reconstructing the environmental history of the last glacial interglacial transition evidence from the isle of skye inner hebrides scotland abstract a new interpretation is presented of the late devensian late weichselian wisconsinan lateglacial and early flandrian holocene environmental history of the isle of skye inner hebrides scotland this reconstruction based on pollen percentage pollen concentration pollen preservation and chemical data differs in a number of respects from previous explanations of the lateglacial environmental history of the island the evidence suggests that throughout the lateglacial and early flandrian variation in degree of exposure to prevailing westerly winds was the dominant factor influencing the development of regional vegetation patterns the data provide a proxy climatic record for western scotland during the last glacial interglacial transition and this is discussed in the context of both onshore and offshore evidence the results from skye demonstrate the importance of pollen preservation studies in the interpretation of pollen taphonomy and in the evaluation of lateglacial and early flandrian radiocarbon dates

geologic thermobarometry of retrograded metamorphic rocks an indication of the uplift trajectory of a portion of the northern scandinavian caledonides kyanite grade pelitic schists from the efjord area 68 15 n 16 45 e northern norway show abundant textural evidence of retrograde reequilibration during late orogenic uplift and cooling of this part of the scandinavian caledonides graphical analysis of mineral compositions in seven samples that show a range of retrograde textures indicates that they reached final chemical equilibrium under nonuniform pressure temperature conditions three element partitioning geothermometers and geobarometers yield consistent pt estimates in individual samples which together define a trend in pt space the sample showing the fewest signs of retrogression yields the highest pressure and temperature estimates whereas samples exhibiting abundant reequilibration textures give lower pt estimates we suggest that the trend indicated by these samples reflects a portion of the pt trajectory assumed by the efjord area during uplift thus the judicious use of element partitioning geothermometers and geobarometers on samples showing signs of retrograde metamorphism may yield important new information concerning the late tectonic evolution of metamorphic terrains

deglacial warming of the northeastern atlantic ocean correlation with the paleoclimatic evolution of the european continent abstract isotopic micropaleontologic and pollen analyses of deep sea cores from the bay of biscay and the northeastern atlantic ocean show that the deglacial warming of this oceanic area was closely correlated with the paleoclimatic evolution of the adjacent european continent temperatures were at least as warm as those of today in the bay of biscay between 13 300 and 11 000 b p coinciding with the combined bolling allerod warm continental events a major spread of polar water occurred between 11 000 and 10 000 b p during this event which coincides with the younger dryas continental cold event marine temperatures were almost as low as those of the last glacial maximum the final deglacial warming of the norteastern atlatntic ocean occurred during the following 3000 yr

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

evidence for two step deglaciation and its impact on north atlantic deep water circulation oxygen and carbon isotope records from benthic and planktonic foraminifera are presented for the past 35 000 years in the northeastern atlantic the results support the idea that the last deglaci ation took place in two major steps1 4 and conflict with theories calling for a strong reduction in north atlantic deep water formation to explain the abrupt cooling of the younger dryas cold period5 7

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

late devensian to early holocene palaeoenvironmental changes in the viking bank area northern north sea abstract lithological and macrofaunal analysis of vibrocores collected from northwest of the viking bank enables the devensian to holocene strata to be subdivided into eight informal units three of which occur widely in the northern north sea for the viking bank area it is suggested that sea level was more than 100 110 m below that at present between 15 500 and 13 600 bp a time when some parts of the area were dry land and others covered by a shallow high arctic sea sea level may have been even lower more than 140 m below its present level prior to 15 500 bp during the windermere interstadial 13 000 11 000 bp polar water was replaced by atlantic water and the environment was low arctic with a regime of strong tidal currents sea level at approximately 12 000 bp had risen to some 80 100 m below present the loch lomond stadial and early holocene generally were characterised by high arctic followed by boreo arctic to boreal faunas relatively low energy conditions and probably rapidly rising sea level

reconstruction of the last deglaciation deconvolved records of δ18o profiles micropaleontological variations and accelerator mass spectrometric14c dating bioturbation acts as a low pass filter in displacing and reducing the amplitudes of stratigraphic signals this often leads to a loss of high frequency events in the stratigraphic record in addition when considering an isotopic signal 18o 14c measured in stratigraphic carriers such as foraminifera bioturbation and carrier abundance changes can create artifacts which may be falsely interpreted as leads or lags in the paleoclimatic record

