how porosity and permeability vary spatially with grain size sorting cement volume and mineral dissolution in fluvial triassic sandstones the value of geostatistics and local regression although it is well known that sandstone porosity and permeability are controlled by a range of parameters such as grain size and sorting amount type and location of diagenetic cements extent and type of compaction and the generation of intergranular and intragranular secondary porosity it is less constrained how these controlling parameters link up in rock volumes within and between beds and how they spatially interact to determine porosity and permeability to address these unknowns this study examined triassic fluvial sandstone outcrops from the uk using field logging probe permeametry of 200 points and sampling at 100 points on a gridded rock surface these field observations were supplemented by laser particle size analysis thin section point count analysis of primary and diagenetic mineralogy quantitative xrd mineral analysis and sem edax analysis of all 100 samples these data were analyzed using global regression variography kriging conditional simulation and geographically weighted regression to examine the spatial relationships between porosity and permeability and their potential controls the results of bivariate analysis global regression of the entire outcrop dataset indicate only a weak correlation between both permeability porosity and their diagenetic and depositional controls and provide very limited information on the role of primary textural structures such as grain size and sorting subdividing the dataset further by bedding unit revealed details of more local controls on porosity and permeability an alternative geostatistical approach combined with a local modeling technique geographically weighted regression gwr subsequently was used to examine the spatial variability of porosity and permeability and their controls the use of gwr does not require prior knowledge of divisions between bedding units but the results from gwr broadly concur with results of regression analysis by bedding unit and provide much greater clarity of how porosity and permeability and their controls vary laterally and vertically the close relationship between depositional lithofacies in each bed diagenesis permeability and porosity demonstrates that each influences the other and in turn how understanding of reservoir properties is enhanced by integration of paleoenvironmental reconstruction stratigraphy mineralogy and geostatistics

heat flux through sea ice in the western weddell sea convective and conductive transfer processes the heat flux through the snow and sea ice cover and at the ice ocean interface were calculated at five sites in the western weddell sea during autumn and early winter 1992 the ocean heat flux averaged 7 2 w m2 from late february to early june and average ice air heat flux in the second year floes depended on the depth of the snow cover and ranged from 9 to 17 0 8 w m2 in late february three of the five sites had an ice surface which was depressed below sea level resulting at two of the sites in a partially flooded snow cover and a slush layer at the snow ice interface as this slush layer froze to form snow ice the dense brine which was rejected flowed out through brine drainage channels and was replaced by lower salinity nutrient rich seawater from the ocean upper layer we estimate that about half of the second year ice in the region was covered with this slush layer early in the winter as the slush layer froze over a 2 to 3 week period the convection within the ice transported salt from the ice to the upper ocean and increased total heat flux through the overlying ice and snow cover on an area wide basis approximately 10 cm of snow ice growth occurred within second year pack ice primarily during a 2 to 3 week period in february and march this ice growth near the surface of the ice provides a salt flux to the upper ocean equivalent to 5 cm of ice growth despite the thick about 1 m ice cover in addition to the ice growth in the small area less than 5 open water regions

a meta study of relationships between fluvial channel body stacking pattern and aggradation rate implications for sequence stratigraphy a quantitative comparison of 20 literature case studies of fluvial sedimentary successions tests common assumptions made in published models of alluvial architecture concerning 1 inverse proportionality between channel deposit density and floodplain aggradation rates and 2 resulting characteristics of channel body geometries and connectedness our results do not support the relationships predicted by established stratigraphy models the data suggest that channel body density geometry and stacking pattern are not reliable diagnostic indicators of rates of accommodation creation hence these architectural characteristics alone do not permit the definition of accommodation based systems tracts and settings and this calls into question current sequence stratigraphic practice in application to fluvial successions

sea ice motion in the weddell sea from drifting buoy and avhrr data a study of sea ice in the northern weddell sea was done relating the ice motion determined using an array of satellite tracked drifters deployed into ice floes to parameters describing the nature of the ice cover obtained from an analysis of advanced very high resolution radiometer avhrr imagery it was found that the ice motion was predominantly wind driven responding to the passage of low pressure systems across the area the correlation length of the strain field over the entire measurement period was around 200 km at high concentrations the ice responded as a rigid body with coherent motion but below a concentration of around 93 differential motion occurred the nature of the ice motion was found to depend upon the lead parameters with low values of pure convergence and divergence and larger values of vorticity and deformation of the ice field the vorticity was found to be well correlated with the atmospheric pressure with a time lag of less than 3 h implying an almost instantaneous response of the ice cover to meteorological forcing

