thickness and extent of the subglacial till layer beneath an antarctic paleo ice stream fast flowing ice streams and outlet glaciers currently account for as much as 90 of the discharge from the antarctic and greenland ice sheets although the deformation of subglacial material has been proposed as the mechanism for this rapid motion such sediment is usually hidden under several kilometers of ice marine geophysical records have allowed reconstruction of the three dimensional thickness of the sedimentary bed beneath a large antarctic paleo ice stream for the first time fast flow is indicated by streamlined seafloor lineations that form the surface of a layer of low shear strength unsorted sediment averaging 4 6 m thick rapid motion of the paleo ice stream was a result of subglacial deformation within this layer

high resolution seismic stratigraphy sedimentary processes and the origin of seabed cracks and pockmarks at nyegga mid norwegian margin abstract densely spaced high resolution topas seismic profiles and em1002 bathymetric data reveal the presence of numerous pockmarks mound like structures and elongated seabed cracks at nyegga offshore mid norway the seabed cracks are located adjacent to the northern escarpment of the storegga slide appearing as graben like structures in the topas data unlike the cracks pockmarks and mound structures are largely associated with vertical zones of acoustic blanking at depth interpreted as pathways for vertically migrating gaseous fluids based on the topas data a new seismostratigraphic framework has been established and correlated to previously published age models of images cores md99 2291 and md99 2289 seismic facies interpretation suggests repeated and rapid deposition of up to 40 m thick glacigenic wedges in the eastern part of the study area around 18 2 14 c ka bp 21 8 cal ka 17 5 14 c ka bp 20 8 cal ka and 16 9 14 c ka bp 20 cal ka towards the west glacimarine deposition has prevailed characterized by progressively increasing sedimentation rates with peak values of 30 m ka during the period from 15 0 14 c ka bp 18 2 cal ka to 15 8 14 c ka bp 19 cal ka as the distribution of the nyegga pockmarks closely coincides with the main late weichselian sediment depocenters we suggest a relation between rapid and repeated sedimentation and periodic overpressure generation at depth ultimately leading to fluid expulsion at the seabed and the formation of the nyegga pockmark field in contrast seabed cracks at nyegga appear to have formed due to local extension which we relate to horizontal stress reduction as a consequence of the storegga slide event potentially this event has been accompanied by renewed vertical fluid migration and the most recent stage of pockmark development

interaction between subsurface ocean waters and calving of the jakobshavn isbrae during the late holocene a marine sediment core from vaigat in disko bugt west greenland has been analysed in terms of lithology dinoflagellate cysts and foraminifera in order to evaluate the influence of oceanographic variability on west greenland glacier stability the data show that during the past 5200 years the atlantic foraminiferal abundance in the subsurface waters of the west greenland current wgc episodically increased indicating periods of increases in the inflow of subsurface warm atlantic water at 2000 1500 cal yr bp and 1300 cal yr bp as well as periods of less pronounced increased bottom water temperatures around 4700 4000 cal yr bp 3100 2800 2600 1000 800 500 400 and at 200 cal yr the sedimentological and dinoflagellate cyst data indicate that these episodes with enhanced advection of irminger sea derived waters are accompanied by increased iceberg rafting which we link to increased iceberg calving in relation to destabilization of the jakobshavn isbrae the long term trend in the data documents the end of a late holocene thermal maximum between 5200 and 4300 cal yr bp and a final onset of the neoglaciation at 3500 cal yr bp increased responses of the iceberg rafting after 3500 cal yr bp reflects a westward seaward advance of the glacier margin in relation to onset of neoglaciation and a development of the glacier into a floating tongue after 2000 cal yr bp a comparison of our record with a record from the eastern north atlantic indicates that a nao like anomaly pattern between subsurface waters in west greenland and atmospheric temperature in the eastern north atlantic may have been operating during most of the late holocene however during the past 1000 years the nao signal may have weakened as some other mode of climate variability overprints the anti phase climate signal in this region

