the late devensian 22 000 bp irish sea basin the sedimentary record of a collapsed ice sheet margin the late devensian 20 ka bp glacial geology of the irish sea basin 4000 km2 is an event stratigraphy recording the entry of marine waters into a glacio isostatically depressed basin and the rapid retreat of the irish sea glacier as a tidewater ice margin marine limits occur up to 140 m o d across much of the central basin the ice margin was uncoupled from its bed exposing a subglacially scoured topography to glaciomarine processes the irish sea glacier was a major drainage conduit of the last british ice sheet calving of the marine ice margin resulted in fast flow surging of ice streams recorded by drumlin fields around the northern basin margin and tunnel valleys rapid evacuation of the basin may have stranded large areas of dead ice in peripheral zones e g cheshire shropshire lowlands and initiated the collapse of the ice sheet thick wedges of ice contact glaciomarine sediments were deposited during ice retreat as morainal bank complexes by successive tidewater ice margins stabilized at pinning points around the irish sea coast where morainal banks occur on the seaward side of drumlin swarms there is a clear sequential relationship between rapid ice loss from calving ice margins the development of fast flowing ice streams drumlinization and the pumping of subglacial sediment to tidewater raised delta complexes are locally associated with marine limits along the high relief coastal margins of wales east central ireland and the lake district associated valley infill complexes record downslope resedimentation of heterogenous sediments into the marine environment during ice retreat co eval offshore deposits are represented by well stratified glaciomarine complexes that infill a subglacially scoured topography that shows networks of tunnel valleys glaciomarine mud drapes occur well to the south of the maximum limit of grounded ice in the basin e g north devon scilly islands southern ireland the age of these distal sediments previously mapped as pre devensian tills is constrained by amino acid ratios basin rebound following deglaciation was rapid with over 100 m recovery in 3 ka and was followed by a low marine still stand peat accumulating in offshore areas now as much as 55 m below sea level has been drowned by the postglacial eustatic rise in sea level the glacio sedimentary model identified in this paper involving rapid ice retreat and related sedimentation triggered by rising relative sea level suggests that isotatic downwarping is an important mechanism for deglaciating continental shelves

upper stratosphere polar jet instability in the southern hemisphere synoptic scale zonal eddies longitudinal disturbances confines to polar latitudes in the southern hemisphere sh upper stratosphere have been observed in fourier analyses of temperature measurements from the limb infrared monitor of the stratosphere lims experiment during april may 1979 eddy activity at 60 degree s 1 mb is characterized by a fourier zonal wavenumber 5 wavelength approximately 4 000 km disturbance of amplitude 2 3 k which exhibits intermittent eastward propagation substantial meridional phase tilt and little vertical phase tilt these wave properties along with evidence of pronounced latitudinal variations in the upper stratosphere zonal wind distribution suggest that the synoptic scale modes may arise from a latitudinal wind shear barotropic instability of the sh polar jet stream this analysis apparently represents the first identification of polar upper stratosphere synoptic scale disturbances from satellite based information heretofore only seen in rocketsonde measurements in northern hemisphere nh polar regions and also predicted by linear model studies the ability to discern these disturbances in satellite temperature data sets offers an opportunity for future studies of the interhemispheric and interannual variability of synoptic scale eddy activity in the stratosphere however and unambiguous determination of dominant wavelength and phase speed in such studies will be precluded by the fact that satellite data alwaysmore will suffer from a certain degree of aliasing if disturbances exist with scales unresolved by the asynoptic satellite sampling less

meltwater floods into the black and caspian seas during heinrich stadial 1 abstract deglaciation of the eurasian ice sheet dispensed vast amounts of meltwater laden with red brown clay into black and caspian sea s freshwater lakes between 16 350 and 15 400 calendar years bp the arriving sediment had a mineral composition and strontium neodymium isotope signatures 87sr 86sr and end consistent with the crystalline bedrock that lay beneath the ice sheet as opposed to sources from landscapes crossed by the rivers that carried meltwater to the lakes the magnitude and rapidity of the shifts of 87sr 86sr and 18o in shells of ostracods and mollusks an eight fold increase in sediment accumulation rate and a plunge of 1250 14c years in the radiocarbon reservoir age indicate a volume of meltwater sufficient to have replaced most or all of the pre existing lake water if the release of 25 000 km3 of water from the caspian into the black sea s new euxine lake was abrupt by judging the magnitude of erosion in the floor of the manych strait spillway this event qualifies as a megaflood deeply scoured furrows channel floor bars and swaths of mounds 5 20 km in length and 5 20 m in height are reminiscent of scabland landscapes the meltwater is coincident with heinrich stadial 1 when the alpine and eurasian ice sheets re advanced and temperatures of the black sea s lake surface remained cold sand grains within the red brown clay indicate they were transported by lake surface ice

deglacial chronology from county donegal ireland implications for deglaciation of the british irish ice sheet in the north of ireland ice advanced northwards onto the continental shelf from inland centres of dispersion at the last glacial maximum we constrain the timing of three subsequent events by accelerator mass spectrometry 14 c dating of marine microfaunas from muds at corvish county donegal early and rapid deglaciation of the continental shelf off northwestern ireland occurred before 17 1 k 14 c years bp when marine muds formed in trawbreaga bay ice subsequently readvanced into the bay some time between 15 0 and 14 0 k 14 c years bp and compressed contemporary sea stacks and beach cobbles into a ridge at ballycrampsey early deglacial muds were deformed during this ice readvance and redeposited with stratigraphically inverted 14 c ages between 16 0 and 15 2 k 14 c years bp the deformed mud is overlain by undeformed laminae deposited during the final deglaciation of the area after 14 1 k 14 c years bp the early deglaciation in the north at c 17 k 14 c years bp is correlative with deglaciation recorded in the irish sea basin western ireland and northeastern scotland indicating a response of the entire british irish ice sheet to early warming of the north atlantic ocean that resulted in a loss of up to two thirds of its mass subsequent ice sheet readvance between 15 0 and 14 1 k 14 c years bp in the north is part of a widespread response of the british irish ice sheet to heinrich event 1 during the killard point stadial high relative sea levels that accompanied deglaciation at 17 k 14 c years bp and again at 14 1 k 14 c years bp indicate substantial loading and attendant isostatic depression by the british irish ice sheet

ice sheet sources of sea level rise and freshwater discharge during the last deglaciation we review and synthesize the geologic record that constrains the sources of sea level rise and freshwater discharge to the global oceans associated with retreat of ice sheets during the last deglaciation the last glacial maximum 26 19 ka was terminated by a rapid 5 10 m sea level rise at 19 0 19 5 ka sourced largely from northern hemisphere ice sheet retreat in response to high northern latitude insolation forcing sea level rise of 8 20 m from 19 to 14 5 ka can be attributed to continued retreat of the laurentide and eurasian ice sheets with an additional freshwater forcing of uncertain amount delivered by heinrich event 1 the source of the abrupt acceleration in sea level rise at 14 6 ka meltwater pulse 1a 14 15 m includes contributions of 6 5 10 m from northern hemisphere ice sheets of which 2 7 m represents an excess contribution above that derived from ongoing ice sheet retreat widespread retreat of antarctic ice sheets began at 14 0 15 0 ka which together with geophysical modeling of far field sea level records suggests an antarctic contribution to this meltwater pulse as well the cause of the subsequent younger dryas cold event can be attributed to eastward freshwater runoff from the lake agassiz basin to the st lawrence estuary that agrees with existing lake agassiz outlet radiocarbon dates much of the early holocene sea level rise can be explained by laurentide and scandinavian ice sheet retreat with collapse of laurentide ice over hudson bay and drainage of lake agassiz basin runoff at 8 4 8 2 ka to the labrador sea causing the 8 2 ka event