a quantitative three dimensional depositional model of gravelly braided rivers a quantitative three dimensional depositional model of gravelly braided rivers has been developed based largely on the deposits of the sagavanirktok river in northern alaska these deposits were described using cores wireline logs trenches and ground penetrating radar profiles the origin of the deposits was inferred from observations of 1 channel and bar formation and migration and channel filling interpreted from aerial photographs 2 water flow during floods and 3 the topography and texture of the river bed at low flow stage this depositional model quantitatively represents the geometry of the different scales of strataset the spatial relationships among them and their sediment texture distribution porosity and permeability in the model are related to sediment texture the geometry of a particular type and scale of strataset is related to the geometry and migration of the bedform type e g ripples dunes bedload sheets bars associated with deposition of the strataset in particular the length to thickness ratio of stratasets is similar to the wavelength to height ratio of associated bedforms furthermore the wavelength and height of bedforms such as dunes and bars are related to channel depth and width therefore the thickness of a particular scale of strataset i e medium scale cross sets and large scale sets of inclined strata will vary with river dimensions these relationships between the dimensions of stratasets bedforms and channels mean that this depositional model can be applied to other gravelly fluvial deposits the depositional model can be used to interpret the origin of ancient gravelly fluvial deposits and to aid in the characterization of gravelly fluvial aquifers and hydrocarbon reservoirs

wintertime heat flux to the underside of east antarctic pack ice in the sea ice zone there is a delicate balance between the heat loss from the surface of the snow covered sea ice and the heat supplied to the underside of the ice by the deep ocean the difference between these two heat fluxes determines the amount of ice growth or melt in global atmospheric models the ocean heat flux is often prescribed and has been shown to be an important parameter in determining how thick sea ice will grow thermodynamically although this ocean heat flux is a critical component in climate models there are relatively few direct measurements in the antarctic sea ice region in this study we use measurements of the temperature gradient through the sea ice and of ice growth during a field experiment to estimate the ocean heat flux in the east antarctic region around 140 e 65 s during august 1995 we find an average ocean heat flux of 13 0 14 5 w m 2 this is more than twice the winter values reported in the western weddell sea under multiyear sea ice but similar to the 19 w m 2 that has been estimated for the entire weddell gyre during august 1995 the air temperature showed large variations ranging from near freezing to 30 c this resulted in the thicker ice floes 50 60 cm alternating between a no growth or melting condition and an active ice growth at the base however it is likely that the thicker 60 cm ridged portions of the floes were continually melting

the effect of snow on antarctic sea ice simulations in a coupled atmosphere sea ice model the effect of a snow cover on sea ice accretion and ablation is estimated based on the zero layer version sea ice model of semtner and is examined using a coupled atmosphere sea ice model including feedbacks and ice dynamics effects when snow is disregarded in the coupled model the averaged antarctic sea ice becomes thicker when only half of the snowfall predicted by the atmospheric model is allowed to land on the ice surface sea ice gets thicker in most of the weddell and ross seas but thinner in east antarctic in winter with the average slightly thicker when twice as much snowfall as predicted by the atmospheric model is assumed to land on the ice surface sea ice also gets much thicker due to the large increase of snow ice formation these results indicate the importance of the correct simulation of the snow cover over sea ice and snow ice formation in the antarctic our results also illustrate the complex feedback effects of the snow cover in global climate models in this study we have also tested the use of a mean value of 0 16 wm 1 k 1 instead of 0 31 for the thermal conductivity of snow in the coupled model based on the most recent observations in the eastern antarctic and bellingshausen and amundsen seas and have found that the sea ice distribution changes greatly with the ice becoming much thinner by about 0 2 m in the antarctic and about 0 4 m in the arctic on average this implies that the magnitude of the thermal conductivity of snow is of considerable importance for the simulation of the sea ice distribution an appropriate value of the thermal conductivity of snow is as crucial as the depth of the snow layer and the snowfall rate in a sea ice model the coupled climate models require accurate values of the effective thermal conductivity of snow from observations for validating the simulated sea ice distribution under the present climate conditions

