winter storm induced hydrodynamics and morphological response of a shallow transgressive shoal complex northern gulf of mexico abstract using extended deployments during seasons of low and high discharge from the atchafalaya river meteorological hydrodynamic and bottom boundary layer parameters were monitored from tiger and trinity shoal complex off louisiana coast usa during winter storms the surface current speed measured at both shoals exceeded 0 5 m s and the entire water column followed the prevailing wind direction the current speed close to the bottom exceeded 0 3 m s during high energy northerly winds the mean water level in the shoal complex increased during southerly winds and decreased during northerly winds such that the difference between wind set up and set down exceeded 0 7 m in tiger shoal and 0 6 m in trinity shoal during high energy frontal passages the swell height was inversely correlated with mean water level and increased during pre frontal phase and decreased during post frontal phase of winter storms the sea short waves height responded quickly to wind direction and speed and within a few hours after the wind shifted and blowing from the north the sea height increased during both deployments bimodal wave frequency spectrum was observed during wind veering from southerly to northerly when both sea and swell intensities were significant the tiger shoal bed sediment texture transformed drastically from mud to shell and shell hash assemblage within a period of two weeks during the december 2008 deployment backscatter signal intensity from a pulse coherent acoustic doppler profiler pcadp and its velocity estimates were used to determine the vertical extend and timing of mud resuspension and their eventual flushing out from the shoal environment when exposed to high energy winter storm passages the computed time frame for a total transformation of bottom sediment texture from muddy bottom to shell and shell hash assemblage was supported by the combined wave and bottom current induced shear stress at shoal bed the bed samples collected from tiger shoal before and after the deployment in spring 2009 consisted of more than 80 shell and shell hash which again confirmed a stable bottom as predicted from the pcadp data however the fine sand and mud dominated bed at trinity shoal was highly dynamic and experienced a few cm of ephemeral sediment deposition during the passage of each cold front as revealed from the analysis of acoustic backscatter data from the pcadp suspended sediment concentration estimated from optical backscatterance sensors obs and pcadp were in good agreement during low river discharge events in december 2008 but significantly diverged during the spring 2009 deployment when a high suspended sediment load was discharged into the shelf from the atchafalaya river and subsequently pushed farther offshore into the deployment sites by wind induced strong currents during the passage of cold fronts

wave mud interactions over the muddy atchafalaya subaqueous clinoform louisiana united states wave supported sediment transport 1 near bottom fluid mud layers were observed during two experiments conducted on the muddy atchafalaya inner shelf subaqueous clinoform louisiana united states on the face of the subaqueous delta 4 7 m water depth first experiment fluid mud layers are produced by seafloor liquefaction and resuspension forced by swells associated with cold front passages and supported by near bed wave induced turbulence the layers are episodic lifetime of 9 12 h form prior to significant postfrontal settling of sediment in the overlying water column and flow seaward downslope at about 5 cm s farther westward on the delta front finer grain size with negligible sand or coarse silt content second experiment similar wave supported fluid mud layers are observed to last longer 2 days show weaker alongshore westward flow of about 1 3 cm s the results suggest a sequence of near bed sediment transport processes triggered by frontal swell activity bed liquefaction resuspension and advection modulated by the bathymetric characteristics of the clinoform that contribute to the formation of clinoform stratigraphy of muddy subaqueous deltas

stochastic reconstruction of the microstructure of equilibrium form snow and computation of effective elastic properties three dimensional geometric descriptions of microstructure are indispensable to obtain the structure property relationships of snow because snow is a random heterogeneous material it is often helpful to construct stochastic geometric models that can be used to model physical and mechanical properties of snow in the present study the gaussian random field based stochastic reconstruction of the sieved and sintered dry snow sample with grain size less than 1 mm is investigated the one and two point correlation functions of the snow samples are used as input for the stochastic snow model several statistical descriptors not used as input to the stochastic reconstruction are computed for the real and reconstructed snow to assess the quality of the reconstructed images for the snow samples and the reconstructed snow microstructure we also estimate the mechanical properties and the size of the associated representative volume element using numerical simulations as additional assessment of the quality of the reconstructed images the results indicate that the stochastic reconstruction technique used in this paper is reasonably accurate robust and highly efficient in numerical computations for the high density snow samples we consider

