self organization in the thermomechanical flow of ice sheets this paper uses a three dimensional thermomechanical ice sheet model to investigate the initiation and evolution of ice streams within ice sheets ice streams are distinguished within general ice sheet flow by their relatively fast of the order of kilometers per year velocity and are thought to be crucial in determining the response of ice sheets to climatic change we show that streaming can arise solely as a consequence of internal feedback between ice sheet flow and temperature inhomogeneities in topography and or geology are not therefore necessary conditions for ice stream development this spatial patterning replaces the large scale surging reported from previous modeling work in one horizontal dimension we suggest that surging is restricted to situations where ice flow is channelized e g valley glaciers and that it is replaced by streaming where horizontal ice flow is unconstrained ice sheets the ice streams in some of our experiments show switching behavior reminiscent of that known from the siple coast ice streams west antarctica the cause appears to be the competition for ice discharge and drainage basin area between adjacent ice streams this may lead to the gradual reduction of a stream s discharge below the threshold necessary to generate enough frictional heat to maintain warm viscous ice at the ice stream bed in this case the stream will stagnate abruptly which then prompts localized ice thickening and the initiation of a new stream in a different location

deglaciation of a marine based ice sheet late weichselian palaeo ice dynamics and retreat in the southern barents sea reconstructed from onshore and offshore glacial geomorphology abstract marine and terrestrial datasets swath bathymetry 2d and 3d seismic and remote sensing data are used to map the megascale glacial geomorphology of the southern barents sea seafloor northern fennoscandia and the kola peninsula giving new insights into the dynamics and behaviour of the barents sea ice sheet during retreat the glacial geomorphology indicates clear spatial and temporal variations in ice dynamics with evidence for both active ice streaming and frozen bed conditions at the maximum and during deglaciation a five stage reconstruction of the late weichselian deglaciation is proposed at the late weichselian maximum ice covered the whole of the barents sea shelf and the configuration and dynamics of the ice sheet were controlled by the bjornoyrenna bear island trough ice stream this was fed by source areas in the central and north eastern barents sea and in the fennoscandian mainland deglaciation was initiated along the western continental margin available dating results show that this occurred after 19 cal ka bp the bjornoyrenna ice stream retreated rapidly ice margin retreat rates of 275 m a 1 but was periodically grounded as evidenced by a well developed series of grounding zone wedges this was followed by an advance of two short lived ice streams from the eastern sector of the ice sheet into the south western barents sea these ice streams advanced and retreated very rapidly with no evidence for ice margin standstills correlation to dated cores suggests an age of around 16 000 cal ka bp for this readvance the period of operation of these two ice streams was coincident with maximum ice extent along the eastern margin in russia the western barents sea ice margin then retreated onshore with deglaciation continuing at a reduced rate the initiation of deglaciation coincided with rising global eustatic sea level acceleration of calving due to grounding line floatation rapidly opened up a major calving bay in bjornoyrenna encouraging rapid loss of the marine based ice the retreat rate stabilised only once the ice sheet retreated onshore and calving ceased we note that the observed pattern of rapid retreat with high variability in ice streaming for the marine based barents sea ice sheet is similar to that of the marine based sectors of the late weichselian british laurentide and west antarctic ice sheets

the sedimentary structure of linear sand dunes linear sand dunes dunes that extend parallel to each other rather than in star like or crescentic forms are the most abundant type of desert sand dune1 but because their development and their internal structure are poorly understood they are rarely recognized in the rock record2 models of linear dune development2 3 4 5 6 have not been able to take into account the sub surface structure of existing dunes but have relied instead either on the extrapolation of short term measurements of winds and sediment transport or on observations of near surface internal sedimentary structures from such studies it has not been clear if linear dunes can migrate laterally2 7 8 here we present images produced by ground penetrating radar showing the three dimensional sedimentary structure of a linear dune in the namib sand sea where some of the world s largest linear dunes are situated these profiles show clear evidence for lateral migration in a linear dune moreover the migration of a sinuous crest line along the dune produces divergent sets of cross stratification which can become stacked as the dune height increases and large linear dunes can support superimposed dunes that produce stacked sets of trough cross stratification these clear structural signatures of linear dunes should facilitate their recognition in geological records

response of jakobshavn isbrae greenland to holocene climate change rapid fluctuations in the velocity of greenland ice sheet gis outlet glaciers over the past decade have made it difficult to extrapolate ice sheet change into the future this significant short term variability highlights the need for geologic records of preinstrumental gis margin fluctuations in order to better predict future gis response to climate change using 10 be surface exposure ages and radiocarbon dated lake sediments we constructed a detailed chronology of ice margin fluctuations over the past 10 k y for jakobshavn isbrae greenland9s largest outlet glacier in addition we present new estimates of corresponding local temperature changes using a continuous record of insect chironomidae remains preserved in lake sediments we find that following an early holocene advance just prior to 8 ka jakobshavn isbrae retreated rapidly at a rate of 100 m yr 1 likely in response to increasing regional and local temperatures ice remained behind its present margin for 7 k y during a warm period in the middle holocene with sustained temperatures 2 c warmer than today then the land based margin advanced at least 2 4 km between a d 1500 1640 and a d 1850 the ice margin near jakobshavn thus underwent large and rapid adjustments in response to relatively modest centennial scale holocene temperature changes which may foreshadow gis response to future warming

multi decadal retreat of greenland s marine terminating glaciers many marine terminating glaciers draining the greenland ice sheet have retreated over the past decade yet the extent and magnitude of retreat relative to past variability is unknown we measure changes in front positions of 210 marine terminating glaciers using landsat imagery spanning nearly four decades and compare decadal scale rates of change with earlier observations we find that 90 of the observed glaciers retreated between 2000 and 2010 approaching 100 in the northwest with rapid retreat observed in all sectors of the ice sheet the current retreat is accelerating and likely began between 1992 and 2000 coincident with the onset of warming following glacier stability and minor advance during a mid century cooling period while it is clear an extensive retreat occurred in the early 20th century a period of increasing air temperatures a comparison of our results with historical observations provides evidence that the current retreat is more widespread the onset of rapid retreat with warming relative to the slow and lagged advance with cooling suggests an asymmetry in the response of marine fronts to external forcing

atmosphere driven ice sheet mass loss paced by topography insights from modelling the south western scandinavian ice sheet abstract marine terminating glaciers and ice streams are important controls of ice sheet mass balance however understanding of their long term response to external forcing is limited by relatively short observational records of present day glaciers and sparse geologic evidence for paleo glaciers here we use a high resolution ice sheet model with an accurate representation of grounding line dynamics to study the deglaciation of the marine based south western norwegian sector of the scandinavian ice sheet and its sensitivity to ocean and atmosphere forcing we find that the regional response to a uniform climate change is highly dependent on the local bedrock topography consistent with ice sheet reconstructions our simulations suggest that ocean warming is able to trigger initial retreat in several fjords but is not sufficient to explain retreat everywhere widespread retreat requires additional ice thinning driven by surface melt once retreat is triggered the underlying bedrock topography and fjord width control the rate and extent of retreat while multi millennial changes over the course of deglaciation are modulated by surface melt we suggest that fjord geometry ice ocean interactions and grounding line dynamics are vital controls of decadal to centennial scale ice sheet mass loss however we postulate that atmospheric changes are the most important drivers of widespread ice sheet demise and will likely trump oceanic influence on future ice sheet mass loss and resulting sea level rise over centennial and longer time scales

the marine based nw fennoscandian ice sheet glacial and deglacial dynamics as reconstructed from submarine landforms abstract the configuration of the marine based nw fennoscandian ice sheet during the last glacial maximum lgm and deglaciation is reconstructed using detailed swath bathymetry and high resolution seismic data the investigated area covers about 10 000 km 2 of the continental shelf off troms northern norway large scale morphology is characterized by cross shelf troughs coast parallel troughs and banks based on mega scale glacial lineations msgl lateral and shear zone moraines and grounding zone systems the extent and dynamics of the ice sheet during the lgm are deduced msgl indicate fast flowing ice streams in the cross shelf troughs while the glacial morphology on the banks indicates more sluggish ice here the marine based part of the fennoscandian ice sheet was sourced from ice domes in the east via fjord and valley systems inshore using a balance flux approach we estimate palaeo ice stream velocities during the lgm to be approximately 350 m year three deglaciation events have been reconstructed i during the torsken 1 event the ice sheet halted or readvanced to form groundings zone wedges gzw and the torsken moraine ii several still stands or readvances characterized the ice behaviour on the shallower banks during the torsken 2 event iii during the flesen event prominent end moraines in the inner parts of the troughs and banks were deposited the locations of the end moraines and gzw in the troughs indicate that the retreat of marine based ice streams in areas of reverse bed slope was episodic probably mainly due to the variation in widths of the cross shelf troughs

the variability of baffin bay seafloor sediment mineralogy the identification of discrete glacial sediment sources and application to late quaternary downcore analysis quantitative x ray diffraction qxrd mineralogy of bedrock ice rafted and fluvial clasts 239 seafloor samples 2 mm and samples from two long piston cores were used to i define regional pa

rapid response of helheim glacier southeast greenland to early holocene climate warming recent changes in speed thinning and retreat rates of marine terminating outlet glaciers have raised concerns about the future stability of the greenland ice sheet establishing a longer term record of outlet glacier retreat rates is essential to provide a context for present day observations and to improve and constrain numerical models of outlet glacier behavior new exposure dating 10be of streamlined bedrock surfaces and glacial erratic boulders of sermilik fjord southeast greenland the present day drainage route of helheim glacier documents rapid retreat 80 m a 1 of this major marine terminating outlet glacier at the close of the last glaciation the glacier front retreated 80 km to within 20 km of the present day 2010 position of helheim glacier in 1 ka ca 10 8 0 3 ka ago retreat followed rapidly rising air temperatures at the start of the holocene and at this temporal resolution there is no evidence that fjord geometry influenced glacier behavior the significant response to climatic amelioration at the end of the last glacial suggests a high sensitivity to abrupt temperature increases which has major implications for the future stability of present day greenlandic outlet glaciers in a warming climate

