extreme detached dust layers near martian volcanoes evidence for dust transport by mesoscale circulations forced by high topography modeling suggests that thermal circulations over mars s highest volcanoes transport water vapor and dust from the surface into the middle atmosphere forming detached layers in these constituents intense vertical mixing also takes place in regional and global dust storms which can generate detached layers that are extreme in both altitude and magnitude here we employ observations by the mars climate sounder mcs on board mars reconnaissance orbiter taking advantage of improved vertical coverage in mcs s aerosol retrievals to discover a new class of extreme detached dust layers eddls observed during minimal dust storm activity and furthermore distinguished by their potentially large and measurable horizontal extent 1000 km these eddls cluster near olympus mons and the tharsis montes from which they likely originate the existence of these eddls suggests that vertical mixing by topographic circulations can be much stronger than previously modeled and more frequent than previously observed

preseismic hydrogen gas anomalies caused by stress corrosion process preceding earthquakes simultaneous monitoring of he h2 ar n2 ch4 and rn in gas bubbles of groundwater from the 1 500 m deep nagashima well in the active yoro fault zone central japan reveals that three microearthquakes with m 1 6 2 6 in the fault zone are accompanied and preceded by increases of h2 as is a moderately large event with m 5 4 in the same fault zone all the focal distances of the earthquakes are within 25 km no comparable anomalies were seen in the gas species other than h2 we suggest that the selective and preseimic increases of h2 in groundwater gas bubbles are geochemical signals of the earthquake nucleation process of stress corrosion mechanism aseismic slips preceding earthquakes in the active fault zone are likely to have enhanced h2 production by mechanochemical reaction of fractured rock surface with water in pre existing fault planes as groundwater conduits

hyperspectral imaging of convective co2 ice clouds in the equatorial mesosphere of mars 1 a unique feature of the martian climate is the possibility for carbon dioxide the main atmospheric constituent to condense as ice co2 ice is usually detected as frost but is also known to exist as clouds this paper presents the first unambiguous observation of co2 ice clouds on mars these images were obtained by the visible and near infrared imaging spectrometer omega on board mars express the data set encompasses 19 different occurrences compositional identification is based on the detection of a diagnostic spectral feature around 4 26 m which is produced by resonant scattering of solar photons by mesospheric co2 ice particles in a spectral interval otherwise dominated by saturated gaseous absorption observed clouds exhibit a strong seasonal and geographic dependence concentrating in the near equatorial regions during two periods before and after northern summer solstice ls 45 and 135 radiative transfer modeling indicates that the 4 26 m feature is very sensitive to cloud altitude opacity and particle size thereby explaining the variety of spectra associated with the cloud images on two orbits the simultaneous detection of clouds with their shadow provides straightforward and robust estimates of cloud properties these images confirm the conclusions established from modeling clouds are thick with normal opacities greater than 0 2 in the near infrared and are lofted in the mesosphere above 80 km the mean radius of co2 ice crystals is found to exceed 1 m an unexpected value considering this altitude range this finding implies the existence of high altitude atmospheric updrafts which are strong enough to counteract the rapid gravitational fall of particles this statement is consistent with the cumuliform morphology of the clouds which may be linked to a moist convective origin generated by the latent heat released during co2 condensation

field observations on hydrodynamic and coastal geomorphic processes off harilaid peninsula baltic sea in winter and spring 2006 2007 abstract investigations of multi layer current regime variations in sea level and wave parameters using a bottom mounted rdcp recording doppler current profiler during 20 december 2006 23 may 2007 were integrated with surveys on changes of shorelines and contours of beach ridges at nearby harilaid peninsula saaremaa island a w storm with a maximum average wind speed of 23 m s 1 occurred on 14 15 january with an accompanying sea level rise of at least 100 cm and a significant wave height of 3 2 m at the 14 m deep rdcp mooring site it appeared that in practically tideless estonian coastal waters doppler based vertical velocity measurements reflect mainly site dependent equilibrium between resuspension and sedimentation the mooring site 1 5 km off the kelba spit of harilaid was located in the accumulation zone where downward fluxes dominated and fine sand settled as a result of storms in january and april the distal part of the accumulative gravel spit advanced by 50 m whereas a 30 50 m retreat of the shoreline in the western and northern parts occurred at cape kiipsaare the location of the beach ridges shows that the development of the spit occurs through relatively short period but infrequent storm events roughly 2 3 times each decade

co 2 degassing in the hartousov mofette area western eger rift imaged by co 2 mapping and geoelectrical and gravity surveys strong subcontinental mantle dominated co2 degassing occurs in the hartousov and bublak mofette fields in the western eger rift the combination of co2 gas flux and soil gas measurements as well as gravity and geoelectric surveys provides insight into the surface and subsurface of this unique mofette area co2 soil gas and gas flux measurements reveal that large amounts of carbon dioxide are released via channels with diameters below 1 m carbon dioxide emissions of several tens and up to more than 100 kg day 1 are ejected via these small seeps measurements with small spacings are necessary to account for the point like focused gas discharge in the lesser degassing surrounding we estimate that between 23 and 97 tons of co2 are released over an area of about 350 000 m2 each day in the hartousov mofette field the application of widely used geostatistical tools leads to estimations of the co2 discharge with very high standard deviations due to the strong positive skewness of the data distribution geophysical investigations via electrical resistivity tomography and gravity measurements were carried out over areas of strong seepage and reveal distinct anomalies in the subsurface below mofettes indicating rock and sediment alterations and or sediment transport by pressurised ascending co2 and water mobilised by it this study reveals that the gas emanations only occur west of a morphological step which is related to a n s oriented fault zone the pocatky plesna fault zone the results of co2 mapping and the geophysical studies can track the course of this fault zone in this area our results fit into a tectonic model in which the mofette fields are in the centres of two independent pull apart basin like structures we hypothesise that the sinistral strike slip movement of the pocatky plesna fault zone leads to a pull apart basin like opening at which the strong mantle derived co2 degassing occurs nowadays since the hartousov and bublak mofette fields only illustrate examples along the n s striking pocatky plesna fault zone its role and other n s striking faults roles of the regensburg leipzig rostock zone for upper mantle degassing might have been underestimated previously

subvisible co2 ice clouds detected in the mesosphere of mars the formation of co2 ice clouds in the upper atmosphere of mars has been suggested in the past on the basis of a few temperature profiles exhibiting portions colder than co2 frost point however the corresponding clouds were never observed in this paper we discuss the detection of the highest clouds ever observed on mars by the spicam ultraviolet spectrometer on board mars express spacecraft analyzing stellar occultations we detected several mesospheric detached layers at about 100 km in the southern winter subtropical latitudes and found that clouds formed where simultaneous temperature measurements indicated that co2 was highly supersaturated and probably condensing further analysis of the spectra reveals a cloud opacity in the subvisible range and ice crystals smaller than 100 nm in radius these layers are therefore similar in nature as the noctilucent clouds which appear on earth in the polar mesosphere we interpret these phenomena as co2 ice clouds forming inside supersaturated pockets of air created by upward propagating thermal waves this detection of clouds in such an ultrararefied and supercold atmosphere raises important questions about the martian middle atmosphere dynamics and microphysics in particular the presence of condensates at such high altitudes begs the question of the origin of the condensation nuclei

pathways of arsenic from sediments to groundwater in the hyporheic zone evidence from an iron isotope study summary ssulfide fe content and heavy fe isotopic signatures of the bulk core sediments all indicate anoxic and sulfidic conditions in the hyporheic zone the relationship between ssulfide and fe contents suggests that fe iii oxides hydroxides are transferred between non sulfidic fe ii minerals and fe ii sulfides under anoxic and sulfidic conditions respectively the fe isotope composition provides further evidence that microbial dissimilatory reduction of fe iii and the formation of fe ii sulfides and non sulfidic fe ii minerals are the dominant fe geochemical pathways and take place at different depths in the hyporheic zone in the upper sections of the core a and b with depth less than 10 m microbial fe iii reduction and non sulfidic fe ii minerals formation govern the fe cycling and the fe isotope composition in hyporheic water and bulk sediments microbial fe iii and so 4 2 reduction and interaction between produced fe ii aq and fe ii sulfides precipitate control 56fe values of sediments and water sample in the midsections 13 19 m of the core a conversely abiotic fe iii reduction by hs determines the bulk 56fe values of core sediments and water in the midsections 13 19 m of the core b microbial so 4 2 reduction is limited and microbial fe iii reduction controls the 56fe values of water and sediments at the bottom of both cores the variation of 56fe values and the as concentration in hyporheic water are similar at each depth indicating that as enrichment in the water is strongly associated with the microbial reduction of fe iii oxides hydroxides and the formation of fe ii sulfides and non sulfidic fe ii minerals the enriched 56fe values of high as water concentrations suggest that microbial reduction of fe iii oxides hydroxides is the dominant process that promotes as mobility in the hyporheic zones

an observational overview of dusty deep convection in martian dust storms abstractdeep convection as used in meteorology refers to the rapid ascent of air parcels in earth s troposphere driven by the buoyancy generated by phase change in water deep convection undergir

