buried late quaternary channel systems in the danish north sea genesis and geological evolution abstract the danish north sea has been subject to extensive seismic surveying both 2d and 3d during the past four decades the 3d seismic data from the area has mainly been used for hydrocarbon exploration but in the last decade it has also been utilized for investigating the quaternary sediments and especially buried incised valleys the erosional and depositional processes involved in forming such valleys are important in paleolandscape reconstruction but are often difficult to determine since sediment deposited by flowing water displays ambiguous geometric structures in this study we combine the analysis of infill geometries from high resolution 2d seismic data with plan view morphology analysis from 3d seismic data and lithological data from borehole reports in order to constrain the origin of buried channels in the danish north sea this data integration makes differentiations of a subaerial vs subglacial origin more robust the study focusses on analyzing a proglacial to fluvial channel system which was initiated as a subglacial tunnel valley system during the last glacial maximum and subsequently evolved as a fluvial system after deglaciation the channel system was active in a marsh environment during a period of subaerial exposure in the late weichselian to early holocene during the holocene transgression the system was gradually flooded leaving estuarine tidal deposits in the underfilled channels once the area was completely flooded the channel system was buried under marine sands

causes consequences and chronology of large magnitude palaeoflows in middle and late pleistocene river systems of northwest europe this study examines the record of high palaeoflow phases in river systems in northwest europe investigating their causes whether due to unique events such as the formation of the dover strait or as characteristic consequences of climate change examining their consequences with regard to landscape evolution and possible effects on climate and determining the chronology of key events large magnitude palaeoflows more than an order of magnitude larger than present day flood peaks are shown to be characteristic of rivers in this region at particular times within the pleistocene these events the most recent of which were during heinrich events 2 and 1 at 25 and 17 ka were evidently caused by the combined effects of glacial outwash rainfall snowmelt and melting of permafrost in some proportion they released such large volumes of water that the thermohaline circulation of the atlantic ocean and thus the climate may well have been affected these large magnitude palaeoflows are thus a significant aspect of the pleistocene earth system that has hitherto gone unquantified

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

the micromorphology of last glacial maximum sediments in the southern north sea abstract the terrestrial ice limits of the last glacial maximum ice sheets are well understood but areas submerged during postglacial sea level rise have proved more difficult to accurately map fine grained diamicts in the southern north sea have been variously interpreted as glacial glacioaqueous or periglacial in origin implying different sedimentary environments this has resulted in contrasting opinions regarding the position of the last ice sheets in this area micromorphology is presented as a useful technique to aid the analysis of such sediments using systematic description of the physical characteristics of the sediments related to an interpreted seismic stratigraphy results indicate that the british ice sheet deposited glaciomarine sediments during an early advance and then advanced over an extensive part of the southern north sea as terrestrial ice

overdeepened quaternary valleys in the eastern danish north sea morphology and origin abstract a system of 100 350 m deep overdeepened and buried valleys has been mapped in the eastern danish north sea individual valleys can be traced for several tens of kilometres and valleys generally begin and terminate abruptly a correlation to buried valleys onshore southwest denmark is possible the valleys post date glaciotectonic structures and are interpreted to be elsterian and possibly saalian in age the origin of valleys in the eastern danish north sea is explained by repeated cycles of sub glacial down cutting of meltwater channels and channel closure due to ice creep eventually producing deeply incised valleys glacial erosion may have been significant in cases where valleys are broad and shallow the origin of overdeepened quaternary valleys in general can be attributed to a combination of three end member processes i steady state drainage of meltwater ii catastrophic outbursts of meltwater and iii glacial erosion the main requirement for sub glacial valley formation is the presence of a melting ice sheet overlying a poorly consolidated substrate permeability variations of the substrate may produce subregional variations in the pattern of valley incision while pre glacial rivers faults or salt structures are of local importance only

absolute transports of mass and temperature for the north atlantic current subpolar front system the flow of subtropical waters carried into the northern north atlantic ocean by the north atlantic current subpolar front system nac spf is an important component of the meridional overturning circulation these waters become colder and denser as they flow through the subpolar region both by mixing with the colder subpolar waters and by atmospheric cooling the relative roles of these two processes remain to be quantified and the mechanisms driving lateral mixing need to be better understood to address those questions a new methodology is developed to estimate the mean absolute transports of mass and heat for the top 1000 dbar in the region of the nac spf for the time period 1993 2000 the transports are obtained by combining historical hydrography with isopycnal rafos float data from the area the mean absolute transport potential field shows an nac spf pipe defined by two bounding transport potential contours this pipe transports 10 0 6 3 5 sv sv 106 m3 s 21 top 1000 dbar from the subtropics into the eastern subpolar north atlantic in contrast to earlier studies the northward flowing nac follows a distinct meandering path with no evidence of permanent branches peeling off the current before reaching the northwest corner as the current enters the northwest corner it loses its tight structure and maybe splits into two or more branches which together constitute the eastward flow along the spf the eastward flow between the northwest corner and the mid atlantic ridge is not as tightly defined because of the meandering and or eddy shedding of the branches constituing the spf as the flow approaches the mid atlantic ridge it converges to cross above the charlie gibbs and faraday fracture zones the mean absolute temperature transport top 1000 dbar by the 10 sv pipe was estimated across 10 transects crossing the nac spf because the mean mass flux is constant in the pipe variations in the mean temperature transports result from lateral exchange and mixing across the pipe s side walls and from air sea fluxes across the surface of the pipe the nac spf current loses 0 18 6 0 05 pw on its transit through the region most of the loss occuring upstream of the northwest corner the heat loss is 10 times the corresponding heat lost to the atmosphere we conclude that cross frontal exchange induced by the steep meanders of the northward flowing nac is the main mechanism by which heat is lost along the current in the region between the tail of the grand banks and the mid atlantic ridge

the origin of major incisions within the pleistocene deposits of the north sea a seismic survey to resolve the geometry of major incisions within the upper pleistocene has been run over an area of 1600 km2 in the mid north sea twelve separate incisions have been identified ranging up to 5 km wide and 25 km long with incised depths from 100 to 350 m deposits categorised into four recurring types infill the incisions to form a flat sea bed the surveyed features are comparable to others widely found beneath the northern continental shelves and lowlands of europe asia and america such incisions have a similar range of sizes and shapes were cut during at least three separate periods in the pleistocene and are down cut into substrates of various lithologies ranging from precambrian to pleistocene in age the major incisions are believed to be the product of a singular mechanism the outburst of intra ice sheet lakes forming jokulhlaup plunge pools except for late stage hollow infills which have interglacial temperate deposits the incision infills are periglacial the former deposits are similar to the sediments accumulating in the present day bathymetric enclosed deeps such as the lambay deep and devil s hole found on continental shelves it is suggested that the enclosed deeps are large kettle holes which resulted from the thawing of ice formerly buried in the incision infills

