geochemical and textural evidence for early shallow diagenetic growth of stratigraphically confined carbonate concretions upper devonian rhinestreet black shale western new york laterally persistent carbonate concretionary horizons are conspicuous to the upper devonian frasnian rhinestreet black shale of the western new york state appalachian plateau field observations including randomly tilted concretions and differential compaction of host sediment laminae around concretions are consistent with early diagenetic growth in unconsolidated sediment further estimates of pre cementation host sediment porosity based on the volume percentage of caco3 cement 74 93 and perhaps most importantly the preservation of a cardhouse clay fabric in mudstones collected from concretion pressure shadow regions suggest that concretionary growth occurred rapidly within perhaps a meter of the seafloor petrographic examination sem of matrix carbonate samples collected from six concretions reveals a relatively porous 4 7 framework of calcite micrite and microsparite euhedral pyrite most abundant near concretion rims disseminated pyrite framboids and randomly oriented detrital clay platelets and domains c isotopic compositions of rhinestreet concretion matrix carbonate range from 13 9 to 1 7 pdb suggesting derivation of c from a mixed source that included depleted and isotopically heavy c slightly to moderately depleted o isotopic compositions 3 8 to 6 8 pdb do not corroborate the shallow depth of concretion growth suggested by field and textural observations the vertically confined nature of most rhinestreet concretions their large size oblate ellipsoidal shape variable c isotope compositions and absence of any evidence that concretions were sited at local concentrations of organic matter suggest an origin by anaerobic ch4 oxidation early pre concretion sulfate reduction and associated pyrite framboid formation that occurred throughout the host sediment was renewed in thin shallow zones of uncompacted sediment the concretionary horizons by ch4 and isotopically heavy dissolved carbonate diffusing upward from the zone of biogenic methanogenesis to the base of the sulfate reduction zone probably little more than a meter below the seabed local variations in the mix of isotopically light ch4 and heavier dissolved carbonate may have been responsible for the wide range of 13c isotopic compositions of rhinestreet concretions crucial to this mechanism is a pause in deposition that would have held the zone of carbonate precipitation at a fixed distance below the ocean floor long enough for the large concretions to grow evidence that sedimentation slowed or even stopped during concretion growth includes 1 laminae that can be traced through concretions with no observed systematic changes in thickness and 2 minimal concretion center to edge variations in estimated pre cementation porosity a resumption of sedimentation and related burial brought concretion growth in each horizon to an end the moderately depleted 18o values of rhinestreet concretions probably reflect the resetting of o isotopic compositions by warm fluids migrating through the permeable concretions during burial

the transport mechanisms of clay and fine silt in the north irish sea abstract the north irish sea represents an area of reworked sediments of very variable mechanical composition a particle size distribution study of these sediments however reveals an underlying correlation between the proportion of m material and the sand mode further throughout the range of samples examined this finer material has a very similar inherant particle size distribution and mineralogical composition the suggestion is made that this size grade is transported as flocs independently of the sand particles and this is supported from the study of flocs formed experimentally from a selection of the samples

spectrally based remote sensing of river bathymetry this paper evaluates the potential for remote mapping of river bathymetry by 1 examining the theoretical basis of a simple ratio based technique for retrieving depth information from passive optical image data 2 performing radiative transfer simulations to quantify the effects of suspended sediment concentration bottom reflectance and water surface state 3 assessing the accuracy of spectrally based depth retrieval under field conditions via ground based reflectance measurements and 4 producing bathymetric maps for a pair of gravel bed rivers from hyperspectral image data consideration of the relative magnitudes of various radiance components allowed us to define the range of conditions under which spectrally based depth retrieval is appropriate the remotely sensed signal must be dominated by bottom reflected radiance we developed a simple algorithm called optimal band ratio analysis obra for identifying pairs of wavelengths for which this critical assumption is valid and which yield strong linear relationships between an image derived quantity x and flow depth d obra of simulated spectra indicated that water column optical properties were accounted for by a shorter wavelength numerator band sensitive to scattering by suspended sediment while depth information was provided by a longer wavelength denominator band subject to strong absorption by pure water field spectra suggested that bottom reflectance was fairly homogeneous isolating the effect of depth and that radiance measured above the water surface was primarily reflected from the bottom not the water column obra of these data 28 of which were collected during a period of high turbidity yielded strong x versus d relations r2 from 0 792 to 0 976 demonstrating that accurate depth retrieval is feasible under field conditions moreover application of obra to hyperspectral image data resulted in spatially coherent hydraulically reasonable bathymetric maps though negative depth estimates occurred along channel margins where pixels were mixed this study indicates that passive optical remote sensing could become a viable tool for measuring river bathymetry copyright 2009 john wiley sons ltd

mixing and the bottom nepheloid layer abstract a close relationship between active mixing and the structure of the bottom nepheloid layer on the oregon shelf is shown by combining mixing information inferred from temperature microstructure with concentration profiles derived from a transmissometer mounted on the microstructure instrument mechanical energy dissipation rates and eddy coefficients are usually consistent with those in an unstratified turbulent boundary layer but an exception was found when stratification due to suspended sediment was required to explain the observations except for this case the suspended particle concentration profiles for observations in approximately 100 m of water are consistent with the assumption of local equilibrium between turbulent diffusion and gravitational settling observations made in deeper 180 200 m water do not show this balance the high gradient region above the nepheloid layer in shallow water impedes diffusion sufficiently that escape of particles by this route is not important winter mixing destroys the layer long before diffusion would this region of low turbulent mixing was not consistently seen in the deeper water where high levels of turbidity were found throughout the water column low density turbidity currents of approximately 1 cm s 1 can be generated by the concentrations found

the influence of an urban stream on sediment geochemistry in goteborg harbour sweden the kvillebacken stream one of three tributaries that discharges into goteborg harbour accumulates organic matter and metals that are mainly derived from urban runoff the relationships between physical and geochemical sedimentary parameters reveal that metals are highly associated with total organic carbon toc in both the stream and harbour sediment but have a negative correlation to fine grained particles 16 m enrichment factors ef and the relationship between total metal and toc content suggest that the stream is contaminated with pb cu zn and hg and the trends in sediment character indicate that the stream observably affects sites within 800 m of its discharge

remote measurement of river morphology via fusion of lidar topography and spectrally based bathymetry this study developed and evaluated a hybrid approach to remote measurement of river morphology that combines lidar topography with spectrally based bathymetry comparison of filtered lidar point clouds with surveyed cross sections indicated that subtle features on low relief floodplains were accurately resolved by lidar but that submerged areas could not be detected due to strong absorption of near infrared laser pulses by water the reduced number of returns made the active channel evident in a lidar point density map a second dataset suggested that pulse intensity also could be used to discriminate land from water via a threshold based masking procedure fusion of lidar and optical data required accurate co registration of images to the lidar and we developed an object oriented procedure for achieving this alignment information on flow depths was derived by correlating pixel values with field measurements of depth highly turbid conditions dictated a positive relation between green band radiance and flow depth and contributed to under prediction of pool depths water surface elevations extracted from the lidar along the water s edge were used to produce a continuous water surface that preserved along channel variations in slope subtracting local flow depths from this surface yielded estimates of the bed elevation that were then combined with lidar topography for exposed areas to create a composite representation of the riverine terrain the accuracy of this terrain model was assessed via comparison with detailed field surveys a map of elevation residuals showed that the greatest errors were associated with underestimation of pool depths and failure to capture cross stream differences in water surface elevation nevertheless fusion of lidar and passive optical image data provided an efficient means of characterizing river morphology that would not have been possible if either dataset had been used in isolation copyright 2011 john wiley sons ltd

patterns of suspended particle distribution and transport in a large fjordlike estuary seasonal and spatial patterns of the distribution and transport of suspended particles in puget sound a large fjordlike estuary are a product of the interaction of the subtidal circulation with surface and bottom particle sources the particle distribution differs from the distribution of hydrographic properties and is characterized by four persistant features 1 a thin 10 m high turbidity surface layer 2 a thick 50 m low turbidity zone centered around the level of no net motion between net seaward and landward flow 3 horizontal particle fronts at the sill entrances and 4 a bottom nepheloid layer maintained by local resuspension removal of particles from the surface waters by advective downwelling at the seaward sill and gravitational settling throughout the basin make puget sound an efficient particle trap particles sedimented on the basin floor are transported preferentially landward by the action of erosion deposition cycles enhanced by fortnightly intrusions of new marine water