foraminifera from the irish sea glacigenic deposits at aberdaron western lleyn north wales palaeoenvironmental implications in a sequence of glacigenic sediments at aberdaron foraminifera were obtained from samples located specifically in order to differentiate between opposing models of depositional environment all the diamict samples yielded remarkably uniform assemblages with similar numbers of benthic specimens and benthic species per unit weight of sediment similar planktic benthic ratios and similar ratios of clearly allochthonous to possibly autochthonous elements this is precisely as predicted by the terrestrial model of sedimentation where all of the sediments are interpreted as being derived from the melting of glacier ice rich in marine debris entrained during passage along the irish sea basin the results lend no support to a glacial marine model since no faunal responses to increasingly distal sedimentary environments are observed however the fauna is dominated by the foraminifera elphidium excavatum terquem forma clavata cushman which is commonly assumed to indicate glacial marine conditions the modern distribution of similar assemblages suggests that it is just as likely to represent the cold reduced salinity conditions that would have prevailed in the northern irish sea basin for much of the quaternary

a shallow marine emergent sequence from the northwestern sector of the last british ice sheet portballintrae northern ireland abstract at portballintrae northern ireland a well preserved emergent facies sequence formed around 17 kyr b p as the late devensian ice sheet withdrew from the continental shelf three main lithofacies assemblages are recognised 1 at the base of the sequence a massive muddy diamict was formed by resedimentation of an unstable sedimentary apron deposited in a tidewater setting 2 rhythmically bedded sand and mud units contain a wide range of wave diagnostic features and are separated from the underlying diamict by both transitional and wave eroded planar contacts palaeowave calculations suggest deposition in a coastal tract open to atlantic waves the preservation and range of boreo arctic foraminifera present are also typical of a lower shoreface storm influenced setting 3 interbedded gravel and sand facies are separated from the underlying rhythmically bedded facies by a planar wave cut surface this facies occurs as crudely organised beds within cross cutting shallow scours which are associated with off shore directed storm induced sediment pulses overall the coarsening upwards sequence is explained by tidewater sedimentation during ice wastage rapid isostatic rebound and isostatic deceleration in the late glacial an isostatic tectonic model comprising a forebulge on the outer continental shelf and a peripheral trough on the inner shelf is presented to resolve the apparent discrepancies between onshore and offshore sea level data

the last glacial maximum british irish ice sheet a reconstruction using digital terrain mapping the use of digital terrain mapping in determining the anatomy of the late devensian british irish ice sheet at a resolution of 500 m cell size is illustrated for boulton et al s 1985 and 1991 models and lambeck s 1995 model of the ice sheet at its maximum extent as an independent ice mass area and volume of the ice sheet are given for each model and the spatial pattern of ice thickness shown in maps the analyses show that if no account is taken of topography beneath the ice surface models will seriously overestimate ice volume it is suggested that as reconstructions of the ice sheet improve detailed models of ice thickness at the resolution given in this paper may be of value in determining the contribution of the ice sheet to sea surface changes as well as in determining the effects of ice loading on glacio isostasy neotectonics and possibly on paraglacial processes in areas of high relief copyright 2007 john wiley sons ltd

a new late weichselian and holocene marine chronology for the western svalbard slope 30 000 0 cal years bp abstract data have been compiled from eleven sediment cores from 76 to 80 n on the western svalbard slope the cores are from water depths between 630 and 1880 m and show clear similarities in lithology and magnetic susceptibility all cores penetrated into mass transported sediments from glacigenic debris flow events and turbidity flow events the mass transport probably occurred when the ice reached the shelf edge the deposits date between 24 080 150 and 23 550 185 calibrated cal years bp the records also include laminated fine grained sediments interpreted as deposits from sediment laden meltwater plumes dated between 14 780 220 and 14 300 260 cal years bp in holocene sediments a diatom rich fine grained layer dates 10 100 150 to 9840 200 cal years bp the eleven cores have been stacked into one record with absolute age control from 35 ams14c dates together with oxygen isotope stratigraphy and contents of ice rafted detritus the stacked record provides a useful chronology tool for cores on the western svalbard slope our study improves the age control of earlier well documented glacial events and shows that the maximum glacial state and the onset of the deglaciation both occurred 2500 3000 years earlier than previously reconstructed for the western svalbard margin the results indicate that during the last 30 000 years advance and retreat of the svalbard barents sea ice sheet was closely linked to the flow of atlantic water and polar water over the margin

response of the irish ice sheet to abrupt climate change during the last deglaciation we summarize 121 14c and in situ cosmogenic 10be and 36cl ages that constrain fluctuations of the irish ice sheet iis since the last glacial maximum lgm that can be linked to abrupt climate changes in the north atlantic region these data provide a robust means to date ice sheet fluctuations because similar age events can be identified from widely spaced sites they are constrained by stratigraphy and they can be related to large changes in the configuration of a dynamic ice sheet the following events are recognized 1 ams 14c ages and 10be and 36cl ages as well as offshore data suggest that the last maximum advance of the iis occurred between 27 and 23 cal ka 2 deglaciation began on the western continental shelf and in the irish sea basin at 23 cal ka dated sites from around ireland constrain subsequent widespread retreat of ice sheet margins from the shelf onto irish coastlines during the cooley point interstadial 20 cal ka ams 14c ages suggest that the cooley point interstadial continued until 18 2 cal ka b p during this interstadial retreat of the ice sheet margin into the northern irish sea basin indicates that the iis may have lost up to two thirds of its mass 3 dated sites from northwestern and eastern ireland indicate that the cooley point interstadial was terminated by ice readvance during the clogher head stadial at 18 2 cal ka 4 the linns interstadial was a brief interval 17 0 16 5 cal ka of ice recession following the clogher head stadial that is identified from raised marine sediments in eastern and northern ireland and cosmogenic ages elsewhere in ireland 5 the iis subsequently readvanced during the killard point stadial reaching its maximum extent 16 5 cal ka indicating that the readvance began sometime earlier 6 widespread retreat of the iis began by 15 5 cal ka during the rough island interstadial 6 readvance of cirque glaciers in western ireland occurred during the younger dryas equivalent nahanagan stadial