comparison of elastic moduli from seismic diving wave and ice core microstructure analysis in antarctic polar firn we compared elastic moduli in polar firn derived from diving wave refraction seismic velocity analysis firn core density measurements and microstructure modelling based on firn core data the seismic data were obtained with a small electrodynamic vibrator source near kohnen station east antarctica the analysis of diving waves resulted in velocity depth profiles for different wave types p sh and sv waves dynamic elastic moduli of firn were derived by combining p and s wave velocities and densities obtained from firn core measurements the structural finite element method fem was used to calculate the components of the elastic tensor from firn microstructure derived from x ray tomography of firn core samples at depths of 10 42 71 and 99 m providing static elastic moduli shear and bulk moduli range from 0 39 to 2 42 gpa and 0 68 to 2 42 gpa respectively the elastic moduli from seismic observations and the structural fem agree within 8 5 for the deepest achieved values at a depth of 71 m and are within the uncertainty range our observations demonstrate that the elastic moduli of the firn can be consistently obtained from two independent methods which are based on dynamic seismic and static tomography and fem observations respectively for deeper layers in the firn below 10 m depth

evolution of regoliths and landscapes in deeply weathered terrain implications for geochemical exploration abstract thick commonly lateritic regoliths are widespread in inter tropical regions of the world and present particular challenges in exploration these are best tackled through a sound understanding of the evolution of the landscapes in which they occur the regoliths formed under humid warm to tropical conditions and although they may have been modified by later climatic changes i e to more humid or more arid conditions many chemical and mineralogical characteristics are retained these include the geochemical expressions of concealed mineralization erosional and depositional processes control the preservation and occurrence of specific regolith units that may be used as sample media and in turn target size element associations and contrast thereby influencing sampling procedures analysis and data interpretation these parameters are best summarized in terms geochemical dispersion models based on the degree of preservation of the pre existing lateritic regolith regolith landform mapping permits an assessment of the terrain in terms of such models in relict regolith landform regimes in which the lateritic regolith is largely preserved broad multi element anomalies in the upper ferruginous horizons lateritic residuum can be detected using sample intervals of 1 km or more in contrast in erosional regimes where this material is absent anomalies in upper saprolite and the soil and lag derived from it are more restricted in area and closer sampling intervals 200 40 m or less may be necessary lag and soil are generally ineffective in depositional areas except where the sediments are very thin e g

modelling snow failure with a fibre bundle model dry snow slab avalanches initiate from a failure in a weak snow layer below a cohesive slab snow is considered as a porous ice structure and the strength distribution of the single elements of this structure i e grains and bonds between grains shows a high degree of disorder on the bond or microstructural level the failure process is believed to start if the fracturing of bonds between snow grains is not balanced by the formation of new bonds we use a statistical fracture model a fibre bundle model to study the failure process in a weak snow layer the model consists of fibres of various strengths representing single snow grains between two rigid plates which represent the slab above and the substratum below the weak layer the fibres deform in a linear elastic manner and break instantly at their rupture strength broken fibres may sinter re bond and regain strength after a finite sintering time we show that the different characteristic times for breaking and sintering lead to the rate dependence of snow strength this is to our knowledge the first statistical model to reproduce the ductile to brittle transition which snow exhibits with increasing strain rate when the model is applied to simulate experimental stress strain curves for different strain rates the model and experimental results are in fair agreement

snow stratigraphic heterogeneity within ground based passive microwave radiometer footprints implications for emission modeling two dimensional measurements of snowpack properties stratigraphic layering density grain size and temperature were used as inputs to the multilayer helsinki university of technology hut microwave emission model at a centimeter scale horizontal resolution across a 4 5 m transect of ground based passive microwave radiometer footprints near churchill manitoba canada snowpack stratigraphy was complex between six and eight layers with only three layers extending continuously throughout the length of the transect distributions of one dimensional simulations accurately representing complex stratigraphic layering were evaluated using measured brightness temperatures large biases 36 to 68 k between simulated and measured brightness temperatures were minimized 0 5 to 0 6 k within measurement accuracy through application of grain scaling factors 2 6 to 5 3 at different combinations of frequencies polarizations and model extinction coefficients grain scaling factors compensated for uncertainty relating optical specific surface area to hut effective grain size inputs and quantified relative differences in scattering and absorption properties of various extinction coefficients the hut model required accurate representation of ice lenses particularly at horizontal polarization and large grain scaling factors highlighted the need to consider microstructure beyond the size of individual grains as variability of extinction coefficients was strongly influenced by the proportion of large hoar grains in a vertical profile it is important to consider simulations from distributions of one dimensional profiles rather than single profiles especially in sub arctic snowpacks where stratigraphic variability can be high model sensitivity experiments suggested that the level of error in field measurements and the new methodological framework used to apply them in a snow emission model were satisfactory layer amalgamation showed that a three layer representation of snowpack stratigraphy reduced the bias of a one layer representation by about 50