new age constraints for the maximum extent of the last british irish ice sheet nw sector this paper presents the first terrestrial age constraints from the outer continental shelf for the maximum extent of the nw sector of the last british irish ice sheet cosmogenic 10be ages from eight glacially transported boulders on the island of north rona show that the late devensian late weichselian british irish ice sheet overrode the island at its maximal stage and retreated c 25 ka bp these new dates supported by other geological evidence indicate that the north western part of the ice sheet was most extensive between 27 and 25 ka bp reaching the outer continental shelf during the global eustatic sea level minimum at the last glacial maximum

the last ice sheet in north west scotland reconstruction and implications recent models of the last scottish ice sheet suggest that nunataks remained above the ice surface in areas peripheral to the main centres of accumulation this proposition has been investigated on 140 mountains over an area of 10 000 km2 in nw scotland outside the limits of the later loch lomond readvance in this area there is evidence for a single high level weathering limit that separates glacially eroded terrain from higher areas of in situ frost debris this limit occurs at altitudes ranging from 425 to 450 m in the outer hebrides to 950 m on the mainland and is best developed on lithologies that resisted breakdown after ice sheet downwastage interpretation of this weathering limit as a periglacial trimline cut by the last ice sheet at its maximum thickness is supported by 1 joint depth and schmidt hammer measurements that indicate significantly more advanced rock breakdown above the weathering limit 2 a much greater representation of gibbsite a pre late devensian weathering product in the clay fraction of soils above the limit 3 cosmogenic isotope dating of the exposure ages of rock outcrops above and below the limit 4 the sharpness of the limit at some sites and its regular decline along former ice flowlines and 5 shear stress calculations based on the inferred altitude and gradient of the former ice surface reconstruction of the ice surface based on trimline evidence indicates that the mainland ice shed lay near or slightly east of the present watershed and descended northwards from 900 m to ca 550 m at the north coast independent dispersion centres fed broad ice streams that occupied major troughs on skye an ice dome 800 m deflected the northwestwards movement of mainland ice but the mountains of rum were over ridden by mainland ice up to an altitude of ca 700 m the outer hebrides supported an independent ice cap that was confluent with mainland ice in the minches extrapolation of the trimline evidence indicates that most reconstructions of ice extent are too conservative and suggests that low gradient ice streams extended across the hebridean shelf offshore wider implications of this research are 1 that blockfields and other periglacial weathering covers are not all of the same age or significance depending on the resistance of different lithologies to frost weathering 2 that the contrasting degree of glacial modification in the western and eastern highlands of scotland may reflect a former cover of predominantly warm based ice in the former and predominantly cold based ice in the latter and 3 that the approach and techniques developed in this study have potential application for constraining ice sheet models not only in areas peripheral to the main centres of ice accumulation in britain and ireland but also in other mountain areas where nunataks protruded through warm based late pleistocene ice masses

new evidence from the south china sea for an abrupt termination of the last glacial period abrupt changes in climatic conditions have been seen at high latitudes in the north atlantic1 and the antarctic2 3 at 13 kyr bp it is important to determine whether this abrupt change was confined to high latitude regions or whether it was global here we present results demonstrating an abrupt change in the rate and character of sedimentation in the south china sea at the close of the last glacial period radiocarbon dating and its position in the oxygen isotope shift suggest that this change may be coincident with the changes found at high latitudes

a 9000 year old ash bed on the faroe islands abstract radiocarbon datings of the saksunarvatn ash bed on the faroe islands indicate an age of 9000 9100 yr b p the saksunarvatn ash bed differs geochemically from both ash zone 1 in the north atlantic and the vedde ash bed of norway and the norwegian sea all mentioned ashes are assumed to originate from iceland the vedde ash has been dated at 10 600 60 yr b p consequently the saksunarvatn and vedde ash beds provide an opportunity for precise dating of events around the pleistocene holocene boundary in marine cores especially from the region where the two plumes overlap

