modern sedimentary processes in the wilmington canyon area u s east coast abstract sedimentary processes active in the wilmington canyon area during the past century are documented from geochronologic sedimentologic and radiographic analysis of sediment cores collected using primarily d s r v alvin site selection for the alvin dives and for collection of box and kasten cores was achieved using sea marc and seabeam data allowing accurate sampling of numerous subenvironments from this extensively dissected area of the continental margin 210 pb sediment accumulation rates from intercanyon areas are highest on the upper slope 1 7 mm yr 140 mg cm 2 yr and decrease with water depth to about 0 4 mm yr 36 mg cm 2 yr on the upper rise within submarine canyons accumulation rates vary dramatically from a maximum of 6 mm yr 500 mg cm 2 yr to less than 0 3 mm yr 22 mg cm 2 yr higher accumulation rates in canyons occur as a result of additional supply of older sediment probably from bioerosion of the canyon walls this is supported by observations from d s r v alvin reduced 210 pb activities and indurated mud clasts observed in several canyon cores extremely low accumulation rates in wilmington and south wilmington canyons are probably the result of strong episodic boundary currents non steady state 210 pb profiles and sedimentologic data indicate small scale mass wasting in south heyes canyon and on the lower slope and rise just north of wilmington canyon

how do bedform patterns arise new views on the role of bedform interactions within a set of boundary conditions one explanation for bedform patterns is self organization in which the pattern emerges because of interactions among the bedforms themselves models remote images field studies and lab experiments have identified bedform interactions that involve whole bedforms only bedform defects or that are remote interactions between bedforms it is proposed that bedform interactions form a spectrum from constructive to regenerative in pattern development constructive interactions including merging lateral linking cannibalization and remote transfer of sediment push the system toward fewer larger more widely spaced bedforms regenerative interactions including bedform splitting defect creation and calving push the system back toward a more initial state other interactions including off center collision defect migration and bedform and defect repulsion cause pattern change but may not be strongly constructive or regenerative although bedform interactions are ubiquitous to any field of bedforms their dynamics flow field modification and impact upon measurable pattern parameters are yet poorly understood most bedform interactions span bedform types and fluids supporting the hypothesis that pattern emerges from dynamics at the bedform level in a hierarchy that includes lower levels of bedform flow and grain fluid interactions bedform interactions alone however cannot account for the rich diversity of bedform patterns in nature it is proposed that field diversity arises because of boundary conditions which are the environmental variables within which a field evolves conceptually boundary conditions modify the shape of the attractor toward which a field evolves possibly by altering the type and frequency of bedform interactions boundary conditions are broadly similar within system types but are unique for each bedform field so that no two are ever exactly alike although aeolian and fluvial systems share some types of boundary conditions flow depth is a unique boundary condition in shallow fluvial systems copyright 2009 john wiley sons ltd

210pb derived sediment accumulation and mixing rates for the washington continental slope abstract total sediment accumulation rates g yr in four canyons indenting the washington continental shelf are about twice those on the nearby open slope even though canyons comprise less than 40 of the depositional area of the entire slope this is because 210 pb derived sediment accumulation rates g cm 2 yr for astoria and quinault canyons are 3 4 times greater than those for willapa and grays canyons and intermediate open slope areas supporting the hypothesis that columbia river derived solids are preferentially transported to these two canyons quinault canyon currently appears to be accumulating solids at rates much greater than its low long term accumulation rate which is attributed to turbidity currents transporting solids down this canyon roughly every 500 years the following four different approaches all show that mixing may cause 210 pb derived sediment accumulation rates for slope and canyon sediments to be 2 3 times higher than true accumulation rates 1 comparison between accumulation rates calculated from 210 pb profiles with and without surface zones in which mixing has obviously affected 210 pb distributions 2 comparison between 210 pb derived and independently determined long term accumulation rates 3 comparison between 210 pb derived accumulation and modern columbia river discharge rates 4 comparison between two and three layer steady state one dimensional diffusion advection decay models mixing coefficients for surface sediments calculated using a one dimensional two layer vertical eddy diffusion model show large differences within the region with most in the 3 30 cm 2 yr range mixing rates are several times larger in canyon sediments from 0 2 1 1 km water depth probably due to physical reworking processes erroneously neglected mixing at depth of no more than 5 of that calculated for the surface mixed layer can cause the 2 3 fold calculated overestimation of true sediment accumulation rates and 2 4 fold calculated underestimation of true mixing coefficients

architecture and structural evolution of an early little ice age terminal moraine at the surge type glacier mulajokull iceland the internal architecture and structural evolution of the arnarfellsmular terminal moraine at mulajokull a surge type glacier in central iceland is described in order to demonstrate submarginal and proglacial glaciotectonic processes during glacier surging as well as constraining the age of the maximum extent of the glacier the moraine is 4 7m high 50 100m wide and composed of a highly deformed sequence of loess peat and tephra that is draped by till up to the crest the internal architecture is dominated by steep high amplitude overturned folds and thrusts in the crest zone but open low amplitude folds on the distal slope section balancing suggests a basal detachment decollement depth of 1 4m and a total horizontal shortening of around 59 this implies that the glacier coupled to the foreland about 70m up glacier from its terminal position to initiate the formation of the moraine the structural evolution is polyphase in that the formation commenced with low amplitude open folding of the foreland followed by overfolding and piggyback thrusting radiocarbon dating and analysis of tephra layers along with historical references indicate that the most likely time of moraine formation was between a d 1717 and 1760 which suggests that mulajokull had its little ice age maximum and most extensive surge earlier than many other surge type glaciers in iceland

geomorphic characterization of four shelf sourced submarine canyons along the u s mid atlantic continental margin abstract shelf sourced submarine canyons are common features of continental margins and are fundamental to deep sea sedimentary systems despite their geomorphic and geologic significance relatively few passive margin shelf breaching canyons worldwide have been mapped using modern geophysical methods between 2007 and 2012 a series of geophysical surveys was conducted across four major canyons of the us mid atlantic margin wilmington baltimore washington and norfolk canyons more than 5700 km2 of high resolution multibeam bathymetry and 890 line km of sub bottom chirp profiles were collected along the outer shelf and uppermost slope depths of 80 1200 m the data allowed us to compare and contrast the fine scale morphology of each canyon system the canyons have marked differences in the morphology and orientation of canyon heads steepness and density of sidewall gullies and the character of the continental shelf surrounding canyon rims down canyon axial profiles for washington baltimore and wilmington canyons have linear shapes and each canyon thalweg exhibits morphological evidence for recent relatively small scale sediment transport for example washington canyon displays extremely steep wall gradients and contains 100 m wide 5 10 m deep v shaped incisions down the canyon axis suggesting modern or recent sediment transport in contrast the convex axial thalweg profile the absence of thalweg incision and evidence for sediment infilling at the canyon head suggest that depositional processes strongly influence norfolk canyon during the current sea level high stand the north walls of wilmington washington and norfolk canyons are steeper than the south walls due to differential erosion though the underlying cause for this asymmetry is not clear furthermore we speculate that most of the geomorphic features observed within the canyons e g terraces tributary canyons gullies and hanging valleys were formed during the pleistocene and show only subtle modification by holocene processes active during the present sea level high stand

