fine scale hydrodynamics influence the spatio temporal distribution of harbour porpoises at a coastal hotspot the coastal runnelstone reef off southwest cornwall uk is characterised by complex topography and strong tidal flows and is a known high density site for harbour porpoise phocoena phocoena a european protected species using a multidisciplinary dataset including porpoise sightings from a multi year land based survey acoustic doppler current profiling adcp vertical profiling of water properties and high resolution bathymetry we investigate how interactions between tidal flow and topography drive the fine scale porpoise spatio temporal distribution at the site porpoise sightings were distributed non uniformly within the survey area with highest sighting density recorded in areas with steep slopes and moderate depths greater numbers of sightings were recorded during strong westward ebbing tidal flows compared to strong eastward flooding flows and slack water periods adcp and conductivity temperature depth ctd data identified fine scale hydrodynamic features associated with cross reef tidal flows in the sections of the survey area with the highest recorded densities of porpoises we observed layered vertically sheared flows that were susceptible to the generation of turbulence by shear instability additionally the intense oscillatory near surface currents led to hydraulically controlled flow that transitioned from subcritical to supercritical conditions indicating that highly turbulent and energetic hydraulic jumps were generated along the eastern and western slopes of the reef the depression and release of isopycnals in the lee of the reef during cross reef flows revealed that the flow released lee waves during upslope currents at specific phases of the tidal cycle when the highest sighting rates were recorded the results of this unique fine scale field study provide new insights into specific hydrodynamic features produced through tidal forcing that may be important for creating predictable foraging opportunities for porpoises at a local scale information on the functional mechanisms linking porpoise distribution to static and dynamic physical habitat variables is extremely valuable to the monitoring and management of the species within the context of european conservation policies and marine renewable energy infrastructure development

glacial lake spillway incision and deposition of a coarse grained fan near watrous saskatchewan the watrous spillway was rapidly incised during a short lived outburst from glacial lake elstow in its outlet area the bed of lake elstow was composed of stagnant ice the 40 km long spillway is

geomorphological evidence of holocene climatic change from northwest ellesmere island canadian high arctic proxy data from the northern coast of ellesmere island are used to reconstruct holocene palaeoclimate and appear to corroborate the ice core record from the canadian and greenland high arctic despite some regional variation geomorphological evidence indicates that deglaciation was associated with a marked climatic amelioration in the late pleistocene early holocene 10 ka bp this contrasts with glaciers on the south side of grant land mountains which started to retreat at 7 5 ka bp perhaps due to significant differences in glacioclimatic regime and the influence of the arctic ocean indicators of sea ice conditions on northern ellesmere island suggest that the early holocene was a period of considerable open water radiocarbon dates on driftwood collected from behind the north coast ice shelves suggest that the ice shelves formed during a mid holocene climatic deterioration geomorphic evidence shows that the ice shelves are presently breaking up and melting in response to recent warming glaciers hav

tunnel channels in southeast alberta canada evidence for catastrophic channelized drainage abstract tunnel channels in southeast alberta are attributed to erosion by channelized subglacial meltwater flows an anabranching tunnel channel network dissects the preglacial drainage divide of the ancestral milk river channel morphology and landform associations are used to evaluate competing hypotheses of tunnel channel formation mechanisms that invoke subaerial channel incision direct glacial erosion or steady state time transgressive erosion at the ice margin cannot explain convex up longitudinal channel profiles anabranching channel networks or confinement to the preglacial drainage divide results conclude that the tunnel channel network in southeast alberta represents late stage erosion by a channelised subglacial flow of catastrophic dimensions interpretations for this tunnel channel network are in agreement with conclusions obtained for the regional subglacial landform assemblage

turbulence transition in stratified atmospheric and oceanic shear flows reynolds and prandtl number controls upon the mechanism 1 we provide detailed analyses of the role of secondary instabilities in the transition to turbulence of stratified shear flows at the high reynolds and prandtl numbers appropriate to the atmosphere and ocean our focus is upon a series of recent observations suggestive of a marked change in the mechanism of transition in this laboratory inaccessible regime our results demonstrate the joint dependance of the transition mechanism on these two nondimensional parameters we discuss the primary transition mechanisms of shear aligned convective instability stagnation point instability and shear instabilities of the braid in detail

response of sediment to ice sheet loading in northwestern germany effective stresses and glacier bed stability laboratory tests on sediment over ridden by the last ice sheet in northwestern germany reveal very low ice induced pre consolidation and high palaeo pore water pressures sediment consolidation at the base of the glacier was largely controlled by hydraulic properties of the substratum generally low permeabilities of the bed caused sustained high pore water pressure in over ridden sediments close to the flotation point this implies a serious possibility of hydraulic lifting of the ice sheet it is believed that the reduced basal coupling limited the transformation of glacier shear stress on to the bed sediments which is indicated by a lack of sedimentological evidence for widespread pervasive bed deformation ice motion was probably focused at the glacier sole by some combination of sliding and ploughing however isolated spots with deformation occur so that the subglacial system in the study area can be characterized as a stable deforming mosaic

the anomalous roxana silt and mid wisconsinan events in and near southern michigan abstract thick deposits of roxana silt are recognized only along the illinois river downstream from the woodfordian terminal moraine and are generally interpreted as being mainly loess with the bulk accumulating from about 40 000 to 30 000 yr ago in association with an altonian age glacier in northeastern illinois yet 11 14c dates indicate that southern michigan was not ice covered during that interval thus any proximate ice must have at best been restricted to great lakes basins an interpretation supported by the absence of late altonian till at critically located michigan and nearby sites late mid wisconsinan ice did however obstruct eastern drainage of the ancestral great lakes such glacial blockage the distribution of many michigan organic deposits within pre woodfordian lacustrine sediments and radiocarbon dates suggest that more than once late altonian lakes associated with the lake michigan basin drained into the illinois river erosion of lake and spillway bluffs along with repeated river fluctuations provided a source for the thick geographically restricted roxana silt meanwhile along other nearby rivers the supply was meager and the loess thin

on the breaking of internal solitary waves at a ridge an experimental laboratory study has been carried out to investigate the propagation of an internal solitary wave of depression and its distortion by a bottom ridge in a two layer stratified fluid system wave profiles density fields and velocity fields have been measured at three reference locations namely upstream downstream and over the ridge experiments have been performed with wave amplitudes in the range 0 2 1 9 times the depth of the upper layer and a ratio between the lower and the upper layer in the range 3 0 8 5 the ridge slope was varied from 0 1 to 0 33 and the maximum ridge height was two thirds of the thicker fluid layer over the ridge the flow has been classified into i cases when the bottom ridge has little influence on the propagation and spatial structure of the internal solitary wave ii cases where the internal solitary wave is significantly distorted by the blocking effect of the ridge though no wave breaking occurs and iii cases for which the internal solitary wave is broken as it encounters and passes over the bottom ridge a detailed description of the processes leading to wave breaking is given breaking has been found to take place when the fluid velocity in the lower layer exceeds 0 7 of a local nonlinear wave speed defined at the top of the ridge the breaking condition is also expressed in terms of the amplitude of the incident wave the layer thickness ratio and the relative height of the ridge the wave breaking can be determined from the input parameters of the experiment the transmitted waves have been found to always consist of a leading pulse solitary wave followed by a dispersive wavetrain the solitary wave amplitude is significantly reduced only when breaking takes place at the ridge internal waves of mode two are generated in cases with strong breaking

the lemniscate loop comparisons with the shapes of streamlined landforms the lemniscate loop is a streamlined geometric form which has a simple algebraic equation containing a parameter whose value governs its overall length to width dimensions the lemniscate has been employed in geomorphology including comparisons with glacial drumlins and erosional streamlined islands in the channeled scabland of eastern washington and within the channels on mars these past comparisons have mainly been visual the present study involves more detailed quantitative comparisons between the lemniscate loop symmetrical airfoils drumlins and various islands formed by water flows the analyses focus primarily on the length to width ratios of these landscape features and their consistency with the analytical lemniscate shape many drumlins are found to be similar to the streamlined lemniscate but an equal number are more closely approximated by an elliptical geometric form the streamlined islands in rivers in the channeled scabland and in the martian channels all have nearly the same ave

experimental modeling of pressurized subglacial water flow implications for tunnel valley formation tunnel valleys are elongated hollows commonly found in formerly glaciated areas and interpreted as resulting from subglacial meltwater erosion beneath ice sheets over the past two decades the number of studies of terrestrial tunnel valleys has continuously increased and their existence has been hypothesized also on mars but their formation mechanisms remain poorly understood we introduce here an innovative experimental approach to examine erosion by circulation of pressurized meltwater within the substratum and at the silicon substratum interface we used a permeable substratum sand partially covered by a viscous impermeable and transparent lid silicon putty below which we applied a central injection of pure water low water pressures led to groundwater circulation in the substratum only while water pressures exceeding the sum of the glaciostatic and lithostatic pressures led to additional water circulation and formation of drainage landforms at the cap substratum interface the formation of these drainage landforms was monitored through time and their shapes were analyzed from digital elevation model obtained by stereo photogrammetry the experimental landforms include valleys that are similar to natural tunnel valleys in their spatial organization and in a number of diagnostic morphological criteria such as undulating longitudinal profiles and tunnel shapes these results are consistent with the hypothesis that overpressurized subglacial water circulation controls the formation of tunnel valleys

