isis may have extended 150 km farther seaward to the shelf edge the glacigenic sequences have not been placed within a secure seismic stratigraphic context and the relationship between glaciation and the linear sediment megaridges observed on the outer shelf of the celtic sea has remained uncertain here we report results of sedimentological geochemical geochronological and micropalaeontological analyses combined with a seismic stratigraphic investigation of the glacigenic sequences of the celtic sea with the aims of establishing maximum extent depositional context timing and retreat chronology of isis eight lithofacies packages are identified six of which correlate with seismic facies lithofacies lf1 and lf2 correlate to a seafloor seismic facies sf1 that we interpret to record the postglacial and holocene transgressive flooding of the shelf lithofacies lf10 till lf3 lf4 and lf8 glacimarine correlate to different seismic facies that we interpret to be of glacigenic origin based on sedimentological geotechnical and micropalaeontological evidence and their distribution supported by geochemical evidence from lithofacies lf8 and lf10 indicate extension of isis as far as the celtic sea shelf break new radiocarbon ages on calcareous micro and macrofauna constrain this advance to be between 24 and 27 cal ka bp consistent with pre existing geochronological constraints glacimarine lithofacies lf8 is in places glacitectonically contorted and deformed indicating ice readvance but the nature and timing of this readvance is unclear retreat out of the celtic sea was initially rapid and may have been triggered by high relative sea levels driven by significant glacio isostatic depression consistent with greater ice loads over britain and ireland than previously considered

streamlined hard beds formed by palaeo ice streams a review fast flowing ice streams occur within modern ice sheets and also operated in pleistocene ice sheets the reconstruction of palaeo ice streams normally relies on the mapping of mega scale glacial lineations msgls and drumlins composed of soft sediment mainly till analysis of new satellite imagery and digital terrain models demonstrates the presence of large fields of kilometre scale glacial lineations comprising rock drumlins megagrooves and megaridges in this paper we describe and analyse a number of such hard bed landform systems from the former laurentide and british irish ice sheets occurring in a variety of palaeo ice stream settings these are attributed to erosion of crystalline and sedimentary rock below fast flowing ice streams bedrock properties such as hardness fracture spacing and bedding and their orientation with respect to ice flow have a profound effect on the occurrence and character of elongate rock bedforms elongate streamlined forms on hard crystalline rock as on the canadian shield only form under special circumstances in contrast sedimentary strata are highly susceptible to form streamlined hard beds specifically if bedrock strike is parallel to ice flow large scale elongate rock bedforms are erosional in origin formed by preferentially focused abrasion or by lateral plucking depending on bedrock type many palaeo ice stream footprints previously mapped in the laurentide ice sheet on the basis of soft bed bedforms are shown to be significantly larger extending up ice across sedimentary strata and onto precambrian crystalline rocks hard bed streamlined forms further show that ice streaming does not necessitate a deformable bed but can equally occur on smooth hard beds

a critical review of the glaciomarine model for irish sea deglaciation evidence from southern britain the celtic shelf and adjacent continental slope in support of their glaciomarine model for the deglaciation of the irish sea basin eyles and mccabe cited the occurrence of distal glaciomarine mud drapes onshore in the isles of scilly and north devon and of arctic beach face gravels and sands around the shores of the celtic sea glacial and sea level data from the southern part of the irish sea in the terminal zone of the ice stream and the adjacent continental slope are reviewed here to test this aspect of the model the suggestion that the glacial sequences of both the isles of scilly and fremington in north devon are glaciomarine mud drapes is rejected an actively calving tidewater margin only occurred early in the deglacial sequence close to the terminal zone in the south central celtic sea relative sea levels were lower and therefore glacio isostatic depression less than envisaged in the glaciomarine model geochronological sedimentological and biostratigraphical data indicate that the raised beach sequences around the shores of the celtic sea and english channel were deposited at or during regression soon after interglacial eustatic highstands evidence for ice rafting at a time of high relative sea levels is restricted to a phase s earlier than the late devensian these data indicate that the raised beach sequences have no bearing on the style of irish sea deglaciation copyright 2001 john wiley sons ltd

the sequence of quaternary glaciation in the bayan har mountains four periods of quaternary glaciation in the pleistocene have been found in the area of the bayan har mountains they represent respectively the two stages of the last glacial age the penultimate ice age and an earlier ice age during the late stage of the last glacial age glaciers developed only near the mountain ridges of the bayan har in the earlier stage glaciers expanded down to the piedmont of the bayan har mountains and were as much as 40 km long in the penultimate ice age an extensive ice cover developed depositing an areally widespread till sheet erratics were transported 60 km from bayan har peak to qingshuihe town to the south and to yematan land to the north granitic erratics are also distributed over elevated geomorphological positions such as chalaping ridge the area of ice cover encompassed up to 50 000 km2 furthermore evidence including glacial landforms and sediments shows that a larger glaciation existed in this area in an earlier time possibly during the third most recent ante penultimate glaciation the scale of this glaciated area is greater than those of the more recent events in the qinghai xizang plateau extending over 80 000 km2 this glaciation covered the source area of the yellow river from xingsuhai in the west to duogerangtan in the east including the areas of gyaring and ngoring lakes based on the extent and locations of the glaciations the bayan har stage and galalahai stage of the last glacial age the yematan ice age and the huanghe glacial age can be recognized

