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

postglacial emergence and distribution of late weichselian ice sheet loads in the northern barents and kara seas russia reconstructions of late weichselian glacier coverage on the continental shelves of the russian arctic range from a large ice sheet terminating in northern siberia to isolated ice caps restricted to arctic archipelagos this disparity in glacier reconstructions reflects the lack of chronological control on glacial and deglacial landforms we present new holocene relative sea level data from franz josef land and northern novaya zemlya russia that place the thickest glacier loads in the northern barents sea and not over novaya zemlya radiocarbon ages from shelf and terrestrial areas at the former ice sheet margin support deglaciation of the northern barents sea between 13 0 and 10 3 ka considerably later than inferred from isotopic records for the arctic ocean this analysis indicates that the barents sea ice sheet was a dominant sea level reservoir in northern eurasia and that glacier loading of novaya zemlya was comparatively limited during the last glaciation

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

size and shape characteristics of drumlins derived from a large sample and associated scaling laws abstract ice sheets flowing across a sedimentary bed usually produce a landscape of blister like landforms streamlined in the direction of the ice flow and with each bump of the order of 102 to 103 m in length and 101 m in relief such landforms known as drumlins have mystified investigators for over a hundred years a satisfactory explanation for their formation and thus an appreciation of their glaciological significance has remained elusive a recent advance has been in numerical modelling of the land forming process in anticipation of future modelling endeavours this paper is motivated by the requirement for robust data on drumlin size and shape for model testing from a systematic programme of drumlin mapping from digital elevation models and satellite images of britain and ireland we used a geographic information system to compile a range of statistics on length l width w and elongation ratio e where e l w for a large sample mean l is found to be 629 m n 58 983 mean w is 209 m and mean e is 2 9 n 37 043 most drumlins are between 250 and 1000 metres in length between 120 and 300 metres in width and between 1 7 and 4 1 times as long as they are wide analysis of such data and plots of drumlin width against length reveals some new insights all frequency distributions are unimodal from which we infer that the geomorphological label of drumlin is fair in that this is a true single population of landforms rather than an amalgam of different landform types drumlin size shows a clear minimum bound of around 100 m horizontal maybe drumlins are generated at many scales and this is the minimum or this value may be an indication of the fundamental scale of bump generation proto drumlins prior to them growing and elongating a relationship between drumlin width and length is found with r2 0 48 and that is approximately w 7 l 1 2 when measured in metres a surprising and sharply defined line bounds the data cloud plotted in e w l space and records a scale dependent maximum elongation limit approximated by emax l1 3 when l measured in metres for a given length for some reason as yet unknown drumlins do not exceed the elongation ratio defined by this scaling law we also report and compare our statistics to an amalgamated sample 25 907 drumlins of measures derived from around 50 published investigations any theory must be able to explain the drumlin statistics and fundamental scaling properties reported herein and they thus provide powerful tests for drumlin modelling

glacial geomorphic features in the northern barents sea direct evidence for grounded ice and implications for the pattern of deglaciation and late glacial sedimentation

relationship between mega scale glacial lineations and iceberg ploughmarks on the bjornoyrenna palaeo ice stream bed barents sea abstract mega scale glacial lineations msgls are ridge groove corrugations aligned in the direction of the former ice flow tens of kilometers long and up to a few hundred meters wide they are the most striking subglacial features on the beds of former ice streams and play an important role in modulating ice flow through their influence on bed roughness and subglacial hydrology despite the importance of msgls their formation remains enigmatic most studies have tended to focus on assemblages of msgls and their relationship to other landforms up ice e g drumlins or bedrock features in ice stream onset zones but fewer studies have examined their characteristics and transition to other landforms towards ice stream grounding lines in this paper we investigate the relationship between an assemblage of msgls and ploughmarks on the bed of the former bjornoyrenna ice stream in the sw barents sea which occurs in the central part of the ice stream bed a sample of msgls is used to test their potential origin based on their metrics width length and diagnostic characteristics predicted by formation theories results show a down flow depth decrease of the msgl grooves and a shallowing tendency once they transition into ploughmarks their width shows an increasing tendency which we link mostly to the strong divergence of the trough and ice flow downstream the prominent continuity from linear to curvilinear features demonstrates that the grooves associated with msgls transition into iceberg ploughmarks this observation is consistent with the hypothesis that the msgls have formed through a mechanism of groove ploughing at least in part the continuity from msgls to iceberg ploughmarks resulted from detachment of large icebergs from the grounded ice wall or grounded ice shelf and their ploughing away from the ice margin

ice stream dynamics of the sw barents sea revealed by high resolution 3d seismic imaging of glacial deposits in the hoop area abstract recent developments in seismic acquisition systems and seismic data visualization have contributed to improve the imaging of seismic geomorphologies over a broad range of topics this study focuses on a new high resolution p cable 3d seismic cube located in the hoop area in the sw barents sea the scientific motivations of the study are 1 to document glacial landforms on a meter scale 2 to study the link of these landforms with the subsurface and 3 to understand ice stream dynamics by detailed interpretation of main horizons including the seabed intra glacial horizons and upper regional unconformity uru the horizons are assessed using the concept of seismic geomorphology and compared with interpretations derived from conventional 3d seismic and state of the art multibeam echosounder technologies to discuss the benefits and limitations of the different geophysical technologies a well defined intra glacial seismic reflection is imaged in the eastern part of the p cable cube this reflection has an overall ne trending ridge shaped morphology which is up to 50 m high and 5 10 km wide and interpreted as a shear margin moraine the top of the moraine displays well defined iceberg ploughmarks and clear slope failure events along its eastern flank the seabed geomorphology which has been directly shaped by glacial processes related to multiple phases of ice streaming appears to be influenced by the buried shear margin moraine mega scale glacial lineations msgls indicative of fast flowing ice streams characterize the seabed west of the moraine infilled msgls and different sets of iceberg ploughmarks with large berms dominate the seabed geomorphology above the moraine the seabed east of the moraine characterized by a smooth morphology and few pockmarks is inferred to reflect more slowly moving ice not resolved by other geophysical techniques seismic attribute maps of p cable 3d allowed the identification of smaller ploughmarks and corrugated ridges related to paleo tides eroded by the larger iceberg ploughmarks these small ploughmarks are suggested to be linked to an earlier rapid disintegration of the barents sea ice stream the new high resolution 3d seismic data have led to the development of a revised ice stream model of the barents sea linking the glacial deposits to different ice stream events

the case against vast glaciation in valles marineris mars abstract the valles marineris of mars form the largest system of interconnected canyons in the solar system where morphological mineralogical and structural evidence of widespread glaciation has been recently reported however neither precipitation models nor global water budgets can account for such a colossal fill and the hypothesis has thus far remained unchallenged by additional scrutiny here we present the first thorough case against a valles marineris glaciation by describing new evidence that precludes the existence of a glacier most crucially we review high resolution imaging science experiment hirise images of chaos terrain in candor chasma previously interpreted as remnant glacial ice and identify layered boulder rich scarps bearing no similarity to scarps of massive ice in promethei terra or the north polar layered deposits we also find no significant differences in the structure morphology and composition of chaos terrain in candor and the chryse planitia region which suggests candor s chaos like chryse s is fractured highland terrain we also review several other key supports for the glacial hypothesis including the coincidence of an apparent glacial trimline with the water bearing mineral jarosite and the apparent presence of glacial features including kettle holes and sandur plains these too are found to have more plausible explanations with non glacial origins including tectonic reorganisation groundwater sapping and chaotic fracturing we conclude that the valles marineris glacial hypothesis is inconsistent with both observed morphology and our understanding of the ancient martian climate and we find no evidence to support its existence

deep draft icebergs from the barents ice sheet during mis 6 are consistent with erosional evidence from the lomonosov ridge central arctic 1 iceberg scour marks on the lomonosov ridge in the central arctic imply that bergs with drafts exceeding 850 m once existed in the arctic whereas similar erosion patterns observed on the yermak plateau suggest that some of these deep keeled icebergs exited the arctic through the fram strait into the nordic seas an intermediate complexity climate model with a dynamic and thermodynamic iceberg model is used to simulate the collapse of the barents ice sheet during mis 6 with the purpose of investigating if deep draft mega icebergs can reach and ground on the lomonosov ridge a number of simulations with different iceberg sizes show that deep draft bergs seeded from near the franz victoria trough could indeed have reached the ridge whereas other bergs crossed the yermak plateau and exited through the fram strait the draft of the bergs mainly determines the trajectory with only minor influence from the mass and length and width of the bergs this work is consistent with previous speculation that these icebergs originated from the disintegration of the barents ice sheet during marine isotope stage 6 mis 6 140 ka bp but suggests their origin was more likely to be from the western rather than eastern major ice stream of that ice sheet the long term impact on the overturning circulation from melting icebergs is more severe than that from a freshwater pulse of equivalent magnitude and a correct representation of icebergs in paleoclimate models is therefore of importance