hydrogeochemistry and weathering on the yilgarn block western australia ferrolysis and heavy metals in continental brines abstract groundwater samples collected from salt lakes over the archean yilgarn block of western australia show the influence of climate on geochemical weathering patterns major element compositions in salt lake groundwaters show little systematic trend but there are marked differences in ph and fe cu and pb concentrations in the alkaline carbonated systems of the arid northeastern part compared to concentrations of the same elements in groundwater systems of the mediterranean type climatic region of the wheatbelt in the southwestern part of the block in this latter region in addition to higher rainfall input the groundwater systems have steeper hydraulic gradients weathering bedrock is closer to the surface and oxidation and hydrolysis of iron ferrolysis is evident in weathering profiles a combination of vertical diffusion and horizontal groundwater flow is thought to be responsible for the development of ferrolysis and acidity in groundwaters in this region anomalously high concentrations of heavy metals particularly lead are observed in some of the acid saline groundwaters the formation of laterite which is a ubiquitous feature of the yilgam block landscape is a process probably closely linked to ferrolysis

observations of nearshore wave dissipation over muddy sea beds 1 wave propagation on the louisiana inner shelf is studied using concurrent measurements at two shallow water ocean observatory sites in sedimentary environments dominated by mud at one site and sand at the other contrary to the widely accepted hypothesis that mud induced wave dissipation is important only for long waves observations show significant damping of high frequency short waves which interact weakly with the bottom the mechanism of short wave dissipation is not understood numerical simulations show that other dissipative processes such as refraction or depth limited breaking do not account for the magnitude of the observed effects independent observations of strong sediment re working during storms suggest that these effects are related to sediment resuspension processes

three dimensional microstructure and numerical calculation of elastic properties of alpine snow with a focus on weak layers abstract the microstructure and stratigraphy of a snowpack determine its physical behaviour weaklayers or weak interfaces buried under a slab are prerequisites for the formation of dry snow slabavalanches and a precise characterization of weak layers or interfaces is essential to assess stability yettheir exact geometry and micromechanical properties are poorly known we cast weak layers and theiradjacent layers in the field during two winters and reconstructed their three dimensional microstructureusing x ray microcomputer tomography the high resolution of 10 20 m m allowed us to study snowstratigraphy at the microstructural scale we quantified the microstructural variability for 32centimetre sized layered samples and we calculated young s modulus and poisson s ratio bytomography based finite element simulations layers in a sample could therefore be differentiatednot only by a change in morphology or microstructure but also by a change in mechanical properties we found a logarithmic correlation of young s modulus with density for two different density ranges consistent with previous studies by calculating the relative microstructural changes within our samples we showed that a large change could indicate a potential weak layer but only when the weak layer andboth adjacent layers i e the sandwich were considered keywords

abstract geologic framework processes and rates of subsidence in the mississippi river delta plain abstract since the 1930 s louisiana has lost an estimated 3 950 km2 of coastal wetlands and barrier islands the loss of these coastal lands resulted primarily from subsidence and erosion rather than the draining and filling of wetlands more than 40 of the coastal wetlands in the u s are found in louisiana and 80 of our nation s total wetland loss occurs here at alarming rates beach erosion rates exceed 10 m yr and the rate of wetland loss is currently measured at 75 km2 yr the causes of louisiana s coastal land loss include delta switching storm impacts man s impacts on this deltaic system and high rates of subsidence recent studies indicate that the highest subsidence and coastal land loss rates occur where the underlying holocene sediments are the thickest this relationship suggests that subsidence through the consolidation and settlement of these young deposits is of primary importance to the coastal land loss problem found in louisiana to understand the role of subsidence in louisiana s coastal land loss problem requires a knowledge of the late quaternary history of the lower mississippi river of the infilling of its incised valley during the holocene transgression and of the processes of delta switching end of record last page 644

