impact of bedrock surface topography on spatial distribution of quaternary sediments and on the flow pattern of late weichselian glaciers on the east european craton russian plain this paper presents the first high quality maps of the bedrock surface topography and the quaternary sediment distribution for the late weichselian glaciation area on the east european craton eec and the reasoning behind the estimated sediment distribution geographic information system gis based three dimensional model of the bedrock surface topography the current digital terrain model dtm and the ice flow pattern of the last glaciation provided the main source data for the analyses and interpretations in the current continental area of the western eec which was covered by the last scandinavian ice sheet sis the bedrock lies overwhelmingly 85 above the contemporary sea level with an average altitude of 54 m above sea level the topography of the bedrock surface is very well reflected in the current topography and an 80 m difference in the ice bed surface altitudes results in the topographic focusing of the ice flow and thus all late weichselian ice streams were accommodated to the depressions in the subglacial surface such depressions are characterised by a thin 10 m layer of sediment with one till bed just 50 m upslope from the bottom of the depressions the thickness of the sediment increases two to threefold and comprises five or more till layers indicating relief enhancement through subsequent glaciations the average calculated thickness of the quaternary deposits in the study area was 49 m and the total volume of sediments was 20 280 km3

millennial scale fluctuations of the european ice sheet at the end of the last glacial and their potential impact on global climate abstract reconstructing northern hemisphere ice sheet oscillations and meltwater routing to the ocean is important to better understand the mechanisms behind abrupt climate changes to date research efforts have mainly focused on the north american laurentide ice sheets lis leaving the potential role of the european ice sheet eis and of the scandinavian ice sheet sis in particular largely unexplored using neodymium isotopes in detrital sediments deposited off the channel river we provide a continuous and well dated record for the evolution of the eis southern margin through the end of the last glacial period and during the deglaciation our results reveal that the evolution of eis margins was accompanied with substantial ice recession especially of the sis and simultaneous release of meltwater to the north atlantic these events occurred both in the course of the eis to its lgm position i e during heinrich stadial hs 3 and hs2 31 29 ka and 26 23 ka respectively and during the deglaciation i e at 22 ka 20 19 ka and from 18 2 0 2 to 16 7 0 2 ka that corresponds to the first part of hs1 the deglaciation was discontinuous in character and similar in timing to that of the southern lis margin with moderate ice sheet retreat from 22 5 0 2 ka in the baltic lowlands as soon as the northern summer insolation increase from 23 ka and an acceleration of the margin retreat thereafter from 20 ka importantly our results show that eis retreat events and release of meltwater to the north atlantic during the deglaciation coincide with amoc destabilisation and interhemispheric climate changes they thus suggest that the eis together with the lis could have played a critical role in the climatic reorganization that accompanied the last deglaciation finally our data suggest that meltwater discharges to the north atlantic produced by large scale recession of continental parts of northern hemisphere ice sheets during hs could have been a possible source for the oceanic perturbations i e amoc shutdown responsible for the marine based ice stream purge cycle or so called he s that punctuate the last glacial period

patterns rates and possible causes of saltmarsh erosion in the greater thames area uk the estuary dominated coast of the greater thames in england has experienced rapid lateral erosion and internal dissection of saltmarshes this paper provides an overview of saltmarsh development in this area and re examines the role of environmental and human forcing factors it draws on documentary evidence including historical maps survey data and time series data of forcing factors lateral marsh retreat began in the 19th century in the medway and blackwater estuaries followed by other estuaries in the greater thames region at the beginning of the 20th century the outer estuaries and the wider parts of the inner estuaries especially have experienced erosion erosion has been modest in wave sheltered areas e g the colne and the inner crouch in the 1960s and more widely the 1970s a phase of rapid erosion took place with erosion rates of up to ca 16 ha year 1 per site notably along the open coast of dengie and foulness and in the blackwater and thames estuaries at all sites vertical sediment accretion was well able to keep up with sea level rise over the past century evidence indicates that there may have been several causes for the erosion of saltmarshes these are notably land claim and embankment construction increasing the tidal range and current velocities and a continuous rise of especially high and extreme water levels the latest episode of rapid erosion in the 1970s is largely attributed to changes in the wind wave climate for example erosion at wave exposed sites coincided with a peak in high magnitude waves combined with a high incidence of southeasterly waves the study shows that many factors including natural forcing factors and human activities have to be taken into account when explaining saltmarsh development

