a conceptual model for glaciogenic reservoirs from landsystems to reservoir architecture abstract glaciogenic sediments are present in many hydrocarbon producing basins across the globe but their complex nature makes it difficult to characterise the reservoir quality sedimentary units despite this ordovician glacial deposits in north africa and carboniferous permian glaciogenic sequences in the middle east have been proven to host significant economical hydrocarbon accumulations additionally discoveries have been made in the shallow

intensification of northern hemisphere glaciations in the circum atlantic region 3 5 2 4 ma ice rafted detritus evidence abstract records of ice rafted detritus ird from ocean drilling program sites 644 and 907 in the nordic seas and deep sea drilling program sites 610 and 607 in the north atlantic ocean are used to determine the growth and history of northern hemisphere glaciations spanning the interval from 3 6 to 2 4 ma the records document that the initiation of large scale glaciation in the circum atlantic region occurred stepwise between 3 5 and 2 4 ma with greenland leading the other areas the first major pulse of ird occurs at 3 3 ma suggesting a distinct expansion of the greenland ice sheet progressive increases in ird occur from 3 0 ma with a synchronous ice sheet development between the greenland scandinavian and north american regions starting around 2 72 2 75 ma the regional records of ird correspond to major trends in the oxygen isotope record suggesting a tight connection between the record of global ice volume and evidence for expanding glaciers in the northern hemisphere it appears as if widespread ird distribution occurs when the global ice volume surpasses certain thresholds similar to the late quaternary situation

modelling greenland ice sheet inception and sustainability during the late pliocene understanding the evolution and dynamics of ice sheet growth during past warm periods is a very important topic considering the potential total removal of the greenland ice sheet in this regard one key event is the full glaciation of greenland that occurred at the end of the pliocene warm period which remains partially unexplained previous modelling studies succeeded in reproducing this full glaciation either by imposing an unrealistically low co2 value or by imposing a partial ice sheet over the surface of greenland although they highlight some fundamental mechanisms none of these studies are fully satisfactory because they do not reflect realistic conditions occurring during the late pliocene through a series of simulations with the ipsl cm5a coupled climate model used to force the grisli ice sheet model we show that a drop in co2 levels does not lead to an abrupt inception of the greenland ice sheet high ablation rates in central and northern greenland combined with low accumulation prevent such an abrupt inception ice sheet inception occurs when low summer insolation and co2 levels below modern values are combined the greenland ice sheet being restricted to the southeast region where high topography favours this build up this ice sheet experiences only partial melting during summer insolation maxima combined with high co2 levels further growth of the ice sheet with recoupling experiments is important at 360 and 280 ppm during insolation minima thus the full glaciation at 2 6 ma could be the result of a cumulative build up of the greenland ice sheet over several orbital cycles leading to progressively more intense glaciations during low summer insolation periods although this result could be a shortcoming of the modelling framework itself the gradual glacial inception interpreted from the oxygen isotope record could support our scenario

subduction megathrust heterogeneity characterized from 3d seismic data megathrust roughness and structural complexity are thought to be controls on earthquake slip at subduction zones because they result in heterogeneity in shear strength and resolved stress however because active megathrust faults are difficult to observe the causes and scales of complexity are largely unknown here we measured the in situ properties of the megathrust of the middle america subduction zone in a three dimensional seismic reflection volume to determine how fault properties vary we quantify spatial variability in the megathrust roughness overburden and rock physical properties heterogeneity in the megathrust roughness exists at length scales of a few kilometres because the megathrust is dissected by active lower plate normal faults which offset the megathrust and renewed fault roughness spatial variations in the rock physical properties at the plate interface are characterized by correlation length scales of hundreds of metres frontal prism taper historical seismicity and the variation in earthquake stress drop values local to the megathrust are all affected by the heterogeneity at these length scales both geometric and rheological complexities may therefore control the mechanical behaviour of the subduction plate interface which includes earthquake rupture characteristics geometric and rheological complexities may control the mechanical behaviour of megathrusts according to an analysis of the heterogeneity in roughness and rock properties of the middle america megathrust from 3d seismic reflection data

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

late pleistocene holocene retreat of the west antarctic ice sheet system in the ross sea part 1 geophysical results in the 1994 1995 and 1998 austral field seasons geophysical research efforts in the ross sea focused on acquiring a high resolution database designed to permit 1 reconstruction of the maximum extent and configuration of the ice sheet during the last glacial maximum i e oxygen isotope stage 2 2 reconstruction of conditions at the base of the ice sheet and 3 assessment of the relative retreat history of the ice sheet following the last glacial maximum five seismic facies are distinguished on the basis of external geometry relationships among features bounding surface amplitude intensity of internal acoustic signature and geometry of internal reflectors seismic facies 1 is a transparent draping unit correlated to diatomaceous mud interpreted as being deposited under open marine conditions seismic facies 2 and 3 are comprised of units displaying subdued massive internal signatures with smooth lower bounding surfaces and hummocky upper surfaces characterized by glacial lineations these units are interpreted to be grounding zone proximal deposits overridden by the expanded ice sheet seismic facies 2 may be a deforming till unit seismic facies 4a is characterized by an internally massive to chaotic signature an erosional often flat lower surface and a hummocky upper surface displaying glacial lineations this unit is interpreted to be till and is divided into deposits associated with the most recent glacial expansion 4a and with an earlier pre last glacial maximum expansion 4b seismic facies 5 is an acoustically laminated ponded and draping deposit interpreted to contain proglacial and sub ice shelf materials deposited continuously since the last interglacial period the associations of these units provide context for the interpretation of the ice edge maximum position conditions at the base of the ice sheet and the relative retreat history of the region there is compelling evidence for a much expanded ice sheet in the ross sea during the last glacial maximum in the western ross sea the maximum grounding position is marked by an isolated grounding zone wedge and placed in the vicinity of coulman island approximately 150 km from the continental shelf edge in the central ross sea the maximum grounding position is close to the continental shelf break based primarily on the presence of an extensive 60 m thick sheet like deposit with a fluted upper surface streaming ice may have occupied bathymetric lows on the continental shelf as suggested by 1 the configuration of bathymetry 2 the presence of glacially eroded troughs 3 the concentration of sediment interpreted to be deforming till within the middle to outer shelf reaches of the troughs and 4 the fluted nature of the upper surface absolute rates of streaming ice flow relative to inter ice stream areas are not implied the western ross sea continental shelf deposits record the retreat history of ice derived predominantly from the east antarctic ice sheet and glaciers of the transantarctic mountains ice flow on the continental shelf is interpreted to have remained fixed in position restricted by the walls of the troughs on the inner shelf of the western ross sea the ice flowed over and eroded lithified sedimentary strata slower moving ice occupied flat topped banks a single grounding zone wedge occurs on the western ross sea central shelf no substantial deposits are observed on the inner continental shelf this lack of grounding zone features reflects a restricted sediment supply and a relatively steady rapid retreat of the ice sheet during retreat ice flow acted independently in each major trough and on the bank tops ice retreated from victoria land basin drygalski trough before it retreated from joides basin ice remained on the bank tops shedding material into the abandoned troughs grounded ice in the central ross sea was derived predominantly from an expanded west antarctic ice sheet the ice sheet remained grounded on the continental shelf edge after retreat of ice from the western ross sea expanded ice eroded the inner shelf and deposited sheets of till on the central and outer shelf ice stream drainage shifted laterally as recorded by rounded laterally accreting ridges that separate bathymetric troughs the central ross sea is the repository for larger volumes of sediment derived from ice flow across basins of relatively thick unlithified sedimentary deposits two till sheets mark grounding zone positions in the central ross sea reflecting the higher sediment supply and a stepped deglaciation ice remained grounded on the pennell bank to the west a series of moraines marks the retreat of ice across the bank mega scale glacial lineations and other streamlined subglacial geomorphic features occur across the continental shelf primarily within the troughs the lineations substantiate the maximum reconstruction and support the interpretation of a deforming substrate beneath the outer reaches of the expanded ice sheet this deforming substrate may have contributed to the onset of deglaciation features associated with meltwater are rare or absent suggesting that basal meltwater played a minor role in retreat of the ice sheet

the crary fan a trough mouth fan on the weddell sea continental margin antarctica abstract multichannel seismic investigations show the presence of a large trough mouth fan deposit on the continental margin in the southern weddell sea a characteristic feature of the fan is relatively few but large canyons and or channels which appear to have been stable for long periods levees associated with the channels may reach thicknesses of more than 1 km drilling during odp leg 113 recorded the presence of glaciers in east antarctica since early oligocene time and the seismic stratigraphic evidence suggests that the submarine fan is largely composed of glacigenic sediments the channel levee systems and complexes indicate several growth phases apparently controlled by glacial interglacial climate fluctuations with maximum fan growth during glacial periods the present interglacial period is characterized by strong and erosive flow of ice shelf water running down the western slope of the fan and carrying only minor amounts of suspended matter the fan is essentially sediment starved during interglacial periods the dimensions of the channel levee complexes and the persistent loci of sediment supply suggest that turbidite sedimentation resulted from melting of wet based glaciers at or near the shelf edge which has consequently prograded 70 80 km seaward