late weichselian glacimarine depositional processes in the southern skagerrak revealed by high resolution seismic facies analysis abstract thirty kilometres of high resolution seismic reflection boomer data were collected in the skagerrak area between norway sweden and denmark to reconstruct the seismic stratigraphy in an area of late weichselian shelf margin progradation by the use of lap out style five depositional units a e were recognised in the boomer profiles no stratigraphic control was available but tentative correlation has been made on the basis of previous studies in the region unit a is interpreted as till in unit b the seismic facies association includes shingled mounded oblique channel fill and parallel bedded reflection configurations which are interpreted to have formed in a channelled proximal pro glacial environment in unit c discrete mounds and semi continuous lensoid bodies with divergent channelled flow style constitute the facies association and are interpreted predominantly as debris flow deposits that accumulated in a distal pro glacial environment in unit d the facies association constitutes mounds and oblique in fill between mounds positive relief and the distribution of facies shows that the deposits were laid down under the influence of a unidirectional current units b d are interpreted as late weichselian in age unit e is interpreted as the holocene marine cover of laminated clay to fine sand this seismic stratigraphic succession reveals a high resolution record of late weichselian deglaciation in this area

seasonal speedup along the western flank of the greenland ice sheet it has been widely hypothesized that a warmer climate in greenland would increase the volume of lubricating surface meltwater reaching the ice bedrock interface accelerating ice flow and increasing mass loss we have assembled a data set that provides a synoptic scale view spanning ice sheet to outlet glacier flow with which to evaluate this hypothesis on the ice sheet these data reveal summer speedups 50 to 100 consistent with but somewhat larger than earlier observations the relative speedup of outlet glaciers however is far smaller 15 furthermore the dominant seasonal influence on jakobshavn isbrae s flow is the calving front s annual advance and retreat with other effects producing outlet glacier speedups an order of magnitude larger seasonal melt s influence on ice flow is likely confined to those regions dominated by ice sheet flow

lithofacies and seismic reflection interpretation of temperate glacimarine sedimentation in tarr inlet glacier bay alaska abstract high resolution seismic reflection profiles of sediment fill within tarr inlet of glacier bay alaska show seismic facies changes with increasing distance from the glacial termini five types of seismic facies are recognized from analysis of huntec and minisparker records and seven lithofacies are determined from detailed sedimentologic study of gravity vibro and box cores and bottom grab samples lithofacies and seismic facies associations and fjordfloor morphology allow us to divide the fjord into three sedimentary environments ice proximal iceberg zone and ice distal the ice proximal environment characterized by a morainal bank depositional system can be subdivided into bank back bank core and bank front subenvironments each of which is characterized by a different depositional subsystem a bank back subsystem shows chaotic seismic facies with a mounded surface which we infer consists mainly of unsorted diamicton and poorly sorted coarse grained sediments a bank core depositional subsystem is a mixture of diamicton rubble gravel sand and mud seismic reflection records of this subsystem are characterized by chaotic seismic facies with abundant hyperbolic diffractions and a hummocky surface a bank front depositional subsystem consists of mainly stratified and massive sand and is characterized by internal hummocky facies on seismic reflection records with significant surface relief and sediment gravity flow channels the depositional system formed in the iceberg zone environment consists of rhythmically laminated mud interbedded with thin beds of weakly stratified diamicton and stratified or massive sand and silt on seismic reflection profiles this depositional system is characterized by discontinuously stratified facies with multiple channels on the surface in the proximal zone and a single channel on the largely flat sediment surface in the distal zone the depositional system formed in the ice distal environment consists of interbedded homogeneous or laminated mud and massive or stratified sand and coarse silt this depositional system shows continuously stratified seismic facies with smooth and flat surfaces on minisparker records and continuously stratified seismic facies which are interlayered with thin weakly stratified facies on huntec records