recent sedimentation on the new jersey slope and rise radiocarbon dating and sedimentological studies of closely spaced cores indicate movement during the holocene of sediments on the new jersey continental slope and upper rise between wilmington and lindenkohl canyons the uneven time stratigraphic thickness of the late quaternary sediment sections between cores and the nonuniform deposition rate at any given core site and among core sites show that the sediment blanket in canyon and intercanyon areas has been affected by downslope gravity driven pocesses during the holocene to the present the reduced rate of deposition on the slope and upper rise between the late pleistocene and the present is largely due to decreased off shelf transport in response to the eustatic rise in sea level very old radiocarbon dates at core tops result from emplacement of older reworked materials from upslope or from truncation of sections by mass wasting processes exposing older material at the sea floor these processes also account for an irregular sequence of dated sections within cores and stratigraphic irregularities of the surficial cover from core to core marked variability in deposition rates on the slope and upper rise is largely a function of topographic configuration proximity and accessibility to sediment source and transport processes seaward of the shelf break moreover higher accumulation rates on the upper rise are attributed primarily to slope bypassing bypassing prevalent during the late pleistocene has continued periodically to the present

high resolution mapping of ice marginal landforms in the barnim region northeast germany abstract despite more than a 100 year long research history timing and position of the last glacial ice margins in the northeast german lowland are still up for debate the barnim region a till plain in the northeast german young morainic landscape is traversed by the contradictorily discussed frankfurt ice marginal position it is located in a key position to reassess the current state of research with help of a geographic information system gis and field methods a qualitative geomorphological analysis of a high resolution lidar digital elevation model dem in the barnim area uncovers a variety of landforms that were previously not described the most prominent discovery is a set of about 10 lobe shaped ridges in the middle barnim area fieldwork and geophysical measurements were carried out to investigate the structure of the ridges the ridges are 1000 1500 m in length and their widths vary from 10 to 15 km they are raised some 6 10 m from their surroundings the frankfurt ice marginal position can only partially be traced in the dem sedimentological and geophysical investigations indicate that the ridges are composed of glacial till that was deposited on glaciofluvial sediments their formation most probably took place during the ice retreat of the brandenburg phase w 1b and hence represents the w 1f phase in the region

seismic stratigraphy of the fault controlled submarine canyon valley system on the shelf and upper slope of anamur bay northeastern mediterranean sea abstract high resolution shallow seismic reflection uniboom and echosounding profiles obtained on the shelf and upper slope areas of anamur bay turkey northeastern mediterranean were studied together with previous data on the onshore geology of the area to investigate the origin and related seismic stratigraphy of the submarine anamur canyon it was found that the main axial trend of the submarine anamur canyon is aligned with the offshore projection of the n s orientated onshore anamur thrust fault of late cretaceous senonian to early tertiary age interpretation of the distinct reflection configurations observed on the seismic profiles reveals the presence of various seismic facies comparable with the depositional sequences resulting from the relative sea level changes during the late quaternary the acoustic basement probably miocene in age is overlain by a sedimentary column mainly plio quaternary which in turn can be divided into two major seismic sequences and 12 seismic facies that show considerable variations in both their lateral and horizontal extent a palaeo deltaic environment sequence i with its typical topset and foreset facies was recognized and the corresponding deposits are interpreted to be indications of coastal deltaic progradation during late pleistocene sea level highstands or during the early phases of the last major eustatic lowering reflections of sequence ii which includes nine distinct facies are marked by onlap configuration and are believed to be marine deposits of the flandrian transgression at least four transgressive cycles are evident from the seismic profiles at 70 90 60 45 and 40 m water depths the two sequences i and ii are now covered with the most recent facies

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

benthic prokaryotic community dynamics along the ardencaple canyon western greenland sea abstract the ardencaple canyon emanating from the eastern greenland continental rise over a distance of about 200 km towards the greenland basin was investigated to determine the effect of enhanced down slope transport mechanisms on deep sea benthic prokaryotic communities the concentration of viable bacterial cells live dead baclight and prokaryotic incorporation rates 3 h thymidine 14 c leucine increased with increasing distance from the continental shelf multidimensional scaling mds results from terminal restriction fragment length polymorphism t rflp analysis indicated a spatial coherence between the benthic bacterial community structure prokaryotic incorporation rates water content protein concentration and the total organic matter in the sediments the community complexity in sediments at 4 5 cm depth was lower in the central parts of the channel compared with the northern and the southern levees while richness in surface sediments of all stations was similar lacking any clear indications for a recent mass sediment transport or funneled shelf drainage flows high similarities between bacterial assemblages in sediments along the canyon course may thus be governed by a combination of an ice edge induced particle flux episodic down slope and canyon guided transport mechanisms

rapid erosion drumlin formation and changing hydrology beneath an antarctic ice stream what happens beneath a glacier affects the way it flows and the landforms left behind when it retreats direct observations from beneath glaciers are however rare and the subglacial environment remains poorly understood we present new repeat observations from west antarctica that show active processes beneath a modern glacier which can normally only be postulated from the geological record we interpret erosion at a rate of 1 m a 1 beneath a fast flowing ice stream followed by cessation of erosion and the formation of a drumlin from mobilized sediment we also interpret both mobilization and increased compaction of basal sediment with associated hydrological changes within the glacier bed all these changes occurred on time scales of a few years or less this variability suggests that an ice stream can reorganize its bed rapidly and that present models of ice dynamics may not simulate all the relevant subglacial processes

from valley to marginal glaciation in alpine type relief lateglacial glacier advances in the piec stawow polskich roztoka valley high tatra mountains poland abstract the piec stawow polskich roztoka valley in the high tatras western carpathians features typical alpine type relief with a deeply incised glacial trough and large compound trough head cirque the prominent hypsographic maximum in the valley 1680 2000 m along with a broad cirque bottom had provided a vast space for recording glacial and periglacial landforms specifically the most recent lateglacial advances the valley has been intensively studied before in the context of glacial chronology in this paper we re establish the post last glacial maximum lgm glacial chronology of the valley via detailed geomorphologic mapping equilibrium line altitude ela reconstruction and schmidt hammer sh dating along with a critical review of previously published cosmogenic exposure age data 36 cl and lacustrine sediment chronology our results indicate that the first four of the five distinguished lateglacial stages roztoka i iii pusta i occurred before the bolling allerod b a interstadial thus virtually the entire valley became deglaciated in course of the oldest dryas cold phase a distinct reorganization of deglacial patterns from valley type to marginal type occurred before b a warming when the ela increased above the valley hypsographic maximum concentrated at the cirque bottom elevation it shows that noticeable deglaciation step can be caused due to topographic reason with a minimal climate forcing this points also to an important role of glaciated valley hypsography in regulating the distribution of moraines which is rarely taken into account in paleoglaciological reconstructions we infer that glaciers vanished in the tatra mountains during the b a interstadial later a renewed advance during the younger dryas pusta ii formed a nearly continuous festoon shaped pattern of moraines and rock glaciers in close distance to cirque backwalls furthermore we discus some paleoenvironmental significance of the geomorphological record in the valley as well the applicability of sh dating in constructing glacial chronology