a morphometric analysis of tunnel valleys in the eastern north sea based on 3d seismic data a 1250 km2 3d seismic volume is used to provide a detailed spatial and geometrical analysis of fifteen pleistocene tunnel valleys in the danish north sea all the valleys are buried they are up to 39 km long 3 4 km wide and up to 350 m deep the valleys are part of a vast tunnel valley province covering an area of some 0 5 million km2 of the formerly glaciated lowland areas of north west europe the valleys consist of non branching non anastomosing troughs they exhibit strongly undulating bottom profiles with numerous sub basins and thresholds and are characterised by adverse end slopes cross cutting relationships and theoretical considerations suggest the occurrence of seven major episodes of valley incision attributed to ice marginal oscillations within a few glacials calculations considering the valley end gradients and theoretical ice surface profiles suggest that the valleys were formed by pressurised subglacial meltwater erosion given a range of theoretical ice surface profiles the adverse end slopes are well beyond the supercooling threshold which suggests that the water was not in thermal equilibrium with the basal ice and that flow was concentrated in substantial conduits with sufficient mass and flux to maintain water temperature well above the freezing point copyright 2007 john wiley sons ltd

micromorphology of some north sea till samples a pilot study in a pilot study three samples of diamictons from boreholes in the dutch sector of the north sea have been thin sectioned in the thin sections the granulometry structure and plasmic fabric of the diamictons have been studied on the basis of this study two of the samples have been interpreted as flow tills while one sample has been interpreted as a basal lodgement till

mesoscale variability transition from the western to the eastern atlantic along 48 n abstract the north atlantic low frequency variability along 48 n is described from 76 year long velocity temperature records obtained as part of the topogulf project whose main objective was to document the effects of the mid atlantic ridge upon the circulation the eddy energy is thermocline intensified and shows a fivefold decrease eastward from 35 to 10 w west of the ridge it penetrates more easily to the ocean floor between 1500 and 2500 m sudden energetic bursts are observed and we argue that they are associated with the passage of sub mesoscale concave cyclonic lenses depleted of labrador sea water at nearly all locations a negative zonal momentum flux u v is observed which may be linked to an energy transfer from the north atlantic current eddy heat fluxes are also obtained and are directed up down the mean gradient west east of the ridge crest

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

the last glacial maximum in the north sea basin micromorphological evidence of extensive glaciation despite a long history of investigation critical issues regarding the last glacial cycle in northwest europe remain unresolved one of these refers to the extent timing and dynamics of late devensian weichselian glaciation of the north sea basin and whether the british and scandinavian ice sheets were confluent at any time during this period this has been the result of the lack of the detailed sedimentological data required to reconstruct processes and environment of sediments recovered through coring this study presents the results of seismic sedimentological and micromorphological evidence used to reconstruct the depositional processes of regionally extensive seismic units across the north sea basin thin section micromorphology is used here to provide an effective means of discriminating between subglacial and glacimarine sediments from cored samples and deriving process based interpretations from sediment cores on the basis of micromorphology critical formations from the basin have been reinterpreted with consequent stratigraphic implications within the current stratigraphic understanding of the north sea basin a complex reconstruction is suggested with a minimum of three major glacial episodes inferred on at least two occasions during the weichselian devensian the british and scandinavian ice sheets were confluent in the central north sea whilst micromorphology can provide much greater confidence in the interpretation of late quaternary offshore stratigraphic sequences it is noted that a much better geochronology is required to resolve key stratigraphic issues between the onshore and offshore stratigraphic records copyright 2006 john wiley sons ltd

pore water controlled grain fracturing as an indicator for subglacial shearing in tills genetic classification of glacial deposits still proves to be highly controversial in many cases it remains unclear whether a particular sediment has been sub glacially deformed in the present paper it is suggested that micromorphological research is helpful where current techniques fail to lead to unambiguous interpretations it is argued that the occurrence of fractured grains in glacial sediments is indicative of subglacial shearing and that such grains may be used as diagnostic evidence of glaciotectonism deformational mechanisms associated with the fracturing process are outlined and explained using a series of thin sections from wijnjewoude the netherlands

repeated advance and retreat of the east antarctic ice sheet on the continental shelf during the early pliocene warm period abstract diatom analysis of a sediment core recovered at iodp site u1358 on the continental shelf off the adelie coast indicated that the lower section of the core contained an assemblage dating back to the thalassiosira innura zone of the lower pliocene that ranges from 4 2 to 5 12 ma based on lithological descriptions at both a macro and micro scale of this early pliocene part of the core four facies were interpreted from the diamictons representing the progressive advance and retreat of the grounding line over the site facies 1a and 1b contain a distinct directional signal from the orientation of the a axis of clasts with several phases of fabric development along with both brittle and ductile deformation features that are common in sediments that have been subglacially deformed facies 1c and 1d are finely laminated and were deposited in open marine conditions the four facies within the depositional model provide for the first time direct evidence for ice advancing across the shelf adjacent to the wilkes subglacial basin on at least four occasions separated by three periods of open marine conditions indicating retreat of grounded ice inland of the site during a warmer than present early pliocene the times of open marine conditions are correlated with previous findings from the neighbouring rise sites that also indicated an oscillating ice margin this has significant implications because firstly it suggests a dynamic east antarctic ice sheet eais that is probably far more sensitive to climatic and oceanic forcing even during relatively short time periods than had previously been thought secondly it suggests that proxies used to interpret the advance and retreat of the grounding line from the rise can be linked with direct evidence of grounding line migration from the shelf it also has important implications for the future behaviour and sensitivity of the eais under present continuing warming conditions together with results from the rise this paper provides a crucial ice extent target for a new ice sheet model of this region during the pliocene

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

sediment deformation beneath glaciers rheology and geological consequences experiments beneath breidamerkurjokull in iceland have led to development of flow laws for the subglacial till relating strain rate to shear stress and effective pressure and assuming either bingham fluid or nonlinearly viscous fluid behavior water pressures in the till are less than ice pressures and it is suggested that this may lead to infiltration of ice into the sediment which inhibits sliding at the ice sediment interface where water pressures are equal or near to ice pressures infiltration does not occur and sliding may result a one dimensional theory of subglacial deformation is developed in which the empirical flow law is coupled with a model of subglacial hydrology and consolidation this predicts stable states in which subglacial sediment either does not deform or a dilatant deforming horizon forms with positive effective pressures at the ice bed interface or unstable states where zero or negative effective pressures are predicted time dependent analyses show that response times following perturbations of the system may be of the order of 103 years and thus that unsteady behavior may be normal on glaciers flowing over unlithified sediment beds it is suggested that the natural variability of material properties in subglacial sediment beds leads to the development of drumlins on the glacier bed it is suggested that unstable deformation at zero or negative effective stress leads to piping in subglacial sediments at the glacier terminus and the growth of sediment floored subglacial tunnels their frequency is that which is sufficient to draw down subglacial water pressures so as to prevent unstable deformation where they discharge large water volumes subglacial sediments flow laterally toward them producing tunnel valleys this sediment is then removed by water flowing along the axial tunnel tunnel valleys can be regarded as the equivalent in soft sediment areas of eskers in bedrock areas

directly measured mid depth circulation in the northeastern north atlantic ocean the circulation of water masses in the northeastern north atlantic ocean has a strong influence on global climate owing to the northward transport of warm subtropical water to high latitudes but the ocean circulation at depths below the reach of satellite observations is difficult to measure and only recently have comprehensive direct observations of whole ocean basins been possible here we present quantitative maps of the absolute velocities at two levels in the northeastern north atlantic as obtained from acoustically tracked floats we find that most of the mean flow transported northward by the gulf stream system at the thermocline level about 600 m depth remains within the subpolar region and only relatively little enters the rockall trough or the nordic seas contrary to previous work our data indicate that warm saline water from the mediterranean sea reaches the high latitudes through a combination of narrow slope currents and mixing processes at both depths under investigation currents cross the mid atlantic ridge preferentially over deep gaps in the ridge demonstrating that sea floor topography can constrain even upper ocean circulation patterns