seasonality of southern ocean sea ice the sea ice cover of the southern ocean undergoes a rapid decrease from mid november to mid january the atmosphere to ocean heat flux is insufficient to account for this melting even in the presence of the high percentage of open water characteristic of the southern ocean sea ice it is estimated that sea air heat exchange in the 60 to 70 s zone can account for roughly 50 of the required spring heating the remainder must be supplied by the relatively warm deep water residing below the southern ocean pycnocline deep to surface water heat flux is accomplished by upwelling of the pycnocline due to the regional ekman divergence of the surface layer and by cross pycnocline mixing it is estimated that the required vertical mixing coefficient for the pycnocline is 1 5 cm2 s this value is considered as realistic in view of the relatively weak pycnocline which is a consequence of low levels of fresh water input to the surface layer it is suggested that the magnitude of fresh water input is a major factor in determining the degree of seasonality of southern ocean sea ice

east antarctic sea ice albedo thickness distribution and snow cover characteristics of springtime sea ice off east antarctica were investigated during a cruise of the australian national antarctic research expedition in october through december 1988 the fractional coverage of the ocean surface the ice thickness and the snow cover thickness for each of several ice types were estimated hourly for the region near the ship these observations were carried out continuously during the 4 weeks the ship was in the ice thin and young ice types were prevalent throughout the region and the observations show a systematic increase in the total area weighted pack ice thickness including open water area from only 0 2 m within 50 km of the ice edge to 0 45 m close to the coast ice thickness averaged over the ice covered region only is also relatively thin ranging from 0 35 m near the ice edge to 0 65 m in the interior these values are probably typical of average winter thickness for the area the average snow cover thickness on the ice increased from 0 05 m near the ice edge to 0 15 m in the interior average ice concentration increased from less than 6 10 near the ice edge to 8 10 in the interior the ship observed concentrations were in good agreement with concentrations derived from passive microwave satellite imagery except in some regions of high concentration in these regions the satellite derived concentrations were consistently lower than those estimated from the ship possibly because of the inability of the satellite sensors to discriminate the appreciable percentage of very thin ice observed within the total area spectral albedo was measured for nilas young grey ice grey white ice snow covered ice and open water at wavelengths from 420 to 1000 nm allwave albedo was computed by using the spectral measurements together with estimates of near infrared albedo and modeled spectral solar flux area averaged albedos for the east antarctic sea ice zone in spring were derived from representative allwave albedos together with the hourly observations of ice types these area averaged surface albedos increased from about 0 35 at the ice edge to about 0 5 at 350 km from the edge remaining at 0 5 to the coast of antarctica the low average albedo is in part due to the large fraction of open water within the pack but extensive fractions of almost snow free thin ice also play an important role

year round pack ice in the weddell sea antarctica response and sensitivity to atmospheric and oceanic forcing using a dynamic thermodynamic numerical sea ice model external oceanic and atmospheric forcings on sea ice in the weddell sea are examined to identify physical processes associated with the seasonal cycle of pack ice and to identify further the parameters that coupled models need to consider in predicting the response of the pack ice to climate and ocean circulation changes in agreement with earlier studies the primary influence on the winter ice edge maximum extent is air temperature ocean heat flux has more impact on the minimum ice edge extent and in reducing pack ice thickness especially in the eastern weddell sea low relative humidity enhances ice growth in thin ice and open water regions producing a more realistic ice edge along the coastal areas of the western weddell sea where dry continental air has an impact the modeled extent of the weddell summer pack is equally sensitive to ocean heat flux and atmospheric relative humidity variations with the more dynamic responses being from the atmosphere since the atmospheric regime in the eastern weddell is dominated by marine intrusions from lower latitudes with high humidity already it is unlikely that either the moisture trans port could be further raised or that it could be significantly lowered because of its distance from the continent the lower humidity source ocean heat transport variability is shown to lead to overall ice thinning in the model response and is a known feature of the actual system as evidenced by the occurrence of the weddell polynya in the mid 1970s

a coupled sea ice mixed layer pycnocline model for the weddell sea a dynamic thermodynamic sea ice model is coupled to a one dimensional model of the oceanic mixed layer and pycnocline and is applied to the weddell sea this model prognostically determines the vertical oceanic heat flux from the mixed layer dynamics in contrast to earlier sea ice modeling where the oceanic heat flux was prescribed in addition to the standard simulation polynya and paleoclimate experiments were performed to investigate the effects of sea ice dynamics furthermore the mixed layer pycnocline model is compared to the original kraus turner approach