southern laurentide ice lobes were created by ice streams des moines lobe in minnesota usa abstract regional mapping in southern minnesota has illuminated a suite of landforms developed by the des moines lobe that delimit the position of the lobe at its maximum and at lesser readvances the ice lobe repeatedly advanced discharged its subglacial water and subsequently stagnated recent glaciological research on antarctic ice streams has led some glacial geologists to postulate that ice streams drained parts of the marine based areas of the laurentide ice sheet i postulate that such ice streams may develop in land based areas of an ice sheet as well and that the des moines lobe 200 km wide and 900 km long was an outlet glacier of an ice stream it appears to have been able to advance beyond the laurentide ice sheet as long as adequate water pressure was maintained however the outer part of the lobe stagnated because subglacial water that facilitated the flow was able to drain away through tunnel valleys stagnation of the lobe is not equivalent to stoppage of the ice stream because ice repeatedly advanced into and onto the stagnant margins stacking ice and debris similar landforms are also seen in other lobes of the upper midwestern united states

processes governing marsh formation in a rapidly subsiding coastal environment abstract processes governing the stability of marshes in louisiana s mississippi river delta plain were examined an accretionary budget was developed for barataria basin fresh brackish intermediate and salt marshes located along a salinity gradient extending inland from the coast the marshes represent a thin veneer overlying sediment stratum deposited by the mississippi river and it s ancestors at many locations rates of vertical marsh accretion were not sufficiently rapid to keep pace with increased water depth accompanying rapid subsidence due to compaction the life span of salt marshes of the mississippi river deltaic plain are estimated to be approximately 100 years the mineral sediment and organic carbon requirement of individual marsh units in response to water level increase is presented organic matter is an important component of accretionary processes and helps the marsh surface to keep pace with water level increase we estimated that at least 600 700 g of c m 2 yr 1 must be supplied to maintain marsh accretion to balance soil oxidation decomposition losses and organic carbon accretion peat formation even though subsidence is the primary factor in marsh deterioration accompanying factors salt water intrusion excess waterlogging stress vegetation and thus reduce the organic carbon source below minimum aggradation requirements inorganic sediment input is also necessary for maintenance of viable marshes many of the marshes within the basin are not receiving sufficient nutrients from sediment source to maintain significant plant growth necessary for organic matter production barataria basin marsh will likely continue disappearing unless means are implemented for reintroducing sediment from the mississippi river

the estimation of global sea level change a problem of uniqueness an objective method of estimating regional averages of coherent sea level sl change is developed the technique is applied to a large set of sl data representative of most of the world s continental margins the results show highly coherent sl changes over many of the regions studied the method is then applied to the regional averages themselves to develop an overall estimate of the coherent pattern of sl variations existing in the historical sl data set the pattern is characterized by a coherent rise of sl in all regions except alaska scandinavia both areas of notorious crustal uplift and southeast asia where sl appears to be falling the analysis suggests little or no change in sl prior to the early 1900 s the period since that time has seen an increase in sl that is optimally fit by a linear trend of 23 cm century the study results suggest that it is not possible to uniquely determine either a global rate of change of sl or even the average rate of change associated with the existing inadequate data set indeed different analysis methods by themselves can cause 50 variations in the estimates of sl trend in the existing data set a signal noise analysis suggests it should be easy to detect small future changes in the sl trends estimated for the period 1930 1980 however detection of theoretically predicted low frequency signals e g caused by co2 warming will be difficult in view of the huge low frequency natural variability associated with glacial tectonic processes

last glacial maximum in poland abstract the last glacial maximum lgm in poland is represented by the leszno phase and occurred after 21 ka radiocarbon years in turn the deglacial poznan phase is estimated at 18 4 ka the pomeranian phase at 15 2 ka the gardno phase at about 14 0 13 8 ka the slupsk bank phase at 13 5 13 2 ka and the southern middle bank phase at 12 7 12 5 ka bp the ice sheet limit at lgm was not synchronous everywhere in poland but occurred as several major and minor ice lobes that reflected a stream like structure of the ice body that radiated southwards from the baltic basin meltwater runoff during the lgm created a complex system of sandur trains and ice marginal spillways with numerous intervening proglacial lakes

high resolution mapping of ice marginal landforms in the barnim region northeast germany abstract despite more than a 100 year long research history timing and position of the last glacial ice margins in the northeast german lowland are still up for debate the barnim region a till plain in the northeast german young morainic landscape is traversed by the contradictorily discussed frankfurt ice marginal position it is located in a key position to reassess the current state of research with help of a geographic information system gis and field methods a qualitative geomorphological analysis of a high resolution lidar digital elevation model dem in the barnim area uncovers a variety of landforms that were previously not described the most prominent discovery is a set of about 10 lobe shaped ridges in the middle barnim area fieldwork and geophysical measurements were carried out to investigate the structure of the ridges the ridges are 1000 1500 m in length and their widths vary from 10 to 15 km they are raised some 6 10 m from their surroundings the frankfurt ice marginal position can only partially be traced in the dem sedimentological and geophysical investigations indicate that the ridges are composed of glacial till that was deposited on glaciofluvial sediments their formation most probably took place during the ice retreat of the brandenburg phase w 1b and hence represents the w 1f phase in the region