plutonium and210pb distributions in northeast atlantic sediments subsurface anomalies caused by non local mixing abstract the depth distributions of 210 pb and 239 240 pu measured in a suite of box cores collected from water depths of 4000 5000 m in the northeast atlantic ocean exhibit pronounced subsurface maxima caused by sediment reworking by benthic infauna small scale spatial heterogeneity in bioturbation rates is indicated by large differences in tracer profiles from duplicate cores separated only by a few centimeters 210 pb and 239 240 pu activity distributions from each subcore exhibit a high degree of correlation and most tracer profiles exhibit one or more subsurface maxima one dimensional biodiffusion analogue models do not adequately simulate the principal features of this data set however an inverse conveyer belt mixing model which simulates subsurface egestion or a functionally equivalent process of surficial material which is enriched both in organic debris and radioactive tracers can reproduce the subsurface tracer maxima single event and continuous subsurface egestion models have been formulated and solved for different feeding rates and background biodiffusive fields the single event model provides a better fit to the data and in particular ensures the observed high degree of correlation between the 210 pb and 239 240 pu activity profiles regardless of the different tracer input functions the most likely candidate responsible for subsurface tracer egestion is a large infaunal worm of the phylum sipunculida which dominates the biomass below a depth of 3 cm

the eyjabakkajokull glacial landsystem iceland geomorphic impact of multiple surges abstract a new glacial geomorphological map of the eyjabakkajokull forefield in iceland is presented the map covers c 60 km2 and is based on high resolution aerial photographs recorded in august 2008 as well as field checking landforms are manually registered in a geographical information system arcgis based on inspection of orthorectified imagery and digital elevation models of the area we mapped subglacially streamlined landforms such as flutes and drumlins on the till plain supraglacial landforms such as ice cored moraine pitted outwash and concertina eskers and ice marginal landforms such as the large multi crested 1890 surge end moraine and smaller single crested end moraines the glaciofluvial landforms are represented by outwash plains minor outwash fans and sinuous eskers extramarginal sediments were also registered and consist mainly of old sediments in wetlands or locally weathered bedrock eyjabakkajokull has behaved as a surge type glacier for 2200 years hence the mapped landforms originate from multiple surges landforms such as large glaciotectonic end moraines hummocky moraine long flutes crevasse fill ridges and concertina eskers are characteristic for surge type glaciers the surging glacier landsystem of eyjabakkajokull serves as a modern analog to the landsystems of terrestrial paleo ice streams

biological mixing intensity and rates of organic carbon accumulation in north carolina slope sediments sediment accumulation rates and biological mixing intensities were determined at three sites on the north carolina slope based on profiles of naturally occurring14c 210pb and234th the three sites all were at a water depth of 850 m with a spacing of 150 180 km between sites sediment accumulation rates increase from south to north from values of 7 cm ky 1 at site i to 160 cm ky 1 at site ii to 1100 cm ky 1 at site iii the organic carbon burial rate at these sites also increases in the northward direction from 0 65 site i to 20 site ii to 150 g corg m 2 year 1 site iii these data indicate that continental margin environment can exhibit highly variable carbon fluxes over relatively small distances on the seafloor the rate of organic carbon accumulation at site iii is one of the highest values reported for the marine environment based on these accumulation rates and dissolved inorganic carbon flux estimates from each site the seabed organic carbon preservation efficiency i e the ratio of corg accumulation rate to corg deposition rate times 100 was estimated to vary from 6 0 to 54 to 88 at sites i ii and iii respectively the14c age of organic matter in surface sediments was older at site iii 1800 years bp than at sites i and ii 800 years bp indicating that site iii receives a greater proportion of old sediment from either up slope areas or from terrigenous sources inventories of excess234th half life of 24 days were used as a tracer for particle flux covering the 100 days prior to the october 1989 july august 1990 and august 1991 cruises the mean234th inventories at the three sites were 4 7 1 9 8 4 6 3and23 1 7 3dpm cm 2 for sites i ii and iii respectively profiles of excess234th activity reveal that the biological mixing intensity is greater at site iii meandb 19 11cm2year 1 n 5 than at either site i meandb 6 0 6 2cm2year 1 n 6 or site ii meandb 4 6 5 2cm2year 1 n 9 in addition to the trend in mixing coefficients the depth of particle mixing on a 100 day time scale generally is greater at site iii than at the other two sites these observations of particle mixing intensity are consistent with the northward increase in the mean abundance of macrofauna 300microns from mean values of 9400 m 2 at site i to 21 400 m 2 at site ii to 55 500 m 2 at site iii for the three study sites off north carolina a strong correlation r2 0 99 p 0 06 exists between macrofaunal abundance and the organic carbon deposition rate an equally strong correlation r2 0 99 p 0 04 occurs between macrofaunal abundance and the234th inventories index of 100 day particle flux fine sand size glass tracer beads were dispersed at these three sites by submersible and then the field plots were sampled 1 year later the vertical distributions of beads at the three sites are consistent with a higher mixing intensity at site iii than at the other two sites but the estimated mixing coefficients generally are lower than those determined from the profiles of234th the slower mixing of the glass beads may be the result of their low food value and or their relatively large size compared to the surrounding fine grained sediments

reconstructing historic glacial lake outburst floods through numerical modelling and geomorphological assessment extreme events in the himalaya westoby m j glasser n f hambrey m j brasington j reynolds j m hassan m a a m 2014 reconstructing historic glacial lake outburst floods through numerical modelling and geomorphological assessment extreme events in the himalaya earth surface processes and landforms 39 12 1675 1692