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

temporal and spatial variability in dune reactivation across the nebraska sand hills usa the nebraska sand hills is a stabilized dune field on the great plains of north america although it is well known that this dune field like several others on the great plains last experienced widespread activity during the medieval climatic anomaly mca ad 900 1300 spatial variation in the timing and nature of drought development is poorly constrained to elucidate spatial trends in dune reactivation samples potentially representing mca activity across the sand hills were collected and dated using optically stimulated luminescence osl ages from the older part of the mca were obtained from eolian sediments in the northwestern sand hills while ages from later in the episode were obtained to the southeast suggesting a geographic trend in the timing of revegetation of the dunes near the end of the drought revegetation likely occurred to the northwest initially as a result of renewed moisture availability from a rising water table in the interdunes which serve as refugia for vegetation during times of drought vegetation then gradually spread to the southeastern sand hills an additional spatial trend in ages is apparent in the chronology of linear dune mobilization across the sand hills linear dunes in the northwest are superimposed on megadunes and originated during the last reactivation while linear dunes in the southeast are built around older cores of dunes and formed during several reactivations our geochronology reveals three episodes of eolian transport including the mca in the formation of linear dunes in the southeast

progressive unpinning of thwaites glacier from newly identified offshore ridge constraints from aerogravity 1 a new bathymetric model from the thwaites glacier region based on icebridge airborne gravity data defines morphologic features that exert key controls on the evolution of the ice flow a prominent ridge with two distinct peaks has been identified 40 km in front of the present day grounding line undulating between 300 700 m below sea level with an average relief of 700 m presently the thwaites ice shelf is pinned on the eastern peak more extensive pinning in the past would have restricted flow of floating ice across the full width of the thwaites glacier system at present thinning rates ice would have lost contact with the western part of the ridge between 55 150 years ago allowing unconfined flow of floating ice and contributing to the present day mass imbalance of thwaites glacier the bathymetric model also reveals a 1200 m deep trough beneath a bight in the grounding line where the glacier is moving the fastest this newly defined trough marks the lowest topographic pathway to the byrd subglacial basin and the most likely path for future grounding line retreat

morphometric analysis of aeolian bedforms in the namib sand sea using aster data the aster global digital elevation model gdem has made elevation data at 30 m spatial resolution freely available enabling reinvestigation of morphometric relationships derived from limited field data using much larger sample sizes these data are used to analyse a range of morphometric relationships derived for dunes between dune height spacing and equivalent sand thickness in the namib sand sea which was chosen because there are a number of extant studies that could be used for comparison with the results the relative accuracy of gdem for capturing dune height and shape was tested against multiple individual aster dem scenes and against field surveys highlighting the smoothing of the dune crest and resultant underestimation of dune height and the omission of the smallest dunes because of the 30 m sampling of aster dem products it is demonstrated that morphometric relationships derived from gdem data are broadly comparable with relationships derived by previous methods across a range of different dune types the data confirm patterns of dune height spacing and equivalent sand thickness mapped previously in the namib sand sea but add new detail to these patterns

sedimentary architecture of an ancient linear megadune barremian neuquen basin insights into the long term development and evolution of aeolian linear bedforms linear aeolian bedforms are the most abundant bedform type in modern earth sand seas and are very common in our solar system despite their abundance the long term development of these bedforms and its impact upon the resulting sedimentary architecture in the geological record is still poorly understood the aims of this paper are to study the exposed record of an ancient linear megadune in order to discuss the factors that impact the development and sedimentary architecture of aeolian linear bedforms the outcrops of the ancient troncoso sand sea barremian neuquen basin argentina provide a unique opportunity to access a preserved megadune record with an external body geometry that unequivocally confirms its linear morphology architectural analysis of the bedform record reveals significant differences for several aspects of cross stratified set bodies and bounding surfaces and allows for the identification of three architectural complexes insights from deterministic models analysis of set body relative chronology and distribution suggest that complexes result from distinctive phases in bedform development it also clearly shows that the megadune s construction was achieved by expansion from a core where the oldest deposits are located and that its development was characterized by sustained growth and strong longitudinal dynamics factors that impact the development and architecture of linear bedforms are identified discussed and compared to bedforms of transverse dynamics finally a scheme of expected styles of sedimentary architecture for linear bedforms is presented this case study shows how growth can be a critical factor conditioning linear bedform architecture and indicates how the preservation of certain styles of sedimentary architecture in the geological record may not be as unusual as previously thought

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

a twenty one year record of surface change on a namib linear dune repeated surveying of two sites on a namib linear dune between 1980 and 2001 provides a 21 year record of dune surface change the surveys con rm the view that the dunes are not inactive relics but are responding to the present day wind regime they also provide no evidence that the dunes are migrating laterally examination of wind data for the survey period provides some evidence that the form of the crest of the dunes is actively responding to the natural year by year climate variability such that an increase in the frequency of easterly winds leads to the development of a double crested form while fewer easterly winds lead to a single crested form copyright 2003 john wiley sons ltd

lateral migration thermoluminescence chronology and colour variation of longitudinal dunes near birdsville in the simpson desert central australia the longitudinal dunes of the simpson desert in the vicinity of birdsville have been reworked largely during the holocene from dunes deposited up to 80000 years ago or earlier the widespread asymmetry of these roughly northward trending dunes with steeper eastern faces and more gentle western faces supports wind rose data showing sand transporting winds from the southwest obliquely intersecting the dunes while this suggests a change in the wind pattern since the dune field was oriented it does not indicate that the dunes are necessarily shifting leeward eastward as a consequence it is hypothesized that the direction of migration is controlled by the extent to which the dunes are vegetated relatively well vegetated dunes can accrete sand on their gentle stoss slopes and erode on their lee slopes causing them to shift westward and hence obliquely into the wind a condition that probably prevails in wetter regions and during episodes of relatively humid climate in contrast in very dry areas or during arid phases sand can move unimpeded up a sparsely vegetated stoss face and over the crest to form an avalanche or slip face on the lee side thereby causing the dunes to shift eastward despite evidence that longitudinal dune crests can shift laterally to some extent the dunes in the western part of the simpson desert have not migrated either westward or eastward more than 100m or so from their pleistocene cores aeolian transport and partial or complete removal of iron cutans from around quartz grains results in dunes of widely varying colour yet of similar age

a decade of surface change on a namib linear dune survey data from return visits to a linear dune in the namib desert provide information about change in dune form over a decade the data demonstrate that although change on these large features is slow there is none the less considerable movement over this time scale the dunes are therefore confirmed to be currently active and not pleistocene relics

bagnold s barchan a 57 yr record of dune movement in the eastern sahara and implications for dune origin and paleoclimate since neolithic times abstract discovery in 1980 of camp 18 of the 1930 bagnold expedition in northwestern sudan has resulted in an exceptionally long record of barchan movement from which an average rate of 7 5 m yr has been calculated measurements of the rate of dune advance since 1980 have not varied significantly indicating a state of quasiequilibrium exists the dune field is moving over an undulating sand sheet exhibiting various stages of holocene pedogenesis and containing neolithic sites the sand sheet overlies pleistocene alluvium with stronger stages of pedogenesis all of these deposits may be a significant source of dune sand wind blown grass fragments trapped by advancing slipfaces mark former slipface positions and indicate late holocene rainfall events which can be radiocarbon dated parabolic forms revealed by spot images at the windward ends of the dune fields are transitional to barchans suggesting sand accumulation in vegetation germinated during a holocene wet period in addition sand streaks from sand sheet undulations suggest that active eolian erosion of sand sheets contributes to the sand supply of dune fields pedogenesis during pluvial periods contributes to silt and clay fractions of bimodal sand sheet sediments from wind streaks on landsat images and an estimated average rate of dune advance positions of dune fields during past hyperarid periods can be estimated

late pleistocene eolian history of the liwa region arabian peninsula the liwa region of the united arab emirates is one of the most distinctive geomorphological features of the rub al khali desert of southern arabia characterized by a sharp crescentic boundary coincident with a n s elevation drop of 65 m with the transverse ridges in al q fa to the north liwa is an area of some of the world9s largest megabarchan dunes deep drilling of continuous cores has provided an opportunity to observe the internal structure and age of these two ergs subsurface stratigraphy is complex reflecting rapid facies transitions between dune and interdune sub environments most of the cored sediment is dominated by cross bedded and structureless sand units of inferred eolian transverse dune depositional origin a total of 56 optical ages for sand sized quartz grains extracted from these cores provide a chronological framework for deposition of the late quaternary ergs a marine isotope stage mis 5 erg is identified north of the liwa crescent in the al q fa region which reaches vertical thicknesses 100 m a mis 1 erg in the form of megabarchan dunes is recorded south of the liwa crescent this was deposited on a pre mis 5 land surface since ca 6 ka over a period of just a few thousand years contemporary bypassing of eolian sands via superimposed dunes in both al q fa and liwa appears to be in equilibrium with the current wind regime a consideration of a variety of factors that control the availability mobilization and preservation of eolian sediments and resulting bedforms leads us to infer that the system is not sediment supply or transport limited instead the system is preservation limited being controlled by a correlated combination of sea level and precipitation both of these factors are strongly linked to global climate variations in the eccentricity ca 100 ka band paradoxically the bulk of the preserved record of eolian activity in the southern arabian peninsula occurs within relatively humid interglacial phases rather than arid intervals evidence of eolian deposition during arid phases may not for the most part be preserved in large areas of the sand sea observed contrasts in the preserved record of eolian activity between al q fa and liwa and the wahiba sand sea may in part relate to contrasting eolian bedform morphology