marine molluscs and late quaternary environmental studies with particular reference to the late glacial period in northwest europe a review abstract although it is now commonly thought that temperature is a minor factor in limiting the distribution of marine invertebrates particularly on a local scale there is evidence to suggest that some boreal molluscs particularly those which occur in similar environments on both sides of the north atlantic are valuable as oceanic temperature indicators this applies particularly to planktotrophic species whose northern limits of distribution are apparently controlled by summer surface temperature the oceanography of the eastern north atlantic is briefly considered in relation to zoogeographic subdivisions based on temperature and it is concluded that the latter are fairly crude and apply only to shelf seas most glaciomarine molluscan faunas are not specific to that environment an exception being that dominated by the bivalve portlandia arctica the role of marine molluscs in palaeoenvironmental research at the local level for the 13 11 ka bp period is illustrated by a site at inchinnan scotland it is concluded that a shell bed at this locality consists partly of a little modified life assemblage and partly of shells which have been gently reworked under conditions of generally rapid deposition during the same time interval the changing composition of molluscan faunas on the nw european seaboard suggests that a weak drift of north atlantic water replaced polar water at or a little later than 13 ka bp off scotland and a few hundred years later off northern norway evidence for relatively warm intervals early and late in the 13 11 ka bp period has been found particulary on the scottish coast and to a lesser extent more generally the later warm interval may be related to the southward movement of the polar front at the beginning of the younger dryas the value of the bivalve shell itself in the determination of temperature seasonality and calendar years is briefly discussed

late weichselian vegetation climate and floral migration at liastemmen north rogaland south western norway palynological results from liastemmen indicate a tripartite division of the late weichselian in the pleniglacial period from deglaciation ca 14000 bp to ca 13000 bp artemisia dominated pioneer vegetation on disturbed mineral soil was strongly influenced by cold winters and katabatic winds the late weichselian interstadial ca 13000 bp ca 11000 bp comprises a salix shrub consolidation phase and from ca 12700 bp a tree birch phase in the last 500 years of this period july and january means are estimated to about 16 c and between 2 c and 6 c respectively in the younger dryas stadial ca 11000 bp ca 10200 bp artemisia dominated vegetation returns three brief climatic deteriorations ca 12 250 bp 11 700 bp and 11 300 bp unfavourable to woody vegetation on humus soils are demonstrated within the interstadial critical climatic factors include cool winters and strong winds exposing vegetation and soil to frost drought and erosion the oldest and strongest oscillation probably involving local deforestation is correlated with the older dryas deterioration boreal circumpolar eurasiatic and arctic alpine plants dominated the late glacial flora for the majority of the late glacial taxa a northward migration is demonstrated this may also apply for papaver radicatum pinguicula alpina and primula scandinavica all with bicentric distributions in norway today

glacial isostasy and water depths in the late devensian and holocene on the scottish shelf west of the outer hebrides

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

the submerged landforms of the st kilda archipelago western scotland abstract a detailed bathymetric map of the area around the st kilda archipelago has been prepared with a 10 m isobath vertical interval the map reveals two major submerged erosional surfaces that culminate in clifflines the lower surface at ca 120 m covers at least 40 km2 and is thought to have been produced during low sea levels coincident with periods of maximum northern hemisphere glaciation the upper surface is complex in origin varying between 80 and 40 m it is thought to have been produced during periods of partial northern hemisphere glaciation the last such period the loch lomond younger dryas stadial being responsible for the production of the ca 40 m cliff platform junction the last 40 m relative rise of sea level has been accompanied by very little marine erosion despite the very exposed situation of the islands and this sea level rise is thought to have taken place during the flandrian

aluminum silicates in the mount raleigh pendant british columbia in regionally metamorphosed pelites of the mount raleigh pendant the fibrolite isograd occurs 5km downgrade from the sillimanite isograd fibrolite formed from the decomposition of biotite a reaction that probably resulted from the late stage influx of acidic volatiles in contrast sillimanite formed by the direct volume for volume replacement of andalusite andalusite and sillimanite coexist in a 3 km wide zone above the sillimanite isograd electron probe analyses of these phases reveal low minor element contents and yield kd x values close to unity the low fe2o3 contents are compatible with reducing conditions implied by the ubiquity of graphite because kd 1 0 the zone of coexisting andalusite sillimanite cannot be attributed to multivariancy resulting from partitioning of minor elements between these phases rather the metastable persistence of andalusite into the sillimanite p t stability field is suggested the modal proportions of sillimanite versus andalusite imply that minimal 5 and alusitesillimanite reaction occurred in a zone 1 5km above the sillimanite isograd in contrast there was a marked increase in reaction progress immediately above this zone with an estimated thermal gradient in the plane of exposure of approximately 20 c km the 1 5 km wide zone of nil reaction suggests that the andalusite sillimanite equilibrium boundary was overstepped by about 30 c before significant reaction occurred inclusion rich areas in andalusite provided favourable sites for sillimanite nucleation however the growth of sillimanite may have been impeded by pinning of sillimanite grain boundaries by inclusions