600 year sedimentary archive of hurricane strikes in a prograding beach ridge plain southwestern louisiana abstract this study tests a novel approach to paleotempestology substituting the lateral time depth of a prograding beach ridge plain for the vertical time depth of an aggrading coastal lake pond lagoon swamp or marsh trenching and coring of a beach ridge plain in southwestern louisiana revealed six sand beds and one shell bed interpreted as hurricane washover deposits the sand beds are readily distinguished from enclosing marsh sediments by their higher sand content lower organic content and contrasting microfossil assemblages based on the modern analogs of hurricanes audrey 1957 rita 2005 and ike 2008 and consideration of nearby landfalling hurricanes in the historical record it was determined that the storm intensity threshold of the study site is equivalent to a category 3 hurricane there is a wide variation in hurricane strike frequency between this site and other sites bordering the gulf of mexico this variation results from differences in site sensitivity and the nature of geologic or geochemical proxies used to derive hurricane strike records the approach demonstrated by this study could have applicability at other sites around the world where beach ridge plains are subject to tropical cyclone strikes

winter storm impacts on the chenier plain coast of southwestern louisiana abstract stormy conditions associated with periodic winter cold front passages are closely related to transport of suspended sediment to the continental shelf coastal erosion and coastal progradation along shoreline sectors where abundant fine grained sediments are stored on the inner shelf cold front passages occur between october and april on three to five day cycles their typical nw to se direction of approach large spatial scales and numerous yearly occurrences 20 30 events year drive physical processes that cause significant coastal change both remotely sensed multispectral and high quality photographic data have been collected from altitudes of 0 9 mi 1500 m 5 6 mi 9000 m and 13 mi 21 000 m before and after cold front passages to form a data base for evaluating coastal change and suspended sediment transport pathways satellite imagery provide a longer term perspective on coastal change remotely sensed data sets are augmented with ground truth measurements of coastal configuration sedimentology and water quality physical processes active in the prefrontal phases of a winter cold front passage are considerably different from those of the post frontal phase along the chenier plain coast prefrontal stages are characterized by prolonged periods on the order of several days of high wave action from the southerly quadrants water level setup along the coast and strong alongshore as well as onshore sediment transport at these times mud from the atchafalaya river stored on the nearshore shelf is transported onshore and alongshore to slightly prograde the chenier coast post frontal conditions bring dry cold winds from the northerly quadrants causing water level setdown along the coast a significant reduction in nearshore wave energy and drying of the newly deposited mudflats fronting the chenier plain rapid drying causes an important increase in sediment strength mud crack formation and effective armoring of the mud flats by dried mud clasts that resist erosion in subsequent cycles

geochemistry of acid brines lake tyrrell victoria australia abstract pore water groundwater and sediments were collected from lake tyrrell to study the evolution of brines in an acidic environment lake tyrrell is a 150 km2 inland salt playa acid saline groundwater enters the playa through springs along the lake margin and is evapo concentrated past halite precipitation the brines were found to contain sea salts but some solutes do not follow the seawater evaporation curve processes that occur in neutral alkaline systems e g gypsum formation occur here but precipitation of alunite kal3 so4 2 oh 6 jarosite kfe3 so4 2 oh 6 and fe oxides also affect solute behavior processes that occur in the recharge area and along the groundwater flow path k uptake calcrete and gypcrete formation affect the brine s chemical signature regardless of the chemical variability found among the samples solutes have evolved from a common source sea salt acidification which appears to occur early in the evolution of the groundwater is related to pyrite oxidation and may be enhanced by precipitation of fe oxides alunite and jarosite and evaporation acidity is maintained in the system because of the lack of buffering capacity of aquifer minerals we suggest that this acid brine from australia is another end member in the eugster jones hardie model for the evolution of water by evaporation in closed basins

observation of temperature gradient metamorphism in snow by x ray computed microtomography measurement of microstructure parameters and simulation of linear elastic properties the process of temperature gradient metamorphism in snow strongly affects the microstructure and associated mechanical properties of the snow the purpose of this study was to 1 examine the temporal variations in three dimensional snow microstructure under the influence of a strong temperature gradient for 6 days using x ray computed microtomography mct and 2 numerically simulate the linear elastic properties of snow from microtomographic data using a voxel based finite element technique the temporal changes in the snow structure were analyzed in terms of density specific surface area ssa thickness distribution of ice matrix and pores structure model index and mean intercept length mil fabric tensor the structural indices and orthotropic elastic compliance matrix were computed over several sub volumes within the reconstructed volume to account for statistical uncertainties the mean density increased by about 14 on day 1 and no significant trend was observed thereafter the ssa decreased by 22 whereas both the ice and pore thickness distributions widened with time the computed young s moduli were 1 5 4 times larger than previously published dynamic measurements and found to be significantly correlated with ice volume fraction and mil fabric measures the increasing trend in computed moduli during the experiment is consistent with the observed development of thicker vertical ice structures multiple linear regression models of elastic compliances using fabric tensor formulation and ice volume fraction could explain 89 9 93 0 of the variance our results suggest a strong dependence of elastic properties on both density and microstructural fabric