deglaciation of the central barents sea abstract the marine based barents sea ice sheet covered the polar continental shelf north of norway and western russia during the last glacial maximum initial ice sheet retreat along the western margin is well established while the retreat pattern in the interior parts of the ice sheet remains poorly known here we present new geological data from the central barents sea the results are based on analysis of several marine geophysical datasets including geomorphological mapping of multibeam swath bathymetry data and analysis of seismic and acoustic stratigraphy the new results provide insights into the configuration and dynamics of the ice sheet during its retreat across the central barents sea in particular they show clear changes in the location of the main ice divides and domes with ice flow becoming gradually more topographically controlled as deglaciation progressed major troughs were characterised by episodic retreat and reoccurring cycles of fast and slow ice flow sometimes leading to stagnation and ice shelf formation meanwhile adjacent bank areas were covered by comparatively slowly retreating ice although evidence of streaming ice is also seen locally

submarine landforms and the behavior of a surging ice cap since the last glacial maximum the open marine setting of eastern austfonna svalbard abstract multi beam swath bathymetry data and topographic parametric sonar topas 3 5 khz sub bottom acoustic profiles were acquired from the inlet of hartogbutka an open marine setting offshore of austfonna northeastern nordaustlandet svalbard the largest ice cap in the eurasian arctic using these marine geophysical data the seafloor morphological and sedimentary evidence of former ice extent and dynamics of the three drainage basins basins 3 4 and 5 adjacent to hartogbukta were examined submarine landforms and landform assemblages that provide evidence of past ice dynamics are described and interpreted in the context of previous studies of surge affected submarine environments elsewhere in svalbard a sequence of four distinct ice flow episodes in hartogbukta from the late weichselian deglaciation to the present is identified to explain the morphological evolution of the seafloor a full glacial ice sheet extended over hartogbukta during the late weichselian flowing ese at intervals throughout the holocene the drainage basins adjacent to hartogbukta probably underwent repeated surges most recently basins 3 and 4 probably surged as one cohesive ice mass in the late 1800s and basin 5 most likely underwent a less extensive surge in the 20th century these ice flow events are interpreted in the context of the glaciology and known glacial history of austfonna and the nw barents sea the 200 km long ice cliffs of eastern austfonna provide an unusual and important analog for open marine deposition that would have been much more prevalent under full glacial conditions where ice sheets in many parts of the arctic advanced from fjord systems onto the adjacent continental shelves

seafloor geomorphology and glacimarine sedimentation associated with fast flowing ice sheet outlet glaciers in disko bay west greenland fast flowing outlet glaciers currently drain the greenland ice sheet gis delivering ice meltwater and debris to the fjords around greenland although such glaciers strongly affect the ice sheet s mass balance their glacimarine processes and associated products are still poorly understood this study provides a detailed analysis of lithological and geophysical data from disko bay and the vaigat strait in central west greenland disko bay is strongly influenced by jakobshavn isbrae greenland s fastest flowing glacier which currently drains 7 of the ice sheet streamlined glacial landforms record the former flow of an expanded jakobshavn isbrae and adjacent gis outlets through disko bay and the vaigat strait towards the continental shelf thirteen vibrocores contain a complex set of lithofacies including diamict stratified mud interbedded mud and sand and bioturbated mud deposited by 1 suspension settling from meltwater plumes and the water column 2 sediment gravity flows and 3 iceberg rafting and ploughing the importance of meltwater related processes to glacimarine sedimentation in west greenland fjords and bays is emphasised by the abundance of mud preserved in the cores radiocarbon dates constrain the position of the ice margin during deglaciation and suggest that jakobshavn isbrae had retreated into central disko bay before 10 6 cal ka bp and to beyond isfjeldsbanken by 7 6 7 1 cal ka bp sediment accumulation rates were up to 1 7 cm a 1 for ice proximal glacimarine mud and 0 007 0 05 cm a 1 for overlying distal sediments in addition to elucidating the deglacial retreat history of jakobshavn isbrae our findings show that the glacimarine sedimentary processes in west greenland are similar to those in east greenland and that variability in such processes is more a function of time and glacier proximity than of geographic location and associated climatic regime

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

seabed morphology and shallow sedimentary structure of the storfjorden and kveithola trough mouth fans north west barents sea abstract this study aims to present an overview of the seafloor morphology and shallow sedimentary structure of the storfjorden and kveithola trough mouth fans tmfs on the northwestern barents sea continental margin data have been compiled from two international polar year ipy cruises svais of the bio hesperides and eglacom of the r v ogs explora that yielded 15 340 km2 of multi beam bathymetry and 9500 km of sub bottom seismic profiles in this area the continental shelf edge defines three wide and subdued sedimentary lobes forming storfjorden tmf one single lobe on kveithola tmf and three inter tmf areas on the continental slope the two northernmost lobes of storfjorden tmf lobes i and ii are composed by thick up to 50 m sequences of glacially derived debris flow deposits interbedded with thin a few metres de glacial and interglacial deposits a network of upper slope gullies incises these debris flow deposits as a consequence of subglacial meltwater release at or near the shelf break gullies evolve into channels whose morphologic evidence disappears midslope leaving place to a subdued chevron like morphological pattern inherited by the preceeding glacial maximum debris flow deposits a drastic change occurs on the continental slope of storfjorden tmf lobe iii and kveithola tmf where are several translational submarine landslides mostly originated in the upper slope the majority of which detach at the contact between middle weishelian glacigenic debris flows and the overlying acoustically laminated plumites dendritic canyon systems only develop in inter tmf areas the data suggest that tmf continental slope progradation depends on short lived episodes of extreme sedimentation during glacial maxima and during the early deglaciation phase and that an important controlling factor is the mechanism of ice stream retreat from the continental shelf edge we suggest that the two northern storfjorden sub ice streams were composed of thicker and perhaps faster ice progressively draining a distal and larger ice source mainly located on svalbard conversely the southernmost storfjorden sub ice stream and the kveithola ice stream were fed by a local smaller marine based ice dome grounded on spitsbergenbanken the ice dome persisted after the lgm maintaining a local ice drainage system close to the shelf edge whose sedimentary evidence can be found on the continental slope of the southern lobe of storfjorden tmf and kveithola tmf the high degree of lateral variability in the style of sedimentation on tmf slopes suggests that ice stream dynamics may vary considerably within the same glacial trough and that such variability affects the long term development of the architecture of tmfs

landscape imprints of changing glacial regimes during ice sheet build up and decay a conceptual model from svalbard the behaviour of ice sheets and their geologic imprints in fjord regions are often multifaceted fjords which were temporarily occupied by fast flowing ice streams during major glaciations and inter fjord areas which were covered by less active ice show different signatures of past glaciations the land and marine records of glaciations over the western svalbard fjord region have been extensively studied during the last few decades we have re examined ice flow records from stratigraphic and geomorphic settings and propose a succession of ice flow events that occurred repeatedly over glacial cycles the maximum the transitional and the local flow style the differently topographically constrained segments of the ice sheet switched behaviour as glacial dynamics developed through each glacial cycle these segments as well as the different flow styles are reflected differently in the offshore stratigraphic record we propose that the glacial geomorphological signatures in the inter ice stream areas mostly developed under warm based conditions during a late phase of the glaciations and that the overall glacial imprints in the landscape are strongly biased towards the youngest events

switching of a paleo ice stream in northwest svalbard ice streams are the fast flowing zones of ice sheets that can discharge a large flux of ice the glaciated western svalbard margin consists of several cross shelf troughs which are the former ice stream drainage pathways during the pliocene pleistocene glaciations from an integrated analysis of high resolution multibeam swath bathymetric data and several high resolution two dimensional reflection seismic profiles across the western and northwestern svalbard margin we infer the ice stream flow directions and the deposition centres of glacial debris that the ice streams deposited on the outer margin our results show that the northwestern margin of svalbard experienced a switching of a major ice stream based on correlation with the regional seismic stratigraphy as well as the results from odp 911 on yermak plateau and odp 986 farther south on the western margin of spitsbergen off van mijenfjord we find that first a northwestward flowing ice stream developed during initial northern hemispheric cooling starting 2 8 2 6 ma a switch in ice stream flow direction to the present day kongsfjorden cross shelf trough took place during a glaciation at 1 5 ma or probably later during an intensive major glaciation phase known as the mid pleistocene revolution starting at 1 0 ma the seismic and bathymetric data suggest that the switch was abrupt rather than gradual and we attribute it to the reaching of a tipping point when growth of the svalbard ice sheet had reached a critical thickness and the ice sheet could overcome a topographic barrier highlights reflection seismic data reveal two glacial fans at northwest svalbard margin the fans are result of ice stream activities during pliocene pleistocene glaciations based on seismic and bathymetric data we find the flow directions of the ice streams we find a switch in ice stream flow direction the switch resulted as the ice sheet became thick and overcame a topographic barrier