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

the northern sector of the last british ice sheet maximum extent and demise abstract strongly divided opinion has led to competing apparently contradictory views on the timing extent flow configuration and decay mechanism of the last british ice sheet we review the existing literature and reconcile some of these differences using remarkable new sea bed imagery this bathymetric data provides unprecedented empirical evidence of confluence and subsequent separation of the last british and fennoscandian ice sheets critically it also allows a viable pattern of ice sheet disintegration to be proposed for the first time covering the continental shelf around the northern united kingdom extensive echosounder data reveals striking geomorphic evidence in the form of tunnel valleys and moraines relating to the former british and fennoscandian ice sheets the pattern of tunnel valleys in the northern north sea basin and the presence of large moraines on the west shetland shelf coupled with stratigraphic evidence from the witch ground basin all suggest that at its maximum extent a grounded ice sheet flowed from se to nw across the northern north sea basin terminating at the continental shelf edge the zone of confluence between the british and much larger fennoscandian ice sheets was probably across the northern orkney islands with fast flowing ice in the fair isle channel focusing sediment delivery to the rona and foula wedges this period of maximum confluent glaciation c 30 25 ka bp was followed by a remarkable period of large scale ice sheet re organisation we present evidence suggesting that as sea level rose a large marine embayment opened in the northern north sea basin as far south as the witch ground basin forcing the two ice sheets to decouple rapidly along a north south axis east of shetland as a result both ice sheets rapidly adjusted to new quasi stable margin positions forming a second distinct set of moraines c 24 18 ka bp the lobate overprinted morphology of these moraines on the mid shelf west of orkney and shetland indicates that the re organisation of the british ice sheet was extremely dynamic probably dominated by a series of internally forced readvances critically much of the ice in the low lying north sea basin may have disintegrated catastrophically as decoupling progressed in response to rising sea levels final stage deglaciation was marked by near shore ice streaming and increasing topographic control on ice flow direction punctuated retreat of the british ice sheet continued until c 16 ka bp when following the north atlantic iceberg discharge event heinrich 1 ice was situated at the present day coastline in nw scotland

rapid rise of sea level 19 000 years ago and its global implications evidence from the irish sea basin supports the existence of an abrupt rise in sea level meltwater pulse at 19 000 years before the present b p climate records indicate a large reduction in the strength of north atlantic deep water formation and attendant cooling of the north atlantic at this time indicating a source of the meltwater pulse from one or more northern hemisphere ice sheets warming of the tropical atlantic and pacific oceans and the southern hemisphere also began at 19 000 years b p these responses identify mechanisms responsible for the propagation of deglacial climate signals to the southern hemisphere and tropics while maintaining a cold climate in the northern hemisphere

resolving discrepancies between field and modelled relative sea level data lessons from western ireland accurate reconstruction of lateglacial and holocene relative sea level rsl histories is complicated where mismatches exist between geological data and rsl curves generated by models of glacio isostatic adjustment gia in ireland such discrepancies have profound implications for interpreting the glacial history of the british isles and for the use of glacial rebound models to predict future sea level changes to address this issue we present new rsl data from four sites along the western coast of ireland including 17 data points from the critical period before 5000 14c a bp for which very few data are available we generate new rsl simulations from an existing gia model incorporating a thickened irish ice sheet component simulated curves from co mayo and co donegal accommodate the higher than present lateglacial rsl inferred from glaciomarine muds while still meeting the requirement for below present rsl indicated by the new terrestrial limiting data points relaxation of trimline constraints on maximum ice sheet thickness provides considerable scope for improved gia performance these results demonstrate inferences about rsl drawn from gia modelling and glacio sedimentary data are not mutually exclusive and represent a significant step towards resolving a long standing debate between the field based and modelling communities

ice sheet variability around the north atlantic ocean during the last deglaciation millennial scale variability in the flux of ice rafted detritus to north atlantic sediments during the last glacial period has been interpreted to reflect a climate forced increase in the discharge of icebergs from ice sheet margins surrounding the northern north atlantic ocean 1 but the relationship between ice sheet variability and climate change is not clear as both the sources of ice rafted detritus and the ice marginal processes are varied and complex 2 4 terrestrial records are helpful in unravelling this complexity because they can demonstrate the scale of ice sheet oscillations and whether the ice sheet or sector was advancing or retreating with respect to climate change here we constrain the age and anatomy of a prominent readvance of the british ice sheet in the northern irish sea region at similar to 14 14 c kyr bp similar to 16 4 calendar kyr bp the analysis indicates that the british ice sheet participated in an iceberg discharge episode known as heinrich event 1 comparison with other terrestrial and marine ice sheet records suggests that the dynamic collapse of the laurentide ice sheet beginning at 14 6 15 0 c 14 kyr bp1 4 similar to 17 2 17 6 calendar kyr bp 5 initiated varied responses from other ice sheet margins around the northern north atlantic region these observations support the argument that the release of icebergs and meltwater during heinrich event 1 disrupted the north atlantic thermohaline circulation 6 8 leading to a delay or reversal of deglaciation of the northern hemisphere and at least as far south as 40 degrees s for two to three thousand years 5 9 10 suggesting a climate forcing and response similar to that of the ensuing younger dryas cold snap 11 12

interpreting iceberg deposits in the deep sea in their report millennial scale instability of the antarctic ice sheet during the last glaciation 9 june p 1815 s l kanfoush et al suggest that increases in ice rafted detritus ird observed in deep sea sediment records from the south atlantic ocean identify times of instability of

upper stratospheric circulations in the two hemispheres observed by satellites a global analysis is made of upper stratospheric circulations with the aid of nimbus 5 and tiros n satellite observations in order to make a comparison of characteristics between the northern hemisphere nh and the southern hemisphere sh it is shown that the reversal of north south gradient of the zonal mean temperature at the stratopause level is always observed in higher latitudes of the sh winter while the temperature gradient of the nh winter is variable because of the occurrence of sudden warmings consequently due to the thermal wind relation the polar night westerlies of the sh stratosphere are generally stronger than those of the nh stratosphere in association with this difference the activity of transient planetary waves of wavenumber 2 is striking in the sh in contrast to the predominance of steady waves in the nh finally the interrelation between the zonal mean field and planetary waves in the upper stratosphere is briefly discussed

ice flow stages and glacial bedforms in north central ireland a record of rapid environmental change during the last glacial termination satellite imagery is a useful tool to assess large scale 10 3 km 2 geological patterns satellite imagery of north central ireland shows cross cut and overprinted subglacial bedform patterns bedform lineations supported by sedimentary evidence are used to reconstruct four ice flow stages named a d during the termination of the last devensian glaciation 22 000 13 000 radiocarbon 14 c years bp flow stage a relates to southwesterly flow of scottish ice across eastern ireland flow stage b during the last glacial maximum c 25 000 22 000 14 c years bp records southeasterly ice flow from dispersal centres in northern parts of ireland transverse subglacial ridges rogen moraines formed during stage b are the largest area of this ridge type in western europe flow stage c records erosional headcutting in the rogen moraine field and sediment streamlining drumlinization by ice streams drawn into the irish sea basin this flow stage is constrained by ams radiocarbon dates from marine microfaunas to around 14 500 14 c years bp flow stage d records drumlinization from an inland centre in the lough neagh basin overall bedform patterns can be used to reconstruct ice mass history and evaluate controls on ice activity including millennial scale changes in amphi north atlantic climate field evidence of bedform relationships also casts doubt on current concepts of drumlinization and the role of pervasive sediment deformation in glacial systems