interplenivistulian mis 3 environmental changes recorded in sub till lake deposits at wildno dobrzyn lakeland polish lowland a complex of clays and sandy silt deposits with mollusc remains covered by a till correlated with the main stadial of the vistulian weichselian glaciation was investigated at wildno in the dobrzyn lakeland polish lowland a few taxa of snails bithynia tentaculata valvata piscinalis theodoxus cf fluviatilis valvata sp viviparus sp as well as bivalves pisidium cf amnicum and sphaerium sp were identified amongst poorly preserved shell fragments no pollen grains were present in mollusc bearing deposits whereas the pollen spectrum of clays lying below the latter points their accumulation in oligotrophic water body in a cool climate pediastrum kawraiskii and woodless area radiocarbon age of shell detritus 4 samples ranges from 43 7 cal ka to c 32 1 0 8 cal ka both the geological situation and the results of dating suggest that sub till sediments with molluscs were deposited in the upper part of interplenivistulian mis 3 the grudzi dz interstadial while accumulation of clays may be correlated with its earlier and cooler part

the signature of strain magnitude in tills associated with the vistula ice stream of the scandinavian ice sheet central poland abstract at oborki in central poland we examined a 3 m thick late weichselian basal till deposited by the vistula ice stream a multi proxy approach involving a study of grain size grain roundness crushing index petrographic composition till fabric and till micromorphology in a closely sampled vertical profile was applied to decipher till formation and ice movement mechanisms the till consists of a succession of four texturally and structurally different units generated by a combination of processes related to effective stresses exerted on the bed by active ice deformation intergranular advection clast ploughing and localized basal decoupling played important roles during till formation micromorphological analysis reveals that the most common s matrix microstructures are grain lineations grain stacks turbate structures till pellets and crushed grains microshears dominate whereas plasmic fabric is not well developed we use grain roundness crushing indices and microshear geometry to determine subglacial strain magnitude in the till matrix microfabric and macrofabric s 1 eigenvalues together with i l indexes indicate low shear strains in the order of 10 10 2 strain estimates vary depending on the particle sizes used suggesting a plastic mode of till deformation all proxies studied suggest complex and temporally variable subglacial conditions under the marginal part of the vistula ice stream probably caused by changes in till rheology related to fluctuating porewater pressures fast ice flow was facilitated by a combination of bed deformation and enhanced basal sliding on a thin water layer our results may also be representative for other terrestrially based pleistocene ice streams moving over soft beds

southwest scandinavia 40 15 kyr bp palaeogeography and environmental change twelve palaeogeographical reconstructions illustrate environmental changes at the southwest rim of the scandinavian ice sheet 40 15 kyr bp synchronised land sea and glacier configurations are based on the lithostratigraphy of tills and intertill sediments dating is provided by optically stimulated luminescence and calibrated accelerator mass spectrometry radiocarbon an interstadial sequence ca 40 30 kyr bp with boreo arctic proglacial fjords and subarctic flora and occasional glaciation in the baltic was succeeded by a last glacial maximum sequence ca 3020 kyr bp with the closure of fjords and subsequent ice streams in glacial lake basins in kattegat and the baltic steadily flowing ice from sweden bordered the norwegian channel ice stream a deglaciation sequence ca 20 15 kyr bp indicates the transgression of arctic waters retreat of the swedish ice and advance of baltic ice streams succeeded by a return to interstadial conditions when ameliorated ice free conditions prevailed in maritime regions glaciers advanced through the baltic and when interstadial regimes dominated the baltic glaciers expanded off the norwegian coast the largest glacier extent was reached in the north sea around 29 kyr bp about 22 kyr bp in denmark and ca 18 kyr bp in the baltic our model provides new data for future numerical and qualitative landform based models copyright c 2003 john wiley sons ltd less

continental scale transport of sediments by the baltic ice stream elucidated by coupled grain size and nd provenance analyses abstract we introduce a methodology for determining the transport distance of subglacially comminuted and entrained sediments we pilot this method on sediments from the terminal margin of the baltic ice stream the largest ice stream of the fennoscandian ice sheet during the last glacial maximum a strong correlation r2 0 83 between the end and latitudes of circum baltic river sediments enables us to use end as a calibrated measure of distance the proportion of subglacially transported sediments in a sample is estimated from grain size ratios in the silt fraction