late quaternary stratigraphy of the northern rockall trough and faeroe shetland channel northeast atlantic ocean a late quaternary deep water stratigraphic framework has been established for the deep water areas 450m of the northern rockall trough and faeroe shetland channel four stratigraphic units 1 4 are identified these are primarily biostratigraphic units based on dinoflagellate cyst evidence unit 1 represents the late weichselian glacial pre 13 000 yr bp unit 2 the late glacial interstadial 11 000 13 000 yr bp unit 3 is of younger dryas age 10 000 11 000 yr bp and unit 4 represents the holocene interglacial post 10 000 yr bp this stratigraphy is supported by the discovery of the mixed vedde ash 10 600 yr bp and north atlantic ash zone 1 and the saksunarvatn ash 9000 9100 yr bp concentrated in units 3 and 4 respectively the sedimentology indicates that the oceanographic regime underwent a major change between the glacial and interglacial stages this is marked by the onset of strong bottom current activity allied to the restoration of overflow of the norwegian sea deep water into the north atlantic towards the end of the younger dryas stadial despite intense bioturbation and bottom current reworking the basic stratigraphic framework is maintained recognition of two volcanic ash markers enables correlation with established onshore and offshore sequences of marine and non marine environments

millennial scale depositional cycles related to british ice sheet variability and north atlantic paleocirculation since 45 kyr b p barra fan u k margin lithology lithic petrology planktonic foraminiferal abundances and clastic grain sizes have been determined in a 30 m long core recovered from the barra fan off northwest scotland the record extends back to around 45 kyr b p with sedimentation rates ranging between 50 and 200 cm kyr the abundance of ice rafted debris indicates 16 glacimarine events including temporal equivalents to heinrich events 1 4 enhanced concentrations of basaltic material derived from the british tertiary province suggest that the glacimarine sediments record variations in a glacial source on the hebrides shelf margin glacimarine zones are separated by silty intervals with high planktonic foraminifera concentrations that reflect an interstadial circulation regime in the rockall trough the results suggest that the last british ice sheet fluctuated with a periodicity of 2000 3000 years in common with the dansgaard oeschger climate cycle

freshwater influx hydrographic reorganization and the dispersal of ice rafted detritus in the sub polar north atlantic ocean during the last deglaciation a sediment core from the north east north atlantic contains high resolution co registered foraminiferal 18o and ice rafted detritus ird records for the last deglaciation these reveal a distinct ice rafting event that occurred at the time of greenland interstade 1d gi 1d a feature also seen in other high resolution cores from the north atlantic the occurrence of a geographically widespread peak in ird at ice distal sites at a time when increased freshwater flux to the surface ocean is inferred to have caused rapid cooling suggests a mechanistic link between the processes analogous to the younger dryas gs 1 cooling episode the general absence of ird at southern locations at other times during gi 1 when the flux of icebergs from surviving ice sheets to northern locations continued suggests that the gi 1d ird peak represents a time of hyrdrographic reorganization which changed ird dispersal while numerous studies have suggested freshwater flux as a major driver of rapid climate oscillations observed around the north atlantic during the last deglaciation the evidence presented here both supports that mechanism and highlights the potential for rapid and major reorganization of the north atlantic s surface hydrography to explain changes in ird flux independently of ice sheet calving dynamics

new constraints on the age of the last ice sheet glaciation in nw england using optically stimulated luminescence dating optically stimulated luminescence osl has been used to date silts interpreted as either primary or colluviated loess deposited in karstic depressions at three sites on the carboniferous limestone of nw england two of the ages presented here constrain the onset of the last late devensian ice in this region to later than ca 27 2 ka and the other two date initial deglaciation prior to ca 19 2 ka in the morecambe bay area and ca 17 2 ka in the karst of the yorkshire dales while these ages are broadly consistent with existing estimates from lacustrine and speleothem evidence they offer the tightest constraints yet published on the presence of the last ice sheet from northern england copyright 2009 john wiley sons ltd