stable channel cross sections of straight sand rivers a mathematical model is presented for defining the size and cross section of self formed straight sand rivers in which sediments are actively transported everywhere as bedload and suspended load a balance of lateral bedload and lateral diffusive transport of suspended sediment is imposed to maintain a stable channel cross section singular perturbation technique is employed to solve the sediment balance equation from which a relation for stable depth is derived a resistance formula for dune covered beds is used to obtain stable width it is revealed theoretically that the channel center depth relative to sediment size is approximately proportional to s 0 8 for natural sand rivers in which s is longitudinal slope the analysis is found to agree reasonably well with available laboratory and field data

seasonal simulation of the southern ocean coupled ice ocean system the southern ocean ice ocean system is investigated using a coupled model developed at princeton university the ocean model uses the primitive equations and solves the second moment closure for turbulent mixing the snow ice model uses a three level thermodynamic scheme resembling semtner s 1976 model the focus here is to study the seasonal variability of the ice covered areas and water mass formation the model simulates reasonably well the seasonal cycle of the ice cover in the southern ocean the annual rapid advance of the ice extent is tied to the ice advection away from the coast toward the antarctic circumpolar current acc where it melts rapidly with the increase of radiative fluxes in the austral spring the european center for medium range weather forecasts climatology tends to produce too little ice in the pacific sector for which the primary cause is a weak meridional wind stress the oceanic heat fluxes are up to 100 w m 2 in open water areas and along the coastal areas except in the weddell and ross seas which are occupied by a year round sea ice cover and have average heat flux of 20 w m 2 or less however there is a small region in the ross sea with high heat loss suggesting deep convection the meridional and zonal heat fluxes are in reasonable agreement with observational estimates the atlantic meridional heat flux is zero at 34 s northern boundary of the model which is an inadequacy in the model in the indian ocean sector the flux is southward while in the pacific sector it is weak and equatorward from the water mass balance we can deduce that the antarctic bottom water aabw t 27 85 annual production is 12 sv in the atlantic sector and 5 sv in the ross sea the total production of 17 sv is in excellent agreement with the observational estimates of 10 20 sv intermediate water types are produced in the indian ocean sector where some of the aabw is lost during that conversion in the atlantic sector 6 sv of the annually formed aabw is advected north across the acc in the pacific sector the northward aabw flow is 7 5 sv which is in excess of the ross sea production suggesting that a considerable portion of the aabw formed in the weddell sea is contributing to that flux

processes facies and architecture of fluvial distributary system deposits abstract there is evidence from the stratigraphic record of examples of fluvial deposits that were the products of deposition from river systems which had decreasing discharge down flow and transitions from proximal channelised to distal unconfined flow these deposits form fan shaped bodies several tens of kilometres in radius and their stratigraphic architecture is aggradational with no evidence of deep incision driven by base level fall the fluvial systems that generated these deposits formed under conditions for which there is no complete analogue today an endorheic basin with a relatively arid climate adjacent to an uplifted area with higher precipitation a conceptual model for fluvial systems of this type has therefore been built on the basis of outcrop examples and a consideration of the controls on sedimentation proximal areas are characterised by amalgamated coarse pebbly and sandy channel deposits with little preservation of overbank facies channel dimensions are generally smaller in the medial areas but sizes are variable deposits are of braided meandering and simple channels which show varying degrees of lateral migration the channel fills may be mud or sand with overbank flow processes playing an important role in filling channels abandoned on the floodplain after avulsion the proportion of overbank deposits increases distally with sheets of sand deposited as lateral and terminal splays by unconfined flow interconnection of sandstone bodies is poor in the distal areas because channel fill bodies are sparse small and are not deeply incised the radial pattern of the sediment body forms by the repeated avulsion of channels active channels build up lobes on the alluvial plain and rivers switch position to follow courses on lower lying areas the term fluvial distributary system is here used to describe a river system which has a downstream decrease in discharge and has a distal zone which is characterised either by terminal splays on to a dry alluvial plain or a lake delta during periods of lake highstand

