submarine landforms and shallow acoustic stratigraphy of a 400 km long fjord shelf slope transect kangerlussuaq margin east greenland kangerlussuaq fjord is a relatively uniform steep walled basin whose floor has an almost smooth surface debris is supplied mainly from icebergs from the fast flowing kangerlussuaq glacier sedimentation after iceberg release from multi year sea ice is mainly by rain out of fine grained englacial debris streamlined glacial lineations and drumlins were produced at the sedimentary bed of an ice sheet that expanded into kangerlussuaq trough at the last glacial maximum lgm bedrock channels and crescentic overdeepenings indicate warm based ice and free water beneath parts of the former ice sheet cross cutting iceberg scour marks which characterise outer kangerlussuaq shelf were produced not only during deglaciation but also occasionally through the holocene by deep keeled icebergs from further north in east greenland the outward convex contours of the shelf edge and slope beyond kangerlussuaq trough and debris flows on the slope suggest a glacier influenced high latitude fan the distribution of streamlined subglacial landforms demonstrates that the greenland ice sheet extended throughout kangerlussuaq fjord and reached at least 200 km across the shelf in kangerlussuaq trough at the lgm streamlined landform orientation indicates ice flow from the interior of greenland down the axis of kangerlussuaq trough there is little evidence for discrete sedimentary depocentres in the trough implying that ice probably retreated rapidly from the outer and mid shelf during deglaciation

past ice sheet flow east of svalbard inferred from streamlined subglacial landforms the pattern of late weichselian ca 20 ka ice flow in the northern barents sea is not well known due mainly to a lack of marine data east of svalbard several years with little summer sea ice have allowed acquisition of swath bathymetric imagery of well preserved subglacial landforms characterizing late weichselian ice flow directions over 150 000 km2 of the northwestern barents sea we show that a major ice dome was located on easternmost spitsbergen or southern hinlopen strait at least 500 km west of its previously inferred position in the northern barents sea this dome controlled the regional flow pattern ice flowed eastward around kong karls land into franz victoria trough and north through hinlopen strait an ice dome west of kong karls land is required to explain the observed ice flow pattern but does not preclude an additional ice dome to the southeast discrepancies with earlier ice sheet reconstructions reflect the lack of previous seafloor observations with evidence limited mainly to past ice loading and postglacial rebound the new pattern of ice flow directions shows predominantly eastward rather than northward flow with franz victoria trough a major drainage pathway with a full glacial balance flux of 40 km3 yr 1

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

glacial morphology and sediment formation in the mertz trough east antarctica abstract the nathaniel b palmer 01 01 cruise produced a seabeam map showing unprecedented detail of the bathymetry in the mertz trough of east antarctica in addition seismic reflection surveys and sediment core collection were completed in the region the morphology of the mertz trough is combined with core data to interpret the sequence of events that occurred in this area since the last glacial maximum these complementary data indicate that an ice sheet once covered the mertz trough which deposited diamicton and formed mega scale glacial lineations during glacial maximal conditions and grounding line wedges during recession an erosional feature caused by subglacial meltwater breaching at least one of the grounding line deposits is also recognized along with a fan of sediment deposited seaward of the breach sediment cores from the mertz trough consist of two distinct units the diamicton deposited subglacially and a diatom mud and ooze deposited after the ice retreated the latter unit has been preferentially deposited in deeper areas of the trough as a hemipelagic drape and shows that a change in the nature of the diatom unit occurred about 3300 14c yr bp