late devensian and flandrian palaeoenvironmental changes on the scottish continental shelf west of the outer hebrides examination of two radiocarbon dated vibrocores taken from south of st kilda at a water depth of about 155 m a short distance within the maximum position of the late devensian dimlington stadial ice sheet suggests that the st kilda basin became free of glacier ice after 15250 yr bp sedimentation in a shallow low energy high arctic muddy environment continued until after 13500 yr bp there followed a higher energy temperate episode during which water depths were roughly about 40 m this is correlated with the latter part of the windermere interstadial and with the warmer interval known in shallow scottish seas about or a little before 11 000 yr bp the loch lomond younger dryas stadial is marked in the vibrocores by the return of muddy sediments and a cold water fauna relatively shallow water conditions seem to have persisted into the earliest flandrian when the water depth was still roughly 60 m corresponding to a sea level in the area 90 100 m below present it is suggested that pack ice was widespread in the northeast atlantic before the windermere interstadial and also during the loch lomond stadial when it transported shards of icelandic volcanic ash into the st kilda basin estimates of sea surface temperature for the last part of the windermere interstadial are close to those derived from the deep sea record for the same period

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

evolution of seasonal stratification in the celtic sea during the holocene seasonal thermocline development in the shelf seas of nw europe results in the formation of pronounced frontal regions which separate stratified from well mixed water numerical m 2 palaeotidal modelling of the nw european continental shelf during successive stages of the holocene transgression indicates that seasonal stratification started to develop in the central celtic sea once a critical threshold water depth had been exceeded at around 9000 years bp this hypothesis has been tested through faunal isotopic and geochemical analysis of an ams 14 c dated british geological survey vibrocore from the celtic deep bathymetric basin a record which spans the last 12 000 years marked positive trends in the stable oxygen isotopic data from the benthic foraminifera ammonia batavus and quinqueloculina seminulum between 9000 and about 5000 years bp represent a 4 5 c cooling in summer bottom water temperature caused by the progressive replacement of tidally well mixed by stratified water stable carbon isotopic data from the same species measured through the same core intervals show a negative trend consistent with net oxygen utilization and decomposition of organic matter beneath the productive frontal zone these geological data indicate the progressive evolution of seasonally stratified water in the celtic sea during the earlier part of the holocene modern shelf sea frontal and thermocline development are known to influence biological productivity sedimentation rates the organic content of shelf sediments and the climate of surrounding landmasses hence these palaeodata have significance in defining the role of shelf sea environments in the climate system

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

dating and rhythmicity from the last deglacial cycle in the british isles in northern britain glaciotectonically thickened sediment piles represent the sediment flux transferred to ice margins by phases of fast ice flow and drumlin streamlining during the last deglacial cycle radiocarbon dating of marine faunas within deglacial muds age constrain phases of drumlinisation shaping to between 19 and 14 5 ka bp individual phases of drumlinization can be correlated with millennial time scale discharge events documented from the circum north atlantic which are probably climate driven the overall deglacial cycle records at least five major millennial time scale ice margin oscillations and phases of sediment sequence rhythmicity

vedde ash layer discovered in a small lake basin on the scottish mainland a thin layer of micro tephra particles has been discovered in a lake sediment sequence from sutherland scotland the tephra is attributed to the vedde ash on the basis of ash geochemistry the vedde ash which has been dated to c 10 300 radiocarbon years bp and which was thus deposited during the younger dryas chronozone has previously been reported from lake sequences in norway from sediment cores from the ne north atlantic and from greenland ice cores but this is the first reported record from the british mainland it is likely that this ash layer also occurs in other lake sediment sequences in northern britain thus providing the potential for more precise correlations of younger dryas sequences than has hitherto been the case the way in which correlation by tephrochronology may revolutionize approaches to reconstructing the sequence of events in thene atlantic region during the last glacial interglacial transition is briefly considered