impact of soil moisture and convectively generated waves on the initiation of a west african mesoscale convective system a mesoscale convective system mcs case study was observed over northeast mali as part of the african monsoon multidisciplinary analysis amma on 31 july 2006 observations of this case suggest that the soil moisture heterogeneity and atmospheric gravity waves emitted from a parent mcs were important trigger mechanisms for this system this study uses high resolution met office unified model metum simulations to assess the importance of the synoptic circulation land surface and gravity waves in the initiation and development of the mcs during the early afternoon shallow convection developed over a region of dry soil within a synoptic scale convergence zone which was caused by the confluence of the southerly monsoon flow with winds associated with the circulation around the saharan heat low two pronounced waves were emitted from a nearby parent storm and propagated towards the convergence zone when the second wave reached the location of the shallow convection deep convection was immediately initiated further convective cells developed later in the afternoon over dry soil many adjacent to strong soil moisture gradients these aggregated with the main storm which later developed into the case study mcs a comparison of model simulations with without the soil moisture heterogeneity and gravity waves shows that the synoptic scale circulation and convergence zones specified by the atmospheric analysis were the most important factors for the successful simulation of the mcs if the location of the initiation of the system is to be forecast accurately the land surface that is the soil moisture must be represented adequately in order to reproduce the timing of the secondary initiation of convection correctly the model must be able to capture gravity waves that are emitted by existing systems

effects of lateral confinement in natural and leveed reaches of a gravel bed river snake river wyoming usa this study examined the effects of natural and anthropogenic changes in confining margin width by applying remote sensing techniques fusing lidar topography with image derived bathymetry over a large spatial extent 58 km of the snake river wy fused dem s from 2007 and 2012 were differenced to quantify changes in the volume of stored sediment develop morphological sediment budgets and infer spatial gradients in bed material transport our study spanned two similar reaches that were subject to different controls on confining margin width natural terraces vs artificial levees channel planform in reaches with similar slope and confining margin width differed depending on whether the margins were natural or anthropogenic theeffects of tributaries also differed between the two reaches generally the natural reach featured greater confining margin widths and was depositional whereas artificial lateral constriction in the leveed reach produced a sediment budget that was closer to balanced although our remote sensing methods provided topographic data over a large area net volumetric changes were not statistically significant due to the uncertainty associated with bed elevation estimates we therefore focused on along channel spatial differences in bed material transport rather than absolute volumes of sediment to complement indirect estimates of sediment transport derived by morphological sediment budgeting we collected field data on bed mobility through a tracer study surface and subsurface grain size measurements were combined with bed mobility observations to calculate armoring and dimensionless sediment transport ratios which indicated that sediment supply exceeded transport capacity in the natural reach and vice versa in the leveed reach we hypothesize that constriction by levees induced an initial phase of incision and bed armoring because levees prevented bank erosion the channel excavated sediment by migrating rapidly across therestricted braidplain and eroding bars and islands

interlaminated ice proximal glacimarine sediments in muir inlet alaska muir inlet in glacier bay alaska is a glacial fjord receiving a tremendous volume of sediment annually the rate of sediment accumulation is greatest proximal to muir glacier about 9 m yr 1 and decreases away from the glacier the primary sediment sources are meltwater streams discharging at subglacial and ice marginal positions to form overflows interflows and underflows continuous turbidity currents overflows and interflows interact with diurnal tidal currents and their volume and sediment concentration varies diurnally and annually with meltwater discharge these effects produce cyclic deposits of a thin fine grained sand or silt lamina that grades normally to a thicker poorly to very poorly sorted mud lamina this lamina couplet is termed a cyclopel underflows are suggested to occur in this glacimarine environment because of conditions unique to subglacial fluvial systems underflow deposits occur only in proximal positions 0 5 km from glacier face and are coarse grained reverse to normal graded and exhibit an increase in sorting and sand content up layer ice rafted debris identified as particles 177 m is ubiquitous though low 5 by weight and occurs as isolated particles frozen pellets or as lenses that in cores may have a lamina appearance proximally ice rafted debris is difficult to identify because proximal sediment is often as coarse grained deposited sediment may be reworked by tidal currents and sediment gravity flows depositional processes operating in muir inlet produce interlaminated sand silt clay that characterizes sediment proximal to a glacier and fines seaward to mud sediment is classified into one of three sediment types 1 1 type i sediment is very fine grained mean 8 65 7 17 o low in sand 0 1 11 2 and very poorly to poorly sorted it is the dominant sediment type in muir inlet and is transported by plumes and deposited by suspension settling 2 2 type ii sediment is fine to coarse grained mean 6 70 3 12 o low to high in sand 5 1 86 6 and very poorly to moderately sorted it represents reworked sediment proximal plume deposits or coarse grained laminae of cyclopels 3 3 type iii sediment is coarse grained mean 3 89 2 38 o high in sand 58 0 100 0 and poorly to well sorted it is deposited by sediment gravity flows or underflows

particle interaction in fjord suspended sediment abstract glacial flour enters the surface layer of howe sound a fjord in southwestern british columbia as a sediment plume which moves quickly down inlet while gradually mixing with the sea water flocculation occurs in the lower brackish waters of the surface layer although mixing and diffusion are the dominant processes for sediment to enter the marine water once in the underlying marine water zooplankton pelletization and biologic agglomeration of inorganic floccules predominate this generates a response in the order of days between the two layers in terms of sedimentation of particulate matter most particles settling in the fjord environment fall as 1 sand and silt grains containing attached clay particles 2 clay clasts possibly related to river mudballs 3 mineral bearing fecal pellets from pelagic zooplankton 4 large grain inorganic and colloidal floccules and 5 inorganic biogenic agglomerates analysis of sediment trap data has led to the following conclusions 1 water turbidity cannot be used to infer the downward flux of particles 2 size distributions of sediment deposited on the sea bed are a function of non lognormal size distributions from particles composing sub laminae

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

the relationship of surface pressure features to the precipitation and airflow structure of an intense midlatitude squall line abstract observations from the oklahoma kansas preliminary regional experiment for storm central ok pre storm have been used to document the surface pressure features accompanying an intense midlatitude squall line with trailing stratiform precipitation three well known features are observed a pre squall mesolow a squall mesohigh and a wake low particular attention is given to the wake low its life cycle and association with the trailing stratiform portion of the squall line during the formative stage the pressure field to the rear of the squall line mesohigh is relatively flat with only weak stratiform precipitation present as the squall line enters the developing to mature stages a pronounced wake low appears at the back edge of the surface stratiform precipitation area the squall line at this time is characterized by a strong rear inflow jet descending from the upper troposphere as far as 500 km behind the leading convective line to the lower troposphere just behind the line the trailin

thermoluminescence properties of fiord sediments from engelskbukta western spitsbergen svalbard a new tool for deciphering depositional environment this study explored the relationship between high arctic fiord depositional environments and the natural thermoluminescence tl signal of sediments the energy and duration of light exposure during transportation and deposition controls the tl level of silicate mineral grains in the sediment the tl signal of sediments rapidly decreases within c 0 5 km of a glacier sediment source the highest tl levels are from tills and ice proximal glacial marine sediments which receive little or no light exposure during transportation and deposition intermediate and consistent tl levels are recorded for ice distal glacialmarine muds c 0 5 5 0 km from the glacier front reflecting slower sedimentation rates the lowest tl levels are for littoral and sublittoral sediments which receive extended light exposure with shoaling the granulometry of the sediments is fairly homogeneous and is not diagnostic of a sedimentary environment with most samples dominated by silt and clay littoral and ice proximal samples exhibit peak abundances in sand these results suggest that the relative tl signal of sediments is sensitive to a depositional environment particularly for environments proximal within 0 5 km to a glacier terminus and in shallow water less than 15 m deep

morphology and sedimentology of deltas in fjord and fjord valley lakes abstract sediment supply depositional processes and the associated morphology and sedimentology of deltas in a fjord and several fjord lakes have been studied two deltas in lakes in eastern norway receive sediments from fluvial erosion of quaternary glacial deposits and are only to a slight extent influenced by modern glaciers the other deltas are situated in western norway in the drainage area of the jostedalsbreen ice cap the meltwater rivers draining this glacier are characterized by a high rate of sediment transport in a wide range of grain sizes the main modes of the grain size distribution curves occur in the silt sand and cobble fractions the sediment transport and the water discharge of the rivers have been measured during the same periods the sedimentation rate of different grain fractions and their downstream variation in the frontal area of the deltas were determined by sediment traps the morphology of the deltas have been investigated with echo sounding differences in downstream sedimentation rates of the various deltas are related to dynamic and geometrical properties of the systems the effect of different factors on delta morphology and sedimentology is discussed

