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

morphological evidence for marine ice stream shutdown central barents sea abstract marine based ice streams are responsible for a significant proportion of the ice mass loss from the present day greenland ice sheet east antarctic ice sheet eais and west antarctic ice sheet wais but the processes controlling their initiation evolution and shutdown remain elusive hindering our understanding of how existing ice masses will respond to predicted future warming the exposed beds of palaeo ice streams offer a unique opportunity to study subglacial processes which are largely inaccessible in contemporary settings we use high resolution multibeam swath bathymetry data from the barents sea to map the geomorphology of a palaeo ice stream bed located in olgastretet olga trough approximately 75 km southeast of kong karls land and 200 km east of central svalbard this reveals evidence for shut down of a marine based ice stream followed by a phase of passive retreat or lift off of the ice stream facilitating preservation of crevasse squeeze ridges csrs subsequently active retreat of the ice margin was re established and is marked by recessional moraine ridges located upstream of the csrs previously csrs have been mainly associated with surging land terminating ice margins however our work adds to recent observations of csrs on the beds of marine based ice streams implying that they may be more common than previously thought it also indicates that marine based ice streams may switch on and off in a surge like manner which has important implications for our understanding of ice stream life cycles and the modelling of ice sheets

earthquake induced sediment failures on a 0 25 slope klamath river delta california on november 8 1980 a major earthquake magnitude 6 5 to 7 2 occurred 60 km off the coast of northern california a survey of the area using high resolution seismic reflection and side scan sonar equipment revealed the presence of extensive sediment failure and flows in a zone about 1 km wide and 20 km long that trends parallel to the shelf on the very gently sloping c and a prominent 1 to 2 m high seaward facing toe scarp on the outer margin of the terrace this toe scarp is sinuous appears to be nearly continuous for a distance of 20 km and closely parallels the 60 m isobath evidence indicates that the toe scarp is the terminus of lateral spreads and lobes of sediment flows side scan sonar records show evidence of gas vents and small 10 3 0 5 m high pressure ridges formed seaward of and parallel to the sediment flow scarp indicators of liquefaction sand boils and collapse craters are present on the sediment flow terrace extensive sediment failure occurred on a sea floor slope of less than 0 25 and we can unequivocally pinpoint the cause as an earthquake of known location magnitude and time

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

the physiography of high arctic cross shelf troughs abstract a comprehensive inventory of high arctic cross shelf troughs is compiled from international bathymetric chart of the arctic ocean ibcao bathymetric data v 3 0 the location of 75 cross shelf troughs is presented alongside a synthesis of their key physiographic characteristics and available glacial geological evidence the troughs are interpreted to have been occupied intermittently and eroded by marine terminating ice streams that traversed the shelf during at least one and often many quaternary full glacial periods considerable variation in cross shelf trough physiography exists in the high arctic trough lengths range between 35 and 1400 km widths from 12 to 260 km and maximum depths from 200 to 1000 m the longest cross shelf troughs extend through inter island channels on the beaufort sea queen elizabeth islands and barents kara sea margins the gradient of the upper slope beyond high arctic glacial troughs which ranges between 0 3 and 13 is shown to have a negative relationship with palaeo ice stream drainage basin area and trough length glacial sedimentary depocentres or trough mouth fans tmfs are inferred on the basis of bathymetric and where available seismic evidence to exist beyond the majority of high arctic cross shelf troughs evidence of shelf progradation or tmf development is absent from the slope beyond several high arctic troughs probably as a result of limited sediment supply to the margin and or sediment by passing of the upper slope on the south greenland continental margin it is likely that steep slopes prevented the development of significant glacial sedimentary depocentres beyond cross shelf troughs or that glacigenic debris has been removed from the upper slope by submarine slope failure