asynchronous response of marine terminating outlet glaciers during deglaciation of the fennoscandian ice sheet this is the accepted manuscript version published version is available at http dx doi org 10 1130 g35299 1

late quaternary linear dune accumulation and chronostratigraphy of the southwestern kalahari implications for aeolian palaeoclimatic reconstructions and predictions of future dynamics abstract the linear dunes of the kalahari now largely inactive have long been identified as having potential palaeoenvironmental significance the application of optically stimulated luminescence osl dating to these dunes in the 1990s provided the first chronology of aeolian accumulation in this region though field methodologies and time consuming multiple aliquot laboratory protocols limited both the depth of sampling in dune bodies and the total number of samples dated in order to permit a more thorough investigation of the potential of these dunes to preserve long chronological records this intensive study presents 71 osl ages from the linear dunes of the southwestern kalahari at witpan south africa sampled with coring equipment at regular and frequent intervals down to bedrock the earliest sand accumulation recorded at witpan is at 104 ka and in spatially discrete locations other evidence of dune activity is recorded at 77 76 57 52 and 35 27 ka although an inherently discontinuous archive the linear dunes of the southwestern kalahari have the potential to record multiple phases of dune construction following the last glacial maximum there is near continuous evidence of dune building with a peak of accumulation recorded from 15 to 9 ka at five individual sites this latter period is generally recognised from other proxy evidence as being unusually arid in this region and such periods of dune activity are likely to be related to intensification of the continental anticyclone during the holocene accumulation has continued at most sites sampled albeit at a lesser intensity this may imply that these dunes are presently not far from thresholds of activation

widespread and accelerating glacier retreat on the lyngen peninsula northern norway since their little ice age maximum the recession of mountain glaciers worldwide is increasing global sea level and in many regions human activities will have to adapt to changes in surface hydrology thus it is important to provide up to date analyses of glacier change and the factors modulating their response to climate warming here we report changes in the extent of 120 glaciers on the lyngen peninsula northern norway where glacier runoff is utilised for hydropower and where glacial lake outburst floods have occurred glaciers covered at least 114 km2 in 1953 and we compare this inventory with those from 1988 2001 and a new one from 2014 and previously dated little ice age lia limits results show a steady reduction in area 0 3 a 1 between their lia maximum 1915 and 1988 consistent with increasing summer air temperatures but recession paused between 1988 and 2001 coinciding with increased winter precipitation air temperatures increased 0 5 c per decade from the 1990s and the rate of recession accelerated to 1 a 1 between 2001 and 2014 when glacier area totalled 95 7 km2 small glaciers 0 05 km2 with low maximum elevations 1400 m experienced the largest percentage losses and if warming continues several glaciers may disappear within the next two decades

experiments and observations bearing on the solubility and diffusivity of carbon in olivine the solubility and diffusivity of c in olivine at 0 1 2 0 and 3 0 gpa have been constrained by annealing single crystals of san carlos olivine in 14c labelled co2 co2 h2o and graphite at 1200 1450 c in nearly all annealed specimens carbonaceous material was observed at the diffusion interface that consisted of either 1 graphite used as a c source 2 elemental c probably graphite formed by reduction of the c o h fluid phase present or 3 carbon rich surface films interpreted as silicate dissolved in the fluid phase at high pressure quenched onto the crystal surface the significant range of 14c beta particles in olivine and photographic emulsion coupled with the presence of carbonaceous material at the diffusion interface gives rise to apparent concentration profiles after removal of the carbonaceous material we retained no unambiguous evidence for c diffusion into olivine the sensitivity and spatial resolution of the beta track method constrain either the solubility to be less than 30 ppmw parts per million by weight c or the diffusivity to be less than 10 12 cm2 s observations and geochemical data on natural rocks bearing on the nature and distribution of c in the earth s upper mantle are discussed in light of these constraints

geological constraints on antarctic palaeo ice stream retreat submarine landforms preserved in bathymetric troughs on the antarctic continental shelf show that the style of ice stream retreat across the shelf following the last glacial maximum varied between different troughs three styles of retreat are inferred from the geological evidence rapid episodic and slow rapid retreat by ice stream floatation and calving is recorded by the preservation of a landform assemblage of unmodified streamlined subglacial bedforms including mega scale glacial lineations msgls that record streaming flow along these troughs these elongate bedforms are not overprinted by recessional glacial landforms formed transverse to ice flow such as moraines or grounding zone wedges and overlying deglacial sediments are thin a second type of landform assemblage consists of msgls overprinted or interrupted by transverse grounding zone wedges this assemblage implies episodic retreat between successive grounding zone positions the third type of landform assemblage is that of numerous closely spaced recessional moraines and intermittent grounding zone wedges that overlie and interrupt msgls this assemblage records the slow retreat of grounded ice across the shelf variation in the style of ice stream retreat between the different bathymetric troughs indicates that antarctic palaeo ice streams did not respond uniformly to external forcing at the end of the last glacial cycle rather their diachronous retreat reflects the dominance of local controls in the form of bathymetry and drainage basin size more broadly these data show that retreat of marine based ice sheets in areas of reverse bed slope is not necessarily catastrophic and they provide important constraints for numerical models that attempt to predict the dynamics of large polar ice sheets copyright 2008 john wiley sons ltd

the influence of ice marginal setting on early holocene retreat rates in central west greenland ice sheet reconstructions from diverse ice margin settings spanning multiple millennia are needed to assess the reaction of the greenland ice sheet gris to millennial scale climatic forcing and to place historical records in a longer term context here we present 18 new cosmogenic 10 be exposure ages and five new radiocarbon ages that constrain the early holocene retreat of the gris in the disko bugt region in both a marine and a land based setting results indicate similar rates of early holocene retreat of 40 50m a 1 from transects in torsukattak fjord marine setting and the naternaq area land based setting we compile seven previously published chronologies of deglaciation from west greenland which yield early holocene retreat rates ranging from 10 to 65m a 1 similar to those determined for our two study areas this work demonstrates that when averaged on millennial timescales retreat rates were remarkably similar along the western gris margin furthermore the retreat rates calculated here demonstrate that terrestrial sectors of ice sheets can retreat at net rates comparable to their marine counterparts copyright 2015 john wiley sons ltd

the experimental deformation of dunite deformation experiments have been carried out on two dunites anita bay of 100 m grain size and aheim of 900 m grain size at strain rates from 10 3 to 10 6 s 1 and temperatures from 1000 c to 1300 c in a gas medium deformation apparatus at 300 mpa confining pressure most of the tests were under wet conditions defined by the presence of small amounts of water from hydrous minerals initially present constant strain rate and relaxation experiments covering ranges of flow stress down to about 70 mpa and 7 mpa respectively show that there is a change in flow law in going below about 100 mpa differential stress and that the coarser grained rock is stronger than the finer grained one power law parameters above the transition are n 4 48 0 31 and q 498 38 kj mol 1 for aheim dunite and n 3 35 0 17 and q 444 24 kj mol 1 for anita bay dunite while below the transition relaxation tests on anita bay dunite give n 2 44 0 18 and q 386 27 kj mol 1 it is concluded that there is a weakening effect of water that this effect is mainly in the grain boundaries and that grain boundary sliding is probably a significant deformation mechanism at the lower stresses under wet conditions

longitudinal dunes can move sideways longitudinal dunes occur in all major sand areas in the world their dominant mode of migration or extension is considered to be either prevailing or resultant wind parallel the dunes extending downwind via accretion of the terminal nose in the qaidam pendi in northwest china a series of active longitudinal dunes extend downwind at 5 10 m yr 1 internal sedimentary structures examined in the dunes however display beds dipping in one direction rather than two opposed directions as is expected analysis of aerial photographs confirms that these dunes migrate laterally up to three metres per year whilst maintaining a symmetrical longitudinal dune morphology

lateral migration of linear dunes in the strzelecki desert australia linear dunes in the strzelecki desert trend roughly south north sand transport which is toward the nne has caused the dunes to migrate eastward while they extend or migrate northward eastward lateral migration is evidenced by 1 asymmetrical shape of the dunes east facing slopes are several times as steep as west facing slopes 2 asymmetrical accumulation of loose recently transported sand relatively abundant on east facing slopes 3 asymmetrical outcropping of older semiconsolidated aeolian sand on the dune surface more abundant on west facing slopes and 4 east dipping foreset beds that underly the west facing flanks of some dunes dunes in the strzelecki desert are still active in the sense that sand is transported along and across many dune crests however the dunes are composed primarily of pleistocene strata indicating that the trend of the dunes was established before the holocene the obliquity of the dunes to the transport direction is not merely an aberration of the wind regime of the last few decades preferential accumulation of sand on east facing flanks indicates that the dunes migrated eastward several metres during the holocene moreover the west facing flanks of some dunes have experienced a minimum of tens of metres of erosion this asymmetric erosion and deposition were caused by dune obliquity and lateral migration that may have begun as early as the pleistocene dunes in the strzelecki desert and in the adjacent simpson desert display a variety of grossly different internal structures computer graphics experiments demonstrate that many of these differences in structure can be explained by different angles of climb of the dunes

impact of bedrock description on modeling ice sheet dynamics recent glaciological surveys have revealed a significant increase of ice discharge from polar ice caps into the ocean in parallel ice flow models have been greatly improved to better reproduce current changes and forecast the future behavior of ice sheets for these models surface topography and bedrock elevation are crucial input parameters that largely control the dynamics and the ensuing overall mass balance of the ice sheet for obvious reasons of inaccessibility only sparse and uneven bedrock elevation data is available this raw data is processed to produce digital elevation models dems on a regular 5 km grid these dems are used to constrain the basal boundary conditions of all ice sheet models here by using a full stokes finite element code we examine the sensitivity of an ice flow model to the accuracy of the bedrock description in the context of short term ice sheet forecast we show that in coastal regions the bedrock elevation should be known at a resolution of the order of one kilometer conversely a crude description of the bedrock in the interior of the continent does not affect modeling of the ice outflow into the ocean these findings clearly indicate that coastal regions should be prioritized during future geophysical surveys they also indicate that a paradigm shift is required to change the current design of dems describing the bedrock below the ice sheets they must give users the opportunity to incorporate high resolution bedrock elevation data in regions of interest