spatial distribution of erosion and deposition during a glacier surge bruarjokull iceland time series of digital elevation models dems of the forefield of the bruarjokull surge type glacier in iceland were used to quantify the volume of material that was mobilized by the 1963 1964 surge the dems were produced by stereophotogrammetry on aerial photographs from before the surge 1961 and after 1988 and 2003 the analysis was performed on two dems of difference dods i e a 1961 2003 dod documenting the impact of the surge and a 1988 2003 dod documenting the post surge modification of the juvenile surging glacier landsystem combined with a digital geomorphological map the dods allow us to quantify the impact of the surge on a landsystem scale down to individual landforms a total of 34 2 11 3 x 10 6 m 3 of material was mobilized in the 30 7 km 2 study area as a result of the most recent surge event of these 17 4 6 6 x 10 6 m 3 of the material were eroded and 16 8 4 7 x 10 6 m 3 were deposited more than half of the deposited volume was ice cored landforms this study demonstrates that although the total mobilized mass volume is high the net volume gain of ice and sediment deposited as landforms in the forefield caused by the surge is low furthermore deposition of new dead ice from the 1963 1964 surge constitutes as much as 64 of the volume gain in the forefield the 1988 2003 dod is used to quantify the melt out of this dead ice and other paraglacial modification of the recently deglaciated forefield of bruarjokull c 2015 elsevier b v all rights reserved less

rapid advance of two mountain glaciers in response to mine related debris loading rapid glacier advance is known to occur by a range of mechanisms however although large scale debris loading has been proposed as a process for causing rapid terminus advance it has rarely been observed we use satellite remote sensing data to observe accelerated glacier terminus advance in response to massive supraglacial loading on two glaciers in kyrgyzstan over a 15 year period mining activity has led to the dumping of spoil of up to 180 m thick on large parts of these valley glaciers we find that the termini of these glaciers advance by 1 2 and 3 2 km respectively at a rate of up to 350 m yr 1 our analysis suggests that although enhanced basal sliding could be an important process massive supraglacial loads have also caused enhanced internal ice deformation that would account for most or all of the glacier terminus advance in addition narrowing of the glacier valley and mining and dumping of ice alter the mass balance and flow regime of the glaciers although the scale of supraglacial loading is massive this full scale experiment provides insight into glacier flow acceleration response where small valley glaciers are impacted by very large volumes of landslide debris

importance of sampling across an assemblage of glacial landforms for interpreting cosmogenic ages of deglaciation deglaciation chronologies for some sectors of former ice sheets are relatively poorly constrained because of the paucity of features or materials traditionally used to constrain the timing of deglaciation in areas without good deglaciation varve chronologies and or without widespread occurrence of material that indicates the start of earliest organic radiocarbon accumulations suitable for radiocarbon dating typically only general patterns and chronologies of deglaciation have been deduced however mid latitude ice sheets that had warm based conditions close to their margins often produced distinctive deglaciation landform assemblages including eskers deltas meltwater channels and aligned lineation systems because these features were formed or significantly altered during the last glaciation boulder or bedrock samples from them have the potential to yield reliable deglaciation ages using terrestrial cosmogenic nuclides tcn for exposure age dating here we present the results of a methodological study designed to examine the consistency of tcn based deglaciation ages from a range of deglaciation landforms at a site in northern norway the strong coherence between exposure ages across several landforms indicates great potential for using tcn techniques on features such as eskers deltas and meltwater channels to enhance the temporal resolution of ice sheet deglaciation chronologies over a range of spatial scales

impact of local morphology on sedimentation in a submarine canyon rov studies in eel canyon northern california u s a abstract despite existing paradigms about marine sedimentation some submarine canyons are receiving large amounts of sediment during the present highstand of sea level these modern examples can be used to unlock secrets of past canyon sedimentation however submarine canyons have complex morphology and consequently dramatic variations in sedimentary processes and deposits can occur over a range of spatial scales as small as meters to tens of meters operations from surface ships usually cannot place sampling devices on the canyon seabed with this level of accuracy the purpose of the present study was to investigate the variability of sedimentation over a range of scales in order to delineate accurate trends along and among channels at the head of a canyon sampling with the rov ventana facilitated detailed examination of microenvironments i e wall thalweg in eel submarine canyon the combination of intense sedimentation from nepheloid layers and gravity flows in a complicated morphologic system leads to clear distinctions between microenvironments as well as some recognizable and unifying trends in sedimentation inherent small scale variability due to canyon morphology is evident in narrow and steep channels at 1 m horizontal resolution cores exhibit consistent sediment fabric but laminae can differ between cores at the 10 m horizontal scale the fabric is not consistent broader more gently sloping channels reveal consistent sediment fabric at the 10 m scale in most cases physical stratification decreases along the thalwegs of channels as water depths increase in contrast channel walls generally exhibit elevated impacts of bioturbation and variable amounts of physical stratification radiochemical profiles 210pb 137cs and the predominance of physical stratification including discrete laminae with high sand content suggest that the northern entrants are receiving more sediment than their southern counterparts however 210pb profiles in this study demonstrate rapid accumulation of sediment everywhere in the head of eel canyon with the highest rates of accumulation 40 mm yr found in the channel thalwegs in thalwegs evidence from sedimentary structures e g erosional bases cross bedded sand layers demonstrates that gravity flows occur frequently many times each year and have been linked by other investigations to storm impacts on the adjacent continental shelf on decadal timescales these processes are temporarily depositing sediment in the head of the canyon which is removed over longer timescales probably as larger gravity flows triggered by earthquakes the radiochemical and sedimentological data collected at the base of entrant channels confirm that modern sediment is moving to deeper portions of the canyon

evaluation of tandem x elevation data for geomorphological mapping and interpretation in high mountain environments a case study from se tibet china abstract digital elevation models dems are a prerequisite for many different applications in the field of geomorphology in this context the two near global medium resolution dems originating from the srtm and aster missions are widely used for detailed geomorphological studies particularly in high mountain environments these datasets are however known to have substantial disadvantages beyond their posting i e data gaps and miscellaneous artifacts the upcoming tandem x dem is a promising candidate to improve this situation by application of state of the art radar technology exhibiting a posting of 12 m and less proneness to errors in this study we present a dem processed from a single tandem x cossc scene covering a study area in the extreme relief of the eastern nyainqentanglha range southeastern tibet the potential of the resulting experimental tandem x dem for geomorphological applications was evaluated by geomorphometric analyses and an assessment of landform cognoscibility and artifacts in comparison to the aster gdem and the recently released srtm 1 dem detailed geomorphological mapping was conducted for four selected core study areas in a manual approach based exclusively on the tandem x dem and its basic derivates the results show that the self processed tandem x dem yields a detailed and widely consistent landscape representation it thus fosters geomorphological analysis by visual and quantitative means allowing delineation of landforms down to footprints of 30 m even in this premature state the tandem x elevation data are widely superior to the aster and srtm datasets primarily owing to its significantly higher resolution and its lower susceptibility to artifacts that hamper landform interpretation conversely challenges toward interferometric dem generation were identified including i triangulation facets and missing topographic information resulting from radar layover on steep slopes facing toward the radar sensor ii low coherence values on leeward slopes iii decorrelation effects over water bodies and iv challenges for phase unwrapping in settings of strong topographic contrasts there is however a high probability that these drawbacks can be overcome by applying multiple interferograms exhibiting different perpendicular baselines as planned for the generation of the final tandem x dem product