were the north atlantic heinrich events triggered by the behavior of the european ice sheets theories explaining the origin and distribution of heinrich layers abrupt massive discharges of ice rafted detritus generally attribute these layers to the laurentide ice sheet however doubt has been cast by the discovery that sediments also originated from european ice sheets here we present isotopic sr nd fingerprints of heinrich layers obtained in cores from the european margin they reveal that for most of the heinrich layers the icebergs were calved first from the european ice sheets predating the laurentide surges accelerator mass spectrometry 14c ages reveal that the oceanic heinrich events were synchronous with their dust equivalents in the greenland ice cores implying a direct ocean atmosphere link the typical laurentide surge seems to have occurred over a short time span after about 1 5 k y of iceberg release from the european ice sheets this suggests that the laurentide ice sheet responded to a stimulus created by events in the european sector

a model for striated boulder pavement formation on glaciated shallow marine shelves an example from the yakataga formation alaska abstract laterally extensive striated boulder pavements crop out within glaciomarine diamicts of the early pleistocene yakataga formation on middleton island alaska boulder pavements consist of planes of one clast thickness with faceted upper surfaces showing consistently oriented striation directions cropping out over several kilometers along strike clasts do not have the preferred long axis alignment nor the characteristic bullet shape of boulders transported at a glacier base and deposited by lodgement processes in most cases pavements identify the planar bounding surfaces of thick up to 100 m tabular units of fossiliferous muddy diamict deposited by the settling of fine grained sands and muds from suspension together with ice rafted debris in water depths between 20 and 250 m diamict facies both underlying and overlying the pavements contain abundant unabraded macro and microfossils and show no evidence of deformation by subglacial shear processes pavements appear to have originated as boulder lag surfaces produced by wave and tidal current winnowing of diamict on relatively shallow bank areas during episodes of relative sea level lowering lags were subsequently overridden and abraded by a grounding ice shelf the glacially abraded pavements are thought to record the repeated expansion of a partially floating ice shelf to the edge of the gulf of alaska continental shelf during the early pleistocene recognition of boulder pavements formed in this manner may help establish the former presence of ice shelves whose depositional record remains enigmatic

lims limb infrared monitor of the stratosphere observation of traveling planetary waves and potential vorticity advection in the stratosphere and mesosphere eastward and westward traveling waves were observed by the nimbus 7 limb infrared monitor of the stratosphere lims during the northern winter 1978 1979 eastward waves were prevalent in early winter and were involved in a minor canadian warming in december 1978 a large westward traveling wave as described by previous authors was observed in january 1979 during a series of minor warmings by comparing these two events it is shown that in both cases the superposition of traveling and quasi stationary waves led to constructive interference that was responsible for the warmings however there was significant asymmetry between eastward and westward traveling components eastward disturbances were confined mostly within the polar vortex whereas quasi stationary and westward traveling components propagated to the vortex periphery and beyond into the tropics and mid latitude mesosphere this behavior is consistent with rossby wave propagation and indicates that the location and magnitude of planetary wave breaking is sensitive to the frequency spectrum entering the middle atmosphere however this asymmetry is also a signature of the nonlinear critical layer as it projects onto the frequency spectrum both interpretations are shown to be valid during wave events observed by lims a local eulerian analysis of potential vorticity pv transport indicates that adiabatic geostrophic advection by the resolvable scales of motion explains qualitatively but not quantitatively the observed potential vorticity tendencies in the lims northern hemisphere winter in particular calculated advection explains the eastward rotation of the main vortex intrusion of low pv air into the polar cap and formation of high pv filaments at the vortex periphery

landform modification by palaeo ice streams in east central ireland in eastern ireland subglacial bedforms including drumlins and rogen moraines were modified by headward erosion along two ice streams which had over lapping flow tracks the ice streams which hadtidewater termini are dated by geochrono metric and morphostratigraphic methods to 5 15 0 14 ckyr bp castleblaney ice stream and 13 8 14 ckyr bp armagh ice stream bedforms along ice stream tracks show a morphological continuum which reflects a down ice increase in the degree of modification by ice stream activity i e resulting in unmodified remoulded overprinted cross cut streamlined bedforms the down ice changes inbedform types are inferred to relate to changes in subglacial drainage and sediment transport mechanisms bedform and sedi mentary evidence suggest that discrete subglacial meltwater channels which developed up ice changed in a down ice direction to unchannelized flows which deepened towards the ice margin meltwater release from subglacial cavities and produced by strain heating at sheared ice stream margins probably helped support ice stream flow which ended as the volume of subglacial meltwater discharge decreased dated millennial scale cycles of ice activity may be related to instability at tidewater margins followed by complex thermal and hydraulic responses within the ice mass

early deglaciation of the british irish ice sheet on the atlantic shelf northwest of ireland driven by glacioisostatic depression and high relative sea level understanding the triggers and pace of marine based ice sheet decay is critical for constraining the future mass loss and dynamic behaviour of marine based sectors of the large polar ice sheets in greenland and antarctica numerical models which seek to predict this behaviour need to be calibrated against data from both contemporary and palaeo ice sheets and the latter requires accurate reconstruction of former ice sheet extent dynamics and timing marine geophysics sediment cores benthic foraminiferal assemblages and radiocarbon dating are used to reconstruct the extent of the last british irish ice sheet biis and the timing and style of its retreat on the atlantic shelf northwest of ireland shelf edge moraines and subglacial till recovered in cores from the outer continental shelf are dated to younger than 26 3 ka cal bp and indicate an extensive ice sheet at the last glacial maximum lgm that was grounded to the shelf edge nested arcuate moraines record the subsequent episodic retreat of the ice sheet across the shelf lithofacies and associated foraminiferal assemblages demonstrate that this retreat occurred in a glacimarine environment as a grounded tidewater margin and that high relative sea level and cold waters prevailed during retreat radiocarbon dates indicate that the timing of initial ice sheet retreat from the shelf edge occurred in the interval between 26 3 and 24 8 ka cal bp during the period of minimum global eustatic sea level and that the ice sheet had retreated to the mid shelf by 24 8 ka cal bp the donegal bay moraine a large moraine at the mouth of donegal bay records a major stillstand and readvance of the ice sheet during deglaciation between 20 2 and 17 9 ka cal bp estimated retreat rates of 5 5 35 m a 1 across the shelf demonstrate that retreat was slow it is noteworthy that retreat was initiated in the absence of ocean warming and when eustatic sea level was at a minimum the sea level rise that initiated deglaciation from the shelf edge therefore is inferred to have been a product of local glacio isostatic crustal depression rather than external forcing this demonstrates that marine based sectors of ice sheets can trigger their own demise internally through glacio isostatic adjustment and it provides an explanation for the early retreat of the biis on the atlantic shelf during the global lgm glgm

environmental processes of the ice age land oceans glaciers epilog knowledge of the state of the earth at the last glacial maximum lgm an interval around 21 000 years ago is an important benchmark for understanding the sensitivity of global environmental systems to change much progress in understanding climates of the lgm has occurred in the 20 years since the end of the climap project of the 1970s climate long range investigation mapping and prediction here we review this progress based on presentations and discussion at a rst open science meeting of the epilog project environmental processes of the ice age land oceans glaciers held in delmenhorst germany may 1999 we outline key controversies and document protocols for epilog contributions so that a new synthesis of the lgm earth can emerge as an open project of the world s community of scientists 2001 elsevier science ltd all rights reserved