the deglacial history of southeast sector of the greenland ice sheet during the last glacial maximum the southeast sector of the greenland ice sheet is currently experiencing rapid changes in mass balance and ice sheet dynamics at low elevations however to what extent these changes are typical of the behaviour of this sector of the ice sheet is uncertain as our understanding of the longer term controls on ice sheet dynamics in this region is limited two models exist for last glacial maximum lgm ice sheet configuration in east greenland the first minimum model envisages a restricted ice sheet with exposed nunataks in coastal areas and limited ice extent onto the continental shelf fed by ice flowing through bedrock troughs a second maximum model entails a thicker ice sheet with limited coastal nunataks and ice filling the coastal valleys and extending across the entire continental shelf radiocarbon dates on foraminifera collected from seabed cores on the southeast greenland continental shelf suggest that the ice sheet reached a maximum extent at ca 22 kcal yr before retreating perhaps as early as ca 17 kcal yr bp and reaching the present coast at ca 10 kcal yr bp this paper presents the results of a study designed to test these different ice sheet models based on geomorphological mapping and cosmogenic isotope analyses in the torqulertivit imiat valley an area to the east of the coastal town of ammassalik 26al and 10be measurements on abraded bedrock surfaces in terrain above local trimlines yield surface exposure ages of ca 11 8 9 9 ka this demonstrates warm based glacial erosion of high level surfaces ca 740 m asl followed by trimline formation during deglaciation and intense postglacial weathering our work constrains minimum ice thickness during the lgm to at least 740 m and supports a maximum ice sheet model in this sector of the gis ice sheet retreat from the continental shelf to the southern edge of sermilik fjord is dated to ca 11 1 9 7 ka and helps to constrain the timing of the early holocene retreat of the helheim glacier ice stream within the torqulertivit imiat valley age determinations from glacially abraded terrain above the local marine limit on the coast 11 1 9 7 ka and those from 10 km up valley 12 8 9 9 ka suggest rapid surface ablation during these intervals coincident with rapid atmospheric warming observed in the greenland ice core records

seafloor geomorphology of the sw barents sea and its glaci dynamic implications abstract three dimensional 3d reflection seismic imaging techniques provide a unique means of identifying large scale submarine geomorphic features produced by former ice sheets we have used such techniques to image the geomorphology of the sw barents sea but using a dense grid of 2d seismic covering a 240 000 2 km large study area supplemented with 3d seismic from selected areas the study area is located at the convergence of ice flow from the former fennoscandian barents sea and svalbard ice sheets the morphology of the major cross shelf troughs is characterized by elongated ridge groove features interpreted to be glacial bedforms produced by fast flowing grounded glaciers mega scale glacial lineations have been grouped into distinct flow sets related to three specific ice flow events these events document the last glacial maximum lgm and two readvances during deglaciation of specific interest is a detailed and well preserved set of seafloor imprints in the bjornoyrenna trough which acted as the main pathway for ice streams draining the surrounding ice sheets the geomorphic features indicate that bjornoyrenna hosted six separate ice stream lobes that diverged fan like at their margins but were not all active simultaneously an end moraine zone 68 km wide up to 85 m high and 300 km long filled the whole width of this major glacial trough as a result of high sediment flux within sub ice stream deformable beds the imprint of this ice stream system can be followed on our seabed images for 500 km however detailed geomorphologic elements demonstrate that these imprints reflect time transgressive behaviour and do not indicate the length or width of single ice streams the seismic derived seafloor geomorphology demonstrates that the barents sea ice behaved in a much more dynamic way during the last glaciation than previously assumed with major shifts between ice originating from the fennoscandian spitsbergen and barents sea ice sheets

ice front variation and tidewater behavior on helheim and kangerdlugssuaq glaciers greenland we used satellite images to examine the calving behavior of helheim and kangerdlugssuaq glaciers greenland from 2001 to 2006 a period in which they retreated and sped up these data show that many large iceberg calving episodes coincided with teleseismically detected glacial earthquakes suggesting that calving related processes are the source of the seismicity for each of several events for which we have observations the ice front calved back to a large pre existing rift these rifts form where the ice has thinned to near flotation as the ice front retreats down the back side of a bathymetric high which agrees well with earlier theoretical predictions in addition to the recent retreat in a period of higher temperatures analysis of several images shows that helheim retreated in the 20th century during a warmer period and then re advanced during a subsequent cooler period this apparent sensitivity to warming suggests that higher temperatures may promote an initial retreat off a bathymetric high that is then sustained by tidewater dynamics as the ice front retreats into deeper water the cycle of frontal advance and retreat in less than a century indicates that tidewater glaciers in greenland can advance rapidly greenland s larger reservoir of inland ice and conditions that favor the formation of ice shelves likely contribute to the rapid rates of advance