submarine landforms and ice sheet flow in the kvitoya trough northwestern barents sea high resolution geophysical and sediment core data are used to investigate the pattern and dynamics of former ice flow in kvitoya trough northwestern barents sea a new swath bathymetric dataset identifies three types of submarine landform in the study area streamlined landforms meltwater channels and cavities iceberg scours subglacially produced streamlined landforms provide a record of ice flow through kvitoya trough during the last glaciation flow directions are inferred from the orientations of streamlined landforms drumlins crag and tail features ice flowed northward for at least 135 km from an ice divide at the southern end of kvitoya trough a large channel cavity system incised into bedrock in the southern trough indicates that subglacial meltwater was present at the former ice sheet base modest landform elongation ratios and a lack of mega scale glacial lineations suggest that although ice in kvitoya trough was melting at the bed and flowed faster than the likely thin and cold based ice on adjacent banks a major ice stream probably did not occupy the trough retreat was relatively rapid after 14 13 5 14c kyr b p and probably progressed via ice sheet bed decoupling in response to rising sea level there is little evidence for still stands during ice retreat or of ice proximal deglacial sediments relict iceberg scours in present day water depths of more than 350 m in the northern trough indicate that calving was an important mass loss mechanism during retreat

submarine glacial landforms and sedimentary environments in vaigattbogen northeastern spitsbergen abstract vaigattbogen is located in northern svalbard the area is currently affected by several tidewater glaciers this study uses multibeam sub bottom acoustic data and four sediment cores to reconstruct the late weichselian and holocene glacial history in vaigattbogen during the last glacial ice flowed northwards through vaigattbogen and fed into the hinlopen strait ice stream streamlined bedforms indicate relatively fast ice flow and their increasing elongation ratios towards the north suggest increasing flow velocities de geer moraines in the shallower parts of vaigattbogen imply that multiple halts and or re advances interrupted the ice retreat in these areas a sediment core suggests that the north basin deglaciated prior to 9 1 cal ka bp in the south basin two large moraine ridges and networks of crevasse squeeze ridges suggest that at least two surge type advances occurred during the holocene the hinlopenbreen glacier surged in the early 1970s and deposited the inner r 2 of the two large moraine ridges radiocarbon ages from a sediment core recovered from the crest of the outer r 1 ridge yield a basal age of 2 6 cal ka bp however the core did not sample subglacial diamict and the age of the ridge could be anything between 2 6 cal ka bp and early holocene the r 1 ridge formed prior to the little ice age lia implying that more than one tidewater glacier has experienced a pre lia surge on the east coast of spitsbergen suggesting that surging during the holocene was a regional phenomenon the r 1 ridge is double crested with small crevasse squeeze ridges between the crests suggesting that more than one surge type advance occurred during the holocene reaching approximately the same location data from eastern svalbard indicate differences in surge landform assemblages suggesting that different mechanisms could have governed surge cycles throughout the holocene

glacial geomorphology of the central barents sea implications for the dynamic deglaciation of the barents sea ice sheet abstract contemporary climate change has resulted in great uncertainty in how glaciers and ice sheets around the earth might evolve it has long been appreciated that the contemporary west antarctic ice sheet wais shares many similarities with the former barents sea ice sheet bsis therefore an increasing number of studies have sought to investigate the barents sea glacial record to better understand marine based glaciation this paper reports the analysis of a new high resolution bathymetric survey covering 55 000 km2 in the central barents sea the relative chronologies of newly mapped glacial landforms such as mega scale glacial lineations grounding zone wedges moraines and crevasse squeeze ridges are used to reconstruct the ice sheet dynamics in the central barents sea our results show that the ice sheet responded dynamically with different periods of retreat advance and stagnation observed these new landform records have been integrated with other geomorphological records in order to reconstruct the retreat pattern of the bsis between 17 14 ka when the fennoscandian ice sheet is thought to have uncoupled from the bsis our data shows that the dynamic drawdown of the ice sheet saddle by ice streams was probably the primary mechanism in separating the two ice sheets after the ice sheets uncoupled the bsis is shown to have retreated episodically with several periods of relative stability geomorphological records such as those from the bsis can be used to constrain ice sheet modelling and will help to develop a clearer understanding of marine based glaciation and the role of ice streams in driving ice sheet evolution

from mountain top to the deep sea deglaciation in 4d of the northwestern barents sea ice sheet abstract the timing of the deglaciation of the northern barents sea ice sheet bsis documented in terrestrial and offshore records from the svalbard archipelago is reviewed we present new cosmogenic nuclide cn ages from formerly unexplored inland areas of northern svalbard to investigate the timing of thinning of past local ice domes cn data are compared with radiocarbon ages from marine and terrestrial deposits 10be isotope cn dates on erratic boulders from interior svalbard suggest that glacier surfaces in northern and western svalbard thinned 950 650 m from 26 4 ka and continued over an extended period until 16 ka initial ice retreat from the western outer to the inner shelf began at 20 5 ka and in storfjordrenna southwest of svalbard around 19 18 ka retreat of grounded ice from the northern outer to the inner shelf did not begin before 15 9 ka we therefore suggest increasing summer insolation and aridification due to atmospheric circulation changes and perennial sea ice cover as the main mechanisms for the ice thinning and grounded ice retreat from the outer shelves before and during the heinrich 1 event the frontal position of the grounded ice sheet however did not change during several millennia despite further thinning in interior northern svalbard the inner shelf areas rapidly deglaciated towards the fjord mouths along the western coasts between 15 and 14 ka and became ice free before and during meltwater pulse 1a mwp 1a the collapse of the ice shelves from the inner shelf towards the fjord mouths and inner fjords occurred on a decadal to centennial time scale based on overlapping radiocarbon ages from marine sediment cores in addition to cn data from erratic boulders in lowlands we suggest that additional mechanisms must have caused this rapid collapse together with reduced moisture supply in the accumulation areas we assume that subsurface warm atlantic water masses that reached the western shelf after 17 5 ka may have accelerated debuttressing of the ice shelves in addition to the bolling warming that kicked in around 15 1 ka due to increased insolation and the global sea level rise called mwp 1a conservative calculations estimate the contribution of only the northwestern part of the bsis to sea level rise with 0 0004 cm yr 1 between 26 and 16 ka and 0 02 cm yr 1 in assumed 300 years between 15 and 14 ka

seismic attenuation tomography of the tonga fiji region using phase pair methods the anelastic structure of the region surrounding the tonga slab and lau back arc spreading center in the southwest pacific is studied using data from 12 broadband island stations and 30 ocean bottom seismographs two differential attenuation methods determine t over the frequency band 0 1 to 3 5 hz for earthquakes in the tonga slab the s p method measures the difference in spectral decay between p and s waves arriving at the same station the p p method measures the difference in spectral decay for p waves with different paths through the upper mantle eight hundred sixty phase pairs are used to invert for two dimensional 1 q structure using a nonnegative least squares algorithm a grid search method determines the q q ratio most compatible with both the s p and p p differential measurements the highest attenuation q 90 is found within the upper 100 km beneath the active portions of the lau basin extending westward to the lau ridge these regions probably delineate the source region for the back arc spreading center magmas expected to be within the upper 100 km based on petrological considerations the high attenuation regions also correlate well with zones of low p wave velocity determined by regional velocity tomography somewhat lower attenuation is found beneath the fiji plateau than beneath the lau basin the entire back arc is characterized by a gradual decrease in attenuation to a depth of 300 to 400 km the slab is imaged as a region of low attenuation q 900 material a q q ratio of 1 75 provides the best fit between the s p and p p data sets upon inversion spectral stacking shows no frequency dependence within the frequency band analyzed

reconstructing the retreat dynamics of the bjornoyrenna ice stream based on new 3d seismic data from the central barents sea the stability of contemporary ice sheets is influenced by the discharge from ice streams corridors of fast flowing ice bounded by ice flowing an order of magnitude slower reconstructions of palaeo ice stream dynamics contribute to our understanding of ice stream sensitivity to the ocean climate system and can aid in the numerical modelling and prediction of future changes in contemporary ice sheets here we use 3d seismic data covering 13 000 km2 in the central bjornoyrenna bear island trough barents sea to investigate the record of ice streaming preserved on the seafloor and on a buried palaeo seafloor surface the unusually broad coverage and high resolution of the dataset as well as its location in the central area of the trough enables improved reconstruction of dynamics of the former bjornoyrenna ice stream in terms of number of streaming events their trajectory and their relative age sequence during deglaciation our results reveal major changes in the configuration and flow dynamics of the ice stream with up to 10 flow switching events identified for the first time we also document ice streaming sourced from the eastern barents sea around the time of the lgm this high degree of flow variability is suggested to have resulted from climate driven changes in ice sheet geometry and ice divide migration and variations in topography that influenced calving at the ice stream terminus

late quaternary ice sheet history of northern eurasia the maximum limits of the eurasian ice sheets during four glaciations have been reconstructed 1 the late saalian 140 ka 2 the early weichselian 100 80 ka 3 the middle weichselian 60 50 ka and 4 the late weichselian 25 15 ka the reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in russia and siberia and with marine seismic and sediment core data the barents kara ice sheet got progressively smaller during each glaciation whereas the dimensions of the scandinavian ice sheet increased during the last ice age the barents kara ice sheet attained its maximum size as early as 90 80 000 years ago when the ice front reached far onto the continent a regrowth of the ice sheets occurred during the early middle weichselian culminating about 60 50 000 years ago during the late weichselian the barents kara ice sheet did not reach the mainland east of the kanin peninsula with the exception of the nw fringe of taimyr a numerical ice sheet model forced by global sea level and solar changes was run through the full weichselian glacial cycle the modeling results are roughly compatible with the geological record of ice growth but the model underpredicts the glaciations in the eurasian arctic during the early and middle weichselian one reason for this is that the climate in the eurasian arctic was not as dry then as during the late weichselian glacial maximum