further evidence that the sound speed algorithm of del grosso is more accurate than that of chen and millero estimates of the bottom depth of the ocean at 11 sites were determined by combining round trip acoustic travel time measurements made by inverted echo sounders on the ocean bottom with sound speed profiles determined from simultaneously measured temperature and salinity profiles these depths were converted into pressures and were compared to independently measured bottom pressures to determine the accuracy of the algorithms used to calculate the sound speed profile the sound speed algorithms tested were those derived by del grosso j acoust soc am 56 1084 1091 1974 and by chen and millero j acoust soc am 62 1129 1135 1977 as well as the corrected version of chen and millero s algorithm recently published by millero and li j acoust soc am 95 2757 2759 1994 the results of this study agree with the results from recent acoustic tomography experiments which indicate that the algorithm of del grosso for the speed of sound in seawater is more accurate than the currently accepted standard algorithm of chen and millero del grosso s algorithm also produces more accurate results than those from the millero and li correction to the chen and millero algorithm

western norwegian fjord sediments age volume stratigraphy and role as temporary depository during glacial cycles abstract the sediments in the western norwegian fjords are described chronologically qualitatively and quantitatively by means of seismic profiling and correlation with dated terrestrial sediments along the fjords five chronostratigraphic units i v are proposed for the fjord sediments using the well established quaternary stratigraphy in the area sediment volumes of the main fjords are calculated using a dense seismic grid combined with map analyses approximately 150 km 3 of sediments are present in the fjords between 59 63 n ninety percent of this material is considered to be deposited during deglaciation of the last weichselian ice sheet less than ten percent of the fjord sediments in this area is older than the last glacial weichselian maximum both glacial and glaciofluvial processes are active in emptying the fjord basins and transporting the sediments to the continental shelf and slope during glaciations

holocene glacimarine sedimentary environments in fiords of disko bugt west greenland abstract acoustic and sedimentary properties of three fiord systems were examined in the region of disko bugt west greenland to understand variability in the processes rates and sources of sediment delivery during the late glacial and holocene kangerluk and kangersooq of western disko are dominated by meltwater inputs of sediment from local ice fields of the island interior modern sediments are delivered primarily via overflow currents rainout occasional bottom currents and small amounts of iceberg rafting where exposure to baffin bay allows penetration of the west greenland current 14 c and acoustic derived accumulation rates for the last 1 2 ka vary from about 1 mm a 1 in distal fiord settings to more than 5 mm a 1 in proximal sites adjacent to actively building deltas these rates are generally larger than has been observed in other greenland and baffin bay fiords the tidewater terminus of inland ice at ikerasak is also meltwater dominated but produces lower than expected sediment accumulation due to low gradients of the outlet ice and resistant substrates these high latitude west greenland fiords are subarctic in character and contrast significantly with colder polar type fiords at similar latitudes in east greenland sediment deposition which was focused in the outer disko fiords during the late glacial and early holocene is due to one of two possible mechanisms standstill of local ice or enhanced rafting of sediment from disko bugt icebergs this study contributes to the debate on the extent of glaciation and holocene spatial variability in fiord processes of west greenland

holocene sedimentation in the skagerrak interpreted from chirp sonar and core data high resolution chirp sonar profiling in the northeastern skagerrak shows acoustically stratified sediments draping a rough surfaced substratum a 32 metre long sediment core retrieved from the survey area encompasses the entire holocene and latest pleistocene the uppermost seismo acoustic units in the chirp profiles represent holocene marine sediments the lowermost unit is interpreted as ice proximal glacial marine sediments rapidly deposited during the last deglaciation the end of ice proximal sedimentation is marked by a strong reflector interpreted to have been formed during latest pleistocene time as a consequence of rapid ice retreat and drastically lowered sedimentation rate the subsequent distal glacial marine sediments were deposited with initially high sedimentation rates caused by an isostatic rebound associated sea level fall based on correlation between the core and the chirp sonar profiles using measured sediment physical properties and ams 14 c dating we propose a revised position for the pleistocene holocene boundary in the seismo acoustic stratigraphy of the investigated area copyright 2005 john wiley sons ltd

