deformation mechanisms in granitic rocks at shallow crustal levels abstract microstructural observations of naturally faulted granitic gneisses show that feldspar grains are weaker than quartz grains at temperatures below 325 c and at depths of less than 8 10 km feldspar grains sustained most of the deformation by grain scale faulting slip along cleavage controlled fractures and cataclasis fracture of feldspar grains within fault zones promoted their alteration to kaolinite quartz grains also deformed by fracturing and often healed to form quartz porphyroclasts and mosaics in a comminuted matrix of feldspar and kaolinite syntectonic alteration of the feldspar grains may have weakened the fault zones over time and resulted in foliated textures within the fault zones this study of naturally deformed rocks confirms published experimental results on the behavior of granitic rocks at low temperatures and pressures and taken together these data show that the theology of the upper 10 km of the crust is greatly influenced by cataclastic processes in feldspar

experimental tests of truncated diffusion in fault damage zones fault zones affect the flow paths of fluids in groundwater aquifers and geological reservoirs fault related fracture damage decreases to background levels with increasing distance from the fault core according to a power law this study investigated mass transport in such a fault related structure using nonlocal models a column flow experiment is conducted to create a permeability distribution that varies with distance from a main conduit the experimental tracer response curve is preasymptotic and implies subdiffusive transport which is slower than the normal fickian diffusion if the surrounding area is a finite domain an upper truncated behavior in tracer response i e exponential decline at late times is observed the tempered anomalous diffusion tad model captures the transition from subdiffusive to fickian transport which is characterized by a smooth transition from power law to an exponential decline in the late time breakthrough curves this article is protected by copyright all rights reserved

antarctic bottom water warming and freshening contributions to sea level rise ocean freshwater budgets and global heat gain abstractfreshening and warming of antarctic bottom water aabw between the 1980s and 2000s are quantified assessing the relative contributions of water mass changes and isotherm heave the analysis uses highly accurate full depth ship based conductivity temperature depth measurements taken along repeated oceanographic sections around the southern ocean fresher varieties of aabw are present within the south pacific and south indian oceans in the 2000s compared to the 1990s with the strongest freshening in the newest waters adjacent to the antarctic continental slope and rise indicating a recent shift in the salinity of aabw produced in this region bottom waters in the weddell sea exhibit significantly less water mass freshening than those in the other two southern basins however a decrease in the volume of the coldest deepest waters is observed throughout the entire southern ocean this isotherm heave causes a salinification and warming on isobaths from the bottom up to the shallow potential tem

large multidecadal salinity trends near the pacific antarctic continental margin abstract ocean temperature and salinity measurements on and near the antarctic continental shelf in the southwest pacific sector are evaluated for evidence of temporal change shelf water in the southwest ross sea has declined in salinity by 0 03 decade 1 from 1958 to 2008 while its temperatures have increased in proportion to the influence of salinity on the sea surface freezing point modified deep water intrusions that reach the central ross ice shelf have freshened at a similar rate and cooled by 0 5 c since the late 1970s salinity has decreased by 0 08 decade 1 in the westward coastal and slope front currents consistent with increased melting of continental ice upstream in the amundsen sea overturning of those near surface waters during winter sea ice formation and mixing across the slope front is sufficient to account for the 5 decade shelf water salinity change a strong correlation between the freshening and change in the southern annular mode index suggests a link with the large scale atmosp

tracer movement in a single fissure in granitic rock some experimental results and their interpretation radionuclide migration was studied in a natural fissure in a granite core the fissure was oriented parallel to the axis in a cylindrical core 30 cm long and 20 cm in diameter the traced solution was injected at one end of the core and collected at the other breakthrough curves were obtained for the nonsorbing tracers tritiated water and a large molecular weight lignosulphonate molecule and for the sorbing tracers cesium and strontium from the breakthrough curves for the nonsorbing tracers it could be concluded that channeling occurs in the single fissure a dispersion model based on channeling is presented the results from the sorbing tracers indicate that there is substantial diffusion into and sorption in the rock matrix sorption on the surface of the fissure also accounts for a part of the retardation effect of the sorbing species a model which includes the mechanisms of channeling surface sorption matrix diffusion and matrix sorption is presented the experimental breakthrough curves can be fitted fairly well by this model by use of independently obtained data on diffusivities and matrix sorption