spatial variation of cold front wind driven circulation and quasi steady state balance in lake pontchartrain estuary abstract circulation in a low salinity estuary with restricted openings to the ocean is mainly driven by wind and to a lesser extent by water level fluctuations at the open boundaries numerical model experiments are conducted using a baroclinic finite volume community ocean model fvcom for wind driven circulations during a period encompassing a total of 16 cold fronts in the lake pontchartrain estuary the work is focused on the examination of the spatial structure of circulation in response to local and remote winds a quasi steady state balance between the surface slope and wind stress is further analyzed the accuracy of the balance is evaluated by comparing the fvcom calculated surface slope with that from the steady state balance equation results show that this balance is more accurate in the cross estuary direction than that in the along estuary direction r2 0 94 vs 0 60 this difference in the accuracy of the quasi steady state balance between the cross and along estuary directions is caused by the open boundary a tidally induced mean slope exists in addition even if the tidal effect is removed the accuracy still decreases toward the open end for slopes in both directions remote wind effect and residual flow through the eastern open boundary tend to introduce a departure from the quasi steady state balance in both along and cross estuary directions remote wind effect decreases into the interior due to bottom friction local wind effect tends to produce downwind flows in coastal shallow water regions and on the surface but upwind flows near the bottom a result consistent with barotropic wind driven circulations while the remote wind effect is important mostly near the open boundary furthermore quasi steady state balance is more accurate in the along estuary direction before cold front passages then after because of the relatively higher occurrence of the wind in that direction before the cold fronts than after in contrast this quasi steady state balance is less accurate in the cross estuary direction before cold front passages than after because of the relatively lower occurrence of the wind in that direction before the cold fronts than after

the thermal conductivity of seasonal snow twenty seven studies on the thermal conductivity of snow k eff have been published since 1886 combined they comprise 354 values of k eff and have been used to derive over 13 regression equation and predicting k eff vs density due to large and largely undocumented differences in measurement methods and accuracy sample temperature and snow type it is not possible to know what part of the variability in this data set is the result of snow microstructure we present a new data set containing 488 measurements for which the temperature type and measurement accuracy are known a quadratic equation where is in g cm 3 and k eff is in w m 1 k 1 can be fit to the new data r 2 0 79 a logarithmic expression can also be used the first regression is better when estimating values beyond the limits of the data the second when estimating values for low density snow within the data set snow types resulting from kinetic growth show density independent behavior rounded grain and wind blown snow show strong density dependence the new data set has a higher mean value of density but a lower mean value of thermal conductivity than the old set this shift is attributed to differences in snow types and sample temperatures in the sets using both data sets we show that there are well defined limits to the geometric configurations that natural seasonal snow can take

mixed energy process interactions read from a compound clinoform delta paleo orinoco delta trinidad preservation of river and tide signals by mud induced wave damping

a life cycle model for wave dominated tidal inlets along passive margin coasts of north america abstract a regional overview of 107 wave dominated tidal inlets along the u s atlantic coast u s gulf of mexico coast and canadian gulf of st lawrence coast yielded a generalized wave dominated tidal inlet life cycle model that recognized the rotational nature of tidal inlets tidal inlets are influenced by concurrently acting processes transpiring over two timescales short term event driven processes and long term evolutionary processes wave dominated tidal inlets are classified into three rotational categories based on net longshore sediment transport direction and rotation direction along the landward back barrier portion of the inlet channel downdrift channel rotation updrift channel rotation or little to no channel rotation lateral shifting of the flood tidal delta depocenter in response to available estuarine accommodation space appears to control inlet channel rotation flood tidal delta deposits fill accommodation space locally within the estuary i e creating bathymetric highs causing the tidal inlet channel to rotate external influences such as fluvial discharge pre existing back barrier channels and impeding salt marsh will also influence inlet channel rotation storm events may rejuvenate the tidal inlet by scouring sediment within the flood tidal delta increasing local accommodation space wave dominated tidal inlets are generally unstable and tend to open concurrently migrate laterally and rotate infill and close channel rotation is a primary reason for wave dominated tidal inlet closure during rotation the inlet channel lengthens and hydraulic efficiency decreases thus causing tidal prism to decrease tidal prism estuarine accommodation space and sediment supply to the flood tidal delta are the primary variables responsible for tidal inlet rotation stability of wave dominated tidal inlets is further explained by stability s tidal prism estuarine accommodation space v volume of annual sediment supply mt rotating wave dominated tidal inlets follow a six stage evolutionary model whereas wave dominated tidal inlets that exhibit little to no rotation follow a five stage evolutionary model