pre andean orogenesis in the coast ranges of central chile an intense structural metamorphic event of probable permian triassic age is inferred from petrologic and field observations of low grade schists from the coast ranges of central chile between latitudes 38 s and 43 s relict almandine rich garnet biotite and aluminous amphibole in mafic schists are replaced by a pervasive assemblage consisting of albite chlorite epidote actinolite sphene quartz stilpnomelane white mica iron oxide chemographic analysis of phase compatibilities based on electron microprobe analyses suggests a regional retrogradation from earlier upper greenschist and or epidote amphibolite to lower greenschist facies a regional northwest southeast trending fabric within the terrane was imposed during the lower greenschist metamorphism which involved widespread reintroduction of fluids into the system this major orogenic event is thought to be the culminating episode in a subduction related accretionary process along the late paleozoic margin of south america convergence may have been markedly oblique to the present north south trending continental margin

a younger dryas ash bed in western norway and its possible correlations with tephra in cores from the norwegian sea and the north atlantic abstract a bed of volcanic ash up to 23 cm thick is found in lacustrine and marine sediments in western norway it is formally mamed the vedde ash bed and its age is approximately 10 600 yr b p i e mid younger dryas the bed consits of pure glass having a bimodal basaltic and rhyolitic somposition the geochemistry of the glass shards suggests an icelandic source by means of stratigraphic position and geochemistry the ash is correlated with ash zones found in cores from the continental shelf the norwegian sea and the north atlatic

autochthonous block fields in southern norway implications for the geometry thickness and isostatic loading of the late weichselian scandinavian ice sheet the consistent geographical and altitudinal distribution of autochthonous block fields mantle of bedrock weathered in situ and trimlines in southern norway suggests a multi domed and asymmetric late weichselian ice sheet low gradient ice sheet profiles in the southern baltic region in the north sea and along the outer fjord areas of southern norway are best explained by movement of ice on a bed of deforming sediment although water lubricated sliding or a combination of the two may not be excluded the ice thickness distribution of the late weichselian scandinavian ice sheet is not in correspondence with the modern uplift pattern of fennoscandia early holocene crustal rebound was apparently determined by an exponential glacio isostatic rise later however crustal movements appear to have been dominated by large scale tectonic uplift of the fennoscandian shield centred on the gulf of bothnia the region of maximum lithosphere thickness

sub ice shelf deposition during the late devensian glaciation in western ireland abstract glacigenic sediments preserved around the margins of clew bay western ireland record deposition in a tidally influenced sub ice shelf environment during the late devensian glaciation 21 13 14 c kyr thick massive to normally graded glacial diamictons tills are interbedded with laminated to massive silt and clay beds these sediments interbed with each other on scales ranging from millimetres to metres in a generally shallowing up sequence associated with a decrease in accommodation space isolated dropstones and a downward going clastic dike are also observed these structures and sediments reflect a waterlain environment with rhythmically varying levels of water energy and sediment supply tidally driven uplift and downdraw of a retreating ice shelf is a likely control on sedimentation patterns and glacial dynamics of this sensitive atlantic facing ice margin

extent and deglacial chronology of the last british irish ice sheet implications of exposure dating using cosmogenic isotopes over 160 10be and 36cl exposure ages pertaining to the extent and chronology of the last british irish ice sheet biis are critically reviewed despite uncertainties inherent in the use of exposure ages this approach has demonstrated that at the last glacial maximum lgm ca 26 21 ka the biis extended over all low ground in scotland and all or almost all of ireland consistent with recent models depicting extension of the last biis to the atlantic shelf edge all exposure ages obtained for high level sites above trimlines on the mountains of northwestern scotland and ireland pre date the lgm this finding confirms that high plateaux in these areas escaped significant glacial erosion probably under a protective cover of cold based glacier ice that remained frozen to the underlying substrate in terms of deglaciation chronology the southern irish sea basin was probably deglaciated by 19 18 ka with extensive deglaciation of low ground in ireland and northeastern scotland prior to ca 14 5 ka ice cover on low ground in northwestern scotland apparently persisted after 14 0 ka suggesting survival of ice in favourable locations during the lateglacial interstade ca 14 5 12 9 ka attempts to date readvances have had mixed success the wester ross readvance in northwestern scotland was initially dated to ca 16 3 ka but more recent research implies a much younger age ca 14 0 13 5 ka exposure ages indicating a prolonged stillstand during ice sheet retreat in the cairngorms at ca 14 5 14 0 ka conflict with ages obtained on postglacial rockslides and basal radiocarbon dates which indicate deglaciation before ca 15 5 15 0 ka exposure dating has been successfully employed to confirm a loch lomond stadial ca 12 9 11 5 ka age for moraines in several mountain areas and to constrain the minimum altitude of the ice cap that extended over the western grampians at that time copyright 2009 john wiley sons ltd