the stability of a remediated bed in hamilton harbour lake ontario canada in situ measurements of lakebed sediment erodibility were made on three sites in hamilton harbour lake ontario using the benthic flume sea carousel three methods of estimating the surface erosion threshold tc 0 from a carousel time series were evaluated the first method fits measures of bed strength to eroded depth the failure envelope and evaluates threshold as the surface intercept the second method regresses mean erosion rate em with bed shear stress and solves for the floc erosion rate ef to derive the threshold for em ef 1 10 5kg m 2 s 1 the third method extrapolates a regression of suspended sediment concentration s and fluid transmitted bed shear stress t0 to ambient concentrations the first field site was undisturbed c and acted as a control the second w was disturbed through ploughing and water injection as part of lakebed treatment whereas the third site oip was disturbed and injected with an oxidant used for remediation of contaminated sediment the main objectives of this study were 1 to evaluate the three different methods of deriving erosion threshold 2 to compare the physical behaviour of lacustrine sediments with their marine estuarine counterparts and 3 to examine the effects of ploughing and chemical treatment of contaminated sediment on bed stability five deployments of sea carousel were carried out at the control site mean erosion thresholds for the three methods were tc 0 0 5 0 06 0 27 0 01 and 0 34 0 03 pa respectively method 1 overpredicted bed strength as it was insensitive to effects in the surface 1 2 mm and the fit of the failure envelope was also highly subjective method 2 exhibited a wide scatter in the data low correlation coefficients and definition of the baseline erosion rate ef is largely arbitrary in the literature method 3 yielded stable high correlation coefficients reproducible and objective results and is thus recommended for evaluation of the erosion threshold the results of this method correlated well with sediment bulk density and followed the same trend as marine counterparts from widely varying sites mass settling rates expressed as a decay constant k of s t were strongly related to the maximum turbidity at the onset of settling smax and were also in continuity with marine counterparts thus it appears that differences in salinity had little effect on mass settling rates in the examples presented and that biological activity dominated any effects normally attributable to changes in salinity bedload transport of eroded aggregates 2 4 mm in diameter took place by rolling below a mean tangential flow velocity uy of 0 32 ms 1and by saltation at higher velocities mass transport as bedload was a maximum at uy 0 4 ms 1 although bedload never exceeded 1 of the suspended load the proportion of material moving as bedload was greatest at the onset of erosion but decreased as flow competence increased given the low bulk density and strength of the lakebed sediment the presence of a bedload component is notable bedload transport over eroding cohesive substrates should be greater in estuaries where both sediment density and strength are usually higher significant differences between the ploughed and control sites were apparent in both the erosion rate and the friction coefficient p and suggest that bed recovery after disruption is rapid 24 h tc 0 increased linearly with time after ploughing and recovered to the control mean value within 3 days the friction coefficient was reduced to zero by ploughing diagnostic of fluidization but increased linearly with time regaining control values within 6 days no long term reduction in bed strength due to remediation was apparent

mars aerosol studies with the mgs tes emission phase function observations optical depths particle sizes and ice cloud types versus latitude and solar longitude 1 emission phase function epf observations taken in 1999 2001 by mars global surveyor thermal emission spectrometer mgs tes support the broadest study of martian aerosol properties to date tes solar band and infrared ir spectral epf sequences are analyzed to obtain first time seasonal latitudinal distributions of visible optical depths particle sizes and single scattering phase functions this combined angular and wavelength coverage enables identification of two distinct ice cloud types over 45 s 45 n type 1 ice clouds exhibit small particle sizes reff 1 2 m and a distinctive backscattering increase they are most prevalent in the southern hemisphere during aphelion but also appear more widely distributed in season and latitude as topographic and high altitude 20 km ice hazes type 2 ice clouds exhibit larger particle sizes reff 3 4 m a distinct side scattering minimum at 90 100 phase angles characteristic of a change in particle shape relative to the type 1 and appear most prominently in the northern subtropical aphelion cloud belt the majority of retrieved dust visible to ir optical depth ratios are indicative of reff 1 5 0 1 m consistent with pathfinder and viking mariner 9 reanalyses however increased ratios 2 7 versus 1 7 appear frequently in the northern hemisphere over ls 50 200 indicating substantially smaller dust particles sizes reff 1 0 0 2 m at this time in addition larger reff 1 8 2 5 m dust particles were observed locally in the southern hemisphere during the peak of the 2001 global dust storm detailed spectral modeling of the tes visible band pass indicates agreement of epf derived dust single scattering albedos 0 92 0 94 with the spectrally resolved results from pathfinder observations

physical behaviour of cretaceous calcareous nannofossil ooze insight from flume studies of disaggregated chalk geomorphic features such as drifts sediment waves and channels have been documented in the upper cretaceous of north west europe these features are interpreted to result from bottom currents and have been used to refine chalk depositional models and quantify palaeocirculation patterns chalk was first deposited as calcareous nannofossil ooze and geomorphic features are the result of sediment reworking after deposition there is limited knowledge on the processes that govern nannofossil ooze mobility thus forcing uncertainty onto numerical models based on sedimentological observations this article provides an extensive view of the erosional and depositional behaviour of calcareous nannofossil ooze based on experimental work using annular flumes a fundamental observation of this study is the significant decrease of nannofossil ooze mobility with decreasing bed porosity erosion characteristics labelled as erosion types vary with total bed porosity and applied shear stress 0 high porosity ooze 80 is characterized by constant erosion rates em at 77 however erosion characteristics showed greater variance surface erosion was typically followed by transitional erosion with asymptotically decreasing em and stages of erosion with constant and exponential erosion rates the estimated erosion thresholds c vary from ca 0 05 to 0 08 pa for the onset of surface erosion and up to ca 0 19 pa for the onset of constant erosion of 60 to 85 variability of deposition thresholds cd from ca 0 04 to 0 13 pa reflects the influence of variable suspended sediment concentration and 0 on settling particle size due to the identified potential for chalk ooze aggregation and flocculation additionally deposition thresholds seem to be affected by the size of eroded aggregates whose size correlates with bed porosity lastly slow sediment transport without resuspension occurred in high porosity ooze as surface creep forming low relief sedimentary features resembling ripples this process represents a previously undescribed mode of fine grained nannofossil ooze transport

effects of bed material properties on cohesive sediment erosion a straight benthic in situ flume was used to measure the erosion rate of cohesive sediments in freshwater and saltwater environments in new zealand the data show an exponential decay of erosion rate with time which is indicative of depth limited erosion two approaches for the calibration of an erosion formula are used both leading to similar results the data show the dependency of erosion rate on bed material properties such as dry bulk density water content organic content and sand content both methodologies also highlight differences between data from freshwater and saltwater environments also shown is a requirement for direct measurements of bed density profiles and bed load transport during in situ investigations

the distribution composition and particle properties of mars mesospheric aerosols an analysis of crism visible near ir limb spectra with context from near coincident mcs and marci observations the compact reconnaissance imaging spectral mapper crism onboard the mars reconnaissance orbiter mro obtains pole to pole observations i e full mro orbits of vertical profiles for visible near ir spectra 0 4 4 0 m which are ideally suited to identifying the composition and particle sizes of mars ice and dust aerosols over 50 100 km altitudes in the mars mesosphere within the coverage limitations of the crism limb data set a distinct compositional dichotomy is found in mars mesospheric ice aerosols co2 ice clouds appear during the aphelion period of mars orbit solar longitudes ls 0 160 at low latitudes 20s 10n over specific longitude regions meridiani valles marineris and at typical altitudes of 55 75 km apart from faint water ice hazes below 55 km mesospheric h2o ice clouds are primarily restricted to the perihelion orbital range ls 160 350 at northern and southern mid to low latitudes with less apparent longitudinal dependences mars mesospheric co2 clouds are presented in crism spectra with a surprisingly large range of particle sizes cross section weighted radii reff 0 3 to 2 2 m the smaller particle sizes reff 1 m appear concentrated near the spatial latitude and altitude boundaries of their global occurrences crism spectra of mesospheric co2 clouds also show evidence of iridescence indicating very narrow particle size distributions effective variance veff 0 03 and so very abrupt co2 cloud nucleation furthermore these clouds are sometimes accompanied by altitude coincident peaks in 1 27 m o2 dayglow which indicates very dry cold regions of formation mesospheric water ice clouds generally exhibit small particle sizes reff 0 1 0 3 m although larger particle sizes reff 0 4 0 7 m appear infrequently on average water ice cloud particle sizes decrease with altitude over 50 80 km in the perihelion mesosphere water ice mass appears similar in clouds over a large range of observed cloud particle sizes with particle number densities increasing to 10 cm 3 for reff 0 2 m near coincident mars climate sounder mcs temperature and aerosol profile measurements for a subset of crism mesospheric aerosol measurements indicate near saturation h2o and co2 conditions for ice clouds and distinct mesospheric temperature increases associated with mesospheric dust loading dayside 3 pm mesospheric co2 clouds with larger particle sizes reff 0 5 m scatter surface infrared emission in mcs limb infrared radiances as well as solar irradiance in the mcs solar band channel scattering of surface infrared emission is most strikingly presented in nighttime 3 am mcs observations at 55 60 km altitudes indicating extensive mesospheric nighttime co2 clouds with considerably larger particle sizes reff 7 m mesospheric co2 ice clouds present cirrus like waveforms over extensive latitude and longitude regions 10 10 as revealed in coincident mars color imager marci nadir imaging solar tides gravity waves and the large orbital variation of the extended thermal structure of the mars atmosphere influence all of these behaviors mesospheric dust aerosols appear infrequently over the non global planet encircling dust storm era of the crism limb data set 2009 2016 and exhibit smaller particle sizes reff 0 2 0 7 m relative to dust in the lower atmosphere one isolated case of an aphelion ls 96 mesospheric dust layer with large dust particle sizes reff 2 m over syria planum may reflect high altitude non local transport of dust over elevated regions

in situ study of the spatiotemporal variability of sediment erodibility in a microtidal estuary abstract seabed erosion is a vital process for sediment transport in estuaries and coasts in this study we investigated the seabed erosion process and its spatiotemporal variability in the pearl river estuary china via in situ observations and laboratory experiments it is found that the seabed was more erodible in the channel than at the shoal in most cases due to the difference in sediment size in a neap spring neap tidal cycle a laminated seabed with different sediment ages was inferred to form due to deposition on flood tides and erosion on ebb tides the seabed was more erodible during spring tides than neap tides because of the difference in sediment availability at the unconsolidated fresh layer furthermore the erosion curve showed evident flood ebb asymmetry which was found to be related to the variations of sediment availability and bottom stress besides erosion experiments with different sediment consolidations revealed that sediment erodibility decreased with the growth of consolidation this study promotes our understanding on the spatiotemporal variability of sediment erodibility and has significant implications for simulation and prediction of estuarine sediment transport and morphological evolution