energy based binary segmentation of snow microtomographic images x ray microtomography has become an essential tool for investigating the mechanical and physical properties of snow which are tied to its microstructure to allow a quantitative characterization of the microstructure the grayscale x ray attenuation coefficient image has to be segmented into a binary ice pore image this step called binary segmentation is crucial and affects all subsequent analysis and modeling common segmentation methods are based on thresholding in practice these methods present some drawbacks and often require time consuming manual post processing here we present a binary segmentation algorithm based on the minimization of a segmentation energy this energy is composed of a data fidelity term and a regularization term penalizing large interface area which is of particular interest for snow where sintering naturally tends to reduce the surface energy the accuracy of the method is demonstrated on a synthetic image the method is then successfully applied on microtomographic images of snow and compared to the threshold based segmentation the main advantage of the presented approach is that it benefits from local spatial information moreover the effective resolution of the segmented image is clearly defined and can be chosen a priori

hydrodynamic and sedimentary responses to two contrasting winter storms on the inner shelf of the northern gulf of mexico abstract results are presented from the deployment of three bottom mounted instrumentation systems in water depths of 6 9 m on the sandy inner shelf of louisiana usa the 61 day deployment included nine cold front passages that were associated with large increases in wind speed two of the most energetic cold front passages were characterized by distinct meteorological hydrodynamic bottom boundary layer and sedimentary responses and may potentially be treated as end member types on a continuum of regional cold front passages arctic surges ac storms have a very weak pre frontal phase followed by a fairly powerful post frontal phase when northeasterly winds dominate migrating cyclones mc storms are dominated by a strong low pressure cell and have fairly strong southerly winds prior to the frontal passage followed by strong northwesterly winds on the basis of measurements taken during this study ac storms are expected to have a lower average significant wave height than mc storms and are dominated by short period southerly waves subsequent to the frontal passage currents are weak and northerly during the pre frontal phase but become very strong and southwesterly following the passage sediment transport rate during as storms was not as high as during mc storms and the mean and overall direction tended to be southwesterly to westerly with low frequency flows producing easterly transport and wind wave flows producing southeasterly transport mc storms had the most energetic waves of any storm type with peaks in significant wave height occurring during both the pre and post frontal phases the wave field during mc storms tended to be more complex than during as storms with an energetic northerly swell band gradually giving way to a southerly sea band as the post frontal phase progressed currents during mc storms were moderate and northerly during the pre frontal phase but became much stronger and southeasterly during the post frontal phase shear velocity was high during both the pre and post frontal phases of the storm although sediment transport was highest following the frontal passage mean and overall sediment transport was directed southeasterly during mc storms with low frequency and wind wave flows producing northerly transport in summary the data sets presented here are unique and offer insight into the morphosedimentary dynamics of mid latitude micro tidal coasts during extratropical storms

the mississippi delta region past present and future the mississippi delta region of south louisiana houses a wealth of resources within a dynamic subsiding landscape foundations for the delta region reflect neogene evolution of the depocenter whereas details of the modern landscape reflect late pleistocene to holocene evolution of the alluvial deltaic plain the holocene delta plain was constructed by cyclical growth of deltaic headlands followed by avulsion and relocation of the fluvial sediment source abandoned headlands were then submerged and reworked while a new headland was created at the site of active fluvial sediment input historic period levees have decoupled the delta plain from its fluvial sediment source at the same time global sea level rise was accelerating which has accelerated delta plain submergence diversions of mississippi river water and sediment are necessary to achieve delta plain sustainability but upstream dams trap 50 of the total sediment load and there is not enough supply to keep pace with subsidence and accelerated