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

ice streams in the laurentide ice sheet identification characteristics and comparison to modern ice sheets this paper presents a comprehensive review and synthesis of ice streams in the laurentide ice sheet lis based on a new mapping inventory that includes previously hypothesised ice streams and includes a concerted effort to search for others from across the entire ice sheet bed the inventory includes 117 ice streams which have been identified based on a variety of evidence including their bedform imprint large scale geomorphology topography till properties and ice rafted debris in ocean sediment records despite uncertainty in identifying ice streams in hard bedrock areas it is unlikely that any major ice streams have been missed during the last glacial maximum laurentide ice streams formed a drainage pattern that bears close resemblance to the present day velocity patterns in modern ice sheets large ice streams had extensive onset zones and were fed by multiple tributaries and where ice drained through regions of high relief the spacing of ice streams shows a degree of spatial self organisation which has hitherto not been recognised topography exerted a primary control on the location of ice streams but there were large areas along the western and southern margin of the ice sheet where the bed was composed of weaker sedimentary bedrock and where networks of ice streams switched direction repeatedly and probably over short time scales as the ice sheet retreated onto its low relief interior several ice streams show no correspondence with topography or underlying geology perhaps facilitated by localised build up of pressurised subglacial meltwater they differed from most other ice stream tracks in having much lower length to width ratios and have no modern analogues there have been very few attempts to date the initiation and cessation of ice streams but it is clear that ice streams switched on and off during deglaciation rather than maintaining the same trajectory as the ice margin retreated we provide a first order estimate of changes in ice stream activity during deglaciation and show that around 30 of the margin was drained by ice streams at the lgm similar to that for present day antarctic ice sheets but this decreases to 15 and 12 at 12 cal ka bp and 10 cal ka bp respectively the extent to which these changes in the ice stream drainage network represent a simple and predictable readjustment to a changing mass balance driven by climate or internal ice dynamical feedbacks unrelated to climate or both is largely unknown and represents a key area for future work to address

monitoring surface change on a namib linear dune in tackling the apparently intractable problem of linear dune initiation and maintenance there has been a move away from large scale deductive models to smaller scale field studies of individual dunes this paper reports a study of surface change on a large complex linear dune in the namib desert southern africa the dune surface responds to a markedly seasonal wind regime in summer westerly winds erode sand from the west flank of the dune and deposit it on the easterly lee side of the dune crest in winter this pattern is reversed easterly winds erode sand from the east slope and deposit it on the west slope the crest therefore moves back and forth some 15 m each year returning at the end of a year s cycle to its position at the beginning the position of the base of the dune appears to remain fixed even though sand is moving throughout the dune system the dune does extend northward along some resultant of the westerly and easterly winds despite relatively high levels of activity especially at the dune crest there is no evidence of the breakdown of the linear dune form the conclusion must therefore be that linear dunes can be maintained in bimodal wind regimes and are not necessarily related to unidirectional parallel regimes as others have suggested

a second look at western sinai seif dunes and their lateral migration abstract tsoar et al tsoar h blumberg d g stoler y 2004 elongation and migration of sand dunes geomorphology 57 293 302 reported that seif dunes in the western sinai desert did not migrate laterally between 1973 and 1999 if the planform sinuosities of the dunes are removed by filtering spatial averaging or linear regression however it is evident that the dunes did in fact migrate laterally roughly 13 m during this 26 year period the measured migration distance is 1 2 orders of magnitude greater than the rms co registration error tsoar et al determined for the first and last air photos that were used to map the dunes the western sinai dunes provide another example demonstrating that linear dunes can migrate laterally and they illustrate some of the difficulties in documenting systematic lateral motion lateral migration of a dune can be important geologically or geomorphologically even where migration is too slow to detect from repeated topographic surveys this article explains the wind conditions for the lateral migration of seif dunes in western sinai and the possible wind occurrences that would not lead to such a migration

ice sheet grounding line dynamics steady states stability and hysteresis 1 the ice sheet ice shelf transition zone plays an important role in controlling marine ice sheet dynamics as it determines the rate at which ice flows out of the grounded part of the ice sheet together with accumulation this outflow is the main control on the mass balance of the grounded sheet in this paper we verify the results of a boundary layer theory for ice flux in the transition zone against numerical solutions that are able to resolve the transition zone very close agreement is obtained and grid refinement in the transition zone is identified as a critical component in obtaining reliable numerical results the boundary layer theory confirms that ice flux through the grounding line in a two dimensional sheet shelf system increases sharply with ice thickness at the grounding line this result is then applied to the large scale dynamics of a marine ice sheet our principal results are that 1 marine ice sheets do not exhibit neutral equilibrium but have well defined discrete equilibrium profiles 2 steady grounding lines cannot be stable on reverse bed slopes and 3 marine ice sheets with overdeepened beds can undergo hysteresis under variations in sea level accumulation rate basal slipperiness and ice viscosity this hysteretic behavior can in principle explain the retreat of the west antarctic ice sheet following the last glacial maximum and may play a role in the dynamics of heinrich events

11 11 dune morphology and dynamics this chapter discusses the key types of sand dunes and how they can be classified and assesses the major controls on their development the processes of dune dynamics are reviewed leading to a discussion of the concept of equilibrium in solitary dune form recent advances in modeling are reviewed that show how interactions between dunes may result in equilibrium at the dune field scale rather than at the single dune scale

early deglaciation of the british irish ice sheet on the atlantic shelf northwest of ireland driven by glacioisostatic depression and high relative sea level understanding the triggers and pace of marine based ice sheet decay is critical for constraining the future mass loss and dynamic behaviour of marine based sectors of the large polar ice sheets in greenland and antarctica numerical models which seek to predict this behaviour need to be calibrated against data from both contemporary and palaeo ice sheets and the latter requires accurate reconstruction of former ice sheet extent dynamics and timing marine geophysics sediment cores benthic foraminiferal assemblages and radiocarbon dating are used to reconstruct the extent of the last british irish ice sheet biis and the timing and style of its retreat on the atlantic shelf northwest of ireland shelf edge moraines and subglacial till recovered in cores from the outer continental shelf are dated to younger than 26 3 ka cal bp and indicate an extensive ice sheet at the last glacial maximum lgm that was grounded to the shelf edge nested arcuate moraines record the subsequent episodic retreat of the ice sheet across the shelf lithofacies and associated foraminiferal assemblages demonstrate that this retreat occurred in a glacimarine environment as a grounded tidewater margin and that high relative sea level and cold waters prevailed during retreat radiocarbon dates indicate that the timing of initial ice sheet retreat from the shelf edge occurred in the interval between 26 3 and 24 8 ka cal bp during the period of minimum global eustatic sea level and that the ice sheet had retreated to the mid shelf by 24 8 ka cal bp the donegal bay moraine a large moraine at the mouth of donegal bay records a major stillstand and readvance of the ice sheet during deglaciation between 20 2 and 17 9 ka cal bp estimated retreat rates of 5 5 35 m a 1 across the shelf demonstrate that retreat was slow it is noteworthy that retreat was initiated in the absence of ocean warming and when eustatic sea level was at a minimum the sea level rise that initiated deglaciation from the shelf edge therefore is inferred to have been a product of local glacio isostatic crustal depression rather than external forcing this demonstrates that marine based sectors of ice sheets can trigger their own demise internally through glacio isostatic adjustment and it provides an explanation for the early retreat of the biis on the atlantic shelf during the global lgm glgm

ice flow patterns and precise timing of ice sheet retreat across a dissected fjord landscape in western norway abstract we reconstruct patterns of ice flow and retreat of the southwestern scandinavian ice sheet from 2900 field observations of glacial striae and elevation measurements of 60 ice marginal deltas from a high resolution lidar dem during the last glacial maximum ice flow was towards the west across the entire area including across several hundred meter deep north south oriented fjords during deglaciation ice flow adjusted to topography and the dominant flow direction switched towards the south west we use a shoreline diagram constructed from relative sea level curves to establish the age of each delta which allows us to constrain the timing of retreat with almost decadal precision rapid ice sheet retreat commenced at the onset of the holocene at 11 600 cal years bp retreat rates were 160 m a 1 in the deepest fjords 60 80 m a 1 in shallower fjords and even slower for land terminating margins the fastest retreat rates 240 m a 1 and 340 m a 1 were experienced in the largest fjords hardangerfjorden and sognefjorden which border the study area to the south and north crosscutting glacial striae indicate that calving bays developed during retreat along the widest fjords the combination of complex fjord topography with fast ice margin retreat by iceberg calving led to isolation of ice remnants on islands and peninsulas a process that accelerated the overall rate of deglaciation ice margin retreat paused between 11 300 11 100 cal years bp probably due to cooling during the preboreal oscillation