long range transport of volcanic ash to the greenland ice sheet betzer et al 1 reported the surprising discovery of giant 75 m mineral particles transported more than 10 000 km from their source we have found volcanic ash containing glass shards as large as 300 m in a section of wisconsinian ice from the dye 3 core in greenland which is similarly unexpected and raises interesting questions concerning the long range aeolian transport of particulate matter as the volcanic ash correlates well with similar ash in deep sea sediment cores from the atlantic it also allows us to date the ice with some confidence

a late devensian ice free area and possible interglacial site on the isle of lewis scotland at the time of the last glacial maximum the last scottish ice sheet has been considered by some1 2 to have extended to the continental shelf edge fig 1a whilst others3 4 have suggested that there were ice free areas in northern scotland no radiocarbon dated strati graphical evidence has been published to support either interpretation we present here data from the isle of lewis establishing that the shelly deposits from the north of that island are of late devensian age but which also show that a late devensian ice margin lay across northern lewis leaving part of the island ice free a peat possibly of interglacial status has been found in the ice free area the last scottish ice sheet therefore did not pass beyond the outer hebrides and may not even have reached the north of the island chain this evidence is also of interest to the debate on the relative expansions of the northern and southern margins of the laurentide and scandinavian ice sheets at the last glacial maximum5 6 for it suggests a restricted glacial expansion of the northern margin of the last british ice sheet at the time of its greatest southerly extent

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

mollusca stable isotope record of a core from lake frassino northern italy hydrological and climatic changes during the last 14 ka a core retrieved from lake frassino northern italy provided evidence of palaeohydrological change in this area during the last 14 ka lithological malacological and in particular stable isotope composition of freshwater shells allowed the delineation of the main phases of lake evolution between the lateglacial and holocene lateglacial conditions were drier than the holocene although a wetter period was inferred before c 14 ka according to the oxygen isotope composition of freshwater shells the holocene showed a clear bipartition the first part which lasted from 9100 to 7000 yr bp was drier and was followed by a rapid increase in humidity at 7000 6800 yr bp between 6800 and 5000 yr bp there were wetter and more stable conditions as indicated by smaller 18 o oscillations of pisidium and valvata shells from c 5000 to 2600 yr bp the record is characterized by larger fluctuations which may indicate that short term and particularly pronounced alternation of wet and dry periods occurred

systematic retrograde metamorphism of sillimanite staurolite schists new salem area massachusetts the new salem retrograde metamorphic zone occupies an approximately triangular area covering 26 km 2 in sillimanite staurolite grade rocks largely pelitic schists of the devonian littleton formation acadian prograde metamorphism at 6 kbar and 600 c produced the common assemblage quartz muscovite biotite garnet staurolite iunenite albite graphite sillimanite pyrrhotite systematic hydration of the prograde assemblages by an influx of h 2 o produced the retrograde assemblages chlorite k feldspar celadonitic musco vite sphene anatase pyrite common and chlorite chloritoid musco vite anatase sphene rare retrograde sillimanite out staurolite out and garnet out isograds have been mapped representing the completion of important retrograde hydration reactions these isograds plus the thicknesses of chlorite rims on garnets 0 and 0 2 mm can be used to subdivide the area into six concentric retrograde metamorphic zones designated r1 to r6 during retrograde metamorphism the exchange reactions k na mn fe mg and fe mg proceeded while more or less consistent tie lines between the sheet silicates and ilmenite were maintained biotite and chlorite became more fe rich owing to staurolite garnet and ilmenite breakdown biotite chlorite and ilmenite became more mn rich owing to garnet breakdown coexisting biotite and muscovite became more k rich during biotite breakdown muscovite also became progressively more celadonite rich chlorite biotite and ilmenite are homogeneous in single thin sections muscovite is zoned with respect to m 2 m 2 al iv and k k na ratios which are higher in muscovite rims there is no evidence for re equilibration of staurolite garnet or albite during retrograde metamorphism temperature and pressure estimates for retrograde metamorphism are poorly constrained to 3 5 kbar and 280 c each kilometre of vertical extent of the retrograde zone required an influx of 0 26 km 3 of h 2 o at stp water may have been derived from a large volume of surrounding rock and concentrated in the study area by a pressure shadow effect around the north end of the prescott intrusive complex