the ice thickness distribution across the atlantic sector of the antarctic ocean in midwinter during the first leg of the winter weddell sea project antarktis v 2 cruise of f s polarstern the entire width of the antarctic sea ice zone was traversed in the vicinity of 0 longitude in the period july 18 to september 10 1986 ice thicknesses were measured by direct drilling and by helicopter profiling using an exstar 100 mhz impulse radar system in addition aerial photography of the ice cover was done from 100 to 2000 m altitude using a 70 mm aerial camera mounted in the helicopter the results of the point measurements drilling are reported in this paper together with an indication of how the radar and photography data will be used to extend them so as to yield area averaged ice thickness distributions it was found that the main ice type across the entire width of the ice cover was consolidated pancake ice occurring in vast floes this formed out of a 250 km wide band at the advancing ice edge which comprised a concentrated field of individual pancakes in a matrix of frazil ice preferred thicknesses of undeformed floes were 40 60 cm of ice covered with 5 15 cm of snow the individual pancakes attained almost all of this thickness before consolidation subsequent congelation growth was slow estimated at 0 4 cm d 1 the floes contained much small scale roughness on the upper and lower surfaces due to rafting of pancakes at the time of consolidation but pressure ridging was modest except in the far south a few very thick 8 11 m multiyear floes were observed embedded in the pack at latitudes beyond 66 s

grain size composition porosity and permeability contrasts within cross bedded sandstones in tertiary fluvial deposits central spain permeability measured with a portable probe pcrmcflmeter on outcrops of cross bcdded sandstones ranges betwecn 0 9 and 19 o the highest pcrmeability 2 19 0 with an avcrage of8 5 d occurs in thc coarsest grained foresct laminae cfl intermediate values 2 120 with an average of 5 3 d occur in fincr grained foreset laminac ffl and thc lowest values 0 9 1 0 0 with un avcrage of 4 8 d occur in boltomsct laycrs bl in the cross bcds the uverage grain sizc rangcs from medium graincd sand in the cfl to finc grained s lnd in thc ffl and bl in all three subf lcies the average size of the primary pores is approximately it unit smaller than the averagc grain size the abundance of unstablc carbonatc clasts correlatcs with incrcasing avcrage grain size micritic clasts being most abundant in the cfl converscly quartz content incrcascs with decreasing grain size and is highest in the ffl and bl oiagenetic destruction of primary porosity by compact ion and cementation as well is generation of sccondary porosity through dissolution were controlled by the original mineralogical composition of the sand contrasts in grain size detcrmine the primary pore size contrasts and differences in composition bctwecn cfl ffl and bl permeability contrasts reflect variations in averagc primary pore size rather than differenccs in total porosity probe permeability contrasts between efl ffl and bl depend on contrasts in llverage pore size and contrasts in mineralogical composition between the subfacies

modeling of antarctic sea ice in a general circulation model a dynamic thermodynamic sea ice model is developed and coupled with the melbourne university general circulation model to simulate the seasonal cycle of the antarctic sea ice distribution the model is efficient rapid to compute and useful for a range of climate studies the thermodynamic part of the sea ice model is similar to that developed by parkinson and washington the dynamics contain a simplified ice rheology that resists compression the thermodynamics is based on energy conservation at the top surface of the ice snow the ice water interface and the open water area to determine the ice formation accretion and ablation a lead parameterization is introduced with an effective partitioning scheme for freezing between and under the ice floes the dynamic calculation determines the motion of ice which is forced with the atmospheric wind taking account of ice resistance and rafting the simulated sea ice distribution compares reasonably well with observations the seasonal cycle of ice extent is well simulated in phase as well as in magnitude simulated sea ice thickness and concentration are also in good agreement with observations over most regions and serve to indicate the importance of advection and ocean drift in the determination of the sea ice distribution

the thickness distribution of sea ice and snow cover during late winter in the bellingshausen and amundsen seas antarctica data collected from a voyage of rv nathaniel b palmer to the bellingshausen and amundsen seas during august september 1993 are used to investigate the thickness distribution of sea ice and snow cover and the processes that influence the development of the first year pack ice the data are a combination of in situ and ship based measurements and show that the process of floe thickening is highly dependent on ice deformation in particular rafting and ridging play important roles at different stages of floe development rafting is the major mechanism in the early stages of development and core structure data show the mean thickness of individual layers of crystals to be only 0 12 m most ice 0 6 m having some surface deformation blocks within ridge sails are typically in the range 0 3 0 6 m thick and ship based observations estimate approximately 25 of the pack exhibits surface ridging when corrected for biases in the observational methods the data show that the dominant ice and snow thickness categories are 0 7 m and 0 2 0 5 m respectively and account for 40 and 36 of the surface area of the pack ice approximately 8 of the pack is open water an estimate of the effects of ridging on the distribution of ice mass within the pack suggests that between 50 and 75 of the total mass is contained within the 25 of the pack that exhibits surface ridging