new age constraints for the limit of the british irish ice sheet on the isles of scilly the southernmost terrestrial extent of the irish sea ice stream isis which drained a large proportion of the last british irish ice sheet impinged on to the isles of scilly during marine isotope stage 2 however the age of this ice limit has been contested and the interpretation that this occurred during the last glacial maximum lgm remains controversial this study reports new ages using optically stimulated luminescence osl dating of outwash sediments at battery tresco 25 5 1 5 ka and terrestrial cosmogenic nuclide exposure dating of boulders overlying till on scilly rock 25 9 1 6 ka which confirm that the isis reached the isles of scilly during the lgm the ages demonstrate this ice advance on to the northern isles of scilly occurred at 26 ka around the time of increased ice rafted debris in the adjacent marine record from the continental margin which coincided with heinrich event 2 at 24 ka osl dating 19 6 1 5 ka of the post glacial hell bay gravel at battery suggests there was then an 5 ka delay between primary deposition and aeolian reworking of the glacigenic sediment during a time when the isis ice front was oscillating on and around the ll n peninsula 390 km to the north

sedimentology and micropalaeontology of glacimarine sediments from the central and southwestern celtic sea thin discontinuous glacigenic sediments occur at or close to the sea bed as far south as 49 n in the celtic sea the northern samples facies a are clast rich overconsolidated lodgement tills or proximal glacimarine sediments containing sparse reworked microfaunas the southern samples facies b are distal glacimarine plastic silty clays containing abundant cold water microfaunas both these facies are correlated with the late devensian scilly till enabling a quantitative reconstruction of ice thicknesses grounding line sea level and shoreline elevations in the celtic sea at 19 000 years bp the ice advance terminated in marine waters towards the shelf edge break and is likely to have constituted a thin lobate surge over deformable marine sediments 1990 the geological society

on the architecture of high latitude continental margins the influence of ice sheet and sea ice processes in the polar north atlantic abstract the presence of ice during the late cenozoic distinguishes the nature and rates of processes on high latitude margins from those elsewhere ice sheets terminating in marine waters deliver icebergs meltwater and debris to high latitude seas sea ice influences ocean salinity structure and downslope water and sediment transfer and also transports fine grained sediments over long distances these cryospheric processes have led to the development of a distinctive sedimentary architecture on modern high latitude continental margins large submarine fans made up almost entirely of stacked debris flows are present around the norwegian greenland sea large slides are located in a variety of settings relative to rates of sediment delivery from quaternary ice sheet margins but no large slides have been mapped on the east greenland margin however extensive channel systems and sediment wave fields are present in the greenland basin probably related to intermittent downslope flow of dense water and turbidity currents the extensive ne greenland shelf was not innundated by ice sheet advance during recent full glacial conditions allowing sea ice and deep water production during both interglacials and full glacials changes in the nature and rate of sedimentation within the greenland basin should provide clues on the rate of dense water production with implications for thermohaline circulation in the north atlantic other erosional and depositional features on the norwegian greenland sea margins include canyons and contourite drifts high relief tectonic features influence sediment reworking by turbidity currents at abyssal depths a simple conceptual model for glacier influenced marine sedimentation summarizes the role of cryospheric processes in high latitude margin sedimentary environments

the fleuve manche the submarine sedimentary features from the outer shelf to the deep sea fans bathymetric seismic and coring surveys have been carried out since the beginning of the 1990s on the outer shelf the slope and the continental rise of the western approaches margin most of the sedimentary features studied belong to a sedimentary system built up since the oligocene and fed by a palaeoriver the fleuve manche that flowed in the english channel during eustatic lowstands a geomorphological map details the spatial distributions of the palaeovalleys on the outer shelf the drainage basin like organised canyons on the slope and the channel levee and lobe complexes on the rise the obvious channel canyon connections and the assessed palaeovalley canyon links demonstrate that the fleuve manche was the single source for terrigeneous fluxes of the armorican deep sea fan when it was one of two sources of the celtic deep sea fan amongst parameters controlling the sedimentation two factors play a major role i subsidence controlled the possibly messinian riverine incision the turbidite activities during lowstands as well as marine infilling of the seawards part of the fleuve manche ii quaternary sedimentary supplies were influenced by the melting ice sheets and the connections with the onshore catchment basins copyright 2003 john wiley sons ltd

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos

sea level change in the irish sea since the last glacial maximum constraints from isostatic modelling models of glacio hydroisostatic sea level change have been published for the british isles that are broadly consistent with the observational evidence as well as with glaciological constraints it has been argued however that the models fail to represent sea level change along the irish sea margins and in southern ireland for the post deglaciation period the argument rests on the interpretation of the depositional environment of the elevated irish sea drift on both sides of the irish sea whether this is terrestrial or glaciomarine the isostatic models for the british isles are consistent with the former interpretation in that sea levels on either side of the irish sea south of about the isle of man are not predicted to have risen above present sea level at any time since the deglaciation of the irish sea this implies that ice over both the irish sea and ireland was relatively thin ca 600 700 m over ireland if the glaciomarine interpretation of the elevated irish sea drift is correct then the maximum ice thickness over central and southern ireland would have to reach 2000 m exceeding that over scotland furthermore for the resulting sea level change to be consistent with the holocene evidence this thick ice sheet could not have extended to the eastern side of the irish sea nor could it have been very thick at its northern and western limits if such an ice model is extreme and incompatible with glaciological observations then the alternative is to accept the interpretation of the irish sea drift as terrestrial in origin copyright 2001 john wiley sons ltd