geophysical constraints on the dynamics and retreat of the barents sea ice sheet as a paleobenchmark for models of marine ice sheet deglaciation our understanding of processes relating to the retreat of marine based ice sheets such as the west antarctic ice sheet and tidewater terminating glaciers in greenland today is still limited in particular the role of ice stream instabilities and oceanographic dynamics in driving their collapse are poorly constrained beyond observational timescales over numerous glaciations during the quaternary a marine based ice sheet has waxed and waned over the barents sea continental shelf characterized by a number of ice streams that extended to the shelf edge and subsequently collapsed during periods of climate and ocean warming increasing availability of offshore and onshore geophysical data over the last decade has significantly enhanced our knowledge of the pattern and timing of retreat of this barents sea ice sheet bsis particularly so from its late weichselian maximum extent we present a review of existing geophysical constraints that detail the dynamic evolution of the bsis through the last glacial cycle providing numerical modelers and geophysical workers with a benchmark data set with which to tune ice sheet reconstructions and explore ice sheet sensitivities and drivers of dynamic behavior although constraining data are generally spatially sporadic across the barents and kara seas behaviors such as ice sheet thinning major ice divide migration asynchronous and rapid flow switching and ice stream collapses are all evident further investigation into the drivers and mechanisms of such dynamics within this unique paleo analogue is seen as a key priority for advancing our understanding of marine based ice sheet deglaciations both in the deep past and in the short term future

basal processes beneath an arctic glacier and their geomorphic imprint after a surge elisebreen svalbard the foreground of elisebreen a retreating valley glacier in west svalbard exhibits a well preserved assemblage of subglacial landforms including ice flow parallel ridges flutings ice flow oblique ridges crevasse fill features and meandering ridges infill of basal meltwater conduits other landforms are thrust block moraine hummocky terrain and drumlinoid hills we argue in agreement with geomorphological models that this landform assemblage was generated by ice flow instability possibly a surge which took place in the past when the ice was thicker and the bed warmer the surge likely occurred due to elevated pore water pressure in a thin layer of thawed and water saturated till that separated glacier ice from a frozen substratum termination may have been caused by a combination of water drainage and loss of lubricating sediment sedimentological investigations indicate that key landforms may be formed by weak till oozing into basal cavities and crevasses opening in response to accelerated ice flow and into water conduits abandoned during rearrangement of the basal water system today elisebreen may no longer have surge potential due to its diminished size the ability to identify ice flow instability from geomorphological criteria is important in deglaciated terrain as well as in regions where ice dynamics are adapting to climate change

size shape and spatial arrangement of mega scale glacial lineations from a large and diverse dataset mega scale glacial lineations msgls are a characteristic landform on ice stream beds solving the puzzle of their formation is key to understanding how ice interacts with its bed and how this in turn influences the dynamics of ice streams however a comprehensive and detailed characterization of this landform s size shape and spatial arrangement which might serve to test and refine formational theories is largely lacking this paper presents a detailed morphometric analysis and comparison of 4043 msgls from eight palaeo ice stream settings three offshore norway and antarctica four onshore canada and one from under a modern ice stream in west antarctica the length of msgls is lower than previously suggested mode 1000 2000 m median 2892 m and they initiate and terminate at various locations on an ice stream bed their spatial arrangement reveals a pattern that is characterized by an exceptional parallel conformity 80 of all mapped msgls have an azimuth within 5 from the mean values and a fairly constant lateral spacing mode 200 300 m median 330 m which we interpret as an indication that msgls are a spatially self organized phenomenon results show that size shape and spatial arrangement of msgls are consistent both within and also generally between different ice stream beds we suggest this results from a common mechanism of formation which is largely insensitive to local factors although the elongation of msgls mode 6 8 median 12 2 is typically higher than features described as drumlins these values and those of their width mode 100 200 m median 268 m overlap which suggests the two landforms are part of a morphological continuum and may share a similar origin we compare their morphometry with explicit predictions made by the groove ploughing and rilling instability theories of msgl formation although the latter was most compatible neither is fully supported by observations 2014 the authors earth surface processes and landforms published by john wiley sons ltd

flow thermal structure and subglacial conditions of a surge type glacier temperature measurements in a subpolar surge type glacier reveal a distinctive thermal structure associated with the boundary between the ice reservoir and receiving areas in the receiving area the glacier is cold based but bottom temperature has increased as much as 0 5 c between 1981 and 1982 and the basal heat flux is roughly 10 times the expected geothermal flux water percolation through permeable subglacial material is the probable energy source deformation of the substrate could destroy this drainage system and trigger a surge