preservation of miocene glacier ice in east antarctica antarctic climate during the pliocene has been the subject of considerable debate one view holds that during part of the pliocene east antarctica was largely free of glacier ice and that vegetation survived on the coastal mountains1a 4 an alternative viewpoint argues for the development of a stable polar ice sheet by the middle miocene which has persisted since then5a 10 here we report the discovery of buried glacier ice in beacon valley east antarctica which appears to have survived for at least 8 1 million years we have dated the ice by 40ar 39ar analysis of volcanic ash in the thin overlying glacial till which we argue has undergone little if any reworking isotope and crystal fabric analyses of the ice show that it was derived from an ice sheet we suggest that stable polar conditions must have persisted in this region for at least 8 1 million years for this ice to have avoided sublimation

ecologic interpretation of deep sea trace fossil communities abstract trace fossil types and their vertical arrangement tiering are closely related to the biotope and hence can provide information on ecological conditions especially on oxygenation benthic food content sedimentation rate and substrate consistency however to use the full potential of trace fossils for environmental analyses various ichnologic criteria are necessary in addition to trace fossil taxonomy based on a taxonomically oriented ichnologic evaluation of modern deep sea environments six ichnologic aspects to ecologic changes have been found to be of major importance 1 1 penetration depth of burrows is influenced by oxygenation benthic food availability and substrate consistency 2 2 the number and vertical extension of tiers varies due to environmental changes a decrease in the vertical extension of tiers telescoping indicates a decrease in oxygenation benthic food content and or sedimentation rate if shallow penetrating traces disappear oxygen may be depleted and if the deepest tiers disappear the benthic food content may be lowered 3 3 the size diameter of specific trace fossils can indicate oxygen and benthic food availability 4 4 degree of bioturbation is related to sedimentation rate and benthic food content and the diversity of the whole ichnocoenoses or within a specific tier is affected by oxygenation benthic food content sedimentation rate and substrate consistency 5 5 the type of burrow wall unlined mucus lined pellet lined mainly refers to substrate consistency and subordinately to pore water oxygenation 6 6 the type of sediment displacement by body appendages used for excavation ingestion sideward pressing or outside pumping is related to substrate consistency and grain size

sedimentologic evidence for outburst floods from the laurentide ice sheet margin in wisconsin usa implications for tunnel channel formation abstract clast supported boulder gravel in outwash fans along the glacial maximum margin of the laurentide ice sheet in wisconsin indicates the occurrence of outburst floods these sediments with clast intermediate axes of up to 2 m are located downstream of tunnel channels and were deposited shortly before cessation of glaciofluvial activity on each fan since tunnel channels with fans are widespread along the ice sheet margin in the western great lakes region these outburst floods were probably common paleodischarge estimates derived from the boulder deposits are poorly constrained but values of at least several hundred m3 s 1 are likely four potential water sources for the floods exist an extreme surface melt event an extreme precipitation event drainage of supraglacial lakes or drainage of stored subglacial meltwater we focus on the storage of subglacial meltwater behind the ice sheet margin as proglacial permafrost was present as ice advanced to its maximum extent and a frozen bed zone upstream from the margin probably impeded drainage through groundwater aquifers decay of this permafrost seal would have eventually allowed trapped water to drain through the tunnel channels we suggest that the 2 m boulders were entrained in an outburst of subglacial water that enlarged a pre existing channel cut by ablation derived flows

glacial landsystems and dynamics of the saginaw lobe of the laurentide ice sheet michigan usa the surficial terrain of the saginaw lobe in southern michigan is divided into 4 landsystems numbered sequentially from southwest to northeast containing related assemblages of sediments and landforms two of which appear to have a genetic relationship with the bedrock units over which they lie landsystem 1 consists of the sturgis moraine a terminal recessional moraine and an adjacent drumlin field the moraine is a high relief ridge with hummocky topography and ice walled lake plains at its crest and thick coarse outwash fans on its distal margin the drumlin field extends up glacier from the sturgis moraine across the subcrop of the mississippian coldwater shale to the subcrop of the overlying marshall sandstone the low permeability of the shale may have increased basal pore pressures into a range in which deformation of basal sediment into drumlins occurred landsystem 2 overlies the subcrop of the marshall sandstone stagnation of the lobe behind a discontinuous moraine in this area is indicated by high relief collapse topography composed of kames eskers and ice walled lake plains a system of tunnel valleys terminates and merges in this landsystem with large outwash fans and plains sloping away from the margin high basal drainage into the sandstone may have facilitated stagnation across a broad area to form this landsystem landsystem 3 may have also developed during stagnation of the lobe but it differs from landsystem 2 by its more subdued relief it contains a network of evenly spaced southwest trending open tunnel valleys that contain discontinuous esker segments landsystem 4 consists of till plains and low recessional moraines formed as the saginaw lobe retreated downslope into saginaw bay of the lake huron basin tunnel valleys are absent in this area

role of overturns in optimal mixing in stratified mixing layers turbulent mixing plays a major role in enabling the large scale ocean circulation the accuracy of mixing rates estimated from observations depends on our understanding of basic fluid mechanical processes underlying the nature of turbulence in a stratified fluid several of the key assumptions made in conventional mixing parameterizations have been increasingly scrutinized in recent years primarily on the basis of adequately high resolution numerical simulations we add to this evidence by compiling results from a suite of numerical simulations of the turbulence generated through stratified shear instability processes we study the inherently intermittent and time dependent nature of wave induced turbulent life cycles and more specifically the tight coupling between inherently anisotropic scales upon which small scale isotropic turbulence grows the anisotropic scales stir and stretch fluid filaments enhancing irreversible diffusive mixing at smaller scales we show that the characteristics of turbulent mixing depend on the relative time evolution of the ozmidov length scale compared to the so called thorpe overturning scale which represents the scale containing available potential energy upon which turbulence feeds and grows we find that when the mixing is most active and efficient since stirring by the largest overturns becomes optimal in the sense that it is not suppressed by ambient stratification we argue that the high mixing efficiency associated with this phase along with observations of in oceanic turbulent patches together point to the potential for systematically underestimating mixing in the ocean if the role of overturns is neglected this neglect arising through the assumption of a clear separation of scales between the background mean flow and small scale quasi isotropic turbulence leads to the exclusion of an highly efficient mixing phase from conventional parameterizations of the vertical transport of density such an exclusion may well be significant if the mechanism of shear induced turbulence is assumed to be representative of at least some turbulent events in the ocean while our results are based upon simulations of shear instability we show that they are potentially more generic by making direct comparisons with data from ocean and lake observations which represent a much wider range of turbulence inducing physical processes

athens subepisode wisconsin episode non glacial and older glacial sediments in the subsurface of southwestern michigan usa abstract we describe the first complete sediment core to bedrock in southwestern michigan of a radiocarbon defined sequence of michigan subepisode marine oxygen isotope stage mis 2 glacial sediments athens subepisode mis 3 non glacial sediments and two older tills using sedimentological lithological and radiocarbon analyses organics from athens subepisode lacustrine and palustrine sediments yield radiocarbon ages of 41 920 42 950 and 43 630 45 340 and 43 500 14 c yr bp we propose the name port sheldon formation for these organic bearing sediments we interpret the underlying diamictons as two basal tills separated by glaciolacustrine fines the youngest till hemlock crossing till lying below the port sheldon formation is a dark gray gravel poor clay loam to loam with a mean kaolinite illite ratio of 0 98 0 04 the oldest till glenn shores till is a dark grayish brown gravel rich clay loam to sandy loam with mean kaolinite illite ratio of 1 22 0 08 about 130 water well records demonstrate that organic sediments and underlying diamictons are common in the subsurface of ottawa county these tills are likely illinois episode mis 6 or older but an ontario subepisode mis 4 age cannot be ruled out deep bedrock basins in lower michigan provide an untapped archive of pre michigan subepisode history

variability of internal frontal bore breaking above opouawe bank methane seep area new zealand large internal wave breaking is observed exceeding a vertical array of 61 high resolution temperature sensors at 1 m intervals between 7 and 67 m above the bottom the array was moored for 5 days at 969 m of opouawe bank new zealand a known methane seep area as breaking internal waves dominate sediment resuspension above sloping topography in other ocean areas they are expected to also influence methane transport despite being visible in single beam echosounder data indications for turbulence due to rising gas bubbles are not found in the present 1 hz sampled temperature records likely the mooring was too far away from the very localized bubble release spot instead the temperature sensors show detailed internal wave turbulence transitions every tidal cycle a solibore a frontal turbulent bore with a train of trailing solitary waves changes shape and intensity these solibores are highly turbulent and they restratify the bottom boundary layer thereby maintaining efficient mixing details of different turbulent bore developments are discussed averaged over a few tidal cycles and over the sensors range mean vertical eddy diffusivity amounts to 3 1 10 3 m2 s 1 and mean turbulent kinetic energy dissipation to 1 6 0 7 10 7 w kg 1 with variations over 4 orders of magnitude such turbulence will affect the distribution of dissolved methane and other geochemical species in the lower 100 150 m above the bottom and their release from the bottom the above mean values are remarkably similar to those found at various other sites in the ne atlantic ocean

trains of large kelvin helmholtz billows observed in the kuroshio above a seamount trains of large kelvin helmholtz kh billows within the kuroshio current at 230 m depth off southeastern taiwan and above a seamount were observed by shipboard instruments the trains of large kh billows were present in a strong shear band along the 0 55 m s 1 isotach within the kuroshio core they are presumably produced by flow interactions with the rapidly changing topography each individual billow resembling a cat s eye had a horizontal length scale of 200 m a vertical scale of 100 m and a timescale of 7 min near the local buoyancy frequency overturns were observed frequently in the billow cores and the upper eyelids the turbulent kinetic energy dissipation rates estimated using the thorpe scale had an average value of o 10 4 w kg 1 and a maximum value of o 10 3 w kg 1 the turbulence mixing induced by the kh billows may exchange kuroshio water with the surrounding water masses