binge purge oscillations of the laurentide ice sheet as a cause of the north atlantic s heinrich events ice rafted debris in sediment cores from the north atlantic suggests that the laurentide ice sheet lis periodically disgorged icebergs in brief but violent episodes which occurred approximately every 7 000 years here i propose that heinrich events i e what these episodes are called were caused by free oscillations in the flow of the laurentide ice sheet which arose because the floor of hudson bay and hudson strait is covered with soft unconsolidated sediment that forms a slippery lubricant when thawed the proposed heinrich event cycle has two phases the growth phase occurs when the sediment is frozen and the lis is stranded immobile on a rigid bed the volume of the lis slowly grows during this phase at a rate dictated by snow accumulation the purge phase occurs when the basal sediment thaws and a basally lubricated discharge pathway i e an ice stream such as those which occur in west antarctica today developes through hudson strait the volume of the lis rapidly equilibrates to the reduced basal friction during this phase by dumping icebergs into the labrador sea the periodicity t k sl2g 2 7000 years of the proposed heinrich event cycle is a function of the thermal conductivity and diffusivity of ice k and respectively the atmospheric sea level temperature sl in degrees celsius and the excess geothermal heat flux defined by g g k where is the atmospheric lapse rate and g is the geothermal heat flux agreement between the predicted t and the apparent periodicity implied by the marine record is the main virtue of the free oscillation mechanism i propose an alternative mechanism in which heinrich events are forced by periodic variations in external climate is implausible because periodic atmospheric temperature perturbations are strongly attenuated with depth in an ice sheet

canyons and late quaternary sedimentation on the north norwegian margin the presence of erosive canyons on high latitude passive margins is unusual such margins are more normally dominated by subsidence and glacially influenced deposition however ten canyons are identified at the edge of the narrow shelf on the north norwegian margin off the lofoten islands between the traenadjupet and andoya slides on the basis of gloria long range side scan sonar and contemporaneous 3 5 khz profiler data combined with a detailed bathymetry the canyons are located down stream of sediments transported through the lofoten drift and the margin is characterized by an absence of cross shelf troughs canyons are up to 420 m deep u shaped display steep gradients in their upper parts and sediments derived from them have short runout distances onto the continental rise the canyons are estimated to be 20 30 ma old being incised into only thinly covered lithified pre miocene sediments as a response to cenozoic uplift late quaternary sedimentation processes associated with the canyons are inferred to occur during both glacials and interglacials glacial sedimentation is probably in the form of direct subglacial debris input in addition to turbid subglacial meltwater plumes interglacial sedimentation processes are probably dominated by the along shelf transport of sediments by strong ocean currents canyon heads capture sediment from the shelf the remobilization of this coarse material and erosion of the canyons occurs through debris flows and turbidity currents canyon preservation and continued development can be attributed directly to the comparatively low sedimentation rates during full glacial conditions as ice streams located to the north and south produce regional depocentres away from this area of relatively slow flowing ice

intensification of the atlantic deep circulation by the canadian archipelago throughflow abstract low salinity water export through the canadian archipelago is one of the main components of the freshwater budget in the arctic ocean nevertheless the canadian archipelago is closed in most global ocean models how it is that deep water formation at high latitudes of the northern hemisphere depends on the opening and closing of the canadian archipelago is investigated an ice ocean coupled model whose horizontal resolution is 1 is used without restoring surface salinity to observed data when the canadian archipelago is open the atlantic deep circulation strengthens by 21 this enhancement is caused by intensification of deep water formation in the northern north atlantic ocean surface salinity in these regions is affected by the east greenland current which flows from the fram strait and increases its salinity when the canadian archipelago is opened the low salinity flow through the canadian archipelago affects surface salinity only in the western part of the labrador sea a cyclonic c

assessing orbitally forced interglacial climate variability during the mid pliocene warm period abstract the traditional view of the pliocene is one of an epoch with higher than present global mean annual temperatures 2 to 3 c and stable climate conditions published data model comparisons for the mid pliocene warm period mpwp 3 3 to 3 million years ago have identified specific regions of concordance and discord between climate model outputs and marine terrestrial proxy data due to the time averaged nature of global palaeoenvironmental syntheses it has been hypothesised that climate variability during interglacial events within the mpwp could contribute to site specific data model disagreement the hadley centre coupled climate model version 3 hadcm3 is used to assess the nature of climate variability around two interglacial events within the mpwp that have different characteristics of orbital forcing marine isotope stages km5c and k1 model results indicate that 20 kyr on either side of the mis km5c orbital forcing produced a less than 1 c change in global mean annual temperatures regionally mean annual surface air temperature sat variability can reach 2 to 3 c seasonal variations exceed those predicted for the annual mean and can locally exceed 5 c simulations 20 kyr on either side of mis k1 show considerably increased variability in relation to km5c we demonstrate that orbitally forced changes in surface air temperature during interglacial events within the mpwp can be substantial and could therefore contribute to data model discord this is especially likely if proxies preserve growing season rather than mean annual temperatures model results indicate that peak mis km5c and k1 interglacial temperatures were not globally synchronous highlighting leads and lags in temperature in different regions this highlights the potential pitfalls in aligning peaks in proxy derived temperatures across geographically diverse data sites and indicates that a single climate model simulation for an interglacial event is inadequate to capture peak temperature change in all regions we conclude that the premise of sustained global warmth and stable pliocene climate conditions is incomplete we also contend that the likely nature of pliocene interglacial climate variability is more akin to interglacial events within the quaternary where the character of interglacials is known to be diverse in the future the utility of pliocene data model comparisons is dependent upon 1 establishing precise chronology of the proxy data 2 providing climate models with fully proxy consistent boundary conditions and 3 in utilising ensembles of climate simulations that can adequately capture orbital variability around any studied interval

the norwegian greenland sea continental margins morphology and late quaternary sedimentary processes and environment the continental margins surrounding the norwegian greenland sea are to a large degree shaped by processes during the late quaternary the paper gives an overview of the morphology and the processes responsible for the formation of three main groups of morphological features slides trough mouth fans and channels several large late quaternary slides have been identified on the eastern norwegian greenland sea continental margin the origin of the slides may be due to high sedimentation rates leading to a build up of excess pore water pressure perhaps with additional pressure caused by gas bubbles triggering might have been prompted by earthquakes or by decomposition of gas hydrates trough mouth fans tmf are fans at the mouths of transverse troughs on presently or formerly glaciated continental shelves in the norwegian greenland sea seven tmfs have been identified varying in area from 2700 km2 to 215 000 km2 the trough mouth fans are depocentres of sediments which have accumulated in front of ice streams draining the large northwest european ice sheets the sediments deposited at the shelf break upper slope by the ice stream were remobilized and transported downslope mostly as debris flows the trough mouth fans hold the potential for giving information about the various ice streams feeding them with regard to velocity and ice discharge two large deep sea channel systems have been observed along the norwegian continental margin the lofoten basin channel and the inbis channel along the east greenland margin several channel systems have been identified the deep sea channels may have been formed by dense water originating from cooling sea ice formation and brine rejection close to the glacier margin or they may originate from small slides on the upper slope transforming into debris flows and turbidity currents

the nature and origin of furrows in lake bed sediments okanagan lake british columbia canada recent sonar surveys of okanagan lake in the central interior of british columbia revealed the presence of linear contour parallel furrows at depths of 50 130 m underwater video imagery shows t

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

geomorphic and shallow acoustic investigation of an antarctic peninsula fjord system using high resolution rov and shipboard geophysical observations ice dynamics and behaviour since the last glacial maximum detailed bathymetric and sub bottom acoustic observations in bourgeois fjord marguerite bay antarctic peninsula provide evidence on sedimentary processes and glacier dynamics during the last glacial cycle submarine landforms observed in the 50 km long fjord from the margins of modern tidewater glaciers to the now ice distal marguerite bay are described and interpreted the landforms are grouped into four morpho sedimentary systems i glacial advance and full glacial ii subglacial and ice marginal meltwater iii glacial retreat and neoglaciation and iv holocene mass wasting these morpho sedimentary systems have been integrated with morphological studies of the marguerite bay continental shelf and analysed in terms of the specific sedimentary processes and or stages of the glacial cycle they demonstrate the action of an ice sheet outlet glacier that produced drumlins and crag and tail features in the main and outer fjord meltwater processes eroded bedrock channels and ponds infilled by fine grained sediments following the last deglaciation of the fjord at about 9000 yr bp subsequent holocene neoglacial activity involved minor readvances of a tidewater glacier terminus in blind bay recent stillstands and or minor readvances are inferred from the presence of a major transverse moraine that indicates grounded ice stabilization probably during the little ice age and a series of smaller landforms that reveal intermittent minor readvances mass wasting processes also affected the walls of the fjord and produced scars and fan shaped deposits during the holocene glacier terminus changes during the last six decades derived from satellite images and aerial photographs reveal variable behaviour of adjacent tidewater glaciers the smaller glaciers show the most marked recent retreat influenced by regional physiography and catchment area size

late weichselian submarine debris flow deposits on the bear island trough mouth fan sedimentary processes on the bear island trough mouth fan during the last glacial were studied using high resolution reflection seismics and gravity cores the fan succession is dominated by large debris flow deposits of up to 24 km in width and 50 m thick debris lobes can be followed over 100 km downslope and the largest cover an area of 1880 km2 the large debris flows were generated when the barents sea ice sheet reached the shelf break glacigenic sediments transported to the grounding line were temporarily stored on the upper slope due to the high sedimentation rate the sediments were unstable and earthquakes oversteepening and or build up of excess pore pressure triggered sediment release generating large debris flows sediments were also eroded and incorporated during the downslope flow debris flows were the most important sediment distributing process due to the relatively high shear strength low flow mobility of the glacigenic diamicton and the low fan gradient the weichselian evolution of the fan was characterized by a relatively low sedimentation rate during the early and mid weichselian the barents sea ice sheet might have reached the shelf break twice during the late weichselian on average one large debris flow comprising 18 km3 of sediments was released between every 35 to 75 years during the last glacial maximum