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

crustal and upper mantle structure beneath the corinth rift greece from a teleseismic tomography study we report here the results of a tomographic lithospheric study in the area of the corinth and evvia rifts greece designed to constrain the mechanism of continental extension sixty seismological stations were deployed in the area for a period of 6 months and 177 teleseismic events were recorded by more than five stations and gave more than 2000 travel time residuals p and pkp phases which were inverted to image the velocity structure down to 200 km depth we use both a linear and a nonlinear method to invert the data set the main result is a long wavelength positive velocity anomaly located in the upper mantle which is interpreted as the subducted african lithosphere the subducted lithosphere is well defined from 7o km depth down to 200 km from synthetic tests as well as from the amplitude of the anomaly more than 7 we conclude that the subduction continues below 200 km in addition a second positive velocity anomaly of about 4 from the surface down to 40 km depth located north of the gulf of corinth has been found this is interpreted as the result of a crustal thinning of several kilometers 5 km shifted to the north from the gulf of corinth and trending obliquily nw se we suggest that this crustal thinning is mainly related to the miocene widespread extension in the aegean and that the quaternary corinth rift initiated where the crust was already thinned the different styles of deformation of the eastern and western part of the rift are consistent with this interpretation no clear velocity anomaly can be related to the evvia rift

palaeo ice stream pathways and retreat style in the easternmost amundsen sea embayment west antarctica revealed by combined multibeam bathymetric and seismic data multibeam swath bathymetry data sets collected over the past two decades have been compiled to identify palaeo ice stream pathways in the easternmost amundsen sea embayment we mapped 3000 glacial landforms to reconstruct ice flow in the 250 km long cross shelf abbot trough this bathymetric feature was occupied by a large ice stream which was fed by two tributaries cosgrove and abbot and reached the continental shelf edge during the last maximum ice sheet advance geomorphological mapping has enabled a clear differentiation between subglacial landforms indicating warm e g megascale glacial lineations and cold based e g hill hole pairs ice conditions on the continental shelf during the last glaciation grounding zone wedges and recessional moraines mapped within the palaeo ice stream troughs and on adjacent sea floor highs referred to as inter ice stream ridges indicate grounding line stillstands or re advances of the west antarctic ice sheet during the last deglaciation of the shelf we observe that the locations of grounding zone wedges coincide with trough constrictions as well as local topographic highs of harder substrate this combination of trough bottlenecks and local pinning points on an otherwise retrograde slope is likely to have modified the pace of grounding line retreat causing the grounding zone to pause and deposit grounding zone wedges the episodic retreat recorded within abbot trough corresponds to post glacial episodic retreat interpreted for the neighbouring pine island thwaites palaeo ice stream trough thus suggesting a uniform pattern of retreat across the eastern amundsen sea embayment locally indications are strong that a change in basal thermal regime of the ice from warm to cold based conditions occurred prior to final retreat as hill hole pairs overprint megascale glacial lineations further the correlation of grounding zone wedges with geological boundaries emphasises the influence of subglacial geology on ice stream flow our new geomorphological map of the easternmost amundsen sea embayment resolves the pathways of palaeo ice streams that were probably all active during the last maximum extent of the ice sheet and the extent of adjacent inter ice stream ridges it reveals information about the style of and the basal thermal regime during the subsequent grounding line retreat such information provides an important empirical framework by which the accuracy of ice sheet models can be gauged