on the total input of antarctic waters to the deep ocean a preliminary estimate from chlorofluorocarbon measurements 1 deep ocean inventories of dissolved chlorofluorocarbon 11 cfc 11 along representative sections off antarctica provide the first estimate of the overall strength of all dense water sources in the southern ocean their formation rates are reported for three density layers that span the main water masses involved in the lower limb of the thermohaline circulation thc the bottom layer is supplied via sinking of antarctic bottom water aabw produced at a few continental shelves the middle layer receives the offshore injection of ventilated modified circumpolar deep water mcdw produced along much of the lengthy antarctic slope front the top layer is ventilated by northward export of antarctic surface water into the upper circumpolar deep water of the antarctic circumpolar current average southern ocean inputs to the upper two layers of the deep ocean for the 1970 1990 period are derived on the basis of the cfc 11 distributions along meridional sections the mean cfc 11 saturations of all water mass ingredients and the inferred mixing leading to production of dense source waters about 5 4 1 7 sv 1 sv 10 6 m 3 s 1 of near freezing shelf water ventilate the bottom layer and 4 7 1 7 sv and 3 6 1 3 sv of cold antarctic surface water ventilate the middle and top layers therefore the total contribution of ventilated southern ocean waters to the lower limb of the global thc is about 14 sv this is close to the about 17 sv estimated for north atlantic near surface sources from cfc 11 inventories their entrainment of 7 4 2 4 sv of cfc poor subsurface lower circumpolar deep water during the formation and sinking of aabw and mcdw raises the total southern ocean input to the deep ocean to about 21 sv

linking aquifer spatial properties and non fickian transport in mobile immobile like alluvial settings summary time nonlocal transport models can describe non fickian diffusion observed in geological media but the physical meaning of parameters can be ambiguous and most applications are limited to curve fitting this study explores methods for predicting the parameters of a temporally tempered levy motion ttlm model for transient sub diffusion in mobile immobile like alluvial settings represented by high resolution hydrofacies models the ttlm model is a concise multi rate mass transfer mrmt model that describes a linear mass transfer process where the transfer kinetics and late time transport behavior are controlled by properties of the host medium especially the immobile domain the intrinsic connection between the mrmt and ttlm models helps to estimate the main time nonlocal parameters in the ttlm model which are the time scale index the capacity coefficient and the truncation parameter either semi analytically or empirically from the measurable aquifer properties further applications show that the ttlm model captures the observed solute snapshots the breakthrough curves and the spatial moments of plumes up to the fourth order most importantly the a priori estimation of the time nonlocal parameters outside of any breakthrough fitting procedure provides a reliable blind prediction of the late time dynamics of subdiffusion observed in a spectrum of alluvial settings predictability of the time nonlocal parameters may be due to the fact that the late time subdiffusion is not affected by the exact location of each immobile zone but rather is controlled by the time spent in immobile blocks surrounding the pathway of solute particles results also show that the effective dispersion coefficient has to be fitted due to the scale effect of transport and the mean velocity can differ from local measurements or volume averages the link between medium heterogeneity and time nonlocal parameters will help to improve model predictability for non fickian transport in alluvial settings

transport and retention from single to multiple fractures in crystalline rock at aspo sweden 2 fracture network simulations and generic retention model hydrogeologic characterization of crystalline rock formations on the field scale is important for many applications but still presents a multitude of challenges neuman 2005 in this work we use

thermal responses to antarctic ice shelf melt in an eddy rich global ocean sea ice model abstractthe response near antarctic waters to freshening by increased glacial melt is investigated using a high resolution 0 1 global ocean sea ice model with realistic antarctic water mass prop

accelerated ice discharge from the antarctic peninsula following the collapse of larsen b ice shelf acceleration exceeds 27 km 3 per year and ice is thinning at rates of tens of meters per year we attribute this abrupt evolution of the glaciers to the removal of the buttressing ice shelf the magnitude of the glacier changes illustrates the importance of ice shelves on ice sheet mass balance and contribution to sea level change index terms 1827 hydrology glaciology 1863 1863 hydrology snow and ice 1827 3349 meteorology and atmospheric dynamics polar meteorology 6924 radio science interferometry 9310 information related to geographic region antarctica citation rignot e g casassa p gogineni w krabill a rivera and r thomas 2004 accelerated ice discharge from the antarctic peninsula following the collapse of larsen b ice shelf geophys res lett 31 l18401 doi 10 1029 2004gl020697