submarine glacial landforms and rates of ice stream collapse the rate of deglacial ice sheet retreat across polar continental shelves and possible ice stream collapse and sea level rise has been much debated high resolution imagery of seafloor morphology is available for many polar shelves and fjords the rapidity of ice retreat is inferred from diagnostic assemblages of submarine landforms produced at ice stream sedimentary beds these landforms exposed by ice retreat across high latitude shelves demonstrate that deglaciation occurs in three main ways rapidly by flotation and breakup episodically by still stands and or grounding events punctuating rapid retreat or by slower retreat of grounded ice submarine landform assemblages imply through the presence of grounding zone wedges overprinting mega scale glacial lineations on many polar shelves that ice stream retreat is more often episodic than catastrophic these observations provide a robust test of the ability of numerical models to predict the varied response of ice sheet basins to environmental changes

giant iceberg plow marks at more than 1 km water depth offshore west greenland abstract during a recent 2006 cruise of rv dana high resolution side scan sonar and sub bottom profiling was carried out on selected shelf and slope transects offshore disko bugt central west greenland available commercial seismic data from the margin indicate here irregular seabed morphology with erosional features locally extending down to c 1100 m water depth the newly acquired side scan sonar data reveal the presence of giant iceberg plow marks extending sub parallel to the slope between about 800 and 1085 m water depth the height difference between bottom of the scours and rim crest is up to 40 m the largest plow marks are about 750 m wide to date no observed modern icebergs including those from antarctica have drafts in excess of c 500 m taking into account maximum glacial sea level lowering of c 120 m the paleo iceberg keel depth was at least 950 m due to the presence of the relatively shallow 1000 m and dimensions of the plow marks are concluded to be exceptional and comparable to glacial scouring features reported from the arctic ocean

late quaternary slumps and debris flows on the scotian slope the scotian slope just west of verrill canyon was surveyed using the sea marc i deep towed sidescan sonar system high resolution seismic reflection profiles and 25 piston cores the generally smooth continental slope has a gradient of 2 5 it is crossed by 2 small valleys that are 1 km wide and 100 m deep much of the sea bed shows evidence of surficial sliding that removed 10 20 m of sediment and the slide scars give the sea bed a steplike morphology from the 600 m isobath to 1 800 m there extend 2 zones of disturbed sediment these disturbed zones have the rough surface and transparent acoustic character previously regarded as characteristic of debris flows but sidescan sonar images and cores suggest that they are principally rotational slide deposits with true debris flows at their distal limits streamlined erosional depressions near the downslope edge of the debris flows cut both the flow and sediment farther down slope these may have been produced by a turbidity current associated with the debris flows sorted coarse sand in piston cores provides further evidence of current activity this widespread sediment failure on relatively low slopes was probably the result of a large earthquake that can be dated from cores as occurring between 5000 and 12000 yr b p

new observations on the relative sea level and deglacial history of greenland from innaarsuit disko bugt relative sea level rsl data derived from isolation basins at innaarsuit a site on the south shores of the large marine embayment of disko bugt west greenland record rapid rsl fall from the marine limit ca 108 m at 10 300 9900 cal yr b p to reach the present sea level at 3500 cal yr b p since 2000 cal yr b p rsl rose ca 3 m to the present when compared with data from elsewhere in disko bugt our results suggest that the embayment was deglaciated later and more quickly than previously thought at or slightly before 10 300 cal yr b p the northern part of disko bugt experienced less rebound ca 10 m at 6000 cal yr b p compared with areas to the south submergence during the late holocene supports a model of crustal down warping as a result of renewed ice sheet growth during the neoglacial there is little evidence for west to east differences in crustal rebound across the southern shores of disko bugt