glacial geomorphology of the central arctic ocean the chukchi borderland and the lomonosov ridge the last decade of geophysical seafloor mapping in the arctic ocean from nuclear submarines and icebreakers reveals a wide variety of glaciogenic geomorphic features at water depths reaching 1000 in these findings provide new and intriguing insights into the quaternary glacial history of the northern hemisphere here we integrate multi and single beam bathymetric data chirp sonar profiles and sidescan images from the chukchi borderland and lomonosov ridge to perform a comparative morphological seafloor study this investigation aims to elucidate the nature and provenance of ice masses that impacted the arctic ocean sea floor during the quaternary mapped glaciogenic bedforms include iceberg keel scours most abundant at water depths shallower than similar to 350 400 m flutes and megascale glacial lineations extending as deep as similar to 1000 m below the present sea level small drumlin like features and morainic ridges and grounding zone wedges the combination of these features indicates that very large glacial ice masses extended into the central arctic ocean from surrounding north american and eurasian ice sheets several times during the quaternary ice shelves occupied large parts of the arctic ocean during glacial maxima and ice rises were formed over the chukchi borderland and portions of the lomonosov ridge more geophysical and sediment core data combined with modeling experiments are needed to reconstruct the timing and patterns of these events

modelling pliocene warmth contribution of atmosphere oceans and cryosphere the relative role of the atmosphere oceans and cryosphere in contributing towards middle pliocene warmth ca 3 ma bp is investigated using the hadcm3 coupled ocean atmosphere general circulation model the model was initialised with boundary conditions from the usgs prism2 data set and a pliocene atmospheric co2 level of 400 ppmv and run for 300 simulated years the simulation resulted in a global surface temperature warming of 3degreesc compared to present day in contrast to earlier modelling experiments for the pliocene surface temperatures warmed in most areas including the tropics 1 5degreesc compared with present day the model predicts a general pattern of ocean warming 1 5degreesc in both hemispheres to a depth of 2000 m below which no significant differences are noted sea ice coverage is massively reduced up to 90 the flow of the gulf stream north atlantic drift is up to 100 mm s 1 greater in the pliocene case analysis of the model predicted meridional streamfunction suggests a global pattern of reduced outflow of antarctic bottom water aabw up to 5 sv a shallower depth for north atlantic deep water formation and weaker thermohaline circulation 3 sv the decrease in aabw occurs mainly in the pacific rather than atlantic ocean model diagnostics for heat transports indicate that neither the oceans nor the atmosphere are transporting significantly more heat in the pliocene scenario rather these results indicate that the major contributing mechanism to global pliocene warmth was the reduced extent of high latitude terrestrial ice sheets 50 reduction on greenland 33 reduction on antarctica and sea ice cover resulting in a strong ice albedo feedback these results highlight the need for further studies designed to improve our knowledge regarding pliocene terrestrial ice configurations

late twentieth century simulation of arctic sea ice and ocean properties in the ccsm4 abstractto establish how well the new community climate system model version 4 ccsm4 simulates the properties of the arctic sea ice and ocean results from six ccsm4 twentieth century ensemble simulations are compared here with the available data it is found that the ccsm4 simulations capture most of the important climatological features of the arctic sea ice and ocean state well among them the sea ice thickness distribution fraction of multiyear sea ice and sea ice edge the strongest bias exists in the simulated spring to fall sea ice motion field the location of the beaufort gyre and the temperature of the deep arctic ocean below 250 m which are caused by deficiencies in the simulation of the arctic sea level pressure field and the lack of deep water formation on the arctic shelves the observed decrease in the sea ice extent and the multiyear ice cover is well captured by the ccsm4 it is important to note however that the temporal evolution of the simulated arctic sea ice cover over the

large scale sedimentation on the glacier influenced polar north atlantic margins long range side scan sonar evidence long range side scan sonar gloria imagery of over 600 000 km of the polar north atlantic provides a large scale view of sedimentation patterns on this glacier influenced continental margin high latitude margins are influenced strongly by glacial history and ice dynamics and linked to this the rate of sediment supply extensive glacial fans up to 350 000 km were built up from stacked series of large debris flows transferring sediment down the continental slope the fans were linked with high debris inputs from quaternary glaciers at the mouths of cross shelf troughs and deep fjords where ice was slower moving but still extended to the shelf break large scale slide deposits are observed where ice failed to cross the continental shelf during full glacials the continental slope was sediment starved and submarine channels and smaller slides developed a simple model for large scale sedimentation on the glaciated continental margins of the polar north atlantic is presented

the glacier influenced scoresby sund fan east greenland continental margin evidence from gloria and 3 5 khz records a major submarine fan gradient about 2 offshore of the scoresby sund fjord system is indicated by the crescentic shape of the shelf break gloria long range side scan sonar imagery was obtained over about 20 000 km2 of the fan along with 1000 km of 3 5 khz records three acoustic facies were defined from gloria backscatter signatures and sea floor morphology and sediment acoustic character on 3 5 khz records facies 1 includes a series of acoustically transparent features 0 5 2 km in width elongate downslope with irregular surface topography which are interpreted as debris flows this makes up the bulk of relatively recent sedimentation on the upper fan diamictic sediments in a core support a debris flow origin facies 2 is featureless on gloria images 3 5 khz profiles reveal irregular former sea floor morphology above which is a draping unit 15 m thick this northern region of the fan is a less active area where hemipelagic sediments and limited ice rafted debris overlie older material formed by past debris flow activity the more distal area of the adjacent ocean basin has a flat floor with parallel sub bottom reflectors of facies 3 this facies is probably an area of low energy hemipelagic sedimentation punctuated by occasional ice rafting and turbidity current activity the debris flows interpreted from gloria and 3 5 khz data are basic building blocks in the long term development of the scoresby sund fan glacier influenced fan volume is about 15 000 5000 km3 based on seismic reflection studies during full glacials in east greenland the inland ice sheet advances to fill the scoresby sund fjord system and extends across the shelf to reach the shelf break in some glacial cycles debris flows form in areas of most rapid sediment flux the scoresby sund fan is relatively similar to the storfjorden fan on the eastern polar north atlantic margin but differs from the larger bear island fan in having a steeper fan gradient much smaller debris flows and no large scale slides

the amplification of arctic terrestrial surface temperatures by reduced sea ice extent during the pliocene abstract many past warm periods exhibited greatly reduced latitudinal temperature gradients as a result of amplified arctic surface temperatures as well as more seasonably equable temperatures the pliocene is a period of particular interest because co2 forcing was comparable to today and yet arctic temperatures were significantly warmer than today here we describe an atmospheric general circulation model experiment assessing the response of terrestrial temperatures in the mid pliocene 3 02 to 3 26 ma to an ice free arctic and we compare the simulation with a compilation of proxy based pliocene paleotemperature reconstructions our experiments indicate that the amplification of arctic surface temperatures is much more sensitive to the extent of sea ice than continental ice the removal of arctic sea ice results in simulated mean annual surface temperatures that better match terrestrial proxy data rmse 2 9 c than experimental conditions that included seasonal sea ice rmse 4 5 c our simulations also show a decrease in the seasonal amplitude of temperatures in the absence of sea ice which is consistent with theory predicting more equable climates in the arctic during warmer intervals in earth s history our results demonstrate that once sea ice is removed latent heat is lost from the ocean to the atmosphere as water vapor that can be circulated by the atmosphere which results in warming of continental interiors although our sensitivity experiment does not help to identify the full array of feedback mechanisms responsible for the amplification of arctic surface temperatures during the pliocene it does demonstrate that arctic terrestrial surface temperatures are extremely sensitive to the spatial and seasonal extent of sea ice

amplified north atlantic warming in the late pliocene by changes in arctic gateways under previous reconstructions of late pliocene boundary conditions climate models have failed to reproduce the warm sea surface temperatures reconstructed in the north atlantic using a reconstruction of mid piacenzian paleogeography that has the bering strait and canadian arctic archipelago straits closed however improves the simulation of the proxy indicated warm sea surface temperatures in the north atlantic in the community climate system model we find that the closure of these small arctic gateways strengthens the atlantic meridional overturning circulation by inhibiting freshwater transport from the pacific to the arctic ocean and from the arctic ocean to the labrador sea leading to warmer sea surface temperatures in the north atlantic this indicates that the state of the arctic gateways may influence the sensitivity of the north atlantic climate in complex ways and better understanding of the state of these arctic gateways for past time periods are needed

large scale ice moulding a discussion of genesis and glaciological significance abstract landsat images reveal a previously unsuspected large scale pattern of streamlining within drift which comprises a number of components drumlins and megaflutes form part of the pattern but in addition there are two previously undocumented ice moulded landform elements streamlined lineations of much greater proportions referred to as mega scale glacial lineations and a distinctive cross cutting topology within the grain consideration of the genesis and glaciological significance of such landforms leads to a number of conclusions it is suggested that mega scale glacial lineations were formed under conditions of fast ice flow and their presence may thus record former locations of ice streams or surge events many lineations of varying scales display a pattern that reveals that they were not formed in sub marginal positions extensive sets of lineations must have been formed approximately synchronously thus indicating that lineation generation occurs over a wide range of glaciodynamic conditions from sub marginal positions to interior portions of ice sheets subglacial deformation of tills has been widely invoked to account for rapid glacier motion criteria for identifying such tills are restricted to structures viewed in cross section and it is thus hard to assess how widespread the processes of deformation may have been lineations provide a surface marker of structure that records subsequent deformation from other ice flow events it is argued that the palaeo flow record including cross cutting patterns provides the surface or plan expression of subglacial deformation the degree of modification to pre existing lineations should permit the identification of zones favoured by deformation and thus assist in an assessment of how pervasive deforming bed processes were in influencing ice sheet dynamics