glacial lake outburst erosion of the grand valley michigan and impacts on glacial lakes in the lake michigan basin abstract geomorphic and sedimentologic evidence in the grand valley which drained the retreating saginaw lobe of the laurentide ice sheet and later acted as a spillway between lakes in the huron and erie basins and in the michigan basin suggests that at least one drainage event from glacial lake saginaw to glacial lake chicago was a catastrophic outburst that deeply incised the valley analysis of shoreline and outlet geomorphology at the chicago outlet supports j h bretz s hypothesis of episodic incision and lake level change shoreline features of each lake level converge to separate outlet sills that decrease in elevation from the oldest to youngest lake phases this evidence coupled with the presence of boulder lags and other features consistent with outburst origin suggests that the outlets were deepened by catastrophic outbursts at least twice the first incision event is correlated with a linked series of floods that progressed from huron and erie basin lakes to glacial lake saginaw to glacial lake chicago and then to the mississippi the second downcutting event occurred after the two rivers advance of the lake michigan lobe outbursts from the eastern outlets of glacial lake agassiz to glacial lake algonquin are a possible cause for this period of downcutting at the chicago outlets

use of nitrogen isotopes and other geochemical tools to evaluate the source of ammonium in a confined glacial drift aquifer ottawa county michigan usa abstract this study utilized several isotopic tracers and geochemical parameters to characterize the source and hydrogeochemical setting of elevated ammonium nh 4 concentrations 2 mg l in a confined glacial drift aquifer in ottawa county michigan results from this investigation indicate that nh 4 is attributed to degrading in situ organic matter and not from surficial anthropogenic sources tritium 18 o and 2 h values suggest that primary recharge in the confined aquifer occurred during the middle to late holocene and before the mid 1900 s geochemical constituents including redox parameters and a suite of common ions demonstrate a compositional difference between the confined and unconfined aquifers in the study area and therefore further support the isolation of the confined aquifer from a significant amount of recent recharge post 1950 s insignificant 15 n nh 4 fractionation 0 81 to 1 38 implies that nh 4 in the confined aquifer originated from degrading in situ organic matter a complete rotosonic glacial sediment core collected to characterize the physical setting of the nh 4 rich aquifer confirmed the presence of in situ organic matter in the confined aquifer a limited set of 15 n no 3 and 18 o no 3 values suggest that the application of manure to row crops may be contributing nitrate up to 10 mg l to nearby shallow residential wells as implemented in this study the use of multiple geochemical and isotopic parameters including 15 n nh 4 can be applied to evaluate the potential source of nh 4 in an aquifer

solibore induced sediment resuspension in the faeroe shetland channel 1 high resolution measurements of temperature and current velocity over the seabed in the faeroe shetland channel fsc reveal an intense internal wave train referred to as a solibore propagating up the continental slope in addition to enhancing turbulent mixing a rotor formed at the leading edge of the solibore generates sediment fluxes o 102 greater than background levels the interaction of solibores which appear to evolve from baroclinic bores with the seabed and the resulting rotor provides a dominant mechanism for the upward transport of sediment over continental slopes that may counteract downward avalanching of material by gravity

erosional origin of hummocky terrain in south central alberta canada we propose that hummocky terrain in south central alberta is the product of subglacial erosion rather than supraglacial letdown during ice disintegration a common view of hummock formation extensive exposures in hummocks contain sediments marking the history of laurentide ice advance and deglaciation in the region regardless of the genesis of those sediments units are abruptly truncated at the surface that represents the hummock and trough morphology indicating that the hummocks are the product of differential erosion subglacial sediments predating the erosion and subglacial eskers overlying the erosion surface suggest that the erosion was also subglacial hummock morphology lithostratigraphy correlated from hummock to hummock truncation at the land surface and widespread coarse boulder lags support a glaciofluvial origin for hummocky terrain in this region

microbial and meiofaunal abundance redox potential ph and shear strength profiles in deep sea pacific sediments vertical profiles of microbial and meiofaunal abundances and of redox potential ph water content and shear strength have been measured in sediment subcores from seven box cores collected in the southern central pacific and the findings have been related to potential effects on pelagic fluxes and sedimentation microbial and meiofaunal abundance decreased exponentially with sediment depth micro organisms were found throughout the depth of the core to 40 cm meiofauna were only present in the top 5 cm to 10 cm meiofaunal metazoans decreased more rapidly than foraminiferans redox potential was always positive decreased below the surface and often rose again deeper in the sediment ph showed no clear cut trend with depth shear strength increased with sediment depth and showed occasional anomalous fluctuations water content decreased progressively downwards with the widest scatter in the top 5 10 cm the most important implications of these results for the water column above are likely to be biologically mediated organic mineralization and nutrient regeneration into the water column and biodeposition of heavy metals and the binding of particulates at and above the sediment water interface by extracellular polymeric material which will in turn lead to differential patterns of sedimentation

predicting fractures in glacially related fine grained materials and a synthetic soil of bentonite and sand using soil texture abstract scientists and engineers from many disciplines have been studying the formation of fractures in fine grained natural geologic materials and fill naturally occurring fractures in the fine grained materials can create preferential flow paths which can allow water to infiltrate quickly resulting in recharge to underlying aquifers but also allowing contaminants to pass through to aquifers potentially threatening ground water drinking water sources they can also create zones of weakness that allow piping in dams and slip zones in fill materials glacially related fine grained materials are widely distributed across the northern hemisphere including the u s states of minnesota wisconsin michigan iowa illinois indiana and ohio canada and much of northern europe it has been difficult to predict the presence of these fractures the objective of this research was to analyze soil textures of fractured soils and determine boundary conditions for predicting the likelihood of fractures in similar materials graphically representing the predictive model on the usda soil texture ternary diagram an extensive midwestern u s data set 275 data points including ohio iowa michigan and wisconsin soil samples was studied the texture data of those glacially related fine grained materials containing fractures indicate that those with 6 5 clay can be predicted to support fractures an auxiliary experiment using bentonite suggests that this predictive model may be applicable beyond the clay mineralogies common to the u s midwest this is a promising method of predicting which soil textures are most likely to form fractures and can be a useful field tool for engineering geologists soil scientists and other environmental professionals it is immediately applicable to the u s midwestern sites and with additional analyses using other soils could be used more widely across glaciated north america and northern europe

late wisconsinan drift stratigraphy of the lake michigan lobe in southwestern michigan three lake michigan lobe till sheets are exposed in a 20 to 25 m high section glenn shores section along the lake michigan shoreline in southwestern michigan the glenn shores till lowest is directly overlain by stratified silt sand and gravel containing organic material dated at 37 150 to 48 000 yr b p the ganges till middle and saugatuck till uppermost are overlain by lacustrine sediments the three till units can be differentiated by the 7a 10a x ray diffraction peak height ratio of their clay size fraction clay mineral analyses of more than 200 samples collected from moraines till plains and multi till exposures 2 to 60 km inland suggest that saugatuck till at the lakeshore is equivalent to till in the lake border valparaiso and sturgis kalamazoo morainic systems whereas ganges till can be traced in the subsurface from the lakeshore to where it crops out within the tekonsha moraine the presence of lacustrine sediments between ganges and saugatuck tills implies that a significant retreat 60 km of the lake michigan lobe occurred between the formation of the tekonsha moraine and that of the sturgis kalamazoo morainic system on the basis of morainal correlations we propose that saugatuck till correlates with wadsworth till in illinois whereas ganges till probably correlates with the upper part of the yorkville till in illinois

late wisconsinan ice flow reconstruction for the central great lakes region late wisconsinan tills from the lower peninsula of michigan can be differentiated with respect to the lake michigan saginaw and huron erie lobes on the basis of their heavy mineral assemblages using discriminant analysis the heavy mineral assemblages can also be associated with specific source areas on the canadian shield these associations suggest that 1 the lake michigan lobe flowed southwestward across a region north of lake huron and then into southwestern michigan 2 the saginaw lobe flowed southwestward across a region northwest of georgian bay and then into south central michigan and 3 the huron erie lobe flowed southwestward across a region north of georgian bay and then southward into southeastern michigan comparison of the heavy mineral assemblages of tills from southeastern michigan with those from younger tills just south of lake huron indicates that a significant westward shift in source area occurred during the retreat of the huron erie lobe from southeastern michigan

on the formation of the tunnel valleys of the superior lobe central minnesota abstract when considering the formation of tunnel valleys most researchers have appealed to basal melting as the primary source of water erosion of the tunnel valleys can then be accomplished by steady state drainage over a long period or by storage and subsequent catastrophic release however field relationships in a large system of tunnel valleys formed by the superior lobe in central minnesota indicate that another source of water must be considered the minnesota tunnel valleys are composed of individual segments 10 20 km long and the segments commonly terminate in subaerial outwash fans at recessional ice margin positions eskers associated with the tunnel valleys are also composed of short segments frequently beginning at moulin kames and terminating at the head of outwash fans the dominant source of the water responsible for tunnel valley formation was seasonal meltwater from the glacier surface that reached the bed through moulins and crevasses the apparent continuity of the valleys resulted from the headward development of the englacial drainage system during ice retreat