extent and retreat history of the barra fan ice stream offshore western scotland and northern ireland during the last glaciation abstract during the last glacial maximum lgm the marine terminating barra fan ice stream bfis a major conduit of the british irish ice sheet biis drained much of western scotland and northwest ireland with ice streaming onto the continental shelf of the malin sea the extent and retreat history of this ice stream across the shelf until now is not well known in particular geochronological constraints on the history of this ice stream have thus far been restricted to deep sea cores or terrestrial cosmogenic nuclide dating onshore with ages across the shelf absent to understand the possible external forcing factors acting on this marine terminating ice stream during retreat improved geochronological constraint on its deglaciation is necessary here we present new geophysical data marine sediment cores and over forty radiocarbon dates to provide important constraints on maximum extent of the bfis as well as the timing and pattern of retreat back across the malin shelf dated moraines and grounding zone wedges gzw seen in seafloor sub bottom profiles provide evidence that the bfis reached the malin shelf edge during the lgm and was at its maximum extent around 26 7 ka bp the presence of two sets of gzws suggests that the style of retreat was episodic the new radiocarbon chronology shows that retreat from the shelf edge was underway by 25 9 ka bp with the majority of the continental shelf ice free by 23 2 ka bp and that glacimarine conditions were present in the sea of hebrides by 20 2 ka bp at the latest collectively these results indicate that the majority of the malin shelf was free of grounded ice by 21 5 20 ka bp which is up to 4000 years earlier than previously reconstructed we attribute this early deglaciation to high relative sea level caused by glacial isostatic depression when the biis reached its maximum extent promoting ice shelf and grounding line instability two deep troughs forming reverse bed slopes aided the continued retreat of the bfis this suggests that local ice loading and bed morphology can be significant controls on the destabilisation of a marine terminating ice stream and can override the influence of ocean and atmospheric temperatures

late weichselian environmental history in southeastern sweden during the deglaciation of the scandinavian ice sheet abstract late weichselian litho bio and chronostratigraphy 14 c and varves in southeastern sweden provide a detailed picture of the deglaciation pattern and dynamics shore displacement late glacial sedimentation and history of the landscape vegetation and climate two plausible glacial models were tested against lithologic chronologic and climatic data permafrost at and outside the ice margin and topographic conditions beneath the ice apparently caused inward spread of frozen glacier bed conditions this led to a buildup of a large zone of debris rich basal ice a climatic amelioration about 12 700 yr b p changed the temperature profile in the ice sheet deposition of basal melt out till began at the previously frozen glacier bed and a rapid recession of the clean ice set in thin exposed debris rich basal ice which was separated from the active ice margin about 150 yr later in this zone of stagnant ice there followed a 200 300 yr period marked by subglacial and supraglacial melt out and resedimentation forming a large hummocky transverse moraine the mild climate favored rapid plant immigration and a park tundra was established the gradual closing of the landscape was interrupted by a 100 to 150 yr period of tundra vegetation and a cool dry climate with local vegetational differences caused by differences in soil moisture about 12 000 yr b p a second climatic amelioration set in and during the next 1000 yr a birch and pine woodland gradually developed soils stabilized and empetrum heaths became abundant as the climate gradually deteriorated at the end of this period by 11 000 yr b p the area had become a tundra again with scattered birch stands dominated by herbs such as artemisia chenopodiaceae grasses and sedges some 500 yr later a birch pine woodland again succeeded and within about 500 yr the vegetation changed to a rather closed woodland as the climate ameliorated further however the time lag between climatic and vegetation change was considerable

petrographic classification of crystal morphology the terms euhedral subhedral and anhedral have limited value as an expression of crystal morphology relating to conditions of crystal formation and rock forming processes the basis of this traditional nomenclature is the presence or absence of crystal faces implying that if a crystal has faces its overall shape is likely to reflect crystal structure experimental reproduction of growth dissolution and melting textures along with an ever increasing awareness of the importance of incomplete and malformed crystals in natural systems is the impetus for presentation here of a more detailed morphological classification of crystals at the petrographic scale the classification is binary based on the degree to which crystals are an expression of crystal structure and on the degree of completeness unlike the traditional scheme the proposed classification is sensitive to faceted crystals that do not have ideal shape and to incomplete crystals variously described as skeletal dendritic cellular