tracer transport in fractured crystalline rock evidence of nondiffusive breakthrough tailing extended tailing of tracer breakthrough is often observed in pulse injection tracer tests conducted in fractured geologic media this behavior has been attributed to diffusive exchange of tracer between mobile fluids traveling through channels in fractures and relatively stagnant fluid between fluid channels along fracture walls or within the bulk matrix we present a field example where tracer breakthrough tailing apparently results from nondiffusive transport tracer tests were conducted in a fractured crystalline rock using both a convergent and weak dipole injection and pumping scheme deuterated water bromide and pentafluorobenzoic acid were selected as tracers for their wide range in molecular diffusivity the late time behavior of the normalized breakthrough curves were consistent for all tracers even when the pumping rate was changed the lack of separation between tracers of varying diffusivity indicates that strong breakthrough tailing in fractured geologic media may be caused by advective transport processes this finding has implications for the interpretation of tracer tests designed to measure matrix diffusion in situ and the prediction of contaminant transport in fractured rock

radionuclide transport in fast channels in crystalline rock recent field investigations in crystalline rock give strong indications that water flows in largely isolated channels in fissured rock the present paper sets out to investigate radionuclide transport in such channels including diffusion into the rock matrix it is shown that the uptake from a cylindrical hole in a matrix is much more effective per unit contact area than a flat surface semi infinite solid comparison of diffusion from cylindrical and slit formed channels shows that the differences in interfacial flux are minor a slit formed channel may therefore be approximated by a cylindrical one diffusional transport in the matrix is then treated as one dimensional instead of two dimensional which gives a considerable numerical simplification a simple estimate of the penetration depth into the cylindrical region i e the location of the diffusional front is proposed by using the integrated finite difference method a number of radionuclide transport calculations are performed for the case of flow and dispersion in a cylindrical channel coupled to diffusion and sorption in the matrix

quantifying antarctic bottom water and north atlantic deep water volumes 1 a near global census of antarctic bottom water aabw and north atlantic deep water nadw is essayed through a nonnegative least squares analysis of conservative and quasi conservative seawater properties aabw thickness generally decreases from south to north modulated by ocean bathymetry likewise nadw thickness generally decreases from north to south in the atlantic ocean nadw dominates below the thermocline of the atlantic ocean at least as far south as the subtropical gyre of the south atlantic with a lesser but still significant influence around the entire antarctic circumpolar current in the indian ocean and in the pacific ocean however in the pacific and indian oceans aabw dominates below the thermocline in addition measurable quantities of aabw reach into the abyssal north atlantic on both sides of the mid atlantic ridge the census results suggest that aabw occupies roughly twice the volume of nadw in the three main oceans and that aabw is in contact with roughly twice the area of the deep main ocean floor compared with nadw however these results are somewhat sensitive to choices of water masses their values of seawater properties and the weightings of the seawater properties used in the analysis

sensitivity of antarctic bottom water to changes in surface buoyancy fluxes abstractthe influence of freshwater and heat flux changes on antarctic bottom water aabw properties are investigated within a realistic bathymetry coupled ocean ice sector model of the atlantic ocean the model simulations are conducted at eddy permitting resolution where dense shelf water production dominates over open ocean convection in forming aabw freshwater and heat flux perturbations are applied independently and have contradictory surface responses with increased upper ocean temperature and reduced ice formation under heating and the opposite under increased freshwater fluxes aabw transport into the abyssal ocean reduces under both flux changes with the reduction in transport being proportional to the net buoyancy flux anomaly south of 60 s through inclusion of shelf sourced aabw a process absent from most current generation climate models cooling and freshening of dense source water is facilitated via reduced on shelf off shelf exchange flow such cooling is propagated to the abyssal ocea

a numerical model of the circulation in knight inlet british columbia canada abstract during spring 1988 a period of low freshwater runoff and summer 1989 a period of high freshwater runoff month long observations of velocity temperature and salinity were made throughout the water column in knight inlet both up inlet and down inlet of the sill measurements were made at depths of 2 4 6 9 and 12 m using s4 current meters at depths down to about 200 m using profiling current meters and at depths deeper than 200 m using aanderaa current meters anemometers were deployed at two locations along the inlet a laterally integrated two dimensional numerical model of the inlet that uses the mellor and yamada level 2 5 turbulence closure scheme and that accounts for the combined influence of the winds tides and freshwater runoff has been used to produce 30 day simulations of the velocity and density field in the inlet the vertical coordinate is transformed in the model so that very fine vertical resolution can be attained near the surface even though the tidal range is larg

rapid subsurface warming and circulation changes of antarctic coastal waters by poleward shifting winds the southern hemisphere westerly winds have been strengthening and shifting poleward since the 1950s this wind trend is projected to persist under continued anthropogenic forcing but the impact of the changing winds on antarctic coastal heat distribution remains poorly understood here we show that a poleward wind shift at the latitudes of the antarctic peninsula can produce an intense warming of subsurface coastal waters that exceeds 2 c at 200 700 m depth the model simulated warming results from a rapid advective heat flux induced by weakened near shore ekman pumping and is associated with weakened coastal currents this analysis shows that anthropogenically induced wind changes can dramatically increase the temperature of ocean water at ice sheet grounding lines and at the base of floating ice shelves around antarctica with potentially significant ramifications for global sea level rise