accounting for rough bed friction factors of mud beds as a result of biological activity in erosion experiments the average bed shear stress and bed friction factor of samples with any roughness was derived from the head loss between upstream and downstream of a test section in an erosion tunnel the method was validated in both hydraulically smooth plexiglass reynolds number less than 25 000 and rough regimes calibrated particles with known roughness as a first step toward using this method on natural sediment this method was tested with experimental mesocosms assembled from field collected materials sieved sediments diatoms bed shear stress measurement precision was high enough in the experiments to detect a positive significant relationship between bed friction factor and core roughness the observed bed friction factor increase could be related to diatom growth but not to diatoms biomass

spatial and temporal variation in cohesive sediment erodibility in the york river estuary eastern usa a biologically influenced equilibrium modified by seasonal deposition abstract sediment erodibility was measured at three sites in the york river a sub estuary of the chesapeake bay monthly to bimonthly from april 2006 through october 2007 erodibility at the three sites was similar during the summer and fall a site near the estuary mouth maintained this level of erodibility greater than 90 of the time while two sites in the more physically dominated mid estuary region exhibited a consistent and pronounced increase in erodibility in the late winter and spring weak to non existent correlations between bed erodibility solids volume fraction and surficial concentrations of organic matter colloidal carbohydrate and extracellular polymeric substances were not sufficient to explain the observed seasonal pattern in bed erodibility digital x radiographs revealed thick sequences 10 20 cm of laminated sediments at the surface in the middle estuary coincident with the period of highest erodibility and more biologically reworked sediment during the rest of the year suggesting that periodic rapid deposition introduced new sediment that was seasonally easy to erode the finding that seasonal deposition influenced erodibility at the mid estuary sites is consistent with previous results indicating the occasional presence of a secondary turbidity maximum comparison of the biologically reworked but still low erodibility condition in the york to other published chesapeake bay erodibility data revealed a consistent critical shear stress range and profile suggesting that this equilibrium critical stress profile may be representative of other similar estuarine environments in the absence of rapid deposition at relatively low stresses and in the absence of rapid deposition we speculate that burrowing and or pelletization may play a role in maintaining high equilibrium bulk water content without reducing the strength of the surface of the seabed

mesospheric co 2 ice clouds on mars observed by planetary fourier spectrometer onboard mars express abstract we have investigated mesospheric co2 ice clouds on mars through analysis of near infrared spectra acquired by planetary fourier spectrometer pfs onboard the mars express mex from my 27 to my 32 with the highest spectral resolution achieved thus far in the relevant spectral range among remote sensing experiments orbiting mars pfs enables precise identification of the scattering peak of co2 ice at the bottom of the 4 3 m co2 band a total of 111 occurrences of co2 ice cloud features have been detected over the period investigated data from the omega imaging spectrometer onboard mex confirm all of pfs detections from times when omega operated simultaneously with pfs the spatial and seasonal distributions of the co2 ice clouds detected by pfs are consistent with previous observations by other instruments we find co2 ice clouds between ls 0 and 140 in distinct longitudinal corridors around the equatorial region 20 n moreover co2 ice clouds were preferentially detected at the observational lt range between 15 16 h in my 29 however observational biases prevent from distinguishing local time dependency from inter annual variation pfs also enables us to investigate the shape of mesospheric co2 ice cloud spectral features in detail in all cases peaks were found between 4 240 and 4 265 m relatively small secondary peaks were occasionally observed around 4 28 m 8 occurrences these spectral features cannot be reproduced using our radiative transfer model which may be because the available co2 ice refractive indices are inappropriate for the mesospheric temperatures of mars or because of the assumption in our model that the co2 ice crystals are spherical and composed by pure co2 ice

in situ flume measurements of resuspension in the north sea abstract the in situ annular flume voyager ii was deployed at three sites in the north sea in order to investigate resuspension events to determine the physical characteristics of the seabed to determine the threshold of resuspension of the bed and to quantify erosion rates and erosion depths these are the first controlled in situ flume experiments to study resuspension in the north sea and were combined with long term measurements of waves and currents resuspension experiments were undertaken at two muddy and one sandy site north of the dogger bank dg water depths 80 m very fine poorly sorted very fine skewed sediment experiencing seasonal thermal stratification of the water column along with oxygen depletion the oyster grounds og 40 m similar bed properties year round water column thermal stratification atlantic forcing and in the sean gas field sgf 20 m moderately sorted very coarse skewed sand and well mixed water column the erosion thresholds of the bed were found to be 0 66 1 04 pa dg and 0 91 1 27 pa og with corresponding erosion depths of 0 1 0 15 mm and 0 02 0 06 mm throughout the experiments evaluation of a year of current velocities from 2007 indicated that at og resuspension of the consolidated bed was limited to on average 8 of the time as a result of tidal forcing alone for short resuspension of bed material and erosion rates were closely related to applied bed shear stresses and eroded depths were significantly correlated with the physical properties of the bed therefore while complex variations in biogeophysical factors affected the critical threshold of erosion once exceeded erosion rates were related to the nature of the sediment

sedimentary environments and postglacial history of the fraser delta and lower fraser valley british columbia the fraser river delta which is about 1000 km2 in area above low tide level has been built into the strait of georgia in southwestern british columbia during the holocene present day sedimentary

the influences of biological activity and consolidation time on laboratory cohesive beds abstract a small annular laboratory flume mini flume was used to investigate the changes in erosion threshold and erosion rate on natural mud taken from an intertidal mud flat surface in southampton water u k mud samples were wet sieved at 2 mm to remove shells and large macrofauna and macroflora and then mixed into a turbid slurry with local estuarine water a mud bed was formed in the flume by letting the sediment deposit in still water at room temperature 20 c the bed was subjected to steady flows of increasing magnitude in a series of steps the flume was subjected to illumination on a dark light cycle of 12 hours to simulate the solar cycle subsequent erosion experiments were carried out after periods of bed consolidation of 2 6 12 24 48 and 96 hours in order to examine changes in bed stability with time this series of experiments was considered the baseline situation in which algal and bacterial binding were present at the end of each experiment the bed was fully resuspended mixed for a period of 5 minutes and then allowed to redeposit a second series of experiments was undertaken using the same sediment but in this case the bed was continuously held in darkness no photosynthesis of microphytobenthos a third series of experiments was carried out in darkness but antibiotics were added to the flume to remove the effects of bacterial activity a final series of experiments was carried out with the addition of 50 ml l 1 of sodium hypochlorite to remove all biological activity in order to examine the effects of electrochemical binding the control the results reveal that under the normal conditions of light day night an increase in sediment stability stabilization index bi of circa 3 was found over that of electrochemical bonding the bed treated with antibiotics suffered an overall stabilization of 1 5 relative to the control

the influence of fish feed pellets on the stability of seabed sediment a laboratory flume investigation superfluous fish food settling below fish farms can have a negative impact on the seabed to aid in the assessment of this impact a series of flume experiments designed to mimic seabed conditions below a fish farm was conducted with the aim of examining the effects of fish pellets on the stability of fine sediments artificial beds with varying quantities of fish pellets incorporated both within the sediment matrix and lying on the sediment surface were allowed to consolidate for different periods of time ranging from 1 to 10 days and then subjected to erosion experiments in flume experiments containing fish pellets a bacterial biofilm developed at the sediment water interface after a few days in the control experiments no fish pellets a diatom biofilm caused extensive stabilisation of the surface sediment the erosion experiments showed that the addition of fish pellets reduced the surface erosion threshold by more than 50 the stability decrease was more pronounced in the experiments with greater amounts of pellets evidence of drag reduction due to high suspended sediment concentration was also observed this phenomenon is discussed and a correction formula is proposed for the effective shear stress experienced by the bed

seismically triggered anomalies in the isotope signatures of mantle derived gases detected at degassing sites along two neighboring faults in nw bohemia central europe the vogtland and nw bohemia region is known for its earthquake swarms the most intensive swarm since 1985 86 occurred in october 2008 to find further indications for the interaction of ascending mantle derived fluids and the occurrence of earthquake swarms detailed fortnightly studies of gas compositions co2 n2 ar he h2 and ch4 and isotope ratios 13c 15n and 3he 4he were carried out between october 2008 and april 2011 at four locations close to the nov kostel focal zone and at the wettinquelle spring bad brambach from the start of the 2008 earthquake swarm seismically induced isotope geochemical anomalies were recorded at locations along the pocatky plesna fault zone ppz and were for the first time also found at degassing locations on the marianske lazn fault zone mlf variations were observed in both the temporal and spatial distributions of the anomalies as well in anomaly strengths probably due to the positions of these fault zones relative to the focal zone and to differences in fluid migration pathways prior to both the 2000 and 2008 swarms 3he 4he ratios 6 ra were recorded at the bublak mofette these anomalous pre seismic 3he 4he ratios suggest that both the 2000 and 2008 swarms may have been associated with the supply of fresh magma from a less degassed reservoir in the lithospheric mantle the temporal 13cco2 pattern from detailed studies at bublak between 2005 and 2011 indicates progressive magma degassing as well as seismically induced variations in the 13c providing additional support to the interpretation derived from the 3he 4he ratios

critical shear stress of cohesive bottom sediments the main purpose of this study is to obtain a simple critical shear stress function for cohesive soft bottom sediments a series of experiments concerning threshold levels of mud transport and two series of tests of their rheological and setting properties were conducted to find some correlation among these indices we defined two threshold levels for mud transport and divided muds into two groups by their characteristics settling type flow curve resuspension behavior etc in discussing the factors determining the characteristics of the two groups we found that natural muds usually belong to the first group in which the two critical shear stresses are given as a function of yield value y1 defined in paper independent of material following a new definition of threshold for sediment detachment from the bed finally the correlation between this yield value and the final settling volume ratio is also discussed