hyperpycnal plume formation from riverine outflows with small sediment concentrations a series of laboratory experiments has been conducted in order to elucidate the sediment induced mixing processes accompanying riverine outflows specifically the discharge of a warm fresh particle laden fluid over a relatively dense cool brine in a parameter regime analogous to recently acquired field measurements hypopycnal surface plumes were subject to a convective instability driven by some combination of heat diffusing out of the warm fresh sediment laden plume and particle settling within it convection was robust in the presence or absence of intense turbulence at sediment concentrations as low as 1 kg m 3 and took the form of millimetre scale sediment laden fingers descending from the base of the surface plume a consequence of the convective instability of the original hypopycnal plume is the generation of a hyperpycnal bottom riding flow the experiments presented here indicate that natural river outflows may thus generate hyperpycnal plumes when sediment concentrations are 40 times less than those required to render the outflow heavy relative to the oceanic ambient the resulting hyperpycnal plumes may play an important role in transporting substantial quantities of sediment to the continental slope and beyond

distribution and dispersal of suspended particulate matter on the ebro continental shelf northwestern mediterranean sea abstract hydrographic data water and bottom sediment samples and a geoprobe tripod experiment were used to examine the distribution and dynamics of suspended particulate matter on the ebro shelf in the northwestern mediterranean sea in the absence of strong winds and storms primary sediment supply from the ebro river is dispersed along the shelf by a general southward flow in such calm conditions suspended matter concentrations on the shelf are lower than 3 mg l and transfer of material from the shelf to the slope takes place principally over the shelf edge north of the columbretes islands very fine sediment deposited in a mid shelf mud belt 30 80 m deep is cohesive and resistant to erosion only relatively rare strong storms are able to resuspend particles from the deeper central region of this cohesive deposit when resuspension takes place suspended particulate matter concentration increases and the general dispersal pattern of suspended matter is altered near the seafloor distribution of suspended matter is greatly influenced by the distribution of the mid shelf muds from which particles are resuspended resuspension occurs more intensively and frequently along the shallower 20 40 m edge of the cohesive deposit and near the delta

glacial and tectonic control on fjord morphology and sediment deposition in the magellan region 53 s chile in the patagonian andes erosion by temperate pleistocene glaciers has produced a deeply incised fjord system in which glacial and non glacial sedimentswere deposited since the late glacial glacier retreat so far fjord bathymetry and structures in the sediment infill were widely unexplored here we report the results of an investigation of morphology and sediment characteristics of a 250 km long fjord transect across the southernmost andes 53 s using multibeam and parametric echosounder data and sediment cores subaquatic morphology reveals continuity of on land tectonic lineaments mapped using field and remote sensing data our results indicate that glacial erosion and fjord orientation are strongly controlled by three major strike slip fault zones furthermore erosion is partly controlled by older and or reactivated fracture zones as well as by differential resistance of the basement units to denudation basement morphology is regionally superimposed by late glacial and holocene subaquatic moraines which are associated to known glacier advances the moraines preferentially occur on basement highs which constrained the glacier flows this suggests that the extent of glacier advances was also controlled by basement morphology subaquatic mass flows fluid vent sites as well as distinct late glacial and holocene sediment infills have furthermore modified fjord bathymetry in the western fjord system close to the strait of magellan subaquatic terraces occur in 20 to 30 m water depth providing an important tag for proglacial lake level during the late glacial

surface pressure and precipitation life cycle characteristics of pre storm mesoscale convective systems abstract extensive observations of the may june 1985 oklahoma kansas preliminary regional experiment for storm central ok pre storm are used to examine the life cycle characteristics of 16 mesoscale convective systems mcss the primary focus is on the surface pressure flow and precipitation structures of the mess it is found that despite the wide variety of initial precipitation structures of the mcss reputable patterns developed in 75 of the cases during their mature to dissipating stages the precipitation structure at this later stage of the life cycle can be described as asymmetric following the definition of houze et al due to the variety of directions of movement the systems are examined in a motion relative quadrant perspective one axis is along the direction of system motion and the other perpendicular to it crossing at the center of the convective line the asymmetry is characterized by 1 a leading convective line containing relatively weak cells on the northern end and a trailing

river incision into bedrock mechanics and relative efficacy of plucking abrasion and cavitation improved formulation of bedrock erosion laws requires knowledge of the actual processes operative at the bed we present qualitative field evidence from a wide range of settings that the relative efficacy of the various processes of fluvial erosion e g plucking abrasion cavitation solution is a strong function of substrate lithology and that joint spacing fractures and bedding planes exert the most direct control the relative importance of the various processes and the nature of the interplay between them are inferred from detailed observations of the morphology of erosional forms on channel bed and banks and their spatial distributions we find that plucking dominates wherever rocks are well jointed on a submeter scale hydraulic wedging of small clasts into cracks bashing and abrasion by bedload and chemical and physical weathering all contribute to the loosening and removal of joint blocks in more massive rocks abrasion by suspended sand appears to be rate limiting in the systems studied here concentration of erosion on downstream sides of obstacles and tight coupling between fluid flow patterns and fine scale morphology of erosion forms testify to the importance of abrasion by suspended load rather than bedload particles mechanical analyses indicate that erosion by suspended load abrasion is considerably more nonlinear in shear stress than erosion by plucking in addition a new analysis indicates that cavitation is more likely to occur in natural systems than previously argued cavitation must be considered a viable process in many actively incising bedrock channels and may contribute to the fluting and potholing of massive unjointed rocks that is otherwise attributed to suspended load abrasion direct field evidence of cavitation erosion is however lacking in terms of the well known shear stress or stream power erosion law erosion by plucking is consistent with a slope exponent n of 2 3 to 1 whereas erosion by suspended load abrasion is more consistent with a slope exponent of 5 3 given that substrate lithology appears to dictate the dominant erosion process this finding has important implications for long term landscape evolution and the models used to study it

incision and differential bedrock uplift along the indus river near nanga parbat pakistan himalaya from 10be and 26al exposure age dating of bedrock straths abstract well preserved river cut bedrock surfaces straths abandoned by the progressive incision of the indus river in northern pakistan were dated using in situ cosmogenic 10 be and 26 al exposure age dating measurements on young and modern straths show no significant ingrowth of 10 be and 26 al implying that strath exposure ages closely approximate their abandonment age strath exposure ages range up to 65 ka and increase with height above the river the straths can be divided into two groups low straths dated at about 7 ka which yield very rapid bedrock incision rates 9 12 m ka and high straths 7 ka in age which yield somewhat slower incision rates 1 6 m ka incision rates for both groups increase by 1 3 m ka downstream toward an active reverse fault the raikot fault that forms the western border of the nanga parbat haramosh massif nphm the downstream increases in incision rates for the low straths mimic downstream increases in the modern gradient suggesting that bedrock incision rates have been proportional to stream power over the last 7 ka gradient increases are probably the result of the creation of knickpoints by bedrock uplift along the raikot fault the longitudinal profile and steep gorge of the indus river in the study area indicate that bedrock incision appears to keep pace with differential vertical motions between the nphm and surrounding regions thus the 1 3 m ka difference in incision rates likely reflects the differential bedrock uplift rate between the nphm and the skardu basin the differential incision rate is consistent with differential exhumation rates obtained from apatite fission track ages assuming geotherms of 80 90 c km in the nphm and 35 c km in the skardu basin this relation suggests that rapid bedrock incision of at least 1 3 m ka has persisted within the nphm for the last 0 5 ma the acceleration of incision rates throughout the study area since 15 ka is likely to be a climatic signal that records an increase in the discharge and or sediment load of the indus river in the study area related to deglaciation of the surrounding terrane

observations simulations and analysis of nonstationary trapped lee waves abstract although considerable understanding of mountain waves has been gained with the aid of the steady state assumption it is clear that mountain waves evolve over time group velocity arguments indicate that this evolution can occur in less than 1 h this study uses observations of trapped lee waves to measure the rate at which their horizontal wavelengths change including a detailed analysis of two events in which such changes are clearly documented in one case doppler lidar observations show a steady increase in horizontal wavelength of 6 h 1 over 4 h and clearly illustrates the relationship between the wave clouds and wave motions in a second case visible satellite imagery reveals an increase in wavelength of 14 h 1 which is related to temporal changes in vertical air motions measured by wind profilers within the wave field hourly vertical profiles of wind and virtual temperature measured by radio acoustic sounding systems rass and wind profilers reveal important changes in the wave env