holocene mass transport activity and climate in outer isfjorden spitsbergen marine and subsurface evidence the analyses of high resolution seismic data swath bathymetry data and sediment cores from the basin svensksunddjupet in isfjorden spitsbergen reveal the deposits of repeated slope failures most of the slope failures occurred during three periods at c 9650 cal bp 8350 8200 cal bp and 3000 cal bp suggested factors causing instability of the slopes include earthquake activity resulting from rapid isostatic uplift excess pore pressure caused by relative sea level fall and or the presence of gas as well as climatic changes mass transport deposits at the mouth of an incision at the southern slope of svensksunddjupet are suggested to mainly relate to runoff from the land based glacier vardebreen the increase of the mass transport activity may indicate that vardebreen either formed or increased in size at c 7000 cal bp

ice sheet dynamics and ice streaming along the coastal parts of northern norway abstract in this paper regional and high resolution bathymetric data are used to reconstruct the pattern and dynamics of ice sheet flow in the fjord and shelf areas of northern norway interpretation of the morphology of the sea floor reveals a series of glacigenic features which are mainly related to the most recent glaciation of the area the shelf area of troms county comprises four cross shelf troughs with intermediate shallow banks glacial features within the cross shelf troughs mega scale glacial lineations msgl lateral shear margin moraines grounding zone wedges are interpreted to have been formed under fast flowing ice streams on the shallow bank areas there are far fewer ice flow indicators and here relatively passive ice acted as interstream ridges outside the finnmark coast to the north and east a coast parallel depression djuprenna deflected rapidly flowing ice from the fjords in a generally east to west direction and then farther out through ingoydjupet and into the bear island trough the fjords guided most of the ice flow and functioned as tributaries to the major ice streams on the shelf including the vast bear island trough ice stream at the last glacial maximum the landform distribution and their cross cutting relationships indicate that major switches in ice stream flow direction took place during deglaciation additionally grounding zone wedges are found within the cross shelf troughs and these reveal temporal variability in ice stream dynamics in different troughs during deglaciation the distribution of glacigenic features on the ice stream beds also reveals a downstream evolution that has been reported by other workers whereby small bedrock features progressively merge into more elongate forms and msgl this downstream evolution in subglacial geology subglacial bedforms implies that the force balance e g basal shear stress of the ice streams also evolves in the downstream direction and more crucially that the flow mechanism of the ice stream is spatially variable along its length

basal sliding of ice stream b west antarctica a tethered stake apparatus is used to measure basal sliding in a borehole on ice stream b west antarctica about 300 km upstream east from its grounding line near the head of the ross ice shelf a metal stake emplaced at the top of a layer of unfrozen till underlying the ice is connected by a tether line to a metering unit that measures the tether line as it is pulled out from the borehole by the stake as a result of basal sliding the measured sliding motion includes any actual slip across the ice till interface and may include in addition a possible contribution from shear deformation of till within about 3 cm of the interface this 3 cm figure follows from a qualitative model of the movements of the stake in the course of the experiment based on features of the record of apparent sliding alternative but less likely models would increase the figure from 3 cm to 10 cm or 25 cm in any case it is small compared to the seismically inferred till thickness of 9 m measured apparent sliding averages 69 of the total motion of 1 2 m d 1 over 26 days of observation if a 3 5 day period of slow apparent sliding 8 of the total motion is included in the average the occurrence of the slow period raises the possibility that the sliding motion switches back and forth between c 80 and c 8 of the total motion on a time scale of a few days however it is likely that the period of slow apparent sliding represents instead a period when the stake got caught on the ice sole if the slow period is therefore omitted the indicated average basal sliding rate is 83 of the total motion in either case basal sliding predominates as the cause of the rapid ice stream motion in the last 2 days of observation the average apparent sliding rate reached 1 17 m d 1 essentially 100 of the motion of the ice stream if till deformation contributes significantly to the ice stream motion the contribution is concentrated in a shear zone 3 cm to possibly 25 cm thick at the top of the 9 m thick till layer these observations if applicable to the west antarctic ice sheet in general pose complications in modeling the rapid ice streaming motion