a pb isotope tracer of ocean ice sheet interaction the record from the ne atlantic during the last glacial interglacial cycle abstract ice sheet ocean interactions are both a response to climate forcing and a source of climate feedback releasing freshwater to the surface ocean and influencing climate and atmospheric co2 through changes in ocean circulation documenting the outcomes of these interactions for recent glacial cycles is important given current and future scenarios of polar ice retreat however this is currently hampered by lack of accurate constraints on ice sheet development and demise marine sedimentary pb isotope records have potential to investigate these aspects of ice sheet feedbacks at high temporal resolution because of the sensitivity of the pb isotope composition to continental weathering intensity and solute flux here we present a pb isotope record sourced from the femn oxyhydroxide fraction in marine sediments from odp site 980 on feni drift 2168 mbsl rockall trough ne atlantic spanning the last 43 ka the location of site 980 at the northern edge of the british irish ice sheet biis makes it well placed to monitor changes in biis development as it responded to migration of the polar front during the last glacial interglacial cycle the data reveal millennial scale cyclicity in pb isotope composition reminiscent of dansgaard oeschger cycles from the start of the record until heinrich event 2 43 24 ka characterised by extreme shifts to radiogenic compositions i e variation in 206pb 204pb from 18 9 to 20 5 the period 24 17 5 ka is also characterised by exceptionally radiogenic and highly variable pb isotope compositions associated with the rapid and repeated expansion and collapse of the biis the presence of such radiogenic pb isotope compositions during periods of maximum ice sheet activity support interpretation of the subglacial environment as an active weathering environment contributing to biogeochemical cycles through the transport vectors of meltwater release and debris laden ice calving

late quaternary deep sea ostracodes in the polar and subpolar north atlantic paleoecological and paleoenvironmental implications two sediment cores from the northern north atlantic one from the iceland plateau and one from the rockall plateau were investigated in order to examine the response of deep sea benthic ostracodes to climate related environmental changes since marine isotope stage mis 7 ostracode fauna was divided into three factor assemblages by using q mode factor analyses and diversity was calculated using the shannon wiener index the iceland plateau revealed an interglacial assemblage dominated by henryhowella a transitional assemblage dominated by eucythere and a background assemblage that consists of the common taxa krithe and cytheropteron the presence of henryhowella is linked to conditions that prevailed during the peak interglacial periods mis 5e and 1 characterized by increased food supply well oxygenated bottom water and lateral advection the presence of eucythere mainly during the interstadial periods appears to be related to slightly increased food supply whereas the background assemblage is considered to be opportunistic and able to cope with decreased food supply as interpreted for glacial times on the rockall plateau the opportunistic background assemblage consisting mainly of krithe argilloecia and cytheropteron shows no obvious relation to climate changes the interglacial assemblage consists of several taxa dominated by pelecocythere but as on the iceland plateau it also contains henryhowella the third assemblage is the glacial assemblage that consists of a variety of taxa several of which are known from the modern arctic ocean and the greenland sea shelf thus this assemblage indicates glacial conditions on the rockall plateau that are comparable to those found in the present day arctic ocean diversity calculations revealed higher ostracode diversities in glacial than in interglacial episodes in both cores and particularly high diversities during periods of increased input of iceberg rafted debris ird in the rockall plateau core both cores reveal lower surface water productivity during the glacial compared to the interglacial periods and particularly low productivity during the ird events as inferred from carbonate contents we assume therefore that ostracode diversity in the study areas is negatively correlated with food flux

late pleistocene mountain glacier response to north atlantic climate change in southwest ireland stephan harrison neil glasser ed anderson susan ivy ochs peter w kubik 2010 late pleistocene mountain glacier response to north atlantic climate change in southwest ireland quaternary science reviews 29 27 28 3948 3955

late pleistocene tidewater glaciers and glaciomarine sequences from north county mayo republic of ireland late pleistocene deposits in north county mayo were deposited in three main glacigenic environments 1 drumlins and basal tills were formed when ice moved from the irish lowlands and local mountain catchments into donegal bay 2 gilbert type deltas accumulated up to 80m i o d on the lowlands and subaqueous moraines formed across minor valleys when marine based ice grounded inland 3 a thick drape of fossiliferous glaciomarine mud along the coastal fringe was deposited from meltwater plumes and by ice rafting immediately outside of these ice limits the muds contain an elphidium clavatum dominated low diversity microfauna which is characteristic of cold water conditions adjacent to glacier termini valves of macoma calcarea from the mud have been 14c dated at 16940 120 and 17300 100 bp the high level delta complex was deposited from tidewater glaciers in a peripheral depression adjacent to the drumlin ice limits of north county mayo although the field evidence cannot be used to determine former sea level history with any accuracy it poses general problems for sea level history and isostatic effects of the last major ice sheet in the west of ireland raised glaciomarine sequences commonly occur in close association with drumlin ice limits elsewhere in ireland and represent marine transgressions prior to glacial unloading it is suggested that the magnitudes and patterns of crustal depression are greater and geometrically more complex at the margins of ice sheets in ireland than hitherto realised

evidence for heinrich event 1 in the british isles in the north irish sea basin isb sedimentary successions constrained by ams 14c dates obtained from marine microfaunas record three major palaeoenvironmental shifts during the last deglacial cycle i marine muds cooley point interstadial dated to between 16 7 and 14 7 14c kyr bp record a major deglaciation of the isb following the late glacial maximum lgm ii terminal outwash and ice contact landforms killard point stadial were deposited during an extensive ice readvance which occurred after 14 7 14c kyr bp and reached a maximum extent at ca 14 14c kyr bp at this time the lowlands surrounding the north isb were drumlinised coeval flowlines reconstructed from these bedforms end at prominent moraines killard point bride st bees and indicate contemporaneity of drumlinisation from separate ice dispersal centres substrate erosion by fast ice flow and subglacial sediment transfer to ice sheet margins in north central ireland bed reorganisation associated with this fast ice flow phase involved overprinting and drumlinisation of earlier transverse ridges rogen type moraines by headward erosion along ice streams that exited through tidewater ice margins this is the first direct terrestrial evidence that the british ice sheet bis participated in heinrich event 1 h1 iii regional mud drapes directly overlying drumlins record high relative sea level rsl with stagnation zone retreat after 13 7 14c kyr bp rough island interstadial elsewhere in lowland areas of northern britain ice marginal sediments and morainic belts record millennial scale oscillations of the bis which post date the lgm advance on to the continental shelf and pre date the loch lomond stadial younger dryas advance in the highlands of western scotland ca 11 10 14c kyr bp in western northwestern and northern ireland killard point stadial h1 ice limits are reconstructed from ice flow lines that are coeval with those in the north isb and end at prominent moraines on the scottish continental shelf possible h1 age ice limits are reconstructed from dated marine muds and associated ice marginal moraines it is argued that the last major offshore ice expansion from the scottish mountains post dated ca 15 14c kyr bp and is therefore part of the h1 event in eastern england the stratigraphic significance of the dimlington silts is re evaluated because evidence shows that there was only one major ice oscillation post dating ca 18 14c kyr bp in these lowlands in a wider context the sequence of deglacial events in the isb widespread deglaciation of southern part of the bis major readvance during h1 ice sheet collapse is similar to records of ice sheet variability from the southern margins of the laurentide ice sheet lis well dated ice marginal records however show that during the killard point readvance the bis was at its maximum position when retreat of the lis was well underway this phasing relationship supports the idea that the bis readvance was a response to north atlantic cooling induced by collapse of the lis 1998 john wiley sons ltd