pathways of inflow and dispersion of warm waters in the nordic seas 1 in this study we use 22 acoustically tracked rafos floats to examine the routes and spreading of warm north atlantic waters entering the norwegian sea between iceland and the faroes the majority of floats crossed the iceland faroe ridge at the eastern end where it is deepest they joined the iceland faroe front but rather than continue north with the outer branch of the norwegian atlantic current into the nordic seas most of them jumped over to the inner branch which continues the inflow through the faroe shetland channel northeast over the voring plateau toward the lofoten basin indeed 17 floats whether deployed near iceland or the faroes did so only 2 floats continued north along the outer branch despite the small numbers these results highlight 1 the strong influence of topography on flow patterns 2 the strong crossover of iceland faroes waters to the inner branch and 3 the rapid and structured spreading into the nordic seas

submarine end moraines as indicators of pleistocene ice limits off northwest britain high resolution sparker seismic profiles reveal evidence for glaciation of the outer part of the northern hebrides and west shetland shelves submarine end moraines suggest glacial ice which locally extended out to the shelfbreak seismic stratigraphic analysis of the glacial succession suggests that the moraines on the northern hebrides shelf are older than those developed on the west shetland shelf whist the stratigraphic evidence indicates at least two phases of widespread outer shelf glaciation the timing of these events remains uncertain

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

micromorphological criteria for discriminating subglacial and glacimarine sediments evidence from a contemporary tidewater glacier spitsbergen abstract sedimentological and micromorphological evidence is presented from four sites within st jonsfjorden western spitsbergen sedimentological and geomorphological evidence is used to distinguish sites comprising undisturbed glacimarine sediments from glacially over ridden glacimarine sediments and subglacial diamicts impregnated thin sections are used to define associations of micromorphological characteristics that allow diamicts formed under these different conditions to be discriminated in situ glacimarine deposits display winnowed textures dropstone structures and distinct vertical orientations of sand grains whilst subglacial conditions result in structures indicative of deformation under moderate to high stress regimes these criteria may help to determine the origin of ancient and quaternary diamicts of questionable subglacial or glacimarine origin

on variations in static stability along lagrangian trajectories abstract by causing an isopycnal float to rise and sink to neighboring density surfaces one can measure layer thickness along a float trajectory and thus variations in static stability we report here on layer thickness measurements that were obtained from the nearly 100 isopycnal floats that were deployed in the 1993 1995 lagrangian study of the north atlantic current layer thickness variations depend significantly upon location and process in the high velocity core of the meandering north atlantic current layer thickness changes correlate with curvature of the flow stretching in troughs compression in crests but this correlation fails in unsteady flows or outside the high velocity center of the current floats also register significant changes in stratification when they cross between the warm waters in the newfoundland basin and the cold waters from the labrador sea as floats enter and exit what appear to be coherent eddy structures significant but not necessarily predictable changes in layer thickness can occur while the technology to measure layer thickness variations performed as well and reliably as we had hoped for the presence of ubiquitous small scale features in the density field together with the fact that the thickness measurements sampled only o 100 m of the total water column limited our ability to isolate and identify the cause of thickness variations to only relatively energetic features

quaternary glaciations in southern fennoscandia evidence from southwestern norway and the northern north sea region abstract based on records from the northern north sea and southern norway quaternary fennoscandian glaciations are described and discussed maximum glaciation defined as the presence of shelf edge glaciation an ice stream flowing out of the norwegian channel and most likely an ice divide over the central part of fennoscandia sweden gulf of bothnia occurred for the first time in the late cenozoic at ca 1 1 myr the fedje glaciation this glaciation was followed by a ca 600 kyr period with at least two glaciations with ice extension somewhat larger than the younger dryas event in the region the first maximum glaciation of the bruhnes chron was during isotope stage 12 and was followed by repeated maximum glaciations within each of the light isotopic stages until stage 2 during the weichselian the southwestern part of the fennoscandian ice sheet reached maximum position three times sometime between 22 and 28 37 and 50 and 60 and 80 ka limited glaciations probably occurred during stadials between the early and middle weichselian interstadials between 500 ka and 1 1 myr and most likely also prior to 1 1 myr deep norwegian sea ice rafted detritus ird records reflecting contributions from several different ice sheets fennoscandian barents sea iceland and greenland each with large variations in history of ice extent to their respective margins yet to some degree they reflect the glaciation of the northern north sea region with an increasing ird input around 1 1 myr and a relatively low input of north sea components during some cycles around the b m boundary maximum glaciations occurred during insolation minima in the earlier part of the middle pleistocene however not all such minima are reflected by maximum glaciation in southern parts of fennoscandia the relatively poor chronological control and non continuous character of the data on weichselian interstadials stadials precludes a clear relationship to atmospheric changes recorded in greenland ice cores as well as to precession and or obliquity cycles in insolation

late pleistocene evolution of the rhine meuse system in the southern north sea basin imprints of climate change sea level oscillation and glacio isostacy high resolution continuous core material geophysical measurements and hundreds of archived core descriptions enabled to identify 13 late pleistocene rhine meuse sedimentary units in the infill of the southern part of the north sea basin the netherlands northwestern europe this sediment record and a large set of optical stimulated luminescence dates 14c dates and biostratigraphical data allowed to establish detailed relationships between climate change sea level oscillation glaciation history and the sedimentary development of the rhine fluvial system during the last glacial cycle marine isotope stages 5e 2 eemian weichselian a well preserved eemian sediment record was encountered as the infill of a late saalian mis6 subglacial basin part of this record reflects groundwater rise controlled fine grained sedimentation as a result of postglacial early eemian sea level rise it shows strong analogy to developments known from the holocene rhine meuse delta outside of the glacial depressions near coastal deposits are only fragmentarily preserved the early glacial rhine sediment record is dominated by organic debris and peat layers marking landscape stability and low fluvial activity part of this record may have been formed under near coastal conditions significant amounts of reworked marine biomarkers in the lag deposits of early pleniglacial mis4 fluvial systems indicate that this period is characterized by extensive reworking of older mis5 near coastal sediments despite the marked early pleniglacial climatic cooling input of new sediment from the drainage basin was relatively low a feature that is related to the presence of regolith protective relic soil complexes in the basin during the early middle pleniglacial a major rhine avulsion indicates the system was in an aggrading mode and that sediment supply into the lower reaches of the rhine had strongly increased this increase in sediment supply coincided with the timing of major climate cooling that occurred from 50 to 45 ka onwards the increase in sediment supply is related to final breakup of the soil complexes in the drainage basin after 24 ka a strong input of coarse grained gravelly sediments was observed which indicates a strong increase in physical weathering processes and periglacial controlled supply of bedload sediment in the catchment a time delay between climate change 30 ka and channel belt aggradation 24 ka is explained as a result of transport path length between source and sink and or effects of higher continental runoff rates after 22 ka the late middle pleniglacial late pleniglacial and lateglacial rhine meuse record testifies for strong influence of glacio isostatic controlled differential upwarping of the study area glacio isostatic controlled forebulge upwarping and lateral valley tilting is shown to have deflected rhine meuse channel belts after 35 ka glacio isostatic upwarping is seen as the main cause for strong incision during the first phase of the late pleniglacial 30 24 ka at later stage glacio isostatic controlled incision was overruled due to high climate controlled sediment input from the catchment and probably initial glacio isostatic subsidence migration of channel belts towards the direction of the former centre of glacio isostatic uplift indicates that glacio isostacy influenced rhine meuse paleogeography until far into the lateglacial 2007 elsevier ltd all rights reserved