early holocene palaeoceanography and deglacial chronology of disko bugt west greenland two new cores from disko bugt a large marine embayment in west greenland are used to assess the deglacial chronology and palaeoceanography of the area during the early holocene deglaciation of the main part of disko bugt is directly dated for the first time to a minimum of ca 10 2 ka cal bp by this time the jakobshavn isbrae ice stream had retreated to the eastern margins of disko bugt initial deglaciation took place before the relatively warm west greenland current wgc was initiated a strengthening in the wgc is identified from ca 9 2 ka cal bp accompanied by retreat of the ice stream to a shallow bank immediately west of the present day jakobshavn isfjord while in this position the calving and melting ice stream produced large volumes of sediment and meltwater the large volumes of meltwater prevented the relatively warm waters of the wgc reaching the eastern margins of disko bugt the ice stream remained grounded on this bank for over a thousand years until ca 7 9 ka cal bp when reduced sedimentation rates and an increase in boreal fauna point to its retreat inside the present day fjord system

glacimarine sedimentary processes and facies on the polar north atlantic margins abstract major contrasts in the glaciological oceanic and atmospheric parameters affecting the polar north atlantic both over space between its eastern and western margins and through time from full glacial to interglacial conditions have lead to the deposition of a wide variety of sedimentary facies in these ice influenced seas the dynamics of the glaciers and ice sheets on the hinterlands surrounding the polar north atlantic have exterted a major influence on the processes rates and patterns of sedimentation on the continental margins of the norwegian and greenland seas over the late cenozoic the western margin is influenced by the cold east greenland current and the svalbard margin by the northernmost extent of the warm north atlantic drift and the passage of relatively warm cyclonic air masses in the fjords of spitsbergen and the northwestern barents sea glacial meltwater is dominant in delivering sediments in the fjords of east greenland the large numbers of icebergs produced from fast flowing outlets of the greenland ice sheet play a more significant role in sedimentation during full glacials sediments are delivered to the shelf break from fast flowing ice streams which drain huge basins within the parent ice sheet large prograding fans located on the continental slope offshore of these ice streams are made up of stacked debris flows large scale mass failures turbidity currents and gas escape structures also rework debris in continental slope and shelf settings even during interglacials both the margins and the deep ocean basins beyond them retain a glacimarine overprint derived from debris in far travelled icebergs and sea ice under full glacial conditions the glacier influence is correspondingly stronger and this is reflected in the glacial and glacimarine facies deposited at these times

basal ice sequences in antarctic ice stream exposure of past hydrologic conditions and a principal mode of sediment transfer 1 the brightness distribution of sequentially extracted borehole camera imagery shows two distinct sequences of basal ice in kamb ice stream the upper sequence 7 3 m comprises clear ice and layers with dispersed and stratified debris the lower sequence 8 2 m consists of accretion ice with alternating layers of stratified and solid debris the two sequences have volumetric debris contents of about 5 and 20 respectively we infer that the upper sequence formed in a tributary where subglacial meltwater was abundant and that the lower sequence formed on the siple coast plain where basal freezing currently dominates the basal thermal regime the basal ice layer contains the equivalent of 2 1 0 4 m of frozen sediment the high volume of sediment is a result of debris rich layers interpreted to have formed by accretion in the stagnant phase of ice stream on off cycles fast ice streaming punctuated by entrainment of debris during stagnation episodes is consistent with inferred past flow of adjacent ice streams and geologic features in the ross sea our results show that sediment wedges near grounding lines may form by melt out of basal ice debris this is different from previous studies where it was assumed that sediment transfer occurs through sediment deformation within layers of subglacial till cumulative freezing in recurring ice stream cycles shows that entrainment of sediment by basal freeze on is an important erosion mechanism and that high sediment fluxes can occur when ice streams override coulomb plastic substrates