late quaternary architecture of trough mouth fans debris flows and suspended sediments on the norwegian margin abstract trough mouth fans are the main marine depocentres for glacier derived sediments in the polar north atlantic but their growth through the late quaternary is complex glacigenic debris flows gdfs are sourced from a common and homogeneous part of the upper fan and only develop as coherent individual flows after downslope transport their genesis and mode of deposition mean that gdfs are confined to particular areas of trough mouth fans accumulation of these subglacial sediments is controlled by a combination of margin glaciology and fan morphology although most of the fan sediment is deposited as gdfs during glacials considerable areas of trough mouth fans are dominated by sedimentation of suspension deposits associated with extensive meltwater release from a warm based ice sheet and probable contour current activity the depositional sequence of these two sediment types may be important in generating the long run out distances of gdfs which are initiated and sustained over low gradients furthermore emplacement of gdfs is interpreted to be a relatively low frequency event and temporally at least fans are not dominated by this mode of sediment emplacement whilst ice sheets are at the shelf break large scale trough mouth fan development is therefore asynchronous and non uniform a result of the interaction between glaciology morphology and oceanography

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

flow of the west antarctic ice sheet on the continental margin of the bellingshausen sea at the last glacial maximum geophysical data show that during the last glaciation the west antarctic ice sheet wais drained to the continental shelf edge of the bellingshausen sea through a cross shelf bathymetric trough belgica trough as a grounded fast flowing ice stream the drainage basin feeding this ice stream probably encompassed southwestern palmer land parts of southern alexander island and the bryan coast of ellsworth land with an area exceeding 200 000 km2 on the inner continental shelf streamlined bedrock and drumlins mapped by swath bathymetry show that the ice stream was fed by convergent ice flow draining from eltanin bay and bays to the east as well as by ice draining the southern part of the antarctic peninsula ice sheet through the ronne entrance the presence of a paleoice stream in belgica trough is indicated by megascale glacial lineations formed in soft till and a trough mouth fan on the continental margin grounding zone wedges on the inner and midshelf record ice marginal stillstands during deglaciation and imply a staggered pattern of ice sheet retreat these new data indicate an extensive wais at the last glacial maximum lgm on the bellingshausen sea continental margin which advanced to the shelf edge in conjunction with ice sheet reconstructions from the antarctic peninsula and pine island bay this implies a regionally extensive ice sheet configuration during the lgm along the antarctic peninsula bellingshausen sea and amundsen sea margins with fast flowing ice streams draining the wais and antarctic peninsula ice sheet to the continental shelf edge

submarine glacigenic debris flows deep sea channels and past ice stream behaviour of the east greenland continental margin abstract former glacigenic debris flow gdf and deep sea channel build up is shown from side scan sonar seismic and sediment core data of the passive continental margin of the greenland sea the well developed deep sea channel systems cross gdf systems and point towards sediment laden meltwater production there is no indication for large scale submarine sliding such as observed on several locations on the norwegian margin where deep sea channels are far less frequent or do not exist whereas seabed erosion gdf stacking and trough mouth fans dominate the observed pattern on the east greenland margin reflects a contrast to the norwegian margin in paleo ice stream extent dynamics and type of sediment delivery a conceptual model for ice sheet behaviour on the continental margin of the greenland sea has been developed based on the characteristics distribution and morphology of gdfs and deep sea channels in four periods at ca 2 5 ma 1 5 ma 0 2 ma and 25 ka we argue that the erosional capabilities of ice streams on the ne greenland margin indicated by aggradation versus progradation were less then those of the fast flowing ice streams of the norwegian margin and that the ice streams in cross shelf troughs remained probably distal from the shelf break during the late weichselian

the east greenland continental margin 65 n since the last deglaciation changes in seafloor properties and ocean circulation nine gravity cores collected on the east greenland continental margin off kangerdlugssuaq fjord reveal a drastic decrease in average sedimentation rates from the cross shelf through the continental slope from 43 2 cm kyrs to 2 2 cm kyrs respectively since the last deglaciation beginning at 2g cm2kyrs at 4000 yrs b p both caco3 and non caco3 accumulation rates became high g cm2kyrs since 3000 yrs b p these rates distinctly decreased melting of glaciers and current activity which drastically changed in space and time controlled the terrigenous sediment input and thus the grain size distribution and the physical properties of sediments across the shelf these observations suggest that current winnowing on sediments is one of the dominant processes at present this is seen in the acoustic reflectivity and in the acoustically hard seafloor particularly at the upper continental slope in addition icebergs transported southward along the continental margin have scoured the sediment surface in water depths 350m