heinrich events sediments a history of terminology and recommendations for future usage abstract we document the history of terms used to describe heinrich h layers and events and which mark major glaciological iceberg discharge events in the north atlantic we argue that the usage heinrich layer heinrich zone or heinrich event should be restricted to only those sediments that can be ascribed to an origin from the hudson strait ice stream and the laurentide ice sheet we also argue that the commonplace understanding of these events as dominated by massive iceberg discharges fails to include the earlier well documented evidence that these events were also massive meltwater events linked to deposition along the north atlantic mid ocean channel namoc in the labrador sea we make five recommendations for future usage of heinrich events which include restricting the usage to those events that can be mineralogically geochemically linked to hudson strait abandoning the term heinrich stadial and promote local terminology for ice rafted events that may be correlated or not with hudson strait heinrich events based on calibrated radiocarbon dates or other appropriate chronological markers

glacial geomorphological mapping a review of approaches and frameworks for best practice geomorphological mapping is a well established method for examining earth surface processes and landscape evolution in a range of environmental contexts in glacial research it provides crucial data for a wide range of process oriented studies and palaeoglaciological reconstructions in the latter case providing an essential geomorphological framework for establishing glacial chronologies in recent decades there have been significant developments in remote sensing and geographical information systems gis with a plethora of high quality remotely sensed datasets now often freely available most recently the emergence of unmanned aerial vehicle uav technology has allowed sub decimetre scale aerial images and digital elevation models dems to be obtained traditional field mapping methods still have an important role in glacial geomorphology particularly in cirque glacier valley glacier and icefield ice cap outlet settings field mapping is also used in ice sheet settings but often takes the form of necessarily highly selective ground truthing of remote mapping given the increasing abundance of datasets and methods available for mapping effective approaches are necessary to enable assimilation of data and ensure robustness this paper provides a review and assessment of the various glacial geomorphological methods and datasets currently available with a focus on their applicability in particular glacial settings we distinguish two overarching work streams that recognise the different approaches typically used in mapping landforms produced by ice masses of different sizes i mapping of ice sheet geomorphological imprints using a combined remote sensing approach with some field checking where feasible and ii mapping of alpine and plateau style ice mass cirque glacier valley glacier icefield and ice cap geomorphological imprints using remote sensing and considerable field mapping key challenges to accurate and robust geomorphological mapping are highlighted often necessitating compromises and pragmatic solutions the importance of combining multiple datasets and or mapping approaches is emphasised akin to multi proxy approaches used in many earth science disciplines based on our review we provide idealised frameworks and general recommendations to ensure best practice in future studies and aid in accuracy assessment comparison and integration of geomorphological data these will be of particular value where geomorphological data are incorporated in large compilations and subsequently used for palaeoglaciological reconstructions finally we stress that robust interpretations of glacial landforms and landscapes invariably requires additional chronological and or sedimentological evidence and that such data should ideally be collected as part of a holistic assessment of the overall glacier system

rapid early holocene retreat of a laurentide outlet glacier through an arctic fjord marine terminating outlet glaciers control the stability of ice sheets exposure ages and radiocarbon dates show that an arctic outlet glacier of the laurentide ice sheet rapidly retreated about 9 500 years ago and imply strong feedbacks between bathymetry and ice movement

rapid changes in ice discharge from greenland outlet glaciers using satellite derived surface elevation and velocity data we found major short term variations in recent ice discharge and mass loss at two of greenland s largest outlet glaciers their combined rate of mass loss doubled in less than a year in 2004 and then decreased in 2006 to near the previous rates likely as a result of fast re equilibration of calving front geometry after retreat total mass loss is a fraction of concurrent gravity derived estimates pointing to an alternative source of loss and the need for high resolution observations of outlet dynamics and glacier geometry for sea level rise predictions

late glacial mountain glacier culmination in arctic norway prior to the younger dryas abstract climate changes during the late glacial period lg 15 11 ka as recorded in greenland and antarctic ice cores show a bipolar pattern between 14 5 ka and 13 ka ago the northern latitudes experienced the bolling allerod ba warm period while southern records feature the antarctic cold reversal acr between 12 9 ka and 11 7 ka ago the north was under the younger dryas yd cold spell while southern latitude temperature rose in parallel to atmospheric co2 concentrations while the southern hemisphere pattern is well documented in mountain glacier moraine records from new zealand and patagonia in northern mid latitudes and the arctic the lg glacier culmination has been connected to the yd stadial apparently confirming the bipolar pattern we present a geomorphic map of mountain glaciers in arctic norway a cosmogenic nuclide chronology from 71 moraine boulders from the lg and the holocene and first order glacier modeling experiments the model and dating results show that the studied mountain glaciers are most sensitive to summer temperature change that their response to those changes is highly correlated to a wider region and that these mountain glaciers in arctic norway reached their maximum lg extent about 14 ka ago prior to the yd following considerable retreat through the first part of the yd glaciers re stabilized in the mid yd and showed slower oscillatory retreat through the latter part of the yd we compare this glacier pattern to updated earlier glacier records in the wider arctic and north atlantic region and propose a pattern of coherent glacier response to climate changes during this interval the lg results from arctic glaciers show consistency to the glacier record from new zealand and patagonia this first order interhemispheric coherency of lg mountain glacier fluctuations driven mainly by summer temperature would support the view that the bipolar seesaw was primarily a northern winter phenomenon during the lg period and the yd in particular more similar experiments need to be performed to further test this scenario

deglaciation of fennoscandia abstract to provide a new reconstruction of the deglaciation of the fennoscandian ice sheet in the form of calendar year time slices which are particularly useful for ice sheet modelling we have compiled and synthesized published geomorphological data for eskers ice marginal formations lineations marginal meltwater channels striae ice dammed lakes and geochronological data from radiocarbon varve optically stimulated luminescence and cosmogenic nuclide dating this is summarized as a deglaciation map of the fennoscandian ice sheet with isochrons marking every 1000 years between 22 and 13 cal kyr bp and every hundred years between 11 6 and final ice decay after 9 7 cal kyr bp deglaciation patterns vary across the fennoscandian ice sheet domain reflecting differences in climatic and geomorphic settings as well as ice sheet basal thermal conditions and terrestrial versus marine margins for example the ice sheet margin in the high precipitation coastal setting of the western sector responded sensitively to climatic variations leaving a detailed record of prominent moraines and other ice marginal deposits in many fjords and coastal valleys retreat rates across the southern sector differed between slow retreat of the terrestrial margin in western and southern sweden and rapid retreat of the calving ice margin in the baltic basin our reconstruction is consistent with much of the published research however the synthesis of a large amount of existing and new data support refined reconstructions in some areas for example the lgm extent of the ice sheet in northwestern russia was located far east and it occurred at a later time than the rest of the ice sheet at around 17 15 cal kyr bp we also propose a slightly different chronology of moraine formation over southern sweden based on improved correlations of moraine segments using new lidar data and tying the timing of moraine formation to greenland ice core cold stages retreat rates vary by as much as an order of magnitude in different sectors of the ice sheet with the lowest rates on the high elevation and maritime norwegian margin retreat rates compared to the climatic information provided by the greenland ice core record show a general correspondence between retreat rate and climatic forcing although a close match between retreat rate and climate is unlikely because of other controls such as topography and marine versus terrestrial margins overall the time slice reconstructions of fennoscandian ice sheet deglaciation from 22 to 9 7 cal kyr bp provide an important dataset for understanding the contexts that underpin spatial and temporal patterns in retreat of the fennoscandian ice sheet and are an important resource for testing and refining ice sheet models

the palaeoenvironmental significance of dune size hierarchies the size of a dune is a function of many factors one of which is the length of the period of consistent wind regime under which it grew ephemeral dunes are defined as those that are adjusted to diurnal wind regimes meso dunes to annual wind regimes and mega dunes to wind regimes that persist for longer periods these longer periods could be major climatic cycles but there seem to be no dunes whose size reaches that allowed by the length of some of these periods there may therefore be a maximum size beyond which mega dunes cannot grow dictated by sand supply aerodynamic processes such as speed up or by the scale of the atmospheric boundary layer these concepts are tested on dunes in the wahiba sands in oman analysed from a landsat image it is hypothesised that a large set of megadunes here formed in the lgm that a smaller set of mega dunes may be of younger dryas age and that there is a meso dune series of holocene age

ice stream stability on a reverse bed slope marine ice streams whose beds deepen inland are thought to be inherently unstable numerical modelling of the maguerite bay ice stream retreat in west antarctica since the last glacial maximum suggests that an ice stream can stabilize on an inland sloping bed owing to increased lateral drag where the ice stream narrows marine based ice streams whose beds deepen inland are thought to be inherently unstable1 2 3 this instability is of particular concern because significant portions of the marine based west antarctic and greenland ice sheets are losing mass and their retreat could contribute significantly to future sea level rise4 5 6 7 however the present understanding of ice stream stability is limited by observational records that are too short to resolve multi decadal to millennial scale behaviour or to validate numerical models8 here we present a dynamic numerical simulation of antarctic ice stream retreat since the last glacial maximum lgm constrained by geophysical data whose behaviour is consistent with the geomorphological record we find that retreat of marguerite bay ice stream following the lgm was highly nonlinear and was interrupted by stabilizations on a reverse sloping bed where theory predicts rapid unstable retreat we demonstrate that these transient stabilizations were caused by enhanced lateral drag as the ice stream narrowed we conclude that as well as bed topography ice stream width and long term retreat history are crucial for understanding decadal to centennial scale ice stream behaviour and marine ice sheet vulnerability