grounding line proximal sediment characteristics at a marine based late stage ice stream margin this is the peer reviewed version of the following article ruther d c winsborrow m andreassen k forwick m 2017 grounding line proximal sediment characteristics at a marine based late stage ice stream margin journal of quaternary science 32 4 463 474 https doi org 10 1002 jqs 2939 which has been published in final form at https doi org 10 1002 jqs 2939 this article may be used for non commercial purposes in accordance with wiley terms and conditions for use of self archived versions

deglacial holocene svalbard paleoceanography and evidence of meltwater pulse 1b abstract better understanding of deglacial meltwater pulses mwps is imperative for future predictions of human induced warming and abrupt sea level change because of their potential for catastrophic damage however our knowledge of the second largest meltwater pulse mwp 1b that occurred shortly after the start of the holocene interglacial remains very limited here we studied fossil ostracods as paleoenvironmental indicators of water depth salinity and temperature in two marine sediment cores from storfjorden svalbard margin the arctic ocean to investigate near field i e areas located beneath continental ice sheets at the last glacial maximum evidence of mwp 1b the depositional environment changed from a cold bathyal environment to a warmer bathyal environment at 11 300 yr bp indicating incursion of warm atlantic water into the nordic seas and eventually to a cold neritic environment by 11 000 yr bp because of melting of the svalbard barents sea ice sheet and resultant isostatic rebound this process corresponds to rapid relative sea level fall of 40 80 m of mwp 1b from 11 300 to 11 000 yr bp

late weichselian local ice dome configuration and chronology in northwestern svalbard early thinning late retreat the chronology and configuration of the svalbard barents sea ice sheet sbsis during the late weichselian lw are based on few and geographically scattered data thus the timing and configuration of the sbsis has been a subject of extensive debate we present provenance data of erratic boulders and cosmogenic 10be ages of bedrock and boulders from northwest spitsbergen nws svalbard to determine the thickness configuration and chronology during the lw we sampled bedrock and boulders of mountain summits and summit slopes along with erratic boulders from coastal locations around nws we suggest that a local ice dome over central nws during lw drained radially in all directions provenance data from erratic boulders from northern coastal lowland reinsdyrflya suggest northeastward ice flow through liefdefjorden 10be ages of high elevation erratic boulders in central nws 687 836 m above sea level ranging from 18 3 1 3 ka to 21 7 1 4 ka indicate that the centre of a local ice dome was at least 300 m thicker than at present 10be ages of all high elevation erratics 400 m above sea level central and coastal locations indicate the onset of ice dome thinning at 25 20 ka 10be ages from erratic boulders on reinsdyrflya ranging from 11 1 0 8 ka to 21 4 1 7 ka indicate an ice cover over the entire reinsdyrflya during lw and a complete deglaciation prior to the holocene but apparently later than the thinning in the mountains lack of moraine deposits but the preservation of beach terraces suggest that the ice covering this peninsula possibly was cold based and that reinsdyrflya was part of an inter ice stream area covered by slow flowing ice as opposed to the adjacent fjord which possibly was filled by a fast flowing ice stream despite the early thinning of the ice sheet 25 20 ka we find a later timing of deglaciation of the fjords and the distal lowlands several bedrock samples 10be from vertical transects in the central mountains of nws pre date the lw and suggest either ice free or pervasive cold based ice conditions our reconstruction is aligned with the previously suggested hypothesis that a complex multi dome ice sheet configuration occupied svalbard and the barents sea during lw with numerous drainage basins feeding fast ice streams separated by slow flowing possibly cold based inter ice stream areas

thermal constraints on the seismogenic portion of the southwestern japan subduction thrust for coastal cities an important factor in earthquake hazard from subduction zone earthquakes is the landward extent of the seismogenic portion of the subduction thrust fault in this study we test the hypothesis that the maximum downdip extent is defined by a critical temperature we have developed a transient thermal model for the nankai subduction zone of southwest japan to allow comparison of the thermally estimated downdip extent of the seismogenic zone with that from 1 seismicity and tsunami data for two great subduction earthquakes 2 the coseismic faulting extent of these events estimated from geodetic deformation data and 3 the interseismic locked zone determined from interseismic geodetic data the nankai margin has extensive heat flow and heat production data to control thermal models and thus crustal temperatures it has earthquake tsunami and geodetic data that constrain the coseismic rupture portion of the subduction thrust fault for past great earthquakes and the portion of the thrust fault that is locked and storing interseismic elastic strain on the nankaido margin off shikoku island the thermal model indicates that a temperature of 350 c taken to be the limit for seismic initiation from laboratory and field data is reached on the subduction thrust fault 150 km from the trench a transition zone into which rupture may extend with decreasing offset taken to be 450 c extends an additional 45 km downdip the thermal model results are in excellent agreement with the maximum downdip extent of coseismic displacement for the 1946 nankaido ms 8 2 earthquake off shikoku island and with the downdip extent of the present locked zone in the region of the 1944 tonankai ms 8 2 earthquake to the northeast the subduction angle is much steeper and the thermal models indicate a narrower downdip seismogenic extent the seismogenic locked zone from earthquake and geodetic data is also narrower thus our analysis of the southwest japan margin indicates that all three constraints on the downdip extent of the seismogenic zone thermal coseismic and interseismic geodetic data are in general agreement the study also supports the hypothesis that the seismogenic portion of subduction thrust faults is limited primarily by temperature the thermal control implies that subduction thrust faults with shallow dip have wider seismogenic zones compared to those with steep dip the subducting plate age and thus heat flow and the thickness of the insulating sediments on the incoming plate are also very important to the thermal regime and thus to the seismogenic width the relation of the maximum seismic rupture area to the interseismic locked zone is particularly important for earthquake hazard estimation on subduction margins such as cascadia where there have been no great historical events

formation of mega scale glacial lineations observed beneath a west antarctic ice stream most discharge from large ice sheets takes place through fast flowing ice streams and their speed is strongly modulated by interactions between the ice and the underlying sediments seismic surveys and investigations through boreholes have revealed a spatial association between fast ice flow and saturated deformable sediments nevertheless our knowledge of the morphology of the interface between ice and sediments is still limited resulting in only rudimentary understanding of the basal boundary conditions beneath ice streams and the generation of subglacial bedforms here we present radar data from the bed of a west antarctic ice stream that reveal the presence of mega scale glacial lineations we combine these data with previously published seismic data and show that these lineations develop in areas of dilatant deforming till and are part of a dynamic sedimentary system that undergoes significant change by erosion and deposition on decadal timescales we find that the mega scale glacial lineations are indistinguishable from those found on beds of palaeo ice streams providing conclusive evidence for the hypothesis that highly elongate bedforms are a characteristic of fast flow regions in ice sheets

push moraines and glacier contact fans in marine and terrestrial environments the local climatic regime and the mass balance state are important determinants of the dynamics of terrestrial and marine glacier fronts which in turn determine the sediments and landforms produced at the glacier front many modern glaciers undergoing overall retreat in areas of maritime climate produce winter push moraines during a late winter readvance followed by a summer retreat whilst in more continental regions no significant winter readvance occurs and annual push moraines are absent the frontal dynamics which lead to these changes are analysed and the form structure sequence and field relations of both terrestrial and marine push moraines are described from iceland spitsbergen and baffin island long term changes in mass balance leading to major glacier advances or readvances also generate large push moraines in terrestrial environments push moraine formation is accompanied by uplift rejuvenation and down cutting of outwash systems whose sediments become closely associated with glaciotectonic structures which permit pre syn and post tectonic sequences to be identified the development of ice marginal fan moraine complexes is modelled as a function of the relative magnitude of two parameters the velocity of ice movement and the calving rate a high ice velocity just exceeded by the calving rate gives closely spaced push moraines and confluent ice marginal fans a high velocity far exceeded by the calving rate produces closely spaced moraines but separate ice marginal fans a low ice velocity in combination with a high calving rate results in well separated and feebly developed push moraines while a low ice velocity and a low calving rate produces feeble push moraines and coalescent fans

statistical analysis of brepollen bathymetry as a key to determine average depths on a glacier foreland abstract the study demonstrates the usefulness of statistical analysis to classify valleys because of the influence of the glaciers that formed them as well as to determine the average depth at their cross section parallel to the glacier front moreover the usefulness of the analysis of shape of the histogram of depth the value of skewness and kurtosis and the relation between the average median and mode of depths to classify valleys is shown the statistical analysis of the normalized shape of the valley cross sections allowed establishment of the relation between the measured depth the location of the measurements and the average depth of the valley cross sections