modelling north american palaeo subglacial lakes and their meltwater drainage pathways this paper presents predictions of palaeo subglacial lakes and their drainage pathways beneath the north american ice sheet during the last glaciation we utilise data on the current topography and seafloor bathymetry and elevation models of the ice and ground surface topography from data calibrated glaciological modelling to calculate the hydraulic potential surface at the ice sheets bed given that specific ice surface elevations are only known from modelled outputs and thus contain significant uncertainty we utilise many such outputs to examine where on the bed that subglacial lakes are likely to have occurred our analysis demonstrates the potential for subglacial lake genesis particularly beneath the former cordilleran ice sheet along the suture zone between the laurentide and cordilleran ice sheets in hudson bay in the great lake basins and deep trenches of the canadian archipelago during the last glacial maximum we suggest that at least 1000 km3 of meltwater could have been stored subglacially as the ice sheet and the bed evolved subglacial lakes repeatedly formed and emptied particularly in hudson bay and the suture zone between the laurentide and cordilleran ice sheets where lakes were characteristically broad and shallow 10 m deep in contrast the cordilleran ice sheet was characterised by deep up to 90 m and persistent lake genesis significantly similar distributions and modes of predicted subglacial lakes are obtained irrespective of the model or model run which suggests the results are robust subglacial meltwater drainage varied between stable networks typically associated with strong topographic controls and convoluted networks that underwent considerable dynamism including repeated meltwater network capture these lake likelihood predictions could usefully form targets for detailed field and remote investigations and we hypothesise and explore the potential that numerous deposits and spillways previously interpreted as arising from ice marginal lakes may have emanated from their subglacial cousins

minimum limiting deglacial ages for the out of phase saginaw lobe of the laurentide ice sheet using optically stimulated luminescence osl and radiocarbon methods

origin and large scale erosional features of glacial lake spillways in the northern great plains deglaciation of the northern great plains produced two basic types of fluvial systems 1 depositional regimes produced by the action of glacial melt water that formed outwash plains and 2 highly erosive systems produced by the sudden rapid drainage of glacial lakes that formed spillways spillways are huge deeply incised trenches that display all of the characteristics of fluvial channels glacial lakes drained in weeks or months and discharges of 10 5 m 3 s were attained at bankfull stage seven spillway systems studied were formed as a consequence of the sudden rapid draining of glacial lakes many other large valleys in the mid continent area and other glaciated regions were probably formed by the same process spillways consist of deeply incised inner channels commonly flanked by broad scoured outer zones initial stages of flow produced shallow anastomosing channels continued erosion produced longitudinal grooves streamlined erosional residuals and surficial boulder lag deposits inner channels developed by the enlargement of one or more centrally located longitudinal grooves the development of erosional residuals was initiated by the incision of shallow anastomosing channels the interchannel areas were progressively modified from irregular quadrilateral or elliptical shapes to an equilibrium minimum drag lemniscate shape as glacial lake drainage proceeded correlations between length and width length and area width and area and length width ratio and k a shape parameter of the lemniscate loop are very high for all erosional residuals studied although only 20 of the residuals display an equilibrium lemniscate shape stable relationships between length width and area of erosional residuals are therefore established very early and are maintained throughout the erosional modification to the lemniscate shape the only shape factor tested which can be used to quantitatively differentiate lemniscate from nonlemniscate erosional residuals is the position of maximum width as measured by the ratio of the length from the lee to the point of maximum width to the total length xm l the mean xm l ratio for erosional residuals in a spillway segment is an indication of the relative duration of flood flows that produced the spillway

biological modifiers of marine benthic seascapes their role as ecosystem engineers benthic organisms in marine ecosystems modify the environment on different spatial and temporal scales these modifications many of which are initially at a microscale are likely to have large scale effects on benthic seascapes this is especially so if the species are ecosystem engineers most species of infaunal and epifaunal invertebrates and macrophytes contribute at a geophysical or geochemical level microorganisms also play a key but currently neglected role in the intertidal and immediately sublittoral zone algae and seagrasses and mussels in mussel beds have received considerable attention a substantial fossil record also exists mathematical modelling of these systems is still in its infancy although several sophisticated mathematical tools have been applied the effects of bioturbation and of microorganisms have been less studied and little is known about the activities of benthic organisms in the deep sea this paper addresses all these effects and places them in the context of large scale benthic seascapes and of the extensive literature on species defined as ecosystem engineers in the sea

outburst flood origin of the central kalamazoo river valley michigan usa abstract geomorphic evidence and stratigraphic information from boreholes suggest that the oversized central kalamazoo river valley ckrv in southwest michigan resulted from a catastrophic outburst flood emanating from subglacial channels under the saginaw lobe of the laurentide ice sheet the ckrv occurs as a deeply incised trench over 2 km wide and in excess of 50 m deep situated in a reentrant formed by the lake michigan saginaw and huron erie lobes the course of the ckrv follows an irregular flow path that bisects the kalamazoo moraine of the lake michigan lobe erosional terraces near the mouth of the channel indicate that lake michigan lobe meltwater drained eastward prior to the westward saginaw outburst prior to valley formation the lake michigan lobe had retreated westward to at least the lake border moraine with the lake michigan lobe absent to impede flow drainage from the ckrv proceeded southwesterly until draining into glacial lake chicago near st joseph michigan the outburst originated from a system of saginaw tunnel channels that display convex up flow profiles and contain eskers meltwater drainage transitioned from subglacial to ice marginal and proglacial environments during the interval represented by the outburst the saginaw lobe appears to have been in a relatively stationary position

sedimentology and paleohydrology of glacial lake outburst deposits in southeastern saskatchewan and northwestern north dakota glacial lake outbursts occurred in the northern great plains as ice marginal lakes suddenly drained forming an interconnected system of glacial lake spillways the outbursts were highly erosive and consequently deposits from such discharges are rare in the spillways glacial lake outburst deposits in the souris des lacs and moose mountain spillways saskatchewan and north dakota have distinct bar shapes and internally are more massive and homogeneous than those of outwash systems in this paper the outburst deposits are described and the sedimentologic and hydrodynamic characteristics of the outburst discharges are interpreted coarse grained sediment eroded from till formed large scale bars in the spillways as much as 2 km long and 30 m thick both as pendant bars and bars in alcoves next to contemporaneous landslides internally the bars consist of homogeneous masses of massive matrix supported very poorly sorted pebbly cobble gravel containing boulders as much as 3 m in diameter the maximum particle sizes in individual bars decrease downstream and toward spillway sides the lithology of the bars resembles the local glacial drift material from the tertiary bedrock in which the spillways are partially incised is not concentrated in the bars paleohydraulic calculations based on data of maximum particle size and on the shields9 entrainment function yield unreasonably large values supplementary calculations based on depth limits established from field observations yield realistic values this method indicates that velocities of 2 9 to 11 7 ms 1 and discharges of 5 8 10 4 to 8 2 10 5 m 3 s 1 were achieved by the outburst sediment water concentrations during the outburst estimated by dividing the volume of sediment eroded by the source lake volume averaged 20 by weight because of this estimate the abundant amount of fine grained material that was eroded and structure of the outburst deposits we infer that outburst flows were hyperconcentrated with sediment water concentrations being as much as 40 by weight in some areas we further infer that sediment transport was extremely efficient and that most particles including coarse gravel were transported in suspension this interpretation is consistent with the sedimentology of the deposits and other conjectural evidence expanding sections caused coarser sediment to be deposited indiscriminate of clast size as poorly sorted massive gravel bars finer grained sediment sand to clay size was transported through the spillway system into downstream glacial lakes

in situ geotechnical characterization of sediments on the nova scotian slope eastern canadian continental margin abstract a seabed 2 m long cone penetrometer and coring system geotechnical module has been used at 17 stations in four transects on the scotian slope to characterise in situ shear strength and induced pore pressure on several different types of late pleistocene and early holocene failure study sites were selected using the sar high resolution deep towed acoustic system equipped with a digital 160 190 khz sidescan sonar and a 3 5 khz subbottom profiler several distinctive types of geotechnical signature were recognised from plots of cone resistance and induced pore pressure with depth in the sediment normally consolidated sediments show a progressive increase in cone resistance with depth to about 75 kpa at 2 m subbottom holocene surficial muds show spectacular apparent overconsolidation reaching a peak of 250 kpa at about 50 cm subbottom and then decreasing down to 1 5 m this overconsolidation is associated with zoophycos burrows late pleistocene sediments exhumed by bedding plane slides show strong true overconsolidation consistent with the original depth of burial inferred from high resolution seismic stratigraphy debris flows show only a slight shear stress gradient with depth 40 45 kpa over 0 5 1 m subbottom with under consolidation due to remoulding of sediment

drumlins and catastrophic subglacial floods shaw j kvill d and rains b 1989 drumlins and catastrophic subglacial floods in j menzies and j rose editors subglacial bedforms drumlins rogen moraine and associated subglacial bedforms sediment geol 62 177 202 a number of lines of evidence are shown to be consistent with drumlin formation by catastrophic meltwater floods drumlins are associated with landforms related to such floods and landscapes produced by outburst floods in extragiacial areas contain drumlin like landforms some drumlins which contain mainly residual materials are compared to similar forms covering a wide range of scales and are interpreted to be scour remnant ridges produced by the action of horseshoe vortices on subgiacial materials these vortices are a product of flow separation in turbulent fluids and this interpretation implies drumlin formation by meltwater other drumlin calied cavity fill drumlins have distinctive shapes that are analogous with infilled erosional marks produced by turbulent separated flows these drumlins are interpreted as the infills of cavities eroded upwards into glacier beds by broad subgiacial meltwater sheetflows the sedimentology and internal structure of the cavity fill drumlins indicate rapid deposition from hyperconcentrated flow clast shape surface texture and lithology are consistent with the short distance of giaciofhivial transport predicted by the cavity fill hypothesis estimates of flow discharge 0 6 6 x 107 m3 s total volume of flow 84 1 103 km3 and flow duration 16 162 days are given for the catastrophic flood proposed to have produced the livingstone like saskatchewan drumlin field subgiacially derived floods are used to explain the sudden drainage of extraglacial lakes and major depositional events in proglacial lakes and it is suggested that they might have contributed to the lid of cold freshwater over the north atlantic held to have caused a late glacial cooling event the flood hypothesis requires extensive subgiacial lakes to have occurred beneath the laurentide and fennoscandian ice sheets which if they existed must have influenced the form and behaviour of these major bodies of ice