a long square barrel gravity corer for sedimentological and geochemical investigation of fine grained sediments abstract large volume undisturbed sediment cores 3 m long are obtained using a modified gravity corer the corer is square in cross section 12 7 12 7 cm and is designed to facilitate acquisition and subsampling of fine grained sediments sedimentological and geochemical data demonstrate that the modified gravity corer obtains undisturbed cores and preserves the sediment water interface

modern sediment dispersal and accumulation in quinault submarine canyon a summary abstract quinault canyon off the coast of washington intersects the dispersal path of modern columbia river sediments on the continental shelf study of the dynamics dispersal and accumulation of these deposits in the canyon indicates that no systematic down canyon transport occurs rather sediment dispersal is controlled primarily by the regional flow pattern suspended particulate matter is resuspended on the shelf primarily during winter storm events and advected northward as a bottom nepheloid layer bnl over the shelf cross canyon advection produces an intermediate nepheloid layer inl over the upper slope and canyon from which the suspended particulate matter settles rapidly probably in amorphous aggregates rapid short term deposition 10 1 g cm 2 yr 1 and enhanced modern accumulation generally 10 10 2 g cm 2 yr 1 are confined to the upper canyon 1600 m where fluctuations in deposition rates and grain size are related to specific shelf sediment resuspension events in the lower canyon 1600 m accumulation is slow and temporally uniform

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

origin evolution and dynamic context of a neoglacial lateral frontal moraine at austre lovenbreen svalbard moraines marking the neoglacial limits in svalbard are commonly ice cored investigating the nature of this relict ice is important because it can aid our understanding of former glacier dynamics this paper examines the composition of the lateral frontal moraine associated with the neoglacial limit at austre lovenbreen and assesses the likely geomorphological evolution the moraine was investigated using ground penetrating radar gpr with context being provided by structural mapping of the glacier based on an oblique aerial image from 1936 and vertical aerial imagery from 2003 multiple up glacier dipping reflectors and syncline structures are found in the gpr surveys the reflectors are most clearly defined in lateral positions where the moraine is substantially composed of ice the frontal area of the moraine is dominantly composed of debris the core of the lateral part of the moraine is likely to consist of stacked sequences of basal ice that have been deformed by strong longitudinal compression the long term preservation potential of the ice dominated lateral moraine is negligible whereas the preservation of the debris dominated frontal moraine is high a glacier surface bulge identified on the 1936 aerial imagery provides evidence that austre lovenbreen has previously displayed surge activity although it is highly unlikely to do so in the near future in its current state this research shows the value of relict buried ice that is preserved in landforms to aiding our understanding of former glacier characteristics

a semi automated method for mapping glacial geomorphology tested at breiðamerkurjokull iceland abstract despite advances in data collection and analytical software mapping of glacial geomorphology is still largely achieved through manual techniques manual mapping is a relatively slow inefficient and potentially subjective process particularly given the extensive spatial coverage of remotely sensed datasets thus glacial geomorphic mapping would benefit from semi automated techniques able to map large areas quickly and efficiently here we develop novel semi automated techniques for mapping glacial geomorphology based on lidar derived data collected from brei amerkurjokull iceland using object based image analysis obia the landforms classified were moraines eskers flutes drumlins and glacio fluvial outwash several land surface parameters lsps were calculated during image segmentation and analysis representing the characteristics of the landforms of interest the segmentation and classification routines were developed in matlab whereas most attempts so far have used specialised obia software our techniques utilised exploratory data analysis where statistical groupings within the data define different landform types accuracy was assessed against a reference map derived using traditional manual mapping techniques landforms were classified to an overall accuracy of 77 our semi automated mapping techniques should with further algorithm development be applicable using other datasets commonly used in palaeo glaciology such as radar derived elevation data and swath bathymetry

correlation of late quaternary moraines impact of climate variability glacier response and chronological resolution abstract the last decade has seen a global surge in the number and resolution of well dated geomorphological reconstructions of mountain glacier fluctuations and former ice sheet extents this has been facilitated by the widespread deployment of large samples of terrestrial cosmogenic nuclide dating tcnd allowing more sophisticated probability analyses for reducing the statistical uncertainty of moraine ages and testing of correlations at local regional and hemispheric scales geochronological advances in the field laboratory and on model calibration have taken place in parallel with modelling of palaeoclimate based on glacier reconstructions and of glacier sensitivity to temperature and precipitation forcing in spite of these advances basic conceptual issues remain this review questions whether the technical leap forward in dating has encouraged us to over reach our interpretive limits particularly in terms of the concept and practice of correlation we propose that to enable reliable correlation glacier chronologies should first be examined for their climatic integrity spatial coherence and chronological robustness even with excellent dating interpretive complexity remains due to complex climate signals and glacier response characteristics and to erosion censoring of the landform record all are issues which must be addressed to avoid either spurious lumping correlation or splitting differentiation of glacier chronologies and thus misinterpretation of the climatic significance of reconstructed glacier advances we suggest that the reliability of correlation is no better than the weakest link in the chain of reasoning which connects climatic fluctuations with dated landforms and sediments improved dating means that poor chronological resolution is less likely to be the limiting factor for correlation but shifts the focus onto other less quantifiable sources of uncertainty these conceptual statements are exemplified with reference to holocene glacial chronologies of contrasting mid latitude environments in southern norway iceland and new zealand

automated drumlin shape and volume estimation using high resolution lidar imagery curvature based relief separation a test from the wadena drumlin field minnesota abstract resolving the origin s of drumlins and related megaridges in areas of megascale glacial lineations msgl left by paleo ice sheets is critical to understanding how ancient ice sheets interacted with their sediment beds msgl is now linked with fast flowing ice streams but there is a broad range of erosional and depositional models further progress is reliant on constraining fluxes of subglacial sediment at the ice sheet base which in turn is dependent on morphological data such as landform shape and elongation and most importantly landform volume past practice in determining shape has employed a broad range of geomorphological methods from strictly visualisation techniques to more complex semi automated and automated drumlin extraction methods this paper reviews and builds on currently available visualisation semi automated and automated extraction methods and presents a new curvature based relief separation cbrs technique for drumlin mapping this uses curvature analysis to generate a base level from which topography can be normalized and drumlin volume can be derived this methodology is tested using a high resolution 3 m lidar elevation dataset from the wadena drumlin field minnesota usa which was constructed by the wadena lobe of the laurentide ice sheet ca 20 000 years ago and which as a whole contains 2000 drumlins across an area of 7500 km 2 this analysis demonstrates that cbrs provides an objective and robust procedure for automated drumlin extraction there is strong agreement with manually selected landforms but the method is also capable of resolving features that were not detectable manually thereby considerably expanding the known population of streamlined landforms cbrs provides an effective automatic method for visualisation of large areas of the streamlined beds of former ice sheets and for modelling sediment fluxes below ice sheets