evolution of subglacial bedforms along a paleo ice stream antarctic peninsula continental shelf geophysical data from the antarctic peninsula continental shelf reveal streamlined subglacial bedforms in a cross shelf trough bedforms exhibit progressive elongation with distance along the trough and record flow of a paleo ice stream from the antarctic peninsula ice sheet during the last glacial maximum downflow evolution of the bedforms indicates increasing flow velocities as the ice stream traversed the shelf this in turn is related to a transition from crystalline bedrock on the inner shelf to a soft sedimentary substrate on the outer shelf although streaming flow operated across both substrates the highest flow velocities occurred over the soft bed spatial variation in the inferred nature of fast flow from sliding to subglacial sediment deformation and or ploughing was also lithologically controlled these data highlight the control of subglacial geology on ice stream dynamics in the geological record and demonstrate a direct relationship between the formation of streamlined subglacial bedforms and paleo ice streams

basal mechanics of ice stream b west antarctica 2 undrained plastic bed model based on the results of our studies of the physical conditions beneath ice stream b we formulate a new analytical ice stream model the undrained plastic bed model henceforth the upb model mathematically the upb model is represented by a non linear system of four coupled equations which express the relationships among ice sliding velocity till strength water storage in till and basal melt rate we examine this system of equations for conditions of ice stream stability over short timescales that permit holding ice stream geometry constant less than hundreds of years temporal variability is introduced into the upb model only by the direct dependence of till void ratio changes e t on the basal melting rate m r since till strength b e and ice stream velocity u b b change as long as till void ratio varies the first condition for ice stream stability is that of constant till water storage 0 the second condition for ice stream stability arises from the feedback between ice stream velocity till strength and the basal melting rate which depends on shear heating m r u b b this is the weak till condition which requires that in a steady state till strength is a small fraction of the gravitational driving stress b n 1 1 d the salient feature of the upb model is its ability to produce two thermo mechanically controlled equilibrium states one with a strong bed and slow ice velocities ice sheet mode and one with a weak bed and fast ice velocities ice stream mode this bimodality of basal conditions is consistent with the available observations of subglacial conditions beneath slow and fast moving ice in west antarctica basal conditions that do not correspond to these two steady states may occur transiently during switches between the two stable modes the upb model demonstrates that ice streams may be prone to thermally triggered instabilities during which small perturbations in the basal thermal energy balance grow leading to generation or elimination of the basal conditions which cause ice streaming

continuous hidden markov models application to automatic earthquake detection and classification at las canadas caldera tenerife abstract a possible interaction of volcano tectonic earthquakes with the continuous seismic noise recorded in the volcanic island of tenerife was recently suggested also recently the zone close to las canadas caldera shows unusual high number of near

the non analogue nature of pliocene temperature gradients abstract the strong warming of the north atlantic and high latitudes in the pliocene 5 3 2 6 million years ago continually fails to be simulated in climate model simulations being the last period of earth history with higher global temperatures and carbon dioxide levels similar to today it is an important target period for palaeoclimate models one of the key features of the pliocene climate is the reduced meridional gradients particularly in the high latitudes of the northern hemisphere here we show that previously unconsidered palaeogeographic changes river routing ocean bathymetry and additional landmass in the modern barents sea in the north atlantic region can produce significant temperature responses at high latitudes along with orbital forcing this can significantly decrease equator to pole temperature gradients in the atlantic ocean these additional forcings show that the large arctic warming and significantly reduced temperature gradients in the pliocene are not analogous to future warming and that careful consideration of all the possible climatic forcings is required to accurately simulate pliocene climate

geomorphological criteria for identifying pleistocene ice streams ice streams are critical regulatory mechanisms in contemporary ice sheets it has been inferred that they also had a significant effect on the dynamics of former ice sheets subsequently many people have invoked their widespread occurrence from a variety of formerly glaciated areas hypothesised locations however have often outweighed meaningful evidence this paper addresses the problem using the characteristics of contemporary ice streams as a basis for their identification from former ice sheet beds a convergence of knowledge gained from contemporary ice stream research coupled with theories of glacial geomorphology allows several geomorphological criteria to be identified as suggestive signatures of ice stream activity it is envisaged that the geomorphological criteria developed here will introduce a more objective approach to the study of former ice streams the criteria are used to construct conceptual land system models of the beds of former ice streams and it is hoped such models can provide an observational template upon which hypotheses of former ice streams can be better based

late weichselian iceberg surface melt and sediment production from the eurasian ice sheet results from numerical ice sheet modelling abstract results from a numerical ice sheet model were matched with geological evidence detailing the extent and timing of the late weichselian ice sheet in the eurasian arctic through simple adjustments in the model s environmental inputs the numerical model predicts the spatial and temporal variation in 1 subglacial sediment transport and deposition 2 rates of iceberg calving and 3 rates of supraglacial melting over the past 30 000 yr the ice sheet is characterised by a series of ice streams occupying bathymetric troughs in the barents sea and west of norway which act as sources for glacial sediment build up and iceberg production our model indicates that significant volumes of sediment are deposited over the bear island fan 3000 km 3 in 12 000 yr franz victoria trough fan 500 km 3 in 8000 yr and a series of smaller fans west of norway which combine to yield 4000 km 3 in 12 000 yr the norwegian channel ice stream operated for only 4000 yr during which time 400 km 3 of sediments were deposited on the adjacent fan the ice sheet experienced two major periods of iceberg production where the rate of calving increased by 50 at about 15 000 and 12 500 yr ago however the time dependent response of iceberg calving to sea level rise for individual ice streams is shown to be more complicated than the generalised ice sheet response the marine portions of the ice sheet decayed after 15 000 yr ago resulting in several embayments at the mouths of bathymetric troughs a second pulse of enhanced iceberg calving at 12 500 yr ago caused further decay of the marine ice sheet and the ice margin retreated back to the shorelines of island archipelagos in the northern barents sea ice loss through surface melting was restricted mostly to the southern margin of the ice sheet

a real time microearthquakes detector based on voice activity detection and endpoint detection an approach to cotopaxi volcano abstract the ring of fire represents a constant threat in the case of possible eruptions due to its 160 active volcanoes consequently several studies have determined that an increase of tectonic and long period events could indicate the beginning of a volcanic eruptive process in this context it is crucial to improve microearthquake detection by using real time automatic recognition systems for this purpose this work aims to improve microearthquake detection based on voice activity detection vad and endpoint detection furthermore we propose the use of signal segmentation considering the signal to noise ratio and adapting vad techniques for microearthquake detection the results tested in real time have demonstrated the reliability of our detector by obtaining 97 89 precision 97 10 accuracy and a value of 0 015 of balanced error rate ber we considered a dataset for real time testing of 744 h of continuous data from cotopaxi volcano in ecuador in these tests the mda detector is 8 89 more precise than the classical sta lta detector

glacigenic debris flows on the north sea trough mouth fan during ice stream maxima abstract numerous short sediment cores which penetrate through the glacimarine section and into glacigenic debris flow debrites gdfs on the north sea fan are investigated the sampled gdfs represent the uppermost of several sequences of these stacked bodies many hundreds of metres thick the gdfs occurred over slopes from 0 3 to 0 7 and examples are found from the shelf break at the mouth of the norwegian channel to the norway basin floor 300 km distant the gdf diamicts are structureless and homogeneous in terms of grain size magnetic susceptibility nrm bulk density water carbonate foraminiferal and rock fragment content this applies both from gdf to gdf across the fan and in a proximal distal sense comparison of the investigated lithologic parameters with weichselian till from a borehole in the norwegian channel 200 km up ice shows striking similarity to the gdf debrites ams 14c dates at the gdf glacimarine contact and stratigraphic relationships indicate voluminous deposition before 18 ka continuing possibly uninterrupted until ca 16 ka and a final phase halting just before 15 ka when the norwegian channel became ice free this chronology the comparable lithologic character between till and gdf debrites and a seismic continuity confirms inferences that the gdfs are directly associated with glacial ice at the shelf break the glacial efflux has not been subject to subsequent sorting and the homogeneity of the gdf is thought to reflect thorough mixing in a deforming till layer beneath a fast flowing ice stream the glacimarine section subsequent to gdfs shows no indications of turbidity flow observations are compatible with a slow non disintegrating cohesive plug flow transport mechanism with little sediment water interaction on the upper surface minor distal differentiation might reflect a change in flow process deposition on the fan margins from water borne glacimarine processes simultaneous with gdf deposition is limited

asynchronous deposition of ice rafted layers in the nordic seas and north atlantic ocean instabilities in ice stream flow within the north american laurentide ice sheet leading to the periodic release of armadas of icebergs into the north atlantic ocean over the past 60 000 years have produced extensive layers of coarse grained iceberg rafted debris heinrich layers in north atlantic sediments1 2 correlation of these layers with iceberg discharge events from the ice sheets on greenland iceland and scandinavia suggested in previous studies for some heinrich layers and in some areas3 4 5 would imply that ice sheet instability had been synchronous across the north atlantic presumably in response to a common environmental cause here we show a lack of widespread systematic correlations both between ice rafted debris layers in different sediment cores from the nordic seas and between the nordic layers and the north atlantic heinrich layers this suggests that the full glacial nordic ice sheets did not exhibit unstable behaviour coincident with iceberg discharge from the vast hudson bay drainage basin of the laurentide ice sheet6 7 off the hudson strait significant ice sheet discharge of melt water is indicated by size sorted sandy and muddy turbidite sediments different from the poorly sorted debris flows which dominate sedimentation on the margins of the nordic seas8 9 10 together these results suggest that the dynamics of quaternary ice sheets surrounding the nordic seas were different from the outlet glacier draining the hudson bay basin and they provide evidence against a common circum north atlantic mechanism driving the discharge of icebergs