glacimarine processes and inductive lithofacies modelling of ice shelf and tidewater glacier sediments based on quaternary examples abstract three variables control the type of glacial debris source and where and when debris is introduced to an ocean 1 type of glacial ice source ice sheet or valley glacier 2 condition of a grounded glacier melting freezing or frozen base and cold or warm internal ice and 3 type of glacier front ice shelf or tidewater using these variables in different combinations eight glacimarine regimes are postulated to exist by integrating information from holocene sediment and pleistocene glacimarine sequences with the eight inductive regimes lithofacies relationships are predicted and modelled the models show a complexity of glacimarine lithofacies the importance of recognizing this complexity lies in realistic interpretations of ancient sequences ice shelf sediment may be limited in the geologic record because of tectonic and climatic constraints required for ice shelf formation alternatively in some tidewater glacier regimes larger volumes of glacimarine sediment are produced than in ice shelf regimes ice proximal sediment is distinctive especially near subglacial meltwater stream effluxes ice shelves and tidewater glaciers may produce similar ice proximal lithofacies e g morainal bank associations and laminites in certain regimes however details of lithofacies may aid in distinguishing ice shelf from tidewater regimes ice shelf and tidewater iceberg zone sediment can be distinguished from each other if basal and high level englacial debris can be distinguished ice shelf zone sediment out from the grounding line has a basal debris source high level englacial debris is deposited in more distal ice shelf zones resulting in sediment by pass in corresponding positions of a tidewater glacier regime iceberg rafted debris comprises mixed basal and high level englacial debris deeper water zones receive large volumes of sediment when a melting freezing base grounding line is at the edge of a continental shelf when the grounding line retreats sediment supply may be drastically reduced because of a back sloping continental shelf and trapping by morainal banks cool water bioclastic carbonates may accumulate once a grounding line has retreated although ice shelf iceberg zones are more extensive than those in tidewater regimes ice shelf icebergs have low debris content and resulting ice rafted debris may be scarce the smallest volume of sediment is produced by a frozen base ice sheet ending as a tidewater front and the largest volume by a melting freezing base valley tidewater glacier glacimarine sediment has a relatively high preservation potential near continental interiors or margins however at continental margins mass flow olistostrome and tectonic melange deposits may be preserved with glacimarine diamictites these deposits may be difficult to distinguish from each other especially if metamorphosed such as at a convergent margin the models presented do not fully represent the glacimarine environment because many other variables are omitted however the principal concepts of generating glacimarine lithofacies associations are considered continued research will verify if each regime exists and will provide data on those regimes that exist today to compare and modify these models

barotropic stability of realistic stratospheric jets abstract the stability of realistic jets is examined in a linearized barotropic model on a sphere approximately non dispersive modes associated with a region of negative basic state absolute vorticity gradient on the poleward side of the jet are examined in detail as in previous studies broader jets and those which peak at higher latitudes produce poleward modes that are less dispersive jet profiles derived from observational data at 10 5 and 2 mb for three southern hemisphere winter months are used in the model and the results are compared with quasi nondispersive features qndf which have been observed in satellite data in the southern hemisphere winter stratosphere characteristics of the barotropically unstable modes compare remarkably well with those of the observed modes the barotropic model results for a month in which these features are not observed indicate the presence of equatorward modes at wavenumbers 3 and 4 which grow considerably faster than the quasi nondispersive poleward modes

timing of the east antrim coastal readvance phase relationships between lowland irish and upland scottish ice sheets during the last glacial termination a submillennial ice readvance from upland centres of ice dispersal in west central scotland into northeastern ireland post dates the retreat of lowland irish ice immediately after the killard point stadial max 16 5 cal ka bp the dimensions of this southerly and westerly ice sheet readvance on the margins of the north channel are reconstructed from subglacial bedform patterns subglacial tectonic deformation of tertiary lignite and glacigenic sediment limiting moraines outwash and glacial stratigraphy morainic ridges at rams island and sandy bay on the eastern margin of the lough neagh basin which mark this ice limit are perpendicular to a well defined field of subglacial bedforms across east county antrim at the ice readvance limits glacial lakes impounded in the lagan valley were partially infilled with subaqueous outwash known as the malone sands this water body drained south along the dundonald comber gap spillway providing sediment which formed extensive late glacial marine terraces at the northern end of strangford lough around 15 15 5 cal ka bp the east antrim coastal readvance is part of a much more extensive readvance southwards along the north channel and adjacent lowlands associated with ice sheet reorganisation and ice sheet growth in west central scotland it is now termed the north channel readvance and may be similar in age to the wester ross readvance moraines in northwestern scotland

temporal patterns and processes of retreat of drumlin coastal cliffs strangford lough northern ireland abstract monthly measurements of erosion pins at sixteen sites around the very low energy marine environment of strangford lough northern ireland were used to investigate temporal patterns and processes of retreat of low cliffs of glacial material erosion rates were extremely varied the mean was 76 49 03 mm a 1 erosion is strongly seasonal with 86 6 of the total erosion occurring during winter september to march periods this seasonal pattern was most exaggerated in some of the more rapidly eroding sites on the exposed eastern side of the lough preparatory processes heavy rainfall desiccation and frost action reduce the compressive strength of the cliff materials and act as important forcing of the erodibility of the cliffs direct wave attack on cliffs around the lough takes place when threshold conditions of wind speed and tidal heights are met tidal levels 1 50 m above o d with wind speed of 15 4 m s 1 30 knots maintaining for more than 4 h during the study period eighteen events exceeding the above criteria were identified extremely low atmospheric pressure has also been identified as important in raising water levels slumps falls topples and slides were the forms of cliff failure observed

glaciomarine facies from the western sector of the last british ice sheet malin beg county donegal ireland the coastal margins and mountainous core of county donegal republic of ireland have been areally scoured and deeply eroded along structural lineaments by major late devensian ice streams which moved generally westwards onto the continental shelf a raised glaciomarine sequence is selectively preserved along a gully at malin beg and comprises mud muddy diamict sand and diamict 1 the mud which was deposited from suspended sediment plumes passes upwards into muddy diamict which reflects an increase in ice rafting the muds contain a redeposited foraminiferal assemblage of ice proximal origin pumped into the water column by jets reworking previously deposited outwash the presence of middle devensian shells have been identified from the mud by amino acid analysis this suggests a late devensian age for the succession 2 the overlying sand indicates an increase in traction current activity at the site 3 there is a sharp planar contact between the sands and the overlying tabular diamict unit 4 a surficial sheet of coarse grained breccia is attributed to intense periglacial weathering along the slopes of leahan mountain this sequence and those at other sites in western ireland e g belderg co mayo provide a record of deep isostatic depression and sedimentation in a peripheral trough at the north western margin of the last british ice sheet directional indicators including drumlin fields and major troughs indicate that the north western sector of the ice sheet was drained by major ice streams these ended in calving bays ice marginal response to ice wastage depended largely on catchment factors such as the magnitude of the ice reservoirs and the length of flow lines ultimately calving led to accelerated ice flow and areal down draw and collapse of the north western sector of the ice sheet