ocean heat flux in the central weddell sea during winter abstract seasonal sea ice which plays a pivotal role in air sea interaction in the weddell sea a region of large deep water formation with potential impact on climate depends critically on heat flux from the deep ocean during the austral winter of 1994 an intensive process oriented field program named the antarctic zone flux experiment measured upper ocean turbulent fluxes during two short manned ice drift station experiments near the maud rise seamount region of the weddell sea unmanned data buoys left at the site of the first manned drift provided a season long time series of ice motion mixed layer temperature and salinity plus a truncated high resolution record of temperature within the ice column direct turbulence flux measurements made in the ocean boundary layer during the manned drift stations were extended to the ice ocean interface with a mixing length model and were used to evaluate parameters in bulk expressions for interfacial stress a rossby similarity drag law and ocean to

contrasting diagenetic histories of concretions and host rock lion mountain sandstone cambrian texas white elliptical calcite cemented concretion nuclei up to 2 m long contrast markedly in color composition and diagenetic history from more glauconite rich concretion rinds and from dark green glaucarenite host rocks concretion nuclei are placers of loosely packed trilobite carapaces and minor quartz and glauconite tightly cemented with an average of 58 calcite cement the nuclei are shell lag deposits that were cemented by calcite at the sea floor or after burial of a few meters concretion rinds composed of sub equal amounts of quartz and compactionally deformed glauconite have an average of only 32 cement which consists of minor quartz overgrowths and later pore occluding calcite cement the rinds underwent burial for several million years to tens of million years to depths of several hundred meters before they were cemented the host rock is predominantly glauconite with very minor quartz and calcite cement 87 sr 86 sr ratios of host rock calcite cement are variable 0 7084 to 0 7093 but the lowest value suggests precipitation during the middle ordovician in the absence of significant amounts of carbonate cement the host rock underwent complete dissolution of trilobite carapaces and maximum compaction with total loss of porosity through squashing of glauconite grains maximum burial during this stage was completed by the end of ordovician time carbon and oxygen isotopic values of calcite from 16 samples show no differences between concretion nuclei rinds and host rocks 13 c ranges from 2 2 to 2 9 pdb and probably reflects derivation of carbon from trilobite carapaces and other skeletal grains 18 o ranges from 4 6 to 6 2 pdb and reflects either the original composition of the cement and trilobites or the modification of original grains by meteoric dominated ground water

relationship between observed liquefaction at kaiapoi following the 2010 darfield earthquake and former channels of the waimakariri river abstract the darfield earthquake caused widespread damage in the canterbury region of new zealand with the majority of damage resulting from liquefaction and lateral spreading one of the worst hit locations was the small town of kaiapoi north of christchurch an area that has experienced liquefaction during past events and has been identified as highly susceptible to liquefaction the low lying town sits on the banks of the kaiapoi river once a branch of the waimakariri a large braided river transporting gravelly sediment the waimakariri has been extensively modified both by natural and human processes consequently many areas in and around the town were once former river channels using historical accounts and maps of the region areas of land reclamation and old channels that had been cut off from the river since the beginning of european settlement in the 1850s were identified these areas correlated well with many of the areas having significant liquefaction damage following the darfield event substantial lateral spreads and sand boils developed in areas of reclamation along the current river path causing significant damage to stopbanks and structures along the river with fissures up to 2 m deep and 1 m wide much of the residential housing was damaged by lateral spreading with cumulative displacement offsets up to 3 m parallel to old channel beds that had aggraded over time due to river shifts in former channel areas that were free of lateral spreading large volumes of ejecta were present over wide areas with depths of up to 400 mm in places houses in these regions were damaged as a result of settlement and tilting in all these areas underground services and roadways were severely impacted as a result of ground deformation the severity of this damage indicates the importance of knowing the location of old channels when defining liquefaction prone regions