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

the north atlantic current and surrounding waters at the crossroads the north atlantic current is a well defined western boundary current that flows north along the east side of the grand banks from 40 to 51 n where it turns sharply to the east and begins its journey across the ocean the current is unique in transporting warm tropical waters to much higher latitudes than any other western boundary current and thus plays a crucial role in ameliorating the climate of the european subcontinent the north atlantic current originates in the gulf stream when the latter curves north around the southeast newfoundland rise a major submarine ridge that stretches se from the grand banks a well defined front delineates the path of the current as long as it flows north as a western boundary current after the current turns east in the north it broadens into a widening band of eastward drift without a sharp or permanent front in the sense of the eastward flowing gulf stream after it separates from cape hatteras the north atlantic current transports more than 40 sv 1 sv 106 m s 1 in the south and about 20 sv by the time it flows east across the mid atlantic ridge the currents along the northward flowing front are quite swift with typical maximum average speeds in the upper 300 m near 1 m s 1 2 knots the current meanders almost as wildly as a snaking river but unlike steep meanders in the gulf stream these meanders appear to be stable and with one exception have not been observed to break off to form pools of warm and or cold waters as frequently occurs in the gulf stream the meanders appear to be induced by major topographic features along the path of the current namely the southeast newfoundland rise the newfoundland seamounts and flemish cap strong recirculations develop on the concave side of the meanders one of these the mann eddy at the first meander crest of the north atlantic current should be regarded as a permanent feature of the north atlantic circulation other meanders also contain recirculations that can persist for months under certain conditions these can merge together to form an extended sw flow recirculation just east of the north atlantic current

description and dating of a submerged beach in the northern north sea abstract an assumed submerged beach bordering the northern part of the north sea plateau towards the norwegian trench at 130 to 160 m waterdepth has previously been described based on interpretation of seismic profiling the seismic unit is parallel to the edge of the plateau for at least 50 km with an eastward dipping bedding soil borings and vibrocorer samples reveal that a stiff to hard clay is overlain by a thin lag deposit of coarse material on the plateau by an up to 40 m thick coarsening upwards sequence of sand and gravel on the upper part of the slope and by gradually finer material further eastwards in deeper water a low sea level is also indicated by the foraminiferal faunas and abundant littoral and aeolian textures on quartz sand grains nine radiocarbon datings of shell material found in sand and gravel from about 1 to 23 m below the sea bed gave ages from 10 800 to 12 500 yrs b p we thus consider the interpretation of the edge of the plateau and the top of the slope as a submerged beach built out in late weichselian time to be confirmed by the sample evidence

isopycnal lagrangian statistics from the north atlantic current rafos float observations one hundred isopycnal floats were tracked on the 27 2 and 27 5 surfaces in the newfoundland basin nfb from july 1993 to july 1995 to study the current structure and exchanges of waters between the subtropical and subpolar gyres the float mapped mean flow consists of weak flows in the nfb and a strong boundary current the north atlantic current nac which separates from the boundary at the northwest corner becoming a diffusive zonal drift the nac meanders are linked to topography and have similar patterns on the two isopycnals despite the fact that the upper layer velocities are twice as fast as the lower layer ones perturbation velocity from the mean is used to compute isopycnal turbulent dispersion and diffusivity this large data set allows us to resolve a narrow mean nac and results in a gaussian turbulence the turbulence approximately follows the classic taylor dispersion theory integral timescales and length scales and turbulent isopycnal diffusivity are of 1 5 2 5 days 20 30 km and 1 7 103 m2 s 1 respectively the timescale increases with depth and decreases with latitude the length scale decreases with depth and longitude and the diffusivity decreases with depth and from nac to nfb compared to previous results from surface drifters and isobaric floats our isopycnal statistics are more isotropic and agree better with the taylor dispersion theory because 1 the mean velocity has a better resolution and 2 the isopycnal floats are better lagrangian followers the diffusivity scales better with the rms velocity and length scale than with the velocity variance and timescale

an alternative hypothesis for the origin of the mediterranean salt lens observed off the bahamas in the fall of 1976 abstract a hypothesis is presented that the original salt lens or meddy observed off the bahamas in the fall of 1976 may have been formed not near the mediterranean outflow but instead in the vicinity of the northwest corner 51 n 43 w of the north atlantic current an eddy was observed near the northwest corner by an isopycnal rafos float deployed during the 1993 95 north atlantic current experiment and had nearly identical temperature salinity properties as those of the bahamas lens hydrographic evidence of thick homogeneous layers with similar properties near the northwest corner suggest a possible formation mechanism by which surface eddies containing warm and saline waters are cooled and subducted a plausible scenario is made whereby a northwest corner eddy might be advected southward in the newfoundland basin by the flow around the high pressure ridge east of the north atlantic current and then enter the recirculation gyre immediately south of the gulf stream such an eddy could be advect

quaternary stratigraphy of the fladen area central north sea a multidisciplinary study based on detailed stratigraphic investigations on a 200 6m long core bgs borehole no 81 26 from the fladen ground area british sector core material from the sleipner field norwegian sector and shallow seismic profiles between the core sites the following conclusions are drawn 1 the north sea was glaciated sometime during th elaterpart of matuyama reversed period a complete glacial interglacial glacial cycle is recorded in these sediments 2 in a period of marine sedimentation in the middle pleistocene a transgression regression cycle under boreal arctic regime is recorded 3 the fladen area has subsided between 0 9 and 0 6 m ka through the later parts of the quaternary 4 a major glacial event dated at between 130 and 200 ka is recorded as a thick till unit in 81 26 this till which was deposited by ice moving from the southwest scotland probably represents a period when the scandinavian and british ice sheets coalesced in the north sea 5 based on the seismic data and the stratigraphy of the sleipner core an ice free open embayment dry land is favoured for the central north sea during the late weichselian 6 from the amino acid data it is shown that there has been an episodic style of sedimentation through the quaternary 7 of the investigated sediments which span the last 1 mill year ca 98 have been deposited under arctic to boreal arctic conditions

luminescence dating indicates radiocarbon age underestimation in late pleistocene fluvial deposits from eastern england robust geochronological control is crucial for interpreting and correlating the environmental record from fragmentary terrestrial sequences from the last glacial period traditional terrestrial stratigraphies are typically reliant on radiocarbon dating although estimates of antiquity for samples older than 40 ka may be unreliable optically stimulated luminescence osl dating of sediments is an alternative for dating the whole of the last glacial period and also provides the opportunity to independently test radiocarbon based chronologies this paper presents a set of nine directly comparable paired osl and accelerator mass spectrometry ams radiocarbon ages from multiple sites within devensian fluvial sediments in lowland britain and shows that it is possible to obtain robust osl age estimates throughout this time period the two techniques agree well for ages younger than ca 29 14c ka bp ca 35 cal ka bp but disagree beyond ca 35 14c ka bp ca 40 cal ka bp this is thought to be due to radiocarbon ages on older organic material having been contaminated by low levels of modern carbon it is therefore suggested that all conventionally pre treated radiocarbon ages greater than 35 14c ka bp should be treated with extreme caution copyright 2009 john wiley sons ltd