constraints on the origin of zonation of the granite complexes in the fichtelgebirge germany and czech republic evidence from a gravity and geochemical study compositional zoning of granitic plutons is a common feature but the spatial variation of zoning is rarely studied in detail it is suggested that important additional information can emerge if the compositional zoning is regarded with relation to the root zones i e with the granite shape at depth a combined geochemical and gravity investigation was performed on the hercynian fichtelgebirge granites which are composed of an older intrusive complex oic and younger intrusive complex yic the oic and yic are distinct from each other with respect to magma origin differentiation pattern shape of the granite complexes at depth and the zonation pattern in relation to the root zone the oic shows normal compositional zoning whereas the yic both reverse yic 1 and normal zoning yic 2 the general zonation pattern of the oic and the yic is the result of a combination of multiple injections of single magma batches and in situ differentiation during magma emplacement in addition to the general zonation pattern local zonation in individual granite bodies of the yic was caused by sidewall crystallisation producing a less differentiated marginal facies g2 and a more differentiated core facies g3 and g4 it is suggested that the complex zonation patterns of the fichtelgebirge granite complexes reflect interactions between the rate of magma output which is partly governed by their rheological properties and the rate of deformation which provides the room for the magma to be emplaced

subaerial exposure and changes in the stability of intertidal estuarine sediments abstract the surface cohesive strength of intertidal sediments at six sites on two estuaries throughout the period of a single diurnal subaerial exposure was investigated stations at different tidal heights were examined at each site hourly measurements were made using a cohesive strength meter which provides an ordinal measure of sediment stability the sediment was most easily eroded immediately after the emersion of the mudflat and there was little difference between the initial stability of the mud at different sites or stations as the subaerial exposure continued the sediment of mid shore and high shore stations began to increase in stability no significant change was found at low shore stations before the return of the tide the surface density of diatom populations was also intermittently measured at each site the greatest increase in sediment stability occurred at high shore stations and this was most extreme where there were also dense populations of epipelic diatoms present at the surface of the sediment this supports laboratory evidence that the extracellular products of diatom populations of sufficient density increase the stability of intertidal sediments

earthquake m 5 1 induced hydrogeochemical and δ18o changes validation of aquifer breaching mixing model in koyna india summary hydrochemical parameters and oxygen 18 18o were measured in groundwater from wells and spring waters from the active seismic area around koyna warna reservoirs over a period of three years 2005 2007 to explore their relationship with seismicity in comparison to average values observed later hydrochemical data of one of the wells revealed increased concentrations of chloride 100 per cent sulphate 300 per cent and fluoride 700 per cent while the 18o value decreased contemporarily to the occurrence of an earthquake of magnitude 5 1 on 2005 march 14 based on the hydrochemical and isotopic characteristics of different well waters in this area we conceptualize a model of aquifer breaching and mixing of deep aquifer water with shallow aquifer water due to the earthquake we estimated the fractions of two components of different aquifer waters mixed using two conservative tracers chloride and 18o the necessary mixing proportions of 50 per cent are unprecedented and call for further work to understand the earthquake related processes causing the observed hydrogeochemical and isotopic anomalies in the koyna warna region

role of fines on cohesive behavior of mine tailings inferred from critical shear stress the significance of fines on the cohesive behavior of mine tailings has been investigated by examining the incipi ent motion of the tailings sixteen laboratory experiments were performed in a plexiglas laboratory annular column on re constituted mine tailings under a 50 cm water cover re suspension was produced by a teflon stirrer and the velocity field in the column was characterized using a laser doppler velocimeter ldv the pressure change in the boundary layer was also measured with a preston tube it was observed that the nondimensional critical shear stresses showed deviation from those of the noncohesive model results at a fines content greater than 50 55 an empirical relation that shows the rela tion between the boundary shear stress deviation and the percent fines in the tailings was proposed regression analysis of the experimental results showed that a power law relationship could reasonably be used to describe the relation between the measured nondimensional excess bed shear stress and the erosion rate it is proposed that the value of b the erosion rate constant could be taken as 1 for mine tailings that show cohesive behavior

mapping the mesospheric co2 clouds on mars mex omega and mex hrsc observations and challenges for atmospheric models this study presents the latest results on the mesospheric co2 clouds in the martian atmosphere based on observations by omega and hrsc onboard mars express we have mapped the mesospheric co2 clouds during nearly three martian years of omega data yielding a cloud dataset of 60 occurrences the global mapping shows that the equatorial clouds are mainly observed in a distinct longitudinal corridor at seasons ls 0 60 and again at and after ls 90 a recent observation shows that the equatorial co2 cloud season may start as early as at ls 330 three cases of mesospheric midlatitude autumn clouds have been observed two cloud shadow observations enabled the mapping of the cloud optical depth 0 01 0 6 with median values of 0 13 0 2 at 1 m and the effective radii mainly 1 3 m with median values of 2 0 2 3 m of the cloud crystals the hrsc dataset of 28 high altitude cloud observations shows that the observed clouds reside mainly in the altitude range 60 85 km and their east west speeds range from 15 to 107 m s two clouds at southern midlatitudes were observed at an altitude range of 53 62 km the speed of one of these southern midlatitude clouds was measured and it exhibited west east oriented speeds between 5 and 42 m s the seasonal and geographical distribution as well as the observed altitudes are mostly in line with previous work the lmd mars global climate model shows that at the cloud altitude range 65 85 km the temperatures exhibit significant daily variability caused by the thermal tides with the coldest temperatures towards the end of the afternoon the gcm predicts the coldest temperatures of this altitude range and the season ls 0 30 in the longitudinal corridor where most of the cloud observations have been made however the model does not predict supersaturation but the gcm predicted winds are in fair agreement with the hrsc measured cloud speeds the clouds exhibit variable morphologies but mainly cirrus type filamented clouds are observed nearly all hrsc observations and most of omega observations in 15 of omega observations clumpy round cloud structures are observed but very few clouds in the hrsc dataset show similar morphology these observations of clumpy cumuliform type clouds raise questions on the possibility of mesospheric convection on mars and we discuss this hypothesis based on convective available potential energy calculations

data interpretation for in situ measurements of cohesive sediment erosion methods for interpreting data from in situ flume measurements of cohesive sediment dynamics are evaluated and a technique for estimating various erosion parameters using in situ measurements is proposed there is currently a lack of uniformity in analysis techniques for cohesive erosion data collected in flumes and with in situ instruments and the proposed technique resolves some of these inconsistencies the data set used in this study was derived from field experiments conducted with a straight benthic in situ flume in different aquatic environments in new zealand the experiments with stepwise increases in flow velocity revealed that peaks in the erosion rate at the beginning of each velocity step are most likely associated with heterogeneous bed structure as transient hydrodynamic effects due to the experimental procedure were found to be insignificant the field data showed an exponential decay of the erosion rate with time that is indicative of depth limited erosion these data are used to illustrate methods for the parameterization of the proposed semiempirical erosion equation taking into account the time dependency of the erosion process

earthquake impact on iron isotope signatures recorded in mineral spring water we investigated the iron isotope signatures of dissolved fe in the water of the wettinquelle mineral spring bad brambach germany by time series sampling covering seismically active periods related to tectonic activity near the eger rift system in central europe our objective was to test whether fe isotopes trace earthquake induced abiotic and biotic changes in the fluid rock interaction of the deep fissured granitic aquifer we found that the dissolved fe isotope signatures in spring water are distinct from the granitic source signature 56fe 0 09 particularly we discovered that water 56fe values are remarkably stable 0 01 0 11 2sd n 4 before and during a strong seismic swarm period in 2000 local magnitudes ml 3 while o2 and h2 concentrations in water decrease and dissolved fe content increases later recurring events of lower 56fe values down to 0 3 are observed in the period from 2001 to 2003 with intermittent seismic events 1 ml 2 6 the observations indicate a time lag between tectonic forcing and fe isotope response the role of abiotic fluid rock interaction and fe utilizing bacteria identified in the mineral spring water on fe isotope fractionation is discussed we explain recurring changes towards isotopically lighter values by a combination of fe dissolution from deep granite and admixture of isotopically light fe generated by a complex combination of abiotic and biotic processes operating in the aquifer when disturbed by swarm earthquakes events we propose a conceptual model scenario of earthquake triggered changes in biogeochemical processes

seismic related variations in the chemical and isotopic composition of thermal springs near acapulco guerrero mexico 1 chemical and isotopic analyses of waters from 4 thermal springs of the guerrero pacific coast the most seismically active area in mexico were performed weekly during a period of 1 5 years october 2002 march 2004 within the same time interval more than 200 earthquakes with 3 8 m 5 3 occurred in the area the data display several anomalies in cl so42 d and 18o always immediately after an event with a relaxation time of 3 4 weeks the responses occurred only to earthquakes with the estimated epicenters very close to the location of a spring these results indicate that 1 at least for earthquakes with m 5 3 within the guerrero seismic gap there were no precursors in the chemical ionic and isotopic composition of thermal waters on a weekly basis 2 two groups of springs near acapulco dos arroyos and paso real are sensitive to seismic activity and therefore further monitoring of these springs may help to unravel the mechanisms of the hydro seismo interaction in the area