nonlinear motions at the internal tide source 1 oceanic internal tidal wave generation is commonly modeled via interaction of a sinusoidal barotropic vertical velocity w with topography however general w above slopes are predominantly nonlinear as appears in some nonhydrostatic models here 1 2 hz sampled observations are presented from 2 84 m above the bottom mab at 1400 m at the bay of biscay continental slope fronts are observed that all propagate upslope having heights 50 mab and more or less 5 occurring at the tidal periodicity they are accompanied by o 10 min pulses of w 0 10 m s 1 w and irregular small scale waves superimposed on an asymmetric tidal signal this nonlinearity is further exemplified by variations in frontal arrival and steepness height form and is causing i internal tidal intermittency of 10 tidal periods ii nonlinear generation of internal tidal higher harmonics at the source the observations suggest internal tide generation in a broadband instead of a monochromatic beam

a composite spectrum of vertical shear in the upper ocean abstract results from three separate velocity profilers operated nearly simultaneously in the northwest atlantic in 1975 are used to form a composite shear spectrum over vertical wavelengths from 100 m down to a few centimeters this exercise constitutes an intercomparison of the three different measurement techniques and reveals a shear spectrum which is approximately fiat at a wkb scaled level from k 0 01 cpm through k0 0 1 cpm then falls as k 1 to a buoyancy wavenumber k0 n3 1 2 determined by the local average vaisala frequency n and the volume averaged dissipation rate various consequences of the observed shear spectral shape are explored

late wisconsinan drift stratigraphy of the saginaw ice lobe in south central michigan clay mineral analyses have been used to define two late wisconsinan till sheets of the saginaw lobe in southwestern michigan bedford till can be traced along the ground surface from the lansing moraine southward to exposures within the kalamazoo moraine and fulton till can be traced in the subsurface southward from the lansing moraine through a series of bore holes to exposures within the tekonsha moraine both tills are sometimes separated by a layer of sand and gravel the presence of sand and gravel between the bedford and fulton tills further suggests that a significant retreat 60 km of the saginaw lobe occurred between the formation of the tekonsha and kalamazoo moraines morpho stratigraphic correlations between moraines of the saginaw and huron erie lobes suggest that the interval between the deposition of the bedford and fulton tills is probably time equivalent to the erie interstade correlations between moraines of the lake michigan and saginaw lobes in southwestern michigan also suggest that the erie interstade occurred in the lake michigan lobe between the deposition of ganges and saugatuck tills

hummocky moraine sedimentary record of stagnant laurentide ice sheet lobes resting on soft beds abstract over large areas of the western interior plains of north america hummocky moraine hm formed at the margins of laurentide ice sheet lis lobes that flowed upslope against topographic highs current depositional models argue that hm was deposited supraglacially from stagnant debris rich ice disintegration moraine across southern alberta canada map and outcrop data show that hm is composed of fine grained till as much as 25 m thick containing rafts of soft glaciotectonized bedrock and sediment chaotic non oriented hm commonly passes downslope into weakly oriented hummocks washboard moraine that are transitional to drumlins in topographic lows the same subsurface stratigraphy and till facies is present throughout these landforms and others such as doughnut like rim ridges flat topped moraine plateaux and linear disintegration ridges are identified as belonging to subglacially deposited soft bed terrain this terrain is the record of ice lobes moving over deformation till derived from weakly lithified bentonite rich shale drumlins record continued active ice flow in topographic lows during deglaciation whereas hm was produced below the outer stagnant margins of ice lobes by gravitational loading pressing of remnant dead ice blocks into wet plastic till intervening zones of washboard moraine mark the former boundary of active and stagnant ice and show hybrid drumlins whose streamlined form has been altered by subglacial pressing humdrums below dead ice the presence of hummocky moraine over a very large area of interior north america provides additional support for glaciological models of a soft bedded laurentide ice sheet

ice fracturing during jokulhlaups implications for englacial floodwater routing and outlet development theoretical studies of glacial outburst floods jokulhlaups assume that i intraglacial floodwater is transported efficiently in isolated conduits ii intraglacial conduit enlargement operates proportionally to increasing discharge iii floodwater exits glaciers through pre existing ice marginal outlets and iv the morphology and positioning of outlets remains fixed during flooding direct field observations together with historical jokulhlaup accounts confirm that these theoretical assumptions are not always correct this paper presents new evidence for spatial and temporal changes in intraglacial floodwater routing during jokulhlaups secondly it identifies and explains the mechanisms controlling the position and morphology of supraglacial jokulhlaup outlets and finally it presents a conceptual model of the controls on supraglacial outbursts field observations are presented from two icelandic glaciers skei ararjokull and solheimajokull video footage and aerial photographs taken before during and after the skei ararjokull jokulhlaup and immediately after the solheimajokull jokulhlaup reveal changes in floodwater routing and the positioning and morphology of outlets field observations confirm that glaciers cannot transmit floodwater as efficiently as previously assumed rapid increases in jokulhlaup discharge generate basal hydraulic pressures in excess of ice overburden under these circumstances floodwater can be forced through the surface of glaciers leading to the development of a range of supraglacial outlets the rate of increase in hydraulic pressure strongly influences the type of supraglacial outlet that can develop steady increases in basal hydraulic pressure can retro feed pre existing englacial drainage whereas transient increases in pressure can generate hydraulic fracturing the position and morphology of supraglacial outlets provide important controls on the spatial and temporal impact of flooding the development of supraglacial jokulhlaup outlets provides a new mechanism for rapid englacial debris entrainment

drumlin formation by subglacial meltwater erosion some drumlins are shown to belong to a family of remnant erosional ridges associated with subglacial meltwater the lengths of these ridges vary in scale from a few tens of millimetres to over 5 km similar form elements are illustrated for three scales of forms it is concluded that some drumlins are composed of preexisting sediment or bedrock left upstanding in ridges as a result of the removal of surrounding materials this erosional theory is related to an earlier theory in which drumlins are held to result from the infilling of subglacial cavities the unifying factor for both theories is the role of sheets of subglacial meltwater

laurentide subgiacial outburst floods landform evidence from digital elevation models various lines of landform evidence in many parts of canada are comprehensively explicable as products of subglacial sheetfloods outburst floods in the northwest territories northern saskatchewan and alberta landform associations such as scoured bedrock tracts cavity fill drumlins erosional drumlins erosional giant flutes remnant ridges tunnel channels channeled scabland and hummocky terrain with upstanding moraine plateaus reflect primary glaciofluvial erosional processes and secondary depositional activities the livingstone lake event major sheetfloods path arcs obliquely upslope from the keewatin district northwest territories through northern saskatchewan and much of alberta into montana u s a hill shaded maps generated from digital elevation models at widely varying scales are used to illustrate regional to local examples of megaflood landform suites complementary maps and diagrams are derived from more conventional data sources speculations regarding extraglacial implications of th

tunnel valleys concepts and controversies a review abstract although erosion of valleys by subglacial meltwater was first proposed more than 100 years ago the processes that produced these valleys under past ice sheets have remained a topic of vigorous debate the most commonly hypothesized mechanisms have included gradual formation by sediment deformation into the incipient valleys under steady state conditions and subsequent transport by meltwater to the ice margin time transgressive formation along a retreating ice margin by drainage of surface meltwater to the bed or release of impounded meltwater behind a marginal permafrost wedge probably catastrophically and rapid erosion during widespread catastrophic basal sheetflood events recent application of new and enhanced imaging techniques has led to the identification of many new tunnel valleys both on land and offshore throughout the regions glaciated during former ice ages in addition new advances in understanding of subglacial hydrology both from modelling and field instrumentation have helped to constrain the drainage of meltwater from past ice sheet beds this work elucidates the role of subglacial groundwater flow systems in evacuating meltwater from the bed but also shows that groundwater flow alone was not enough to maintain ice bed meltwater pore pressures below the level of ice flotation both modelling and field observations indicate that subglacial conduits oriented parallel to glacial flow lines reorganize groundwater flow systems into basins containing lateral flow toward conduits cut upward into the ice or downward into the bed because of the inability of groundwater flow to account for all the meltwater produced by basal melting other drainage mechanisms involving both non channelized and channelized meltwater flow have been proposed the notion of catastrophic drainage of impounded basal meltwater is still favored by many and the discovery of hundreds of subglacial lakes beneath the antarctic ice sheet and the likelihood of similar lakes beneath pleistocene ice sheets provides a source of water for those advocating catastrophic formation for tunnel valleys proponents of catastrophic drainage consider the valleys to be channels reflecting the width and perhaps depths of flows that formed them tunnel valleys produced by the scandinavian ice sheet have been described and mapped on land as well as on the sea bed valleys and networks of valleys some of which are totally buried have been linked to 3 or more glaciations tunnel valley networks from the last weichselian glaciation in denmark can be related to specific ice margins developed during ice retreat in north america most research has focused on tunnel valleys associated with ice margins formed by the last wisconsin glaciation along the southern margin of the laurentide ice sheet