depositional facies of late pleistocene heinrich events in the labrador sea late pleistocene heinrich ice rafting events produced layers rich in ice rafted debris in major parts of the north atlantic north of 40 n a high detrital carbonate content points to the hudson strait outlet of the laurentide ice sheet as a dominant source of the icebergs heinrich events were coupled with short term climate fluctuations during the last and penultimate glaciations and provide evidence for cryosphere hydrosphere atmosphere interaction in pleistocene climate change an unsolved problem with heinrich layers has been their high concentration of fine grained detrital carbonate 80 of the total detrital carbonate which cannot have been delivered by icebergs alone we propose combinations of different processes that deposited four sedimentologically different types of heinrich layers ice rafting alone for the coarser sand to gravel sized fractions and the fine fractions in distal regions type iv heinrich layers whereas nepheloid flows deposited the bulk of the fine sediment in regions proximal to the hudson strait type i heinrich layers on the labrador slope turbidity currents spilling over from canyons were also involved in transporting the fine grained carbonate rich material causing an alternation of mud turbidites and thin laminae of ice rafted debris in type ii heinrich layers on the levees of the northwest atlantic mid ocean channel the thickness relationship is reversed mud turbidites deposited by occasional spillover of currents from the channel are thin and alternate with thicker laminae of ice rafted debris type iii heinrich layers

detrital carbonate rich sediments northwestern labrador sea implications for ice sheet dynamics and iceberg rafting heinrich events in the north atlantic much of the bed of the central and eastern sectors of the laurentide ice sheet was underlain by paleozoic carbonates we propose that pulses of detrital carbonate rich sediments in two cores from the northwestern labrador sea reflect episodes when an ice stream from the hudson strait extended to the shelf break and delivered sediment onto the slope and deep sea plain atomic mass spectroscopy 14 c dating of planktonic foraminifera in cores hu75 009 iv 55 2 4 km water depth and hu87 033 009 1 4 km water depth and 150 km north northwest indicates that the youngest event occurred between ca 14 and 15 ka and another occurred between 19 and 21 ka the two carbonate intervals in northwestern labrador sea cores are coeval with heinrich events 1 and 2 in the eastern north atlantic lat 45 50 n long 20 w where they are associated with an increase in lithic fragments and a drastic reduction in the numbers of foraminifera these changes have been linked with the massive production of icebergs associated with ice sheet surges our evidence indicates that heinrich events 1 and 2 are associated with the dynamics of the hudson strait ice stream and denote considerable glaciological instability

mid pliocene warmth stronger greenhouse and stronger conveyor abstract three million years ago prior to the onset of northern hemisphere glaciation global mean temperatures may have been as much as 3 5 c warmer than at present we present evidence based on the carbon isotopic composition of marine organic matter that atmospheric co2 levels at this time were on average only about 35 higher than the preindustrial value of 280 ppm we also present carbon isotopic evidence for stronger thermohaline circulation in the atlantic ocean during the warmest intervals and propose that the north atlantic conveyor belt may act as a positive feedback to global warming by enhancing sea ice retreat and decreasing high latitude albedo based on our results it seems unlikely that the mid pliocene warm period was a doubled co2 world

extent and basal characteristics of the m clintock channel ice stream abstract the m clintock channel palaeo ice stream drained the northwestern margin victoria island arctic canada of the laurentide ice sheet functioning for 200 years prior to 10 ka bp from its bed imprint it is reconstructed as 720 140 km with a cross sectional area of 100 km2 comparable in size to the hudson strait ice stream it drained an estimated 80 000 km3 of ice enough to significantly affect the shrinking ice sheet and drive the keewatin ice divide south eastwards such discharges likely produced heinrich events and influenced the temperature and salinity of the western arctic ocean ice stream location was controlled by a topographic trough but glaciological regulation rather than properties of the bed controlled margin locations and hence ice stream width the ice stream eroded into pre existing unconsolidated sediments and left a pattern of subglacially produced landforms recording a snapshot view of the bed prior to shutdown frictional shutdown occurred once downcutting through sediments reached bedrock in places high sediment availability appears critical for ice stream functioning with a drift thickness of 50 m required to sustain its 200 year lifespan debris discharge was exceptionally high 73 000 m3 a 1 m 1 this ice stream demonstrates non steady response of ice sheets to climate change and their large impact on mass balance and stability of ice sheets

ice sheet numerical modeling and marine geophysical measurements of glacier derived sedimentation on the eurasian arctic continental margins long range side scan sonar images of the barents sea continental margin have been analyzed in conjunction with results from previous geophysical investigations to determine a qualitative model for sedimentation over the bear island and storfjorden trough mouth fans these data indicate that gravity driven debris flows are major processes in the downslope transport of glacial material delivered to the shelf break when ice sheets advanced across the continental shelf during late weichselian time 4000 km 3 of sediments were deposited over the bear island fan 280 000 km 2 while 700 km 3 of sediments were deposited over the storfjorden fan 40 000 km 2 a numerical ice sheet model including sediment deformation and transport beneath ice streams reconstructs the glacial conditions required to transport large volumes of sediment to the late weichselian eurasian continental margin model results indicate that glaciation of the eurasian high arctic occurred after 28 ka and that ice streams within bathymetric troughs were active by ca 25 ka the maximum ice sheet thickness over the barents sea was about 1400 m there was a secondary dome 1 0 13 cm yr 1 averaged over the fan the rate was 6 cm yr 1 equivalent to 0 6 cm yr 1 over the fan over the storfjorden trough mouth the modeled sediment volume at the continental margin of the bear island and storfjorden troughs agrees well with the volumes of late weichselian sediment inferred from seismic records from these large prograding submarine fans sensitivity experiments show that adjustments to model environmental inputs do not significantly affect the results

provenance of heinrich layers in core v28 82 northeastern atlantic 40ar 39ar ages of ice rafted hornblende pb isotopes in feldspar grains and nd sr pb isotopes in the fine sediment fraction abstract several correlatable layers of sediment rich in ice rafted grains have been documented in the north atlantic the most notable within the last glacial cycle are the heinrich layers layers extremely rich in ice rafted detritus and generally barren of foraminifera within the north atlantic ice rafted detritus ird belt the view of these layers is that they represent events where great armadas of icebergs were launched into the north atlantic the importance of the heinrich layers lies in their connection with abrupt climate change in the north atlantic and perhaps globally there is a growing number of published provenance studies of the heinrich layers in the north atlantic based on a variety of methods however there is little overlap of methods applied to the same samples in this contribution we present a multi component provenance study of heinrich layers h1 h2 h4 and h5 from core v28 82 in the eastern north atlantic our results indicate that virtually the entire inventory of terrigenous clastic detritus in heinrich layers h2 h4 and h5 came from ancient continental sources surrounding the labrador sea although heinrich layer h1 is similar in many respects it appears to have some significant differences relative to the other three

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

bathymetric controls on pliocene north atlantic and arctic sea surface temperature and deepwater production the mid pliocene warm period mpwp 3 3 to 3 0 ma is the most recent interval in earth s history in which global temperatures reached and remained at levels similar to those projected for the near future the distribution of global warmth however was different than today in that the high latitudes warmed more than the tropics multiple temperature proxies indicate significant sea surface warming in the north atlantic and arctic oceans during the mpwp but predictions from a fully coupled ocean atmosphere model hadcm3 have so far been unable to fully predict the large scale of sea surface warming in the high latitudes if climate proxies accurately represent pliocene conditions and if no weakness exists in the physics of the model then model boundary conditions may be in error here we alter a single boundary condition bathymetry to examine if pliocene high latitude warming was aided by an increase in poleward heat transport due to changes in the subsidence of north atlantic ocean ridges we find an increase in both arctic sea surface temperature and deepwater production in model experiments that incorporate a deepened greenland scotland ridge these results offer both a mechanism for the warming in the north atlantic and arctic oceans indicated by numerous proxies and an explanation for the apparent disparity between proxy data and model simulations of pliocene northern north atlantic and arctic ocean conditions determining the causes of pliocene warmth remains critical to fully understanding comparisons of the pliocene warm period to possible future climate change scenarios

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

seismic architecture and sedimentology of a major grounding zone system deposited by the bjornoyrenna ice stream during late weichselian deglaciation abstract a 280 km wide sediment wedge in outer bjornoyrenna bear island trough south western barents sea has been investigated using 2d and 3d seismic data sediment gravity cores as well as regional swath and large scale bathymetry data the bathymetry data indicate a division into an up to 35 m high frontal wedge with large depressions and an upstream part characterized by mega scale glacial lineations msgl from seismic sections increasing erosion is demonstrated for the upstream part coinciding with the location of msgl whether the latter are depositional features postdating an extensive erosional event or formed by erosion remains inconclusive based on the distinct morphology and internal structures we infer that the system was deposited during a rapid readvance whereby the ice front pushed and bulldozed predominantly soft diluted proglacial sediments analyses in the eastern part of the sediment system reveal the existence of imbricated thrust sheets in the frontal part of the wedge this is suggested to imply upstream erosion of sedimentary rock and incorporation of thrusted blocks into the moraine forming a composite ridge locally we argue that observed large scale depressions are dead ice features in the marine environment it is envisioned that intense englacial thrusting may have developed into a decollement as the cold glacier snout got overrun by ice masses from the interior thereby enabling the inclusion of slabs of ice in the push moraine mass radiocarbon dates indicate that the sediment wedge was deposited around 17 090 cal yrs bp 14 530 14 c yrs bp and that the ice front probably remained stable until 16 580 cal yrs bp 13 835 14 c yrs bp

micropaleontological evidence for increased meridional heat transport in the north atlantic ocean during the pliocene the middle pliocene approximately 3 million years ago has been identified as the last time the earth was significantly warmer than it was during the last interglacial and holocene a quantitative micropaleontological paleotemperature transect from equator to high latitudes in the north atlantic indicates that middle pliocene warmth involved increased meridional oceanic heat transport