drumlin evolution and ice sheet oscillations along the ne atlantic margin donegal bay western ireland abstract satellite imagery of donegal bay northwestern ireland reveals two streamlined subglacial bedform sets produced during the late devensian glaciation ca 22 000 15 000 yrs b p the first bedform set trends northeast southwest and records fast ice flow from inland ice domes onto the eastern atlantic continental shelf the second bedform set trending east west crosscuts and partially reorientates the first morphological and sedimentary evidence show that the second set corresponds to the last phase of fast ice flow drumlinization in northwestern ireland morphological characteristics of the donegal bay drumlin field and sedimentary characteristics of the mullinasole drumlin donegal bay support a two stage interpretation of drumlin evolution these are the following 1 deposition of glaciomarine mud and diamict facies at a tidewater glacier margin stratified diamicts record debris flow events and sediment reworking this facies sequence is erosionally truncated 2 deposition of subglacial diamict and sand facies recording ice readvance and drumlinization drumlinization sediment streamlining reflects ice mass balance destabilization episodic fast ice flow and ice marginal oscillation and may be correlated with millennial time scale climate changes in the circum north atlantic

new data for the last glacial maximum in great britain and ireland abstract understanding the history of the british and irish ice sheet biis at the last glacial maximum lgm has been advanced by new approaches in particular by cosmogenic nuclide surface exposure dating aminostratigraphy of shelly glacial deposits ams radiocarbon dating and the evidence from continental margin marine cores all of which supersede the previously weak geochronologic control it was formerly believed that great britain and ireland was largely ice free between the last interglacial oxygen isotope sub stage 5e and the late devensian when the lgm occurred as such the biis was effectively out of phase with laurentide and scandinavian ice sheets as well as inferences of ice volume from oxygen isotope stratigraphy the biis during the late devensian maximum was also perceived as having been relatively stationary new evidence shows that the lgm was an important event during the evolution of an earlier biis when the extent of ice was greater repeated iceberg rafting events over the past 50 ka are shown by marine cores while the derivative inference of numerous corresponding glacial advances is supported by several clusters of 36 cl ages on glaciated surfaces and glacial boulders that are indicative of deglacial events between 40 and 12 ka these appear to be associated with heinrich events the earliest being inferred as heinrich 4 at about 40 ka during this advance the biis and scandinavian ice sheet sis were in contact and all of ireland was glaciated the ice sheet appears to have fluctuated several times between 40 and 25 ka although evidence for this is poorly preserved but the 36 cl and 14 c evidence is clear that the biis reached its lgm maximum size about 22 ka soon after heinrich event 2 when the biis and sis were not in contact one cluster of 36 cl and 14 c ages at 21 4 1 3 ka records an initial pulse of deglaciation that was followed by extensive deglaciation about 17 4 0 4 ka just before heinrich event 1 when the ice sheet readvanced contrary to previous views the biis probably existed throughout much of devensian time as a mobile and sensitive ice sheet during which the lgm advance was but one important event in places glacial deposits of the earlier devensian glaciation have previously been incorrectly identified as products of the later lgm glaciation

ams c 14 dating of deglacial events in the irish sea basin and other sectors of the british irish ice sheet sedimentary sequences deposited by the decaying marine margin of the british irish ice sheet biis record isostatic depression and successive ice sheet retreat towards centres of ice dispersion radiocarbon dating by accelerator mass spectrometry ams of in situ marine microfaunas that are commonly associated with these sequences constrain the timing of glacial and sea level fluctuations during the last deglaciation enabling us to evaluate the dynamics of the bus and its response to north atlantic climate change here we use our radiocarbon dated stratigraphy to define six major glacial and sea level events since the last glacial maximum 1 initial deglaciation may have occurred 18 3 kyr c 14 bp along the northwestern irish coast in agreement with a deglacial age of similar to 22 cl 36 kyr bp for southwestern ireland ice retreated to inland centres and areas of transverse moraine began to form across the north irish lowlands 2 channels cut into glaciomarine deglacial sediments along the western irish sea coast are graded to below present sea level identifying a fall of relative sea level rsl in response to isostatic emergence of the coast 3 marine mud that rapidly infilled these channels records an abrupt rise in global sea level of 10 15 m similar to 16 7 c 14 kyr bp that flooded the irish sea coast and may have triggered deglaciation of a marine based margin in donegal bay 4 intertidal boulder pavements in dundalk bay indicate that rsl similar to 15 0 c 14 kyr bp was similar to present 5 a major readvance of all sectors of the biis occurred between 14 and 15 kyr 14 c bp which overprinted subglacial transverse moraines and delivered a substantial sediment flux to tidewater ice sheet margins this event the killard point stadial indicates that the bus participated in heinrich event 1 6 subsequent deposition of marine muds on drumlins 12 7 c 14 kyr bp indicates isostatic depression and attendant high rsl resulting from the killard point readvance these events identify a dynamic biis during the last deglaciation as well as significant changes in rsl that reflect a combination of isostatic loading and eustatic changes in global sea level c 2005 elsevier ltd all rights reserved

glaciomarine facies deposited by retreating tidewater glaciers an example from the late pleistocene of northern ireland lithofacies variability lithofacies relationships and sedimentary structures indicate that well exposed late pleistocene glaciogenic sequences in south county down northern ireland formed in subaqueous environments regional considerations of ice flow patterns and isostatic depression indicate that the sediments accumulated in a glaciomarine basin four major lithofacies associations are identified the first consists of muds diamictic mud and stratified sand gravel beds deposited by dispersed and concentrated meltwater sources the second occurs as a thick apron of massive and stratified diamictons formed by rainout from debris rich icebergs and resedimentation seaward of tidewater grounding zones the third association is preserved as fills in large subaqueous channels eroded into the diamicton apron these ills are characterized by slumping and debris flow interbedded sand gravel diamicton and mud from channel flanks interactions between underflows and overflows rhythmically bedded mud along channel axes and traction current activity prograded sand aprons at the top of the sequence the fourth comprises a late glacial emergent beach facies sand and gravel that truncates the earlier deposits along the entire exposure abrupt variations in dominant clast type erratics and matrix carbonate content within the sediment pile reflect indirect glacial input from three distinct geological provenances into the glaciomarine basin variability of this type should not be used for stratigraphic correlations in place of direct glacial stratigraphy this type of situation may be more common than hitherto realized in the late pleistocene mid latitude forelands characterized by complexly interbedded diamicton sequences which formed when isostatic depression exceeded sea level fall

sedimentation at the margins of a late pleistocene ice lobe terminating in shallow marine environments dundalk bay eastern ireland late pleistocene morainic sequences around dundalk bay eastern ireland were deposited in a variety of shallow glaciomarine environments at the margins of a grounded ice lobe the deposits are essentially ice proximal delta fan and apron sequences and are divided into two lithofacies associations lithofacies association 1 occurs as a series of morainal banks formed at the southern margin of the ice lobe in a body of water open to influences from the irish sea the morainal banks consist mainly of diamictic muds deposited from turbid plumes and by ice rafting with minor occurrences of turbidites cross bedded gravels subaqueous outwash and massive boulder gravels high density debris flows lithofacies association 2 was deposited in a narrow arm of the sea at the north eastern margin of the ice lobe the deposits consist mainly of a series of coalescing ice proximal gilbert type fan deltas which are interbedded distally with tabular and lens shaped subaqueous deposits the latter are mainly ice rafted diamictons debris flow deposits and subaqueous sands and gravels both lithofacies associations are draped by diamictons formed by a combination of rain out debris flow and traction current activity at a few localities the upper parts of the sequence have been sheared by minor oscillations of the ice sheet margin these sequences form part of an extensive belt of glaciomarine deposits which border the drumlin swarms of east central ireland lithostratigraphic variability is partially related to the arrival of large volumes of debris at the ice lobe margin when the main lowland ice sheet surged during drumlin formation complex depositional continua of this type lack any major erosional breaks and should not be used either as climatic proxies or for stratigraphic correlations