numerical simulation of the weddell sea pack ice to investigate the role of ice dynamics on the seasonal cycle of antarctic sea ice a series of 2 year simulations of the weddell sea pack ice are carried out the simulations employ the dynamic thermodynamic model developed by hibler 1979 and use a 1 day time step on an 18 15 grid with a resolution of 222 km daily atmospheric data from 1979 are used to drive the simulations with atmospheric temperature fields modified to reflect buoy observations the simulations yield a seasonal cycle of ice with maximum and minimum extents close to that observed except for portions of the western weddell the advance of the ice is found to be primarily thermodynamic in nature while the rapid decay depends critically on the presence of both leads and lateral ice advection the average fraction of open water is substantial even in winter and varies from a minimum of 10 in september to a maximum of 35 in march these values are in general agreement with estimates from satellite microwave data in early summer the ice motion causes a residual tongue of ice to extend eastward from the antarctic peninsula in agreement with observations mean ice thicknesses are consistent with observations and vary from about 3 m in the perennial ice in the western weddell to 1 m in first year ice in the eastern weddell possible feedback between the ice extent and atmosphere are investigated by simulations with the surface air temperatures constrained to below freezing values in the presence of ice these coupled simulations yield a more realistic rapid decay in summer with dynamics included but an unrealistically small decay without dynamics simulated ice drift results yield mean drift rates of about 5 km day in good agreement with buoy drift observations but with slightly inadequate northward transport in the western weddell near the ice edge the drift rates are relatively insensitive to the ice strength near the coast however lower strengths are found to yield a decrease in northward drift rates

determining the floe size distribution of east antarctic sea ice from digital aerial photographs floe size within the antarctic pack ice is an important parameter that affects both the ocean ice atmosphere energy exchange and the mechanical properties of pack ice in this paper we present a computer based algorithm to extract floe size distribution information from digital aerial photographs of antarctic sea ice the algorithm segments digital images of sea ice into distinct floes from which the size of each floe is calculated and floe size distributions are derived through a recursive application of the morphological erosion operator each floe is eroded towards its centre while each pixel s erosion number is recorded this ensures no information is lost while individual floes are identified the algorithm combines image processing techniques with some manual input to accurately identify the boundaries of individual floes within an image to demonstrate the functionality of the algorithm six images representing regions along a 22 km south to north transect through a transitional zone of pack ice near 65 s 140 e have been processed regional variations in the floe size distributions show an increase in the number of smaller floes relative to larger floes and a decrease in the dominant floe size in terms of areal coverage from south to north these results are consistent with ship based observations

southern ocean winter mixed layer austral winter 1986 observations from the polarstern along the greenwich meridian from the ice edge to the antarctic margin show the mixed layer beneath the winter sea ice cover to be significantly depressed in oxygen saturation incorporation of weddell deep water wdw into the winter mixed layer responsible for this undersaturation also introduces heat and salinity into the surface layer which strongly influences the mixed layer sea air exchanges and sea ice formation processes the total wdw transfer into the mixed layer averages 45 myr 1 implying a residence time for the surface water of 2 5 years the associated winter heat flux is 41 w m 2 which limits ice thickness to about 0 55 m agreeing quite well with observations the air temperatures during the cruise are just sufficient to remove the wdw heat input in the presence of observed ice thickness and concentration this suggests that the sea ice cover and wdw heat input into the mixed layer are in approximate balance by midwinter the annual heat flux from wdw to the surface layer and hence into the atmosphere is estimated as 16 w m 2 extrapolation of the greenwich meridian wdw entrainment value to the full circumpolar 60 70 s belt yields total up welling of 24 106 m3 s 1 similar extrapolation of the heat flux value gives a circumpolar total of 2 8 1014 w as a consequence of circulation topography interaction the maud rise water column stands out as an anomaly relative to the surrounding region with a significantly more saline and dense mixed layer below the mixed layer the water column over the crest of the rise is identical to that over the flanks if the latter water column is upwelled by 400 m this uplifting is believed to be a response of the upstream flow encountering the rise increased upstream flow would be expected to increase maud rise upwelling and the dependent salinity density of the mixed layer slight increases in the mixed layer density could trigger a convective mode and generation of a polynya it is hypothesized that spin up of the weddell gyre s barotropic circulation induced by an increase of the regional wind stress curl would enhance the probability of polynya development over maud rise

a simple parameterization of ice leads in a general circulation model and the sensitivity of climate to change in antarctic ice concentration we present a simple parameterization of the effect of open leads in a general circulation model of the atmosphere we consider only the case where the sea ice distribution is prescribed i e not interactive and the fraction of open water in the ice is also prescribed and set at the same value at all points in the southern hemisphere and a different value in the northern hemisphere we approximate the distribution of sea ice over a model grid box as a part of the box being covered by solid ice of uniform thickness and the complement of the box consisting of open water at a fixed 1 8 c because of the nonlinearity in the flux computations separate calculations are performed over the solid sea ice and over the open leads the net fluxes conveyed to the atmosphere over the grid box are determined by performing the appropriate area weighted average over the two surface types we report on an experiment designed to assess the sensitivity of the modelled climate to the imposition of a 50 concentration in the winter antarctic sea ice significant warming of up to 6 c takes place in the vicinity of and above the antarctic sea ice and is associated with significant changes in the zonal wind structure pressure reductions are simulated over the sea ice being particularly marked in the weddell sea region and an anomalous east west aligned ridge is simulated at about 60 s very large changes in the sensible heat flux in excess of 200 wm 2 are simulated near the coast of antarctica