extent and dynamics of the west antarctic ice sheet on the outer continental shelf of pine island bay during the last glaciation abstract swath bathymetry and topas sub bottom profiler acoustic data reveal the presence of a major cross shelf bathymetric trough containing streamlined subglacial bedforms formed in soft till that extends to the continental shelf edge of outer pine island bay amundsen sea west antarctica the new data indicate that the west antarctic ice sheet wais extended to the shelf edge of pine island bay during the last glaciation and was drained by a grounded fast flowing palaeo ice stream through this outer shelf trough topography and subglacial geology are likely to have exerted a strong control on the development and location of palaeo ice streams in pine island bay topas records show that mega scale glacial lineations are formed in an acoustically transparent sediment layer interpreted to be soft till and are inferred to be the product of subglacial sediment deformation beneath the palaeo ice stream the flat to irregular nature of the basal reflector of the acoustically transparent layer of soft till implies that a combination of groove ploughing of the substrate and subglacial sediment deformation were important processes beneath the palaeo ice stream in the outer trough of pine island bay as well as palaeo ice streams elsewhere in antarctica therefore the formation of the soft till layer and possibly associated subglacial bedforms are likely to be a function of these palaeo ice stream processes in a regional context the wais extended to the continental shelf edge of the bellingshausen amundsen and ross seas and was drained by a number of palaeo ice streams during the last glaciation

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

keel depths of modern antarctic icebergs and implications for sea floor scouring in the geological record abstract icebergs affect the geological record through the scouring or ploughing action of their keels reworking sediments where they contact the sea floor satellite radar altimeter measurements of the surface elevation of the marine margins of the antarctic ice sheet are inverted to produce ice thickness values these data are assumed to represent the keel depths of newly calved icebergs there are three peaks in the frequency distribution of antarctic iceberg keel depths a about 140 200 m in thickness associated with smaller ice shelves fringing antarctica e g wilkins george vi and brunt ice shelves b about 250 300 m from large ice shelves e g ross ronne amery and c approximately 500 600 m from fast flowing ice sheet outlet glaciers e g pine island and dibble glaciers together with the filchner ice shelf controls on iceberg keel depth are ice thickness at the grounding line creep thinning and the rate of melting freezing at the floating ice shelf base with distance to the calving margin the distribution of sea floor scours produced by iceberg grounding is dependent on the changing form and flow of the glaciers and ice sheets from which icebergs are derived and on berg drift tracks and melt rates sea floor evidence for icebergs with particularly deep keels has sometimes been interpreted to indicate the presence of extensive former ice shelves however the largest modern antarctic ice shelves do not produce large numbers of icebergs thicker than about 350 m implying that sea floor scours found in deeper water are unlikely to be an indicator of extensive past ice shelf development iceberg scours found at water depths in excess of about 500 m in the geological record are instead probably indicative of either a the former presence of fast flowing ice sheet outlet glaciers b ice shelves fed from major interior basins where lateral spreading is constrained topographically or c a pulse of large icebergs released during major deglaciation or ice sheet collapse

influence of melting icebergs on distribution characteristics and transport of marine particles in an east greenland fjord a detailed study of distribution of suspended sediments in an east greenland fjord with a high iceberg production rate reveals the existence of intermediate nepheloid layers inls observed inls extended from the head to the mouth of the fjord at water depths between 100 and 400 m particulate organic carbon and nitrogen chlorophyll a and nutrient measurements and observation by microscope and energy dispersive x ray analyses were used to characterize marine particles particles in the inls are composed of glacial flour including 50 m quartz and feldspar grains with angular and sharp edges considered to be released from melting icebergs in situ photographs show large aggregates 1 mm at high concentration 300 particles per liter in and below inls these aggregates in comparison with the dispersed particle size distribution demonstrate that smaller size particles e g clay settle effectively along with larger single size grains in kangerlugssuaq fjord the mass transport of marine particles was governed by the subsurface iceberg melting producing observed inls rather than the surface meltwater plume this suggests that the subsurface water temperature controls release of iceberg debris and the existence of warm subsurface water as well as the spread of cold and fresh water in the surface layer needs to be considered to evaluate the occurrence of ice rafted debris layers including heinrich layers this study provides the field evidence of a modern analogue on ocean conditions that could form iceberg rafted layers