the geochemistry of fallout plutonium in the north atlantic i a pore water study in shelf slope and deep sea sediments abstract the distribution of fallout plutonium between pore waters and sediments in the northwest atlantic is examined in order better to define the potential for pu migration from and within marine sediments along a transect of seven cores collected between woods hole and bermuda the solid phase 239 240pu 210pbex and 137cs results do not suggest that any of these tracers are preferentially mobile within the cores pore water pu activities appear to be controlled primarily by the distribution of pu in the solid phase with an operationally determined distribution coefficient kd in the range of 0 2 23 104 there is a trend in the kds along the transect with higher values in the 104 105 range on the shelf and slope to lower values 239 240 pu cm 2 year sediment mixing models are not significantly altered by the inclusion of pu diffusion terms since the pore water terms are so small relative to typical sediment mixing rates

high resolution mapping of supra glacial drainage pathways reveals link between micro channel drainage density surface roughness and surface reflectance this paper reports on the use of a small unmanned aerial vehicle suav carrying a standard compact camera to construct a high resolution orthomosaic om and digital elevation model dem over the lower reaches of the glacier midtre lovenbreen svalbard structure from motion sfm techniques were used to build the om and dem and together these reveal insights into the nature of supra glacial drainage major meandering supra glacial drainage pathways show clear dynamism via meander cutoffs and abandoned channels in addition the imagery reveals a very extensive network of smaller channels that may well carry substantial amounts of water this network of channels is in part controlled by the structure of the glacier but in turn these channels have a significant impact on the ice surface roughness of the ice surface is higher where channels are most extensive in addition we find a relationship between channel density and surface reflectance such that greater channel density is associated with lower reflectance values given the role of surface reflectance and roughness in the energy balance of glaciers it is therefore apparent that extensive networks of small supra glacial channels across such glaciers have the potential to have an important impact on energy exchanges between the atmosphere and the ice surface copyright 2015 john wiley sons ltd

an ice sheet scale comparison of eskers with modelled subglacial drainage routes eskers record the signature of channelised meltwater drainage during deglaciation providing vital information on the nature and evolution of subglacial drainage in this paper we compare the spatial pattern of eskers beneath the former laurentide ice sheet with subglacial drainage routes diagnosed at discrete time intervals from the results of a numerical ice sheet model perhaps surprisingly we show that eskers predominantly occur in regions where modelled subglacial water flow is low eskers and modelled subglacial drainage routes were found to typically match over distances of 10 km and most eskers show a better agreement with the routes close to the ice margin just prior to deglaciation this supports a time transgressive esker pattern with formation in short 10 km segments of conduit close behind a retreating ice margin and probably associated with thin stagnant or sluggish ice esker forming conduits were probably dominated by supraglacially fed meltwater inputs we also show that modelled subglacial drainage routes containing the largest concentrations of meltwater show a close correlation with palaeo ice stream locations the paucity of eskers along the terrestrial portion of these palaeo ice streams and meltwater routes is probably because of the prevalence of distributed drainage and the high erosion potential of fast flowing ice

pleistocene glaciations in chukotka russia moraine mapping using satellite synthetic aperture radar sar imagery abstract using satellite synthetic aperture radar sar imagery we are able to identify many glacial features on the russian landscape that were previously unobservable by scientists outside russian institutes observations from sar imagery provide information on glacial extent moraine morphology and non sedimentary glacial features such as valley morphology and flow direction moraine sequences in several areas of chukotka record multiple pleistocene glacial events moraine position along with several morphologic characteristics such as relative degradation and surface slope can be determined from sar imagery and used to estimate relative age of glacial features by conducting comparative studies on moraines of known age in alaska we are able to estimate the ages of moraines in russia and develop a framework for the correlation of glacial history across bering strait our study of these images suggests that the last major glaciation late wisconsin was much less extensive than older pleistocene events whose marks remain on the landscape beyond the younger moraines

mantle flow and the evolution of the lithosphere abstract the evolution of the lithosphere is mainly controlled by time dependent forces due to 1 plate tectonic processes and 2 sublithospheric mantle flow plate tectonic processes like continental collision may provide strong thermal disturbances and after completion may trigger secondary convection beneath the lithosphere without such mantle flows lateral variations of temperature and associated variations of lithospheric thickness hl or seismic velocities will equilibrate after time scales which are considerably shorter than the geologic ages of several provinces in europe we will discuss the role of sublithospheric mantle flows on the evolution of the lithosphere and the asthenosphere and compare the results with observations from the european lithosphere steady state convection models with a rheology based on laboratory data on lherzolite show that there exists a simple relationship between mantle heat flow and hl however steady state may be reached only after transition times of the order of 1 ga during such times hl shows strong lateral variations if such variations were inherited from plate tectonic events the role of sublithospheric convection would be to prolong their lifetime considerably at higher heat flows sublithospheric mantle convection becomes strongly time dependent with a time scale of 25 50 ma on this time scale variations of hl are small altogether we observe no strong direct correlation between upwelling mantle flows and thin lithosphere in some cases the correlation is even reversed on the other hand the presence or absence of a partially molten asthenosphere may be strongly affected by sublithospheric convection and may show strong lateral variations as well these variations in space and time can be correlated with the laterally heterogeneous lvz with seismic tomography data and with intraplate volcanism in europe mantle convection mantle diapirs and variations in thickness of the lithosphere may exert forces on the lithosphere and crust they will lead to bending of the lithosphere changes in surface topography and thinning or thickening of the crust induced by lateral flows within the lower crust depending on the time scale of loading and unloading of the lithosphere and the relaxation time associated with lower crustal flows characteristic relations between moho depth and surface topography are predicted comparison with observed correlations between moho depth surface topography and lithospheric thickness of european crustal age provinces show some trends in agreement with the proposed crustal deformation model