palaeo ice streams abstract the location and behaviour of ice streams is one of the most important controls on ice sheet configuration and stability in order to reconstruct former ice sheets we need to know ice stream location and timing once identified the beds of palaeo ice streams provide an unprecedented opportunity to glean information about their basal environment something that remains very difficult under contemporary ice streams this paper represents the first synthesis and discussion of palaeo ice stream research from a variety of former ice sheets and includes new insights relating their configuration and activity to the evidence they leave behind the ambiguous use of the term ice stream is addressed and four possible configurations for ice streams are presented diagnostic landforms and landform assemblages that we would expect an ice stream to produce are discussed and the temporal context of bedform generation is described as either a rubber stamped or smudged bedform imprint resulting from isochronous or time transgressive landform generation in particular we focus on the configuration of terrestrially terminating ice streams for which there are no modern analogues technological advances in marine geophysics are helping to generate a convergence of interest between antarctic glaciology and palaeo glaciology it is suggested that investigations around the fringes of contemporary ice sheets i e west antarctica can provide evidence that directly links the geomorphological record of palaeo ice streams with their contemporary counterparts in addition computational advances and modelling adaptations have permitted the incorporation of ice streams within ice sheet models we argue that data from palaeo ice stream beds are invaluable to ice sheet stream modelling experiments and will help us understand ice stream operation and the linkages between climate perturbations and both palaeo and contemporary ice sheets

quaternary glaciations of northern europe this paper presents the outcome of a workshop held in berlin in february 2009 concerned with current research on the glacial history of northern europe including the british isles the methodologies presently used to resolve this topic are outlined particular attention is given to new analytical methods deriving from high resolution remote imaging of glacial terrain both on land and on the sea bed key new stratigraphic sections higher resolution results from conventional geochronological methods like radiocarbon and more recently developed technologies such as luminescence and cosmogenic radionuclide dating the relationships between the results derived from these two methods are discussed in further detail along with possible explanations for these differences an outline of a most likely glacial history of the scandinavian and british and irish ice sheets is presented along with possible links to global climate change as represented by the marine isotope mis record tentative evidence for glaciation is identified in mis 22 16 12 10 8 6 4 and 2 and correlations of phases within the last glaciation are also explored for both the scandinavian and british and irish ice sheets the results show that the character and extent of glaciation in different parts of the region are not synchronous and much more geochronological work is required before regional correlations can be established with confidence

from morphostratigraphy to geochronology on the dating of ice marginal positions abstract this study focuses on the glacial landscape of northern germany as a part of the southwestern sector of the scandinavian ice sheet sis as it has a research history reaching back about 130 years since the glacial theory replaced the drift theory in the late 19th century it has experienced a number of key changes including the introduction of the concept of polyglaciation or the differentiation of ice advances within one glaciation which is closely linked to the morphostratigraphical definition of ice marginal positions with the development of numerical dating methods the rather static morphostratigraphically based chronologies which are deeply rooted in research history have been confronted with a growing number of geochronometrical data obtained from glacigenic deposits in order to date ice marginal positions the two most commonly used dating methods for that purpose are optically stimulated luminescence osl and surface exposure dating of erratic boulders this study highlights the dependency of the significance of results from different dating methods on the sampling position within the geomorphological framework results from osl and surface exposure dating for the same ice marginal position in theory cannot be the same as the methods date different processes in the development of the glacial landscape osl dating of fluvioglacial sandur sediments dating the process of active sedimentation at the ice front and surface exposure dating of boulders on end moraines dating the process of stabilisation of end moraines after the retreat of the ice front often qualify as the most useful combination of techniques in order to define a time interval for the formation of the landforms at a specific ice marginal position methodological drawbacks which might occur unfortunately tend to widen the process induced offset between osl and surface exposure ages incomplete bleaching of fluvioglacial sediments might cause an offset towards a maximum osl age for an ice marginal position whereas delayed stabilisation or post exposure relocation of boulders might cause a shift towards a minimum age of key importance are the influence of periglacial processes and the effects of melting of buried ice on landform stabilisation which remain to be quantified a possible solution to this problem combining osl and surface exposure dating is suggested in this study nevertheless the possibility exists to date different geomorphological processes by applying different dating methods to glacigenic deposits this allows for a differentiated reflection of morphostratigraphically based chronologies against the background of the modern concept of dynamic ice sheets in contrast to the traditional morphostratigraphical definition of ice marginal positions a time based definition is proposed because it offers the possibility of a more detailed reconstruction of ice sheet dynamics at a certain point in time