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

till and moraine emplacement in a deforming bed surge an example from a marine environment the glacier sefstrombreen in spitsbergen surged across an arm of the sea between qsr 1882 and 1886 and rode up onto the island coraholmen marine and terrestrial geological observations and archive records show that the glacier advanced on a deforming carpet of marine mud which was eroded from its original location transported and smeared over the sea bed and coraholmen as a deformation till the glacier emplaced about 210sm 0 2 km 3 of drift in the terminal 2 km of its advance in a maximum of 14 years leaving a thickness of up to 20 m on coraholmen which was doubled in size as a result during the surge subglacial muds were characterised by high water pressures low effective pressures and low frictional resistance to glacier movement original sedimentary inhomogenities permit fold structures to be identified but repeated refolding and progressive remoulding produce mixing and homogenisation of deformation tills the surge was probably shortlived and as the heavily crevassed glacier stagnated underlying water saturated muds were intruded into crevasses and then extruded on the glacier surface reticulate crevasse intrusion ridges on coraholmen and the sea floor reflect the orientation of surge generated crevasses water and sediment was also extruded beyond the glacier at its maximum extent to form extensive flows producing till tongues both on coraholmen and the sea floor extending over 1 3 km from the glacier it is argued that subglacial deformation of pre existing sediment will almost invariably be associated with glaciation of marine areas and that this process will not only produce deformation tills through remoulding of pre existing sediments but will also play a fundamental role in glacier dynamics criteria which perrait glacial tills produced by such events from marine and glaciomarine muds are discussed copyright 1996 elsevier science ltd

particle and aggregate mobility in till microscopic evidence of subglacial processes abstract microscopic studies of tills show that the deforming bed of glaciers is made up of minute rotational elements or wheels consisting of a nucleus alone or a nucleus with spiralling arms of fine grains these fine grains can move from one wheel to the next providing a process of high grain mobility within a deforming subglacial till recognition of this process explains a variety of glacial distribution patterns i e the mineralogical reflection of subjacent lithologies in the till matrix the side by side occurrence of far travelled erratics and locally derived matrix and the shape of geochemical anomalies

palaeogeographical changes in response to glacial interglacial cycles as recorded in middle and late pleistocene seismic stratigraphy southern north sea offshore stratigraphic records from the north sea contain information to reconstruct palaeo ice sheet extent and understand sedimentary processes and landscape response to pleistocene glacial interglacial cycles we document three major middle to late pleistocene stratigraphic packages over a 401 km2 area norfolk vanguard boreas offshore wind farm offshore east anglia uk through the integration of 2d seismic borehole and cone penetration test data the lowermost unit is predominantly fluviatile yarmouth roads formation marine isotope stage mis 19 13 including three northward draining valleys the middle unit swarte bank formation records the southernmost extent of tunnel valley fills in this area of the north sea providing evidence for subglacial conditions most likely during the anglian stage mis 12 glaciation the yarmouth roads and swarte bank deposits are truncated and overlain by low energy estuarine silts and clays brown bank formation mis 5d 4 smaller scale features including dune scale bedforms and abrupt changes in cone penetration test parameters provide evidence for episodic changes in relative sea level within mis 5 the landscape evolution recorded in deposits of mis 19 5 are strongly related to glacial interglacial cycles although a distinctive aspect of this low relief ice marginal setting are opposing sediment transport directions under contrasting sedimentary process regimes

the jaeren area a border zone of the norwegian channel ice stream abstract the coastal lowlands of jaeren southwestern norway have an extensive cover of quaternary sediments lithological biostratigraphical and geochronological investigations of a series of boreholes across jaeren have allowed us to combine earlier and new information on these deposits into a temporal model of quaternary sedimentation the cores show evidence of at least four ice free episodes with marine deposition during mainly arctic conditions the oldest of these is considered to be ca 200 ka old and the youngest one is the sandnes interstadial which is 14 c ams dated to 32 ka bp interbedded between these units are 10 40 m thick units of till with components of marine material these findings together with a re evaluation of distinct morphological features on jaeren as well as earlier provenance studies strongly suggest that jaeren has been a boundary zone between an ice stream following the norwegian channel draining a substantial part of the southern region of the fennoscandian ice sheet and local ice from south western norway through multiple periods of glaciation starting ca 1 1 myr million years ago the norwegian channel ice stream has been the main conduit of erosion products from southern scandinavia to the deep norwegian sea comparison with ice stream profiles from antarctica suggests that the deposition of relatively young marine sediments as high as ca 200 m a s l on jaeren is a result of glacial isostasy rather than regional tectonic movements

amino acid geochronology and the british pleistocene secure stratigraphical framework or a case of circular reasoning aminostratigraphy is central to the recently revised correlation of quaternary deposits in the british isles providing a link between terrestrial deposits and marine oxygen isotope stages the central tenet of british aminostratigraphy however that shells from the same interglacial yield very similar ratios so that the characteristic ratios from different interglacials are distinct remains uncertain the data available suggest that amino acid ratios from different interglacials do not fall into discrete groups but overlap considerably it is therefore not valid to assign individual shells to oxygen isotope stages simply on the basis of their amino acid ratios which means that filtering data to remove high or low values on the assumption that they represent reworked shells is unacceptable the range of characteristic ratios assigned to british warm stages may have been underestimated and the degree of separation between them overestimated amino acid ratios should be treated as sample data that are naturally variable copyright 2002 john wiley sons ltd

the quaternary succession in the northern north sea abstract studies of core material show that the upper 200 m of sediments deposited in central parts of the north sea span the last ca 1 ma in the norwegian trench the upper 120 m span the last ca 500 ka sedimentation in both areas was characterized by rapid rates over short intervals separated by long hiatuses in the central area fine grained shallow water sediments dominate the pleistocene sequence these sediments were redeposited transported by rivers flowing northward from the british isles and the continent during periods of low sea level through the quaternary the extreme low stands of sea level are also indicated by river channels cut in the sequence in the northern north sea in the norwegian trench thick glacial and glacial marine diamictons make up ca 80 of the record in the middle and late pleistocene sequence the northern north sea was glaciated as early as 850 ka evidence of possibly the most extensive glaciation of the north sea basin has been dated to between 200 and 450 ka in cores from the fladen area the british and scandinavian ice sheets probably did not coalesce in the north sea during the late weichselian maximum

valley asymmetry evidence for periglacial activity in the central north sea present day open valleys with distinct asymmetric profiles have been studied from the central north sea the bulk of the valleys exhibit steep north facing and shallow south facing slopes this asymmetry is ascribed to preferential slumping of the south facing slope under periglacial climatic conditions exceptions to the regional asymmetric trend are probably the result of more localized factors such as fluvial and microclimatic processes and the effects of local geology the recognition of this type of within valley asymmetry associated with slumping in buried valleys within the quaternary sequence may be indicative of former periglacial activity