accumulation of modern sediment in quinault submarine canyon abstract twenty box cores have been studied from quinault submarine canyon a major pathway between the washington continental shelf and the deep sea for silt and clay originating from the columbia river sediment accumulation rates on a 100 yr time scale are calculated from profiles of excess 210pb and of 137cs accumulation rates decrease with increasing distance downcanyon from 14 10 2 g cm 2 yr 1 in the upper canyon lower head to 3 10 2 g cm 2 yr 1 in the lower canyon in the upper canyon lower head channel floor areas have a higher mean accumulation rate 12 10 2 g cm 2 yr 1 than channel wall areas 5 10 2 g cm 2 yr 1 the difference in accumulation rate between channel floor and channel wall areas indicates preferential accumulation i e focusing in topographic lows the decrease in accumulation rate from high rates in the channel floors of the upper canyon to low rates in the lower canyon may be caused by progressive depletion of a nepheloid layer source and or may be an artifact of sediment focusing in the upper canyon the silty clay and clayey silt accumulating in the canyon show no significant trend in grain size or clay mineralogy with depth in cores or with distance downcanyon the lack of sorting probably results from the transport of sediment in aggregate form with a nearly random distribution of size and mineralogy within aggregates quinault canyon is accumulating approximately 5 5 10 5 mt of sediment yr 1 the lithogenic component 64 accounts for 1 4 of the columbia river discharge similarity of sediment trap deposition rates including storm events and 210pb accumulation rates indicates that the vertical flux is a major input of sediment to quinault canyon and that storms are important in the accumulation of sediment on a 100 yr time scale

drumlin sedimentology in a hard bed lowland setting connemara western ireland implications for subglacial bedform generation in areas of sparse till cover cores of coastal drumlins in connemara contain stratified diamictons that interdigitate with gravelly clinoforms and finer grained rhythmites the diamictons are interpreted as subaqueous mud apron deposits delivered by subglacial till advection to continuously failing subaqueous ice contact fans whose strata were being syn depositionally over steepened by glacitectonic deformation the localized nature of the stratified sediments reflects the emergence of subglacial deforming tills and meltwater deposits in a glacilacustrine environment to produce interdigitated mass flow diamictons and grounding line fans wedges these depo centres became glacitectonized and subglacially streamlined during glacier overriding and hence regional drumlin sedimentology reflects the varying degrees of inheritance of pre existing glacigenic deposits and suggests that drumlin production relates more to the position of localized sediment accumulations at the glacier bed than full depth till deformation processes e g instability mechanisms within the same drumlin field till cored drumlins give way down ice to stratified cored drumlins with till caps and then to stratified drumlins this zonation is compatible with the increased lateral variability in drumlin composition that would arise from the occurrence of linear assemblages of glacifluvial esker and subaqueous grounding line sediments in an otherwise marginal thickening till sheet

petrologic and foraminiferal evidence for active downslope transport in wilmington canyon abstract the texture and composition of surficial sediment collected by drsv alvin in a meandering part of wilmington canyon on the upper rise off the mid atlantic states indicate that deposition from gravity flow or bottom current or both has occurred in this sector in recent time the marked petrologic and foraminiferal variations between closely spaced sample sites across the canyon axis show a distinct pattern that is closely related to the configuration of the thalweg the sediment distribution pattern recalls that in sinuous fluvial systems the presence of higher proportions of sand terrigenous grains and displaced shallow water shelf upper slope foraminifera close to the incised part of meanders is a result of active erosion the irregular down core variations of texture terrigenous grains and biogenic components tend to favor a discontinuous stop and go transport process the nature and distribution of mixed assemblages of shallow and deep lower slope and rise benthonic and planktonic foraminifera also indicate a downslope directed transport process involving several pulse like redepositional phases some material was introduced at the head of the canyon but much sediment has also entered the canyon channel by displacement down canyon walls it appears that sediment between the shelf edge and the rise must reside sufficiently long in transit to pick up and incorporate an important mix of deep water faunas as the material is displaced seaward

extensive mis 3 glaciation in southernmost patagonia revealed by cosmogenic nuclide dating of outwash sediments abstract the timing and extent of former glacial advances can demonstrate leads and lags during periods of climatic change and their forcing but this requires robust glacial chronologies in parts of southernmost patagonia dating pre global last glacial maximum glgm ice limits has proven difficult due to post deposition processes affecting the build up of cosmogenic nuclides in moraine boulders here we provide ages for the rio cullen and san sebastian glacial limits of the former bahia inutil san sebastian bi ssb ice lobe on tierra del fuego 53 54 s previously hypothesised to represent advances during marine isotope stages mis 12 and 10 respectively our approach uses cosmogenic 10be and 26al exposure dating but targets glacial outwash associated with these limits and uses depth profiles and surface cobble samples thereby accounting for surface deflation and inheritance the data reveal that the limits formed more recently than previously thought giving ages of 45 6 ka 139 9 14 3 for the rio cullen and 30 1 ka 45 6 23 1 for the san sebastian limits these dates indicate extensive glaciation in southern patagonia during mis 3 prior to the well constrained but much less extensive mis 2 glgm limit this suggests the pattern of ice advances in the region was different to northern patagonia with the terrestrial limits relating to the last glacial cycle rather than progressively less extensive glaciations over hundreds of thousands of years however the dates are consistent with mis 3 glaciation elsewhere in the southern mid latitudes and the combination of cooler summers and warmer winters with increased precipitation may have caused extensive glaciation prior to the glgm

the structural geometric and volumetric changes of a polythermal arctic glacier during a surge cycle comfortlessbreen svalbard various parameters of the most recent surge of the polythermal glacier comfortlessbreen in northwest svalbard have been assessed through a combination of remote sensing and ground observations analysis of a digital elevation model time series shows a marked change in the geometry of the glacier from quiescence 1990 and earlier into the late surge phase 2009 the transfer of 0 74 km3 of ice caused up to 80 m of surface drawdown in the reservoir area above the equilibrium line whilst ice built up in a spatially concentrated manner in the receiving zone below the equilibrium line a ramp of ice c 100 m above quiescent level developed in the lower reaches of the glacier late in the surge also in the lower reaches of the glacier structures attributable to the passage of a kinematic wave are identified and the migration of a surge front on the glacier is thus inferred in a conceptual model we consider that a bend in the valley in which the glacier resides and convergence with tributary glaciers to be significant factors in the style of surge evolution their flow restrictive interference results in slow initial mass transfer and the growth of a surge front within 3 4 km of the terminus copyright 2015 john wiley sons ltd

reconstruction of palaeo ice sheets the use of geomorphological data the article discusses the nature of the glacial inversion problem which is defined as the extraction of time slice ice sheet flow patterns from the patchy and partly overprinted landform record present in former ice sheet areas a coherent inversion model for derivation of flow patterns and interior ice sheet configuration from geomorphological data is presented glacial landscapes are classified according to the three criteria of internal age gradients presence or absence of meltwater traces aligned to flow traces and basal condition frozen bed thawed bed inferred from morphology the inversion model uses landscapes classified accordingly spatially delineated into fans as input data relative chronologies at fan intersections are used to sort fans in a relative age stack that can be linked to stratigraphic dating information

ice streaming in the laurentide ice sheet a first comparison between data calibrated numerical model output and geological evidence 1 despite the importance of rapidly flowing ice streams to ice sheet mass balance their incorporation into numerical ice sheet models is a major scientific challenge this introduces large uncertainties in model output and inhibits a more complete understanding of the role of ice streams in overall ice sheet stability recent computational advances have enabled more realistic representations of ice streaming but few studies have attempted to compare model output against known locations of ice streams this paper compares predictions of ice streaming derived from a large ensemble analysis of a glacial systems model of the laurentide ice sheet against independent geological evidence compiled from previously published studies although the precise dating of paleo ice stream locations is problematic our analysis includes comparisons at six different time steps 18 to 10 cal ka bp during deglaciation results indicate that the model is successful in predicting all of the major marine terminating ice streams but there is mixed success in simulating terrestrial ice streams in the right place and at the right time which is vital in guiding future model development the model also reveals that whilst some ice streams persist throughout deglaciation the focus of mass loss associated with ice streaming switches through time with dynamic changes in ice stream catchments and tributaries this implies that major changes in ice stream activity are to be expected in a deglaciating ice sheet with important implications for contemporary ice sheet dynamics