seven million years of glaciation in greenland glacial till glaciomarine diamictites and ice rafted detritus found in marine cores collected off the shore of southeast greenland record multiple late cenozoic glaciations beginning in the late miocene distinct rock assemblages and seismic stratigraphic control correlate the diamictites with glaciation of the southeast greenland margin glaciers advanced to the sea during several intervals in the pliocene and pleistocene north atlantic glaciation may have nucleated in southern greenland rather than further north because of the high mountains and the high levels of precipitation in this region

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

cold tongue and warm pool enso events in cmip5 mean state and future projections abstractthe representation of the el nino southern oscillation enso under historical forcing and future projections is analyzed in 34 models from the coupled model intercomparison project phase 5 cmip5 most models realistically simulate the observed intensity and location of maximum sea surface temperature sst anomalies during enso events however there exist systematic biases in the westward extent of enso related sst anomalies driven by unrealistic westward displacement and enhancement of the equatorial wind stress in the western pacific almost all cmip5 models capture the observed asymmetry in magnitude between the warm and cold events i e el ninos are stronger than la ninas and between the two types of el ninos that is cold tongue ct el ninos are stronger than warm pool wp el ninos however most models fail to reproduce the asymmetry between the two types of la ninas with ct stronger than wp events which is opposite to observations most models capture the observed peak in enso

the origin of massive diamicton facies by iceberg rafting and scouring scoresby sund east greenland almost 90 of 39 m of core material recovered from scoresby sund and the adjacent east greenland shelf is massive diamicton interpreted to be formed predominantly by the release of iceberg rafted debris and reworking by iceberg scouring there is also likely to be a contribution from suspension settling of fines derived from glaciofluvial sources model calculations suggest that the 14c derived holocene sedimentation rate of 0 1 0 3 m 1000 yr 1 in scoresby sund can be accounted for mainly by iceberg rafting of debris a further 4 of core material is of gravel or coarse sand lenses interpreted to reflect iceberg dumping of debris intensive iceberg scouring which reworks sea floor sediments is observed on acoustic records from over 30 000 km2 of the scoresby sund fiord system and the adjacent east greenland shelf 69 72 n and 75 n the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg rafting and scouring may be important over a significant proportion of the 500 000 km2 area above the shelf break the relatively extensive modern occurrence of massive diamicton formed by iceberg rafting and scouring together with suspension settling of fines suggests that it may also be a significant facies in the glacier influenced geological record the recognition in the geological record of the massive diamicton facies described above may also indicate the former presence of fast flowing ice sheet outlet glaciers

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

history of a stable ice margin east greenland during the middle and upper pleistocene abstract the east greenland record of glaciation and environmental change is based on a combination of onshore and offshore studies glaciological work on contemporary outlet glaciers provides background for interpreting the glaciation styles of the past the scoresby sund fjord system the single largest outlet of the inland ice in east greenland and the adjacent continental shelf and slope were the main working areas the regionality of these results was tested with onshore and offshore work on sites further to the north in the east greenland fjord zone the record spans the period since isotope stage 7 ca 240 ka the most extensive glaciation phases were the lollandselv and scoresby sund glaciations isotope stages 7 and 6 the langelandselv interglaciation isotope substage 5e comprises shallow marine sediments at more than 20 sites onshore and cibicides wuellerstorfii carrying sediments on the continental slope summer temperatures were 2 3 warmer than the holocene optimum and there was vigorous advection of warm atlantic water into the fjords the warm period seems to be accompanied by a eustatic sea level rise of ca 20 m during the weichselian there were three major glacier advances the aucellaelv jyllandselv and flakkerhuk stades isotope substages 5d 5b and stages 3 2 all three advances mark a shift from one topographically determined stable position to another in each phase the glaciers occupied almost the same space in the fjord basins and had their fronts on the inner shelf but the glacial regime and duration was different the aucellaelv stade lasted ca 10 ka and the regime resembled that of present day outlet glaciers 600 km further to the north the flakkerhuk stade lasted for ca 50 ka but left only thin and sporadic till as well as glaciolacustrine sediments in ice dammed river valleys the regime was polar similar to present day glaciers in antarctica its culmination the last glacial maximum in the period between 22 and 14 ka is shown by a maximum in ird deposition on the continental slope after 12 ka and before 10 ka the outer fjord basins in the southern fjord zone had been abandoned by the glaciers and at ca 9 5 ka the last resurgence the milne land stade had ended