collapse of marine based outlet glaciers from the scandinavian ice sheet abstract we present a reconstruction of the timing and retreat rates of more than 2000 m thick younger dryas yd fjord glaciers in western norway using a detailed chronology of 10 be exposure ages from lateral moraines and 14 c dated end moraines a primary conclusion is that ice margins retreated up the 120 170 km long fjords at mean rates of 240 340 m yr 1 during the early holocene we further show that part of the south western sector of the scandinavian ice sheet collapsed in two distinct steps the first step occurred between 19 5 and 18 5 ka bp as break up of the norwegian channel ice stream which drained the ice sheet during the last glacial maximum lgm the second step was the rapid retreat up the fjords mentioned above dated to 11 6 11 1 ka bp during the intervening 7000 years no net retreat occurred despite oscillations of the ice margin this stepwise ice margin retreat strongly contrasts with the more monotonic decay of the ice sheet as a whole indicating that water depths set the pace for climate triggered ice margin retreat in this part of the ice sheet calving and melting of marine margins has dominated mass loss from modern ice sheets in recent decades however the mechanisms and long term 100 1000 yr rate of ice front retreat is less certain and empirical examples such as those given here may help in developing better numerical models

accelerating ice loss from the fastest greenland and antarctic glaciers 1 ice discharge from the fastest glaciers draining the greenland and antarctic ice sheets jakobshavn isbrae ji and pine island glacier pig continues to increase and is now more than double that needed to balance snowfall in their catchment basins velocity increase probably resulted from decreased buttressing from thinning and for ji breakup of their floating ice tongues and from reduced basal drag as grounding lines on both glaciers retreat ji flows directly into the ocean as it becomes afloat and here creep rates are proportional to the cube of bed depth rapid thinning of the pig ice shelf increases the likelihood of its breakup and subsequent rapid increase in discharge velocity results from a simple model indicate that ji velocities should almost double to 20 km a 1 by 2015 with velocities on pig increasing to 10 km a 1 after breakup of its ice shelf these high velocities would probably be sustained over many decades as the glaciers retreat within their long very deep troughs resulting sea level rise would average about 1 5 mm a 1

magnitude and frequency of grain flows on a desert sand dune preliminary studies of the magnitude and frequency of lee side avalanches grain flows on a namib crescentic dune show that the frequency of grain flows for a given segment of the lee face is dependent on the wind speed and sand transport rate for the period preceding their initiation and the magnitude of the flows as described by their area is inversely proportional to the interval between flows and thus wind speed and sand transport rates these studies indicate the potential of using a simple digital video camera technique to document the magnitude frequency and geometry of grain flows on desert sand dunes

autonomous underwater vehicle auv observations of recent tidewater glacier retreat western svalbard abstract recent studies have highlighted the need to improve our understanding of the relationship between glacial front bathymetry and oceanography in order to better predict the behaviour of tidewater glaciers the glaciomarine fjords of western svalbard are strongly influenced by temperate atlantic water advected from the west spitsbergen current marine terminating tidewater glaciers locally influence many svalbard fjords through fluxes of sediments nutrients and freshwater however their response to ocean warming and the imprint left by their recent retreat on the seabed remains unresolved here we present glacial front data collected by an autonomous underwater vehicle auv from four tidewater glaciers fjortende julibreen krossfjorden conwaybreen kongsbreen and kronebreen kongsfjorden the seabed adjacent to the glacial terminus has been mapped providing high resolution bathymetry 0 5 m 1 0 m grid cell size side scan and photographs with additional simultaneous oceanographic observations the aim being to survey the glacial front submarine landforms to identify the water mass structure and to observe any melt water plume activity the bathymetry data displays a diverse assemblage of glacial landforms including numerous retreat moraines glacial lineations crevasse squeeze ridges and sediment debris flows reflecting the dynamic depositional environment of the glacial front the age of the features and the annual rate of retreat have been estimated using satellite remote sensing imagery to digitise the glacial front positions over time the glacial landforms have been produced by the last few years of retreat as these glaciers gradually become land terminating the auv also observed in situ subglacial meltwater plumes at the two most active glaciers kongsbreen and kronebreen and an associated signature of warm atlantic water occurring at the glacier face the presence of relatively warm oceanic waters enhances subsurface melting accelerating the ablation rate while fresh melt water injection at depth influences local water mass structure and the wider fjord circulation at the glacial fronts of kongsbreen and kronebreen sedimentation from subglacial meltwater plumes dominate the ice proximal zone and settling from suspension is more prevalent away from the glacier this study shows how sensitive dynamic glaciomarine systems are to change in the local marine environment and how the use of autonomous vehicles can greatly aid in the monitoring of glacial change by collecting simultaneous high resolution in situ datasets where vessel based observations are lacking

intermediate water ventilation in the nordic seas during mis 2 1 a high resolution marine record from the northern norwegian continental margin off lofoten is used to reconstruct changes in the oceanography of the nordic seas during marine isotope stage mis 2 including the last glacial maximum and early deglaciation circa 25 to 16 ka the period was characterized by generally warm subsurface water temperatures 2 c and inflow of atlantic surface water several events were characterized by decrease in ventilation of the intermediate water and low subsurface temperature and salinity they correlate with colder atmospheric temperatures as seen in ice cores the events terminated with gradual strengthening of the intermediate water ventilation and increase in subsurface temperature the generation of intermediate water was unstable and experienced climate and ventilation changes on millennial and centennial timescales the changes appear consistent with modeling experiments that predict short lasting circulation stops during mis 2 due to release of meltwater in the nordic seas

a reevaluation of the flow data for olivine abstract the solid medium deformation experiments on polycrystalline olivine at pressures of 500 1500 mpa show steadily increasing creep strength with decreasing water content thus water content can significantly influence the strength of olivine room pressure experiments on olivine single crystals have been conducted under conditions of low p h 2 o and therefore should be compared with solid medium experiments on dried samples deformed under anhydrous conditions the single crystals flow more rapidly by 2 3 decades in strain rate for a given stress three hypotheses regarding the origin of this strength discrepancy are 1 1 solid medium sample strengths are higher due to the finite strength of the confining medium 2 2 temperature gradients in the solid medium samples render them stronger 3 3 the application of high confining pressure has significantly increased strength these hypotheses have been analyzed and none of them appears to alter strain rates by more than a decade another hypothesis that dislocations are pinned by iron oxide precipitates in the dry solid medium experiments also does not appear likely unless some unknown effect in the solid medium apparatus results in anomalously high strength for olivine the discrepancy must be attributed to fundamentally different behavior of the single crystal and the aggregate

geomorphology of desert sand dunes a review of recent progress through the 1980s and 1990s studies of the geomorphology of desert sand dunes were dominated by field studies of wind flow and sand flow over individual dunes alongside these there were some attempts numerically to model dune development as well as some wind tunnel studies that investigated wind flow over dunes as developments with equipment allowed field measurements became more sophisticated however by the mid 1990s it was clear that even these more complex measurements were still unable to explain the mechanisms by which sand is entrained and transported most importantly the attempt to measure the stresses imposed by the wind on the sand surface proved impossible and the use of shear or friction velocity as a surrogate for shear stress also failed to deliver at the same time it has become apparent that turbulent structures in the flow may be as or more important in explaining sand flux in a development paralleled in fluvial geomorphology aeolian geomorphologists have attempted to measure and model turbulent structures over dunes progress has recently been made through the use of more complex numerical models based on computational fluid dynamics cfd some of the modelling work has also suggested that notions of dune equilibrium form may not be particularly helpful this range of recent developments has not meant that field studies are now redundant for linear dunes careful observations of individual dunes have provided important data about how the dunes develop but in this particular field some progress has been made through ground penetrating radar images of the internal structure of the dunes the paradigm for studies of desert dune geomorphology for several decades has been that good quality empirical data about wind flow and sand flux will enable us to understand how dunes are created and maintain their form at least some of the difficulty in the past arose from the plethora of undirected data generated by largely inductive field studies more recently attention has shifted although not completely to modelling approaches and very considerable progress has been made in developing models of dune development it is clear however that the models will continue to require accurate field observations in order for us to be able to develop a clear understanding of desert sand dune geomorphology

understanding linear dune chronologies insights from a simple accumulation model abstract dunefields are today often found in regions where environmental conditions are no longer conducive to widespread aeolian transport and deposition and are thus seen as potential archives of palaeoenvironmental information some dune types are more suitable for this purpose than others and linear dunes used here synonymously with longitudinal dunes have been most frequently employed they are commonly found in dryland and dryland marginal regions and they are apparently less migratory than some other dune forms thereby offering the potential for longer environmental histories most recent studies have employed optical osl dating surveys which directly date the emplacement of dune sands to attempt to produce a representative history of aeolian accumulation at a dunefield scale yet such studies have not always given due consideration to the geomorphology of linear dune accumulation although linear dunes do not rework their sand as readily as say barchans dunes it is clear that sand deposited during an aeolian event is likely to have been removed from elsewhere on the dunefield s surface for this reason all dune archives must be assumed to be discontinuous over long timescales the effect of sediment redistribution on dune preservation and thus palaeoenvironmental interpretation is difficult to observe and poorly understood we present a simplified probabilistic model to replicate deposition erosion of sand at a linear dune crest thus simulating the type of profile sampled in many field studies in order to produce a local accumulation history the modelled sand flux incorporates various feedbacks and the simulations are run with varying boundary conditions in which the simulated surface is assumed to be in equilibrium over the multi millennial timescales of the model s duration periodic instabilities in the landscape are generally well recorded by the modelled dune accumulation history particularly when the events involve the system as a whole briefly functioning out of an equilibrium state i e the probabilities of deposition and reworking are not equal however under forcing conditions where the probabilities are unchanged throughout the duration of the model run the results can show apparent structure within the data when sample sizes are low although at large sample sizes the preservation potential decays with burial age according to a power law the model confirms the importance of rigorous sampling strategies for such studies but also suggests that if such precautions are taken the reworking inherent to linear dune aeolian systems does not preclude their use as a quaternary palaeoenvironmental archive of environmental change