resuspension potential of surficial sediments in saguenay fjord quebec canada abstract a flash flood that occurred in july 1996 in the saguenay area quebec canada deposited a bed of cohesive sediments average of 10 60 cm thick over an area of 65 km 2 of the deep fjord basin of the upper saguenay fjord because this turbidite covered contaminated sediments the resuspension potential of surficial sediments is an important parameter in determining the efficiency of the 1996 layer as a natural capping layer this is because contaminants that may have diffused through the 1996 layer may be resuspended the resuspension potential of surficial sediments in saguenay fjord was investigated in situ over a 3 yr period at fifteen sites in the baie des ha ha and the north arm using a benthic flume the miniflume in addition geotechnical measurements photographs of benthic sediments and recordings of benthic current velocities were also carried out the measured critical velocities of sediment resuspension u c vary between 7 and 15 cm s 1 the maximum bottom current speed recorded in the north arm and in baie des ha ha from may to august 2000 was 27 cm s 1 erosion depths were determined from miniflume data combined with laboratory measurements carried out with an axial tomography scanner which provided variation of sediment density at an interval of 0 13 mm a general relationship between depth of erosion ze mm and shear stress applied on the bed b pa was determined as saguenay fjord sediment characteristics vary greatly from one station to another the potential for resuspension of surficial sediments shows the same trend

co2 ice clouds in the upper atmosphere of mars recent sept 1996 sept 1997 observations of mars submillimeter co lines from the james clerk maxwell telescope jcmt on mauna kea hawaii have revealed surprisingly cold temperatures as typical of the mars atmosphere over the 50 80 km altitude region measurements of these j 2 3 and j 3 4 rotational transitions of mars atmospheric 12co provide unique seasonal coverage of global averaged dayside temperatures within this poorly observed mesophere of mars at solar longitudes ls of 8 90 150 and 187 in 1996 97 the mean atmospheric temperature for the 70 80 km 2 0 0 3 bars altitude region is observed to be at or below 120 k which is only 10 15 k above the vapor saturation temperature for the co2 mars atmosphere consequently local co2 saturation conditions at these altitudes would be likely to exist and in fact were observed during the 3 am descent entry of the pathfinder spacecraft on july 4 1997 we argue that the blue wave clouds imaged from the pathfinder lander 35 100 minutes prior to sunrise on sol 39 are evidence of such co2 ice formation within the 60 100 km altitude region and that the 4 3 m co2 lines of solar scattered flux in mariner 6 and 7 infrared limb spectra of mars are a direct spectral identification of co2 ice cloud formation in the dayside mars mesosphere simple considerations of these pathfinder and mariner 6 and 7 observations suggest 0 1 0 3 m cloud particle radii and particle number densities of the order 10 cm 3 on the basis of a variety of such day and night time measurements we assert that the mesosphere of mars does not exhibit extreme 25 k diurnal temperature variations as maintained by the pathfinder meteorology team and that it is often substantially colder 20 k than determined from the viking descent measurements in 1976 due to temporal variations in dust loading of this region

new near ir observations of mesospheric co2 and h2o clouds on mars 1 carbon dioxide clouds which are speculated by models on solar and extra solar planets have been recently observed near the equator of mars the most comprehensive identification of martian co2 ice clouds has been obtained by the near ir imaging spectrometer omega crism a similar instrument with a higher spatial resolution cannot detect these clouds with the same method due to its shorter wavelength range here we present a new method to detect co2 clouds using near ir data based on the comparison of h2o and co2 ice spectral properties the spatial and seasonal distributions of 54 crism observations containing co2 clouds are reported in addition to 17 new omega observations crism co2 clouds are characterized by grain size in the 0 5 2 m range and optical depths lower than 0 3 the distributions of co2 clouds inferred from omega and crism are consistent with each other and match at first order the distribution of high altitude 60 km clouds derived from previous studies at second order discrepancies are observed we report the identification of h2o clouds extending up to 80 km altitude which could explain part of these discrepancies both co2 and h2o clouds can exist at high mesospheric altitudes crism observations of afternoon co2 clouds display morphologies resembling terrestrial cirrus which generalizes a previous result to the whole equatorial clouds season finally we show that morning omega observations have been previously misinterpreted as evidence for cumuliform and hence potentially convective co2 clouds

dusty deep convection in the mars year 34 planet encircling dust event dusty convection convective activity powered by radiative heating of dust is a ubiquitous phenomenon in mars s atmosphere but is especially deep that is impactful on the middle atmosphere and widespread during planet encircling dust events pede that occur every few mars years my yet the relative roles of dusty deep convection and global dynamics such as the principal meridional overturning cell pmoc and the radiative tides in dust storm development and the vertical transport of dust and water are still unclear here observations from the mars climate sounder on board mars reconnaissance orbiter mro mcs are used to study dusty deep convection and its impact on middle atmospheric water content during the my 34 pede commenced june 2018 additional context is provided by mro mcs observations of the my 28 pede commenced june 2007 this investigation establishes that a few localized centers of dusty deep convection in the tropics formed in the initial phases of both pede simultaneously with a substantial increase in middle atmospheric water content the growth phase of the my 34 pede was defined by episodic outbreaks of deep convection along the acidalia and utopia storm tracks as opposed to less episodic more longitudinally distributed convective activity during the my 28 pede the most intense convection during both pede was observed in southern eastern tharsis where mro mcs observed multiple instances of deep convective clouds transporting dust to altitudes of 70 90 km these results suggest that martian pede typically contain multiple convectively active mesoscale weather systems

cohesion influences on erosion and bed load transport 1 studies on erosion and transport rates of cohesive sediment mixtures containing gravel are not reported so far in the literature to the best of our knowledge results from laboratory experiments on the process of erosion of cohesive sediment mixtures by open channel flow are presented the sediment used for experimentation consisted of fine gravel mixed with clay in proportions varying from 10 to 50 and fine gravel fine sand in equal proportion by weight mixed with clay proportions again varying from 10 to 50 by weight experimental observations have revealed that the process of detachment of cohesive sediment mixtures containing gravel is significantly different from that of cohesionless sediments also it is different from the detachment process of cohesive sediment mixtures not containing coarser size material experimental data on transport rates of the bed load of the cohesive sediment mixtures are presented on the basis of dimensional considerations a computational procedure is proposed to determine the bed load transport rates generated from erosion of the different size fractions of sediment mixtures clay percentage and unconfined compressive strength of the sediment bed were the main parameters controlling bed load transport rate of such sediments in the absence of cohesion the proposed method reduces to the patel and ranga raju 1996 method for bed load transport rate computation of nonuniform cohesionless sediments

vertical distribution of dust and water ice aerosols from crism limb geometry observations 1 near infrared spectra taken in a limb viewing geometry by the compact reconnaissance imaging spectrometer for mars crism on board the mars reconnaissance orbiter provide a useful tool for probing atmospheric structure specifically the observed radiance as a function of wavelength and height above the limb enables the vertical distribution of both dust and water ice aerosols to be retrieved more than a dozen sets of crism limb observations have been taken so far providing pole to pole cross sections spanning more than a full martian year radiative transfer modeling is used to model the observations taking into account multiple scattering from aerosols and the spherical geometry of the limb observations both dust and water ice vertical profiles often show a significant vertical structure for nearly all seasons and latitudes that is not consistent with the well mixed or conrath v assumptions that have often been used in the past for describing aerosol vertical profiles for retrieval and modeling purposes significant variations are seen in the retrieved vertical profiles of dust and water ice aerosol as a function of season dust typically extends to higher altitudes 40 50 km during the perihelion season than during the aphelion season 20 km and the hellas region consistently shows more dust mixed to higher altitudes than other locations detached water ice clouds are common and water ice aerosols are observed to cap the dust layer in all seasons

the stability of fine grained sediments from the fraser river delta the stability and erodibility of benthic fine grained sediments on the foreshore and upper foreslope of the fraser river delta were measured using thein situbenthic flume sea carousel the erosion threshold c 0 which varied between 0 11 and 0 50 pa was inversely related to erosion rate it was also proportional to sediment wet bulk density b in the form c 0 7 10 4 b 0 47 this trend agreed with those obtained from four other sites across canada that encompassed a wide range in sediment densities 1000 b 2000 kg m 3 erosion threshold shields parameter c was positively related to grain reynolds number over the silt clay size range 0 01 re 5 c 2 86re0 58 this was similar to earlier findings for water saturated sediment this trend is also in continuity with published threshold values measured in biostabilized sand 5 re 50 copyright 1997 academic press limited three erosion types were observed type ia erosion was a surface phenomenon caused by the presence of a thin organic fluff layer it occurred at current speeds less than 0 3 m s 1 type 1b erosion asymptotically decaying with time characterized the mid portions of each erosion time series and occurred at current speeds of 0 3 0 9 m s 1 type i ii erosion transitional was largely found on the foreslope and occurred at current speeds in excess of 0 8 m s 1 the erosion process began in all cases under turbulent transitional flows the change from type i to type ii erosion corresponded to the onset of turbulent rough flows 60 re 70 this is supported by video observations which showed type i erosion to be largely the result of entrainment of small aggregates and flocs whereas type ii erosion was the result of enlargement of surface irregularities and subsequent undercutting and release of large aggregates mean erosion rate em was independent of either azimuthal current speed or bed shear stress it was largely constant throughout each deployment and varied between 1 4 and 7 4 10 4 kg m 2 s 1

modeling diagnosis of suspended sediment transport in tidal estuarine system a three dimensional time dependent hydrodynamic and suspended sediment transport model was performed and applied to the danshuei river estuarine system and adjacent coastal sea in northern taiwan the model was validated with observed time series salinity in 2001 and with salinity and suspended sediment distributions in 2002 the predicted results quantitatively agreed with the measured data a local turbidity maximum was found in the bottom water of the kuan du station the validated model then was conducted with no salinity gradient no sediment supply from the sediment bed wind stress and different freshwater discharges from upstream boundaries to comprehend the influences on suspended sediment dynamics in the danshuei river estuarine system the results reveal that concentrations of the turbidity maximum simulated without salinity gradient are higher than those of the turbidity maximum simulated with salinity gradient at the kuan du station without bottom resuspension process the estuarine turbidity maximum zone at the kuan du station vanishes this suggests that bottom sediment resuspension is a very important sediment source to the formation of estuarine turbidity maximum the wind stress with northeast and southwest directions may contribute to decrease the suspended sediment concentration when the freshwater discharges increase at the upstream boundaries the limits of salt intrusion pushes downriver toward river mouth suspended sediment concentrations increase at the upriver reaches in the danshuei river to tahan stream while decrease at kuan du station