analysis of gravity waves generated at the top of a drainage flow abstract drainage or katabatic flows are common mesoscale circulations established as a result of differential radiative cooling of near surface air masses in sloping terrain the initial irruption of these flows with sudden shifts in wind speed and direction may result in vertical displacements of air parcels from their equilibrium position which prove to be a common source of internal gravity waves this paper illustrates this mechanism and describes the main features of the oscillations following the study of observational data gathered throughout one night during the stable atmospheric boundary layer experiment in spain 2006 sables2006 field campaign pressure differences measured by microbarometers set at different levels of a tower help to interpret the evolution of other atmospheric variables provide a detailed picture of the irruption of a drainage current and reveal the formation of gravity waves at its top the main parameters of the waves are derived from wavelet cross correlation of p

in situ observations of floc settling velocities in glacier bay alaska abstract in situ floc settling velocities and diameters of particles ranging in size from 0 63 to 5 05 mm equivalent circular diameter were measured under a buoyant discharge plume by deploying a bottom tripod mounted floc camera assembly fca in tarr inlet glacier bay alaska these observations were used to estimate floc effective densities three results emerge from this work first fits of settling velocity and effective density to diameter are consistent with expressions published for other environments suggesting that common controls on floc size and settling velocity operate across diverse marine environments second the raw data show considerable scatter with upper and lower 95 prediction intervals on settling velocity and excess density differing by about a factor of 7 analysis of sources of error suggests that the variability is caused by differences in component grain composition among flocs and turbulent stirring within the stilling box third bin averaged effective densities and settling velocities are highly correlated with diameter thus while it is not possible based on diameter to predict accurately the settling velocity of a single floc it is possible to estimate the mean settling velocity of a population of like sized flocs

knickpoint initiation and distribution within fluvial networks 236 waterfalls in the waipaoa river north island new zealand if knickpoints transmit signals of base level fall in river networks then improvements in our understanding of their retreat rate and basin wide distribution helps constrain the transient response following perturbation many studies of knickpoint retreat focus on the response of trunk streams to base level fall here we examine the response of an entire fluvial network as recorded by 236 active knickpoints distributed within the waipaoa river on the north island of new zealand base level fall within the waipaoa catchment initiated 18 000 years ago in response to a climatically triggered and tectonically exacerbated pulse of incision using observations from field work aerial photo analysis and a digital elevation model dem we study the knickpoint positions within the network we find that 70 of the knickpoints are located at drainage areas between 1 10 5 m 2 and 1 10 6 m 2 and more than half are b1 km upstream of a large change in drainage area for the knickpoints b1 km upstream of large tributary junctions we find that the retreat distances were well correlated with the tributaries drainage areas in order to determine how a pulse of incision distributes itself throughout a fluvial network we develop two simple end member models and compare their behavior to the observed knickpoint distribution in the waipaoa in the first model we propose that a knickpoint initiated at the basin outlet retreats upstream and distributes the signal throughout the network at a rate that is a power law function of drainage area in the second model we propose that knickpoints form near a threshold drainage area below which channels cannot incise with the same efficiency as possible in downstream reaches though neither model addresses the along stream variability in substrate or knickpoint form the misfit between the modeled and the observed knickpoints along stream positions are surprisingly low b1 km 1 25 of the total stream length for knickpoints with drainage areas b1 10 6 m 2 large misfits up to 3 5 km are observed for knickpoints with present day drainage areas greater than 1 10 6 m 2 the large single step in channel elevation that characterizes knickpoints presently observed in tributaries of the waipaoa river may not characterize the base level fall signal that propagated through the trunk streams evidence for progressive rather than instantaneous incision in the trunk streams the knickpoints vicinities to tributary junctions and the equivalent success of the two end member models lead us to conclude that the present positions of the 236 observed knickpoints are largely a consequence of thresholds in channel incision at low drainage areas

convectively generated gravity waves and their effect on the cloud environment this study uses a two dimensional cloud resolving model to examine how convectively generated gravity waves modify the environment of an isolated convective cloud the model is initialized with an idealized sounding and the cloud is initiated by adding a locally buoyant perturbation the modeled convection generates a spectrum of gravity waves with vertical wavelengths that are harmonics of the depth of the troposphere it is shown that the first three wave modes significantly modify the cloud environment the modification of the cloud environment is quantified in terms of the convective available potential energy cape and convective inhibition cin the first two wave modes travel fastest away from the cloud and are responsible for the changes in cape whereas the third wave mode causes low level lifting and hence a reduction in cin the maximum far field perturbations in cape and cin are approximately 15 and 33 of the initial background values respectively these results agree with previous studies of more organized convection predicting the existence of a region surrounding the convective system that favors the development of new convection

contemporary squamish river sediment flux to howe sound british columbia squamish river drains 3600 km2 in the southern coast mountains of british columbia to howe sound at squamish some 50 km north of vancouver this study uses differencing of digitized bathymetric surfaces based on the canadian hydrographic services surveys of 1930 1973 and 1984 at the head of howe sound to yield a long term sedimentation rate for squamish river delta the sediment flux from squamish river to howe sound is determined to be 1 29 106 m3 a 1 or 1 81 109 kg a 1 rates consistent with loads calculated from flow and sediment concentration regimes measured in the estuary in 1973 1975 and 1987 1988 the latter data indicate that the modal discharge effectiveness class is 600 700 m3 s 1 moving 13 of the annual suspended sediment load discharges up to 1400 m3 s 1 constitute 99 8 of all flows and are responsible for transporting 81 5 of the annual load a very significant 18 5 of the load is moved by large magnitude floods 1400 m3 s 1 which occur less than 0 2 of the time squam

sedimentary organic matter geochemistry of clayoquot sound vancouver island british columbia surface sediment samples from three interconnected fjords of clayoquot sound british columbia were density fractionated 1 6 g cm 3 to isolate discrete organic debris od from mineral associated organic matter mom total organic carbon oc values varied greatly ranging from 0 1 to 8 8 by weight with a general decreasing trend from fjord head to the continental shelf within the sediment terrestrial om was present either as vascular plant debris or soil mom down fjord the woody vascular plant material in the od fraction acquires nitrogen which is hypothesized to be due to the bacterial incorporation of nitrogen from the water terrestrial oc in the mom is incompletely replaced by marine oc within the fjords resulting in a 65 net loss of mom sediments deposited under oxic and intermittently anoxic water column conditions have organic carbon to surface area ratios oc sa ranging from 0 4 to 1 2 mg c m 2 similar to that of typical continental margin sediments given that temperate fjords contain an estimated 12 of the continental margin sediment deposited during the last 100 000 yr and that they bury at least a margin equivalent amount of oc either weight or surface area normalized we hypothesize that temperate fjords may contain 12 or more of the sedimentary oc buried during this time

boundary layer oscillations from thunderstorms at sydney airport abstract analyses of wind velocity and air pressure data acquired by a set of low level anemometers at sydney airport australia indicate the passage of a set of three remarkably smooth atmospheric boundary layer oscillations that traveled ahead of a thunderstorm on 27 december 1991 the oscillations were probably generated by a nearby thunderstorm outflow propagating into a stably stratified atmospheric layer it is likely that the phenomenon was initiated by the degenerating of an outflow gravity current into a family of amplitude ordered solitary waves although reasonable agreement can be obtained on the propagation speed using a linear theory the weakness of the trapping mechanism for this solution and an overestimation of the weakly nonlinear wave half width leads to a conclusion that the waves fully nonlinear

modelling channel incision and alpine hillslope development using laser altimetry data this paper presents a new approach to simulate drainage basin evolution and demonstrates that high resolution elevation data can be used as useful tool for a dynamic simulation of alpine landscape development in which channel incision is incorporated in high spatial detail a vector channel incision model cim uses 1 m high resolution laser altimetry data for simulation of longitudinal profile development the cim is combined with a grid cell based hillslope erosion model to incorporate the hillslope response to incising bedrock rivers in a simulation of landscape evolution the combined simulation model is applied to a geologically diverse alpine catchment to simulate landscape development from reconstructed late glacial conditions towards the current situation the model is time efficient and realistically adapts to contrasting geological substrata while spatially and temporally variable incision values knick point recession and variable hillslope development result in a realistic simulation of post glacial landscape evolution high resolution elevation data in combination with dynamic geomorphological simulation models facilitate research of complex and difficult to access alpine terrain at greater detail than before it potentially paves the way for more efficient landscape evolution research and can contribute to increasing the understanding of the functioning of geo ecological systems