deep water deposits of the tanqua and laingsburg subbasins southwest karoo basin south africa analog for the gulf of mexico abstract the tanqua and laingsburg subbasins in south africa had near contemporaneous formation and filling and contain permian age basin floor and slope fans that display characteristics similar to deposits in the northern gulf of mexico outcrop area for each subbasin is about 650 km2 and individual fans range from 150 to 450 km2 with lateral continuity of individual fans up to 34 km with a sandstone shale ratio of 75 90 the arenaceous fans vary in thickness from 20 to 60 m with interlying shales ranging from 20 to 75m in thickness both subbasins were influenced in their formation and in the architecture of their deposits by structures and events associated with the cape fold belt having undergone little tectonic tilting the highly continuous outcrops in the tanqua subbasin expose two fans continuing from mid fan channel complexes with associated levee overbank deposits to sheet like outer fan lobes while three other fans expose outer fan depositional lobes paleocurrent directions for four of the fans are from ssw to s and a direction of w to wnw for the fifth these fans most likely had a single point source which migrated over the time of basin fill unrestricted deposition suggests an open basin depositional setting the laingsburg subbasin was strongly influenced by the tectonism associated with the cape fold belt deposition occurred in a deeper and narrower basin and the deposits except for the overlying deltaics cannot be correlated with those of the tanqua subbasin the two subbasins while associated with an active margin were likely filled at slightly different times both had a distant source area which led to deposits exhibiting characteristics of a passive margin depositional environment understanding the evolution of the subbasins and the tectonic conditions under which the submarine fans were deposited leads to the determination of the mechanisms that influenced the formation of the fans and their resulting architecture these fans permit detailed studies on their architecture necessary to 1 increase our understanding of fine grained low sandstone shale ratio fans 2 determine influences of paleostructures and tectonics on basin fill 3 carry out detailed reservoir simulation programs and 4 make predictive models of deep water sands in the northern gulf of mexico end of record last page 646

summertime tidal flushing of barataria bay transports of water and suspended sediments the edges of the inlet the net flux of total suspended sediment out of the bay was determined to be 8800 t of which 20 was organic matter demonstrating a significant source of organic matter to the base of the coastal ocean detrital food chain the time evolution and net fluxes of water and suspended sediments showed that the net flow resembles conventional estuarine circulation patterns with net outward flow on the surface and shallow ends of the inlet and with net inward flow in the center and at the bottom of the center of the inlet the west side has a much larger outward flow than the east side while the east side is fresher these differences suggest that the louisiana coastal current from around the bird s foot delta derived from the mixing of shelf water with the mississippi river freshwater may have entered the bay this must have been mostly from the east side during the survey which resulted in a smaller outward flow on the eastern side a numerical experiment further confirmed this assumption and the model was verified by field observations on 5 may 2010

snow replica method for three dimensional x ray microtomographic imaging visualization and quantification of snow structures at a scale of a few millimetres is important in understanding the mechanical thermal and electromagnetic properties of snow surface sections and to an even greater degree three dimensional 3 d reconstructions of cast snow samples are difficult to prepare and automatic image processing is notoriously difficult and often requires manual evaluation here we present a new method to measure the 3 d structure of cast snow samples snow samples cast with diethyl phthalate dep and frozen are cut to a sample size a few centimetres in diameter and up to 10 cm in height the ice of these samples is then sublimated in high vacuum and the remaining negative structure replica is imaged using x ray microtomography micro ct the accuracy of the method is demonstrated by comparing micro ct scans of the original snow structure and the replica the method described here allows easy transportation of samples requires little manual interaction has a very high spatial resolution of up to 10 m and is environmentally friendly

a porosity based biot model for acoustic waves in snow phase velocities and attenuation in snow cannot be explained by the widely used elastic or viscoelastic models for acoustic wave propagation instead biot s model of wave propagation in porous materials should be used however the application of biot s model is complicated by the large property space of the underlying porous material here constant properties for ice and air and empirical relationships are used to estimate unknown porous properties from snow porosity using this set of equations phase velocities and plane wave attenuation of shear and compressional waves are predicted as functions of porosity or density for light snow the peculiarity was found that the velocity of the first compressional wave is lower than that of the second compressional wave that is commonly referred to as the slow wave the reversal of the velocities comes with an increase of attenuation for the first compressional wave this is in line with the common observation that sound is strongly absorbed in light snow the results have important implications for the use of acoustic waves to evaluate snow properties and to numerically simulate wave propagation in snow