sedimentary and stratigraphic evidence for subglacial flooding south central michigan usa abstract the glacial landscape in south central michigan is a dissected surface with streamlined residual and upland blocks surrounded by lowland valleys dominated by outwash the upland surface has ridges hills and hummocks composed of boulder gravel which are transitional to drumlins in a down ice direction and is dissected by tunnel channels with eskers within them sedimentary descriptions from 14 gravel pits indicate a consistent stratigraphy across a width of 15 km the upland consists of bedrock covered by a lower till with subglacial melt out or lodgment characteristics above the lower till is a sand and gravel facies that passes upward into a boulder gravel facies nestled within depressions on the boulder gravel surface is a discontinuous facies of laminated sand and silt above the gravel is an upper till with supraglacial melt out and flow till characteristics analyses of the till and gravel indicate an upward change in clast lithology from locally derived carbonates to clastics and finally to crystallines from the lower till through the gravel facies into the upper till the transition mimics the bedrock lithology up ice of the study area and is explained by meltwater erosion of bedrock previously deposited subglacial sediment and overlying debris rich basal ice the systematic change in clast lithology and the stratigraphic position of the gravel facies between a subglacial and supraglacial till strongly suggests that the gravel facies sediment was deposited subglacially and that the entire till gravel till sequence resulted from the same glacial advance

bottom pressure observations of deep sea internal hydrostatic and non hydrostatic motions in the ocean sloping bottom topography is important for the generation and dissipation of internal waves here the transition of such waves to turbulence is demonstrated using an accurate bottom pressure sensor that was moored with an acoustic doppler current profiler and high resolution thermistor string on the sloping side of the ocean guyot great meteor seamount water depth 549 m the site is dominated by the passage of strong frontal bores moving upslope once or twice every tidal period with a trail of high frequency internal waves the bore amplitude and precise timing of bore passage vary every tide a bore induces mainly non hydrostatic pressure while the trailing waves induce mainly internal hydrostatic pressure these separate internal wave pressure terms are independently estimated using current and temperature data respectively in the bottom pressure time series the passage of a bore is barely visible but the trailing high frequency internal waves are a bore is obscured by higher frequency pressure variations up to similar to 4 x 10 3 cpd approximate to 80n cpd cycles per day n the large scale buoyancy frequency these motions dominate the turbulent state of internal tides above a sloping bottom in contrast with previous bottom pressure observations in other areas infra gravity surface waves contribute little to these pressure variations in the same frequency range here such waves do not incur observed pressure this is verified in a consistency test for large reynolds number turbulence using high resolution temperature data the high frequency quasi turbulent internal motions are visible in detailed temperature and acoustic echo images revealing a nearly permanently wave turbulent tide going up and down the bottom slope over the entire observational period the spectral slope and variance of bottom pressure are equivalent to internal hydrostatic pressure due to internal waves in the lower 100 m above the bottom by non hydrostatic pressure due to high frequency internal waves and large scale overturning the observations suggest a transition between large scale internal waves small scale internal tidal waves residing on thin similar to 1 m stratified layers and turbulence

depositional record of a glacial lake outburst glacial lake souris north dakota glacial lake souris located in what is now north dakota was inundated by about 74 km3 of sediment laden water from the outburst of glacial lake regina saskatchewan glacial lake outbursts were common during the late pleistocene but detailed studies of outburst deposited sediments in lake environments have not been done the purpose of this paper is to document the sedimentologic effects of the outburst on lake souris and to develop a depositional model the outburst deposited sediments in lake souris are grouped into three lithofacies on the basis of textural analyses of subsurface samples and surficial mapping 1 sand 2 matrix rich gravel and 3 matrix deficient gravel sand is the most common sediment and generally overlies other lithofacies lignite particles are present in most sands and at depth are significantly larger than other particles matrix rich lignite bearing gravel generally occurs at the base of the outburst sections matrix deficient gravel occurs near the ground surface overlying other outburst lithofacies in the inlet area deposition of the outburst sediment is attributed to three main processes low density turbidity currents the predominant process high density turbidity currents and aggradation in braided rivers continuous low density turbidity currents caused by the influx of sediment laden flows and by residual currents from high density flows characterized the outburst event in lake souris most high density flows resulted from the initial influx of the outburst or from continuous avalanching as a result of rapid deposition thick homogenous sections of outburst sediments a gradual systematic fining of sediments distally from the souris spillway and the scarcity of silt sized and clay sized sediment indicate that there was little decrease in flow energy during the outburst nonrepetitive vertical sequences showing little textural variation indicate that there was little migration of individual depositional processes the described characteristics may be used to identify and interpret other outburst events in similar settings and to help evaluate the pleistocene sedimentary record in the marine offshore zone

a deep ocean kelvin helmholtz billow train 1 detailed overturning is observed between 0 5 and 50 m above the sloping side of great meteor seamount canary basin using 100 moored temperature sensors 1 mk accurate sampling at 1 hz while previously reported frontal bores of 40 m amplitude can form with vigorous near bottom motions and sediment resuspension at the beginning of the upslope phase of large e g tidal carrier waves the downslope phase presented here is more permanently turbulent away from the bottom this turbulence is inferred from high resolution temperature space time series which reveal ubiquitous finger like structures it occurs during the clear water tidal phase with low amounts of acoustic scatterers the high frequency finger like motions n n the buoyancy frequency are observed simultaneously with local mode 2 near n inertio gravity waves and overall shear s n they show large temperature variations 5 10 m vertical amplitudes and occasionally develop kelvin helmholtz billows the typical eulerian period of these firstly observed deep ocean billows amounts 50 10 s

rapid laurentide ice sheet advance towards southern last glacial maximum limit during marine isotope stage 3 abstract marine isotope stage mis 3 58 28 ka is a period of intermediate global ice volume between mis 4 and the last glacial maximum of mis 2 here we report geologic evidence for southern laurentide ice sheet rapid growth to near its last glacial maximum extent after a period with limited ice in the southernmost hudson bay lowland a14c age on wood in lacustrine sediments interbedded with glacial tills in central eastern wisconsin dates a laurentide ice sheet advance southwards to an extent at least equivalent to at least its 17 ka deglacial limit by 39 1 0 4 ka this advance ended before 30 4 0 9 ka based on another 14c date on wood in lacustrine sediment overlying the till layers this advance is consistent with 14c ages from michigan and iowa and gulf of mexico runoff records that support a concurrent southern laurentide ice sheet advance we infer changes in north american ice volume using ice sheet model simulations from a large ensemble that are consistent with 14c data and gulf of mexico discharge constraints the simulations show the laurentide ice sheet growing from a volume equivalent to 25 30 m of global mean sea level gmsl before 40 ka to 40 45 m of gmsl at 40 ka and reaching 65 70 m gmsl by 30 ka consistent with glacial isostatic adjustment assessments of near to intermediate field sea level data we thus show from our terrestrial field data and ice sheet model simulations that an individual ice sheet can grow rapidly which has only been inferred previously for global ice volume from gsml records

morphological analysis and evolution of buried tunnel valleys in northeast alberta canada abstract tunnel valleys are large elongated depressions eroded into unconsolidated sediments and bedrock tunnel valleys are believed to have been efficient drainage pathways for large volumes of subglacial meltwater and reflect the interplay between groundwater flow and variations in the hydraulic conductivity of the substrate and basal meltwater production and associated water pressure variations at the ice bed interface tunnel valleys are therefore an important component of the subglacial hydrological system three dimensional modelling of geophysical and lithological data has revealed numerous buried valleys eroded into the bedrock unconformity in northeast alberta many of which are interpreted to be tunnel valleys due to the very high data density used in this modelling the morphology orientation and internal architecture of several of these tunnel valleys have been determined the northeast alberta buried tunnel valleys are similar to the open tunnel valleys described along the former margins of the southern laurentide ice sheet they have high depth to width ratios with undulating low gradient longitudinal profiles many valleys start and end abruptly and occur as solitary straight to slightly sinuous incisions or form widespread anastomosing networks typically these valleys are between 0 5 and 3 km wide and 10 and 30 m deep although the depth of incision along some thalwegs exceeds 100 m several valleys extend for up to 60 km but most are between 10 and 30 km long valley fills comprise a range of lithofacies including stacked sequences of diamict glaciofluvial sands and gravels and glaciolacustrine silts and clays displaced bedrock presumably of glaciotectonic origin also occurs within several anastomosing valleys several channel bodies are exposed along a number of valley sections suggesting progressive valley development through repeated cycles of sediment discharge cut and fill structures that are capped by fine grained sequences of rippled sand and mud rich drapes within these channel bodies suggest unstable flow regimes within the valley and the discharge of sediment laden basal meltwater under flood like conditions followed by wane flow events or periods of lower meltwater discharge likely concomitant with localized modification by glacial ice basal meltwater is inferred to have been released as episodic jokulhlaups beneath the western laurentide ice sheet which at times re used existing valley systems which were spatially and temporally stable features and at other times incised new valleys

saginaw lobe tunnel channels laurentide ice sheet and their significance in south central michigan usa abstract a network of tunnel channels in southern michigan records substantial subglacial meltwater activity beneath the saginaw lobe of the laurentide ice sheet the channels are incompletely filled with outwash contain eskers and in many places crosscut and continue beyond upland ridges previously mapped as recessional moraines the presence of the tunnel channels and drumlins on these upland ridges indicate that the ridges are not recessional moraines instead outwash fans and minor ridges record deglaciation in the area a palimpsest relationship between buried bedrock valleys and tunnel channels records the presence of multiple generations of tunnel channels evidence for a subglacial meltwater sheetflow consists of sheets of boulder gravel in upland 15 km wide with a hummocky upper surface the hummocks transform down flow into erosional remnant drumlins possibly the result of flow acceleration on a negative slope tunnel channels at the distal end of the drumlin swarm suggest collapse of the sheetflow into a channelized flow the tunnel channels then end at the sturgis moraine at the heads of large outwash fans the observed geomorphic relationships between tunnel channels moraines and drumlins in south central michigan are applicable to glacial landform studies elsewhere and indicate the important role of meltwater in landscape evolution