the sizes frequencies and freeboards of east greenland icebergs observed using ship radar and sextant the scoresby sund fjord system east greenland contains the most productive fast flowing outlet glaciers draining east from the greenland ice sheet calving 18 km3 a 1 of icebergs the sizes frequencies and freeboards of 1900 icebergs were measured from f s polarstern using ship x band radar and sextant radar beam spreading exaggerates iceberg width by 60 m per nautical mile of range beyond the first mile data sets on iceberg size e g that collated for antarctic icebergs collected using ship radars which do not take this effect into account will overestimate iceberg dimensions significantly the location and concentration of icebergs within the fjord complex can be explained by 1 the locations of the principal source glaciers and 2 fjord topography and bathymetry iceberg concentration maximum 0 6 icebergs km 2 declines with distance from the major iceberg sources we found that 69 of icebergs within the fjord system are 1 km in length the largest is 2 7 km long icebergs become spread more evenly over the range of size classes in the outer fjord and shelf modal iceberg keel depth calculated from freeboard measurements is 4 500 m in the inner fjords shifting to lower values in the outer fjords reflecting shallower bathymetry radar measurements of iceberg width cannot be used to infer keel depths accurately because width and keel depth are only weakly correlated comparison between freeboards and keel depths for icebergs from east greenland and the barents sea indicates that the iceberg source i e floating or grounded exerts a fundamental control on iceberg dimensions the drift pattern of icebergs is from the head to the mouth of the fjord system although fjord bifurcations bathymetry and currents provide additional complications the trends in observed iceberg size and frequency and in inferred keel depth in the scoresby sund region are likely to be applicable to other fjords and shelves around greenland

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

iceberg scouring in scoresby sund and on the east greenland continental shelf modern and relict scours produced by iceberg keels have been reported from a number of high latitude continental shelves in the northern hemisphere and antarctica but observations are largely absent from the east greenland shelf about 18 km3 yr 1 of icebergs are calved into the scoresby sund fjord system east greenland these icebergs have submarine keels with drafts up to 550 m modern iceberg contacts with the sea floor are inferred from calculated keel depths and stationary icebergs identified on sequential landsat imagery acoustic profiles parasound 3 5 khz of the sea floor show that scouring is a significant process in water depths 550 m iceberg scouring intensity varies inversely with water depth the most intense scouring occurs at depths of 300 400 m iceberg scours were observed on over 25 000 km2 of the east greenland shelf at 69 72 n and 75 n scours are being actively produced on the modern shelf but relict scours probably dating back to the late weichselian are also present the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg scouring is important over a significant proportion of the 500 000 km2 area above the shelf break around greenland

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

mapping tide water glacier dynamics in east greenland using landsat data landsat multispectral scanner and thematic mapper images were co registered for the kangerdlugssuaq fjord region in east greenland and were used to map glacier drainage basin areas changes in the positions of tide water glacier termini and to estimate surface velocities of the larger tide water glaciers statistics were compiled to document distance and area changes to glacier termini the methodologies developed in this study are broadly applicable to the investigation of tide water glaciers in other areas the number of images available for consecutive years and the accuracy with which images are co registered are key factors that influence the degree to which regional glacier dynamics can be characterized using remotely sensed data three domains of glacier state were interpreted net increase in terminus area in the southern part of the study area net loss of terminus area for glaciers in upper kangerdlugssuaq fjord and a slight loss of glacier terminus area northward from ryberg fjord local increases in the concentrations of drifting icebergs in the fjords coincide with the observed extension of glacier termini positions ice surface velocity estimates were derived for several glaciers using automated image cross correlation techniques the velocity determined for kangerdlugssuaq gletscher is approximately 5 0 km a 1 and that for kong christian iv gletscher is 0 9 km a 1 the continuous presence of icebergs and brash ice in front of these glaciers indicates sustained rates of ice front calving