lateglacial retreat chronology of the scandinavian ice sheet in finnmark northern norway reconstructed from surface exposure dating of major end moraines abstract we report results from a comprehensive surface exposure dating campaign in eastern finnmark located in the northernmost part of norway and close to the norwegian russian border this is a palaeo glaciologically important region as it sits near the proposed border zone between the former scandinavian and barents sea ice sheets however until now the deglaciation history has few direct dates onshore and the chronology of ice front retreat is instead found by correlating ice marginal deposits with isostatically raised shorelines and marine sediment cores we measured the content of 10 be n 22 and 36 cl n 17 from boulders located at the crest of major moraine ridges at four localities kjaes kongsfjorden vardo and kirkenes these are key localities of existing regional reconstructions of ice recession in this area despite some spread in age results from each locality due to methodological challenges associated with surface exposure dating the large numbers of samples from each site except kjaes still allow for obtaining clusters of similar ages which are used for arriving at a likely chronology of ice front retreat our results show that the kongsfjorden and vardo moraines were deposited 14 3 1 7 ka and 13 6 1 4 ka respectively and thus point to a older dryas age of the proposed outer porsanger deglaciation sub stage moraine ridges belonging to the main sub stage near kirkenes were dated to 11 9 1 2 ka corresponding well with the ice retreat chronology farther west in northern norway and suggesting that the maximum younger dryas ice sheet extent was attained in the late younger dryas along a more than 500 km long stretch in northernmost scandinavia

age and dynamics of linear dunes in the namib desert bristow c s duller g a t lancaster n 2007 age and dynamics of linear dunes in the namib desert geology 35 6 555 558 sponsorship american chemical society

rapid response of helheim glacier in greenland to climate variability over the past century during the early 2000s the greenland ice sheet experienced the largest ice mass loss of the instrumental record 1 largely as a result of the acceleration thinning and retreat of large outlet glaciers in west and southeast greenland 2 5 the quasi simultaneous change in the glaciers suggests a common climate forcing increasing air 6 and ocean 7 8 temperatures have been indicated as potential triggers here we present a record of calving activity of helheim glacier east greenland that extends back to about ad 1890 based on an analysis of sedimentary deposits from sermilik fjord where helheim glacier terminates specifically we use the annual deposition of sand grains as a proxy for iceberg discharge our record reveals large fluctuations in calving rates but the present high rate was reproduced only in the 1930s a comparison with climate indices indicates that high calving activity coincides with a relatively strong influence of atlantic water and a lower influence of polar water on the shelf off greenland as well as with warm summers and the negative phase of the north atlantic oscillation our analysis provides evidence that helheim glacier responds to short term fluctuations of large scale oceanic and atmospheric conditions on timescales of 3 10 years the forcings behind the rapid increase in mass loss from the greenland ice sheet in the early 2000s ref 1 are still debated it is unclear whether the mass loss will continue in the near future and ifso atwhatrate theseuncertaintiesareaconsequenceofour limited understanding of mechanisms regulating ice sheet variability and the response of fast flowing outlet glaciers to climate variability in southeast greenland helheim glacier one of the regions largestglaciers thinned acceleratedandretreatedduringtheperiod 20032005

dependence of creep in olivine on homologous temperature and its implications for flow in the mantle creep data for olivine when normalized by the melting temperature can be extrapolated directly to the pressure temperature and chemical environment of the upper mantle by using the appropriate solidus and geotherms the data presented here collected over a broad pressure range predict effective viscosities that are consistent with geophysical and tectonic constraints for a dry upper mantle these systematics suggest that the effective viscosity of the mantle has risen over the age of the earth as outgassing has progressively raised the solidus

width height and slope relationships and aerodynamic maintenance of barchans the allometric relationship between the height of barchan dunes and horn to horn widths is re examined the addition of new data from barchans in the namib desert and elsewhere confirms the relationship that the height of a barchan is approximately one tenth of the width of the dune height and width of the dune are closely linked to the three dimensional morphology of the dune in particular the relatively constant mean angles of around 11 at which the side slopes of the dune are maintained we suggest that the 3 d barchan form is directly controlled by aerodynamic processes constant feedback between three dimensional stoss face windward shape of the dune slipface height and horn to horn width and shear stress produces an equilibrium dune form

recent retreat of major outlet glaciers on novaya zemlya russian arctic influenced by fjord geometry and sea ice conditions substantial ice loss has occurred in the russian high arctic during the past decade predominantly on novaya zemlya yet the region has been studied relatively little consequently the factors forcing mass loss and the relative contribution of ice dynamics versus surface melt are poorly understood here we evaluate the influence of atmospheric oceanic forcing and variations in fjord width on the behaviour of 38 glaciers on the northern ice cap novaya zemlya we compare retreat rates on land versus marine terminating outlets and on the kara versus barents sea coasts between 1992 and 2010 90 of the study glaciers retreated and retreat rates were an order of magnitude higher for marine terminating outlets 52 1 m a 1 than for land terminating glaciers 4 8 m a 1 we identify a post 2000 acceleration in marine terminating glacier retreat which corresponded closely to changes in sea ice concentrations retreat rates were higher on the barents sea coast which we partly attribute to lower sea ice concentrations but varied dramatically between individual glaciers we use empirical data to categorize changes in along flow fjord width and demonstrate a significant relationship between fjord width variability and retreat rate results suggest that variations in fjord width exert a major influence on glacier retreat

analyzing dune dynamics at the dune field scale based on multi temporal analysis of landsat tm images abstract studying dune dynamics at the dune field scale requires intensive fieldwork and a relatively huge dataset however this is not always possible with the high cost and the limited availability of data here we present a technique based on the analysis of multi temporal landsat tm images for studying the dynamics of different dune morphologies from five dune field sites around the world a pair of landsat tm images for each site has been used after performing several steps of image pre processing and enhancement i e image co registration radiometric calibration and histogram equalization rgb clustering is a commonly used algorithm for data compression and iso clustering in this study we implemented this technique as an unconventional change detection algorithm with 32 clustering partitions per band a bi temporal layerstack of the near infrared bands was the input for the rgb clustering process rgb clustering produced thematic maps that gave an immediate insight into the dune dynamics at the dune field scale given the availability of landsat images the technique gave the best results with dunes developed under uni directional wind pattern in addition it was also easier to detect migration of simple dunes than in compound or complex dunes these maps can be used as a bi temporal digital atlas of large dune systems and help in defining areas for detailed field measurements on dune dynamics and migration moreover it can be implemented in analyzing aeolian systems where field measurements are practically impossible i e large and extra terrestrial aeolian systems

rapid retreat of a scandinavian marine outlet glacier in response to warming at the last glacial termination abstract marine outlet glaciers on greenland are retreating yet it is unclear if the recent fast retreat will persist and how atmosphere and ocean warming will impact future retreat we show how a marine outlet glacier in hardangerfjorden retreated rapidly in response to the abrupt warming following the younger dryas cold period approximately 11 600 years before present this almost 1000 m deep fjord with several sills at 300 500 m depth hosted a 175 km long outlet glacier at the western rim of the scandinavian ice sheet we use a dynamic ice flow model constrained by well dated terminal and lateral moraines to simulate the reconstructed 500 year retreat of hardangerfjorden glacier the model includes an idealized oceanic and atmospheric forcing based on reconstructions but excludes the surface mass balance elevation feedback our simulations show a highly episodic retreat driven by surface melt and warming fjord waters paced by the fjord bathymetry warming air and ocean temperatures by 4 5 c during the period of retreat result in a 125 km retreat of hardangerfjorden glacier in 500 years retreat rates throughout the deglaciation vary by an order of magnitude from 50 to 2500 m a 1 generally close to 200 m a 1 punctuated by brief events of swift retreat exceeding 500 m a 1 each event lasting a few decades we show that the fastest retreat rates occur in regions of the bed with the largest retrograde slopes ice shelf length and fjord water depth is less important our results have implications for modern glacial fjord settings similar to hardangerfjorden where high retreat rates have been observed our findings imply that increasing air temperatures and warming subsurface waters in greenland fjords will continue to drive extensive retreat of marine outlet glaciers however the recent high retreat rates are not expected to be sustained for longer than a few decades due to constraints by the fjord bathymetry