the drift des demoiselles on the magdalen islands quebec canada sedimentological and micromorphological evidence of a late wisconsinan glacial diamict the deposits identified as being the drift des demoiselles which is the upper unit of the southern magdalen islands quebec canada belong to two units of different origin glacial and glaciomar

isopycnal rafos floats as roving hydrographers in the north atlantic current region the properties measured by isopycnal floats can be compiled to provide hydrographic information about the sampled surfaces the height and temperature of two specific volume anomaly surfaces reported by 84 rafos floats deployed in the north atlantic current nac region are compared here with the climatological hydrographic database the mean pathway of the nac and other prominent features of the region are similar in float derived and climatological surfaces the most striking difference between floats and climatology an extended trough in the nac path at 44 n in the float derived surface reflects the sampling time scales the baroclinic transport of the nac estimated from rafos floats using the observed climatological relationship between the potential energy anomaly and the height of the specific volume anomaly surfaces was 42 sv at 42 n and 24 sv at 47 n in reasonable agreement with climatological estimates

a relict ice scoured erosion surface in the central north sea abstract the interpretation of shallow seismic records from the central north sea has revealed the existence of an irregular erosion surface within late pleistocene sediments a morphological study of this surface has identified two main types of relief 1 an irregular rough topography with depressions varying in depth from 1 to 6 m and in width from 25 to 300 m and 2 a much smoother topography with relatively few depressions on a palaeobathymetric map the rough topography extends from ca 110 to 160 m below sea level od while the smoother topography extends beyond the 160 m below od contour this surface is interpreted as an ice scoured erosional feature formed by the grounding of sea ice in a shallow shelf environment the stratigraphic position of the ice scoured surface shows it to be a relict late weichselian feature formed at ca 17 000 18 000 b p

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

the quaternary geology of the north sea basin the north sea is a shallow 50 400 m deep 500 km wide marine embayment that separates the uk from scandinavia and northern europe fig 1 this epicontinental shelf area has had a long and complex geological history with its present day structural configuration largely being the result of rifting during the jurassic early cretaceous followed by thermal subsidence glennie and underhill 1998 zanella and coward 2003 since the middle cenozoic the central graben region of the north sea basin has accumulated up to 3000 m of oligocene to holocene sediments which locally includes more than 800 m of quaternary sediments caston 1977 1979 gatliff et al 1994 although a detailed understanding of the depositional history recorded by this sedimentary succession is yet to be fully established these sediments preserve evidence for the advance and retreat of several ice sheets into the north sea from the adjacent landmasses at different times during the quaternary these ice masses not only resulted in periodic erosion but also made a significant depositional contribution to the infill of the basin

pathways of cross frontal exchange in the north atlantic current the north atlantic current nac forms part of the boundary between the subtropical and subpolar gyres in the north atlantic ocean the current has topographically controlled stationary meanders that appear to grow and decay a region east of the current in the newfoundland basin contains water of mixed subpolar subtropical properties suggesting that there is exchange across the nac this study considers data from isopycnal rafos floats launched in the nac region from 1993 to 1995 we use the rafos data to define the frontal zone as a pressure range where the jet is most likely to be found this definition requires a latitudinal dependence as the nac shoals to the north floats shallower and deeper than this range are defined to be on the subpolar and subtropical side respectively these definitions are used to estimate mixing that occurs between the current and its surroundings and to estimate the relative quantity of exchange of water parcels between the two gyres only small quantities of mass exchange from one gyre to the other are found but there is a distinct asymmetry leading to a mean flux from the subpolar to subtropical sides we also find that floats spend significant time in the frontal region and are frequently exchanged between fast and slow moving waters particularly at the meander extrema diffusion while in the jet leads to eddy cross frontal exchange which is important for the exchange of properties across the nac

theory of glacial erosion transport and deposition as a consequence of subglacial sediment deformation a theory of erosion transport and deposition of unlithified sediments by glaciers is presented it predicts the large scale areal distribution of zones and rates of erosion and deposition in time and space through a complete glacial cycle together with the resultant intensity of large scale lincations drumlins which will be incised in the landscape the theory also predicts the dispersal patterns of subglacial lithologies together with the form of dispersal trains derived from distinctive sources and the vertical and horizontal distribution of lithologies within a till it predicts major erosional discontinuities within tills and the formation of boulder pavements it suggests that the dominant proportion of the lowland tills produced by pleistocene mid latitude ice sheets was generated by subglacial deformation and explains why they are predominantly fine grained the theory is based on an analysis of glacier dynamic processes and therefore can be used to infer the dynamic behaviour of former ice sheets from the distribution of tills and their lithologic composition

lagrangian studies of fluid exchange between the gulf stream and surrounding waters abstract between spring of 1988 and winter of 1990 75 rafos floats were released east of cape hatteras near the center of the gulf stream on the 26 8 t surface o 15 c the purpose of this sequential deployment was to investigate the spatial and temporal characteristics of the meandering stream and the lagrangian properties of fluid motion in the upper thermocline these new observations were also intended to provide a database for comparative studies of fluid motion in the upper thermocline with similar observations made earlier 1984 85 in the middle and lower thermocline sixty one of the 75 rafos float trajectories in the 13 16 c layers have been analyzed from both a lagrangian and eulerian point of view the results reconfirm the strong baroclinic structure of the gulf stream established earlier and reveal enhanced cross stream motion with increasing depth and over the new england seamounts float trajectories tend to be more convoluted east of the seamounts reflecting the large amplitude meand

the history of quaternary sedimentation in the uk sector of the north sea basin reconnaissance seismic and sampling surveys have shown that up to 500 m of lower and early middle pleistocene deltaic sediments are preserved in the uk sector of the north sea the distributions of delta related facies record the progressive expansion of peripheral delta systems northwards across the southern north sea during the early pleistocene a late middle pleistocene unconformity is present throughout the uk sector and sedimentation above the unconformity was dominated by glacial erosional and depositional processes a complex system of deeply incised valleys was eroded during each of three regional middle and upper pleistocene glaciations and the valleys have been filled or partially filled by glaciolacustrine or glaciomarine and interglacial marine sediments the valleys of the earliest elsterian glaciation are up to 400 m deep in the southern north sea the saalian and weichselian valleys are commonly more than 100 m deep they are eroded through their contemporary tills nearshore but occur well beyond the limits of these tills offshore the origins of these valleys are attributed to a combination of fluvial subglacial and periglacial processes

glacial incisions indicating middle and upper pieistocene ice limits off britain from the recognition that major incisions formed at lowland or tidewater ice sheet margins during each of the last three glacial stages it is assumed that a standard quaternary stratigraphy is applicable to the deposits geophysically profiled on the continental shelf off britain ice limits for each glacial stadial can be mapped from the geographical distribution of the incisions during the next glacial stage major incisions will be downcut on the present continental shelf or coastal lowlands to some 350 m below the ambient surface this will have important environmental consequences regarding the long term burial of hazardous wastes