modern deposition rates and patterns of organic carbon burial in fiordland new zealand fjords are disproportionately important for global organic carbon oc burial relative to their spatial extent and may be important in sequestering atmospheric co2 providing a negative climate feedback within fjords multiple locally variable delivery mechanisms control mineral sediment deposition which in turn modulates oc burial sediment and oc sources in fiordland new zealand include terrigenous input at fjord heads sediment reworking over fjord mouth sills and landslide events from steep fjord walls box cores were analyzed for sedimentary texture sediment accumulation rate and oc content to evaluate the relative importance of each delivery mechanism sediment accumulation was up to 3 4 mm yr in proximal and distal fjord areas with lower rates in medial reaches x radiograph and 210pb stratigraphy indicate mass wasting and surface sediment bioturbation throughout the fjords sediment accumulation rates are inversely correlated with oc spatial heterogeneity in sediment depositional processes and rates is important when evaluating oc burial within fjords

rapid late pleistocene incision of atlantic passive margin river gorges the direct and secondary effects of rapidly changing climate caused large rivers draining the atlantic passive margin to incise quickly into bedrock beginning about 35 000 years ago measured in samples from bedrock fluvial terraces 10 beryllium shows that both the susquehanna and potomac rivers incised 10 to 20 meter deep gorges along steep convex lower reaches during the last glacial cycle this short lived pulse of unusually rapid down cutting ended by 13 000 to 14 000 years ago the timing and rate of downcutting are similar on the glaciated susquehanna and unglaciated potomac rivers indicating that regional changes not simply glacial meltwater initiated incision

how turbidity current frequency and character varies down a fjord delta system combining direct monitoring deposits and seismic data submarine turbidity currents are one of the most important processes for moving sediment across our planet they are hazardous to offshore infrastructure deposit petroleum reservoirs worldwide and may record tsunamigenic landslides however there are few studies that have monitored these submarine flows in action and even fewer studies that have combined direct monitoring with longer term records from core and seismic data of deposits this article provides one of the most complete studies yet of a turbidity current system the aim here is to understand what controls changes in flow frequency and character along the turbidite system the study area is a 12 km long delta fed fjord howe sound in british columbia canada over 100 often powerful up to 2 to 3 m sec 1 events occur each year in the highly active proximal channels which extend for 1 to 2 km from the delta lip about half of these events reach the lobes at the channel mouths however flow frequency decreases rapidly once these initially sand rich flows become unconfined and only one to five flows run out across the mid slope each year many of these sand rich channelized delta sourced flows therefore dissipated over a few hundred metres once unconfined rather than eroding and igniting upflow migrating bedforms indicate that supercritical flow dominated in the proximal channels and lobes and also across the unconfined mid slope these supercritical flows deposited thick sand beds in proximal channels and lobes but thinner and finer beds on the unconfined mid slope the distal flat basin records far larger volume and more hazardous events that have a recurrence interval of ca 100 years this study shows how sand rich delta fed flows dissipate rapidly once they become unconfined that supercritical flows dominate in both confined and unconfined settings and how a second type of more hazardous and much less frequent event is linked to a different scale of margin failure

multiscale evolution of a derecho producing mesoscale convective system abstract in this paper the authors address one type of severe weather strong straight line winds the case of a mesoscale convective system that developed in eastern colorado on 12 13 may 1985 was studied the system formed in the afternoon was active until early morning and caused strong winds during the night a multiscale nonhydrostatic full physics simulation was performed to formulate a conceptual model of the main airflow branches of the system and to gain understanding of the physical processes involved in the strong wind generation in this storm four telescopically nested grids covering from the synoptic scale down to cloud scale circulations were used a lagrangian model was employed to follow trajectories of parcels that took part in the updraft and downdraft and balances of forces were computed along the trajectories the strong nocturnal winds were caused by downdrafts reaching the surface and by a dynamically forced horizontal pressure gradient force the most important branch of the do

review of wave turbulence interactions in the stable atmospheric boundary layer flow in a stably stratified environment is characterized by anisotropic and intermittent turbulence and wavelike motions of varying amplitudes and periods understanding turbulence intermittency and wave turbulence interactions in a stably stratified flow remains a challenging issue in geosciences including planetary atmospheres and oceans the stable atmospheric boundary layer sabl commonly occurs when the ground surface is cooled by longwave radiation emission such as at night over land surfaces or even daytime over snow and ice surfaces and when warm air is advected over cold surfaces intermittent turbulence intensification in the sabl impacts human activities and weather variability yet it cannot be generated in state of the art numerical forecast models this failure is mainly due to a lack of understanding of the physical mechanisms for seemingly random turbulence generation in a stably stratified flow in which wave turbulence interaction is a potential mechanism for turbulence intermittency a workshop on wave turbulence interactions in the sabl addressed the current understanding and challenges of wave turbulence interactions and the role of wavelike motions in contributing to anisotropic and intermittent turbulence from the perspectives of theory observations and numerical parameterization there have been a number of reviews on waves and a few on turbulence in stably stratified flows but not much on wave turbulence interactions this review focuses on the nocturnal sabl however the discussions here on intermittent turbulence and wave turbulence interactions in stably stratified flows underscore important issues in stably stratified geophysical dynamics in general

climate driven bedrock incision in an active mountain belt measurements of fluvial bedrock incision were made with submillimeter precision in the east central range of taiwan where long term exhumation rates and precipitation driven river discharge are independently known they indicate that valley lowering is driven by relatively frequent flows of moderate intensity abrasion by suspended sediment is an important fluvial wear process and channel bed geometry and the presence of widely spaced planes of weakness in the rock mass influence erosion rate and style

sources of mesoscale variability of gravity waves part i topographic excitation abstract aircraft measurements of winds and temperatures collected during the gasp program are used to study the effects of topography as a source of mesoscale variability variances of fluctuations at the mesoscale over rough terrain are enhanced up to nearly two orders of magnitude compared to nonsource regions in some cases and are frequently enhanced by an order of magnitude the implications of these episodic enhancements of variances for the vertical transports of energy and momentum are considered in the framework of gravity wave theory the observed flight data are used to estimate the momentum flux u w on several flight segments results show that the flux is generally negative with mean value 0 26 m2 s 2 and with magnitudes ranging up to 1 5 m2 s 2 spectral analysis shows that the largest contributions to the net flux come from horizontal scales of 25 x 60 km finally the observed momentum fluxes are used to infer the anisotropy factor of gravity waves over rough terrain which is foun

origin of shale fabric by mechanical compaction of flocculated clay evidence from the upper devonian rhinestreet shale western new york u s a abstract most workers attribute the preferred grain orientation that defines the shale fabric to the mechanical collapse of a high porosity clay microfabric under increasing overburden pressure scanning electron microscope analysis of samples of the upper devonian frasnian rhinestreet shale of western new york state collected from near early diagenetic carbonate concretions provides further evidence of this mechanism specifically mudstones recovered from pressure shadows immediately adjacent to lateral edges of concretions are characterized by an open fabric of randomly arranged clay domains the cardhouse fabric laterally equivalent shale samples collected only 0 2 to 0 3 m distant the pressure shadows however reveal a low porosity strongly oriented shale fabric in which clay particles mold around incompressible quartz silt and euhedral pyrite grains and pyrite framboids these observations suggest that the organic rhinestreet shale accumulated as water rich flocculated clay the open clay fabric observed in pressure shadow mudstones was preserved by the incompressible concretions during burial flocculated clay beyond the shielding effect of the concretions however collapsed during progressive burial to form the strongly oriented shale fabric

step by step error assessment in braided river sediment budget using airborne lidar data abstract sequential airborne lidar surveys were used to reconstruct the sediment budget of a 7 km long braided river channel in southeastern france following a 14 year return period flood and to improve its accuracy step by step data processing involved i surface matching of the sequential point clouds ii spatially distributed propagation of uncertainty based on surface conditions of the channel and iii water depth subtraction from the digital elevation models based on water depths measured in the field the respective influence of each processing step on sediment budget computation was systematically documented this showed that surface matching and water depth subtraction both have a considerable effect on the net sediment budget although dem of difference thresholding based on uncertainty analysis on absolute elevation values had a smaller effect on the sediment budget this step is crucial for the production of a comprehensive map of channel deformations a large independent data set of rtk gps checkpoints was used to control the quality of the lidar altimetry the results showed that high density 7 9 points m 2 airborne lidar surveys can provide a very high level of detection of elevation changes on the exposed surfaces of the channel with a 95 confidence interval level of detection between 19 and 30 cm change detection from lidar data revealed that 54 of the pre flood active channel was reworked by the flood the braided channel pattern was highly disturbed by the flood owing to the occurrence of several channel avulsions