thermal regime of the southwest japan subduction zone effects of age history of the subducting plate abstract during a mid miocene at about 15 ma tectonic reorganization an ocean spreading ridge perpendicular to the strike of the nankai trough subduction zone stopped spreading since that time there has been subduction of the cooling fossil spreading ridge in the present study we have developed a time dependent thermal subduction model for this region using the finite element method there are good seismological and geological constraints for the plate geometry and for the subduction history of the past 15 ma boundary conditions are specified so that the oceanic plate subducting at the nankai trough becomes cooler as it gets older the model results agree with the present heat flow trend that decreases landward and explain the paleothermal regime of high mid miocene temperatures inferred from land geological studies the tectonics of the region prior to 15 ma has some uncertainties assuming subduction of an active spreading ridge or an 80 ma old lithosphere prior to 15 ma give the same results for the present thermal regime of the seaward portion of the forearc but different results for the most landward region 250 km the thermal history of the forearc since 15 ma can be summarized as a rapid warming period as a consequence of ridge subduction followed by a cooling trend to the present as a result of the aging of the subducting plate the results illustrate the thermal consequences of one type of ridge subduction they also demonstrate that the thermal regime of a subduction zone depends critically on the age history of the subducting oceanic lithosphere especially if it is young as well as such parameters as the subducting plate dip angle and thickness of insulating sediments on the incoming oceanic crust this dependence is especially important when the thermal regime is used to constrain the seismogenic behaviour of the subduction thrust fault

fast glacier flow ice streams surging and tidewater glaciers fast flowing glaciers are unusual but important jakobshavns glacier in western greenland illustrates this point figure 1 considered to be the world s fastest glacier its maximum observed flow rate measured in midsummer near the floating terminus is 8360 m yr 1 lingle et al 1981 except for a tidal influence near the terminus the flow is believed to be fairly steady bindschadler 1984

thermal structure of the subduction zone in western japan derived from seismic attenuation data 1 we use a well determined three dimensional attenuation model to infer the temperature distribution of the subduction zone in western japan the tomographic attenuation model was derived from about 19 000 t determinations for p waves recorded at 128 stations the attenuation model with a previously determined velocity model was used to infer the temperature distribution of the subduction zone from depths of 15 to 80 km using the high temperature background method we can clearly see the cooler slab 400 c to 700 c that is being subducted under the hotter mantle material 425 c to 850 c we also show that the deep low frequency earthquakes are occurring in regions just above the slab with temperatures of about 500 c to 600 c

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

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

evidence for full glacial flow and retreat of the late weichselian ice sheet from the waters around kong karls land eastern svalbard abstract marine geophysical and geological data from the seafloor surrounding kong karls land in eastern svalbard are used to reconstruct late weichselian full glacial flow dynamics and retreat history of the barents sea ice sheet bsis grounded ice extended over the entire area during the last glacial maximum lgm and produced streamlined sedimentary landforms in the broad bathymetric troughs that flank the kong karls land archipelago the landforms were produced in subglacial till as a result of subglacial processes at the base of the ice sheet drumlins and hill hole pairs confirm that regional ice flow was towards the east northeast through the troughs based on the absence of ice margin recessional features deglaciation in olga strait erik eriksen strait and the unnamed deep northeast of kong karls land appears to have been rapid in the deeper outer parts of the troughs in contrast in the shallower parts of the troughs ice recession was slower and minor readvances still stands of the ice margin resulted in the formation of recessional moraines during deglaciation temporary calving bays formed in the deeper parts of the troughs and calved icebergs were evacuated away from the ice margin through the troughs grounding zone features formed in olga strait indicate that retreat here was gradual and punctuated by longer still stands the transition from a grounded ice sheet to ice proximal settings is marked locally by a laminated mud sequence deposited from meltwater plumes from a nearby ice margin the presence of meltwater derived facies suggests that melting may have also been a significant ice loss mechanism during retreat in a broader context this study is one of the first investigations of the seafloor east of svalbard providing evidence that ice drained towards the east northeast during full glacial conditions ice from this part of the bsis was an important contributor to the palaeo ice stream in the large franz victoria trough during the lgm

a review of postglacial emergence on svalbard franz josef land and novaya zemlya northern eurasia the pattern of postglacial emergence in the barents sea is pivotal to constraining the timing of deglaciation and extent and thickness of the last ice sheet in northern eurasia this review unites records of holocene relative sea level from svalbard franz josef land and novaya zemlya to better understand the geometries of past ice sheet loads emergence data from northern eurasia confine the maximum area of glacier loading to the northwestern barents sea where 100 m of emergence is measured on kongs ya deglacial unloading commenced on western and northern spitsbergen c 13 12 14 c ka ago and by c 10 5 14 ck a on eastern svalbard and more distal sites on franz josef land and novaya zemlya the marine limit phase c 13 12 14 c ka on western and northern spitsbergen is characterized by the construction of spits indicating a dominance of long shore drift over stormgenerated fetch reflecting extensive sea ice coverage of coastal areas at sites in proximity to the ice sheet margin on western and northern spitsbergen there is evidence for a transgressive regressive cycle c 6 4 14 c ka possibly reflecting back migration of displaced mantle material a modern transgression is inferred from the marine erosion of 17th century cultural features and 14 c ages of whalebone and terrestrial peat buried by modern storm gravels that place sea level at its present position by c 2 to 1 ka ago the greatest observed emergence on franz josef land occurs on bell island with a marine limit at 49 m aht formed c 10 14 c ka available emergence data since 9 ka show rising strandlines toward the southwest at b0 3 m km the northern limit of emergence on franz josef land is poorly constrained because relative sea level data is sparse north of 80 30 0 n in contrast to svalbard and franz josef land the marine limit on northern novaya zemlya is only 10 15 m above high tide and formed between 6 5 and 5 0 14 c ka when global sea level was stabilizing all sites show little apparent emergence during the past 2 ka with the youngest raised landforms at identical heights to storm beaches this minimal glacio isostatic signature on novaya zemlya and on vaygach island where deglaciation commenced 10 ka ago indicates ice sheet thicknesses of o1 5 km the spatial variation in emergence for the barents sea indicates that western and northern spitsbergen and novaya zemlya were near the reactive margin of the ice sheet and these areas sustained the briefest ice coverage 2 6 ka and were probably not in isostatic equilibrium in contrast central and eastern svalbard and southern franz josef land were beneath a substantial ice load and probably sustained this load for c 10 14 c ka and achieved isostatic equilibrium isostasy residual from an ice sheet model portrays well the general pattern of uplift and load response at the centre of ice sheets but deviates substantial at the ice sheet margin or areas covered by thin ice like novaya zemlya

late weichselian deglacial history of the svyataya saint anna trough northern kara sea arctic russia abstract marine sediment core and seismic records from the svyataya saint anna trough provide new insight into the distribution of late weichselian glacial coverage ice retreat pattern and post glacial environments in the northern barents and kara seas these records indicate that the saint anna trough was filled with grounded glacier ice which likely reached the shelf edge during the late weichselian maximum several radiocarbon dates suggest early deglaciation of the deep axial part of the trough prior to 13 3 ka two sandy beds in the deglacial section of the cores imply distinct pulses of iceberg calving and or melting which were probably associated with stepwise retreat of the ice margin morainic ridges and glacial sole markings in the western part of the saint anna trough indicate that the northern central barents sea was a site of a large ice mass during deglaciation a smaller ice cap is inferred for the northern kara plateau at later stages ice retreat on the western flank of the trough was directed towards franz josef land and was presumably facilitated by a separation of the barents sea and novaya zemlya ice domes deglaciation of the saint anna trough was completed by ca 10 ka high post glacial sediment fluxes between 10 and 8 ka were probably related to sea floor coastal erosion and or siberian river discharge during the rising sea level

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

high resolution geophysical observations of the yermak plateau and northern svalbard margin implications for ice sheet grounding and deep keeled icebergs high resolution geophysical evidence on the seafloor morphology and acoustic stratigraphy of the yermak plateau and northern svalbard margin between 79 20 and 81 30 n and 5 and 22 e is presented