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

the last glacial maximum of svalbard and the barents sea area ice sheet extent and configuration abstract the timing extent and configuration of the late weichselian barents ice sheet has been debated for several decades this debate has arisen largely because of the limited or conflicting field evidence on which most models have been based in particular reconstruction of the marine parts of the former barents ice sheet has been controversial this paper aims to review the geological observations and interpretations regarding the size and timing of the late weichselian ice sheet combined with numerical modelling of its formation in order to produce a reconstruction of ice sheet extent and behaviour sub glacial till with overlying glacimarine deposits dated to the late weichselian is found over most of the barents sea floor and the continental shelf west of svalbard glacially induced debris flow deposits on the large bjonoya and isfjorden trough mouth fans strongly support the idea of ice sheet extension to the shelf edge during maximum glaciation isobase maps show a centre of post glacial uplift in the north central barents sea and glaciological and isostatic modelling suggest that the ice sheet was 2000 3000 m thick in this area the ice sheet was confluent with ice over the kara sea but the interaction between the barents and kara ice sheets is not yet fully understood the deglaciation of the barents ice sheet started ca 15 ka probably by calving within the deeper troughs by 12 ka most of the central barents sea was ice free and ice remained over the svalbard franz josef land and novaja zemlya archipelagos and adjacent shallow shelf areas the coasts and fjords of these islands were ice free by 10 ka

sediment characteristics in iceberg dominated fjords kangerlussuaq region east greenland abstract sediment cores from three east greenland fjords contain sediment lithofacies and depositional processes in an iceberg dominated glacial marine setting three major lithofacies diamicton fine grained mud and sand are deposited by two processes sediment rain out and sediment gravity flows the sediments in kangerlussuaq fjord are predominately fine grained muds deposited by rain out from icebergs and glacier meltwater with sediment gravity flows acting as secondary agents of deposition miki fjord records rain out of fine grained muds from a river plume emanating from a proglacial delta at the fjord head alternating units of diamicton and fine grained mud in nansen fjord are deposited by sediment rain out from icebergs particle size is governed by the oceanographic conditions in the fjord at the time of deposition despite their proximity to each other each fjord is distinguished by a distinct sedimentological signature kangerlussuaq fjord has low total organic carbon contact miki fjord has high mass magnetic susceptibility and nansen fjord has high amounts of ice rafted debris comparison of the east greenland iceberg dominated and alaska glacial meltwater dominated environments indicates few major differences between sediments deposited in these two settings this similarity raises doubt as to how well glacial marine sedimentary sequences can be used to interpret and reconstruct differences between glacial marine environments in the past without knowledge of sediment accumulation rates environmental conditions at the time of sediment deposition and comparable sedimentological data between studies

the effects of the water flow through the canadian archipelago in a global ice ocean model numerical experiments are conducted with a global ice ocean model in order to evaluate the influence of the water flow from the arctic ocean to baffin bay through the canadian archipelago on the water mass properties of the arctic ocean and adjacent seas and more generally on the global ocean circulation the results indicate that this flow plays a significant role in controlling the freshwater budget of the arctic ocean when the canadian archipelago passage is open in the model the arctic pycnocline experiences a noticeable increase in salinity furthermore the flow of relatively fresh arctic waters through the passage yields a pronounced decrease of surface salinity and density in the labrador sea which leads to a diminution of convective activity there as a result the north atlantic deep water outflow in the model is reduced by about 5 deep convection in the norwegian sea exhibits almost no change and this despite a weakening of the inflow of relatively fresh arctic waters through fram strait

distribution of glacial geomorphic features on the antarctic continental shelf and correlation with substrate implications for ice behavior surveys were conducted seaward of all the major drainage outlets of the antarctic ice sheet from the pennell coast north victoria land to marguerite bay antarctic peninsula the results show that the ice sheet extended onto the outer shelf glacial troughs occur offshore of all major glacial outlets where the substrate is crystalline bedrock ice flow tended to follow the structural grain of the bedrock deposited little sediment and eroded the underlying bedrock where ice flowed over relatively soft more easily eroded sedimentary strata the direction of ice flow was more directly offshore and depositional features characterize the sea floor in these areas the signature of the grounded ice consists of till deposits and large scale geomorphic features drumlins occur within the region of contact between crystalline and sedimentary substrates the different geological substrates are interpreted to have exerted a fundamental control on the behavior of past ice sheets the troughs in the areas of bedrock composed of sedimentary substrate are interpreted to have been occupied by relatively fast flowing ice ice streams and the troughs in the areas of crystalline substrate are interpreted to have been occupied by slower moving ice the area between these two zones was characterized by ice acceleration and is marked by drumlins

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

the late weichselian glaciation of the franz victoria trough northern barents sea ice sheet extent and timing high resolution seismic profiles parasound 4 khz and three sediment cores from the franz victoria trough and the adjacent continental slope were studied in order to constrain the timing and extent of the northern svalbard barents sea ice sheet during the late weichselian glaciation stacked debris flow lobes and layers of glacimarine diamicton on the lower continental slope indicate that large quantities of glacially derived sediments were deposited by the northern svalbard barents sea ice sheet directly onto the upper continental slope at approximately 23 14 c ka a grounding line advance to the shelf break is supported by the identification of diamicton interpreted as till in the seismic profile near the shelf break after several ice sheet instabilities marked by significant input of ice rafted detritus to the continental margin the disintegration of the northern svalbard barents sea ice sheet termination ia is indicated by a distinct pulse of ice rafted detritus at 15 4 14 c ka and the transition to an isotopically defined meltwater signal the drastic change in sedimentary pattern on the upper continental slope dated to about 13 4 14 c ka is interpreted as grounding line retreat from the shelf edge a further stepwise retreat of the northern svalbard barents sea ice sheet is indicated by pulses of ice rafted detritus which appear to be contemporaneous with the onset of distinct ice rafting events in adjacent areas and pulses of glacimarine sedimentation in the southwestern barents sea q 2000 elsevier science b v all rights reserved

rapid changes in the mechanism of ocean convection during the last glacial period high amplitude rapid climate fluctuations are common features of glacial times the prominent changes in air temperature recorded in the greenland ice cores1 2 are coherent with shifts in the magnitude of the northward heat flux carried by the north atlantic surface ocean3 4 changes in the ocean s thermohaline circulation are a key component in many explanations of this climate flickering5 here we use stable isotope and other sedimentological data to reveal specific oceanic reorganizations during these rapid climate change events deep water was generated more or less continuously in the nordic seas during the latter part of the last glacial period 60 to 10 thousand years ago but by two different mechanisms the deep water formation occurred by convection in the open ocean during warmer periods interstadials but during colder phases stadials a freshening of the surface ocean reduced or stopped open ocean convection and deep water formation was instead driven by brine release during sea ice freezing these shifting magnitudes and modes nested within the overall continuity of deep water formation were probably important for the structuring and rapidity of the prevailing climate changes

abrupt changes heinrich events in late quaternary north atlantic marine environments a history and review of data and concepts in the last several years evidence has mounted that a series of abrupt changes in sediment delivery and palaeoceanography effected the north atlantic they are recorded in a variety of proxy records but most dramatically in changes of grain size and mineralogy associated with postulated iceberg rafting events specifically heinrich h events this review paper examines the evidence for such evidence prior to the development of the heinrich event concept 1988 1992 and then examines the explosion of data and correlations that stemmed from the acceptance and use of this paradigm specific attention is focused on ideas pertaining to the cause s of glaciological mechanisms sediment delivery and sediment source and major gaps in our understanding of the underlying glaciological glacial geological and glacial marine processes are stressed abrupt changes across boundaries associated with h 2 in the labrador sea are illustrated from core hu87033 009lcf the case is made that correlations between records need to be more rigorous especially within the range of radiocarbon dating but it appears that abrupt changes in the delivery of iceberg rafted debris which characterize these intervals are multisourced it is unclear how global climate can simultaneously influence the abrupt behaviour of ice margins in different parts of the world for marine based margins changes in relative sea level are one possibility a qualitative model is presented for triggering h events which includes global changes in mass balance changes in relative sea level at ice margins due to glacial isostasy and changes in the basal thermal regime of tidewater ice streams 1998 john wiley sons ltd

deep sea floor evidence of past ice streams off the antarctic peninsula the past existence of a giant ice stream off the northern end of the antarctic peninsula is suggested by a convex upward elongated sediment body now at a mean water depth of 1000 m because of its morphological characteristics i e a set of parallel to subparallel ridges and grooves to 100 km long with an overall width of 25 km we call this depositional body a bundle structure we hypothesize that bundle structures form by accumulation of basal deformation till under their parent ice streams from its location size and overall characteristics the bundle structure described here constitutes the best preserved largest deepest and relatively low latitude evidence of giant ice streams that flowed offshore antarctica during glacial maxima bundle structures reveal the very dynamic behavior of ice caps in the northern antarctic peninsula during the last glacial maximum with catchment areas draining rapidly under marine based critical subglacial conditions bundle structures represent a new megascale streamlined glacial landform