circulation and sedimentation of suspended particulate matter in new zealand fjords abstract circulation in the new zealand fjords is estuarine with a seaward flowing brackish layer overflowing saline water despite an extremely high rainfall 6000 mm yr 1 terrestrial dediment input is low and concentrations of suspended particulate matter spm rarely exceed 1 mg 1 1 the terrestrial influence is barely detectable anywhere in the fjords spm in near surface waters is dominated by phytoplankton in surface waters spm components remain separate as they settle they are clustered into larger groups by agglomeration faecal pelletization and flocculation phytoplankton produce a secondary spm maximum at the top of the deep zone deep waters are barren of living plankton with clustered spm and broken phytoplankton settling from above the low terrestrial spm input and high organic biogenic concentrations are reflected in low sedimentation rates and high organic carbon content of bottom sediments the estuarine stratification is broken up in the fjord entrances by ocean waves which also resuspend sediment off the entrance sills thereby increasing spm concentrations in bottom waters high spm concentrations are found in basins cut off from the main fjord by shallow sills which inhibit deep water renewal

evidence against a late wisconsinan ice shelf in the gulf of maine abstract proposals for the formation of a late wisconsinan ice shelf in the gulf of maine during the retreat of the laurentide ice sheet are considered to be inappropriate an antarctic type ice shelf does not fit the field data that indicate temperate glacial terrestrial and marine climates for the region between 18 ka and 12 ka a temperate ice shelf has no modern analogues and may be physically impossible the preponderance of stratified drift in the gulf of maine region supports temperate climates during late wisconsinan time it also indicates that glacial meltwater rather than ice in either an ice sheet or ice shelf was the primary transport mechanism of glacial sediment and the source for the glaciomarine mud for these reasons we have proposed glacial analogues for the deglaciation of the gulf of maine that consist of temperate or subpolar marine based glaciers characterized by depositional environments dominated by meltwater discharge directly to the sea or the sea by way of subaerial meltwater streams these analogues include alaskan fjord glaciers glaciers on the alaskan continental shelf that discharged meltwater directly into the sea in the not too distant past and austfonna nordaustandet svalbard norway that is presently discharging meltwater in the sea along a grounded ice wall this last example is the best modern day analogue for the depositional environment for most of the glaciomarine mud in the gulf of maine and deglaciation of the gulf

particle transport processes in a small marine bay particle transport in elliott bay a 20 km2 embayment in puget sound washington was studied in an integrated program employing shipboard ctd transmissometer observations moored sediment traps and moored transmissometer current meter observations surface and bottom high turbidity layers are present throughout the bay during both summer and winter seasons particles added to the surface layer by river input and phytoplankton production are rapidly advected out of the bay and provide only a minor contribution to the local sedimentation rate the benthic nepheloid layer is maintained not by local resuspension but by particles advected into elliott bay with turbid deep water from the adjoining main basin of puget sound a severalfold drop in mean current speed as main basin water enters elliott bay results in increased particle fallout within the benthic nepheloid layer a high sedimentation rate and the embayment functioning as a sink for particles from throughout puget sound

near monochromatic ducted gravity waves associated with a convective system close to the pyrenees near monochromatic gravity waves gws associated with a mesoscale convective system mcs were detected during the boundary layer late afternoon and sunset turbulence bllast field campaign in lannemezan france on 21 june 2011 these gws are analyzed using available instrumental data e g an array of microbarometers a microwave system humidity and temperature profiler hatpro and an ultra high frequency uhf wind profiler pressure oscillations of up to 0 5 hpa were recorded after a pronounced pressure drop of 1 4 hpa identified as the mcs weak low wavelet analysis and evaluated wave parameters confirm the occurrence of such gws period 9 min horizontal wavelength 7 km which propagated from southwest to northeast i e in the same direction of propagation as the mcs observational evidence suggests the downdraughts associated with the rear inflow jet at the weak low zone of the mcs as the most likely generator mechanism of the gws however the complex orography and proximity of the pyrenees to the field campaign could also play an important role wave propagation was possible through the ducting mechanism favoured by the existence of a critical level in a wind sheared environment around 2000 m above ground level wave like motions related to the passage of the gws were also observed in other atmospheric parameters close to the surface and within the lower troposphere the effects of gws on the surface fluxes have also been analyzed through multi resolution flux decomposition mrfd methods

the mysteries of mammatus clouds observations and formation mechanisms mammatus clouds are an intriguing enigma of atmospheric fluid dynamics and cloud physics most commonly observed on the underside of cumulonimbus anvils mammatus also occur on the underside of cirrus cirrocumulus altocumulus altostratus and stratocumulus as well as in contrails from jet aircraft and pyrocumulus ash clouds from volcanic eruptions despite their aesthetic appearance mammatus have been the subject of few quantitative research studies observations of mammatus have been obtained largely through serendipitous opportunities with a single observing system e g aircraft penetrations visual observations lidar radar or tangential observations from field programs with other objectives theories describing mammatus remain untested as adequate measurements for validation do not exist because of the small distance scales and short time scales of mammatus modeling studies of mammatus are virtually nonexistent as a result relatively little is known about the environment formation mechanisms properties microphysics and dynamics of mammatus this paper presents a review of mammatus clouds that addresses these mysteries previous observations of mammatus and proposed formation mechanisms are discussed these hypothesized mechanisms are anvil subsidence subcloud evaporation sublimation melting hydrometeor fallout cloud base detrainment instability radiative effects gravity waves kelvin helmholtz instability rayleigh taylor instability and rayleigh benard like convection other issues addressed in this paper include whether mammatus are composed of ice or liquid water hydrometeors why mammatus are smooth what controls the temporal and spatial scales and organization of individual mammatus lobes and what are the properties of volcanic ash clouds that produce mammatus the similarities and differences between mammatus virga stalactites and reticular clouds are also discussed finally because much still remains to be learned research opportunities are described for using mammatus as a window into the microphysical turbulent and dynamical processes occurring on the underside of clouds

sill processes related to deep water renewal in a fjord observations of the gravitational circulation over the sill at the entrance to puget sound indicate a fortnightly modulation of the two layer flow with a corresponding variation in stratification gravitational circulation and stratification reach a maximum during neap tides and a minimum during spring tides the modulation appears to be a function of the turbulence generation by tidal flow over the sill which varies as a function of tidal amplitude the enhanced gravitational circulation during neap tides augments the flux of dense water across the sill region and episodes of bottom water renewal in puget sound result intrusions of dense water in the main basin of the sound show a fortnightly periodicity with a phase lag appropriate for the propagation of an internal bore from the sill region commencing at the neap tide observations indicate that the intrusions take the form of gravity currents propagating at approximately 20 cm s 1 down the main basin the detailed dynamics of the turbulent mixing processes that modulate the onset of inflow were not resolved in this study but the integrated effect of tidal mixing on the low frequency circulation is clearly demonstrated

sediment transport by fecal pellets in british columbian fjords abstract monthly sediment traps moored near the surface and bottom of saanich and jervis inlets were examined for fecal pellets and lithologic composition three major categories of pellets were observed cylinders threads and small spheroids cylinders occurred throughout the year and were composed of an undifferentiated mixture of particles including lithic material dominant during winter months and diatoms dominant from spring through fall threads occurred only in the fall in jervis inlet and were also of mixed composition spheroids occurred throughout the year but were more common in late spring and summer they were composed only of fine particles and in some cases of monospecific fragments of small diatoms the monthly trend of pellet flux in saanich inlet is inverse to that of total mass and of diatom flux being at a minimum during spring and early summer blooms this trend is interpreted as reflecting the relative rates of pellet production and destruction with the latter process predominating during the productive period in jervis inlet pellet flux is in phase with mass and diatom flux and pellet production rate controls the flux pellet flux decreases with increasing depth throughout the year indicating that destructive processes dominate the deep waters possible mechanisms include coprophagy and physical disaggregation perhaps enhanced by bacterial action estimates of loss rate suggest that pellet destruction is linear with depth in both fjords given the composition of the pellets and the destruction of most of them with depth it is probable that this mode of transport does not have a marked effect on the lithologic or fossil taxonomic composition of the sediments