pleistocene architecture and stratigraphy in the contact zone of ice streams and lobes in the south eastern part of the baltic region rich material obtained during the glacigenic topography researches shows that the advance of the ice sheet and deglaciation of the area took place in a shape of ice streams substreams and lobes during the last glaciation the south eastern part of the baltic region had been covered by ice on a form of three ice streams which in its continental part were dividing into smaller substreams and lobes differently named in the scientific literature the goal of the present study is to discuss the glacial multilayerness of the pleistocene strata in the se baltic region as a phenomenon of palaeo ice streams substreams and lobes in the contact zone the material of previous researches is analysed as well as published data and new findings of the authors are used the material available on the middle pleistocene emaitija till occurring at the depths from 10 to 175 m along the nw se distribution of the deposits shows differences in petrographic composition of gravel and pebble beds for the western and eastern sectors the deposits of the middle pleistocene occurring at the surface the ashmyany upland and the lida plain in this region are thought to be a result of two different asynchronous ice substreams in the area of the last nemunas glaciation the ice sheet of two stages maximum gr da and the younger baltija also formed tills differing in features and composition thus testifying the result of different ice streams and substreams the statistical correlation analysis for the most widely occurring palaeosurfaces of tills in the south lithuania revealed that the positive coefficient of adjacent surfaces was increasing with the occurrence depth a conclusion is made that different dynamic activity of ice streams and substreams is a natural and objective phenomenon therefore an ice stream substream or a lobe of the same glaciation but of different stages phases could move into a depression formed by another adjacent substream or lobe the multilayered character of the pleistocene strata in the south lithuania can be explained by different manifestation of glacial till layers formed by ice streams substreams or lobes of the same glaciation but of different stages phases application of this conception makes easier the stratigraphic interpretation of the pleistocene deposits in the region

sedimentation accretion and subsidence in marshes of barataria basin louisiana1 vertical accretion and sediment accumulation rates were determined from the distribution of 137cs in cores collected from freshwater intermediate brackish and salt marshes in the barataria basin louisiana vertical accretion rates vary from about 1 3 cm yr l in levee areas to 0 7 in backmarshes mineral sediment content of the marsh soil profile decreased with distance from the coast however vertical accretion rates were about equivalent in areas of the same type autochthonous organic matter appears to be an important factor defining the process and rate of vertical accretion especially in the freshwater marshes except in natural levee areas marsh accretion rates are less than subsidence measured by water level data however this alone cannot account for observed land loss patterns in the basin area

sedimentological record of subglacial conditions and ice sheet dynamics of the vistula ice stream north central poland during the last glaciation abstract deposits of the vistula ice stream draining the scandinavian ice sheet during the last glaciation were investigated at four field sites in north central poland using micro and macroscale features the study reveals several till units with specific structural textural and lithological characteristics the individual till units are either macroscopically massive or bedded and the contacts between the units are either sharp or transitional the nature of the contacts with the underlying sediments ductile deformation structures largely undeformed clayey clasts tectonic lamination thin horizontal stringers of sorted sediments ploughing marks boulder pavements and striated upper surfaces of pebbles in the till indicate both bed deformation and enhanced basal sliding under high subglacial water pressure conditions it is suggested that the till is a hybrid deposit generated by some combination of lodgement deformation and ploughing punctuated by periods of basal decoupling the depth of deformation at any point in time was thinner up to several decimetres than the maximum till thickness c 2 5 m the ice sliding velocity estimations indicate velocities of less than 100 to over 2000 m yr 1 which suggests an unstable and highly dynamic ice lobe consistent with spatial variability of till characteristics sand wedges in the deposits beneath the till and the nature of the till bed interface indicate permafrost under the advancing ice sheet we suggest that under the increasing ice thickness a layer of thawed water saturated sediment formed on top of the still frozen ground due to inefficient drainage and contributed to ice streaming by promoting pervasive deformation and basal sliding

development of the topography controlled upper odra ice lobe scandinavian ice sheet in the fore mountain area of southern poland during the saalian glaciation abstract during the saalian drenthe glaciation the upper odra ice lobe constituted the most southern part of the scandinavian ice sheet in central europe the lobe was situated in an area with varied topography in the foreland of a mountain range the ice lobe had a complex form because it was subdivided into several smaller sublobes the primary factors that controlled the lobe were investigated it was found that the ice lobe development depended largely on the topography but the lithology of the ice sheet substratum was also highly important the topography controlled the main movement direction of the ice and caused a concentration of the ice flow in the axial part of the silesian lowland between subglacial morphological barriers which thereby formed a corridor of relatively fast flowing ice which was probably streaming and which supplied the lobe the topography also determined the ice flow within the lobe which strongly matched the valley system the presence of sediments with relatively low permeability at the base of the lobe the quaternary deposits are underlain by neogene clays caused high pore water pressure in the subglacial zone and triggered the basal movement of the ice sheet which promoted a rapid flow of the ice and favoured the development of the lobe the basal tills deposited from the active and passive ice and extant till patches without a fluvioglacial cover atop some parts of the studied area indicate spatially varying ice flow dynamics especially in the later stage of glaciation certain parts of the lobe underwent stagnation while in other parts the ice was probably still active the varied behaviour of the ice within the lobe was determined primarily by the topography and lithology of the substratum which produced spatially varied marginal compression and basal friction a model of the development of the lobe is proposed