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

analysis of lagrangian potential vorticity balance and lateral displacement of water parcels in gulf stream meanders abstract the balance of potential vorticity components following fluid parcel motion in gulf stream meanders was studied using rafos float data from the synop experiment by introducing curvature dependent variations to the velocity and density fields the authors relaxed the rigid field assumption used in earlier studies and examined closely 61 floats in the upper layers 13 16 c of the main thermocline float trajectories were segmented according to transition from crest to trough and trough to crest and grouped by their positions relative to the current center a total of 154 segments were collected to estimate the horizontal divergence and the mean lateral displacement of parcels under two distinct regimes growing and decaying meanders both spatial and temporal changes in curvature affect the regions of divergence in a meandering stream on the one hand horizontal divergence increases with increasing curvature magnitude while on the other hand the divergence pattern itself changes going from g

the extension of the late weichselian late devensian ice sheets in the north sea basin the distribution of large channel like features comprising weichselian devensian incisions in the western north sea provides evidence for a much larger extension of the last ice sheet than currently assumed morphological comparison of the incisions with those in north germany and poland reveals a striking similarity in shape and distribution the features on the north sea floor are interpreted as being formed by meltwater erosion within the margin of the ice sheet the widespread absence of weichselian devensian till in the area under consideration may be attributed to later erosion large scale reworking and redistribution of sediments is indicated by the complete sediment infill of the majority of the incisions

till fabric patterns and significance particle response to subglacial stress abstract the analysis of particle arrangements within glacial sediments fabric has long been considered to reflect the behaviour of the ice that transported and deposited or deformed the sediment particles can develop specific fabric arrangements as a response to bulk sediment strain driven by effective stress at the bed of a glacier as such fabric analysis has been used to try and understand the complex relationship between glacier and ice sheet dynamics and the geological evidence of former glaciation developments have focused on the use of stereonet patterns and statistical measures vector and eigenvector analysis of clast fabric to infer the process of sediment deposition deformation and consequent ice flow directions and dynamics however as this study identifies fundamental processes of particle orientation march jeffery and taylor rotation mechanisms would suggest more complex explanations than have been previously reported this study reports the results of a detailed field and laboratory investigation of macro scale clast and microfabrics from a till sequence in central scotland the results suggest a systematic behaviour of different particle size fractions which may be interpreted in terms of the strain response of sediment three fabric patterns are identified that illustrate consistent progressively shifting and more complex particle behaviour it is suggested these orientation patterns indicate the degree to which subglacial sediment has undergone strain and the nature of the deforming bed erosional or accretionary it is concluded that this approach may yield fundamental information about the strain conditions underlying different ice masses providing critical data linking glaciological modelling with the sedimentary evidence of glaciation

deep water formation the subpolar gyre and the meridional overturning circulation in the subpolar north atlantic on interannual to decadal times scales model simulations suggest a strong relationship between anomalies in the deep water formation rate the strength of the subpolar gyre and the meridional overturning circulation in the north atlantic whether this is valid can only be confirmed by continuous long observational time series several measurement components are already in place but crucial arrays to obtain time series of the meridional volume and heat transport in the subpolar north atlantic are still missing here we summarize the recent developments of the deep water formation rates and the subpolar gyre transports we discuss how existing observational components in the subpolar north atlantic could be supplemented to provide long term monitoring of the meridional heat and volume transport through a combined analysis of observations and model results the temporal and spatial scales that had to be covered with instruments are discussed together with the key regions with the highest variability in the velocity and temperature fields

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

mechanical discontinuities monitoring at merapi volcano using kinematic gps merapi volcano java indonesia is in almost continuous activity with growth of an andesitic lava dome this dome frequently collapses to form potentially deadly glowing avalanches explosions and nuees ardentes to monitor the evolution of surface displacements and to model the associated magmatic sources we established a global positioning system gps network in 1993 and have measured it each year using the static gps method however the limited number of benchmarks and the geometry of the network did not allow us to precisely locate major mechanical discontinuities within the edifice precisely locating these discontinuities is of central importance because they delimit areas of potential instability and provide means to evaluate potential volumes of falling material the kinematic gps method offers a way to partially solve the problem of temporal and spatial sampling of the displacement field but its accuracy is usually insufficient to monitor small displacements we propose here a strategy of field measurements and adjustments which combines kinematic positioning 1 min and rapid static baselines 15 min to get a 1 5 cm error 95 confidence at merapi summit we have installed about 50 benchmarks covering the area around the main crater field measurements of this new network with our method take a few hours and the data processing has been automated we present the results of 8 surveys from 1999 to 2002 a period that includes a dome collapse in january 2001 our results show large horizontal displacements towards the northwest starting in july 2000 and reaching about 50 cm in amplitude in november 2000 that we interpret as precursors to the dome collapse we also locate two presently active discontinuities at the summit of the volcano this approach can be implemented easily on other active volcanoes

direct observation of subtropical mode water circulation in the western north atlantic ocean abstract eighteen degree water edw is the dominant subtropical mode water of the north atlantic subtropical gyre and is hypothesized as an interannual reservoir of anomalous heat nutrients and co2 although isolated beneath the stratified upper ocean at the end of each winter edw may re emerge in subsequent years to influence mixed layer properties and consequently air sea interaction and primary productivity here we report on recent quasi lagrangian measurements of edw circulation and stratification in the western subtropical gyre using an array of acoustically tracked isotherm following bobbing profiling floats programmed to track and intensively sample the vertically homogenized edw layer and directly measure velocity on the 18 5 c isothermal surface the majority of the clivar mode water dynamics experiment climode bobbers drifted within the subtropical gyre for 2 5 3 5 years many exhibiting complex looping patterns indicative of an energetic eddy field bobber derived lagrangian integral time and length scales 3 days 68 km associated with motion on 18 5 c were consistent with previous measurements in the gulf stream extension region and fall between previous estimates at the ocean surface and thermocline depth several bobbers provided evidence of long lived submesoscale coherent vortices associated with substantial edw thickness while the relative importance of such vortices remains to be determined our observations indicate that these features can have a profound effect on edw distribution edw thickness defined using a vertical temperature gradient criterion exhibits seasonal changes in opposition to a layer bounded by the 17 c and 19 c isotherms in particular edw thickness is generally greatest in winter as a result of buoyancy forced convection while the 17 19 c layer is thickest in summer consistent with seasonal ekman pumping contrary to previous hypotheses the bobber data suggest that a substantial fraction of subducted edw is isolated from the atmosphere for periods of less than 24 months seasonal to biennial re emergence principally within the recirculation region south of the gulf stream appears to be a common scenario which should be considered when assessing the climatic and biogeochemical consequences of edw

mid pleistocene thin skinned glaciotectonic thrusting of the aberdeen ground formation central graben region central north sea this paper presents the results of a high resolution 2d seismic survey of mid pleistocene glaciogenic sediments in the central graben region of the central north sea sediments have undergone major glaciotectonic thrusting and folding associated with the repeated southerly advance of a mid pleistocene ice sheet the total observed length of the thrust stacked section is approximately 5 6 km comprising a series of discrete thrust slices which range in length from 700 m the basal detachment of the thrust complex occurs at a depth of ca 220 m below the sea bed within the upper aberdeen ground formation a thin skinned glaciotectonic model involving proglacial to ice marginal glaciotectonic thrusting followed by post tectonic deposition is proposed initial ice advance led to the over pressurizing of groundwater within a laterally extensive sand sheet in the upper aberdeen ground formation promoting the formation of a major decollement surface at the base of the developing thrust stack over pressurization of the groundwater system is thought to have occurred in response to rapid ice advance suggesting that the development of large scale thrust complexes may be associated with surge type behaviour the proposed model evidences complex dynamics of mid pleistocene ice sheets within the central north sea