ice stream retreat dynamics inferred from an assemblage of landforms in the northern barents sea abstract palaeo records of rapid ice stream retreat are important as they can be used to identify the processes involved and inform investigations of present day ice masses here we document a previously unknown retreat stage in northernmost bjornoyrenna bear island trough in the northern barents sea representing the youngest stage in a stepwise retreat of the bjornoyrenna ice stream we present a descriptive landsystem model for retreat of a marine based ice stream which provides new insights into the glacial dynamics of the episodic retreat stages this model captures the landforms produced during a cycle of 1 fast ice stream flow 2 intense calving of large icebergs locked in a dense matrix of smaller icebergs probably from a collapsed ice shelf 3 ice stream stagnation 4 ice stream floating off forming an ice shelf as the grounding line retreats and eventually 5 ice shelf disintegration we hypothesize that the presented ice stream retreat model reflects glacial surging the formation of corrugated furrows in the study area is consistent with interpretation of similar features in pine island bay west antarctica which are interpreted to have been formed during a massive ice shelf break up and associated grounding line retreat two directions of past ice flow are indicated from streamlined glacial landforms in the study area ice flow from north north east is indicated for the last glacial maximum and an early phase of deglaciation whereas a shift to flow from north north west from an ice dome located over hinlopenstretet svalbard is indicated for the latest deglaciation phases of the bjornoyrenna ice stream

kamb ice stream flow history and surge potential a basal zone tens of meters thick of debris laden ice was observed in kamb ice stream west antarctica using a video camera lowered into boreholes made by hot water drilling the debris content varies sometimes abruptly forming a sequence of layers that reflect the complex history of fast ice flow and bed interaction in most parts the concentration of debris is low a few percent by weight with particles often mud clots dispersed in a matrix of clear ice the nature of the debris distribution can be interpreted in terms of specific time intervals in the history of fast motion of kamb ice stream including processes leading up to the termination of its streaming behavior and possible reactivation

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

continued slowing of the ross ice shelf and thickening of west antarctic ice streams as part of the ross ice shelf geophysical and glaciological survey riggs ice velocities were measured on the ross ice shelf ris during 1973 78 comparisons of these with velocity estimates at the same locations derived from radarsat synthetic aperture radar sar measurements in 1997 and 2009 show velocity reduction in the southeast quadrant of the ice shelf by almost 200 m a 1 with deceleration rates increasing with time large areas of ice shelf in this region are lightly grounded forming an ice plain that increases local buttressing of the ice streams icesat measurements show this ice plain to be thickening the observed decrease in ice shelf velocities implies a total reduction in the mass of ice flowing into the ris from the west antarctic ice sheet wais by 23 gt a 1 shifting the mass balance of the wais drainage basin from strongly negative in the 1970s to strongly positive in 2009 the resulting decrease in ice advection should lead to ice shelf thinning further seaward of the ice plain this thinning would reduce the lateral drag and back stress of the shelf ice further contributing to thinning through an increase in spreading rate icesat measurements show recent thinning of most of the freely floating ice shelf

arctic ocean glacial history while there are numerous hypotheses concerning glacial interglacial environmental and climatic regime shifts in the arctic ocean a holistic view on the northern hemisphere s late quaternary ice sh

aligned glaciotectonic rafts on the central barents sea seafloor revealing extensive glacitectonic erosion during the last deglaciation 1 erosion rates on glaciated continental shelves are remarkably high especially within ice stream troughs although glaciotectonic erosion may have considerably contributed to enhanced glacial erosion of these landscapes entrainment mechanisms of glaciotectonically emplaced megablocks and rafts remain little understood here we report a northeast southwest trending chain of over 1300 glacial rafts observed on the seafloor in bjornoyrenna a paleo ice stream trough with particularly high erosion rates the landform assemblage adjacent to the glacial rafts includes streamlined bedforms and crevasse squeeze ridges and may represent a lateral shear zone where a paleo ice stream met cold stagnant ice during the last deglaciation individual glacial rafts along the chain are up to 30 m high tend to be elongated with lengths and widths on the order of tens of meters and are oriented from northeast southwest to north south the north southern rearrangement of rafts may reflect a compressional strain regime along the ice stream margin

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