palaeoenvironmental reconstructions from linear dunefields recent progress current challenges and future directions abstract this paper reviews recent progress in the use of linear dunes as geoproxies of late quaternary environmental change summarises the challenges facing their use and explores some potential solutions to these challenges large areas of the swathes of linear dunes which occupy the continental interior of southern africa australia and parts of central asia and southern america currently have limited or negligible aeolian activity they have been recognised as offering potential information about past environments for more than a century but only with the widespread application of luminescence dating during the 1990s did they realistically start to offer the prospect of being an extensive dateable proxy of late quaternary palaeoenvironments and possibly palaeoclimates dating aeolian dune sands with luminescence methods is generally although not always relatively straightforward over the past twenty years a large number 1000 of luminescence ages have been added to the global dataset yet there has also been significant criticism of some of the rationale underpinning much of the interpretation of the records derived at the landscape scale developments of arguably equal importance have come from improved geomorphological understanding based on the wider availability of remotely sensed data and the paradigm of dunefield evolution as a self organising complex system current challenges are identified in three key regions incomplete understanding of how the process geomorphology of linear dunes affect the accumulation and preservation of sediment a lack of clarity regarding the temporal and spatial scale of the response in a dynamic environmental setting and uncertainty surrounding the drivers of changing rates of net accumulation solutions to these challenges lie within diverse research methodologies certainly further field study is required with improvement required in understanding system responses to changing environmental stimuli at scales from sedimentological to landscape in parallel the full implications of complex systems approaches to aeolian geomorphology for linear dunes lag behind the adoption of the concept to some other dune forms e g barchans the relationship between observed dune complexity and age from field data complicates previous suggestions that dune patterning may be purely a function of development time parallel to this lies the need to improve interpretation of the results of dune geochronological studies a suggestion is offered which aims to test the statistical significance of dune accumulation time series by comparison with a modelled system with unchanging external forcing despite the initial promise of linear dune records as a revolutionary source of palaeoenvironmental information in drylands the outcomes to date have been coarse although still valuable in resolution perhaps the most valuable realization has been that geomorphological understanding of these widespread landforms is incomplete

the role of water in the deformation of dunite specimens of two natural dunites anita bay of 100 m grain size and aheirn of 900 m grain size have been deformed in experiments at temperatures between 1200 and 1400 c and constant strain rates between 10 4 and 10 6 s 1 in a gas medium deformation apparatus at 300 mpa confining pressure prior to these experiments the specimens were given a heat treatment in a controlled oxygen fugacity furnace at 1200 c for 60 hours to dehydrate the trace layer silicate minerals present and drive off adsorbed water the predried specimens are much stronger than specimens tested under wet conditions in an earlier study the predried specimens also do not show the apparent grain size dependence seen under wet conditions infrared absorption measurements on the present specimens and those of the earlier study indicate that for a given rock flow stress can be correlated with the intensity of a residual water related broad absorption the addition of water to a predried specimen results in both a mechanical reweakening and an intensifying of the broadband infrared component the weakening of the dunites under wet conditions is probably strongly influenced by the presence of small amounts of a water related species in the grain boundaries but intragranular weakening may also be contributing it is suggested that the concentration of the water related species in the grain boundaries is governed by its concentration in the small melt fraction present the amounts of water that have been found to be of importance for the strength of these dunites are of the order of 0 01 wt amounts much less than most estimates of the water content of the earth s undepleted upper mantle such water may have an important role in determining upper mantle flow behavior stress strain curves for all experiments are available with entire manuscript on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b84 008 2 50 payment must accompany order

deformation of peridotite in the mantle and extraction by kimberlite a case history documented by fluid and solid precipitates in olivine abstract during an extensive study of the microstructure of peridotite xenoliths from kimberlite pipes coprecipitation of fluid and solid phases has been observed in olivine one specimen which displays these precipitates particularly well contains three generations of olivine 1 a original coarse grained highly deformed porphyroclasts 2 b dynamically recrystallized neoblasts 3 c statically recrystallized tablets all three generations display precipitates on virtually all dislocations indicating that exsolution occurred during transport to the surface analysis by a variety of analytical techniques has determined that the solid phase is chrome aluminum spinel and the fluid phase is probably co 2 the deformation and the exsolution microstructure allow construction of a detailed model of the p t path followed by the xenolith to the surface and further allow refinement of our earlier diapiric model of kimberlite genesis

late glacial holocene clay minerals elucidating glacial history in the sw barents sea abstract detailed investigations of the distribution of clay minerals of late glacial holocene sediments from the sw barents sea provide important new information about the provenance and transport paths of the sediments this information leads to better understanding of the onset of the last deglaciation and subsequent advances retreats of the barents sea and fennoscandian ice sheets the results show interaction and changes in the fennoscandian ice sheet and bjornoyrenna ice stream during the last deglaciation high illite content and maximum kaolinite content 18 700 cal yr b p indicate glacial erosion from both the fennoscandian ice sheet and bjornoyrenna ice stream lgm ii the occurrence of a c reniforme dominated benthic foraminiferal assemblage 18 700 cal yr b p indicates that the northern most cores site in ingoydjupet had already been deglaciated and was probably situated in a glacier distal environment in addition smectite content reaching its highest level concurrent with the presence of neogloboquadrina pachyderma sin dominated planktic foraminifera can be related to the strengthening of the atlantic current the inflow of the atlantic water may have triggered deglaciation of the fennoscandian ice sheet bolling interstadial a rapid increase in illite content reflecting strong melting of the fennoscandian ice sheet 15 000 cal yr b p indicates the onset of deglaciation in a core closer to the continent decrease of illite and ird content together with the deposition of laminated sediments during the older dryas stadial 15 000 14 000 cal yr b p indicates colder conditions and formation of at least seasonal sea ice in addition increased kaolinite content indicates increased glacial erosion of the bjornoyrenna ice stream the highest values of illite content and increased ird content 14 000 13 000 cal yr b p can be related to strong melting of the fennoscandian ice sheet a slight indication of the younger dryas cold period is given by the decrease in illite and ird contents all clay contents are more stable during holocene compared to lgm and the last deglaciation

late cenozoic environmental changes along the norwegian margin abstract our ability to understand the rates and consequences of contemporary climate change is limited by the insufficient duration of instrumental records thus we are not able to fully understand the processes that provide a fundamental control in driving climate changes across different timescales palaeo climate archives like those preserved offshore norway provide our only real window through which to observe long term rates and styles of climate change this paper reviews the extensive geological and geophysical data available from the late cenozoic atlantic margin of norway along the margin periods of erosion and deposition have been controlled by agents including fluvial glacial and oceanographic processes current controlled sedimentation along the margin provides insight into the connection of the arctic and atlantic oceans from the miocene onward plio pleistocene shelf edge progradation of up to 150 km can be linked to the grounding of ice sheets on the continental shelf through observations of buried grounding zone wedges and mega scale glacial lineations the margin is also important for understanding the ability of glaciation to cause topographic relief changes and generate offshore geohazards such as the storegga slide which mobilised some 3000 km 3 of sediments during the holocene whilst the processes operating along the norwegian margin are well understood through the late cenozoic there is little geochronological control with which to constrain the environmental changes that have been observed concomitant with the wealth of knowledge and the extensive data that are currently available we propose that the norwegian margin is an ideal location to be considered for future ocean drilling the observations of multiple processes acting independently and together means ocean drilling could yield information of global significance due to the bridging location of norway s atlantic margin between the arctic and lower latitudes

landform assemblages and sedimentary processes along the norwegian channel ice stream abstract several regional and detailed bathymetric datasets together with 2d and 3d seismic data are compiled to investigate the landform assemblages and sedimentary processes along the former path of the norwegian channel ice stream ncis at the broad scale the glacial geomorphology and sedimentary architecture reveals three different zones along the ice stream path characterized by 1 glacial erosion in the onset zone and inner shelf area 2 sediment transport through the main trunk of the ice stream across the mid shelf and 3 a zone of deposition towards the outer continental shelf edge along the first 400 km of the ice stream bed outer oslofjord skagerrak stavanger a major overdeepening is associated with suites of crag and tail features at the transition from the crystalline bedrock to the sedimentary bedrock together with evidence of glaciotectonic thrusting in the form of hill hole pairs here we interpret extensive erosion of both sedimentary rocks and quaternary sediments this zone is succeeded by an approximately 400 km long zone through which most of the sediments eroded from the inner shelf were transported rather than being deposited we infer that sediment was transported subglacially and is likely to have been advected downstream by soft sediment deformation the thickness of till of inferred weichselian age generally varies from 0 and 50 m and this zone is characterized by mega scale glacial lineations msgls which we interpret to be formed in a dynamic sedimentary system dominated by high sediment fluxes but with some localized sediment accretion associated with lineations towards the shelf break the north sea fan extends to the deep norwegian sea and reflects massive sedimentation of glacigenic debris onto the continental slope numerous glacigenic debris flows accumulated and constructed a unit up to 400 m thick during the last glacial maximum the presence of these three zones erosion transport deposition is consistent with observations from other palaeo ice streams and their significance arises from their potential to feedback and impact on ice stream dynamics

origin and morphology of barchan and linear clay dunes in the shuhongtu basin alashan plateau china abstract clay dunes are characterized by a relatively high content of silt and clay and are typically developed on the lee side margin of closed basins in arid and semi arid areas although they are widely distributed aeolian landforms on earth little is known about their development and distribution in asia our field investigations have identified for the first time the occurrence of clay dunes in the alashan plateau north china the clay dunes occur in three isolated lowland areas of the suhongtu sht basin and their morphologies barchans hooked barchans asymmetrical barchans and linear or seif dunes differ substantially from those of the well studied clay dunes in australia africa and north america these differences could be mainly attributed to the asymmetrical bimodal wind regime prolonged drought and sediment physical properties which indicate that dunes of any type can be formed in sand silt or clay based on the known evolution of the sht paleo lake basin and regional climate change we infer that the landscape of modern clay dunes in the desert of the alashan plateau does not predate mis 5 and probably formed during the late holocene analyses of grain size distributions and the contents of trace and rare earth elements combined with geomorphological characteristics indicate that the source sediments of the clay dunes are mainly local cretaceous tertiary and quaternary red fluvial lacustrine mudstone and sediments while the ultimate source is the weathered and denuded products of granitoids of the east altay mountains comparison of the morphology and alignment of the clay dunes with the prevailing wind pattern tends to support tsoar s 1984 model of the transition in dune shape from barchans to seif or linear dunes during 2003 2013 the seif or linear dunes of the sht basin migrated laterally and elongated northeastward at rates of about 2 4 m yr and 16 20 m yr respectively