day night variation of intertidal flat sediment properties in relation to sediment stability the majority of investigations that have measured sediment properties related to intertidal sediment stability have been undertaken during daylight subaerial exposure periods as a consequence models based upon such data represent only partially the intertidal flat surface conditions within any 24 h period in this contribution a comparison is made between surface sediment properties related to sediment stability measured during six consecutive day night semi diurnal subaerial exposure periods at three stations on an intertidal sand flat in late march 1999 the study site was selected on the basis of its suitability for sampling and data collection at night with special regard to safety and logistics seawater temperatures ranged from 4 1 to 9 6 c and salinities from 33 9 to 34 8 eleven parameters related to intertidal flat sediment stability were measured or derived these variables included the critical erosion shear stress c chlorophyll a phaeopigment and colloidal carbohydrate content mean grain size and settling velocity of the surface 0 1 mm sediment fraction bed elevation was described using an acretion erosion parameter aep west and west 1991 whilst additional physical terms included ambient seawater salinity and temperature as well as tidal range and wind speed during the preceding immersion periods one way anova was used to detect significant differences between day and night time emersion periods similarly principal components analysis pca was applied to detect continuous variation between properties the results show a high degree of temporal and spatial variability between day and night time intertidal flat variables the pca differentiating clearly between day and night conditions surface sediments across the intertidal flat exhibited varying degrees of biostabilisation the maximum biostabilisation coefficient 18 was recorded at night in high microalgal biomass areas the minimum 5 occurred during both day and night in areas with lower microalgal biomass all surface sediment parameters varied rhythmically between day and night time significant differences were found between day and night time biostabilisation coefficients however differences between day and night time c values were not detected it is suggested that sediment stability at night is enhanced in high microalgal biomass areas as a result of degradation products from bound extra cellular polysaccharides eps not easily detected using standard extraction procedures

the vertical structure of limb hazes in the martian atmosphere abstract profiles of scattered light above the planetary limb from over 100 viking orbiter images are used to constrain the temporal and spatial behavior of earosols suspended in the martian atmosphere the data cover a wide range of seasons locations and viewing geometry providing information about the aerosol optical properties and vertical distribution the vertical resolution of the data is about 1 5 km with an absolute elevation accuracy of 1 to 4 km viking orbiter camera colibration algorithms provided reflectance accuracies to 7 absolute allowing meaningful radiometric analysis the typical atmospheric column contains one or more discrete optically thin ice like haze layers between 30 and 90 km elevation depending on season whose composition is inferred to be water ice below the detached hazes there is a continuous haze extending to the surface the continuous haze is rarely observed above 50 km and is much redder in color than the detached hazes above implying a composition that has a strong dust component the aerosol distribution exhibits a strong seasonal control inferred to be driven by the variable solar flux around the orbit of mars

turbidity limits gas exchange in a large macrotidal estuary in estuaries the gas transfer velocity k is driven by a combination of two major physical drivers wind and water current the k values for co2 in the macrotidal gironde estuary were obtained from 159 simultaneous pco2 and floating chamber flux measurements values of k increased with wind speed and were significantly greater when water currents and wind were in opposing directions at low wind speeds 0 2 g l 1 had a significant role in attenuating turbulence and therefore gas exchange this result has important consequences for modeling water oxygenation in estuarine turbidity maxima for seven low turbidity estuaries previously described in the literature the slope of the linear regression between k and wind speed correlates very well with the estuary surface area due to a fetch effect in the gironde estuary this slope follows the same trend at low turbidity tss 0 2 g l 1 but is on average significantly lower than in other large estuaries and

mars equatorial mesospheric clouds global occurrence and physical properties from mars global surveyor thermal emission spectrometer and mars orbiter camera limb observations 1 we report the occurrence of a new type of cloud in the mars dayside 1300 1400 local time atmosphere apparent as high altitude 60 to 80 km vertically discrete aerosol scattering layers mars global surveyor mgs limb observations from the thermal emission spectrometer tes visible channel indicate peak frequencies at the beginning and end of the aphelion northern summer season ls 30 and 150 where they are confined to equatorial 15 s 15 n latitudes and two longitude ranges 40 e 2 w and 50 w 120 w limb images from the mgs mars orbiter camera moc indicate significant horizontal variations in these mars equatorial mesospheric mem clouds on 20 50 km scales on the basis of the distribution of projected limb heights mem clouds exhibit peak optical depths over 70 75 km altitudes that are substantial nadir vis of order 0 01 for the low pressure region of formation 1 bar averaged tes limb infrared spectral 5 40 m and solarband radiance profiles corresponding to mem occurrence indicate dust aerosols reff 1 5 2 0 m vis 0 4 at 0 25 km altitudes capped by water ice clouds reff 1 5 2 0 m vis 0 2 at 20 45 km altitudes the lack of detectable infrared radiances at mem cloud heights precludes distinction of water versus co2 ice but indicates 1 m particle sizes for water or 1 5 m for co2 ice compositions more recent mars express observations point toward mars mesospheric co2 clouds although current dynamical and radiative models do not indicate sufficiently cold temperatures at mem cloud locations to produce daytime co2 saturation conditions

a multiannual record of gravity wave activity in mars s lower atmosphere from on planet observations by the mars climate sounder abstract gravity waves in mars s atmosphere strongly affect the general circulation as well as middle atmospheric cloud formation but the climatology and sources of gravity waves in the lower atmosphere remain poorly understood at earth the statistical variance in satellite observations of thermal emission above the instrumental noise floor has been used to enable measurement of gravity wave activity at a global scale here is presented an analysis of variance in calibrated radiance at 15 4 m 635 665 cm 1 from off nadir and nadir observations by the mars climate sounder mcs on board mars reconnaissance orbiter mro a major expansion in the observational data available for validating models of martian gravity wave activity these observations are sensitive to gravity waves at 20 30 km altitude with wavelength properties h 10 100 km z 5 km that make them likely to affect the dynamics of the middle and upper atmosphere we find that 1 strong moderately intermittent gravity wave activity is scattered over the tropical volcanoes and throughout the middle to high latitudes of both hemispheres during fall and winter 2 gravity wave activity noticeably departs from climatology during regional and global dust storms and 3 strong intermittent variance is observed at night in parts of the southern tropics during its fall winter but frequent co 2 ice clouds prevents unambiguous attribution to gw activity the spatial distribution of wave activity is consistent with topographic sources being dominant but contributions from boundary layer convection and other convective processes are possible

an evaluation of bed shear stress under turbid flows this paper investigates the effect of various turbidity levels on the drag coefficient and bed shear stress in decelerating flows over a smooth bed turbid flows were simulated in a laboratory annular flume lab carousel using clay suspensions of different known mass concentrations flow velocity measurements were taken in the turbulent boundary layer and the values of bed drag coefficient and shear stress were calculated using the method of flow deceleration results showed that the bed drag coefficient responds significantly to an increase in the suspended sediment concentration up to 20 g l showing a decrease of up to 50 in drag due to turbulence suppression however subsequent increases in mass concentration resulted in an increase in the drag coefficient reaching the clear water value at approximately 200 g l because of the influence of viscosity thus the application of the law of the wall in flows of high concentrations of suspended cohesive sediments up to 200 g l results in overestimation of the bed shear stress

great differences in the critical erosion threshold between surface and subsurface sediments a field investigation of an intertidal mudflat jiangsu china abstract understanding of bottom sediment erodibility is necessary for the sustainable management and protection of coastlines and is of great importance for numerical models of sediment dynamics and transport to investigate the dependence of sediment erodibility on degree of consolidation we measured turbidity waves tidal currents intratidal bed level changes and sediment properties on an exposed macrotidal mudflat during a series of tidal cycles we estimated the water content of surface sediments in the uppermost 2 cm of sediment and sub surface sediments at 2 cm below the sediment surface bed shear stress values due to currents c waves w and combined current wave action cw were calculated using a hydrodynamic model in this study we estimate the critical shear stress for erosion using two approaches and both of them give similar results we found that the critical shear stress for erosion ce was 0 17 0 18 n m2 in the uppermost 0 2 cm of sediment and 0 29 n m2 in sub surface sediment layers depth 2 cm as determined by time series of cw values and intratidal bed level changes and values of ce obtained using the water content of bottom sediments were 0 16 n m2 in the uppermost 2 cm and 0 28 n m2 in the sub surface depth 2 cm sediment these results indicate that the value of ce for sub surface sediments depth 2 cm is much greater than that for the uppermost sediments depth 0 2 cm and that the ce value is mainly related to the water content which is determined by the extent of consolidation our results have implications for improving the predictive accuracy of models of sediment transport and morphological evolution by introducing variable ce values for corresponding sediment layers and can also provide a mechanistic understanding of bottom sediment erodibility at different sediment depths on intertidal mudflats as related to differences in the consolidation time

the deposition and erosion of cohesive sediments determined by a multi class model sediment properties were studied experimentally using a laboratory flume and sediments sampled from both fresh and saltwater systems i e the rhone river and the adjacent continental shelf golfe du lion mediterranean sea an experimental protocol is proposed which includes the development of an analytical method based on a multi class model in order to determine the erosion and deposition fluxes of these sediments this approach highlights the presence of a fluff layer characterized by a very low critical erosion shear stress and a second layer with a significantly larger critical erosion shear stress if a global model is used i e only one class of particles is considered this distinction between the two layers cannot be made as sediment parameters are identified for the whole eroded particles including the fluff layer critical shear stresses of erosion were 0 05 0 04 and 0 025 n m 2 respectively for the first class of particles eroded at rhone 1 rhone 2 and sofi stations the second class of particles showed critical shear stress 10 20 times higher around 0 20 n m 2 the use of the multi class model allowed estimation of the erosion rates in the order of 2 5 10 6 6 2 10 5 and 2 10 6 kg m 2 s 1 for rhone 1 rhone 2 and sofi settling velocities were in the order of 0 012 0 045 mm s 1 for the first class and between 0 05 and 0 09 mm s 1 for the second class for the river experiments it is shown that the fluff layer corresponding to the first class of particles being eroded is mainly representative of recent deposits of suspended particles probably trapped in the overlying water column during sediment sampling this highlights the difficulties in sampling sediments and transporting these from field to lab and more generally into flumes and the limits of applying a global model to flume experiments when studying sediment properties