microscopic evidence of subglacial deformation abstract subglacial deformation is by now a well established process however recognition of this process in pleistocene tills is not always clear studies of thin sections of pleistocene tills show that there are a variety of microscopic features caused by deformation this paper gives a review of microscopic evidence for subglacial deformation and starts with a case where deformation could be established macroscopically then traces the microscopic features through planar and rotational movements which are described and separated accordingly attention is also given to features caused by crushing of grains and sediment dewatering these studies indicate that almost all basal tills show evidence of subglacial deformation rather than sedimentary derivation this implies that if we want to understand subglacial processes such tills should be described in tectonic rather than sedimentary terminology

potential vorticity balances and horizontal divergence along particle trajectories in gulf stream meanders east of cape hatteras abstract trajectories of 37 isopycnal rafos floats launched in the gulf stream off cape hatteras have been analyzed to examine the dynamics of meanders from a lagrangian viewpoint using the float data in conjunction with information on the structure of horizontal velocity shear from the pegasus study halkin and rossby variations in planetary curvature and shear vorticity have been estimated along the float trajectories changes in fluid layer thickness were then inferred assuming potential vorticity is conserved following the floats this analysis shows that curvature vorticity changes are typically 10 20 of f planetary vorticity as fluid parcels travel between meander troughs and crests lateral shear changes on the order of 20 30 of f are common as parcels move laterally relative to the jet axis between meander extrema although changes in these two terms are usually of opposite sign and tend to compensate significant layer thickness changes do occur with some parcels exhibiting 30 change

surficial sediments in the norwegian sector of the north sea between 60 30 and 62 n abstract based on grain size distribution and sea floor photographs the sea bed sediments between bergen and maloy have been divided into four groups a sand with coarse material on the northern part of the north sea plateau and the maloy plateau b very well sorted sand on the southern part of the north sea plateau and the upper part of the western slope of the norwegian trench c silty clayey sand in lower part of the slopes d silty sandy clay in the central part of the norwegian trench large local variations are found in the group a sediments on the maloy plateau partly caused by relict iceberg plough marks the net deposition after the transition to boreal conditions with atlantic water about 10 000 yrs ago is mostly between 0 and 30 cm on the northern part of the north sea plateau and exceeds 200 cm in the deepest parts of the norwegian trench the total thickness of sediments above assumed overconsolidated material has been mapped based on sparker records on the northern part of the north sea plateau the sediment cover above a supposed wavecut platform is less than 1 m over large areas while a late weichselian coastal unit fringing the plateau consists of up to 40 m of sand and gravel on the southern part of the plateau and the upper part of the western slope of the norwegian trench up to 10 30 m of sediments are found probably dominated by sand formed by wave and tidal current action during a period of low sea level in the central part of the trench a total thickness of up to 40 m of clay deposited during varying environments is found most of the investigated area is believed to be underlain by a till deposited by a north northwestward moving ice sheet

spatial and temporal evolution of a gulf stream crest warm core ring interaction an intensive near synoptic hydrographic study of the reabsorption of a warm core ring into the gulf stream at a meander crest was conducted near 70 w in fall 1988 using a mixture of measurement techniques and statistical optimal interpolation to map the velocity and density fields the study documents how the normally robust cross stream structure of the gulf stream breaks down and the process by which a high pressure ridge between the stream and the ring develops examination of the layer potential vorticity lpv structure on two specific volume anomaly surfaces approximately 18 c and 10 c showed different characteristics of cross stream lpv structure on the shallower surface the cross stream lpv structure was dominated by the cross stream gradient of layer thickness on the deeper surface the much weaker cross stream lpv structure reflected the structure of the relative vorticity field during the 10 day period of ringstream contact considerable water was exchanged rupturing the ring and eventually resulting in the ring s reentrainment by the gulf stream time varying transports as large as 30 sv were exchanged to the north and south between the surface and 5 c the gulf stream bifurcates in such a way that the anticyclonic southern side continues through the meander crest uninterrupted while the cyclonic side is diverted to the north to replace the low potential vorticity waters of the ring with waters of high potential vorticity contact between the ring and the stream is established first at the surface and progresses downward with increasing time the decreased time needed to remove the ring s vorticity in the lower layers is consistent with the geometrical picture of the gulf stream colliding with a bowl shaped ring the flushing time for the lens of 18 c water in the ring is on the order of 5 days slightly longer than the 2 3 days for the relative vorticity of the 10 c surface

thin section production of diamicts problems and solutions abstract thin section production of diamict samples presents many problems primarily as a result of incomplete impregnation this problem is investigated in diamicts of known glacial glaciomarine and subaerial origin the inherent sedimentological characteristics rather than particular mode of deposition appears to influence resin impregnation of diamicts a technique of surface impregnation is presented to overcome this problem when samples fail to impregnate fully during initial preparation and is incorporated into current techniques within a flowchart in the majority of cases this technique results in successful production of a useful thin section

quaternary erosion and depositional processes western norwegian fjords norwegian channel and north sea fan abstract the southern norwegian fjords the northern north sea and north sea margin represent major pathways of sediment flux from the southern part of fennoscandia to the deep sea basin volumes genesis and chronology of the temporary and semi permanent quaternary sediment repositories are reviewed the fjord infill is dominated by sediments from the last deglaciation 150 km 3 the norwegian channel is occupied by tills and glaciomarine marine sediments 5000 km 3 the north sea fan comprises glacially fed debris flow fingers lobes constituting 80 of deposits in the mid to late pleistocene together with hemipelagic and mass transport slide sediments totalling 15 000 km 3 the norwegian channel represents a dynamic transport conduit whereby during peak glaciation a fast flowing ice stream has drained large parts of the southern fennoscandian ice sheet several times the sediment flux to the deep sea is temporarily interrupted between glacials when stored in the channel but under glacial maxima the channel is probably largely bypassed with material transported as subglacial load and deposited as debris flows on the north sea fan sediments on the fan have a much longer storage time numerous glaciation cycles but are further transported to the deep sea in large slide events the volume of quaternary sediments found along this sediment pathway plus that which slid to the deep sea total at least 25 000 km 3 corresponding to an averaged 120 m of erosion across southern norway

the pre weichselian glaciations of north west europe abstract in north west europe no evidence has been found for glaciations older than the elsterian the elsterian seems to consist of at least two separate ice advances with a minor interval in between during the elsterian in the area south of the baltic sea over 400 m deep channels were cut into the underlying substratum by a combination of glacial erosion and meltwater activity the channels were active until the late elsterian and were subsequently filled with meltwater deposits and glaciolacustrine silt and clay during the saalian no comparative channels were being formed three different ice advances can be distinguished within the saalian the stratigraphical correlation of which is to be discussed no convincing evidence was found for any interglacial within the saalian sequence there are good reasons to assume that the ice advances were only separated from each other by minor ice free intervals