energetic plumes over the western ross sea continental slope rapid descent of dense drygalski trough western ross sea antarctica shelf water over the continental slope within 100 to 250 m thick benthic plumes is described speeds of up to 1 0 m s are recorded flowing at an average angle of 35 to the isobaths entraining ambient lower circumpolar deep water en route this process is predominant in determining the concentration and placement of the shelf water injected into the deep sea as a precursor antarctic bottom water nonetheless a 4 hour duration pulse of undiluted shelf water was observed at depth 1407 m directly north of the drygalski trough moving at around 90 degrees to isobaths and at a speed of 1 4 m s thus the export of ross sea shelf water to the deep sea is accomplished within plumes descending at moderate angle to isobaths punctuated by rapid downhill cascades

implications for mechanical properties of brittle faults from observations of the punchbowl fault zone california field observations of the punchbowl fault zone an inactive trace of the san andreas are integrated with results from experimental deformation of naturally deformed punchbowl fault rocks for a qualitative description of the mechanical properties of the fault and additional information for conceptual models of crustal faulting the punchbowl fault zone consists of a single continuous gouge layer bounded by zones of extensively damaged host rock fault displacements were not only localized to the gouge layer but also to discrete shear surfaces within the gouge deformation in the exposure studied probably occurred at depths of 2 to 4 km and was dominated by cataclastic mechanisms textural data also suggest that significant amounts of pore fluids were present during faulting and that fluid assisted mechanisms such as dissolution diffusion and precipitation were operative the experimental data on specimens collected from the fault zone suggest that there is a gradual decrease in strength and elastic modulus and an increase in relative ductility and permeability toward the main gouge zone the gouge layer has fairly uniform mechanical properites and it has significantly lower strength elastic modulus and permeability than both the damaged and the undeformed host rock for the punchbowl fault and possibly other brittle faults the variations in loading of the gouge zone with time are primarily governed by the morphology of the fault and the mechanical properties of the damaged host rock in addition the damaged zone acts as the permeable unit of the fault zone and surrounding rock it appears that the gouge primarily governs whether displacements are localized and it therefore may have a significant influence on the mode of slip

eddy driven exchange between the open ocean and a sub ice shelf cavity the exchange between the open ocean and sub ice shelf cavities is important to both water mass transformations and ice shelf melting here we use a high resolution 500 m numerical model to investigate to which degree eddies produced by frontal instability at the edge of a polynya are capable of transporting dense high salinity shelf water hssw underneath an ice shelf the applied surface buoyancy flux and ice shelf geometry is based on ronne ice shelf in the southern weddell sea an area of intense wintertime sea ice production where a flow of hssw into the cavity has been observed results show that eddies are able to enter the cavity at the southwestern corner of the polynya where an anticyclonic rim current intersects the ice shelf front the size and time scale of simulated eddies are in agreement with observations close to the ronne ice front the properties and strength of the inflow are sensitive to the prescribed total ice production flushing the ice shelf cavity at a rate of 0 2 0 4 106 m3 s 1 depending on polynya size and magnitude of surface buoyancy flux eddy driven hssw transport into the cavity is reduced by about 50 if the model grid resolution is decreased to 2 5 km and eddies are not properly resolved

determining glacier flow direction from till fabrics abstract field and experimental data indicate that fabrics of sheared basal tills based on particle orientations and on anisotropy of magnetic susceptibility are inclined relative to the macroscopic plane of shear as a result if this plane is tilted with a transverse component one of the longest standing axioms of glacial geology that particles in basal till are preferentially oriented parallel to the direction of shear is not strictly true the resultant correction to the shearing direction increases with the transverse and longitudinal components of shear plane inclination and with the magnitude of the fabric inclination relative to the shear plane azimuthal corrections calculated herein range from being negligible to a few tens of degrees for reasonable ranges of shear plane tilt the past success of fabric azimuths as indicators of flow direction despite the absence of this correction likely reflects the clustering of shear planes about the horizontal in basal tills however on the flanks of accreting subglacial bedforms shear plane attitudes may well conform to the local bedform slope as illustrated with hypothetical fabrics of drumlins and flutes azimuthal corrections can in that case be sufficiently large and systematic to seriously affect interpretations of bedform genesis