drag reduction in turbulent muddy seawater flows and some sedimentary consequences turbulent saline flows which contain low concentrations of suspended clay 10 g 1 1 have previously been reported to possess dramatically different boundary layer characteristics from clearwater flows and to exhibit the phenomenon of drag reduction drag reduction causes significantly lower friction factors and higher erosion thresholds in muddy saline flows than predicted by experimental data gained from fresh water flows using the law of the wall to estimate bed shear stress confirmation is given by experimental results on drag reduction using non intrusive laser doppler measurements in seawater flows with 2 2 g 1 1 maximum concentration of suspended clay increasing the concentration of clay caused progressively lower velocities near the wall due to a gradual thickening of the buffer region of the turbulent boundary layer several aspects of sediment transport deposition and bedform development in natural marine environments are thus considered to be significantly affected by the drag reduction process

characterization of the bacterial flora in mineral waters in upstreaming fluids of deep igneous rock aquifers 1 the bacterial community of the mineral spring wettinquelle in the vogtland nw bohemian region german czech border was characterized by sequence analysis of amplified small subunit ribosomal rna genes the acidulous spring water consists mostly of old groundwater from deep aquifers which is mixed with 15 20 young water from upper groundwater horizons the spring water contains high concentrations of iron ca2 and so42 ions a remarkable attribute is the high radon activity of 27 kbq l 1 water free escaping spring gas consists mainly of co2 originating from the mantle n2 1 2 and traces of other gases like methane and helium close relatives of gallionella ferruginea a micro aerobic oxidizer of ferrous iron contributed most to the clone library clones with sequences related to thiobacillus aquaesulis members of the sulfuricurvum cluster and members of several branches of the op11 group were present in significantly lower numbers but still with some microdiversity these bacterial groups which contributed strongly to the clone library and have known physiology obviously depend on the oxygen in the younger water and reduced compounds from the below

results of the mars pathfinder atmospheric structure investigation we report on a thorough analysis of the mars pathfinder atmospheric structure investigation asi accelerometer data spanning the altitude range 161 8 9 km entry descent and landing occurred within 850 km of the viking 1 lander and somewhat later in northern summer the early morning entry 0300 hours provided the first opportunity to study mars nighttime atmospheric structure the close proximity to the viking 1 site has permitted a search for changes in atmospheric structure during the 21 years between the landings our results confirm and refine the major features of the atmospheric structure discovered in the initial analysis of the asi results reported by schofield et al 1997 the current analysis has yielded a much better definition of the temperature structure above 90 km altitude pathfinder measured a thermospheric peak temperature of 153 k at 134 km which is 30 k colder than the value found by viking 1 between 110 and 88 km pathfinder found a broad nearly isothermal plateau at 127 k which correlates very well with a similar structure evident in viking 1 data at the same pressures although the pathfinder layer is 25 k colder at levels above 88 km wavelike oscillations with a wavelength 5 km and amplitudes of 2 3 k are evident possibly reflecting gravity or planetary wave activity between 90 and 60 km the average temperature is 20 30 k cooler than viking 1 values large amplitude 10 20 k long wavelength 20 40 km oscillations which show a remarkable correspondence to equivalent structures found in the viking 1 profile at the same pressures occur in this region and are likely due to a diurnal tidal mode between 85 and 77 km a minimum of one oscillation results in temperatures up to 7 k below the saturation temperature of co2 well outside the uncertainties in the measurements and the vapor pressure curve and comparable to observed supersaturations of water in earth s mesosphere between 55 and 16 km temperatures are close to or warmer than viking 1 values superposed long wavelength oscillations correspond well with similar structures observed by viking 1 between 16 and 9 9 km the temperature profile shows an unexpected strong thermal inversion which may reflect radiative cooling due to a water cloud at the base of the inversion temperatures begin to increase abruptly until the last measurement at 8 9 km the viking like temperatures in the lower atmosphere are consistent with the viking like dust optical depths observed by the mars pathfinder imager the cool temperatures in the middle and upper atmosphere may be indicative of significant nighttime cooling at these levels although other interpretations are possible

detection of mesospheric co 2 ice clouds on mars in southern summer this paper reports the first detections of two high altitude nighttime co2 clouds on mars during southern summer ls 264 and ls 330 with stellar occultation measurements by the imaging ultraviolet spectrograph on board the mars atmosphere and volatile evolution spacecraft interpretation of the transmission spectra with mie theory indicates particle radii of 90 110 nm assuming a mono disperse distribution the altitude profile of extinction indicates that the cloud layers are confined horizontally to sizes less than 500 700 km examination of the co2 density and temperature profiles reveals strong wave like perturbations supersaturated temperatures occur at the maximum negative extent of these wave like perturbations which are organized in longitude with a dominant m 3 zonal harmonic this suggests that tides are important in the formation of co2 clouds

natural laboratory nw bohemia comprehensive fluid studies between 1992 and 2005 used to trace geodynamic processes comprehensive studies of co2 rich fluids close to the swarm earthquake region nov kostel at the czech german border have been started 15 years ago and have in particular included two extended chemical and isotope monitoring studies lasting for several years each the regional surface distribution patterns of the fluid signatures including the identification of the origin of fluid components are the focus of the detailed studies three degassing centers cheb basin marianske lazn and karlovy vary with high co2 flux and the same level of 13c values but different levels of 3he 4he ratios have been identified the studies have located the co2 source and have investigated seismically induced changes in fluid characteristics on the basis of unique weekly sampling campaigns at selected locations a seismically triggered release of crustal helium was confirmed by both monitoring campaigns finally indications for a presently active magmatic process beneath the cheb basin have been found in contrast to volcanically active regions magma accumulation in the study area takes place at the crust mantle boundary and is not yet accompanied by heat transfer to the surface likewise reactive magma derived components are absent in the degassing fluids the area of investigation has the potential to be a natural laboratory for fundamental studies of active geodynamic processes the results of our fluid monitoring including the stunning observation of mantle derived free fluids marked by 3he 4he ratios within the subcontinental mantle range are supported by geophysical findings from seismic studies and geologic indications

the effect of sediment stratification on tidal dynamics and sediment transport patterns 1 the western tip of southwest korea is characterized by a tidally dominated turbid coastal environment there are well developed tidal flats along the coast and around islands together with offshore sand ridges several tens of kilometers long in the west the effects of bottom boundary layer bbl sediment stratification on sediment transport and tidal dynamics in this environment were examined using a sediment transport model coupled with a three dimensional tidal hydrodynamic model model experiments using two scenarios with and without the effect of sediment induced stratification showed that bbl sediment stratification influenced the spatial distribution and reduced the magnitude of net sedimentation the presence of a sediment stratified bbl also led to a reduction in suspended sediment fluxes and an increase in the vertical gradient of sediment concentrations in the water column these variations occurred because sediment induced bbl stratification leads to not only a reduction in bottom shear stress but also a decrease in buoyancy production ofturbulent kinetic energy and an associated dampening ofturbulence the significant reductions in turbulence and bottom shear stress result in changes to the vertical current structure of the m 2 tide including alteration of the tidal ellipse configuration and an increase in vertical shears of the tidal current amplitude and phase these reductions also lead to a slight increase in tidal amplitudes due to the decreased tidal energy dissipation the model results indicate that feedback between the sediment transport dynamics and hydrodynamics is an important factor in modeling sediment transport dynamics in tidally dominated turbid coastal environments such environments include the west coast of korea and the yellow sea a suitable approach to simulating the effects of this feedback may be the use of a modified bottom drag coefficient as a stability function together with the inclusion of the effect of sediment stratification on the hydrodynamics

erosion of soft cohesive sediment deposits erosion behavior of soft cohesive sediment deposits has been investigated in laboratory experiments such deposits are representative of the top active layer of estuarial beds an experimental procedure involving layer by layer erosion under a range of bed shear stresses b of successively increasing magnitude was utilized interpretation of the resulting concentrationtime data together with bed density profiles yielded a description of the variation of the bed shear strength s with depth as well as an expression for the rate of surface erosion in general s increased with depth and was also influenced by the type of sediment bed consolidation period and salinity the rate of erosion was found to vary exponentially with b s 1 2 in modeling estuarial bed erosion it is essential to take these characteristics of s and the rate of erosion into account