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

numerical reconstructions of the eurasian ice sheet and climate during the late weichselian abstract geological investigations undertaken through the quaternary environments of the eurasian north programme established ice sheet limits for the eurasian arctic at the last glacial maximum lgm sedimentary records of palaeo ice streams and uplift information relating to ice sheet configuration and the pattern of deglaciation ice sheet numerical modelling was used to reconstruct a history of the eurasian ice sheet compatible with these geological datasets the result was a quantitative assessment of the time dependent behaviour of the ice sheet its mass balance and climate and predictions of glaciological products including sediments icebergs and meltwater at the lgm ice cover was continuous from scandinavia to the arctic ocean margin of the barents sea to the north and the kara sea to the east in the west along the continental margin between the norwegian channel and svalbard the ice sheet was characterised by fast flowing ice streams occupying bathymetric troughs which fed large volumes of sediment to the continental margin that were deposited as a series of trough mouth fans ice streams may also have been present in bathymetric troughs to the north between svalbard and franz josef land further east however the ice sheet was thinner across the kara sea the ice thickness was predicted to be less than 300 m while on severnaya zemlya the ice cover may have been thinner at the lgm than at present it is likely that the taymyr peninsula was mainly free of ice at the lgm in the south the ice margin was located close to the shoreline of the russian mainland the climate associated with this ice sheet is maritime to the west and in stark contrast desert like in the east atmospheric general circulation modelling has revealed that such a contrast is possible under relatively warm north atlantic conditions because a circulation system develops across the kara sea isolating it from the moisture laden westerlies which are diverted to the south ice sheet decay began through enhanced iceberg calving in the deepest regions of the barents sea which caused a significant ice embayment within the bear island trough by about 12 000 years ago further iceberg calving reduced ice extent to the northern archipelagos and their surrounding shallow seas ice decay was complete by about 10 000 years ago

submarine landforms and glacimarine sedimentary processes in lomfjorden east spitsbergen understanding the role of fjords in modulating the long term interaction between ice sheets and glaciers with the surrounding ocean requires the investigation of glacigenic landform and sediment archives in svalbard there is a wealth of data from fjords in west spitsbergen that constrains the glacial history of this sector of the svalbard barents sea ice sheet sbis since the last glacial maximum lgm and the nature and timing of subsequent ice retreat in contrast however very little is known about the glacial history of fjords in east spitsbergen this paper combines multibeam swath bathymetry sub bottom profiles lithological data and radiocarbon dates from lomfjorden svalbard to provide the first insights into the dynamics of tidewater glaciers and associated glacimarine sedimentary processes in a northeast spitsbergen fjord at the lgm a fast flowing ice stream drained the sbis through lomfjorden serving as a tributary to a south north flowing ice stream in hinlopenstretet ice advance is recorded by streamlined bedrock glacial lineations and drumlins a radiocarbon date of 9 7 ka bp from the outer fjord provides a minimum date for retreat of this ice stream and suggests that lomfjorden was ice free earlier than fjords in west spitsbergen ice retreat occurred in a slow and step wise manner indicated by the presence of recessional moraines and de geer moraines by 4 5 ka bp the local tidewater glaciers had probably retreated inland of their present positions the limited extent of glacigenic landform assemblages in front of these glaciers implies that any holocene re advances were probably restricted the principal sedimentary processes during deglaciation were suspension settling from meltwater causing deposition of weakly stratified bioturbated mud in ice distal settings at rates of 0 02 0 08 cm a 1 and gravitational mass flows forming sandy turbidites in ice proximal areas iceberg ploughmarks and ice rafted debris provide evidence for the presence of large icebergs during deglaciation our data suggest an early and extensive deglaciation in east spitsbergen fjords and show that previous reconstructions of the extent of the sbis need to be revised as new data emerges from east spitsbergen the data confirm that tidewater glaciers from different regions of spitsbergen behaved differently since the lgm and that variations in landform sediment assemblages occur even within geographically adjacent fjords

the svalbard barents sea ice sheet historical current and future perspectives abstract the history of research on the late quaternary svalbard barents sea ice sheet mirrors the developments of ideas and the shifts of paradigms in glacial theory over the past 150 years since the onset of scientific research there in the early 19th century svalbard has been a natural laboratory where ideas and concepts have been tested and played an important but rarely acknowledged role in the break through of the ice age theory in the 1870 s the history of how the scientific perception of the svalbard barents sea ice sheet developed in the mid 20th century also tells a story of how a combination of fairly scattered and often contradictory observational data and through both deductive and inductive reasoning could outline a major ice sheet that had left but few tangible fingerprints since the 1980 s with increased terrestrial stratigraphical data ever more marine geological evidence and better chronological control of glacial events our perception of the svalbard barents sea ice sheet has changed the first reconstructions depicted it as a static concentric single domed ice sheet with ice flowing from an ice divide over the central northern barents sea that expanded and declined in response to large scale late quaternary climate fluctuations and which was more or less in tune with other major northern hemisphere ice sheets we now increasingly perceive it as a very dynamic multidomed ice sheet controlled by climate fluctuations relative sea level change as well as subglacial topography substrate properties and basal temperature in this respect the svalbard barents sea ice sheet will increasingly hold the key for understanding the dynamics and processes of how marine based ice sheets build up and decay

seismic attenuation and mantle wedge temperatures in the alaska subduction zone 1 anelastic loss of seismic wave energy or seismic attenuation 1 q provides a proxy for temperature under certain conditions the q structure of the upper mantle beneath central alaska is imaged here at high resolution an active subduction zone where arc volcanism is absent to investigate mantle thermal structure the recent broadband experiment across the alaska range beaar provides the first dense broadband seismic coverage of this region the spectra of p and sh waves for regional earthquakes are inverted for path averaged attenuation operators between 0 5 and 20 hz along with earthquake source parameters these measurements fit waveforms significantly better when the frequency dependence of q is taken into account and in the mantle frequency dependence lies close to laboratory values inverting these measurements for spatial variations in q reveals a highly attenuating wedge with q 500 assuming frequency dependence comparison with p results shows that attenuation in bulk modulus is negligible within the low q wedge as expected for thermally activated attenuation mechanisms bulk attenuation is significant in the overlying crust and subducting plate indicating that q must be controlled by other processes the shallowest part of the wedge shows little attenuation as expected for a cold viscous nose that is not involved in wedge corner flow overall the spatial pattern of q beneath alaska is qualitatively similar to other subduction zones although the highest wedge attenuation is about a factor of 2 lower the q values imply that temperatures exceed 1200 c in the wedge on the basis of recent laboratory based calibrations for dry peridotite these temperatures are 100 150 c colder than we infer beneath japan or the andes possibly explaining the absence of arc volcanism in central alaska

constraints on the late weichselian ice sheet over the barents sea from observations of raised shorelines abstract direct evidence for late weichselian grounded glacier ice over extensive areas of the barents sea is based largely on indirect observations including elevations of old shorelines on svalbard and arguments of isostatic rebound such isostatic models are discussed here for two cases representing maximum and minimum ice sheet reconstructions in the former model the ice extends over the kara sea whereas in the latter the ice is limited to the barents sea and island archipelagos comparisons of predictions with observations from a number of areas including spitsbergen nordaustlandet edgeoya kong karls land franz josef land novaya zemlya and finnmark support arguments for the existence of a large ice sheet over the region at the time of the last glacial maximum this ice sheet is likely to have had the following characteristics conclusions that are independent of assumptions made about the earth s rheological parameters i the maximum thickness of this ice was about 1500 2000 m with the centre of the load occurring to the south and east of kong karls land ii the ice sheet extended out to the western edge of the continental shelf and its maximum thickness over western spitsbergen was about 800 m iii to the north of svalberg and frans josef land the ice sheet extended out to the northern shelf edge iv retreat of the grounded ice across the southern barents sea occurred relatively early such that this region was largely ice free by about 15 000 bp v by 12 000 bp the grounded ice had retreated to the northern archipelagos and was largely gone by 10 000 bp vi the ice sheet may have extended to the kara sea but ice thicknesses were only a fraction of those proposed in those reconstructions where the maximum ice thickness is centered on novaya zemlya models for the palaeobathymetry for the barents sea at the time of the last glacial maximum indicate that large parts of the barents sea were either very shallow or above sea level providing the opportunity for ice growth on the emerged plateaux as well as on the islands but only towards the end of the period of fennoscandian ice sheet build up

pleistocene iceberg dynamics on the west svalbard margin evidence from bathymetric and sub bottom profiler data large icebergs leave evidence of their drift via ploughing of the seabed thereby providing a geological record of episodes of calving from thick ice sheets we interpret large scale curvilinear depressions on the western svalbard margin as ploughmarks produced by the keels of icebergs that grounded on the seafloor as they drifted through this area iceberg ploughmarks were identified at modern water depths between 300 m and 1000 m and in two distinct stratigraphic units combining data from sediment cores with seismic stratigraphy from sub bottom profiler data suggests that the ploughmarks developed in two phases 1 during marine isotope stage mis 6 and 2 during mis 2 indicating the presence of large drifting icebergs on the western svalbard margin during both the late saalian and late weichselian glaciations sediment core data along the western svalbard margin indicate a sharp increase in mass transported sediments dated at 23 7 0 2 ka consistent with the mis 2 age of the younger iceberg ploughed surface the ploughmarks are oriented in two main directions sw ne and s n s n oriented ploughmarks which shallow to the north indicate iceberg drift from the south with a sw ne component marking the zone of splitting of the west spitsbergen current wsc into the yermak slope current ysc and north spitsbergen current nsc large mis 6 and mis 2 icebergs most likely had an arctic ocean source we suggest that these icebergs probably left the arctic ocean southward through fram strait and circulated within the norwegian greenland sea before being transported northwards along the svalbard margin by the wsc an additional likely source of icebergs to the western svalbard margin during mis 2 was the ice sheet terminating in the western barents sea from which icebergs drifted northward