fast flow of the lake michigan lobe evidence from sediment landform assemblages in southwestern michigan usa abstract the dynamics of the late wisconsin lake michigan lobe of the laurentide ice sheet as interpreted by sediment landform assemblages along its southeastern margin are consistent with fast flow driven by high subglacial pore pressures a major advance of the lake michigan lobe terminated at the kalamazoo moraine where proglacial glaciotectonic activity marginal stagnation and release of subglacial meltwater marked the extent of the advance a large portion of the valparaiso moraine west of the kalamazoo moraine is actually a drumlinized till capped upland plain rather than an ice marginal landform assemblage lacustrine sediment underlying the surficial diamicton in the valparaiso upland is glaciotectonically deformed to a depth of 10 m the deformed interval consists of folded sandy and silty lacustrine sediment which is in places sharply truncated by the overlying diamicton decoupling of the glacier from its bed is suggested by a discontinous thin bed of sand at the base of the diamicton and by the sharp truncation of deformed lacustrine sediment the association of drumlins proglacial and subglacial deformation marginal stagnation and major ice marginal outwash fan deposition are indicative of fast flow perhaps in a surge these characteristics are consistent with a terrestrial ice stream model for the lake michigan lobe

biogeomorphological implications of microscale interactions between sediment geotechnics and marine benthos a review abstract at the foundations of biogeomorphological processes in the sea lie interactions between the activities of marine benthic animals and the geotechnical properties of their sedimentary environments the potential significance of these interactions which take place at a microscale level of millimetres to metres for the large scale geomorphology of the seabed has rarely been appreciated in the context of this review large scale is defined as greater than 50 m to hundreds of kilometres the present review addresses this link drawing examples from a wide range of marine environments including estuaries the intertidal zone continental shelves and slopes and the deep sea it firstly considers sediment stabilisation slope failure sediment mixing biodeposition sediment compaction and hydrodynamic effects this is followed by a consideration of two extremes of the ecological pyramid the effects of marine meiofauna and marine vertebrates the final section draws attention to the central role of faunal mucus and extracellular polymeric material ecpm in many of the microscale interactions that we describe the implications of these microscale biological processes and features are discussed in terms of their influence on and control of the large scale geomorphology of the seabed

on the formation of large subglacial lakes the role of subglacial water storage beneath continental ice sheets is investigated primarily for a deformable bed subglacial ponding is shown to occur under most regions of warm based ice sheets and large subglacial lakes can become established for example in the hudson bay basin the formation of large lakes depends upon the fact that the ice surface gradient is reduced once subglacial ponding occurs and upon the feedback between the reduced ice surface gradient and increased subglacial ponding subglacial ponding likely played a large role in determining the ice sheet topography during late deglaciation and in speeding up the deglaciation process

bioturbation in deep sea pacific sediments bioturbation structures have been recorded in sediment cores from 5000 m to 5300 m water depth collected from the pacific ocean using subcores from spade box cores shear strength and eh profiles were also taken the results have been related to pelagic fluxes and sedimentation bioturba tion structures consist of holes and chambers of various sizes running vertically and horizontally whose abundance size and shapes have been measured values did not decrease exponentially with sediment depth but end abruptly at depths ranging from 30 cm to 45 cm in many instances there were subsurface peaks of vertical and horizontal burrows there was also evidence of lateral galleries large deep in filled burrows were observed these consisted of light and dark brown sediment having different shear strengths eh profiles showed that the sediment was aerobic with slightly lower values near the sediment surface possibly associated with meiofaunal and bacterial activity the most important implications of this work for pelagic processes are likely to be increased transfer of dissolved and particulate material between the sediment and the water column due to the physical network of burrows within the sediment and increased surface roughness caused by burrow openings mucus binding of particulates and faecal pelletization are also likely to be important all of these effects will be most noticeable at high burrow densities

incipient tunnel channels abstract glaciated terrains in east central alberta and south central michigan contain channels that have hummocks and transverse ridges separating depressions along their floors this association imparts a linked pothole appearance similar channels are often interpreted as tunnel channels or subaerial channels partly filled with sediment from a subsequent glacial advance a stagnating ice roof or slumped sediment from the channel margins however the truncation of sedimentary packages in the channel walls and intrachannel hummocks indicates that they are erosional landforms cut into glacial sediments till bedrock or gravel eskers overlie and are found within a few channels indicating that these channels formed before the final stagnation that produced the eskers these two characteristics combined with the observation that many channels have convex up long profiles indicate that the channels were eroded by pressurized subglacial water because the formative mechanisms for this type of channel are not clear and modern environments that could produce this type of landform are inaccessible we draw on several morphologic analogues to propose mechanisms for channel erosion we conclude that the erosion of these linked pothole channels incipient tunnel channels was the product of the complex interaction between complex turbulent flow structures and various scales of roughness elements

pseudobreccias revealed as calcrete mottling and bioturbation in the late dinantian of the southern lake district uk two types of pseudobreccia one with grey and the other with brown mottle fabrics occur in shoaling upward cycles of the urswick limestone formation of asbian late dinantian carboniferous age in the southern lake district uk the grey mottle pseudobreccia occurs in cycle base packstones and developed after backfilling and abandonment of thalassinoides burrow systems burrow infills consist of a fine to coarse crystalline microspar that has dull brown to moderate orange colours under cathodoluminescence mottling formed when an early diagenetic aerobic decay clock operating on buried organic material was stopped and sediment entered the sulphate reduction zone this probably occurred during progradation of grainstone shoal facies after which there was initial exposure to meteoric water microspar calcites then formed rapidly as a result of aragonite stabilization the precipitation of the main meteoric cements and aragonite bioclast dissolution post date this stabilisation event the brown mottle pseudobreccia fabrics are intimately associated with rhizocretions and calcrete which developed beneath palaeokarstic surfaces capping cycle top grainstones and post date all depositional fabrics although they may also follow primary depositional heterogeneities such as burrows they consist of coarse inclusion rich microspar calcites that are always very dull to non luminescent under cathodoluminescence sometimes with some thin bright zones these are interpreted as capillary rise and pedogenic calcrete precipitates the d 18 o values 5 to 8 pdb and the d 13 c values 2 to 3 pdb of the pseudobreccias are lower than the estimated d 18 o values 3 to 1 pdb and d 13 c values of 2 to 4 pdb of normal marine calcite precipitated from late dinantian sea water reflecting the influence of meteoric waters and the input of organic carbon

characterization of the sub mesoscale energy cascade in the alboran sea thermocline from spectral analysis of high resolution mcs data part of the kinetic energy that maintains ocean circulation cascades down to small scales until it is dissipated through mixing while most steps of this downward energy cascade are well understood an observational gap exists at horizontal scales of 103 101 m that prevents characterizing a key step in the chain the transition from anisotropic internal wave motions to isotropic turbulence here we show that this observational gap can be covered using high resolution multichannel seismic hr mcs data spectral analysis of acoustic reflectors imaged in the alboran sea thermocline shows that this transition is likely caused by shear instabilities in particular we show that the averaged horizontal wavenumber spectra of the reflectors vertical displacements display three subranges that reproduce theoretical spectral slopes of internal waves x 100 m kelvin helmholtz type shear instabilities 100 m x 33 m and turbulence x 33 m indicating that the whole chain of events is occurring continuously and simultaneously in the surveyed area

a meltwater origin for antarctic shelf bedforms with special attention to megalineations the geomorphology of troughs crossing the antarctic shelf is described and interpreted in terms of ice stream hydrology the scale of tunnel channels on the inner shelf and the absence of sediment at their mouths are taken to infer catastrophic drainage drumlins on the inner and outer shelves with pronounced crescentic and hairpin scours are also interpreted as products of catastrophic flow gullies and channels on the continental slope and turbidites on the rise and abyssal plain point to abundant meltwater discharge across the shelf attempts to explain this morphology and sedimentology in terms of release or discharge of meltwater by pressure melting strain heating darcian flow or advection in deforming till are shown to be unrealistic we suggest that meltwater flow across the middle and outer shelves might have been in broad turbulent floods which raises the possibility that megascale glacial lineations msgl on the shelf might originate by erosion in turbulent flow this possibility is explored by use of analogs for msgl from flood and eolian landscapes and marine environments an extended discussion reflects on objections that stand in the way of the flood hypothesis

evidence for the intra glenwood mackinaw low water phase of glacial lake chicago a 14c age estimate of 13 470 130 bp isgs 1378 from organic material at the base of transgressive lake deposits exposed in a southern lake michigan shore bluff near riverside michigan confirms

internal wave turbulence pressure above sloping sea bottoms an accurate bottom pressure sensor has been moored at different sites varying from a shallow sea strait via open ocean guyots to a 1900 m deep gulf of mexico all sites show more or less sloping bottom topography focusing on frequencies sigma higher than tidal the pressure records are remarkably similar to within the 95 statistical significance bounds in the internal gravity wave continuum iwc band up to buoyancy frequency n the iwc has a relatively uniform spectral slope log p sigma alpha log sigma alpha 2 1 3 the spectral collapse is confirmed from independent internal hydrostatic pressure estimate which suggests a saturated iwc for sigma n all pressure spectra transit to a bulge that differs in magnitude this bulge is commonly attributed to long surface waves for the present data it is suggested to be due to stratified turbulence internal wave coupling which is typically large over sloping topography the bulge drops off at a more or less common frequency of 2 3 x 10 2 hz which is probably related with typical turbulent overturning scales