210pb geochronology of flood events in large tropical river systems floodplain sedimentation removes particles from fluvial transport and constructs stratigraphic records of flooding biogeochemical sequestration and other aspects of the environmental history of ri

ancestral head of wilmington canyon a 12 channel seismic reflection survey over parts of the head of wilmington canyon and the surrounding shelf revealed four major buried valleys and many small channels the data indicate that the ancestral delaware river valley was the most recent of a series of valleys to enter the canyon from the west the head of wilmington canyon probably was eroded and then filled at various times from late miocene to late pleistocene time thick sedimentary sequences indicate a sediment supply from both the north and west a large buried valley entering the canyon from the north was not mapped with the data presented here but it is possible that such a valley exists this is one of the first documentations of the long history of erosion of the united states east coast canyons

clay size minerals as indicators of modern sedimentary processes in submarine canyons application to the wilmington canyon system recent sedimentary processes in the wilmington canyon area u s east coast are interpreted using high resolution profiles of clay size minerals from sediment cores collected using d s r v alvin and the r v atlantis ii modern surficial sediments 100 years old of the wilmington canyon system contain uniformly high relative abundances of illite 55 65 and chlorite 25 35 where these assemblages occur downcore relatively continuous hemipelagic sedimentation is inferred anomalously high concentrations of expandable minerals to 58 and kaolinite to 15 occur at discrete intervals within several cores from the wilmington canyon area these anomalous intervals are bounded by sediments deposited within the past 100 years previous studies of dsdp sites along the u s atlantic margin revealed relatively high abundances of montmorillonite and kaolinite in late cretaceous tertiary strata similar signatures in the wilmington canyon system probably indicate that these sediments are derived from late cretaceous tertiary outcrops on the canyon walls during episodic sediment transport events intervals rich in detrital clay size minerals quartz feldspar pyroxene and amphibole also occur in cores from the wilmington canyon area and are probably derived from pleistocene sediments which were delivered to the continental slope in great quantities during periods of lower sea level the presence of distinct mineral zonations on the floor of the wilmington canyon suggests that local erosional forces rather than large scale turbidity currents probably dominate the canyon area at present surficial sediments from the intercanyon area northeast of wilmington canyon reveal a downslope decrease in illite and corresponding increase in expandable minerals suggesting an increased contribution of pre holocene sediments derived from erosion of the slope

the effect of sediment mixing on pb 210 accumulation rates for the washington continental shelf abstract nine cores from the washington continental shelf were examined by radiochemical techniques in order to evaluate the effect of mixing on the calculation of sediment accumulation rates from pb 210 profiles th 234 profiles indicate mixing coefficients of 140 cm 2 yr 1 for the seabed offshore from the columbia river and 47 cm 2 yr 1 for the seabed of the mid shelf silt deposit 75 km north of the columbia river these large mixing coefficients demonstrate that particles can penetrate to the base of the intensely mixed surface layer 10 cm within one year after emplacement at the seabed surface observed depths of cs 137 penetration within the seabed are compared with depths predicted from the surface mixed layer thickness and the pb 210 accumulation rate the observed and predicted depths agree well at all but one station at this station a combination of th 234 co 60 pb 210 and cs 137 profiles suggests that active mixing occurs below the intensely mixed surface layer the agreement of pb 210 and cs 137 data at the other stations however indicates a general absence of deep mixing on the washington shelf thus the apparent accumulation rates calculated from pb 210 profiles below the intensely mixed surface layer on the washington shelf generally reflect the true rates of sediment accumulation

landscape preservation under fennoscandian ice sheets determined from in situ produced 10be and 26al some areas within ice sheet boundaries retain pre existing landforms and thus either remained as ice free islands nunataks during glaciation or were preserved under ice differentiating between these alternatives has significant implications for paleoenvironment ice sheet surface elevation and ice volume reconstructions in the northern swedish mountains in situ cosmogenic 10be and 26al concentrations from glacial erratics on relict surfaces as well as glacially eroded bedrock adjacent to these surfaces provide consistent last deglaciation exposure ages 8 13 kyr confirming ice sheet overriding as opposed to ice free conditions however these ages contrast with exposure ages of 34 61 kyr on bedrock surfaces in these same relict areas demonstrating that relict areas were preserved with little erosion through multiple glacial cycles based on the difference in radioactive decay between 26al and 10be the measured nuclide concentration in one of these bedrock surfaces suggests that it remained largely unmodified for a minimum period of 845 418 461 kyr these results indicate that relict areas need to be accounted for as frozen bed patches in basal boundary conditions for ice sheet models and in landscape development models subglacial preservation also implies that source areas for glacial sediments in ocean cores are considerably smaller than the total area covered by ice sheets these relict areas also have significance as potential long term subglacial biologic refugia

reconnaissance in dsrv alvin of a fluvial like meander system in wilmington canyon and slump features in south wilmington canyon three dives in dsrv alvin on the atlantic continental rise in wilmington and south wilmington canyons off the east coast of the united states allowed examination and sampling of morphological features in water depths of 2 300 to 2 400 m that were observed in midrange sidescan sonar data in wilmington canyon a fluvial like meandering system was confirmed the meandering channel had steep undercut outer banks and gently sloping inner banks localized slumping is inferred from many steplike depressions on the steep outer banks although the meander system is as much as 500 m wide and has many characteristics typical of a fluvial system extreme depth and evidence of episodic ongoing sedimentary processes preclude a true fluvial origin currents of unknown origin that is downcanyon turbidity flows appear to be the only agent capable of sculpturing the observed features a meander system was not observed in south wilmington canyon channel floor features including deformed and displaced sediment support a previous suggestion of large scale slumping in the area these sediments include upturned clay beds disaggregated gravels loosely bound gravel conglomerates in a reddish brown matrix and a tubular structure resembling a tree root cast within a thinly bedded reddish brown sandstone