stratigraphic architecture of upper jurassic oxfordian reefs in the northeastern gulf coast u s and the eastern paris basin france abstract the late jurassic was a major period of reef expansion many jurassic reefs are potential hydrocarbon reservoirs but their stratigraphic distribution has been difficult to predict examination of the stratigraphic architecture of oxfordian reefs in the northeast u s gulf coast and the eastern paris basin france affords a comparison of mixed coral algal sponge reefs versus microbial dominated reefs the smackover formation in the northeastern gulf coast contains microbial dominated reefs the smackover represents deposition during a major transgression and reefs occur within late transgressive system tract tst deposits reefs of mixed coral algae and sponges characterize the oxfordian of the eastern paris basin in the ardennes lorraine reefs appear after the maximum flooding event of a stratigraphic sequence and are maintained through the highstand systems tract hst deposition and into the overlying stratigraphic sequence in burgundy reefs occur in association with the maximum flooding event of the upper stratigraphic sequence dominated by platy microsolenids reef growth begins in the tst this interval is traditionally called the lower reef complex more diverse reef growth the upper reef complex continues above the maximum flooding event through the early hst reef growth ceases by deposition of the late hst with the introduction of grainstones and other high energy lithologies all reefs in this examination regardless of biota are associated with maximum flooding events the sequence stratigraphy of the oxfordian reefs in france and the gulf coast provides a framework for studying jurassic reefs of both mixed and microbial dominated assemblages

quaternary seismic stratigraphy of the north sea fan glacially fed gravity flow aprons hemipelagic sediments and large submarine slides abstract approximately 1000 km of high resolution sleeve gun array transects on the north sea fan located at the mouth of the norwegian channel reveal three dominant styles of sedimentation within a thick 900 m quaternary sediment wedge comprising numerous sequences these are interpreted as terrigenous hemipelagic sedimentation large scale translational slides and aprons of glaciogenic debris flow deposits contributing to considerable fan construction four large buried translational slides involved sediment volumes upwards of 3000 km 3 each and preceded the similarly dimensioned first storegga slide on the ne fan flank several thick 100 m terrigenous hemipelagic deposits apparently represent long lived 150 200 kyr periods of sedimentation whose distribution indicates fan input via the norwegian channel the upper sequences are each made upper sequences are each made up of one or several thick 100 m aprons comprising stacked lensoid and or lobate forms which range from 2 to 40 km in width and 15 to 60 m in thickness they characterize debris flows attributed to periodic input from several phases of a norwegian channel ice stream reaching the shelf edge subsidence in the outer norwegian channel allowed preservation of several glaciation cycles represented by sheet erosion bounded tills and progradational units much of the shelf slope transition has been preserved allowing a preliminary chronology of the fan sequences through correlation with borehole sediments in the norwegian channel debris flows which signal the initial shelf edge glaciation are not recognized from the initial glaciation in the channel 1 1 myr but are associated with a middle pleistocene and all following glacial erosion surfaces ges in the outer norwegian channel this was followed by six further sequences probably totalling over 13 000 km 3 of sediment at least four of these were shelf edge ice maximum events the last of which was late weichselian age 14 c ams considering earlier glaciation related hemipelagic sedimentation material since removed by the large slides and extensive unmapped areas total quaternary fan sedimentation was in the vicinity of 20 000 km 3

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

bottom current controlled sedimentation a synthesis of the contourite problem abstract an overview of the main items concerning deep bottom current controlled deposits is presented these include the definition of contourites their processes of deposition and facies characteristics contourite drift types and seismic patterns the interplay of turbidity and bottom current processes and the correlation between bottom current processes and global changes in climate sea level from this discussion several of the more significant problems are highlighted which we believe should be priority targets for future research 1 identification of contourites especially in ancient series where they are interbedded with turbidites and other facies 2 refinement of the numerous parameters used as tracers of palaeocirculation patterns 3 understanding the interaction between the different types of bottom currents and also between bottom current and other deep water processes 4 distinction in the sedimentary record between the effects of short time scale bottom current variations due to regional causes like benthic storms and geological scale current fluctuations related to climatic or astronomic control 5 understanding the control of glacial interglacial climatic cycles on the nature and rate of contourite deposition