internal lee waves and baroclinic bores over a tropical seamount shark hot spot abstract oceanographic observations were made with a subsurface oceanographic mooring over the summit and flanks of two neighbouring seamounts in the tropical indian ocean to identify processes that may be responsible for the aggregation of silvertip sharks carcharhinus albimarginatus in the deep water drop off surrounding the summits the seamounts which are in the chagos archipelago in the british indian ocean territories are narrow in horizontal extent 15 sides that rise from depths of 600 m and flat summits at a depth of 70 m they are subjected to forcing at subinertial basin scales and local scales that include a mixed tidal regime and storm generated near inertial waves at the drop off at a depth of between 70 and 100 m isotherms oscillate at both diurnal and semidiurnal frequencies with amplitudes of 20 30 m the waves of tidal origin are accompanied by short period 5 min internal waves with amplitudes o 10 m and frequencies close to the local buoyancy frequency n within the thermocline which is the maximum frequency possible for freely propagating internal waves the tidal oscillations result from internal lee waves with 30 m vertical wavelength generated by the prevailing currents over the supercritical seamount flanks whereby the bottom slope is greater than the internal tide wave slope the near n waves are due to enhanced shear associated with the hydraulic jumps that form from the lee waves due to the abrupt transition from steeply sloping sides to a relatively flat summit the jumps manifest themselves as bottom trapped bores that propagate up the slope towards the summit further observations over the summit reveal that the bores subsequently flush the summits with cold water with tidal periodicity the bores which have long wave phase speeds more than double that of the bore particle velocities are characterised by intense vertical velocities 0 1 m s 1 and inferred local resuspension but relatively little turbulence based on temperature overturns our results strongly implicate lee waves as the dynamic mechanism of leading order importance to the previously observed accumulation of biomass adjacent to the supercritical slopes that are commonplace throughout the archipelago we propose that further investigation should identify the spatiotemporal correlation between internal wave activity and fish schooling around the summit and whether such schooling attracts predators

structure and generation of turbulence at interfaces strained by internal solitary waves propagating shoreward over the continental shelf abstract detailed observations of the structure within internal solitary waves propagating shoreward over oregon s continental shelf reveal the evolving nature of interfaces as they become unstable and break creating turbulent flow a persistent feature is high acoustic backscatter beginning in the vicinity of the wave trough and continuing through its trailing edge and wake this is demonstrated to be due to enhanced density microstructure increased small scale strain ahead of the wave trough compresses select density interfaces thereby locally increasing stratification this is followed by a sequence of overturning high density microstructure and turbulence at the interface which is coincident with the high acoustic backscatter the richardson number estimated from observations is larger than 1 4 indicating that the interface is stable however density profiles reveal these preturbulent interfaces to be o 10 cm thick much thinner than can be resolved with shipboard velocity measurements by as

a sediment mixing process model of till genesis using texture and clay mineralogy data from saginaw lobe michigan usa tills we present a sediment mixing process model of till genesis based on data from surface tills of the saginaw lobe terrain in lower michigan our research uses a spatial approach to understanding glacial landsystems and till genesis we sampled calcareous till at 336 upland sites and at 17 sites in lacustrine sediment of the saginaw lake plain the loamy tills have bimodal grain size curves with a fine texture mode near the silt clay boundary and a sand mode spatial grouping analysis suggests that tills can be divided into six groups each with different textures and clay mineral compositions that vary systematically down ice the similarity among groups with respect to the silt clay mode and clay mineralogy argues for a common origin for the fines illite rich lacustrine sediment of the saginaw lake plain fine textured sediments were probably entrained transported and deposited down ice as till which also becomes sandier and enriched in kaolinite reflecting increasing mixing with shallow sandstone bedrock with distance from the lacustrine clay source clayey tills on the flanks of the saginaw terrain may reflect proglacial ponding against nearby uplands a process model of progressive down ice mixing of preexisting fine lake sediments with crushed abraded sandstone bedrock helps to better explain till textures compared with a purely crushing abrasion process model

tunnel channels and associated landforms south central ontario their implications for ice sheet hydrology the peterborough trenton drumlin field and associated meltwater erosion marks s forms were interpreted as the products of erosion by turbulent separated flows within a catastrophically released subglacial meltwater sheet the algonquin event recent theoretical modelling of ice sheet hydrology suggests progressive channelization of meltwater during the collapse of such a sheet inductive testing of this hypothesis using observations in south central ontario forms the crux of this paper a geometric model of the interaction of rough ice base and bed surfaces gives inferred meltwater flow patterns such a rough interactive geometry is suggested as the bed is drumlinized and flows responsible for drumlins may be expected to have eroded similar forms into the ice base three landforms in south central ontario namely tunnel channels megachannels and late stage sheet flow scours are described and interpreted as evidence of progressive channelization and flow diversion processes governed by the geometri

the formation and evolution of an isolated submarine valley in the north channel irish sea an investigation of beaufort s dyke beaufort s dyke is a submarine depression located in the north channel of the irish sea with a maximum depth of 312 m the dyke is one of the deepest areas within the european continental shelf integration and interpretation of 450 km of sparker seismic data and full coverage bathymetric data derived from multi beam echo sounder surveys allow for the investigation of the formation processes of beaufort s dyke and the evolution of geomorphological features within it the dyke formed by composite subglacial processes dominated by subglacial meltwater discharge is interpreted as a tunnel valley the regional isolation of beaufort s dyke may be explained by the bounding of the north channel by the bedrock masses of ireland and scotland coupled with the exploitation of structural weakness along a fault plane and presence of halite in the eroded substrate enhancing the erosive potential of the overlying glacier beaufort s dyke has probably been maintained as an open feature by strong rectilinear tidal currents the morphology of lunate sediment waves and a large parabolic bedform towards the south of the dyke contradict the observed dominant s n mean hydrodynamic flow recorded within the north channel suggesting an alternative hydrodynamic regime either within the dyke or during bedform creation

internal bores and breaking internal tides on the oregon continental slope abstractobservations of breaking internal tides on the oregon continental slope during a 40 day deployment of 5 moorings along 43 12 n are presented remotely generated internal tides shoal onto the slope steepen break and form turbulent bores that propagate upslope independently of the internal tide a high resolution snapshot of a single bore is captured from lowered acoustic doppler current profilers ladcp ctd profiles in a 25 h time series at 1200 m the bore is cold salty over 100 m tall and has a turbulent head where instantaneous dissipation rates are enhanced e 10 6 w kg 1 and sediment is resuspended at the two deepest slope moorings 1452 and 1780 m similar borelike phenomena are observed in near bottom high resolution temperature time series mean dissipation rates and diapycnal diffusivities increase by a factor of 2 when bores are present w kg 1 and m s 1 and observed internal tides are energetic enough to drive these enhanced dissipation rates globally the authors estimate

the kankakee torrent and other large meltwater flooding events during the last deglaciation illinois usa abstract evidence of the kankakee torrent ekblaw and athy 1925 includes boulder bars formed on a scoured bedrock surface west of kankakee illinois and overflow channels that connect several moraine dammed basins wauponsee watseka and pontiac willman and payne 1942 geomorphic evidence of a large scale flood event in the illinois valley includes features such as erosional residuals hajic 1990 the age of the kankakee torrent is about 19 000 cal yr bp based on the pooled mean of four radiocarbon ages of tundra plant stems and leaves from the oswego channel complex median probability 18 930 cal yr bp 1 range 18 870 18 970 cal yr bp analysis of recently obtained sediment cores from the middle illinois river valley near havana illinois has revealed the bedrock surface is defended by a mantle of bouldery debris buried by 15 m of mostly slackwater lake sediment radiocarbon ages of needles archived in the lake sediment reveal evidence for an early lake phase that post dates the kankakee torrent 18 030 17 530 cal yr bp and a later lake phase 15 690 13 040 cal yr bp the radiocarbon ages indicate that the deeply buried bouldery rubble was deposited by the kankakee torrent consideration of isostasy indicates that the earlier lake phase at havana may have been associated with downward flexure of land surface in response to glacier loading the younger lake phase was caused in part by deposition of a sediment dam the savanna deer plain terrace at the mouth of the illinois river the lake shoaled due to passing of the isostatic forebulge across the area

temperature statistics above a deep ocean sloping boundary we present a detailed analysis of temperature statistics in an oceanographic observational dataset the data are collected using a moored array of thermistors 100 text m 100 m tall and starting 5 text m 5 m above the bottom deployed during four months above the slopes of a seamount in the north eastern atlantic ocean turbulence at this location is strongly affected by the semidiurnal tidal wave mean stratification is stable in the entire dataset we compute structure functions of order up to 10 of the distributions of temperature increments strong intermittency is observed in particular during the downslope phase of the tide and farther from the solid bottom in the lower half of the mooring during the upslope phase the temperature statistics are consistent with those of a passive scalar in the upper half of the mooring the temperature statistics deviate from those of a passive scalar and evidence of turbulent convective activity is found the downslope phase is generally thought to be more shear dominated but our results suggest on the other hand that convective activity is present high order moments also show that the turbulence scaling behaviour breaks at a well defined scale of the order of the buoyancy length scale which is however dependent on the flow state tidal phase height above the bottom at larger scales wave motions are dominant we suggest that our results could provide an important reference for laboratory and numerical studies of mixing in geophysical flows

hydraulics and mixing in a laterally divergent channel of a highly stratified estuary author posting american geophysical union 2017 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in journal of geophysical research oceans 122 2017 4743 4760 doi 10 1002 2016jc012455