ice sheet grounding and iceberg plow marks on the northern and central yermak plateau revealed by geophysical data abstract we present new evidence for a grounded ice sheet and subsequent erosion by large fields of coherent icebergs for the central and northern yermak plateau 80 6 n to 82 2 n sediment echosounder and swath bathymetry data were combined with seismic reflection profiles and reveal at least three different glacial events marked by erosional unconformities i an erosional unconformity was observed at 70 90 m below seafloor down to depths of more than 850 m present water depth extending to 82 n the erosional unconformity is overlain by an acoustically chaotic layer of 50 m thickness interpreted as a diamicton originating from a grounded ice sheet the erosional unconformity and the overlying diamicton can be correlated to the overconsolidated sediments found at odp site 910 at a sediment depth between 19 and 70 95 m the oldest sediments just above the overconsolidated sediments are of late early pleistocene age mis19 20 and provide a minimum age for the grounding event ii parallel to sub parallel mega scale lineations are observed on large parts of the plateau west and northeast of the sverdrup bank at water depths between 725 and 850 m these lineations are mainly oriented nne ssw and were quite likely formed by the keels of deep draft mega scale tabular icebergs entrapped in a coherent mass of icebergs and sea ice the lineations are of late middle pleistocene age iii smaller scale curvilinear plow marks were found in the southernmost part of our study area at water depths between 640 and 775 m these were possibly caused by single icebergs and are of late pleistocene age iceberg scours are also found on three basement heights on the yermak plateau these however cannot be assigned to specific events they might as well originate from additional glacial phases the western at 850 m water depth and eastern at 1000 1200 m water depth flanks of the yermak plateau are relatively featureless and indicate the maximum depth of a grounded ice sheet and of iceberg armadas probably entrapped in sea ice

submarine landforms and the reconstruction of fast flowing ice streams within a large quaternary ice sheet the 2500 km long norwegian svalbard margin 57 80 n morphological interpretation of regional and detailed bathymetric data sets on the 2500 km long norwegian shelf from the north sea 57 n to svalbard 80 n has revealed a dynamic ice flow pattern along the western marginof the scandinavian and barents svalbard ice sheets about 20 cross shelf troughs with megascale glacial lineations msgl elongate ridges and grooves oriented parallel to trough long axes are interpreted as former pathways for fast flowing ice streams studies of large scale margin morphology and seismic profiles have identified large submarine fans at the mouths of several major cross shelf troughs less dynamic ice probably existed on shallower banks the two largest paleo ice streams were the norwegian channel ice stream and bear island trough ice stream each 150 200 km wide at the mouth the lengths of individual msgl vary from hundreds of meters to several tens of kilometers and the distance between ridges varies from 0 1 to 3 km msgl amplitudes reach 15 m but are commonly 10 m the onset of msgl and hence fast ice flow is generally close to the outer coast at the border zone between crystalline rocks and softer sedimentary rocks transverse submarine ridges on various scales commonly parallel to the shelf edge reflect either the maximum ice sheet position or the recessional pattern of the ice sheet lateral ice stream moraines several tens of kilometers long have also been mapped along the sides of several cross shelf troughs identifying the border zone between fast ice flow and stagnant or slow flowing ice on intervening banks

magnetostratigraphy and paleontology of ait kandoula basin high atlas morocco and the african european late miocene terrestrial fauna exchanges abstract a magnetostratigraphic study has been carried out on a middle miocene to upper pliocene lacustrine sedimentary deposit in the central part of the ait kandoula basin which contains micromammal faunas and is situated in the southern high atlas morocco in total 113 samples were subjected to paleomagnetic analysis 60 out of the 113 studied samples representing 52 different stratigraphic levels yielded a paleomagnetic direction and at least the polarity could be recognized in 42 specimens eleven specimens were submitted to af demagnetization the mean direction for normal polarity samples was d 349 4 i 50 7 n 36 95 4 5 k 27 and for reversed polarity samples d 191 2 i 53 4 n 16 95 12 32 k 9 these results yielded a polarity sequence which we interpret as spanning from chron c5n 2n to the beginning of chron c3n 4n this interpretation relies on biostratigraphic data previously proposed for a part of the continental fauna found in the basin this result is in agreement with the 40ar 39ar dating previously carried out on a volcanic ash layer which provided an age of 5 9 0 5 ma 1 and which is shown here to be reversely magnetized this layer is correlated here with the reverse polarity zone corresponding to chron c3r biostratigraphic studies on the same section have shown that the micromammal levels extend here only from middle vallesian to upper turolian upper miocene four localities have yielded western european species of micromammals indicating trans mediterranean terrestrial faunal exchanges between these two continents during the late miocene the european murid rodent occitanomys is recorded for the first time in north africa in level 8 of the afoud section an age younger than 5 32 ma being assigned to this level by the present study level 1 of the same section yields the lagomorph prolagus cf michauxi with an age of 6 1 ma the magnetostratigraphic data suggest therefore that the beginning of terrestrial faunal exchanges between north africa and western europe took place in subchron c3an 1n at about 6 1 ma some 0 4 myr before the beginning of the messinian salinity crisis

the updip and downdip limits to great subduction earthquakes thermal and structural models of cascadia south alaska sw japan and chile this study examines thermal and structural controls of the updip and downdip rupture limits of great subduction thrust earthquakes data on past great earthquake seismic limits have been compiled for four continental subduction zones cascadia sw japan south alaska and chile these limits have then been compared to the predictions of several models for what constrains great earthquake rupture temperatures on the subduction thrusts have been estimated by finite element numerical models the landward limits of the observed updip aseismic zones correspond to the position where the thrust temperature reaches about 100 c that is depths of about 2 to 10 km for the subduction zones studied this temperature agrees with the dehydration of stable sliding smectite clays to illite chlorite the temperatures in this region are controlled mainly by the thickness of sediment on the incoming crust and by the crustal age and thus heat flow the downdip limits correspond to the depth on the thrust where either 1 the temperature reaches about 350 c which corresponds to thermally activated stable sliding behavior for crustal rocks with a transition to 450 c or 2 about 40 km depth if 350 c is reached at greater depth depths of about 40 km approximately correspond to the intersection of the thrust with the continental forearc moho and this downdip limit may be a consequence of stable sliding serpentinite or talc and other hydrated forearc mantle rocks the primary temperature controls on the downdip region are the age of the subducting oceanic plate and the thrust dip profile secondary control comes from the thickness of incoming sediment the convergence rate and the radioactive heat generation in the overlying forearc the 100 c updip limit occurs near the trench for young subducting plates with a thick sediment section such as cascadia 6 8 ma and up to 80 km landward for older oceanic crust such as south alaska 50 ma the 350 c downdip thermal limit is applicable for young oceanic plates e g cascadia and nankai whereas the forearc mantle limit applies for older plates e g south alaska and chile except near the chile rise for the margins studied that have experienced great earthquakes there is generally good agreement between the postulated thermal and moho limits and the rupture or seismogenic zone as defined by the distribution of aftershocks and by waveform tsunami and dislocation modeling the downdip limit of the interseismic locked zone from dislocation modeling is also in agreement with these limits

reconstruction of ice sheet retreat after the last glacial maximum in storfjorden southern svalbard abstract storfjorden is a large north south trending sound located in the southern part of svalbard in the northwestern barents sea presently several glaciers drain into the northern and western part of storfjorden our study area covers the southern part of the sound which is divided by a north south striking basement ridge the mid ridge into a narrow western trough little storfjorden and a broader eastern trough storfjorden in the latter three grounding zone wedges gzws were discovered in 2005 showing evidence of former grounded ice here we confirm the existence and map the extent of the gzws and reconstruct the pattern and timing of ice retreat in storfjorden during the deglaciation the study is based on high resolution seismic and shallow acoustic profiles and swath bathymetry combined with information of lithology and radiocarbon dates from sediment cores the results show that the three gzws stretch across the fjord and that all three are located south of higher basement areas that were upstream of the gzws and which acted as pinning points during ice retreat the mid ridge imposed a lateral drag to the ice resulting in an uneven ice retreat across the fjord outside of the gzws only a thin cover of glacial deposits was found the cores were taken in vicinity of the gzws and all reached till deposits overlain by glacimarine or hemipelagic sediments enabling dating of the gzws altogether we find that the fjord and basement topography played an important role in the ice retreat ams 14c dates show that the formation of the three gzws correlate with three well known atmospheric warming phases start of bolling interstadial allerod interstadial and holocene interglacial respectively associated with inflows of warm atlantic water indicating a strong ocean climate control on the deglaciation of storfjorden

dating high arctic holocene relative sea level changes using juvenile articulated marine shells in raised beaches high arctic raised beaches provide evidence for changes in relative sea level rsl sea ice extent storminess and variations in sediment supply in many high arctic areas driftwood and whale bone are usually the preferred targets for radiocarbon dating with marine shells a third choice because of their often large age and height uncertainties with respect to former sea level here we detail a new approach to sampling marine shells that reduces these problems by targeting juvenile articulated specimens of astarte borealis that are washed onto the beach under storm conditions and become incorporated into the beach crest radiocarbon dates from articulated valves of a borealis from eight raised beaches from billefjorden svalbard provide a chronology for holocene beach ridge formation and rsl change that compares favourably to the most precise records developed from elsewhere in svalbard using driftwood or whale bone we demonstrate the value of this new approach by comparing our record with previously published rsl data from eastern svalbard to test different models of late weichselian ice load in this region we find support for a major ice dome centred south and east of kong karls land but no evidence for a significant ice dome located over easternmost spitsbergen or southern hinlopen strait as proposed from recent marine geophysical survey the approach is potentially applicable elsewhere in svalbard and the high arctic to address questions of rsl change and beach ridge chronology and hence wider questions regarding palaeoclimate and ice load history