iron isotope fractionation during leaching of granite and basalt by hydrochloric and oxalic acids abstract transport of iron fe within hydrothermal and soil environments involves the transferral into aqueous solutions by leaching of complex polyminerallic rocks understanding the isotope fractionation mechanisms during this process is key for any application of the fe isotope system to biogeochemical studies here we reacted biotite granite and tholeiite basalt with 0 5 m hydrochloric acid and 5 mm oxalic acid solutions at ambient temperature solution aliquots were recovered over a seven day period and analysed for major and trace element concentrations and fe isotopic compositions in all experiments fe initially released into solution was isotopically lighter with 56fesolution rock as low as 1 80 in the granite hydrochloric acid system the oxalic acid experiments showed similar patterns but smaller fractionation in all experiments the 56fesolution rock reduced over time which would be in line with the formation of a leached layer as proposed before brantley s l liermann l j guynn r l anbar a icopini g a and barling j 2004 fe isotopic fractionation during mineral dissolution with and without bacteria geochim cosmochim acta 68 15 3189 3204 granite and basalts reacting with hydrochloric acid reached apparent steady state values of 0 60 0 15 and 0 40 0 20 respectively whilst experimental values with oxalic acid were 1 0 0 15 and 0 50 0 15 during the granite experiments alteration of biotite to chlorite followed by dissolution of chlorite were likely the dominant processes whilst in the basalt experiments dissolution of pigeonite was likely the principal source of fe variations in ph during the hydrochloric acid experiments were minimal remaining below 0 5 at all times in oxalic acid solutions the ph increased to over 4 leading likely to precipitation of secondary minerals and adsorption co precipitation of fe onto mineral surfaces these processes could contribute to the greater fractionation observed in the final stages of the oxalic acid experiments our results highlight the importance of mineralogy and fluid composition on the fe isotope systematics during weathering the fractionation processes identified for granites and basalts are in line with those inferred from field observations in soils sediments groundwater and hydrothermal deposits and from laboratory studies of single mineral leaching

the effects of suspended sediment on turbulence within an estuarine turbidity maximum predictions of cohesive sediment transport are hampered by poor understanding of the effects of sediment suspensions upon the nature of near bed turbulence in this study current velocities associated turbulence and flow characteristics were measured within an estuarine turbidity maximum during two spring ebb tides measurements at two heights both within and above a near bed high concentration layer show the importance of intermittent internal waves the ratio of vertical to horizontal turbulence intensities exceeded 1 0 when waves were present the waves were more significant above the layer than within it comparison between the turbulent kinetic energy and the reynolds stresses showed inactive turbulence occurring at stresses less than about 0 2 n m 2 during these periods negative suspended sediment fluxes occurred indicating that the turbulence could enhance settling of the sediment the effect of the intermittent internal waves on the turbulent bursting structure and their interaction with the concentration profile appears to increase the variability of the reynolds fluxes of suspended sediment and cause downwards reynolds fluxes especially beneath the lutocline

comparison of iron isotope variations in modern and ordovician siliceous fe oxyhydroxide deposits abstract formation pathways of ancient siliceous iron formations and related fe isotopic fractionation are still not completely understood investigating these processes however is difficult as good modern analogues to ancient iron formations are scarce modern siliceous fe oxyhydroxide deposits are found at marine hydrothermal vent sites where they precipitate from diffuse low temperature fluids along faults and fissures on the seafloor these deposits exhibit textural and chemical features that are similar to some phanerozoic iron formations raising the question as to whether the latter could have precipitated from diffuse hydrothermal fluids rather than from hydrothermal plumes in this study we present the first data on modern fe oxyhydroxide deposits from the jan mayen hydrothermal vent fields norwegian greenland sea the samples we investigated exhibited very low 56fe values between 2 09 and 0 66 due to various degrees of partial oxidation the fe oxyhydroxides are with one exception either indistinguishable from low temperature hydrothermal fluids from which they precipitated 1 84 and 1 53 in 56fe or are enriched in the heavy fe isotopes in addition we investigated fe isotope variations in ordovician jasper beds from the lokken ophiolite complex norway which have been interpreted to represent diagenetic products of siliceous ferrihydrite precursors that precipitated in a hydrothermal plume in order to compare different formation pathways of fe oxyhydroxide deposits iron isotopes in the jasper samples have higher 56fe values 0 38 to 0 89 relative to modern high temperature hydrothermal vent fluids ca 0 40 on average supporting the fallout model however formation of the ordovician jaspers by diffuse venting cannot be excluded due to lithological differences of the subsurface of the two investigated vent systems our study shows that reliable interpretation of fe isotope variations in modern and ancient marine fe oxyhydroxide deposits depends on comprehensive knowledge of the geological context furthermore we demonstrate that very negative 56fe values in such samples might not be the result of microbial dissimilatory iron reduction but could be caused instead by inorganic reactions

in situ estimation of erosion and deposition thresholds by acoustic doppler velocimeter adv abstract field based estimations of bed shear stress have been made using sontek ysi 10 mhz advs a coustic d oppler v elocimeter at the kongsmark mudflat danish wadden sea in order to test if it was possible to estimate erosion and deposition thresholds in situ by use of unidirectional tidal and orbital wave currents the results were promising and erosion thresholds were in the same range as those observed in eromes erosion experiments carried out at the same site similarly the short term erosion rates which could be calculated matched closely those obtained with eromes and were in the same range as those published for a large annular flume sea carousel from another fine grained site this indicates that the erosion rates obtained with those two erosion instruments are reasonable estimates of the actual erosion taking place under natural tidal current and waves one advantage of the use of advs to characterize sediment erodibility is that measurements can be carried out for long periods which makes it possible to examine the temporal variation of erosion threshold erosion rate and sedimentation the maximum bed shear stresses which was observed during a strong storm in january 2005 was only 0 7 n m 2 which is three to four times lower than the highest thresholds measured by eromes experiments on sediment with biofilms during previous studies this shows that such strong biofilms at this site will not get eroded unless degraded or physically disrupted by some other mechanism a prerequisite for the determination of any of the erodibility and sedimentation parameters is that the actual bed level changes at the measuring site are known in detail this information is obtained automatically by the advs used in the present study accurate estimates of the bed shear stress under waves in very shallow water are difficult to obtain and in the present study a simple method based on instantaneous velocities and assumption of a logarithmic velocity profile was used further field studies are required of the boundary layer under these extreme conditions in order to refine this simple method of calculating bed shear stresses

influence of cohesion on the incipient motion condition of sediment mixtures 1 previous investigations on initiation of motion and erosion of cohesive sediment mixtures have not included gravel within the mixtures experimental results on the incipient motion characteristics of cohesive sediment mixtures containing gravel are presented in this paper the sediment used consisted of fine gravel mixed with clay in proportions varying from 10 to 50 by weight and fine gravel with fine sand mixed in equal proportion with clay proportions again varying from 10 to 50 by weight the stages of the incipient condition of motion were visually identified three modes of initiation of motion of cohesive sediment mixtures were noticed namely pothole erosion line erosion and mass erosion the modes of initiation of motion changed mainly with clay percentages in the mixture its antecedent moisture characteristics and the applied shear stress analysis of the experimental data from the present study and the literature revealed that depending upon the flow and sediment characteristics the critical shear stress of the incipient motion condition in cohesive sediment mixtures can be up to 50 times larger than the critical shear stress of cohesionless sediments having similar arithmetic mean size as the cohesive sediments on the basis of dimensional considerations a relationship is proposed for the determination of critical shear stress of the incipient motion condition in cohesive sediment mixtures also containing gravel the variables namely clay percentage void ratio and unconfined compressive strength of the sediment bed are noticed to be the main parameters controlling the incipient motion condition of the cohesive sediments in the absence of cohesion the proposed relationship reduces to the critical shear stress for the incipient motion condition of the cohesionless sediment mixture having the same arithmetic mean size the condition for the threshold of erosion of cohesive sediment mixtures by the flow is thus parameterized in the present study

determination of the critical erosion threshold of cohesive sediments on intertidal mudflats along the dutch wadden sea coast abstract the bed shear strength on an intertidal mudflat bordering salt marshes along the dutch wadden sea coast was determined by means of an in situ erosion flume isef characteristic erosion patterns type i and type ii erosion were observed for most measurements the critical erosion threshold varied between 0 11 0 18 pa for all measurements and erosion rates varied between 5 10 5 and 3 10 3 kg m 2 s 1 no clear relationship was found between distinct parameters like bed density moisture content or biological activity and the critical erosion threshold a more pronounced effect of the erodability of the mudflat was found when the erosion rate was taken into account basically two clusters were distinguished high mean peak erosion rates of the substratum were found at locations which were characterized by a low mud content of the substratum below 20 mud by weight in these situations bed load transport is expected to be the most important process which determined erosion of the bed and erosion of predominantly the sand fraction was found at higher rates of the mud content over 20 mud by weight mean peak erosion rates decreased substantially an order 6 to 10 times lower and both erosion of the mud and sand fraction was found

postglacial deltaic sediments southern fraser river delta british columbia the fraser river delta the largest delta on the west coast of canada has been built into the strait of georgia during the holocene drill hole and seismic reflection records reveal a succession of sedimentary units deposited during early holocene progradation of the delta these overlie an irregular surface developed on pleistocene drift mud and silt similar to sediments presently accumulating off the mouth of fraser river in the southern strait of georgia are conformably overlain by a thick unit of sandy foreset beds dipping gently to the south southwest into boundary bay and deposited in a foreslope environment the foreset unit is sharply overlain by a much thinner topset sequence comprising silt and sand deposited in intertidal fluvial channel and overbank environments and peat deposited in swamps and bogs fifteen accelerator mass spectrometry radiocarbon dates on shell and wood indicate that most of the deltaic sediments south of the main channel of fraser river were deposited between ca 7

dynamics of erosion and deposition events on an intertidal mudbank at burringham river trent uk measurements using an automatic bank level monitoring technique the photoelectronic erosion pin peep system over a 70 day period between 16 march and 27 may 1997 have revealed a complex pattern of erosion and deposition on an intertidal mudbank on the river trent at burringham comparison of mean daily changes in bank elevation at upper and lower bank positions suggest that wave activity induced by high wind speeds causes erosion while high tidal range leads to deposition as a result of higher suspended solids concentrations a greater variability in mean daily erosion and deposition events at the lower bank compared with the upper bank appears to indicate that higher bed shear stresses as well as a greater availability of sediment for settling owing to higher concentrations and a greater depth of water lead to a more dynamic exchange of material at this position the peep data also show longer term trends in sedimentation with the mean deposition for the period exceeding mean erosion manual erosion pin measurements at a lower frequency over a longer seven month period confirm this and also highlight the advantage of the peep system in monitoring events at a finer temporal resolution copyright 1999 john wiley sons ltd