the last glacial maximum extent of the scandinavian ice sheet in the valday heights western russia evidence from cosmogenic surface exposure dating using 10be abstract recent synoptic studies have summarized the former spatial extent and chronology of the last scandinavian ice sheet sis and provide exceptional compilations of empirical datasets the latter represent the primary source of information for the modelling community to test and develop thermomechanical ice sheet model which are then further embedded into climatic and general circulation models the last glacial maximum lgm extent and chronology of the sis across continental europe were highlighted as being the least well known thus generating the biggest uncertainties in the reconstruction of the ice sheet while early geomorphological studies of the ice sheet marginal belts are numerous and detailed in western russia geochronological data are virtually inexistent in an attempt to fill in this gap we conducted a series of sampling campaigns for surface exposure dating using 10be in the western and northwestern regions of russia we present here the first results from the valday heights where glacial deposits constitute well preserved margins of the sis a total of 16 samples firmly establish the timing of the lgm in the valday heights at 20 1 0 4 ka the valday heights acted as a natural wall for the last maximum advance of the sis during mis2 constraining the eastern flank of the ladoga ilmen lovat ice stream to the west of the hills the valday heights were only overran by previously more extensive glacial advances as suggested by older exposure ages obtain on erratic boulders 31 2 1 4 to 47 1 1 5 ka located east of the lgm limit

sedimentary record of a scandinavian ice sheet drainage system and till deposition over subglacial obstacles promoting basal sliding an example from southern poland abstract subglacial obstacles occurring in the path of advancing ice sheets generally generate higher longitudinal compression and higher frictional drag than a flat substrate however in the case of a soft sediment substratum they can have a very different effect on ice sheet behaviour this study concerns a substrate composed of very fine grained sediments with low permeability the relationship between subglacial obstacles and the overriding scandinavian ice sheet was studied in an area of southern poland where a small intervalley neogene clay ridge 40 m high was present based on sedimentological and structural analysis of subglacial till and gravelly sandy sediments the basal depositional processes and subglacial conditions and their influence on ice sheet behaviour were analysed the till and related deposits within the ridge reflecting high water pressure conditions and lack of glacitectonic deformations indicate that the clay ridge did not generate much resistance against the advancing ice sheet but instead favoured basal slip the impermeable substratum weakened the ice bed coupling and promoted ice detachment from the substratum gravelly sandy inclusions at the till clay contact indicate that during the first stage of ice sheet overriding a canal drainage system developed at the ice substrate interface varied geometry size and location of inclusions of sorted sediments suggest periodic instability of the canal system which could lead to its transformation from initially uniform to being composed of conduits of different sizes during later stages of ice sheet overriding a traction till was deposited and occasional drainage through a water film was sufficient to evacuate basal meltwater the resulting change in the character of subglacial drainage was probably related to variations in water pressure gradient during progressive ice sheet advance

patterns of deformation within a subglacial shear zone implications for palaeo ice stream bed evolution abstract this paper presents macro and microsedimentological data recording subglacial deformation of a sediment succession at przeszkoda in north central poland under the vistula ice stream at the southern fringe of the scandinavian ice sheet during the weichselian glaciation the sediment succession consists of i undeformed outwash sand ii deformed outwash sand iii bedded till and iv massive till these deposits were examined in a closely sampled vertical profile for kinematic structures macrofabrics grain shape characteristics and micromorphology detrital components microstructures clast microfabrics the analyzed parameters suggest that the deposits were generated by a progressive homogenization and mixing of local material with far travelled detritus successively released from the active ice sole grain crushing and abrasion characteristics lack any obvious trends in the vertical profile indicating that the deformation was focused in a thin cm scale layer which progressively migrated upwards parallel with sediment accretion the closely spaced thin sections were collected in the deformed outwash sand bedded till and massive till units these revealed formation and evolution of stress induced foliation in the glacier bed whereby three microfabric generations including s1 earliest s2 and s3 latest foliation were recognized the geometry of these microfabrics is consistent with their formation in response to the development of subhorizontal y type shears and up ice dipping p type and down ice dipping r type riedel shears within the subglacial shear zone the geometry and cross cutting relationships between the microfabrics throughout the succession reflects changing deformation styles within a thin deforming bed that migrated time transgressively up the profile during till accretion strain magnitude accumulated in the whole sediment succession was low in the range of 101 to 102 suggesting that enhanced basal sliding was an important component contributing to fast flow of the ice stream