a novel method for estimating sandbody compaction in fluvial successions clastic sedimentary successions are subject to variable amounts of compaction which causes a decrease in both the thickness and porosity of sand rich depositional units methods for estimating the degree of sediment compaction are needed for characterizing changes in the geometry and petrophysical properties of depositional elements in relation to their burial history conventional methods for estimating compaction of rock successions through the application of several empirical equations return estimations whose uncertainties can be significant and integrative approaches that can produce reliable estimations are therefore desirable to this end a new method is proposed here for the estimation of the degree of compaction of sandbodies in ancient channelized fluvial successions for outcropping fluvial successions the compacted geometry of channel fill margins cut into non cohesive deposits can be measured whereas the decompacted angle of repose of the material originally forming the channel banks can be estimated experimentally sediment compaction can therefore be estimated by comparing the observed geometry of the uppermost part of a channel fill margin with the angle of repose of the non cohesive bank material the proposed method has been applied to three different sand prone fluvial successions seen in outcrop for the purposes of i illustrating the approach and ii testing it through a comparison of its estimations against results produced by a conventional method based on thin section observations the comparison demonstrates that the two methods yield similar results highlighting how the proposed approach can be readily applied to the assessment of compaction in clastic successions for scopes of both pure and applied geological research

evolution of the southern ocean winter mixed layer and sea ice open ocean deepwater formation and ventilation an analytical model has been developed to describe the nature of the winter ocean sea ice interaction in the southern ocean to determine the principal processes responsible for maintaining stability in this marginally stable region and to predict the response to changes in the external forcing and initial conditions the model accurately describes the sparse winter observations and the general temporal evolution of the ice mixed layer depth and salinity for the period following the elimination of the seasonal pycnocline by rapid fall ice growth a scale analysis and sensitivity study reveal the system parameter dependence this indicates that the magnitude of entrainment is proportional to fst h0 s where fs is the external salt flux h0 the depth of the winter mixed layer and s the salinity gradient through the pycnocline thermodynamic ice growth reflects predominantly the competition between the oceanic diffusive heat gain across the base of the mixed layer and the loss to the atmosphere through the ice and leads a strong thermal gradient across the pycnocline leads to a significant diffusive flux which balances most of the heat lost to the atmosphere this limits the amount of ice growth possible and plays the principal role in maintaining the system stability since the ice growth is required for destabilization through haline rejection during the growth process the system is also sensitive to the large ratio of heat to salt in the pycnocline this introduces a negative feedback where increasing ice growth induces entrainment by the associated salt flux which in turn drives an entrainment heat flux which compensates for heat lost to the atmosphere this moderates the ability to grow ice and drive further entrainment the absolute strength of the salinity gradient on the other hand dictates the effectiveness which a same magnitude external salt flux will have in driving entrainment the effectiveness with which changes in these parameters as well as several other external parameters can influence the southern ocean stability is explicitly evaluated through the sensitivity study and analysis

sediment induced amplification and the collapse of the nimitz freeway the amplification of ground motion by low seismic velocity surface sediments is an important factor in determining the seismic hazard specific to a given site the ms 7 1 loma prieta earthquake of 17 october 1989 was the largest event in the contiguous united states in 37 years and yielded an unparalleled volume of seismic data from the main shock and aftershock sequence1 these data can be used to image the seismic source to study detailed earth structure and to study the propagation of seismic waves both through bedrock at depth and through sediment layers near the surface near the edge of san francisco bay site conditions vary considerably on scales of hundreds of metres the collapsed section of the two tiered nimitz freeway in oakland was built on san francisco bay mud whereas stiffen alluvial sediments underlie a southern section that was damaged but did not collapse here we analyse high quality digital aftershock recordings from several sites near the nimitz freeway and conclude that soil conditions and resulting ground motion amplification may have contributed significantly to the failure of the structure