deformation of till beneath ice stream b west antarctica the behaviour and possible instability of the west antarctic ice sheet depend fundamentally on the dynamics of the large ice streams which drain it model calculations show that most ice stream velocity arises at the bed1 2 and radar sounding has shown the bed to be wet3 but the basal boundary condition is not well understood seismic evidence from the upstream b camp upb on the siple coast of west antarctica4 shows that the ice stream there rests on a layer of unconsolidated sediment averaging 5 or 6 m thick in which the water pressure is only 50 kpa less than the overburden pressure because this thin layer occurs well inland beneath an active ice sheet and rests on a surface showing flutes4 characteristic of glacial erosion5 we presume that it is glacial till we propose here that deformation within the till is the primary mechanism by which the ice stream moves and we discuss implications of this hypothesis

glacimarine sedimentary processes and depositional environments in an embayment fed by west greenland ice streams abstract the extent and behaviour of the central west greenland sector of the greenland ice sheet gis during the last glacial maximum lgm and the following deglaciation remains poorly constrained to investigate deglacial marine environments and sedimentary processes in an area fed by several lgm ice streams we now report findings from a 3 5 khz sub bottom profiler survey acquired in and around disko bay in 2009 sediment thicknesses and volumes in three glaciated areas disko bay southern vaigat and egedesminde dyb are fully constrained for the first time acoustic facies types and distributions were also mapped the largest sediment thicknesses 256 m and widest variation in acoustic character was observed in disko bay adjacent to the mouth of jakobshavns isfjord significant sediment thicknesses were also observed in isolated basins in the egedesminde dyb trough and in a trough in southern vaigat strait up to 110 m given low modern sedimentation rates these thick sediment packages are inferred to record the retreat of glaciers from the middle shelf through disko bay and into both the jakobshavns and torssukatak fjord systems in central west greenland our results highlight similarities in deglacial sedimentary processes across the study area when the margins of retreating glaciers supplied large volumes of sediment to the marine environment from sediment laden meltwater plumes and melting icebergs we estimate the sediment flux for the palaeo jakobshavn ice stream while the ice margin was stable at a fjord entrance sill to be 1 6 3 6 10 7 m 3 a 1 assuming a flux at the upper end of our range for the torssukatak fjord system requires the grounded ice margin to be stable for about 450 years during retreat the sediment fluxes we estimate are within the range of previously calculated fluxes for other arctic and antarctic ice streams and suggest that large volumes of meltwater and sediment were available at the base of the outlet glaciers during deglaciation even during periods of quasi stability retreat of the ice margins into the fjord systems is characterised by a rapid transition to ice distal sedimentation by rainout of iceberg rafted detritus ird and hemipelagic material accumulation rates drop to 2 mm a 1 this study demonstrates the variability in glacimarine processes and environments on high latitude continental margins and highlights the importance of local factors such as bedrock morphology as well as glacio dynamic factors on sedimentation

variable north atlantic climate seesaw patterns documented by a late holocene marine record from disko bugt west greenland abstract the reconstruction of past sea surface conditions in the labrador sea is essential for understanding climate fluctuations in the north atlantic region we here study late holocene sea surface conditions off west greenland in order to elucidate the possible relationship between a north atlantic seesaw and centennial to millennial scale climate fluctuations in the labrador sea region for that purpose we have studied the particulate organic matter especially dinoflagellate cysts and acritarchs from two marine sediment cores from disko bugt central west greenland our data show significant variations in sea surface temperature and sea ice cover during the last ca 3200 years after a cooling at ca 2 9 ka cal bp presumably related to the neoglacial cooling seen in large parts of the northern hemisphere the area was subjected to significant variability both in the entrainment of atlantic water west greenland current water and in atmospheric temperatures from 2 0 1 5 ka cal bp corresponding to the later part of the roman warm period the area experienced a return to a stronger influx of atlantic water and an increased fresh water influx from land probably related to increased precipitation or to melt water outflow from the nearby inland ice the dark ages 1 5 1 3 ka cal bp were characterised by an only minor cooling of the surface waters however as seen in other records from the labrador sea region the beginning of the medieval warm period 1 3 0 9 ka cal bp signified a severe cooling presumably due to a significant reduction in atlantic water entrainment the cold conditions continued through the little ice age after 0 9 ka cal bp although the area seems to have experienced a minor decrease in sea ice cover until 0 5 ka cal b p after which sea ice cover may again have increased the period of modern warming is not represented in our data our study shows that a north atlantic oscillation type pattern played a significant role in the late holocene centennial to millennial scale climate fluctuations in the labrador sea region however this cannot explain the full complexity of the climate signal the fact that a simple pattern of cold versus warm climate scenario does not exist demonstrates that it will hardly be feasible to select the correct baseline data set when modelling future climate development