effects of remote generation sites on model estimates ofm2internal tides in the philippine sea abstractthis study investigates the impact of remotely generated internal tides on model estimates of barotropic to baroclinic tidal conversion for two generation sites bounding the philippine sea the luzon strait and the mariana island arc a primitive equation model is used to characterize the internal tides generated by the principal semidiurnal tide m2 over a domain encompassing the two generation sites energetic internal tides are generated at the luzon strait where nearly 17 gw of barotropic tide energy is converted to baroclinic energy of which 44 4 78 gw is radiated eastward into the philippine sea from the mariana arc baroclinic energy propagates westward into the philippine sea as a result of 3 82 gw of barotropic to baroclinic energy conversion simulations that focus on each generation site without influence of the other are performed and comparisons show that remotely generated internal tides have a significant effect on local conversion at the two sites total conversion is greate

palaeoglaciology of an ice sheet through a glacial cycle the european ice sheet through the weichselian abstract satellite images provide unique means of identifying large scale flow generated lineations produced by former ice sheets they can be interpreted to reconstruct the major elements which make up the integrated large scale structure of ice sheets ice divides ice streams interstream ridges ice shelves calving bays the evolving palaeoglaciological structure of the european ice sheet during its decay from the last glacial maximum lgm is reconstructed by reference to these components and in the context of a new map showing isochrons of retreat during the retreat phase in particular the time dependent dynamic evolution of the ice sheet and the pattern of ice stream development are reconstructed crossing lineations are widespread the older ones are suggested to have formed during molten bed phases of ice sheet growth and preserved by frozen bed conditions during the glacial maximum particularly in areas which lay during deglaciation beneath ice divides and inter ice stream ridges both areas of slow flow and possibly frozen bed conditions four phases of growth a1 to a4 and five phases of decay r1 to r5 are used to describe the major climatically and dynamically determined stages in the evolution of the ice sheet through the last glacial cycle the growth and decay patterns are quite different and associated with major shifts in the ice divide reflecting growth from the fennoscandian mountains and decay away from marine influenced margins these patterns were determined by the locations of nucleation areas spatial patterns of climate and calving at marine margins the prevalence of streaming within the retreating ice sheet suggests that the mean elevation of the ice sheet was lower than predicted from glaciological models which do not include streaming and that this might reconcile glaciological models and earth rheology models which infer paleao ice sheet thickness by inverting sea level data

terrestrial ice streams a view from the lobe abstract the glacial landforms of minnesota are interpreted as the products of the lobate extensions of ice streams that issued from various ice sheds within the laurentide ice sheet low relief till plains trough shaped lowlands boulder pavements and streamlined forms make up the subglacial landsystem in minnesota that is interpreted as having been formed by streaming ice extremely uniform tills are created subglacially in a way that remains somewhat mysterious at the ice margins thrust moraines and hummocky stagnation topography are more common than single crested simple moraines if the ice lobes had repeated advances subglacial drainage features are obscure up ice but are present down ice in the form of tunnel valleys eskers spooner hills and associated ice marginal fans ice streaming may occur when basal shear stress is lowered as a result of high subglacial water pressure subglacial conditions that allow the retention of water will allow an ice lobe to extend far beyond the ice sheet as long as the ice shed also supports the advance by supplying adequate ice even with adequate ice flux however the advance of an ice lobe may be terminated at least temporarily if the subglacial water is drained through tunnel valleys or perhaps a permeable substrate thrust moraines and ice stagnation topography will result from sudden drainage although climate change is ultimately responsible for the accumulation of ice in the laurentide ice sheet the asynchronous advances and retreats of the ice lobes in the mid continent are strongly overprinted by the internal dynamics of individual ice streams as well as the interaction of ice sheds which obscure the climate signal

successive subglacial depositional processes as interpreted from basal tills in the lower vistula valley n poland abstract three basal till facies from the lower vistula valley were examined the lowest facies a sandy diamicton with characteristic sand inclusions forming detached and attenuated folds is overlain by a bedded till characterized by alternating diamictons and sorted sediment layers the uppermost till facies is a homogeneous diamicton the three till facies must have been formed by complex subglacial sedimentary processes during the first late weichselian ice advance the lowest till facies is interpreted as a deformation till and accumulated during the initial stage of the ice advance the middle facies represents a stagnation phase during the initial ice advance and was deposited during recurrent periods of subglacial melt out followed by meltwater sedimentation the upper till facies was deposited by direct subglacial melt out during a stage of stagnant ice it is suggested that bed deformation and temporarily enhanced basal sliding have been caused by ice streaming at the time of the ice sheet advance and just before its stagnation