modeling pliocene warmth modeling studies relevant to the question of pliocene warmth are reviewed although significant regional climate variations may be due to pliocene changes in orography and ocean circulation these changes do not appear sufficient to explain inferred globally increased warmth climate modeling studies for a doubling of co2 suggest high latitude temperature increases approximately comparable to inferred warming during the pliocene i suggest that such a co2 increase may be primarily responsible for the pliocene temperature increase downdraw of co2 since the pliocene is consistent with some geochemical indications of enhanced weathering in the pleistocene however additional proxy testing of this hypothesis is required the co2 models also predict tropical sea surface warming of 2 3 c and winter temperature warming in central eurasia 50 70 n of 4 10 c predictions that distinguish co2 from some other mechanisms enhanced scrutiny of pliocene records from the above regions may prove a valuable test of the co2 hypothesis finally although a co2 increase may be responsible for pliocene warmth this time interval should not be cited as a direct analog for a future greenhouse warming as the future climate will have a significant nonequilibrium response because of the rapid rate of change of forcing despite these limitations enhanced study of pliocene climates may be very valuable as an independent source of validation of co2 doubling simulations

iceberg production debris rafting and the extent and thickness of heinrich layers h 1 h 2 in north atlantic sediments the pattern of heinrich layer distribution for the last two events h 1 14 5 and h 2 21 1 ka mapped from magnetic susceptibility analysis of more than 50 north atlantic ocean cores provides the most detailed information to date on their extent and thickness an integrated spatial average thickness for the layers is 10 15 cm and there is a strong distance decay eastward the pattern of deposition over the north atlantic is similar for events h 1 and h 2 indicating that icebergs followed similar drift tracks rates of iceberg production and sediment flux from the hudson strait drainage basin of the north american laurentide ice sheet the major iceberg source for the events were calculated by using a mass balance approach this provides an envelope of sedimentation rates and the prediction that it would take between 50 and 1250 yr of iceberg sediment delivery to accumulate a heinrich layer averaging 10 cm thick over the north atlantic depending on the model assumptions used the most likely duration of heinrich events is 250 1250 yr

the glacier fed fan at the mouth of storfjorden trough western barents sea a comparative study the middle and late pleistocene succession on the glacier fed fan at the mouth of storfjorden trough was studied using high resolution seismic data seven glacial advances to the shelf break during middle and late pleistocene resulted in episodic high sediment input to the fan with real sedimentation rates of up to 172 cm 1000 years separated by sediment starved interstadials and interglacials on the upper fan the high sediment input resulted in frequent slides and slumps generating debris flows which dominate the mid fan strata compared with the larger neighbouring bear island trough mouth fan the storfjorden trough mouth fan has a steeper fan gradient narrower thinner and shorter debris flow deposits and lower frequency of large scale sliding glacier fed submarine fans receive their main sediment input from a glacier margin at the shelf break as opposed to river fed fans where sediment input occurs through a channel levee complex as a result the depocentre of a river fed fan is found on the mid fan and the upper slope is mainly an area of sediment bypass whereas the glacier fed fan has an elongated depocentre across the uppermost fan the river fed fans are dominated by deposition from turbidity currents whereas glacier fed fans are dominated by debris flow deposits

implications of arctic sea ice changes for north atlantic deep convection and the meridional overturning circulation in ccsm4 cmip5 simulations 1 using ccsm4 climate simulations for 1850 2300 with four different future forcing scenarios we show that the maximum strength of the atlantic meridional overturning circulation moc decreases proportionally to the applied co2 forcing this weakening of the overturning is caused by a reduction or shut down of north atlantic na deep convection due to a surface freshening in the labrador sea the surface freshening is caused by strongly increased liquid freshwater exports from the arctic which are largely due to the decrease in the arctic sea ice cover in the strongest forcing scenario rcp8 5 the arctic becomes summer ice free by the end of the 21st century and year round ice free by the end of the 23rd century as a result of the associated freshening all na deep convection ceases by 2145 which leads to a 72 18 sv decrease of the moc strength by the end of the simulation in 2300

holocene glacimarine sedimentation inner scoresby sund east greenland the influence of fast flowing ice sheet outlet glaciers abstract holocene glacimarine sedimentation associated with fast flowing outlet glaciers draining the greenland ice sheet is investigated using sedimentary and acoustic data from inner scoresby sund east greenland sedimentation in inner scoresby sund is dominated by three processes which are influenced by differences in proximity to fast flowing outlet glaciers extent of glacier ice cover and fjord bathymetry 1 sediment gravity flow principally in the form of turbidity currents and debris flows 2 suspension sedimentation from turbid meltwater plumes and 3 iceberg rafting these processes result in texturally and sedimentologically heterogeneous lithofacies proportionally fine grained muds laminated stratified and massive facies dominate cores recovered from inner scoresby sund accounting for 80 of the total whereas diamict facies account for only 15 abundant fine grained muds demonstrate that meltwater flux and sedimentation is significant in this high arctic glacimarine environment in settings proximal to fast flowing outlet glaciers with increasing distance from these glacier termini muds are replaced progressively by iceberg rafted coarse grained sediment the dominance of this iceberg rafted sediment in outer scoresby sund reflects both its more distal location from fast flowing glacier termini and the high calving flux associated with these ice masses laminated muds deposited by turbidity currents and suspension settling from overflow plumes in inner scoresby sund are similar to lithofacies produced in temperate and subpolar glacimarine systems this implies a similarity in sedimentation processes and resulting facies across a wide spectrum of climatically glaciologically fast flowing and non fast flowing ice masses and oceanographically variable glacimarine settings recognition of laminated fine grained facies in the geological record therefore does not necessarily indicate a temperate palaeo glacial setting however the predominance of iceberg rafted diamict facies in ice distal sedimentary records suggests the former presence of relatively cold environmental conditions in which iceberg sedimentation played a dominant role

seafloor evidence of a subglacial sedimentary system off the northern antarctic peninsula swath bathymetry data and high resolution seismic reflection profiles allow us to portray a subglacial sedimentary system off the northern tip of the antarctic peninsula in the central bransfield basin during the last glacial maximum with unprecedented detail postglacial reworking and sedimentation are weak enough for the subglacial morphology of the last glacial maximum to be preserved on the present seafloor the studied sedimentary system extends 250 km from 1000 m above sea level to 2000 m water depth the data set supports a model for subglacial sedimentary systems that consists of 1 an upper ice catchment or erosional zone on the innermost continental shelf extending onshore 2 a transitional erosional depositional zone on the inner shelf with drumlinized seafloor 3 a depositional outer shelf zone with mega scale bundle glacial lineations and 4 a debris apron on the continental slope and base of slope formed under floating ice shelves with debris delivery linked to grounding lines along the shelf break

modeling iceberg rafted sedimentation in high latitude fjord environments 1 an iceberg model sedberg has been developed to simulate sedimentation in high latitude glaciated fjords sediments deposited in fjords provide an important record of glaciological response to changing climatic conditions the model simulates the formation drift and melt of a population of icebergs utilizing monte carlo based techniques with a number of underlying parametric probability distributions to describe the stochastic behavior of iceberg formation and dynamics the model captures iceberg dynamics and melt in fjord environments and has been applied to kangerdlugssuaq fjord in east greenland as an example of an iceberg dominated sedimentary environment sedimentation has been simulated over the past 1500 years encompassing the climatic intervals of the medieval warm period mwp and the little ice age lia model results have been compared with the observed sedimentary record the model demonstrates that the glaciological regime e g basal debris thickness mean annual calving rate mean iceberg size plays a more important role than the direct influence of climate ocean and air temperatures on iceberg sedimentation rate although often changes in climate result in changes to the glaciological regime

late pleistocene holocene retreat of the west antarctic ice sheet system in the ross sea part 2 sedimentologic and stratigraphic signature sedimentologic geotechnical geochemical and accelerator mass spectrometer ams radiocarbon data from two marine geologic cruises in the ross sea have allowed us to constrain facies relationships and temporal changes in the west antarctic ice sheet the selection of core sites was facilitated by the use of multibeam bottom imagery and a good quality chirp subbottom reflection system a complex but consistent succession of facies documents a number of environments from subglacial to open marine massive mud rich diamictons have low water contents contain in places a calcareous microfossil assemblage show minimal textural variation and contain low and uniform total organic carbon values this reflects a subglacial setting this unit passes upward into a stratified thin granulated facies consisting of pelletized sandy muddy gravel that is loosely compacted and contains a variable water content and concentrated horizons of pebble sized clasts this facies reflects the lift off zone or thin water film between the basal debris and sea floor overlying this unit are silty clays that contain a well sorted very fine grained sand component there are no coarse grains within this unit this facies is in part laminated and reflects deposition beneath an ice shelf near and away from the grounding line zone the ice shelf facies passes upward into a siliceous mud and ooze unit that represents deposition in an open marine setting a sandy volcaniclastic rich subfacies marks the transition from ice shelf to open marine environments found at the calving line the 86 ams radiocarbon dates on organic matter provide an accurate chronology for 19 cores ice shelf conditions were established in the outer drygalski trough by 11 0 25 ka and perhaps earlier this transition took place in the joides basin by 10 8 ka the calving front of the ross ice shelf passed over the drygalski trough at 74 s by 9 5 0 25 ka the timing of deglaciation in the ross sea calls into question current models for the contribution of antarctic glacial ice to holocene sea level rise and suggests that recession was relatively gradual and more closely aligned with northern hemisphere deglaciation and its associated eustatic pulse