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

laurentide ice sheet dynamics in the bay of fundy canada revealed through multibeam sonar mapping of glacial landsystems abstract recent multibeam sonar data collected in the bay of fundy canada interpreted in conjunction with geophysical profiling and sediment sampling reveal in unprecedented detail a suite of glacial landforms associated with the southwest margin of the laurentide ice sheet these landforms constitute four glacial landsystems 1 subglacial landsystem i in southwestern bay of fundy the elongated grand manan basin contains ice contact sediments of possible mid wisconsinan age overlain by late wisconsinan ice contact sediments strongly imprinted by iceberg furrows and pits in places possible mid wisconsinan glaciomarine sediments have been eroded by late wisconsinan ice creating streamlined landforms eroded bedrock and megafluted ice contact sediment on the flanks of grand manan basin indicate the southwest direction of topographically steered ice 2 subglacial landsystem ii along the southern margin of the bay of fundy an array of drumlins with superimposed esker complexes was formed by glacial ice that emanated northwest from the interior of nova scotia and was deflected to the southwest by the ice flowing out of the bay of fundy to the gulf of maine the esker complexes formed later when the nova scotia ice sheet stagnated and meltwater escaped northwest via topographic gaps 3 ice marginal landsystem i in northern bay of fundy both small de geer moraines and larger basin bounding moraines were created when retreating late wisconsinan ice became grounded in relatively shallow water new radiocarbon ages show that the owen basin moraine in this landsystem was abandoned prior to c 14 600 14 c yr bp cal bp 17 015 17 270 0 7 17 286 17 405 0 3 4 ice marginal landsystem ii this distinctive landsystem consists of numerous arcuate moraines commonly superimposed on one another this landsystem was formed by thin 170 m lightly grounded ice that retreated northeast into the bay of fundy the splayed pattern of the ice margin was a response to a large accommodation space and velocity variations within the ice the isle haute moraine is a large lobate moraine its age is poorly constrained by shells from glaciomarine sediments 13 750 60 14 c yr bp cal bp 15 970 15 996 0 03 16 047 16 665 0 97 but the moraine may be coeval with the onset of a terrestrial ice margin established at the head of the bay of fundy by c 14 300 14 c yr bp cal bp 16 824 17 013

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

late quaternary ice flow and sediment delivery through hinlopen trough northern svalbard margin submarine landforms and depositional fan abstract the morphology and distribution of submarine landforms in hinlopen trough northern svalbard margin and the upper continental slope beyond are investigated using swath bathymetric data together with side scan sonar acoustic profiler records and sediment cores sun illuminated images reveal a number of landform assemblages on the sea floor of hinlopen trough and confirm that this depression was occupied by an ice stream during the late weichselian glaciation around 20 ka before present the geomorphology of the inner shelf is characterised by bedrock drumlins and ice sculpted bedrock there is a middle shelf transition from a rock bed to an unconsolidated sedimentary bed that contains highly attenuated drumlins and megaflutes formed within a dark grey matrix supported diamict interpreted as subglacial till outer shelf landforms are mainly iceberg ploughmarks the geomorphological imprint identified from hinlopen trough is similar to that of many former ice streams the trough is dominated by elongate landforms orientated parallel to the inferred flow direction and is lacking in transverse features indicative of inter ice stream locations a characteristic down flow progression in landform elongation is also observed suggesting an increase in ice velocity across the continental shelf the lack of grounding zone features imaged from swath bathymetric data implies that deglaciation was probably rapid within the trough a large depositional fan exists on the upper continental slope beyond the trough characterised by debris flow deposits relating to the down slope transport of glacigenic sediment order of magnitude calculations of the volume of glacigenic sediment on the continental slope indicate that the ice stream provided high rates of debris delivery of around 5 7 5 m ka this suggests that hinlopen trough ice stream represented a major route for the transfer of ice and debris to the hinlopen fan on the northern continental margin of svalbard during the late weichselian glaciation

postglacial emergence of western franz josef land russian and retreat of the barents sea ice sheet uncertainty remains on the timing and extent of late weichselian glaciers over the qsr barents and kara sea shelves franz josef land russia is a critical area for deciphering the record of glacier fluctuations and postglacial relative sea level change coastal forelands on the archipelago are covered by a well preserved raised beach sequence containing abundant and pristine driftwood whalebone and shell 4c dating of these materials provides site specific emergence records for the archipelago and some of the oldest ages on deglaciation of 10 400 bp three apparent still stands in emergence are inferred from morphology of the raised beach sequence and 4c dating between 9900 and 6200 bp and at ca 5500 bp and 3500 bp the earliest sea level arrest after formation of the marine limit reflects a balance between glacio isostasy and eustasy concomitant with the final phase of global sea level rise the latter two sea level arrests during the middle to late holocene are less pronounced and may indicate increased height of the ocean surface with greater storminess and extended open water conditions raised beaches at 1 2 m a s l and j4c dated at 1000 to 2000 bp give contemporary emergence rates of 1 to 2 mm year the low current rates of emergence on franz josef land are similar to areas in fennoscandinavia that sustained modest late weichselian glacier loads 1500 m within a few 100s of km of the inferred ice sheet margin the pattern of postglacial emergence and strandline tilts indicates that past glacier loads were greater over the adjacent barents sea than franz josef land marine and terrestrial records from franz josef land place retreat of glaciers from coastal areas by 10 400 bp whereas the adjacent franz victoria trough was deglaciated by 13 000 bp retreat of the barents sea ice sheet was probably underway by 13 500 bp coincident with rising global sea level and elevated summer insolation we infer that iceberg calving through the deep troughs bordering the barents sea particularly with rapidly rising sea level ca 12 000 bp was an important process controlling the demise of the barents sea ice sheet copyright 1996 elsevier science ltd

palaeoglaciology of the alexander island ice cap western antarctic peninsula reconstructed from marine geophysical and core data abstract the glacial history of the continental shelf northwest of alexander island is not well known due mainly to a lack of targeted marine data on antarctica s palaeo ice sheets in their inter ice stream areas recently it has been argued that the region was ice free at the last glacial maximum lgm and thus a potential site for glacial refugia in this paper multibeam swath bathymetry sub bottom profiles and sediment cores are used to map the alexander island sector of the antarctic peninsula margin in order to reconstruct the shelf s palaeoglaciology sea floor bedforms provide evidence that an independent ice cap persisted on alexander island through the lgm and deglaciation we show that this ice cap drained via two major previously undescribed tidewater outlets rothschild and charcot glaciers sourced from an ice dome centred over the west of the island and near shore areas the glaciers grounded along deep fjord like cross shelf troughs to within at least 10 20 km of the shelf edge and probably reached the shelf break only one small outer shelf zone appears to have remained free of ice throughout an otherwise extensive lgm during retreat grounding line geomorphology indicates periodic stabilisation of charcot glacier on the mid shelf after 13 500 cal yrs bp while rothschild glacier retreated across its mid shelf by 14 450 cal yrs bp the timing of these events is in phase with retreat in nearby marguerite trough and we take this as evidence of a common history and forcing with the antarctic peninsula ice sheet the fine details of ice flow documented by our new reconstruction highlight the importance of capturing complex ice flow patterns in models e g in inter stream areas for understanding how region specific parts of antarctica may change in the future moreover the reconstruction shows that glacial refugia if present cannot have been extensive on the alexander island shelf at the lgm as indicated by previous biological studies instead we argue that any ice free refugia were probably restricted to isolated outer shelf pockets that opened closed or were maintained through diachronous ice sheet advance and retreat

seismic consequences of warm versus cool subduction metamorphism examples from southwest and northeast japan warm and cool subduction zones exhibit differences in seismicity seismic structure and arc magmatism which reflect differences in metamorphic reactions occurring in subducting oceanic crust in southwest japan arc volcanism is sparse and intraslab earthquakes extend to 65 kilometers depth in northeast japan arc volcanism is more common and intraslab earthquakes reach 200 kilometers depth thermal petrologic models predict that oceanic crust subducting beneath southwest japan is 300 to 500 c warmer than beneath northeast japan resulting in shallower eclogite transformation and slab dehydration reactions and possible slab melting

past ice flow in wahlenbergfjorden and its implications for late quaternary ice sheet dynamics in northeastern svalbard wahlenbergfjorden is a fjord situated in the western part of nordaustlandet in northern svalbard it leads into the 400 m deep hinlopen strait located between nordaustlandet and spitsbergen high r