a fluctuating ice front over an esker near ryssjon s sweden as a cause of a giant load cast abstract a well exposed section in an esker near ryssjon s sweden strongly affected by several phases of glacitectonism showed two phenomena that are uncommon and that seem to have a causal relationship the first phenomenon is the occurrence of a load cast consisting predominantly of gravel in deposits formed just inside or outside a tunnel mouth the load cast is over 3 m high and 8 m wide a size that has previously not been described from unconsolidated sediments two nearby somewhat smaller load casts consisting mainly of sand also have dimensions of over 2 m indicating that the formation of huge load casts was apparently a feature related to the special conditions under which loading could develop at this site the second remarkable feature is that not only is a till present in the succession above the load cast thus indicating re advance of the ice but deposits overlying this till are also deformed by glacitectonism proving that at least a second phase of ice re advance must have occurred this situation has not previously been documented it is concluded that the varying differential overburden of sediment and particularly the retreating and re advancing ice in this area were responsible for the formation of the extremely large load casts possibly triggered by seismic shocks related to isostatic adjustment caused by oscillations of the ice front

radiocarbon calibration curve spanning 0 to 50 000 years bp based on paired 230 th 234 u 238 u and 14 c dates on pristine corals abstract radiocarbon dating is the most widely used dating technique in the world recent advances in accelerator mass spectrometry ams and sample preparation techniques have reduced the sample size requirements by a factor of 1000 and decreased the measurement time from weeks to minutes today it is estimated that more than 90 percent of all measurements made on accelerator mass spectrometers are for radiocarbon age dates the production of 14 c in the atmosphere varies through time due to changes in the earth s geomagnetic field intensity and in its concentration which is regulated by the carbon cycle as a result of these two variables a radiocarbon age is not equivalent to a calendar age four decades of joint research by the dendrochronology and radiocarbon communities have produced a radiocarbon calibration data set of remarkable precision and accuracy extending from the present to approximately 12 000 calendar years before present this paper presents high precision paired 230 th 234 u 238 u and 14 c age determinations on pristine coral samples that enable us to extend the radiocarbon calibration curve from 12 000 to 50 000 years before present we developed a statistical model to properly estimate sample age conversion from radiocarbon years to calendar years taking full account of combined errors in input ages and calibration uncertainties our radiocarbon calibration program is publicly accessible at http www radiocarbon ldeo columbia edu along with full documentation of the samples data and our statistical calibration model

relationships among vertical accretion coastal submergence and erosion in a louisiana gulf coast marsh abstract vertical accretion in a southwest louisiana spartina patens brackish marsh has not kept pace with coastal submergence during the past three decades the rate of accretion determined from 137cs dating and the use of artificial marker horizons averaged 0 8 cm yr 1 whereas coastal submergence obtained from tide gauge data averaged 1 2 cm yr 1 conversion from marsh to open water bodies closely paralleled the increase in coastal submergence if the resulting aggradation deficit continues the marsh will likely complete its transformation to an open bay in less than 40 years in view of recent projections of increasing sea level rise the results presented may foreshadow a more widespread phenomenon

record of the vistula ice lobe advances in the late weichselian glacial sequence in north central poland during the last glacial maximum lgm the vistula ice lobe was one of the key morphological elements at the southern margin of the scandinavian ice sheet in north central poland the area of the vistula ice lobe experienced two ice sheet advances of varied extent the older one is correlated with the leszno brandenburg phase and the younger one is correlated with the poznan frankfurt phase sedimentological research and luminescence dating of the late weichselian glacial sequence in the vistula ice lobe area was conducted a new scenario of the late weichselian ice events in the area is presented the limit of the leszno phase within the vistula ice lobe was much smaller than had been accepted previously and its age is estimated to be about 20 300 bp significant ice sheet retreat was

laurentide glacial landscapes the role of ice streams glacial landforms of the north american prairie can be divided into two suites that result from different styles of ice flow 1 a lowland suite of level to streamlined till consistent with formation beneath ice streams and 2 an upland and lobe margin suite of thick hummocky till and glacial thrust blocks consistent with formation at ice stream and ice lobe margins southern laurentide ice lobes hypothetically functioned as outlets of ice streams broad branching lowlands bounded by escarpments mark the stable positions of the ice streams that fed the lobes if the lobes and ice streams were similar to modern ice streams their fast flow was facilitated by high subglacial water pressure favorable geology and topography in the midcontinent encouraged nonuniform ice flow and controlled the location of ice streams and outlet lobes