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

timing of the last glacial maximum from observed sea level minima during the last glacial maximum ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today but few direct estimates exist of the volume of the ice sheets or the timing and rates of change during their advance and retreat here we analyze four distinct sediment facies in the shallow tectonically stable bonaparte gulf australia each of which is characteristic of a distinct range in sea level to estimate the maximum volume of land based ice during the last glaciation and the timing of the initial melting phase we use faunal assemblages and preservation status of the sediments to distinguish open marine shallow marine marginal marine and brackish conditions and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio hydroisostatic modelling our results indicate that from at least 22 000 to 19 000 calendar years before present land based ice volume was at its maximum exceeding today s grounded ice sheets by 52 5 x 10 exp 6 cu km a rapid decrease in ice volume by about 10 percent within a few hundred years terminated the last glacial maximum at 19 000 250 years

intertidal forms produced by floating ice in vestfirdir iceland forms produced by the action of intertidal ice in the fjord of kaldalon vestfirdir iceland are described and interpreted in terms of their morphogenetic environment isolated boulders resting on top of undisturbed fine sediments are interpreted as dropstones from floating intertidal ice following rockfall events boulder pavements and ridges which occur in the upper intertidal zone are related to the onshore movement of ice packing and bulldozing boulders together the occurrence of such ice formed features in kaldalon is attributed to their preservation within a low energy environment in spite of a limited ice climate the paucity of such forms preserved in the sedimentary record suggests that opportunities for burial and preservation are limited except where local infill is rapid

a model of subaqueous sedimentation at the margin of the late midlandian irish ice sheet connemara ireland and its implications for regionally high isostatic sea levels abstract the geomorphology and sedimentology of a series of late midlandian glacigenic sites in connemara western ireland are described and a set of commonly occurring sedimentary assemblages identified these form components of a simple model of ice contact subaqueous sedimentation involving progressive down current transition from subglacial esker tunnel fill through proximal tunnel mouth fans proximal and distal subaqueous fans into basin floor sediments in two of the sites aggradation to the water line passes into fan delta topsets and foresets all sites abut into inferred water bodies to their west and imply minimum water surface heights of between 35 and 65 m irish od or in the case of the two deltaic sites shoreline heights of between 75 and 80 m these high water levels very close to and facing directly into the immediately adjacent open atlantic ocean are difficult to explain as ice dammed glaciolacustrine water bodies without invoking improbable ice sheet marginal geometries they may however be explained as a set of successive fjord head grounding line depositional systems that trace temporary still stands in the phased retreat of the irish ice sheet from its offshore maximum this possibility not yet confirmed by the discovery of in situ marine fauna implies a degree of late midlandian isostatic depression and subsequent response unexplained by currently applied crustal response models but supported by previously constructed glacio sedimentary models

the importance of the terrigenous fraction within a cold water coral mound a case study in the nineties cold water coral mounds were discovered in the porcupine seabight ne atlantic west of ireland a decade later this discovery led to the drilling of the entire challenger cold water coral mound eastern slope porcupine seabight during iodp expedition 307 as more than 50 of the sediment within challenger mound consists of terrigenous material the terrigenous component is equally important for the build up of the mound as the framework building corals moreover the terrigenous fraction contains important information on the dynamics and the conditions of the depositional environment during mound development in this study the first in depth investigation of the terrigenous sediment fraction of a cold water coral mound is performed combining clay mineralogy sedimentology petrography and sr nd isotopic analysis on a gravity core md01 2451g collected at the top of challenger mound sr and nd isotopic fingerprinting identifies ireland as the main contributor of terrigenous material in challenger mound besides this a variable input of volcanic material from the northern volcanic provinces iceland and or the nw british isles is recognized in most of the samples this volcanic material was most likely transported to challenger mound during cold climatic stages in three samples the isotopic ratios indicate a minor contribution of sediment deriving from the old cratons on greenland scandinavia or canada the grain size distributions of glacial sediments demonstrate that ice rafted debris was deposited with little or no sorting indicating a slow bottom current regime in contrast interglacial intervals contain strongly current sorted sediments including reworked glacio marine grains the micro textures of the quartz sand grains confirm the presence of grains transported by icebergs in interglacial intervals these observations highlight the role of ice rafting as an important transport mechanism of terrigenous material towards the mound during the late quaternary furthermore elevated smectite content in the siliciclastic glaciomarine sediment intervals is linked to the deglaciation history of the british irish ice sheet biis the increase of smectite is attributed to the initial stage of chemical weathering processes which became activated following glacial retreat and the onset of warmer climatic conditions during these deglaciations a significant change in the signature of the detrital fraction and a lack of coral growth is observed therefore we postulate that the deglaciation of the biis has an important effect on mound growth it can seriously alter the hydrography nutrient supply and sedimentation processes thereby affecting both sediment input and coral growth and hence coral mound development

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

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

a late pleistocene intertidal boulder pavement from an isostatically emergent coast dundalk bay eastern ireland late pleistocene sequences around dundalk bay eastern ireland record glaciomarine sedimentation near the margin of a grounded ice lobe around 15 ka sp a coastal exposure at cooley point consists of four major facies deposited outside this ice limit 1 a basal mud facies deposited from sediment plumes accumulated following the initial ice marginal retreat inland it contains a well preserved arctic microfauna dominated by the foram elphidium clavatum and the ostracod roundstonia globulifera 2 a flat to undulating boulder facies pavement mostly one clast thick is found pressed into the mud and is characterized by bevelled and striated upper clast surfaces pavement attributes are a result of intertidal activity in a cold climate the boulder source is due to rafting by ice flees from glacigenic debris deposited during an ice advance 3 laminated sand facies drape the pavement and are a result of variable current activity 4 the overlying gravel facies is separated from the sand facies by a marine erosion surface the gravel facies is subaqueous channelized and is overlain by late glacial raised beach ridges locally the gravels have been deformed by ice pressure from partially floating ice flees facies changes record terrestrial submergence and provide evidence for changes in relative sea level during part of the last deglacial cycle the boulder pavement and deformed gravel facies suggest that ice flees and sea ice effects may be more common within stratigraphies along emergent coasts than previously thought though they have a low preservation potential extreme conditions during the deglacial favoured opportunistic microfaunas during mud deposition this event may be related to a major meltwater event within the irish sea basin