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

cyclic steps review and aggradation based classification abstract cyclic steps are a type of upper flow regime bedform consisting of trains of upstream and upslope migrating bed undulations the overriding flow is characterised by a series of hydraulic jumps occurring in the troughs of the undulations cyclic steps form in open channel flows such as rivers and comprise a common bedform in subaqueous density flows in oceans lakes and reservoirs cyclic steps are associated with alternating froude subcritical and froude supercritical flow on respectively the stoss side and lee side of individual bedforms the transition between these flow states is embodied by the hydraulic jump in the trough of the bedform leading to the permanent or quasi permanent morphology of cyclic steps over the past decade numerous studies affirmed the dominant role of cyclic steps in generating bed undulations in modern and ancient glacial outwash fluvial delta and turbidite environments as reviewed here cyclic steps were previously discriminated as net depositional climbing transportational and net erosional falling in different parts of sedimentary systems the following cyclic step descriptors with distinct depositional signatures are proposed fully depositional partially depositional transportational partially erosional and fully erosional partially depositional cyclic steps are most common they are associated with backset bedded sets high aggradation rate and nested scours filled with massive to backset bedded deposits low aggradation rate the new classification can be used as a predictive tool in the reconstruction of modern and ancient sedimentary successions using repeat bathymetry seismic reflection or outcrop data it is applied in three turbidite case studies classical deep sea system small scale delta slope and line sourced carbonate slope

the interaction of plankton and suspended sediment in fjords abstract the interaction of plankton with suspended sediment affects both the plankton and the sediment trace metals organics and nutrients that are adsorbed onto suspended particles affect the supply of these materials to phytoplankton and zooplankton ingestion of suspended sediment by zooplankton exposes the particulate minerals to physical and chemical breakdown occasionally strong enough to produce changes in particle mineralogy fecal pellets produced from undigested material package fine particulate material and thus increase their rate of sedimentation this is particularly important in fjords an aqueous environment that is dominated by the vertical flux of suspended sediment pelletization also allows the transport of undigested food to greater depths providing an important source of organic material to benthic sediments and food to deep water organisms

sedimentation and iithostratigraphy of the north sea drift and lowestoft till formations in the coastal cliffs of northeast norfolk england the most complete terrestrial sequence of anglian elsterian glacial sediments in western europe was investigated in northeast norfolk england in order to reconstruct the evolution of the contemporary palaeoenvironments lithostratigraphically the glacial sediments in the northeast norfolk coastal cliffs can be divided into the northn sea drift and lowestoft till formations three of the diamicton members of the north sea drift formation happisburgh walcott and cromer diamictons were deposited as lodgement and or subglacial deformation till by grounded ice but one the mundesley diamicton is waterlain and was deposited in an extensive glacial lake sands and fine sediments interbedded between the diamictons represent deltaic sands and glaciolacustrine sediments derived not solely from the melting ice in the north but also from extra marginal rivers in the south the lowestoft till formation is not well preserved in the cliffs but includes lodgement till marly drift till and most probably associated meltwater deposits extensive glaciotectonism in the northern part of the area is shown to relate to oscillating ice that deposited the cromer diamicton and also partially to the ice sheet that deposited the marly drift till it is suggested that during the anglian stage the present day northeast norfolk coast was situated on the northwestern margin of an extensive glaciolacustrine basin this basin was dammed by the scandinavian ice sheet in the north and northeast because the grounding line of this ice sheet oscillated in space and time part of the north sea drift diamictons were deposited directly by this ice however during ice retreat phases glaciolacustrine deposition comprised waterlain diamicton sands and fines when the scandinavian ice sheet was situated in northernmost norfolk the british ice sheet responsible for depositing the marly drift facies entered the area from the west this ice sheet partially deformed the north sea drift formation sediments in the northern part of the area but not in the south where the british ice sheet apparently terminated in water the interplay of these two ice sheets on the northern and western margins of the glacial lake is thought to be the major determining factor for the accumulation of thick glacial deposits in this area during the anglian glaciation

an episode of rapid bedrock channel incision during the last glacial cycle measured with 10be we use 10 be to infer when how fast and why the susquehanna river incised through bedrock along the u s atlantic seaboard one of the world s most prominent and ancient passive margins although the rate at which large rivers incise rock is a fundamental control on the development of landscapes relatively few studies have directly measured how quickly such incision occurs either in tectonically active environments or along passive margins exposure ages of fluvially carved bedrock strath terraces preserved along the lower susquehanna river demonstrate that even along a passive margin large rivers are capable of incising through rock for short periods of time at rates approaching those recorded in tectonically active regions such as the himalayas over eighty samples collected along and between three prominent levels of strath terraces within holtwood gorge indicate that the susquehanna river incised more than 10 meters into the appalachian piedmont during the last glacial cycle beginning 36 ka incision rates increased dramatically and remained elevated until 14 ka the northern half of the susquehanna basin was glaciated during the late wisconsinan however similar rates and timing of incision occurred in the unglaciated potomac river basin immedi ately to the south the concurrence of incision periods on both rivers suggests that glaciation and associated meltwater were not the primary drivers of incision instead it appears that changing climatic conditions during the late pleistocene promoted an increase in the frequency and magnitude of flood events capable of exceeding thresholds for rock detachment and bedrock erosion thus enabling a short lived episode of rapid incision into rock although this study has constrained the timing and rate of bedrock incision along the largest river draining the atlantic passive margin the dates alone cannot explain fully why or by what processes this incision occurred however cosmogenic dating offers compelling evidence that episodes of rapid incision into bedrock are tied to glacial cycles and changes in global climate these results and the methods we employ provide valuable insights into the nature of bedrock channel incision not only along the susquehanna river and passive margins but also across a wide range of settings around the globe because river incision into bedrock transmits the effects of changing climate and tectonics through fluvial networks to hillslopes comprehending when where and why rivers incise has important implications for the evolution of land scapes

origin evolution and finescale structure of the st valentine s day mesoscale gravity wave observed during storm fest part iii gravity wave genesis and the role of evaporation abstract on 14 february 1992 a long lived moderate amplitude mesoscale gravity wave formed in kansas during the storm scale operational and research meteorology fronts experiment systems test storm fest wave formation was evident in correlated surface pressure and wind fields the wave of depression accompanied by a weak rainband tracked across the state a wealth of data was collected on the mature wave as it passed over the storm fest dual doppler domain however the mechanism of genesis remained difficult to ascertain since wave formation occurred in a region of less comprehensive observations the genesis of the storm fest gravity wave is successfully simulated using the fifth generation pennsylvania state university national center for atmospheric research penn state ncar mesoscale model mm5 which was run at 6 km grid spacing in the innermost domain the lee cyclone movement dry airmass development and gravity wave formation over kansas were successfully captured by the model results

sedimentary processes of fine grained material and the effect of seawall construction in the daeho macrotidal flat nearshore area northern west coast of korea abstract sedimentary processes on the lower tidal flat of the reclaimed seosan bay daeho tidal flat at the west coast of korea have undergone significant changes since 1984 when seawalls over 8 km long were constructed at the bay mouth comparison of pre and post construction tidal flow models indicates that in general tidal currents have increased considerably in front of the daeho tidal flat with tidal flow directions having changed from shore normal to shore parallel the 12 h measurements of currents and suspended sediment concentrations at four anchored hydrographic stations show nearshore suspended sediments drifting southward throughout the year bypassing the daeho tidal flat cyclic seasonal variations occur prominently in the grain texture of the tidal flat sediments and associated sedimentation rates in summer fine grained sediments deposit at a rate of 2 6 mm month particularly in sheltered places during the winter monsoon erosional processes are greatly enhanced by the interplay of tidal currents and waves up to 30 mm month this sedimentary seasonality is reflected in the variations in the concentration of nearshore suspended matter the concentration of suspended matter is much higher in winter 60 80 mg l because of vigorous resuspension activities compared with the summer concentration 10 30 mg l the direct effect of seawall construction coupled with strong natural seasonality can be seen from the continuous monitoring of sedimentation rates on the tidal flat the 2 year 1993 1995 measurements indicate that the entire daeho tidal flat was eroded during that period at the abnormally high average rate of 10 cm year the causal blocking of bayward sediment and water movements by any artificial structure might lead to similar erosional conditions to many other bays facing the yellow sea on the both chinese and korean coastlines subjected to energetic winter wave attack