reply to comment by f boano et al on pore water flow due to near bed turbulence and associated solute transfer in a stream or lake sediment bed

isolation basin stratigraphy and holocene relative sea level change on arveprinsen ejland disko bugt west greenland this paper presents the results of an investigation into holocene relative sea level rsl change isostatic rebound and ice sheet dynamics in disko bugt west greenland data collected from nine isolation basins on arveprinsen ejland east disko bugt show that mean sea level fell continuously from ca 70 m at 9 9 ka cal yr bp 8 9 ka 14c yr bp to reach a minimum of ca 5 m at 2 8 ka cal yr bp 2 5 ka 14c yr bp before rising to the present day a west east gradient in isostatic uplift across disko bugt is confirmed with reduced rebound observed in east disko bugt however rsl differences up to 20 m at 7 8 ka to 6 8 ka cal yr bp 7 ka to 6 ka 14c yr bp also exist within east disko bugt suggesting a significant north south component to the area s isostatic history the observed magnitude and timing of late holocene rsl rise is not compatible with regional forebulge collapse instead rsl rise began first in the eastern part of the bay as might be expected under a scenario of crustal subsidence caused by neoglacial ice sheet readvance the results of this study demonstrate the potential of isolation basin data for local and regional rsl studies in greenland and the importance of avoiding data compilations from areas where the isobase orientation is uncertain copyright 1999 john wiley sons ltd

discovery of till deposition at the grounding line of whillans ice stream we report on the discovery of a grounding line sedimentary wedge till delta deposited by whillans ice stream west antarctica our observation is that grounding line deposition serves to thicken the ice and stabilize the position of the grounding line the ice thickness at the grounding line is greater than that of floating ice in hydrostatic equilibrium thus the grounding line will tend to remain in the same location despite changes in sea level until sea level rises enough to overcome the excess thickness that is due to the wedge further our observation demonstrates the occurrence of rapid subglacial erosion sediment transport by distributed subglacial till deformation and grounding line sedimentation which have important implications for ice dynamics numerical modeling of ice flow and interpretation of the sedimentation record

laminated sediments in glacimarine environments diagnostic criteria for their interpretation abstract fine grained laminated deposits are often reported from contemporary and ancient glacimarine sedimentary sequences laminated glacimarine sediments form by a variety of processes including suspension settling from turbid overflow plumes turbidity current deposition and contour current activity subglacial deformation of pre existing sediments may also produce laminated deposits in the form of glacitectonite and deformation till the development of diagnostic criteria for genetic discrimination of laminated glacimarine sediments is important both for their correct interpretation in sedimentary sequences and also for the accurate reconstruction of former glacier extent and geometry as laminated sediments may form in subglacial ice proximal and ice distal environments this paper reviews the processes by which laminated glacimarine sediments form and their resulting sedimentology the aim is to provide a synthesis of diagnostic sedimentological criteria for laminated glacimarine deposits that will assist in the interpretation of such sediments in the geological record laminated sediments are genetically differentiated on the basis of sedimentary structures bedding contacts stratigraphic relationships and macrofaunal content bioturbation these attributes also facilitate discrimination between glacimarine and glacilacustrine rhythmites the paper concludes by discussing the glaciological significance of laminated glacimarine sediments in terms of glacier hydrology reconstructions of former ice dynamics and basal thermal regime