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

arctic and antarctic submarine gullies a comparison of high latitude continental margins abstract submarine gullies are common features of high latitude continental slopes and over the last decade have been shown to play a key role in continental margin evolution submarine erosion downslope sediment transport slope deposits and the architecture of petroleum reservoirs however the processes that form these gullies the timescales over which they develop and the environmental controls influencing their morphology remain poorly constrained we present the first systematic and comparative analysis between arctic and antarctic gullies with the aim of identifying differences in slope character from which we infer differences in processes operating in these environments quantitative analysis of multibeam echosounder data along 2441 km of the continental shelf and upper slope and morphometric signatures of over 1450 gullies show that six geomorphically distinct gully types exist on high latitude continental margins we identify distinct differences between arctic and antarctic gully morphologies in the arctic data sets deep relief 30 m gully incision depth at 50 m below the shelf edge and shelf incising gullies are lacking these differences have implications for the timescales over which the gullies were formed and for the magnitude of the flows that formed them we consider two hypotheses for these differences 1 some antarctic gullies developed through several glacial cycles and 2 larger antarctic gullies were formed since the last glacial maximum as a result of erosive flows i e sediment laden subglacial meltwater being more abundant on parts of the antarctic margin over longer timescales a second difference is that unique gully signatures are observed on arctic and on antarctic margins environmental controls such as the oceanographic regime and geotechnical differences may lead to particular styles of gully erosion observed on arctic and antarctic margins

earthquake classification location and error analysis in a volcanic environment implications for the magmatic system of the 1989 1990 eruptions at redoubt volcano alaska abstract determination of the precise locations of seismic events associated with the 1989 1990 eruptions of redoubt volcano posed a number of problems including poorly known crustal velocities a sparse station distribution and an abundance of events with emergent phase onsets in addition the high relief of the volcano could not be incorporated into the hypoellipse earthquake location algorithm this algorithm was modified to allow hypocenters to be located above the elevation of the seismic stations the velocity model was calibrated on the basis of a posteruptive seismic survey in which four chemical explosions were recorded by eight stations of the permanent network supplemented with 20 temporary seismographs deployed on and around the volcanic edifice the model consists of a stack of homogeneous horizontal layers setting the top of the model at the summit allows events to be located anywhere within the volcanic edifice detailed analysis of hypocentral errors shows that the long period lp events constituting the vigorous 23 hour swarm that preceded the initial eruption on december 14 could have originated from a point 1 4 km below the crater floor a similar analysis of lp events in the swarm preceding the major eruption on january 2 shows they also could have originated from a point the location of which is shifted 0 8 km northwest and 0 7 km deeper than the source of the initial swarm we suggest this shift in lp activity reflects a northward jump in the pathway for magmatic gases caused by the sealing of the initial pathway by magma extrusion during the last half of december volcano tectonic vt earthquakes did not occur until after the initial 23 hour long swarm they began slowly just below the lp source and their rate of occurrence increased after the eruption of 01 52 ast on december 15 when they shifted to depths of 6 to 10 km after january 2 the vt activity migrated gradually northward this migration suggests northward propagating withdrawal of magma from a plexus of dikes and or sills located in the 6 to 10 km depth range precise relocations of selected events prior to january 2 clearly resolve a narrow steeply dipping pencil shaped concentration of activity in the depth range of 1 7 km which illuminates the conduit along which magma was transported to the surface a third event type named hybrid which blends the characteristics of both vt and lp events originates just below the lp source and may reflect brittle failure along a zone intersecting a fluid filled crack the distribution of hybrid events is elongated 0 2 0 4 km in an east west direction this distribution may offer constraints on the orientation and size of the fluid filled crack inferred to be the source of the lp events

the origin of heinrich layers evidence from h2 for european precursor events recent well dated isotopic sr nd fingerprinting of heinrich layer ice rafted detritus ird on the european margin indicates supply from european ice sheets as precursors to laurentide ice sheet lis supply f e grousset et al geology 28 2000 123 126 h snoeckx et al mar geol 158 1999 197 208 these precursorevents lead lis input by up to 1 5 ka f e grousset et al geology 28 2000 123 126 and have been interpreted to indicate lis collapse during heinrichevents stimulated by events originating on the european side of the atlantic f e grousset et al geology 28 2000 123 126 such phasing of ird supply from different sources within heinrich layers therefore has implications for the origin and mechanics of heinrichevents we present evidence here that the ird comprising heinrich layer 2 h2 20 21 14c ka bp on the european continental margin contains detrital campanian upper chalk deriving from bedrock sources eroded on the celtic shelf by the british ice sheet bis in addition to lithic material sourced from the lis high resolution radiocarbon chronology indicates chalk grain deposition as discrete pulses both before and coincident with supply of lis sourced detritus the specificity of the chalk fingerprint to the bis enables a 700 1000 yr lag between the bis and lis events to be identified this phasing indicates a more rapid response of the outlet lobes draining the smaller bis than those draining the lis and implicates external climatic forcing of heinrichevents it is unlikely that this precursorevent represents ird event 18 the recently identified 1 2 ka ird cycle event which immediately precedes h2 because the lag between precursor and main event is here less than 1 5 ka and because such pervasive periodicity is not apparent in european continental margin ird records the later synchroneity between the bis and lis input in h2 identifies glacio eustatic sea level rise associated with lis discharges as a possible feedback mechanism causing destabilisation of ice streams elsewhere during heinrichevents

mega scale glacial lineations and cross cutting ice flow landforms landsat images reveal a previously unsuspected large scale pattern of streamlining within drift that is assumed to reflect former phases of ice flow such a glacial grain can be regarded as a landform assemblage comprised of a number of components drumlins and megaflutes form part of the pattern but in addition there are two previously undocumented ice moulded landform elements streamlined lineations of much greater proportions referred to as mega scale glacial lineations and a distinctive cross cutting topology within the grain the ice moulded landform assemblage is described and illustrated with reference to examples from canada possible modes of genesis of such landforms are discussed and their glaciological implications outlined the discovery of this pattern indicates the pervasive nature of subglacial deformation of sediment and demands a radical re interpretation of ice sheet dynamics

shingled quaternary debris flow lenses on the north east newfoundland slope debris flow deposits are the principal component of quaternary continental slope sediments between the north east newfoundland shelf and central orphan basin in seismic profiles these deposits occur as shingled elongate acoustically transparent lenses with their long axes orientated downslope deposits of individual flows form positive mounds on the sea floor subsequent flows were diverted by the pre existing topography into bathymetric lows between older debris flow deposits these deposits show a large variation in the area of sea floor covered by individual flows about 60 1000 km2 average thickness of deposits 9 37 m and volume of sediment displaced 1 27 km3 the ratio of average thickness to a measure of deposit diameter termed the aspect ratio has a threefold variation from 0 0006 to 0 0021 very low depositional slopes and low aspect ratios suggest relatively low viscosities probably due to inmixing of water during downslope transport stratified sediments form three distinct horizons and are locally interbedded with the debris flow deposits these are mainly hemipelagic deposits the slope and rise to the west of the orphan basin are constructional in character the apparent absence of upper slope erosional features and the abundance of debris flow deposits on the slope suggest that the supply of sediment to the continental slope occurred predominantly during times of maximum extent of quaternary glacial ice the ice sheet grounding line during several glacial maxima must have been situated at or near the present shelf break supplying vast amounts of sediment directly to the upper slope oversteepening and subsequent slope failures fed material into deeper water

trough mouth fans palaeoclimate and ice sheet monitors abstract trough mouth fans are fans at the mouth of transverse troughs channels on glaciated continental shelves on the northwest european glaciated continental margin eight trough mouth fans varying in size between 2700 and 215 000 km 2 have been identified the trough mouth fans are depocentres dominated by debris flows accumulated in front of ice streams draining the former large northwest european ice sheets the debris flow units are separated by hemmipelagic interglacial interstadial sediments it is inferred that the number of debris flow units record the number of shelfbreak positions of the ice sheet margins the number found varies between three in the south and eight in the north typical trough mouth fans and related debris flow units seem to have been formed later than the early mid pleistocene thus the north european ice sheets did not form ice streams extending to the shelfbreak in any appreciable length before the mid pleistocene besides being loci for sediment deposition the trough mouth fans were also the main sites of fresh water supply to the ocean in the form of icebergs during the mid late pleistocene ice ages

glacial flow systems in the zone of confluence between the scandinavian and novaja zemlya ice sheets abstract the glacial geomorphology of the eastern kola peninsula northwestern russian plain pechora lowland northern ural mountains and southern novaya zemlya 1 000 000 km 2 was mapped using landsat satellite imagery glacial flow parallel lineations and marginal and interlobate features were identified the directions of glacial flow and the patterns of deglaciation were reconstructed the scandinavian ice sheet expanded northeastwards into the southern barents sea while the novaya zemlya ice sheet spread southwestwards into the same area the two coalesced in the kanin region and subsequently flowed from the barents sea towards the land during the deglaciation of the scandinavian ice sheet flow was initially oriented from the white sea region towards the barents sea subsequently several ice streams controlled by the regional topography were formed the growth of the novaya zemlya ice sheet occurred east of the islands whereas during the decay there was more ice on the western side a compilation of dated sequences up to 300 km inland from the coast indicate a late weichselian age of deglaciation separation of the two ice sheets occurred along the saddle between the kanin and kola peninsulas at about 13 000 bp 15 500 cal years bp which became the locus for discharge of the proglacial dvina pechora lake into the sea beyond the presumed late weichselian limits older flow patterns are recognised these patterns along with dispersal of erratics suggest that the growth of a more extensive glaciation started in the novaya zemlya region later the scandinavian ice sheet occupied areas previously covered by the novaya zemlya ice sheet