cryospheric science muddying greenland s meltwaters satellite measurements indicate that greenland s meltwater rivers are exporting one billion tons of sediment annually a process that is controlled by the sliding rate of glaciers this rate is nearly 10 of the fluvial sediment discharge to the ocean

observations of a mesoscale ducted gravity wave abstract this paper reports coordinated observations of a mesoscale gravity wave made during the fronts 84 field experiment conducted in southwestern france in the summer of 1984 the observations were unique in the sense that all relevant wave characteristics including its detailed vertical structure could be directly ascertained and shown to be mutually consistent the wave was observed to be ducted the static stability structure of the atmosphere was favorable for the existence of such a duct a critical level where the phase velocity of the wave matches the wave parallel background wind speed was present in or just above a layer of low static stability that capped a stabler layer at a still lower level the observed vertical structure was that of a standing wave with the top of the stable lower layer corresponding roughly to an antinode and one half the vertical wavelength below the critical level the wave was observed when there was extensive activity associated with two line of deep convection

subglacial meltwater discharge in the open marine tidewater glacier environment observations from nordaustlandet svalbard archipelago the ice proximal environment of the nordaustlandet tidewater ice cap svalbard archipelago is one of the best analogues for understanding glacial geologic processes of northern continental shelves during initial pleistocene deglaciation investigations of the proglacial region in 1980 1983 showed that the sedimentary environment is dominated by numerous meltwater outflows which discharge sediment laden water from subglacial meltwater streams during the summer two large stable meltwater outflows were observed in embayments along the southern part of the ice front landsat images show that both outflows have been in approximately the same position since at least 1976 they are located at the intersection of glacial drainage basins and centered over depressions in the underlying bedrock an outflow valley extending away from the ice front was observed in front of the western meltwater outflow sidescan sonar profiling along the glacier front showed a 200 m wide gap in acoustic reflection at the base of the western meltwater outflow probably caused by meltwater effluence enhanced sediment accumulations in this region observed as a 3 ms sediment drape in front of the outflow and large arcuate ridges in the outflow valley testify to the transport efficiency of the subglacial meltwater stream several mounds up to about 25 m high and 200 m wide are observed on sidescan and 3 5 khz profiles directly in front of the outflow although samples from these structures are absent they are most likely composed of sediment and are similar to beaded eskers observed in pleistocene glacimarine sequences indicating locally very high sedimentation rates fine grained components of the subglacial discharge incorporated in the buoyant meltwater plume are usually entrained in a westerly coastal current elevated suspended particulate material concentrations are observed within the coastal waters in a region extending about 15 km perpendicular to the glacier front and at least 60 km along the ice front extending into the northwestern barents sea

basin sedimentation and the growth of prograding deltas a theoretical model is developed for the infilling of a basin by the progradation of a delta the model simulates four mechanisms for the transfer of sediment from the land to the sea 1 bed load dumping along the delta front 2 hemipelagic sedimentation under the seaward flowing river plume 3 proximal slope bypassing by turbidity currents and 4 the combined effects of both short term wave and tidal action and long term creep and small slides downslope diffusion of the accreting sediment mass the general model is of relatively low precision useful for predicting basin infilling on time scales greater than a few hundred years the river plume portion of the model can predict sedimentation on time scales of less than a year and is designed to reflect the dynamics of a free two dimensional buoyant jet that transports a composite size population of suspended particles the general model allows the prediction of lithologies changing with time and space the model has been used to simulate infilling processes for knight and bute inlets two grabenlike fjord basins along the coast of british columbia model simulations of delta progradation over the last 10 000 years favorably predicted the modern seafloor bathymetry and sediment accumulation rates to within a factor of 2 of measured 210pb 137cs and sediment trap rates

a case study of an unusually intense atmospheric gravity wave abstract a remarkable long lived large amplitude gravity wave in the carolinas and virginia on 27 february 1984 is investigated by means of a subsynoptic scale case study the wave was characterized by a minor wave of elevation followed by a sharp wave of depression with a period of 2 3 h a horizontal wavelength of 100 150 km and surface pressure perturbation amplitudes of 3 14 mb the wave propagated toward the east southeast at 1 5 m s 1 accelerating to more than 20 m s 1 after it crossed the atlantic coast wave passage was accompanied by gusty surface easterly winds reaching 30 m s 1 and an abrupt termination of precipitation with the rapid surface pressure fall the synoptic criteria identified by uccellini and koch as common to many cases of large amplitude gravity waves were present in this case gravity waves were first detected across western tennessee and northern mississippi in a wake depression region to the rear of an advancing squall line an amplifying wave emerged out of the wave packet

global cyclostratigraphy a model of carbonate growth patterns abstract cyclostratigraphy is the study of cyclic depositional patterns produced by climatic and tectonic processes a global scale quantitative cyclostratigraphic model is described which simulates carbonate growth patterns controlled by tectonic and climatic processes the model uses seven factors simulating the effects of physical and chemical environments on the deposition rates of carbonate accumulations these factors are sea level change the rate of basement subsidence food supply influence of nutrients available sunlight temperature salinity and dissolved oxygen the factors are considered as functions of climatic and tectonic processes the model also integrates milankovitch induced short term climatic changes with the long term tectonic evolution of basins to examine the potential carbonate accumulation patterns the two dimensional computer model results provided here show that 1 carbonate growth patterns in different climates and under different tectonic processes can be modelled quantitatively 2 carbonate production increases towards the equator decreasing latitude as the temperature and nutrition supply increase in tropical belts and production changes because of expansion or contraction of the tropical belt in different climatic periods 3 when matched with the turbidity the model describes different carbonate accumulation patterns in different climatic patterns 4 at either abnormally high or low salinity carbonate accumulation rates decline sharply and the salinity becomes normal away from the strand line and 5 cyclic sea level changes cause a cyclic change of carbonate accumulation a case study is presented from the upper pennsylvanian of texas the simulation results indicate that carbonate growth patterns observed from field well or seismic data are accurately modelled by the quantitative procedure given here

properties of suspended sediment over the hebble area on the nova scotian rise abstract twenty samples from 20 40 250 and 1000 m above bottom were analysed by coulter counter for size using three overlapping tubes giving a size range of 1 59 256 m the principal features are a fine mode in the region 2 8 m and a coarser one between 20 and 60 m aperture shear was probably responsible for lack of particles counted over 100 m log log cumulative particle number distributions are mainly wavy or curved but have segments particularly 1 6 10 m with a slope approaching 3 signifying equal particle volumes in logarithmic size grades if waviness and coarse end truncation are ignored there is a rough overall fit to 3 in many cases the samples were also filtered to determine weight concentration and examined by scanning electron microscope aggregates were common in most samples particularly with associated mucus blobs and strings of mucus were common with and without particles apparent density of particles a increases with overall concentration but b decreases with increasing concentration when only larger particles are included this probably reflects a aggregation during ageing of a suspension and b presence of more mucus in larger coarse mode populations

accuracy assessment of lidar derived dems of bedrock river channels holtwood gorge susquehanna river 1 we evaluate the accuracy of 1 m lidar derived dems of an exposed bedrock channel and use these high resolution terrain models to calculate erosional fluxes between four levels of strath terraces dated previously with 10be recent investigations into the timing rates and processes by which rivers incise their bedrock channels have greatly enhanced our understanding of landscape evolution however measuring channel geometries in 3 dimensions is difficult thus volumes of bedrock eroded during incision events are rarely considered although our analysis successfully demonstrates the proportionality between incision rates and erosional fluxes for terraces high above the channel floor in this gorge unusually high river flows on the date of acquisition inundated lower bedrock surfaces preventing accurate volume estimates to ensure optimal low flow lidar coverage for fluvial environments we discuss methods to improve the scheduling of data acquisition by using archived discharge records and predictive models based on real time data

sediment character and provenance in a complex fjord howe sound british columbia howe sound is a complex fjord in terms of geomorphology and circulation pattern sediment is presently being deposited in its deep basins from four distinct sources 1 land derived sediment from the squamish river 2 suspended sediment originating from surface waters influenced by discharges from the nearby fraser river 3 reworked pleistocene lag deposits found on some shore platforms and sills throughout the sound and 4 mine tailings from a defunct cu zn mine a less distinct source is sediment deposited via gravity flows from fjord wall slopes including side entry fanglomerate deltas and the major squamish river delta grain size data have been used to differentiate depositional versus nondepositional environments in addition surficial sediment samples collected from depositional basins could be modelled in terms of their size frequency distribution and distance from source those that deviate from a predicted grain size distribution were found to be bimodal partitioning of their probabili